# Mosfet Control Circuit Problem

Discussion in 'Homework Help' started by Engr, Mar 22, 2010.

1. ### Engr Thread Starter Member

Mar 17, 2010
114
5
Hi Guys,

I have a problem with my control circuit for Mosfets. The source of the Mosfet that I will be using will be connected to -10V while the drain will be connected to a resistor then the resistor will be connected to ground. I need to connect 15V to the gate of the mosfet and I want it to have a switch so that I can connect and disconnect the 15V from the mosfet turning the mosfet on and off. I have a control signal for the switch that has 0V(low level) and 12V(high level) level. This control signal will control the circuit by disconnecting the 15V from the gate of the mosfet. I need help on designing the circuit. I can only use Mosfets, resistors and BJT for the control circuit.

See attached file for the illustration of the circuit.

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2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
293
Hint - the FET is off when the gate-source voltage is 0. It is full on when the G-S voltage is 10 volts.

3. ### shortbus AAC Fanatic!

Sep 30, 2009
5,916
3,374
Your battery, V3-10+, should be connected to R2 instead of the ground symbol. Then the source of the FET is connected to ground.

4. ### Engr Thread Starter Member

Mar 17, 2010
114
5
The mosfet circuit is already existing, the only circuit that can be change is the control circuit and I am having problem designing a control circuit since the source of the mosfet is connected to -10V and the control signal starts from 0V. I need to have a control circuit that will turn off the mosfet when the control signal is 0V and turn on when the control signal is 12V.

5. ### jpanhalt Expert

Jan 18, 2008
6,558
1,303
Also, be aware that most mosfets have a Vgs rating of only 20V. So, you will be exceeding that with -10 for source and 12 for gate.

John

6. ### hobbyist AAC Fanatic!

Aug 10, 2008
885
85
Here is a quick schem. to get the wheels turning,

Think in terms of electronic switching.

It won't work as an actual circuit, just use this for a idea to get you started in a direction of some sort.