Power supply circuit with overcurrent protection for an illuminating device

摘要

According to one embodiment, a power supply circuit (14) includes a DC-DC converter (21) and an overcurrent protection unit (25). The DC-DC converter (21) converts a first DC voltage into a second DC voltage and supplies the voltage to a DC load (12). The overcurrent protection unit (25) performs feedback control of the DC-DC converter (21) based on current which flows through the DC load. The DC-DC converter (21) includes a normally-on type switching element (41). The switching element (41) includes a first electrode, a second electrode, and a third electrode for controlling current which flows between the first electrode and the second electrode, and includes a first state, and a second state where the current which flows between the first electrode and the second electrode is smaller than that of the first state. The overcurrent protection unit (25) sets the switching element (41) in the second sate, when the current which flows through the DC load (12) is larger than a reference value.