| 摘要 |
<p>PURPOSE:To provide a hot water feeder having a less-expensive and safe water- less heating prevention device by a method wherein a temperature sensor circuit, a differential circuit, a water level sensing circuit, a relay driving element triggered by an output from the differential circuit and a relay for use in controlling a heater device are provided in an electrical series-connected state. CONSTITUTION:A detecting temperature of a thermistor 13 is lowered, a voltage at an output terminal of a comparator 19 is increased, a + voltage is applied to a coil 36 of a relay, a transistor 27 and a transistor 30 are turned ON by a voltage charged in a capacitor 26, the voltage is supplied to a comparator 36 and a voltage is supplied to an electrode 32. At this time, if there is no water within a tank 1, a water resistance is approximately limitless, a voltage at an inverting input terminal of the comparator 36 is high, a voltage at the output terminal of the comparator 36 is not increased more than the voltage at a non-inverting input terminal of the comparator 36 and a gate current of a thyristor 41 is not flowed, resulting in that the thyristor 41 is kept OFF, the coil 39 of the relay is not energized and a heater 11 is not heated.</p> |
