0
\$\begingroup\$

I have a few lcd open panel screens I've modified with higher powered led strips instead of ccfl. In doing this I needed to add led drivers for voltage and current regulation. When utilizing the same power source there is so much noise and static and interference that the screen shuts down. When not changing anything except running the power to the drivers via a seperste power source (even non-grounded AC/dc) I get no interference at all. I built an LC filter which helped a bit but these are still unusable. I need to use them off the same power source because they are portable. I can't seem to figure out how to reduce the interference. Any ideas?

\$\endgroup\$
  • \$\begingroup\$ Can you put a DC LISN in the power input to the LED drivers, then get us scope/specan shots of what they're dumping back onto the line? \$\endgroup\$ – ThreePhaseEel Dec 10 '16 at 5:19
  • \$\begingroup\$ DC LISN I dont have - Scope I can do but I'll need to find another way to measure the RF noise. It definitely is coming from the LED driver side though as by not moving a single component, just wiring the driver to an external power source (whose lines run nearly parallel) to the battery wires, the interference is gone. I originally thought it was an issue with grounding but thats not it. Not sure how to test for the fix though. \$\endgroup\$ – RJ44 Dec 10 '16 at 18:22
  • \$\begingroup\$ you probably could (quite carefully) DIY a DC LISN -- the base circuit is a 50uH inductor in series with each power line, and then 1uF film caps from each power input terminal to earth, a 100nF film cap from each power load terminal to each signal output's center terminal, and a 1kOhm resistor from each signal output's center terminal to earth, all built into a well shielded and earthed metal box. Good lead dress is important, though, to avoid unwanted parasitics and get the frequency response desired. \$\endgroup\$ – ThreePhaseEel Dec 10 '16 at 18:32
  • \$\begingroup\$ Thanks ThreePhaseEel, Im up for a challenge. I wired a separate cc/cv from the same power src as the LCD (bypassing/isolating the driver completely) and the interference lives-Thought then maybe its LEDs themselves but that wdnt make sense bec I ran the other set of LEDs (1 strip top 1 bottom) from the ext src through the driver and no interference-If the driver+LED+LCD are on the same power src - interference. If the driver+led(stripA) on external source and LCD separate - no interference. Lastly - if the LCD + separate cc/cv are on the same src while LED(stripB) is ext powered, interference. \$\endgroup\$ – RJ44 Dec 10 '16 at 19:20
1
\$\begingroup\$

Ok - figured this out (but I don't understand how the solution works). It is a grounding issue that causes the interference (static on the LCD). If I run two separate power and ground cables to the same battery source, static appears (tried everything, LC filter, twisted wires, inductors, caps. No difference). To solve the issue I needed to run the ground (and vcc) cable from the power source and attach it to the LCD controller. I then run a long ground cable from each component to the actual back of the LCD (which is metal as it is open frame). I stripped and exposed a couple inches of wire from each cable and put them on opposite corners, the further the better. Attached them by wedging them on the corners - couldn't solder as it is aluminum back panel. This was the only way to remove the static on the screen, having ground go through the panel. Issue solved - why this works I don't know.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.