While testing some TFT screens I've noticed some requiring a 12v back light power even though its a 3.3v display.
My initial thoughts where that 12v as a back light will just end up making the end device more complicated with an additional power conversion and rails.
Just wondering anyone's thoughts on this?
Think about it. You always have multiple LEDs in a backlight.
You are either going to put them in parallel or series.
e.g. 4 white LED with 3.1V forward voltage @ 25mA
If they are in parallel, the current will vary greatly with a 3.3V supply. You need to drop 200mV i.e. 3.3V - 3.1V. The LEDs are unlikely to divide the current equally (unless you use separate dropper resistors.
It is difficult to control the 100mA.
If they are in series, they might need 12.4V but it is easy to control this current. All LEDs share the same 25mA current.
TFT controller chips generate their own voltages internally.
But backlight voltage generators require a separate chip and inductor.
From the user's point of view. An SSD1963 800x480 display has external electronics on the pcb.
You just provide 5V/3.3V to power the external electronics and provide 3.3V GPIO logic for the TFT controller.
Short answer. Series LEDs are easier to control with a constant current.
David.