Hitachi RAS-25CNH2 Service Manual page 52

6. Rotor Magnetic Pole Position Detection Circuit
A
R101 R102 R103
C106
C104
C105
C101 C102
R104
R105 R106
0V
Voltage at point
B - transis-
tor ON
Fig. 6 — 1
Motor-induced voltage signal (voltage at point A ) is phase-shifted by 90° by passing lowpass filter
G
consisting of R101, R104 and C101 to make triangular wave (voltage at point B ). In HIC, 3 phases of
this triangular wave are synthesized to produce composite wave (voltage at point C ). This composite
wave becomes a triangular wave with period of 1/3 times compared with original triangular wave.
Voltages at points B and C are compared by comparator to make voltage at point D.
G
Voltage at point D is taken into microcomputer and timing of switching from V – transistor to W – transistor
is made by rising waveform, and timing of switching from V + transistor to W + transistor is made by failling
waveform.
For other 2 phases (V phase and W phase), the operation is the same and phases are shifted by 120°
G
and 240° respectively compared with U phase waveform.
B
C103
C
A about 260V-380V
0.6V
Voltage at point
Voltage at point
C - transis- B + transis-
tor ON tor ON
Rotor magnetic pole position detection circuit and voltage waveform at each part
+12V
–5V
Voltage at point B
C
D
C + transis-
tor ON
– 55 –
+5V
D
20
18
19