Ordering SMD LED for backlight

[Mcologist]

Hello,

I am currently working on a Haier 55UFC2500b that has two backlight LED's out.

my question is does anyone know of a model number to order individual SMD LED's that works on most backlight strips? I have it narrowed down to 3001 results on digikey.ca based of Physical dimension alone.

Thanks!

[Wilderone]

Re: Ordering SMD LED for backlight

Measure the dimensions of the smd ie 2.8mm * 3.5mm would be (2835) there will be differences in the pads & color (warm white/cool white) check this against your old ones.

For example LG 2835;
https://s.click.aliexpress.com/e/cb1GobpA

[budm]

Re: Ordering SMD LED for backlight

You need to know the Forward Voltage (Vf) rating, the current rating, and the footprint I.E large solder pad is Anode or Cathode.
You need to remove the bad one and look at the solder pad, you can also measure Vf.
Current rating of 400mA is typical for backlights application.
Pictures of your LED's?
LED strip P/N?
Dimension?
LED drive Voltage/Currnet rating as printed on the board?

[Mcologist]

Re: Ordering SMD LED for backlight

Okay so size is 3mmx3mm, large pad is - small pad is +. As for current or voltage there is nothing printed on any of the LED strips for it and there is nothing I can see on the power board that indicates either value.

[Diah]

Re: Ordering SMD LED for backlight

yours SMD LED 3030 6V 1-2 W easily can find them with Lens or just the LED

[Mcologist]

Re: Ordering SMD LED for backlight

How do you know it is a 6V?

[Diah]

Re: Ordering SMD LED for backlight

How do you know it is a 6V?

you have 55 size TV. the range of SMD LED with 5600K 4.7V. as yours..

in the market there are 3030 Single LED of 3 Volts and 6 Volts. if you use now at yours set 3 Volts it will burn other old LED

[Mcologist]

Re: Ordering SMD LED for backlight

Thanks everyone for the help I have ordered a few and hopefully can test it out before the end of the week

[budm]

Re: Ordering SMD LED for backlight

How do you know it is a 6V?

Set meter to diode mode, the 3V LED will dimmly lights up and look at the readout on the meter, the 6V probably will not due to meter does not have high enough potential Voltage to bias on 6V LED.

[Diah]

Re: Ordering SMD LED for backlight

Set meter to diode mode, the 3V LED will dimmly lights up and look at the readout on the meter, the 6V probably will not due to meter does not have high enough potential Voltage to bias on 6V LED.

SMD LED when it say 6V. mean maximum. with DM diode mode. most DM are 9.volts Battery this will not make sense. average all direct LED back light are 4.7 V. this is my calculation always on how many mount of LED used on one LINE. of course each Brand use 1 line or 4 line or 2. but still PSU will provide 126V for line. BTW Haier Pure Chinese. which they use 3030 6V SMD LED

[budm]

Re: Ordering SMD LED for backlight

If meter can forward on the 6V LED (Vf will be much lower at low current which the meter is limited to, so the readout on the meter will be <6V, the meter in diode mode will show Vf of the semiconductor. So the 3V LED may show something like 2.7V on the meter. Easy enough for OP to use his meter to test his working LED to verify, no t hard to do, is it? The spec of the meter will also show what the output limit is in diode mode.
LG 3030 Dual-LED.

[Diah]

Re: Ordering SMD LED for backlight

also show what the output limit is in diode mode.

you are right with RGB SMD LED, this will not work at white 5600K designed for TV back light. VF here in TV don't play any roll. but current yes and this why we have 0.5W- 1W-2W etc and all of those use 12V for example

[budm]

Re: Ordering SMD LED for backlight

"VF here in TV don't play any roll" What do you mean Vf of LED does not play any roll?
OP just have to use his meter in diode mode and report what the Vf shows on the meter. If is is single 3V LED it should show something on his meter in diode mode.Why just not wait and find out the result from OP?
BTW, my FLUKE 87 uses 9V Battery, in Diode mode it has open circuit of 3.50VDC, and 1mA (shorted current).

[Diah]

Re: Ordering SMD LED for backlight

"VF here in TV don't play any roll" What do you mean Vf of LED does not play any roll?

budm.. sorry to say you still don't have the deep understanding of LED in General and how it built with LID and Ziner D on opposite direction.
volts had nothings to do... only current CURRENT .. go back refer to yours attached pdf.. where are the VF ? and how it calculated with current forward.

many years ago i posted here complete post on General TV LED back light edge and direct one. sorry .. if you believe what you write here VF volt forward...o say.. its wrong and i should correct it with my respect to yours knowledge

[budm]

Re: Ordering SMD LED for backlight

Sorry I am just too stupid to understand that you have to have enough Voltage potential on the semiconductor to bias it on for it to start conducting current. BTW, you use curve tracer before, correct?
BTW, I only from 1978 ~ 1986 at Fairchild Semiconductor Discrete Division which makes Transistor, MOSFET, Diode, and LED.
Please look at the VF/If chart of the LG spec I provided.

[Mcologist]

Re: Ordering SMD LED for backlight

I measured the voltage on the LED connector on the power board and am getting 252V so drop across all 50 LEDs would be about 5v each. Diah is correct in his answer of 4.7V or 6V LED's I believe.

[budm]

Re: Ordering SMD LED for backlight

252V reading with ref. to chassis GND and working LED in place? I thought you have bad LEDs so the LED string does not light up. It is always best to verify.
BTW, most power supply board will have Voltage chart showing the Voltage and current rating for each outputs.

[budm]

Re: Ordering SMD LED for backlight

BTW, what is the LCD panel number?
You may want to really think about replacing just the bad LED's only or not, it is big screen so if some already went out, the other may well go bad later on, it is big panel which will be bad if you have to take it apart aging if some other LED's go out. They drive those LED at the max rating without good thermal management.

[Mcologist]

Re: Ordering SMD LED for backlight

Measured the voltage with the bad LEDs in place as they are failed open. And the only voltage chart is for the main board power connector this brand seems bad with their marking and obviously their engineering as the tv is not very old. I'm planning to just replace the two burnt out LEDs and apply thermal paste to the back of the strips to help transfer the heat better to the back panel of the tv.

[budm]

Re: Ordering SMD LED for backlight

That is why you are getting 252V because there is no load due to open circuit, that is how it will react when no load is present for constant current power supply source.
Can we see good clear pictures of the power supply/LED driver board?
How many are there on the LED connector?
LCD panel number?
BTW what does it show on your meter when you check 1 LED with your meter in diode mode?
If you look at the LED Vf VS If I porvided for the LG LED, Vf is a 6.5V at 175mA so total Vf of the LED string (if all 50 LED's are connected in series o form one large LED string) will be 6.5V x 50 LED's = 325V + the Vdrops on the PWM Control MOSFET on the low side for maintaining constant current (25 ~ 30V is typical, it will vary with the current) and on the current sensing resistor.

LED strip P/N CRH-K55EMD30301005684
https://www.shopjimmy.com/haier-crh-...-strips-10.htm