| 摘要 |
PURPOSE:To ensure a stable operation for a switching element such as a relay, by feeding back the driving output of the switching element to change the difference of potential of a bridge circuit and then producing the hysteresis to the output of a comparator. CONSTITUTION:A potential difference detecting resistance R4 becomes equivalent to a resistor which is connected in parallel to a fixed registor R3 when a cooking heater R conducts since the output of a comparator CV2 is set at L. As a result, a reference potential Vs is set at a low level, and the output of an A/D conversion changes with every step. Meanwhile a thermistor Th reaches a set resistance value, and accordingly the output of the A/D converter changes from H to L. And the threshold potential rises up in accordance with the rise of the potential Vs which is caused by the comparator CV2 and based on the signal of the R terminal of a microcomputer MC. Thus the hysteresis is caused to vary the working point of a comparator CV1. Then the R output terminal of the MC is turned off in a stable way to turn off a relay RY. Thus the electric conduction is inhibited to the heater R. |
