| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To maintain lifetimes of LEDs by disallowing an excessive current to flow to an array of normal LED units even if the array of LED units enters an open state. <P>SOLUTION: The voltage of a power source 11 is stepped down by a DC/DC converter 12 based upon a switching signal of a pulse width modulation circuit. An output voltage Vd of the converter 12 is supplied to first and second LED units 13 and 14 which are connected in parallel to make the LED units illuminate. Currents flowing to the LED units 13 and 14 are converted by resistances R1 and R2 into voltages, which are ORed by an OR circuit 16, and the output voltage Vd is controlled with a duty of switching pulses from the pulse width modulation circuit 18 which turns ON and OFF a transistor of Q of the converter 12 so that the currents flowing to the LED units 13 and 14 become constant. The voltages converted by the resistances R1 and R2 are ORed, so that the constant output voltage Vd is obtained even if one of the LED units 13 and 14 enters an open state. <P>COPYRIGHT: (C)2012,JPO&INPIT</p> |
