I can't get my MOSFET to work...

Thread Starter


Joined Jan 22, 2007
Ok, I want to test out my N-Channel MOSFET (an IRF620). I plugged it into my breadboard and wanted to try a simple test: connect a battery to an LED, and control whether the LED is on by attaching/detaching a second battery from the gate.

All of my resistors are 100k-Ohms. The setup is: the middle-pin of the MOSFET goes to a resistor, to the LED, to the positive end of the battery. The negative end of the battery goes to another resistor, and finally to the right-most pin of the MOSFET. I assume that those are source and drain, correct?

Well, even if nothing is plugged into the gate, the LED lights. What am I doing wrong, and how do I set up the circuit properly?



Joined Sep 20, 2005
Get datasheet of the transistor, and you should also know that the gate has some capacitance, so you have to discharge it to switch the transistor off.

In fact to switch it on you touch the gate with + voltage, to switch it off you touch the gate with ground.