What chips should be used to drive LCDs negative contrast

[Lak]

Hello,
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.

 

[ayeong]

Try **broken link removed**

Look for

MAX749
MAX686
MAX634
MAX629

Hope that it helps !

Best Regards

 

[k-electron]

You can use LMC7660 form National Semiconductor

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

**broken link removed**

Regards

k-electron

 

[Lak]

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.

 

[joco]

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

 

[smx86]

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

 

[algilsan]

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

 

[fuzcub]

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