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DRV8251A: low RPM control scheme

SRB
Intellectual 830 points
Part Number: DRV8251A

For small brushed motors -

Ignoring cost, efficiency, and solution size, what control scheme will provide the best variable speed operation down to speeds well below the motor's nominal RPM:

-- a variable voltage or
-- PWM at the motor's nominal voltage?

In this case, "best" includes smooth, quiet operation and resistance to stalling.  Regarding stalling, it seems that PWM is best as this applies the maximum torque (at least momentarily).  Just looking for an expert opinion.

  • +1
    TI__Mastermind 18505 points

    Hello SRB, 

    For brushed DC motors to get them spinning at first, you need the large inrush current. A larger voltage with a high duty cycle will get you that result and then you could lower the duty cycle for lower RPM. If quiet operation is necessary then PWM will also be beneficial as if the PWM frequency > 20 kHz, then the noise should be reduced. There is a minimum duty cycle that is required for it to spin, and it determined by the motor time constant (L/R). The high time and low time should be greater than that time constant.

    Best,

    Keerthi