| 摘要 |
PURPOSE:To display a power-on state and a voltage reduction state by turning on/off of a light emitting diode by turning on the light emitting diode only when a power source is in on-state and its voltage is higher than a rated voltage. CONSTITUTION:The source voltage VCC applied to equipment L as a load is applied to the light emitting diode D1 as well through a current limiting resistance R4 and a transistor (TR) Q1. The voltage VD applied to this light emitting diode D1 is VD=R3VCC/(R2+R3)-VBE, and when the VCC drops, the light emitting diode D1 turns off. Therefore, resistances R2 and R1 are so set that the voltage at which the TRQ1 turns on and off is the lowest operation voltage of the equipment L; when the source voltage VCC of the equipment L is higher than the lowest operation voltage, the TRQ1 conducts to turn on the light emitting diode D1. On the other hand, when the source voltage VCC drops below the lowest operation voltage, the TRQ1 turns off to turn off the light emitting diode D1. |
