PWM driver for an inductive load with detector of a not regulating PWM condition

A method for generating a not.sub.-- regulating signal, in a PWM driver circuit having a driver transistor and an inductive load and including a pulse-width-modulator (PWM) load-current controller, the method being of the kind including connecting the output of a set-dominated set-reset latch to the gating input of a transistor driver transistor, repeatedly at times t.sub.1 setting the latch by a timer-pulse generator that generates timer pulses of a predetermined width, from t.sub.1 to t.sub.2, setting and blocking the latch from being reset during a timer pulse, sensing the inductive load current and generating a sensing voltage that is proportional to the load current, generating a PWM-control reference-voltage, and during each PWM period between adjacent times t.sub.1 resetting the latch when the sensing voltage exceeds the reference voltage, wherein the improvement comprises:

• a) defining a predetermined sample-time interval, t.sub.2 to t.sub.3, during each PWM period;
• and
• b) generating a not.sub.-- regulating pulse during the predetermined sample-time interval only when the sensing voltage exceeds the reference voltage, so that the not.sub.-- regulating pulse indicates an operating condition wherein the PWM control circuit is not regulating the load current and the width of the not.sub.-- regulating pulse is a measure of the degree to which the PWM system fails to regulate.

A pulse width modulated (PWM) driver circuit including a driver transistor;

• a pair of driver-circuit load terminals to which an inductive load may be connected;
• a load-current sensing transducer for producing a sense voltage that is directly related to the load current, said driver transistor and said pair of load terminals connected in series between a pair of DC supply voltage busses;
• a PWM reference-signal input conductor to which a driver-control reference voltage may be applied;
• and a sense-comparator having one input connected to said sensing transducer and having another input connected to said reference-signal input conductor for producing at time t.sub.a a pulse at the output of the sense-comparator when the sense voltage exceeds the applied reference voltage, wherein the improvement comprises:
• a PWM control circuit means connected to the output of said sense-comparator and having an output connected to the control element of said driver transistor for repeatedly producing at the gating element of said driver-transistor during each PWM period a gating pulse for turning on said driver transistor, the gating pulse starting at a time t.sub.1 ;
• a sample-time logic means connected to said PWM control circuit for producing logic pulses that include a first logic-level transition at time t.sub.2 occurring after t.sub.1 and while said driver transistor is still on, and further includes a second logic-level transition at time t.sub.3 occurring after t.sub.2, to define a sample time from t.sub.2 to t.sub.3 during each PWM period;
• and
• a not.sub.-- regulating pulse generator means having one input connected to said sample-time logic means and having another input connected to said sense-comparator for producing a not.sub.-- reg pulse only when during a sample-time in each PWM period the sense voltage exceeds the driver-control reference voltage that may be applied to said reference signal input conductor.

A method for generating a not.sub.-- regulating signal in a PWM driver circuit having a driver transistor with an inductive load comprising:

• a) repeatedly generating timer pulses at successive times t.sub.1 to initiate each of a plurality of successive PWM periods;
• b) sensing the load current and generating a sense voltage that is proportional to the load current;
• c) generating a reference control voltage of a level at which the sense voltage level, and that of the corresponding load current, are desired to be controlled;
• e) during each PWM period producing at a time t.sub.a an excess-load-current detection pulse when sense voltage corresponding to the load current first exceeds the applied reference control voltage;
• f) generating a gating pulse at the gating-element of said driver-transistor initiated at each time t.sub.1 and turning on said driver transistor by the gating pulse, said driver transistor delaying turning off until a time t.sub.d after the occurrence of the excess-load-current detection pulse at time t.sub.a ;
• g) during each PWM period producing a sample-logic pulse that includes a first logic-level transition at a time t.sub.2 after t.sub.1, and producing a second logic-level transition at a time t.sub.3 after t.sub.2 to define a sample.sub.3 time t.sub.2 to t.sub.3 ;
• and
• h) during a sample-time, t.sub.2 to t.sub.3 in each PWM period generating a not.sub.-- regulating pulse only when simultaneously the load current exceeds the reference-control current.