Constant Current Dummy Load for Power Supply

Constant Current Dummy Load for Power Supply

This project is made out of few junkbox parts and builds a useful constant current load for switch mode power supply, battery testing, and other applications. A dummy load is traditionally a big resistor you connect across the output of a power device when testing it.

These are used to test power supply designs and instead of just chaining resistive loads together every time so the builder decided to look into building a tool for the job. It is a reliable constant current load that can be dialed anywhere from 1.5 mA up to just over 1A. There’s even an onboard meter to probe the setting before use.

adjustable constant current load

It may look like a design off to the board house for production but that’s actually a re-purposed PCB. And it is capable of up to 10amps at 40volts. Unlike conventional resistive loads, the dummy load maintains a constant but adjustable load current for voltages in the range of 40 volts. Thus the circuit is powered by an external 12V supply. An RC filter was added for this supply to reduce the ripple noise. It is simple to build but with a minimum protection circuit.