Led blinker circuit using transistor

 LED Blinker or LED flashing circuit is most basic circuit to understand switching of transistor in cut off and saturation region. In this article we will discuss about the circuit, it's components and it's working.

Components Required:- 

1. One npn transistor (bc547)

2. One pnp transistor (2n3906)

3. Resistors 1 MΩ, 1kΩ, 22 Ω, all of 1/4 watt

4. Electrolytic Capacitor 2.2 μF, 25 Volt

5. 9 Volt Battery 

6. Bread Board 

7. Connection wires

Circuit Diagram:- 

Fig. 1 LED Blinker circuit using transistors

In this circuit bc547 transistor switching is done using a 2n3906 transistor and capacitor. When bc547 transistor acts in saturation mode LED starts glowing and when bc547  transistor acts in cut off mode LED does not glow.

Working :- When 9 V supply is given to the circuit upper pn diode of 2n3906 i.e. pnp transistor conducts and charges 2.2 μF capacitor. Once the capacitor get fully charged it discharges through 1 MΩ resistor which provides base current to 2n3906 transistor and transistor starts conducting. As shown in fig1. Collector of 2n3906 is connected to base of bc547 transistor which drive this transistor into saturation mode and collector current passes through transistor to emitter and LED starts glowing.

When capacitor get fully discharged base current of 2n3907 transistor becomes to small to drive it. 

Bread Board circuit:- 

Fig.2 Bread Board Connection 

Application:- This circuit can be used in two colour (Red/Green) torch for giving signals in railways, for decoration, in toys, security purpose and also as indicator.

Author:- Amarjeet Singh Jamwal authored articles on Basic Electronics Engineering, Electric Traction, and Electronics Practical for INFO4EEE Website