3 Volt LED Flasher Light Circuit using Transistors

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An LED flasher circuit is a circuit that flashes the LED i.e. turns it ON-OFF. In this tutorial, we will demonstrate how to make a LED Flasher Circuit with a cheap, easy, and economical design. All the parts of the circuit are available on market or you can make it from the junk box.

This circuit blinks a white LED. The circuit usually operates on 3 volts and consumes only 1.8mA during operation. This low consumption of current causes the battery to survive longer.

BC 557 is a PNP bipolar junction transistor made up of a TO-92 small package while BC547 is an NPN Bipolar junction transistor and is commonly used to amplify current. Both BC 557 and BC 547 transistors are general-purpose transistors, which can be used as switches or amplifiers in electronic circuits. A combination of BC 557, a silicon low power PNP transistor, and BC 547, a bipolar junction NPN transistor is used in this project for switching purposes.

Hardware Components

S.no	Components	Value	Qty
1.	Silicon low power PNP transistor	BC 557	1
2.	Bipolar junction NPN transistor	BC 547	1
3.	Electrolytic capacitor	10 µF	1
4.	Electrolytic capacitor	100 µF	1
5.	Nonpolar capacitor	10 nF	1
6.	Resistor	100kΩ, 10kΩ, 1kΩ, 47Ω	1,1,1,1
7.	LED	White	1
8.	Battery (AA, AAA, or button cell)	3 Volt	1

Circuit Diagram

Circuit Operation

The above circuit uses a combination of BC 557 and BC 547 transistors in such a way that BC 547 NPN transistor conducts for a very brief time making the LED light. The combination of resistors and capacitors determines the timing of the flasher, and the time duration is proportional to ‘R x C’. Capacitors charges through the resistors. When the capacitors have sufficient charge, it discharges through the emitter junction of BC 557 transistor thus conducts it thereby powering the white LED.

The positive voltage at the base junction of the BC547 NPN transistor will cause it to saturate while BC 557 PNP transistor requires a negative or zero voltage at the base to saturate. The use of low power LED with a series of resistors causes the circuit to consume very little power thus the battery lasts for many weeks.