| 摘要 |
<p>PURPOSE:To extend the life of a backup battery and make a device small- size, by using a Zener diode, a photocoupler, etc. to eliminate practically the noise output of a voltage comparator which detects the lowering of a power source voltage. CONSTITUTION:When the voltage of a device power source U-Bu becomes a prescribed value or lower, the output of a voltage comparator 1 is lowered, and a photocoupler 2 is turned on through an LED 21 connected to a Zener diode 3, and transistors (TRs) 51 and 52 are switched, and the power source is switched to a battery Bu, and a chip select terminal CS of a memory 4 is still in high- level. When the voltage of the power source U-Bu is lowered furthermore and the comparator 1 in the unoperable state outputs a noise, this noise is eliminated practically through the diode 3, and the state of the coupler 2 is not varied. Consequently, it is unnecessary to back up the comparator 1 with the battery, and a memory device including a chip select controlling circuit where the life of the backup battery is extended and which is made small-sized is attained.</p> |
