A light source driving circuit for powering a first light source and a second light source by a DC voltage includes a first control circuitry and a second control circuitry. If the DC voltage is within a first range, then the first control circuitry controls a first switch and the second control circuitry controls a second switch to turn on the first light source and to regulate a current flowing through the first light source. If the DC voltage is within a second range, then the first control circuitry controls a third switch and the second control circuitry controls a fourth switch to turn on the first light source and the second light source and to regulate a current flowing through the first light source and the second light source.