Okay, so I wanted to mess around with some MOSFETs for a little project I’m working on. Nothing too crazy, just switching some LEDs on and off. But first, I needed to figure out which pin was which, you know, the gate, drain, and source. That’s what they call the “pin configuration.”
I grabbed a few MOSFETs from my parts bin. I think they were IRF540N, pretty common ones. First thing I did was pull up the datasheet. Gotta have that! You can usually find them by just searching the part number online. The datasheet has a little diagram that shows you the pinout.
Finding the Pinout
Usually looking at the mosfet with the label/text facing you, it goes like this from left to right:
- Gate
- Drain
- Source
But, to be absolutely sure, I like to double-check with my multimeter. It’s a good habit to get into, saves you from frying components. I set my multimeter to the “diode test” mode. It usually has a little diode symbol.
Then, I did some testing. With the datasheet and multimeter, I figured it out.
Verifying with a Multimeter
Next, I connected the positive (red) probe of my multimeter to what I thought was the drain, and the negative (black) probe to the source. You should get some kind of reading, not an open circuit.
Now, here’s the trick to find the gate. Without moving the probes from the drain and source, I briefly touched the positive probe to the gate pin as well. This “charges” the gate a little. Then, I put the positive probe back on the drain only.
Boom! If everything is right, the multimeter reading should stay low, meaning the MOSFET is “on”. It’s conducting because I gave the gate that little charge.
To turn it “off,” I touched the negative probe to the gate, while still having the negative probe on the source. This discharges the gate. After that, when I put the probes back on the drain and source, the reading should be high again, showing it’s not conducting.
I played around with this a few times, charging and discharging the gate, just to make sure I had it right. It’s pretty cool to see it work.
So yeah, that’s how I figured out the pin configuration of my MOSFETs. It’s not rocket science, but it’s definitely something you need to know before you start hooking them up in your circuits. Always double-check that datasheet, and use your multimeter to be extra sure!
