| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To keep the light emission quantity of a semiconductor light source irrespective of the temperature of the light source. <P>SOLUTION: When an LED 20 is lighted up, the voltage V2 of a capacitor C5 heightens bit by bit with a longer light-up time of the LED 20, while the amperage I<SB>2</SB>of a resistor R2 lessens bit by bit. As a result, a control circuit 16 conducts such a control as increasing gradually the output current of a switching regulator 12 in order to make constant the voltage of a current sensing terminal 34, and the photo-quantity of the LED 20 can be maintained constant even if the forward voltage Vf of the LED 20 lowers. When the LED 20 is lighted, the value of the voltage V2 is maintained high with a shorter put-off time, and the amperage I<SB>2</SB>lessens at starting the lighting to cause a large current to be supplied to the LED 20, which enables maintaining the photo-quantity of the LED 20 constant. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
