A hardware development project for a galvanically isolated, fully programmable laboratory power supply. The design combines a tracking synchronous buck preregulator with a fast linear post-regulator to provide high efficiency without giving up low output noise.
Development status: the schematic and the PCB layout are complete for this revision and the KiCad sources are published. Firmware is in development, and no board has been etched or brought up yet — every figure below is a design target, not a measurement.
| Parameter | Target / current design |
|---|---|
| Output voltage | 0–50 V programmable; expected practical lower limit approximately 20–50 mV |
| Voltage setting increment | approximately 0.84 mV; 1 mV user step |
| Current setting increment | 1 mA in firmware |
| Output ripple | no more than 1 mV target |
| Present transformer capability | approximately 5–6 A continuous, 8 A peak — the limiting element today |
| Pass-element thermal budget | 7 A continuous with the current heatsink and a silicone insulator; 10 A in short bursts under NTC foldback |
| Power-stage design target | up to 10 A after the transformer rewind (a mica insulator is then required on the pass FET) |
| Operating modes | CV, digital CC, programmable foldback, controlled output ramps |
| Controller | STM32G474 |
| Voltage reference and DAC | REF5025 + 16-bit DAC8830 |
| Voltage/current monitor | 20-bit INA228 with a Kelvin-connected 10 mΩ shunt |
The schematic is an A1 sheet. Open the SVG directly for lossless zoom.
Two home-etched single-sided boards: a main board of about 260 × 152 mm and an auxiliary flyback board that generates the +67 V / −5 V rails for the post-regulator. Connections that cannot be routed on one copper layer are made with 25 documented wire jumpers.
More views, layout details and the conventions used → PCB page
The mains front end is based on a modified 500 W ATX supply. Its active PFC stage creates an approximately 380 V DC bus, followed by a two-switch forward converter that provides galvanic isolation and an approximately 55 V secondary rail.
An STM32G474 controls a synchronous buck stage through HRTIM. The buck output tracks the requested output voltage while maintaining only about 2–2.5 V across the linear pass MOSFET. A damped C–L–C filter attenuates switching components before the OPA454-based linear post-regulator removes the remaining ripple.
A 16-bit DAC8830 and REF5025 establish the voltage setpoint. An INA228 measures terminal voltage and shunt current; firmware implements the programmable current limit and foldback characteristic. Fast short-circuit interception does not depend on that digital loop: the STM32 analog front end drives the hardware comparator and HRTIM break input, while firmware simultaneously clears the voltage DAC and opens the output relay.
The output stage also includes reverse-polarity detection, external-voltage detection before relay closure, overvoltage protection, backfeed supervision, a fuse, surge clamps, thermal monitoring, and an independent thermal relay interlock.
- System architecture and protection design
- Auxiliary +67 V / −5 V flyback converter
- PCB design and boards
- Русская техническая документация
The complete KiCad 10 project is in hardware/: schematic, layout, the project footprint library, hand-written 3D models with the Python scripts that generate them, and the SKiDL script the netlist is built from.
The documentation, the schematic and the hardware design files are published under CC BY-NC-ND 4.0: read them, study them, share them with attribution, but no commercial use and no publishing of modified versions. Building a single unit for your own private use is explicitly permitted — the exact terms are in NOTICE.md.
The firmware is not published. The hardware does not run without it, so if you build this board the control software is yours to write. Firmware and a video of the working device will follow once the hardware has been built and tested.
Aleksei Subbotin — embedded electronics and power control, France / remote. Open to freelance and contract work: github.com/Aleksei327 · alsubfr@hotmail.com
This project contains rectified mains and an approximately 380 V DC bus. It is an engineering prototype, not a certified product. Construction and testing require appropriate isolation, current limiting, discharge procedures, protective equipment, and experience with lethal-voltage power electronics.