“The term varactor is the shortened form of a variable reactor, which refers to the voltage-variable capacitance of a reverse-biased p-n junction.”
Varactor diode is also known as a variable diode, vericap diode, tuning diode, variable reactance diode, or variable capacitance diode.
Symbol of Varactor Diode:
Symbol of Varactor Diode
How does a varactor diode work?
Working principle of varactor diode:
At this point the junction capacitance be influenced by on the instigated voltage and the design parameter of the junction. A junction with constant reverse biasing can be utilized as a capacitance. Usually, the variable diode is designed to employ the voltage-variable characteristics of junction capacitance. For instance, a varactor may be hand-me-down in the radio receiver’s tuning stage to supplementary of the large variable plate capacitor. The measurement of the resulting circuit can be reduced, and its dependability is increased. All the uses of varactor diode comprise with harmonic generation, microwave frequency amplification, and active filter applications. In an abrupt P-N junction, the capacitance changes as the reverse bias Vr‘s square root.
In a graded junction, the capacitance can regularly be written as,
Cj∝ Vr-n for the condition Vr >>V0
In a linearly categorized junction, the exponent n is always one-third. That’s why, varactor diodes are prepared by ‘ the epitaxial growth methodology’ or by ‘the ion implantation technique’. The epitaxial layer can be devised to get junctions for which the exponent n is more significant than one-half. Such junctions are called hyper abrupt junctions.
Structure of Varactor Diode
Structure of Varactor Diode or Varicap , Image Credit: No machine-readable author provided. Shaddack assumed (based on copyright claims)., Varactor, marked as public domain, more details on Wikimedia Commons
I-V Characteristic of Varactor Diode:
V-I Characteristic of Varactor Diode
Doping Profiles of Varactor Diode
The Doping Profiles of variable diode
Three different doping profiles has been explained above with the junction is devalued as p+ -n so that the depletion layer width W is extended originally into the n side. We can observe that the exponent n is 1/(m + 2) for the p+-n junction.
The hyper abrupt junction16 with m = -3/2 is particularly interesting for specific varactor applications for this case, n = 2, and the capacitance is equivalent to Vr-2. If a capacitor is connected with an inductor L in a resonant circuit, the resonant frequency varies linearly with diode’s applied voltage.
For the reason that of the wide variability of Cj vs. Vr reliance on doping profiles selection, variable diodes can be utilized in various specific uses. In one of these case, varactors can be designed to exploit the forward-bias charge storage capacitance for high-frequency applications.
Ohmic Loss of Varactor Diode:
While deriving the diode equation, we assumed that the device’s voltage appears solely over the junction. For most of these diode, the voltage drop in the neutral regions are negligible and the doping require is comparatively higher. The resistivity of each of the neutral region is small, and a characteristic diode area is outsized compared to the length.
Sometimes the ohmic loss is explained in a diode by inclusion of a simple resistance in series with the junction. The effects of voltage drop exterior to the development region are important because the voltage decline be influenced on the current, explained by the voltage across the junction. For instance, if we expressed the series resistance of a p and n constituencies by Rp and Rn, correspondingly, the junction voltage V is
V = Va – I[Rp(I) + Rn(I)]
Where Va is a voltage applied externally to the device. There is a on the rise voltage drop in the resistance region Rp and Rn correspondingly when the current become higher and the junction voltage V is declined. An additional complication of loss calculation may occur if conductivity has been increased in neutral region with cumulative carrier injection. Though, at high injection levels, with the injected surplus carriers’ conductivity inflection can reduce Rp and Rn considerably. The Ohmic losses are often avoided in properly-outlined devices. For that reason, deviations of the current in general give the impression only for very high currents operating beyond regular region.
The forward and reverses current-voltage characteristics in a semi-log scale
The forward and reverses current-voltage characteristics of a p-n junction on a semi-log scale
The forward and reverses current-voltage characteristics of a p-n junction on a semi-log scale has been explained above. We observe a straight line on a semi-log plot for the ideal forward-biased diode, corresponding the exponential relationship of current on voltage. Considering the second-order properties, we realize different operation modes. The enhanced generation–recombination current is directed to a further distinguished diode with ‘ideality factor’ (n = 2). For neutral currents, we get an excellent low-level injection and diffusion-limited current (n = 1). At more currents, we can get a higher injection level and n = 2, while at even greater currents, the ohmic drops initiated and space charge-neutral regions become critical.
At reverse biasing, a constant reverse saturation current has been observed, during this current is independent to voltage change. However, in substance, we receive an increased, voltage-dependent leakage current. The avalanche or Zener effects cause break down in sufficiently high reverse biasing.
Advantages of using a Varactor Diode:
Since the varactor diode has low noise compared to the p-n junction diode, there is less power loss in this diode. variable diodes are lightweight and easily portable due to its small size.
Applications of Varactor Diode:
variable diodes are used in a variable resistant tank, which is generally an L-C circuit.
variable diode can be used as a frequency modulator.
It is used as RF phase shifter.
variable diodes are utilized in a microwave receiver.
A tantalum capacitor is one kind of electrolytic capacitor, which is a passive electrical device. It uses a capsule of spongy tantalum metal as an anode. An insulating layer of oxide covers the anode. The oxide layer further generates the dielectric. It is surrounded by a solid or non-solid electrolyte, which serves as a cathode.
Tantalum capacitors are characteristics of high capacitance per volume or high volumetric efficiency because of its very reasonable and high permittivity dielectric layer. The increased capacitance value differentiates the tantalum capacitor from other types of electrolytic capacitors. It is also a more expensive capacitor than any different electrolytic kind.
This type of capacitor is polarized inherently. To form a non-polarized or bipolar tantalum capacitor, two polarized capacitors are connected in series. Their anodes are oriented in opposite directions.
Electrolytic capacitors store electrical energy as a typical capacitor. It holds electrical power by separation charge in an electric field in the dielectric oxide layer between two conductors.
The solid electrolyte is the cathode, forming another electrode of the capacitor. An electrolytic capacitor is different from supercapacitors or electrochemical capacitors, where the electrolyte is generally the ionic conductive connection.
A positive valued voltage is applied at the anode side of the tantalum electrolyte capacitor. The applied voltage causes the generation of a thin oxide layer. This oxide layer functions as the dielectric material of the capacitors.
The characteristics of the oxidised layer can be depicted using the below table.
Anode Material
Dielectric Material
Relative Permittivity
Structure of Oxide
Breakdown Voltage (V/μm)
Tantalum Metal
Tantalum pentoxide [Ta2O5]
27
Amorphous
625
Niobium
Niobium pentoxide [Nb2O5]
41
Amorphous
400
The electrolytic works as a cathode for a tantalum electrolytic capacitor. Several types of electrolytes are used. In general, two types of electrolytes are used – soli and non-solid.
Any liquid medium that has an ionic conductivity medium can be treated as a non-solid electrolyte. Concrete types of electrolytes have electron conductivity, and that is why solid electrolytes are more sensitive to voltage sparks. The oxide layer can be damaged if all of a usdden the polarities of the input voltage is reversed.
The working principle of an electrolytic tantalum capacitor is based on a ‘plate capacitor.’
The capacitance can be defined as the below-mentioned formula –
C = ε * (A /d)
C gives the value of the capacitance; A gives the area of the electrode, d represents the distance between the plates, and ε gives us the value of permittivity.
Capacitance can be increased if the electrode area is increased, and the dielectric permittivity is increased.
If we look in detail, a tantalum electrolytic capacitor has a tinny dielectric layer, and its construction is in the range of nm/volt. Also, the voltage strengths of the formed oxide layer are high enough. Now, this thin dielectric is combined with high voltage oxide dielectric and generates high volumetric capacitance. That is why an electrolytic tantalum capacitor has a higher capacitance than an ordinary capacitor. There are also some influences behind the increase in capacitance. That is the rough surface area due to etched and sintered anodes.
The desired voltage rating of an electrolytic capacitor can be easily produced as the oxide layer is dependent on the applied voltage on the anode. Tantalum Electrolytic capacitors have a high “CV product,” explained as the product of capacitance of the capacitor and voltage divided by the volume.
A standard tantalum electrolytic capacitor is a blemish capacitor and made up of tantalum powder and sintered into a capsule, which works as the capacitor’s anode. The oxide layer, which works as a dielectric, is made up of tantalum pentoxide. The cathode of the capacitor is a stable manganese dioxide electrolytic.
As mentioned previously, a tantalum capacitor usages tantalum powder as an anode. The powder is manufactured from pure tantalum metal. Capacitor times volts is the parameter to measure the figure of merit of the powder.
The metallic powder is bounded by tantalum wires (riser wire) to form the capsule or ‘pellet.’ The bounding wire works as the tantalum capacitor’s anode connection.
Larger surface areas give higher capacitance value. That is why powders having high CV/g and smaller average particle sizes are used for high capacitance low voltage parts. A specific voltage can be achieved if we can choose the correct type of powder and an almost perfect temperature for sintering. A suitable sintering temperature can be around – 1200-1800 degrees Celsius.
Dielectric
An electrochemical process named anodization forms the dielectric over the tantalum particles. The primary step to creating this is that the ‘pellet’ is submerged into a very frail solution of an acid and the supplied DC voltage.
Like any other electrolytic capacitor, the thickness of the dielectric layer depends upon the total applied voltage. At the beginning of the process, the power supply is kept in steady current mode until and unless the dielectric thickness is reached. After that, the voltage is held, and the current can decay to get zero value. This process provides an unvarying consistency throughout the device.
The chemical equations are represented below.
2 Ta → 2 Ta 5+ + 10 e−
2 Ta 5+ + 10 OH− → Ta2O5 + 5 H2O
Formation of oxides also took place on the surface of the material during the process. The oxide ultimately grows into the material. There is a specific way the oxide grows. Each unit thickness of oxide growth, the two-third share goes inside, whereas one-third share goes outside. The limit of the maximum voltage rating is also due to the limit in the oxide growth.
There is a safety margin in the oxide layer thickness.
Cathode
The process to form the cathode is the pyrolysis of manganese nitrate into the manganese dioxide. After the pellet submersion, that is baked to produce the dioxide cover at around 250 degrees Celsius. The chemical equations are represented below.
Mn (NO3 )2 → MnO2 + 2 NO2
To build up a thick layer of the coat over both internal and external service areas, the process is repeated repeatedly through fluctuating specific gravities of nitrate solutions.
Types of the Tantalum Capacitors
There are several styles of tantalum capacitors.
Tantalum Chip Capacitors: 80% of tantalum capacitors are of this type. They are categorized for surface mounting.
Tantalum ‘Pearls’ capacitors: They are specially designed for PCB mounting. They are dipped in resin.
Axial leaded tantalum capacitors: Mostly used in military, medical and space applications. It has both tangible and non-solid electrolyte.
Capacitors are designated as an ideal series equivalent circuit with electrical constituents. But, tantalum capacitors can not be marked as idealistic capacitors.
C is the capacitor’s capacitance; RESR is the equivalent series resistance, which takes into account all the ohmic losses. LESL is the self-inductance of the capacitor. Bleak is the leakage resistance.
Capacitance, standard values, and tolerances
The construction of electrode determines the electrical characteristics of an electrolytic tantalum capacitor. The capacitance also depends on the frequency and temperature parameters. The unit of the capacitance of an electrolytic tantalum capacitor depends on microfarad (mu f).
Particular applications determine the required tolerance of capacitance.
This does not need narrow tolerances.
Ready and Category voltage
The allowable operating voltage for a tantalum electrolytic capacitor is known as rated voltage or nominal voltage.
Applying higher voltage than the rated one may lead to the destruction of the tantalum electrolytic capacitor. Applying lower voltage has also influenced the capacitor. A lower voltage can extend the lifetime. Sometimes it increases reliability for it.
Surge Voltage
IEC/EN 60384 standardized surge voltage is the maximum amount of peak voltage which is supplied as input to the capacitors. It is measured for the duration of the capacitor’s applications in no of cycles.
Transient voltage
If a transient voltage or a current spike is applied to tantalum electrolytic capacitors, which ha stable manganese dioxide as the electrolytic material, that will lead the capacitor to fail.
Reverse voltage
A typical tantalum electrolytic capacitor is polarized and, in general, have need of the anode must be positive relative to cathode.
Tantalum capacitors can withstand reverse voltage for a short period. Sometimes the reverse voltage may be used for applications in permanent AC circuits.
Impedance
A standard capacitor is considered as a storage component in electrical energy. Sometimes capacitors are deployed in Alternative Current circuits as resistive elements. An electrolytic capacitor is used as a decoupling capacitor in a course. It blocks the DC component of the signal with the help of the dielectric material.
Leakage Current
The leakage current of tantalum capacitors differentiates these type of capacitors or it can be the identity of these capacitors. The value of leakage current be influenced by on the anode’s applied voltage and temperature.
Symbol of capacitor
Electrolytic capacitors have a particular type of symbol for representing circuits. It is almost similar to the regular capacitor symbol, but a plus sign makes a difference.
A ceramic capacitor is a type of electronic component commonly used in various electrical circuits. It is made of ceramic materials and consists of two conductive plates separated by a dielectric material. The dielectric material in a ceramic capacitor is usually made of ceramic compounds such as titanium dioxide or barium titanate. Ceramic capacitors are known for their small size, high capacitance values, and low cost. They are widely used in electronic devices such as computers, televisions, mobile phones, and automotive systems.
Key Takeaways
Property
Description
Small Size
Ceramic capacitors are compact and take up less space in electronic devices.
High Capacitance
They have high capacitance values, allowing them to store and release electrical energy efficiently.
Low Cost
Ceramic capacitors are cost-effective compared to other types of capacitors.
Wide Application
They are used in a wide range of electronic devices and systems, including computers, televisions, and automotive systems.
Class 1 type ceramic capacitors are a type of ceramic capacitor that are known for their high stability and low losses. They are made using dielectric materials such as mica or ceramic, which have a low temperature coefficient and low dielectric losses. These capacitors are commonly used in high-frequency applications due to their excellent performance at high frequencies. Class 1 ceramic capacitors have a high capacitance value and are often used in electronic circuits where accuracy and stability are crucial.
Class 2 type Ceramic Capacitor
Class 2 type ceramic capacitors are another type of ceramic capacitor that are widely used in various electronic applications. They are made using multilayer ceramic capacitor (MLCC) technology, which allows for a high capacitance value in a small package size. Class 2 ceramic capacitors have a higher capacitance value compared to Class 1 capacitors, making them suitable for applications that require higher capacitance values. These capacitors are commonly used in power applications, decoupling circuits, and filtering applications.
Multi-layer ceramic capacitor (MLCC)
Multi-layer ceramic capacitors, also known as MLCCs, are a popular type of ceramic capacitor used in a wide range of electronic devices. They are constructed using multiple layers of ceramic material, with alternating layers of ceramic and electrode material. MLCCs offer a high capacitance value in a compact size, making them ideal for space-constrained applications. They are commonly used in various electronic devices, including smartphones, computers, televisions, and automotive electronics.
Ceramic Power Capacitors
Ceramic power capacitors are designed to handle high power and high voltage applications. They are specifically designed to provide high capacitance values and low impedance at high frequencies. These capacitors are commonly used in power electronics, such as power supplies, inverters, and motor drives. Ceramic power capacitors are known for their high energy storage capabilities and low ESR(Equivalent Series Resistance), making them suitable for applications that require high power handling and low losses.
Tubular Ceramic Capacitor
Tubular ceramic capacitors are a type of ceramic capacitor that have a tubular shape. They are commonly used in applications that require high capacitance values and high voltage ratings. Tubular ceramic capacitors are known for their high temperature stability and low leakage current. They are often used in power applications, lighting fixtures, and industrial equipment.
Monolithic Ceramic Capacitor
Monolithic ceramic capacitors are compact, surface mount capacitors that are widely used in various electronic devices. They are constructed using a single ceramic block with embedded electrodes. Monolithic ceramic capacitors offer a high capacitance value in a small package size, making them suitable for miniaturized electronic devices. They are commonly used in consumer electronics, telecommunications equipment, and automotive electronics.
In summary, ceramic capacitors come in various types, each with its own unique characteristics and applications. Class 1 and Class 2 ceramic capacitors are differentiated by their dielectric materials and capacitance values. MLCCs offer high capacitance in a compact size, while ceramic power capacitors are designed for high power applications. Tubular ceramic capacitors are used for high voltage applications, and monolithic ceramic capacitors are compact surface mount capacitors used in miniaturized electronic devices.
Ceramic capacitors are widely used electrical components in various applications due to their high capacitance values and excellent performance at high frequencies. The construction of ceramic capacitors involves the use of dielectric materials, such as ceramic, which determines their capacitance and other electrical properties.
One of the most common types of ceramic capacitors is the multilayer ceramic capacitor (MLCC). MLCCs are constructed by stacking multiple layers of ceramic material, each coated with a conductive material on both sides. These layers are then stacked together, alternating between the positive and negative electrodes, to form a compact and efficient capacitor.
The size of the ceramic chip used in MLCCs can vary, depending on the desired capacitance value and the space available on the circuit board. The miniaturization of MLCCs has been a significant advancement in recent years, allowing for higher capacitance values in smaller packages. This miniaturization is achieved by reducing the size of the ceramic layers and optimizing the internal structure of the capacitor.
MLCCs also feature different termination styles, which are the contact points that connect the capacitor to the circuit board. The most common termination styles include the traditional “end contact” and the newer “side contact” designs. The choice of termination style depends on the specific application and the desired impedance characteristics of the capacitor.
MLCC Miniaturizing
The miniaturization of MLCCs has revolutionized the field of electronic circuits, enabling the development of smaller and more compact devices. This advancement has been made possible by reducing the size of the ceramic layers and optimizing the internal structure of the capacitor.
The miniaturization process involves stacking multiple ceramic layers, each with a thickness of only a few micrometers. This allows for a higher number of layers within the same overall size, resulting in increased capacitance values. Additionally, advancements in manufacturing techniques have enabled the production of MLCCs with smaller electrode sizes, further contributing to their miniaturization.
The miniaturization of MLCCs has also led to improvements in their electrical performance. Smaller capacitor sizes result in lower parasitic inductance and resistance, allowing for better high-frequency performance. This makes MLCCs ideal for applications that require high-frequency filtering or decoupling.
Ceramic Capacitor Construction
Apart from MLCCs, ceramic capacitors are also available in other construction styles. One such style is the ceramic disc capacitor, which consists of a ceramic disc coated with a conductive material on both sides. The leads of the capacitor are attached to the coated surfaces, allowing for easy integration into electronic circuits.
Ceramic capacitors are available in various capacitance values, voltage ratings, and temperature coefficients. These specifications determine their suitability for different applications. For example, capacitors with high capacitance values are suitable for power applications, while those with high voltage ratings are ideal for use in high-voltage circuits.
In terms of construction, ceramic capacitors are known for their reliability and long lifespan. They have a low equivalent series resistance (ESR) and can withstand high temperatures, making them suitable for demanding environments. However, it is important to consider the dielectric breakdown voltage and leakage current when selecting ceramic capacitors for specific applications.
In summary, ceramic capacitors, including MLCCs, are versatile components that find applications in a wide range of electronic circuits. Their construction, capacitance values, and other specifications make them suitable for various high-frequency and power applications. The miniaturization of MLCCs has further expanded their usability, allowing for smaller and more efficient electronic devices.
Ceramic capacitors are widely used electrical components in various applications due to their excellent electrical properties and compact size. They are made using different dielectric materials and come in various types such as multilayer ceramic capacitors (MLCCs), ceramic disc capacitors, and surface mount capacitors. In this section, we will explore the electrical characteristics of ceramic capacitors, including their series equivalent circuit, capacitance, impedance, ESR (Equivalent Series Resistance), and more.
Series Equivalent Circuit
The series equivalent circuit of a ceramic capacitor represents its electrical behavior in a circuit. It consists of the actual capacitance, equivalent series resistance (ESR), and inductance (ESL). The capacitance is the ability of the capacitor to store electrical energy, while the ESR represents the resistance encountered by the capacitor in a circuit. The ESL, on the other hand, represents the inductance associated with the capacitor’s leads and internal construction.
Capacitance, Standard Values, and Tolerances
Capacitance is a crucial parameter of ceramic capacitors, indicating their ability to store electrical charge. The capacitance value is measured in farads (F) and can vary depending on the specific capacitor type and construction. Ceramic capacitors are available in a wide range of capacitance values, from picofarads (pF) to microfarads (μF). They also have standard values and tolerances that determine their accuracy in capacitance. Capacitor manufacturers follow specific codes to indicate the capacitance value and tolerance, such as the ceramic capacitor code.
Impedance
Impedance is a measure of the opposition to the flow of alternating current (AC) in a circuit. In ceramic capacitors, impedance varies with frequency due to the inherent characteristics of the dielectric material used. At low frequencies, the impedance of ceramic capacitors is mainly capacitive, while at high frequencies, it becomes inductive. Understanding the impedance characteristics of ceramic capacitors is crucial for their proper application in electronic circuits.
ESR, Dissipation Factor, Quality Factor
ESR, or Equivalent Series Resistance, is an important parameter that affects the performance of ceramic capacitors. It represents the resistance encountered by the capacitor in a circuit due to various factors such as the internal construction, electrode materials, and dielectric properties. A low ESR is desirable for efficient energy storage and discharge in capacitors. The Dissipation Factor (DF) and Quality Factor (Q) are related to the ESR and represent the energy loss and efficiency of the capacitor, respectively.
Ceramic Capacitor ESR
Ceramic capacitors have a unique ESR characteristic compared to other capacitor types. The ESR of ceramic capacitors is generally low, making them suitable for high-frequency applications. However, it is important to consider the ESR when selecting ceramic capacitors for specific applications, as it can affect their performance and reliability. Factors such as temperature, frequency, and voltage can also influence the ESR of ceramic capacitors.
In summary, the electrical characteristics of ceramic capacitors play a crucial role in their performance and application. Understanding the series equivalent circuit, capacitance values, tolerances, impedance, and ESR is essential for selecting the right ceramic capacitors for different electronic circuits and ensuring their reliable operation.
Understanding Ceramic Capacitors
Ceramic capacitors are essential electrical components used in a wide range of applications. They are commonly found in electronic circuits and are known for their reliability and versatility. In this article, we will explore the working principle of ceramic capacitors, their physical appearance, symbols, polarity, markings, and how to read their values using the ceramic capacitor code.
How Ceramic Capacitor Works
Ceramic capacitors utilize a dielectric material, typically made of ceramic, which separates two conductive plates known as electrodes. When a voltage is applied across the electrodes, an electric field is created within the dielectric material, causing it to store electrical energy. The capacitance value of a ceramic capacitor determines its ability to store this energy.
What Does a Ceramic Capacitor Look Like
Ceramic capacitors come in various shapes and sizes, but they are typically small and cylindrical or rectangular in shape. They are often referred to as multilayer ceramic capacitors (MLCCs) due to their construction, which consists of multiple layers of ceramic and electrodes stacked together. The size of a ceramic capacitor can vary depending on its capacitance and voltage rating.
Ceramic Capacitor Symbol
In circuit diagrams, ceramic capacitors are represented by a symbol that consists of two parallel lines representing the electrodes, with a gap between them indicating the dielectric material. The symbol may also include additional markings to indicate the capacitor’s capacitance value and voltage rating.
Ceramic Capacitor Polarity
Unlike electrolytic capacitors, ceramic capacitors are non-polarized, meaning they do not have a specific positive or negative terminal. This makes them suitable for use in both AC and DC circuits. However, it is important to note that some ceramic capacitors have a polarity marking, indicating the side that should be connected to the lower voltage potential in certain applications.
Ceramic Capacitor Markings
Ceramic capacitors often have markings printed on their surface to indicate important specifications. These markings may include the manufacturer’s logo, capacitance value, voltage rating, and sometimes the temperature coefficient. Understanding these markings is crucial when selecting the right capacitor for a specific application.
How to Read Ceramic Capacitor
Reading the values of ceramic capacitors can be done by decoding the ceramic capacitor code. This code consists of alphanumeric characters that represent the capacitance value, voltage rating, and sometimes the tolerance of the capacitor. By referring to a ceramic capacitor code chart, one can easily determine the specifications of a ceramic capacitor based on its code.
Ceramic Capacitor Code
The ceramic capacitor code is a standardized system used to represent the capacitance value, voltage rating, and tolerance of ceramic capacitors. It typically consists of three digits followed by a letter or two digits. Each digit represents a specific value or multiplier, while the letter or two digits indicate the tolerance. By understanding this code, one can quickly identify the characteristics of a ceramic capacitor.
In conclusion, ceramic capacitors are widely used in various electronic applications due to their reliability, compact size, and versatility. Understanding how they work, their physical appearance, symbols, polarity, markings, and how to read their values using the ceramic capacitor code is essential for selecting the right capacitor for specific circuit requirements.
Ceramic Capacitor vs Electrolytic Capacitor
Comparison of Characteristics
When it comes to choosing the right capacitor for your electronic circuits, two popular options are ceramic capacitors and electrolytic capacitors. Each type has its own unique characteristics and applications. Let’s take a closer look at the differences between these two capacitor types.
Ceramic Capacitors:
Dielectric Materials: Ceramic capacitors use a ceramic material as the dielectric, which is a non-conductive material that separates the capacitor’s plates.
Capacitance Value: Ceramic capacitors are available in a wide range of capacitance values, from picofarads (pF) to microfarads (µF).
Capacitor Construction: They are typically constructed using multilayer ceramic capacitors (MLCCs) or ceramic disc capacitors.
Capacitor Ratings: Ceramic capacitors have high voltage ratings and are suitable for various applications.
Capacitor Applications: They are commonly used in high-frequency applications, such as RF circuits, power supply decoupling, and noise filtering.
Electrolytic Capacitors:
Dielectric Materials: Electrolytic capacitors use an electrolyte as the dielectric, which is a conductive material.
Capacitance Value: Electrolytic capacitors have higher capacitance values compared to ceramic capacitors, ranging from microfarads (µF) to farads (F).
Capacitor Construction: They are typically cylindrical in shape and have two electrodes immersed in an electrolyte.
Capacitor Ratings: Electrolytic capacitors have lower voltage ratings compared to ceramic capacitors.
Capacitor Applications: They are commonly used in power supply circuits, audio amplifiers, and applications that require high capacitance values.
When to Use Each Type
Now that we have compared the characteristics of ceramic capacitors and electrolytic capacitors, let’s discuss when it is appropriate to use each type.
Ceramic Capacitors:
High-Frequency Applications: Ceramic capacitors are ideal for high-frequency applications due to their low impedance and high resonance frequency.
Compact Size: They are available in small sizes, making them suitable for space-constrained electronic devices.
AC Coupling: Ceramic capacitors are commonly used for AC coupling in audio circuits and signal processing applications.
Temperature Stability: They have a low temperature coefficient, which means their capacitance value remains relatively stable over a wide temperature range.
Electrolytic Capacitors:
Power Supply Filtering: Electrolytic capacitors are commonly used for power supply filtering and energy storage in electronic devices.
High Capacitance Requirements: When a high capacitance value is needed, electrolytic capacitors are the preferred choice.
Polarity: Electrolytic capacitors have polarity, meaning they must be connected with the correct orientation to avoid damage.
Low-Frequency Applications: They are suitable for low-frequency applications where size and cost are not major constraints.
In summary, ceramic capacitors are often used in high-frequency applications and where compact size is important, while electrolytic capacitors are commonly used for power supply filtering and applications that require high capacitance values. Understanding the characteristics and applications of each type will help you choose the right capacitor for your specific needs.
Ceramic Capacitor Failure Modes
Ceramic capacitors are widely used in electronic circuits due to their small size, high capacitance values, and excellent stability. However, like any electrical component, ceramic capacitors can experience failure under certain conditions. Understanding the failure modes of ceramic capacitors is crucial for ensuring the reliability and longevity of electronic devices.
Causes of Failure
There are several factors that can contribute to the failure of ceramic capacitors. These include:
Dielectric breakdown: Excessive voltage or a voltage spike can cause the dielectric material in the capacitor to break down, leading to a short circuit or open circuit failure.
Capacitor aging: Over time, ceramic capacitors can experience a decrease in capacitance value and an increase in equivalent series resistance (ESR), which can affect their performance.
Thermal stress: Rapid temperature changes or exposure to high temperatures can cause the ceramic material to expand and contract, leading to mechanical stress and potential failure.
Mechanical stress: Excessive mechanical stress, such as vibration or physical impact, can cause cracks or fractures in the ceramic capacitor, compromising its functionality.
How to Test Ceramic Capacitor in Circuit
Testing ceramic capacitors in circuit can help identify any potential issues. Here are a few methods to test ceramic capacitors:
Visual inspection: Check for any physical damage, such as cracks or bulges, on the ceramic capacitor. This can indicate a failure.
Capacitance measurement: Use a multimeter or a dedicated capacitance meter to measure the capacitance value of the ceramic capacitor. Compare the measured value with the specified value to ensure it falls within an acceptable range.
ESR measurement: Measure the equivalent series resistance (ESR) of the ceramic capacitor using an ESR meter. Higher ESR values can indicate a potential failure.
Dielectric breakdown test: Apply a high voltage to the ceramic capacitor and monitor for any signs of breakdown, such as excessive current flow or voltage leakage.
Do Ceramic Capacitors Fail?
Yes, ceramic capacitors can fail under certain conditions. The failure rate of ceramic capacitors can vary depending on factors such as operating conditions, quality of manufacturing, and environmental factors. However, with proper design considerations and regular testing, the risk of failure can be minimized.
How Long Do Ceramic Capacitors Last?
The lifetime of ceramic capacitors can vary depending on various factors, including operating conditions, voltage stress, temperature, and quality of manufacturing. Generally, ceramic capacitors have a relatively long lifespan and can last for several years or even decades under normal operating conditions. However, it is important to monitor their performance over time and replace any capacitors that show signs of degradation or failure.
In conclusion, understanding the failure modes of ceramic capacitors and implementing appropriate testing methods can help ensure the reliability and longevity of electronic circuits. Regular inspection, capacitance measurement, ESR measurement, and dielectric breakdown testing are essential for identifying potential issues and preventing failures. By taking these precautions, the lifespan of ceramic capacitors can be maximized, contributing to the overall reliability of electronic devices.
Applications of Ceramic Capacitors
What is Ceramic Capacitor Used For
Ceramic capacitors are widely used in various electronic circuits due to their excellent electrical properties and compact size. They are commonly used for decoupling, bypassing, filtering, and coupling applications. The high dielectric constant of ceramic materials allows for high capacitance values in small packages, making them ideal for space-constrained designs.
In addition to their small size, ceramic capacitors offer low impedance at high frequencies, making them suitable for high-frequency applications. They are commonly used in RF circuits, microwave circuits, and high-speed digital circuits. Their low equivalent series resistance (ESR) and low equivalent series inductance (ESL) make them effective in reducing noise and improving signal integrity.
Where are Ceramic Capacitors Used
Ceramic capacitors find applications in a wide range of electronic devices and systems. Some common areas where ceramic capacitors are used include:
Consumer Electronics: Ceramic capacitors are used in smartphones, tablets, laptops, televisions, and other consumer electronic devices. They are used for power supply filtering, decoupling, and noise suppression.
Automotive Electronics: Ceramic capacitors are used in automotive electronics for various applications such as engine control units, infotainment systems, and safety systems. They are used for voltage regulation, EMI suppression, and filtering.
Industrial Equipment: Ceramic capacitors are used in industrial equipment such as power supplies, motor drives, and control systems. They are used for power factor correction, noise filtering, and voltage regulation.
Telecommunications: Ceramic capacitors are used in telecommunications equipment such as routers, switches, and base stations. They are used for signal conditioning, filtering, and impedance matching.
Medical Devices: Ceramic capacitors are used in medical devices such as patient monitors, imaging systems, and implantable devices. They are used for power supply filtering, noise suppression, and signal conditioning.
Are Ceramic Capacitors Good for Audio
Ceramic capacitors are commonly used in audio applications, but their suitability depends on the specific requirements of the audio circuit. Ceramic capacitors offer advantages such as small size, low cost, and high capacitance values. However, they also have some limitations.
One limitation of ceramic capacitors is their non-linear behavior at high voltages, which can introduce distortion in audio signals. Additionally, ceramic capacitors may exhibit piezoelectric effects, which can cause microphonic noise in audio circuits. For high-quality audio applications, other capacitor types such as film capacitors or electrolytic capacitors may be preferred.
When to Use Ceramic Capacitor
Ceramic capacitors are suitable for a wide range of applications, but there are certain factors to consider when deciding to use them:
Frequency: Ceramic capacitors are well-suited for high-frequency applications due to their low impedance at high frequencies. They are commonly used in RF circuits, microwave circuits, and high-speed digital circuits.
Size: Ceramic capacitors are available in small packages, making them ideal for space-constrained designs. They are commonly used in portable electronic devices and miniaturized electronic systems.
Temperature: Ceramic capacitors have a wide operating temperature range, making them suitable for both low-temperature and high-temperature environments. They are commonly used in automotive, industrial, and aerospace applications where temperature variations are significant.
Cost: Ceramic capacitors are generally more cost-effective compared to other capacitor types such as film capacitors or electrolytic capacitors. They offer a good balance between performance and cost, making them suitable for cost-sensitive applications.
In summary, ceramic capacitors have a wide range of applications in various industries and electronic devices. Their small size, high capacitance values, and low impedance at high frequencies make them a popular choice for many electronic circuits. However, it is important to consider the specific requirements of the application and the limitations of ceramic capacitors before selecting them.
Practical Guide to Ceramic Capacitors
Ceramic capacitors are essential electrical components used in a wide range of applications, from electronic circuits to power systems. In this practical guide, we will explore various aspects of ceramic capacitors, including how to make them, find their value, check their value, measure them with a multimeter, calculate their value, use them effectively, solder them, and understand how they are made.
How to Make Ceramic Capacitor
Making a ceramic capacitor involves the use of dielectric materials, which are insulating materials that can store electrical energy. The most common type of ceramic capacitor is the multilayer ceramic capacitor (MLCC), which consists of multiple layers of ceramic material stacked together. These capacitors are widely used due to their small size, high capacitance, and excellent performance at high frequencies.
How to Find Ceramic Capacitor Value
To find the value of a ceramic capacitor, you can refer to the markings on its surface. Ceramic capacitors are often labeled with a code that indicates their capacitance value. This code typically consists of alphanumeric characters that represent the capacitance value, tolerance, and voltage rating of the capacitor. By decoding the markings, you can determine the capacitance value of the ceramic capacitor.
How to Check Ceramic Capacitor Value
Checking the value of a ceramic capacitor is important to ensure its suitability for a specific application. One way to check the value is by using a capacitance meter or a multimeter with a capacitance measurement function. By connecting the leads of the meter to the capacitor terminals, you can measure its capacitance value. This allows you to verify if the capacitor meets the required specifications for your circuit.
How to Measure Ceramic Capacitor with Multimeter
Measuring a ceramic capacitor with a multimeter is a straightforward process. Set your multimeter to the capacitance measurement mode and ensure that the capacitor is discharged. Connect the multimeter leads to the capacitor terminals and observe the reading on the display. This measurement provides an accurate value of the capacitance, allowing you to assess the performance of the capacitor.
How to Calculate Ceramic Capacitor Value
Calculating the value of a ceramic capacitor is useful when you don’t have access to its markings or if you want to verify the value obtained from other methods. The capacitance of a ceramic capacitor can be calculated using the formula:
C = (k * ε₀ * A) / d
Where: – C is the capacitance in farads
– k is the dielectric constant of the ceramic material
– ε₀ is the permittivity of free space
– A is the area of the capacitor plates
– d is the distance between the capacitor plates
By plugging in the appropriate values, you can determine the capacitance of the ceramic capacitor.
How to Use Ceramic Capacitor
Ceramic capacitors find applications in various electronic circuits, ranging from decoupling and bypassing to filtering and timing. Their high capacitance and low impedance make them suitable for high-frequency applications. Additionally, ceramic capacitors are used for energy storage, voltage regulation, and noise suppression. Understanding the specific requirements of your circuit will help you select the appropriate ceramic capacitor for optimal performance.
How to Solder Ceramic Capacitor
Soldering ceramic capacitors requires careful handling to prevent damage to the component. Start by cleaning the capacitor terminals and the soldering iron tip. Apply a small amount of solder to the tip to ensure good heat transfer. Place the capacitor on the circuit board, aligning the terminals with the solder pads. Heat the joint with the soldering iron while applying solder to create a secure connection. Avoid excessive heat and prolonged soldering time to prevent thermal stress on the ceramic capacitor.
How Ceramic Capacitors are Made
Ceramic capacitors are manufactured through a precise process that involves the construction of multiple layers of ceramic material. The ceramic layers are coated with a conductive material, typically a metal, to create the capacitor plates. These layers are then stacked together, and the edges are terminated to provide electrical contact. The size and shape of the capacitor can vary depending on its intended application. Capacitor manufacturers employ advanced techniques to ensure high-quality and reliable ceramic capacitors.
By following this practical guide, you can gain a better understanding of ceramic capacitors and their various aspects, from making and finding their value to measuring, calculating, using, soldering, and understanding their manufacturing process. Ceramic capacitors play a crucial role in modern electronic systems, and knowing how to work with them effectively is essential for any electronics enthusiast or professional.
Ceramic Capacitor Kits
Overview of Kits
Ceramic capacitor kits are a convenient and cost-effective solution for engineers and hobbyists who frequently work with electrical components. These kits contain a variety of ceramic capacitors with different capacitance values, voltage ratings, and package sizes. They are designed to provide a comprehensive selection of capacitors for various applications in electronic circuits.
The ceramic capacitors included in these kits are made using different dielectric materials, such as multilayer ceramic capacitors (MLCCs) and ceramic disc capacitors. MLCCs are the most common type of ceramic capacitors and are widely used due to their high capacitance values and small size. Ceramic disc capacitors, on the other hand, are suitable for applications that require high voltage ratings.
The capacitor kits typically come with a range of capacitance values, allowing users to experiment with different values to achieve the desired performance in their circuits. Capacitor values are measured in farads (F) or its subunits, such as microfarads (μF) and picofarads (pF). The kits may also include capacitors with different ratings, such as voltage ratings and temperature coefficients, to cater to a wide range of applications.
To make it easier for users to identify and select the right capacitor for their needs, the kits often provide a code or marking system. This system helps users determine the capacitance, voltage rating, and other specifications of the capacitors. It is important to understand these codes to ensure the correct usage of the capacitors in electronic projects.
How to Choose the Right Kit
When choosing a ceramic capacitor kit, there are several factors to consider to ensure it meets your specific requirements. Here are some key considerations:
Application: Determine the specific application for which you need the capacitors. Different applications may require capacitors with specific characteristics, such as high frequency, high voltage, or high temperature capabilities.
Capacitor Type: Consider the type of capacitor that best suits your needs. Ceramic capacitors are suitable for a wide range of applications due to their excellent performance in terms of capacitance, frequency response, and stability.
Capacitance Value: Identify the required capacitance value for your application. This value determines the amount of charge the capacitor can store and release. It is crucial to choose a kit that offers a range of capacitance values to cover your specific needs.
Package Size: Consider the available space in your circuit board or project enclosure. Ceramic capacitors come in various package sizes, such as surface mount capacitors (SMD) and through-hole capacitors. Choose a kit that includes capacitors with package sizes suitable for your project.
Voltage Rating: Determine the voltage requirements of your application. Ceramic capacitors have different voltage ratings, and it is important to choose a kit that includes capacitors with ratings that meet or exceed your application’s voltage requirements.
Temperature Coefficient: If your application involves temperature variations, consider the temperature coefficient of the capacitors. This coefficient indicates how the capacitance value changes with temperature. Choose a kit that includes capacitors with temperature coefficients suitable for your application.
By considering these factors, you can select a ceramic capacitor kit that provides the necessary components for your specific project or experimentation needs. These kits offer a convenient way to have a diverse range of capacitors readily available, saving you time and effort in sourcing individual components.
Remember to consult the datasheets and specifications provided with the kit to ensure proper usage and compatibility with your electronic circuits.
In conclusion, ceramic capacitors are widely used in various electronic devices due to their numerous advantages. They offer high capacitance values in a compact size, making them ideal for miniaturized circuits. Ceramic capacitors also have excellent stability, low cost, and low equivalent series resistance (ESR). They can operate at high frequencies and withstand high temperatures, making them suitable for a wide range of applications. However, it is important to consider the specific requirements of your circuit and choose the appropriate type of ceramic capacitor, such as multilayer ceramic capacitors (MLCCs) or ceramic disc capacitors. Overall, ceramic capacitors are a reliable and versatile choice for electronic circuitry.
Frequently Asked Questions
Q1: What is a ceramic capacitor and how does it work?
A ceramic capacitor is a type of capacitor that uses ceramic material as the dielectric. It works by storing energy in an electric field between two conductive plates, separated by the ceramic dielectric material. The ceramic material’s properties allow the capacitor to store and release electrical energy.
Q2: How can I identify the value of a ceramic capacitor?
The value of a ceramic capacitor can be identified by the markings on its body. These markings usually represent the capacitance value and the voltage rating. If the markings are unclear, a multimeter can be used to measure the capacitance value.
Q3: What are the different types of ceramic capacitors?
There are several types of ceramic capacitors, including disc, multilayer, and monolithic ceramic capacitors. Disc capacitors are simple and inexpensive, while multilayer and monolithic capacitors offer higher capacitance values and are used in more complex electronic circuits.
Q4: What is the purpose of a ceramic capacitor in a circuit?
In a circuit, a ceramic capacitor is used to store and release electrical energy. It can also be used for filtering, where it passes alternating current (AC) and blocks direct current (DC). Additionally, ceramic capacitors are used for coupling and decoupling applications in electronic circuits.
Q5: How can I check if a ceramic capacitor is functioning correctly?
A ceramic capacitor can be tested using a multimeter. By setting the multimeter to the capacitance setting and connecting the probes to the capacitor’s leads, the displayed value should be close to the capacitor’s rated capacitance. If the value is far off or the multimeter displays an error, the capacitor may be faulty.
Q6: Do ceramic capacitors have polarity?
Unlike some other types of capacitors, most ceramic capacitors do not have polarity. This means they can be installed in either direction in a circuit. However, some special types of ceramic capacitors do have polarity, and these are usually clearly marked.
Q7: What is the role of the dielectric in a ceramic capacitor?
The dielectric in a ceramic capacitor plays a crucial role in storing and releasing electrical energy. The properties of the ceramic dielectric material, such as its permittivity, determine the amount of energy the capacitor can store.
Q8: What are the common applications of ceramic capacitors?
Ceramic capacitors are commonly used in a wide range of electronic devices. They are found in power supply circuits for filtering, in audio and RF circuits for coupling and decoupling, and in timing circuits for oscillators and wave generators.
Q9: How long do ceramic capacitors last?
The lifespan of a ceramic capacitor depends on several factors, including its quality, operating conditions, and the electrical load it experiences. Under normal conditions, a ceramic capacitor can last for many years without failure.
Q10: What causes a ceramic capacitor to fail?
Ceramic capacitors can fail due to a variety of reasons, including excessive voltage (which can cause dielectric breakdown), physical damage, and aging. In some cases, manufacturing defects can also lead to early failure.
Discover the vital role of capacitors in electronic circuits: learn about their varieties, applications, and significance in energy management.
Capacitor – Definitions & Overview
Capacitor is one of the most important passive equipment which is able to store electrical energies.It is a two-terminal device.Capacitance is known as the effect of the capacitor.
Ancient forms of capacitor was innovated in the year 1704s. A European experiment back then discovered that electric charge could be reserved in a water-filled glass. Later in 1745, Ewald Georg from Germany found that series-connected high-voltage electrostatic generators can store the amount. Previously capacitors were known as condensers or condensator. Alessandro Volta coined the term in 1782. The term capacitor came into existence in 1926.
There are lots of types of capacitors. The capacitors have at least two conductors in the form of a metallic flat surface separated by a dielectric materials. The conductor may be an electrolyte, foil, thin film, etc. the non-conductor is the dielectric substance, increasing the capacitor’s charge capacity. Materials like – air, plastic film, paper, mica, ceramics are used as a dielectric for the capacitor.
When an external voltage is applied at the terminals of a capacitor, an electric field is produced across the dielectric material. Thus, a positive charge is collected on one plate, and a negative amount is collected on another scale. Capacitors are used in almost every electrical and electronic circuit. The difference between a resistor and a capacitor is that a resistor dissipates energy, whereas an ideal capacitor does not.
As mentioned earlier, a capacitor has two conductors separated by a dielectric medium. A capacitor works on the principle of Coulomb’s Law. Coulomb’s law states that –
Thus, a charge on one conductor will generate the force on the other conductor’s carrier, which further attracts opposite polarity charges and ripples the same type of charges. That is how an opposite polarity charge is induced on the other conductor’s surface.
Both the conductors hold an equal amount of charges, and the dielectric material develops the electric field.
Capacitance and Units of capacitance:
The capacitance of a standard capacitor is defined as the charge’s ratio to the conductor to the conductors’ voltage.
C = Q / V
C is the capacitance, Q is the charge on each conductor’s surface, and V is the voltage between two conductors.
The S.I unit of capacitance is given by – Farad(F).
One Farad capacitance is defined as the amount of capacitance a capacitor can generate if one coulomb of charge is applied to each conductor having one volt of voltage.
In practical devices, Capacitance is given by –
C = dQ / dV
* Most of the capacitors available in the market have capacitance rang in micro-farad.
A capacitor may behave differently at different times if it is placed in an active electrical circuit. Its behavior can be characterized by a long time limit and a short time limit.
Long time equivalence of a capacitor acts like an open circuit configuration (no current passes).
The short time equivalent of capacitors act like a short-circuit configuration.
V (t) = Q (t) / C = (1/C) * [ ∫t0t I (τ) dτ ] + V (t0)
Taking the derivatives, we get –
I (t) = dQ (t) / dt = C * [ dV(t) / dt ]
Symbol of Capacitor
There are different kinds of capacitor available. Different types of symbols are also there to represent them. Some of them are represented below using the diagrams. They are very useful to describe the circuit.
Different symbols to represent capacitor
A capacitor in a DC Circuit
Let us discuss a DC circuit where a capacitor and a resistor are kept in series with a constant voltage source – V0.
Let’s assume the capacitor was previously uncharged, and the opened switch is closed at time t0.
From Kirchhoff’s Voltage Law, we can write –
Vo = VR (t) + VC (t)
VR (t) is the voltage across resistor ‘R’ at time instant ‘t,’ and VC (t) is the measured voltage across the circuit’s capacitor at time instant t.
Vo = i (t) * R + (1/C) * [ ∫t0 t I(τ) dτ ]
Taking derivative on both sides, we get –
RC * [ di (t) / dt] + i(t) = 0
At time t, let say tis zero. The voltage of the resistor is Vo and of the capacitor is zero.
At that time, current would be – Io = Vo / R. Now solving the differential equations –
I (t) = (Vo /R) * e (-t / τ0)
V (t) = Vo (1 – e (-t / τ0))
τ0 = RC.
It refers to as the “Time constant” of the circuitry.
A capacitor in an AC Circuit
In an AC circuit, the capacitor produces impedance, which is the vector sum of resistance and reactance. Capacitor’s impedances and reactance is given by the following expressions.
The impedance depends inversely on capacitance. Increasing the capacitance and frequency causes a decrease in impedance and vice-versa.
Q factor:
Q Factor or Quality Factor of a capacitor is defined as the ratio of reactance to its resistance. The q factor is a measure of efficiency. The formula can be written as –
Q = Xc / R = 1 / ωCR
ω is the angular frequency, C is the capacitance of the capacitor, Xc is the reactance, and R is the equivalent resistance.
Capacitor in Series
The diagram represents the capacitors in the series connection. It shows that the separation distance is added up instead of the plate area. The series of the capacitance acts as a capacitor less than any of its components.
Series connection of capacitors
The equivalent capacitance of the given connection, is –
1/Ceq = ∑ 1 / Ci = 1 / C1 + 1 / C2 + … + 1 / Cn
Capacitors in Parallel
The diagram represents the capacitors in parallel connection. An equal amount of voltage is applied to every capacitor. Here the capacitances of the capacitors are added up. The connection of the capacitance acts as an adder.
Parallel connections of capacitors
The equivalent capacitance is –
Ceq = ∑ Ci = C1 + C2 + … + Cn
Capacitor Types
There is an enormous number of capacitor types, available in the market based on numerous classification parameters. Type of the dielectric material, the device packaging, and the plates’ structure are some of the determining factors to classify capacitor types.
Dielectric Material
Almost every capacitor types have a dielectric substance. Dielectric substances are placed in between two conductors, the charge capacity can be increased. It is best to have a high permittivity material or high breakdown voltage as a dielectric substance.
There are various dielectric materials available like – paper, plastic, mica, ceramic, glass, air, etc.
Based on dielectric materials, some capacitor types are –
There are also other types, some capacitor types are –
Voltage-dependent Capacitor
Frequency-dependent Capacitor
Parallel Plate Capacitor
Decoupling Capacitor
Applications of Capacitors
Capacitors are one of the essential devices which are required for almost every electrical circuit. It has numerous applications in various fields. Some of the most important are –
Energy Storage
A capacitor has the property of charging and discharging. It can store energy when it is disconnected from the charging source. Using this property, capacitors can be used as a battery or rechargeable battery.
Super-capacitors can accept and deliver charges faster than typical batteries and tolerate a more significant number of charging and discharging cycles than a standard rechargeable battery. But it is more extensive.
The quantity of charge stored in the dielectric layer is equal to or greater than the charge stockpiled in a plate of capacitor.
Pulsed power
Capacitors are used in pulsed power applications. Mainly groups of large, primarily constructed, high voltage, and low inductance capacitors are used here.
Banks of capacitors are also used in power supplies to produce smooth outputs in half-wave or full-wave rectifier. Reservoir capacitors can be used for charging up pump circuits.
Industrial Use
This helps to shunt away and hide fluctuations of current from the primary source to ensure a clean power supply for the control circuits. Audio circuits also use several capacitors.
Signal Coupling and Decoupling
Capacitors pass the AC signal but block the DC signals. That’s why capacitors are used in separating AC circuits. The process is recognized as – AC coupling or ‘capacitive coupling.’
A decoupling capacitor safeguards one area of the circuitry from other. They are used in power supply grounds. These are also known as a Bypass capacitor. Decoupling capacitors has applications in the biasing of transistors.
Memory
Dynamic digital memories for binary computers can be made using capacitors.
In this article we will discuss about photo diode detector as follows:
Definition of a photodetector
Different types
Circuit Diagram
Applications
What is a Photodiode
Features of a photodiode
Working principle
Avalanche photodiode
Circuit Diagram
Applications
Advantages & disadvantages
Phototransistor vs. photodiode
What is a Photo Detector?
Definition of a Photo Detector:
“Photodetectors are important elements, possess the ability to transform light into electrical signals.”
“Photodetectors are important elements useful in image processing, optical communication, security, and night vision and motion detection.”
Types of Photo Detectors:
Photo Detector Types
Important Applications of Photo Detectors:
Photo Detectors can be employed for properties like optical power, luminous flux measurements.
These are used in various types of optical-sensor and microscope design.
Photo detectors are essential for laser rangefinders.
Fast photodetectors are commonly utilized in optical-fiber communication, frequency metrology etc.
What is a Photo Diode?
Definition of a photodiode:
“A photodiode is basically a typically p-n junction diode.“
When a photon strikes the diode, it will excite electron and generates a moveable electron and a positive charge hole. The absorption happens in the junction’s depletion area, the carrier will removed from the junction by the depletion region’s built-in potential.
How does a photodiode work?
Working Principle of photodiode:
A photodiode is a p-n junction or a P-I-N configuration. If a photon strikes the diode, it produces the electron and a positively charged hole. When there’s any absorption happens in the juncture’s depletion area, these carriers have been trapped in the juncture from the built-in area of this depletion region that created a photocurrent.
Photodiodes are widely used under inverse biasing or without biasing. The light or photon can drive a current across this circuitry, which gives to the forward bias, which subsequently causes ‘Dark current’ from the reverse direction to the photocurrent. This is referred to as the natural effect and can be the foundation of solar cell design. A solar panel is just a combination of multiple effectual photodiodes.
Reverse bias produce minor current along exactly identical direction. Apart from that, the photodiode exhibits less noise.
Avalanche photodiodes have a similar prearrangement, but it’s normally operated with a greater reverse biasing. This enables every single photo-generated provider to be multiplied with avalanche breakdown, leading to photodiode’s internal effects and improves the device’s overall responsivity.
Materials for a photo diode:
Material used in photodiode:
Silicon
Germanium
Lead Sulfide
The materials used for the construction of photodiode is important to describing its properties because only photons with appropriate energy can excite electrons in bandgap and able to produce substantial photocurrents.
It is important to remember that, silicon-based photodiode have greater band-gap and because of this it is capable to produce less noise than germanium-based photodiodes.
Since transistors and ICs are prepared by semiconductor material too and comprise p-n junctions, may act like a photodiode. This is not the accepted, an opaque housing is mandatory to remove this effect. Though these is not entirely opaque towards high energy radiations, may still cause ICs to malfunction for induced photocurrent.
Applications of a Photo Diode:
Photodiodes are used in consumer electronic i.e., CD players, fire and smoke detectors, remote controls, lighting etc.
These are also employed in various medical applications, detector and high-energy physics etc.
Advantages and Disadvantages of a Photo Diode:
ADVANTAGES-
Low noise
Low cost
Compact and lightweight.
Long Lifetime
No high voltage is required.
High quantum efficiency.
DISADVANTAGES-
Small area
No internal gain
Much lower sensitivity
Response time is slower.
What are the characteristics of a Photo Diode?
There are two types of characteristics of photo diode
Shunt Resistance (RSH) is used to estimate the thermal noise when no reverse bias is applied. It’s the ratio of voltage to current.
It is computed from the slope of the photodiode’s V-I curve at the origin.
SERIES RESISTANCE
Series resistance is give by Rs and it comes from the resistances of silicon. The expression is given by the following equation –
JUNCTION CAPACITANCE, (Cj)
Junction Capacitance (Cj) is the capacitance of the diode at a given reverse bias.
The junction capacitance is proportionate to the diffusion area and inversely proportionate to the width of depletion area.
RISE AND FALL TIME ( tr , tf )
The time taken to reach Ninety percent from ten percent is known as Rise Time and the time taken to fall from Ninety percent to Ten percent is known as Fall time. This parameter commonly expressed in frequency response of 3dB decay as follows.
QE is extensively recognized as the percentage of the incident photons that contribute to the photocurrent.
QE=R obs/R Id (100%)
RESPONSIVITY, R
The responsivity of a silicon photodiode is the measurement of the sensitivity to light. It is given by the ratio of Ip to the coming power of light (P) for the given wavelength.
R=IP/P at specific wavelength
NON-UNIFORMITY
It is well-defined as the variations of responsivity witnessed over the active photodiode surface area with a trivial spots of light.
NON-LINEARITY
A silicon photodiode characteristic is linear in nature though minor change in current regulates photocurrent linearity.
Noises in a Photo Diode:
In a photodiode, two types of noises are introduced; they are
Shot Noise
Johnson Noise.
Shot Noise
It is expressed by the following equation.
Thermal Noise or Johnson Noise
The photodetector may produce Johnson noise because of the thermal generation of carrier. The magnitude of this generated current noise is:
Hence, the total noise is,
Explain Avalanche and Zener Mechanisms:
Avalanche breakdown happens only at the higher voltages. Assume the electric field (E) in the transition region is enormous. Then, an e– incoming from the P side may get accelerated with kinetic energy to collide with the lattice and produce ionization. The interactions will create carrier multiplication; the original electron and generated electron are swept to the N side, and the create hole is flounced to the P. This process is Avalanche since each incoming carrier be able to initiate the large number of carriers.
Zener effect happens once tunneling of electrons take place from the P-side valance band to N-side conduction band, may causes reverse current flow from N to P terminal. Basic inevitabilities for tunneling current are a large number of electrons that are detached from a substantial quantity of unoccupied state by a tinny barrier. Since the tunneling probability be governed by the barrier width, doping must be great.
· Electrical Symbol of digital-to-analog converter
· Types of digital-to-analog converter
· Applications of digital-to-analog converter
· Advantages and Disadvantages of Digital to Analog Converter (DAC)
Digital to Analog Converter (DAC)
A digital to analog converter is an electronic device that does a conversion operation. As the name suggests, it converts a digital input signal into an analog output signal. Digital signals such as digitized music can be converted into analog sounds using a digital to analog converter. It is one of the types of data converters.
A digital to analog converter is also known as DAC, d to a converter, dac converter, D / A converter, etc. An analog to digital converter (ADC) does the reverse operation. A DAC is required almost every time in the circuit whenever there is a need for ADC.
A digital to analog converter is an equipment working for digital to analog conversion. A digital signal is defined as the discrete in time and discrete in the amplitude signal. At the same time, an analog signal is defined as the time-continuous and continuous amplitude signal. A DAC covert a fixed-point binary number (abstract adequate precision number) into a physical measurement.
The transformation has several steps in it. A typical digital to analog converter converts abstract data into conceptual sequences of impulses. Then the series is processed using a reconstruction filter.
A digital to analog converter works based on the Nyquist-Shannon sampling theorem. It states that – an input signal can be recovered from its sampled output if the sampling rate is twice greater than or equal to the highest frequency component present in the input signal.
There are several parameters to measure the performance of a digital to analog converter. The bandwidth of the output signal, the signal to noise ratio are some of the parameters.
Electrical Symbol of a DAC
The below symbol represents a digital to analog converter.
Symbol of Digital to analog converter
Types of digital to analog converters
The conversion of digital input bits into analog signals can be achieved through different processes. Let’s discuss some of the types –
A. DAC using the weighted resistors method
Let’s get started with a 4-bit digital number. We will convert it into analog. Let the digital number – B3B2B1B0
The decimal equivalent will be – N = 23B3+22B2+21B2+20B0
Here B3 is the most significant digit (MSB) whereas, the B0 is the least significant digit (LSB). The circuit here operates to produce an analog output signal weighted according to the bit positions and add them together.
In the circuit, logic voltages, which represents the binary input, is applied to the corresponding resistors using switches. The resistors of the circuits (except feedback resistor Rf) are connected in a weighted way so that the successive ratio is 2. That is – R0 / R1 = R1 / R2 = R2 / R3 = 2. The resistors are also inversely proportional to their numerical significance of the appropriate binary bit.
When the binary bit is zero (0), the switch is turned ON and connected to the ground. If the binary bit is one (1), the controller is closed and connected to the reference voltage VR.
The current i which will be supplied to the non-inverting terminal is –
Substituting the values of R0, R1, R2, R3 we get –
i = (VR / R) * (23B3+22B2+21B2+20B0 )
Since G is virtual ground, the output voltage vo =
Vo = -i * Rf = – ( VR / R ) * Rf * ( 23B3+22B2+21B2+20B0 )
Now we can observe that the output voltage is proportionate to the numerical value of the binary digits.
The DAC accuracy depends on the resistor’s ratios and their ability to track each other when the temperature varies.
This type of digital to analog converters has some disadvantages. It requires a wide range of resistors to construct the converter if the binary input consists of a large number of bits. The R-2R ladder type converter overcomes this disadvantage.
B. R – 2R Ladder Type DAC
A ladder of resistances can convert a binary word into analog. This type of DACs is known as R – 2R Ladder-type converters.
R – 2 R Ladder Type Digital to analogue conversion. Image source – Wiki Analog
To understand the circuit’s operation, let us assume that the terminal B0 is connected to VR, and the rest of the terminals (B1, B2, B3) are connected to the ground. The resulting figure is shown in the circuit –
We apply Thevenin’s theorem to the nodes a0, a1, a2, a3 concerning ground. We get the Thevenin’s equivalent circuit, which is further shown in the below course –
The equivalent source has a voltage of VR/16 in series with a resistance 3R.
Again, if the terminal B1 is connected to Vr and the terminals B0, B2, B3 are connected to the ground, then applying Thevenin’s theorem also, it can be shown that the source has a voltage VR /8 in series with a resistance 3R.
Similarly, when B2 is connected with VR and rest inputs are connected to the ground, we will find that the Thevenin’s equivalent circuit has a source voltage of VR / 4 in series with a resistance 3R.
Same for B3’s connection with VR. The equivalent circuit gives the source voltage as VR / 2 and the series resistance of 3R.
The current i obtained by the principle of superposition –
i = ( Vr / 3R ) * ( B0/16 + B1/8 + B2/4 + B3/2 )
Since G is virtual ground, the output voltage vo =
Here and now we can realize that the output voltage is proportionate to the numerical value of the binary digits. This circuit can easily convert large binary digits as it is easily extensible. All we need to add is additional switches and extra resistors for the ladder.
One of the vital features of a digital to analog converter is that the circuit’s smallest change defines its resolution.
Applications of digital to analog converter
The modern era has a high demand for digitized data. That is why there is an increasing demand for an analog to digital converter. But we have to keep in mind that we use analog signals in our day-to-day life, and the world is analog. So, whenever we need an analog to digital converter, we need a digital to analog converter. Both DACs and ADCs have contributed most to the digital revolution.
Let us take a real-world example to understand their need. Consider a telephone call. At first, the caller starts speaking. The speech is an analog signal, which is changed into a digital signal using an analog to digital converter or ADC. When the digitized signal is transported to the receiver’s end, it again needs to be converted into an analog signal; otherwise, the receiver will not understand the sent data. Here a digital to analog converter serves the purpose.
Audio Processing:
Music and other audios are stored in digitized format in today’s era of digitalization. When we need to hear them in speakers or headphones, then the digitized form must be converted into an analog signal. That is why DACs are found in every device which can play music like – MP3 Music player, DVD player, CD player, Laptops, Mobile Phones, etc.
High-end hi-fi systems use specialized standalone DACs. Similar DACs are found in modern digital speakers such as USB speakers, sound cards, etc.
In voice over IP communications, the source is digitized. Thus a DAC is needed to reconstruct the digitized part into an analog signal.
Video Encoding:
The video encoder system processes a video signal and sends digital signals to ICs.
Digital Display:
The graphic controller typically uses a lookup table to generate signals sent to analog outputs such as RGB signals to drive the display.
Calibration:
A digital to analog converter can provide calibration of dynamic types to increase the test system’s accuracy.
Controlling Motor:
Digital to analog converters are also used in motor control devices where the voltage control signal is required.
DACs are also used in data distribution systems, digital potentiometer, software radio, and many other places.
Advantages and Disadvantages of Digital to Analog Converter (DAC)
Advantages of DAC
As mentioned earlier a digital to analog converter is as important as an Analofg to digital converter, it has too several points to discuss. Every electrical and electronic device has both its advantages and disadvantages. DACs are no exception. Some of its benefits are –
Large digital – binary inputs can be converted into its analog form easily.
· Working Principle of an analog to digital converter
· Electrical Symbol of analog to digital converter
· Types of analog-to-digital converter & Explanations
· Applications of analog to digital converter
· Testing of an analog-to-digital converter
· An ADC IC
Definition & Overview of Analog-to-digital Converter
An analog to digital converter is an electronic device. As the name predicts, the supplied analog signal is converted into a digital signal which is produced at output.Analog signals such as voice recorded by a microphone can be converted into a digital signal using an analog-to-digital converter.
An analog to digital converter is also known as ADC and A to D converter, etc.
Working of an Analog to digital converter
An analog signal is defined as the time-continuous and continuous-amplitude signal. At the same time, a digital signal is defined as the discrete-time and discrete-amplitude signal. An analog signal is converted into a digital signal with the help of an analog-to-digital converter. The transformation has several steps, like sampling, quantization, and others. The process is not continuous; instead, it is periodic and limits the input signal’s allowable bandwidth.
An analog-to-digital converter works based on the Nyquist-Shannon Sampling Theorem. It states that – an input signal can be recovered from its sampled output if the sampling rate is twice greater than or equal to the highest frequency component present in the input signal.
There are several parameters to measure the performance of an analog to digital converter. The bandwidth of the output signal, the signal to noise ratio are some of the parameters.
Electrical Symbol of an ADC
The below symbol represents an Analog to digital converter (ADC).
Types of Analog to digital converters
The conversion of input analog signals into digital signals can be achieved through different processes. Let’s discuss some of the types in detail –
A. Flash ADC
Flash ADC is known as direct-conversion type’s analog to digital converter. It is one of the fastest types of analog-to-digital converters. It comprises a series of comparators with the inverting terminals connected to a voltage divider ladder and the non-inverting terminals connected to the analog input signal.
As the circuit shows, a ladder of well-matched resistors is connected with a reference or threshold voltage. A comparator is used at each tap of the resistors’ ladder. Then there is an amplification stage, and after that, the code is generated as binary values (0 and 1). An amplifier is also used. The amplifier amplifies the voltage difference from the comparators and also suppresses the comparator offset.
If the measured voltage is above the threshold voltage, then the binary output will be one, and if the measured voltage is less than the binary work will be 0.
Recently improved ADCs are modified with digital error corrections systems, offset calibrations, and also, they are a smaller size. ADCs are now available in integrated circuits (ICs).
This type of analog-to-digital converters has a high sampling rate. Thus, it has applications in high-frequency devices. Detection using radars, wide-band radios, various testing equipment are some of them. NAND Flash memory also uses flash type analog-to-digital converters to store up to 3 bits in a cell.
Flash type ADCs are fastest in operation speed, simple in circuitries, and conversion coincides instead of sequentially. Though, these requires considerable numbers of comparisons than different types of ADCs.
Successive approximation type ADC is another type of analog-to-digital converter which uses binary search through quantization levels before conversion into the digital domain.
The whole process is divided into different sub-processes. There is an ample and hold circuit, which takes the analog input, Vin. Then there is a comparator that compares the input analog voltage with the internal digital-to-analog converter. There is also a successive-approximation register (SAR), which takes input as clock pulse and comparator data.
The SAR is primarily initialized to make the MSB (most significant bit) as logic high or 1. This code is supplied to the digital-to-analog converter, which further provides the analog equivalent to the comparator circuit compared to the sampled analog input signal. If the voltage is more than the input voltage, then the comparator resets the bit. Else the bit is left as it is. After that, the next bit is set to a digital one, and the whole process is again done until every bit of the successive-approximation register is tested. The final output is the digital version of the analog input signal.
There are two types of successive-approximation types analog-to-digital converters available. They are – Counter type and Servo tracking type.
These types of ADCs give the most accurate results than other types of ADC.
As the name implies, this type of ADCs converts continuous-time and continuous amplitude input analog signal into a digital signal using an integrator (an integrator) to apply an operational amplifier that takes a usual input signal and gives time-integrated output signal).
An unidentified analog input voltage is applied at the input terminal and allowed to ramp for a certain period, known as the run-up period. A pre-determined reference voltage of opposite polarity is then applied to the integrator circuit. That is also allowed to ramp until and unless the integrator gives the output as zero. This time is known as the run-down period.
The run-down time is generally measured in units of the ADC’s clock. So, longer integration time results in higher resolution. The speed of this type of converter can be improved by compromising with the solution.
As the speed and resolution are inversely proportional, this type of converters does not find digital signal processing or audio processing applications. Preferably, they are used in digital measurement meters (ammeters, voltmeters, etc.) and other instruments where high accuracy is crucial.
This type of ADCs has two kinds – charge balancing analog to digital converter and Dual-slope ADC.
– D. H. Wilkinson first designed this type of analog-to-digital converter in the year 1950.
At first, capacitor gets charged. A comparator checks this condition. After getting to that specified level, now the capacitor starts discharging linearly, producing a ramp signal. A gate pulse is also initiated in the meantime. The gate pulse remains on for the rest of the time while the capacitor discharges. This gate pulse further operates a linear gate which further receives input from an oscillator clock of high-frequency. Now, when the gate pulse is ON, several clock pulses are being counted by the address register.
E. Time Stretch Analog to Digital Converter (TS – ADC):
This type of Analog-to-digital converter are functioned on a combined technology of electronics and other techs.
It can digitalize a very high bandwidth signal that cannot be done using an ordinary ADC. This is often termed as “Photonic Time Stretch Digitizer”.
It not only analog to digital but also used for high-throughput real-time equipment such as imaging and spectroscopy.
There are several other types of other analog-to-digital converters.
The analog to digital converter is one of the most important electronic devices in this modern era. This is an era of digitalization, but our world is analog in real-time. Converting analog data in the digital domain is the need of this hour. That is why they are so important. Some of the significant applications of an ADC are –
A. Digital signal processing
– Analog to digital converters are essential for editing, modifying, processing, storing, and transporting data from the analog field to the digital area. Microcontrollers, digital oscilloscopes, and critical software find applications in this domain. Devices like digital oscilloscopes can store waveforms for later use, whereas an analog oscilloscope cannot.
B. Microcontrollers
– Microcontrollers makes a device smart. At present, almost all microcontrollers have analog to digital converters inside them. The most common example may be the Arduino. (It is built on an ATMega328p microcontroller) The Arduino provides a useful function of ‘analogRead(),’ which takes analog input signals and returns digital data generated by the ADC.
C. Scientific Instruments
– ADCs are useful for making various necessary electronics instruments and systems. Digital imaging for the digitization of pixels, radar technologies, and many remote sensing systems is an example. Devices like sensors produce an analog signal for measuring temperature, light intensity, light sensitivity, air humidity, air pressure, pH of a solution, etc. All these analog inputs are converted by ADC to generate a proportionate digital output.
D. Audio Processing:
-ADC has a vital application in the field of audio processing. The digitization of music enhances music quality. Analog voices are recorded via microphones. Then they are stored in digital platforms using an ADC. Many tunes recording studios record in PCM or DSD formats and then down sampled for digital audio productions. They are used for broadcast on televisions and radios.
Testing of an analog to digital converter
To test an analog-to-digital converter, first of all, we need an analog input voltage source and electronics equipment to send and control signals and receive the digital output data. Some of the ADCs also requires a source of reference signals. There are some parameters to test an ADC.
Some of them are –
Signal to noise ratio (SNR),
Total harmonic distortion (THD),
Integral nonlinearity (INL),
DC offset error,
DC gain error,
Power Dissipation, etc.
ADC IC
ADCs are commercially available as ICs in the market. Some of the commonly used ADC ICs are ADC0808, ADC0804, MPC3008, etc. They find applications in devices like Rasberry pi and other processors or digital electronics circuits where an ADC is needed.
In this article we will learn about PN junction diode and it’s characteristics as follows:
What is PN junction diode ?
Definition of PN junction diode:
Working Principle of PN junction diode
Properties of PN junction diode
Circuit and symbol of PN junction diode
Equivalent Circuit of PN junction diode:
PN junction Current flows
Ideal current-voltage relationship
PN junction Characteristics
Diode quasi-fermi levels
Applications of PN junction Diode
What is a PN junction diode?
Definition of PN junction diode:
“A pn junction diode is two-terminal or two-electrode semiconductor device.“
“A diode is called as P-N junction diode if it is formed by P-type on one side and N-type on the supplementary one or reverse direction.”
“The diode has to be in forward biased condition to permit the electric current flow. through it.“
If a positive voltage is connected to the P terminals, the current then pass through from the P to N region as positive voltage helps to cross the depletion region. When we use a negative voltage is applied to the p-type, the depletion zone increases and prevents the current from flowing.
How does a PN junction Diode work?
PN junction diode
Working Principle of PN junction diode:
In a PN junction Diode, we will consider the p-n junction with a forward-bias voltage employed. We can determine the current-voltage characteristics. The potential barrier of this p-n junction is reduced when a forward-bias voltage is applied to it. It will allow e- and hole to leak through the space charge region.
When holes begin passing through the p region throughout the space charge area, they get excess minority carrier namely, hole and extra minority carrier from drift, recombination and diffusion process.
Likewise, when electrons in the region initiate flowing through the space charge region to P. They get surplus minority carrier electrons.
When semiconductor apparatus with p-n junctions are employed in linear amplifiers, as an instance, time-varying signs are overlaid on the dc currents and voltages. A tiny sinusoidal voltage apply to on a dc voltage applied across a p-n junction will initiate a small-signal current.
The proportion of the current to voltage generate the small-signal admittance of this p-n intersection. The admittance of a forward-biased p-n intersection includes both the conductance and capacitance parameters.
What is the PN junction current?
When a forward-biased voltage is applied to a p-n junction, a current gets generated in the device. That is known as P-N junction current.
Define the ideal current-voltage relationship:
Ideal PN junction current:
The ideal current at a p-n intersection relies on the important components of the fourth principle mentioned previous section. The total current at the intersection is the summation of these electrons and hole currents, that stay steady through the depletion area.
The gradients from the minority carrier concentrations create diffusion currents, and because we’re considering that the electrical field to be ‘0’ at the space-charge edge, we can ignore drift current for minority in this approach.
Equivalent Circuit of PN junction diode:
The small-signal equivalent circuit of the forward-biased p-n junction is derived from an equation.
Y =gd+ Jωcd
Equivalent Circuit of P-N junction diode
It is required to add the junction capacitance in parallel to the diffusion resistance (rd) and diffusion capacitance. The last element for the equivalent circuit is a series of resistance. The neutral n and p regions have a ‘C’ numbers pf resistances, so the actual p-n junction includes a series resistance which complete equivalent circuit is represented in above Figure.
Forward-biased I-V characteristics for p-n junction diode with the effect of series resistance
The above figure is V-I characteristics that reveals the impact of the series resistance. A voltage, that can be greater in general, is needed to find the exact same present value when a streak of immunity is included. In the majority of the diodes, the show resistance will probably be negligible.
In certain semiconductor apparatus with p-n junctions, but the series resistance will belong into some feedback loop.
Reverse Biased Recombination Current:
If a PN junction diode is in reverse biasing, It was learnt that mobile holes and electrons were wiped from the space-charge section. The negative signal explains a negative recombination rate; therefore, we’re actually generating electron-hole pairs inside the reverse-biased space charge region.
The recombination of excess holes and electrons at the procedure during the attempt to re-establish the thermal balance. Considering that the concentration of holes and electrons is essentially zero at the reverse-bias area, holes and electrons become generated through the trap level, which also attempts to revive the thermal balance.
Since the holes and electrons are generated, they are trapped from the space-charge area by the electrical field. The flow of charge is at the current direction of a reverse-biasing. This reverse-bias production current, which is principally a result of the creation of holes and electrons at the space-charge region, is added to the reverse-bias ideal saturation current.
Forward Biased Recombination Current:
For a reverse-biased PN junction, electrons and holes are cleared up mostly from the Space charge region. Under forward bias, however, electrons and holes are injected across the space charge region; during that some extra carrier charges may be at the space charge region.
There are certain possibility exists that some of these electrons and holes will recombine also during that time.
“A diode is a special electronic element with two electrodes termed as the Anode and the Cathode”.
Different types of diodes
Most of the diodes are made of semiconductors such as silicon, germanium, or selenium.
How does a Diode function?
Working Principle of diode:
The basic characteristics of a diode is to carry electric current in only one direction. If the cathode is negatively charged at a voltage greater than the anode, a certain current called ‘forward break over’ starts flowing through it.
When the cathode is +ve charged in respect of the anode, it will not conduct any current. These can be operated as a rectifiers, switches and limiters.
The forward break over voltage is approximately 0.6 Volt for silicon, 0.3 Volt for germanium and 1 Volt for selenium material respectively.
At the forward break over point, if an analog signal flow through the diode the signal waveform is inaccurate and distorting. All the signals that get generated are harmonic and integral multiples if the input frequency. These generally produce signals at microwave frequency with the correct level and polarity of voltage application.
Symbol of Diode:
Diode Symbol
Important features of Diodes:
Diode is a two terminal electronic component
It has lower resistance in one direction and higher in another direction
Most of the diodes are made of silicon
The voltage drop under a forward bias condition is 0.7 volts approximately.
In the reverse biasing the region of depletion layer, will increase.
Different types of diode:
1. P-N junction diode –
“A diode is a P-N junction with P-type on one side and N-type on the other side”.
2. Light Emitting Diode (LED) –
“LED is a semiconductor light source that emits light when current flows through it”.
3. Photo Diode –
“This is a semiconductor-based P-N junction diode, if exposed to light produce a potential difference”
4. Schottky Diode –
“This is designed by the junction of a semiconductor with a metal. Sometime known as hot carrier diode”.
5. Tunnel Diode –
“ A semiconductor diode that has effectively negative resistance due to the tunnelling”.
6. Varactor diode –
“A diode with changing internal capacitance with the changes of the reverse voltage”.
7. Zener Diode –
“A special type of diode, designed to allow current to carry backwards when a reverse voltage is applied”.
What are the Ideal Diodes?
In an ideal diode, when it is in forward bias the current starts flowing freely from the device. In an ideal one usually without voltage drop when forward biased. All the other voltage sources are dropped across the circuit resistors. When reverse biased, in an ideal diode there is zero current flow and will have infinite resistance.
What are Practical Diodes?
In a practical diode, some of the resistances allow the current to flow if forward bias. Due to the presence of the resistances, some power is dissipated when the current starts flowing through the forward biased. When it’s in reverse biased, due to the high resistance it can conduct.
A diode is normally is P-N junction.
It is a barrier potential. To overcome this problem by applying an extra voltage to the p-n junction, it can be able to conduct.
So current will pass through p-n junction when the barrier potential is omitted.
It is with two metallic conducts is known as p-n junction.
The process of external voltage applying is channel biasing.
If voltage is applied to p-n junction diodes –ve terminal is connected to the p-type semiconductor. Similarly, +ve terminal is connected to the n-type.
Holes from p-side are attracted towards the -ve terminal. Whereas the free electrons from n-side are attracted towards +ve terminal.
The reverse bias increases in steps and diode current is observed.
When the reverse bias increases VBR the diode reverse current increases very shortly.
Switching property of diodes:
In forward bias when a small voltage is applied the diode conducts which exceeds the cut in voltage known as on-state.
In reverse bias only small voltage current sources with reverse applied voltage that is less than the breakdown value is known as off-state
In switching property of a diode is switched from forward bias on-state to reverse bias off-state or vice versa.
Applications of a diodes
Rectification:
A diode is usually acting as a rectifier, flattening an AC power source into a constant power supply. This can achieve this task by obstructive the flow in one direction and pass through the other direction.
Light emission:
LED provides a much more efficient source of light. The bulbs are cost more than their incandescent counterparts, in part because they require additional control circuitry to work with AC power.
Inductive Load Dissipation:
Diodes are used in this application, when an inductive load is switched off, the energy it has stored must go somewhere. Without the proper circuit protection, the stored energy can lead to voltage spikes that can arc across the switch and potentially overload a transistor this configuration allows the current to dissipate across the inductor and it feeds back into the power supply and protects the circuit.
Sensing and Control:
Semiconductors can easily generate electrical charges based on the optical effects. In general, these devices are packaged in such a way that it blocks out light to avoid unintended electrical activity. Photodiodes are built to optimize this effect. These photodiodes are often used in the infrared spectrum, such as inside consumer remote controls.
