Hitachi RAC-25FPA, Service Manual

Page: 56 / 117

-1 ) (
min
5
4
3
2
1
0
T1
T2
T2
T1
◯
B
Microcomputer
No. of
rotation output
No. of
rotation detect
35V line
M
45
68
0V 0V
5V
Q751
A
0V
C
CN10
0V
B
R751 L751
R752
C751
R631
C631
6
4
3
2
1
5V line
Fan Motor
Voltage of point (V)
3. Fan Motor Drive Circuit
The waveform of
voltage at the
point
The waveform of
voltage at the
point
The waveform of
voltage at the
point
T1 = Low No. of rotation
T2 = High No. of rotation
At T2
At T1
Fig. 3-3
Fig. 3-1
Fig. 3-2
Rotation
56
(about 1200)
The 610Hz PWM pulse shown in Fig. 3-2 from the microcomputer
pin 45 is output to point . The width of this pulse 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 and number of
rotations becomes as shown in Fig. -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 68 . The frequency of
this pulse is 12/60 of the number of rotations. (Ex: 1000min
-1
12/60=200Hz) The microcomputer observes this frequency and to
make it as the instruction number of rotation all the time, adjusts
the output pulse width of pin 45 .
If the feedback pulse becomes lower than 100min
-1
caused by
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.
3