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H-bridge with 4 N-ch FETs

Discussion in 'General Electronics Discussion' started by BlackMelon, Oct 11, 2012.

  1. BlackMelon

    BlackMelon

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    Aug 7, 2012
    I want to design H-bridge to drive 12V DC Motor at rate of 12A with Pulse Width Modulation
    but the problems is the FETs which can drive the motor with that high current are N-ch (The P-ch is so expensive because it's extremely rare in my area) so I have to put 4 N-ch FETs in the H-bridge and 12V battery to drive the motors
    But the problems is how to drive the gates of FETs correctly? and how the circuit will be?
    (I've got a Microcontroller which can give me only 5-0V pulse,and one 12V battery)
     
  2. BobK

    BobK

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    You need a high-side driver. They use a bootstrap capacitor to raise the voltage above V+ in order to turn on the gate even though the source is at a high voltage.

    The are often packaged as a high and low in one package to drive half a bridge. There might even be full bridge drivers.

    Bob
     
  3. BlackMelon

    BlackMelon

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    Aug 7, 2012
    Yes,There are full bridge drivers... but they can't withstand such a high current that I'm gonna use T___T
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    They're not designed to drive the motor, they're designed to drive the mosfets which drive the motor.

    And yes, a mosfet can have a gate current measured in amps!
     
  5. BobK

    BobK

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    But, hopefully, only for microseconds.

    Bob
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Hopefully, several orders of magnitude less than that!
     
  7. BobK

    BobK

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    Yeah, you're right, nanoseconds.

    Bob
     
  8. BlackMelon

    BlackMelon

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    Aug 7, 2012
    Sorry I can't get your idea about using Full bridge drivers to drive 4FETs in h-bridge...
    Plz. explain me more with the circuit diagram
    Thank you
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Give me a part number. I will find the datasheet for you and show you (unless we're talking bout different things)
     
  10. BobK

    BobK

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    A full bridge driver usually means an IC that drives the motor directly. What you need is a MOSFET gate driver with high-side and low-side drivers. I think most of these come with one of each per package. I don't seem to be able to find any that have 2 of each in a package, so you will need 2 high-side + low-side driver chips to drive a full bridge.

    Bob
     
  11. BlackMelon

    BlackMelon

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    Aug 7, 2012
    ok sorry for making confusions..
    I think I'm gonna use chips that BobK has spoken of
    but how the circuit will be?
     
  12. BobK

    BobK

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    Pick out a chip and it will have examples in the datasheet. The high-side and low-side drivers will go between your signals from the microcontroller and the gates of your power MOSFETs.

    Bob
     
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