On Wed, 24 Sep 2008 18:03:28 -0700, Jim Thompson
wrote:

Doesn't take much to make a CD Ignition, see....

http://analog-innovations.com/SED/CD-Ignition-Basic.pdf

Thanks. What is the theory of operation?

All of the control circuitry is not shown.

(1) Transistor turns on
(2) When current in inductor reaches 5A, transistor turns off, dumping
energy into capacitor (~350V)
(3) When transistor turns on again, capacitor dumps into ignition coil
(conventional ratio) firing plug; and inductor charging begins again.

Works great... I've used it to saw Plexiglas ;-)

What I have now, connects
one side of the coil to the battery and the other side to the ignition
module. In that circuit, D3 D2 would stay forward biased if the coil
goes to B+.

This circuit is supposed to dump a largish negative spike to the coil?

What kind of voltage does the transistor have to stand off?

I used 500V BVCEO (NPN) devices.

There are probably Power MOSFET's now that would work better... HV
NPN's have lousy beta, requiring beta correction circuits in the
current sensing.

...Jim Thompson
Thanks, I'll give it a try.
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