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bare bones charge pump
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OM222O:
I need to generate a negative rail for my op amps from a +12V input. The simplest way would be a an inverting charge pump and I do have two schottky diodes and suitable capacitors, the problem will be the oscillator ... I'm not sure how to create one using the parts I have on hand (some transistors and mosfets, capacitors, resistors and MCP6002). mos people have recommended a 555 or comparator based oscillator but I don't have any on hand.

I'm currently traveling, so if I can make the circuit with what I have (I'm not sure how to purchase chips here), that would be preferable.Before I travel, I bought a 7912 LDO not realizing that it needs a negative supply to begin with  :palm:

The main issue is that the MCP6002 has a max VCC of 6V and even with an inverting charge pump, I can get about -4V (fed from a 5V LDO) which is 1/3 of the -12V goal. maybe I can cascade them somehow? even then I'm not sure about the output current capacity? maybe I can create the oscillator with the op amp and use the transistors as a voltage and current booster stage?

Edit: the current goal is about 100 to 150mA (which I know is a bit large for a charge pump)
StillTrying:
Producing a stable -12V @ 150mA from what you've got is just about impossible, :) I think you're going to have to change something.
Audioguru:
Opamps work fine without a negative supply if you bias the (+) input at about half the supply voltage and use coupling capacitors for input, output and feedback ground.
duak:
Looking up "opamp relaxation oscillator" returns a number of links.  Here's one: http://www.analogzoo.com/2015/01/relaxation-oscillator-design/

Are you able to take it from here?
David Hess:
If you have transistors available, then a 2 transistor astable multivibrator will do it.
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