strange problem with H-bridge induction heater

Discussion in 'The Projects Forum' started by ajrenzetti, Mar 30, 2011.

  1. ajrenzetti

    Thread Starter Member

    Dec 20, 2010
    Ive been working for a while on this induction heater, and my latest problem is the strangest so far. I have included the schematic in the picture attached, and the link to a video clip of my oscilloscope when i attempt to run the circuit. For some reason the inverter doesn't seem to start working until a little after i switch off the driver. Im using 2 igbt's to drive the circuit. In the video clip, i turn off the driver exactly 1 second after i start it(when the waveform starts).

    the link for the video is here:

    what is going on here? how could i fix this?
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    Your problem may be the zener diodes - D2, D3. When using a gate driver you don't need a zener between gate and source. The circuitry of the driver chip makes the voltage level shift needed to turn on the gate. Adding the zener just allows the output from the driver to loop back to the source, keeping the gate voltage at what ever the zener voltage is. The gate needs to be at 10V + source voltage to turn on.