I need to select an inductor for my power supply conducted emissions testing. The inductor will be placed in series with the power supply line ( multiple power supplies onboard). the max current for one of the power supply is about 10A with other power supplies being lower than that.
but the requirement is to measure the conducted emissions up to 3GHz, for which I need to make sure that the inductor impedance profile would remain flat up that freq. I was looking for inductor with current rating >=10A and with a resonant freq of >=3GHz but none are available. many of the power inductors have high impedance at the resonant freq much closer to <100MHz or so. Is there something I am missing here?
Hello,
Thank you for your post.
In regards to an inductor that matches your requirements, I was not able to find a good match.
I do see that we have some that are rated for more than 10A, but the highest frequency I saw in those options was 565MHz. That would be our part number 541-IHLP1616ABER47NM01CT-ND
https://www.digikey.com/short/qw50w4d3
When one starts speaking of GHz frequencies, things as mundane as the size of the PCB pads used to plant a component start to have an effect on observed behaviors. Filters for such can often be implemented using PCB features alone.
That said, it may be useful to consider ferrite bead products such as a BLM31SN500SH1L; these are designed to appear resistive at higher frequencies, in order to dissipate energy at such rather than simply confining it, as would occur if one could build a filter from ideal components. Which are of course on backorder presently due to shortages of unobtanium…
I just realized that I didn’t specify the value of the inductor - > 5uH is needed. There were none matching the criteria.
Agree that the RF freq can affect many of the characteristics.
If I understand correctly, the ask here is for a >5uH inductor capable of handling >10A that’s more or less linear past 3 GHz. Take a look at the inductors that are perhaps closest, note where the limits of listed products start to fall short, and consider the underlying factors involved in building such an inductor:
- 10A is a fair bit of current, meaning the windings need to be pretty beefy.
- 3GHz is pretty fast; most magnetic core materials start to go wonky before that, so one is likely going to be stuck with a non-magnetic core.
- With a non-magnetic core, it takes more turns to achieve a given inductance.
- More turns tends to mean turns that are closer together, increasing the capacitance between them and thereby lowering the self-resonant frequency.
- Spacing those windings out to reduce inter-winding capacitance makes the overall device larger, and start looking a lot like an antenna.
Bottom line: if a device meeting your specifications is physically practical, we don’t have one among our current listings.
From whence does this set of requirements arise? I’d assumed at first that you were looking for something to incorporate into a product to aid in passing emissions, but the question changes somewhat if operating on the side of the test apparatus.