-5v - from an ATX psu?

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Bikerbob
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-5v - from an ATX psu?

Post by Bikerbob »

Anyone enough of an electrical engineer to know how to convert say the 3.3v volt on the psu to -5v we need for TT and megaSTE? also old IBMs etc..

There was a guy selling a cable on ebay.. no longer.

I got some perfect sized ATX power supplies. I just need to create the -5v somehow.

James
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Re: -5v - from an ATX psu?

Post by terriblefire »

Bikerbob wrote: Wed Dec 11, 2019 9:45 pm Anyone enough of an electrical engineer to know how to convert say the 3.3v volt on the psu to -5v we need for TT and megaSTE? also old IBMs etc..

There was a guy selling a cable on ebay.. no longer.

I got some perfect sized ATX power supplies. I just need to create the -5v somehow.

James
ATX has a -5v rail. If its not powerful enough use a 7905 regulator.

http://powersupply33.com/atx-power-supply-pinout.html
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Re: -5v - from an ATX psu?

Post by Bikerbob »

Every ATX I am looking at does not have -5v.. maybe its still in there but not being brought out to the plug.

What I am reading is ATX ver3 standard did away with the -5v.


This was in the link you provided...

The ATX power supply generates three main voltage outputs that are: +3.3 V ; +5 V ; and +12 V. Low-power −12 V and +5 VSB (standby) supplies are also generated by this power supply. The −5 V output was originally needed since it was supplied on the ISA bus, however it became obsolete with the removal of the ISA bus in modern day PCs and has been removed in later versions of the standard ATX power supply.


James
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Re: -5v - from an ATX psu?

Post by terriblefire »

You need the regulator then. 7905 type job.
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indicates how much hurting you shall receive."
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Re: -5v - from an ATX psu?

Post by Bikerbob »

SO found this.

https://czh-labs.com/audiowind-5v-dc-ne ... p0695.html

but the -12v output on the PSU is only .3 amp.. will that power this circuit and whatever else it needs?

James
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Re: -5v - from an ATX psu?

Post by Bikerbob »

terriblefire, I assume you have some pretty good electrical knowledge because of the boards your building etc.. maybe thats what you do for a living.

In the ST world the TT and the megaSTE use -5v on their PSU .. hard to find now.. I have found a nice size replacement a Delta DPS-88ab-2 but it does not put out -5v. Would there be a small circuit you might suggest using that 7905 that could do that?

The board I found needs low ac input or negitive voltage input. the output on the -12v rail is only .3amp.. How do I calc what would be used in running this board.. still left for what the computer needs.. and is it enough for the -5v supply??

James
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Re: -5v - from an ATX psu?

Post by terriblefire »

There are definitely inverting linear regs out there. I'd remembered 7905 from my uni days but maybe its a different part.

Ian Steadman did a nice version for the amiga that produces all the right voltages.

http://www.ianstedman.co.uk/Amiga/amiga ... ATXAdaptor

I have one. I dont tend to do power supplies myself as they are complicated and need a lot of time and energy.. and unless you're doing something specific like @exxos does for the ST/E its usually just worth buying off the shelf.
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Re: -5v - from an ATX psu?

Post by exxos »

Theres a neg-gen in the STFM circuit, generates -12 for the RS232.. I have looked into it before recently , but I haven't found any good solution to this. You either have to have a proper PSU with the voltages you want or build a small circuit using a transformer and a 7905.

http://www.theorycircuit.com/dual-power-supply-circuit/
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Re: -5v - from an ATX psu?

Post by stephen_usher »

Bikerbob wrote: Wed Dec 11, 2019 10:23 pm SO found this.

https://czh-labs.com/audiowind-5v-dc-ne ... p0695.html

but the -12v output on the PSU is only .3 amp.. will that power this circuit and whatever else it needs?

James
That's 4 watts. So at -5V that would be just under an Amp, minus conversion loss, so say 750mA. Is that enough?
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Re: -5v - from an ATX psu?

Post by terriblefire »

NIce...

Here is more info on the Ian Stedman stuff... including a github link with all his schematics.

http://www.ianstedman.co.uk/Amiga/desig ... aptor.html

I distinctly remember creating -5V from 5V with a 7905.
———
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indicates how much hurting you shall receive."
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