| 摘要 |
PURPOSE:To keep a stable discharge state by providing a heating element circuit connected in parallel to the series circuit of each discharge lamp, and a relay contact provided in parallel to a main heating element and kept in the closed state by the heat generation of a sub-heating element. CONSTITUTION:When the voltage between terminals of a fluorescent lamp 7a is excessive, for example, 80V, a large current of operating current or more is continuously carried to the series circuit of the heating elements 10, 11 of a thermal relay 9. The calorific values of the heating elements 10, 11 are increased, and a relay contact 12 is immediately closed to bypass the main heating element 10. Then, the resistance value between the terminals 9a, 9b of the relay 9 is reduced to the low resistance value of the sub-heating element 11 which is sufficiently smaller than a rated discharge resistance R, and the relay 9 forms the short-circuit bypass passage for the fluorescent lamp 7a to stop the discharge of the lamp 7a. When the remaining fluorescent lamps 7b-7d are lighted, then, the contact 12 is held in the closed state by the heat generation of the sub-heating element 11 after the discharge of the lamp 7a is stopped. Thus, the voltage is properly shared to the remaining lamps 7b-7d, and the lamps 7b-7d are normally lighted to keep stable discharge state. |
