Power Circuit For P.w.b.; Shifting From Off To On - Hitachi RAS-25CNH1 Service Manual

4. Power Circuit for P.W.B.

Fig. 4-1 shows the power circuit for P.W.B. and waveform at each point.
3A fuse
R805
AC 220V
In the power circuit for P.W.B., power voltage for microcomputer, peripheral circuits, and power module
drive and, as well as DV35V, are produced by switching power circuit.
Switching power circuit performs voltage conversion effectively by switching transistor Q1 to convert
DC270V voltage to high frequency of about 20kHz to 70kHz.
Transistor Q1 operates as follows:

(1) Shifting from OFF to ON

DC about 270V is applied from smoothing capacitors C810
With this power, current flows to base of transistor Q1 via R1 and Q1 starts to rurn ON. Since voltage in
the direction of arrow generates at point C at the same time, current passing through R5, R6 and D2 is
positive-fed back to Q1
R 3
R1
C810
D1
R2
L1
Q1
D2
R5 R6
C3
C2 C5 VR2
C811
Q2
R8
R4
ZD3
C4
Fig. 4-1 Power circuit for P.W.B.
D61
a (12 - C)
C61
b (12 - C)
D62
(12 - C)
c
C62
(12 - D)
d
D63
(12 - D)
e
C63
(12 - E)
f
C1
D64
(12 - E)
g
C64
(12 - H)
h
C RC61
M52
C65
D4
D65
R 9
C66
RC62
C67
C6
R51
R52
4 1
R53
P151
3 2
C51
R54
M51
and C811
– 70 –
12V
5V
0V
—5V
C711 R62 R64
C712 R63
in the control power circuit.
I / F 35V
I / F GND