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Detect low battery and light an LED

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MikeMl

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bestcallumuk

New Member
Sorry for my ignorance but could you please make a diagram on how I could make this work with resistor types (if needed) and how to wire up the voltage low battery thing. As I said sorry.
 

electronspeed

New Member
First you need to decide what should be the voltage V, to be called for low battery.Then use a transistor in voltage divider bias with a zener diode of breakdown voltage V connected in reverse bias between base voltage divider resistors.Your Vcc should be such that initial voltage between zener should be greater than V.Use your battery as source for Vcc & cascade it with an inverter containing led at load side.You can use transistor as switch for making an inverter.
 

MikeMl

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This circuit will light the LED when the battery voltage is below ~8V (1V per cell for an Alkaline is quite dead). It draws ~1mA before it turns on; then about 7mA after it turns on, with most of that going to the LED. If your battery-powered device has an On/Off switch, wire this circuit on the load-side of the switch, so when the switch is Off, this device is too.

ps: LM431 is a substitute for a TL431.
 

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