> -----Original Message-----
> From: Russell McMahon [SMTP:apptech@PARADISE.NET.NZ]
> Sent: Saturday, April 26, 2003 7:36 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: Electronic ignition coil driving <== Re: [AR] SV: [AR]
> mosfet problems
>
> With a 100:1 turns ratio say the primary may rise to typically 200 volts
> (20
> kV at secondary) prior to spark initiating.
> During driver on time the primary will only be 12 volts and the ouitput
> therefore 1200 volts. They could make the turns ratio whatever they wanted
> to get best amp-turns magnetisation in the dwell time available as the
> turns
> ratio plays essentially no part in the spark generation process.
>
Like most things it's a compromise. With a lower ratio the primary voltage
would have to rise to very high values, causing problems for any
semiconductor switches, and the higher inductance would require longer dwell
times.  With a very high turns ratio, the primary current would have to be
very large, leading to heating problems.

Mike


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