Main Circuit Operation Description; Reset Circuit - Hitachi RAF-25NH4 Service Manual

ESCRIPTION OF MAIN CIRCUIT OPERATION
MODEL RAD-25QH4, RAD-40QH4

1.Reset Circuit

ZD201
Voltage
35V
27V
5V
Power is ON
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 poewr is ON and OFF.
¥ When power is supplied, the voltages on the 35V and 5V DC lines rise, and when the 35V DC line
becomes approx. 27V, 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. 27V, ZD201 turns off,
Q201 and Q202 turn off, and the reset input of the micro computer goes "Lo" to reset it.
5V
35V
0V
Q202
Normal:Hi
Reset :Lo
RES
10
Micro computer
Fig.1-1
35V DC Line
5V DC Line
Base of Q201
Power is OFF
Collector of Q202
Fig.1-2
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