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Stepping down a negative voltage supply
http://forum.lcdinfo.com/viewtopic.php?f=6&t=1420
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Author:  penjuin [ Tue Nov 22, 2005 10:41 ]
Post subject:  Stepping down a negative voltage supply

I have a circuit that gives me -12v DC. I have two small problems though:

-> The maximum for the drive voltage on my lcd is -10v. How can I step down the -12v to -10v or lower?

-> Is 1A likely to kill my 128x64 LCD? Should I just get a massive resistor and whack it on?

Author:  One~Zero [ Wed Nov 23, 2005 3:47 ]
Post subject:  Re: Stepping down a negative voltage supply

penjuin wrote:
-> Is 1A likely to kill my 128x64 LCD? Should I just get a massive resistor and whack it on?


It's MORE than likely...it WOULD kill your LCD. What type of display is it? And do you have a data sheet. That would be very helpful. :D

Author:  penjuin [ Wed Nov 23, 2005 9:55 ]
Post subject: 

I have a 128x64 glcd; model number CM12864-10. It's from Futurlec; there is a partially translated piece of datasheet here. The controller is T6963C.

What would be a good current? I have an AT psu from an old computer that gives 500mA@-12v if that is better.

Author:  Hamishyaba [ Fri Jan 11, 2008 13:24 ]
Post subject: 

hi penjuin,

I also bought the same LCD from Futurlec. Did you know you can go to the americian futurlec site www.futurlec.com and down load the Toshiba T6963 driver data sheet. Your -12V could be used on the LCD but you would need to connect the earths together with the 5V supply and on the -12V supply use a resister and zener combination to clamp the voltage at -10V. I dont thinks the -10V Vo connection would pull any more than 20-50mA, as the LCD can only dissapate so much heat. :)

Futurlec say this is a 5V LCD but I don't think it is, I think it is a 5V,-10V display - Gruuuuuuuuuu. :(

I would be interested how you go with your project, are you connecting it to a PIC?. If you are we could share some code.

Author:  Hamishyaba [ Mon Jan 21, 2008 12:56 ]
Post subject: 

I have been working on a 5V to -10V power supply for the LCD and I finally finished it and it works. If you want a kit for this power supply you can contact me at marni@alphalink.com.au

Author:  Hamishyaba [ Sat Oct 20, 2012 14:19 ]
Post subject:  Re: Stepping down a negative voltage supply

Update to past comments

The CM12864-10 is actually a single 5V power supply LCD display.
The Vo noted on the futurlec data sheet is an output.
Dont connect a power supply to it or you will probably blow it up, like I did.
Connect the Vo and Vss to the ends pins of a variable resistor.
Use 20K to 50K ohms variable resistor. A non linear resistor mabe a good choice, make sure its around the right way.
Connect the variable resistor slider pin to Vee(FG) and good luck
Futurlec, :)

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