Aug 312020

What is Half Wave Rectifier?

The half-wave rectifier only passes half of the input sine wave and rejects the other half. The output of the half-wave rectifier is pulsed DC voltage. The ripple in the output waveform can be reduced by using an electrolytic capacitor.

The half-wave rectifier is mainly used in low power applications due to two main disadvantages:

1. The output amplitude is less than the input amplitude.
2. Because there is no output during the negative half cycle, the output is a pulsed DC voltage with excessive ripple.

Half-wave rectifier rectification process

The current and voltage, that the energy supplier companies deliver to our homes, offices, shops, etc., is alternating current (AC). But the electronic devices that we have on these places use direct current (DC). Then, the alternating current (AC) should be converted to direct current (DC).

To make the rectification process, we use a rectifier circuit made of semiconductor diodes. An electric transformer is used to reduce the line voltage from 110 / 220 volts AC or other, to a lower voltage such as 24, 12, 15  or 9 volts AC.

The rectifier circuit is placed at the output of the transformer. The voltage at the transformer secondary winding is alternating, and it has positive and negative half cycles.

Forward Biased Diode

During each “positive” half cycle of the sine wave, the diode is forward biased, allowing current to flow through it. If the diode is considered ideal, it is like a short circuit. Then all the transformer voltage  secondary winding goes directly to the load resistor.

Diode Forward Bias - The Half-wave rectifier

Reverse Biased Diode

During each “negative” half cycle of the sinusoidal input waveform, the diode is reverse biased, the current supplied by the transformer secondary winding will attempt to flow in the opposite direction to the diode arrow (the diode is reverse biased). If the diode is considered ideal, it is like an open circuit and no current flows through the diode.

Diode Reverse Bias - The Half-wave Rectifier

The output waveform of a half-wave rectifier is shown in the diagram below. As you can see only the positive part of the original wave is obtained in the output of the half-wave rectifier.

Half-wave Rectifier Output

Half wave rectifier output

Note: Half Wave Rectifier = Half-wave Rectifier

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