Dummy electrical Load v1.0

Purpose: -

Recently, I purchased a power supply that claimed a max current of 2A and 0~15V. So I wanted to test it. I had a 36 watts bulb (used in motor cycles), but that was too much. Then, I thought of the dummy load that is explained by Dave in his video blog.

My version is similar, but I changed certain components to my liking (and what ever was already available with me).

Following are changes: -

1. I used MCP6002 -- rail-to-rail opamp (both input and output). Supply voltage = 5V. Using rail-to-rail opamp simplifies the hardware design a lot and using this opamp, I was able to control current all the way from 1mA to 1A (and more). I also tried using LM358 (pin compatible, so remove MCP6002 from socket and insert LM358). But then, my max current was limited. That is either due to the lower limits of inputs/ outputs for this opamp. I could tweak the resistor to make the circuit work, but then, I had a bunch of MCP6002 lying with me as well, so better use them.

2. Power transistor as TIP122 -- darlington, perfectly suitable for 1A or 2A current. Also, due to property of darlington, the current drawn by base (from output of opamp) is very small. Also, I had a bunch of these darlingtons lying in my box for a long time. So use them.

There are some disadvantages of using darlington -- their speed is limited, but that does no bother me, as my current/ voltage will not vary more than few Hz. Also, due to higher Vce_sat, these transistor do heat up more for a given current.

3. Shunt as 2X0.5E real shunts -- I had them as well with me for a long time. These are real shunts, each rated for 5W, so perfect for the purpose.

4. Instead of multi turn pot, I used 2 pots in series -- for fine and coarse adjustments.

Schematic: -

Picture of hardware: -

Demo (video of dummy load working): -