Hitachi RAD-25NH7 Service Manual page 61

4. Power Circuit for P.W.B.
Fig. 4-1 shows the power circuit for P.W.B. and waveform at each point.
G
Diode stack 2
(RC2)
+
R002
+
In the power circuit for P.W.B., power supply for microcomputer, peripheral circuits, and system power
G
module driver circuit and, as well as DC 35V, are produced by switching power circuit.
Switching power circuit performs voltage conversion effectively by switching transistor IC901 to convert
G
DC 330V voltage to high frequency of about 20kHz to 200kHz.
Transistor IC901 operates as follows:
G
(1) Shifting from OFF to ON
DC about 330V is applied from smoothing capacitors C010 Œ and C011 œ in the control power circuit.
G
With this power, current flows to pin
voltage in the direction of arrow generates at point
D903 is positive-fed back to IC901.
Switching transformer (T1)
R902
R901
D911
IC901
D903
3 4
3 PQ1
1
2 5
+
4
L901
R907
D905
C906
C908
R911
D906
Fig. 4-1 Power circuit for P.W.B.
4
C909
20
D907
21
1
22
D908
R915
C901
18
19
9
R917 D909
16
R910
12
17
C913
C
15
D910
14
13
11
R920
C918
4 1
3
PQ2
2
2
C924
3
R922
of IC901 via R903 and R904 and IC901 starts to tum ON. Since
at the same time, current passing through R910 and
C
– 71 –
35V
+
R914
C910
17V
I/F0V
L902
+
R916
C911
FM–15V
0V
+
C912
R918
FM–0V
12V
L903
+ +
1
1
2
Q706
0V
D912
5V
1 2
4 3
REG1
+
0V