A charge pump is a kind of DC to DC converter that uses capacitors as energy-storage elements to create either a higher- or lower-voltage power source.

Is it possible to create a charge pump without using capacitors? What characteristics of capacitors make them useful in charge pump applications which are normally seen in level shifters?


The name gives you the answer : you need to store charge and move that stored charge around.

Charge storage devices are either batteries (not very practical) or capacitors (practical, cheap and common).

The only alternative I can see is to store charge on an insulator, move the insulator, and reclaim the charge from it elsewhere. A rubber belt makes a suitable insulator for the job. Thus a Van de Graaff Generator (the machine not the band) is a charge pump of sorts.

But capacitors and rectifiers (or even spark gaps used as switches) are a more practical approach, as in the Cockroft-Walton multiplier.


The name 'charge pump' is the name given to devices that change voltages using capacitors as the main energy storage element, Boost/Buck regulators are the names given to devices that change voltages up or down using inductors as the main element respectively. A charge pump has the advantage over a level shifter that it can generate a voltage either higher or of opposite polarity than the input, level shifters can only generate outputs that are within their supply rails, charge pumps do not have this limitation as they are full DC-DC converters as opposed to a glorified switch.


Is it possible to create a charge pump without using capacitors?

Yes you could use rechargable batteries as well but it would be impractical as these are usually larger, they age and wear out. Also most rechargable batteries do not like to be completely discharged so the circuit would have to be more complex to avoid that.

Also when the charge pump is off the rechargable batteries would still hold a voltage. Maybe a circuit would be needed to disconnect the rechargable batteries from the load or from the circuit.

Rechargable batteries are more expensive than capacitors.

Capacitors do not mind being discharged completely. They age but much less than rechargable batteries.

As far as I know there is no other way you can build a charge pump without using capacitors or rechargable batteries. You need an element which can store charge which is what capacitors and rechargable batteries do. OK, rechargable batteries actually store the energy of the charge as chemical energy and not as an electrical charge as a capacitor does. But for a chargepump like circuit that does not matter.

You could also make a increased voltage using an inductor but that is not a charge pump but a boost converter.

  • 3
    \$\begingroup\$ CP with battaries is kinda steampunk. They should use robotic arms instead transistors to literally move the batteries. \$\endgroup\$ – Gregory Kornblum May 16 '16 at 9:54
  • \$\begingroup\$ Or clicking relays to connect and disconnect them. With batteries you would not want a high switching frequency so robots or relays should be entirely possible. But capacitors is easier ! \$\endgroup\$ – Bimpelrekkie May 16 '16 at 10:06

Level-shifters don't store any energy. This means they only work within the highest voltage available to them. Typically they are connected to the two voltages they are shifting. Level shifters act like a switch with some power converted to heat.

Some level shifters use 'transformers' to communicate a change of voltage between the two sides. However, even these don't store energy to function, they are still acting as switches.

A DC-DC converter uses its power source to either produce a larger or smaller voltage. A DC-DC converter stores energy in the capacitor. When it's creating a larger voltage, a DC-DC converter can step well beyond its power supply voltage, unlike a level shifter.

A DC-DC converter, depending on its circuit structure, steps up a voltage, with reduced current (compared to its power source), or steps it down with increased current. Of course, this process has losses. However a step-down DC-DC converter can be much more efficient than a linear regulator.

An alternative short-term energy storage device would be an inductor.


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