– 126 –
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:
DC about 330V is applied from smoothing capacitors C010 + and C011 - in the control power circuit.
With this power, current flows to pin of IC901 via R903 and R904 and IC901 starts to turn ON. Since voltage in the
direction of arrow generates at point at the same time, current passing through R910 and D903 is positive-fed back to
IC901.
Fig. 4-1 shows the power circuit for P.W.B. and waveform at each point.
4. Power Circuit for P.W.B.
(1) Shifting from OFF to ON
+
+
+
+
+
+
+
+
+
RC2
IC901
L901
R911
C906
R907
D905
R902
C901
R901
R902
R910
D911
D903
PQ1
PQ2
REG1
C010
R010
C011
R906
C905
R903
D904
R908
C907
R909
C903
R904
D902
R011
3
4
C908
D906
3
4
1
2
C924
R920
Q706
0V
2
2
1
1
3
D910
FM-0V
R918
C912
FM-15V
D909
C913
D912
L903
R917
R915 D908
C911 R916
L902
C909
D907
C910
R914
35V
17V
12V
0V
Switching transformer
5V
0V
I/F0V
R922
R921
R923
REG2
C914
JW8
PQ1
JW9
R919
R924
ZD904
C919
C920
C921
2
3
4
1
3
4
5
11
12
9
1
20
21
22
18
19
16
17
15
14
13
C
2
1
C918
Fig. 4-1 Power circuit for P.W.B.