> Does anyone know of any good tutorials on ballast? A
> good circuit diagram with some good explanation would
> be very helpful to me.
>
> Thanks,
> John
>


I don't have any tutorials or schematics handy, but the solid state
designs are very clever! I first saw a schematic of one while working with
a company that makes fluorescent fixtures for television studios.

In their ballast, the had an H bridge generating a 50kHz square wave. From
one side of the bridge, there was an inductor, then one lamp filament,
then a capacitor, then the other lamp filament, then back to the H bridge.
The inductor and capacitor are resonant, so we have a series resonant
circuit causing a high current through the filaments, making them light.
In addition, the series resonant circuit creates a high voltage across the
capacitor (Q times applied voltage), so we have high voltage to fire the
lamp. When the lamp fires, it shorts out the capacitor with a relatively
low resistance (the resistance of the arc). The inductor now becomes a
current limiter, just like in old "magnetic" ballasts.

I thought the whole thing was pretty clever!

I think http://www.irf.com has stuff on ballast design.

Good luck!

Harold


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