DJ Delorie wrote: >> 4.5 watts? That must be one hell of a flashlight. > > It's a big 6v rechargable one. The flashlight doesn't work, but the > bulb does. >
We got one of those big yellow Lowes deals. You can make a street sign half a mile away light up with it. $10 including charger, 8 years old, used daily, gel cell in there, still works, amazing. >>> One of these days I'm going to make a digitally-controlled load. It's >>> just a monster FET with some control circuitry, right? >> Basically, yes. But in order to dial in resistances you must find two >> that are nearly identical (pairs are rare in the power class) > > I saw an appnote about one FET that had a different temperature > coefficient, so could be used paired (for heavier loads), because if > one overheats it *reduced* its conductivity - they ended up balancing. > But I suspect that's not what you're talking about - you're talking > about a current mirror, yes? > No, a real servo. But for that they must remain at identical die temperatures. Not easy at large loads. >> and servo it with an opamp. > > I knew that part. > >> Or just command currents, then it's down to one big FET. > > One FET, one current sense resistor, and an opamp, plus however you > derive the control setting for it. > Yep. You can also set load resistance that way if you also sense the voltage and divide by the sensed current. Either a reasonably fast uC or an "analog computer chip" from Analog Devices (will be a bit pricey). -- Regards, Joerg http://www.analogconsultants.com/ _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user