Help, My Mosfets are Burning Out !!

[FLY_PT]

Hello,

Please I need some Help, I don't know what is wrong with this design, It works fine for a while but after a few minutes two Mosfets of the bridge just not work any more. Temperature aparently is Ok, Their get warm but not hot at all.

I'm using PWM for driving the bridge on both directions.

I' sending the schematics so any Idea I appreciate it.

The driver circuit(PWM) is connected in A1 and B1 and diodes D1-D4 are not placed in the board. The Mosfets I'm Using are FQA22P10 and FQA33N10. Voltage source is not 12VDC is 36VDC. I must say the power supply comes from a transformer and a Bridge rectifier.

Regards,

FLY_PT

 

[IanP]

I can't see anything wrong with your circuit.
Ii looks like the MOSFETS are rated for to low voltage: 55V rating in 36V circuit is not enough.
You should select Mosfets rated for at least twice the supply voltage, and I would say 150V rating would not hurt..
After all, you are switching an inductive load..
Regards,
IanP

 

[Btrend]

The driver circuit(PWM) is connected in A1 and B1 and diodes D1-D4 are not placed in the board.

I think the diode must be included in the board, cause the inductor will generate reverse high voltage whenever it is from state ON to OFF, and this reverse high voltage will find some way to leak away, if u don't add D1-D4, the only path to leak these high voltage are the "body diode" of the MOS which are not large enough to provide good leak path.

 

[FLY_PT]

The mosfets I'm Using are FQA33n10 and FQA22p10 wich are 100 volts rated, so I realy don't know if that could be the reason.

I will try the circuit placing the diodes as well.

Thanks

 

[rellutzu]

Hy!
Just take a look on the data sheet of the Mos and make sure that it doesn't have a built-in diode between drain and source, for fly-back voltage purpose.
It would be futile to put another one in the circuit!