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Help finding missing component values

Discussion in 'High Voltage' started by lokeycmos, Feb 24, 2013.

  1. lokeycmos

    lokeycmos New Member

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    on the attached pic of an ignition coil driver R and C need to be determined so that the inductive kick will be below the maximum safe voltage of about 400V for a IRF740 MOSFET. The frequency wont be fixed at 300hz as in the example. my question is, what would be some good starting values for R and C. how would i go about calculating these? i know it says to experiment, but im looking for a ball park value to start with. Thanks

    i actually have 3 ignition coils here are primary specs if you need it:

    1) 6.7mH 1.5Ohm
    2)5.9mH .8Ohm
    3)6.8mH 1.5Ohm
     

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  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Are you trying to drive a spark plug? If so, then when the air in the spark gap ionizes the impedance of arc coupled from coil secondary to the primary does a good job of clamping the peak voltage on the primary. Have you ever looked at the voltage across a magneto or point type ignition with a 'scope?
     
  3. lokeycmos

    lokeycmos New Member

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    This is what im doing:

    http://www.youtube.com/watch?v=OMAEF0ScuCs
     

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