Importance

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Abstract

A digital input signal is fed through an interface to a logic phase control which decodes the signal to provide a plurality of phase signals in a predetermined relationship for driving a sychronous DC stepper motor. The phase signals are fed to corresponding phase drivers which amplify the pulses of the phase signals before they are applied to the corresponding phase windings of the stepper motor. Each phase driver includes an operational amplifier and a power transistor connected in a closed loop to provide a current pulse having a constant predetermined peak amplitude to the corresponding phase winding during acceleration of the motor. The inductive time constant of the motor phase windings is thus overcome so that an applied mechanical load can be rapidly accelerated without stalling and the absence of dropping resistors minimizes power dissipation and heat generation. A pulse detector turns off the phase drivers after a predetermined time interval following the last pulse of the digital input signal to provide a time brake holding torque and near zero standby power comsumption. Components in the circuit are provided for protecting the power transistors from breakdown due to back emf signals generated in the phase windings.

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First Claim