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Re: gEDA-user: powermeter power supply update



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


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