A full-wave rectifier uses both half-cycles of the AC input instead of throwing one away. It flips the negative half-cycles upright, so the output is always positive and consists of back-to-back humps with no gaps. Two standard topologies do this: the Center-tapped full-wave rectifier and the Bridge rectifier.
What’s wrong with half-wave
A Half-wave rectifier discards half of every cycle. The output is ragged: a hump, then a long flat gap at zero, then another hump. Its DC component is only (see DC value of a rectified waveform), and the long gaps make it hard to smooth. A filter capacitor has to hold the voltage up across an entire missing half-cycle, so it has to be large or the Ripple voltage is bad. On top of that, half the available power goes unused.
A full-wave rectifier fixes both problems. Using the negative half-cycle too means there’s a hump every half-period, no gaps. Two payoffs:
- Higher DC component. The full-wave average is , double the half-wave value.
- Output frequency is twice the input frequency. A peak every half-cycle, not every cycle. For a 60 Hz line the rectified output ripples at 120 Hz. That helps smoothing: the capacitor only holds the voltage for half as long between refills, so for the same Ripple voltage you need half the capacitance.
The two topologies
- Center-tapped full-wave rectifier: a transformer with a centre tap and two diodes, each conducting on one half-cycle. Only one diode drop in the load path, but it needs a centre-tapped transformer and each diode must withstand a Peak inverse voltage of .
- Bridge rectifier: four diodes in a diamond around the load, single secondary, two conducting each half-cycle. No centre tap and PIV is only , but two diode drops sit in series with the load.
The choice between them trades transformer cost against diode count and voltage rating.