| 摘要 |
PURPOSE:To dispense with the detecting resistor of a load current, and besides, to make a heat generation smaller, and further, to eliminate the change of a temperature set value against the fluctuation of a power source by opening the resistance measuring part of a heater at the time when the heater is charged by electricity, and measuring under a low voltage only when it is necessitated. CONSTITUTION:An AC power source 1 is half-wave-rectified, and a capacitor 6 is charged by the Zener voltage of a voltage regulator diode 4. A control circuit 11 outputs periodically a signal to close a switch circuit 10, while the trigger pulse (PT) of a triode AC switch (TA) 2 is not outputted. When the circuit 10 is closed, a current flows in a resistor 8, and a voltage drop is obtained. When the temperature of the heater 3 is low, the resistance is also low, and the voltage of the resistor 8 is larger than a reference voltage 9. The circuit 11 controls the output/stop of the trigger signal and the close/open of the circuit 10 while storing these data. The TA 2 heats the heater 3 during the output of the pulse PT. Accordingly, because the voltage of the resistor 8 goes down lower, if the resistance value is set so that it comes just to be temperature set value when the voltage of the resistor 4 comes lower than the voltage 9, the TA 2 continues an OFF state during an interval until the circuit 10 is closed next time after the circuit 10 is closed.
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