ATX psu > lab-ish psu - need help with protections

[neclovek]

Hi, before i start i just want to
since unmodified ATX psu pretty much sucks as a lab supply, I decided to make it into one. Internet is full of "tutorials" how to do such thing but all of them are just useless bull**it because they only show you how to put a linear regulator or whatever into it. So i made one on my own by disconnecting pins 1 and 2 of TL494 and connecting them so pin 2 is around 1,5V (voltage divider from VREF on tl494) and pin 1 is connected to gnd with one resistor and to 12v with potentiometer. It works really great but i have one problem - protections. On old crappy supply i had i just desoldered 8 pin protection chip and grounded some pins but then it lost short circuit protection and i "accidentaly" fried it (love that burnt semiconductor smell). Now i got myself some really nice psu - lots of imput filtering, high current everything(transistors, rectifiers,...), lots of output filtering as well, good quality output caps, etc. It has protections probably somehow made through lm339. I wouldnt mind them - still works from 1,5 to 17 volts with high currents but i would like to remove all unnecesary coils, caps, etc from other outputs since i dont plan to use them. Problem is that i cant. Even when i removed output cap from -12 volts the damn thing refused to start. I guess I can just remove all "unneeded" circuitry but i really want short circuit protection on this thing.

Is there anyone who would like to help me with this?
Some photos: http://imgur.com/a/rZbAZ

[selldoor]

Re: ATX psu > lab-ish psu - need help with protections

Please post your photos on this site not offsite - use manage attachments

[dmill89]

Re: ATX psu > lab-ish psu - need help with protections

I suppose it depends on what you are looking for in "protections". On my lab/test PSU (Converted from an ATX PSU) I just used automotive fuses on the outputs, simple and works pretty well (of course you have to keep spare fuses on hand for when you blow one).

[neclovek]

Re: ATX psu > lab-ish psu - need help with protections

selldoor: Thanks for telling me. But is it really that much of a problem? I mean I dont have any problem with that, I just think that using imgur is better because images are loading at least 5 times faster and also they are easy to manage.

dmill89: I was thinking about using fuses too but I think that built in short circuit protection would be much better, I just need some help figuring out what is preventing the supply from starting when some rail is not present.

[SteveNielsen]

Re: ATX psu > lab-ish psu - need help with protections

selldoor: Thanks for telling me. But is it really that much of a problem? I mean I dont have any problem with that, I just think that using imgur is better because images are loading at least 5 times faster and also they are easy to manage.

"Imgur is over capacity!

Sorry! We're busy running around with our hair on fire because Imgur is over capacity! This can happen when the site is under a very heavy load, or while we're doing maintenance.

Please try again in a few minutes."

[selldoor]

Re: ATX psu > lab-ish psu - need help with protections

selldoor: Thanks for telling me. But is it really that much of a problem? .

Its no problem at all, I just wont look at them and neither will some others who might be able to help you.

We also like the pictures on site so that they stay with the thread, which is sometimes meaningless when you have no picture to refer to.

Off site pictures often get deleted by the poster or the site.

[neclovek]

Re: ATX psu > lab-ish psu - need help with protections

"ERROR 500 - Internal Server Error!
The following eror occurred:
This requested URL caused an internal server error."

...Yeah, uploading photos to the attachments works flawlessly!

[Stefan Payne]

Re: ATX psu > lab-ish psu - need help with protections

Do what they say!

Because the attached photos stay here as long as the forum exist.
The ones on imgur will be deleted in a year or two and than this thread makes no sense!

So it's always preferable to use attachments in Forums if possible...

[neclovek]

Re: ATX psu > lab-ish psu - need help with protections

Okay, i know but it has 2 problems:
1.st - I dont think that anyone is going to be losing his time helping me with this (today i feel really pessimistic, sorry for that)
2.nd - The damn thing doesnt let me to post those friggin attachements and keeps failing with that internal server error. I tried photos, I tried ziping them, I tried uploaded smaler photos and always same error. So how the hell am i supposed to attach those photos when it doesnt work?

I am gonna try one more time and if its gonna fail, i will probably go somewhere alone and cry that my life hates me...

EDIT: MAAAAN, this ONE pixel made so much trouble??????? I am starting to hate attachments...no wonder i dont use them, its like the most unconfortable way to share content

[noppa]

Re: ATX psu > lab-ish psu - need help with protections

Maybe this could help.

http://www.chirio.com/switching_power_supply_atx.htm

[neclovek]

Re: ATX psu > lab-ish psu - need help with protections

That will surely help! Thanks a lot! But i would rather keep original short circuit protection but if i wont find out how ill probably make it from the tutorial

[domas]

Re: ATX psu > lab-ish psu - need help with protections

I was through a simmilar project recently. I followed the tutorial for the first part (converting atx to 13.8v p/s) where you really throw everything out you don't need, keep 12v rail only. The control chip was DR0183, and according to tutorial one would fake +3.3 and +5 voltage input to chip by routing +5vstby to them with according voltage dividers to keep the controller chip happy.

As I have moded the atx to 2.5 to 25V p/s, I had to keep the OV protection but removing the UV protection. The problem was that it had 1 pin monitoring both things, and the limit was broad for chip iself - 3 to 5 V to make it happy. So I have made an adjustable voltage divider with diode to that pin adjusted to trigger OV protection @ 24.6V but the problem was that this would trigger UV protection @ 10 or so volts. So I have added another diode from 5vstby rail to keep the pin at 4.3v (5Vstby - diode vdrop) no matter what, and another adjustable resistor network to increase voltage at the pin to trigger the respective OV voltage adjusted to 24.5V. I did this in case feedback reg. potentiometer wires are damaged which will result in skyrocketing voltage. Did not fiddle with short circuit / oc protection though - wasn't even sure how it worked, so I added automotive fuse. but this was not needed, as the protection was still there.

Just play around with pins going to lm 339 from 12v rail, and in case you want to remove +3 and +5 V rails you might need to fake few lm339 outputs, but I would advice making a diagram first.

That is the way to go.