Abstract: A lighting circuit for lighting a vehicular lamp including a light-emitting diode, includes: a switching regulator for applying an output voltage based on a power-supply voltage received from a DC power supply provided in the outside thereof to the light-emitting diode so as to supply a supply current to the light-emitting diode; an abnormal state detector for detecting an abnormal state of the lighting circuit based on at least one of the output voltage of the switching regulator, the supply current and the power-supply voltage; and an output controlling unit for controlling the output voltage of the switching regulator based on the supply current or the output voltage of the switching regulator and lowering the output voltage of the switching regulator in a case where the abnormal state detector detected the abnormal state.

Abstract: A switching regulator circuit for controlling power supplied to a load, includes: a switching device for repeatedly going on or off to control a voltage or a current applied to the load; a detector for detecting a supply voltage or a supply current supplied to the load; and a controller for controlling a duration ratio of a period in which the switching device is on or off based on the supply voltage or supply current detected by the detector, so as to control a value of the voltage applied to the load.

Abstract: A lighting circuit for lighting a vehicular lamp including a plurality of light-emitting diodes, includes: a selection unit for selecting the number of light-emitting diodes to be connected in series in the vehicular lamp based on an instruction from the outside; a switching regulator for applying an output voltage based on a power-supply voltage output by an external DC power supply to the selected number of light-emitting diodes to be connected in series, so as to supply a supply current to the selected number of light-emitting diodes; and an output controlling unit for controlling the output voltage of the switching regulator based on the supply current.

Abstract: A switching regulator circuit for supplying two input potentials to a passive device that is driven by a potential difference between the two input potentials irrespective of potential differences between the two input potentials and a ground potential, includes: a low-voltage input terminal for receiving a lower input potential that is lower one of the two input potentials; a coil provided between the low-voltage input terminal and the passive device in series; and a switching device, provided between the low-voltage input terminal and the passive device to be in series with the coil, for making the coil generate a potential higher than the lower input voltage by repeatedly switching whether or not a current is allowed to flow in the coil, so as to supply the generated potential to the passive device.