IRFP064 gets burnt

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Please view the attachment of SMPS circuit which was modified by me to fulfill my requirements. I made three PCB's of the above SMPS (Output about 220V/1.5A DC). The problem is that one PCB is working fine and delivering my desired voltage & current (i.e. 220V/1.5A DC). But in the remaining two PCB's, power MOSFET (IRFP064) gets burnt within 2-3 minutes.
My question is that when the three PCB's are identical, so why one board is working satisfactorily & other two boards are not functioning properly? I thoroughly checked everything in all PCB's but remained unsuccessful. Hence please help in this respect.

Further another question is that can I use power transistors (e.g TIP35) despite using MOSFET's? By providing sufficient driving to the transistors?

Note: The IC is TL494
Best regards
 

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The fact that one works says to me that the schematic & layout must be good. I think your assumption that they are all identical is flawed.

Did you wind you own transformers? A reversed winding could cause problems.

Did you make your own PCB's if so, there could be fine hair thin strands shorting out some traces.

If the trace/pad pitch is very fine you could have solder shorts.

Get a good lens and really look hard at that section of board & triple check all component value, type and orientation. I'm sure you will find a difference.
Good luck:)
 
Thanks for replying. The PCB's was not made by me. Three samples were got made with PCB manufacturer. I made the transformer ETD44 with turns ratio [(2+2 turns of nine #24 SWG)/55 turns for secondary]. I changed the transformer from the circuit which works fine to the problem PCB's, but the MOSFET's get burnt. So I think the problem might be in the driving stage. But question arises that how the one circuit is working fine?
 
your get driver is not correct, if you really want to use totem pole stage then consider using sg3525, if slow turn on/off is ok for you then remove totem pole stage and connect each gate with say 33ohm to emitter of the pnp,

as you connect all the gate without a resistor for each gate so only one mosfet takes all the load at turn on/off causing it to overheat,

well only 2 mosfet is ok i guess, if they are well driven then they can go over 400watts,
 
After receiving suggestions, I tested all three boards with frequency counter and found that even the one board is working satisfactorily but the frequency at the gates of MOSFET's is displaying randomly (ranging from 200KHz to 500KHz), when I disconnected the gates driving resistors (10 Ohms), the frequency counter displayed the actual frequency of the circuit (which is about 36KHz). I then removed the driving circuit (consisting of BD139/BD140) & also removed the diodes D2/D3 (1N4148) with 220 Ohms resistor and then again connected the gates. The frequency counter displaying 36Khz in one side & other side the frequency is showing as 64KHz (just double) but the frequency remained stable. I also tried with different values of resistor but both channels are showing different frequencies (36KHZ & its multiple) but the frequency remains constant in all cases, also tried the circuit function with different frequencies (from 20KHz to 60KHz) but same situation. The transformer (2+2turns/50 turns) I again rewound but the situation still remained unchanged. I also connected two capacitors of 2200uF/25V for decoupling, & snubber circuitry (0.01uf with 4.7 Ohms resistor in series) is also attached.
So, I think that this is the problem within gate driving section, so please help me for resolving the trouble.
 

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I do not have an oscilloscope, but a frequency counter.
I agree with (AREZA) that get driver is not correct. I removed the BD139/BD140 stage (can be seen in the modified schematic in the attachment 3-e.zip), and connected only one MOSFET/side but the situation is unchanged
 
in the schematics “I” marked point (near pin 1 and 16 of U1) should be ground through some very low ohm resistor used as current sense, they are missing, may be this is the reason the pwm sending very narrow turn on pulse and blow the fets,

well your schematics is not complete , so do the smps, your turn ratio is a bit high for 220v , may be there is some layout issue present as well,

dont worry about saturation at this moment , this converter should not enter into saturation if the schematics and layout is optimised.
 
Please see the attached waveforms taken from oscilloscope. The pattern (A) shows the waveform of MOSFET's gates when the positive supply (12V) not connected to the push-pull transformer. When it is connected, the waveform (B) produces (too much noise/spikes) even the snubber is connected. After changing frequency from 36KHz to around 50KHz, waveform (C) appears which seems better but the MOSFET's gets very hot within one minute at 30% load. I changed the circuit with SG3525 (totem pole output) but the same result. So, the most suspected thing is transformer. changing the turns ratio or frequency slightly change the waveform. So, what is the solution?
 

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xyz9915 said:
choke was not used in the output stage, is it necessary?

The output stage is isolated from input, but the ground of bridge was wrongly shown as input ground symbol. it is connected to c28/c30 of output capacitors

If you're running closed loop then yes. Without a choke you're feeding those caps with very high current- practically a dead short. If you're running open loop (ie no regulation and no feedback) and close to full pulse width then you can get away without a choke since the current pulses in the caps will be just slivers.
 
Hello to all & EVA!
The attached file contain waveforms taken from oscilloscope. The problem is that about 70% of the load, the MOSFET's get suddenly hot and if the power supply is not disconnected, they burn within 3-5 minutes. I increased MOSFET's from 1 to 5 each side but the result is same, MOSFET's gets burnt. So, please help me is this respect.
 

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