| 摘要 |
PURPOSE:To attain stable and economical voltage detection for both a main power supply and a spare power supply by providing a reference voltage generating circuit and a power supply voltage change detecting circuit and activating them based on the same reference voltage. CONSTITUTION:A reference voltage generated from a reference voltage generating circuit 3 is fed in common to differential amplifiers 4a, 4b and a deviation of the threshold level of the amplifiers 4a, 4b is suppressed to a value of nearly 10mV. Further, a specified volage depends on the amplifier 4a of a reference voltage generating circuit 20 and the detected voltage depends on the amplifier 4b of a power supply voltage change detecting circuit 21, then the detected voltage is set with an error of nearly 10mV. When the reference voltage and the detected voltage are set in this way and when the main power supply VCC is normal, an output voltage VOUT2 of the amplifier 4b is 0 level and the main power supply VCC is fed to a RAM10. In this case, when the value of the main power supply VCC is set larger than the voltage of the battery 12 of the spare power supply. Thus, the stable and economical voltage detection is attained for the main power supply and the spare power supply. |
