A full-wave rectifier uses both half-cycles of the AC input instead of throwing one away. It effectively 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 achieve this: the Center-tapped full-wave rectifier and the Bridge rectifier.
Why bother — what’s wrong with half-wave
A Half-wave rectifier discards half of every cycle. That has two consequences. First, the output is very 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. Second, half the available power is simply not used.
A full-wave rectifier fixes both. By using the negative half-cycle as well, the output has no gaps — there is a hump every half-period. Two practical benefits follow:
- Higher DC component. The full-wave average is , double the half-wave value.
- Output frequency is twice the input frequency. There is a peak every half-cycle, not every cycle. For a 60 Hz line the rectified output ripples at 120 Hz. This matters for smoothing: the capacitor only has to hold the voltage for half as long between refills, so for the same Ripple voltage you need half the capacitance.
The two topologies in brief
- Center-tapped full-wave rectifier: a transformer with a centre tap and two diodes. Each diode conducts on one half-cycle. Simple, only one diode drop in the load path, but 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 diodes conduct each half-cycle. No centre tap needed and PIV is only , but two diode drops are in series with the load.
Both turn the same ragged-half-wave problem into a smooth-able, gap-free, double-frequency waveform; the choice between them is a trade of transformer cost against diode count and voltage rating.