Alright, guys, so today I wanted to mess around with some MOSFETs I had lying around. I needed to figure out if they were still good or if they’d gone to that great electronics graveyard in the sky. So, I grabbed my trusty multimeter and got to work. Here’s how I did it:
Getting Started
First things first, safety! Make sure the power is OFF to whatever circuit the MOSFET was in. You don’t want any nasty shocks. I double-checked, even triple-checked, just to be sure.
Identifying the Pins
Next, you need to know what you’re looking at. MOSFETs have three pins: Gate, Drain, and Source. Usually, the datasheet is your best friend, But I find it by google, because I lost mine. I find some pictures that showed the pinouts for the specific MOSFETs I had, some common ones, and all TO-220 packages. Phew!
Testing Time!
Now for the actual testing. I set my multimeter to the diode test mode. It usually has a little diode symbol. Here’s the process I followed:
- Step 1: Check the Gate-Source. I put the black probe on the Source and the red probe on the Gate. I shouldn’t get a reading. If I do, it’s probably bad. Then I switched them around, red on Source, black on Gate, still expecting no reading.
- Step 2: Check the Drain-Source. This is where it gets interesting. Black probe on Source, red probe on Drain. I’m looking for an open circuit (no reading) initially.
- Step 3: The “Turn-On” Test. Keeping the black probe on the Source, I briefly touched the red probe to the Gate (to charge it up) and then moved the red probe back to the Drain. NOW, I should get a low resistance reading, meaning the MOSFET is “on”.
- Step 4: The “Turn-Off” Test. Again, black probe on Source, I briefly touched the red probe to the source to discharge and then moved the red probe back to the Drain,I should get a high resistance reading, meaning the MOSFET is “off”
Interpreting the Results
If I followed those steps and got those readings, my MOSFET was probably good. If I got weird readings at any point, like a short circuit (low resistance) between Gate and Source, or if I couldn’t get it to “turn on” and “turn off,” then the MOSFET was likely toast. I did find one that kept showing a short between Drain and Source, no matter what I did. That one’s definitely going in the bin.
If discharge is slow, the resistance will not be instant change, and it will need some time to back the normal state.
Wrapping Up
That’s pretty much it! It’s a relatively quick and dirty way to check MOSFETs. It’s not a 100% guarantee, of course, but it’s a good starting point. I managed to sort through my pile and weed out the bad ones. Now I can get back to my actual project without worrying about faulty components. Hope this helps someone out there!