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nwbell

Stupid power supply question

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So I'm trying to put together a replacement power supply for a DVR I snagged today. The original was configured as such: ftp://files155.cyberlynk.net/uploads/Classic%20Recorder%20Power%20Pin%20Out.pdf

It needs to put out +12VDC, +5VDC, and -12VDC. At first glance, I'd think a plain old AT power supply would work fine, since it would put out +12VDC and +5VDC at more than sufficient amperages.

But what about the -12VDC? As I understand it, -12VDC is merely +12VDC with swapped polarity. But I don't know how I'd be able to get + and - out of the same supply without shorting its outputs to its grounds.

Can anyone enlighten me on what I'm missing?

--nwbell

Edited by nwbell
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So I'm trying to put together a replacement power supply for a DVR I snagged today. The original was configured as such: ftp://files155.cyberlynk.net/uploads/Classic%20Recorder%20Power%20Pin%20Out.pdf

It needs to put out +12VDC, +5VDC, and -12VDC. At first glance, I'd think a plain old AT power supply would work fine, since it would put out +12VDC and +5VDC at more than sufficient amperages.

But what about the -12VDC? As I understand it, -12VDC is merely +12VDC with swapped polarity. But I don't know how I'd be able to get + and - out of the same supply without shorting its outputs to its grounds.

Can anyone enlighten me on what I'm missing?

--nwbell

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I just finished building my bench power supply this weekend from an old ATX power supply. This site has a lot of information on how to build one.

Yellow: +12v

Red: +5v

Orange: +3.3v

Black: Ground

Blue: -12v

Brown: +3.3vs (+3.3v remote sensing)

Green: Power On

Purple: +5vsb (+5v stanby)

Grey: Power OK

White: -5v (most newer ATX power supplies may not have -5v)

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But what about the -12VDC? As I understand it, -12VDC is merely +12VDC with swapped polarity. But I don't know how I'd be able to get + and - out of the same supply without shorting its outputs to its grounds.

Can anyone enlighten me on what I'm missing?

As Rift pointed out, computer supplies do provide -12V and generally make pretty good bench supplies. The thing about the -12V side is that it's not really just +12V with the polarity swapped, it's a bipolar supply. Between the -12V and +12V leads, you have 24V.

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As Rift pointed out, computer supplies do provide -12V and generally make pretty good bench supplies. The thing about the -12V side is that it's not really just +12V with the polarity swapped, it's a bipolar supply. Between the -12V and +12V leads, you have 24V.

Right and between other leads you can get different voltages as well. +5v with +12v will get you +7v (+5v as your gnd lead) or -12v (gnd lead) and +5v is +17v and so on.

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