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

44 Replies to “LED Tube Light Circuit”

    1. 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.

    2. Few doubts sir…
      Pot 1k three terminal
      1 st terminal postive of bridge rectifier
      2nd terminal 100ohms resistor input
      3rd one is ground..

      Is it correct…

      We r applying 1a in pot…
      Did pot will accept 1a..did pot will damage.

  1. 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???

    1. 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.

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

      Any circuity with SMD LEDs????

  2. 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 .

  3. 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.

    1. 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.

  4. 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


    1. 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.

  5. 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

    1. 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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