Patent ID: 7724219
Filing Date: 2010-05-25
Classification: H05B

Abstract:
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, wherein the voltage detection circuit outputs a predetermined operation stop signal to the power supply circuit when the output voltages of the plurality of the current sources all become greater than or equal to the minimum set voltage and wherein the voltage detection circuit comprises: a plurality of comparators each configured to compare a drain voltage of a respective one of the plurality of current sources with the minimum set voltage, wherein each of the plurality of comparators performs the comparison in a predetermined order; a drain voltage output circuit configured to exclusively output one of the drain voltages of the plurality of current sources which is smaller than the minimum set voltage according to results of the comparison performed by the plurality of comparators, wherein the drain voltage output circuit outputs the drain voltages in the predetermined order; and an operation stop signal output circuit configured to output the predetermined operation stop signal to the power supply circuit to cause the power supply circuit to stop operating when operation stop signal output circuit detects from the results of the comparison performed by the plurality of comparators that the drain voltages of the plurality of current sources are all greater than or equal to the minimum set voltage.