A rectifier is a diode circuit that converts an alternating-current (AC) input into a unipolar output — one that is always positive (or always negative). Rectification is the first step in turning the AC from a wall socket into the DC that electronics actually run on, so the rectifier is the front end of every DC power supply.
Why it is needed
The wall socket delivers a sinusoid that swings symmetrically positive and negative; its average value is zero. Almost every electronic circuit needs a steady DC rail. You cannot get DC out of a zero-average waveform by averaging it — you first have to make it one-sided. The Diode’s one-way-valve behaviour does exactly that: it lets one polarity of the input through and blocks the other, producing a lumpy but unipolar waveform that a smoothing capacitor can then average into something close to DC, and a Zener voltage regulator or active regulator can clean up further.
Rectifiers are the building block of the DC power supplies that power electronic equipment.
The three families
Three families: half-wave, full-wave (centre-tapped or bridge), and peak rectifier with a smoothing capacitor.
- Half-wave rectifier — a single diode in series with the load. Passes only one polarity’s half-cycles; throws the other half away. Simplest, but wasteful and very lumpy.
- Full-wave rectifier — uses both half-cycles by flipping the negative ones upright. Two standard topologies: the Center-tapped full-wave rectifier (centre-tapped transformer, two diodes) and the Bridge rectifier (single secondary, four diodes). Output frequency is twice the input.
- Peak rectifier — any of the above with a smoothing capacitor across the load. The capacitor holds the voltage near the peak between conduction bursts, producing approximately DC with a small Ripple voltage.
These are not separate devices; they are arrangements of diodes around a load. Which one you pick trades off diode count, transformer cost, Peak inverse voltage rating, and output smoothness.