Looking for an LCD controller chip

[Modelworks]

I have some displays that are 128x64 graphic LCD and the interface really isn't a problem, standard 8 bit stuff. The problem is the voltages the displays need. 5V, -48VDC, 200VAC @ 100khz. I can generate the -48vdc using a transistor/inductor/capacitor setup that is driven off a PWM channel of the micro but the 200VAC @100khz really adds more complexity to using the displays than I want. Getting 200vac off 5vdc means stepping up the dc then switching it through a transformer at 100khz, more than I want to do and adds a lot more parts to the mix.

I guess the one good thing is the current needed is really low , -48vdc @ 5ma and 200VAC @ 2ma.

5v is the VCC
-48vdc is LCD Bias
200VAC is for the EL backlight

These displays were pretty common before LED backlighting and I wondered if someone hadn't heard of a single ic maybe that was designed for these displays to generate the voltages with fewer external parts. I thought of replacing the backlight but there is zero clearance between the back and the display, just enough for a EL strip.

Thoughts ?

 

[PottedMeat]

i haven't heard of a single VCC/bias/backlight driver. heh i'm sure if you comb though enough national semiconductor datasheets you'll find a circuit like that when modified heavily will do all three using a hard to get IC.

what's the logic interface - 3.3 to 5?

200VAC @100khz

you sure about this? ELs are usually a few hundred hz

how many square inches?

there are some little 4-5 pin EL drivers that need just a capacitor/diode/inductor ( some even inductorless )


have you seen what the display looks with graphics and the EL backlight working? i've used a vikay 128x32 display with a Linear IC + transformer for a lathe readout and the contrast was awful no matter how much i adjusted it.

 

[William Gaatjes]

I once had to repair devices with an EL back-light display inside.
I noticed that the EL driver was a 90V DC voltage. That is possible but i do not know how much back-light intensity you need.

I think for the way Electro Luminescence effect, the DC voltage should not matter that much. But my knowledge is very limited on this subject.

 

[Modelworks]

what's the logic interface - 3.3 to 5?
you sure about this? ELs are usually a few hundred hz
how many square inches?
there are some little 4-5 pin EL drivers that need just a capacitor/diode/inductor ( some even inductorless )
have you seen what the display looks with graphics and the EL backlight working? i've used a vikay 128x32 display with a Linear IC + transformer for a lathe readout and the contrast was awful no matter how much i adjusted it.

The logic is 5V and the EL is 400Hz. Not sure where I got 100khz for those displays. The contrast is very good for these displays which is why I wanted to use them but not if I have to do too much that I couldn't just replace them with something easier to use.

 

[Modelworks]

I once had to repair devices with an EL back-light display inside.
I noticed that the EL driver was a 90V DC voltage. That is possible but i do not know how much back-light intensity you need.

I think for the way Electro Luminescence effect, the DC voltage should not matter that much. But my knowledge is very limited on this subject.

I tried them with 120VAC from the regular wall outlet and they glow but not very bright. I was told that frequency was the important thing to determine output and color. EL is a new area for me as well as I really haven't much experience with it.

 

[William Gaatjes]

The logic is 5V and the EL is 400Hz. Not sure where I got 100khz for those displays. The contrast is very good for these displays which is why I wanted to use them but not if I have to do too much that I couldn't just replace them with something easier to use.

I think i know where you got the 100kHz from.
Most smps do 100kHz easy as a pwm signal to drive the switching power transistor.
If you really need AC, you are in for a treat. I do not think a high frequency pwm signal is a problem for electro luminescence back-lights. Then you could maybe get away with small ferrite core transformer.

200VAC * 0.002ma = 0.4 Watts. 0.5 Watts circuit should be enough.
But as you already mentioned, you have the use some switching components.
The 90V DC of the devices i had to repair, was created from a single coil (step up). But i agree 200V is just to much for such an configuration at 0.5 watt(assuming 80 % efficiency).
Maxim-ic and linear technology might have some smps controllers you can use.

Maybe those back-light converters for laptops are something you can use.
The converters for those CCFL tubes. But you have to do some modification i am afraid.