Flyback on reversed polarity driving multiplier? - Page 1
Forum section: electronics / projects

author: nsled
author_rank: Contributor
timestamp: February 04, 2024, 10:43:46 am
content: Is there anything flawed with the attached picture?I want to achieve 20kV out of 10kv flyback transformers, then multiply to 120kV(ish).So the primaries are wired in parallel but with reversed polarities, giving reversed polarities at the secondaries that produce a 2x potential difference at the multiplier input.Is this workable? Does this configuration have a name that I can research?I was going to wire the transformers secondaries in series but is this option better?Thankyou.EDIT: I should note that I need the 20kv AC output as well as the 120kV DC, so no lengthening the multiplier nor using a bipolar multiplier.

author: Andy Chee
author_rank: Super Contributor
timestamp: February 04, 2024, 11:03:34 am
content: What is inside each of the square blocks marked with "primary" & "secondary"?If this is a transformer, then as wired in your picture, you will actually short circuit the 100V output.

author: nsled
author_rank: Contributor
timestamp: February 04, 2024, 11:13:50 am
content: It's just the primary and secondary winding transformer, nothing more. There's no short that doesn't flow through the coil it's just transformers wired in parallel.I've noticed the colours of the secondary to multiplier are wrong, flip colours on bottom transformer. Though makes no difference to the wiring.

author: Andy Chee
author_rank: Super Contributor
timestamp: February 04, 2024, 11:18:07 am
content: If the transformer winding phasing is consistent with your red and blue, then you most definitely have a short across 100V.Otherwise, please redraw your diagram indicating proper phasing.The below diagram is a short circuit.

author: nsled
author_rank: Contributor
timestamp: February 04, 2024, 11:51:16 am
content: You've drawn parallel transformers, output +10kv/0kV, I need +10kv/-10kV.

author: jonpaul
author_rank: Super Contributor
timestamp: February 04, 2024, 12:36:54 pm
content: flybacks have a Low and HV side.Low - start near core must be near ckt groundCannot use in seriesj

author: Andy Chee
author_rank: Super Contributor
timestamp: February 04, 2024, 12:44:34 pm
content: Quote from: nsled on February 04, 2024, 11:51:16 amI'm just interpreting your diagram, which appears to be also drawn as parallel transformers.

author: Andy Chee
author_rank: Super Contributor
timestamp: February 04, 2024, 01:01:13 pm
content: To create a bipolar supply with two identical transformers, connect the transformers like so:However, you have mentioned that these are flyback transformers. Flyback transformers cannot be connected like this.Please post a picture of your intended transformer.

author: nsled
author_rank: Contributor
timestamp: February 04, 2024, 01:59:33 pm
content: I'm confident you can connect flybacks in series, it just might not always be a good idea. The Chinese CO2 laser power supply flybacks are connected in series.https://ae01.alicdn.com/kf/H3cdaed050e80492187e7f66aa8c75104a.jpgdepending on length of tube it can be 1, 2 or 3 in series.My 10kV transformer is run via a ZVS and its input and output is a perfect sine wave, I don't see a problem with assuming the wiring is the same as any power transformer when driven this way. There's not much to look at its just a cast resin block E core transformer. I've only one atm or I'd test it myself.I'm confused Andy isn't that last picture just a series output config. +20kV/0v. Which is something I may end up doing if I cannot work out +10kV/-10kV.

author: Andy Chee
author_rank: Super Contributor
timestamp: February 04, 2024, 02:20:57 pm
content: The secondary winding of a flyback transformer forms part of an autotransformer. They do not "add up" like connecting conventional isolated secondaries in series. Use LTspice to see for yourself.In my last picture, the grounded centre is the 0V reference point, top wire supplies +V, bottom wire supplies -V.If you're getting confused, perhaps you should re-evaluate your design specification i.e. do you actually need +/-10kV for your application?What is your application?

author: nsled
author_rank: Contributor
timestamp: February 04, 2024, 03:46:08 pm
content: Correct me if I'm wrong but the definition of a "flyback" isn't exactly black and white and has more to do with the core material, configuration, optimisation and the way its driven than the windings. For the purposes of this topic its 2 separate windings coaxially wound on a ferrite E core with 240:1 ratio. I found a pic before the secondary was wound, attached.I think I found the term I'm looking for, "antiparallel" configuration. Though cannot find relevant examples of it.So in your schematic is the centre ground attached back to the primary? I've no real access back to a common ground. I see what confused me, you kept saying the 100v side was shorted but you meant the 10kV side correct?I'm attaching pic as to where I'm at in thoughts, the primary is still "antiparallel", that way the secondaries should hit +10kV and -10kV respectively at the same time and the ground is shared with the primary in the same way it is in an ignition coil.

author: Andy Chee
author_rank: Super Contributor
timestamp: February 04, 2024, 04:11:26 pm
content: Quote from: nsled on February 04, 2024, 03:46:08 pmThe picture in the link you previously showed with the Chinese television flyback transformers, will likely be autotransformer construction, not 2 separate isolated windings.In any case, once you get the transformer in your physical hands, you should use a multimeter to confirm isolation.Quote from: nsled on February 04, 2024, 03:46:08 pmNo, I was correct. If you get the 10kV secondary phasing incorrect, you will short the 100V supply.

author: Andy Chee
author_rank: Super Contributor
timestamp: February 04, 2024, 04:42:48 pm
content: Incidentally, you might consider winding your transformer using UU cores like the guys in the attached pdf.Note the simulated the voltage stress heat maps (i.e. likely place for arcing).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 04, 2024, 04:58:29 pm
content: If you want high voltage, just specify a high voltage transformer."Flyback transformer" implies much more than any random transformer alone. At the least, it implies a transformer intended for such application, usually with a high voltage diode or tripler attached to it, and the turns ratio may be lower than expected due to the voltage multiplication that a high duty cycle (or DCM) flyback can offer.The average example, is probably a "flyback transformer" for use in a CRT TV/monitor, which aside from early examples (50s-70s?), integrates the rectifier, focus divider, and dynamic focus/pincushion network if applicable. The latter type obviously cannot be used here as its output is DC only.There are many HV transformer types available for various purposes, including resonant application, which may be most suitable here.Tim

author: Marco
author_rank: Super Contributor
timestamp: February 04, 2024, 10:29:11 pm
content: AFAIR when using "recent" TV "flybacks", the HV tinkerers/arc-pullers count on the Royer/ZVS/Mazilli driver to just blow the two stage diode/capacitor multiplier short through overvoltage. Because in principle the driver requires a transformer without the output multiplier. It's designed for a symmetrical load for the MOSFETs and the internal multiplier isn't, you can make a symmetrical multiplier but the one in there isn't.Those TV "flybacks" are not strictly speaking flybacks either, they are hybrid forward/flyback. A true flyback delivers unidirectional current on the output and that obviously can't drive a multiplier.