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
