Reusing TV LED Strips

Thread Starter

Kubes

Joined Jan 31, 2023
7
I am reusing LED strips from a TV for my light in my shop.

I posted this https://forum.allaboutcircuits.com/threads/tv-led-strips.192286/ (I did not want to cross-post) to identify the LEDs, but I have had no responses at all. So at this point, I am looking for "professional" advice, meaning some with more than my basic knowledge. Who can help guess what the correct forward current and voltage might be? Or how to try to figure that out. A table in the other post has voltage, current, and dissipated heat.

Thanks for any advice!
 
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MisterBill2

Joined Jan 23, 2018
18,928
This is a way to characterize LEDs, either single or strings, well enough to use them for experimenter uses such as general illumination.

Usually the meters on an experimenter grade power supply are not accurate enough to be of much use in characterizing an LED or LED string. So the TS will need a digital voltmeter or digital multimeter that can read voltage. A fairly stable power supply that can deliver a half an amp will also be required. Also a variable resistor able to carry 50 milliamps without damage will be required if the power supply is not adjustable. It the supply is adjustable then a 100 ohm (or fairly close to 100 ohm) resistor would be required.
And finally, some of the LED strings to be characterized, with some connection wires that will stay attached while doing the evaluation.. A variable resistor can be a substitute for a variable DC power supply.

The first step is to make a guess at the voltage needed to light however many LEDs are in series in the string., and to gues which end is the positive end. Mostly LEDs will illuminate with less than 4 volts across each one, so with a series of six LEDs the supply could be up to 24 volts. But the safe way to start is to apply about 2 volts per LED to the string, with the resistor in series, and see if there is any glow at all. If not, increase the voltage or decrease the resistor until there is a bit of glow, not bright. Measure this voltage across an LED and know that this is toward the bottom of the curve. As the voltage rises above this level in small increments the current will increase quite rapidly and the glow will get much brighter. Measure these voltages and se that the current is also rising quite a bit with small increases in voltage. At some point the LEDs will continue to draw more current but not seem much brighter, this is beyond the best operating point for a reasonable life. Now you can measure the exact voltage across the LEDs and know what to adjust for in the installation. If you are able to also measure the current then you can know just what voltage and current you should adjust for.
 

bassbindevil

Joined Jan 23, 2014
836
For what it's worth, I rescued the LED backlighting from my friend's dead 40" Samsung TV. There were 6 strips of 9 SMD LEDs, and the power supply silkscreen said 194V 430 mA, which is plausible since that's 3.6V per LED.
 

Externet

Joined Nov 29, 2005
2,232
Defunct TVs that I removed the LCD glass panel and all boards inside, repurposed as ceiling lamps in my basement. I remember using a higher voltage supply, perhaps ~ >60 volt but cannot remember. Just observe the wiring and calculate.
Screen diffussors left in place, original LEDs strips untouched. The LED driver supply was from Aliexpress attached to the back of the TV case, been working 5 years. The nearest one was a Samsung. There is more in the same basement ceiling.1678058729151.png
 
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