| 摘要 |
PURPOSE:To detect over load condition at a terminal period of a lamp or during lighting when excessive current runs so as to protect a device from breaking and prevent error operation owing to rush current at the initial stage of electric power application by constructing a protection circuit in the way so that a high frequency inverter is stopped when the number of the times at which a lamp current surpasses the threshold value is counted synchronously with alternating current power source and the counted number reaches a prescribed number. CONSTITUTION:A high frequency inverter 1, to which a branched electric power source is supplied and which lights an incandescent lamp by a high frequency power source, and a protection circuit 2, which stops the high frequency inverter when the number of the times at which lamp current surpasses a prescribed threshold value is counted synchronously with alternating current power source and the counted value reaches a prescribed number, are installed. If the counted number is set not to reach a prescribed value in the case that a lamp current damps gradually like a rush current, the rush current is not detected and over current only at that time of secondary short-circuit or the time of over load can be detected. Further, the counted number is set to come up close to the prescribed number by the rush current, the period during stress is applied to the circuit of the high frequency inverter becomes short and high protection function is achieved at the time of secondary short-circuit and the time of over load. |
