The problems with the transformer debate are primarily due to an incorrectly
applied simpification: The 'transformer rule', that the secondary voltage
equals N times the primary voltage. It is only valid for a steady state
periodic waveform, such as a sinewave. For transient waveforms, any analysis
of the circuit will require consideration of the basic inductor relationship
V=L*dI/dT, as noted by many. This is the basis of practically all automotive
ignition systems. The coil is initially 'charged' up to a primary current,
which is then interrupted, resulting in a very large dI/dT and resulting
voltage pulse. This pulse is multiplied by N, but the actual value of
discharge current is controlled by the spark itself.
Eric von Valtier K8LV
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