View Full Version : DC Electronic load another project to the list

03-06-2014, 08:01 PM
While testing an scoping the prototype of my LM723 i quickly designed a quick dc electronic load around a TL072 and an IRF540 and used it to test the PSU for light loading. Looking a little bit around an thinking a little bit long term i searched and bit an managed to extend the load to do constant voltage and constant current at simulation level. I still have to breadboard the CR and CV but the constant current is working great. I am still trying to find a way to make it work in constant power and pulse loading(this one should be easy). It took a little time to kill all the oscillation in the CC mode but i have a constant loading on my PSU and plus what i really like is that its variable. The IRF540 has to be bolted to a heatsink and a fan used to cool it down. I do find this method safer and more controlled than "dip power resistors into a sealed oil can" or use any other form of resistive loading which can be dangerous when it heats up unless its housed in some protective case and variability is not available unless disconnecting things or the like. The downside however is the number of mosfets required to achieve a heavy loading but time has proven that plenty of electronics to do a work is better than one dedicated mechanical device due to reparability, repeatability and control variation. Of course thats my point of view if you devote you time to build a single 1000W psu its just better to get a big power resistor and throw it in. If i had an electronic load when i started building SMPS it would have saved me a lot of time.

Of course linear PSU/SMPS testing might not require so many functions as i mentionned above some are related to battery chargers which is different a simple constant current load is enough.

I also like to check whats available on the market and see what some monsters can do and i was surprised to see that some of the electronic loads can even simulate loudspeaker impedance. Thats a lot of time/effort gained compared to buying a very high power sepaker and then recoil it everytime in case it gets damaged during amplifier testing.

The method of control is also very easily implemented using either multiturn pots, mutiple single turn pots or what i like ADC read and DAC voltage control.

Anyone around here ever dived into something like that? I would also be interested to hear if any of you have ever (though its extreme) to do a pulse load test on your SMPS to see how it reacts to such transients. Thanks

08-12-2015, 06:56 PM
Past some test and simulations and having now some MCP492 handy I am slowing going into this project. I will post more details + schamtic soon. the version I am thinking of building will be at most a 1A/3A version. The reason being I don't need very high currents SMPS/PSU and I prefer to add a big heatsink + fan + temperature sensor and have it run reliably.