Soft-starting phase-control circuit for low voltage load
First Claim
1. A circuit for phase-controlling both the starting and normal operating flows of current from an A.C. source to a load, comprising:
- power switching means for selectively respectively enabling and disabling a connection of said source to said load, responsive to respective first and second states of a control signal;
means for generating at least one signal having a transition in a selected direction occurring substantially at each of a sequential plurality of zero crossings of the source signal waveform and for also providing a lock signal only if said at least one signal selected transition occurs essentially at each sequential one of said source signal waveform zero crossings;
means for generating a ramp signal commencing at a first magnitude responsive to the selected transition of each of said at least one signal and reaching a second magnitude, greater than said first magnitude, by the occurrence of the selected transition of the next successive one of said at least one signal;
means for providing said first control signal state responsive to the instantaneous magnitude of said ramp signal exceeding a predetermined magnitude and for thereafter providing said second control signal state responsive to the selected transition of the next successive one of said at least one signal;
first means, responsive to the presence of said lock signal, for controlling the slope of said ramp signal to increase the second magnitude thereof over a plurality of time intervals each between successive ones of the selected transition of said at least one pulse signal, from a magnitude less than said predetermined magnitude to a magnitude greater than said predetermined magnitude, to cause said power switching means to enable a starting load current flow increasing from a substantially zero initial magnitude toward a magnitude greater than the desired normal operating magnitude;
second means, monitoring a selected parameter of said load, for controlling the slope of said ramp signal to cause said second magnitude to vary responsive to the sensed load parameter; and
switching means for enabling said first means to control said ramp signal slope until said sensed load parameter approaches a preselected value thereof and for then switching control of said ramp signal slope to said second means for controlling the duration of current flow during each source waveform cycle thereafter to cause said load current flow to maintain substantially the said preselected value of said sensed load parameter.
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Accused Products
Abstract
A soft-starting phase-control circuit for controlling both the cold in-rush and normal operating flows of current through a load from an A.C. source. The load may be resistive, may have a non-zero resistance temperature coefficient and may require a load voltage thereacross lower than the voltage provided by the A.C. source connected to the load and the control circuit. The control circuit utilizes at least one power switching device for selectively enabling and disabling the connection between source and load responsive to turn-on and turn-off states of a control signal provided at the output of a gate subcircuit. The gate subcircuit provides a turn-on state at a time, after each zero crossing, variably responsive to either a sensed load parameter when the load is in the normal operating condition, or to a selected starting sequence each time the load is initially energized (either intentionally or responsive to recovery from a detected fault condition) to limit in-rush current to a relatively low multiple of the normal operating current. The start-up sequence of load turn-on states is responsive to gate enabling signals provided by comparison of a reference level with the instantaneous magnitude of a ramped signal, itself terminated and restarted at each line zero crossing. Only if a phase-locked loop has been synchronized to the source line voltage zero crossings can the gate means be driven to the turn-on state. The exact time when the ramp signal reaches the reference level is controlled by integration of the sum of the outputs of selected ones of a plurality of current sources.
31 Citations
28 Claims
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1. A circuit for phase-controlling both the starting and normal operating flows of current from an A.C. source to a load, comprising:
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power switching means for selectively respectively enabling and disabling a connection of said source to said load, responsive to respective first and second states of a control signal; means for generating at least one signal having a transition in a selected direction occurring substantially at each of a sequential plurality of zero crossings of the source signal waveform and for also providing a lock signal only if said at least one signal selected transition occurs essentially at each sequential one of said source signal waveform zero crossings; means for generating a ramp signal commencing at a first magnitude responsive to the selected transition of each of said at least one signal and reaching a second magnitude, greater than said first magnitude, by the occurrence of the selected transition of the next successive one of said at least one signal; means for providing said first control signal state responsive to the instantaneous magnitude of said ramp signal exceeding a predetermined magnitude and for thereafter providing said second control signal state responsive to the selected transition of the next successive one of said at least one signal; first means, responsive to the presence of said lock signal, for controlling the slope of said ramp signal to increase the second magnitude thereof over a plurality of time intervals each between successive ones of the selected transition of said at least one pulse signal, from a magnitude less than said predetermined magnitude to a magnitude greater than said predetermined magnitude, to cause said power switching means to enable a starting load current flow increasing from a substantially zero initial magnitude toward a magnitude greater than the desired normal operating magnitude; second means, monitoring a selected parameter of said load, for controlling the slope of said ramp signal to cause said second magnitude to vary responsive to the sensed load parameter; and switching means for enabling said first means to control said ramp signal slope until said sensed load parameter approaches a preselected value thereof and for then switching control of said ramp signal slope to said second means for controlling the duration of current flow during each source waveform cycle thereafter to cause said load current flow to maintain substantially the said preselected value of said sensed load parameter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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Specification