Hello All, I was playing around with a small circuit that used a MOSFET to pulse power from my DC power supply into a small coil that I wound (I was messing around with BEMF in the coil). I was driving it with a small function generator, connecting the function gen's output directly to the gate of the MOSFET. I realized that I probably should have put a resistor between the gate and source to drain off some of the charge (it wasn't switching very well) so I put a 2 KOhm resistor there and then it didn't work at all. So I dropped the resistance to a 200 Ohm resistor and still it wasn't working. Confused and a little frustrated, I got the bright idea to connect a small capacitor (40 nF) between the gate and the source (just to see what would happen). When I turned on the function generator, the MOSFET immediately ran away switching up into the low MHz while I was still pulsing it at around 10 kHz! I thought this phenomena was pretty interesting and was wondering how common it is to do something like this with a MOSFET? Also, I'm wondering how one would tune the frequency of oscillation of the FET (I used an IRF840). I posted a circuit diagram of my setup below. Any insights welcome. Thanks, Jason O P.S. I should also note that the 300V cap on the 50 turn coil doesn't have to be there. It still works if there is just a piece of wire across the coil. It doesn't seem to work without that though. My thought is that the coil's BEMF is recycled through that loop when the MOSFET is shut off.