The reason to modulate the headlight is for visability. If you see something in your rearview mirror flashing at 240 cycles per minute, it will stand out. That makes motorcyclists safer. This isn't a new idea. Jim, I could use an N-Channel, but if my load is connected between source and ground, the gate turn on voltage will be (if it is a logic level FET) ~ 12V + 5V. Without using a charge pump IC, 17V isn't available easily on a standard automotive application. That is the reason of a P-Channel. ----- Original Message ----- From: "jim" To: Sent: Thursday, June 28, 2007 9:16 PM Subject: Re: [EE]: Modulating a headlight > Miles, > > If you want a low RDSon, shouldn't you use an N channel device? > And I have had no problems driving a FET if I use a pullup resistor, > (or pulldown if that's what I need). > > Regards, > > Jim > ----- Original Message ----- > From: Miles McKinnon > To: > Sent: Thursday, June 28, 2001 3:27 PM > Subject: [EE]: Modulating a headlight > > > > I am building a motorcycle headlight modulator using a PIC to monitor > > ambient light and a few other things. Anyway, the PIC has to modulate the > > headlight ( ~ 4Amps) at a arount 240Hz or so. > > > > There are a few legal stipulations. They say that you cannot switch the > > ground, you must switch the +12V to the headlight. I want to use a low > Rds > > HEXFET or simular transistor, but I think I would need a P-Channel device. > > > > Is a P-Channel Mosfet difficult to drive from a TTL logic level, such as a > > PIC. > > > > Thanks for any help. > > > > -- > > http://www.piclist.com hint: The PICList is archived three different > > ways. See http://www.piclist.com/#archives for details. > > > > > > > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body