Hitachi RAS-80YH5A - Page 70

– 79 –
9. Reset Circuit
● Reset circuit performs initial setting of the microcomputer program when power is turned on.
● Microcomputer resets program with reset voltage set to Lo, to enable operation at Hi level.
● Fig. 9-1 shows the reset circuit, and Fig. 9-2 shows waveform at each point when power is turned on/
off.
● After power is turned on, 12V line and 5V line voltages rise: When 12V line voltage reaches 7.2V (Zener
voltage of ZD201), ZD201 turns ON and Q211 and Q205 turn on, and reset voltage becomes Hi. Reset
voltage is not set to Hi until VDD of microcomputer rises to 5V, enabling operation, due to ZD201.
● After power turns off, when 12V line voltage drops, ZD201 also turns OFF.
12V line
12V line
5V line
5V line
Reset voltage
Reset voltage
12
6
0
Voltage when power is turned ON
12
6
0
Voltage when power is turned OFF
Time
Time
Fig. 9-1
0V
0V 0V
C224
5V
Q212
C223 R368
R369 R367
R365
C351
R366
Q205
R345
48
12V
ZD201
Reset
(AX-6V01)
Outdoor
Microcomputer
Fig. 9-2