CFAG240128LYYHTZ backlight specification

[mare]

Hello everybody!

When looking through the CFAG240128LYYHTZ datasheet, I came across backlight specs. According to the spec ILED is 900mA typical and 1350mA maximum. That's seems awfully high! Is this correct? Why is it so high? I checked other displays in the same category and they all have lower currents. Can anyone confirm this?

I did some calculations and it turned out that if I want to power the backlight through 12V that I would need R=(12-4.2) / 0.9 = 8.6 ohms ... and P = 7.02W ! That's awfuly big! If I want to use car's 12V that would be even trickier since the voltage there is around 14,2V!

Are there any other suggestions? How exactly should I limit such current ?

Thanks!

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[cosmicvoid]

You will probably find that the backlight brightness would be acceptable with a lower current. How much lower? I don't know, since I don't own this display; you'd have to experiment. I'd imagine that 300~600 mA might be adequate.

As for methods, you could use the calculated resistor value, or you could rig up an active current source, such as a LM317 hooked up in current-mode, if you are using a source voltage higher than 6 volts. The advantage of the active current source is that the output current would be independant of any source voltage variations, and adjustable via a small pot.

The problem with either method is dissapating the wasted power. The resistor should be rated at double the calculated power. The LM317 would have to be on a heat sink.