Single Transistor LED Flasher Circuit

It is possibly the smallest 12 V LED flasher to date, which is able to flash an LED ON/OFF infinitely using a single transistor, a resistor, and a capacitor.

Can you imagine making a great looking LED flasher or blinker with just a single transistor and a couple of other passive parts? That's exactly what we learn in this post! This is perhaps the world's simplest and the tiniest LED flasher you can get!

How it Works

I came across this phenomena some eight years ago (2006), accidentally, while trying to make a smallest possible motorcycle side indicator flasher, and was surprised the phenomenon.

However, then I realized that the phenomenon was already discovered by Mr. Dick Cappels while investigating the negative resistance theory in BJTs by the Japanese researcher Mr. Reona Esaki (Aka Leo). Reona Esaki's thesis work in the relevant field and on tunnel diodes ultimately won him the Nobel Prize in 1972.

That looks too good to be true, however the following diagram will simply prove that it's really possible to create a working LED flasher circuit using just one general purpose transistor as the main component.

Then I did have not any idea that it was happening due to the negative resistance characteristics of the transistor.

The circuit actually exploits the negative resistance factor in transistors to produce the blinking effect.

I'll be soon writing a comprehensive article on this and we'll see there how the concept can be modified in many different ways.

Parts List for the proposed single transistor LED flasher circuit

• R1 = 2K7,
• R2 = 100 Ohms,
• T1 = BC 547,
• C1 = 100 uF to 470 uF
• LED = Any Type, any color

The flashing rate could be varied either by changing the value of R1 or C1 or both together. But the supply voltage not be less than 9V otherwise the circuit might fail to work correctly.

You may also love to read this article: Blinking LED Circuit using LDR

Circuit Diagram

Connecting an External Transistor for Higher Loads

Video Clip:

PCB Design