Power Supplies – Why Use Through Hole Components?


Why are power supplies almost always made using through hole components? Every computer PSU I've taken apart uses through hole components, though occasionally (not in all cases) surface mount components are found on the bottom. Don't these have to be hand assembled? (before reflow or wave soldering) If so, why are they still doing this, even though labour costs are low in China, it still must cost less for a machine to pick and place SMT stuff… or am I missing something?

Best Answer

Because PSUs use many big lumpy parts that are not SMDable and/or need good mechanical fixing. Also, for minimum cost they like to use single-layer PCBs - TH is a little more amenable to this as parts act as jumpers over tracks. TH parts can be machine-inserted - e.g. http://www.youtube.com/watch?v=eOQ3pZkKX24 (30kparts/hour!)