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bare bones charge pump

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MarkL:
How about a DC-DC converter instead of a charge pump?  There are some inexpensive non-isolated ones that can be connected to produce either positive or negative outputs.

For example, the CUI VXO78012-500 can give you -12V regulated @ 150mA, USD$2.36:

  https://www.cui.com/product/resource/pdf/vxo78-500.pdf

OM222O:

--- Quote from: MarkL on July 15, 2019, 12:48:12 pm ---How about a DC-DC converter instead of a charge pump?  There are some inexpensive non-isolated ones that can be connected to produce either positive or negative outputs.

For example, the CUI VXO78012-500 can give you -12V regulated @ 150mA, USD$2.36:

  https://www.cui.com/product/resource/pdf/vxo78-500.pdf

--- End quote ---

Only if I could ... at the first post I mentioned that I'm traveling (Iran  :palm:) so digikey, mouser, etc are out of the question since nobody ships here. I also have no clue where the local suppliers are to buy from them. making a charge pump or finding a 12v battery are my only options rn and the charge pump idea just needs a tiny bit more tweaking to work (the issue with low voltage to be regulated by the LDO) so I'd rather stick to it.

duak:
Here is a complementary clock driver with low voltage loss using bipolar transistors.  I use Linux and the only circuit design package I have right now is Oregano and it has many, many bugs that I don't have time to fix.  I hope it will give you an idea of how to proceed.

The Input square wave is applied to V1 and the complementary outputs are the two test points.  The output devices are connected as common emitter to minimize voltage loss by being saturated.  Q3 & Q4 are drivers that use the same current twice to drive the complementary output devices out of phase.  D1 & D2 should be 8.2 or 9.1V - high enough so that only one conducts at one time.  An improvement would be to use a diode gate so that operation isn't so dependant on supply voltage.

The 2N2219/2N2905A transistors shown should be capable of about 150 mA but are not the best choice.  Something capable of 1 A or greater would be better.

Ian.M:
Hmmmm.  I'd be concerned about shoot-through.  Also is it fast enough? 

The size of the capacitors required in a charge pump is inversely proportional to the frequency and directly proportional to the required output current so there is a strong incentive to use a fairly high operating frequency.

Another concern is output voltage sag under load - if you need symmetrical rails, you are going to need a voltage doubling charge pump + post-regulation.  With Vcc much greater than typical Vbe drop and Vce_sat losses that removes most of the incentive to drive as close to rail to rail as possible, as a doubler will have fairly generous headroom for post-regulation anyway.


If you've got a suitable choke and  P-MOSFET for the high side switch, you might well be better off cobbling together a switched mode inverting buck-boost converter.  The controller could be scratch-built from discretes and OPAMPs.


@Duak: Can't your system run LTspice under Wine?

duak:
Ian.M - I'm an old retired guy with too many things to do in the twilight of my life - I'm helping a friend with racing a Bugeye Sprite and still trying to finish up a renovation.  Until then my lab and workshop is so full of crap that CAD is the least of my problems.  I came from a time when the company paid $$$ for SPICE and CAD (PCAD and then Protel/Altium) and there was no way to get it to run at home with the licensing or copy/execute protection.  I never used SPICE much professionally but decided to at least try something simple so I went for Oregano - not a good idea.

So, LTspice under Wine is the way to go?  I downloaded a copy of Eagle CAD recently but haven't installed it yet.  Is Eagle a good choice and does it work with LTspice?

Thx & Cheers,

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