Importance

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Abstract

A pulse width modulated (PWM) transistor driver circuit, for driving an inductive load, has a load-current sensing resistor and a comparator having an input connected to the sensing resistor and another input to which a PWM control reference voltage may be applied. A PWM driver-control circuit includes a set-dominant PWM latch, and a not.sub.-- regulating detector that may be composed entirely of logic circuit blocks or a combination of logic and analog circuits. By either means, the PWM bridge-control circuit includes a timer for repeatedly generating control pulses that set and hold a PWM latch beginning each PWM period, and the comparator resets the latch each time after the timer pulse the load current rises to exceed a corresponding reference voltage level. A sample-time-interval is defined beginning at the time of termination of a control pulse and a not.sub.-- regulating pulse generator produces a not.sub.-- regulating pulse only during the sample-time when the load current exceeds the level of the applied reference signal, indicating that the PWM system is failing to regulate the load current. Further, the not.sub.-- reg pulse width is, under most load conditions and over a wide range of applied reference voltage levels, a measure of the degree of failure of the PWM driver to regulate.

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First Claim