Products > Test Equipment
Programmable resistive load
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Nogtail:
I've got a PWM LED driver I'd like to test across a large range of voltages, frequencies and loads. The PWM rate can be relatively high (over 100 kHz) which doesn't seem to play nicely with most DC loads.

So far I've been manually switching in a bank of power resistors. Unfortunately the ones I have are wire wound and more inductive than I'd like. I'd also like something I can automate to test at a variety of loads.

Does anyone know of some equipment that can handle 10-20 W at around 100 kHz? Something purely resistive is ideal, but a DC load that can handle a 100 kHz square wave would also do the trick. Bonus points if it's not ridiculously expensive!

Thanks!
slugrustle:
I was going to cheekily suggest a rheostat, but you've already tried (assuming wirewound) power resistors and they were too inductive.  A rheostat wouldn't fix that.

If spiffy equipment is not available, there are non-inductive power resistors available.  They typically come in a package that needs to be mounted to a heatsink.  I recently bought some resistors like this for a test at work; they were effectively TO-220 case parts and rated to 30W.  The nice thing about these kinds of resistors is they tend to have isolated packages, often ceramic backed.

Here's an example of a 100W 100Ω resistor in TO-247.  Datasheet says 11.7nH inductance.
https://www.digikey.com/en/products/detail/riedon/PF2472-100RF1/2447861
https://riedon.com/resistors/view/to-247-power-film-resistors-pf2470

Worth saying twice that you'll need a heatsink.

EDIT: The trouble with E-Loads is they pretend to be resistors (CR mode) by modulating the gate inputs to a bank of power MOSFETs with a control loop.  It would have to be a screaming fast control loop to make a power MOSFET look like a programmable resistance to a 100kHz square wave.  You might be able to set up a "dumb" essentially open loop current sink with a large power BJT, an emitter resistor, and a voltage source to set the base-to-ground voltage.  I know it's not a resistor, but it is a programmable open loop current sink.

EDIT2: Resistance wire of a suitable diameter bent into a non-inductive shape (squiggle line) that minimizes path length.  Mount it on a high temperature substrate and tap into the wire at various points with a clip that can handle the current.
Nogtail:
My backup plan was to get a few of the thick film resistors, wire them in series and short them out with some chunky relays to vary the load. I was hoping there was some existing equipment that does what I wanted but I haven't come across anything yet. Thankfully I've got a giant heatsink I salvaged from an old solar inverter that should be perfect for keeping them cool.
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