IR2304 Output Issues

Discussion in 'General Electronics Chat' started by ianfcrowley, Jan 22, 2011.

  1. ianfcrowley

    Thread Starter New Member

    Jan 22, 2011
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    I am currently working on a project wherein I am building an H-bridge using 2 IR2304 half-bridge drivers, with 4 IRFPA460As as my MOSFETs. Right now, I'm building and testing the circuit at low voltage, with an H-Bridge bus voltage of 20V. Eventually, that bus will be 170V (hence the beefy MOSFETs). My VCC is 10V as well.

    My two bridges are wired exactly as in the IR2304 datasheet, with boot-strap capacitors of 100nF, and input filter capacitors of 0.01uF.

    My input signal is a PWM signal which goes from 0V low to 10V high, with a 50kHz switching frequency, and the sine-wave which the PWM encodes is 60Hz. The circuit seems to be working at this point except for a strange problem. Occasionally, the HO of the bridge which is currently high duty cycle cuts off, and anywhere between one and 3 or 4 high cycles will stay low, before the gate begins switching high again.

    One half-bridge is doing it worse than the other, but both are doing it. All I can think of as a reason is that for some reason, the shoot-through prevention logic is kicking in once in a while. It does seem to happen more when each H-bridge is high duty cycle, but it also happens sometimes around 50%. It never seems to happen below 50% though.

    Anyway, any help with this issue would be greatly appreciated.

    Ian
     
  2. ianfcrowley

    Thread Starter New Member

    Jan 22, 2011
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  3. SgtWookie

    Expert

    Jul 17, 2007
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    Your bootstrap caps are too small at 100nF. Keep those as close as possible to the driver IC, but add a larger cap nearby.

    You really need to post your circuit as it's constructed. Photos and a board layout.
     
  4. ianfcrowley

    Thread Starter New Member

    Jan 22, 2011
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    0
    The value for the bootstrap that I'm using is higher than what I calculated as a minimum using the AN-978 equation, which gave me a minimum of 67nF, so I just rounded it up to 100nF.

    As far as the board layout, the circuit itself is exactly like the datasheet circuit for each half-bridge, with the two load connections for half-bridge connected together and then connected to each side of a load, which in this case is a 7.5kOhm resistor.

    I'll try to get a picture and post it.

    Ian
     
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