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Let me start by saying that I am not talking about the free energy or "overunity" idea of back EMF. When searching around for information I can only seem to find information from free energy sites, which isn't too helpful (perpetual motion and all of that).

With that said, I see a lot EMF suppression and flywheel circuits that take back EMF from an inductive load. These seem to be largely designed to protect other circuitry, but one has to wonder, can't you harvest this EMF, store it in a capacitor for the next cycle? Is there a downside I am not seeing, perhaps the gain is not worth the extra circuitry?

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Normally, like you say, the little bit of energy saving isn't worth the complexity.

But yes, this can be done. In fact, this is the basis for how boost converter and flyback power supplies work. In those cases it is done deliberately to get power at a different voltage/current tradeoff than the input power.

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  • \$\begingroup\$ Ah, I don't know why it didn't occur to me that boost converters use the same principle... duh! And as I thought, you would usually wouldn't bother with the extra circuitry just for the bit of energy in return. \$\endgroup\$ – Jarrod Christman Aug 26 '14 at 20:27
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If you have a circuit that you need to operate at a considerable high voltage with respect to the supply voltage, the 'back EMF' is your friend. Say, you have a 3.7 Volts power supply but you need 10 Volts to produce (2 Watts as in Cell Phones), you can use this technology. It is usually not that complex. You 'must' use the right value of inductor for the right value of voltage (since the inductor is the primary determiner of the induced voltage - if input voltage is constant)...the rest is a simple rectifier. This same principle is behind the 'Joule Thief' works.

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