Converting AC to DC with single and multiple diodes
A half-wave rectifier uses one diode to block the negative half-cycle of AC, passing only positive pulses to the load. This is simple but wastes half the AC cycle and produces a ripply, low-average DC voltage. A full-wave rectifier with a center-tapped transformer uses two diodes, each passing one half-cycle, producing twice the average voltage and lower ripple. A bridge rectifier uses four diodes arranged in a square to pass both half-cycles through the same load, achieving the benefits of full-wave without needing a center tap. Bridge rectifiers are the most common topology for modern AC-to-DC power supplies.
Ripple filtering and rectifier selection
All rectifiers produce a pulsating DC output that must be filtered by a capacitor and inductor (LC filter) to smooth it to clean DC. Larger filter capacitors produce lower ripple but slow the response to load changes. A half-wave rectifier needs 4 times more filtering than a bridge rectifier to achieve the same ripple. Higher rectifier frequencies (using switched-mode power supplies instead of 50/60 Hz line frequency) reduce filtering requirements dramatically. Modern AC-DC converters use high-frequency switching and digital control to achieve tight output voltage regulation, small size, and efficiency above 90 percent.