LED Tube Light Circuit

Using white LEDs for illuminating our homes is becoming popular nowadays, due to the high power efficiency involved with these devices. The diagram shows a straightforward configuration involving many LEDs, arranged in series and parallel.
Refrring to the shown LED tube light circuit using transformer we see the LEDs are driven by a general purpose 24 V power supply for illuminating the LED bank very brightly. The  power supply incorporates standard bridge and capacitor network for the required rectification and filtration of the supply voltage to the LEDs.

The arrangement of the LEDs is done in the following way:
The supply voltage being 24, dividing it by the forward voltage of a white LED which is around 3 volts gives 24/3 = 6, meaning the supply voltage will be able to support at the most 6 LEDs in series.
However since we are interested to include many LEDs (132 here), we need to connect many of these series connected strings of LED through parallel connections.
That's exactly what we do here.
Total 22 strings of LEDs having 6 in each are connected in parallel, as shown in the figure.
Since current limiting becomes an important issue with the white LEDs, a limiting resistor is added in series with  each of the strings. The value of the resistor may be optimized by the user for adjusting the overall illumination of the LED tube light.
The proposed design will provide enough light for illuminating a small 10 by 10 room brightly, and will consume not more than 0.02 * 22 = 0.44 Amps or 0.44 * 24 = 10.56 watts of power.

24 Volt, LED Tube Light Circuit Using Transformer, Circuit Diagram




LED Tube Light Circuit



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42 comments

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June 19, 2012 at 9:14 PM delete

what should i change if i use 1 watt LEDs ?

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June 20, 2012 at 8:24 PM delete

you may reduce the resistor values and check.

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Anonymous
July 5, 2012 at 6:20 PM delete

Hi,

what would be wattage for 220vAC.

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Anonymous
August 23, 2012 at 10:09 PM delete

which POT should i use and where if i want to have variable intensity light

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August 24, 2012 at 3:20 PM delete

disconnect the LED positive link from the bridge rectifier, take a 1K 1 watt pot, connect its center lead with the LED positive link, connect one of the ends of the pot to the bridge positive and connect the other end of the pot to ground or the negative supply......start dimming.

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Anonymous
August 25, 2012 at 9:46 AM delete

thanks!!! awesome blog :)

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Anonymous
August 25, 2012 at 10:13 AM delete

i have 5mm straw hat LED
< http://www.onsale-usa.com/Wholesale-Discount-USA/usa-on-sale-25205-5mm-straw-hat-led-with-flange-120-140-viewing-angle-white-color-1800-2500mcd-1000pcs-one.jpg >
would these work for the circuit????

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August 25, 2012 at 11:31 AM delete

Thanks Buddy, appreciate it....

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August 25, 2012 at 11:43 AM delete

Yes you may use the shown LED for this project.

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Anonymous
August 25, 2012 at 7:02 PM delete

hi Swagatam.....
i made the circuit and its working fine BUT i think the power supplied is too much(i mean the LED are glowing very bright an generate some heat). How do i reduce the power???

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August 26, 2012 at 7:48 AM delete

Change all the resistors to 150 Ohms 1/2 watt

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Anonymous
August 26, 2012 at 9:17 AM delete

i already soldered them. any changes that i can make in other part of circuit?? where desoldering would be less???

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August 26, 2012 at 11:11 AM delete

You can try connecting any value between 10 to 22 Ohm 2 watt resistor in series with the positive of the circuit

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Anonymous
August 26, 2012 at 1:40 PM delete

i connected 100ohm 1w resistor there(thats what i had right now). but dint have much effect. How about some POT so that i can vary the light as per my need.

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August 26, 2012 at 1:49 PM delete

You may connect a 1K pot in series with the positive.

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Anonymous
August 28, 2012 at 5:45 PM delete

SUPERB GENTLEMAN.

S. Tushar +919892105582

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Anonymous
September 12, 2012 at 12:15 AM delete

hi swagatam plz help me for the circuit of smd led 5050 i want to make tube light of smd led 5050
what will be the circuit diagarm

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September 12, 2012 at 1:23 PM delete

OK I'll design the circuit soon and let you know...stay tuned.

Thanks.

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Anonymous
September 26, 2012 at 8:35 PM delete

Circuit is working awesome. i connected a 100ohm pot which gives me perfect intensity control.
Thanks for the circuit.

Any circuity with SMD LEDs????

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September 26, 2012 at 9:03 PM delete

That's great....for smd LEDs too the present configuration will work well.

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October 26, 2012 at 10:21 PM delete

hi if use 12v supply explained by you in "How to Calculate and Deduce Current, Voltage Parameters in Transformerless Power Supplies"article will it work properly i mean brightness etc .

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October 27, 2012 at 8:44 AM delete

The article is meant for only capacitive power supplies, not for transformer type power supplies, so won't apply for 12v transformer supply.

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December 9, 2012 at 6:33 PM delete

Hi swgatham,
Can you suggest some circuit to operate directly from mains without transformer

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December 10, 2012 at 9:06 AM delete

Hi John,

Please refer to this circuit:

http://homemadecircuitsandschematics.blogspot.in/2012/04/how-to-make-led-bulb-circuit.html

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August 15, 2014 at 8:35 PM delete

Sir,What is the difference between 0-24V and 12-0-12V ?
As far I know 0-24V means 24V DC at the ouput of the Transformer.Then what 12-0-12v means then ?
Please correct me if I am wrong.

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August 16, 2014 at 10:32 AM delete

Ajay, both are one and the same, when an extra center tap terminal is taken out from a 0-24V winding it becomes a 12-0-12V transformer.

12-0-12 is nothing but a 0-24 divided into two halves by removing a wire from its middle of the winding.

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April 2, 2015 at 12:58 AM delete

For 1watt led heat sink Will be required

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April 5, 2015 at 8:54 PM delete

If I nt use heat sink for 1watt led then wat will happen

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September 24, 2015 at 4:57 PM delete

Hello,

In relation with your first circuit diagram and your solution of "diodes in series with the supply", whereby as the voltage of the battery drops, the diodes in series are reduced to two and subsequently to one making sure only the desired amount of voltage reaches the LED bank, could you please clarify how the S1 Switch (with changeover contacts) succeeds that? From the circuit I take it rather as manual changeover, or not? Is there an automatic switch and how would it be connected?

Many thanks and Best Regards

Stavros
.

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September 25, 2015 at 7:30 AM delete

Hello,you have posted the question under the wrong article,

anyway, yes it is a manual action and needs to be initially kept with the maximum number of diodes in series, and then as the light diminishes, the switch is required to be shifted step-wise until all the diodes have been bypassed.

automatic is possible but that would make the circuit much complicated.

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November 22, 2015 at 1:39 PM delete

Hellow sir
I was wondering if you could use 12-18v power supply what wil you change and why did you choose to use such high voltage

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November 23, 2015 at 9:27 AM delete

for 12V just reduce the number of LEDs proportionately on each series...higher voltage allows more LEDs to be included easily without the need of increasing current.

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November 23, 2015 at 9:52 AM delete

Thanx sir for the fast reply
But can i be open and ask this question . in led connected in series how can i calculate the value of limiting resistor effectively?
The formular i know is (supply voltage-forward voltage)/forward current

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November 23, 2015 at 4:59 PM delete

yes the formula is correct, for series connection the forward voltage is obtained by adding the forward voltages of all LEDs in series, but the forward current value is taken for a single LED because current does not add up when LEDs are in series.

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November 23, 2015 at 11:41 PM delete

One more interesting question .whats the advantage of connecting led in series or parallel ? Which is the best configuration??

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November 24, 2015 at 10:20 AM delete

if you have excess voltage in hand then you must connect the LEDs in series, otherwise parallel is the only option that can be applied.

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November 24, 2015 at 12:09 PM delete

and to ensure led will last long how can i calculate the power dissipated by each led in both series and parallel connection

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November 24, 2015 at 5:03 PM delete

I have not yet researched about that because it's not so critical, and can be tackled it by adding a current controller stage and an adequate heatsink...

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