24v DC to 12v DC converter for LED backlight

[Heckler]

I did try to use 2 strips in series but didn't work so well.

Why did that not work?? It seems like it should have. You also should be able to supply an external Power resistor to drop half the supply voltage (which would be wasted as heat, not so good).

One thing you might consider would be to drive the ULN2003's using a PWM (pulse width modulated) signal at 50% duty cycle (or less for less brightness) and still use the native 24V supply.

Using the LMxxx regulators you are also going to be wasting half the consumed power as heat, dropping the 24v to 12v. A switching regulator (something I'm not vary familiar with) is the more efficient way to go.

Again, I would go back and find out why the parallel LED strips arent working. You would probably need to make sure each of the LED strips have the same number of LED's in each strip. Then just feed into one strip, cross over to the second strip and then to ground.

PS what is your source of LED strips?? I have been looking for some for a project.