Charge Pump

Discussion in 'General Electronics Chat' started by blah2222, Dec 31, 2013.

  1. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Hi all,

    In short, I am in need to create a single-ended supply for a high-voltage op-amp of around +50V from either a lithium (coin) or alkaline battery (AAs or 9V).

    Wondering if it would be possible to stack charge-pump (inductorless) boost converters in series to arrive at the desired voltage or if I need to go with an inductor-based boost converter.

    I have been looking at parts from TI for the sake of getting samples and the charge-pumps have outputs up to 5V which is a lot lower than I need.

    Any help is much appreciated.

    Thank you.
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I don't see why not as long as the current is fairly low. I would use the 9 volt option to reduce the number of stages.
     
  3. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Is there an IC that would get a 9V up to around 40V? Current won't be more than around 50 mA.
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Given the 50 ma requirement at 50 volts off of a 9 volt source the input load would be somewhere around 280 - 300+ ma.

    Getting to 50 volts form a 9 volt source with just charge pumps can be done but its going to take a fair amount of work to do. More than likely it would require a 6 or 7 stage system.
     
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
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    If you really need 50 ma. you might be better off with a little boost converter. But either way it sounds like it is going to be more than what you were thinking about battery capacity wise. I'm having trouble visualizing a 50 volt 50 ma. op amp. Is it a power amp?
     
  6. ronv

    AAC Fanatic!

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  7. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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  8. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    That can't be 50mA constant current. If that is more than a very low duty cycle max current pulse lasting for just a few milliseconds then you might not be talking about a good candidate for battery power. Even a 9V stack of 6 good D cells is going to struggle to run that power level for more than a minute.

    The charge pump route is not well developed for this purpose. There are reasons for that. I don't want to explain diode and adsorption losses.

    Just take some advice and use a boost switching converter. You should be able to find lots of help and resources on setting one up or even ebay a ready made module.
     
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  9. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Thank you for the reply. I guess I should have been clearer on my part.

    Output current: 50mA @ 30Hz with a 10us on time.
     
  10. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Much better. 0.03% duty cycle is possible with battery power.
    To get that much current in a 10us pulse you will need a low inductance load.

    Was there a reason that you wanted to use a charge pump?
    Maybe you need to have super low magnetic signature or something like that; then sure use a charge pump because it can be done. Build it from discrete components if you need to.

    I stand by the recommendation of a switching supply solution otherwise.
     
  11. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    I was just wondering if I could get away without using an inductor for this. I guess the concensus is to just use a boost converter with an inductor then?
     
  12. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Your current requirements are very low. Your inductor can be very small especially if you are using a high switching frequency; anything over about 120kHz.
     
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  13. #12

    Expert

    Nov 30, 2010
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    Did you forget that you can buy 22.5 volt batteries that are the same size as 9V batteries?
     
  14. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Couldn't of forgotten as I have never heard of them. Don't seem to be very common and I have lots of 9V lying around.
     
  15. #12

    Expert

    Nov 30, 2010
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    Being the same size as 9V batteries, you have to assume they carry about the same number of watt hours, but you can get to 45 volts with only 2 of them. They are still available at Mouser..I think.
     
  16. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Thanks for the suggestion. I will check out that option as well.
     
  17. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
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    Could I not just use this MC34063A buck-boost-inverter regulator from TI?

    Seems to go up to 40V which is what I need. Anyone have experience using this IC?
     
  18. #12

    Expert

    Nov 30, 2010
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    I was wrong. The little 22.5V batteries are no longer available at Mouser.

    Edit: or any other place I can find.
     
    Last edited: Jan 1, 2014
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  19. tcmtech

    Well-Known Member

    Nov 4, 2013
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    That's the way I would go. That IC and variations of it are used all over the place in small buck converters so I suspect they are pretty well designed and easy to set up.
     
  20. RichardO

    Well-Known Member

    May 4, 2013
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    This gives you no margin for tolerances and overshoot/ringing. You really need a part that has a switch with, more like, a 50 volt breakdown specification. I don't know of a single chip version off the top of my head. I do know that they are somewhat rare.

    It takes more parts but you may have to use a switching regulator "controller" that drives an external transistor switch.
     
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