| 摘要 |
<p>PURPOSE:To obtain a power supply control circuit where the consumption of an incorporated battery even though a normal drive power supply is frequently switched on and off, by supplying the power to switch a microcomputer to a low power consumption mode through a capacitor when the normal drive power supply is cut off and then supplying the power to the microcomputer from the battery. CONSTITUTION:When a normal drive power supply 1 for microcomputer, is turned off, the voltage level is first set at Vf=0 at a point (f). In such a case, the electric charge stored in a capacitor C2 is supplied to a VDD for the time being. Thus no current flows from a battery B. While the voltage Ve=0 is obtained at the point (e) when the Vf=0 is obtained at the point (f). Then a transistor Q is turned off to secure Vb=0. A microcomputer 3 knows that the power supply 1 is cut off and is shifted to a low power consumption mode from a normal power consumption mode. Here the capacitor C2 is previously selected so that a current is supplied to the VDD from the capacitor C2 for a period during which the low power consumption mode is secured. In such a way, a large current flowing out of the battery B is prevented when the power supply 1 is cut off.</p> |
