Hitachi RAM-18QH5E, Руководство по обслуживанию

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4. Power Circuit for P.W.B.
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Fig. 4-1 shows the power circuit for P.W.B.
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In the power circuit for P.W.B., power voltage for microcomputer, peripheral circuits, and system power
module drive and, as well as DV35V, are produced by switching power circuit.
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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
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DC about 330V is applied from smoothing capacitors C020
Œ
and C021
œ
in the control power circuit.
With this power, current flows to pin
4
of IC1 via R701 and R702 and IC1 starts to tum ON. Since voltage
in the direction of arrow generates at pin @ of Switching Transforwer at the same time, current passing
through R708 and D702 is positive-fed back to IC1.
Fig. 4-1 Power circuit for P.W.B.