Electronic ignition enhancing circuit having both fundamental an

Details Electronic ignition enhancing circuit having both fundamental an Electronic ignition enhancing circuit having both fundamental an

1995-03-31

1998-08-18

Pascal, Robert

Electric lamp and discharge devices: systems

Current and/or voltage regulation

Automatic regulation

315224, 315DIG7, 315DIG4, 315276, H05B 3702

Patent

active

057962162

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates generally to energy management systems for electric loads. Utility of the invention is found in power supplies and in lamp ballasts, such as used in the operation of discharge lamps, such as high intensity discharge (HID) lamps. More particularly, a high frequency electronic ballast circuit responsive to a highly dynamic load is described. The ballast circuit includes a transformer having primary and secondary flux paths to vary the flux, linking a secondary winding coupling the ballast to a load; and, due to the varying flux linkage, the transformer also isolates the ballast-circuit from the operating dynamics of the load.
Discharge lamps such as fluorescent, mercury, metal halide and high pressure sodium lamps are popular sources of light because of their high efficiency in converting electrical energy into light. For the high efficiency operation of such lamps, a high efficiency ballast circuit must be provided. Likewise, there are many applications in which a power supply responsive to a highly dynamic load is required.
Due to the highly dynamic characteristics of operation of certain loads, which may change from an effective open circuit to a very low impedance close to zero in a matter of nanoseconds, for example, upon ignition of a HID lamp, high efficiency ballast circuits have been very expensive. The high costs of prior art high efficiency ballast circuits are due to the requirements of expensive circuitry for high speed current limiting with high power ratings, which are necessary to construct ballast circuits in accordance with conventional circuit designs.
Accordingly, there is a need for an improved ballast circuit which can survive the hostile conditions imposed by starting and running dynamic loads at high efficiencies, yet which utilizes low cost components, such that the cost of the improved ballast circuit is substantially reduced in comparison to currently available ballast circuits.
Power supplies in many applications also experience highly dynamic behaviour that requires complex control mechanisms to prevent variations in output voltages. To provide adequate control, many analog components are added to provide regulation in each needed output. The introduction of these analog regulators also introduces high losses, and therefore, results in low efficiency. The high losses in the output regulators also require large physical size to allow dissipation of the heat generated in analog regulators.


SUMMARY OF THE INVENTION

These ballast and power supply needs are met by the invention of the present application wherein a high frequency electronic ballast circuit includes a transformer having a primary winding which is coupled to a secondary winding via a primary flux path from which flux can be diverted by a secondary flux path including an air gap, preferably an adjustable air gap. For one mode of operation, a portion of the secondary winding is switched out of the circuit including a connected load. Alternately, for another mode of operation a resonance element is connected in circuit with the load and a load driver operated around the resonance frequency. The frequency of operation can be adjusted, manually or via a frequency control signal generated by a signal source or feedback loop, for power control and for stability. A conventional operating frequency of devices of this type is in the range of 20-30 Khz, although the invention is not so restricted and may be designed for operation in frequencies in much broader range, estimated to be between about 15 Khz and about 500 Khz.
Use of the transformer permits operation from a rectified alternating current power source which can be compensated by a high frequency power supply to present a favorable power factor to the alternating current power supply. The ballast circuit preferably includes catastrophic transient protection to extend life expectancy of the high frequency ballast circuit.
In accordance with one aspect of the present invention, a high frequency ballast circuit for

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