Ok, I’m building a test circuit that uses a power MOSFET. The microcontroller I’m using emits 3.3 volts on a pin. When I dug around the “parts bin” aisle at the local Fry’s Electronics, I found a “logic level” MOSFET that needs 5 volts instead of 3.3. I could have ordered a 3.3 volt mosfet, or a gate driver online, but let’s do it the fun way.
Just need a simple circuit to let the 3.3 volt microcontroller output control the MOSFET. So a quick perusal of youtube found this nifty video. Looks about right.
So I went to radio shack looking for the 2N3904 shown in the schematic. Ended up with a 2N3906. Figured that was close enough, bought it and went home.
Well, turns out, the 2N3906 is a PNP type transistor. The kind I was supposed to buy is an NPN transistor. The last digit is actually a big deal. The state school I attended did not think that power transistors was a needed part of the curriculum for the computer engineering program, so while they taught me all about various filters and the software side of things, I don’t know how to switch power.
Can I just flip the diode portion of the transistor (the emitter and collector) and use the same circuit? Or is a more serious overhaul needed to use the BJT to drive the mosfet.
A little visual aid :
https://dl.dropboxusercontent.com/u/16656673/IMG_0248.JPG
State schools also don’t cover how to use perfboard. Turns out this is a really great, easy to do way to make a test circuit. Beats the heck out of breadboarding - permanent, cheap, easy, good solid electrical connections. Wish I had known about perfboard when doing senior project…