| 摘要 |
<p>PURPOSE:To reduce the consumption of an auxiliary power supply, by switching forcibly a load to a holding state from an active state with a transistor which is turned off when a primary power supply has the voltage less than a certain level and then switching the primary power supply to the auxiliary power supply when the voltage of the primary power supply lowers further. CONSTITUTION:When the constant voltage Vm supplied from a primary power supply battery Bm, a resistance R1 and a Zener diode Dz becomes lower than a certain level, the base voltages of resistances TR1 and TR2 drop. At the same time, the TR1 and TR3 are turned off. As a result, an active/holding state switching terminal Run/Hold of a load circuit L is set at a low level regardless of the ON/OFF of a switch SW. This is equivalent to the fact that the SW is turned on. Thus the load L is set in a holding state to reduce the power consumption. When the voltage of the primary power supply lowers further, both the TR2 and TR4 are turned off whch a TR5 turned on. Then the voltage of an auxiliary power supply battery Bb is applied to a terminal Vdd of the load L. This prevents the waste of the battery Bb. Such a power supply circuit is suited to a computer.</p> |
