Electronic Load

[EntropyWizard]

I built a small electronic load based initially off Dave's video on the subject (EEVblog #102)as well as some extentions by others around the internet. The final is pretty much unique though (I haven't seen a version with a gate input) so I thought I'd post it here in case anyone else wants to build a similar one. It's a no-frills, manually controlled load up to 2.5A, can dissipate about 25W, and has thermal overload protection and a gate input. I also welcome idea's for improvements, I'm thinking of building a larger one at some point.

This version is built on protoboard and housed in an old DB-25 port switcher box from a thrift store. The heatsink is from some older model CPU I guessed could handle 20-30W. The MOSFET (Toshiba 2SK3561) is from a scrapped tube TV switchmode supply, but most any power MOSFET should work since this is only hitting about 2.5A. The thermistor is epoxied to the heatsink next to the MOSFET and the thermal overload circuit tuned via RV1 in operation to trigger at about 25W. The gate schmitt trigger has threshholds at 1 and 2 volts approx. and is held high (on) if nothing is connected.

I've attached comparison traces using the load on a simple linear (7805 based I think) lab supply and a switched (old PC) power supply at 5V. The electronic load gate is driven with a 200Hz square wave from a signal generator and average load was set at 1A. The scope settings were 0.1V/div, 1ms/div.

[German_EE]

Nice to see that I'm not the only one building one-off projects on protoboard, and extra marks for reusing that case which is too good to throw away.

How about posting your schematic as well?

[EntropyWizard]

The schematic should be there now -- I was swapping it from pdf which doesn't preview to jpg.