| 摘要 |
PURPOSE:To discriminate the level value of a DC input voltage by lighting of a light emitting diode, by lighting the light emitting diode only when the DC input voltage is within a DC reference voltage of a small difference between respective DC reference voltages of two differential amplifier type amplitude comparing circuits. CONSTITUTION:When a DC input voltage Vin is within a range from VZ to (VZ+VF), the potential of the output terminal of a differential amplifier type amplitude comparing circuit A21 is about VCC, and the potential of the output terminal of a differential amplifier type amplitude comparing circuit A22 is about -VEE, and therefore, a potential difference of about (VCC+VEE) is applied to both terminals of the series connection of a light emitting diode D21 and a resistance R22, and the light emitting didoe D21 is lit. When the input voltage Vin is equal to or higher than (VCC+VEE), potentials of output terminals of differential amplifier type amplitude comparing circuits A21 and A22 are both about -VEE, and no potential difference is generated in both ends of the light emitting diode D21, and the diode 21 is not lit. |
