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-15v contrast supply for Graphics LCD

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djsb:
I need to supply a -15V voltage to the contrast pin on a Graphics LCD. I have discovered the following options for myself.

1/ Feed a 100Khz PIC pin output into a diode charge pump.
2/ Use the -9v output of a MAX232 transceiver (if fitted).

Are there any easy DC-DC convertor solutions I can use or any other straightforward solutions. I know I should have bought a LCD module with the negative voltage convertor built in but you live and learn.

David.

allanw:
Currently I'm using TC962 in a project to generate -15V. It's a beefier version of the smaller TC7662.

mikeselectricstuff:
I wouldn't advise using output of max232 as you may find voltage will change when transmitting, causing screen flicker.
Charge pump from a PWM output on PIC is the cheapest if you can get sufficient current- you could also PWM it for contrast control. There are several standalone charge pump chips out there. Good old 555 timer + charge pump is another option.

NiHaoMike:
How much current do you need? If it's a few mA or less, the charge pump is probably the best way. You could actually drive the charge pump from the MAX232 and use a simple shunt regulator.

Psi:
You can also buy tiny power supply modules in DIP/SIP type packages.
You could either get a -15v one or a +15v isolated one.

It wont be the cheapest option but will probably be less expensive than your thinking.
Also it will look nice and be real easy to implement.

here's two real quick example of ones at digikey, +5v input ->  isolated 15v output.
Link + output to your gnd and you have -15v on the - output

USD$4.98
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=945-1222-ND  

USD$6.70
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=102-1362-ND

They cant handle huge capacitive loads though, dunno if that will be a issue for your application or not

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