John, Thanks for the quick reply.
John Luciani wrote: > Why wouldn't you use the transistor or the FET? An MMBT3904 or an > N-channel > FET is more suitable for this application than a 1G125. I would go > with the MMBT3904 > since you have a low voltage system. I used these to drive pager > motors in a haptic > compass. I'm concerned about leakage. This device will probably sit on a shelf for some time (with battery inserted, pic in sleep mode). I wanted to make sure there wasn't a trickle of current through the motor. > I am not sure about the duty-cycle of the motor but have you looked at > the coin-cell life > and the voltage dip when the motor is on? Make sure your coin-cells > are rated for high > pulse currents or factor the decreased battery life into your > specification. Overall "ON" battery life is pretty short, ~100 hours, and the motor only runs for a few seconds at a time when the device is turned on or off. It's the shelf life I'm concerned about. Unfortunately, physical constraints and legacy design lock me in to a CR2032. Sure wish I could use a CR123... I found this [1] transistor on digikey and then used this [2] guide to calculate an Rb of 174ohms when Rload is 29ohms, Vs is 3V, hfemin is 30, and Ic is 100mA. I just can't seem to divine when my Vbe is < 0.7V (ie, transistor OFF), what will my Ic (or Rce) be? It's not perfect, right? thx, Jason. [1] - http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MMBT3904FSCT-ND [2] - http://www.kpsec.freeuk.com/trancirc.htm _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user