Center Tap Transformer: What, Why, Working, Applications, Detailed Facts


This article describes the center tap transformer, its components, working and other important details. A center tap is a wiring drawn from the midway of a transformer, a resistor, an inductor or a potentiometer.

A Center Tap transformer functions almost in the same way as an ordinary transformer. The only difference is that the tap present in the secondary winding of the center tap transformer divides the transformer into two parts, therefore, we can get two individual voltages across the two line ends if the transformer.

What is center tap transformer?

A center tap transformer is a device that has tapping through the middle of its secondary winding. This way, we can get half of the voltage induced in the secondary winding from the center tap to either of the tap ends.

A center tapped transformer is also known as the ” two phase three wire” transformer. These transformers work best in rectifier circuits and step down actions as it provides two output cycles for a single input cycle. For example, a V volt transformer measures V/2 Volts each across its two half windings made by center tapping it. 

Why do you center tap a transformer?

Center tap transformers play a pivotal role in uninterrupted and even voltage. Tapping helps in voltage regulation by changing the coil turn ratio. It can increase or decrease the voltage to compensate for the rise/loss. 

Center tapped transformer is essential as it converts the total AC input into DC output. Center tap in the secondary winding of the transformer generates a closed circuit in both first and second half cycle of the AC input. Therefore, center tap on the secondary is important in getting the positive half cycle on the load. 

Center tap transformer working

The working principle of the center tapped transformer is the same as any other transformer. When AC current flows through the primary coil of the center tap transformer, it creates a magnetic flux in the core of it.

When the secondary winding comes near to the primary, a magnetic flux induces in the secondary winding. This happens because the flux flows through the iron core and changes the direction with each AC cycle. Thus the AC current also passes through the two halves formed in the secondary winding and flows to the entire circuit.

Center tap transformer applications

Full wave rectifiers are the most significant application of center tap transformers. A full wave rectifier needs the entire DC output from the AC signal. The center tap transformer does this by allowing current in both cycles.

Other DC rectifier circuits use center tap transformers for converting full AC waves to DC. A normal transformer generates the output in only one direction while tapping through the mid of the transformer provides both direction output. Also, center tapping is seen in general step down transformers for AC-AC conversion.

Center tap transformer diagram

center tap transformer
Center tapped transformer diagram

In a center tap transformer, along with the usual coils, an extra wire is connected from the midpoint of the secondary. This point acts as a neutral point and divides the secondary voltage into two equal halves.

A center-tap transformer is designed in such a way that it can produce two secondary voltages with the same connection. Two voltages VS1 and VS2 obtained by the center tap, are shown in figure 1. These voltages are proportional to the primary voltage VP and the values are the same. So, the power in each coil is equal.

Center tap transformer- FAQs

Center tap transformer winding

In a center tap transformer, the secondary winding is coiled in the same direction as the primary winding, such that both the secondary half winding voltages can add up. The equivalent structure is shown in figure 2.

Here, the end points of the primary winding are P1 and P2. The middle point of the secondary winding between the ends S1 and S2 is S’, the center tapped point . When we apply AC voltage between P1 and P2 , voltage gets induced between S1 and S2. Each half-winding voltage, sums up to the full winding voltage.

Center tapped transformer winding

Delta center tap transformer

Delta center tap transformer, or a high leg delta transformer, is a component in which the secondary winding is connected in delta configuration and it is center tapped. The equivalent circuit is shown in the image below..

Delta Center Tap Transformer
High leg delta transformer; Image Credits: Wikipedia

We can see, one coil in the delta circuit is center tapped. The voltages of the delta coils are the same. Therefore the voltage difference from one end of the center tapped winding and from any two of the other end points to the tapping point are respectively half and √3/2 of the voltage difference between two ends.

Kaushikee Banerjee

I am an electronics enthusiast and currently devoted towards the field of Electronics and Communications . My interest lies in exploring the cutting edge technologies. I'm an enthusiastic learner and I tinker around with open-source electronics. LinkedIn ID- https://www.linkedin.com/in/kaushikee-banerjee-538321175

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