What is the suitable deadtime for Hbridge SMPS with IRFP460 MOSFETS?????

[billu8660]

hi,
I am making this SMPS with 50khz frequency, so far i have exploded 12 IRFP460 MOSFETs and 4 IRFPG50 MOSFETS, when i apply 60Vdc to this SMPS its seems to work fine, when 310Vdc is applied booom :-( , i have set 880ns as deadtime for this, i want to know what should be the safe deadtime for this SMPS.

 

[kabeer02]

well for the dead time you can simply use a diode in parallel with the 10ohms resistor and also try and out 10k resistor from gate to source of each fets.

 

[BradtheRad]

i have set 880ns as deadtime for this, i want to know what should be the safe deadtime for this SMPS.

Speaking theoretically...

You have a charged coil. Suddenly it sees high impedance when you shut off the mosfets.

The time constant (L/R) becomes a small value divided by a very large value. It is tiny. Hence the coil's flux fields collapse quickly, generating a pulse that has to go somewhere immediately.

In one millionth of a second, it can generate a high-voltage spike, positive at one end, negative at the other end.

Could that be what's making mosfets go boom?

This is just theory talking.

 

[kabeer02]

Unhh yes i can agree with bradtherad "spike" can also damage your mosfet but try and put the resistors.