| 摘要 |
PURPOSE:To achieve stable operation even at a low voltage by connecting an active resistance between a bridge circuit and a non-inverting input terminal of an operational amplifier. CONSTITUTION:A heater temperature sensor 12, a temperature compensation temperature sensor 14, a variable resistance 22 and resistances 16, 18 form a bridge circuit 20. The circuit 20 is connected to an input side of an operational amplifier 24. A feedback transistor 28 is connected to an output side of the operational amplifier 24. Moreover, an active resistance 26 is connected between the sensor 14 and a non-inverting input terminal of the operational amplifier 24. A current is let to flow in the sensor 12 to heat the sensor. When the flow of the air comes in touch with the sensor 12 thereby to take the heat, the resistance of the sensor 12 is changed. Accordingly, the wind velocity is detected. Even if the transistor 28 is turned OFF, a voltage decrease is brought about by input bias currents IB1, IB2, and a large voltage is impressed more to the non-inverting input terminal of the operational amplifier 24 by the resistance 26 as compared with an inverting input terminal. Therefore, the operational amplifier 24 is kept active, thereby securing stable operation. |
