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

  • US 5,708,578 A
  • Filed: 07/11/1996
  • Issued: 01/13/1998
  • Est. Priority Date: 07/19/1995
  • Status: Expired due to Term
First Claim
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1. A pulse width modulated (PWM) bridge including four driver transistors, a pair of bridge load terminals to which an inductive load may be connected, and a load-current sensing transducer for producing a sense voltage that is directly related to the bridge load current;

  • and a sense-comparator having one input connected to said sensing transducer and having another input to which a driver-control reference voltage may be applied for producing at time ta a pulse at the output of the sense-comparator when the sense voltage exceeds the applied reference voltage, wherein the improvement comprises;

    a PWM bridge-control circuit means capable of operating said PWM bridge in either a four quadrant control mode or a in two quadrant control mode, said PWM bridge-control circuit means connected to the output of said sense-comparator and having an output connected to a gating element of at least one of said driver transistors for repeatedly producing at said gating element of said at least one driver-transistor a gating pulse initiated at time t1 for turning on said one driver transistor for a first portion of each PWM period, the second and remaining portion of each PWM period being a load-current decay portion;

    a sample-time logic means connected to said PWM bridge-control circuit for producing logic pulses that include a first logic-level transition at time t2 after t1 during the first portion of the PWM period, and producing a second logic-level transition at time t3 after t2, to define a sample time t2 to t3 ;

    a not-- regulating pulse generator means connected to said sample-time logic means and to said sense-comparator output, and having a mode-control output, for producing a not-- regulating pulse at said mode-control output during the sample-time in each PWM period when the load current rises to exceed the level at which the sense voltage exceeds the driver-control reference voltage that may be applied to said reference signal input conductor;

    a mode control circuit means connected to said PWM bridge-control circuit means and connected to said mode-control output for when a not-- regulating pulse occurs during the sample time of a PWM period, operating said bridge driver in the four quadrant mode during an initial part of the ensuing PWM-period decay portion until at a time tm operating said bridge driver in the two quadrant mode for the remainder of the PWM-period decay portion.

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