| 摘要 |
A voltage supplied from a power supply is boosted by a boosting circuit unit to generate a direct-current voltage, and the pulse-shape direct-current voltage is applied to LED while a constant-voltage control unit controls the direct-current voltage. The operation of LED is controlled by a control unit and a PWM unit. When the current is passed through LED, the constant-voltage control unit obtains information on the current passed through LED from a potential difference between both ends of a resistor, and on-and-off control of the voltage applied to LED from the boosting circuit unit is performed at a high frequency based on the information. Therefore, the voltage applied to LED can be controlled to keep the current passed through LED constant.
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