Fail-safe mechanism

摘要

When failure of a system is detected, feeding electric power to a driving circuit is interrupted to stop the system with reliability, and power source is not applied to the driver circuit unless a driving power source is restarted. A fail-safe mechanism is provided with a main switch circuit (9) connected between a driving power source (4) and a driver circuit (2); a sub switch circuit (5) connected between the driving power source (4) and the main switch circuit (9), and maintaining an OFF state in normal times; a timer circuit (7) allowing the sub switch circuit (5) to be fed with electric current for a predetermined time period after said driving power source (4) is turned on; a failure detector circuit (6) connected between the main switch circuit (9) and a controller (1); and a sub switch control means (8) brining the sub switch circuit (5) to an OFF state when the feeding of electric current is cut off. The main switch circuit (9) is turned OFF when the failure detector circuit (6) detects an abnormal condition of the controller (1). <IMAGE>