| 摘要 |
PURPOSE:To prevent a source voltage from dropping due to a rush current by comprising an input cutoff means by using an output buffer circuit which lowers a signal inputted to an input terminal to an L level compulsorily when a switch signal is inputted to a control input terminal, or pulls it up to an H level. CONSTITUTION:A power source switching means 46 switches a power source for CMOS input type IC 36 from a main power source to a backup power source 38 based on a power source switching command. Simultaneously, the CMOS input type IC 36 drives the input cutoff means 60-1 to 60-n comprising of the output buffer circuits 62 and 64 provided at the rear stage of each input terminal 52 based on the power source switching command inputted to its control input terminal 52, and performs control to lower the signal inputted to each input terminal 52 to the L level compulsorily, or to pull it up to the H level. Thereby, it is possible to prevent the rush current from flowing on the CMOS input type IC 36 for a long time when the power source is switched from the main power source to the backup power source 38, and to prevent the voltage drop of the backup power source small in capacity occurring. |
