| 摘要 |
<p>PURPOSE:To increase the lifetime of a relay contact, by latching the coil of a latch relay connected to a heater with the signal which is supplied via a Schmitt circuit and a hysteresis means by the temperature of detection and therefore reducing the opening/closing times of the relay contact. CONSTITUTION:Transistors TR27 and TR26 are turned on and off when the temperature of a heater 2 is lower than that set by a volume 25 with a high level of resistance of a thermistor 31. At the same time, a temperature detecting means A is set at an H output, and TR15 and TR14 of a Schmitt circuit B are turned off and on respectively with TR4 and TR11 turned on. Thus an inverting means D has an L output, and a TR8 is turned off. Then a charging current flows instantaneously to a capacitor 6 to close and latch a contact 3A. When the heater 2 conducts to raise up the temperature, the state of each part is inverted. Then the capacitor 6 is discharged to release the latching state. In this case, the temperature of the thermistor 31 drops, and the TR15 is turned on. Thus the base potential of the TR26 is set at a high level owing to a diode 22 and a resistance 21, and the temperature of the thermistor 31 is lowered less than the level obtained when the heater 2 is turned off. Then the thermistor 31 is finally turned on to draw a hysteresis.</p> |
