Half Wave Rectifier Circuit

- notes and details of the diode half wave rectifier circuit often used in power supplies and other applications..

The half wave rectifier circuit is the most straightforward rectifier circuit that can be used.

Although the half wave rectifier circuit may not provide the level of performance needed for many applications, its simplicity lends it to use in many circumstances.

In view of this advantage, the half wave rectifier circuit can often be seen within large items of electronics equipment.

Basic half wave rectifier circuit

The half wave rectifier circuit can be used in a number of different applications. The half wave rectifier circuit normally utilises a single diode. This passes one half of the cycle, and blocks the other. In this way only half of the cycle is used, but current is only allowed to flow in one direction.

Basic diode half wave rectifier circuit
Basic diode half wave rectifier circuit

The half wave rectifier circuit can often be used with a transformer if it is to be used for powering equipment in any way. Normally in this application the input alternating waveform is provided via a transformer. This is used to provide the required input voltage.

Diode half wave rectifier circuit with transformer
Diode half wave rectifier circuit with transformer

Half wave rectifier diode requirements

When designing a half wave rectifier circuit, it is necessary to ensure that the diode is capable of providing the required performance. While there are very many parameters that define individual diodes, and these may need to be taken into account for a given design, some of the major parameters are detailed below:

  • Forward current:   It is necessary that the diode is able to handle the levels of average current and peak current flowing through it in a half wave rectifier circuit. The current will peak as a result of the capacitor smoothing circuit. As the current only flows as the capacitor charges up, the current is in short bursts which are much higher than the average current.
  • Peak inverse voltage:   The diode must be able to reliably withstand the peak reverse or inverse voltages that appear across it. The peak voltages are not just the output voltage, but higher. The peak inverse voltage rating of the diode should be at least 2 x √2 times the RMS voltage of the input. This is because the output is normally smoothed by a capacitor, and this will take a value that is the peak of the input waveform. This will be √2 times the RMS voltage. With this voltage on the output, the input waveform on the "blocked" half of the cycle will fall and reach a peak value at the bottom of the crest of √2 times the RMS value. The maximum reverse value seen across the rectifier diode is the sum of these two voltages.

    There should also be a significant margin, especially when used in a mains or line power supply. This is because voltage spikes can appear on the line.

By Ian Poole

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