H-bridge

Discussion in 'General Electronics Chat' started by Dritech, Feb 21, 2012.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi all,

    I am working on a project which involves moving a motor clockwise and counterclockwise. The motor is supplied by 12V and consumes approx 1.5A (maximum 3A when loaded). If i use the H-bridge in the attached picture, will it work fine? and will i need to use a heatsink?

    Thanks.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Depending on how much current your motor actually consumes, you may not be able to get away with the small signal 1n4148 diodes as your flyback protection.

    hgmjr
     
  3. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,
    Assuming the motor will not consume more than 3A, what diodes shell i use? and can i connect the base pins of the TIP directly to a PIC18F ?

    Apart from the diodes, is the H-bridge circuit correct ? and will i need heat sink?

    Thanks
     
  4. Felo

    Member

    Feb 20, 2012
    91
    13
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You forgot to look at the datasheet for a TIP120 darlington transistor.

    With a motor current of 3A then the maximum saturation voltage from collector to emitter for the bottom TIP120 is 2.0V.

    If the top TIP120 has enough base voltage (it doesn't) then its emitter voltage will be a minimum of +3.0V due to its max collector to emitter saturation voltage of 2.0V.
    Then the input to its base resistor must be about +8.5V for the motor to get only 1V.
    But you don't have +8.5V, you have only about +4.5V to feed the base resistor.

    You should use complementary logic-level Mosfets that have a very low voltage drop.
     
  6. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi, thanks for your replies.

    If i use IRFZ44N mosfets instead of the TIP122, will it work?
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    No.
    You need P-channel Mosfets (which are complementary to the N-channel IRFZ44 Mosfets) at the top or you will need a Mosfet driver IC to drive N-channel Mosfets at the top.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The IRFZ44 should not be driven directly by logic-level ICs (including PICs) because they are standard level MOSFETs; Vgs needs to be 10v in order for the MOSFET to be considered fully turned ON, and have a low Rds(on). You need logic-level MOSFETs; with this type, Rds(on) is generally specified at both 4.5v and 10v instead of just 10v.

    International Rectifier's standard level MOSFETs generally start with IRF, and their logic-level MOSFETs start with IRL. This is not true for ALL of their MOSFETs, but it is for the vast majority.
     
  9. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,

    What is the complementary P-channel Mosfets please?
     
  10. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    We don't know what is available in your country. In North America EVERYTHING is available.

    You must find a P-channel logic level Mosfet that has a suitable max voltage and suitable on-resistance that you need.
     
  11. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,

    It is difficult to find certain electronic components in Malta, but i can order them from RS Malta and they will arrive within 3 days.
     
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