Inductive Spike for Push-Pull car audio supply

Discussion in 'The Projects Forum' started by maxmavin, Feb 20, 2016.

  1. maxmavin

    Thread Starter New Member

    May 11, 2013
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    I am facing this problem, which is causing the two push-pull MOSFET to extreme stresses.

    I am using this to power TAS5630 amp. the boost converter is converting the 12V DC voltage to 36V DC (unregulated). As this is a car amplifier so the battery voltage can be 10V to 14.5V.

    Everything is ok upto 13.5V DC input. But when the input voltage is higher than that, inductive spike is seen at the MOSFET drain and they becomes hot.
    At 13.8V or higher the kick exceeds the max Vds 40V and the FETs are starting to runaway.

    I have attached some screenshot and unsnubbed oscillation at MOSFET drain. Please help me to remove the inductive kick @15V. 0drain-gnd1 @14.5V2.png
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Whats the circuit for the booster?
     
  3. maxmavin

    Thread Starter New Member

    May 11, 2013
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    the schematic is inside the zip file. anyway I am again uploading...
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    what is the signal like on the gates when the voltage is altered?

    You can put an ultrafast diode like MUR460 across the drains to batt positive to clamp it.
     
    Last edited: Feb 21, 2016
    maxmavin likes this.
  5. Lestraveled

    Well-Known Member

    May 19, 2014
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    Are these scope photos with the power supply loaded or unloaded??
     
  6. maxmavin

    Thread Starter New Member

    May 11, 2013
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    Thanks Dodgy for your reply. Attached is the gate waveshape. I will try to add an ultra-fast diode to see if anything is improved. Thought the snubber will be sufficient to absorb everything (ringing ,spike etc.)
     
  7. maxmavin

    Thread Starter New Member

    May 11, 2013
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    These are unloaded waveforms.
     
  8. Lestraveled

    Well-Known Member

    May 19, 2014
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    Look at the waveforms with the power supply loaded.
     
  9. maxmavin

    Thread Starter New Member

    May 11, 2013
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    Probably this is caused by the primary leakage inductance. I am thinking about rewinding the transformer. Is there any tips or guide about the winding procedure so that leakage inductance is minimum ?
     
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