How to Make a Simple 12 Volt LED Lantern Circuit


We have discussed white LEDs comprehensively through many of my earlier articles and have learned how efficient these lights are with power consumption.

In this article we will study a very simple configuration for making a LED lamp or a LED lantern.


New electronic enthusiasts often get confused with the wiring intricacies while configuring many LEDs in groups.

Here we’ll see how we can connect as many as 64 LEDs for making the proposed unit.

The circuit diagram details may be understood from the following points:

White LEDs typically have a forward voltage drop of about 3 volts.

When operated at the above voltage level, the device is able to produce lights at optimum levels and the spec also maintains better life expectancy.

The minimum current required at the above voltage level is around 20 mA, which again is an optimal magnitude and is ideally suited for a white LED.

That means for driving a single white LED in the most straightforward way we would require 3 * 0.02 = 0.06 watts, that’s pretty negligible compared to the relative illumination received from it.

The best thing is that as long as the above voltage and current spec is observed, the device continues to consume 0.06 watts irrespective of the number of LEDs connected.

In the present circuit, the maximum voltage available is 12, dividing 12 by 3 = 4, meaning 4 numbers of LEDs can be accommodated at this voltage and yet we are able to limit the power to 0.06 watts.

However the above calculation would make the circuit quite vulnerable to voltage drops and if the voltage dropped even by a single volt would make the LED too dim or might just shut them OFF, we don’t want this to happen.

Therefore though the efficiency may drop a bit, we opt for a configuration which would enable the circuit to work even at lower voltages. We include only two LEDs in the series @ o.06 watts.

Now it’s all about connecting the desired number of strings of two LEDs each in parallel until all the 64 bulbs are included in the circuit.

However connecting in parallel would mean multiplying current. Since we have 32 parallel connections means the total consumption will now become 32 * 0.06 = 1.92 watts, still pretty much reasonable.


The connection details can be easily traced from the given schematic.

Your simple LED lantern is ready and may be taken anywhere outdoors with you, probably during night time explorations.

Pats List

All resistors are = 470 Ohms, 1.4 watts,
All LEDs are = white, 5mm, hi-efficiency
Diode = 1N4007

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46 comments

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Anonymous
February 9, 2012 at 7:41 PM delete

the resistors 1/4 or 1.4 watts.

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February 9, 2012 at 7:45 PM delete

Sorry, it's 1/4 watts,

Thanks!

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Anonymous
February 10, 2012 at 7:50 PM delete

why to connect a diode.

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February 11, 2012 at 8:59 AM delete

No need of it actually, it's just to protect the circuit from accidental reverse polarity connection that might take place due to human error.

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Anonymous
February 11, 2012 at 7:10 PM delete

Thank u for ur good works. Please i built the 'high efficiency emergency LED lamp' you posted on brighthub and it was working until now. It does not light unless u short C and E of the transistor. I replaced d BD140 with TIP42 then found out that d light only flashes when u connect to d battery then goes off. I found that it lights when you short circuit capacitor C2 but when i removed the capacitor it does not even flash. Same thing happened when i replaced with d BD transistor. Pls help. THANK YOU

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February 11, 2012 at 8:40 PM delete

Thanks for pointing out the problem.
Firstly, the LEDs will never light up as long as mains voltage is present, however if the problem is happening even after the circuit is removed from the mains socket, it can be simply corrected by reducing the resistor value connected across the base and the ground of the transistor.
Reduce and try different values until the LEDs light up with sufficient brightness.

Regards.

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Anonymous
February 12, 2012 at 11:45 AM delete

thank u sir for your timely response. The problem happens with battery i.e not mains voltage. Pls is using the TP42 transistor ok? The biasing resistor R2 reads fine ie 10k when i tested it (though it was still connected in d circuit when i tested it). I hav also noticed that bypassing the base resistor makes it light but the transistor becomes hot. Could it be that the resistor is open and therefore not conducting hence sending the current through the capacitor C2?

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February 12, 2012 at 1:40 PM delete

If you short the 10K resistor, it will damage the transistor permanently, probably you might have already made it weak.
As I explained in the previous comment, the resistor value should be reduced to, say, 1K or 2K etc until the LEDs light up brightly, but you cannot short it.

Regards.

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Anonymous
February 3, 2013 at 12:44 PM delete

Mr. Swagatam, what is the watts brightness of this lantern circuit?

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February 3, 2013 at 10:19 PM delete

watts will be around 15.

not sure about the brightness.

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April 9, 2013 at 7:37 PM delete

I have a doubt that y r u connecting Vcc 12v positive terminal passing through all the LED's and at right side corner connecting with negative terminal. Isn't become short circuit.???? Reply immediatly

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April 21, 2013 at 11:49 AM delete

ok thank you....you r good i used ur inverter(Astable multivibrator) in my college project its working.....

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Anonymous
September 11, 2013 at 9:41 PM delete

how u have calculated that there are 32 parallel connections.????
pls explain..

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September 12, 2013 at 1:07 PM delete

Each of the shown Two LEDs with the series resistor becomes one string, count how many are there.

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Anonymous
October 13, 2013 at 1:09 PM delete

hello swagatam,in this lantern circuit on to line u r connecting resistors to -ve of leds
then in second line u r connecting resistors to +ve of leds.
i didnt understand whats the point.
pls explain.
thnks in advance.

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October 13, 2013 at 5:00 PM delete

resistors can be connected anywhere in the line, the position is not important.

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January 21, 2015 at 7:37 PM delete

Dear sir,

May I know which software is used to draw the schematic in this post?

Thank you.

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January 22, 2015 at 2:00 PM delete

Dear Srinivas, I use CorelDraw......

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May 9, 2015 at 11:15 PM delete

Wat is the ampere of battery

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May 10, 2015 at 9:45 AM delete

for 5mm leds it can be 4AH, and for 1 watt it should be 25Ah or 40 AH

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May 10, 2015 at 5:58 PM delete

Can I use piranha led if yes then ampere for piranha led will be 4AH or it is changed and wat will the resistor value for piranha led and 1watt led.... Thanks

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May 11, 2015 at 10:33 AM delete

yes you can use piranha LEDs also without changing anything in the circuit,

but 1 watt leds cannot be used in this circuit, it will require completely different configuration

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May 12, 2015 at 10:35 AM delete

Thanks for the reply............. Sir I want ur email address..........

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May 12, 2015 at 1:24 PM delete

for discussing circuits you can feel free to ask your questions here....I use email only for business related discussions.

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May 12, 2015 at 2:34 PM delete

Ok sir but..... I want to send a video to u so that's why I wanted ur email..........

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May 12, 2015 at 5:24 PM delete

OK, send it to:

hitman2008(at)live.in

replace (at) with @

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November 13, 2015 at 3:39 PM delete

good day! is it the same process if i use different color of led light for my lantern?

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November 13, 2015 at 8:41 PM delete

if you use approximately 3.3V LEDs then it'll be the same regardless of the color...

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November 16, 2015 at 7:00 PM delete

thanks for the info, I was wondering if you can take old LEDS from old LED flash lights that have quit working and make a simple working light for hooking to a 12 volt battery to make a light for when the power goes out.

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November 17, 2015 at 9:27 AM delete

If the LEDs are in a a working condition then definitely you can use them with an external battery for emergency lighting....

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November 19, 2015 at 4:57 PM delete

Ok thanks. My question is the two lights I have is one has 7 LEDS in

parallel with a 32 ohm resistor at each light and 5 in parallel with

one 6.8m ohm resistor up front, can you just add another resistor to make

them work off 12 volts if so what sizes please or do I need to rewire

the whole thing, Just a little about me I took half a course in

electronics about 45 years ago, so I know what things do and how to

take them apart and replace parts but I missed or forgot the part about

building circuits, I can build from a DWG, so I am half smart, If I was

totally smart I would build me a overunity motor or magnet motor, just

love that stuff, Many thanks Buddy

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November 19, 2015 at 6:24 PM delete

OK, but I'll also need to know what supply voltages these two lamps used...only then I'll able to judge the LED specs and then accordingly would be able to tell you the resistor value and the wiring detail for connecting these together with a 12V supply.

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November 20, 2015 at 3:36 AM delete

Thanks for the help, I do not know the supply voltage the bat went dead and would not charge and it does not have any markings on it or the light all it has is a marking of a number of the circuit board, SS272-B one of those china made or some place does not have a brand name, sorry Buddy

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November 20, 2015 at 8:53 PM delete

OK but without the voltage I wouldn't be able to calculate the resistor value...so it can be difficult to configure the design

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November 21, 2015 at 6:30 AM delete

thanks for the help, So I am confused if you have an white led with a 32 ohm resistor you can not just add another resistor to use with 12 volt batt, what about just taking that resistor out and just replacing it with one that works with 12 volts, I think I will make it easy just cut that resistor out put in a jumper in to connect two LEDS and put in the resistor you have shown above and be done with it, what do you think, or am I missing something which is almost all ways, thanks for your thoughts, buddy

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November 21, 2015 at 10:10 AM delete

either I have to know the original voltage spec used in the unit, or you can tell me the LED current (mA) rating...any of the two will be sufficient for calculating the resistor value....if neither of this is known then it would be impossible to calculate the correct resistor value.

the other method is to try by trial and error method which can be fatal for the LED or can make them work inefficiently

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November 21, 2015 at 4:11 PM delete

Thanks for your reply, I did miss something I thought all white LEDS had the same (ma) rating and voltage draw, I told you I know just enough to get my self in trouble, I guess it is going to be trial and burnout method, they are free now and if I can not make them work I was going to throw them away anyway, going to hook them as they are to a 5 volt phone charger first to see if they burn or burn HA HA, it is never easy when you are trying to recycle free electronics< if you do not snap, crackel and pop you are not learning, that is like I crashed 3 computers before I learned how to use dos and now you use windows do not need dos, thanks Buddy

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November 22, 2015 at 9:17 PM delete

sure buddy, you won't learn unless you sacrifice a few of the valuable things...

you can experiment on a single LED, by applying 12V to it through an arbitrarily selected high value resistor such as a 1K, then go on reducing this value until you find the resistor getting to hot or may be the LED on the verge of getting destroyed, this will tell you which value of resistor was actually optimal during the procedure...

wish you all the best.

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November 23, 2015 at 5:13 AM delete

Ok thanks, if does not work I will just build one of your Emergency circuits thanks Buddy

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December 12, 2015 at 5:46 AM delete

Could I still build this circuit if I used 18V (2 x 9V batteries connected together) and used about 150 LEDs and 150 470Ohm resistors?

IF I could do this, how long would it light for?

Many thanks in advance.

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December 12, 2015 at 5:22 PM delete

yes it's possible just make sure each string now includes 5 LeDs in series with 150 ohms in each series

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December 12, 2015 at 5:30 PM delete

Thanks for your speedy answer.

Unfortunately, time is of the essence here, and I won't get the 150ohm resistors in the mail before the project is due.

Could I alternatively use a string of simply 470 ohm resistor with each individual led (in parallel) instead of 5 leds with 150ohm resistor? Like this:


│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│
│ │
│led+470 ohm resistor│

etc.

Thanks again for any help you can give.

Patrick

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December 13, 2015 at 10:15 AM delete

18 - 3.3 / 0.02 = 735 ohms

470 will burn the 5mm 20 mA LEDs at 18V

as per the calculations it will need to be at least 735 ohms.

you could for a 680 ohm or even a 1K.

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