Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
2000-03-17
2001-09-04
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C315S276000, C315S2090SC
Reexamination Certificate
active
06285136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a discharge lamp lighting driver using a piezoelectric transformer which his designed to provide stable emission of light.
2. Background Art
Japanese Patent No. 2767730 discloses a conventional discharge lamp lighting driver. This driver is designed to apply the voltage having a frequency higher than a driving frequency of a piezoelectric transformer required to develop the voltage for igniting a discharge lamp and then sweep that frequency to a lower side until the discharge lamp is ignited. After the discharge lamp is ignited, the lighting driver continues to sweep the frequency of the voltage applied to the piezoelectric transformer to the lower side until the current required to keep stable emission of light from the discharge lamp is reached.
However, if a difference between the driving frequency of the voltage applied to the piezoelectric transformer required to produce the voltage for igniting the discharge lamp and that required to supply the current to the discharge lamp for keeping the stability of lighting of the discharge lamp is great, a discharge lamp lighting driver of the above described type encounters a drawback as will be discussed below.
FIG. 2
illustrates the relation between the current and voltage outputted to the discharge lamp from the piezoelectric transformer and the driving frequency of the voltage applied to the piezoelectric transformer.
The ignition of the discharge lamp is, as shown in the drawing, achieved by applying the voltage having a first frequency a to the piezoelectric transformer to output a first voltage A (X point), to the discharge lamp and lowering the first frequency a to a second frequency b required for stabilizing the lighting of the discharge lamp. The current supplied to the discharge lamp is then kept at B (Y point). If, however, a difference between impedance of the discharge lamp before ignited and that when the discharge lamp is placed in a stable condition is great, it will result in an increased interval between the first frequency a and the second frequency b, which may make it difficult to sweep the driving frequency of the voltage applied to the piezoelectric transformer from a to b within a short period of time. Specifically, the voltage having a frequency c (Z point) which is higher than the frequency b required for the stability of lighting of the discharge lamp is undesirably applied to the piezoelectric transformer. Therefore, after the discharge lamp is ignited, the voltage suitable for keeping the stable emission of light from the discharge lamp is not applied to the piezoelectric transformer, resulting in lack of current supplied to the discharge lamp.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a discharge lamp lighting driver capable of keeping stable emission of light from a discharge lamp after ignited.
According to one aspect of the invention, there is provided a lighting driver for a discharge lamp designed to be ignited in response to application of a voltage higher than a given set voltage and to maintain stable emission of light through supply of a current having a given value. The lighting driver comprises: (a) a piezoelectric transformer connected electrically to the discharge lamp, the piezoelectric transformer being responsive to application of a first voltage having a first driving frequency to develop a voltage higher than the given set voltage required to ignite the discharge lamp and also responsive to application of a second voltage having a second driving frequency to supply a current to the discharge lamp which allows the discharge lamp to maintain stable emission of light; (b) a lighting detecting circuit detecting a status of the discharge lamp to provide a signal indicating whether the discharge lamp has been ignited or not; (c) a first voltage source circuit generating the first voltage having the first frequency; (d) a second voltage source circuit generating the second voltage having the second frequency; and (e) an applied voltage switching circuit switching between a first communication of the first voltage source circuit with the piezoelectric transformer and a second communication of the second voltage source circuit with the piezoelectric transformer, when it is required to ignite the discharge lamp, the applied voltage switching circuit establishing the first communication between the first voltage source circuit and the piezoelectric transformer to apply the first voltage having the first frequency to the piezoelectric transformer, after the discharge lamp is ignited, the applied voltage switching circuit being responsive to the signal from the lighting detecting circuit indicating that the discharge lamp has been ignited to block the first communication while establishing the second communication between the second voltage source circuit and the piezoelectric transformer to apply the second voltage having the second frequency to the piezoelectric transformer.
In the preferred mode of the invention, the lighting detecting circuit measures a current supplied to the discharge lamp to determine whether the discharge lamp has been ignited or not.
The first voltage source circuit first applies a voltage having a frequency higher than the first frequency and then sweeps at least the voltage to a lower side until the first frequency is reached.
A current controlling circuit is further provided which controls a current supplied to the discharge lamp, after the discharge lamp is ignited. The current controlling circuit controls the frequency of a voltage applied from the second voltage source circuit to the piezoelectric transformer to maintain the current supplied to discharge lamp at the given value.
REFERENCES:
patent: 5854543 (1998-12-01), Satoh et al.
patent: 5886477 (1999-03-01), Honbo et al.
patent: 5998937 (1999-12-01), Nishigaki
patent: 6075325 (2000-06-01), Kouno et al.
patent: 6118221 (2000-09-01), Kumasaka et al.
patent: 2767730 (1994-06-01), None
Fujii Akira
Fukagawa Yasuhiro
Kataoka Takumi
Denso Corporation
Lee Wilson
Pillsbury & Winthrop LLP
Wong Don
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