Hitachi RAS-25QH1 Technische Information Seite 133

9. DC Fan Motor Drive Circuit (RAS-25QH1, RAS-32QH1)
@ Fig.9-1 shows the indoor DC fan motor drive circuit.
Micro computer
Indoor DC
fan motor
Fan motor
current (9)
detection
OV OV Terminal boad D
Fig. 9-1
@ The circuit produces the fan motor drive voltages, 8-33V, from 35V DC supplied from the outdoor unit and
controls the fan motor speed.
@ Q903 is switched on and off according to the signal at fan PWM output pin 6? to control the voltage
which is smoothed by D901, L901 and C901 to drive the fan motor.
@ The output voltage is divided by R901 and R903 and is input to divided voltage output pin ©); the micro
computer controls the fan PWM output so the output voltage is set to the specified value. The chopper
frequency of the fan PWM output is 15.7kHz.
@ The fan current detector detects the current on the 35V line using R906-915 and inputs it via fan current
detector pin @. The microcomputer compares it with the current detection value that corresponds to the
fan speed, to detect an overcurrent.
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