The bridge rectifier is a Full-wave rectifier built from four diodes arranged in a diamond around the load, fed from a single (no centre tap required) transformer secondary. On each half-cycle two diagonally-opposite diodes conduct, always pushing current through the load in the same direction.
How the four diodes work
Picture the four diodes as a diamond with the AC source connected to the left and right corners and the load connected across the top and bottom corners.
- Positive half-cycle (left corner positive): current flows from the source, through one diode into the top of the load, down through the load, out of the bottom, and back through a second (diagonally opposite) diode to the source. The other two diodes are reverse biased and off.
- Negative half-cycle (right corner positive): the other diagonal pair conducts. Crucially, the path is arranged so the current still flows the same way through the load — top to bottom — even though the source polarity reversed.
So the load always sees current in one direction: full-wave rectification, output frequency twice the input, no gaps.
Four diodes in a diamond; two conduct diagonally each half-cycle, current always one way through the load.
Advantages over the centre-tapped version
The whole transformer secondary is active on every half-cycle (no idle half-winding), so the bridge uses the transformer copper more efficiently than the Center-tapped full-wave rectifier, and it needs no centre tap.
Its Peak inverse voltage is only , about half the that each diode in a centre-tapped rectifier must withstand. The off diodes in a bridge are protected by the conducting diodes, so no single diode ever sees more than one peak.
Bridge PIV , ~half the centre-tapped value, and needs no centre tap.
The cost: two diode drops
The price is that the conduction path always goes through two diodes in series, not one. With the Constant-voltage-drop model each drops V, so the peak output is
instead of the of a single-diode-path rectifier.
CVD worked example: two series diode drops cost ~1.4 V from the peak output.
Worked example. Suppose the secondary peak is V and V. The peak output is V. The two diode drops cost about V — negligible at high voltages but a significant fraction of a low-voltage supply, which is exactly when a centre-tapped or active arrangement may be preferred. For mains-level voltages the bridge’s lower PIV and better transformer use usually win, which is why the bridge is the most common rectifier in practice.