I am trying to build a controllable resistive load for a test system=20
and I was hoping that someone has solved this problem before.

   The over all design is meant to drive four parallel LEDs & resistor=20
pairs and to detect if any of them are open or shorted. The driving=20
circuit has a 12v supply with a current sense and the low side is an FET=20
that is PWM controlled to Gnd.

   I need to design a variable load that can sink between 20mA and 300mA=20
and will emulate the LED/Res load.  This means that the resistance would=20
be 60 to 600 Ohms.

   I have looked at the programmable resistance chips like the MCP4012=20
or the AD5246 but the operating current range is too small.

   I have also looked at commercially available ones but they are very=20
expensive and meant for carrying 15Amps.

   Cost is not a significant factor since I only need to build about=20
three of these but I would hate to waste couple of thousand dollars when=20
a couple of hundreds (or less) would do.

   Any suggestions would be appreciated.

-Phil-

--=20
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