Over Voltage Protection _ Ac Shutdown Latch Circuit - Panasonic TC-26LX20 Technical Manual

Over Voltage Protection _ AC Shutdown Latch Circuit

This protection circuit is responsible for forcing the AC _On voltage to a low if any of
these protected voltages mentioned in the next paragraph become excessive. The AC
_On voltage is used to activate the relay RL7001, which is used to power up the unit.
AC Shutdown Latch Circuit
Figure 17
T ransistor Q822 monitors the Sub_+3.3V, Sub_9V, Main_11.2V, DVD_5.9V, and
DVD_1.8V; Drive 12V, Sub_5V, and Sub_9V lines. If any of these supply lines incr ease
in voltage, transistor Q822 goes into conduction causing its collector to go low. As a
result, Q823 conducts causing the AC _On voltage to drop. Transistor Q822 and Q82 3
form a latch that keeps the unit from being turned back on until it is unplugged from the
AC outlet and plugged in again.
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