PWM inductive load bridge driver for dynamically mixing four and two quadrant chopping during PWM period off time

A bridge for driving one phase of a stepping motor includes a PWM driver control circuit that repeatedly turns on at least one of the driver transistors. A sense voltage is produced that is directly related to the bridge load current. When a driver-control reference voltage Vref is applied to the driver-control input, a sense-comparator pulse is generated when the sense voltage exceeds the applied reference voltage for turning off the one driver transistor. The remaining "decay" portion of the PWM period ensues after the driver transistor turns off. A not-regulating pulse is generated during a predetermined sample time portion of each driver on-time when the load sense voltage exceeds the applied Vref. In each PWM period, when a not-regulating pulse occurs the bridge driver is operated in the four quadrant decay mode during an initial part of the PWM-period decay portion until time tm and operating in the two quadrant decay mode for the remainder of the PWM-period decay portion. The not-regulating pulse may have a width that is directly related to the time interval during which the sense voltage exceeds the driver-control reference voltage, and the time tm may be delayed in the PWM period by an amount that is directly related to the not-regulating pulse width, and/or delayed by an amount that is inversely related to the value of the applied Vref.