High frequency electronic ballast with reactive power compensation
First Claim
1. A ballast circuit, comprising:
- a transformer including a primary and a secondary winding, wherein said primary winding of said transformer receives an AC voltage and current;
at least one lamp coupled to said secondary winding;
said circuit having an optimized magnetizing inductance, said optimized magnetizing inductance causing said transformer input voltage and current to be in phase relative to each other.
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Accused Products
Abstract
A lamp ballast circuit which provides a magnetizing inductance to a lamp ballast circuit transformer. A DC voltage and current supply source energize a pair of transistors which provide an AC voltage and current. The transformer includes a primary winding that receives the AC voltage and current. At least one lamp is coupled to the transformer secondary winding via a capacitor. The circuit has an optimal magnetizing inductance such that the transformer input voltage and current are substantially in phase with each other, thereby substantially reducing or eliminating the reactive power transferred through the output transformer. In a preferred embodiment, the magnetizing inductance, L102, is given as:
wherein ωs is an operating frequency, C1 is the capacitance of the capacitor, R1 is the resistance of the at least one lamp, and n is the secondary-to-primary side turns ratio of the transformer.
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Citations
28 Claims
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1. A ballast circuit, comprising:
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a transformer including a primary and a secondary winding, wherein said primary winding of said transformer receives an AC voltage and current;
at least one lamp coupled to said secondary winding;
said circuit having an optimized magnetizing inductance, said optimized magnetizing inductance causing said transformer input voltage and current to be in phase relative to each other. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
Lm=[1+(ω
sC1R1)2]n2ω
s2C1,wherein ω
s is an operating frequency, C1 is a capacitance of said capacitor, R1 is a resistance of said at least one lamp, and n is a secondary-to-primary side turns ratio of said transformer.
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5. The circuit according to claim 4, wherein said at least one lamp comprises a plurality of parallel-connected lamps, and said resistance R1 is an equivalent resistance of said plurality of said lamps.
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6. The circuit according to claim 5, wherein said plurality of parallel-connected lamps are coupled in series to a corresponding plurality of capacitors, and said capacitance C1 is an equivalent capacitance of said plurality of said capacitors.
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7. The circuit according to claim 1, wherein said circuit further comprises a magnetizing inductor coupled in parallel across said primary winding for providing said magnetizing inductance.
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8. The circuit according to claim 4, wherein the primary-to-secondary turns ratio n of said transformer is selected so as to optimize said magnetizing inductance.
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9. A method of operating a ballast circuit, said method comprising the steps of:
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receiving an AC voltage and current at a primary winding of a transformer, said transformer having said primary winding and a secondary winding;
coupling at least one lamp to said secondary winding;
providing a transformer magnetizing inductance having an optimized value which causes said transformer input voltage and current to be in phase relative to each other. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
Lm=[1+(ω
sC1R1)2]/n2ω
s2C1,wherein ω
s, is an operating frequency, C1 is a capacitance of said capacitor, R1 is a resistance of said at least one lamp, and n is a secondary-to-primary side turns ratio of said transformer.
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13. The method according to claim 12, wherein said coupling step further comprises coupling a plurality of parallel-connected lamps, and said resistance R1 is an equivalent resistance of said plurality of said lamps.
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14. The method according to claim 13, further comprising coupling said plurality of parallel-connected lamps in series to a corresponding plurality of capacitors, and said capacitance C1 is an equivalent capacitance of said plurality of said capacitors.
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15. The method according to claim 9, further comprising the step of providing in said circuit a magnetizing inductor coupled in parallel with the transformer primary winding, said magnetizing inductor configured to provide said magnetizing inductance.
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16. The method according to claim 9, further comprising the step of selecting the primary-to-secondary turns ratio n of said transformer so as to optimize said magnetizing inductance.
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17. A high frequency electronic ballast circuit for one or more discharge lamps, the ballast circuit comprising:
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input terminals for connection to a source of DC supply voltage, means coupled to the input terminals for deriving an AC voltage and current, a transformer having a primary winding which receives said AC voltage and current, a load circuit including at least one discharge lamp in series circuit with a capacitor, means for coupling the load circuit to a secondary winding of said transformer, and means including a magnetizing inductance having an optimized value for compensating reactive currents in the transformer by bringing the transformer primary winding voltage and current in phase with one another. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
an LC resonant circuit including an inductor coupled to the AC voltage and current deriving means and to the transformer primary winding and a resonant capacitor coupled across the transformer primary winding.
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23. The high frequency electronic ballast circuit as claimed in claim 17 wherein the load circuit is directly coupled to the transformer secondary winding.
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24. The high frequency electronic ballast circuit as claimed in claim 17 wherein the magnetizing inductance is determined, at least in part, by one of the following circuit parameters, the circuit operating frequency (ω
- s), the resistance (Ri) of the at least one lamp, the capacitance (Ci) of the capacitor, and the turns ratio (n) of the transformer.
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25. The high frequency electronic ballast circuit as claimed in claim 17 wherein said means for deriving the AC voltage and current comprise a DC/AC converter coupled to the input terminals.
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26. The high frequency electronic ballast circuit as claimed in claim 17 wherein said magnetizing Inductance includes a magnetizing inductor coupled in parallel with said transformer primary winding.
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27. The high frequency electronic ballast as claimed in claim 17 wherein said magnetizing inductance, Lm, is given as:
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28. The high frequency electronic ballast as claimed in claim 17 wherein the value of the magnetizing inductance is chosen so as to optimize the current (Im) therein and thereby bring the transformer primary winding voltage and current in phase with one another and substantially reduce the level of any reactive power transferred through said transformer.
Specification