Teardown of a PC Power Supply

Re:Teardown of a PC Power Supply by formerly_proven on Sunday May 23, 2021 @05:07PM (#27258604)

-12 V was used for RS-232, which uses +12 V and -12 V levels (with a very wide tolerance band). Having a separate supply for this was a design decision which was pretty much instantly obsolete with integrated charge pumps: All RS-232 outputs are running off of charge pumps running at (-2) and (+2) ratios, so +-10 V levels with a 5 V supply.

I don't know what -5 V was used for. Maybe some analog circuits somewhere, very early MOS logic also often had awkward supply voltages (charge-pumps made this obsolete too, just like high-voltage supplies for EEPROMs).

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Re:Teardown of a PC Power Supply by kens on Sunday May 23, 2021 @05:35PM (#27258799)

Early DRAM chips like the MK4116 required -5 V, +5 V, and +12 V. (-5 was the substrate back bias for the chip.) So the ISA standard required -12 V, -5 V, +5 V, and +12 V.

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Re:Teardown of a PC Power Supply by toast0 on Sunday May 23, 2021 @05:41PM (#27258846)

-5v was often used in sound cards for audio amps, I believe. I've got an arcade machine with an AT supply that uses -5v for the audio amp anyway.

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Re:Teardown of a PC Power Supply by SomeHacker44 on Sunday May 23, 2021 @11:10PM (#27260766)

I have a number of 80s and early 90s computers. They had some circuits that used ECL, which required a negative voltage. One I had to recently adjust had a power supply that outputted (when properly adjusted) +5V and -5.2V.

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