| 摘要 |
PROBLEM TO BE SOLVED: To provide a light emitting diode driving circuit which is hardly affected by the decrease of a power supply voltage and the dispersion of the forward voltage drop of a light emitting diode, can allows the power supply voltage just before the forward voltage drop of the light emitting diode and also prevents battery consumption by suppressing a consumption current in the area outside a constant current in order to solve the problem that a battery driver of a low voltage has to prepare a step-up voltage because the forward voltage drop of a white light emitting diode is large in comparison with those of the light emitting diodes of the other colors even if a back light for a portable terminal such as a portable telephone and a PHS has to use the white light emitting diode. SOLUTION: A voltage controlled constant current circuit is connected to the light emitting diode, a control circuit for turning on the voltage controlled constant current circuit with an incoming signal to the portable telephone or a signal such as the depression signal of a light emitting button is provided, and a constant current is supplied to the light emitting diode only when the light emitting diode operates to make the light emitting diode emit light. |
