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Adjustable current load 2014-03-16

Sometimes it is useful to be able to draw a specified amount of current from a circuit you a working on - such as when fault-finding a power supply or testing the capacity of a battery. It can also be useful to insert an adjustable current-limit into a circuit - if you suspect that the output stage of your amplifier may fail short, etc.

I've described here a two-terminal DC current load that you can hook up to your circuit under test in these situations. The design is new, so it's not been subject to a great deal of use "in anger", but it has behaved quite well in the tests that I have done thus far.

The load is usable on load voltages between 3.3 and 200V (although you may not get full performance at 3.3V), and is theoretically capable of sinking 20A - again you may not quite reach this, but I've definitely seen 10A (I don't have a supply capable of delivering 20A). These figures are dependent upon the SOA of the output devices, which you could tailor to suit your needs.

The unit's main feature is that it does not need a separate supply, meaning that it is somewhat more convenient to use than many commercial devices.

I've uploaded two files here: The schematic and a circuit description.
Please get in touch if you have any questions or comments, or if you've spotted an error.

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