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What chips should be used to drive LCDs negative contrast

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Junior Member level 3
Jun 10, 2001
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I need to drive a 240x128 graphic lcd so what chips can be use to drive the negative contrast voltage. The spec calls for -18V typical. Any better ICs to drive -18V from 5V? (or 12v)

Is 1.1A current for the LED backlight at 5V normal/typical ?

The LCD uses L7891 Sanyo or HD61830.
Anyone with experience ,pls advise.

Many thanks.

Try **broken link removed**

Look for


Hope that it helps !

Best Regards

You can use LMC7660 form National Semiconductor

Use two in cascade (-15V from +5V) as showed in datasheet:

**broken link removed**



Yep, tried cascade 2 ICL7662 to get ~ -15V but last line of the graphic display not too clear. Maybe the L7891 or the lcd suckz. Anyway will source for a 18V supply and invert it.
Thanks to all for replies.
May many fortunes go your way.

If you don't what to use inverter chip, voltage can be made by negative charge-pump. Little oscillator and some diodes and capasitors...

You can use a ready-to-use DC/DC converter, as NME0515 from C&D technologies (previously Newport) (, if the cost is not important...

I think the best result you will have with an DC/DC converter. You can generate a negative supply with a battery of 1.5v por example.
The other option tou have is to use charger pumps, like used in rs232 transcevers and the third option is to use a negative linear voltaje regulator like 7912 with some diodes in the 2 pin, like this regulator have a quiescent current of abaout 4 mA, you will have sufficient current to biassing diodes and they will drop about 0.7 v. I think there are variable negative voltage regulators. like lm317 for positive voltaje. Check National.

I hope you be usefull

Re: LCD Negative

For a "black box" aproach , If you've got any old network cards around they often have a dc>dc converter on the PCB, it's usually a black block about 15mm x 30mm x10mm it takes +5 in and provides an isolated reguated 9v out. link 2 of these together in series to get -18v at 150ma. Try a google search on the part number on the unit for the pinout

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