Electronics > Projects, Designs, and Technical Stuff

5uH Aerospace LISN: How dumb would I be to "throw one together"?

<< < (7/11) > >>

TimNJ:

--- Quote from: Jay_Diddy_B on July 28, 2020, 03:29:26 am ---Hi,

The Coilcraft model is only valid over a limited frequency range:

*======================================================================
* SPICE Model generated by Coilcraft
* Coilcraft Part Number : SER1590-102
* Inductance = 1uH
*======================================================================
* Model Parameters:
*   Valid Frequency Range = 0.1MHz-10MHz
*   Ambient Temperature = 25 degC
*   Inductor Frequency Model
*   Use model for Frequency Domain simulations
*======================================================================

They say here:

https://www.coilcraft.com/en-us/models/howto/using-coilcrafts-models-in-ltspice/

When running simulations, note the upper and lower frequency limits for which the model is valid. This information is shown on the Coilcraft SPICE model document for each inductor series.

Which make it pretty useless for looking at the SRF frequency.

The Wurth model seems to be correct. It matched the measurements that I made with a VNA.

Regards,
Jay_Diddy_B

--- End quote ---

Thanks. I saw this too. Not sure what Wurth is doing to get a reasonably accurate model and why Coilcraft can't (or doesn't care) to model the high frequencies. Perhaps they decided it's outside the "useful" frequency range of the inductor (i.e. few people would try to design a switching power supply above a few megahertz anyway.) Maybe low frequency model accuracy suffers if try to fit the model to high frequencies as well. Not sure.

TimNJ:

--- Quote from: Jay_Diddy_B on July 28, 2020, 04:44:32 am ---
--- Quote from: TimNJ on July 28, 2020, 04:32:04 am ---

Floating electrode as in MLCC with flexible termination? If so, interesting thought, though since these will be hand-soldered, I'd still feel a little queasy about the whole idea. Inductance of those 40x20mm MKP caps is probably not so great at the high frequencies is I guess what you are suggesting. I suppose I could bypass with Y-caps or similar to get some better MHz range performance. I suppose those should be located closer to the AC (or DC) input? Or maybe it's more important to keep the inductance between parallel caps down, exact position of HF bypass caps less critical?

Thanks.

--- End quote ---

The floating electrode, is a type of capacitor construction where there are two (or more capacitors) in series inside the capacitor.
The Wima FKP1 shown here:

(Attachment Link)

Has two capacitors in series.

This reduces the ac voltage across each of the internal capacitors by a factor of two.

Typically one section is used for every 200V of ac voltage rating.

The 10uF capacitor in the EMC application do two things:

1) the define the impedance at low frequencies  say less than 100kHz. Good RF performance is not needed for this part.

2) Act as a filter for noise coming from the input side. This is probably the main reason for having them. Good RF performance is needed for this.
(In your application with the Chroma Source) you might not need this function).

Regards,
Jay_Diddy_B

--- End quote ---

Ah! Didn't know about those capacitors. Learn something new every day. Thanks.

Regarding the capacitance, I don't really know how the AC source synthesizes the AC voltage and what the noise signature of it is. Definitely some sort of switching topology, maybe some sort of DDS thing.

I simulated with 1uF and 10uF in that position. As you said, the low frequency impedance is indeed affected, although when comparing to the DO-160 LISN limits, seems it would still be in the allowable range. Then tried with 4.4uF (2x2.2uF). Impedance is really not that much different between the two.

Yellow = 1uF
Blue = 4.4uF
Red = 10uF

Perhaps the 10uF is somewhat of a historical artifact. Maybe the 400Hz sources of the past were very dirty/noisy. (Perhaps EMC test labes were even using mechanical 400Hz generator?)

Unless a higher impedance below 10KHz is for some reason a problem, seems like a lower capacitance would be okay.

edit: As we know, something's gone wrong with the attachments function. It was showing an image I posted in another thread. Should be fixed now.

TimNJ:
Hi all,

Here's the planned schematic and layout. Earthed mounting holes mate directly to the die-cast aluminum chassis via M3.5 screws. Planning to use panel mount BNCs with a small 50ohm coax jumper from PCB to BNC. (Too many misaligned holes on previous projects.)

I've changed the inductors to SER2011-122 (1.2uH). 100% inductance to over 30A. I've added the option to populate two ceramic Y-caps on the "mains" side. Undecided if it's a good idea yet. The bottom side will have a matching earth polygon pour.

Any feedback welcome. Thanks.

Jay_Diddy_B:
Hi,

What capacitors are you using?

I like to use Y caps for the 0.1uF. If they fail they will destroy the analyzer.

You need to use a transient limiter (or at least a 10dB) attenuator with this LISN if you connect the output to a spectrum analyzer.

Regards,
Jay_Diddy_B

TimNJ:
The 3 * 3.3uF caps are X2. Planning to use this one: https://www.digikey.com/product-detail/en/kemet/F861DY335M310ZLH0J/399-17029-ND/8346549

Since posting, I've added a MOV across each, to keep the voltage stress on the caps as low as possible. For my case, should always be powered from a well controlled source but for anyone else who might attempt this, can't guarantee that.

The 0.1uF were also X2. As others and you have mentioned, large physical size and high frequency usually doesn't bode well, so was trying to keep the size and series inductance low. Not sure if it's relevant in that position. However, based on your recommendation, I will plan to use this: https://www.digikey.com/product-detail/en/wima/MKY22W31005D00KSSD/1928-1791-ND/9370699

Regarding the transient limiter I've installed two back-to-back 5V ESD diodes. I know the Tekbox 5uH uses a Bourns GDT rated at 60V. Necessary? Recommended? Anything else? If I add an HP11947 style limiter with 10dB, I'm just a little worried about insertion loss roll-off/deviation with frequency. Presumably I'd have to compensate on the SA somehow.

By the way, I bought a NanoVNA and am excited to learn how to use it. Hopefully I can give an accurate analysis of the impedance characteristics of this LISN once built.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod