I have seen a schematic for a line following robot, but there is something that I can't understand and is shown in the figure below, what is the purpose of the Op Amp circuit? I know that BREAK input in H-Bridge is independent on other pin. Could some one explain what this circuit does?

enter image description here

  • \$\begingroup\$ note that the BREAK G is refer to BREAK D \$\endgroup\$
    – Learner
    Dec 28, 2013 at 18:04

1 Answer 1


The device that looks like an opamp is a comparator, it compares the REF_I_MAX input with ISENSE_G input. The output is low unless the sense level becomes higher than the reference voltage in which case the BRAKE_G output becomes high.

Seems to be a brake mechanism that is activated when the current of the motor exceeds the reference level (for whatever reason).

  • 1
    \$\begingroup\$ does the current of DC motor growing with time ? i think that the amount of current remain constant \$\endgroup\$
    – Learner
    Dec 29, 2013 at 6:26
  • \$\begingroup\$ @Hassan The motor uses more current at startup and as it accelerates the current gradually drops. The motor current can also increase where there is a load that resists the spindle rotation and tries to slow the motor down (like an obstacle in the case of the robot). \$\endgroup\$
    – alexan_e
    Dec 29, 2013 at 10:16
  • \$\begingroup\$ That does not make sense at all. An op-amp has very high input impedance - it cannot take current as an input. For a transresistance configuration like this, the current can't be driven directly into the input terminals. Is this perhaps more of a block diagram? \$\endgroup\$
    – sherrellbc
    Jun 28, 2014 at 14:20
  • \$\begingroup\$ @sherrellbc . . it would seem that ISENSE_G could be a current sensor with a voltage output. \$\endgroup\$
    – Marla
    Jun 28, 2014 at 14:38

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