Patent ID: 8120283

Claim:
An LED driver for driving one or plural LEDs (light emitting diodes) connected in series with each other electrically to emit light, comprising: a DC power source that outputs a DC LED driving voltage; a constant current driving circuit connected in series with said LED with respect to said DC power source for providing a constant LED driving current in said LED; and a headroom voltage monitoring circuit for said DC power source to perform dynamic variable control of the voltage level of said LED driving voltage so that the headroom voltage obtained at the current terminal of said constant current driving circuit is kept within a predetermined range of a first reference voltage; wherein said DC power source comprises: a switching power source part, which has a first switching element that can be turned ON/OFF at a high frequency, and which switches said first switching element ON/OFF and converts said input voltage to said LED driving voltage; a switching control part, which controls the ON/OFF operation of said first switching element in said switching power source part; and a first feedback circuit that feeds back said LED driving voltage to said switching control part, wherein said headroom voltage monitoring circuit has a second feedback circuit that feeds back said headroom voltage to said switching control part of said DC power source.