Circuit and method of effectively enhancing drive control of light-emitting diodes
First Claim
1. A light-emitting diode drive circuit, comprising:
- a plurality of light-emitting diodes;
a power supply circuit configured to supply a variable voltage to supply electric power to each of the plurality of light-emitting diodes;
a plurality of current sources each configured to drive a corresponding one of the plurality of light-emitting diodes;
a bias voltage setting circuit configured to generate and output a reference voltage for causing each of the plurality of current sources to have a current having a predetermined constant value, and a minimum set voltage for causing each of the plurality of current sources to have the current having the predetermined constant value when the reference voltage is input to each of the current sources; and
a voltage detection circuit configured to sequentially compare output voltages of the plurality of current sources with the minimum set voltage to supply one of the output voltages which is smaller than the minimum set voltage, wherein the power supply circuit is configured to control the variable voltage so that the output voltage output from the voltage detection circuit becomes greater than or equal to the minimum set voltage output from the bias voltage setting circuit.
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Accused Products
Abstract
An LED drive circuit includes a plurality of LEDs, a power supply circuit for outputting a variable output voltage to supply electricity to the LEDs, a plurality of drive transistors for driving the respective LEDs, a bias voltage setting circuit for generating and outputting a reference gate voltage for causing the drive transistors to have drain currents having a predetermined constant value, and a minimum drain voltage for causing the drive transistors to have the predetermined constant drain currents when the reference gate voltage is input to the drive transistors, and a voltage detection circuit for sequentially comparing drain voltages of the drive transistors with the minimum drain voltage to output one of the drain voltages smaller than the minimum drain voltage, wherein the power supply circuit controls the output voltage so that the drain voltage output from the voltage detection circuit becomes greater than or equal to the minimum drain voltage.
59 Citations
7 Claims
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1. A light-emitting diode drive circuit, comprising:
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a plurality of light-emitting diodes;
a power supply circuit configured to supply a variable voltage to supply electric power to each of the plurality of light-emitting diodes;
a plurality of current sources each configured to drive a corresponding one of the plurality of light-emitting diodes;
a bias voltage setting circuit configured to generate and output a reference voltage for causing each of the plurality of current sources to have a current having a predetermined constant value, and a minimum set voltage for causing each of the plurality of current sources to have the current having the predetermined constant value when the reference voltage is input to each of the current sources; and
a voltage detection circuit configured to sequentially compare output voltages of the plurality of current sources with the minimum set voltage to supply one of the output voltages which is smaller than the minimum set voltage, wherein the power supply circuit is configured to control the variable voltage so that the output voltage output from the voltage detection circuit becomes greater than or equal to the minimum set voltage output from the bias voltage setting circuit. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of controlling a circuit for driving a plurality of light-emitting diodes, comprising the steps of:
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supplying a variable voltage to supply electric power to each of the plurality of light-emitting diodes;
driving the plurality of light-emitting diodes by using a plurality of current sources;
generating a reference voltage for causing each of the plurality of current sources to have a current having a predetermined constant value;
outputting the reference voltage;
generating a minimum set voltage for causing each of the plurality of current sources to have the current having the predetermined constant value when the reference voltage is input to each of the current sources;
outputting the minimum set voltage;
sequentially comparing output voltages of the plurality of current sources with the minimum set voltage;
outputting one of the output voltages which is smaller than the minimum set voltage; and
controlling the variable voltage so that the output voltages of all the current sources become greater than or equal to the minimum set voltage.
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Specification