Hitachi RAC-18WPB, Service Manual

Page: 73 / 148

Switching power circuit
Fig. 1-1
· An AC power supply from outdoor unit passes through the 3.15 A fuse, varistor (VA001), and noise filter circuit and rectified
and smoothed by DB1 and C003 to become a DC current 325 V. It is then supplied to indoor fan motor drive circuit,and
switching power circuit.
· The switching power circuit, as controlled by IC001, drives the primary winding of the transformer (T001) to produce a
specified voltage at the output winding. [The output terminal (pin ) of IC001 has a switching voltage. But it changes in
voltage peak and oscillation period depending on the power load. usually,the oscillation frequency when the air condition
operation is about 67 kHz. In the standby state, the oscillation frequency is lowered to a level as low as 20 kHz or so to
reduce the standby power.]
①
· The outputs of the output windings of the transformer is rectified and smoothed to become DC voltages at primary 18.5 V,
12 V, and 8.5 V respectively. The primary 18.5 V is supplied to the drive circuit of the indoor fan motor, the 12 V is supplied
to each vane motor and to the drive circuits of the cleaning unit driving motor and other equipment, and the 8.5 V is adjusted
to a stable 5 V by the 3-terminal regulator IC (IC101,IC103) and supplied to the microcomputer peripheral circuit.
If a failure in a part or circuit has produced an abnormal current in the power supply, the 3.15 A fuse will melt down to
prevent further damage. If the 3.15 A fuse melts down, check the indoor fan motor, switching electrical circuit, and other
components and replace any defective part.
If an abnormally high voltage is applied to the power supply, the 3.15 A fuse and varistor (VA001) will prevent further
damage. If a high voltage results in the 3.15A fuse melted down, the varistor (VA001) should have deteriorated and
destroyed. Therefore replace it at the same time.
The primary circuit of the transformer (T001) has a voltage to ground. Guard against electric shocks.
Check
Check
Caution
1. Control power circuit
DESCRIPTION OF MAIN CIRCUIT OPERATION
RAK-18PPB /25PPB /35PPB /50PPB
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