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High Side Active Load


Jeff Johnson

Jan 1, 1970
I guess it's better to say what I'm trying to do. I'm am trying to create an
active load that is on the high side of a circuit(has to be for various
reasons) used for automating a test procedure. I figured a mosfet would work
nicely but since I need AC a SSR configuration should work. I can parallel
several of these for power handling and heat disspation reduction. The only
issue is driving them. The load is on the order of 10's of ohms at about
110V rms but may be temporarily shorted(there is an additional fixed load).
Current and voltage will be monitored and can be used as a feedback to set
the desired gate votage.

I was thinking of using floating gate drive and an opto but not sure if I
can get the accuracy needed(say about 1% of the load).

I would rather use a monolithic device rather than try and roll my own but I
can't find anything that will work for ac and variable drive(all are

It's not necessary that I use mosfets and BJT's may be easier to use but
unless there is compelling reason to go with BJT's I'd rather use mosfets(I
have plenty on stock and might need to parallel them).