Half bridge inverter/mosfet question.

Discussion in 'Homework Help' started by Runs212, Apr 28, 2015.

  1. Runs212

    Thread Starter Member

    Mar 12, 2015
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    I'm using a half bridge driver to drive a mosfet fqa55n25. It's input is above 10v, vdd is at least 12v. I noticed the 100ohms resistor connecting the driver to the mosfet was heating up. I also noticed my input frequency was at 400hz. Could the low frequency explain why it was heating up?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Hard to say.
    Post your schematic.
     
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  3. Runs212

    Thread Starter Member

    Mar 12, 2015
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    This is my last resort before i have to do a demonstration for the semester and I'd appreciate some help. Attached is a schematic of my project and teh waveforms i'm getting on the driver. I didn't connect it to the mosfet yet because the second signal was outputing ~5V. The first signal is correctly outputing the needed ~10V. I can't seem to figure out why one output on the driver is wrong. The current frequency is about 2Khz. I'm expected to use 110Khz but at that frequency, the signal gets seriously distorted. I'd appreciate any help that can be offered. This is for my senior design first semester project due in 2 days.
     
  4. #12

    Expert

    Nov 30, 2010
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    I can't find an IRS2103 or an IR52103 datasheet.
     
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  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Here's the datasheet
     
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  6. Runs212

    Thread Starter Member

    Mar 12, 2015
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  7. kdillinger

    Active Member

    Jul 26, 2009
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    Why is the COM pin floating?
     
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  8. crutschow

    Expert

    Mar 14, 2008
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    What's the purpose of the 39nF caps across the MOSFETs?
     
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  9. kdillinger

    Active Member

    Jul 26, 2009
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    VS is the return for the high-side floating MOSFET, so the 39nF cap on the low-side MOSFET is not providing anything.

    But he said above the MOSFETs are not in circuit yet.

    So first thing is first. Ground your COM pin.
     
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  10. Runs212

    Thread Starter Member

    Mar 12, 2015
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    The mosfets were not connected yet because I was getting less than 10v on one of the signals to drive one mosfet.
     
  11. Runs212

    Thread Starter Member

    Mar 12, 2015
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    The COM was grounded. I mistakenly omitted that on the schematic. also the cap value to the right is 4.7uF.
     
    Last edited: Apr 29, 2015
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  12. kdillinger

    Active Member

    Jul 26, 2009
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    If you zoomed in on the falling edge of the channel that is giving you problems (which channel BTW?) is there any funny business?
    The time base from your first scope plot is 100us/div. If this is happening when nothing is connected to the outputs, then one possibility is a bad part. You have a 80us time constant on the falling edge and that should not happen. Looks like you have a blown output stage, IMO. Some high resistance interacting with the gate capacitance.
    Is this on a breadboard or PCB?
     
  13. Runs212

    Thread Starter Member

    Mar 12, 2015
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    Thanks for your responses. I agree the mosfet driver is probably blown. Both HIN and LIN are receiving the same input (~5V) and should have a similar output (>10V). This is on a breadboard btw.
     
  14. kdillinger

    Active Member

    Jul 26, 2009
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    One thing to be careful of is the actual breadboard. I have seen parts shorted out because the person pushed the pins with enough force to get underneath the strip metal and into the next column.
     
  15. Runs212

    Thread Starter Member

    Mar 12, 2015
    55
    1
    Hello Everyone, progress has been made in the project. However, when I connect a load to my circuit or connect it to a receiver circuit, my MOSFET heats up quickly. I am thinking something shorting somewhere. I could be wrong. Could you look at my schematic and bounce off some ideas with me? Thanks.
     
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