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Old 31st December 2008, 06:03 PM   #1
xyz9915 is offline xyz9915  Pakistan
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Default IRFP064 gets burnt

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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File Type: pdf 3-c.pdf (93.3 KB, 241 views)
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Old 31st December 2008, 06:35 PM   #2
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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
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Old 31st December 2008, 06:45 PM   #3
xyz9915 is offline xyz9915  Pakistan
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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?
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Old 31st December 2008, 07:28 PM   #4
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Maybe there's a wrong value on the good board that stops the FET from overheating.

I still think theres a difference between the good & bad boards
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Old 31st December 2008, 07:32 PM   #5
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If you take the fuse out, are the waveforms on the gates of the FETS correct?
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Old 31st December 2008, 11:44 PM   #6
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Well if you have one that works it's easy to compare waveshapes. Look at gate drives, currents, drains, diodes, etc.
You will find it.
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Old 1st January 2009, 06:03 PM   #7
areza is offline areza  Bangladesh
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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,
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Old 3rd January 2009, 03:16 PM   #8
xyz9915 is offline xyz9915  Pakistan
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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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File Type: zip 3-e.zip (98.6 KB, 56 views)
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Old 3rd January 2009, 04:07 PM   #9
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Do you have an oscilloscope?
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Old 3rd January 2009, 05:49 PM   #10
xyz9915 is offline xyz9915  Pakistan
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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
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