| 摘要 |
PURPOSE:To previously prevent a failure to be caused by the abnormal heating, by forcibly breaking the electric conduction to a heat source in case when a thermistor has a disconnection. CONSTITUTION:A transistor TR7 is connected in series to a resistance 6, and a control pulse 8 is supplied to the base of the TR7. The point of connection between the collector of the TR7 and the resistance 6 is connected to the base of a TR10 inserted between a relay 9 and a DC power supply 1 via a buffer 11, a resistance 12, a diode 13 and a capacitor 14 respectively. If a thermistor 5 has a disconnection, the high potential does not exist any more at the point of connection between the resistance 6 and the collector of the TR7. Then the output of the buffer 1 is set at a low level of potential to make the TR10 conduct. As a result, the relay 9 works to open a constantly closed contact 9a. Thus the electric conduction is forcibly broken to a heater 15. |
