Transistor Based LED Chasing Flashing Circuit

A Transistor Based LED Chasing Flashing Circuit is a simple and interesting project.

This circuit turns LEDs ON and OFF one by one, so it is called a chaser circuit.

Simple transistors are used instead of ICs which the beginners can understand it easily.

It is mainly used for learning and decoration.

The components are with low cost and easily available.

Circuit Working:

Parts List:

When power is given to the circuit the capacitor C1 starts charging through resistor R3.

At the same time transistor Q1 turns ON, because of this LED1 glows.

After some time C1 becomes fully charged and then the voltage at base of Q2 changes.

So transistor Q2 turns ON and LED2 glows.

At the same time Q1 turns OFF.

Next, capacitor C2 starts charging through resistor R5.

After a short delay transistor Q3 turns ON and LED3 glows.

At the same time LED2 turns OFF.

Now capacitor C3 discharges and gives signal back to Q1.

Therefore, the process repeats again and hence the LEDs glow one by one continuously.

Formulas with Calculation:

1. Formula for base resistor calculation:

Rb = (Vcc – Vbe) / Ib

Assume:

• Vcc is 9V
• Vbe is 0.7V
• Ib is 0.8mA

Rb = (9 – 0.7) / 0.0008
Rb = 8.3 / 0.0008
Rb = 10375 ohm

So 10k resistors are used.

2. LED current limiting resistor:

Rled = (Vcc – Vled) / Iled

Assume:

• Vled is 2V
• Iled is 15mA

Rled = (9 – 2) / 0.015
Rled = 7 / 0.015
Rled = 466 ohm

So 470 ohm resistors are used.

How to Build:

To build a Transistor Based LED Chasing Flashing Circuit following steps are required for connection steps:

• First, assemble all the parts as shown in the circuit diagram.
• Now transistor Q1 emitter goes to 9V battery negative.
• Then collector goes to LED1, R2 and C1 anode.
• Next, base goes to R1 and capacitor C3 cathode.
• After that transistor Q2 emitter goes to 9V battery negative.
• Then collector goes to LED2, R4 and C2 anode.
• Next, base goes to R3, VR1 and capacitor C1 cathode.
• Similarly transistor Q3 emitter goes to 9V battery negative.
• Then collector goes to LED3, R6 and C3 anode.
• Next, base goes to R5 and capacitor C2 cathode.
• And finally the battery positive goes to one end of resistor R1, VR1, R4 and R6.

Conclusion:

This Transistor Based LED Chasing Flashing Circuit is very useful for beginners.

It helps to understand transistor switching and RC timing clearly.

Also, no IC is used so the design is very simple and easy to build and test.

More LED stages can be added if needed.

So, this circuit is good for learning and decoration use.

References:

Explanation of blinking circuit with transistors