Alarm Signal Sending Circuit - Panasonic KX-NS500AG Service Manual

4.10. Alarm Signal Sending Circuit

This section describes the operation of the circuit that sends the AC alarm/DC alarm signal
1) Alarm Circuit Power Supply
This power supply consists mainly of Q301, D301. The output of the main converter (described in section 2) drops from 41V to
around 26V for a more stable supply.
2) AC alarm signal sending circuit
When the AC Detection Circuit (described in section 1 (5)) detects AC input as "Yes", the Secondary side transistor of PC80
turns ON. This action turns Q312 ON and then a LOW signal is sent to AC alarm output.
However, if the AC input is detected as "No", the Secondary side transistor of PC80 turns OFF. This action turns Q312 OFF and
then AC alarm sending output becomes OPEN. (Open collector output)
3) DC Alarm Signal Sending Circuit
When 41V is output normally, transistors Q303 and Q304 in the output voltage detection circuit turn ON. Q302 also turns on and
then DC alarm sending output becomes LOW.
When 41V output becomes abnormal, transistors Q303 and Q304 turn OFF, Q302 turns OFF and DC alarm sending output
becomes OPEN. (Open collector output)
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KX-NS500AG