| 摘要 |
PROBLEM TO BE SOLVED: To provide a driving circuit for a light emitting diode which can save an electric power and downsize. SOLUTION: A voltage detection circuit 4 outputs a voltage detection signal S4 which is H when a cathode voltage of a light emitting diode 1 is above 0.7 V (minimum level voltage which a constant electric current driving circuit 2 can supply a constant electric current), and whish is L when the cathode voltage is below 0.7 V. After a one-chip microcomputer 5 receives a start signal for a power supply S6 which indicates a control start, it increases a power supply voltage Vcc every 0.05 V from 0 V until the voltage detection signal S4 changes to H from L. When the voltage detection signal S4 changes to H, the one-chip microcomputer 5 stops a voltage increase of the power supply voltage Vcc and finishes a set-up of the power supply voltage Vcc.
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