transformer for CDI(capacitive discharge ignition)

Hmm, what exactly are you trying to accomplish - a CDI for internal combustion ignition purposes, or a CDI for HV generation? What number of cylinders? Max voltage desired? How much current can you supply? What voltage? What is the frequency source? You must be more specific.

Have you searched google for "CDI transformer" yet?

I'll assume this if for an automotive application. You need a power supply that will put out enough power to charge a 1 uF capacitor to at least 300 volts several hundred times per second... For example an 8 cylinder car running at 6000 rpm fires 400 times per second. I'll let you figure out the required amperage from that. Here is a link to a web site that will get you started with some information on the size of ferrite cores required for various power levels.

Amidon's web site has some pretty good info on ferrites. They have ferrites big enough to run a car CDI. If you are going to wind your own, consider using an E-core, it should be a lot easier to wind than a toroid.

The CD I built from a kit back in 1972 was a center tapped half bridge converter based on a saturating core multivibrator. Simple (no feedback control system) but not very efficient. If I designed one, today, I think I would go with a flyback design with current controlled primary and secondary voltage feedback. The flyback is more efficient dumping power into a wide voltage range load (storage capacitor that goes from zero to full voltage each spark).

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John Popelish