Need help protect burn Mosfet H bridge circuit

Discussion in 'General Electronics Chat' started by mpcotuong, Nov 18, 2010.

  1. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Hi All,

    I am using Mosfet P and N channel for H bridge circuit, once my Motor stuck the whole circuit has burned. Do you know how to make protect Mosfet H bridge circuit? Please let me know. The Voltage is 12VDC for Motor.

    Thanks,
    Kevin
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    There is an ancient device made from a low temperature fusible metal.

    It's called a fuse. It might help protect your motor from large current flows, and in the process it will keep your H bridge from bursting into flames :)
     
  3. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Last edited: Nov 18, 2010
  4. SgtWookie

    Expert

    Jul 17, 2007
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    MOSFET internal diodes won't protect against overcurrent.

    When a motors' rotor is locked/stalled, current flow is perhaps 10x as much as when it is running no-load.

    Another option is to use a chopper driver, which limits the maximum current without a fuse; however a fuse is always good protection against other circuit failures.
     
  5. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    I am using IRF630 and IRF9520PBF

    Thanks,
    Kevin
     
  6. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    It look like you suggest using the fuse. Do you know any fuse for 12VDC?

    Thanks,
    Kevin
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    What is your MOSFET Peak Current rating?

    Add a fuse inline with the motor of an automotive blade type, say 10 Amp or whatever, and you have that part covered.
     
  8. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Please see my N and P channel device IRF630 & IRF9520. I am using for 12VDC motor
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Then use a 2A fuse rated for 32v or higher.

    I don't know why you're using such high-voltage MOSFETs, unless you just can't find any that are lower voltage. Your Rds(on) is quite high at 0.6 Ohms.
     
  10. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    I am using the high Mosfet because would like to use strong motor of 12VDC. How to connect the Fuse. Is that connect it before the input of 12VDC?

    Thanks,
    Kevin
     
  11. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    If you have other Mosfet please recommend.

    Thanks,

    kevin
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    You would get a much lower Rds(on) if you used lower Vdss rated MOSFETs. 20v to 60v would be much lower.

    You can put it on either power supply/return wire to the H-bridge. My personal preference would be to interrupt the positive side.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    I would not use a P-ch MOSFET. The gate charge is 2.5 times higher in order to get the same Rds(on) for the same Vdss rating as an N-ch power MOSFET.

    I would use a high and low-side driver IC for each side of the H-bridge, and use identical N-ch power MOSFETs for all four.

    The IRLR8721/IRLU8721 would be a far better match for your application. Rds(on) is 0.0084 Ohms vs 0.6 Ohms for the P-channel you're using now; your power dissipation is over 71 times as high as it would be with these MOSFETs.

    The total gate charge at 8.5nC is ~half your current 16nC-22nC total gate charge; but as an added benefit the MOSFETs I'm suggesting are logic level rather than standard level.

    As I said though, you will need to use a high & low side driver IC for both sides of the H-bridge.
     
  14. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Thanks, I will consider lower Mosfet as you suggestion. Will it make my 12VDC motor move slow?

    Kevin
     
  15. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The motor may actually move faster due to lower resistance internal to the MOSFETs. The motor is still only supplied 12V, even if the MOSFETs are rated for 600V or more, 12V is all that is available.

    An H-Bridge driver IC may be the ticket, some include current sensing and shutdown as well.
     
  16. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    What H bridge IC you suggestion?

    Thanks,

    Kevin
     
  17. sgardner025

    Active Member

    Nov 5, 2009
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    The HIP4081 by Intersil is a good driver.
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    The VNH2SP30-E by ST Microelectronics is a very capable Automotive Fully Integrated H-Bridge Motor Driver, capable of up to 30A @ 41V (maximum), 19m Ohms per leg; 20kHz PWM, really too many great features to mention in one post, all for about $10/ea - if you can find any. For some reason, they appear to be sold out virtually everywhere, and new stock won't be arriving for a month or two.
     
  19. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Thanks, to both of you for suggestion of the H bridge IC. I will check the part and purchase.

    Kevin.
     
  20. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Do you have the diagram how to connect for both H bridge IC chip which you are recomend?

    Thanks,
    Kevin
     
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