Patent ID: 7081708

Claim:
A lighting circuit for lighting a vehicular lamp comprising a plurality of light source blocks respectively comprising a plurality of light-emitting diodes connected in series, comprising: a selection unit operable to select at least one of the plurality of light source blocks, thereby selecting a number of light-emitting diodes to be connected in said vehicular lamp based on an external instruction; a switch operable not to flow a current through at least one of the light source blocks not selected according to the selection of said selection unit; a switching regulator operable to apply an output voltage based on a power-supply voltage output by an external DC power supply to said selected number of light-emitting diodes, to supply a supply current to said selected number of light-emitting diodes; and an output controlling unit operable to control said output voltage of said switching regulator based on said supply current, wherein said vehicular lamp comprises two light source blocks connected in series, said switch is connected in parallel to a first of said two light source blocks while being connected in series with a second of said two light source blocks, said selection unit makes said switch conductive in a case where said first of said two light source blocks is not selected, and said switching regulator outputs said supply current having approximately the same magnitude irrespective of whether said first of said two light source blocks is selected.