SDG #217 FULL BRIDGE RECTIFIERS and some alternative technologies for high efficiency

Full bridge rectifiers are one of the least glamorous parts in a power supply, and also one of the most wasteful. This build examines what is actually given up by fitting a generic bridge, then compares it against two higher efficiency routes: discrete Schottky diodes and active rectification using MOSFETs driven by dedicated controller ICs.

The test vehicle is a small custom PCB, populated by pick and place so that each variant is assembled to the same standard and measured under comparable conditions. That matters, because forward voltage drop is only half the story. A silicon bridge with two conducting junctions in series at any instant loses roughly 1.4 V to 2 V in total, which at even modest currents becomes watts of heat, a heatsink, and a thermal budget to design around. Schottky parts cut that drop noticeably but bring higher reverse leakage and a tighter voltage ceiling. Ideal diode and active rectifier controllers driving low RDS(on) MOSFETs can push conduction losses lower still, at the cost of part count, board area and a control IC that has to switch cleanly at line frequency.

The cost breakdown deserves attention. A commodity bridge costs pennies; a four MOSFET active stage plus controllers is an order of magnitude more expensive and more complex to lay out. The measured results show where that expenditure is justified, generally at higher current, low input voltage or in sealed enclosures where dissipating heat is the real constraint, and where a plain bridge remains the sensible engineering choice.