VOGONS


First post, by adalbert

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Recently i had to build a new power supply for my Toshiba T3200SXC because all capacitors in original PSU had leaked and the PCB got toasted. It was an AC/DC power supply, I decided to replace it with DC-DC converters, so now I am using 19V laptop power brick. Or an USB-C PD powerbank (with PD 20V trigger) 😀

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I made some schematics and PCB, but beware that this PCB's layout is only for reference and should be redesigned. I made a prototype on protoboard and you can see how it looks now. My design had soft-power on functionality (you power off the converters by shorting ENABLE pins to ground), but I ommited that function in the prototype and just wired the DC input to the switch.

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It has following outputs:

1. COVER (toggles LCD on/off, high=off: this is dedicated for Toshiba T3200SXC)
2. -12V
3. -5V
4. GND
5. +12V1
6. GND
7. GND
8. +5V
9. +5V

Fan connector:
+12V1
GND

LCD connector:
+12V2 (second converter)
GND

Input voltage: 15V to 24V, could be potentially stressed further

Max current:
around 8A for +5V (Pololu D36V50F5)
around 2A for +12V1 (Pololu D24V22F12)
around 2A for +12V2 (second D24V22F12, this is not needed in regular AT PSU)
-200mA for -5V,
few hundred miliamps for -12V

You can see necessary parts in the schematic, the most expensive ones are Pololu step-down converters. I used them because they were the only ones that were branded and I believe that they have all the protective measures they claim (undervoltage, overvoltage, thermals, reverse polarity). But you can make that in theory with a fraction of cost using noname converters.
You can see all different variants here, the more amps you need the more expensive it gets: https://www.pololu.com/category/131/step-down … tage-regulators

I used CD4066 to toggle +12V2 ENABLE pin with signal from motherboard. That's an overkill, but i have dozens of those chips in my drawer.

I used voltage inverting MC34063A module https://www.ebay.com/itm/MC34063A-Reverse-Vol … ha/362986986675
to create -15V. Then I created -12V with LM7912. This is because I don't believe MC34063 would have proper protection if something failed. A protective diode is also used.

I created -5V from +5V with LM2662 module: https://www.ebay.com/itm/200mA-LM2662-Switche … le/174254048914
I could have probably just added LM7905 after LM7912, but I had these modules laying around. And it won't stress MC34063A. There is protective schottky diode so -5V will have slight voltage drop. But I don't want +5V be passed to -5V rail if something fails.

Overall economics of this projects are pretty poor (around 50 USD + cost of power brick for not-so-powerful PSU), if you need something beefier it's better to adapt regular ATX PSU or use Pico PSU, but for some specific cases maybe that project will be useful. You can just use some parts if you need them, like converting +5V to -5V with LM2662, that could be used with ATX PSUs, or added to Pico PSU.

I attach project files, so you can use or improve something if you like. I'm not 100% sure that it is a perfectly safe PSU, it's a prototype so if you see some hazards you can let me know. I just rely on protection measures of Pololu converters, polyfuses on negative rails and main fuse. There could be an watchdog microcontroller added etc.

Attachments

Repair/electronic stuff videos: https://www.youtube.com/c/adalbertfix