Center taped Full wave rectifier construction and working

#Technical Studies – Study 4

Definition

Full wave rectifiers are the circuits those convert an AC signal into pulsating DC signal using the both half cycles of the input signal.

Construction:

Full wave rectifier uses two diodes, one step down center taped transformer, load resistor and an AC source.

Two diodes are connected to the both positive terminals of the transformer, load resistor is connected to the diodes in parallel and AC source is supplying power to the circuit.

Operation:

As the transformer is centre taped it acts as two step-down transformers so we can say full wave rectifier is combination of two half wave rectifiers.

During positive half cycle of the signal diode D1 is in forward bias and D2 is in reverse bias. Therefore diode D1 conducts and the voltage across load resistor is equal to supply voltage. The output is in positive polarity.

During negative half cycle of the signal diode D1 is in reverse bias and D2 is in forward bias. Therefore diode D2 conducts and the voltage across load resistor is equal to supply voltage. The output is in positive polarity.

During the operation of both the cycles the load voltage is in same polarity and the load current is in same direction. So in the output signal the negative half wave form is shifted to positive side.

Input and output wave forms

Output frequency:

The input AC voltage has a frequency of 50Hz,

Time period=1/f=1/50 Hz=20 ms

The time period of the output signal of full wave rectifier is half of the input period.

T out= 0.5(20 ms) = 10 ms

f out= 1/Tout=  1/10=100 Hz

The frequency of full wave output is double of the input frequency.

So f out= 2fin

Dc value of full wave signal:

Full wave rectifier has double number of positive half cycles compared to half wave signal, so the dc value will be

Vdc=2Vp/π

If we assume Vp is 1, then

Vdc= 2/π=0.636 V

So Vdc ≈ 0.636Vp

Ripple factor:

The ripple factor of full wave rectifier is approximately 0.482.

Form factor:

Form factor is defines as the ratio of the rms value of the output voltage to the average value of the output voltage.

Ff =rms value of output/ average value of output

Form factor of full wave rectifier is 1.11.

Efficiency:

Efficiency is the ratio between DC output power to AC input power.

Ƞ= dc output power/ AC input power

Efficiency of full wave rectifier is 81.2%.

Peak inverse voltage:

Peak inverse voltage for full wave rectifier is 2*Vs max.

Advantages:

1.Efficiency is higher than half wave rectifier.

2.Ripple factor is less compared to high wave rectifier.

Disadvantages:

1.Output is not pure dc

2.High cost

Full wave rectifier with filter:

The output of full wave rectifier contains both AC and DC components. The application needs pure dc. So the rectified output requires further processing. The unwanted AC component can be reduced by adding a filter to the rectifier.

Below circuit shows a full wave rectifier with capacitor filter.

Full wave rectifier wave forms with filter

Please write in the comment box below if you have any questions.

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