Pico ATX PSU, schematic? what IC is used? - Page 1
Forum section: electronics / projects

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 09, 2015, 12:55:55 am
content: I've just ordered one of these:http://www.aliexpress.com/item/12V-160W-Pico-ATX-switch-PSU-Car-Auto-MINI-ITX-ATX-Power-Supply-24pin-DC-ATX/32415238164.htmlFrom ebay, not Ali, but it looks the same.I don't need 3.3volts, but rather need a regulated 12volts at a few amps.The plan is to replace the 3.3volt inductor, and modify the feedback circuit, to get a regulated 12 and 5volt, from 19volts input.But does anyone know what chip they use? if its rated for 12volts, and possibly what they're using to get the -12volt rail...Sure, I could wait for it to arrive, but who has time for that!Cheers!

author: lapm
author_rank: Frequent Contributor
timestamp: August 09, 2015, 05:42:56 am
content: Stupid but obvious question, why all this modding? When there's already PSU units to provide those 12/5V.Its impossible to say what chip they us without opening it and taking a look, there's just too many chips out there.

author: eas
author_rank: Frequent Contributor
timestamp: August 09, 2015, 05:49:18 am
content: My impression was that the 12v versions of those things don't regulate the 12v at all, they pass-through the 12v they are supplied with.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 09, 2015, 05:51:39 am
content: Got a link to a small board that will do 5volts at 5amps, 12volts at about 3amps, and -12volts?Correct, they don't regulate the 12volts, which is why I plan to modify the 3.3v output to give 12volt.

author: funkathustra
author_rank: Regular Contributor
timestamp: August 09, 2015, 05:54:20 am
content: One of the pico supplies floating around uses the LM2642 -- I assume one channel supplies 5V and the other supplies 3.3V. If they're not using that chip, it'd be something similar.It goes without saying that you'll need to verify that every relevant part on the board can handle that kind of voltage -- 20V is a typical cut-off for some HV CMOS processes, so you may run into some issues with the switching transistors, especially.Seems like it'd be easier to just build something from scratch instead of trying to hunt down traces on a board, but I guess to some people, that's a fun adventure! Good luck!

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 09, 2015, 06:01:03 am
content: I saw that ic used, this board has less pins :p

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 09, 2015, 06:59:38 am
content: Quote from: funkathustra on August 09, 2015, 05:54:20 amAnd, I really can't see it being easier, cheaper, or quicker designing from scratch, having to source parts, then design, and have a PCB made, when IC's like the LM2642 will take the 20 volt input, and can do the 12volt output I need...I know the input capacitors, and capacitor on the 3.3volt line will need to be changed for the higher voltages.

author: hs3
author_rank: Regular Contributor
timestamp: August 09, 2015, 07:45:36 am
content: ISL6440 ?https://www.intersil.com/en/products/power-management/switching-controllers/multiple-output-controllers/ISL6440.htmlhttp://www.intersil.com/content/dam/Intersil/documents/isl6/isl6440.pdf

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 09, 2015, 08:37:09 am
content: Quote from: hs3 on August 09, 2015, 07:45:36 amsure looks like it!Thankyou very much!

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 31, 2015, 08:52:56 pm
content: This PSU arrived yesterday! Too slow China, too slow!I've tested it at about 5amps on the 5volt line, and the same on the 3.3volt.Seems well made, and handles it quite well, but before I set about modifying the 3.3volt rail to do 12volt, I decided to wind up the input voltage.... 13volts, and it shut down, it has a "power good" IC, for if any of the rails go out of range...

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: September 10, 2015, 10:10:08 am
content: This PSU has a wt751002 "power good" IC, and I can't figure out how to bypass it...http://www.hardwaresecrets.com/datasheets/WT751002.pdfI assumed I could simply wire from pin 1, to pin 8 (with the IC removed) but the power supply doesn't function.What am I missing here?Thanks!

author: lapm
author_rank: Frequent Contributor
timestamp: September 10, 2015, 12:26:14 pm
content: Quote from: AmmoJammo on September 10, 2015, 10:10:08 amOpen drain outputs. thats what your missing. Try pin 8 wired to ground

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: September 10, 2015, 12:27:31 pm
content: Didn't work either.Pin 2 to pin 3 however did work! Lol