- Sep 12, 2007
Plan is to measure at LD+, LD- and RS+, all referenced to GND.
While the ground plane is low resistance, it is not zero resistance. In fact, it may even be comparable to the shunt you use, which will throw the current reading way off. If you want high accuracy, you want to sense the voltage across the shunt (directly - kelvin sense).
Have considered swapping the transistor(s) out for MOSFETs
I tried that. I couldn't get it to stabilize and actually popped a pricey diode when I THOUGHT I had it figured out . It can be done, obviously, as the flexmod is FET based. But it seems a lot harder for some reason.
I have a real beefy TO-3 heatsink, easily big enough to handle the heat
The heat sink isn't always the limitation. It's sometimes the thermal resistance to case, and the case resistance to the heat sink when it comes to high dissipation. It is possible for the heat sink to be barely above room temperature, while the junction is over 100C. Just monitor the case temperature and don't start with full power.
Friend has an O-scope
I hope it has single shot. You'll want to capture power on, power off, quick power cycle, and rms noise at several different input voltages and output currents.