Hitachi RAM-60QH4 Manuel De Service page 84

4. Power circuit for P.W.B.
• Fig. 4-1 shows the power circuit for P.W.B. and waveform at each point.
Diode stack
R505
• In the power circuit for P.W.B., power voltage for microcomputer, peripheral circuits, and system power module drive and, as
well as DC35V, are produced by switching power circuit.
• Switching power circuit performs voltage conversion effectively by switching transistor IC1 to convert DC330V voltage to high
frequency of about 20kHz to 200kHz.
• Transistor IC1 operates as follows:
(1) Shifting from OFF to ON
• DC about 330V is applied from smoothing capacitors C020 ○ + and C021 ○ - in the control power circuit. With this power,
current flows to pin ④ of IC1 via R701 and IC1 starts to turn ON. Since voltage in the direction of arrow generates at point ○ C
at the same time, current passing through R708 and D702 is positive-fed back to IC1.
R702 R701
+
+
IC1
3 4
1
2 5
FB1
R715
C732
R726
Fig. 4-1 Power circuit for P.W.B.
Switching transformer
16
17
1
18
C714
R703
19
D709
13
9
14
D702 R708
12
15
C
+
D731
20
11
R722
21
D715
R724
22
C733
4
C725
3 PQ8
D708
C724
R725
– 96 –
+17V
R713
R717
+
C718
+15V
R710
R718
+
C707
+12V
C735
REG1
+
D705
C708
+
D706
R723
-5V
C734
+
D707
R713
R710
1
R711
1
2
2
3
R712
R714
+5V
+
C721 C716
0V
C740