What is the meaning of MOSFET ? It means Metal Oxide Semiconductor Field Effect
Transistor. Mosfets are some kind of transistors generally used for switching and
amplifying. Mosfets comes with three leads as shown below,
Gate ( G )
Source ( S )
Drain ( D )
The physical appearance of a mosfet and a transistor may same but mosfets are voltage
control power device and transistors are current driven devices. There are tow type of
mosfets ,N channel and P channel.
Testing a Mosfet using a analog multimeter
Testing a mosfet is not easy compare with other electronic devices like diodes, capasitors
and transistors. But if you do lot of test again and again for many mosfets you will be a
expert. Now get a analog multimeter and put the selector in to the diode testing mode.
Then connect the source ( S ) lead to the multimeter negative probe.
If you want you can hold the mosfet by it's body or the case but do not touch the other
two leads by your fingers. Now touch the Gate ( G ) pin with the positive probe once and
move the probe to the Drain ( D ). Now you should get a low reading if the mosfet is
Remember the test is not yet finished ! Now without lifting the positive probe on the
drain pin touch the Gate and Source pins by your finger. Now the Gate should discharge
through your finger and multimeter should show low reading.
If you observe above two results for a mosfet then we can assure that the mosfet is good.
But remember this is not 100% correct way to determine the status of a mosfet.