Flyback transformer driver ideas, best setup

[NetworKing]

I have seen different hacky ways online people re-use flybacks from old CRT gear. Many for some reason seem to totally bypass the transformer internals winding things on an outer ferrite bar which I don't think is always available and seems silly to me as it has to at least have a primary winding already. I have a couple flybacks from some old gear but have yet to make a driver for them. I'd like to figure out a good driver setup but i would rather use the transformer as is rather than hacking windings on to it, etc. I think be nice too if had some way to control the voltage on it too so probably variable frequency of some sort? In theory, it seems simple a 555IC, some passive parts, a potentiometer, capacitor, a power transistor or MOSFET and flyback and you have a driver circuit or am I missing something? I have some function generators so i could get a driver power source setup feed in from function generator till get further into the details perhaps?

[moffy]

There are a lot of Youtube videos about flyback PSUs.

[Andy Chee]

My favorite:

https://franzolielectronics.com/easy-flyback-i/



You will find that the existing primary winding was designed only for mains voltage (240V), whereas all the designs with supplementary winding are designed for lower voltage, typically 12V (car battery) or 19V (laptop power supply).

By all means use the existing 240V primary at 12V, but don't expect long streamers like the video above!

[NetworKing]

Ok that makes sense, but if USA would these not run 120V or are these running on the 240V that would be after the SMPS mains side has rectified and doubled it? I don't see issue use existing winding low voltage at first then verify it works and maybe throw in some opto isolators perhaps and run at mains power.

[Andy Chee]

Given that flybacks are dangerous enough as it is, that explains why you don't see many circuits retain the use of the original mains primary input.

But yes, if you're confident enough with mains and are able to properly isolate small signals with optoisolators, then good luck to you!  That's usually the technique they use with larger mains powered tesla coils, but works just as well with flybacks.

[inse]

Maybe there is confusion about which transformer you are talking about.
The TV sets used to have two flyback transformers: one for the power supply and the HV FBT.
In most TV sets, the HV FBT was driven from the so called B+ rail which came from the power supply and was 90..130V usually.
So if you want to re-use the FBT to generate high voltage, applying new windings suitable for a lower drive voltage suddenly makes sense.

[NetworKing]

Referring to HV FBT in like a CRT TV, monitor, etc. ~25KV output.