Okay, so I was messing around with some MOSFETs the other day, and I wanted to really nail down how to figure out their threshold voltage – you know, that magic number where the thing actually starts to conduct. It’s more hands-on than you might think, so here’s how I got it to make sense for me:
Setting Things Up
First, I grabbed the MOSFET I was working with, I am using IRFZ44N. and hooked it up in a simple test circuit. This is super basic:
- Connect the drain to a power supply (I used a variable one, makes life easier) through a resistor. The resistor’s there to limit the current, so things don’t go boom.
- Tie the gate and drain together. I know, it sounds weird, but trust me on this one. It puts the MOSFET in its “saturation” region, which is what we want.
- Connect the source to ground. Gotta complete the circuit, right?
Getting Down to Business
With everything wired up, I started by cranking up the power supply voltage slowly. I mean really slowly. You’re watching for that tiny, tiny increase in current flowing through the drain.
I kept an eye on the voltage between the gate and the source (VGS) using my trusty multimeter. I was also watching the drain current (ID). At first, not much happens. The current is practically zero.
But then, as I increased the voltage, there’s this point where the drain current starts to creep up. It’s not a sudden jump, more like a gentle nudge. That’s your clue! The VGS at which that current starts to become noticeable – that’s your threshold voltage (Vth).
My Rough Result
I increased my voltage supply slowly and I noticed the tiny changes in my ammeter, and the voltage between gate and source at the tiny changes is the threshold voltage, which is about 2.0 to 4.0V, that completely makes sense, it is in the given range of values on the datasheet!.
It’s not a perfect science, since “noticeable” is kinda subjective, but it gives you a really good ballpark figure. And honestly, for most hobbyist stuff, that’s plenty good enough. I just wanted to share how I personally did it – no fancy lab equipment required!