| 摘要 |
PURPOSE:To prevent malfunction of a logic circuit by controlling the quantity of voltage drop at a holding power source with inverse voltage of a Zener diode. CONSTITUTION:In case a regulator 20 to make the voltage +5V for a logic circuit is connected to a holding power source 3, suppose the in- and output voltage difference necessary for the regulator 20 is VREG, the input voltage necessary for the regulator 20 will be (VREG+5)V. Consequently, let the maximum drooping voltage +VL(MIN) at the holding power source 3 be the voltage higher than (VREG+5), and the voltage +5V for the logic circuit will be stable without being affected by the drooping characteristic of the holding power source 3 that may be caused when the high voltage power source 2 and the holding power source 3 are switched over. That is, suppose the voltage across the base and emitter of a control transistor 22 be VBE22, the voltage for the logic circuit can be stabilized without increasing the capacity of the holding power source 3 by selecting a Zener diode 24 of which the inverse voltage VZD satisfies an equation I. |
