Tuesday, February 7, 2012

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


  1. the resistors 1/4 or 1.4 watts.

  2. why to connect a diode.

    1. 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.

  3. 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

    1. 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.


  4. 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?

    1. 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.


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

    3. watts will be around 15.

      not sure about the brightness.

  5. 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

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

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

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

  7. 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.

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

  8. Dear sir,

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

    Thank you.


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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.
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