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Stupid power supply question


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#1 nwbell

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Posted 16 November 2011 - 05:05 PM

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, 16 November 2011 - 05:06 PM.


#2 nyphonejacks

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Posted 16 November 2011 - 08:32 PM

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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#3 Rift

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Posted 17 November 2011 - 11:12 AM

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)

#4 systems_glitch

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Posted 17 November 2011 - 08:32 PM

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.

#5 Rift

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Posted 18 November 2011 - 01:23 AM

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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