EASA / CAR Part-66 · Module 4 · 4.1.1 Diodes · Cat B1/B2
A diode only lets current pass one way. See how one diode (half-wave) or four in a bridge (full-wave) turn an AC input into a one-direction (DC) output.
Blue is the AC input; green is the rectified output across the load. Half-wave passes only the positive halves (the negative halves are blocked). A full-wave bridge flips the negative halves up too, giving smoother DC. A smoothing capacitor (not shown) would fill the gaps.