Friday 11 April 2014


This circuit is simple and easy to build & has only a few discrete components.
This indicates the 12V battery safe operating voltage.

Diode D1 protects the circuit when the battery polarity is reversed.
The LED glows with full brightness when the battery voltage is above the set threshold.

The threshold is set with the zener diode D2. for this circuit the threshold will
 Vds+VBEq1 ~= 11.5V

When the Battery voltage is above 10.8V the LED glows with very little brightness & increases with increase in battery voltage.
When it is above 11.5V the LED glows with full brightness.

The resistance R1 limts the current flow through the LED, R2 limits base current.
The current consumption is very less. Approx 10mA for battery voltage above 13V & very lesser current consumption (in few uA) when battery voltage drops below 10.5V.


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