Controlling LCD B/L

[Charles Linquis]

Wow! Thanks!
I have an application that can use that. My PIC circuit is powered by a tiny AC -> 5V switcher (1"X2"), and I barely have enough extra power to run the backlight. This display solves the problem.

[Acetronics2]

Hi, Charles

And keep in mind those "new" backlights need " not so far " from 5 v supply !!!

Mine are rated 5v @ 0°C and 4.7v @ 25°C ...

Regards

Alain

[Melanie]

Hmmm... this 5v business is debateable... I've run them from close to 24vDC (with a suitable current limiting Resistor of course - at the end of the day it is no more than an LED). I must admit, the early ones (back from 2004) that have been run 24/7/365 at about 70% brightness are starting to get a bit dim, and you need to turn the brightness up to about 90% to achieve the same level as a new unit... We've have ONE dud B/L LED in that five-year period (after 3 years service at near 100% brightness supplied from about 20vDC).

Hey, nice picture Alain - nice to know what folks look like... *smiles*

[Charles Linquis]

I think the confusion here is the trouble that a lot of people have with LEDs:
You can't just run them like a lamp, you need a current-limiting resistor.

The forward voltage of most backlights is 4.2-4.7V, so if you need to provide them with 100mA of drive, you need (5-4.5) = .5V/100mA = 5 ohms in series.
You can power the same backlight from 24V, but then you would need (24-4.5 = 19.5/100mA = 195 ohms in series. Please note that in the latter case, the resistor would dissipate close to 2watts.

A few LCDs have the resistors "on board", but most require external current-limiting resistors.

[Acetronics2]

Hey, nice picture Alain - nice to know what folks look like... *smiles*

Hi, Mel

I knew you would love it ...

You've always been a romantic girl ...

BTW ... Try to find the Film " Always " by Steven Spielberg, starring R. Dreyfuss ...

you'll love it.

really

Best Regards

Alain

[Ioannis]

I must admit, the early ones (back from 2004) that have been run 24/7/365 at about 70% brightness are starting to get a bit dim...

Well, 5 years are almost half the LED life provided that LED are kept cool at room temperatures.

If the temperature is higher than 25C, then the 44.000 hours seems resonable enough.

Ioannis