What is synchronous rectification and when is it beneficial?

Synchronous rectification replaces diodes with actively controlled MOSFETs to reduce rectification losses. MOSFET Rds(on) loss can be much lower than diode forward voltage drop, especially at low output voltages. For example, at 5V/10A, a diode drops 0.5V (5W loss), while a 5mOhm MOSFET drops 50mV (0.5W). Most beneficial for low-voltage, high-current outputs. Requires control circuitry for proper timing (prevent shoot-through). Control can be self-driven (from transformer) or controlled (from PWM controller).