What causes a MOSFET to fail?

The cause of this failure is a very high voltage, very fast transient spike (positive or negative). If such a spike gets onto the drain of a MOSFET, it gets coupled through the MOSFETs internal capacitance to the gate.

Do MOSFETs fail open or short?

A typical failure mode for a MOSFET is a short between source and drain. In this case, only the source impedance of the power source limits the peak current. A common outcome of a direct short is a melting of the die and metal, eventually opening the circuit.

How to test a MOSFET?

This method requires the assembly of a test circuit to test whether the MOSFET is functioning appropriately. Conducting this test is straightforward as one only needs a multimeter with diode mode. A MOSFET has an internal body diode. Therefore, in an NMOS, the body diode is usually from the source to the drain.

What is the n-channel MOSFET?

The most commonly used MOSFET is the N-Channel MOSFET, also known as NMOS. The testing of the N-Channel MOSFET requires the following elements: One measuring meter- This can be either an Ohmmeter or multimeter with a resistance range.

What is the forward drop of a MOSFET?

For most of the MOSFETs, the forward drop is approximately between 0.4V to 0.9V. When an NMOS is in reverse bias, the diode operates as a circuit. A diode that does not read within this range is probably defective. A diode that also reads zero on the multimeter is also faulty.

How to identify drain to source resistance of MOSFET?

The threshold voltage should be within the range of the multimeter for optimum performance. Use the resistance test to identify the drain to source resistance. It would help if you recorded the value of drain to source resistance of the MOSFET while in off condition. You will use this value for reference in the next step.