LC Resonance circuit question

Discussion in 'General Electronics Chat' started by warp, Apr 30, 2015.

  1. warp

    Thread Starter New Member

    Jan 20, 2014
    18
    0
    Hi,
    I am trying to make an LC resonant circuit for driving a small resonant transformer and or experimenting with wireless power transfer
    .
    I have noticed that there are quite a few different possible combinations of L and C that will resonate at the same frequency.

    What I am looking for is the combination that will give the most aggressive oscillations in the tank.

    Can this be calculated by finding the sum of the L and C impedences and choosing the combination that has the lowest values or perhaps by some other means.

    Thanks in advance
    Regards.
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,748
    4,796
    What do you define an aggressive oscillation?

    For a given resonant frequency the product of L and C must be a constant. The ratio of L and C determine the Q factor. The higher the L the better the Q. But you quickly run into practical limitations regarding realizable component values, particularly if you want to keep the parasitic resistances from rearing their ugly heads.
     
  3. warp

    Thread Starter New Member

    Jan 20, 2014
    18
    0
    Thanks for you reply.

    What I was meaning by aggressive was the one that allows the most energy to oscillate backward and forward in the tank. Perhaps this means Q. Actually Im not really sure what Q means. The closest I could gather about that was it has a narrow band width for tuning.

    Thanks
    Regards.
     
    Last edited: Apr 30, 2015
  4. warp

    Thread Starter New Member

    Jan 20, 2014
    18
    0
    did a quick search and came up with

    Let's define what Q really is. Q = 2*Pi*(maximum stored energy)/(energy dissipated per cycle) .

    That sounds good. Perhaps what I should have asked is what is the best ratio for a resonant transformer.
     
    Last edited: Apr 30, 2015
  5. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    The Q factor is determined by the resistance in the circuit as well as the L and C.
    For a series RLC circuit the Q approaches infinity as the resistance goes to zero (Q = ω0L / R).
     
    Last edited: Apr 30, 2015
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  6. warp

    Thread Starter New Member

    Jan 20, 2014
    18
    0
    Thanks for the tips on Q. I have noticed that when the L value on my colpitts (still on bread board) goes up the input power goes down. Is it storing more energy in the tank needing less to top it up or does less energy circulate in the tank.
     
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