Hi, I just made a first working prototype of a DC-DC PSU board for AT / old ATX PCs, preferably ones with lower-to-mid power usage, but this design can be scaled up if needed.

The idea was to make a modular board that will have built-in protections and supervision ICs, will have a place where you can install DC-DC converters, and will also take care of generating -12V and -5V rails, PSON/PGOOD signals etc.

Features:

• can generate 12V, 5V, 3.3V, -5V, 12V rails
• works in AT and ATX mode: you decide which converters you plug, and what cabling you use
• uses microcontroller as a supervisor and soft-OVP/UVP protection
• uses TL431 with SCR crowbar for analog brute-force OVP protection (along with TVS diodes for additional clamping)
• modular: you can use on-board DC-DC converters, or solder screw terminals/wires and use custom, external modules
• designed around HW-468 TPS40057-based modules (which are surprisingly good for the price) for main voltage rails, and SIP-3 modules for additional rails
• should be easy hackable/modifiable, so you can power various kinds of computers, with custom wiring

Why not just use a Pico PSU (which is smaller and more integrated)? First, Picos are often limited to a 12V input, which requires finding a proper power brick. Today, 19V laptop PSUs or 20V USB-C PD PSUs and powerbanks are much more easily available and more convenient to use (especially small GaN chargers), so I wanted this PSU to be able to work with modern chargers.

Second, most existing DC-DC PSUs that I know of use pretty simple overvoltage protection, relying on disconnecting an input P-MOSFET after a simple supervisor IC like the TPS3510 triggers a fault state. But these ICs often have OVP trip points set dangerously high. And if the P-MOSFET itself goes short, there is no way of saving the hardware. Also, the MOSFETs on buck converters can go short, causing the input voltage to go directly to the +5V or +3.3V rail and frying the CPU/mainboard. Therefore, I added a crude, but effective "brute-force" SCR crowbar, which is meant to short the input to ground and blow the fuse in case an overvoltage happens.

Third, old builds require negative rails (-5V, -12V), and picos or other PSUs usually have really weak charge pumps with small current capacity, and provide only -12V. Here, I used a 3-pin DC-DC converter module in inverting mode to generate -12V, and stepped that down to -5V with a linear regulator. I also put TVS diodes and small fuses for OVP on the negative rails.

And fourth, as we know, most modern power supplies are designed around the +12V rail and have a weak +5V rail. Though in my experience a lot of old PCs, especially Socket 3, Socket 7 builds and earlier don't require as much power from the 5V rail as one might expect (total system power draw can be well below 60W). However, if someone wants to power a 5V-hungry PC, there is an option to plug in a beefy, external industrial DC-DC converter that can generate all the 5V current one would ever want (though first it would be a good idea to solder a copper bar on top of the 5V trace and I exposed some copper to make that possible if needed).

You can also build only what you need: if you want to skip using connectors and screw terminals, you can just solder the wires directly. If you don't need 3.3V or -5V rails, you can skip those converters and their protection circuitry. And if you feel brave and don't think you need separate analog OVP, you can even skip the TL431 ICs and rely only on the digital, programmable supervisor, or the other way around.

Currently this is the first revision of the hardware, a working prototype. I have done some basic testing with a Zida 4DPS PC with Cyrix 5x86 and the PSU works fine, but I am planning on doing some extensive testing and tuning everything further.

PCB design, schematics, firmware (early) currently is available here: https://hackaday.io/project/207195-atxanythin … u-for-retro-pcs
I also made a GitHub placeholder: https://github.com/adbrt/atxanything

Test video (with no commentary for now): https://www.youtube.com/watch?v=ex6VxK59p4k

This is work in progress, so certainly there is a lot to be tuned and optimized, but that's a starting point. This design uses mostly 0805 parts and components on one side, so it is not "dense" by modern standards. But you could scale it down and make it much smaller if needed, especially if only AT mode is needed.