LED Emergency Light 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

PLEASE CONNECT A 10 OHM RESISTOR IN SERIES WITH THE LED CHAIN FOR SAFEGUARDING IT FROM HIGH BOOSTED VOLTAGE.

INCREASING THE VALUE OF R2 SHOULD INCREASE THE BRIGHTNESS OF THE LEDs AND VICE VERSA.

Need Help? Please send your queries through Comments for quick replies!




Comments

avijeet agrawal said…
Hello sir,
What is the value of t1 in above circuit.
Can i use a ring type core having internal dia about 14mm and extrnal dia about 21mm and wire used in sec winding of 0-12 750mA trafo
Swagatam said…
Hello Avijeet,

T1 = TIP122

I am not sure what would be the results with a torroid type core, but there's no harm in trying it.
Swagatam said…
measure the voltage across the inductor and divide it with 3.3, you'll get the answer.
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!
Swagatam said…
Dear Truong, yes you can do it, but the 7V input must be appropriately rated with amps, at least 1.5amps
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.

Thanks
Swagatam said…
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
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.
Swagatam said…
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.
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.
Swagatam said…
Hello Sherwin, it'll give 24V 5amp because the trafo is actually a 0-24V 5amp transformer, it just has a center tap attached
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.
Swagatam said…
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
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.
Swagatam said…
Thanks Sherwin,

you can try the circuit presented in the following article for getting a push pull response at the output:

https://homemade-circuits.com/2013/09/half-bridge-mosfet-driver-ic-irs21531d.html
can i use these ckt to charge a cellphone? 3.7v to 5v ?
Swagatam said…
yes can be tried...
Anirudh Kundu said…
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.

Thanks.
Swagatam said…
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.
Hii sir ur email is not working sir.
If you don't mind please Hi to my email:
k.ssrao.2015@gmail.com sir please sir
I have small douts regarding my led projects

please sir contact me sir....
Swagatam said…
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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