Hitachi RAM-90QH5, Service Manual, Page: 53 / 83

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4. Power Supply Circuit
●
Fig. 4-1 shows the power circuit.
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There are two switching power supply in Power PWB.
●
Switching power supply 1 is generating the secondary power for control circuits and DC35V for indoor
unit no. 5.
●
Switching power supply 2 is generating the DC12V for expansion valve and DC35V for indoor unit 1 and 2.
●
Switching power supply 3 is generating the DC12V for expansion valve and DC35V for indoor unit 3 and 4.
●
Switching power supply performs voltage conversion effectively by switching transistor IC1 to convert DC330V
to high frequency of approximately 20kHz to 200kHz.
●
Transistor IC1 operates as follows:
(1) Shifting from OFF to ON
●
DC about 330V is applied from smoothing capacitors C020 + and – in the control power circuit. With
this power, current flows to pin
7
of IC1 and IC1 starts to turn ON. Since voltage in the direction of arrow
generates at point c at the same time, current passing through R705 and D702 is positive-fed back to IC1.
Fig. 4-1 Power circuit for P.W.B.
3A
FUSE
C790
C705
C776
C734
FB3
R771
R770
R772
C767
C766
D733
C768
D732
C771
R790
R720 C774 C775
C780
R778
R777
R773
D730
C769
R775
C776
D731
R774 ( 6
C770
D735
C773
L702
— B
— B
— B
— B
C777
R779
D736
3
IC3
— A
— A
— A
— A