L272 driving Stepper motor, issue

Discussion in 'General Electronics Chat' started by zodiac565, Aug 9, 2016.

  1. zodiac565

    Thread Starter New Member

    Aug 9, 2016

    two small stepper motor's from scanner's. each of them bipolar motors (4-wires).
    i have made a PCB with 2xL272's summing 4 Opamps to drive one stepper motor.
    the circuit used is found in the datasheet.

    datasheet of the chip

    I used the same voltage for IN_REF as for the supply for the Opamps(on the schematic)
    i fed 2 square waves with low frequency, one 90° phase shifted into the two inputs, and it really worked. however after some time the motor began to rattle loudly. and also with more than 5Volts the motor begins to get too hot and also the IC. could someone help me to figure out what happened ? i really don't understand what happened cause at the beginning my circuit went fine.
    Last edited: Aug 9, 2016
  2. CEJones

    New Member

    Feb 12, 2016
    What motor are you using. The op-amps are rated for 1A and it's important to remember that op-amps are not designed to be driven to the rail so will often be lossy used in this manner. This heat could possibly be reduced by changing to an equivalent comparator circuit. I would suggest measuring you opamp output waveform. My guess is that the rattling is coming from noise caused by the op-amps starting to fail.

    It's always best to separate variables for debugging. Try the opamp when driving a resistive load to determine if they have failed.