Mosfet Control Circuit Problem

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

  1. Engr

    Thread Starter Member

    Mar 17, 2010
    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.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    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
    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
    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

    AAC Fanatic!

    Jan 18, 2008
    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.

  6. hobbyist

    Distinguished Member

    Aug 10, 2008
    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.