| 摘要 |
PROBLEM TO BE SOLVED: To provide an inexpensive backlight dimming control device capable of setting and adjusting an luminosity optionally and miniaturizing the size without using a constant voltage circuit and making the luminosity of a LED dependent on a supplied voltage. SOLUTION: The backlight dimming control device includes a light-emitting circuit 20 composed of one or more LEDs connected in series, which emit light by electric power from a power source +B, a current control circuit 21 serially connected to the light-emitting circuit 20 and making an emitter current of a transistor TR variable by controlling a base voltage of the transistor TR in an emitter follower connection, a current output circuit 22 serially connected to the current control circuit 21, determining its operating current, and determining an operating current of the transistor TR0 of the light-emitting circuit 20, and a modulation circuit 23 carrying out PWM of the current of the light-emitting circuit 20. For example, a lighting period is increased for a current reduced by a voltage drop of the power source +B by detecting a voltage supplied to the light-emitting circuit 20 from the power source +B by a voltage detection circuit 10, and by adjusting a pulse width of PWM based on the detected voltage by the voltage detection circuit 10. COPYRIGHT: (C)2010,JPO&INPIT
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