What is Half wave rectifier?

#Technical Studies-Study 3

Rectifiers

Rectifier is an electronics circuit that converts AC signal into DC. It is very useful because electronics circuits operate on DC voltage.

Rectifier is two types:

1.Half wave rectifier

2.Full wave rectifier

Full wave rectifier is of two types

1.Center taped full wave rectifier

2.Bridge rectifier

This study is about half wave rectifier

Definition:

Half wave rectifier is a circuit that converts half of a sinusoidal waveform into pulsating DC.

Construction:

Half wave rectifier can be constructed by using a step down transformer, a PN junction diode, an AC source and a load resistor.

AC source is connected to transformer, transformer steps down the voltage and then supplied to the diode and the resistor is connected as a load.

Operation:

positive half wave rectifier

Above figure shows the operation of the half wave rectifier.

AC source is in the form of sinusoidal waveform. In the positive half cycle of the source the diode is forward bias and allow the current to flow.

 In the negative half cycle of the source the diode is reverse biased so it doesn’t allow the current to flow.

If we consider a full cycle of wave applied to the diode in the output only positive half cycle appears and during negative half cycle it remains zero.

This operation can be called as positive half wave rectifier because only positive half cycle of the signal is rectified.

negative half wave rectifier

If we conduct this operation by reversing the diode we can see that the negative half cycle of the signal appears at the output and the positive half cycle is blocked. It can be called as negative half wave rectifier.

Output frequency:

In half wave rectifiers the output frequency remain same as the input frequency.

fout =fin

Ripple factor:

The output of the half wave rectifier is not pure dc, it is pulsating dc. It has unwanted AC component in it. That is called ripple voltage.

To measure the amount of voltage present in the output signal we use a factor which is called ripple factor.

It is denoted by γ 

Ripple factor= Ripple voltage ratio /DC voltage

\gamma =\sqrt{(\frac{Vrms}{Vdc})^2}-1

The ripple factor for half wave rectifier is 1.21.

DC value of half wave signal:

The dc value of a half wave signal is same as the average value. The formula for calculating dc voltage is

Vdc=\frac{Vp}{\pi }

If we calculate for one cycle

Vdc=\frac{1}{\pi }=0.318

So  Vdc \approx 0.318Vp

Pick Inverse voltage:

Pick inverse voltage is the maximum reverse bias voltage that a diode can withstand. If more than that voltage is applied to the diode then diode will be destroyed.

In reverse bias the diode doesn’t allow current to flow. So the voltage applied to the diode drops across the diode.

Thus PIV = Vs max.

Efficiency (Ƞ):

Rectifier efficiency can be defined as the ratio of output DC power to input AC power.

Ƞ=o/p power/i/p power.

The efficiency of half wave rectifier is 40.6%.

Form factor:

Form factor can be defined as the ratio of rms voltage to dc voltage.

FF= Rms value/DC value.

The form factor for half wave rectifier is 1.57.

Advantages:

1.Low cost

2.Easy to construct

Disadvantages:

Power loss

Output is pulsating dc

Half wave rectifier with filter:

The output of a half wave rectifier is not pure dc it is pulsating dc. But in application pure dc is required. To use the output of half wave rectifier further filtration is needed.

Therefore half wave rectifier uses a filter at the output.

Below circuit shows a half wave rectifier with capacitor filter.

Half wave rectifier with filter

This study was about Half wave rectifier, in next studies we will study other types of rectifiers.

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

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