Discharge lamp ballast with dimming

• US 20030222593A1
• Filed: 05/27/2003
• Published: 12/04/2003
• Est. Priority Date: 05/31/2002
• Status: Active Grant

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamamoto, Norikazu
• Granted Patent: US 6,788,006 B2
• Time in Patent Office: Days
• US Class Current: 315/219
• CPC Class Codes: H05B 41/2806 with semiconductor devices and specially adapted for lamps without electrodes in the vessel, e.g. surface discharge lamps, electrodeless discharge lamps
• CPC Class Codes: H05B 41/3921 with possibility of light intensity variations
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

A ballast includes a rectangular wave generating circuit that generates a rectangular wave signal; a driving signal generating circuit supplied with the rectangular wave signal and a dimmer signal of a PWM waveform of a frequency lower than that of the rectangular wave signal and outputting a driving signal of an output obtained by extracting the rectangular wave signal for a period corresponding to “on” period of the dimmer signal; a pulse transformer which is supplied with a rectangular wave voltage based on the driving signal, step up the rectangular wave voltage and applying it to a discharge lamp. A rectangular wave reset circuit is provided so as to reset the generation of the rectangular wave signal at a rising of the dimmer signal. The driving signal generating circuit extracts the rectangular wave signal for a period starting from when the dimmer signal is turned on, until a time at which the dimmer signal and the rectangular wave signal are both off.

Claims

1. A discharge lamp ballast comprising:

a rectangular wave generating circuit that generates a rectangular wave signal of a predetermined frequency;

a driving signal generating circuit into which the rectangular wave signal and a dimmer signal of a PWM waveform of a frequency lower than that of the rectangular wave signal are input, and which outputs, as a driving signal, a signal obtained by extracting the rectangular wave signal for a period corresponding to a period in which the dimmer signal is on; and

a pulse transformer in which a rectangular wave voltage based on the driving signal is applied to the primary side, and the rectangular wave voltage is stepped up and applied to a discharge lamp;

wherein a rectangular wave reset circuit is provided so as to reset the operation of generating the rectangular wave signal with the rectangular wave generating circuit at a rising of the dimmer signal, and

the driving signal generating circuit extracts the rectangular wave signal for a period starting from when the dimmer signal is turned on, until a time at which the dimmer signal and the rectangular wave signal are both off.

2. The discharge lamp ballast according to claim 1, wherein the rectangular wave reset circuit is configured so as to reset an oscillation of the rectangular wave generating circuit.

3. The discharge lamp ballast according to claim 2, wherein the rectangular wave reset circuit comprises:

a first differential circuit into which the dimmer signal is input; and

a first switching circuit that is driven by the output of the first differential circuit;

wherein a node between a capacitor and a resistor composing a CR oscillator in the rectangular wave generating circuit is connected to a ground potential via the first switching circuit.

8. The discharge lamp ballast according to claim 1 or claim 4, wherein the rectangular wave generating circuit includes a timer circuit.

9. The discharge lamp ballast according to claim 1 or claim 4, wherein the discharge lamp is an external electrode type discharge lamp, in which at least one electrode of the discharge lamp is provided at an outer surface of a arc tube.

10. The discharge lamp ballast according to claim 9, wherein the discharge material of the discharge lamp includes a rare gas.

4. A discharge lamp ballast comprising:

a rectangular wave generating circuit that generates a rectangular wave signal of a predetermined frequency;

a driving signal generating circuit into which the rectangular wave signal and a dimmer signal of a PWM waveform of a frequency lower than that of the rectangular wave signal are input, and which outputs, as a driving signal, an output obtained by extracting the rectangular wave signal for a period corresponding to a period in which the dimmer signal is on; and

a pulse transformer in which a rectangular wave AC voltage based on the driving signal is applied to the primary side, and the rectangular wave AC voltage is stepped up and applied to a discharge lamp;

wherein an output reset circuit is provided so as to input a pulse voltage in phase with the rectangular wave AC voltage to the pulse transformer immediately after the end of the rectangular wave AC voltage in response to the completion of the ON period of the dimmer signal, the secondary side output of the pulse transformer being attenuated by application of the pulse voltage.

5. The discharge lamp ballast according to claim 4, further comprising a second switching circuit that is inserted between the driving signal generating circuit and the pulse transformer, and has two switching elements that are alternately driven in response to the driving signal;

wherein by inputting the output of the switching elements to the pulse transformer, the rectangular wave AC voltage is applied to the pulse transformer, and wherein, the output reset circuit supplies an output reset signal that momentarily drives the switching element that was not being driven immediately prior to the end of the rectangular wave AC voltage.

6. The discharge lamp ballast according to claim 5, wherein the output reset circuit further comprises a second differential circuit into which the driving signal is input, and in which the output of the second differential circuit is supplied as the output reset signal.

7. The discharge lamp ballast according to claim 5, wherein the pulse width of the output reset signal not greater than one-quarter of one cycle of the waveform of the driving signal.