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Single Transistor LED Flasher

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.

However, 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

Circuit Diagram


single transistor LED flasher circuit



Video Clip:





PCB Design


pcb design for single transistor flasher


Need Help? Please leave a comment, I'll get back soon with a reply!




Comments

  1. 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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  2. you can try this one:

    https://homemade-circuits.com/2011/12/make-yourself-simple-led-flasher-at.html

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  3. What are the formulas to calculate the timing of the flash?

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  4. t = -log((V-Vc)/V)R*C

    To calculate Vc at a specific time, the formula can be modified to:

    Vc = V-(V*exp(-t/(R*C)))

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  5. 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?

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  6. 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?

    ReplyDelete
  7. 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.

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

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  9. hi my name is madhu i want electronic variable wattage choke circuit diagram for flurocent tube. pls send to the mail below
    email: madhubabu.sv@gmail.com

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  10. sorry, presently I do not have this circuit.

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  11. HI
    will this circuit work for 16v?

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  12. 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

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

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

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  14. Can you tell me in technical prospectivem, why cant we use this circuit??

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  15. 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.

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  16. 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

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  17. It will need to be tweaked and verified practically for those results....there are no formulas for it.

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  18. Hi, can you please tell me how the transistor is activated without the base connected?

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  19. 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

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  20. 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..

    ReplyDelete
  21. Mukesh you cannot use the above circuit, instead you can try any of the following designs:

    https://homemade-circuits.com/2012/01/how-to-make-any-light-strobe-light.html

    ReplyDelete
  22. Hi Swagatam, were you able to write the comprehensive article explaining how this works?

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  23. 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.

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  24. Nice bro I am satisfied with this ckt. Can you please help me to blink some more faster

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  25. thanks bro, just decrease the value of C1 to make it blink faster

    ReplyDelete
  26. 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.

    ReplyDelete
  27. Hi Mohan, you can refer to the following circuit and do it accordingly for getting the required results:

    https://homemade-circuits.com/2011/12/how-to-make-efficient-led-emergency.html

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  28. how to test transistor emitter Base collector

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  29. Hi, how could I make this circuit flash twice every second like a police or ambulance vehicle?

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  30. 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

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  31. Paul,

    it may be possible, but you will have to add an additional BJT buffer stage for powering the lamps.

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  32. 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..

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  33. 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.

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  34. 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!

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  35. 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.

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  36. Ha! If I did not see the video i would not have believed it.
    Does not work in simulator.
    www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+12.050203812241895+53+5+50%0AR+656+160+656+80+0+0+40+12+0+0+0.5%0Ag+656+464+656+528+0%0Ar+656+160+656+256+0+2700%0Ar+656+464+576+464+0+100%0A162+576+352+576+464+1+2.1024259+1+0+0+0.01%0At+384+336+576+336+1+1+0.00012985325697745242+-0.30249585765328524+500%0Aw+576+320+576+272+0%0Aw+576+272+656+256+0%0A209+656+256+656+464+0+0.00033299999999999996+0.8571050617707789+1%0Ao+4+64+0+4099+0.625+0.00009765625+0+2+4+3%0A

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  37. that's exactly why I never rely or use simulator softwares, they are no match for an human brain.

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  38. 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...)

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  39. 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.

    ReplyDelete

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