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Original question:

DRV8825: Why the actual current is lower than the set-up current?

DRV8825: The current of 24V power supply is 0.04A occasionally，which is always about 0.13A .

Lu Feiyue
Intellectual 660 points
Part Number: DRV8825

I  drive the motor to rotate a  half-circle.

When the motor is running , I set the chopping current to 1.33A,

When the motor stops,   I set the chopping current to 0.24A, and in  most case, the supply current of 24V  is about 0.13A when the motor stops.

But in some cases , the supply current of 24V  is about 0.04A when the motor stops.and the motor can be rotated manually wiith few resistance.

what's  the reason ?

Then  I  try  the fast decay mode  :  when the motor stops.,the supply current of 24V   is also about 0.04A  and the motor can also  be rotated manually wiith few resistance.

So I  guess maybe the current decreased  to 0 during chopping.   Would the situation I decribed happen?

So,  I  plan to  incease the chopping current when the motor stops, or  I  want to  try to increase the value of C11. Here  is my schematic:(some value is not the same as what I use to test.)

  • 0
    TI__Genius 14487 points
    Hi Feiyue,

    The current regulation doesn't work as well for low currents, especially if VREF is between 0 V and 1 V. I believe that this is likely causing your problem.

    If you have a current probe, can you take oscilloscope pictures of the current in your motor during the times you describe?

    When the current drops very low, the motor torque decreases, which is why the motor is easy to spin by by hand when the current is low.
  • 0 in reply to James Lockridge19
    Intellectual 660 points
    Thanks for your reply, I think I understand.

    I'll try to use fast-decay mode and increase the chopping current as well.
  • 0 in reply to Lu Feiyue
    TI__Genius 14487 points
    Feiyue,

    I hope that works for you. I recommend trying several decay modes, not just fast decay. If you have a current probe, I recommend looking at the current on an oscilloscope, and choosing the decay mode that minimizes current ripple as much as possible for your operating conditions.