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Typical LCDs VEE current draw

mitchjs

New member
I got a LCD that need a negative supply for contrast

whats the typical current draw of VEE?

i got a Optrex graphic lcd 240 x 64 ( i think)

It cant be much...

why i ask, there is a dc-dc convertor that supplied -8.5 v to the VEE circuit(thermister/pot)

and its dead, i cant find a 8.5 dc-dc converter, so im gonna use 9v
. when i put -9v in now, its a little messed up, 8.5 really works best, so i want to use a zener at 8.5v, and i need to know how much current i need to limit the zener too



mitch
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I'd estimate that Vee uses a few hundred microamps, at most. Zener diodes are probably more trouble than they're worth. They are not very stable with temperature change, and they need a minimum current to reach the knee voltage, probably several mA even for a low power zener. You might do better just putting a 50K ohm pot across the -9v supply, and connect the wiper to Vee, then you can set the contrast just right.
 
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