I'm having a bit of an issue with switching a +12Vdc solenoid off using a p-channel MOSFET (IRFR9220). I've attached the circuit as it sits currently on the breadboard.
The problem I'm facing is that when I apply +12vdc to the solenoid (power source PSU-1 in diagram), the solenoid is on, even though the MOSFET isn't being driven (PSU-2 is at 0V). I've experimented with different gate-source resistor values (current value is 100kohm) with no change in behavior.
I've replaced the solenoid with a 6vdc buzzer and have been able to switch the buzzer ON and OFF with the circuit shown in the attached schematic.
I'm using a p-channel FET because the final drive circuit that will replace PSU-2 is an n-channel MOSFET on an external driver board.
Any suggestions would be appreciated.