On Tue, Apr 19, 2011 at 10:55 PM, Oli Glaser wrote= : > On 20/04/2011 03:26, V G wrote: > > Or should I do active control with a microcontroller? I can have the > > microcontroller read the output of the opamp and control the Darlington > pair > > through a DAC. > > You could, but I think that would be overkill for a simple constant > current load. Unless you want to make it programmable for different > tests, like pulsing the current, or ramping up/down at different rates. > If not, you have everything you need with the opamp. At the very least, > it's probably best to understand the simple version before adding > complexity. > > Seems like I'm going to do active control. I did a .step simulation with my original circuit and found that adjusting the gain on the opamp yielded a non-linear graph. For this circuit, I prefer a linear graph. I then did another simulation simply by varying the voltage via .step param V1 1 5 0.1 and the graph looked a lot more linear. It should also be far easier to mak= e a simple current control program for a microcontroller and will provide options in the future. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .