| 摘要 |
<p>PROBLEM TO BE SOLVED: To obtain a voltage monitoring circuit which requires little energy and reliably responds to changes in a power supply voltage by operating a switch to be controlled according to a switching signal obtained from an alarm signal from the first comparator or from a control signal from the second comparator. SOLUTION: By comparing a voltage present at a tap point 20 i.e., the signal input 12 of a comparator 10 with a voltage present at a preference input 14, it is possible to monitor the voltage of a power supply voltage line 22 in effect. The voltage of the tap point 20 is changed by leakage currents in reality. Therefore, a ratio between the voltage of the tap point 20 and a power supply voltage is not same as a ratio set by ratios between capacitors C1 and C2 and resistance R1 and R2 . This voltage monitoring circuit is provided with a means to update the voltage of the tap point 20 at all times to be at a correct ratio to or in a correct relationship with a power supply voltage Vcc to be monitored. This operates as if not monitoring a voltage obtained from the voltage Vcc and accumulated in the capacitors but directly monitoring the voltage Vcc. A comparator 50 generates a control signal for the updating operation.</p> |
