| 摘要 |
Using a simple circuit arrangement, a brightness of the lamp is controlled in accordance with an ambient brightness. A light sensor (10) produces an analog signal of which the signal level depends on an ambient brightness. An A/D converting circuit (307) converts the analog signal into a digital signal of which the pulse width depends on the signal level of the analog signal. An FET QA is on/off controlled in accordance with the digital signal (PWM), and hence an average value of current flowing through a head light (L1) is controlled in level. As a result, a brightness of the head light (L1) is controlled in accordance with the ambient brightness.
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