Electronics

List of Topics

• Rectification & Rectifier
• Types of Rectifier
• Bridge Rectifier
• Bridge Rectifier Circuit and Diagram
• Working of a bridge rectifier
• Differences between Bridge Rectifier and Full Wave Rectifier
• Mathematical problems

Rectification

Rectification: The process through which AC voltage is converted into Dc voltage is known as the rectification. Rectifier is the electronics device to perform the rectification

Types of Rectifiers

Rectifiers are mainly three types. They are –

1. Half-Wave Rectifiers (HWR)
2. Full-Wave Rectifiers (FWR)
3. Bridge Rectifier (BR)

Bridge Rectifiers

Bridge rectifiers are kind of rectifiers that converts ac to dc that is alternating current to direct current. This type of rectifier allows both halves of the ac input voltage to pass through the circuit. Four diodes are necessary to make a bridge rectifier.

Bridge Rectifiers Working & Circuit

A bridge rectifier is shown in the below circuit.

Full-wave rectification can also be implemented with the help of a rectifiers, which includes four diodes. As shown in the circuit, two diodes of the opposite arms conduct current simultaneously while the other two diodes remained in OFF state. For Now, the current flows through the diode D1 and D3 but no current flows through the D2 and D4 diodes. This happens because of the instantaneous polarity of the secondary windings of the transformer.  A current I thus pass through the load resistance RL in the shown direction.

Now, the next half of the cycle comes. This time the transformer’s polarity changes. Current flows through the Diode D2 and diode D4 and no current flows through the diodes D1 and D3. The direction of flow of current remains the same as the previous half of the cycle.

Know about How a Transformer works!

Bridge Rectifier Formula and Equations

From the standard Bridge rectifier circuit,

Vi is the input voltage; Vb is the diode voltage, rd is the dynamic resistance, R is the load resistance, Vo is the output voltage.

Average O/p voltage:

V_o = V_mSinωt; 0 ≤ ωt ≤ π

V_av = 1/π * ∫₀^2πVo d(ωt)

Or, V_av = 1/π * ∫₀^2πV_mSinωt d(ωt)

Or, V_av = (V_m/π) [- Cosωt]₀^π

Or, V_av = (V_m / π) * [-(-1) – (-(1))]

Or, V_av = (V_m/ π) * 2

Or, V_av = 2V_m / π = 0.64 V_m

The average load current (I_av) = 2* I_m/π

The RMS (Root Means Square) Value of current:

I_rms = [1/π * ∫ ₀ ^2π I²  d(ωt)]^1/2

I = I_mSinωt; 0 ≤ ωt ≤ π

Or, I_rms = [1/π * ∫ ₀ ^2π I_m²  Sin²ωt d(ωt)]^1/2

Or, I_rms = [I_m²/π *∫ ₀ ^2π Sin²ωt d(ωt)]^1/2

Now, Sin²ωt = ½ (1 – Cos2ωt)

Or, I_rms = [I_m²/π *∫ ₀ ^2π (1 – Cos2ωt)d(ωt)]^1/2

Or, I_rms = [I_m²/2] ^½   Or, I_rms = I_m/√2

The RMS voltage = V_rms = V_m/√2.

The significance of the RMS value is that it is equivalent to DC Value.

Provided that RMS value is ≤ Peak Value

Peak Inverse Voltage (PIV):

Peak inverse voltage or PIV is referred to as the maximum permissible voltage that can be applied to a diode before its breakdown.

Peak inverse voltage of a bridge rectifier is calculated as PIV >= V_m

Applying greater voltage than the peak inverse voltage will damage the diode and effect other circuit elements if associated.

Bridge Rectifier graph

The following graph shows the input output signal of a bridge rectifier. It is same as Bridge Rectifier.

Form Factor

The form factor of a bridge rectifier is the same as a full-wave rectifier and is defined as the ratio of RMS (Root Means Square) Value of load voltage to the average value load Voltage.

Form Factor = V_rms / V_av

V_rms = V_m/2

V_av = V_m / π

Form Factor = (V_m/√2) / (2*V_m/ π) = π/2√2=1.11

So, we can write, V_rms = 1.11 * _Vav.

Ripple Factor

Ripple factor of a bridge rectifier is the percentage of Alternating Current component present in the output of the bridge rectifier.

The ‘γ’ represents the ripple factor.

I_o = I_ac + I_dc

Or, I_ac = I_o – I_dc

Or, I_ac = [1/(2π) * ∫₀^2π(I-Idc)²d(ωt)]^1/2

Or, I_ac = [I_rms² + I_dc²– 2 I_dc²]1/2

Or, I_ac = [I_rms² – I_dc²]1/2

So, Ripple factor,

γ = I_rms² – I_dc² / I_dc²

or, γ = [(I_rms² – I_dc²) – 1] ^1/2

γ_FWR = 0.482

Transformer Utilization Factor

The ratio of DC power to the rated AC power is known as the Transformer utilization factor or TUF.

TUF = P_dc/ P_ac(rated)

V_s / √2 is the voltage rated for the secondary winding and I_m/2 is the current flowing through the winding.

So, TUF = I_dc² R_L / (V_s/ √2) * (I_m / √2)

TUF = (2I_m/ π)²R_L / ( I_m² (R_f +R_L)/(2√2) = 2√2/ π ² * (1 / (1 + R_f/R_L))

If R_f << R_L, then,

TUF = 8 / π ² = 0.812

The more the TUF, the better the performance.

Bridge Rectifier Efficiency

Efficiency of bridge rectifier is defined as the ratio of the DC power supplied at the load to the input AC power. It is represented by the symbol – η

η = P_load / P_in *100

or, η = I_dc² * R/ I_rms² * R , as P = VI, & V= IR

Now, I_rms = I_m/√2 and I_dc = 2*I_m/π

So, η = (4I_m²/ π²) / (I_m²/2)

η = 8 / π² * 100% = 81.2%

Efficiency of an ideal Bridge Rectifier Circuit is = 81.2%

Specify Difference Between Bridge and Full Wave Rectifier

Some Problems with Bridge Rectifiers

1. A bridge rectifier has a load of 1 kilo- ohm. The applied AC voltage is 220 V (RMS value). If the diodes’ internal resistances are neglected, what will be ripple voltage across the load resistance?

a. 0.542 V

b. 0.585 V

c. 0.919 V

d. 0.945 V

The ripple voltage is = γ * Vdc / 100

Vdc = 0.636 * Vrms * √2 = 0.636*220*√2 = 198 V.

The ripple factor of an ideal full-wave rectifier is 0.482

Hence the ripple voltage = 0.482*198/100 = 0.945 V

2. If the peak voltage of a bridge rectifier circuit is 10 V and the diode is silicon diode, what will be the peak inverse voltage on the diode?

Peak inverse voltage is an important parameter defined as the maximum reverse bias voltage applied across the diode before entering the breakdown region. If the peak inverse voltage rating is less than the value, then breakdown may occur. For a full-wave rectifier, the diode’s peak inverse voltage is the same as the peak voltage = Vm. So, peak inverse voltage =5 volts.

3. A input of 100Sin 100 πt volt is applied to a full-wave rectifier. What is the output ripple frequency?

V= V_mSinωt

Here, ω= 100

Frequency is given as – ω/2 = 100/2 = 50 Hz.

Thus, the output frequency = 50*2 = 100 Hz.

4. What is the main application of a rectifier? Which device does the opposite operation?

A rectifier transforms the AC voltage to the DC voltage. An oscillator converts a DC voltage to AC voltage.

5. For a bridge rectifier, the input voltage applied is 20Sin100 π t. What will be the average output voltage?

Now we know that, V= V_mSinωt

V_m = 20

So, the output voltage = 2V_m / π = 2*20 / π = 12.73 volts

The output voltage is = 12.73 volts.

• What is a Voltage regulator
• Types of a voltage regulator
• Voltage regulator Circuit
• Zener Diode as a voltage regulator
• Difference between series regulator & shunt regulator
• Series regulator
• Shunt regulator
• Regulated power supply
• The function of the voltage regulator
• Percentage regulation
• Applications of a voltage regulator

Definition of voltage regulator:

“A voltage regulator is a DC regulator that offers a constant DC output voltage that is fundamentally independent of applied input voltage, output load current, and temperature.”

Also, the regulator output can be changed as per the requirement. Hence, the function of a voltage regulator is two-fold 1. The output voltage can be regulated at the desired level. 2. The regulated voltage at the output can be maintained constant despite disturbances in supply voltage or change in load.

Voltage Regulator Types:

• The Zener Diode Based Shunt Regulators
• The Transistor Based Shunt Regulators
• The Transistor Series Regulators
• The Transistor Current Regulators
• The Transistor Controlled Series Regulators
• The Op-amp based Shunt Regulators
• The Op-amp based Series Regulators
• The Switching Voltage Integrated Circuit Regulators
• The Monolithic Regulators

Voltage Regulator Circuit:

The following figure refer to the Zener diode of a regulator.

The input current, I_S=V_S-V_Z/R_S

Where V_S= d.c input voltage to the regulator circuit V_Z= Zener voltage

The voltage across Zener diode terminals,

V_L=V_Z + I_Z r_z

V_L=V_Z (I_tr_z is negligible)

I_L=V_L/R_L

Input current, I_S=I_Z + I_L or I_Z= I_S – I_L

Zener Diode as Voltage Regulator:

In this circuit, a Zener diode is joined in reverse biased parallel with a variable voltage source supply. The Zener diode in this circuit will operate when the voltage at the reverse breakdown voltage. Then, the diode’s relatively low impedance retains the voltage.

This is a typical voltage regulation circuit with an input voltage, V_IN. This voltage is regulated down to a stable output voltage, namely V_OUT. The breakdown diode voltage is stable over a wide current range and maintains V_OUT at relatively constant even though the relative voltage may fluctuate during this operation.

As per Ohm’s law diode current, flowing through the diode, a load is placed across the diode, and as long as the Zener diode operates in a reverse breakdown, the diode will deliver a stable voltage to the load. Zener diodes in this stage are often used as a stable regulator for more advanced circuitry.

Series Regulator Circuit:

The basic block diagram of the series regulator circuit is shown below. The control element is connected in series with the load in between i/p and o/p terminal. The sampling circuit detects the variation in the output voltage. The comparator circuit will compare sample voltage with a reference one. The control element will compensate during that period and will retain a constant output. The control element conducts more when V₀ reduces and conducts less when V₀ increases.

Here a simple series regulator is presented. Transistor Q is the controlling element that is in series. The Zener diode provides the reference voltage.

Shunt Regulator Circuit:

In the linear voltage regulator category, in the shunt regulator circuit, the output is monitored, and the feedback signal initiates changes in input signals to maintain the desired output. However, in series regulators, the control unit or regulating unit is in series, and in shunt regulators, the control unit is in the shunt. The basic block diagram is shown below,

In the case of shunt regulators, as the control element is in shunt, it conducts more to provide regulation by shunting current away from the load.

What is Regulated Power Supply?

A regulated power supply is a stand-alone unit. It is able to supply a stable voltage to a circuit. This has to be operated within specific power supply limits. The regulated power supply output might be alternating or unidirectional but it is nearly a DC in standard operation.

The type of stabilization be limited to confirm that the output remains within absolute limits under a number of load condition.

The specification parameters are:

• The Input Voltage parameter
• The Output Voltage parameter
• The Output Current parameter
• Stability factor
• Ripple factor
• The Stored Energy
• The Pulsed operations
• The Load Regulation
• The Line regulation
• The Dynamic Regulation
• The Efficiency.

Comparison between Shunt and Series Regulator

What is the function of a Voltage Regulator?

A voltage regulator is to provide a constant DC output which is independent of the input voltage, output load current, and the temperature. It is an important component of a power supply circuitry. Its input voltage supplied from the rectifier circuit. The low capacity (500VA) regulators are in general used for domestic applications, for television, refrigerator, air-conditioner, etc. and for necessary equipment like computers. In these medical instruments, the sudden changes in voltages can affect the equipment leading to erroneous results and may get damaged ultimately.

What is the Percentage Regulation?

The basic performance measures for a regulator are line regulation and load regulation parameter. The line regulation is defined as the change in percentage of the output voltage for a given change in the input voltage as explains follows:

Uses of Voltage Regulators:

• Voltage Regulators is used in low output voltage switching power supply circuits.
• It is used in error amplifiers design.
• In design of the current source and  the sink circuits
• These are used for voltage monitoring and maintenances.
• It is used to design the Precision current limiter circuitry. It is applied in Analog and Digital Circuits for precision reference.
• It is used in adjustable voltage or current linear circuitry etc.

Rectification

Rectification is the electrical process to convert an alternating current (or voltage) to direct current (or voltage).

A rectifier is a device that has a low resistance to current in one direction and higher resistance in another order.

Types of Rectifier

Rectifiers can be classified into three types –

1. Half Wave Rectifier
2. Full Wave Rectifier
3. Bridge Rectifier

Full Wave Rectifier

Full-wave rectifiers are kind of rectifiers that converts ac to dc that is alternating current to direct current. This type of rectifier allows both halves of the ac input voltage to pass through the circuit. Two diodes are necessary to make a full-wave rectifier.

Full Wave Rectifier Working & Circuit

A full-wave rectifier is shown in the below circuit.

There is a transformer T on the input side. The transformer T steps up or steps down the AC voltage supplied at the primary side. It is a center-tapped transformer. An ac input voltage of V = nV_oSinwt is applied in the circuit. N is the turn ratio of the center-tapped transformer. Two diodes are connected to the course. Current flows through one diode for the first half of the cycle and flows through the other diode for the next half of the process. That is how a unidirectional current flow towards the load.

This is a modified and also an improved version of the half-wave rectifier. We use a center-tapped transformer. Each half of the transformer’s secondary has an equal number of turns; the voltage induced in each half of the secondary is equal in values and opposite in phase.

Now for any instance of the input half-cycle, point A has a positive voltage concerning O (center). The lower point B has an equal voltage but negative in magnitude (It is the center-tapped transformer). So, diode D1 conducts current, and diode D2 does not appear at this half of the cycle. For the next half of the process, diode D1 is at revere biased, and diode D2 is forward biased. So, diode D1 does not conduct the current while D2 does for this half of the input cycle. The load current is the sum of current from diode D1 and diode D2 from both the input voltage cycles.

Diodes D1 and D2 are identical, so the average value of load current for a full-wave rectifier circuit is double that of a half-wave rectifier.

As both halves of the cycle passed through the circuit, this is known as a Half wave rectifier. 

How a transformer works? Click to Know!

Full Wave Rectifier Formula & Equations

From the circuit,

Vi is the input voltage; Vb is the diode voltage, rd is the dynamic resistance, R is the load resistance, Vo is the output voltage.

Average O/p voltage:

V_o = V_mSinωt; 0 ≤ ωt ≤ π

V_av = 1/π * ∫ ₀ ^2π Vo d(wt)

Or, V_av = 1/ π * ∫ ₀ ^2π VmSinwt d(wt)

Or, V_av = (V_m/π) [- Cosωt]₀^π

Or, V_av = (V_m / π) * [-(-1) – (-(1))]

Or, V_av = (V_m/ π) * 2

Or, V_av = 2V_m / π = 0.64 V_m

The average load current (I_av) comes as = 2* I_m/π

The RMS (Root Means Square) Value of current:

I_rms = [1/π * ∫ ₀ ^2π I²  d(ωt)]^1/2

I = I_mSinωt; 0 ≤ ωt ≤ π

Or, I_rms = [1/π * ∫ ₀ ^2π I_m²  Sin²ωt d(ωt)]^1/2

Or, I_rms = [I_m²/π *∫ ₀ ^2π Sin²ωt d(ωt)]^1/2

Now, Sin²ωt = ½ (1 – Cos2ωt)

Or, I_rms = [I_m²/π *∫ ₀ ^2π (1 – Cos2ωt)d(ωt)]^1/2

Or, I_rms = [I_m²/2] ^½   Or, I_rms = I_m/√2

The RMS voltage comes as – V_rms = V_m/√2.

The significance of the RMS value is that it is equivalent to DC Value.

Provided that RMS value is ≤ Peak Value

Peak Inverse Voltage (PIV):

Peak inverse voltage or PIV is an important parameter. It is defined as the maximum reverse bias voltage applied across the diode before entering the Zenner Region or Breakdown Region.

For a full-wave rectifier. Peak inverse voltage is given as PIV >= 2V_m

If, at any point, PIV<V_m, the diode will be damaged.

The load current of a rectifier circuit is fluctuating and unidirectional. The output is a periodic function of time. Using the Fourier theorem, it can be concluded that the load current has an average value superimposed on which are sinusoidal currents having harmonically related frequencies. The average of the dc amount of the load current is – I_dc = 1/2π *∫₀^2πI_load d(ωt)

Iload is the instantaneous load current at time t, and  is the source sinusoidal voltage’s angular frequency. A more excellent value of Idc implies better performance by the rectifier circuit.

Full Wave Rectifier graph

The following diagram represents the input and output graph.

Form Factor

The form factor of a full-wave rectifier can be defined as RMS’s ratio (Root Means Square) Value of load voltage to the average value load Voltage.

Form Factor = V_rms / V_av

V_rms = V_m/2

V_av = V_m / π

Form Factor = (V_m/√2) / (2*V_m/ π) = π/2√2=1.11

So, we can write, V_rms = 1.11 * _Vav.

Ripple Factor

Ripple factor is given as the RMS (Root Means Square) Value of AC Component to the Average value of the output. The output current consists of both the AC and DC components. The ripple factor measures the percentage of AC components present in the rectified output.  The symbol represents the ripple factor – γ

I_o = I_ac + I_dc

Or, I_ac = I_o – I_dc

Or, I_ac = [1/(2π) ∫ ₀ ^2π (I-Idc)*(I-Idc) d(ωt)* ^1/2

Or, I_ac = [I_rms² + I_dc²– 2 I_dc²]1/2

Or, I_ac = [I_rms² – I_dc²]1/2

So, Ripple factor,

γ = I_rms² – I_dc² / I_dc²

or, γ = [(I_rms² – I_dc²) – 1] ^1/2

γ_FWR = 0.482

Transformer Utilisation Factor

The transformer utilisation factor is defined as the DC power ratio supplied to the transformer’s AC power rating load.

TUF = P_dc/ P_ac(rated)

Now, to find the Transformer Utilisation Factor, we need the rated secondary voltage. Let us say that V_s. / √2. RMS current through the winding is I_m/2.

So, TUF = I_dc² R_L / (V_s/ √2) * (I_m / √2)

TUF = (2I_m/ π)²R_L / ( I_m² (R_f +R_L)/(2√2) = 2√2/ π ² * (1 / (1 + R_f/R_L))

If R_f << R_L, then,

TUF = 8 / π ² = 0.812

The average transformer utilization factor comes as =

(0.574 + 0.812)/2 = 0.693

Increase in Transformer utilisation factor suggests a better performance of the full wave rectifier.

Full Wave Rectifier Efficiency

Efficiency of Full Wave Rectifier is defined as the ratio of the DC power available at the load to the input AC power. It is represented by the symbol – η

η = P_load / P_in *100

or, η = I_dc² * R/ I_rms² * R , as P = VI, & V= IR

Now, I_rms = I_m/√2 and I_dc = 2*I_m/π

So, η = (4I_m²/ π²) / (I_m²/2)

η = 8 / π² * 100% = 81.2%

Efficiency of a ideal Full Wave Rectifier Circuit is = 81.2%

Difference Between Half Wave and Full Wave Rectifier

Problems with Full Wave Rectifiers

1. A full-wave rectifier has a load of 1 kilo- ohm. The applied AC voltage is 220 V (RMS value). If the diodes’ internal resistances are neglected, what will be ripple voltage across the load resistance?

a. 0.542 V

b. 0.585 V

c. 0.919 V

d. 0.945 V

The ripple voltage is = γ * Vdc / 100

Vdc = 0.636 * Vrms * √2 = 0.636*220*√2 = 198 V.

The ripple factor of a full wave rectifier is 0.482

Hence the ripple voltage = 0.482*198/100 = 0.945 V

2. If the peak voltage of a full-wave rectifier circuit is 5 V and the diode is silicon diode, what will be the peak inverse voltage on the diode?

Peak inverse voltage is an important parameter defined as the maximum reverse bias voltage applied across the diode before entering the breakdown region. If the peak inverse voltage rating is less than the value, then breakdown may occur. The diode’s peak inverse voltage is twice the peak voltage = 2Vm -Vd for a full-wave rectifier. Vd is the diode cut-in voltage. Now for a silicon diode, the cut-in voltage  = 0.7 v. So, peak inverse voltage =2* 5 -0.7volts = 9.3 volts.

3. A input of 200Sin 100 πt volt is applied to a full-wave rectifier. What is the output ripple frequency?

V= V_mSinωt

Here,  ω= 100

Frequency is given as – ω/2 = 100/2 = 50 Hz.

The output frequency of a center-tapped frequency is doubled the input frequency. Thus the output frequency = 50*2 = 100 Hz.

4. What is the main application of a rectifier? Which device does the opposite operation?

A rectifier transforms the AC voltage to the DC voltage. An oscillator converts a DC voltage to AC voltage.

Introduction to Rectifiers

Rectifiers play a crucial role in the field of electrical engineering and power electronics. They are essential components in electronic circuits that convert alternating current (AC) to direct current (DC). In this section, we will explore the definition of rectification and the role of rectifiers in changing AC to DC.

Definition of Rectification

Rectification is the process of converting an AC electrical signal into a DC signal. AC voltage and current change direction periodically, while DC voltage and current flow in only one direction. Rectifiers are electronic devices that enable this conversion by utilizing the properties of semiconductor diodes.

Role of Rectifiers in changing AC to DC

The primary function of a rectifier is to convert the alternating current (AC) waveform into a direct current (DC) waveform. AC voltage and current oscillate between positive and negative values, while DC voltage and current maintain a constant polarity and direction. Rectifiers ensure that the output waveform has a unidirectional flow, allowing for the consistent supply of power to electrical devices.

Rectifiers are widely used in various applications, including power supplies, battery chargers, and electronic devices. They are especially important in situations where a constant and steady DC voltage is required. By converting AC to DC, rectifiers enable the efficient utilization of electrical energy and power in electrical systems.

There are different types of rectifiers, including half wave rectifiers and full wave rectifiers. In this article, we will focus on the half wave rectifier, which is a simple and commonly used rectifier circuit.

In the next section, we will delve into the working principle of a half wave rectifier and understand how it converts AC to DC.

Half Wave Rectifier

The half wave rectifier is a fundamental electronic circuit used in power electronics and electrical engineering. It is a simple yet important component that converts alternating current (AC) into direct current (DC). In this section, we will explore the explanation, circuit diagram, working principle, derivation of formulas and equations, graphical representation, and calculations associated with the half wave rectifier.

Explanation of Half Wave Rectification

Half wave rectification is the process of converting an AC waveform into a unidirectional DC waveform. It is achieved by using a diode, which is a semiconductor device that allows current to flow in only one direction. The diode acts as a switch, allowing current to pass through when it is forward-biased and blocking current when it is reverse-biased.

Circuit Diagram of Half Wave Rectifier

The circuit diagram of a half wave rectifier is quite simple. It consists of a diode, a load resistor, and an AC input source. The diode is connected in series with the load resistor, and the AC input source is connected across the diode. The load resistor is used to limit the current flowing through the circuit.

Working Principle of Half Wave Rectifier

The working principle of a half wave rectifier is based on the fact that a diode allows current to flow in only one direction. When the AC input signal is positive, the diode is forward-biased and conducts current. This positive half-cycle of the AC waveform appears across the load resistor, resulting in a positive half-cycle of the output waveform. However, when the AC input signal is negative, the diode is reverse-biased and blocks current flow. As a result, the negative half-cycle of the AC waveform is suppressed, and no output is obtained during this period.

Derivation of Half Wave Rectifier Formula and Equations

The formulas and equations associated with the half wave rectifier can be derived by analyzing the circuit. The key parameters to consider are the peak value of the input voltage, the peak value of the output voltage, and the average value of the output voltage. By applying basic principles of electrical circuits and diode characteristics, these values can be calculated.

Graphical Representation of Half Wave Rectifier

A graphical representation of the half wave rectifier waveform helps visualize the conversion process. The input waveform, which is an AC signal, is transformed into a unidirectional output waveform. The positive half-cycle of the input waveform appears as the positive half-cycle of the output waveform, while the negative half-cycle is suppressed.

Calculation of Average Output Voltage

The average output voltage of a half wave rectifier can be calculated using the formula:

[ V_{text{avg}} = frac{V_{text{p}}}{pi} ]

where ( V_{text{avg}} ) is the average output voltage and ( V_{text{p}} ) is the peak value of the input voltage.

Calculation of RMS Value of Current

The RMS value of the current flowing through the load resistor in a half wave rectifier can be calculated using the formula:

[ I_{text{rms}} = frac{I_{text{p}}}{sqrt{2}} ]

where ( I_{text{rms}} ) is the RMS value of the current and ( I_{text{p}} ) is the peak value of the input current.

Calculation of Peak Inverse Voltage (PIV)

The peak inverse voltage (PIV) is the maximum voltage that appears across the diode when it is reverse-biased. In a half wave rectifier, the PIV is equal to the peak value of the input voltage.

In conclusion, the half wave rectifier is a fundamental component in power electronics and electrical engineering. It converts AC into DC by utilizing the properties of a diode. Understanding the circuit diagram, working principle, and calculations associated with the half wave rectifier is essential for designing and analyzing electronic circuits.

Form Factor of Half Wave Rectifier

The form factor of a half wave rectifier is a measure of how closely the rectified waveform resembles a pure DC (direct current) waveform. It is an important parameter to consider when designing and analyzing rectifier circuits. The form factor is defined as the ratio of the RMS (root mean square) value of the output voltage to the average value of the output voltage.

The form factor of a half wave rectifier can be calculated using the following formula:

Form Factor = (Vrms) / (Vavg)

where Vrms is the RMS value of the output voltage and Vavg is the average value of the output voltage.

The form factor provides an indication of the quality of rectification achieved by the half wave rectifier. A perfect rectifier would have a form factor of 1, indicating that the output waveform is a pure DC voltage with no ripple. However, in practice, the form factor of a half wave rectifier is always greater than 1 due to the presence of ripple in the output waveform.

Ripple Factor of Half Wave Rectifier

The ripple factor of a half wave rectifier is a measure of the amount of AC (alternating current) ripple present in the rectified output waveform. It is defined as the ratio of the RMS value of the AC component of the output voltage to the average value of the output voltage.

The ripple factor can be calculated using the following formula:

Ripple Factor = (Vrms(ac)) / (Vavg)

where Vrms(ac) is the RMS value of the AC component of the output voltage and Vavg is the average value of the output voltage.

The ripple factor provides an indication of the amount of ripple present in the output waveform. A lower ripple factor indicates a smoother output waveform with less AC ripple, while a higher ripple factor indicates a more distorted waveform with greater AC ripple.

In a half wave rectifier, the ripple factor is relatively high compared to other rectifier configurations. This is because the rectification process only utilizes one half of the input waveform, resulting in a higher amount of ripple in the output waveform. To reduce the ripple factor and achieve a smoother output waveform, additional filtering techniques such as the use of capacitors can be employed.

Overall, the form factor and ripple factor are important parameters to consider when designing and analyzing half wave rectifier circuits. They provide valuable insights into the quality of rectification achieved and the amount of ripple present in the output waveform. By understanding and optimizing these factors, engineers can design more efficient and reliable rectifier circuits for various applications.

Full Wave Rectifier

A full wave rectifier is a type of rectifier that converts alternating current (AC) into direct current (DC). It is an essential component in power electronics and is widely used in various electronic circuits. In this section, we will explore the introduction, circuit diagram, working principle, advantages over half wave rectifier, and the importance of a center-tapped transformer in a full wave rectifier.

Introduction to Full Wave Rectification

Full wave rectification is the process of converting the entire cycle of an AC waveform into a unidirectional DC waveform. Unlike a half wave rectifier, which only utilizes one half of the input waveform, a full wave rectifier makes use of both halves. This results in a more efficient conversion of AC to DC.

Circuit Diagram of Full Wave Rectifier

The circuit diagram of a full wave rectifier consists of a transformer, two diodes, and a load resistor. The transformer is used to step down the input voltage to a suitable level. The diodes, which are semiconductor devices, allow the flow of current in only one direction. The load resistor is connected in parallel with the diodes to provide a path for the current to flow.

Working Principle of Full Wave Rectifier

The working principle of a full wave rectifier is based on the concept of diode rectification. When the input AC voltage is applied to the primary winding of the transformer, it induces a voltage in the secondary winding. This induced voltage is then applied to the diodes, which conduct current in only one direction. As a result, the negative half-cycle of the input waveform is rectified by one diode, while the positive half-cycle is rectified by the other diode. This ensures that both halves of the input waveform are converted into a unidirectional DC waveform.

Advantages of Full Wave Rectifier over Half Wave Rectifier

A full wave rectifier offers several advantages over a half wave rectifier. Firstly, it provides a higher average output voltage compared to a half wave rectifier. This is because a full wave rectifier utilizes both halves of the input waveform, resulting in a higher overall rectification efficiency. Secondly, a full wave rectifier produces a smoother output waveform with less ripple. This is due to the fact that the rectification occurs during both the positive and negative half-cycles of the input waveform. Lastly, a full wave rectifier has a higher efficiency compared to a half wave rectifier, as it utilizes the entire input waveform.

Importance of Center Tapped Transformer in Full Wave Rectifier

A center-tapped transformer is an essential component in a full wave rectifier. It provides a means of obtaining two equal and opposite voltages, which are required for the rectification process. The center tap of the transformer is connected to the ground, while the two ends are connected to the diodes. This allows the diodes to conduct current in opposite directions during each half-cycle of the input waveform. The center-tapped transformer ensures that the rectification process is carried out effectively, resulting in a smooth and efficient conversion of AC to DC.

In conclusion, a full wave rectifier is a crucial component in power electronics and electronic circuits. It offers advantages over a half wave rectifier, such as higher average output voltage, smoother output waveform, and higher efficiency. The presence of a center-tapped transformer is essential for the proper functioning of a full wave rectifier. By understanding the working principle and circuit diagram of a full wave rectifier, we can appreciate its importance in converting AC to DC for various electrical applications.

Comparison between Half Wave and Full Wave Rectifiers

Rectifiers are electronic circuits used to convert alternating current (AC) into direct current (DC). They are essential components in various electrical devices and systems. Two commonly used rectifiers are the half wave rectifier and the full wave rectifier. While both serve the purpose of converting AC to DC, there are significant differences between the two. Let’s explore these differences and understand the advantages and disadvantages of each.

Key Differences between Half Wave and Full Wave Rectifiers

Half Wave Rectifier

A half wave rectifier is the simplest form of rectifier circuit. It uses a single diode to convert the positive half of the AC waveform into DC. The negative half of the waveform is blocked, resulting in an output waveform that contains only the positive half cycles. Here are the key differences between a half wave rectifier and a full wave rectifier:

1. Efficiency: The efficiency of a rectifier refers to how effectively it converts AC to DC. In this aspect, the half wave rectifier falls short. It has lower efficiency compared to a full wave rectifier due to the fact that it utilizes only half of the input waveform.

2. Output Waveform: The output waveform of a half wave rectifier is characterized by a pulsating DC signal. It contains only the positive half cycles of the input waveform. As a result, the output voltage is not constant and has a higher ripple factor compared to a full wave rectifier.

3. Voltage Ripple: The voltage ripple is a measure of the variation in the output voltage. In a half wave rectifier, the voltage ripple is higher due to the absence of the negative half cycles. This can lead to fluctuations in the output voltage, which may not be suitable for certain applications.

Full Wave Rectifier

A full wave rectifier, on the other hand, utilizes both halves of the input waveform to produce a smoother DC output. It employs either two diodes or a bridge rectifier circuit to achieve this. Here are the key differences between a half wave rectifier and a full wave rectifier:

1. Efficiency: The full wave rectifier is more efficient than the half wave rectifier. By utilizing both halves of the input waveform, it effectively doubles the output voltage and reduces the voltage ripple. This makes it more suitable for applications that require a stable and constant DC voltage.

2. Output Waveform: Unlike the half wave rectifier, the full wave rectifier produces a continuous DC output waveform. It contains both the positive and negative half cycles of the input waveform, resulting in a smoother output voltage.

3. Voltage Ripple: The full wave rectifier has a lower voltage ripple compared to the half wave rectifier. This is because it utilizes both halves of the input waveform, reducing the fluctuations in the output voltage.

Advantages and Disadvantages of Half Wave Rectifier

Advantages:
– Simple and inexpensive circuit design
– Requires fewer components compared to a full wave rectifier
– Suitable for applications where a low output voltage is acceptable

Disadvantages:
– Lower efficiency compared to a full wave rectifier
– Higher voltage ripple
– Not suitable for applications that require a stable and constant DC voltage

Advantages and Disadvantages of Full Wave Rectifier

Advantages:
– Higher efficiency compared to a half wave rectifier
– Lower voltage ripple
– Suitable for applications that require a stable and constant DC voltage

Disadvantages:
– More complex circuit design compared to a half wave rectifier
– Requires additional components such as diodes or a bridge rectifier circuit
– Relatively higher cost compared to a half wave rectifier

In conclusion, both the half wave rectifier and the full wave rectifier have their own advantages and disadvantages. The choice between the two depends on the specific requirements of the application. While the half wave rectifier is simpler and cheaper, it has lower efficiency and higher voltage ripple. On the other hand, the full wave rectifier offers higher efficiency and lower voltage ripple, but at the cost of a more complex circuit design.

Applications of Half Wave Rectifier

The half wave rectifier is a fundamental component in electrical engineering and power electronics. It finds numerous applications in various electronic devices and circuits. Let’s explore some common uses and the significance of the half wave rectifier in these applications.

Common Uses of Half Wave Rectifier

The half wave rectifier is widely used in electronic circuits where the conversion of alternating current (AC) to direct current (DC) is required. Here are some common applications of the half wave rectifier:

1. Battery Chargers: Half wave rectifiers are commonly used in battery chargers to convert the AC voltage from the power source into DC voltage suitable for charging batteries. The rectifier ensures that the battery receives a steady and constant flow of current in one direction, enabling efficient charging.

2. Power Supplies: Half wave rectifiers are used in power supplies to convert the AC voltage from the mains into a DC voltage that can be used to power electronic devices. The rectifier ensures a smooth and constant DC output, which is essential for the proper functioning of electronic components.

3. Voltage Multipliers: Half wave rectifiers are also used in voltage multiplier circuits, where they help increase the voltage level. These circuits are commonly used in applications such as cathode ray tubes (CRTs), X-ray machines, and other high-voltage applications.

4. Signal Demodulation: In communication systems, the half wave rectifier is used for signal demodulation. It extracts the original modulating signal from the carrier wave by rectifying the amplitude variations of the modulated signal.

Significance of Half Wave Rectifier in Electronic Devices

The half wave rectifier plays a crucial role in various electronic devices and circuits. Here are some key reasons why it is significant:

1. Conversion of AC to DC: The primary function of the half wave rectifier is to convert the AC voltage into DC voltage. This conversion is essential for powering electronic devices that require a constant and steady DC supply.

2. Simplicity and Cost-effectiveness: The half wave rectifier is a simple circuit consisting of only one diode and a load resistor. Its simplicity makes it cost-effective and easy to implement in electronic devices and circuits.

3. Efficiency: While the half wave rectifier is not as efficient as full wave rectifiers, it still offers reasonable efficiency in converting AC to DC. The rectifier allows only half of the input waveform to appear at the output, resulting in a lower average DC voltage. However, for applications where high efficiency is not critical, such as low-power devices, the half wave rectifier is a suitable choice.

4. Waveform Filtering: The output waveform of a half wave rectifier contains significant ripple due to the absence of a smoothing capacitor. However, in some applications where a small amount of ripple is acceptable, the half wave rectifier can be used without a filter capacitor, reducing the complexity and cost of the circuit.

In conclusion, the half wave rectifier finds a wide range of applications in electronic devices and circuits. Its simplicity, cost-effectiveness, and ability to convert AC to DC make it an essential component in power supplies, battery chargers, voltage multipliers, and signal demodulation circuits. While it may not offer the same level of efficiency as full wave rectifiers, its significance in various applications cannot be overlooked.

Precision Half Wave Rectifier

A precision half wave rectifier is a type of electronic circuit used to convert an alternating current (AC) electrical signal into a direct current (DC) signal. It is commonly used in various applications, including audio amplifiers, power supplies, and signal processing circuits. In this section, we will explore the definition and purpose of a precision half wave rectifier, as well as its circuit diagram and working principle.

Definition and Purpose of Precision Half Wave Rectifier

A precision half wave rectifier is designed to rectify only the positive half cycles of an AC waveform while blocking the negative half cycles. Unlike a standard half wave rectifier, which uses a diode and a capacitor to rectify the waveform, a precision half wave rectifier provides a more accurate and precise rectification process.

The purpose of a precision half wave rectifier is to ensure that the rectified output waveform closely follows the positive half cycles of the input waveform. This is particularly useful in applications where a precise and accurate rectification is required, such as in instrumentation and measurement systems.

Circuit Diagram and Working Principle of Precision Half Wave Rectifier

The circuit diagram of a precision half wave rectifier typically consists of an operational amplifier (op-amp), a diode, and a feedback resistor. The op-amp is configured in an inverting amplifier configuration, with the diode connected in the feedback loop.

The working principle of a precision half wave rectifier is as follows:

1. During the positive half cycle of the input waveform, the diode conducts and allows the current to flow through the feedback resistor and into the inverting input of the op-amp. This causes the op-amp to amplify the voltage across the feedback resistor.

2. The amplified voltage is then fed back to the non-inverting input of the op-amp, which causes the op-amp to output a negative voltage. This negative voltage effectively cancels out the positive half cycle of the input waveform, resulting in a rectified output waveform that closely follows the positive half cycles.

3. During the negative half cycle of the input waveform, the diode blocks the current flow, preventing any feedback to the op-amp. As a result, the op-amp does not produce any output voltage during the negative half cycles, effectively blocking them from the rectified output waveform.

By utilizing the feedback resistor and the inverting amplifier configuration of the op-amp, a precision half wave rectifier ensures that the rectified output waveform closely follows the positive half cycles of the input waveform, providing a precise and accurate rectification process.

In conclusion, a precision half wave rectifier is a specialized electronic circuit used to accurately rectify the positive half cycles of an AC waveform. By utilizing an operational amplifier, a diode, and a feedback resistor, it provides a precise and accurate rectification process, making it suitable for applications where precise rectification is required.

Half Wave Rectifier Efficiency

A half wave rectifier is an electronic circuit that converts alternating current (AC) into direct current (DC). It is a simple and commonly used circuit in power electronics and is widely used in various applications. One important aspect to consider when analyzing the performance of a half wave rectifier is its efficiency.

Calculation of Efficiency for Half Wave Rectifier

Efficiency is a measure of how effectively a device converts input power into useful output power. In the case of a half wave rectifier, efficiency is calculated by comparing the DC power delivered to the load with the AC power supplied to the rectifier. The formula for calculating efficiency is as follows:

Efficiency = (DC power output / AC power input) * 100%

To calculate the DC power output, we need to determine the average value of the rectified waveform. Since a half wave rectifier only conducts during the positive half cycle of the input waveform, the average value can be calculated by taking the integral of the positive half cycle and dividing it by the time period. This can be expressed as:

DC power output = (Vp / π) * (1 - cos(π))

Where Vp is the peak value of the input voltage waveform.

The AC power input can be calculated by multiplying the RMS value of the input voltage waveform with the RMS value of the input current waveform. For a half wave rectifier, the RMS value of the input current can be calculated as:

Irms = (Im / √2)

Where Im is the peak value of the input current waveform.

Once we have the DC power output and the AC power input, we can substitute these values into the efficiency formula to determine the efficiency of the half wave rectifier.

It is important to note that the efficiency of a half wave rectifier is relatively low compared to other rectifier configurations, such as full wave rectifiers. This is because a half wave rectifier only utilizes half of the input waveform, resulting in a lower average output power. However, despite its lower efficiency, a half wave rectifier is still widely used in applications where cost and simplicity are more important factors than efficiency.

In summary, the efficiency of a half wave rectifier can be calculated by comparing the DC power output to the AC power input. Despite its lower efficiency compared to other rectifier configurations, the half wave rectifier remains a popular choice in various applications.
Conclusion

In conclusion, the half wave rectifier is a simple and commonly used circuit that converts an alternating current (AC) input signal into a pulsating direct current (DC) output signal. It utilizes a diode to allow only the positive half cycles of the input signal to pass through, while blocking the negative half cycles. This results in a rectified output waveform with a significant amount of ripple. Despite its simplicity, the half wave rectifier has certain limitations, such as low efficiency and high ripple content. However, it still finds applications in various electronic devices where a low-cost and basic rectification is sufficient. Overall, the half wave rectifier serves as a fundamental building block for more complex rectifier circuits and provides a basic understanding of rectification principles.

Frequently Asked Questions

Q: What is a half wave rectifier and how does it work?

A: A half wave rectifier is an electronic circuit that converts alternating current (AC) into direct current (DC) by allowing only one half of the input waveform to pass through. It uses a diode to block the negative half of the waveform, resulting in a pulsating DC output.

Q: What is the derivation of a half wave rectifier?

A: The derivation of a half wave rectifier involves analyzing the circuit and understanding the behavior of the diode. It includes calculations of voltage and current waveforms, as well as the average and peak values of the rectified output.

Q: What is the difference between a half wave rectifier and a full wave rectifier?

A: A half wave rectifier allows only one half of the input waveform to pass through, while a full wave rectifier allows both halves of the waveform to be utilized. This makes a full wave rectifier more efficient in converting AC to DC compared to a half wave rectifier.

Q: Why is a full wave rectifier center tapped?

A: A full wave rectifier is center tapped to provide a balanced output waveform. The center tap allows the use of two diodes in a bridge configuration, which ensures that both halves of the input waveform are rectified, resulting in a smoother DC output.

Q: What is the circuit diagram of a full wave rectifier?

A: The circuit diagram of a full wave rectifier consists of a transformer, a center-tapped secondary winding, and four diodes arranged in a bridge configuration. This arrangement allows for full wave rectification of the input AC waveform.

Q: What is the efficiency of a half wave rectifier?

A: The efficiency of a half wave rectifier is the ratio of DC power output to the AC power input. It is typically lower than that of a full wave rectifier due to the fact that only half of the input waveform is utilized.

Q: How can I calculate the output voltage of a half wave rectifier?

A: The output voltage of a half wave rectifier can be calculated by multiplying the peak value of the input voltage by the rectification factor, which is typically around 0.5.

Q: What is the symbol for a half wave rectifier?

A: The symbol for a half wave rectifier is a triangle with a vertical line intersecting it, representing the diode used in the rectification process.

Q: When is a half wave rectifier used?

A: A half wave rectifier is used in applications where a lower DC output voltage is acceptable, such as in battery charging circuits or low power applications.

Q: What is the purpose of a capacitor in a wave rectifier circuit?

A: The capacitor in a wave rectifier circuit is used to smooth out the pulsating DC output by storing electrical energy during the positive half of the waveform and releasing it during the negative half. This helps in reducing the ripple voltage.

• Definition of BJT
• Types of BJT
• Configurations
• Applications
• Advantages & disadvantages
• Different Modes and Characteristics.

Definition of a Bipolar Junction Transistor:

A Bipolar Junction Transistor (also well-known as BJT) is a special type of semiconductor device with three terminals made of p-n junctions. They are able to amplify a signal as well they control current i.e., they are called as current controlled device. The three terminals are Base, Collector & Emitter.

Types of BJT:

There are two types of BJT –

• P-N-P Transistor.
• N-P-N Transistor.

The BJT has three parts named emitter, collector and base. Here, the emitter-based junctions are forward biased and the collector-based junctions are reverse biased.

PNP Bipolar Junction Transistor:

These types of transistors have two p-region and one n region. The n region is sandwiched between two p region.

NPN Bipolar Junction Transistor:

“NPN transistor is a type of Bipolar Junction Transistor (BJT) that consists of three terminals and three layers and function as either amplifiers or electronic switches.”

NPN BJT with forward-biased E–B junction and reverse-biased B–C junction

What is punch through breakdown in BJT?

In the reverse biasing configuration, the collector junction is increased, the effective base region decreases. At a certain reverse bias of the collector junction, the depletion region covers the base reducing the effective base width to zero. As the collector voltage penetrates the base, and potential barrier at the emitter junction is reduced. As a result, an excessively large emitter current flows. This phenomenon is known as Punch Through.

Applications of Bipolar Junction Transistor:

There are so many applications of a BJT, some of them are-

• In logic circuits BJT is used.
• Bipolar junction transistor is used as an amplifier.
• This type of transistor utilized as switches.
• To design a clipping circuits, Bipolar Junction Transistor is preferred for wave shaping circuits.
• In demodulation circuits, BJTs are also being used.

Advantages and Disadvantages of a Bipolar Junction Transistor:

A BJT is a one type of a power transistor. It is used in the amplifiers, multi-vibrators, oscillators etc. A BJT also has few disadvantages besides its advantages, they are:

Advantages –

1. BJT has a better voltage gain.
2. BJT has a high current density.
3. Higher Bandwidth
4. BJT gives stable performances in higher frequencies.

Disadvantages-

1. Bipolar Junction Transistor has a low thermal stability.
2. It usually produces more noise. So noise prone circuit.
3. It has a small switching frequency.
4. The switching time of BJT is not very fast.

Bipolar Junction Transistor Characteristics:

Transistor Characteristics-

Transistor Modes:

The three modes of a transistor are

• CB (Common -Base)
• CE (Common -Emitter)
• CC (Common Collector)

CB-Common Base, CE-Common Emitter and CC- Common Collector Mode of PNP and NPN Transistor has been discussed as follows:

Input Characteristics:

Input characteristics of a transistor is drawn between the Emitter current and Emitter-base Voltage with collector base voltage as a constant.

Output Characteristics:

Out characteristics of a transistor is drawn between the Collector current and Collector-base Voltage with emitter current as a constant.

The output characteristics is distributed into different sections:

The Active Region –

In this Active mode, all together the junctions are in reverse biased and no current pass through the circuitry. Therefore, the transistor stays in the OFF mode; operate as an open switch.

The Saturation Region –

In this Saturation mode, both junctions are forward biased and current pass through the circuitry. Hence, the transistor stays in the ON mode; operate as a closed switch.

Cut-off Region –

In this Cut-off mode, one of the junction is in forward biased and other one is connected in reverse biasing. This Cut-off mode is utilized for current amplification purpose.

CB (Common Base)

In the Common Base mode operation the base is grounded. The E-B junction is connected at forward biased during the standard operation; the input characteristics are analogous to p-n diode. I_E get increased with the increase of |V_CB|. If the functional voltage at |V_CB| increases, the size of the depletion region at the C-B junction enlarged, thereby reducing the effective base region. The “variation of the effective base width” by the voltage applied in collector terminal is termed as early effect.

From nodal analysis we know,

I_E=I_B+I_C

Now, α= the ratio of I_C & I_E

So, α=I_C/I_E

       I_C= αI_E

       I_E=I_B+ αI_E

      I_B=I_E (1- α)

Input characteristic common-base silicon transistor:

Output characteristic common-base silicon transistor:

CE (Common Emitter)

In CE mode, the emitter is grounded and the input voltage is applied in between emitter and base and output is measured from collector and emitter.

β=ratio between I_C & I_B

β=I_C/I_B

I_C= βI_B

I_E=I_B+ βI_B

I_E=I_B (1+ β)

The Common Emitter mode, the emitter is common to the input and output of the circuitry. The input current I_B  is plotted to the voltage V_BE with output voltage V_CE in the time being. This is because width of depletion region at collector emitter junction increases. This is called Early Effect.

Input characteristic common-emitter silicon transistor

Output characteristic common-emitter silicon transistor

CC (Common Collector)

In CC or Common Collector mode collector has to be grounded and the input is applied from base collector and output is taken from collector to emitter.

The ratio, I_E/I_B = I_E/I_C.I_C/I_B

Or, I_E/I_B = β/α

We know α= β (1- α)

                 β = α β+ α

               I_E=I_B (1+ β)

Relationship between α & β:-

We know,

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• What is photo transistor ?
• Working principle of photo transistor
• Photo transistor uses
• Photo transistor symbol
• Characteristics of photo transistor
• Advantages and disadvantages of photo transistor

The photo transistor is an transducer which is capable of converting the light energy into the electrical energy. The parameters like wavelengths, alignments, interfaces, etc. should be considered with higher importance while designing the circuit.

Definition of Photo Transistor:

“The phototransistor is a semiconductor device that is able to sense light levels and alter the current flowing between emitter and collector according to the level of light it receives.”

As the name suggests, the phototransistor is a transistor which can sense the light and vary the flow of currents in-between the terminals of the transistor.

In general transistors are sensible to lights. This property of transistors are used in phototransistors. NPN type photo transistor is one of the types.

Here, in a phototransistor light striking the base supplants the voltage, actually applied to the base, so a phototransistor amplifies disparities as per the light signal. The phototransistors may or may not be have a base terminal in it. If it is present, the base region permits it to biasing the phototransistor’s light impacts.

• This type of transistor is controlled by exposure of light. It is like a photodiode controlling a BJT.
• Photo Transistor can be any one type such as BJT or FET.
• These types of transistors are typically covered with the plastic materials and one of the part is kept open or transparent for light.

Symbol of Photo Transistor:

Examples Photo Transistor:

• KDT00030TR
• PS5042
• OP506A, OP550A, OP506B
• TEKT5400S, TEMT1030
• SFH314-2/3, SFH 325 FA-Z
• QSE113E3R0
• BPW17N, BPV11F, BPW85C etc.

Working Principle of Photo Transistor

Output of a photo transistor is taken from its emitter terminal; hence the light rays are allowed to the base region.

A photo-transistor can be three or a two terminal device as per our requirement. The base of the photo-transistor is used for only biasing purpose. For NPN transistor, the base is made +ve in respect to the emitter terminal, and in a PNP transistor the collector terminal is made –ve in respect to the emitter terminal.

At first, the light ray enters the base region of a photo transistor and generates an electron hole pairs. This process mainly occurs under reverse biasing. The active region of this type of transistor is used for generating current. The cut-off and saturation region are used to operate the particular transistor as a switch.

A photo-transistor and its working depends on so many internal and external factors, such as:

• The intensity of the photocurrent will be more with higher DC current gain.
• Luminous sensitivity is given by the ratio of the photo electronic currents to the incoming luminous fluxes.
• If the wavelength gets increased, the frequency will be decreased.
• If the area of the collector-base junction gets wider, the Amplitude of the photo current engendered by the photo-transistor will be higher.

Characteristics of Photo Transistor:

Here the X axis is V_CE– denotes the voltage applied to the collector-emitter lead and the Y axis is I_C – denotes the collector current that carrying through the circuit in mA.

As we can see, the curve is clearly indicating that current is increasing with the intensity of the radiation which is at the base region.                  

Advantages of Photo Transistor:

• The efficiency of this type of transistor is greater than a photodiode. The transistor’s current gain is also more compare to photodiode; even if incident light is same, the photo transistor will produce more photo current.
• In compared to a photo diode, the response time of a photo transistor is more. So, it means this type of transistor has a faster response time.
• The photo-transistors are immune to any noise interference.
• Photo-transistors are less costly.
• The circuitry of a this type of transistor is less complicated.

Disadvantages of Photo Transistor:

• The efficiency of the phototransistor decreases with the electromagnetic field interferes.
• At higher frequencies, photo transistors do not function properly. Due to this problem it fails to convert the photo current effectively at high frequency.
• Electric Spikes occur frequently.

Applications of Photo Transistor:

• Photo-transistors are used in counting systems.
• This type of transistors are utilized in the computing system.
• This type of transistor can be used to generate variable voltage.
• These types of transistors are used in.
• Due to high light to current conversion efficiency these are widely used in remote, printing machine.
• The most important application of this type of transistor is to use it as a light detector. It can also detect very less light also.
• They also play important role in making punch cards.
• This type of transistors are crucial optoelectronics device which are also used in optical fibers

Why is phototransistor reverse biased?

Photodiodes are connected in reverse bias to decrease the charges area and narrow the capacitance at the junctions. This permits higher bandwidth. The light acts as I_B, so in an NPN phototransistor the collector have +ve voltage by a resistive load, whereas the emitter will be grounded one.

Difference between photo resistor and phototransistor

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Points of Discussion:

• Definition
• Construction
• Working
• Applications
• Frequently asked questions on step up transformers.

Definition of Step up Transformer

A transformer transfers electrical energy. Step up transformer is one type of electrical transformer. A step-up transformer increases the input voltage and provides increased voltage as the output. In the process of transferring the power, the power and the frequency of the power remains constant.

Construction of Step up Transformer

Step-up transformer construction means the construction of core and construction of the windings.

Core Construction:

Transformer’s core is a specially build part which is created with spongy metals. The reason behind choosing the spongy metals for core is that magnetic flux can pass through those types of metals. The core is surrounded by the coils. The design of the wrapping decides the types of the core.

A transformer core will be called as a Closed core transformer if the core is bounded by the coils from the outside.

A transformer is called Shell core transformer if the core is surrounded by the coils from inside.

For industry purpose a shell type of core is being chosen over a core type because a core type has the shortcoming of ‘leakage Flux’.

Windings:

Windings are another important part of transformer which are basically coils of wire and carries current. The Primary and secondary windings are made up of copper and Aluminium. Primary windings take the input voltage and the secondary voltage provides the output voltage. The classification of step-up or step-down is done here. Now, for a step-up transformer the number of turns in secondary windings is more than the number of turns in secondary windings.

Step Up Transformer Working principle

Step up transformer has the same principle as a normal transformer. Step-up transformers take a lower voltage and provides a higher voltage. Their working is based upon the laws of Faraday and the turn ratio theory.  

Inside a step-up transformer, current flows due to the input voltage. The current flow induces a magnetic flux around the windings and the flux passes through the core of the transformer.

The voltage in the secondary windings is induced by the secondary-winding.

The next working principle is the turn ratio. Turn ratio is given as the ratio of primary winding’s turn number to the secondary winding’s turn ratio. It is also described as the ratio of the input voltage to the output voltage.

Turns ratio = N_primary/N_secondary =V_primary/V_secondary ———————- (i)

Or, Vsecondary = Vprimary *(Nsecondary /Nprimary) ———————(ii)

Here, Nprimary = Primary windings number of turns

Nsecondary = Secondary windings number of turns

Vprimary = Primary side’s voltage

Vsecondary = Secondary side’s voltage

Using the (ii) marked equation we try to calculate the secondary voltage. It is clear that the input voltage is constant. Now changing the turn ratio, we can get the wanted output voltage. A step-up transformer is used to produce a higher voltage at the output side. That is why the Ratio of (Nsecondary/Nprimary) is fixed to greater than 1.

Now, from the equations, we can observe that the Nsecondary will be greater unlike step-down transformer. That is why a step-up transformer consists of higher number of turns in the secondary windings.

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Applications of Step up transformer

Step-up transformer has several applications. Most of the applications are very specific and from different fields.

• Applications in Power Systems: Step-up transformer is one of the most important part of power distribution system. A step-up transformer helps to step-up the supplied voltage as per the need.  
• Electronics device and Instruments: Step-up transformers is used inside numerous electronics devices and instruments. Devices like rectifiers, ADC and DAC converters use this type of transformer.
• Electric motor and generators, microwave ovens, X-Ray machines and various home appliances use to step up transformers.

Frequently asked questions on step up transformers

1. How do you identify a step up and step down transformer?

A step up transformer supplies increased voltages on the load whereas a step down transformer supplies reduced voltages on the load. Measuring the input voltage at the primary winding and output voltage at the secondary windings, one can identify the type of transformer. One can check the current value of input and output also. If the current value is more than the supplied, then that is step up type, else that is step down. This was a process. Another process will be to check the turn ratio. If the turn ratio is less than one, then it is step up else it is step down transformer. 

Checking the types of wire will be another way.  For a step up transformers, primary windings have thicker wire density than the wire density of secondary windings.

2. What is the need of a step-up transformer?

A step-up transformer delivers increased supplied voltages to its load. So, if there is a need to step-up or increase the supplied voltage for our workings, then it is advised to use a step-up transformer. But that the current value gets decreased. So if we need a higher voltage source with the same current, then a step up transformer would not serve our purposes.

3. What is the purpose of a step up transformer?

Step up transformer helps to increase the voltage. So, the purpose is relatively straight, that is to step up the voltage supplied to it.

4. What is the turn ratio for a step up transformer?

Turn’s ratio is an important parameter of electrical transformers. It is given by the ratio of the primary winding’s number of turns to the secondary winding’s number of turns.

Turns ratio = N_primary/N_secondary

Nprimary is the primary winding’s number of turn and Nsecondary is the secondary winding’s number of turns.  

Step up transformer has no ideal turns ratio. But in general, the turn ratio is less than 1 in case of a step-up transformer.

5. Write about practical significances of Step-Up Transformers

Step up transformers are very much important for our daily life. It is quite impossible to supply electric if there are no step-up transformers. In a power distribution system, when power is supplied from the power stations, the supplied voltage gets decreased due to the resistance of the supplying conductors. Step-up transformers are required at this time to increase the voltage again keeping the power constant. That is the practical significance of a step-up transformer.

6. Differences between a step-up transformer and step-down transformer?

The objective of step-up and step-down transformer differentiates the transformers. The objective of step-up transformer is that it step-up the voltage provided and step-down transformer provides the decreased supplied voltage. Some other differences are given below.

7. Does a step up transformer increase current?

No, a step up transformer does not increase current. Instead, it increases the voltage and decreases current. The power of the signal remains constant, though.

8.  Number of turns of a winding of an Electrical transformer is 3000. Another winding has number of turns = 1500 where an AC voltage of 50 volts is applied. Find out the voltage at the lesser number of turns. Find out the type of transformer.

Voltage is applied at the 1500 turn side. So, that is the primary winding and the number of turns of wire = 1500. Let’s say that is Np.

3000 turn side is the secondary side. So this is the secondary winding and the number of turns of wire = 3000. Let’s say that is ns.

50 volt is supplied at the primary side, so that is primary voltage and let’s say that = Vp

We have to calculate the voltage at the secondary side; let’s say that = Vs.

We know that turn ratio = Np/Ns

That is also= Vp/Vs

So, Np/Ns = Vp/Vs

Or, Vs = (Ns/Np) * Vp

Substituting the values, we get-

Vs = (3000/1500) * 50

Or, Vs = 100 volt

The voltage at the secondary side will be  = 100 volt.

Now as we can see, the voltage is higher than the supplied voltage, so this is a step up transformer.

Points of Discussion:

• Definition of step down transformer
• Construction
• Working
• Applications
• Frequently asked questions on step down transformers.

Definition

A transformer transfers electrical energy. Step down transformer is one kind of it. A step-down transformer decreases the voltage applied on primary windings and supplies reduced voltage on the secondary side. However, the power and frequency remain constant in the process.

Construction of Step Down Transformer

The construction process of a step-down transformer lies in its core and windings, and it is very much similar to a step-up transformer.

Construction of Core of a Transformer:

Core of a transformer is made of soft iron-like metals. It allows the magnetic flux to pass through it. The coils of both the windings are wrapped around the core. The core can be of two types based on the wrapping up of the locks. If the coils are wrapped outside the body, then that is Closed Core Transformer. If the windings are inside the iron core, then that will be Shell Core Structure. A closed core type transformer suffers a problem of ‘Leakage Flux’ while a shell type does not. That’s why a shell core structure is more preferred rather than a closed core. 

Read more about How To Convert Step Down To Step Up Transformer

Transformer Windings:

Windings are the conductors of current inside the transformer. They are made of a coil of wires. The material of the wire is copper or aluminium. Windings are of two types – Primary windings and Secondary windings. Primary windings receive the applied voltage, and the secondary windings supply the induced voltage to load. Though electrical energy transfers from the primary side to secondary windings without metallic contacts—the main classification parameter to decide whether a transformer is a step up or step down lies here.

In case of a step-down transformer, the number of turns in primary windings is more than the number of turns in the secondary windings. However, the density of wire is thinner in primary windings than the thickness of the secondary windings.

Working of a Step Down Transformer

The working principle of a step-down transformer is the same as a typical transformer. A step-down transformer gives higher output voltages than a lower input voltage and works on Faraday’s law and Turn Ratio.

Due to the applied voltage in the primary windings, the current flows through the wires. The flow of alternating current generates magnetic flux around the windings. The core of the transformer allows this magnetic flux to flow through it.

Change in magnetic flux further induces a voltage in the secondary windings.

Now the turn ratio factor comes into action.

Turns ratio = N_p/N_s =V_p/V_s ———————- (i)

Or, Vs = Vp *(Ns /Np) ——————— (ii)

Here, Np = number of turns in the primary windings.

Ns = number of turns in the secondary windings

Vp = voltage at the primary side

Vs = voltage at the secondary side.

Now in the equation (ii), we are calculating Vs – the secondary voltage. We can see Vp is constant as the applied voltage is constant. Now increasing or decreasing the (Ns/Np) ratio, we will able to get our desire voltage at the output side. While using a step-up transformer, our motive is to generate lesser voltage than the input. So, we have to keep the Ratio of (Ns/Np) less than 1.

That means the value of Np should be higher than the magnitude of Ns. As we know, Np is the number of turns in the primary windings, that’s why a step-down transformer is designed with higher no. of turns in the primary winding side. As mentioned earlier, the power of the electrical signal remains the same. The voltage gets reduced, and to keep the power constant, the current gets increased. The frequency of energy also remains unchanged.

Read more about Mutual Inductance Transformer

Applications of Step down transformer

Transformers have various applications. Step down transformer is designed to do some specific tasks and has a wide range of applications in both electrical and electronics circuitries.

• Power System: Step down transformers are used in power distribution systems. In a various phase of supplying power, step down transformers is used to reduce voltage whenever necessary.
• Electronic devices: Step-up transformers are used in various electronics device where the device works on lower voltages than the supplied voltage. Tools like adapters of different electronic devices and low voltage applications use this type of transformers.
• Transformers, which we found at streets near our home step down transformers.

Know about different types of transformers and their applications! Click to navigate!

Frequently asked questions on a step down transformer

1. Does a step down transformer decrease current?

No, a step down transformer does not decrease or reduce current. Instead, it reduces the voltage and increases current. The power of the signal remains constant, though.

2. Why do we need to step-up transformers?

The name of the transformer helps us to find out what it does. A step-down transformer delivers reduced supplied voltages to its load. So, when we need to step down or reduce the voltage provided for our workings, then we should use a step-down transformer. But that the current value gets increased. So if we need to minimise voltage source with the same current, then a step-down transformer would not serve our purposes.

3. A transformer has 2000 turns of copper wire wrapped in a side, and 1000 turns of copper wire surrounded at another side. If an AC voltage of 440 volts is applied at 2000 turn side, what will be the voltage at the 1000 turn side? Also what type of transformer is this?

Voltage is applied at the 2000 turn side. So, that is the primary winding and the number of turns of wire = 2000. Let’s say that is Np.

1000 turn side is the secondary side. So this is the secondary winding and the number of turns of wire = 1000. Let’s say that is ns.

440 volt is supplied at the primary side, so that is primary voltage and let’s say that = Vp

We have to calculate the voltage at the secondary side; let’s say that = Vs.

We know that turn ratio = Np/Ns

That is also= Vp/Vs

So, Np/Ns = Vp/Vs

Or, Vs = (Ns/Np) * Vp

Substituting the values, we get-

Vs = (1000/2000) * 440

Or, Vs = 220 volt

The voltage at the secondary side will be = 220 volt.

Now, as we can see, the voltage is lower than the supplied voltage, so this is a step-down transformer.

Read more about How Does A Transformer Work

4. Write some differences between step up and step down transformers

The fundamental difference of step up and step down transformers lies in their working. Step-up transformers increase the supplied voltage, whereas step down transformers reduces that. Here are some of the more differences. Click Here!

5. Practical Significance of Step-Down transformers

Step down transformers have impacts on our day to day life. The power which generates at a power station is of high voltages (Range of Megawatt to Gigawatt). If there are no step-down transformers, then there would not be electricity in households. When we need to transfer power from power stations to the home, then it is necessary to use a step-down transformer. Using a step-down transformer, we can reduce the high voltage and can be supplied to houses.

6. What is the turn ratio for a step-up transformer?

The turn’s ratio of a transformer is an essential parameter for the calculation of power. It is given by the balance of the number of turns of the wire in primary windings to the number of the arches of the wire in secondary windings. The equation gives the ratio –

Turns ratio = N_p/N_s

Np is the number of turn in the primary windings, and Ns is the number of bend in the secondary windings.

Step down transformer has no ideal turn’s ratio. It varies as per the need. But to work as a step-down transformer, the turn ratio must be greater than unity.

Read more about How Do Transformers Increase Voltage To Decrease Current

• Power transformer definition
• Power transformer design
• Power transformer diagram
• Power transformer rating
• Power transformer losses
• Power transformer efficiency
• Power transformer application ( in a substation)
• Power transformer maintenance
• Power transformer failure

Power transformer definition

A typical transformer can be defined as “A device that transfers electrical energy between electrical circuits.” It is a passive and static device. A power transformer is one of its kind. Power transformers are used to interface step down and step up voltages in the power distribution system. 

A typical power transformer has a life span of around 30 years.

Power transformer Design

A typical transformer consists of parts –

• A. Metallic core
• B. Two windings made up of coils

A power transformer has the same components as a normal one. Additionally, it has a cooling system and a metallic skeleton, which is laminated with sheets. Depending on the core structure, a power transformer may be either shell type or core type. This may also be three-phase or single phase-type. A three-phase can be made from three single-phase transformer.

Primary and secondary windings are wrapped using conductors either from inside or from outside the core. Single-phase and three-phase both the transformers need ‘bank’ to place the windings. If we use three single-phase transformers, then it is necessary to identify each bank isolated from others. If one of the banks fails, then also the transformer will ensure continuous service. But in the case of a single three-phase transformer, it won’t work if a bank fails.

All these settings with the core are kept inside a skeleton. The skeleton is absorbed inside a fire-protected oil. The oil both does the job of isolation and cooling. There is busing (isolators), which allows the conductor to do their job without interfering with the outer structure. Transformers need a cooling device too. A fan or some other process may serve the process.

Power transformer Diagram

Power transfer rating

Transformers are rated based on the power it can deliver to the load. If a transformer gives 5 volts and 4 amperes current as output, then the transformer’s rating will be 5*4 = 20-volt ampere. That’s why transformers are rated in Volt – Ampere (VA) or Kilovolt – Ampere (kVA). It usually work for higher voltages and are rated in kilovolt ampere.

A power transformer is a costly part of a distribution system. If the power rating isn’t done correctly, then the transformer may be burnt out. So, it is necessary to rate a power transformer accurately. The current value can be calculated using the diameter of the coil of the windings. The voltage can be calculated using the number of turns or using the turns ratio.

Power transformer losses

A power transformer suffers loss as it is not an ideal transformer. A transformer loss means loss of power. Losses of the transformer can be divided into four categories. They are –

• A. Core Loss / Iron Loss (Hysteresis Loss & Eddy Current Loss)
• B. Dielectric Loss
• C. Copper loss or Ohmic Loss
• D. Stray Loss

A. Core Loss / Iron Loss:

These losses are also termed as “No Load Losses”. This transformers suffer such losses whenever it is plugged in with power even it has no load connected with it on the secondary side. These types of losses are constant and do not fluctuate. Iron loss is also of two kind –

• a. Hysteresis losses
• b. Eddy current losses

a. Hysteresis losses:

• An alternating magnetizing force occurs inside the core of the transformer. Due to the magnetizing leverage, a hysteresis loop traced out and power dissipated in the form of heat. Hysteresis losses cause a 50% to 80% no-load loss.

P_h = η * B_max * n * f * V

P_h = Hysteresis Loss

η = Steinmetz hysteresis coefficient

B_max = Maximum flux density

n = Steinmetz exponenet

f  = frequency of magnetic reversals per second

V = volume of magnetic material

b. Eddy Current Loss:

• Eddy current loss occurs due to Faraday’s law of induction. An emf is induced in the core circuit due to the magnetic flux. This emf cause flow of current through the core structure as it is made up of iron. This current is known as Eddy Current. Eddy current is not useful for working in this circuit. So, the power loss due to this current is known as eddy current loss. Eddy current losses are accountable for 20% to 50% no-load loss.

The loss is given by –

Pe = K_e * B_max² * f * V * t²

P_e = Eddy Current loss

K_e = Eddy current constant

B_max = Maximum flux density

f  = frequency of magnetic reversals per second

V = volume of magnetic material

t = magnetic thickness

B. Dielectric Losses:

• Insulators placed inside transformers are the reason behind this loss. It is not a significant loss and contributes 1% of the total no-load losses.

C. Copper loss or Ohomic loss:

• This type of loss in a power transformer can be called Load Losses as transformers suffer this type of loss due to short circuit conditions or when connected with the load. The resistance of the wire’s windings is the source of this loss. As most of the cables are made up of copper, the loss is named after that.

D. Stray Loss:

• This loss occurs due to the leakage flux. The leakage flux depends on several parameters like – winding’s geometrical structure, the tank’s size, etc. Changing these parameters can also reduce loss. It is a negligible loss.

There are some other losses too. One of them is Auxiliary losses. The cooling system of the transformer causes this type of loss. Also, imbalanced and distorted power results in some extra losses.

Power Transformer Efficiency

The efficiency of an Electrical device is given as the ratio of output power to the input power.  It is given by – η.

η = Output / Input * 100%

In a practical scenario, a transformer has losses, as mentioned earlier. This loss is numerically equal to the difference between the Input power and Output power, that is –

Loss = Input Power – Output Power

Or, Output Power = Input Power – Loss

Now, efficiency can be written –

η = (Input Power-Loss) / Input Power * 100%

η = 1- (Loss / Input Power)  * 100%

It can also be written as –

η = (V₂I₂Cosϕ / ( V₂I₂Cosϕ+ P_i+ P_c ))* 100%

Where,

V₂ = Secondary voltage

I₂ = Secondary current

Cos ϕ = Power Factor

P_i = Iron Loss / Core Loss

P_c = Copper Loss

A large power transformer can achieve efficiency by up to 99.75%, and a small one can achieve efficiency by up to 97.50 %. If a power transformer’s efficiency stays in a range of 98 to 99.50%, it will be considered good.

The need for power is increasing by leaps and bound. In the case of the distribution of power, a power transformer is one of the essential tools needed. Though these are designed for higher efficiency, the need is high for more efficiency with a concern towards the environment and reduced usage of power. The reduction of losses is the way towards this goal.

Power transformer Application (Power transformer in a substation)

Transformers are one of the essential and most incredible innovations in the field of Electrical Engineering. Power transformers have the most use in the power distribution system. Some of the applications are –

• Power transformers are used in power generation and distribution systems.
• Power transformers are used in Sub-stations. A substation transforms higher electrically voltages to lower voltages, and a power transformer does this work. these are the most critical device of a power substation.
• To reduce power losses in power transmission. Transformers help to minimize power, and thus electricity can be supplied throughout the areas.
• To step up and step-down voltages as per the need.
• Power transformers work continuously, ensuring supply for 24 * 7. Thus, when we need to do always, a transformer can be used.
• These are also find application in Earthing transformers, isolation transformers.

Power transformer maintenance

Power transformers are expensive, bulky, and an essential part of a power distribution system. So, a transformer needs a high quality of maintenance. Maintenance can be two types – a daily basis and at the time of emergency. Regular maintenance is highly recommended for this type of transformer, which is placed in a substation. Some maintenance types are given below –

Regular Maintenance:

1. Checking of oil level
2. To keep the oil level at the desired level.
3. To seal up leakage if any detected.
4. To replace the silica gel if the colour changes to pink.

Monthly Maintenance:

1. Oil level to avoid damage.
2. To check up the bushings.
3. Cleaning of the skeleton.

Half Yearly Maintenance:

1. To check the IFT, DDA, flashpoints.
2. To check acidity, water content, and dielectric strength.

Annual Maintenance:

1. Check the condition of the oil—the situation in terms of moisture content and dielectric strength.
2. To check up on all alarm and control switches.
3. Measuring and checking the earthing connection.
4. Checking of bushings and cleaning them up.
5. To check a press release device.

Power transformer failure

A typical electrical transformer is quite complex in its circuitries. A power transformer is more complicated as it has some additional elements. A transformer fails by burning out or shut down of a transformer. A transformer’s failure may occur due to several reasons. Mechanical faults, periodic maintenance, natural calamity like lightning may lead a transformer to destruction.

• Transformers generates heat during operation. If there are low-quality material for isolation, then the generated heat would lead towards burning.
• Overloaded condition is another cause for transformers.
• Old transformers can cause failure. Mechanical faults are prominent for old transformers.
• If the oil’s moisture content fluctuates from the rated values, that may also lead to failure.

The power failure may be prevented by doing regular maintenance. Information based on previous failures also helps to detect signs of a power failure before the incident occurs.

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