Testing a MOSFET
Contents
Testing a MOSFET
If a MOSFET passes all 4 tests, it is likely a good device. If any of the tests are not satisfied, the part has been damaged.
*Once the Gate is charged, it will remain charged for several minutes. Long enough to do the tests. You just have to be careful not to disturb the gate lead and accidentally discharge it.
nFET
Test #1 --Source
Probe the Gate with the BLACK lead and the Source with the RED<
Test #2 - Test Drain-Source
Being turned off, the Drain-Source should be an open circuit. Test by probing with the BLACK lead on the Source and the RED lead on the Drain. The expected reading is an open circuit. The nFET has a reverse protection diode built in. To test this diode, reverse the polarity of the leads placing the RED on the Source and the BLACK on the Drain. The meter should read the forward voltage of the diode. If it shows as an open circuit, then the diode has been damaged.
=== Test #3 -
Probe the Gate with the RED lead and the Source with the BLACK lead. The expected reading is an open circuit. This double checks the Gate for short circuits and turns the device on.
Test #4 - Check Drain-Source junction for proper conduction
Make sure that you have not touched the Gate lead since you turned the device on. Probe with the RED on the Drain and the BLACK on the Source. The expected reading is a short circuit. Then probe with the polarity reversed with the RED on the Source and the BLACK on the Drain. This should also show a short circuit. If either of these shows an open circuit, then the Drain-Source is blown open.
pFET
Test #1 --Source
Probe the Gate with the RED<
Test #2 - Test Drain-Source
Being turned off, the Drain-Source should be an open circuit. Test by probing with the RED lead on the Source and the BLACK lead on the Drain. The expected reading is an open circuit. The pFET has a reverse protection diode built in. To test this diode, reverse the polarity of the leads by placing the BLACK on the Source and the RED on the Drain. The meter should read the forward voltage of the diode. If is shows as an open circuit, then the diode has been damaged.
=== Test #3 -
Probe the Gate with the BLACK lead and the Source with the RED lead. The expected reading is an open circuit. This double checks the Gate for short circuits and turns the device on.
Test #4 - Check Drain-Source junction for proper conduction
Make sure that you have not touched the Gate lead since you turned the device on. Probe with the RED on the Drain and the BLACK on the Source. The expected reading is a short circuit. Then probe with the polarity reversed with the RED on the Source and the BLACK on the Drain. This should also show a short circuit. If either of these shows an open circuit, then the Drain-Source is blown open.
