About: Now I am a retired person, who enjoys life and making small things to pass the time keep myself busy.


I had to do this project for many of my young friends who are interested in LED’s but do not know how to go about it.

I also had the same problem but was fortunate enough to get HELP from my friends at

This is not about any calculation or study but a set of proven rules to follow and get results,

which anybody can do if he has the mind to.

Here I have shown you many types of power supply which can be used to glow a LED.

I have also shown here how different types LED's can be made to glow and use it in you project.


A 15 mm LED has two legs, the long one is the Positive and the short one is the Negative.

It consumes 15 milli Ampere of current and can glow on 3 Volts DC Current, or a 3 volt battery.

LED’s are Diodes and the current can only pass through the POSITIVE side.

Always remember to maintain the POLARITY of the LED, that is (plus to plus) and (minus to minus) otherwise it will not work.

LED is a one way street. Now you know how to connect an LED in your circuit.


If you are interested, here you can see the different parts on an LED.


This set of rules will help to build a Project, follow them.

Here I have shown the Resistors to be used with 6 volts, 9 volts and 12 volts DC.

You can go on adding any numbers of LED's.

Remember that the first line of LED should be in series and  the second line onwards should be in Parallel.


LED can be run on AC or DC current.

If you want to run it on DC that is Battery Then you must use Resistors.

If you want to run it on AC then use a Step down AC Transformer. (220VAC to 12 VAC)

Here we will deal with AC Transformer

Now what is the load the AC Transformer will take? For that you will have to measure the output voltage of the AC Transformer with a Multimeter, say it comes to 14volts.

The subject transformer was 14VAC 500mA output without load.

First, we have to be aware that the 14V rating is known as the RMS voltage, and is the effective average power of the sine wave. The maximum voltage, which we will subject our LED’s to, is about 1.4 times higher.

So we should expect a peak voltage of 1.4 x 14v =19.6

So, we will be using 19.6 volt as the basis of our calculations.

We know that most white and blue LED’s range between 3 and 3.6 volts. So by dividing our PEAK voltage by an average LED voltage, we get an idea of the number of LED’s our transformer can support:

19.6 / 3.5 = 5.6, which we round up to 6 LED’s.

But remember, that AC has an identical NEGATIVE cycle! Which means we can add a mirror circuit that work on alternate phases,

that is 6+6. The advantage of using voltages to start our calculations is that, as long as we stay with similar LED’s, and stay within

its operating voltages, the current will stay within safe limits. So, by adjusting the number of LED’s in use, we can handle most AC

transformer outputs. We can multiply the light output up to 15 times just by adding chains of 6+6 LED’s arranged the same way

across the supply! 15 times means 90+90=180 LED’s

Step 5: LED's CAN GLOW DIRECT ON 220volts or 120 Volts AC MAINS.

You can use LED’s directly on 220 volt or 110volt AC.

Same principal applies, one line opposite to the other while using AC.

The value of the Condenser and Resistors are given in the diagram for 220 volts and 110 volts.

The condensers must be non-polar.

You can use 30 + 30 LED's on a string, after that if you start adding more LED's the light starts to get dimmer.


Step 6: USING 1 WATT LED’s

Here you can see the various types of 1 watt LED’s.

Their polarity are marked on the legs or body.

They glow on 3 volt and consume 350mA of current,

so you must calculate the power source to be used with this LED.


Every thing is explained in this Diagram.


You can use different types voltage and resistors with this LED as shown in the Diagram.


Everything is clearly explained in the Diagram and it is very easy to use strip LED's.

Now you can make your own LED projects.

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101 Discussions

what power supply can I use with a 2m leds strip 5v what is the amp requied and can I use batteries 3 nmh rechargeable. These are addressable RGB Leds ?

If I want to run 6 led of 1 watt with 5 volt supply can my led glow up?

Hi I am building a model airport runway, And will be using 550 led diode 3 and 5 mm. Of various colours. What I like to know is how many led diode can I connect to a 12v DC Transformer ?. I am using resistors on each diode. Thanks for your help regards.

1 more answer

Hi Do anyone have a answer for this question? Thank you.

Whomever produced that first image of the LED diagram must have taken art lessons from Escher... Pretty cool.


sir can you help with this please 220 colour changing leds wired in parrallel what power supply to use

I have an 1w x 7 light. I,m set this lights serios system. Then can i connect a 12v ups battery without any cercuit? Sir, please exlain me.

Hi Sir, I got a led project that I assume is similar to your "step 4" the ac transformer.

I have a power supply that step down to 9VAC and 200ma. I am using the 1 watt LED, which is exactly the one you have on your step 7.

My question is: I assume I can put minimum 8? : 4 in series ( 9 x 1.4= 12.6v) and 4 more on the negative cycle.

My second question is: What is the max number I can put them? I assume is 15 x 8, so 120?

Thank you for your time and the help

1 reply

i might not be your good sir ,but i know i can learn,witch is that what you have there is ether a rectified transformer or a smps (switch mode power supply) witch are both dc not ac in outer words half of your led's wont light up

to make it easier to understand just treat that transformer as a battery follow step 8 and you should be good

Sir can you tell me the ampere rating of the step down transformer required to glow a single 1 watt LED light from a 220v source?

Hello I want to connect 20 1W LED. which one should I use power supply?

My Prof recommend me to use 3V-20W but I cannot find it. what is another option to do it? I can divide 10/10 so 2 groups. this project is killing me.

1 reply

Use this circuit it is easy and reliable...

1 watt LED's.jpg

Hello, i have a question about connecting 1W, 350mA leds to a power bank.
I was wondering if i could connect 7 1W, 350mA 3.2-3.6V Leds to this powerbank,
and what would be the best way to do it?
I think i should connect them parallel, and add resistor, but i dont know which DC output i need to consider for this? It says it is 5.1V, 2.1A(3.6A max), but battery is 3.6V.
7x350 is 2,450, but if i connect them either way, each led will get 300mA and should work just fine but dimmer?
But i need help with figuring out the voltage, and what resistor if any to use.

1 reply

Hi Dipankar,

This is my first project. I have a 30w led I would like to power from a wall outlet with as few components as possible. I found an led driver made by Introcircuit with an output "DC 12v, 2.5a, 30w". It has 110 power outlet plug coming out of one end of the driver and a red (+)and black (-) wire coming out of the other end.

Do I need anything else for this to work?

The led (pic attached) I have doesn't have a (+) or (-) indicator on either connector. Does it matter which connector I solder the wires to?

Thank you for your help!

3 replies

Should have a (+) or (-) indicator on either connector. It Does matter because LED are Diodes and it should have a + and - poles.
Go to Google Image and find out.

The driver I listed above is constant voltage and if I am right I actually need constant current driver. I found a 30W CC driver on Ebay ( but the output states it is DC 20 - 36V.

Will this driver do the job without blowing out the led?

Is there a better place to buy reliable drivers than Ebay?

I took the protective cover off and found the + and - poles. They can also be seen in the pic.

Excellent presentation;the use of "one line opposite to the other" while using a stroke of genius which i have not come across in many of the online texts i have read.i wish you had also given on how to use solar power for the one watt LED.