| 摘要 |
PURPOSE: To avoid the repeated application of a stress to a ballast circuit component generated by the repeated renewal of a self-resonance mode, by displaying the operability of a ballast by detecting the overload condition of the voltage of a lamp terminal. CONSTITUTION: This ballast circuit is composed of the first and the second control circuits 24 and 26 to turn on and off switches S1 and S2 alternatively by forming a DC bus power source 17, a starting pulse generating circuit 48, and their respective gate circuits, and a ballast 10 to drive a gas discharge lamp RL by a resonance load circuit 18 and the like to which the lamp RL is connected. In this ballast 10, an overcurrent detecting circuit 42, a ballast operability display unit 46, and a switch S3 are provided, so as to detect whether the voltage applied to the terminal of the lamp RL exceeds an overload level or not by the circuit 42, and the display unit 46 displays the operation possibility and the operation stop of the circuit 10 according to the overload condition, depending on the above detecting result. Consequently, the repeated application of the stress to the composing element of the ballast circuit by the repeated reopening of a self resonance mode can be prevented. |
