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:

V_AVG = 2V_p/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 V_in 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 = (V_p(sec)/2 – 0.7) – (-V_p(sec)/2)

= (V_p(sec)/2 + V_p(sec)/2 – 0.7)

= V_p(sec) – 0.7

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

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

– Thus, the PIV across each diode becomes:

PIV = 2V_p(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:

V_p(out) = V_p(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 = V_p(out) + 0.7 V