IRFP064 gets burnt

Discussion in 'General Electronics Chat' started by xyz9915, Dec 31, 2008.

  1. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    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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  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    C5 is a single 10uF cap. I suspect that you're using an electrolytic. Unless it's a low ESR type, it may be causing an abnormally high rise/fall time.
    Add a 100nF cap from pin 11 to ground, and another 100nF cap from pin 8 to ground. Keep the leads as short as possible.

    You don't have any bypass capacitors on the collectors of your BD139's. This could be causing the gates of your IRFP064's to be charging slowly (excessive rise times).

    Total gate charge of the IRFP064's is 170nC's, which is quite large.
    Try removing the fuse from the battery supply to the transformer center tap, and compare the gate rise/fall times between your two "burner" boards and your good board.
     
  3. Alberto

    Active Member

    Nov 7, 2008
    169
    36
    I would place two ultra fast recovery diodes (as BYV28/200 for example) to protect the mosfet from the reverse induced voltage produced by the transformer.

    Alberto
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Good catch, Alberto.

    I think I'd opt for something a bit heavier duty though, like an MUR3020PT.
     
  5. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    snubber circuitry was also used (not shown in the schematic mistakenly). collectors of your BD139's is bypassed with 1000uf/25 capacitor but the problem still unresolved. I think this a gate drive issue and BD139/BD140 complementary pairs are not properly charging/discharging the (5+5) MOSFET's. If I reduce the number of MOSFET's from 5 to 2 in each side, the MOSFET's gets too much hot, so please suggest a better gate drive circuitry
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You might go to Microchip's website and download AN799 - Matching MOSFET drivers to MOSFETs.

    It will be lots easier to use driver ICs than so many discrete components.
     
  7. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    Someone informed me that since the circuit is running in voltage mode... a push-pull running that way can be subject to "flux walking".
    Therefore, my question is that how I prevent the core from reaching saturate in this push pull mode?
     
  8. xyz9915

    Thread Starter Member

    Feb 24, 2008
    23
    0
    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?
     
  9. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    I noticed that you have used 1N4148 for D2 and D3 at the two MOSFET gates drive circuit.

    You need to use Schottky diodes instead as normal diode don't recover fast enough for this application.
     
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