300W Resistive load?

[JosephKK]

Maybe two or three electric irons in parallel.

If this will be anything other than a temporary lashup,
you'll want a fuse rated to interrupt 200VDC.

A typical electric clothes iron (flatiron for those that remember) is
about 450 W rated, with a bang-bang temperature controller.

 

[JosephKK]

Small electric heater with switch able power level.

I don't know about now, but in the distant past hardware stores sold
heating elements that screwed into porcelain light sockets. The
intended use was for chicken incubators.


John Ferrell W8CCW

I have actually seen those sold for room heaters (with dish reflector)
at powers a high as 1000 W.

 

[JosephKK]

Finned heat sinks, arranged as a square tunnel, fins inward, file,
mill, whatever so they fit together nicely, and the "square" is
muffin-fan size... which fits on one end.

...Jim Thompson

Yup. Also works fine with pairs and any air blocker to make a tunnel.
There will be a thermal gradient along the tunnel, with FETs this
works in your favor though.

 

[JosephKK]

If you use transistors that can handle 200V (or way more) like I did
there is no problem.

Plus it allows for all kinds of interesting test scenarios.

 

[Nico Coesel]

But not up at 200V? Low voltage, high current is easy, transistor
SOA at high voltage not so easy?

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.

 

[Grant]

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.

 

[Tim Williams]

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.

http://en.wikipedia.org/wiki/Avalanche_transistor#Second_breakdown_avalanche_mode

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

 

[Steve]

http://en.wikipedia.org/wiki/Avalanche_transistor#Second_breakdown_avalanche_mode

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

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