April 22, 2008, 01:20 PM
CFAX12864CP1-WGH EL backlight driver
I purchased a CFAX12864CP1-WGH LCD (with EL backlight) and the demo board. The demo works beautifully, so I built a PCB with a smaller EL driver than the big black box on the demo board. I used a chip that is designed for 3 in.sq. EL backlights that works at 160Volts peak to peak. The problem is that the backlight does not light up bright enough. It is so dim that in a lit room I cannot tell if the backlight is ON or not. But with the demo board the backlight is very bright even in a bright room. So I started comparing the the two circuits and found that the demo board is driving the backlight at over 320Vp-p.
The chips I have tried are MIC4826 which is spec'ed at 160Vp-p, MIC4832 (220V p-p) and HV857. I have tried to change the driving frequency between 200 and 1100Hz. The frequency has a big impact on the brightness, but I don't come close to that of the demo board.
I have trouble believing that such a tiny LCD needs such a huge driver for its backlight. There must be some way of driving the backlight to a proper brightness without the huge inverter?
Can you suggest a design or a chip that I can use to drive the backlight at this voltage/frequency without a big inverter?
Can you tell me if the same LCD with the LED backlight as the same brightness as this LCD with the demo board? If so, perhaps I can change the design to use the LED backlight LCD instead of the EL backlight.
April 22, 2008, 11:13 PM
EL backlights are typically chosen for thinness, and traditionally (before white LEDs) chosen for low power.
Brightness is not one of their strong points.
The darker the room, the less light you need. If you can't see the backlight in a bright-lit room, but you can see the display, then the reflective part of the "transflective" display is doing its job, allowing the display to be visible, while still using no power for the backlight.
If you want a "bright" display, you probably want to use the white LED version.