🔧 How to Test a N Channel & p Channel MOSFET with a Multimeter (Step-by-Step Guide)

Testing a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is an essential skill for electronics repair and troubleshooting. Whether you’re working on a power supply, motor controller, or other electronic device, identifying a faulty MOSFET can save time and money. This guide will walk you through how to test N-channel and P-channel MOSFETs using a digital multimeter.

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🧰 What You Need

• Digital multimeter (with diode test mode)

• The MOSFET you want to test (removed from the circuit is best)

• Basic understanding of the MOSFET’s pinout (Drain, Gate, Source)

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📘 Understanding the MOSFET Terminals

• Gate (G): Controls the current flow

• Drain (D): Where current enters (for N-channel)

• Source (S): Where current exits

Always consult the datasheet of your MOSFET to identify the pins correctly.

 

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🔍 How to Test an N-Channel MOSFET

1. Initial Checks (Body Diode Test)

1. Set your multimeter to diode mode.

2. Connect the positive (red) probe to Source and the negative (black) probe to Drain.

3. You should see a voltage drop between 0.4V to 0.9V (body diode forward voltage).

4. Reverse the probes: It should show OL (no conduction).

✅ This confirms the body diode is healthy.

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2. Gate Charge Test (Turn-On Behavior)

1. With the multimeter in diode mode, touch the Gate and Source together to discharge the gate.

2. Now connect the positive probe to Drain, negative probe to Source → It should show OL (off state).

3. Briefly touch the Gate with the positive probe and the Source with the negative probe (this charges the gate).

4. Now again connect positive probe to Drain, negative to Source → It should now show low resistance, indicating the MOSFET is turned ON.

✅ The MOSFET responds to gate voltage = working properly.

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3. Reset the Gate

Touch the Gate and Source together again to turn the MOSFET OFF.

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🔁 How to Test a P-Channel MOSFET

The steps are similar but with reversed polarity:

1. For the body diode, connect black probe to Source, red to Drain → You should get 0.4V–0.9V.

2. Charge the gate by touching Gate with negative probe, Source with positive.

3. Test from Source to Drain — you should now see low resistance.

4. Discharge the gate by shorting Gate and Source to reset.

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⚠️ Important Tips

• Always remove the MOSFET from the circuit before testing for best results.

• Make sure your fingers don’t touch multiple pins while testing — body capacitance can affect results.

• If the MOSFET shows short between Drain and Source with no gate activation, it’s likely faulty.

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🏁 Conclusion

Testing a MOSFET with a multimeter is quick and effective. With a little practice, you’ll be able to diagnose faulty components in power electronics confidently.

For a better idea, we suggest you watch the video below