LED Emergency Light Circuit Using Boost Converter

The following emergency light circuit uses a very common voltage boost converter concept for making a group of white LEDs illuminate at relatively lower power supplies.

Let's learn how to make this interesting and useful little LED boost emergency light circuit.

Yet again we take the help of the evergreen work horse, the IC555 for implementing the proposed actions.

boost converter circuit using IC 555

Using IC 555 as the Main Component

The figure shows a very simple circuit configuration where the IC 555 has been rigged as an astable multivibrator.

In an astable multivibrator design the various components are wired such that the output generates trains of pulses which are self sustaining and keeps coming as long as the circuit remains powered.

In the present configuration the output of the IC which is the pin #3 generates pulses at a frequency determined by the resistors R1 and R2 and also the capacitor C2.

R2 may be typically adjusted or made variable type for enabling dimming control of the LEDs.

However here the value of R2 has been fixed for acquiring optimum brightness from the LEDs.

The pulses available at pin#3 of the IC is used for ddriving the transistor T1 which in turn switches in response to the positive pulses.

The switching of the transistor pulls the supply voltage through the inductor in a pulsed mode.

As we know when alternating or pulsed voltage is applied across an inductor it tries to oppose the current and in the process kick an equivalent high voltage for compensating the applied current force.

This action of the inductor is what constitutes the boost action, where the voltage is stepped to higher levels than the actual supply voltage.

How L1 Functions

The above functioning of the inductor has been exploited in this circuit also.

L1 boosts the voltage in an attempt to restrict the applied AC, this high voltage generated across the coil during the non conducting phases of the transistor is fed across a series connected LEDs for illuminating them under lower current levels.

This process helps to illuminate the LEDs at relatively lower power consumption.

L1 winding is not so critical, it is a matter of little experimentation, the number of turns, wire guage, the diameter of the core, all are directly involved and affect the boost levels, therefore must be optimized carefully.

In the prototype I had used 50 turns of 22 SWG over an ordinary ferrite rod, which is normally used in small MW radio receivers.

The LEDs used by me were 1 watt, 350 mA types, however you may use different types if you want.


boost LED emergency light circuit using IC 555



Parts List

R1 = 100K
R2 = 100k pot,
R3 = 100 Ohms,
R4 = 4k7, 1 watt
C1 = 680pF,
C2 = 0.01uF
C3 = 100uF/100V
L1 = see text
IC = LM555
T1 = TIP122
D1 = BA159



62 thoughts on “LED Emergency Light Circuit Using Boost Converter

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Hi Swagatam, i've got problems with L1, its getting heated rather than boosting the voltage. Can I use inductor like 10uH or other value rather built it myself?


    • Hi Menanti,

      If the coil is heating up means your IC is not generating the oscillations at high frequencies.

      First check whether the IC is generating the required pulses at the base of T1.

      Connect a 1uF cap in series with R3, if the transistor stops conducting would mean the IC is not working.

    • Thanks, but i only can found elco 1uF, cap that has 1uF always in high voltage (i.e. 400v), which one should i use?


    • 2N3055 might not work, use TIP122 only because it's a Darlington transistor and has better gain than 2N3055.

      By the way for a single 1 watt LED you won't need this circuit, just connect it directly in place of the coil with a 22 Ohm series resistor.

    • L1 is a copper coil over a ferrite core.

      Connect the LEDs parallel to the coil as shown in the figure.

      Battery charger has not been provided here, you may refer any suitable charger circuit published in this blog.

  3. Hi Swagatam
    how many 5mm white leds colud be connected in series?
    further C1 and C2 are electrolytic or ceramics? please explain

    • First you'll have to measure the voltage across the coil without connecting any LEds, then divide it with 3.3, that will give you the number of LEDs which can be connected.

      C1/C2 are ceramic

  4. hi swagatam, its me again.
    I have li-po battery, 3.7v 4900mA. can I use it with this circuits?
    Is there any change? Please explain.


    • great, i'll make it on next weekend.
      which trickle charge i can use with it? So it can
      connected to the line all the time, and on when
      the line is down?
      Thanks a lot


    • how about the current? How many the current should we use it for trickle charging. I know in standard charging, it better use 1/10 of the capacity the battery, how about trickle charging?

      The second question is, how about if when trickle charging in process, the battery has full, should we use the cut off? Or its not necessary?

      THe last, how to made the simple cut off, i.e 3.7 v, 6v, or 12 v batteries?

      Thanks a lot Swagatam,

    • trickle charging involves very very low current just to stop the battery from discharging naturally. trickle charging does not need a cut off because the current is very small.

      for cut off you will have to use an opamp circuit, simple circuits won't give proper results.

    • Thanks a lot swagatam, i understood the basic concept of trickle charging now.

      Next, i have 350mA trafo, and i will use ic 7805 and one 1K resistor at the output, it is ok? (this trafo was the smallest current that I could find here).

      Hey i still don't understand yet about opamp circuit…may can you explain it? (If not disturbing you….he he…)

      Again, thanks a lot, your helping me a lot…
      God Bless you swagatam….happy new year…

  5. I want to construct 6 watt&10 watt cob led portable light ,whose configration is_vf-37.5, i-350 ma( for 6 watt) vf-19 to 21v' ,i-500 ma(for10watt),I would like to operate it by 12 volt battery ,kindly do the needful
    Regard' anand

  6. I have a couple of question concerning this circuit: Are the LEDs you used 1W 350ma are called high power LEDs like Cree type rather than regular LEDs, right? All your resistors are at 0.25w regular ones including the one that you asked to add a 10ohm to the leds series? I am having difficulty finding L1 materials (ferrite rod and wire you mentioned) though, could you please give me some suggestion. Is there anything readymade I can substitute for L1? Can a sealed lead acid battery 6v 4.5AH be used? Thanks for your response.

    • yes i had used 1 watt, 350 mA leds

      10 Ohm should be 1 watt rated.

      My L1 was built by winding 22 swg copper wire over an ordinary MW radio antenna coil ferrite rod, about 50 to 80 turns. you may need to experiment a bit.

      yes an smf battery can be used.

    • Thank you very much for your quick response. It seems to be hard to find a MW radio antenna here in the US. But I can purchase ferrite rod on ebay but I saw the only available sizes are 3x15mm or 4x20mm or 5x10mm or 8x30mm for Ham radio antenna chokes and they are a kind of expensive (plus the wire to wind around the rod needs to be purchase separately) for these types of experiment. That is why I was seeking for an alternative ready made inductor, if any. And lastly, how should I calculate how long the lights (6 to 8 in series) will run using a fully charged SLA 6V 4.5AH battery? Thank you, in advance, for your reply.

    • Could you please tell me the length of ferrite rod for 50 to 80 turns so that I purchase the right one because it is hard to find it here in the US. Thank you.

    • I won't recommend buying anything costly initially, try making the above circuit, and L1 using parts from your electronic junkyard, or you may ask your local TV, DvD technician to look for a suitable ferrite core…even a small T-25 torroidal core will also do.

    • you will have to experiment with different inductor configurations to get a voltage across it which may be around 3 times more than total number LEDs in series….this would illuminate the LEDs with optimum brightness.

    • I don't know the exact specs Swagatam used but you can calculate inductance (L) yourself. Since he used 50-80 turns of SWG22 wire (diameter 0.0253 in.), my guesstimate is something like 5.8-9.8 microhenries. Is this right, Swagatam?

    • Can't confirm the exact value.

      I don't keep the circuits intact with me…I have probably dismantled everything, and used the components for other circuit prototypes.

      As mentioned in the article, the coil parameter is not critical, and can be tweaked to get the best possible results by the user.

  7. Hi sir,
    Can you help me to connect 5*1w LED to a 3.6v mobile phone battery? I need to connect LED in parallel. Will it be okay if I connect them without a resistor? but they get hot very much in that case? help me pls.


  8. Dear Sir! With this circuit, I can supply about 7v, and I use 1 download moto 12v dc – 500ma. Sir Please comment on this, whether it was feasible? Because I want this application circuit for fan 12v emergency power failure. I'll have more integrated circuits and circuit switching charger. Thank you Sir!

  9. Hello sir,
    This is Sherwin.
    What is the output frequency of the 555 ic?
    What is the function of c2 in schematic?
    I have a 6v 4.5amp sla batt and is it OK to provide the full batt current directly to the 555 without using a resistor between positive rail and vcc?
    please help in such thoughts.

    Again, what is the minimum voltage and current required by 555 for it normal operation.


    • Hello Sherwin,

      frequency is 12khz
      C2 is required at pin5 for stability
      any voltage between 5 and 15 can be used directly across 555 IC
      minimum voltage is 4.5V and current 5mA

  10. Hi sir,
    since 555 outputs a square wave with the given circuit details,
    the output waveform at the inductors points will be square so my thought is that when i am to measure the voltage at the inductor points, setting the DMM to ac scale:
    1. can multimeter read square wave inputs to it properly and give a stable reading?
    2. can the peak output voltage from inductor damage the multimeter by any chance??
    Please help in such thoughts. I am going to build this project.

    • Hi Sherwin,

      Selecting the AC range may not be required here, because the output is a DC pulsating voltage, so you can use the DC range of the meter

      The reading on the meter will give 50% of the actual value since the waveform is in a pulsed form….to get the peak value just multiply the reading with 2.

      The peak voltage or current will not harm the meter since it won't be significantly out of range.

  11. Hello sir,
    Thanks for your kind replies till now.
    I have purchased a 12-0-12V 5A transformer and my query is that:
    1. Taking power from the 12v taps will give me 24v at 2.5a, am i right?
    Please help.

  12. Hello sir,
    i am to build a 555 switching power supply circuit.
    i have the following questions.
    I am to amplify the output from 555 using transistor and mosfet. I have made a rough diagram about the connection, i would describe it and please correct me if i am wrong.
    1. First to the transistor, output from 555 will go to base
    2. Emitter will go to GND since im using NPN transistor.
    3. Amplified output will be at collector.
    4. This amplified output will go to gate of mosfet.
    5. Source pin of mosfet will go to GND since i'm using N-channel mosfet.
    6. Finally better amplified output at Drain pin of mosfet.
    are these connections right?
    What about darlington transistor like TIP122 could i use this in place of ordinary transistor?
    Please help.

    • Hello Sherwin,

      using 2 devices will not double the voltage or current….the final output will be equal to the supply levels unless you are using a coil for boosting voltage.

      The mosfet can be directly connected with pin3 of 555, the extra NPN is not required……use a 22 ohm 1./4 watt resistor at the gate of the mosfet…. for a better response put a parallel 1n4148 diode across the 22 ohm….anode to gate, cathode to pin3 of 555

  13. Yes dear,
    Thanks for your kind info.
    I will be using the mosfet in my circuit, but one thing here i need a waveform changing its polarity from pos to neg and not pulsating DC because i want to pass output to ferrite transformer.

    Your circuit shown in this blog is real and correct circuit i've tried it. It works well. I had no problems of inductor heating as i engineered it very carefully just that TIP122 gets warm, NO doubts you are really great i really appreciate your work.
    but for now i want to pass the output to a ferrite transformer and prepare a switching power supply.
    Please guide me against any component changes
    Again, i trust your circuits since they are meaningful.

    Once again Thanks for your kind help till date. And keep up with the smart work.

  14. Hello sir,

    I was in the process of making the circuit with the method and guidance you gave but during the process i learnt that is circuit uses AC voltage at the end to light up the led's. Since am making it to be used as a video light, i may see the flicker that the camera captures. Maybe am wrong about the AC thing. Please correct me. Else guide me sir. Am tryin to light some 60+ led's from a usb power bank.


    • Hello Anirudh,

      The output is not AC, rather a pulsating DC…..but the presence of C3 will clean the ripples and will turn it to almost pure DC, you can try adding more number of 100uF/100V caps in parallel for getting more filtering, or may be a single 1000uF/100V will also do.

    • Hi Shanmuka, all my emails are working perfectly.

      However, you will expect best possible response from me if you interact with me here, through this commenting platform, because I normally don't find time to respond to emails.

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