In conjunction with my independent study of switching converters using textbooks, I am more or less obsessively tearing apart all the low-ish power (say 5 - 25 Watt) switching converters I can find. I'm finding myself increasingly able to explain what's happening inside and generally learning a lot about the practicalities of the topic:
I was surprised to discover that all but one of the offline converters I've explored so far use discrete rectifier diodes to form the mains voltage rectifier bridge. This has a few downsides I can see:
- increased PCB area
- increased component population effort
- perhaps increased parasitic C and L, although I don't know that for a fact nor whether anyone would care at that particular part of the circuit
I have a couple hypotheses about why these downsides might be outweighed:
- Lower cost?
- Increased thermal coupling for better dissipation without a heat sink?
Anyway, can someone with experience with these designs help me understand the design reasoning that might explain this apparently common choice?