A lighting circuit structured to turn on a plurality of semiconductor light sources (102_1:102_N), comprising: a plurality of current sources (210_1:210_N) each of which is to be coupled to a corresponding semiconductor light source (102_1:102_N) in series; a switching converter structured to supply a driving voltage across each of a plurality of series connection circuits each formed of the semiconductor light source (102_1:102_N) and the current source (210_1:210_N); and a converter controller employing a ripple control method, wherein the plurality of current sources (210_1:210_N) each comprise: a series transistor (M2) and a sensing resistor (RS) arranged in series with a corresponding semiconductor light source (102_1:102_N); and an error amplifier structured to adjust a voltage at a control electrode of the series transistor (M2) based on a voltage drop across the sensing resistor (RS), and wherein the converter controller is structured to turn on the switching transistor (M1) of the switching converter in response to an output voltage (VG1:VGN) of the error amplifier included in any one of the plurality of current sources (210_1:210_N) satisfying a predetermined turn-on condition, wherein the converter controller turns off the switching transistor (M1) in response to the driving voltage reaching an upper limit voltage, characterized in that the upper limit voltage is feedback controlled such that the switching frequency of the switching transistor (M1) approaches a target frequency. a plurality of current sources (210_1:210_N) each of which is to be coupled to a corresponding semiconductor light source (102_1:102_N) in series; a switching converter structured to supply a driving voltage across each of a plurality of series connection circuits each formed of the semiconductor light source (102_1:102_N) and the current source (210_1:210_N); and a converter controller employing a ripple control method, wherein the plurality of current sources (210_1:210_N) each comprise: a series transistor (M2) and a sensing resistor (RS) arranged in series with a corresponding semiconductor light source (102_1:102_N); and an error amplifier structured to adjust a voltage at a control electrode of the series transistor (M2) based on a voltage drop across the sensing resistor (RS), a series transistor (M2) and a sensing resistor (RS) arranged in series with a corresponding semiconductor light source (102_1:102_N); and an error amplifier structured to adjust a voltage at a control electrode of the series transistor (M2) based on a voltage drop across the sensing resistor (RS), and wherein the converter controller is structured to turn on the switching transistor (M1) of the switching converter in response to an output voltage (VG1:VGN) of the error amplifier included in any one of the plurality of current sources (210_1:210_N) satisfying a predetermined turn-on condition, wherein the converter controller turns off the switching transistor (M1) in response to the driving voltage reaching an upper limit voltage, characterized in that the upper limit voltage is feedback controlled such that the switching frequency of the switching transistor (M1) approaches a target frequency. <EOS>