Published:2009/7/9 23:07:00 Author:May | From:SeekIC
Input terminal VIN is connected to the + V line of the circuit that the indicator is to monitor, and the grounds of both circuits are connected together. The position of potentiometer R1's wiper deter-mines Q1's base voltage. As long as the transistor gets enough bias voltage to remain on, the low voltage at the collector will keep the SCR from firing. As the battery voltage starts to fall, the transistor's base voltage will fall as well. When Q1 turns off VIN drops), the collector voltage increases. That voltage provides enough gate drive to turn on the SCR, which turns on the LED. The LED could also be a buzzer or almost any other type of waming device.
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