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I keep promising myself I will build an Electronic DC Load and have kept defering it, well no longer, I finally ot it designed and tested on a breadboard and will be following up with a completed unit in a project case
It can go way above 30V (60 to be precice and upto 5Amps), the MOSFET I used the IRFP064 is able to go to 70Amps but thats more than my wiring would stand and way more than i need so I designed the load to go upto 5Amps for now. All I need to do though is change the current sense resistor and it can easily become a 10Amp unit
For the heatsink I tested with a standard one but subsiquently found an old CPU heatsing with a Fan attached which looks like it will do a grand job of cooling the MOSFET etc so it will be the one I use in the build.
Testin showed I can load as little as 250mV and still control upto an Amp which is great and once im over 1V source voltage I can go all the way to 5Amps with ease.
Now you all know the math "Power = Volts * Amps) so therefor will know that at 30V an 5Amps theres 150W being dissipated in the MOSFET and thats a lot of heat. I am pretty sure the CPU heatsing even with the fan will still get pretty hot and I look forward to characturizing it once the bukd is done. till then I have no idea how well it will work but I am sure it will be better than the one I tested the circuit with
for now, here is the schamitic I came up with
It will use between 12 and 24V for the DC in, has a REF02 Voltage reference to provide the manual setting via a 10 Turn pot and has a trimmer to accuratly set the top output to precisly 5A if so desired.
I also included a BNC input as an alternate control allowing a signal generator to control the load enabling many more test scenarious to be executed like transient response testing, noise response, Waveform based profile, pulse response etc.
The design does have a frequency limit before the output falls off of only a few hundred Hertz but that should be more than enough for this. It may be way better once it is off the bread board and the wiring is significanly shorter too but I wont be able to test that till the buld is complete. I will add a video to this blog once that is done and tested
anyway, enough banter, here is the video (Yes Im back to my 1+ hour videos... sorry I tried)
Hope you enjoy
Thanks to Vishay Precision Group ( VPG) Bulk Metal Film division for their kind donation of the current sense resistors and precision metal film resistors used in the resistor divider part of the design. It takes the use of this project to the next level by bringing stability to the key parts of the design in the order of a few parts per million... oh yaaaa.
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