1. Home
  2. Electronics Design
  3. LCD displays and EMC

LCD displays and EMC

The LCD display itself ought to be pretty inoffensive - the voltages are low, the currents are very low, and there is no necessity for fast edges.

The back-lighting can be a problem. Jim Williams of Linear Technology has written a number of application notes of the subject - I've found AN-81, AN-65 and AN-55 on the Linear Technology web-site - which refer to generating kilovolts to drive cold cathode lamps at ten of kiloherz.

He does recommend a resonant inverter (an example of a Baxandall class-B oscillator, thogh Jim Williams calls it a Royer inverter), which minimises the switching transients.

---------- Bill Sloman, Nijmegen

Reply to
bill.sloman
Loading thread data ...

Possibly your biggest problem is the hole in the case needed to view a display. That'll let in and out all manner of garbage. I doubt that the display itself will be of any great concern.

Graham

Reply to
Pooh Bear

I have an application where I require 2 line by 8 character (minimum, but more characters would be OK) LCD modules. The character hight should be around 4-6 mm. They have to be "intelligent" in as much as they can be driven directly by RS232. The end product will have a total of six modules.

There's quite a number of these items on the market, but the end product spec has to meet a fair amount of MIL-STD-461E for EMI/EMC.

Has anybody found LCD modules that are especially quiet and that easily passed 461E or similar? I would much prefer not to use conductive mesh or the like to reduce emissions and susceptibility.

Barry Lennox

Reply to
Barry Lennox

The hole noted by Graham will probably be your biggest issue, although you don't say what material the box is to be made of.

If it's conductive, you can get EMI gaskets to fit between the LCD display and the cutout in the box.

As to backlight inverters, they are always noisy ( I have one in a design now, and it had to be shielded so the internal gubbins worked correctly, let alone get through EMC ;)

Cheers

PeteS

Reply to
PeteS

The box is 6061 alloy. and right now I'm looking at a simple LED backlight. Efficiency or heat is not too much of an issue.

I'd prefer not to use EMI material for screening the displays. It's pricey and obstructs vision to some extent. However, it can be kept ready as a last resort. If it fails RE or RS via the viewing hole (about 10 x 50 mm) I can just throw a sheet of it at the problem.

Thanks for the comments.

Barry Lennox

Reply to
Barry Lennox

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.