Patent ID: 8305001

Claim:
A light-emitting diode driver circuit comprising: a first rectifier circuit configured to output a first rectified voltage obtained by rectifying an AC voltage; a transformer including a primary coil provided on a primary side, a secondary coil provided on a secondary side, and an auxiliary coil inductively coupled to the primary coil or the secondary coil, the primary coil configured to be applied with the first rectified voltage; a transistor connected in series to the primary coil to control a current passing through the primary coil; a second rectifier circuit configured to output a second rectified voltage obtained by rectifying a voltage generated in the auxiliary coil; a capacitor configured to be charged with the second rectified voltage; and a voltage-dividing circuit configured to divide a charging voltage of the capacitor; and a control circuit configured to control on and off of the transistor based on a divided voltage output from the voltage-dividing circuit so that the charging voltage becomes equal to a predetermined voltage, the secondary coil outputting a voltage that varies with a frequency corresponding to a frequency of the first rectified voltage and that corresponds to a turns ratio between the primary coil and the secondary coil, as a voltage for driving a light-emitting diode.