| 摘要 |
PURPOSE:To decrease the number of members of the whole device and also reduce the size and manufacturing cost of a device by connecting plural stages of constant circuit elements which have mutually different constant voltages. CONSTITUTION:A rectifying circuit 13 is connected to an AC power source 11 through a power transformer 12 as a voltage converting circuit. When an input voltage Vd to a constant voltage circuit 15 drops below a preset value, a Zener diode 29 turns off in a DC voltage drop derecting circuit 18 and a reset signal outputted from a reset terminal 33 changes to a low level. Consequently, an input voltage Vp the the 2nd constant voltage circuit element 19b is held constant because Vp>Vl as far as an input voltage Vd to the 1st constant voltage circuit element 19a of the circuit 15 is normal. Therefore, only the input voltage Vd to the circuit 15 is necessarily monitored. Thus, the number of constituent members is decreased. |
