Is it possible to increase a DC voltage with capacitors and switching circuitry?

Discussion in 'General Electronics Chat' started by realflow100, Apr 17, 2016.

  1. realflow100

    Thread Starter New Member

    Apr 17, 2016
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    I was thinking there would be a way to switch multiple transistors on to multiple capacitors in such a way that the capacitors would have a series voltage output higher than the voltage of the power supplies voltage without using a transformer to increase the voltage

    its similar to charging two capacitors seperately then putting them in series and using the doubled voltage of them in series
    If you had about 8 capacitors. lets say you would charge each of them up to 12v and the switching circuitry would switch rapidly between all of them to juggle the voltage as quickly as possible charging each capacitor to 12v simulate a higher voltage on the output of the capacitors
    I was thinking multiple clocks syncronized rapidly switching transistors to charge each capacitor up to the voltage of the power supply (or battery)
    and it would create a higher voltage on the output than if connected directly to the power source possibly higher voltage DC on the output)

    If that would be true. then you could efficiently power a 12v DC to AC 120v inverter with a 6v 10A solar panel and minimal losses from circuitry.
    as long as the switching circuitry could keep the capacitors charged up to a decent total voltage?

    Would this be possible? and effective in any way? I thought it sounded like a great idea.

    It sounds like it would only work for DC but would be much more efficient than using a transformer with an inverter circuit and a rectifier and regulator..
     
  2. #12

    Expert

    Nov 30, 2010
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    "Effective" and "efficient" are the key words.
    The answer is: Not yet.
    You described a well known charge pump, but that chip is only good for about 0.01 amp and 10 volts. If the switched capacitor method could be done better than the transformer method, they would already be available for cheaper than the transformer method. Reality intrudes.:(
     
  3. realflow100

    Thread Starter New Member

    Apr 17, 2016
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    I was thinking using stronger transistors (bigger) and fast switching. with big capacity capacitors..
    instead of using micro-sized circuitry. It could be a larger version of the same thing with tougher and bigger components.
    like using two 16,000uF capacitors to double the voltage with another capacitor on the output to smooth the voltage. with stronger/larger switching components to handle the higher amount of current?

    the circuitry I'm thinking of looks like a few transistors going in an upside down pyramid pattern to charge each capacitor individually and rapidly.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You can get 100% efficiency using Flux capacitors....:confused:
     
  5. realflow100

    Thread Starter New Member

    Apr 17, 2016
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    i'm not trying to make a joke here.. I was thinking it would actually be useful for a situation like this.. It would have close to the same power current as the power supply's from what i can think of.
     
  6. #12

    Expert

    Nov 30, 2010
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    Do you think engineers and designers all over the world are not watching for the day when that becomes the better solution?
    If you do, then go ahead and make the design. You will have lots of money very soon.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Give it a try... your solution may be unique and more successful than anything tried before.
    Or you could discover something totally new not even related to what you are trying to do.
    But, if you are like the rest of us...you will discover another way that doesn't work and will actually learn something about electronic circuit design that is useful to you along the way.
    Don't be scared to fail at this because it will ultimately help you win in the end.
     
    roadey_carl, Rodney Phillips and absf like this.
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    There are plenty of solutions for getting a higher voltage with a lower source..
    This is typically done with a "boost" switching regulator.. Efficiency is pretty good depending on the choice of boost IC's..
    But watts are still watts and you can't make more power than the input..
    So if you for example have a 6V 60W (10 Amp) supply then you can get close (depending on efficiency of the boost circuit) to 12V @ 5A (60W still) or 60V @ 1A (60W still).. They are usually around 80% or more efficient.. So you can usually get 48W from a 60W supply or more.
     
  9. Lestraveled

    Well-Known Member

    May 19, 2014
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    Here is what you are talking about. When the fet is off, the caps are being charged in parallel through the inductors. When the fet is on (pulse) the caps are effectively in series.

    [​IMG]
     
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  10. realflow100

    Thread Starter New Member

    Apr 17, 2016
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    I was thinking of doing it soley with capacitors and switching circuitry without inductors (only if they're needed to control the switching circuitry but not for the actual voltage boost)
    using maybe resistors and capacitors to control and make the switching circuitry for the main drive circuits for charging the capacitors. with a few FET's or mosfets as the "main" drive switching components that actually charge each capacitor to handle the amount of current..
    I was thinking it'd work reasonably well even if it needs complex switching circuitry before the actual drive components that charge the capacitors.
     
  11. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Sounds like you want to build a multi-phase multi-stage charge pump circuit.

    Sorry but not a new technology. The most effective is a three or four phase system where each charge pump section runs 90 - 120 degrees off from the previous one so at least two are always charging or discharging at any time.

    As for efficiency capacitor ESR is going to be your primary efficiency eater. After that diode forward voltage drops and switching device forward voltage drops are next.

    It can be done and done effectively but to be honest once all the small losses for each stage is factored in from start to finish then multiplied for each phase it still won't beat inductor/transformer based conversion efficiency.

    You may be able get close to the efficiency of an induction based system but you won't beat any decently designed one and your parts count for the equivalent voltage step ups will be way higher.
     
    Last edited: Apr 18, 2016
  12. Lestraveled

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    May 19, 2014
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    You can replace the inductors, with resistors, but you will loose a lot of efficiency.
     
  13. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Inductors rule for voltage conversion applications.

    The reason being that the circuit can be designed to avoid high instantaneous currents that generate high losses.

    Capacitor charge pumps require charging the capacitors rapidly, resulting in very high currents and therefor high losses in the ESR of the capacitors and switching element resistance.
     
  14. highvoltpower

    New Member

    Apr 5, 2016
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    Go ahead, I think your clarification is unique but there are many solution available for high voltage with low source and I hope u will successful to making these kind of design. bst lk
     
  15. Tonyr1084

    Active Member

    Sep 24, 2015
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    So you want to charge a bunch of capacitors in parallel then switch them to discharge in series. Is that right? Sort of what I've drawn below? Condition A is charging; condition B is discharging.

    I've always wanted to charge a bunch of 12 volt batteries from a 12 volt alternator but use diodes so they can individually charge but discharge in series, sort of like what you're wanting to do. So far I haven't figured that one out. Let me know if you figure this one out.

    Condition A.png
     
  16. realflow100

    Thread Starter New Member

    Apr 17, 2016
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    bridge rectifier? that would make it impossible to feed back into the source at all. if thats what your thinking of.
    a bridge rectifier to each battery seperately would work. if the diodes can handle the current.

    Then just connect the ~~'s of all the bridge rectifiers to your charging source and it should give each battery the right polarity.

    You might need a diode like used with solar panels in series between each battery.
    So the batteries can be charged. but not block each other from getting a separate 12v

    It might introduce some voltage loss but it should be negligible..
     
  17. Tonyr1084

    Active Member

    Sep 24, 2015
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    Thanks, but no, that's not what I was thinking.

    Ten 12 volt batteries in series (120 VDC). Kept charged by a 12 volt charger. The problem is that the positive pole of one battery connected to the negative pole of the next would short out the alternator.

    In other words what I was trying to impress on you is that it will be very difficult to find a way to charge your capacitors (like my batteries) without encountering potential shorts. I suppose you could build a transistor network that will force your capacitors into a parallel state for charging then switch them into a series state for discharging (powering something) without running into the problems of timing and potential massive current discharges through a transistor.

    I think your idea is interesting but figuring a way to do it is beyond me. Still, like mcgyvr said; Watts is Watts. You can't get more watts out of something that's not there. You can double voltages but you'll half the wattages. (or something similar - respectively). In other words you'll never get more out than you put in. If you figure that one out you'll be the first human in the whole world history to have done what so many have tried before only to fail.

    I'm not saying what you want to do can't be done. You'll have to figure out the circuitry of connecting caps in parallel while isolating them from their series configuration, then switch them from parallel into series mode while isolating them from their parallel configuration. In doing so you have to be careful of the timing between when you isolate the caps and the time you switch them into one mode or the other. Otherwise you'll have a massive short and all those capacitors will dump their energy through your transistors and likely leak the smoke out of the component(s).

    One word of advice: Wear a face shield when you test your first prototype. That may protect your eyes and face from a potentially nasty burn (assuming you're working with fairly high voltages).
     
  18. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    A Cockcroft-Walton voltage multiplier does what you are describing using diodes instead of transistors as the switches. Since diodes cannot saturate, the circuit is not as efficient. However, it has *zero* control electronics, gate drivers, etc.

    https://en.wikipedia.org/wiki/Cockcroft–Walton_generator

    ak
     
  19. tcmtech

    Well-Known Member

    Nov 4, 2013
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    That one's easy. Just use a DPDT relay/solenoid or switch on each battery.

    Connect the battery + and - to the center connections and wire the 12 volt power to the appropriate NC terminals corresponding with the battery + and - then wire up the NO contacts from one relay to the next so that when activated they put each battery in series.

    10 batteries 10 relays/solenoids/switches and you're good to go.

    If you want to go solid state then each DPDT device would have to be replaced with a H-bridge of the appropriate sized switching devices and sets of high side/low side driver IC's.


    That said for the work and costs involved it would be easier to just take a cheap power inverter and hack into the HV DC side of the power supply ahead of the output stage and tweak its feedback loop to make it have the right voltage range for charging the 120 VDC battery bank.

    Either that or tap into the alternator's AC power ahead of its output bridge rectifiers and use three step up transformers to take the AC off that stator and step it up to the 120 volts you need to charge the batteries.
     
  20. Tonyr1084

    Active Member

    Sep 24, 2015
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    Thanks Tcmtech, but this is not my thread. I used my example only to highlight the problems I was looking at. I'm sure there IS a solution but I'm not currently searching for one. Perhaps the OP needs to use relays to switch capacitors between parallel and series. AND I'm not even sure that's what he was looking for.
     
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