Author Topic: how to run these guys?  (Read 672 times)

Offline Alberto

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how to run these guys?
« on: January 16, 2021, 12:21:23 AM »
Hi everyone.


I have these flybacks. They are from a CO2 laser.



I don't know what is the best way to run them.

Should I have to use its own primary or is it better if I make others by winding wire on the ferrite core?

In the second case, I will only need a feedback coil, right?

Thank you

Kind regards
« Last Edit: January 16, 2021, 01:27:49 AM by Alberto »

Offline davekni

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Re: how to run these guys?
« Reply #1 on: January 16, 2021, 05:00:46 AM »
Are you wiring the two secondaries in series?  If so, it may not last too long.  Internal insulation from the HV low-side is not designed to handle high voltage relative to the primary winding and ferrite core.

The internal primary will have much less leakage inductance to the secondary compared to adding an external primary winding on the other ferrite core leg.  Leakage inductance can be useful or problematic depending on the drive circuit you plan to use.
David Knierim

Offline Alberto

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Re: how to run these guys?
« Reply #2 on: January 16, 2021, 11:21:13 PM »
Thank you for your answer.

I was thinking in mazzilli driver, or an 555 oscillator.

Thething is, they are in series, so, the output voltage will be double no?

I bought them tihinking in that, but they could handle that voltage?

Maybe the best option will be make my own primary. How should I conect them in series or parallel? In parallel I´ll get higher voltages I think.

So, one feedback coil in one of them and the 2 primarys in parallel

What do you think?


Offline davekni

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Re: how to run these guys?
« Reply #3 on: January 17, 2021, 03:37:28 AM »
If driving these with a ZVS (ie. mazzilli) oscillator, then some leakage inductance is necessary.  Otherwise oscillation drops out when drawing an arc.  The arc load drops Q too low without leakage inductance.  Primary windings on the other core leg would be appropriate.

If driving as a flyback, then leakage inductance is undesirable.  Use the existing primary windings.  I think that is what you mean by 555 - feeding a single HV FET.  These transformers are designed for flyback drive.

Secondaries doubles the voltage as long as the insulation survives.  I don't know the internal construction of your particular flyback transformers.  Expect the second one in the series connection will fail before too long.  Experimenting is the way to learn!  Paralleling the outputs doubles current, making thicker arcs.

For primaries, two 10-turn windings in parallel behaves about the same as two 5-turn windings in series.  Optimum turn count depends on drive circuit and transformer characteristics.  Have fun experimenting!
David Knierim

Offline SteveN87

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Re: how to run these guys?
« Reply #4 on: January 17, 2021, 02:20:09 PM »
I have a very similar unit to yours, marked "LASER HIGH-VOLTAGE" "HS-16-40W" The core is not gapped (and from the photo, it looks like yours isn't either), so it can't be driven as a true flyback. Also, mine has a full-wave rectifier and a built-in capacitor of about 240pF on the output. The primary is 3.3mH with 0.6 ohm DCR. Looks like it was intended for half-bridge drive from rectified mains.

I added a separate primary and a gap to the core and drove it as a true flyback (that's how I found it had full-wave rectification). The overall result was disappointing, because there was strong dielectric barrier discharge from the plastic casing to the core, and sparks rather than arcs on the output.

A ZVS driver would turn this into a nice HVDC power supply, but pushing it too far will likely cause that built-in capacitor to fail.

Offline davekni

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Re: how to run these guys?
« Reply #5 on: January 17, 2021, 08:04:54 PM »
Steve, thank you for the info on these laser HV transformers.  I falsely presumed they were like CRT flybacks.  Looking more closely at the picture, it is now obvious that they have two separate HV leads rather than a low-side pinned out with the primary as with CRT flybacks.  No-gap seems likely too, although I have seen flybacks that appear to have an internal gap and not an external one.
David Knierim

Offline Alberto

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Re: how to run these guys?
« Reply #6 on: January 17, 2021, 09:55:24 PM »
Thank you for your answers.

Ok, I´m getting a little bit lost haha.

I thought they were flybacks. What are they? What is de difference?

And how can I know if a HV transformer gives DC or AC?

I´m not sure what are you talking about the gap.

I have took this photo



Offline davekni

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Re: how to run these guys?
« Reply #7 on: January 17, 2021, 11:29:04 PM »
Try a Google search for "gapped core".  Generally necessary for DC current.  Flyback drive relies on relatively-large DC component of current.

High voltage high frequency AC transformers are hard to find.  Most include rectification within the potted package.  Flyback HV transformers are half-wave rectified.  Per Steve, these are likely full-wave (bridge) rectified and have an internal filter capacitor across the output.

Experiment and have fun (carefully)!
David Knierim

Offline Alberto

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Re: how to run these guys?
« Reply #8 on: January 18, 2021, 12:26:26 AM »


Thanks for all your help!!

Yes, they aren´t gapped



So a Flyback is a HF transformer with DC output right?

In the other hand,if I have understood you, to run them as a flyback means use their own primary giving by an oscillator the desired frequency. And If I use a ZVS I have to make my own primaries conecting them in parallel and usin only 1 feedback coil.

Sorry for all my questions.

Finally, I dont know where to conect in parallel the coil for the second transformer in the mazilli driver. In A or B?



If mazilli doesn´t work for 2 flybacks, waht simple driver I could use?

Or Maybe I could do this,

https://www.youtube.com/watch?v=pqGkUqstn0A&feature=emb_title




Offline klugesmith

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Re: how to run these guys?
« Reply #9 on: January 18, 2021, 01:03:48 AM »
>> Yes, they aren´t gapped

I can't tell from your picture, but a well engineered air gap might be only 1/2 mm, hidden inside the bobbin for windings.

>> So a Flyback is a HF transformer with DC output right?

A flyback is a power converter that depends on energy storage in coupled inductors.
Unlike a transformer, in which instantaneous primary and secondary currents are proportional, and energy storage is ideally zero.

In many applications, for example wallplug USB chargers, flyback topology is chosen for cost reasons.  Single transistor primary, single diode secondary.  Magnetic components may look like tiny ordinary transformers.

In the original CRT-TV application that gave the circuit its name, and familiar core shape, the HV rectifying diode is separate.   So "transformer" delivers AC, with unsymmetric voltage, current, and time in positive and negative half-cycles. 
If a contemporary component has built-in rectifier diode, then unavoidably there's DC current in secondary.  I think that favors, but doesn't require, flyback drive on primary.  We find DC secondary current in the ungapped-core transformers of self-rectifying 60 Hz dental X-ray generators.

As others have mentioned, those "flyback looking" components can often be driven as flybacks or as transformers.   Gapped core indicates that original intent was a flyback circuit, since I think the gap does no good when used as a transformer.  There might be an exception in intentionally-resonant applications.



« Last Edit: January 18, 2021, 01:18:07 AM by klugesmith »

Offline Alberto

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Re: how to run these guys?
« Reply #10 on: January 18, 2021, 11:50:22 PM »
Thank you for your answer.

Ok ok now I see the difference between Flyback and ferrite core transformer.

Offline Alberto

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Re: how to run these guys?
« Reply #11 on: January 30, 2021, 12:09:25 AM »
Thank you for all your help. I have tried them today, connecting my own primaries in parallel and using an 555 oscillator. And yes, the give twice voltage if I run them at the same time.

And I saw in other flyback, between the ferrites, a small disc of pastic. That must be the gap. I tried the flyback with and without the disc, but I din´t see diference.

I have look up in the internet about flybacks and other ferrite core transformers to understand the diference, but I don find anything. Does anybody knows a web or document to learn about that?


Offline davekni

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Re: how to run these guys?
« Reply #12 on: January 30, 2021, 01:00:46 AM »
Search for "gapped core" as I'd suggested in reply 7.  Here are a couple of the search results:
https://www.powerelectronics.com/content/article/21861299/why-have-an-air-gap
http://info.ee.surrey.ac.uk/Workshop/advice/coils/gap/index.html

Yes, that small piece of plastic is the gap.

If you are driving with a symmetric waveform at a fixed frequency, the gap may not make an obvious difference.  The gap increases magnetization current.  If the drive impedance is low enough, that additional current doesn't matter.

If driving with a single transistor as a flyback (boost converter) or in any resonant circuit, the gap is necessary for reasonable performance.
David Knierim

Offline Alberto

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Re: how to run these guys?
« Reply #13 on: January 30, 2021, 06:43:12 PM »
Thank you for your answer.

I didn´t see this results when I look up. I´m going to read them!

High Voltage Forum

Re: how to run these guys?
« Reply #13 on: January 30, 2021, 06:43:12 PM »

 


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