PA Board SOS Detection Circuits
Over-Voltage Detection of Main Voltage (10 Blinks)
Figure 39
The transistor Q5644 monitors the MAIN_3.3V, MAIN_5V, MAIN_9V, and MAIN_2.5V
lines. If any of these supply voltages becomes excessive, the inline zener diode goes
into conduction and turn on transistor Q5644. As a result, a voltage drop appears at the
base of Q5641, causing it to turn on and output a high to pin 111 of the MPU, IC4005, to
trigger the SOS condition.
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