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How to Check High-Power MOSFETs

Transistors are semiconductor devices that are used to amplify or switch electrical signals. MOSFETs are a special type of transistor made from metal oxides and silicon. Unlike regular transistors, MOSFETs only need a voltage in order to operate. This characteristic makes them useful for power switching, and thus they are found in devices such as flash memory, microprocessors and power supplies.

Power MOSFETs are designed to work with high currents and voltages. They are extremely sensitive to static electricity, and so must be tested for damage. To check a power MOSFET, use a MOSFET tester. Alternatively, check it with a digital multimeter.

Things You'll Need

N-Channel Power MOSFET
MOSFET datasheet
Digital multimeter

Instructions

- 1
  Identify which of the MOSFET leads are the gate, drain and source. Use the package or datasheet to find the information.
- 2
  Place the multimeter on the diode setting, which is marked by an arrowlike symbol. Hold the red probe on the drain and the black probe on the source. The display should show that the MOSFET is nonconducting.
- 3
  Turn the MOSFET on by briefly holding the red probe against the gate and then placing it back on the drain. The MOSFET will now be conducting, and the multimeter will display a low voltage reading.
- 4
  Turn the MOSFET off. One method is to leave the red probe on the drain, but to remove the black probe and then touch the gate and source with a finger. A second method is to hold the black probe on the drain and the red one on the gate. The multimeter will show a typical silicon diode reading of 0.5 to 0.7 volts. Reverse the probes, and the multimeter will show that the MOSFET is again nonconducting.

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