Patent attributes
The supply of a predetermined current to LEDs is controlled by using series regulators. In accordance with the controlled states of the series regulators, a switching regulator adjusts an output voltage relative to the LEDs to the maximum voltage. When a ground fault occurs at the anode of one of the LEDs, and when a short circuit occurs at the output terminal of the switching regulator and the output voltage drops abnormally, the operation of the switching regulator is halted. When the gate voltage of an NMOS transistor is raised due to the disconnection of one of the LEDs, or when the drain voltage of the transistor is raised due to a short circuit at one of the LEDs, a Zener diode becomes conductive and an NPN transistor and a PNP transistor are rendered on. Then, a current flows through a diode, and as the gate voltage has been lowered, the operation of the NMOS transistor is halted, so that the remaining, normal LEDs are protected when an abnormality occurs.
