Any one have any advice for CCFL to LED convertion?

[jeffescortlx]

An Acer x193w 19" monitor was given to me. It has a bad CCFL.
I want to convert it to LED backlit.

This is the LED's I have picked out:
http://www.mouser.com/Search/Product...rkeXLRgw%3D%3D

They are a white "9000 K" (how ever white that is) short 5mm. (hope it fit's)
"Through Hole" so I can just solder them up, in series groups of 4 (they are 3.2v each).
I'm just gonna use the 12v supply that's there for the inverter, and use a transistor off the inverter enable trigger signal to turn them on.

They are a 110º LED, should have a nice wide beam so I don't get bright stripes. I'm wondering if I can get away with 8 on top and 8 on bottom. I could do 12 or 16 top/bottom.
So it will cost $3.04 to $6.08.

Any one have any advice? Will they fit in place of the CCFL lamp, and will the Wavelength/Color Temperature of 9000 K be white enough to not screw with the display color?

[JimmysTGP]

You sure got me thinking about something like this, However you do understand that theirs active lines that go to each LED array, which may make the Brightness seem to high in some areas and the contrast seem low in others. Thats the reason why they calculated all these factors in to be able to get the best whites and blacks to the areas neccessary. But the Idea would most definitly have my interest if you were to take this project on. Fill us in on the progress if attempted.

[999999999]

I doubt it's going to work out well for 3 reasons.

1) 9000K is a very blue tinted light. Typical CCFL is closer to 5K though I'm not sure about those in monitors. You might or might not be able to boost red and green and reduce blue with monitor controls or the video source but you're already at a disadvantage.

2) They won't produce nearly as much light as a couple CFL tubes.

3) It'll be unlikely that they end up producing uniform light. Even when professionals design lighting systems with CFLs, even they can't avoid a little bleedthrough around the edges.

[jeffescortlx]

I am moving forward with this project. The LED's came in a few day's ago.

I haven't had a chance to install the LED's yet, but I did test one of the LED's to get an idea on how well/bad it will go.
So far, I think it might work out OK. It's a lot less blue then I was expecting, and the beam is spread out very wide, so I don't think I will see any streaking or bright strips of light. It wasn't super bright, with a lit room, I could light up my hand about 10" away. But I will have 16 on top and 16 on bottom, and it's only a 19" panel, so I'm confident I'll have plenty of light.

And if it turns out a failed project, I'm only out $6 for parts and $6 for shipping.
I had gotton the monitor for free, and my other option was to just throw it away.

[budm]

Do you have any plan yet for dimming?

[momaka]

Keeps us posted how it goes.

I have an old 15" LCD I want to put LEDs in since it has a dead CCFL on the bottom and the top one is very dim (probably on its way out too).
I'm thinking if I should use pre-built LED strips, though. They are very cheap on ebay, and you won't need resistors or drivers or anything like that. Just hook them up straight to 12V.

However, the only concern I have about those LED strips is the quality. Currently we have 2 sets at my workplace, both working 12 hours a day for the past 2-3 months. One of them has started to develop many dead or dim LEDs, while the other is fine. The LED strips are from different companies, though, so I guess there's a bit of luck involved there. So if anyone decides to use cheap LED strips from eBay, just be advised of their quality.

Originally Posted by budm

Do you have any plan yet for dimming?

I don't know about dimming, but he will definitely need to do something about driving them properly so they don't burn out. Most simple way would be to put 3 LEDs max in series and then use a resistor to drop 2.4V with a resistor. The resistor should be chosen to allow the proper current to the LEDs.

Since these LEDs are rated for 25mA @ 3.2V each: 3 of them in series will require 9.6V @ 25mA to run. That means the resistor will have to drop 2.4V. So the resistor value will need to be 2.4 V / 0.025 A = 96 Ohms. A 100 Ohm resistor should work fine.

Before putting the LEDs in the screen, I would strongly advise to use a multimeter to measure the current going to the LEDs to see if any adjustments need to be made to the resistor values.

If you want dimming, I would guess the easiest route would be to use a PWM controller.

[budm]

He will need to build analog variable constant current source for Dimming, max current will be about 30 mA and go down from there. Or PWM using 555 TIMER.

[jeffescortlx]

Originally Posted by budm

Do you have any plan yet for dimming?

Yep. Set it up, and if it's too much light, I'll add resistance until it looks good.
I really dont see the need to go over board on a monitor that can be replaced in good working order for 40 bucks on craigslist.

Originally Posted by momaka

I'm thinking if I should use pre-built LED strips, though.

I looked at these at mouser, and they were all pretty expensive.
Plus with individual LED's I have a little more freedom with spacing and voltage control.

Originally Posted by momaka

Since these LEDs are rated for 25mA @ 3.2V each...

The 12v power supply is on the high side, so I can use 4 in series. I might not need any resisters at all, but I'll check the voltage across each LED and measure the current once I get it set up.

[999999999]

You'd be better off with 3 in series and a resistor to limit current so you have the (nearly) exact drive current you want.

[jeffescortlx]

Originally Posted by 999999999

You'd be better off with 3 in series and a resistor to limit current so you have the (nearly) exact drive current you want.

True.

But, I'm putting this project on hold until I run across another panel with bad back lighting. I was given a used panel that was intended to be used to scavenge parts from. It wasn't suppose to work, but just for the heck of it I hooked it up and it's been running great all afternoon.
The screen is in better shape then the one I was going to do the conversion to.

[momaka]

Originally Posted by jeffescortlx

I looked at these at mouser, and they were all pretty expensive.

Under $2 on ebay with free shipping from China. The only downfall is the slightly longer wait times. I think I will buy a set for my 15" LCD if I find the right size. Maybe even a few more for other various projects.

Originally Posted by jeffescortlx

Plus with individual LED's I have a little more freedom with spacing and voltage control.

True.

Originally Posted by jeffescortlx

The 12v power supply is on the high side, so I can use 4 in series. I might not need any resisters at all, but I'll check the voltage across each LED and measure the current once I get it set up.

Just like diodes, LEDs are highly non-linear devices. That is, near their turn-on voltage, their resistance changes quite drastically. So for example, at 3.15 V your LEDs may be very dim, but near 3.2 V, they may be fully bright, and near 3.22 V they may burn out. Most switching power supplies (LCD, PC, and other electronics) tend to have +/-5% tolerance - more than enough to make your LEDs either too dim one instant and burn out the next.

To get even brightness from your LEDs without having the PSU variations affect them, you need to control the current going to the LEDs.