Hitachi RAS-18YH4 Service Manual page 42

2. Power circuit
This circuit is to convert the power from AC which is provided from the terminal A and B to DC voltage
And produces an AC current which does not exceed the harmonic amplitude limit of the IEC61000-3-2.
When the compressor is stopped, the AC voltage becomes about 300 V and while the compressor
operates, it is about 280 V.
Main parts
(1) DB2
The DB2 rectifies the AC voltage.
The possible causes for the DB2 failure are as follows. The 15 A fuse may be blown out or the IPM
for the main P.W.B. may have a failure. In such a case, check the 15 A fuse for blowout and replace
the main P.W.B. if necessary.
(2) DB3, L1, C023 and L2
The DB3, L1, C023 and L2 shape waveform of the input current.
When the current runs through the L1 is taken for I1 and the current runs through the L2 is taken for
I2 as shown in Fig. 2-2, I1 becomes an input current to the capacitor which peak value was crushed
by the L1 and I2 becomes a resonance current which causes the LC resonance using the L2 and
C023. By combining the I1 and I2, the input current from the main power shapes a waveform shown
in the right side of Fig. 2-3, indicating that the waveform is similar to sine wave. The more the
waveform is similar to the sine wave, the lower the harmonic current becomes.
If the C023 has any failure, the protection unit activates and the C023 in open mode. In such a case,
replace the failed parts.
DB3
C023
Fig. 2-2
Fig. 2-1
I
1
L1
I
1
I
2
L2
I
2
+
Fig. 2-3
– 45 –
I
S