Coil/Transformer identification

[Tarien]

Hello im struggling to copy NCH8200HV step up converter for powering nixie tubes. All data from chips and tranistors are milled. But i figure it out at 90% including chip wich is MAX669 . But im getting problem with figuring out what is that Coil or Transformer thing . The size is 7,25mm x 6,3mm with two wirings (down middle pin is NC) with resistance as in pic, onnly marking is J054 wich sugest 50mH 5%? I drove the schematic. Any sugestion what that migh be?

[bostonman]

Maybe it has a company logo on the bottom? Might be worth removing to see.

[T3sl4co1l]

Holey moley, an actually good design?!

Yes, it'll be something like that.  How the secondary is returned (to which end of pri) is kind of whatever, it could be a standard flyback with the ends wired together (+V or GND), or in series as a tapped inductor (or boost with extended winding, same thing).  The ratio will be in the 1:10 range give or take (flyback is pretty tolerant of ratio so it could be anything from say 1:5 to 1:40).

Part will either be standard for some other application (offline SMPS / phone charger would do; photoflash charger maybe; or maybe even CCFL, but those aren't used much anymore), or custom.  Custom magnetics aren't exactly expensive so it could be whatever.

Taking it apart, measuring inductances, counting turns (and layer arrangement), measuring and looking up the core type, and air gap if possible, basically tells you everything you need to know about it.

Tim

[Tarien]

I take it off for measurment but no marking

[Tarien]

Okay due to chines meter the green marked wiring is 1mH (this connected with diode), the red one go 0.01mH. I seen the same transformer in a lot of chiness copy so i guess its serial production. Does its some typical package for transformers?

[floobydust]

I thought it was the never ending battle 555 verses MC34063 for these nixie power supplies lol.

Coilcraft Transformers for Capacitor Charging like CJ5143 for the NCP5080. Camera flash/strobe applications. They have reference design parts, maybe the Maxim IC is there.

That PCB photo I would say you need HV spacings for some traces but don't see it.

[T3sl4co1l]

Core might be EFD, you'll have to take a closer look yourself. Example: https://product.tdk.com/en/search/ferrite/catalog there are dozens of manufacturers, particularly in China; even if it's a nonstandard part (shape or dimensions), you can probably find something close, if you search hard enough.  SMT bobbins are quite standard for EFD and other small and low-profile cores.  Add some e.g. 3M #92 polyimide tape, and magnet wire, and you can make your own.

Tim

[jbb]

I'm guessing that's a .  It's likely a good choice for this application: high step-up ratio and fairly low power.

Turns ratio is probably sqrt(1mH / 0.01mH) = 10:1.  Leakage inductance in the tapped inductor is undesirable, so the windings need to be designed accordingly.

Please note that the 'end' of the inductor will go negative (to about 5V * -1 * 10 = -50V) and so the diode will need to block more than 170 V.

[moffy]

The easiest and best method is to remove the transformer from the board and measure the inductances and ratio using a signal generator and a scope plus a resistor or two.