Electronic Circuits and Projects Forum



Help with L298 DUAL FULL-BRIDGE DRIVER

  1. 6th November 2007 11:58 AM #1
    Scorpio Scorpio is offline

    Help with L298 DUAL FULL-BRIDGE DRIVER

    It's my first time to write in a forum, so excuse me if am not clear.

    I am making a robot using the L298 H-Bridge to drive 2 (24v-3A) motors, Max. rating from data sheet is that the L298(Dual-Bridge) can drive 2 DC motors each of 2A or 3A motor if the 2-bridges are connected in parallel configuration.
    The micro-controller (AVR) have a 2 built-in pwm channels which i used to control the speed of the motors, the micro-controller board is isolated from the motor-control board(board with H-Bridge) by opto-couplers.

    Q1 - The H-Bridge get very hot and it fails"burn" (Data sheet operating temp. = -25 to 130 C - i think the hot part is solved)
    Q2 - The opto-coupler o/p is always either 5v ot 0v and i pass the pwm signal through it
    ( if i measure the signal from micro using multimeter and the signal pulse width was say 50% the multi-meter reads 2.5v but the o/p of the opto reads 0 or 5v)

    Any idea how to isolate the 2 boards in anthor way than using opto-couplers and any idea of high rating H-Bridge
    Last edited by Scorpio; 6th November 2007 at 12:07 PM.
  2. 6th November 2007 02:53 PM #2
    audioguru audioguru is offline
    Each half of an L298 has a max allowed continuous current rating of 2A. If your motors have an operating current of 3A then it might be 30A when they are started or when they are stalled.

    You forgot to attach your schematic so we can't see why your optos don't work. What is the PWM frequency?
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  3. 6th November 2007 06:54 PM Thread Starter #3
    Scorpio Scorpio is offline
    so what can i do to avoid the 30A current ??

    There's the schematics of the micro-controller board, the micro-controller is connectors to the opto-coupler and then the opto-couplers are connected to o/p connectors which will be connected to the H-Bridge (L298) in the motor control board.

    There are 6-opto (3 for each motor) (2 for the direction and one for the pwm).
    The pwm i tried from 10 khz to 20 khz.
    Attached Files
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  4. 6th November 2007 06:57 PM #4
    blueroomelectronics blueroomelectronics is offline
    What make / model are the motors?
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  5. 6th November 2007 07:00 PM #5
    Nigel Goodwin Nigel Goodwin is offline
    Super Moderator
    Quote Originally Posted by Scorpio
    so what can i do to avoid the 30A current ??
    You need a decent size H-Bridge, the one you're attempting to use is only for little toy motors.


    The pwm i tried from 10 khz to 20 khz.
    I would suggest that's much too high, PWM is usually lower - usually only in the low single KHz range.
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  6. 6th November 2007 08:54 PM #6
    audioguru audioguru is offline
    What are the LM324 quad opamps for on the motor board?
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    Uncle $crooge
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