| 摘要 |
PURPOSE: To establish efficient dimming control of a fluorescent lamp by allowing the lamp to emit a large light quantity, when the sensed illuminance lies in the low region, and emit a small light quantity when the sensed illuminance lies higher than the low region. CONSTITUTION: During the operation, transistors Q1 -Q4 have a power operating from a photo-interface circuit in connection with a fluorescent lamp or a ballast resistor 131. Adjustable resistors R2a -R2c work as a threshold control means or a selecting means. The transistor Q1 works as a main current sink whole the transistor Q2 works as an amplifier for adjustment and a partial current sink, and the others Q3 and Q4 work in the atmosphere with low level natural light so that they have a high current gain. The transistor Q4 is saturated at a high natural lighter level, and this becomes a relatively low current gain of the amplifier formed by the transistors Q3 and Q4 . Thereby an efficient dimming control of a fluorescent lamp is established.
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