I have to make low power SMPS operable up to several hundred volts. For obvious reasons, it would be good to use off the shelf SMT inductors. In datasheets, they always specify inductor max. current, however they don't say anything about max. voltage.
Any advice or relevant experience?
Vladimir Vassilevsky DSP and Mixed Signal Designs
First I'd make sure the pads are far enough apart to stand off whatever voltage you expect to create (+ safety factor of three or so).
Then, have you looked here:
Mark L. Fergerson
Yes. If you're going to ask the the electronics equivalent of a question that would earn you a "Stupident" title change from some guy named Vladimir Vassilevsky on comp.dsp -- change your ways.
-- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
"Vladimir Vassilevsky"
** Why not get a few likely candidates and test them to destruction ?Then you will know the absolute max and can de-rate from there.
Eg: place the DUT in series with a high voltage ceramic cap and drive the combo at resonance with a sine wave from an amplifier - should be easy enough to get a few hundred volts RMS across the inductor.
.... Phil
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I love to cook with wine. Sometimes I even put it in the food.
If you had a sample, the insulation rating of the wire would be a good starting point for the upper limit...
-- Cheers, James Arthur
I call that the "diode" method. Good for weeding out devices that definitely won't work...but says nothing about those that pass, out of the next batch...and the batch two years from now after the vendor quits making 'em. Certainly better than nothing, but nowhere near as helpful as contacting the vendors.
Having a clear goal, like "several hundred volts" helps a lot.
Several people really hate this method. The purchasing agent who has to source the thing. The safety compliance agent who's looking at something potentially unsafe with no specification. The manufacturing manager waiting for you to get the line back up. The guy in Field Returns who has to fix 'em. Your successor saddled with your comfort with risk taking.
But, at least, you had fun smoking some.
If you had a sample, the insulation rating of the wire would be a good starting point for the upper limit...
** That assumes the ends of the coil are adjacent.Normally, the voltage between adjacent turns is divided by the number of turns, for a single layer coil.
Real tests need to be done on a real example - cos insulation to the ferrite may be the first to fail.
.... Phil
** My idea is to test *every example* at several times the max expected peak voltage - assuming this gives you a high pass rate. ** When using an un-speced parameter - one is on ones own.
... Phil
Tests good, but you're missing the point...SPECS BETTER!
Shoot-From-The-Hip designers are a nightmare. Back in the day, there was a whole building full of engineers who did nothing but verify components met their specs. Hard to do when they don't have a spec. They would not let us do unspecified things that seemed to over-stress the technology...unless we didn't tell 'em. My engineers were trained to create reliable stuff. YMMV
** No - YOU are missing the point.
The makers are not simply supplying a spec and any figure given after a request would not be credible.
Also, IF the devices fail the test - then the OP has his answer.
BTW:
Film resistors come with max voltage specs - right?
But you cannot believe them.
Given time, applying the rated DC voltage will destroy most.
Even half the same figure will destroy a great many.
... Phil
I'd be surprised of any commercial inductor would break down at a few hundred volts. Magnet wire is generally good for that much.
You could test a candidate inductor to destruction. That's always fun.
What topology did you have in mind?
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
It's a question I've wondered about before. It's definitely something to apply, say, 700V at ~unlimited current reserve to an inductor and hope it'll work.
I don't think I've ever seen a winding voltage spec. It's much harder to test than a capacitor current limit (which is also often omitted), because, yes you can make it resonate, but because the Q is lower, getting the voltage that high will incur a lot more power than a mere signal generator can generate. The Q even of very good inductors is less than the average film cap.
Also, testing low-gap ferrite transformers is problematic because the inductance depends on amplitude: I've seen bistable frequency spectra from resonators built using them.
Tim
-- Deep Friar: a very philosophical monk. Website: http://seventransistorlabs.com "Vladimir Vassilevsky" wrote in message news:cYGdnTKwAsJqYhvMnZ2dnUVZ_qCdnZ2d@giganews.com... > > I have to make low power SMPS operable up to several hundred volts. For > obvious reasons, it would be good to use off the shelf SMT inductors. > In datasheets, they always specify inductor max. current, however they > don't say anything about max. voltage. > > Any advice or relevant experience? > > Vladimir Vassilevsky > DSP and Mixed Signal Designs > www.abvolt.com
the first question is:
do you mean the voltage from terminal to terminal
or do you mean the voltage from terminals to ground
I'm trying to imagine a situation where you would have that high of a voltage terminal to terminal. Resonance maybe
Mark
How about when the output capacitor is discharged and the "several hundred volts" is applied on start up?
John
Normally not allowed. Every dielectric strength test that reaches near the potential limits will usually age the barrier some. Permanent damage occurs, little by little. This is why the working voltage on parts such as opto-isolatros is much lower than the 1min max breakdown rating.
Not always. If the datasheet doesn't mention the breakdown voltage to adjacent turns and to the core my advice to Vladimir is to write to the manufacturer. If this is for a product design make sure you get a written answer, and not just an "Oh, it's usually ok to put on 300V" via the phone.
-- Regards, Joerg http://www.analogconsultants.com/
"Jerk"
** Pedantic crap.There is NO safety barrier involved here - f****it.
** Go f*ck yourself.
Just remembered that a while back I tested a twisted pair of #40 magnet wire for breakdown. This was at about 1200 volts DC, as I recall.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Any inductor can have a voltage rating; that depends on the wire insulation (lacquer, beldasol, etc) and should be less that the volts per turn mitigated by how many turns from one wire to physically next wire. At high frequencies, it is prolly reduced a lot.
Assume 50V max for SMT, if specced higher; be happy.
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