ccfl controler

[cnctony]

I have repaired my 19" LCD screen by replacing the CCFL inverter board with a generic 12V inverter. I would like to control the Voltage to the driver board. I have a control signal that ranges from 100%=0.035v 75%=1.173v 50%=2.389v 25%=3.6v 0%=4.79v I intend to use an op amp to control the output. The max current of the 2 driver boards is 1.75amps when connected to 12V. I know how to connect the op amp 5Vto A+, sig across 1k res to -A 12v to v+ and 0 to V. I cant seam to figure what device to control the 12v from the output. An LM317? or what? Please help.

Thanks
Anthony

 

[Blueteeth]

Hi,

From my experience, CCFL driver boards rarely use a simple voltage to control the brightness of the tube on its output...its usually PWM, even on 'generic' boards. Running the 12v driver board at a lower voltage, it might not be able to reach the CCFL's start voltage, and if it does, the output probably wouldn't be linear to your control voltage.

However, if I understand your problem correctly....you have a control 'voltage' that is inversely related to the 'brightness'...so 0v = 100%, 5v = 0%, 70% = 1.5v? correct? And, you wish to control the driver boards power supply using this control voltage. Hmm, a LM317 might actually be able to do this. However, there are many here who are far more versed in 317 designs (Hero999, RonH?), I fear I would be out of my depth.

The reason I'm posting is I just don't think varying the driver boards power is a good way change the CCFL's brightness, almost all inverters I've seen have a 'control' pin. This is usually PWM, but not always, sometimes it uses a voltage as a reference, which will not draw much power at all, and can be controlled by an opamp circuit effectively.

If it does happen to have PWM control, a simple sawtooth (or traingle) wave generator and a comparator should do it. Seeing as how your control voltage is inverse to the output, you would simply swap the inputs to the comparator.
If it doesn't, then I'm out of idea's

You could always check ebay for ccfl driver boards for your monitor..theres loads on there.

 

[Hero999]

You might even be able to power PWM the driver board, you'd need a much lower frequency than the driver's switching frequency, 200Hz might be enough. I very much doubt you'll be able to get that much of a brightness control though, can't you get holf of a board with built-in brightness control?

 

[cnctony]

Thanks for the quick reply!

I do have a couple of scopes to check the PWM signal and did try and to my supprise there was a voltage signal not a PWM. I am pretty well versed in electronics and am just trying to get some advice on my circuit design. I did use a 2SD1061 and a pot to control the 12V signal to the inverter and was able to brighten and dim the lamps quite reliably. I also found out the hard way the the 1.75 amps was too much and actually one or more of the lamps was causing an excessive current draw and melted down my inverter board to the bottom 3 lamps. The top 3 lamps only draw 400mA at full voltage. I think I have got it down now. I do have a cad program to make a PCB and the ability to populate it, parts, soldering iron, drill. But just wanted some ideas. I guess its on to the bread board. Was hopeing someone has tackeled this before.
I have searched for this board and the cheapest I can find it for is $99.00 +S&H thats just tooooooo much to light a ccfl. I did check the board and could not find a problem. Now I know 1 or more of the lamps are bad I might try to replace the lamp(s) But I think it would be more fun to come up with my own solution and to hell with the expensive parts! Ambit 6633TZA015A. And come up with a solution for others.
Thanks
Anthony

 

[j777dragon777j]

hey all - I had the same problem with my gateway monitor and browsing the internet I found a forum where someone said that it had to do with the 4 100uf/25V capacitors on the backlight/inverter board. I just took my board out tonight as I was going to take it somewhere and get the capacitors or order them online...am I right with the specs on the capacitors because I have no idea and I want to order the right ones??? Please reply if you know. The name of the board is AMBIT 6633TZA015A Inverter 6CCFL Lamps TFT Module. THANKS!!!

Capacitance: 100 uF
Dimensions: 6.3 mm D x 11 mm L
Operating Temperature Range: - 40 C to + 85 C
Product: General Purpose Electrolytic Capacitors
Termination Style: Radial
Tolerance: +/- 20 %
Voltage: 25 V
Product Category: Radial Electrolytic Capacitors

 

[Nigel Goodwin]

Don't order '- 40 C to + 85 C' ones, order 105 C ones instead, the originals were probably 85 C, and that's why they fail!.