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TC Circuit Question

  1. Jun 1, 2007 #1

    theres no image tags on this forum?

    but yea what happens in this circuit?

    I know what's supposed to happen is that the tank cap is supposed to charge until the gap breaks down and then you have an LC resonance circuit in the primary side that excites the LC circuit, composed of the coil inductor and the stray capacitance betwee nthe top load and ground, in the secondary.

    lol run-on sentence.

    what i don't understand is that if the capacitor charges to the voltage of the power supply, only, why would the gap breakdown due to the voltage across the cap and not the voltage across the power supply? isn't the voltage across the power supply the same voltage that will eventually be across the cap?
  2. jcsd
  3. Jun 1, 2007 #2
    In this case the high voltage power supply is the mains transformer, like from a neon sign or an ignition coil. And yes the voltage across them is the same, but these transformers are heavily insulated that prevent sparking. Without insulation, they spark like crazy and burn the dielectric.

    In theory, the cap and inductor form a voltage divider for the AC voltage, so AC wise the voltage across is less than input. But during the first AC (60 Hz) quarter cycle, voltage across the gap will reach a maximum and it begins to spark thus completing the DC circuit. During this time, energy stored in the cap will be dumped to the inductor back and forth at resonant frequency. In theory the voltage across the cap should be less than input, but given such low inductance, the initial voltage across cap will be same as input voltage.
    Last edited: Jun 1, 2007
  4. Jun 1, 2007 #3
    across what?
    i thought the cap discharging overvolted the gap
    no initially the voltage across the cap is zero in a capacitative circuit, one with low inductance
    Last edited: Jun 1, 2007
  5. Jun 2, 2007 #4
    The primary coil inductor has low inductance therefore its reactance @ 60 Hz is so low you can call it a short. Therefore the 60 Hz voltage across the cap is the same as it is across the gap.
  6. Jun 3, 2007 #5
    can someone give me some more assistance
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