Abstract: Methods and apparatuses are provided for use in driving a multiple-phase brushless motor. The methods and apparatuses include generating a slewed phase control signal for each phase of the motor. The slewed phase control signals are substantially proportional to a speed control signal during non-transitioning periods, and are slewed from one state to the next state over time during transitioning periods. The transitioning periods being associated with a commutation point. The slewed phase control signals are used to generate pulse width modulated (PWM) driving signals, for each phase of the motor. Thus, the shape of the resulting PWM driving signal will include additional PWM pulses during the transitioning period that provide for a trapezoidal shaping of the current supplied to each of the phase coils in the motor. The result is that torque ripple is reduced because the overall current applied to the motor and the torque resulting therefrom will tend to be more constant during commutation.

Abstract: A brushless DC motor system using PWM switching, in which the PWM switching is temporarily frozen whenever a zero crossing is expected in the back EMF. This avoids disruption of zero-crossing detection due to switching transients from the power transistor.

Abstract: A pulse width modulated (PWM) motor drive with back EMF monitoring of the floating phase of a polyphase motor is arranged so that zero crossings of the back EMF can be read without interference by PWM switching. A measure is taken of an interval between two zero crossings and, in the next interval, the PWM switching is stopped near to and before the next expected zero crossing, based on the time of the last prior interval. A period counter counts up during the first interval and another counter, loaded with the previous count reached by the period counter, counts down at the same rate during the second interval until a certain number is reached, near to but before zero, to generate a signal that results in stopping PWM switching until after the next zero crossing is detected.