| 摘要 |
<P>PROBLEM TO BE SOLVED: To minimize change of loss for variation of power supply voltage and to simplify the circuitry. <P>SOLUTION: When the power supply voltage Vs varies (drops), a driving current I<SB POS="POST">LD</SB>flowing to a light source 1 decreases. However, as the variation of the power supply voltage Vs (droppage for a rated voltage) increases, control means 4 controls selection means 2 to increase the number of light-emitting diodes LDi selected (short-circuited) not to feed the driving current I<SB POS="POST">LD</SB>and to decrease the number of light-emitting diodes LDj selected to feed the driving current I<SB POS="POST">LD</SB>. In other words, the light-emitting device according to an embodiment utilizes a resistance component existing in the light-emitting diode LD as a current limit element and decreases the number of light-emitting diodes LDj through which the driving current I<SB POS="POST">LD</SB>flows according to variation of an input voltage (power supply voltage Vs). Consequently, change (increase) of loss for variation of the power supply voltage Vs is minimized and the circuitry can be simplified. <P>COPYRIGHT: (C)2012,JPO&INPIT |
