Full Wave Rectifier Circuit

The bridge rectifier provides significant advantages over the half wave rectifier, allowing better smoothing and better efficiency.

Diode Rectifier Circuits Include:
Diode rectifier circuits     Half wave rectifier     Full wave rectifier     Two diode full wave rectifier     Full wave bridge rectifier     Synchronous rectifier    

Although the half wave rectifier finds applications in signal and peak detection, it is not widely used in power rectification. It is within the power rectification arena that the bridge rectifier is the most common form of rectifier.

The full wave rectifier is more complicated than the half wave version, but the full wave rectifier offers some significant advantages, and as a result it is almost exclusively used in this area.

Full wave rectifier: basics

The concept of the full wave rectifier is that it utilises both halves of the waveform to provide an output and this greatly improves its efficiency.

Comparison between the half wave and full wave rectifier operation showing that in a full wave rectifier both halves of the waveform are used.
Comparison between the half wave and full wave rectifier operation

A further advantage when used in a power supply is that the resulting output is much easier to smooth. When using a smoothing capacitor, the time between the peaks is much greater for a half wave rectifier than for a full wave rectifier.

With a shorter gap between peaks the full wave rectifier enables better smoothing
Full wave rectifier enables better smoothing

It can be seen from the circuit diagram, that the fundamental frequency within the rectified waveform is twice that of the source waveform - there are twice as many peaks in the rectified waveform. This can often be heard when there is a small amount of background hum on an audio circuit.

Full wave rectifier advantages and disadvantages

Although the full wave rectifier circuit requires more diodes than a half wave rectifier circuit, it has advantages in terms of utilising both halves of the alternative waveform to provide the output.

Full wave rectifier advantages

  • Utilises both halves of the AC waveform
  • Easier to provide smoothing as a result of ripple frequency

Full wave rectifier disadvantages

  • More complicated than half wave rectifier
  • The twice frequency hum on an audio circuit may be more audible

Types of full wave rectifier circuit

There are two main forms of full wave rectifier circuit that can be used. Each type has its own features and is suited for different applications.

  • Two diode full wave rectifier circuit:   The two diode full wave rectifier circuit is not so widely used with semiconductor diodes as it requires the use of a centre tapped transformer. However this rectifier circuit was widely used in the days of thermionic valves / vacuum tubes. As a rectifier circuit using four valves would be large, the two diode version was much more preferable.
    Full wave rectifier using two diodes and a centre tapped transformer
    Full wave rectifier using two diodes and a centre tapped transformer
  • Bridge rectifier circuit:   The full wave bridge rectifier circuit configuration is far more widely used these days. It offers a more efficient use of the transformer as well as not requiring a centre-tapped transformer. The additional cost is two additional diodes - not an expensive addition these days. Often four diode bridges can be bought as single items, making construction of the overall circuit much simpler.
    Full wave rectifier using a bridge rectifier
    Full wave rectifier using a bridge rectifier

In view of their advantages, full wave rectifier circuits are virtually always used in preference to half wave circuits. The increased efficiency coupled with the better smoothing ability arising from the shorter time between peaks means that their advantages outweigh the disadvantages by a long way. Only occasionally, often for low requirement supplies would a half wave rectifier be used in preference to the full wave rectifier circuit.

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