I am surprised that no-one has already asked this question (unless I've missed it), because it affects all those DIY guys dealing with high voltage. I have spent hours on the web to find how to use a CRT television flyback transformer to generate high voltage, and indeed, there are infinitely many schematics etc. on this subject: Basically, all the circuits I've seen use a supply somewhere between 12-30V DC, 3-5A, and they need an external wiring around the primary (not the internal primary coil). They almost never say if their circuit works with an internally rectified flyback (or not). Furthermore, these circuits are in general very inefficient (they dissipate a lot of heat). But that's not the point here. In CRT televisions, I know that the flyback works at 150V DC bias (what does it mean exactly?), in the rare cases where it is possible to find the spec of the flyback, it is very incomplete (e.g it says nothing about the inductances of the coils, the capacitance, the internal rectifiers). Even more annoying, I was unable to find any "real CRT television flyback" circuit that would have explained to me how they made the high voltage production efficient inside televisions. Well, I guess there are reference books on how to build a television, but even if I find them, it will probably be too hard a task for me to obtain these informations. To sum up my questions are:

  1. How the 150V bias is used to improve the efficiency of the flyback (this question must probably be linked with the third question)

  2. I know there are different kind of flyback topologies (resonant, quasi-resonant etc.). Is there a usual topology used in CRT television flyback (quasi-resonant?)

  3. A schematic using the topology of your choice that explain only the high voltage production in CRT televisions (not the other features also related to the flyback like the electron beam deviation). To put bones on flesh, here is one of the most detailed flyback schematic I've found in the web. It can be used to answer the question, but that's not mandatory.

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    \$\begingroup\$ You might want to check out Sam Goldwasser's excellent primer on how the old CRT horizontal deflection circuits worked. You won't likely find a lot of public info on FBTs but it's not hard to make measurements and infer things from the application schematics. \$\endgroup\$ May 17, 2017 at 7:50
  • \$\begingroup\$ What the name of Sam Goldwasser's excellent primer ? \$\endgroup\$
    – MikeTeX
    May 17, 2017 at 7:54
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    \$\begingroup\$ It's at repairfaq.org \$\endgroup\$ May 17, 2017 at 7:54
  • \$\begingroup\$ The 1B2 was common flyback rectifier tube, with filament driving from a tiny winding at 15,000 cycles per second. \$\endgroup\$ May 17, 2017 at 15:04

1 Answer 1


Your schematic is missing one of the most important components, which is the horizontal deflection yoke/coil (that is mounted on the neck of the CRT) which is in parallel with the primary winding of the transformer.

Most of the energy exchange during an horizontal cycle, including the resonant flyback pulse, is with the horizontal yoke (not the flyback transformer). Only a small fraction of the energy goes through the flyback transformer. Some of the energy is siphoned off through the flyback transformer during the flyback pulse to generate the high voltages.

  1. The horizontal voltage in combination with the inductance of the horizontal yoke determines the current ramp that is required to deflect the electron beam from the left edge to right within the prescribed horizontal period. That voltage can be 12 to 15V for a small 12" CRT with a small yoke or it would be higher for a large CRT, so it is not necessarily 150V.

  2. From what I have seen, I would guess that most if not all raster CRT horizontal deflection circuits employ this resonant flyback scheme. (Obviously, a vector CRT display, like in an analog oscilloscope, would be different.)

  3. Here is a good app note on the CRT horizontal deflection circuit: https://www.fairchildsemi.com/application-notes/AN/AN-9009.pdf

  • \$\begingroup\$ Thx. Actually, this is not my schematic but the schematic of the seller. Your answer is informative and interesting, though not exactly what I am expecting, as I'm not interested in the mechanism of electron beam deflection, but only in the high voltage production. I'll have a look at the link you've indicated. \$\endgroup\$
    – MikeTeX
    May 18, 2017 at 8:58

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