H-bridge

Discussion in 'General Electronics Chat' started by Dritech, Feb 18, 2012.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi,

    I want to control a motor (12V, 2A) using an h-bridge from a PIC microcontroller. To do so, i am going to use the IRFZ44N transistors. Is it a good decision to use these transistors? will i need to use heatsinks for them?

    Is it ok if i wire the h-bridge as the picture attached?

    Thanks.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    You are going to find that the upper mosfets will never turn on properly, since their gates can never be taken higher than their sources by the necessary Vgs.

    For the configuration you have chosen, you will need a high side drive IC.

    hgmjr
     
  3. hgmjr

    Moderator

    Jan 28, 2005
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    Here is a link to an example IC. I have provided this link for reference only. There are other devices that perform the same function.

    hgmjr
     
  4. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,

    Can this problem be solved without using a high side drive IC ?? and is the H-bridge circuit bellow better?

    http://schematics.circuitdiagram.net/images/jdv1235544233p.jpg

    Thanks
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    The circuit to which you link should work fine. You will notice that it uses p-channel mosfets in the upper legs and n-channel mosfets in the lower legs. This allows it to get around the need for a highside driver IC.

    One thing that you will need to do is carefully structure your software so that it avoids turning on the upper and lower mosfet on the same side of the bridge. You should be able to provide a software controlled dead-zone in which you make sure that both upper devices are off before you switch between the lower mosfets.


    hgmjr
     
    Dritech likes this.
  6. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
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    Thanks for your help.
     
  7. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    You can run a high drive charge pump with a couple of diodes and capacitors, and an NPN transistor or small mosfet, pulsed by a spare pin of the Microcontroller.

    That will work very well if you are only running forward and reverse. If you are running PWM for speed control the High Side Drive will work harder to keep up. Pulsing makes it more complicated because you need to be sure it can keep the gates charging repeatedly instead of only once. It might still be easy enough.

    It also depends on your 12Volt power supply. If your main supply drops to 9 Volts under a high motor load then the high side drive might drop to as low as 16Volts.

    This kind of highside is just a charge pump that doubles the Power Rail voltage minus diodes and some droop.

    IRFZ44N would probably survive with only 7 volts of drive overhead even if we are looking at highest load situations. You say your motor is 2 Amps, so assuming 10 Amps for stall is safe we can hope. At 7 Volts drive the FET would be 10 Amps and less than half a volt Drain to Source. 5 watts should be in its survival zone even without a heat sink.

    But this is all quick look guesses and I am very frequently wrong.
     
  8. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,
    I decided to design an h-bridge myself. The attached figure shows the design. For the transistors i am going to use the IRFZ44N and 1N4501 for the diodes.

    Is the design correct and will i work? and what opto isolator can i use?

    Just as a reminder, the motor is supplied with 12V and consumes approx 2A.
     
  9. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
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    Any help please?
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    The one thing I noticed is a serious lack of a discharge path for the gate. Remember, the gate of a MOSFET is a capacitor. You need to charge it fast and discharge it just as fast.

    The MOSFET driver chips have this feature, in the form of push pull transistors.
     
  11. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    I will suggest you to use L298 for 2Amps if you want to control large current go for MOS and don't forget to add a series DIODE in path of power supply (VCc and GND) to avoid damage of internal diode in MOS in case of wrong connection of power source.( i have also damage my H_BRIDGES thats why...(IRF9540/540))
     
  12. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi ,

    Thanks for your replies.

    Is there an H-bridge similar to the L298 but with a single h-bridge?
     
  13. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    I think no......
     
  14. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Do you know its number please? it tried google it but i cannot find any.
     
  15. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    I already said there is no chip with single BRIDGES....
     
  16. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Sorry i thought you said 'i think so'.

    I bought the L298 but when i give signal to its inputs, the PIC (which is connected to the same supply) is restarting. I noticed that i am having voltage on ground when the h-bridge is active (this only happen at start up of the motor).
    Do you know what can be causing this??

    Thanks in advance.

    EDIT: By the way, i am using the attached circuit diagram.
     
  17. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Any help please?
     
    Last edited: Mar 19, 2012
  18. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    I noticed that when i disconnect the motor, the PIC is working fine. The problem is when i connect the motor. The PIC is also restarting when i connect the motor directly to the supply.
    BTW is motor is a small DC one so its should not trip the supply.
     
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