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CFAG12864B-WGH-V EL Backlighting Circuit

neil2501_h8

New member
Hi,

It is my first time to design a EL backlighting circuit to drive CFAG12864B-WGH-V module.

I have searched the net and found Supertex HV8XX IC series that should do the job. I choose HV830 in particular because it provides it seems to provide one of the highest Vpp (typ. 200Vpp) among the other HV8XX series. Referring to the specs of LCD module, the typical Vrms required is 110V.

The basic conversion between Vpp & Vrms is given below:
() Vrms = Vpp / Sqrt(8)
() Vpp = Vrms * Sqrt(8)

Then Vpp(required) = 110Vrms * Sqrt(8) = 311Vpp
From the above calculation, it means the HV830 IC is only capable of providing 70% of the typical Vrms required for LCD module! Will this be a problem for the EL brightness?

In my design, I use a 2M ohm resistor connected to pin 8 of HV830 to give an output wave of 400Hz. Will frequency of the output wave affects the color of EL backlight?

Please advise if the circuit incorporating HV830 can be further optimised or it has to be replaced with another circuit. I can only find Supertex ICs available for sales online (@ www.mouser.com) that provides EL backlight driving features.




Many Thanks in Advance!
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All the EL driver chips that I've seen have output voltages in the range of 100~160 Vpp (not counting the Supertex). This makes me suspicious as to whether there is a typo error in the data sheet, and the rating should be Vpp instead of Vrms. Otherwise, none of the common driver chips would seem to fill the requirements. Perhaps CF Tech can clarify this.
Will frequency of the output wave affects the color of EL backlight?
Yes, slightly.

As a crude test of the EL's illumination, you could try using 110 Vrms @ 60 Hz from your AC mains (assuming thats what you have in Singapore). If the real spec should be Vpp, then it might damage the EL.
 
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Here is an off-the-wall idea: use a transformer to boost the voltage. A small audio transformer, like a telephone coupling unit, would have a 1500 volt dielectric rating, and 2 - 600 ohm CT windings. Use half of one winding as the primary, and get a 2X voltage gain. That would let you use a driver with 155 Vpp output, which are common from Sipex, Toko, Zywyn, Supertex, etc.

example: http://www.digikey.com/scripts/DkSearch/dksus.dll?PName?Name=237-1121-ND&Site=US
 
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neil2501_h8

New member
Hi cosmicvoid,


Thanks for your help and ideas! However, the audio transformer is way too big to be inserted unto the PCB board. I will email to CrystalFontz technical support directly for an answer.
 

CF Tech

Administrator
We have a little inverter available. It is CFAIEL2 or something like that. Just takes in 5v and gives out a nice EL supply. You can e-mail sales and they can hook you up with one. You can see it on the CFAX ZIF demo board:

 
Are any specs available for that inverter?

BTW, when I went to the CFA site page of graphic displays, I see that only one of the CFAX ZIF DEMO pix has the new board, the other pic still has the version with the Sipex chip.
 
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