I'm getting some wierd behavior on the gate of a simple n-channel MOSFET circuit. The circuit is:
A TTL input from a function generator putting out a single 5usec pulse.
That feeds a TC4427 MOSFET driver chip running at 12V.
That feeds the gate of an NDP4050 MOSFET through a 24ohm resistor.
A 200k resistor shunts the gate to ground.
The source of the MOSFET is connected to ground.
The drain is connected to a 6ohm wirewound load resistor. There is a freewheeling diode across the wirewound resistor in case of inductive kick.
The other end of the load resistor is connected to Vdd which may be as much as 30V.
A battery powered floating scope is looking at the gate voltage Vgs, with a good x10 probe.
That's it. Not much to it.
When Vdd < 5V Vgs looks fine. Above that, Vgs rings for a bit at a very high frequency on the trailing edge of the pulse. The higher Vdd the longer the ringing. Above about 12V Vgs starts freely oscillating after the input pulse. The MOSFET starts heating up and would probably burn itself up if I didn't kill the power.
I tries another NDP4050 and got the same behavior. And it is very consistent.
What would cause the gate voltage of a MOSFET to go into oscillation??
A TTL input from a function generator putting out a single 5usec pulse.
That feeds a TC4427 MOSFET driver chip running at 12V.
That feeds the gate of an NDP4050 MOSFET through a 24ohm resistor.
A 200k resistor shunts the gate to ground.
The source of the MOSFET is connected to ground.
The drain is connected to a 6ohm wirewound load resistor. There is a freewheeling diode across the wirewound resistor in case of inductive kick.
The other end of the load resistor is connected to Vdd which may be as much as 30V.
A battery powered floating scope is looking at the gate voltage Vgs, with a good x10 probe.
That's it. Not much to it.
When Vdd < 5V Vgs looks fine. Above that, Vgs rings for a bit at a very high frequency on the trailing edge of the pulse. The higher Vdd the longer the ringing. Above about 12V Vgs starts freely oscillating after the input pulse. The MOSFET starts heating up and would probably burn itself up if I didn't kill the power.
I tries another NDP4050 and got the same behavior. And it is very consistent.
What would cause the gate voltage of a MOSFET to go into oscillation??