Hitachi RAC-18SX8 Service Manual page 129

3. Drive circuit of the indoor fan motor
Primary 18.5 V
3
Power signal of indoor fan
(from pin %8 of microcomputer)
Rotation speed feedback signal (to pin ^8 of microcomputer)
Output signal of indoor fan (to pin $5 of microcomputer)
< Typical circuit waveform >
Voltage at pin $5 of microcomputer (between 0 V and pin $5 )
When slow (700min -
1.7ms.
5V
・ The indoor fan motor receives VDC (motor drive power supply), VCC (power supply for the control circuit inside the motor),
and VS (speed command voltage) from CN2. The indoor fan motor returns an FG signal of a frequency that matches the
rotation speed.
・ VCC stabilizes the primary 18.5 V power supply into 15 V by using Q201 and supplies it.
・ While on standby for a remote control signal, the Q201 shuts down the VCC and reduces the standby power.
・ The VS receives a command voltage from the microcomputer (IC601). The VS terminal undergoes an analog voltage that
matches the Lo level time ratio of the pulse signal from pin $5 of the microcomputer. (See Fig. 3-2.)
・ The FG terminal undergoes a signal of 12 pulses per revolution of the motor shaft. By counting the pulse rate, the
microcomputer (IC601) recognizes the motor speed, thereby performing feedback control.
Caution
The indoor fan motor and drive circuit are connected to the primary power supply. They therefore have voltage to ground.
Guard against electric shocks.
Caution
While the product is energized, do not under any circumstances detach or reattach a connector. Any such practice would
cause a high voltage to run, resulting in the indoor fan motor and board circuit being destroyed. (Check the discharge of
the C003 before detaching or reattaching the connectors.)
Q201
12V
D201
14
IC683
Primary 0 V
When fast (1200min -
1 1
) )
1.7ms.
15V
5V
(DC311V-325V)
5V
R201
5V
+
−
R233
0V 0V
Fig. 3-1
FG voltage of fan motor (between pins ④ and ⑦ of CN2)
When slow (700min -
When fast (1200min -
1 )
7.1ms.
4.2ms.
15V
Fig. 3-2
– 162 –
CN2
VDC
1
C208
GND
4
VCC
5
C203
VS
6
FG
7
Indoor fan motor
+
−
Relationship between the VS voltage of fan motor
(between pins ④ and ⑥ of CN2) and its rotation
speed (a guide)
1
)
1300min -
1
2.1V
M
5.4V