Hitachi RAF-25FX8 Service Manual page 78

6. Fan Motor Drive Circuit
Microcomputer
No. of
40
rotation output
No. of
14
rotation detect
Waveform of
voltage at the
point
At T2
At T1
Waveform of
voltage at the
point
T1
Waveform of
voltage at the
point
T2
The 15.7 kHz PWM pulse shown in Fig.6-2 from the micro
computer pin is output to point
40
changes with instruction number of rotations.
This pulse changes to analog voltage by R751 and C751 and it is
applied to the fan motor as instruction voltage number of
rotations. The relationship between the voltage of point
number of rotations becomes as shown in Fig.6-3. (The gap may
arise depending on the condition of unit.)
The feedback pulse of number of rotation is outputted from the
fan motor and input to micro computer pin
this pulse is 12/60 of the number of rotations. (Ex: 1000min
12/60=200Hz) The micro computer observes this frequency and
to make it as the instruction number of rotation all the time,
adjusts the output pulse width of pin
If the feedback pulse becomes lower than 100min
lock or failure of a fan motor, the fan output stops temporary as
the fan lock is faulty. The pulse will output again after 10 seconds.
If the abnormal in fan lock is detected twice in 10 minutes, the
unit is completely stopped and change to the fault mode which
the timer lamp blinks 10 times.
A
R751
C751
0V
R631
C631
C
0V
T1
T1 = Low No. of rotation
T2
T2 = High No. of rotation
. The width of this pulse
. The frequency of
14
.
40
-1
CN10
35V line
6
0V
4
5V line 3
B
2
1
Fig. 6-1
Fig. 6-2
and
(about 1200)
-1
X
( min -1 )
caused by
– 96 –
M
Fan Motor
2
0 1 3
Voltage of point ⃝ (V)
B
Fig. 6-3
4 5