# LED Tubelight circuit - voltage and current requirements

#### vaibh_p

Joined Jan 11, 2020
10
Hi , I take out the LED strip from one of the LED Tubelight which stopped working.
Its Rating was: 220V AC - 22W

I take out the circuit and LED Strip , disconnected the circuit and put the 12V DC 2A power supply directly to the LED strip , but nothing works.

I have checked each LED on the strip and every LED is good to go.

They are connected as 33 LED in Series and 4 such parallel connected combinations
|1---2---3---------31---32---33|
GND ________|1---2---3---------31---32---33|________ +12V
|1---2---3---------31---32---33|
|1---2---3---------31---32---33|

So I am not getting what's the problem , isn't the 2A source enough ? but then I thought that at least all LED should glow with some minimum brightness.

So need help on this , how to debug ?

#### LesJones

Joined Jan 8, 2017
2,726
As each LED of the string will require about 3.2 volts across it a string of 33 LEDs in series will require about 106 volts between the ends. As LEDs are current driven devices you will need something to limit the current. As the rated power was 22 watts each string will require about 5.5 watts. As there are 33 LEDs in the string each LED will be consuming 5.5/33 watts = 0.17 watts.so the current required through each LED will be about 53 mA. If you want to run them off 12 volts you will need to break them down into groups of three LEDs in series with a resistor in series with each group of three. The required resistor s will be about 45 ohms. 47 ohms is the nearest standard value.

Les.

#### Dodgydave

Joined Jun 22, 2012
9,666
The fitting will probably have a transformer-less PSU and a bridge rectifier with a series resistor or on a cheaper scale they put the LEDs back to back without a bridge rectifier and two sets work on each cycle of the mains, at 115 V AC . Are you in India.

Can you take pictures of the fitting as well.,?

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#### vaibh_p

Joined Jan 11, 2020
10
The fitting will probably have a transformer-less PSU and a bridge rectifier with a series resistor or on a cheaper scale they put the LEDs back to back without a bridge rectifier and two sets work on each cycle of the mains, at 115 V AC . Are you in India.

Can you take pictures of the fitting as well.,?
Yes , I am from India.
I have very less knowledge about electronics circuit designing.
I am attaching the images of the circuit , any guess what's wrong in it?

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#### bertus

Joined Apr 5, 2008
20,881
Hello,

It looks like there are also parts on the bottom of the board.
Could you post a photo of the bottom of the board?

Bertus

#### vaibh_p

Joined Jan 11, 2020
10
Hello,

It looks like there are also parts on the bottom of the board.
Could you post a photo of the bottom of the board?

Bertus

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#### Dodgydave

Joined Jun 22, 2012
9,666
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