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Single Transistor LED Flasher Circuit

Single Transistor LED Flasher Circuit

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Can you imagine of making a formidable little LED flasher or blinker using just a single transistor and a couple of other passive parts.

How it Works

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

I came across this phenomena some eight years ago, accidentally, while trying to make a smallest possible motorcycle side indicator flasher, and was really amazed.

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.

Circuit Diagram

LED flasher circuit using single transistor

Connecting an External Transistor for Higher Loads

Video Clip:

PCB Design

single transistor flasher PCB design
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About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!



51 thoughts on “Single Transistor LED Flasher Circuit”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!

  2. Hi sir,

    1)In above circuit,can the blinker time be adjusted.(like “ON” for 1sec and “OFF” for 1 sec.).
    And instead of led,how can i connect transistor which can act as a switch.(the transistor switch will be “ON” for 1sec and “OFF” for 1sec.)

    2)The circuit diagram is shown in the link below
    https://drive.google.com/file/d/10bVfTV6iDspl3Ma76lMcr33gFKMPpgy8/view?usp=sharing

    how to adjust the blinker time ((like “ON” for 1sec and “OFF” for 1 sec.).
    And instead of led,how can i connect transistor which can act as a switch.(the transistor switch will be “ON” for 1sec and “OFF” for 1sec.)

    Thank you

  4. I have a switch with implemented LED which is extra connected to minus. Is it somhow possible to get the LED flashing while switched on? I had to connect this circuit somehow after the LED on the negative pol.

  6. Ha! If I did not see the video i would not have believed it.
    Does not work in simulator.
    http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+12.050203812241895+53+5+50R+656+160+656+80+0+0+40+12+0+0+0.5g+656+464+656+528+0r+656+160+656+256+0+2700r+656+464+576+464+0+100162+576+352+576+464+1+2.1024259+1+0+0+0.01t+384+336+576+336+1+1+0.00012985325697745242+-0.30249585765328524+500w+576+320+576+272+0w+576+272+656+256+0209+656+256+656+464+0+0.00033299999999999996+0.8571050617707789+1o+4+64+0+4099+0.625+0.00009765625+0+2+4+3

      • Considering simulators like LTspice can easily simulate op-amp and power supply circuits, it should easily be able to simulate your circuit, but try as I might, I too cannot get it to simulate.

        BC547 A, B or C ?
        LED: which one did you end up using (what breakdown voltage, forward current, partnumber…)

        • When only BC547 is written it means any BC547 can be used since the supply voltage is only 12V, in the video you can see that the LED is a 5mm 20mA type.

          A simulator may have difficulty in simulating because the circuit works with unconventional principles.

  8. Hi Swagatam,

    I have seen it’s possible to make this LED stop blinking by disconnecting the capacitor. Is it possible to disconnect / reconnect the capacitor by means of an additional transistor on the cap side of the circuit? I would like the LED to be on then when the second transistor gets signal the cap is connected and flashing starts. I’ve achieved this with relays but as I will have many of these in my circuit the cost of relays isn’t a good choice.
    Thanks for an excellent website!

    • Thank you Theuns, yes that may be possible, but instead of modifying the C1 section, I would recommended you to configure the ground supply line of the above circuit with an NPN such that when the NPN is triggered the circuit gets activated. For this you may connect the collector of the NPN with the ground line of the circuit,and the emitter with the supply negative.

  10. Thank you for your response sir.. How can i accomplished that? Can you please show me a circuit diagram with BJT circuit that i can follow sir..
    Thanks again sir..

    • Paul, I’ll explain you verbally:

      In the above circuit, remove the LED and join R2 directly with collector of T1, but make R2 = 1K

      now take a TIP127 BJT, connect its base directly with the above junction of R2 and T1 collector, join its emitter with the +12V line…and connect the collector with the bulb…bulb other end will go to the ground line…I hope you understood.

  12. Sir Swagatam,

    Can I use this circuit as replacement for my turn signal flasher on my motorcycle? or is there another circuit you can refer to me..
    As a 12v signal flasher for 12v led light.

    Thank you very much..
    Paul

  18. Hi Mr swagatam,
    Can you guide me to make an automatic switching for my led emergency light using Transistors? I have connected 50 no's of led and planned for 6V/4.5 Ah battery.pl explain with circuit diagram.

    • Hi Siddarth, sorry no I could not complete it due to lack of time and other more complex assignments…you can Google "Esaki single transistor flasher circuit" to learn more about it.

  26. Hey buddy,i have installed 12v3led strip in my bike and i need them to blink.i knw i can use this circuit but what all i need to alter?to adjust speed and to power led 12v..

    • In the circuit, the capacitor is charged by R1 until the voltage becomes large enough to get the emitter-base junction to avalanche which lights up the LED and also discharges the capacitor to trigger a fresh cycle….it basically takes place due to the negative resistance characteristic of the BJT

  30. Hi,

    thanks for your prompt response.
    Could you Just modify the circuit for this specifications LED Flasher Circuit with Input : 9V-16V, On time : 0.5s +/- 10%, Period : 1s +/- 10%, Reverse polarity protection required, by using any other stage of RC or any other way. Using astable multivibrators is cost effective for my project, need a simple circuit. Hope for your response.

    Thanks in advance

    • the above circuit is not configured in a conventional manner so could have limitations in terms of interval setting accuracy…you can try it out, though.

  34. I want to design a LED Flasher Cirrcuit with Input : 9V-16V, On time : 0.5s +/- 10%, Period : 1s +/- 10%, Reverse polarity protection : required can you help me with the above circuit? Will it work for this conditions?
    need your response
    thank you

    • the above circuit won't be appropriate, search for:

      transistor astable multivibrator circuit …..or 555 astable multivibrator circuit

  40. I am trying to imitate cloud to cloud lightning using the smallest possible circuit. I found this project that uses only the flashing LEDs and a battery (Candle Flicker Hair Bow). I found 3mm flashing LEDs (3-3.4V, 20mA, 1 Hz flash frequency)
    Can I power 2-3 of these (amber and/or white) using one CR2032 battery? Can I get them to flash at different rates? …I think that may drain the battery too quickly since there are no resisitors used, is that correct?

    • you can include a 22 ohm resistor in series with the LEd in order to make the battery drain slower.
      alternatively you can employ a joule thief circuit for making the batt last for ages.

    • a flashing LEd could have an automatic flash rate changer built-in, so it could go on changing the flash rate by itself.

  42. I am trying to imitate cloud to cloud lightning using the smallest possible circuit. I found this project that uses only the flashing LEDs and a battery…www.youtube.com/watch?v=Rj5tqhGypAE&feature=player_embedded. I found 3mm flashing LEDs …lighthouseleds.com/led-component-lighting/animated-leds-flashing-blinking/3mm-led-flashing-round-top.html
    Can I power 2-3 of these (amber and/or white) using one CR2032 battery? Can I get them to flash at different rates? …I think that may drain the battery too quickly since there are no resisitors used, is that correct?

  50. i used all the components shown and it didn't work the first time. it works now because i changed out the transistor until the led started blinking

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