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Old 13th March 2007, 09:51 AM   #1
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Question At Pc Power Supply Conversion??.

Hi

I'd Like to know if it is possible to Convert a old Pc Powersupply
to a +-35v Supply?...

I was thinking of Rewinding the Secondary
& repacing the Caps & Filter
But dont know how 1 wld go about with the feed back

Dose anybody have plans on doing that?

or Else does Some1 outthere have a schemetic
of building 1 from scratch?

I'm Very interested in SMPS at the moment

Thanks in advance
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Old 13th March 2007, 05:32 PM   #2
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Did you search?

There are several threads in the Power Supply Design forum on converting old AT & ATX powerboxes: Some from the +/-5V & +/-12V to +13.8V, Some to (+/-) Medium Voltage (for Audio Use), and others for converting to 12V input, etc.

As far as converting the secondary side to do this, sure, it's possible, depending on the model of the PSU (there are literally thousands), how the board is layed out, and of there is a space on the +12V line for a filtercap after the BIG yellow Toroid, but before the output filter choke. Most AT & ATX skip this.

Also, these mods work best for half-bridge units (easily identifiable by a TL494 on the secondary side, and two transistors on the primary side). If you encounter an 8-pin dip UC3842, '43, '44, or '45 PWM chip on the primary side driving a single hiogh-voltage transistor, then you have a flyback unit, and then things are somewhat more complicated.

Hope this helps..


Steve
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Old 14th March 2007, 01:32 PM   #3
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I would use a PSU that has a half bridge design as N-Channel stated, it's a lot simpler to work with.

Also you should try to find a PSU with the largest transformer in it, it makes winding easy and gives you lots of room for extra windings (wich is what you need).

Here's a schematic of one too (you'll have to remove the over/under voltage protection on the left but other than that it's reletivly simple.)

P.S this is not my schematic it belongs to the original author.

Edit: typo's
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Old 15th March 2007, 03:50 PM   #4
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Thanx for the reply the 1 I have is like the 1 on the above schemetic (except 4 the component numbering)
also using a tl494 & transistors

Does any1 have a Idea how to modify the feedback
for 35v?

wold replacing the trans former with a E39 have any bad effects
(i wld rewind the primary with same no of turns as the original one)

Thankx again will keep u posted on my results
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Old 16th March 2007, 12:04 AM   #5
jkeny is offline jkeny  Ireland
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I posted on this a little ways back modyfing a pc switchmode for B+

Although this is about changing AT supply to higher V+ levels I'm sure it can be adjusted for 35V+.

You'll find the article in here: http://rapidshare.com/files/12323786/siliconic.rar.html

John
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