| 摘要 |
PURPOSE:To improve the recognition properties of lighting and non-lighting by making a constant current circuit, in which output currents from a constant- voltage generating circuit driven at supply voltage are determined, and a light- emitting diode driven by output currents from the constant current circuit to be contained. CONSTITUTION:VF=VCC-VCE holds in the forward voltage VF of a light- emitting diode 7. When a forward voltage threshold where the light-emitting diode 7 is lit is represented by VFT at that time, the diode 7 is lit when VFT<=VF =VCC-VCE holds, and the diode 7 is not lit at all when VF=VCC-VCE<VFT holds. Consequently, when the constant voltage value VZ of a constant voltage diode 5 is set previously at a value slightly lower than the forward voltage threshold VFT, the light-emitting diode 7 is not lit at all when supply voltage extends over a constant voltage value V2 or lower, and the diode 7 is lit at sufficient luminance when supply voltage is larger than the constant voltage value V2. Accordingly, the recognition properties of the lighting and non-lighting of the light-emitting diode 7 are improved. |
