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.

Search This Blog

Loading...

Monday, December 19, 2011

Simple Current Controlled LED Tube Light Circuit Diagram

The given circuit of a current controlled LED tube light uses a couple of high voltage transistors which works on a very basic principle for implementing the required current control operation. Resistor R2 is placed for converting the rising current to voltage across itself.
This voltage is sensed by R2 which immediately conducts and grounds T1s base rendering it inactive, the instantaneous process initiates a switching effect, producing the desired current control and safeguarding of the LEDs. Each channel consists of 50 white LEDs in series. R2 is calculated with the following formula:

R = 0.7 / I, where I = Total safe current consumed by the LEDs.

The whole circuit of the current controlled LED tube light may be understood in this manner:

When input AC is applied to the circuit, C1 drops the input current down to a lower level which can be considered to be safe for operating the involved electronic circuit.

The diodes rectify the low current AC and feeds to the next current sensing stage consisting of T1 and T2.
Initially T1 is biased through R1 and conducts fully illuminating the entire array of LEDs.

As long as the current delivered by T1 or rather current drawn by the LEDs is within the specified safe limit, T2 remains in a non-conducting state, however of the current drawn by the LEDs begins to cross the safe limit, the voltage across the limiting resistor R2 begins to develop a small voltage across it.
When this voltage exceeds 0.6, T2 begins to leak through its collector emitter pin outs.
Since the collector of T2 is connected to the base of T1, the biasing current to T1 now starts leaking to ground.
This inhibits T1 from conducting fully and its collector current stops rising any further. Since the LEDs form the collector load of T1, the current through the LEDs also gets restricted and the devices are safeguarded from the rising current intake.

Ths above rise in the current takes place when the input AC rises, producing an equivalent increase in the LED current consumption, but the inclusion of T1 and T2, ensures that anything that's dangerous to the LEDs is effectively controlled and curbed.

Parts List for the proposed current controlled LED tube light circuit

T1 and T2 = KST42
R1, R2 = To be calculated.
R3 = 1 M, 1/4 W
Diodes = 1N4007,
C1 = 2 uF / 400 V,




19 comments:

  1. can i use this circuit in 110Vac?

    ReplyDelete
    Replies
    1. same circuit or there is a modification for 110v?

      Delete
    2. The LED series cannot be more than 25nos per channel, the 2uF cap may be rated at 250V for reducing the cost and space.

      Delete
  2. Dear Mr.Swagatam,
    I'm Niro
    # Can you please give 01 or 02 example for calculating R1 and R2.
    # Can I use only one or two 50 white LED in series?

    Thanks.............

    ReplyDelete
    Replies
    1. R1 = (Supply V - Total LED fwd V) / LED required Current.

      R2 = 0.7 / LED required current

      Delete
  3. Hi Swagatam,

    What will happen under the the following conditions.

    1. one of the LEDs in a string short circuits?
    2. one of the LEDs in a string open circuits?

    Thanks,
    D

    ReplyDelete
    Replies
    1. Hi D,

      Normally such conditions will never happen, under short circuit other LEDs will remain lit, under open, all LEDs in the string will shut off.

      Delete
  4. hi swagatam
    can i use BC548, 547 or 549 (easily available parts)?

    ReplyDelete
    Replies
    1. Hi Max,

      The transistors should be able to handle in excess of 220V, BC54X can handle up to 65V maximum....so not suitable here.

      You may try MJE340...

      Delete
  5. i am trying to design a greeting card with a circuit and LEDs in it, but it should be like when we open the card the LEDs should be on and when we close the card they should go off, can you pleas help me with it?

    ReplyDelete
  6. i am trying to design a greeting card with a circuit and LEDs in it, but it should be like when we open the card the LEDs should be on and when we close the card they should go off, can you pleas help me with it?

    ReplyDelete
    Replies
    1. I've noted down your request, will try to design and post it soon...

      Delete
  7. Dear Swagatam,

    I want to use 50 led in 2 series(total 100 led) with 50mA/string. As per my calculation R1 is 1.6 ohm and R2 is 6.8 ohm.pls help

    ReplyDelete
    Replies
    1. Dear Ganesh,

      How did you get the 50mA current, is it your LED spcification?

      Anyway with 50mA, R1 = (300 - 50*3)/0.05 = 3000 Ohms or 3K

      and R2 = 0.6/0.05 = 12Ohms

      Delete
  8. what should be watts for R1 I placed 1.35 k 1/2 watt for 100 ma string it burned

    ReplyDelete
  9. What should be watts of R1, I connected 1.35 k 1/2w for 100 ma LED string it burned. R1 was calculated as R1=(300-3.4*50)/.1

    ReplyDelete
    Replies
    1. R1 = (300 - 3.3x50)hfe/0.1
      hfe = gain of transistor

      example (300 - 3.3x50)200/0.1 = 270k

      Delete

Readers are requested not to include external links while commenting. For consulting a diagram, upload it on Google Drive and provide the link here.