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Do MOSFETs normally fail open or closed?
The short answer is I would expect a MOSFET to fail as an open circuit due to over-temperature conditions. This wikipedia article suggests that: Increase in drain-to-source resistance.
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.
Do MOSFETs fail closed?
Yes, transistors and mosfets can go defective.
Can a normally closed MOSFET be turned on?
Normally closed MOSFETS (ON with 0V gate to source voltage or depletion-mode) are uncommon. Most MOSFETS are OFF with Vgs = 0V. A Vgs voltage must be applied (enhancement-mode) to turn them ON (positive for N-MOSFETs and negative for P-MOSFETs). The data sheet will tell you the Vgs voltages required to turn on the MOSFET.
What should the temperature of a MOSFET be?
Since the RTP has to sense the temperature of the MOSFET, it naturally follows that the two should remain in close proximity. The RTP resistance will allow up to 80A of current at 120V AC through the MOSFET as long as the temperature of the MOSFET remains below the Open Temperature of the RTP, which can be between 135-145ºC.
What happens when the body of a MOSFET blows up?
MOSFET body diodes generally have a long reverse recovery time compared to the performance of the MOSFETs themselves. If the body diode of one MOSFET conducts when the opposing device is on, a short circuit arises resembling the shoot-through condition.
Why are my MOSFETs so hot after connecting?
Even after connecting everything correctly you find the mosfets in your circuit becoming HOT and blowing off within minutes. This is quite a common issue faced by most new as well as experienced hobbyists while designing and optimizing mosfet based circuits especially the ones which involve high frequencies.