VEHICLE LAMP AND LIGHTING CIRCUIT THEREOF

A lighting circuit, which is mounted in a vehicle lamp, can change the luminance at high speeds. The lighting circuit is used together with a semiconductor light source and makes up a vehicle lamp. A switching converter supplies power to the semiconductor light source. A converter controller controls the switching converter. A current detection circuit detects a current IDRV which is supplied from the switching converter to the semiconductor light source. A hysteresis comparator compares the detected current value with an upper threshold voltage and a lower threshold voltage and generates a control pulse according to the results of the comparison. A threshold voltage generating circuit receives a variable control voltage which indicates a target amount of a current and generates the upper threshold voltage and the lower threshold voltage according to the control voltage.