AIR FLOW CONTROL CIRCUIT OF AIR CONDITIONER FOR CAR

摘要

PURPOSE:To prevent phase lag which is caused by the fluctuation of power supply voltage by using the voltage value in which the power supply voltage is divided as the control reference voltage in a circuit and making each resistivity of negative feedback signal and preset voltage sections equal to the said partial voltage ratio. CONSTITUTION:An air flow preset circuit 2 consisting of a resistor R and the OP amplifier A of an air flow control circuit 3 are connected to the output end of a constant voltage source 1 consisting of a resistor 5 and a zener diode ZD. The voltage Vr in which the power supply voltage VB is divided by resistors R1 and R2 is applied to the reverse input terminal of the OP amplifier A. On the other hand, resistors R3 and R4 are connected to a non-reverse input terminal. The R3 is connected to the air flow preset circuit 2 and the R4 to the collector of a power transistor Tr4. Moreover, a blower motor 5 is connected to the collector of the Tr4 and the output terminal of the OP amplifier A is connected to the base of the Tr4 through a resistor R6. By obtaining a circuit constant in which a relationship of R1/R2=R4/R3 is established, a desired purpose is achieved.