uController PSU

Every (home)lab needs a good variable powersupply and so does mine. I wanted to design something with a microcontroller to set the voltage and current limit. Using a microcontroller also brings the possibility to use an LCD and fancy rotary encoders for control. The control loops themselves are pure analog.

I made this powersupply mostly from components I already had.


The schematic contains two pages. The first for the microcontroller and it’s peripherals. The second page contains the analog and power parts.


The heart of the powersupply is an Atmel ATmega8 microcontroller. It controls the LCD, DAC, output voltage, maximum current and two relays. Inputs are the rotary encoder, an analog voltage that represents the output current, program headers and a temperature sensor. You can read about rotary encoders here.

Microcontroller PSU schematic 1

Click the picture to open the PDF


Analog powerstage

This is the actual powersupply that regulates the output voltage and -if needed- limits the current. You can see the voltage amplifier that amplifies the outputs of opamps U4A (voltage setting) and U4B (current limit). U5A inverts and amplifies the voltagedrop of R1, which is the current sense shunt.

There are also some regulators to provide all Atmel the voltages needed for the opamps and the digital part.

Microcontroller PSU schematic 2

Click the picture to open the PDF



The final PCB is currently being routed. I already have a prototype, but this has a few modifications.


The case is made from an old industrial pc. Some paint and new aluminium front and back panels and it’s quite nice.

Microcontroller PSU 3

Microcontroller PSU 4

Microcontroller PSU 2

Microcontroller PSU 1


I am not a programmer, so the mde software is quite basic. You can find the AVR Studio project here.


Right now I can think of a few modifications that will improve the performance of the powersupply. These include:

  • a seperate ADC with a higher resolution Tube to get more accurate readings of the drawn current
  • solid state solutions for the relays

At the moment I don’t feel the urge to put these improvements in the design, but if I had to design another one…

3 thoughts on “uController PSU

  1. I’m thinking of building something like your design. Where did you get that transformer?
    Do you have photos of your board?
    You can reply to my e-mail address.

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