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

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billu8660

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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.
 

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kabeer02

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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

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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

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

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