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Back EMF

  1. Sep 23, 2010 #1
    I have always wondered if anyone has ever developed an understanding of why Back EMF happens?

    All I know is it happens when the the field inside of a transformer collapses at some low frequency during the collapse of the coil when the transistor shuts off creates a huge spike hundreds of times the supply voltage is created within the coil. is there a new understanding of why this happens?

    I appreciate any help in in expanding my knowledge of this phenomena.

  2. jcsd
  3. Sep 23, 2010 #2


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    Staff: Mentor

    If I'm not mistaken, it is because the electromagnetic field of the transformer actually stores energy, and when you shutoff the transformer, the electromagnetic field collapses, sending that energy back as a spike of power.
  4. Sep 23, 2010 #3
    Remember also, that back EMF collapse, regardless of high voltage or not, has a power factor slightly less than that which created it.
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