capacitive power transfer

[jmole]

was thinking about this conceptually, but figured I'd ask a wider audience.

Is is possible to power an LED (at 5mA or so) with a capacitively coupled, single-ended signal?  I.E., could you run one wire  to a chip with some rectification/filtering circuitry and LED, and power it?

[ejeffrey]

Capacitively coupled, yes. Without a return path?  No.

[pinkysbrein]

You could use parasitic capacitance to ground as the return path (ie. Attach a large piece of metal to the other side of the LEDs, you need 2 because the current is AC.)

[IanB]

Yes, you could in theory, but you would be getting into borderline RF territory.

At "low" frequencies, I don't think a single ended (one wire) path would get you anywhere close to the kind of delivered power (5 mA through an LED) you are asking for.

As far as "run one wire to a chip with some rectification/filtering circuitry and LED, and power it" -- no, not unless you create a secondary two wire power supply for the chip and LED system tapped off the one wire power supply.

Why did you want to do this? I think the reason you don't see it in practice is because there are simpler and more practical engineering solutions to the problem of an isolated power supply.

To visualize how such a circuit might work, consider the antenna section of a radio receiver. The antenna couples an AC signal into a coil, and an output signal is tapped off that coil, filtered, detected and amplified. However the antenna signal is tiny and delivers very little power.

If you took the same basic circuit and coupled the AC signal into the "antenna" through a capacitor rather than by radio waves you could get the result you are looking for. But I think it would be cumbersome and inefficient.

[Zero999]

Connect a Schottky diode in reverse parallel with the LED and you have a very simple voltage doubler.