300W Resistive load?

Unless it was slightly less old and used TO-3 MOSFETs, which Idunno, might be worth something on eBay. :^)

handle the voltage just fine, as long as there's enough for the power.

I had one power BJT per FACE... 400W audio amplifier ;-) ...Jim Thompson

I still fail to see why it wouldn't work. The only failure mode I can think of is the case in which the emitter resistors are too small to divide the load properly at low currents / high voltages.

Not saying it cannot work, but you'd need big expensive transistors to make an active load for 200V at hundreds of watts.

I'm working on a power DAC at the moment, only going up to about 30V and 30A, non-trivial when you want the same circuit to hold to the output to nearest mV or mA ;)

First version with transistors leaked and drifted too much, current version being designed & built with MOSFET switched resistor banks and analog power amp to make up the small stuff seems far more viable.

But here I'm drifting OT as I'm making a precision load, not a simple test load, but that explains why my focus is more on the reliability of an active load.

Recently I built a 1A current sink, while it didn't fail, it was cooking a power MOSFET on large heatsink, but without fan, at only 30W. So I pulled the plug at 20 hours operation. Then realised I could use a bridge circuit instead of accurate current sink. Side stepped a problem, finding a better solution :) I ordered $5 worth of precision resistors 10:1 ratio.

Grant.

So either the transistors seems to avalanche, i.e. current goes way = higher than expected, or voltage starts pulling down, or it burns out = altogether.

Tim

--=20 Deep Friar: a very philosophical monk. Website:

On Tue, 20 Jul 2010 23:24:52 -0500, "Tim Williams" = put together some random words that came up with:

nche_mode

higher than expected, or voltage starts pulling down, or it burns out = altogether.

I used a 220V electric water heater element for a load when I build a = power supply for an argon laser. It worked great.

Steve