On 5 Apr 2007 at 9:13, Harold Hallikainen 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
> 
> 

	It is interesting that those ballasts don't need the filaments.
	One can get a lamp with burned filaments and short circuit them.
	The lamp will light normally.

	Mark Jordan

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