H-bridge ready to be built.

Discussion in 'The Projects Forum' started by hobbyist, Sep 17, 2009.

  1. hobbyist

    Thread Starter AAC Fanatic!

    Aug 10, 2008
    Looks like for this application, (simple mobile robot vehicle), I can use the H-bridge I designed a while back, I am now using a 9volt battery for the logics unit, and 2 AA batteries for the H-bridge drive voltage, the motor I'm using is a small 5volt, hacked servo motor.

    I have built and run extensive tests on this and I am satisfied that this will work for THIS application.

    The reason for extrememly high resistanace is to not load the battery so much.

    First here is the data I gathered during the test run.

    H-bridege data.jpg

    Here is the original schematic
    the motor is run off of 2 AA batteries, and the logic is run off of 9 volt battery.

    H-bridege for small robot motor rev.2.jpg

    here is the unit breadboarded for one motor only.

    breadboard before test.jpg

    Here is the dynamic test applying a squarewave signal to the unit.
    I had to use a resistive dummy load so as to check the switching ability of circuit.

    100 hZ.

    osciloscope, 100Hz.jpg

    200 Hz.

    osciloscope, 200Hz.jpg

    and 400 Hz.

    osciloscope, 400Hz.jpg

    This unit will only be switching during sensor inputs (no need for fast switching), such as bumper switches and infra-red obststacle avoidance, most of the time the motor will be in continuous run mode.

    After an hour the mosfets were still cool to the touch.

    Thanks everyoe for the info on my last thread I appreciate the time you took to exoplain things.
    Last edited: Sep 17, 2009

    AAC Fanatic!

    May 26, 2009
    A real marvel, hobbyist! What, may I ask, is the signifance of having those diodes at the bases of your transistors?
  3. hobbyist

    Thread Starter AAC Fanatic!

    Aug 10, 2008
    They are used to keep the bases isolated from each other, otherwise problems could arise as current through the bases interact with each other.

    As well as kepping base currents away from the sensor circuits, this way the sensor circuits will have the full drive, and not interact with the base currents.
  4. hgmjr

    Retired Moderator

    Jan 28, 2005
    I am afraid you may have a problem turning on the upper two MOSFET transistors. The problem is that the gate on these two FETs has to go 5 to 10 volts higher than the source. Since your gate driver for these two devices can not go more positive than the positive supply, you will not be able to turn these devices on.

    There are available high-side drivers made for the express purpose of driving these gates to voltage greater than the positive supply just for this purpose.

    An alternative would be to use P-channel Mosfets in the two upper switching devices. You will need to change the gate driver circuit to accommodate the p-channel mosfets.

  5. hobbyist

    Thread Starter AAC Fanatic!

    Aug 10, 2008

    Sorry my fault on the schematic. I used the old drawing with the old supplies.

    My new drawing should have 3 volts, for the motor, and 9 volts for the logic circuits.
  6. Audioguru


    Dec 20, 2007
    The old IRF610 is for high voltage and low current. But your requirements are the opposite.
    If its gate is at +9V then it might not supply any current to the motor since its gate-source turn on voltage is 10V. For its source voltage to the motor to be +3V then its gate voltage must be +13V.
  7. hobbyist

    Thread Starter AAC Fanatic!

    Aug 10, 2008
    This is the 2 H-Bridges been built into PC Boards. So far.

    2 H-Bridges PC board foil side before loading.JPG

    after loading.
    2 h-bridges with schematic and foil artwork map.JPG

    closeup both PC boards.
    closeup of both bridges.JPG

    closeup view 2.JPG

    size reference using a 9 volt battery.
    size reference.JPG

    The 5 headers at the bottom row are for
    sensor inputs.

    1. side bumper switch.
    2. fromt bumper switch.
    3. Infra-Red detector.
    4. Aux. 1
    5. Aux. 2.

    closeup view 1.JPG