Daniel Rubin wrote: > Morgan wrote: > >Remove the back-emf diode, and use a transistor in emitter follwer > >configuration. (that will also dissipate the back EMF) =No more > >components than today. You will get 1V drop across the tranny though. > > If I use a transistor I'll have to add a resistor. Anyone know of any > transistors (in a SMD package) that don't require a resistor between the > PIC and it's base? Emitter follower means that the load goes between the emitter lead and ground (assuming NPN here); no resistor in base or collector required. When the transistor cuts off, the coil will drive the emitter below ground, drawing current through the base and collector until the energy is dissipated. The base current will come from the low-side pin driver MOSFET and/or the protection diode -- you may need to make sure this current doesn't cause any problems for the PIC. You could also configure a PNP as a low-side switch, but a similar issue arises when the output goes high. -- Dave Tweed -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads