Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
2003-05-29
2004-09-14
Vo, Tuyet T. (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S291000, C315S307000, C315S244000
Reexamination Certificate
active
06791281
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-pressure discharge lamp lighting apparatus for lighting a high-pressure discharge lamp with a high-frequency AC voltage. Moreover, the present invention relates to a luminaire using such a high-pressure discharge lamp lighting apparatus.
BACKGROUND OF THE INVENTION
Generally, a discharge lamp lighting apparatus is provided with an inverter circuit and an LC resonance circuit. At the time of starting a discharge lamp, a high frequency AC voltage is initially applied from the inverter circuit to the discharge lamp through the LC resonance circuit. The frequency of the AC voltage is then gradually lowered close to a resonance frequency of the LC resonance circuit. Thereby, the output voltage of the LC resonance circuit rises. As the output voltage of the LC resonance circuit reaching a glow discharge of the discharge lamp, the glow discharge is started. After the operation of the high-intensity discharge lamp has transferred from the glow discharge to an arc discharge, an arc-spot generates on a main portion of the electrode. Then, the discharge lamp is lit up. After the discharge lamp has been lit up, the frequency of the inverter circuit is further lowered so as that the discharge lamp is steadily lit up at a frequency not involving acoustic resonance in the discharge lamp.
On the other hand, the applied voltage must be kept high for a predetermined time to ensure the glow discharge to arc discharge transition of the high-pressure discharge lamp. A prior art, JP2000-58284-A, discloses' a ballast having a booster circuit provided in preceding the inverter circuit. In a starting operation, the booster circuit boosts up the applied voltage higher than the steady lighting voltage for starting the operation of the high-pressure discharge lamp.
There exists an astable operation window, i.e., a frequency range where acoustic resonance occur in the high-pressure discharge lamp. Thereby, at the time of starting as well as in the steady lighting, a frequency in a stable operation window, i.e., a frequency range where acoustic resonance never occur in the high-pressure discharge lamp. The resonance frequency of the LC resonance circuit is set up in the stable operation window in the vicinity of or higher than the steady lighting frequency.
In this prior art, since the glow discharge causing frequency, a glow discharge to arc discharge transition causing frequency, and the steady lighting frequency reside in the stable operation window, acoustic resonance never occurs.
However, in such frequencies load characteristics of the half-bridge type inverter circuit has a stable current characteristics of generating almost constant current independently from load impedances. Moreover, when the lamp voltage varies, the lamp operating power changes extensively. Furthermore, the lamp operating power extensively changes in accordance with a frequency change. Therefore, the lamp operating power varies extensively even if a frequency slightly shifts according to a change of ambient temperature around the inverter control circuit. In the high-pressure discharge lamp, there is also a problem that a color temperature changes according to the change of the lamp operating power. Consequently, the lamp operating power is expected to be controlled to have a constant value. However, for that purpose, the high-pressure discharge lamp lighting apparatus is upsized and becomes expensive.
Furthermore, in case of switching the output voltage of the booster circuit JP2000-58284-A, the inverter control circuit becomes complicated. Furthermore, since the output voltage of the booster circuit is raised higher than the voltage in the steady lighting operation, more large-sized high electric strength components are required, and the high-pressure discharge lamp lighting apparatus is upsized. Particularly, in the high-pressure discharge lamp using a small-size bulb base, it is desirable for preventing a breakdown at the bulb base that the starting voltage generated by this high-pressure discharge lamp lighting apparatus is lowered whenever possible and that the amplitude of the starting voltage generated in every starting operation has little dispersion for every starting operation.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a discharge lamp lighting apparatus with a little change in its lamp power to a change of a lamp voltage, and little dispersion in its starting voltage for every starting operation.
AD first aspect of the high-pressure discharge lamp lighting apparatus according to the present invention, comprises an LC resonance circuit, wherein the LC resonance circuit has a resonance frequency set up in two to three times the steady lighting frequency of the high-pressure discharge lamp, and the LC resonance circuit is connected to the high-pressure discharge lamp; a DC power source; an inverter circuit, wherein the inverter circuit has an input terminal connected to the DC power source, and an output terminal connected to the high-pressure discharge lamp through the LC resonance circuit, and the inverter circuit converts the DC power of the DC power source into an AC power, and causes to start and steadily operate the high-pressure discharge lamp; and an inverter control circuit, wherein the inverter control circuit is connected to a control terminal of the inverter circuit, the inverter control circuit operates the inverter circuit at a frequency around or higher than the resonance frequency of the LC resonance circuit at the time of starting the operation of the high-pressure discharge lamp, and the inverter control circuit operates the inverter circuit at a frequency in a range lower than the resonance frequency of the LC resonance circuit and free from acoustic resonance in the steady lighting operation of the high-pressure discharge lamp.
In this application, some terms are defined to have the following technical meanings, unless otherwise specified.
The term “high-pressure discharge lamp” means a mercury lamp, a metal halide lamp, a high-pressure sodium lamp, etc. The term “high-pressure discharge lamp” also admits a ceramic discharge lamp which uses an alumina for the arc tube. The arc tube is filled with at least rare gas, such as Neon (Ne), Argon (Ar), etc, as discharge agent.
The inverter circuit has, for example, a half-bridge type configuration by using two switching elements. These two switching elements alternately switch ON and OFF a DC power source so that the high-frequency AC voltage is obtained on the output side of the inverter circuit. An LC resonance circuit is connected to the output side of the inverter circuit. The resonance frequency of the LC resonance circuit is adjusted to the steady lighting frequency of the high-pressure discharge lamp. By the way, the inverter circuit may be a single-transistor type or a four-transistor type configuration.
The LC resonance circuit outputs the AC voltage at a high output rate, when the frequency of the high-frequency AC voltage applied from the inverter circuit is close to the resonance frequency. The inverter circuit is set up so that it may operate at a frequency in two to three times the resonance frequency of the LC resonance circuit at the time of starting the operation of the high-pressure discharge lamp. Thereby, the inverter circuit can steadily operate the high-pressure discharge lamp at an operating point voltage thereat the load power becomes almost maximum. The inverter circuit can prevent that the inverter circuit oscillates at an advancing phase. Therefore, a switching loss of the inverter circuit is restricted.
An inverter control circuit controls the inverter to oscillate at a frequency around or higher than the resonance frequency of the LC resonance circuit at the time of starting the operation of the high-pressure discharge lamp. And after the high-pressure discharge lamp has lit up, the inverter control circuit controls the inverter circuit to oscillate at a frequency lower than the resonance frequency of the LC resonance circuit and not
Pillsbury & Winthrop LLP
Toshiba Lighting & Technology Corporation
Vo Tuyet T.
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