shumifan50
- Jan 16, 2014
- 579
- Joined
- Jan 16, 2014
- Messages
- 579
I have a circuit that is powered from 2 plugs from the same battery. The one plug powers the logic including a micro controller. The ground of the other plug gets switched by a N=channel mosfet. The only PCB connection between the logic and the mosfet is the gate. When both plugs are connecyed the ground is connected externally through the battery (this I am sure is the problem). The logic switches the mosfet fine while both plugs are connected. If I unplug the power to the logic, which also means there is no longer a resistor holding the gate to ground, the mosfet slowly starts turning on until it is fully on, still with nothing connected to the gate. It is like the voltage on the gate is slowly creaping to the source voltage.
The problem is easily fixed by either connecting the logic ground to the ground of the mofet, or place a pull-down resistor on the mosfet to hold the gate low when the logic power is removed.
My confusion is this: As the transition is quite quick from off to full on, it seems there is quite a bit of current flowing causing the gate voltage rise. The source is connected to 12V.
Does this mean that if I have a pull down resistor on the gate, there will always be current flowing through the mosfet?
Note: MOSFET is ST95N2LH5
The problem is easily fixed by either connecting the logic ground to the ground of the mofet, or place a pull-down resistor on the mosfet to hold the gate low when the logic power is removed.
My confusion is this: As the transition is quite quick from off to full on, it seems there is quite a bit of current flowing causing the gate voltage rise. The source is connected to 12V.
Does this mean that if I have a pull down resistor on the gate, there will always be current flowing through the mosfet?
Note: MOSFET is ST95N2LH5
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