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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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[quote name='nwbell' timestamp='1321481129' post='359553']
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 [url="http://web2.murraystate.edu/andy.batts/ps/powersupply.htm"]site[/url] 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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[quote name='nwbell' timestamp='1321481129' post='359553']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?[/quote]
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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[quote name='systems_glitch' timestamp='1321579930' post='359567']
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.
[/quote]

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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