Simple 500 mA high voltage biasable current source

This project contains a simple OpAmp and MosFET based current supply that can be controlled using a serial port. The whole project is built around an IRF540N MosFET that's driven by an LM358 OpAmp in a way to keep the voltage drop over a sense resistor constant - thus it provides a controllable current source (note that there is no temperature compensation but that was not necessary for this application).

The reference voltage is provided by an MCP4822 SPI digital to analog converter that's controlled by an ATMega328P. The serial port that's used to control the current source is isolated using two PC816 optocouplers - this is necessary since the whole board will be biased to -2 kV with respect to the controlling system. The load is powered by an 12V isolation transformer, the controller uses the same power supply and derives it's 5V supply for DAC and microcontroller using a simple LM317 linear voltage regulator.

The schematic

The schematic can be found in KiCAD format in the /kicad/currentcontroller directory

A PCB design

This repository includes also a simple PCB design

Microcontroller firmware

The firmware for the microcontroller can be found in mcusrc and is built using avr-gcc. The firmware can be flashed by using the Makefile:

make flash

The ACSL annotations are work in progress.

Test script

To test the communication using a simple serial TTL to USB converter a simple Python library is available (currently no PyPi package) at mcusrc/sertest