| 摘要 |
PROBLEM TO BE SOLVED: To fix the voltage level of external power source into a constant voltage at the time of power source switching and to prevent instantaneous power failure from being generated at the time of power failure by comparing the output voltage of driving circuit due to the external power source with a reference voltage and driving a power source switching relay based on the compared result. SOLUTION: A comparator circuit CP 1 having hysteresis characteristics compares the output voltage of external power source with the reference voltage. Based on this compared result, a relay driving circuit TR operates the control contact of power source switching relays Rc and Ry by selectively changing the voltage to be impressed to the control coil of power source switching relays Rc and Ry to high or low level. Therefore, the voltage level of external power source in the case of performing power source switching is not dispersed by the characteristics of relay circuit. Namely, a power source switching voltage is decided regardlessly of the impressed and non-impressed voltages of power source switching relays Rc and Ry. Therefore, when the external voltage is made a fixed voltage, power source switching is surely performed. |
