I am clueless about flyback transformers

[Johton]

Recently I got my hands upon some old flyback transformer from an old Sony CRT TV. As I started tinkering with it in order to find where are its primary and flyback coils, as I entered its model number (859882200) I got only a few Russian sites where they were selling these transformers types, no datasheet whatsoever. So my plan B was to measure the resistance of its pins, and that's where I got confused, a lot of pins had very similar and sometimes the same resistances. I made a fast graph of my results which I attached as a png file bellow, so please help me to identify the pins of my transformer.

[SteveN87]

The HRDEIMEN website gives the following match:

https://www.hrdiemen.com/search/index?utf8=%E2%9C%93&orig=859882200

And schematic (HR 8520):

https://www.hrdiemen.com/reparation/flyback/scheme/8520

Sony flybacks seem particularly good - I have one (which doesn't have the focus outputs) that has been pushed to 80kV output and is still going strong.

[MRMILSTAR]

I am assuming that you want to use it to generate HV for some application. If so you don't need any of the primary coil pins. All that you need is the HV output lead and the HV return pin. So your task is to determine which of the pins is the HV return pin. I am assuming that the HV output lead is obvious. Do you know if the flyback is an AC type or a DC type? The DC type has a built in diode, actually a string of lower voltage diodes, which converts the flyback's secondary coil output from AC to DC. DC flybacks usually have a rectangular bulge on the side which contains the diode and some pots. There may be 2 adjustable screws on the side of a DC flyback. These are potentiometers for TV use. AC flybacks are usually, but not always, completely round. There will not be any adjustable pots.

If its an AC flyback then its simple to locate the HV return pin. Your ohmmeter should show significant resistance, typically around 1000 ohms, between the HV output wire and the HV return pin.

If its the DC type then an ohmmeter won't work because of the internal HV diode. An ohmmeter doesn't supply enough voltage to overcome the forward voltage drop in the HV diode which could be 20 to 50 volts or so. You could use a voltage source with at least 30 volts output or at least enough to overcome the diode forward voltage drop, a current limiting resistor, and a voltmeter to find the return pin. I have a 0 to 1000 volt DC power supply so I just use 100 volts to make sure but you can get by with less.

Another method for locating a DC flyback HV return pin is to wind a center-tapped 10 turn coil around the unused ferrite core leg and drive this coil with one those cheap Chinese ZVS drivers (about $10). This would also require a DC power source with an output between 15 and 36 volts capable of supplying at least 5 amps to the ZVS driver. Then simply move the HV output lead from pin to pin until you get an arc. When you get an arc, that is the HV return pin.

[Alberto]

You can run in this way, but be carefull.

https://www.youtube.com/watch?v=q9iSQSR9SHM

[John123]

I'll just leave this here, if you want true flyback operation then done right with a good layout this one is bulletproof. If you use a higher voltage fet then you can reduce the capacitor across the primary for more voltage out. I also added a TVS diode from drain to source and a zener diode in anti parallel to the fets gate for added protection along with a pulldown resistor of a few k ohms. If its unstable then add a 10 ohm resistor in series with the gate turn off diode.

Use UC3845 if you want the chip to run off 12v instead of 18v and also make sure that big 10m/50v capacitor is a low ESR type, even if you use an already filtered DC supply still put some kind of low ESR bulk capacitor there right across the DC bus rails very close to the driver (it sees large peak currents).

Its the adjustable peak current sensing on this driver which makes it suited for arc drawing.