Hitachi RAS-50WX8 Service Manual page 86

4. Power Circuit for P.W.B.
Fig. 4-1 shows the power circuit for P.W.B. and waveform at each point.
RC2
+
R902
+
In the power circuit for P.W.B., power voltage for microcomputer, peripheral circuits, and power module drive and, as well
as DC35V, are produced by switching power circuit.
Switching power circuit performs voltage conversion effectively by switching transistor IC901 to convert DC330V voltage to
high frequency of about 20kHz to 200kHz.
Transistor IC901 operates as follows:
(1) Shifting from OFF to ON
DC about 330V is applied from smoothing capacitors C010 + and C011 - in the control power circuit.
With this power, current flows to pin
direction of arrow generates at point
IC901.
Switching transformer
R902
R901
C901
D911
IC901
D903
R910
3 4
1
3
2 5
+
L901 PQ1
4
R907
D905
C906
C908
R911
D906
Fig. 4-1 Power circuit for P.W.B.
of IC901 via R903 and R904 and IC901 starts to turn ON. Since voltage in the
at the same time, current passing through R910 and D903 is positive-fed back to
C909
20
+
21 D907
C910
1 22
R915 D908
18
+
C911 R916
19
FM-15V
9
D909
R917
16
+
C912
12
17
C913
C
15
D910
+
14
13
11
R920
C918
4 1
1
2
3
PQ2 2
C924
3
R922
– 126 –
35V
R914
17V
I/F0V
L902
0V
R918
12V
FM-0V
1
L903
4
+
1
2
Q706
0V
D912
5V
2
3
+
REG1
0V