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A ready-made solution is available - Traco Power make a module (TEN 8-1212) which accepts 9 to 18 v in and produces a floating 12v at upto 665mA. Connect the output pos to supply neg and you have a -12v rail.
The device is a bit expensive - £29.60 UK pounds but is almost bomb-proof.
the problem is that i dont live in U.K. and so there might be a problem in finding the device. so i was looking for a schematic. maybe even less current. theoreticly all i need to do is to generate -12V from +12V and keep the ground. right?
i need to use them simultaneous! dont you think that i would have thought to reverse the polarity.....
the first one looks ok, but too low current. the second is quite OK. but hard to find components. ill keep looking.
all i need it to keep the voltage over(i mean under) -11V@100mA load and it's all ok.
silly answer: nope!
it will be simpler like that. but as i said i have GND and +Vcc=12V and i want to get -12V, GND(the same one) +12V(i can use the original one) so the problem is to generate -12V from +12V..... the 555 converted Kinjalgp showed me is something similar to what i have, but i still need one to suply 100mA and have a voltage descrease at the full load(100mA) of max 1V
I have an idea. But it's only an idea. Maybe silly as well. I know it's possible to make voltage duplicators with two or three diodes. Let's search for that. We can see if the result fits your needs ¿what do you think about it?
this is a good idea, but not so good. i can build a voltage doubler from 2 caps and 2 diodes, but i need a.c. if i have sinusoidal a.c. i can generate a positive and negative voltge, as i want with 2 caps. but it is not that easy to generate a.c. sinusoidal.
ok, i got this circuit(sorry for the bad scanning). and i was wondering if it will work(with out the transformer) with a square wave genetared with a 555...?