Hitachi RAM-60QH4 Manuel De Service page 112

13. Outdoor DC fan motor control circuit
Microcomputer
AX-6M00
16
Fan lock
Fan chopper
75
• In the same way as compressor control, speed of outdoor DC fan motor is controlled by switching supplied current
according to rotation position of fan motor magnet pole rotor: The switching order is shown in Fig. 13-2.
Upper arm
transistor
Lower arm
transistor
• Lower arm transistor is modulated by chopper signal of about 20kHz.
• Fig. 13-2 shows switching period of time T, and relationship with fan rotation speed is shown by the following formula:
N = (60/4) × (1/T)
• Fig. 13-2 shows voltage waveform at point A (U phase). (V and W phases are the same) Voltage waveform of each
phase can be observed at anode terminal of D904-D906.
Voltage at
◯
point A
300-330V
0V
5V
R242
R279
＋
V
−
U
＋
U transistor ON
DC300-330V
Drive
circuit
12V
Chopper
circuit
5V
0V
-5V
Duty command
circuit
4-bit microcomputer
＋
−
C901
Fig. 13-1
＋ ＋
W U
−
V
T
Fig. 13-2
＋
U transistor chopper
T
Fig. 13-3
– 124 –
I N V
FAN-HIC
Triangular wave
generation circuit
Current limiter
circuit
Over-current
limiter circuit
Filter
Position detection
circuit
circuit
＋
V
−
−
U
W
Chopper period (about 50μs)
A
DC motor
1
3
5
CN24
VH-3P
Time