Description Of Main Circuit Operation - Hitachi RAC-70YH7 Service Manual

DESCRIPTION OF MAIN CIRCUIT OPERATION

RAS-70YH7
1. Reset Circuit
12V
0V
12V
7V
5V
Micro computer
Pin 7
5V
The reset circuit is used to reset the program to its initial settings when the power is turned on or when the
G
power is recovered after a power failure.
The micro computer is reset when the reset input is "Hi", and operation is possible when the reset input is
G
"Lo".
The waveforms at each point when the power is turned on and off are shown in the diagrams.
G
When the power is turned on, the voltages of the DC 12V line and DC 5V lines are increased. When the
G
voltage of DC 12V lines reaches about 7V, ZD202 is turned ON, the potential of Q201's base rises and Q202
is turned ON. Since Q202's collector is set to "LO" at this time, Q202 is turned OFF and the reset input of
the micro computer is set to "Lo". The DC 5V line voltage has already become 5V at this time and the micro
computer starts operation.
When the power is turned OFF, the voltage of the DC 12V line decreases. When it becomes about 7V, ZD202
G
is turned OFF, then Q201 is turned OFF, Q202 is turned ON the reset input of the micro computer is set to
"Hi' and the micro computer is set to the reset mode.
5V
Q202
Q201
POWER ON
C202
0V
DC12V Line
DC5V Line
Base
– 61 –
Micro computer
AX-7X30
7 RES
POWER OFF