I am designing a 1.7 kV @ 6 mA flyback power supply. The issue I have is that it seems to be extremely difficult to find any type of high voltage flyback transformers for the design. I bought a cheap generic CRT flyback to experiment with, but being generic it has no datasheet to speak of. I assume I can derive the winding ratio easily enough, but what about the other parameters? For example, to figure out the optimum frequency can I just do a frequency sweep until I find the highest output voltage?
Electronic – Derive Parameters for Unknown Flyback Transformer
flybacktransformer
Related Solutions
It's a little unclear what exactly you are trying to accomplish. If the point is just to experiment with full wave bridges and see all the signals, then do it at a low voltage like JonnyBoats said. You can probably find a old transformer somewhere that is rated in the range 6-12V AC at 1 Amp or so. That's a good size to put a full wave bridge after, and then you also get a useful DC voltage to do lots of other things with.
As Jonny mentioned, there are also wall wart type transformers that are rated for less power but you can do mostly the same things with. The advantage is that these things are cheap nowadays. You can probably find something in the 3-5 Watt range for $5. Jameco has a broad selection of such things. That's a good place to look around.
If you really want to experiment with a full wave bridge driven by a function generator, then you should power the function generator from a isolation transformer. These are 1:1 transformers meant to take line power in and put line power out, except that the output can float. These will cost a bit more since they are usually intended for 100 W or more. Sometimes they even come in a box with a line cord for the primary of the transformer and a regular output connected to the secondary. You simply plug the cord into a wall outlet, and the thing you want isolated into the outlet on the box.
One gotcha you have to be careful of with these things is that they may not come wired up fully isolated. I bunch of years ago I bought a 500 W "isolation transformer" that was just as I described above. I used it to float a device under test so that I could hook up a grounded scope to it at various places. The first time I touched the scope ground clip to part of the power supply there was nice spark and the fuse blew. It turns out there was actually a deliberate ground wire inside the isolation transformer box connecting the ground from the line cord to the grounds on the output sockets. That's not what I consider "isolation", but someone else apparently does. Once I disconnected the two sides of the transformer and carefully verified there was no conduction path, it worked as intended.
Another possibility (in addition to those in the previous answer and comments) is that the pins of the secondary connection are swapped -- or equivalently, the pins of the primary connection are swapped.
If the connection to one of the windings has a flipped polarity, this circuit will work as a forward converter instead of as a flyback converter. Given the turns ratio of the transformer (1:10.2 or 1:12) and the 24-volt supply, the circuit can still charge the capacitor bank to 200 volts. But unlike a flyback converter, a forward converter has no intrinsic current limiting, so the peak transformer currents will be very high while charging the capacitors, which can damage the transformer (and other components).
In a flyback configuration, the output diode should be off when the transformer-driving transistor is on. The on time of the transistor charges the transformer with a current ramp limited by the primary inductance. When the transistor turns off, the diode conducts and the magnetic energy stored in the transformer transfers to the output capacitor. Because of the controlled energy transfer, a flyback converter can efficiently charge a capacitor starting at zero volts.
In a forward-converter configuration, both the transistor and diode conduct at the same time. The only things that limit the current are circuit and winding resistances, plus a very small amount of transformer leakage inductance. Not only are the peak currents very high, but directly charging a capacitor from zero volts with a forward converter dissipates half the energy into the circuit resistances. This results in a best-case efficiency of only 50 percent. If efficiency is not a concern, it's okay to use a forward converter to charge capacitors, but the design should include a resistor in the primary or secondary circuit to limit the peak charging current.
One thing that contradicts this hypothesis is your measurement that shows a maximum current of 1 amp. Was this a measurement of the transformer primary current or of the average input current to the circuit? Was the capacitor bank already partially charged when this measurement was taken?
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Best Answer
To determine the core saturation and permeability you probably need a function generator with the ability to generate a high enough voltage/power.
I am not sure what the primary looks like in your case but I am thinking of an audio amp or maybe the type of amplifiers EMC people use in there test. The latter are expensive and not easy to come by for the average hobbyist.
Use an oscilloscope to measure the current over a series resistance to determine the impedance and saturation point at different frequencies. Then work you way back through the typical solenoid formulas do determine the core properties.