Electronic ballast with high voltage protection
AssigneeMagneTek, Inc.
InventorJohn Lindquist
Life of this patent
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Abstract
A solid-state ballast for discharge lamps includes circuitry for limiting the maximum output voltage produced when a lamp is first being ignited or is removed. The ballast includes a signal controlled oscillator that provides the operating signal for a resonantly driven lamp load. The voltage across the load is sensed and a signal representing this voltage is fed back to a circuit when controlling the oscillator so as to limit the maximum load voltage during initial start-up and when a lamp is removed. In accordance with a second embodiment, the voltage is cycled between a low level and a level high enough to ignite the lamp, so long as the lamp is not ignited.
Claims21
In a solid-state ballast for discharge lamps, the ballast being of the type including an oscillator providing an operating signal to the discharge lamp load through a driver, the improvement comprising:
- said oscillator being a signal controlled oscillator having a frequency control input and providing an output signal with a frequency determined by the value of a signal applied at said frequency control input;
- control means sensing the instantaneous current flowing within the load for producing a first control signal representing this load current;
- comparator means differentially responsive to the voltage across the load and a predetermined reference voltage for producing a second control signal representing the polarity of the difference between said voltages, said reference voltage corresponding to a load voltage substantially in excess of the voltage across a normally discharging lamp;
- coupling means jointly responsive to said first and second control signals for producing a composite control signal to said frequency control input, said composite control signal being substantially identical to said first control signal when said second control signal has a polarity indicating that the load voltage is not excessive, said composite control signal being equal to a predefined signal when said second control signal has polarity indicating that the load voltage is excessive, said predefined signal being effective to operate said oscillator so as to reduce the voltage across said load to a predetermined minimum value.
Dependencies are inferred from the claim text.