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Faizan
A metal-oxide semiconducting field effect transistor (MOSFET) is similar to a junction transistor but uses less current and can be switched on and off faster. They come in two basic varieties, depletion and enhancement, each having "P" and "N" subtypes. If you have a single MOSFET device you suspect may not be working, test it with a multimeter's ohmmeter function. As a MOSFET is easily destroyed with static electricity, always ground yourself before working with one.
Preparation
Identify which pins of the MOSFET are its source, gate and drain leads. Look up the device's part number in the MOSFET catalog to verify its lead layout. Also identify whether the device's type is depletion or enhancement.
Slip the wrist strap on your wrist and clip or connect it to a solid earth ground, such as a cold water pipe or electrical ground.
Turn the multimeter on and set its function knob so it reads resistance.
Test Enhancement Type
Set one of the meter's probes to the MOSFET's drain lead and the other probe to the source lead. Read the resistance on the meter's display. Reverse the probes and read the resistance. Both ways, you should read infinite resistance.
Touch the meter's red or positive probe to the MOSFET's gate lead. Touch the black or negative probe to the drain lead and note the resistance reading. Touch the black probe to the source lead. Both readings should indicate infinite resistance.
Set the black probe on the gate lead. Touch the red probe to the source lead and note the resistance. Touch the red probe to the drain lead and read resistance on the meter's display. Both readings should indicate infinite resistance. If the device fails any of these tests, replace it.
Test Depletion Type
Put one of the meter's probes to the MOSFET's drain lead and the other probe to the source lead. Note the resistance on the meter's display. Reverse the probes and note the resistance. Both ways, you should read the same resistance.
Touch the meter's red (positive) probe to the MOSFET's gate lead. Touch the black (negative) probe to the drain lead and note the resistance reading. Touch the black probe to the source lead and read the resistance. Both readings should show infinite resistance.
Connect the black probe to the gate lead by touching it. Touch the red probe to the source lead and note the resistance. Touch the red probe to the drain lead and read resistance on the meter's display. Both readings should have infinite resistance. If the device fails any of these tests, replace it.
Preparation
Identify which pins of the MOSFET are its source, gate and drain leads. Look up the device's part number in the MOSFET catalog to verify its lead layout. Also identify whether the device's type is depletion or enhancement.
Slip the wrist strap on your wrist and clip or connect it to a solid earth ground, such as a cold water pipe or electrical ground.
Turn the multimeter on and set its function knob so it reads resistance.
Test Enhancement Type
Set one of the meter's probes to the MOSFET's drain lead and the other probe to the source lead. Read the resistance on the meter's display. Reverse the probes and read the resistance. Both ways, you should read infinite resistance.
Touch the meter's red or positive probe to the MOSFET's gate lead. Touch the black or negative probe to the drain lead and note the resistance reading. Touch the black probe to the source lead. Both readings should indicate infinite resistance.
Set the black probe on the gate lead. Touch the red probe to the source lead and note the resistance. Touch the red probe to the drain lead and read resistance on the meter's display. Both readings should indicate infinite resistance. If the device fails any of these tests, replace it.
Test Depletion Type
Put one of the meter's probes to the MOSFET's drain lead and the other probe to the source lead. Note the resistance on the meter's display. Reverse the probes and note the resistance. Both ways, you should read the same resistance.
Touch the meter's red (positive) probe to the MOSFET's gate lead. Touch the black (negative) probe to the drain lead and note the resistance reading. Touch the black probe to the source lead and read the resistance. Both readings should show infinite resistance.
Connect the black probe to the gate lead by touching it. Touch the red probe to the source lead and note the resistance. Touch the red probe to the drain lead and read resistance on the meter's display. Both readings should have infinite resistance. If the device fails any of these tests, replace it.
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