| 摘要 |
PROBLEM TO BE SOLVED: To surely discontinue the operation of a high voltage circuit, when a grounding wire is disconnected from a connection part and other disconnection is produced. SOLUTION: If the disconnection of a grounding wire 14a or 14b, etc., is produced, a current flows between an S-phase and an R-phase through respective light-emitting diodes (27a and 27b) and (28a and 28b) of 1st and 2nd photocouplers 27 and 28 and 1st and 2nd phototransistors 27c and 28c are electrically continuous except in a range where a current flowing through the light- emitting diodes 27a, 27b, 28a and 28b is close to zero. Although an electrolytic capacitor 48 is charged while the two phototransistors 27c and 28c are not electrically continuous, the time constant of a charging circuit is so predetermined as to have the charged voltage of the electrolytic capacitor 48 lower than a voltage level by which a drive transistor 45 is turned on, until the two phototransistors 27c and 28c are turned on again. As a result, a 2nd switching contact 18 is opened, and a power supply to a high voltage power supply unit 3 is cut off. |
