Full bridge rectifier operation

A full-bridge rectifier converts AC into pulsating DC using four diodes connected as a bridge, so both half cycles of the input are used.

        A (AC in)
       /  \
     D1    D4
     /      \
   (+)-RL-(-)
     \      /
     D3    D2
       \  /
        B (AC in)

D1 and D2 conduct together on one half cycle; D3 and D4 conduct on the other. Each pair connects the load to the supply.

Operation:

• Positive half cycle (A positive, B negative): D1 and D2 are forward biased, and D3 and D4 are reverse biased. Current flows A → D1 → load (from + to −) → D2 → B.
• Negative half cycle (B positive, A negative): D3 and D4 conduct. Current flows B → D3 → load (again from + to −, the same direction) → D4 → A.

The current through $R_L$ has the same direction in both half cycles, so the output is a pulsating unidirectional waveform with two pulses per cycle (frequency $2f$).

Average (DC) output voltage. If the secondary peak voltage is $V_m$ (ignoring diode drops):

$$V_{dc}=\frac{1}{\pi}\int_0^{\pi}V_m\sin\theta\,d\theta=\frac{2V_m}{\pi}=0.637\,V_m$$ $$I_{dc}=\frac{2I_m}{\pi}, \qquad V_{rms}=\frac{V_m}{\sqrt2}, \qquad \text{ripple factor}=0.48, \quad \eta_{max}=81.2\%$$

With silicon diodes, two diodes conduct at a time, so $V_{dc}\approx\frac{2(V_m-1.4)}{\pi}$. The peak inverse voltage of each diode is $V_m$. No centre-tapped transformer is needed.