> > Uhoh..just realized something (that should have been obvious to me
> > before). My battery is only 1.2v, so is there a flipflop that I can use
> > that will run that low?
>
>         Ouch, 1.2V? You will probably be able to find a flop that runs
that low,
> the big problem will be finding a FET that runs with so little a gate
> voltage. It'll take some looking, none of the "standard" variety of parts
> out there will be able to function with that low a voltage. TTYL

If I was doing this I would almost certainly use a bipolar transistor as the
power switch (or a relay :-) ). The Zetex FETs I referred to will do the job
but they are unusual, only available in SMD packages and are working at the
lower end of their operating range. With 1 volt or so on the gate they will
work but will not be fully enhanced and will not meet their specified Rdson.
Using one of the higher current ones will help as the Rdson decreases with
increasing current.

But a small bipolar transistor will be easily driven with the available
voltage and will probably achieve an adequately low Vsat. I don't think you
have specified operating current but I imagine that it is tens of milliamps.
A BC337 has a Vsat of 700 mV at 500 mA and approximately proportionately
less at lower currents. At 50 mA that would be perhaps 70 mV which should be
acceptable.The equivalent FET Rdson would be 0.070V/0.050A = 1.4 Ohm so the
FET would probably be better electrically but still be hard to work with in
a one off and available from a limited range of suppliers.



            Russell McMahon

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu