General Help Question-12V Ballast

[acoles1619]

So this is a pretty simple circuit, but would someone be able to explain it in a little greater detail?

http://www.kinoflo.com/PDF/repair/6800042.pdf

I just don't really understand how it is able to go from DC to AC. I mean, wouldn't the constant DC voltage across the inductive windings produce no voltage on the secondaries? I thought there had to be some sort of a change in the voltage.

 

[davenn]

very basically, the transistors are switching the DC voltage on and off across the windings.

Dave

 

[acoles1619]

Thanks Davenn, but it seems to me that the transistors are constantly saturated, it looks like they both have a bias voltage at the base at all times. Any direction is helpful.

 

[davenn]

well you have no component values on that cct so a valid response is difficult

 

[acoles1619]

Yeah, this is all that was provided. I mean, Q2 seems to constantly be conducting. Without some kind of switching circuitry it isn't making much sense to me. Assuming there were component values, how would this change things?

 

[duke37]

This is a classical invertor circuit. One transistor will be more enthusiastic than the other and will turn on a little. The base will then be turned on harder through the winding on the transformer. The transistor will therefore turn hard on and stay there until it cannot supply the rising currrent, then the whole operation will switch over.
Th frequency will depend on the current capability of the transistors and the inductance and saturation characteristics of the transformer.