Description Of Main Circuit Operation; Reset Circuit - Hitachi RAS-25CNH1 Service Manual

DESCRIPTION OF MAIN CIRCUIT OPERATION

Model RAS-25CNH11

1. Reset Circuit

ZD201
Voltage
35V
24V
5V
5V
The reset circuit initializes the program when power is supplied or power is restored following a power failure.
RESET "Lo" or SET "Hi" activates the micro computer.
Fig. 1-2 shows the waveforms in each circuit when power is ON and OFF.
When the power is supplied, the voltages on the 35V and 5V DC lines rise, and when the 35V DC line becomes approx.
24V, ZD201 turns on and the voltage at the base of Q201 rises to turn Q201 on. Since the collector of Q201 goes "Lo"
at this time, Q202 turns on and the reset input of the micro computer goes "Hi". The 5V DC line has already been 5V
at this time and the micro computer starts operation.
When power is OFF, the voltage on the 35V DC line drops, and when it is approx. 24V, ZD201 turns off, Q201 and Q202
turn off, and the reset input of the micro computer goes "Lo" to reset it.
35V 5V 5V 12V
+
–
0V
Power is ON
5V
Q202
NORMAL HI
RESET LO
17
RES
MICRO
COMPUTER
Fig. 1-1
35V DC line
5V DC line
Base of Q201
Power is OFF
Collector of Q202
Fig. 1-2
– 55 –