| 摘要 |
<p>PURPOSE:To ensure actuation of a hot-wire flowmeter through simple constitution when power is applied to the hot-wire flowmeter. CONSTITUTION:An operational amplifier 250 feedback controls the base voltage of a power transistor 5 so that the temperature of a temperature sensing resistor 7 is held constant and the amount of electricity transmitted to the temperature sensing resistor 7 is output as a signal indicative of the amount of air. Three- stage emitter-follower circuits are provided to the output of the operational amplifier 250 and the voltage drop of the circuits is 3XVBE wherein VBE is the base-emitter voltage drop of transistors 324, 325, 326. Therefore, the base voltage of the transistor 5 of Dahlington connection becomes higher than the base-emitter voltage drop 2XVBE of the transistor 5. Thereby electricity is surely transmitted to the temperature sensing resistors 7, 8 even during power application so as to surely actuate a feedback control loop.</p> |
