LCD backlight overheats 7805

[keithdoxey]

So lets say I move the lcd backlightpower to the source before my 7805 regulator which is powered by a 12v wall wart adapter. Do i need a voltage divider before feeding the power to the LCD backlight?

You just need a bigger resistor instead of the 11 ohm you currently have.

With your 11 ohm resistor you have 50mA flowing through the backlight.

11 * 0.05 = 0.55V dropped across the resistor so your LED backlight has a forward voltage of 4.45 volts.

For a 12v supply you need the resistor to drop 7.55v

7.55/0.05 = 151 so 150 ohm 0.5 watt resistor for 12V supply @ 50mA

For the 18v supply you need the resistor to drop 13.55v

13.55 / 0.05 = 271 so 270 ohm 1 watt resistor 18V supply @ 50mA