Designing HV transformers.

Mebart,

With a piezo trasnformer, is there any way to "roll your own" like there is with conventional transformers? I'd love to experiment with piezo transformers in some switching power supplies, but it's unclear to me how you can do that in small quantities. Places like

seem to want to do a custom design?

Thanks,

---Joel Kolstad

Joseph,

You didn't mention your location or the power level needed.

If you need 6 to 40 watts at up to 3 KV, you might look into a piezotransformer. They have high step up ratios and do not suffer from shunt capacitance problems like conventional wire based transformers do.

To get a few watts, use a piezoinverter from a CCFL inverter which are available here in the US. If you need more power (up to 30 watts, or slightly more), you can use the newer radial piezotransformer available in Europe.

Regulation is easily obtained as well, you didn't mention whether you needed regulation.

They operate from 50 kHz to around 200 kHz and produce AC, with the majority at the lower end of that frequency range.

Regards,

M

How high in voltage rating are they available? 5kV, 10kV? What are some suppliers of these new European radial piezotransformers?

How is that done, servo the primary supply voltage?

Especially at higher voltages I suppose?

--
 Thanks,
    - Win

Hi Mebart,

Thanks for the detailed reply; it's most informative.

It sounds like this could be one of those items that would work well via "eBay distribution" if we could find a supply who's sell, say, 100 at a time.

Yeah, I found the Panasonic units at DigiKey and was amazed to see that Panasonic then doesn't actually know anything about them on their web site. Sheesh!

Specs would be nice, but I (think) characterizing them empirically would be OK.

I have a pet project of a CCFL driver, but it's somewhat higher power than most (~25W) and making the driver board more efficient and smaller is always desirable. Constant current regulation (adjustable for the sake of dimming) is what I'm using. I do have access to a network analyzer.

Sure! Although I'm not certain I actually have any e-mail accounts that'll accept a file that big. I don't suppose there's an FTP or HTTP site you could place a ZIP archive of them all?

Thanks,

---Joel

Greetings. In the past I succesfully built HV transformers for a 2KV voltage sourse. I drive the primary with a 20KHz sinwave. I used to use UU cores like those in flyback transformers. But now I am having great difficulty getting those type of cores - a MAJOR stockist of Ferroxcube etc tells me they are very hard to get! So my question is: will cores such as etd54 do the job? Why are single loop UU type cores always used in flyback transformers? Regards Joseph Casey.

Hi Joel,

You asked the million dollar question! If you want a few units, you can get them....but the supply isn't reliable in the US for commercial purposes. Places that want to design them are selling you design time, and won't even produce it for you unless you want to buy them by the ton:>:

I've followed the development of these ever since learning about them in the 1999, thanks to an article in EDN Magazine. Lots of outfits claim to make them, but they turn out to be BS claims-they don't advertise their standard products and there is no real content when you look for info on their websites. Been there, did that, plenty!

I've even looked in Asia via the web. The Asian suppliers don't even want to talk to you unless you want to order 200,000 units per year from them. In general, Asia is a waste of time-take it from someone who has tried. One Asian vendor tried to hit tried to sell me samples shipped from .tw, they wanted 12 dollars each unit and $200 for shipping 3 units. Needless to say, I did not reply:>:

Regarding the roll your own effort.... They are not terribly hard to make although you will have to attach wires and build a holder to contain your piezoelement. The supports have to be placed at 1/4 and

3/4 of the physical length or else the movement of the piezoelement will cause it to fracture. You can't solder wires to them either, connections must be low mass. If you can deposit silver (very thin, can't have much mass) on the piezo, anyone in the semiconductor biz can attach wires for you.

If you want characterized units, you can do it yourself with an HP network analyzer. I have a Spice model for one that actually works! The internal parameters are very important with respect to the driver.

All the CCFL inverters on the market today use constant current regulation, if you want to regulate it with respect to voltage output, you gotta roll your own driver. This is not impossible, but forget a single chip solution:>:

I have megabytes and megabytes of info I've collected on them over the years, there is alot of good ifo on the web too. Keep in mind, some call them 'piezotransformers' others call them "piezoelectric transformers" or "piezo transformer" etc. Google turns up lots of hits....but getting some of the units themselves will be a challenge.

If you want to play with higher powered button or circular devices, they are available from a European supplier. The circular ones put out

5 times more power than the conventional rectangular Rosen type devices.

You can buy a development kit from TI that comes with driver chips (constant current type) and piezotransformers on a PCB. You can also buy Panasonic units (without a source of specs) from digi-key. Not cheap, I might add and they are selling them until the stock runs out.

I found a single US supplier that actually has the units in stock for immediate sale, but they don't even know what a Spice Model is......again, these are devices without complete specs.

I am working on a photomultiplier supply using one of these units, hope it will be efficient.

Hey, what are you trying to do with them, and what do you have for test equipment?? A network analyzer I hope?? Having a network analyzer will allow you to characterize your own unit, you won't be reliant on a manufacturer for specs.

In closing, I can say that these devices are appearing in so called 'personal air purifiers'. They generate high voltage, and the sellers claim breathing ozone is healthy for you:>: The FDA is confiscating them as fast as they enter the country, but some are on the market (surplus, ebay and other non-reputable sellers have them). Search for piezo+air+purifier on ebay, you will have many hits. I haven't looked inside any of these yet, but they might have a constant voltage driver although it's probably not regulated well.

So, tell me more...........

Want 20 or 40 mb worth of web info on them?? Ive got a big collection of files in my personal library. Say the word and I'll ship them via email.

M

Hello Joseph,

I have used regular cores and mostly toroids for transformers that had to comply with IEC601, plus they needed to be defibrillator proof. In essence that means they must withstand a 5KV blow.

The main thing is an absense of any sharp edges, wire with certified insulation properties and very detailed and well guarded production procedures.

For UU cores you may have to contact Asian manufacturers such as Dongying Xinji. That's the region where most TVs are built these days and the ones with CRTs need such cores for their flyback transformer.

Regards, Joerg

Currently, the industry believes that if if ain't for a ccfl inverter, then your application has no merit. This is not an exaggeration. Most have ratings of 6 to 8 kV peak to peak. There is actually very little that limits the output however, except that the devices aren't built with larger spacings to allow higher outputs.

Sample the output and feed it to a conventional error amp feedback loop circuit.

No, actually not at all. The higher operating frequency devices are generally physically smaller and therefore have a higher frequency of operation and put out less power because they are smaller. Again, this isn't necessarily the way it could be....except that it is the mindset of the designer. Again, if it ain't for a ccfl inverter, it doesn't count:>:

There are some first class technical references on the web. Some of these go into great depth regarding the physical dimensions and the particular material used to make them and many questions are answered regarding what makes 'em tick.

Hope this helps. Feel free to ask other questions or I'm happy to send a care package in the form of web documents I've collected over the recent history of these devices.

M

Hi Mebart,

OK.

Yahoo! messenger runs whenever this PC is on (more or less work hours) and it alerts me whenever I have new Yahoo! mail.

Sure, that'd be great. Try sending... say... 5MB chunks, I'm pretty sure Yahoo! mail will swallow that.

The e-mail address in the header is correct after removing the "HATESSPAM" part. :-)

Thanks,

---Joel

Hello Joseph,

Mostly to avoid corona or arcing. Far enough away from the winding it isn't so important. Another concern is if the wire is to be wound directly onto the bare or taped core. Any burrs can damage the insulation.

Regards, Joerg

Why is this important? I do notice that the TV ones are rounded inside next to the winding but have corners outside.

Ireland. The power is about 10 watts intermittent use.

It is regulated. I don't want to change the design so I'll stick with wound transformers but the piezo transformers would be fun to experiment with.

Thanks JC

This is fairly typical of the entire industry. No one has specs listed, and the one single vendor who does has some serious errors in his listing! Complete characterization necessary for Spice simulations is non-existant. I am NOT kidding about this!

I'm not sure-I know yahoo gives 20 mb of free web space if you start a mailing list. I have 10 mb of personal web space, but that won't even start to cover all the materail I have.

How often do you check your mail??? I can forward a mb or two each day till you holler STOP. Is your email address in the header ok?

Regards,

M

Cores are likely to be available according to market demand.

I find the ETD and EE series to be best supported overall for general purpose.

Doesn't matter if it's flyback or forward.

Download Epcos's Ferrite Magnetic Designer utility. It's great.

Graham

Large winding area was traditionally good to accomadate the necessary safety margins.

Use triple insulated wire and your problems go away.

Graham

No, many fewer turns are required at higher frequencies, and in most instances the core area can be smaller as well.

--
 Thanks,
    - Win

Are they reliable to 180C? Are small ones available - similar to the FerroxCube size P14/8?

Hey! That looks handier than a rat! I wonder how they make their living?

Cheers! Rich

"Joel Kolstad" a écrit dans le message de news: snipped-for-privacy@corp.supernews.com...

it

Make a zip of all files and just use

You upload your file (up to 1GB), then the other guy receives an email with a link to download it.

--
Thanks,
Fred.