A simple LED torch circuit that would light up 3 white LEDs from a 6 volt supply and would make your battery last forever is described here.
A useful voltage doubler circuit is incorporated here to make a highly efficient circuit using just a handful of components.
Introduction
Learn more how to build it. White LEDs are quite renowned for producing dazzling lights at very low currents.
But, if they are not configured cleverly can in fact be pretty poor in the above respect. Learn the simple trick to optimize and make a highly efficient LED torch at home.
Illuminating 6 LEDs from a 3V Source
You may find it impossible illuminating 3 white LEDs fully, at 6 volts/20 mA without incorporating complex inductor assemblies.
Such a LED torch can be truly handy as the light output produced from it is reasonably high with battery lasting almost forever.
Moreover nothing could be as satisfying as building this beautiful circuit right in your home. We know that, LEDs in series always provide better results.
Simply because, just by increasing the required voltage appropriately, we are able to drive the whole series using the same amount of current as required for a single LED.
For example, if we consider a single white LED, it requires about 20 mA of current at 3.8 volts to illuminate brightly, so if we connect 3 such LEDs in parallel, would mean a current consumption of 60 mA – that’s huge, and would discharge a small battery pretty fast, within minutes.
However, if we connect the above LEDs in series and step up the voltage to about 10 volts, it would become possible to light them up using just 20 mA of current, making the whole circuit very efficient.
Using IC4049 Circuit as an Oscillator
Using the versatile IC 4049, which contains six inverter gates or NOT gates in one package, a very simple voltage stepper can be wired.
By configuring two of its gates as an oscillator, we find that 4 of its gates can be tied up in parallel to produce the required buffering to the oscillator output and step this buffered output to drive a single series of 3 LEDs.
To add up more such series you would just require increasing the number of gates (ICs) and using them as buffers for the relevant LED series.
One oscillator will be enough and may be used commonly to drive all these added buffers and the LED series.
Let’s track down the proposed circuit’s working principle.
How it Works
In the adjoining figure (click to enlarge) we see how simply a single IC 4049 and few other passive components are used to drive three white LEDs from a 6 volt source at just 20 mA current.
The present configuration ensures almost 100 % efficiency and thus a good battery life.
Gates N1 and N2 along with R1 and C1 are all wired up as an oscillator with a frequency determined by the values of R1 and C1.
The remaining gates N3, N4, N5 and N6 are all joined in parallel as buffers, i.e. their inputs are all linked together and connected to the frequency source from the oscillator.
Their outputs are also made into a single common outlet and terminated to the following voltage enhancer circuit.
The Voltage Multiplier Circuit
A standard configuration using two diodes and the same number of electrolytic capacitors are used to create a voltage multiplier circuit.
The above configuration will work only for alternating voltages and will double the received input.
The applied oscillating frequency from the buffers is successfully made almost twice by the above multiplier circuit.
Three high efficiency white LEDs in series are integrated at the output of the voltage multiplier circuit to complete the unit.
The LEDs receive the suitable voltage from the circuit and illuminate quite brightly.
Parts List
R1 = 68K,C1 = 680pF,
C2, C3 = 100 uF/ 25V,
D1, D2 =1N4148,
N1, N2, N3, N4 = IC 4049,
LEDs White = 3 nos.
GeneralPurpose PCB = As per size,
Ni-Cd Cells = 5 nos. 1.2 volts each (rechargeable)
Suitable Enclosure = Small plastic box to hold the circuit, batteries and the LEDs.
How to Assemble
Building the circuit of this LED torch is pretty easy, just procure all the components and solder them together with the help of the given circuit schematic.
Then it’s just a matter of connecting the battery pack to the circuit and checking its illumination.
If possible check the current consumption of the circuit using a milliammeter, should not be more than 15 to 20 mA.
Enclose the whole unit inside a suitable plastic box; make sure that the LEDs suitably protrude out of the box’s front surface.
You can use suitable reflectors to increase its light output. A fully charged battery pack should last for a very long time, almost more than five years even if used quite frequently.
PCB Layout
Craig says
Hi.
I’m going to give this circuit a run as I’m making some DIY lanterns for friends.
My issue is that i’m not sure if 3 LEDS are going to be bright enough. I was considering putting a second ‘leg” of 3 LEDs in parallel with the first string. I know doing this I should put an individual resistor on each parallel branch instead of just one leading into the LED part of the circuit. But looking at your circuit you a voltage balancing resistor doesn’t seem to be leading into the LED path. SO the question is how would adding a second branch of 3 LEDs in parallel change the circuit.
Swag says
Hi,
Actually the above circuit does not make sense, because we can simply connect the LEDs in parallel directly with the battery with individual series resistors. So Please remove the circuit and just connect the LEDs in parallel directly with the battery, with each LED having its own calculated series resistor. I had designed this circuit 10 years ago and perhaps I failed to understand this basic point then…
Craig says
Well it does make sense in that LEDs in parallel burn themselves out much easier and tend to cascade fail when they do as the multiple paths can create voltage/current differentials based on badly binned and dissimilar forward voltage-d LEDs and if you get one (even of the same color/batch) that is draws less voltage it’s going to hog enough current that it might cook itself and then each one down the line likely would as well without individual series resistors on each branch. Now having a resistor in series with each parallel LED (or LED grouping) would likely limit this or prevent it entirely but its more parts and just feels less elegant.
Series is a safe way to go if you can provide enough voltage.
My electrical engineering is 3 years of college about 25 years ago so it’s all pretty murky at this point and I tend to really double check things and in truth I don’t understand/recall the properties of most individual specialized items anymore… certainly not off the top of my head.
That all said my question is this. lets just look at this as a voltage boosting circuit. Does any part of it act as a voltage sink (which is what the in series resistor to an LED should/would do) to limit/take up the rest of the available voltage above what the LEDs forward voltage (~9.6 if the LEDs in your schematic above if they are white/blue) is in your series connection of them (and also limit milliamps to say 20)
Or
Is the full doubled voltage without any current limiting going through the branch of the circuit with the LEDs as things are shown. In which case I can “black box” the voltage booster away from whatever LED branches I want to run and figure out their series resistor based on whatever they are just knowing that at the beginning of that part of the circuit i’ve got 12 volts to account for.
In part I ask because i already picked up the components to tinker with this circuit and so I might as well play around with it… and also because I am trying to relearn and understand a few things and even if it turns out that I don’t need a voltage doubler (for the LED setup i’m trying to put together) I still want to understand whats going on up there… and I might end up using it for something else.
Swag says
Sorry, your assumption regarding LEDs doesn’t seem to be correct. Whether it is series or parallel both can be absolutely safe for LEDs, as long as the current is limited and distributed correctly. However the efficiency of the configuration can be optimized depending on the available supply voltage, for example we have 5V then adding parallel LEDs with separate resistors will be more appropriate, on the contrary suppose if we have 12 V as the source then a series connection will work better.
Now coming back to the above circuit, since you are interested to connect more branches in it, you can do it by adding separate resistors on each branch or string. The circuit originally does not include any current control mechanism in it, therefore you will have to add those series resistors separately with each of the strings to make the illumination uniform…however the circuit would be able to support current to a given nominal level beyond that the voltage may begin dropping drastically.
A much better alternative could be studied in the following article:
https://www.homemade-circuits.com/1-watt-led-driver-using-joule-thief/
Craig says
Thanks. Will go take a look.
Sidhesh dessai says
Hi sir I cannot see the circuit diagram in this page can u pls send me the pic of circuit diagram , and also circuit for 3 v , 1 watt led touch which will run on 4 volt 1.5 ah battery which run for 10 hours
Swag says
Hi Sidhesh, I have corrected the issue please check it now,
a 1 watt LED will not run for 10 hours from a 4V/1.5 AH battery, it may run for a maximum of 5 hours
Sidhesh dessai says
Thanks sir it’s visible now ,
Sidhesh dessai says
Even less led also do
Sidhesh dessai says
Hi sir Same circuit can u alter for 4 v 1.5 v battery , or any other circuit which run the led for whole night in my farm to make frightening wild animals ,
Swag says
Hi Sidhesh, your battery is 1.5 ah, due to possible inefficiencies we can assume it as a 1 ah battery, now if you multiply 4 x 1 gives 4 watt hour, that means for a 1 watt LED the back up cannot go beyond 4 hours, no matter what circuit you try?
if you connect a series resistor with the 1 watt LED such that its current consumption is reduced to 150mA then probably it may run for 10 hours.
Sidhesh dessai says
How to reduce to 150 ma
Swag says
add a 5 ohm, 1 watt resistor in series with your LED
Sidhesh dessai says
Ok sir but how do I do that
Ranganathan rangarajan says
Sir can I use 4 volt 500 milliamps battery for this circuit if not possible means kindly design me a led torch light circuit using the above mentioned battery. Thanks in advance.
Swagatam says
Ranganathan, 4V will produce 8V at the output which won't be sufficient for illuminating 3 LEDs, therefore cannot be used here.
Actually a circuit is not required at all, you can simply connect your LEDs in parallel with your 4V battery terminals….but make sure each of the LEDs has a resistor having a value, which can be calculated with the following formula
4 – 3.3 / LED current
Ranganathan rangarajan says
Sir can I use 20E 1/4 watts resistors
Swagatam says
You will have to solve the above mentioned formula for getting the right value….if it's as per the above formula then it should be correct
Unknown says
the circuit is wudwerful. how can the battery be recharged?
Swagatam says
thanks….through an external source
Kuntal Paul says
i want to make a head torch for…..outdoor treeking… so is it possible…..with this circuit
Swagatam says
yes it is possible!
Kuntal Paul says
sir can i connect 3x AAA batteries.. means 4.2 volt….
Swagatam says
Kuntal, yes you can use 3 AAA cells in series with the above circuit….the back time will depend on the battery charge level and overall condition, I cannot say it specifically.
alternatively you can try this software:
https://homemade-circuits.com/p/battery-calculator.html
Kuntal Paul says
sir, can i connect 3x AAA batteries..means 4.5 volt……then pls say the time of lightning is so longer.. or shorter because …. i want to build it for my outdoor camping……
eshkariel tapiador says
What's the Formula for the Frequency? tnx
Swagatam says
Not sure about the formula, could be as given in the following article:
https://en.wikipedia.org/wiki/RC_time_constant
eshkariel tapiador says
the only draw back is we can't go below 5v..for it's the supply required by the IC4049 :(…is that right?
Swagatam says
4049 can work from 3V to 15V, it's the 74XX version which has this limitation
eshkariel tapiador says
ohh!!. so it means I can use 2 x 1.5v battery cell??? 😀 🙂 ^_^
Swagatam says
it should be slightly over 3V, lower than 3V can cause malfunctioning
Anil Kumar. K says
Hi Swagatham, thanks for this great idea.
The CD4049UB and CD4050B devices are inverting and
non-inverting hex buffers, respectively.
I have one CD4050B, can I use this ic instead of 4049, after some modification in the circuit….if yes how…..?
Swagatam says
Hi Anil,
you can probably try the following with your IC.
remove the gate N3 and place it between pin4 of N2 and C1 top end…this should allow the circuit to function in the same way as with 4049 IC
Swagatam says
….and you might also need to put another gate in series with N1…so you can remove another gate N4 from the buffer stage and connect it in series with pin3 of N1
Yusnizam Yusop says
Thank sir…
Yusnizam Yusop says
Hello sir ..i want to put ldr to cntrol the led..where shoulf i put it…tq
Swagatam says
hello yusinizam, connect pin4 with the pin9 junction through a 10k resistor, and then connect the LDR across positive and pin9 rail
Arun Kumar says
What is illumination please tell me sir
Swagatam says
it's the the level of brightness
Arun Kumar says
Which types led used long battery Backup please tell me sir
Swagatam says
depends on how much illumination you require,
low illumination more back-up, high illumination low back-up
Arun Kumar says
Iwant power saver led light circuit diagram used 3.7v battery
Swagatam says
provide more details regarding LEDs, voltage etc.
Arun Kumar says
I want 3.7v battery used power saver high effective lights circuit
Swagatam says
power saver or power bank?
Arun Kumar says
How modify 3.7v mobile battery used what types led used this mobile battery please tell me sir
Swagatam says
you can try the second circuit from this article:
https://homemade-circuits.com/2013/04/1-watt-led-emergency-lamp-circuit-using.html
Swagatam says
tell me what's your exact requirement
Neeraj Kumar Sharma says
Hi
I am Neeraj
Is this circuit applicable for 6v 4.5ah battery
and I have 3 led of 3v 300ma. can I connect these led's using this circuit
to get more back up from the battery
Swagatam says
Hi Neeraj, the above circuit is rated for 20mA only, you can use the following circuit instead:
https://homemade-circuits.com/2012/09/led-emergency-light-circuit-using-boost.html
make sure the coil has no more than 20 turns and use a 6 ohms 2 watt resistor in series with the LED string
Neeraj Kumar Sharma says
Hi
I am Neeraj
Is this circuit applicable for 6v 4.5ah battery
basit momin says
Then which type of 5mm led will be better for it……….. Flat head type, round led type, or straw hat type
Swagatam says
any type that's rated to work at 20mA current
basit momin says
Sir if I want to use 8mm 0.50 watt straw hat white leds this led will be suitable for this circuit
Swagatam says
No, this is a low current design, it won't handle 1/2 watt LeDs
basit momin says
I want to add a on off switch to it so were I fix it
Swagatam says
in series with battery positive
maganti udaya bhaskar says
why did we use ic4049 in this circuit as well as the diodes……how would we justify it…..
Swagatam says
it has been explained in the article.
maganti udaya bhaskar says
I need the project report of this experiment……………….plsss mail it to mbpoint3@gmail.com or else mail me what are the important points needed to be covered in the project report………………………..
maganti udaya bhaskar says
I want the details of the gates n5 & n6……………………….n I need the information of the circuit in video mode…………………pls reply fast guys I need to submit the project…………………………………………..by the way ur xplanation is exceptional
Swagatam says
more info is given here:
https://homemade-circuits.com/2011/12/simple-dc-to-dc-voltage-doubler-circuit.html
Anonymous says
so can i change the capacitance of c2 and c3?
Swagatam says
it's due to the stored charge inside C2, C3….
achilles hector says
is it correct that if i connect the circuit to a power source for a minute then disconnect it, the light is still glowing even there is no power source? That is what happened to my circuit! I just made it yesterday.
Jinnamuru Xunte says
you mean I cant use 1 watt led in the above circuit? why(sobbing)…
Swagatam says
NO, you cannot use 1 watt led
Jinnamuru Xunte says
if I use single 1 watt led with 12v battery in this circuit what value of resistor will I use?
how many 1 watt led can I use in series using 12v battery in this circuit?
Swagatam says
yes you can combine all these circuits together.
for 1 watt LED the above circuit won't work, and is not required.
you can simply connect the LED directly with the battery using a 20 ohm 1 watt series resistor.
Jinnamuru Xunte says
can i put this circuit at the output of the circuit
"Simplest Automatic Emergency Light Circuit Using IC555"?
and
can i combine the three circuits of yours? like:
"Make this 10 Step Battery Voltage Monitor Circuit"
"Simplest Automatic Emergency Light Circuit Using IC555"
"How to Build a Simple Hi Efficiency LED Torch Circuit at Home"
Jinnamuru Xunte says
you mean up to 12v battery can be used in this circuit?
will 12v last longer than 6v battery?
can I use 2.4v-4.8v nimh battery?
thamks a lot for your help sir!!!
I will always acknowledge you in my projects!!!
Swagatam says
12V will work longer than 6V if the LEDs are connected in series.
4.8V battery will work but not 2.4V.
achilles hector says
what are the ranges of voltage (minimum to maximum) that can be used in this circuit?
Swagatam says
with 6v supply only three LEDs and with 12V supply upto 6 LEds in series….eDs shouldbe 5mm/20mA type
salman basit says
hello
can i use 4.2v laptop battery cell for it
Swagatam says
yes you can use it.
Jinnamuru Xunte says
can i use ic MN4049B?
Jinnamuru Xunte says
can i use ic MN4049b
Swagatam says
yes….
Jinnamuru Xunte says
Just making sure:
the IC4049 has 16 pins right?
And the pin#16 and pin#13 has no connection in your circuit right?
thanks for the answer?
By the way how much is the maximum input for 7812 voltage regulator? how will I know if i used the right capacitors?
Swagatam says
4049 has a few blank pinouts, you may refer to its datasheet.
mayur says
Hi Swagatam,
my name is mayur.I have two battery's of 4V, 0.5Ah and 4V, 0.9 Ah. I want to make a circuit in such a way that the the input will be a this two battery's.and output will be our mobile charger.It Is possible.if possible please tell me the Ciruit Description.
Swagatam says
Hi Mayur,
I did not understand your question?
ra66ju99 says
Hi Swagatam,
I have used 4 AA rechargeable batteries and the brightness of the LEDs were amazing. Now I want to use 1 watt LED (one or two)with the above circuit. Is it possible and if yes please help me with any modification.
Regards
Nagaraj
Swagatam says
Hi Nagaraja,
This circuit won't hold a 1 watt led….you may connect a single 1 watt LED with a 2 Ohms resistor directly to the 4.5V battery pack….that would work great.
ra66ju99 says
Dear Swagatam,
I had built the above circuit with 9v battery and 7 mm LEDs. Though the circuit works very well, the brightness i suppose is not up to the mark. So now i am planning to go back on your above suggested batteries and 5 mm LEDs. In this regard, exactly how many batteries are required (AA or AAA). I also tried to add more LEDs (5 mm in series) as suggested by you but they did not work.
Regards
Nagaraj
Swagatam says
Dear Nagaraj,
Use AAA batteries, four of them would be enough.
ra66ju99 says
Hi Swagatam,
I had built the above circuit and was good to construct as it has very few components. My battery input is 9v. But when i powered the circuit, it did not give sufficient brightness. It was as if i connected just only one LED. what might have gone wrong. kindly help me.
Regards
Nagaraj
Swagatam says
Hi Nagaraj,
9 volt batts are low in AH therefore will not be as effective as AAA cells, which are high with AH.
You can connect two more LEDs in series to increase the total illumination.
ra66ju99 says
Hi Swagatam,
The above circuit is very good and I am planning to construct this one also but with a slight modified requirement. Instead of using 4 batteries to get 6v, can i connect one 9v battery with some modification as this will be more simple. Please suggest.
Regards
Nagaraj
Swagatam says
Hi Nagaraj,
Yes you can do it!