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ATX to PSU?? No negative?

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gooseEL34:
Ok folks.
I am just starting my interest in EE projects and knowledge acquisition.
I see a lot of vids on Youtube about converting a computer ATX power suppy unit to a benchtop voltage supply.

Here's my question....

With ICs, don't you usually need + AND - voltages?
For example, I have a solid state guitar amp that uses 741s and 4558 ICs.
Those are operated on +/- 15.

Am I missing something?  Or are there many instances where one would only need a positive DC voltage supply?
Thanks
Tim

nctnico:
An ATX power supply is the worst choice for a bench PSU. It can push out way too much current and is poorly regulated.

cyr:
Generally you only need a negative supply for audio and some other analog applications, you don't need it for stuff like microcontrollers.

But I agree, an ATX supply is a horrible choice for a lab PSU, the only thing it is good for is making things blow up in your face if you make a mistake.

alm:
I agree with ntcnico that an ATX power supply makes for a very poor lab supply. But to answer your question, no, modern electronics does not generally need negative rails. For example, many modern (from seventies onward, like the LM324) op-amps are often designed for single supply operation, which means that the op-amp can swing to its negative rail (ground in that case). Common digital ICs and micro-controllers don't need negative voltages either.

The µA741 is an ancient late-sixties design, when symmetrical +/- 15 V power supplies were common. You can be sure the amplifier in your smart phone won't have +/- 15 V power supplies, however.

nctnico:
Actually many opamps (including the LM324) can't swing to the positive or negative rail. For that you need an opamp which is specifically designed for rail-to-rail output. And there is also something called rail-to-rail input. In other words: read the datasheet carefully regarding input levels and output swing.

You can use a single supply voltage and use a resistive divider to keep the inputs halfway the supply voltage.

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