Electric OU: Supplement: MOSFETs… How DO They Work?? Part 4
When an N channel mosfet is configured to switch a high side low impedance load, the Drain voltage is HIGH when the mosfet is OFF, and when the mosfet is ON, the drain voltage is LOW. Also, gate charge stays on the mosfet unless there is some way for it to leave. Either a resistance pathway to the source, or just leakage through the air and the supporting woodwork. As the resistive pathway is removed and the gate charge is allowed to leak slowly away through the wood and paint and wet air, the drain voltage rises slowly and the bulb dims slowly as the mosfet slowly turns off through its linear conductance operation region.