DC motor

Discussion in 'General Electronics Chat' started by firend, Jun 29, 2013.

  1. firend

    Thread Starter Member

    Feb 18, 2012
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    Hello everyone!
    I am controlling DC motor 12V. I am going to use H bridge to control. Circuit in PDF FILE. Can anyone give a advise?
    Thanks a lot.
     
  2. Shagas

    Active Member

    May 13, 2013
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    Why is there a BJT in the Forward 1 and reverse 1 between the signal and the mosfet?
     
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    You circuit is wrong, you need N-fets and P-fets use this type of design

    Clockwise = A Gnd ,B V+
    Anticlockwise A V+, B Gnd.

    If AB are at same supply motor is in stop mode.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Your design will work if...
    - You can prevent "shoot through" in your MOSFETS. That is, make sure the MOSFETS that control forward turn off completely before the reverse MOSFETS turn on.

    - You have Vgs between 10 and 15 volts to insure it is completely on. This means you cannot control th N-fets with only a Microcontroller. Your p-MOSFETS will be fine with the 2N3904 pulling them down.

    - you should have about 10ohm resistor going into each gate

    - you need a resistor at the base of each 2N3904 to limit current into them.

    I recommend a "logic level" mosfet for your n-MOSFETS instead of the ones you have. That way, 5-volts will drive the gate cleanly into saturation.
     
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  5. firend

    Thread Starter Member

    Feb 18, 2012
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    Thanks you. You can recommend me a "logic level" mosfet. Do i have a question? I read IRF610 datasheet, VGS(th)=2-4V. voltage of microcontrller is 5V.
     
    Last edited: Jun 30, 2013
  6. firend

    Thread Starter Member

    Feb 18, 2012
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    I use it to open P-MOS.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Threshold voltage is where the mosfet starts to turn on. It is not saturated at that point.

    I have a stash of STP55NF06L
    But just search digikey.com for discrete MOSFETS. Logic level is one of the search options (check the drop-down menus).

    Also, I forgot to mention that you will need 4 diodes in reverse bias to protect your MOSFETS. The symbol for your mosfet shows a diode but that is just the symbol, that "diode" does not protect anything. Put them across drain and source with cathode to the more positive leg.
     
    Last edited: Jun 30, 2013
  8. firend

    Thread Starter Member

    Feb 18, 2012
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    Thank you.
    I read document again. I know VGS(on)= VGS(sat)>VGS(th). But I can't find VGS(sat) in datasheet. Normally, does it has in datasheet, VGS(sat)?
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    usually as a graph. Your definition of Vgs(sat) will depend on the current flow you require.
     
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  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    One last suggestion. On the N-Mosfets, add a 10k ohm resistor from the gate to ground. This way, the MOSFET will be off until the microcontroller sets pin assignments during startup. If not pulled to ground, you could get shoot-through and burn your MOSFETs. Your P-MOSFETs are already protected with the 1k pull-ups connected to the 2N3904.

    Also, if you are using PWM to control motor speeds, do not use PWM on both the N-MOSFET and P-MOSFET at the same time. Just turn on the P-MOSFET and pulse the N-MOSFET. To reverse, just off both of your forward drivers then turn on the reverse P-MOSFET, and finally start the PWM on the N-MOSFET. That will keep switching fast and clean with little heat build-up on the p-MOSFET.
     
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  11. firend

    Thread Starter Member

    Feb 18, 2012
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    Hello GopherT!
    In my country, It is difficult to buy a logic level MOSFET. I read IRF540 datasheet. At voltage Vgs=4.5V, current ID(on) > 2A. My max motor current has =2A. If I use it,is my circuit safe?
    Thank you!
     
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