Problem with my output of Full bridge MOSFET

Discussion in 'The Projects Forum' started by julius64, Jul 1, 2008.

  1. julius64

    Thread Starter New Member

    Jun 17, 2008
    6
    0
    Hi.
    I write if you can help me with my problem:
    I feed my full bridge MOSFET B25NM60N, Mosfet 600 V, with 29.3 VDC, and working good, but I feed the circuit with 29.8 VDC and my signal in the output (with resistance as load) is very wrong. My circuit gate is with 2 IR2111 with boostrap capacitor is .1 uF.
    The signal i show the next:
    Without problem:
    [​IMG]

    This is my problem:
    [​IMG]
    If you can help me, very thank.
     
    Last edited: Jul 1, 2008
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Try lowering your supply back down to the tolerances specified in the datasheet: 25V or less. 29V is too much.
     
  3. julius64

    Thread Starter New Member

    Jun 17, 2008
    6
    0
    But the MOSFET is for 600 VDC?? I dont understand, as this mosfet I want to feed with 600 VDC. Now, the 25 V is the max Gate-source voltage. The feed is VDS, different that Gate supply. Gate supply voltage is VGS, is the 15 VDC, as I feed the drivers IR2111.
    My pulses I generate is a PWM signal the 40 KHZ, I dont believe that this frequency is a problem.
    If you gcan help me, very thank.
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
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    Perhaps a schematic would help. Where are you putting your 29V?
     
  5. julius64

    Thread Starter New Member

    Jun 17, 2008
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    I Attach the schematic of my circuit.

    [​IMG]

    Beetwen nodes a and b exist a resistance of 100 ohms 250 W as load.
    The voltage Vgs is 15 V, supply the drivers IR2111, as show the next schematic.
    [​IMG]

    If you can help me, very thank.
     
    Last edited: Jul 2, 2008
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    I apologize for misunderstanding your comments earlier.

    This is indeed a mystery. If you have connected everything according to your schematic, and if your drive signal is correct, the Vdd of your bridge should not matter.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Your UD4007 diode may be breaking down, or the voltage rating of your 0.1uF bootstrap capacitor may not be high enough, or the cap may be defective.
     
  8. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    Do you have VS connected to either "a" or "b"?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Julius, please attach your files to your posts. They are no longer showing up from the site you posted them on.

    I suggest saving them in .PNG format before you upload them, as the files will be quite compact.
     
  10. julius64

    Thread Starter New Member

    Jun 17, 2008
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    Yes I have conected VS in this point
     
  11. thingmaker3

    Retired Moderator

    May 16, 2005
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    The only thing connected to a and b should be the load.:confused: The schematic does not show Vs connected to a or b. Nor should it.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Thingmaker3,
    Attached is a typical application suggestion from page 1 of International Rectifier's datasheet for the IR2111. Please note that VS is connected to the middle of the bridge.

    The bootstrap circuit will not work properly unless that connection exists.
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
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    Ah. Wrong "Vs." Never mind.
     
  14. julius64

    Thread Starter New Member

    Jun 17, 2008
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    I have conected as datasheet. My apologize
     
  15. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    My apologies, actually. I misunderstood "Vs." You had it right.

    I really have no idea why the circuit would not be working, save that some components or connections may be faulty.
     
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