| 摘要 |
PURPOSE:To prevent the malfunction due to the leakage current, an open state of load connection, etc., by detecting the conduction or non-conduction state to the load through a current transformer. CONSTITUTION:The collector of a transistor Q3 has a high impedance at the time of an abnormal, i.e., in case a current flows to a fixing heater H with no input of a drive signal. The voltage level at a point (f) is increased by a constant tau determined by R8 and R9 and C2 and reaches a Zener voltage ZD1. Then a TR Q4 is turned on when the voltage level of the point (f) reaches a level where a TR Q2 is turned on. Then a TR Q5 is turned on. Here the TR Q4 is kept under an ON state after the TR Q5 is once turned on and therefore the TR Q5 is kept under an ON state. Thus the TR Q5 is set at a low level and the base voltage of a TR Q6 flows to the TR Q5. Then the TR Q6 is turned off to open the contact of a relay RL and the supply of the AC voltage is cut off. Thus the relay RL is protected.
|
