Okay, so today I wanted to mess around with MOSFETs, specifically depletion and enhancement types. I’ve heard about them, but never really got my hands dirty, you know?
Getting Started
First, I gathered all my stuff. I grabbed a breadboard, some jumper wires, a few resistors (I always seem to need more resistors!), a 9V battery, and of course, the MOSFETs. I made sure I had both depletion-type (J108) and enhancement-type (2N7000) MOSFETs. You can’t do this experiment with just one type, gotta have both to really see the difference.
The Basic Setup
I started with the enhancement-type MOSFET. I remembered that these guys are normally “off,” meaning they don’t conduct unless you apply a voltage to the gate. I connected the source pin to the negative rail of my breadboard, the drain pin to a resistor (I think I used a 220-ohm one), and the other end of the resistor to the positive rail. I added an LED the Drain pin and resistor,so that is easier to check if the circuit is working or not.
- Source to ground.
- Drain to resistor, then to positive.
- Gate initially left unconnected.
Testing the Enhancement MOSFET
With no voltage on the gate, the LED stayed off. Makes sense, right? Then, I touched a jumper wire from the positive rail to the gate. Boom! The LED lit up. I disconnected the gate wire, and the LED turned off. Just like it should. It’s like a little switch controlled by voltage.
Switching to the Depletion MOSFET
Now for the depletion-type MOSFET. This one’s a bit different. These are normally “on,” so they conduct without any gate voltage. I swapped out the enhancement MOSFET for the depletion MOSFET, keeping the same basic wiring. I made a similar circuit as the enhancement MOSFET.
- Source to ground.
- Drain to resistor, then to positive.
- Gate initially left unconnected.
Testing the Depletion MOSFET
Right away, the LED lit up! No surprise there. Now, to turn it off, I needed to apply a negative voltage to the gate. I connected the gate, through a resistor, to the ground,The LED dimmed.The more negative voltage that add to the gate,the dimmer the LED will be,Pretty cool!
The “Aha!” Moment
It finally clicked. Enhancement MOSFETs need a positive voltage to turn on, while depletion MOSFETs need a negative voltage to turn off. Playing with them side-by-side really showed me the difference. It’s one thing to read about it, but it’s totally different to actually see it happen.
That’s my little MOSFET adventure for today. Simple, but satisfying! I feel like I have a much better grasp on these things now. Next time, I might try building a simple amplifier circuit or something. We’ll see!