Light-emitting diode driver circuit and lighting apparatus
View Patent ↗A light-emitting diode driver circuit includes: a first-rectifier circuit to output a first-rectified voltage; a transformer including primary and secondary coils and an auxiliary coil inductively coupled to the primary or secondary coils, the primary coil being applied with the first-rectified voltage; a transistor connected in series to the primary coil; a second-rectifier circuit to output a second-rectified voltage obtained by rectifying a voltage generated in the auxiliary coil; a capacitor to be charged with the second-rectified voltage; and a control circuit to control on and off of the transistor based on a charging voltage of the capacitor 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 and secondary coils, as a voltage for driving a light-emitting diode.
1. 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.
2. The light-emitting diode driver circuit of claim 1 , wherein
the first rectifier circuit includes a full-wave rectifier circuit.
3. The light-emitting diode driver circuit of claim 2 , further comprising
a current detecting circuit configured to output a detection voltage corresponding to a value of a current passing through the transistor, wherein
the control circuit controls on and off of the transistor so that a value of a current passing through the transistor varies according to the first rectified voltage as well as the charging voltage becomes equal to a predetermined voltage, based on the charging voltage, the detection voltage, and the first rectified voltage.
4. The light-emitting diode driver circuit of claim 3 , wherein
the voltage-dividing circuit divides the charging voltage at a voltage division ratio according to a control signal; and
the control circuit controls on and off of the transistor so that a value of a current passing through the transistor varies according to the first rectified voltage as well as the divided voltage becomes equal to a predetermined voltage, based on the divided voltage output from the voltage-dividing circuit, the detection voltage, and the first rectified voltage.
5. A lighting apparatus 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;
a voltage-dividing circuit configured to divide a charging voltage of the capacitor;
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; and
a light-emitting diode,
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 the light-emitting diode.