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Flyback tranformers are wonderful little things, cheap, easily available, easy (somewhat) to work with, and very simple to drive. And, they create voltages at about 15-30kV, at a high frequency, perhaps 20kHz or so. In that, the quality and nature of the output is very similar to that of a very minuscule Tesla Coil.
Flyback transformers can be used to power plasma globes, like the one shown on the index.htm page here, also small jakob's ladders, tiny tesla coils, and thier usual commercial purpose: Cathode Ray Tubes.
Flyback transformers can be found in the back of any device containing a CRT, black and white TVs, color ones, computer monitors, even oscilloscopes, or any strange old thing that has a television-like display. (I once salvaged a flyback supply from a strange readout on an echocardiogram machine)
The best variety, as far as building any of these circuits will go, is the older design with disc-shaped secondaries. These are most often found in old b&w televisions.
The configuration and shape of the core, primary, secondary, and the mounting structure may vary wildly, but they all follow this same basic pattern. On some, the primary windings may be wound underneath the secondary, and should just be ignored. If the primary windings are on the opposite leg as shown, then they should be removed. Once the mounting bracket has been removed from the transformer, often times the core will slide apart into two halves, and the primary and secondary coils can be easily removed. There may be spacers in between the core sections, these should be retained and used when the the thing is reassembled.
Any new primary windings can be wound directly onto the core, on the leg opposite the secondary. Else wind them on a plasric or carboard bobbin that can be slid over on core half, the other sliding into it then. Be careful not to break off or otherwise damage the HV return wire when disassebling the flyback.
If you are powering a plasma globe or other single-ended display, then ground the HV return wire. If you use the elctrical ground or neutral, then ground it through a 10kV .01µF capacitor (ceramic works fine). This will prevent the plasma from possibly conducting the 60Hz mains voltage into your outstrecthed hand...
Easiest, simple, (I think best) way
Only uses 1 transistor (2N3055 works well with 10-18VDC), and two resistors, plus two primary coils.
Use 5W for R1, and 1W for R2. This circuit works with a wide variety of transistors, but each one may require a different number of feedback turns, so try varying it by two or more. The circuit, as pictured, has always worked fine for me with no tweaking. Use Something like 18 gauge, and not much smaller for the coils.
Here are some pix of a nice setup of this type
Rather Blurry, but, it shows the whole Thing, power supply
transformer and all.
This shows
the the single transistor, and a large bridge rectifier in the DC
power supply.
There are far more complex ways of driving flybacks, as you can see in this picture of one advanced circuit that I never did get to work...
This shows an entire tesla coil system running from a flyback
transformer. Vary R1 and R2 between 1K and 11K to find the best
frequency to drive the flyback at. .01µF is a good starting
value for C1. Try various numbers of primary turns on the
flyback, 5-10 being a good starting point. The value of C2 isn't
critical, since the diode (either within the flyback itself or
added) supplies the tank circuit with DC. Try values starting at
2000pF or 3000pF.
More to come later...
email: electrophile@juno.com