Electronic – dual of the transformer


Capacitors and inductors are duals of each other.

A transformer is made of two inductors, and transfers power through mutual inductance, through the magnetic near-field (right?) Also, you can vary the ratio of voltages or currents by changing the ratio of turns on the core. You could think of this as coupling a single primary loop with many secondary loops, and then stacking the secondary loops so their output voltages are summed.

Is there an electric dual of the transformer? Something that uses capacitance and transfers power through the electric near-field over an isolation barrier? Some way to couple a single primary capacitor with multiple secondary capacitors and then stack them to do power conversion by summing their outputs?

I know that an isolated supply can be built using two capacitors, but I'm not sure if that's exactly a dual, or if there's an equivalent to adjusting the ratio of turns:

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Or maybe something related to this?

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For example, there are capacitive voltage dividers, but these only reduce voltage, they can't increase it like an autotransformer. There are charge pumps, but those require active elements like switches or diodes, which aren't present in a transformer.

More succinctly: Is there a way to transform power (1 V, 5 A on primary to 5 V, 1 A on secondary) using electric fields instead of magnetic fields, and passive components only? If not, why not? (Electric field screening?)

Best Answer

Actually, this is a common thing to wonder.

There is a dual to this. When you have devices sharing a common winding and magnetic flux(Magnetic "current") it makes a perfect dual for devices sharing a common electric conductor. Nice picture from wikipedia:

wikipedia image of flux in a transformer2

You can also take a look at "Magnetic Circuits". You can start learning some fun terms when you go into these concepts in detail, like "Magnetic Capacitance," it seems that my flux does have capacitance.

The way you can determine how much energy passes through a transformer can be broken down into a magnetic circuit that works just like an electric circuit with different units. Magnetic Circuits are an analog of Electric Circuits, which are much easier to work with for many many reasons.

Think of it like a voltage source or a current source. They are direct analogs, but when you build a voltage source it is a hell of a lot easier than a current source.

Side Note

The magnetic flux is shared in a core due to the fact that magnetic flux is perpendicular to the wire, the issue with electric flux is that it points between two surfaces, not looped around. If it looped around a dielectric would get the job done.

In relation to the capacitor inside the other

IF the smaller becomes bigger, it will end up acting like two coupling capacitors with a series resistor between them, as it gets smaller, the overall electric field will be minimal, but you could put a big big E-Field in there, not nearly as effective as a transformer.