LCD/LED TV panel

[Nigel Goodwin]

Just thought I'd share this you.

I've just dismantled an LCD panel out of a 46 inch Sony TV, in this particular case the LCD is a Sharp model.

Interestingly it's edge lit top and bottom, with two modules on the top, and two on the bottom, each containing 47 LED's in series. The modules are connected in pairs in series as well, so it uses two series chains of 94 LED's - and four wires are brought accordingly, actually split left and right rather than top and bottom.

I've just measured the voltage drop across a single LED, and it's 2.7V fed from 12V via a 390 ohm resistor - s0 that makes just over 250V for the entire series chain of 94.

So what to do with them now?

 

[Externet]

Unlikely they are 250V. Usually strips are several paralleled sets of 3 to 4 LEDs, for 12V operation.

Make them under-cabinet lights.

 

[Nigel Goodwin]

Unlikely they are 250V.

No, it's normal for high voltage series chains in TV back-lights - so 250V sounds perfectly reasonable - and the wires feeding them are very thin as well, as you're only talking about a few tens of mA.

 

[alec_t]

So what to do with them now?

Christmas is coming. Time to make something to dazzle the neighbourhood .

 

[Tony Stewart]

Sounds like an inexpensive way to drive 188 regulated LED's to me, with a low current.
If these are driven at 60mW then 188 LED's would be 11.3Watts for a 0.6 square meter display

If designed for the standard display brightness of 250 lumens /meter squared and the LED's are driven at 20mA,
Then the display would be 250 * 0.6 = 150 lumens and the efficacy would be 132 lumens per watt. which is pretty good.

 

[dr pepper]

You can get indicator lamps from china, pygmy lamp sort of size, and they are a capsule with a shed load of leds in series running at about 210v.

 

[Externet]

Something else I learned today... 250V led strips ! Thanks.
If any spare time, could you post a picture of its power supply ?
Thank you.

 

[Nigel Goodwin]

Something else I learned today... 250V led strips ! Thanks.
If any spare time, could you post a picture of its power supply ?
Thank you.

The power supply is on the main PSU, which they don't supply a schematic for (or any details at all) - I also don't have it, as the set went back to the customer repaired (but Sony didn't want the old panel back, so I stripped the LED modules out )

 

[k7elp60]

For last halloween I made a single string of LED's for about 160 volts. All the LED's were in series and a blinking LED in the series string so all the LED's ran off the power supply. It was a lot of work as the LED's were spaced about 4'" apart so I had to connect wires to some of the LED's.
Nigel I think you will come up with a idea for the modules.

 

[Nigel Goodwin]

Nigel I think you will come up with a idea for the modules.

At the moment I'm still trying to find a simple way to get a current limited 125V or so to feed one string to see how bright they are

 

[k7elp60]

Nigel, if I did the math correctly (12-2.7)/390=23.8mA. That seems a little high for the current. You got my mind working on a current limiter for 125V though. Is the 23.8mA the current limit you want, or is some other value? Please let me know.
Ned

 

[Nigel Goodwin]

Nigel, if I did the math correctly (12-2.7)/390=23.8mA. That seems a little high for the current. You got my mind working on a current limiter for 125V though. Is the 23.8mA the current limit you want, or is some other value? Please let me know.
Ned

The 390 ohm resistor was just one I randomly grabbed, so as to roughly measure the voltage drop across the LED - I had no intention of specifying that as a suitable current

As I've no idea what, if anything, I'm going to do with them I've got no assumptions on the current. I would like though to light up at least one entire string, just to see how bright it is.

Incidentally, the LED's are SM (obviously) and have six pins - although only two look to be used.

 

[k7elp60]

The 390 ohm resistor was just one I randomly grabbed, so as to roughly measure the voltage drop across the LED - I had no intention of specifying that as a suitable current

As I've no idea what, if anything, I'm going to do with them I've got no assumptions on the current. I would like though to light up at least one entire string, just to see how bright it is.

Incidentally, the LED's are SM (obviously) and have six pins - although only two look to be used.

Nigel, I am not sure what you may have in test fixtures to light up one string. Since the voltage is about 125 volts, if it were me I would use a isolation tranformer and a 1/2 wave rectifier and then use a variac on the primary of the isolation transformer. I would put a resister in series with the string and adjust the voltage with the variac. I still have an 100W isolation transformer and a 1A variac that I got over 25 years ago. Occasionally they come in handy.
Ned

 

[Nigel Goodwin]

Nigel, I am not sure what you may have in test fixtures to light up one string. Since the voltage is about 125 volts, if it were me I would use a isolation tranformer and a 1/2 wave rectifier and then use a variac on the primary of the isolation transformer. I would put a resister in series with the string and adjust the voltage with the variac.

I'm considering doing that, if I knew where the variac at work was

We moved to a MUCH smaller workshop a couple of years ago, and I'm not sure where it went? - I knew exactly where it was in the old workshop.

 

[dr pepper]

Is that 2 years since, time flies.

 

[Nigel Goodwin]

Is that 2 years since, time flies.

It's hard to remember

As you say, time flies.

 

[k7elp60]

I'm considering doing that, if I knew where the variac at work was

We moved to a MUCH smaller workshop a couple of years ago, and I'm not sure where it went? - I knew exactly where it was in the old workshop.

Nigel, another suggestion. If you have a lamp dimmer, how about keeping the lamp in the circuit and using a 1/2 wave rectifier and a series resistor connected to one side of the lamp and the LED string connected to the residtor and the other side of the lamp. As you know the voltage across the lamp will vary with the lamps intensity.
Ned