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How to Use an Op-Amp for a MOSFET

A metal-oxide semiconductor field-effect transistor, or MOSFET, is frequently used to convert voltages on a CPU board. The MOSFET transistor consists of a gate, source and drain. The gate voltage enhances the current that goes from the source to the drain. Operational amplifiers, or op-amps, take two source inputs and amplify them as a single output. Op-amps are used with MOSFETs as part of a device to create distortion when playing an electric guitar.

Things You'll Need

PC board
Op-amp
Power supply
Resistors
MOSFET

Instructions

- 1
  Connect a current to the input of the op-amp. The op-amp needs a bipolar power supply. Use a capacitor on the board or a biased 9-volt battery.
- 2
  Place your resistors. For a non-inverting op-amp, the power is connected to the "+" input, and the two resistors loop between the "-" input and the output. For an inverting op-amp, ground the "+" input, and connect the power to the "-" input through the two resistors.
- 3
  Connect the output of the op-amp to the MOSFET gate. The gate-to-source voltage will equal -(resistor 1 divided by resistor 2) divided by the drain-to-source voltage.

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