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I am converting a ATX computer power supply into a bench power supply and I was wondering if I would need the -5 volts. I know I might need the -12 volts for op amps but is there any point of using a binding post for the -5 volts.

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    \$\begingroup\$ Perhaps you should change the question title, as you're asking about the use of -5v outside a PC. \$\endgroup\$
    – John U
    Commented Aug 27, 2013 at 8:04
  • \$\begingroup\$ my original question was about the use of - 5 volts in electronics (I meant would I need it as a hobbyist) but the question was edited. But I think this is also ok. \$\endgroup\$
    – khiz
    Commented Aug 27, 2013 at 8:09
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    \$\begingroup\$ N.b.: The -5V rail is not used in modern PCs and was therefore dropped from ATX PSUs some time ago. \$\endgroup\$
    – JimmyB
    Commented Aug 27, 2013 at 9:03
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    \$\begingroup\$ @khiz, I guess the title was edited because you only mention the ATX power supply. If you want to expand to the full field of electronics you'll have to edit the question, but I think it is better the way it is. \$\endgroup\$ Commented Aug 27, 2013 at 9:18

2 Answers 2

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As well as the +/- 12V you've mentioned for op-amps many will run from +/-5V as well, sometimes that can be handy because you can use something like a TPS60400 charge pump to get -5V from a 5V supply. You might like to include it for that reason so you can test your analog section before you've made the final power supply.

It might also be a useful test input for bipolar ADCs and other analog stages that accept a negative input voltage, for example you might want a negative input that is not right on the supply rail with a +/- 12V circuit (although for most of those cases you could also use a voltage divider).

I suspect it's not the sort of thing you'd use often but for the sake of a binding post it's probably worth including in case you ever need it.

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A common output voltage for an ac transformer is 6v, 0V, 6V i.e. a 12V secondary with a centre pin. After the bridge rectifier you'd get dc voltages of + and -7V relative to the centre pin and many circuits will use + and - 5V regulators to derive a stable and clean DC supply for various circuits.

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