Looks like a good circuit for me to understand.
Thanks.

John


--- Harold Hallikainen <harold@hallikainen.org> wrote:

> 
> > 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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