Lighting circuit and lighting device
First Claim
Patent Images
1. A lighting circuit comprising:
- a noise filter having input terminals arranged for connection to a low frequency AC power supply and having output terminals;
a series circuit including first and second capacitors, joined at a node therebetween, the series circuit being connected across output terminals of the noise filter;
a full wave rectifier circuit having an input connected to the output terminals of the noise filter and having first and second DC output terminals;
a smoothing element connected across the DC output terminals of the full wave rectifier;
a load circuit, which has first and second ends, having a discharge lamp with electrodes, a first current limiting inductor and a capacitor connected in parallel with the electrodes;
a first switching element connecting the first DC output terminal of the full wave rectifier with the first end of the load circuit;
a second switching element connecting the second DC output terminal of the full wave rectifier with the first end of the load circuit;
means for driving the first and second switching elements to open and close alternately;
a high frequency current passage for conducting high frequency current from the second end of the load circuit to the node connecting the first and second capacitors; and
a fourth capacitor connected between the second end of the load circuit and a DC output terminal of the rectifier.
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Abstract
The present invention provides an improved power factor and lower harmonic distortion in the power supply circuit of a high frequency discharge lamp. An "extra" circuit path is provided so that the driving power to the lamp will "see" a load that significantly reduces the harmonic distortion and tends to cause the power factor to approach "1". In a preferred embodiment of the invention this is accomplished by providing a third capacitor with which the load circuit forms an in-series resonance circuit with the discharge lamp and its associated current-limiting inductance. The new circuit arrangement provides a high frequency current passage not provided in known lighting circuits of this type that raises the power factor and lowers harmonic distortion.
17 Citations
9 Claims
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1. A lighting circuit comprising:
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a noise filter having input terminals arranged for connection to a low frequency AC power supply and having output terminals; a series circuit including first and second capacitors, joined at a node therebetween, the series circuit being connected across output terminals of the noise filter; a full wave rectifier circuit having an input connected to the output terminals of the noise filter and having first and second DC output terminals; a smoothing element connected across the DC output terminals of the full wave rectifier; a load circuit, which has first and second ends, having a discharge lamp with electrodes, a first current limiting inductor and a capacitor connected in parallel with the electrodes; a first switching element connecting the first DC output terminal of the full wave rectifier with the first end of the load circuit; a second switching element connecting the second DC output terminal of the full wave rectifier with the first end of the load circuit; means for driving the first and second switching elements to open and close alternately; a high frequency current passage for conducting high frequency current from the second end of the load circuit to the node connecting the first and second capacitors; and a fourth capacitor connected between the second end of the load circuit and a DC output terminal of the rectifier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A lighting device comprising:
a frame structure and a lighting circuit contained within the frame structure, the lighting circuit comprising; a noise filter having input terminals arranged for connection to a low frequency AC power supply and having output terminals; a series circuit including first and second capacitors, joined at a node therebetween, the series circuit being connected across output terminals of the noise filter; a full wave rectifier circuit having an input connected to the output terminals of the noise filter and having first and second DC output terminals; a smoothing element connected across the DC output terminals of the full wave rectifier; a load circuit, which has first and second ends, having a discharge lamp with electrodes, a first current limiting inductor and a capacitor connected in parallel with the electrodes; a first switching element connecting the first DC output terminal of the full wave rectifier with the first end of the load circuit; a second switching element connecting the second DC output terminal of the full wave rectifier with the first end of the load circuit; means for driving the first and second switching elements to open and close alternately; a high frequency current passage for conducting high frequency current from the second end of the load circuit to the node connecting the first and second capacitors; and a fourth capacitor connected between the second end of the load circuit and a DC output terminal of the rectifier.
Specification
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Current AssigneeToshiba Lighting & Technology Corporation (Toshiba Corporation)
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Original AssigneeToshiba Lighting & Technology Corporation (Toshiba Corporation)
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InventorsOhtake, Hirokazu
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Primary Examiner(s)Philogene, Haissa
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Application NumberUS09/292,672Time in Patent Office284 DaysField of Search315/307, 315/244, 315/209 R, 315/207, 315/238, 315/DIG. 2, 315/DIG. 7, 315/247, 363/34, 363/44-47, 363/89, 363/98, 363/126, 363/132US Class Current315/307CPC Class CodesH05B 41/28 using static convertersY10S 315/02 High frequency starting ope...
