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App Note: Isolated power using capacitors

Posted on Saturday, May 28th, 2011 in app notes by Ian

rsdio tipped us to an app note on isolated power-supply circuits:

Wow! It’s quite interesting to see how to substitute capacitors for a transformer. Without digging deeper, though, it’s not clear whether voltage boost can be achieved.

An integrated H-bridge driver for isolated power-supply circuits (MAX256) usually drives the primary of a transformer, but it can also drive a pair of capacitors that substitute for the transformer in providing isolation and power transfer.

Thanks rsdio!

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2 Responses to “App Note: Isolated power using capacitors”

  1. Drone says:

    “Without digging deeper, though, it’s not clear whether voltage boost can be achieved”

    Why not feed diode/capacitor voltage multiplier stages instead of the bridge rectifier. Voltage multipliers are used to boost an AC signal to a higher DC voltage. Getting high-current might be a bit of a design challenge. Plus I would need to look at the way the H-bridge drives the multipliers through the caps with no common DC ground point – but off the top of my head, I think it would work.

    http://en.wikipedia.org/wiki/Voltage_multiplier

    Rgds, David

  2. Drone says:

    Also keep in-mind, this cap-coupled circuit doesn’t not provide code-compliant isolation. Unwanted transients appearing on the caps will cross the caps.

    Rgds agn, David

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