Lucas and Spehro (got it right that time!) - Thanks for the replies. Logic level N channels would be ideal -- in another place. Unfortunately, this is an automotive app and the return is through the frame. I don't mind using the IRF5305. It has a very low resistance for a P channel (.06) and it's priced right -- .55USD in 100's. The unit has two or four of these PIC driven channels per unit. Each unit is potted for complete weatherproofing. I definitely will add the diode to the base of the NPN. In previous apps the NPN was part of an optocoupler, but is just a jelly bean transistor now. I will also get rid of the diode across the load. I'll run a couple without the 6A diode and run some destruct / temp tests to see what I get. Thanks, Bill -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Spehro Pefhany Sent: Tuesday, February 10, 2004 1:46 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE:] yet another MOSFET output question At 11:37 AM 2/10/2004 -0500, you wrote: >I have a question about the 6 amp diode actually. I put in the diode >in case the power and ground were connected backwards. Is this diode >really needed? The only reason I ask is I need to connect more lights >(about 10 amps worth) and this is the limiting factor. It's mounted on >the PCB and anything bigger will be a TO-220 or stud mounted device -- >ugly and cumbersome but doable. If it's just lamps, you don't need the diode across the load. If you do put it there, it will take out the MOSFET and maybe the diode if the polarity is reversed. The fuse might go first, but I wouldn't count on it. The IRF5305 is avalanche rated so it can deal with overvoltage from a bit of stray wiring inductance all on its own. Yes, you can leave the 6A diode out too, BUT you MUST put a diode from the base of the BJT to ground for reverse polarity protection as thus: -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads