Post by thread:[EE]: Mosfet student question.

I have never used a Mosfet before. (3)|Source-----757 Lamp--- + 12V +12v & 0v-----100 ohm------Gate(1)| (2)|Drain -------------- -12V Common (0v) IRF540N Mosfet The 757 Lamp is 24v, glows dim on 12v. Should this circuit switch the lamp on & off? Am I blowing another Mosfet each try? Do I have the right pinout? Or is it I have a bad batch of '540N's from EBAY? John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" {Original Message removed}

Try this John: It sounds like you are wanting to do some switching. I don't know how many watts the lamp is that you mention, but the '540 will switch a fairly large load - even larger than an auto headlamp - so it may be overkill for your application, but should still work. The Source should be toward your lowest potential, or most likely your DC ground. The load can be on either side - that is above the drain or between the source and Gnd. Unlike a bipolar transistor, this thing needs a positive voltage of somewhere between 2 and 4 V, as related to the source(that's why the data sheet labels it Vgs) for it to switch and conduct. it does not need current at the gate the way a bipolar needs to be biased, just volatge, so think in terms of a voltage divider tapped to bring the Gate to at least 4V if you want all parts to work all the time. The full 12V on the gate shouldn't hurt it, according to the data sheet, but may not be most desirable. If you tried them this way they should have worked. Now all you have to do is figure out if you have it connected correctly and get the The pinout in the IRF540 is G, D, S as viewed from the front (printed) side with the tab away from you. The source, or pin 3 How many do you have, and what is your application? C {Quote hidden}> > May Be I have it fixed now... > John Ferrell > 6241 Phillippi Rd > Julian NC 27283 > Phone: (336)685-9606 > Dixie Competition Products > NSRCA 479 AMA 4190 W8CCW > "My Competition is Not My Enemy" > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

It sounds like I have the polarity backwards. I will take another look at the data sheet in the morning and see how I missed that. I probably have a dozen or so IRF540N's. I bought them on EBAY just to experiment. I don't really have a specific project in mind, just trying to develop a little better foundation for PIC'n! John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" {Original Message removed}

Ouch! It don't get any more basic than that... The data sheet specifies at the very top: "Vdss 100v" I had the +12 on the source. The internal diode did its job just fine. Thank you... John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.