On Fri, 2009-01-16 at 17:53 +0000, Peter Clifton wrote: > On Fri, 2009-01-16 at 12:30 -0500, DJ Delorie wrote: > > > Not digital, but this is similar to a load circuit I built in the lab. > > > > Yeah, something like that. > > > > Kudos to email-able schematics :-) > > > > > The actual circuit ended up with most of RLoad in the emitters of > > > the FETs to ensure better balancing. > > > > Did your FETs have positive or negative thermal coefficients? > > Not sure, but the emitter resistors ought to help them share. (Not that > they were drawn in the schematic). > > > The FETs were SPP80N03. Charts show threshold voltage drops with > increasing temperature, R_DS(on) increases. I'm not sure what the > overall effect would look like. > > The emitter resistors are all 10-25W metal heat-sink mount resistors > (not got the rating to hand), mounted on a heat-sink with each > transistor next to its power resistor, a common gnd-bus-bar threaded > through the power resistors, and a power bus bar soldered to the > transistor drains. > > This was all semi-dead-bug style, as the gate resistors are also > supported in space by their leads, one end on the mounted FET. another > on a gate-bus bar, terminated on a connector plate mounted one end of > the heat sink. > > I can't quite recall, but I think the final design used more than 4 > paralleled channels. The whole thing was supposed to burn up to 600W > peak, and was used for programmable load cycling of batteries under > test. > > For low voltage cells I had to bootstrap the battery with a lab > power-supply, as the circuit started to have stability problems once it > ran out of head-room. > > The control input in my case was a cheap National Instruments DAQ card > analogue output. I did think of designing a switched mode load, but in > the end the simplicity of linear won out. > -- Peter Clifton Electrical Engineering Division, Engineering Department, University of Cambridge, 9, JJ Thomson Avenue, Cambridge CB3 0FA Tel: +44 (0)7729 980173 - (No signal in the lab!)
Attachment:
inst_amp.pcb
Description: application/pcb-layout
Attachment:
inst_amp_embedded.sch
Description: application/geda-schematic
_______________________________________________ geda-user mailing list geda-user@xxxxxxxxxxxxxx http://www.seul.org/cgi-bin/mailman/listinfo/geda-user