PC AT Querries

[RX5]

hello all,

I got some questions regarding PC AT power supply...

I wanted to mod it by making/getting MORE current from the +12V...

PC PSU has only 1 chip........ TL494...

All I have done (for now)
-change 220uF/200V capacitors to 470uF/200V..got some from dead
PSU

-change the transformer to a bigger one... (EI-33CAL).. it has much
thicker windings...

-re-wired the output choke filter so +12V has much thicker gauge wire..

.... that is all for now....

I WAS planning to RE-wind transformer.. BUT i cant figure it it... Until I read from past posts (Eva) that said transformer is series wind...its one (12-0-12) coil only?? with +5V "tapped" from that winding... am I correct? or maybe I have miss-read....

each "12V" output from winding has 2 diodes, FR302 and FR153.... for the "5V" out, it has SB1040 and FR153... so meaning FR302 and
SB1040 are the MAIN rectifiers for +12V/+5V....right? I dont know
where the FR153's supply runs... maybe it powers -12V or -5V..

dunno... I got no diagram here..

now my question/s are:

>> what voltage does the TL494 "monitor" for it to regulate??? from +12V or +5V??

>> can I remove the SB1040?? im just going to use +12V since...there is FR153 going off to somwhere..from the "5V" windings...

.. IS it safe to assume to just leave the transformer alone and just
"beef up" the FR302 for a higher output current of 12V??

thanks in advance 😀
Raff

An externally hosted image should be here but it was not working when we last tested it.

 

[N-Channel]

Raff-

Some of the better supplies used separate windings for the 12V and 5V outputs, while the cheaper Chinese ones tapped the 12V winding at 5V.

What EVA means by series, if I'm understanding her correctly, is that the primary is two windings in series. Half the turns inside of the secondaries, and the other half wound outside the saecondaries. This is to provide good magnetic coupling between the primasry and secondary windings, and to minimize leakage inductance, right Eva? 😉

The TL494 monitors the +5V line, because its regulation is the most critical. In some designs, it also monitors the +/-12V and -5V outputs, but with less sensitivity. In other designs, the TL494 montiors the +5V line, and uses feedback from the other outputs to adjust the deadtime of the PWM chip.

Do a search for AT/ATX psu mods. There are about 8-10 threads.

Nice pic, BTW. Notice how there is no EMI/RFI filter at the AC input? Some of the cheap chinese units get away with so much, and the FCC regs (US) are not being enforced.

Steve

 

[RX5]

while the cheaper Chinese ones tapped the 12V winding at 5V.

you mean to say 5V IS tapped from 12V? or the reverse??

What EVA means by series, if I'm understanding her correctly, is that the primary is two windings in series. Half the turns inside of the secondaries, and the other half wound outside the saecondaries. This is to provide good magnetic coupling between the primasry and secondary windings, and to minimize leakage inductance,

I totally understand this 🙂 its what Honda(and perhaps other) CDI (capacitive Discharge Ignition) have.... It does HELP A LOT in coupling the pri to sec....I have build one... big difference from "single" pri compared to split "pri"...

WHat I mean to say is the secondary part...🙂 I know the pri is "split in two".. I managed to de-wound one.... have never managed to put back the secondary.. hehehe bad move 😀 NOw I know the cheaper AT PS have "12-12" windings with /wc 5V is "tapped" from there... ok.. NOW I get it....

The TL494 monitors the +5V line, because its regulation is the most critical. In some designs, it also monitors the +/-12V and -5V outputs, but with less sensitivity. In other designs, the TL494 montiors the +5V line, and uses feedback from the other outputs to adjust the deadtime of the PWM chip.

ok.... hhhmmmmmmm I think there are two "tapped" diode sets.. in +5V.. one is the SB1040(schottky barrier) and FR153(fast recovery).... I think IT wont hurt removing SB1040??? it has NO connection whatsoever to the TL494 ..just pure output of "+5V"/..... the FR153 HAS.... I think thats the rectifier/monitor... 🙂

anyways, maybe last MOD is "beef-up" the FR302 so something more higher current diodes...for +12V..


--------------------BTW-----------

what WILL happen if lets say, it monitors the +5V and there is NO +5V??? will it simply TURN OFF?? or explode?


Thanks

Raff

 

[ifrythings]

N- Channel - Notice how there is no EMI/RFI filter at the AC input?

It's there, see the nice blank spot, it's right in there 😀 😀

what WILL happen if lets say, it monitors the +5V and there is NO +5V

Well it woun't explode 😀 , but if they use seperate windings for the +5V and +12V, you'll get very poor regulation. If it's one big winding there should be modderate regulation.

If your really concerned about regulation you could always change the 2-3 resistor divider network to make it monitor the +12V.

 

[RX5]

EMI/RFI filter at the AC input?

I removed it....😀 gives me the -shock- when I touch chassis and im standing barefoot..

Well it woun't explode , but if they use seperate windings for the +5V and +12V, you'll get very poor regulation. If it's one big winding there should be modderate regulation.

its one BIg winding.. 😀 not separate....

 

[wine&dine]

>>EMI/RFI filter at the AC input?
> I removed it....😀 gives me the -shock- when I touch chassis and im standing barefoot..

Yikes ...

Well, you get a shock 'cause an EMI filter has capacitors from both live and neutral to chassis, which is supposed to be firmly grounded; your bare feet are NOT supposed to be grounded (electrically, heh) when you're working on line-connected stuff.

Aren't you - how to put it politely - stretching the limits of your knowledge beyond the breaking point on this project? I'm asking because we hate to lose forum members to stupid electirical accidents ...

 

[RX5]

>>EMI/RFI filter at the AC input?
> I removed it....😀 gives me the -shock- when I touch chassis and im standing barefoot..

Yikes ...

Well, you get a shock 'cause an EMI filter has capacitors from both live and neutral to chassis, which is supposed to be firmly grounded; your bare feet are NOT supposed to be grounded (electrically, heh) when you're working on line-connected stuff.

Aren't you - how to put it politely - stretching the limits of your knowledge beyond the breaking point on this project? I'm asking because we hate to lose forum members to stupid electirical accidents ...

opps .. not THAT kind of -SHOCK-

😀

I meant to say -sting-... 🙂 not deadly ...but it " I HATE IT" hehehe read that mods from searching google...removing those caps... now, DC OUTPUT is really isolated...
Btw, I removed the +5V.. and "huuuummmmmm"... yep, I guess you get regulation from monitoring the +5V... ok... I can live with that.. but I changed the FR302(for the 12V rectifier) with MBR3045 🙂 15A(per leg?) @ 45V...and put 4x 2200/16V caps at 12V output.... nice

 

[wine&dine]

> read that mods from searching google...
> removing those caps... now, DC OUTPUT is really isolated...

You found some bad advice there from someone else who doesn't know what he's doing. The case has got to be grounded, and the filter should stay. The output can be disconnected from chassis ground on the OUTPUT side with no further harm.

Consider the possibility that one of the primary caps blows and electrolyte forms a connection between V+ and the case. Then you come along and touch that case ... you'll wish you had grounded it even if your feet were not bare.

 

[Bakmeel]

.... Unless you are willing to put the entire supply in a plastic enclosure with no touchable metallic parts.

Secondly, you will notice your fine PSU has become a nice radio, and there will be no AM radio near that PSU 😎

Bakmeel

 

[kartino]

parallel with sagarverma's thread?

I thought I put very clear for modded PC PSU at this forum. As you read and do carefully (also from ELECTRIC SHOCK!), I guarantee you will have cheap SMPS psu for you amps, that is for your goal, isn't it?