Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
2000-03-17
2001-09-25
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C315S224000, C315S291000, C315SDIG005
Reexamination Certificate
active
06294879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a ballast for a discharge lamp, more particularly a high density discharge lamp such as a metal halide lamp and a mercury lamp.
2. Description of the Prior Art
As disclosed in Japanese Laid-Open Patent Publication No. 7-142182, a prior ballast for a discharge lamp is generally known to have a DC-to-DC converter supplying a DC voltage from a DC voltage source, a DC-to-AC inverter providing an AC voltage from the DC voltage source for operating the discharge lamp, a booster generating a boosted DC voltage, and a starter receiving the boosted voltage and providing a starting voltage of sufficiently high level for starting the lamp. The booster includes a capacitor which accumulates the boosted DC voltage to be supplied to the starter for developing the starting voltage. A problem remains in the ballast that, even if the ballast is deactivated as a consequence of that the discharge lamp fails to start due to absence of the lamp or the lamp reaching its end of operation life, the residual capacitance in the capacitor of the booster may cause the starter to develop the starting voltage or at least gives the boosted voltage to the starter, thereby giving unnecessary high voltage which may give undue stress to the components of the starter and create a possible electrical shock hazard to a personnel who accidentally touch the connection between the booster and the starter.
SUMMARY OF THE INVENTION
In view of the above problem, the present invention has been achieved to provide a safety ballast for a discharge lamp which is capable of disconnecting a supply of high voltage upon failure of starting the lamp, thereby avoiding undue occurrence of the high voltage and protecting a personnel from the electrical shock hazard. The ballast in accordance with the present invention includes a DC-to-DC converter providing a DC power voltage of a predetermined level from a DC voltage source, and a booster including a booster's capacitor which is charged through the DC-to-DC converter by the DC voltage source to accumulate a boosted voltage to be supplied to a starter so that the starter generates a starting voltage for starting the discharge lamp. Also included in the ballast is a DC-to-AC inverter which receives the DC power from the DC-to-DC converter to provide an AC power to operate the discharge lamp. The DC-to-AC inverter has a plurality of switching elements controlled to turn on and off for providing the AC power. Further, the ballast includes a controller which provides a no-load signal when the lamp is not started. The inverter is controlled by the controller to establish a supply path of supplying the boosted voltage from the booster's capacitor through the inverter to the starter. The one switching element is also controlled by the controller so as to be turned off in response to a condition where the discharge lamp fails to start within a predetermined time period, thereby interrupting the supply path. Thus, when the no-load condition continues over a predetermined starting period as indicative of the that the lamp has been removed or the lamp reaching its end of life, the booster's capacitor bearing the boosted voltage is disconnected from the starter, applying no voltage to the starter and therefore preventing the starter from being activated to generate unnecessary starting voltage. Further, since the boosted voltage is not applied to the connection between the starter and the booster, it is possible to protect personnel accidentally touching the connection from an electrical shock hazard which would be otherwise presented.
The controller may provides a disable signal when the no-load signal lasts over the predetermined starting period so as to turn off the one switching element, thereby interrupting the supply path. In this connection, the load detector may includes a timer which provides the disable signal when the discharge lamp fails to start within the predetermined time period as indicative of that the discharge lamp is disconnected.
In a preferred embodiment where the DC-to-DC converter, the booster, and the controller are integrated into a single driver module, the inverter has first and second output terminals through which the inverter is connected to the starter, and the booster has a third output terminal such that the booster is connected to the starter through the third and the second terminals. The booster's capacitor has its one end connected to the third terminal and has the other end connected to the second terminal through the switching element of the inverter so as to supply the boosted voltage to the starter. The switching element of the inverter is connected to the controller and is turned off in response to the disable signal, thereby interrupting a discharge loop starting from the booster's capacitor through the third and second output terminals.
Thus, the booster's capacitor responsible for supplying the boosted voltage is disconnected from the second and the third terminal by the switching element when the lamp is removed, thereby preventing an electrical shock hazard due to the boosted voltage, even if the user touches the connection between the third and second terminals.
Preferably, the booster's capacitor has its one end connected to the third output terminal and has the other end connected to the first terminal through another switching element of the inverter which is turned off in response to the disable signal. Thus, even if there is a short-circuit between the third and first output terminals, the booster's capacitor can be prevented from discharging the current through these terminals, therefore avoiding another possible electrical shock hazard.
It is preferred that the DC-to-AC inverter includes two pairs of switching transistors arranged in a full-bridge with each pair of the transistors disposed on opposed sides of the full-bridge. One pair of the transistors are controlled to turn on and off alternately with the other pair of the switching transistors to provide said AC power. The full-bridge has inputs connected to receive the DC power from the DC-to-DC converter and having outputs defining the first and second output ends, respectively. One of the switching transistors defines the switching element connected to the second terminal, while another transistor defines the switching element connected to the first terminal. Thus, the prevention of undue activation of the starter and the electrical shock hazard can be made by utilization of the switching transistors of the inverter responsible for providing the AC power to the lamp.
In a preferred embodiment, the DC-to-DC converter, the booster, the DC-to-AC inverter, and the load detector are accommodated in a single housing to form a driver module with the first, second and third output terminals for detachable connection with a lamp module integrating the discharge lamp and the starter. Thus, the ballast can be easily installed for detachable connection with the lamp module.
These and still other objects and advantageous features of the present invention will become more apparent from the following description of the preferred embodiments when taken in conjunction with the attached drawings.
REFERENCES:
patent: 6107754 (2000-08-01), Kim
patent: 7-142182 (1995-06-01), None
Kataoka Hisao
Nagase Haruo
Satou Noriyuki
Taga Yoshitaka
Ueno Masatoshi
Matsushita Electric & Works Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Vu David
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