use spare led backlights from one tv to test the led driver of another tv?

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

ok ok im reading! thanks again

[budm]

Re: use spare led backlights from one tv to test the led driver of another tv?

Yes it can be done, you just need to know the power supply voltage, the LED forward voltage which about 3~4V, as shown in one of the link, you put in the Vf of the LED, the quantity of the LED is series, it will give you the result.
You need to study those links and make up the circuits otherwise you will not learn.

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

thanks for all the reading material... but can you tell me first if theres a light at the end of this tunnel or if im chasing wild geese?
if it can be done, it hardly seems right that it should be ME, the lowliest of noobs to figure it all out for everyone... i was wondering if someone has figured this out before?

either way im reading all those links.
thanks bud!

[budm]

Re: use spare led backlights from one tv to test the led driver of another tv?

http://ledcalc.com/
http://www.ohmslawcalculator.com/led...calculator.php
http://www.pcboard.ca/kits/led_notes/
http://www.daycounter.com/Calculator...lculator.phtml
http://www.hobby-hour.com/electronics/ledcalc.php
You have to do some research on your own to learn.


http://www.hebeiltd.com.cn/?p=zz.led...tor.calculator

http://electronics.stackexchange.com...iting-resistor

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

can you tell me before i ask a bunch more dumb questions, if what im trying to do is even possible? or is every LED strip different based on the panel and theres no way to know if you're going to fry stuff by swapping??

like..what if i just wanted to power some strips on my own. what voltage and amps would i have to give them? could i hack an ordinary ac adapter or ATX power supply from a PC to power these things?

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

Ok that makes sense. So how does one measure a diode that has a voltage drop greater than what his meter puts out?

[budm]

Re: use spare led backlights from one tv to test the led driver of another tv?

You cannot test the resistance of the LED strip, your meter does not out out enough Voltage to bias on all the LED string which the LEDs are connected in series. Each LED requires 3~4V for the Vf (Forward Voltage). You need to understand how Diode function then you will know why. Do the research on how Diode function. Some meter also may not put out enough Voltage to test each White LED either.

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

ok so i got some edge lights from a panasonic TC-L47E50 that had a cracked screen. i also have all the other boards so i can probably get them powered. but what i would like to do is use the LGP4750 to power them.

some things i discovered from looking at these edge lights for a bit:
there are 48 LED lights in each edge
they are broken into 6 groups of 8
there are 8 pins going from the LED driver board (which is a separate board from the PSU in this tv) to the left edge light
and 8 pins going to the right edge light
2 of those pins are + and the other 6 are -
on the edge led strip you can see that the 2 + pins are grouped together and shared by all 6 groups of 8 LED's
the remaining 6 negative pins each go to the negative side of one of the 6 groups of 8 LEDs on the strip.
so they all share the same + but they all have separate grounds?
i dont know enough to guess at why its setup like this but im just in the observing stage...

again i cant seem to get a resistance reading on anything. even putting the probes on either side of one LED yields infinite resistance..

guess ill try put this tv back together somewhat and see what voltage is coming out of the driver board?

is it possible to use these edge lights to test a led driver circuit that was designed to power direct lit instead?

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

ok on the LGP4750-13PL2 i have ~30vdc on both of the VLED- pins and ~120vdc on the VLED+ pins...how do i test the resistance of the LED strips? ive tried putting the probes any way i can think of on the vled pins and on the strips themselves and its all infinite resistance

[budm]

Re: use spare led backlights from one tv to test the led driver of another tv?

You know you have this:
https://www.badcaps.net/forum/showpo...03&postcount=1
So why don't you treat as an unknown board for you to try to figure out what kind of load you will need to make to test LED dummy load to hook up to this power supply board.
And also do what I suggest here:
https://www.badcaps.net/forum/showpo...9&postcount=14
You have to do the research to understand how it works then you will know what you need to do.
You have that working unit for you to do hands on learning with it.
You can see the IC, the MOSFETs, etc, in the LED driver circuit as shown in the pictures.
The power supply board in post 1 LGP4750-13PL2:
http://www.shopjimmy.com/media/catal...801-bottom.jpg

http://www.shopjimmy.com/media/catal...810801-top.jpg

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

i was thinking it could get around the problem budm brought up with the light bulb drawing too much current when it first turns on because of low initial resistance until it heats up..
why wouldnt this work to counteract that?


just fishing for a way to reliably test LED strips here which i think we can all agree is something we need!

[Agent24]

Re: use spare led backlights from one tv to test the led driver of another tv?

is there a reisistor that starts out high resistance at room temperature and then goes low resistance as it heats up?

Yes, an NTC thermistor does that. They are used as inrush current limiter in SMPS to reduce the current drawn as the main capacitor charges up when first turned on.

I don't think it would be of much use here though.

Edit: Dammit, too slow again!

[budm]

Re: use spare led backlights from one tv to test the led driver of another tv?

"is there a reisistor that starts out high resistance at room temperature and then goes low resistance as it heats up?" Yes, it is called NTC (Negative Temperature Coefficient) Thermistor which uses a lot for inrush current limiter.

http://www.ametherm.com/thermistor/w...ntc-thermistor

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

is there a reisistor that starts out high resistance at room temperature and then goes low resistance as it heats up?

[Alastair E]

Re: use spare led backlights from one tv to test the led driver of another tv?

Always summit--Innit!

These damned things are getting too clever by half!

[budm]

Re: use spare led backlights from one tv to test the led driver of another tv?

40W cold resistance will have cold resistance around 36 Ohms (Hot reistance will be 360 Ohms) so the current sensing circuit will cause the power supply to go into shutdown mode due to current of of over 2A @ 83V at first power applied.

[Alastair E]

Re: use spare led backlights from one tv to test the led driver of another tv?

How about using a 20-40W 120v bulb in place of the LED to see if the supply runs it....?

[budm]

Re: use spare led backlights from one tv to test the led driver of another tv?

27 LEDS x 3.1V (or 4V) = 83.7V (or 108V) so measure the Voltage at LED + LED -, the Voltage reading will not show up as calculated since the are may be PWM driven. So check the voltage to see what you get. Getting the IC spec sheet will give you more details.

[triplefour]

Re: use spare led backlights from one tv to test the led driver of another tv?

i did trace it... there are 2 +- pairs and they each drive 3 led strips in series

we call those 3 strips in series a string?

so yes it is 27 per string...27 per +- pair

so its safe to check those voltages? and amps too?

[budm]

Re: use spare led backlights from one tv to test the led driver of another tv?

You can check the Voltage at those caps close by, they are for the power supply for the LED. If the backlights are working then you measure the Voltage at the LED+, LED -. It looks like it has two LED strings.
Since this https://www.badcaps.net/forum/attach...7&d=1413982161 is working, why don't you see how the LED strings are connected and count how many LED are in the stirngs. There are 54 LEDs total so see how they are connected, Is it 27 LED per LED+ LED-? You trace them out and also look at the ICs around that area of the LED connector to see which one is for the LED driver, that is how you learn, you have do the research.