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Okay here is some sircuits for powering lcd displays. Most of these will give negative 9-12V, but there is also some that give -15V or even up to -48V.
All of these works from +12V

http://www.p5taylor.btinternet.co.uk/11.pdf

http://www.reconnsworld.com/power_voltinvert.html

http://w1.859.telia.com/~u85920178/power/vconv_01.htm

http://www.hantronix.com/down/neg-invr.pdf

http://www.aaroncake.net/circuits/vinvertr.htm

I'm using one of those 555 based sircuits with an additional 7909 regulator and it seems to work fine.

Thanks, I'm sure these will be useful.

Your welcome. Here is one more(ICL7660 and ICL7662) this has almost 100% conversion effiency!
http://www.intersil.com/design/parametric/productresults.asp?t=55&i=216&i=219&i=1045
You only need this chip and 2 capasitors. Cannot go much easier

Those are also quite cheap about 2-4€

That sounds very good. With the chip and 2 caps it would be a very easy way to make the negative voltage.

Do you know where to get these chips easily ?

http://www.spelektroniikka.fi Suomalaiset voi katsella tuolta.
Tarvii vielä etsiä josko löytyisi jokin toinen paikka.
For those of You that doesn't live in finland You can find these ICL7660 and ICL7662 from RS-COM http://www.rswww.com
There probaply is other places, but I dont wanna go thrue all those. Then there is also Intersil's own webshop, but i dont know do they deliver for end user. You could always try.

Thanks for the Links

The one i'm using uses 3 voltage regulators and some capacitors , it has been designed by me to powerup the lcd externaly , it uses an 2 x 24v 3VA Tranformer to get the midle point has ground , then after the rectifier circuitr contitued by a rectifier bride ,two 1000 uF (one for eache chanel), 2 100 nF capacitor's rigt after the 1000uF , then comes the voltage regulators for 5 v (7805) , and the voltage regulators for -20 (7920) and the -8 (7908) right next come two more 10 uf cacpcitors , betwen the Vin and Vout if The ic's there is also an diode to prevent short's ans inverse curent's , it's also a very cheap and functional power suply , i've already head of those chips , but due to my display need of -20 volt i've made one off these , all componentts are easy to find and very cheap (about 8 € including the circuit board)


As soon i have the schematic done i'll post it here in eagle format

Samtech

Your welcome. Here is few voltade doubler sircuits. Other is made with ICL7660 and I believe it might be possible to do an inverting voltage boubler with one icl7660 or 7662 chip.
I just ordered that ICL7662. Altought my 555 based inverter worked fine. Just want something that doesn't have so many components.

http://www.diystompboxes.com/pedals/vdbl.html
http://www.reconnsworld.com/power_voltdoubler.html

Just little note for useng those icl7662. There might be the need of use some external stabiling for examp. Zener diodi. You could also try to change that output capasitor.
I used resistor and zener diod. With out those my lcd goes crazy when I adjust contrast.

Hello,
which things I would need to get on the cheapest and simplest way
-24 Volt from a ATX Pc suply ?
that´s the last thing to connect my lcd

thx

DC/DC-Converter SIM1-524S.

Look here: http://www.reichelt.de/index_direkt.html?SIM1-0524S%20DIL8+PpK-x9S4AQ4AAHWFQYY+D481.

It's a german shop but you should get this (or a similar type).

are you shure thats it
I need negative -21 Volt

you could also use a LT1051.with 5 parts you can get the negative voltage out of a pos. 12 volts.

Simply connect the positive output to ground and at the negative you have the -24V. Input and output have no connection therefore you can put Vin- and Vout+ both to ground.

TI provide a built-in componant to do it alone :



http://focus.ti.com/docs/prod/productfo ... ber=PT5023

WOW expensive thing euro 27 without the tax at Farnell, for the -12 volt version. Very handy though.