On Wed, 7 Jun 2006, Dwayne Reid wrote:

> At 07:30 AM 6/7/2006, Peter wrote:
>
>> Jinx <joecolquitt <at> clear.net.nz> writes:
>> 
>> > http://home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif
>> 
>> Also, the voltage/current metering device using Q3 and Q4 looks like it 
>> would introduce the Vgs of the open 2N7000s in
>> series with the measured voltage. No ?
>
> Assuming (from the voltage divider ratios) that the voltage at AN2 is less 
> than 3V and given that Vgs for a 2n7000 is less than 2V (1.3V for some 
> variants), there should be no problem.  This also assumes that the voltage 
> drop across the current sense resistor is low enough that the body diode of 
> the inactive 2n7000 does not conduct.
>
> It actually looks like a competent design.

I would use a tc66 gate to do this or two mosfets back to back. Maybe it 
works as shown but I would be worried about reverse leakage and such 
when a mosfet is closed.

Peter
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist