Maxim Integrated Products, Inc.
METHOD AND CIRCUIT ASSEMBLY FOR SENSORLESS LOAD DETECTION IN STEPPER MOTORS

Abstract:

A method and a circuit assembly are described with which, in a stepper motor, a mechanical load applied to the motor shaft of which can be detected without a sensor in a voltage-based operating mode in which a nominal coil current is generated by applying a predetermined coil voltage (Us) to the coil. The coil is connected in a bridge branch of a bridge circuit formed from a first to fourth semiconductor switch (S1, . . . S4), wherein the predetermined coil voltage (Us) is applied to the coil with a variable duty cycle (T) by switching the semiconductor switch in the form of at least one PWM voltage (U(A1), U(A2)). The motor load is detected in the form of a load indicator signal (L) which represents a phase shift between a zero crossing of the predefined coil voltage (Us) and the next zero crossing of the coil current (Icoil) generated thereby, wherein a zero crossing of the coil current (Icoil) is defined when, in those time intervals (tm) in which the PWM voltage (U(A1), U(A2)) applied to the coil is zero, a polarity change occurs in a voltage dropping across the internal resistances of the semiconductor switches due to the coil current.