Lighting device and vehicle headlamp

摘要

A switching circuit includes an active element connected in parallel to a second light source block and having an impedance that varies in accordance with a control signal input into a control terminal, and switches the second light source block between a lit condition and an extinguished condition by switching the active element ON and OFF. The switching circuit adjusts the impedance of the active element so that a current flowing to the active element matches a target value set by a switching control circuit. When the active element is to be switched ON, the switching control circuit varies the target value gradually over time, and therefore an excessive load current can be prevented from flowing while the active element shifts from an OFF condition to an ON condition.

主权项

1. A lighting device comprising:
a power supply circuit that supplies a constant current to a light source group in which a first light source block and a second light source block are connected in series; and a switching circuit that includes an active element connected in parallel to the second light source block, and extinguishes the second light source block by applying a current to the active element such that the current bypasses the second light source block, wherein the active element includes a control terminal, has an impedance that can be varied in accordance with a control signal input into the control terminal, and lights the second light source block when the impedance reaches or exceeds a predetermined value, and the switching circuit includes: a control unit that controls the impedance of the active element such that a current flowing through the active element or an end-to-end voltage of the active element matches a target value; and a switching control circuit that sets the target value and to monotonically increase or reduce the target value so that the current flowing through the active element monotonically increases or reduces over time at a rate based on the target value.