Hitachi RAM-50CNHZ2, Service Manual, Page: 74 / 107

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6. Rotor magnetic pole position detection circuit
When the DC brushless motor is rotated, it also operates as power generator, generating reverse electromotive
force according to number of rotations. This reverse electromotive force is voltage-divided by R503-R505 and
R604-R011, and appears as point
A voltage. IC3 compares and digitalizes point A voltage with point B voltage
(in which DC voltage (Vd) is voltage-divided by R501, R502 and R608), and inputs this to microcomputer as
position detection signals for points
C , D and E . Microcomputer switches inverter using optimum timing based
on position detection signals, in order to control the rotation of the brushless motor.
Microcomputer of outdoor unit
18
59
C
1
2
13
14
12
8
9
10
11
4
5
6
7
3
D
B
A
E
19
20
C605
C606
OV
OV
+5V
+12V
OV
OV
OV
OV
C607
IC3
R601
R253
R500
R502
Inverter
DC brushless motor
for compressor
+
+
+ +
R501
R604
R605
R606
R607
R608
R611 R610 R609
R503 R504 R505
W V U
C604 C603 C602 C601
C205
R602
R603
+
+
+
+
Fig. 6-1 Rotor magnetic pole position detection circuit