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LCD LED backlight question

Hi,

I just installed this LCD:

formatting link

to replace the dead one in an Alesis QuadraVerb (this doesn't really matter, it's more of a generic question).

The LCD display itself work fine but to get power to the backlight I ran the 5V source and ground that supplies the LCD part to the LED blacklight and it works too. However I'm wondering if I need to add a resistor to limit the current to the backlight like I normally would with regular 5mm LED. I've read the specs on the backlight but they aren't given as simply as:

# 30mA (max) # Typical Voltage is 2.0, with a maximum voltage of 2.8V

like I'm used to.

Can anyone point me in the correct direction?

Thanks!

Reply =BB

Reply to
stoneattic
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See page 11 of the spec sheet. VF(typ) = 4.1V @ IF = 112ma.

So you will need a series resistor sized to drop .9V at 112ma.

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James T. White
Reply to
James T. White

Thanks! That's actually what I thought but I wasn't sure I was reading that correctly on the spec sheet. So an 8 ohm resistor is the way to go? I assume a 1/4w would be fine?

Thanks again

Reply to
stoneattic

In a pinch you can start with a 500 ohm or so pot, then set it to max resistance, measure the current with a DMM and adjust the pot to get the desired current/brightness and then disconnect the pot, measure the resistance of that and choose a fixed resistor as close as you can get.

1/4W should be plenty, 1/8W should work too.
Reply to
James Sweet

Since I use this thing in the dark mostly I would lean towards the brightest I could get out of it which would be at a resistance of 0. hehe Obviously that's not a good idea. Do you think the 8 ohms would give me the best brightness and still protect the LED enough? I've got

10ohms resistors (1/8 and 1/4W) laying around so I may toss one of those in and call it done. How does that sound?

Thanks again!

Reply to
stoneattic

Reply to
M Berger

Measure the current, don't exceed 20mA or the LED will not last long.

Reply to
James Sweet

Don't I want (nominally) 112mA?

Reply to
stoneattic

I put a 10 ohm resistor in and get 90mA on the ammeter. Nice bright backlight too.

Reply to
stoneattic

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