| 摘要 |
PURPOSE:To facilitate the design, etc., of a protection circuit, by limiting the voltage applied to a main transistor of an inverter by the sum voltage of operating voltage of constant voltage elements and DC input voltage of a chopper. CONSTITUTION:A power unit is composed of a rectification circuit 1, a chopper 2, and an inverter 3 and feeds the current to a fluorescent lamp FL, the load, from the secondary winding WS of an output transformer 1. An inverter abnormal voltage protection circuit 4 is provided and the anode of a Zener diode ZD is connected to the midpoint of the abovementioned output transformer 1, while the cathode is connected to the positive side output terminal of a rectification circuit 1 through a diode DS for reverse-current prevention and a resistance RS to constitute a power unit. Abnormal voltage is thereby generated by the abnormal oscillating mode in starting, etc. If this voltage is larger than the sum of the Zener voltage of protection circuit 4 and the output of rectification circuit, the abnormal voltage will be fed back and absorbed to the input side of the chopper 2. |
