Electronics > Projects, Designs, and Technical Stuff
5uH Aerospace LISN: How dumb would I be to "throw one together"?
T3sl4co1l:
X caps are safe for mains transients because they self-heal. Self-heal dumps spikes into the system; not the greatest idea.
Running from a synthesized source? Even better! No worry for transients at all. Hrm, well, beyond hot-plugging I suppose. Even nominally rated capacitors will do (but a little extra, and/or the use of floating-electrode types, isn't a bad idea).
This may be one of those situations where staggered capacitor sizes and values proves beneficial -- you can get the stray inductance between them low enough that it doesn't make things worse at the inbetween resonant frequencies. Also may be a good reason to choose PE dielectric (MKT and other types) over PP, the Q is a bit lower. Anyway, bypassing on the DC side shouldn't be too important thanks to the dominant impedance of the decoupling inductor, which is really the star here.
Tim
Jay_Diddy_B:
--- Quote from: TimNJ on July 28, 2020, 02:24:40 am ---Just did a sanity check on the Coilcraft Model...The SFR is not showing at all. Might explain why it's so flat...although 115MHz SFR sounds good regardless. You're right about the saturation point. Perfect inductance is really only maintained to 10-12A which isn't a huge upgrade over a standard Tekbox model. On the other hand the SER2011/SER2013 series are bigger and more expensive. I'll think about it.
Here's the model. Not sure what everything is exactly. Wurth model in the same setup shows SFR just fine.
--- Quote ---.subckt SER1590-102_freq port1 port2 PARAMS: Cpar=27.7pF Ind=1uH
X1 port1 port2 Model1A PARAMS:
+ R1=535
+ R2=0.02
+ C= {Cpar}
+ K1=1E-09
+ K2=0.341
+ K3= {Ind}
+ K4=0.012
+ K5=0.00001
+ L=0
+ Is=0
+ a=0
+ L_Z0=0
+ L_EL=0
+ L_F0=0E6
+ PkZ=186.791125
.ends SER1590-102_freq
--- End quote ---
Regarding the 10uF capacitance...you are right that Y-class capacitors are technically appropriate here. I was looking for Y-class caps in large value today, but somehow did not come across this series, so I decided X2 might be okay for *laboratory use only*. The cost of Y2 film caps is very high, not to mention the size is enormous...close to 10x the size of X2.
I am definitely hesitant to say any of this on a public forum.
Warning to anyone reading: X-class capacitors are built to be safer than normal film capacitors, but still are not intended to go from line/neutral to earth. If a capacitors in that position fails, it has the potential to put the chassis at a high potential. X capacitors are not advised in the position I mentioned.
At the same time, for a properly earthed system, an internal short to earth should blow the internal or building fuse/breaker. I'm a little bit on the fence.
--- End quote ---
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
Jay_Diddy_B:
--- Quote from: TimNJ on July 28, 2020, 02:38:51 am ---This doesn't necessarily make it right but the Tekbox TBLC08 LISN (teardown EEVBlog #993) uses Vishay MKP1847
https://www.vishay.com/docs/28172/mkp1847ac.pdf
...not even X2. Just a normal film cap.
The LISN at work (Atten brand) also only uses X2 capacitors. I wonder what a Rhode and Schwarz uses.
--- End quote ---
The datasheet for the MKP1847ac capacitors used by Tekbox says:
I like the idea of using a better cap that is intended for connecting either from L to N (X rated)
or
L to GND (Y rated)
Although you might not need the mains rated caps in your application at 400Hz with the Chroma AC Source, why not build one that is safe as possible to use on the line?
There is some logic in building a small one for the DC application and a bigger one for the AC application.
Regards,
Jay_Diddy_B
TimNJ:
--- Quote from: T3sl4co1l on July 28, 2020, 03:26:10 am ---X caps are safe for mains transients because they self-heal. Self-heal dumps spikes into the system; not the greatest idea.
Running from a synthesized source? Even better! No worry for transients at all. Hrm, well, beyond hot-plugging I suppose. Even nominally rated capacitors will do (but a little extra, and/or the use of floating-electrode types, isn't a bad idea).
This may be one of those situations where staggered capacitor sizes and values proves beneficial -- you can get the stray inductance between them low enough that it doesn't make things worse at the inbetween resonant frequencies. Also may be a good reason to choose PE dielectric (MKT and other types) over PP, the Q is a bit lower. Anyway, bypassing on the DC side shouldn't be too important thanks to the dominant impedance of the decoupling inductor, which is really the star here.
Tim
--- End quote ---
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.
Jay_Diddy_B:
--- 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:
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
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