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Comment by londons_explore | Hacker News Reader

Bear in mind this is a very old power supply.

A modern supply would use the same principles, but would probably have mostly surface mount components, a single controller IC, and probably separate switching supplies for each different supplied voltage.

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The power supply is from 2005. By my standards that's not very old, but maybe because I've also been looking at power supplies from the 1940s :-) Specifically a 100-pound Teletype power supply from the Navy that used mercury-vapor thyratron tubes.

http://www.righto.com/2018/09/glowing-mercury-thyratrons-ins...

Two great articles, Ken!

Last time I looked at it it was not especially cost effective to build PC power supplies on multilayer boards. That leads to exactly the kind of construction as in this power supply: large almost completely through hole single-sided board with power components and one or more higher density perpendicular sub-boards with control logic.

2 layer boards with smd components are now cheaper than single layer and through hole - simply because through hole requires more labour to place components and has a substantially higher failure rate (bad joints).

Obviously some components in a power supply still need to be through hole for mechanical reasons, but it isn't many.

It is not that clear-cut. Obviously the optimal case is SMD-only, but there is a threshold when THT-only becomes cheaper than SMD/THT mix. Another thing is that power supplies tend to use higher temperature board material (presumably to allow for thinner copper plating) which is somewhat rare and expensive in dual layer configurations.

More than old, it is low-end OEM power supply. Even back in 2005 we already had stuff like 80 Plus ratings, active PFC, universal input, 600+ W output ratings etc.

I thought the same thing, how could there be no PFC? The UC3842B is not that old. [1] But I guess time has flown... The PFC requirement was part of Energy Star 5.0 which was 2009. [2]

[1] https://www.ti.com/lit/ds/symlink/uc2845.pdf Great generic current mode control circuit good for lots of things, not just supplies. Still in active use today. Datasheet is like a textbook. [2] https://en.wikipedia.org/wiki/Power_factor#cite_note-30

Are you talking about a laptop power supply vs an ATX desktop power supply? Even most enthusiast ATX power supplies that I've seen don't use SMT for the main power board, probably because of the weight of the components.

For example, Here's a (very packed!) modern 1600 watt (!) powersupply from Corsair: https://cdn.cplonline.com.au/media/description/POW-COR-AX160...

You can definitely see that SMT is used for the distribution side, but you can see single-layer boards used closer to the A/C side as well.

Not really true. A lot of supplies sold use old designs. Some components, due to their power requirements, are only cheap in through-hole designs.

Surface mount components exist in some cases that are very compact but you pay a large premium.

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