Full-wave Rectifiers

Full-wave rectifiers

Half-wave rectifiers have some applications.

However, full-wave rectifiers are the most commonly used ones for dc power supplies.

A full-wave rectifier is exactly the same as the half-wave, but allows unidirectional current through the load during the entire sinusoidal cycle (as opposed to only half the cycle in the half-wave).

Average value of output becomes twice that of the half wave rectifier output:

VAVG = 2Vp/p

There are two main types of full wave rectifiers:

i) Center-tapped full-wave rectifier.

Two diodes connected to the secondary of a center-tapped transformer.

Half of Vin shows up between the center tap and each secondary.

At any point in time, only one of the diodes is forward biased.

This allows for continuous conduction through load.

Note that the peak inverse voltage (PIV) across D2 is:

PIV = (Vp(sec)/2 – 0.7) – (-Vp(sec)/2)

= (Vp(sec)/2 + Vp(sec)/2 – 0.7)

= Vp(sec) – 0.7

Since Vp(out) = Vp(sec)/2 – 0.7, we get:

Vp(sec) = 2Vp(out) + 1.4

Thus, the PIV across each diode becomes:

PIV = 2Vp(out) + 0.7 V

ii) Bridge full-wave rectifier.

When the input cycle is positive, diodes D1 and D2 are forward biased.

When the input cycle is negative, diodes D3 and D4 are the ones conducing.

The output voltage becomes:

Vp(out) = Vp(sec) – 1.4 V

The reason we’d rather use a full bridge rectifier than a center-tap, is that the PIV is a lot smaller:

PIV = Vp(out) + 0.7 V

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