One LED Low Voltage Flasher Circuit using IC LM3909

Low voltage indication is very important, especially for battery operated circuits.

Because battery can discharge anytime and so a simple indicator is required.

Therefore, this One LED Low Voltage Flasher Circuit using IC LM3909 is designed.

It uses only one LED and also uses minimum components and moreover, it works on very low voltage.

Hence, this circuit is useful for small projects and is useful for beginners also.

Circuit Working:

Components	Value	Quantity
Resistors (All resistors are 1/4 watt)	22k	1
	47Ω, 1.5k	2 each
Capacitors	Electrolytic 470μF 25V	1
	Ceramic 0.01μF	1
	Any standard LED	1
	IC LM3909	1
	ON/OFF switch	1
	Battery 3V DC	1

This circuit is based on IC LM3909 and it is a low voltage LED flasher IC which works from 1.5V to 5V.

First, battery supplies 3V power and then the power reaches LM3909 IC.

Pin 5 gets positive supply and pin 4 is connected to ground.

Now, capacitor C2 starts charging and it charges through resistor R3 and R2.

After that capacitor discharges and this discharge happens through internal IC circuit.

As a result the LED turns ON and then this LED turns OFF again.

Thus, flashing action is created and meanwhile resistor R4 limits LED current, so LED remains safe.

Switch S1 is used and it turns circuit ON or OFF.

Therefore, LED flashes continuously and it continues as long as battery is connected.

LED current formula with calculation:

LED current = (Supply voltage − LED forward voltage) / Series resistor

Battery voltage = 3V

LED forward voltage = 2V (approx)

Series resistor R4 = 47 ohm

LED current = (Battery voltage – LED voltage) / R4

LED current = (3 – 2) / 47
LED current = 1 / 47
LED current = 0.021 A
LED current = 21 mA

So LED is safe.

To build a One LED Low Voltage Flasher Circuit using IC LM3909 follow the below steps for connection:

Start, the circuit by collecting all the circuit parts:
Then start with IC pin 2 which is connected to R2 and timing network capacitor C2 cathode.
Pin 4 of IC is connected to ground pin of battery negative.
Pin 5 of IC is connected to positive supply pin.
Pin 8 of IC is the feedback pin and is connected to one end of switch S1.
Connect other end of Switch S1 to one end of resistor R1 and C1 which are in parralel.
Connect resistor R4 and LED at positive supply between pin 2 and pin 5 of IC .
Finally, connect resistor R5 between pin 5 of IC and battery positive and negative of battery connect to GND.

To conclude, this One LED Low Voltage Flasher Circuit using IC LM3909 is a very simple and easy design to build.

It uses very few components and it also works at low voltage.

Therefore, it is best for beginners and it is also useful for battery monitoring.

Finally, one LED flashing gives clear warning, so user can replace battery on time.