Newbie Trying to control CCFL

Community PCB Design
1

Hey guys!! I am attempting to mod a laptop in order to hold more than one video card when it really isn’t supposed to.

I have a large question for you.

The new video card is not working properly with the inverter, aka. there is not any backlight brightness control and its stuck at the lowest setting.

Now I believe it’s controlled through pwm. And I was going to buy a whole new inverter that I’d use with a switch in order to make work correctly. However I have some questions regarding it. I’d really like to be able to keep my original inverter and be able to change the brightness using a dial aka pot trim or smth. Do you know enough about inverters and pwm in order to help me out, aka design a circuit that could change the pwm signal it’s SUPPOSED to get from the video card and put it to another source? Also where would I put the video card’s wires to the inverter afterwards.

The last thing is, my original idea was to use a seperate dc - ac inverter with hopefully a pot that would allow me to change the amperage and for it to keep up the high voltage needed for the cold cathode flourescent lamp. I wanted to have a switch to choose when to turn that on, or to use the seperate inverter. (I was thinking about a switch for which inverters output voltage goes to the lamp, but I think there are issues when the voltage is that high in just blocking off the circuit. or are there?_

As you can see I have a lot of questions, and appreciate any help you could give me. Thanks a million, I’ll put you in my credits for the project :stuck_out_tongue:

Sincerely,

myke

PS. I’m quite a newbie at this so if you have amazing ideas please do it kindergarden style. Im hoping to learn alot but not need a course in order to get this to work.

Thanks alot again :slight_smile:

2

First off, this sounds like an extremely complex project for a self-described newbie to be undertaking; I salute your initiative but take it slow (especially around the high voltages that CCFL supplies put out!)

If your CCFL brightness is indeed controlled by PWM (you need to make absolutely sure of this), there are a few ways to generate it. Most of us around here would program up a microcontroller like an AVR to read a pot and generate the PWM. However there are simpler ways of doing this, such as using a 555 timer chip: http://www.dprg.org/tutorials/2005-11a/index.html. You’ll need to figure out what voltage the PWM signal needs to be, and run the above circuit at that voltage. PWM also uses a base frequency, and you should try to get close to what the CCFL supply wants. If you had access to an oscilloscope you could look at the existing signal to get an idea of its parameters.

As for your other questions about which wires to hook up to and adjusting the amperage, I haven’t a clue and wouldn’t want to even hazard a guess because of the danger to yourself and your equipment… this is really a situation where an experienced tinkerer should be there to help you in person.

Good luck with your project!

-Mike, SparkFun Electronics

“I mean, being a robot’s great but we don’t have emotions and sometimes that makes me very sad” - Bender Bending Rodriguez