-5v - from an ATX psu?

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

Post by DoG » Wed Dec 11, 2019 10:45 pm

Check the archives for what is needed of the PSU in the MegaSTe.

Meanwell does some nice PSU. The RQ65 for example can maybe work. Got -12V and -5V. It seems in specs. Input 115V or 230V. Should fit nicely.

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

Post by Bikerbob » Wed Dec 11, 2019 11:45 pm

Thanks DoG might do that.. I picked these up for $10 ea.. and they work fine for other projects.. but if I could use it here would be great..

ANYWAY..

This is the part of the schematic I am interested in. .. But why is the Fan in the -12v area??

If I built a small board that has a 7905 on it.. with the large lead in cap and the following stabilizing cap.. should I not just be able to grab from the -12v output and that will give me my -5v??

James
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ari.tao
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Re: -5v - from an ATX psu?

Post by ari.tao » Thu Dec 12, 2019 8:54 am

Specs linked by DoG tell max. load on -12V is 0,3A - so better not pull 750mA from that.
I wonder about the spec. min. load of 0,2A on +12V, as the normally attached fan Nidec BETA SL takes only 150mA. The fan should protect the PSU from being damaged by too less load.
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stephen_usher
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Re: -5v - from an ATX psu?

Post by stephen_usher » Thu Dec 12, 2019 11:52 am

ari.tao wrote:
Thu Dec 12, 2019 8:54 am
Specs linked by DoG tell max. load on -12V is 0,3A - so better not pull 750mA from that.
I wonder about the spec. min. load of 0,2A on +12V, as the normally attached fan Nidec BETA SL takes only 150mA. The fan should protect the PSU from being damaged by too less load.
12V @ 0.3A is 4 watts.
5V @ 0.72A is 4 watts. (So, ok, with conversion loss you're probably looking at 0.7A max.)
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Atarian Computing
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Re: -5v - from an ATX psu?

Post by Atarian Computing » Thu Dec 12, 2019 12:16 pm

terriblefire wrote:
Wed Dec 11, 2019 10:41 pm
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.
I can vouch for Stedy's adapter. I have it specifically for the -5V and my TT works from it.
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Bikerbob
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Re: -5v - from an ATX psu?

Post by Bikerbob » Thu Dec 12, 2019 1:38 pm

So the point of this..

I am adding things to my MegaSTE and to my TT030 .. and I thought.. at what point am I going to deal with issues relating to high draw?

I can recap to my hearts content, but it does not allow more power out. What can I do?

I also have a PAK68/30 for my megaST4 - and the ATX is perfect for that.. as I am going to have to mount the whole thing in a desktop case anyway.. so a nice small ATX 75w psu should be able to power all in that nicely.

So that meanwell RQ65-B - is getting rare it would seem. Also not really much of a boost in power, if not a slight bit less.

Thanks for the link on the Steadman item.. that might be the way to go if I run into problems.. but I guess for now.. build.. see what everything draws and go from there.

James

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

Post by terriblefire » Thu Dec 12, 2019 2:33 pm

My approach is always wait until you have an actual problem before solving it.

Just something to think about.
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ari.tao
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Re: -5v - from an ATX psu?

Post by ari.tao » Thu Dec 12, 2019 4:28 pm

terriblefire wrote:
Thu Dec 12, 2019 2:33 pm
My approach is always wait until you have an actual problem before solving it.
Just something to think about.
Well, that´s the difference between brothers Prometheus & Epimetheus. I tend to be a fan of Prometheues (the one who put us on fire).
Did Steadman something like PicoPSU? With Pico you´ll have 12V in and everything out...
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Re: -5v - from an ATX psu?

Post by terriblefire » Thu Dec 12, 2019 7:13 pm

Most PicoPSUs are rubbish. The one i got wont even power an Amiga 2000.
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Re: -5v - from an ATX psu?

Post by Tomswork » Fri Dec 13, 2019 5:08 am

The white wire on atx supply is minus 5v same as that Atari supply'

Tom

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