of each of the switching elements q 1 q 2 and q 3 is commonly connected to a current power source terminal vdc a gate terminal is connected to pulse output terminals p 1 p 2 and p 3 of the control unit 140 additionally a source terminal of each of the switching elements q 1 q 2 and q 3 is connected to anode terminals of the first red led the first green led and the first blue led resistors r 1 r 2 and r 3 of the feedback unit 130 are connected to cathode terminals of the last leds the feedback unit 130 includes resistors r 1 r 2 and r 3 connected to the cathode of the last leds respectively a voltage applied to the resistors r 1 r 2 and r 3 is applied to feedback terminals fb 1 fb 2 and fb 3 of the control unit 140 the control unit 140 outputs pulse signals through pulse output terminals p 1 p 2 and p 3 to turn on or off the switching elements q 1 q 2 and q 3 of the switching unit 120 and thus the leds 111 112 and 113 can be turned on or off.