Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
2002-07-22
2003-11-11
Wong, Don (Department: 2817)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C315S290000, C315S224000
Reexamination Certificate
active
06646389
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-222721, filed on Jul. 24, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a discharge lamp ignition device for igniting a discharge lamp filled with a discharge medium mainly including a rare gas. The invention also relates to equipment and image forming apparatus using such a discharge lamp ignition device.
2. Description of the Related Art
A rare-gas discharge lamp is adapted to emit light from a phosphor with ultraviolet radiation produced by discharge of a rare gas. The lamp has a good rising characteristic of light flux at low temperatures because the amount of light emission is independent of temperature but is low in light emission efficiency in comparison with a mercury-vapor discharge lamp.
To improve the light emission efficiency, on the other hand, pulse-based ignition of a discharge lamp which radiates visible light by exciting a phosphor layer with ultraviolet rays produced by discharge of a rare gas has been disclosed in Japanese Unexamined Patent Publications Nos. 58-135563, 2-174097, 9-199285, and Japanese Patent Publication No. 8-12794. In addition, a discharge lamp ignition device has also been proposed which improves the light emission efficiency by applying a high-frequency alternating-current voltage having its waveform adjusted by being superimposed with a direct-current voltage between paired electrodes of the discharge lamp. At least one of the paired electrodes is placed on the outer surface of the discharge container.
However, the discharge lamp equipped with paired electrodes at least one of which is placed on the outer surface of the discharge container utilizes dielectric barrier discharge and hence is generally very high in starting voltage and lamp voltage.
For this reason, if the high-frequency power supply continues operation at no-load time, it will not so long before that power supply breaks down due to the high voltage generated by the power supply itself. In addition, the application of the aforementioned high voltages will cause the discharge lamp, a feeding harness line and the high-frequency to be subject to dielectric breakdown. The dielectric breakdown leads to a serious problem of occurrence of an abnormal discharge.
Accordingly, we invented protection devices which involve detecting the no-load state of a discharge lamp utilizing dielectric barrier discharge and applied for patents in Japanese Patent Applications Nos. 2000-362207 and 2001-046321. According to this invention, a dielectric barrier discharge lamp is ignited by high-frequency voltage generator having switch and an output transformer, and high-frequency operation detector, controller and no-load detector are provided. The controller feedback controls the switch so that a high-frequency operation detect signal from the high-frequency operation detector goes to a first level to thereby make the high-frequency output constant. Upon detecting the no-load state of the secondary circuit of the output transformer, the no-load detector changes the high-frequency operation detect signal input to the controller to the second level, thereby allowing the switch in the high-frequency voltage generator to perform a protective operation.
When incorporating the discharge lamp utilizing dielectric barrier discharge into equipment, such as an image forming apparatus, as a light source of the reading unit, the discharge lamp and the ignition circuit are commonly connected by a feeding harness line. The harness line is formed of parallel conductors in almost all portions except connecting portions at both ends.
Depending on equipment into which the lamp is incorporated, the feeding harness line may be required to be 200 mm or more in length. It was found that such a long harness line makes the distributed static capacitance of the parallel conductor portion so large that it cannot be neglected for the high operating frequency. That is, in the event of a no-load state due to the discharge lamp being out of connection by way of example, when only the harness line is connected, the load seen by the high frequency generator becomes the distributed capacitance of the harness line. This distributed capacitance is considerably smaller than the interelectrode static capacitance within the discharge container. Moreover, at no-load time, the high frequency generator outputs a high-frequency oscillating current at a resonant frequency which is determined by the distributed capacitance of the harness line and the inductance of the output transformer and which is considerably higher than the normal operating frequency. The no-load detector is prone to recognize erroneously the state where the high-frequency oscillating current is being output as a load state. The erroneous recognition by the no-load detector results in failure to perform the inherent function of detecting the no-load state for protection.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a discharge lamp ignition device which, even if the feeding harness line used is long, exactly responds to a no-load state to perform a protection operation and equipment and image forming apparatus using such an ignition device.
It is another object of the present invention to provide a discharge lamp ignition device which, even if the feeding harness line used is long, exactly responds to a no-load state to perform a protection operation and, when the no-load state is removed by the discharge lamp being restored, provides automatic recovery and equipment and image forming apparatus using such an ignition device.
An ignition device igniting a dielectric barrier discharge lamp according a first embodiment of the present invention comprises: a discharge lamp including a dielectric discharge container filled with a discharge medium; a pair of electrodes at least one of which is disposed on the outer surface of the discharge container and between which a discharge is generated in the container; high-frequency voltage generator, comprising a switch configured to generate a high-frequency voltage and an output transformer which outputs a high-frequency voltage, configured to ignite the discharge lamp by applying the high-frequency output voltage of the output transformer between paired electrodes of the discharge lamp; a feeding harness line having its one end connected to the high-frequency voltage generator and its other end connected to the discharge lamp, the harness line having parallel conductors whose length is 200 mm or more; and a lowpass filter which bypasses a high-frequency oscillating current which flows at no-load time mainly due to stray capacitance associated with the feeding harness line.
A discharge lamp ignition device according to the first embodiment of the present invention comprises: a discharge lamp including a discharge container filled with a discharge medium mainly including a rare gas and a pair of electrodes at least one of which is disposed on the outer surface of the discharge container; a feeding harness line having its one end connected to the discharge lamp, the harness line including parallel conductors the length of which is 200 mm or more; and an ignition circuit connected to the other end of the feeding harness line to ignite the discharge lamp,
the ignition circuit including: high-frequency voltage generator, comprising a switch configured to generate a high-frequency voltage and an output transformer which outputs a high-frequency voltage, configured to ignite the discharge lamp by applying the high-frequency output voltage of the output transformer between the paired electrodes of the discharge lamp; no-load detector configured to detect a no-load state based on a current which flows in the secondary circuit of the output transformer; high-frequency oscillating current bypass coupled to the no-load detector configured to
Cooper & Dunham LLP
Harison Toshiba Lighting Corp.
Vu Jimmy T.
White John P.
Wong Don
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