Conducted emissions issue with multiple Mean Well AC/DC converters  - Page 1
Forum section: electronics / projects

author: prasimix
author_rank: Unknown
timestamp: June 08, 2020, 03:47:08 pm
content: I started the EMI testing procedure of the EEZ Bench Box 3 which is carried out in an accredited lab. I was informed that the results of the conducted emissions were negative and that I should try to correct it.I was in the lab today and got a slightly better picture of the situation, and the situation is complex. Here's what it's about. On mains voltage I have the following Mean Well AC/DC converters: 2 xIRM-10(for +5 V and +12 V for 10 W each) and up to 3 xLRS-150F(for + 48V / 155 W) but I tested with only one. Mean Wells have some input filters, and the simplified wiring diagram and "conducted emissions" results look like this:It is important to note that the MCU module is not a simple ohmic load. The picture is similar if the LRS converter is removed from the scheme and only IRMs remain. The first suspect is a 5 V IRM that powers the MCU module. For this reason, I tried to insert a filter in front of the IRMs, temporarily removed the LRS and it gave positive results:However, the luck was short-lived because as soon as I added the LRS converter even without any load the situation got worse and the test did not pass:Since the LRS has filter at the AC input, I also tried to connect it directly to 230 Vac and leave the IRMs behind the filter, but that didn’t help. At one point I doubted the CE certifications of the Mean Well module, so to dispel that doubt I connected them directly to 230 Vac, and loaded both IRMs withohmicloads. The results are then good:My conclusion is that an IRM loaded with a non-ohmic load combined with an LRS even without a load generates the problem. All the filters I prepared (6 of them) failed to fix this issue. I don’t know if it’s because they all had CM chokes with insufficiently high inductance (below 2.2 mH). I also had a seventh filter that had a CM choke of 2 x 40 mH but unfortunately it turned out that one was not working (one of its lines is broken).Your input and suggestions are welcome. Many thanks in advance.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 08, 2020, 04:23:12 pm
content: I'm not very sure this will work, but I'll try to put some resistors at the output of each Meanwell power source (as a constant load). My assumption is the current either varies too wildly, or it's too small. Those are switching power supply, they try to keep the required voltage by altering the switching frequency or the on/off ratio, it depends on their type.If they already have a constant load, the real load won't affect the switching frequency/period so much. Also, a switching power supply will struggle with no load, sometimes it might not even work without a minimum load. Either way, an extra resistor or a small light bulb to ensure a minimum current should help.No idea if this is the main cause, but at least it's easy to test. Put some load onallthe Meanwell sources and see if the noises decrease enough to pass the tests.

author: jbb
author_rank: Super Contributor
timestamp: June 08, 2020, 08:00:50 pm
content: Like RoGeorfe said, some minimum load might help.If Mean Well supplies are base on flyback (very traditional for an off line supply, nothing wrong with it) they will be in Discontinuous Conduction Mode (DCM) at low loads. In DCM the switch nodes will likely exhibit some ringing. Try loading things up to 50% load and see what happens...A possible extra complication; when the assorted supplies are paralleled up, their EMC filter caps are somewhat in parallel, which may shift filter resonances around.

author: jkostb
author_rank: Regular Contributor
timestamp: June 08, 2020, 10:46:11 pm
content: I suspect that the conducted emission issues are caused by common mode currents (L/N -> MCU -> PE). This is confirmed by your experiment where you added a net filter consisting of a common mode choke.The problem with adding an unloaded ACDC adapter is that the combination of netfilter and unloaded AC DC adapter can cause stability issues. You always need to ensure that the output impedance of the netfilter is lower than the input impedance of the regulator (which in your case is unloaded). When the power supply gets instable you can get conducted emission issues!Have you tried to add a common mode choke just before the MCU module (and remove net filter) before the meanwell power supplies? I would also add some ceramnic caps over the V+/V- lines to the MCU (100nF) for additional diiferential filtering.Lastly Meanwell power supplies are very cheap, but you get what you pay for. I know that some Meanwell power supplies have inadequate netfiltering especially for reactive load. If your MCU module is properly filtered you can always try ACDC modules from other manufacturer (TDK-Lambda)

author: trobbins
author_rank: Frequent Contributor
timestamp: June 08, 2020, 11:14:04 pm
content: The MCU is shown with an internal PE link to negative supply rail. Can that link be modified to provide a lossy high-frequency impedance, but still provide an acceptably low galvanic resistance and protective current conduction capability (which I presume is a requirement)?

author: prasimix
author_rank: Unknown
timestamp: June 09, 2020, 07:13:51 am
content: Many thanks to all of you. I missed to add into initial post results of all three Mean Well directly connected to the AC mains and without any load. Mean Well seems to be doing its job well for that money:I believe @jkostb guessed what the problem might be: connected GND to PE on the MCU module side. I suspected this at the end of the test, but I was not able to disconnect the GND and see what the result would be. It’s definitely something I’ll try right away the next time I go to the lab.I will also prepare a configuration where it will be possible to insert a CM filter between the Mean Well and the MCU module.@trobbins I'm not sure I really need low galvanic resistance from GND to PE, but I could put some Ferrite bead for the test, or just separate it with HV caps (e.g. 1 to 4n7) to collect spikes when connecting a USB cable from a PC.

author: jbb
author_rank: Super Contributor
timestamp: June 09, 2020, 07:51:47 am
content: Glad you’re narrowing it down!At my previous workplace the serious EMI researchers had specially modified LISNs (3 phase too) where you could select the per phase, differential mode (3 modes for 3 phase pairs) or common mode.You know, ribbon cables are infamous for EMI issues. Could you clip on a ferrite choke around the whole ribbon between the Aux board and MCU board?

author: prasimix
author_rank: Unknown
timestamp: June 09, 2020, 08:11:42 am
content: Quote from: jbb on June 09, 2020, 07:51:47 amGood point. I will put this on the TODO list for the next lab visit.

author: Dave
author_rank: Super Contributor
timestamp: June 09, 2020, 09:29:15 am
content: I'd consider buying/renting/making a LISN box to do some preliminary testing on the bench. Frequent lab visits tend to get quite expensive when you're basically kicking around in the dark, hopelessly trying to please the EMC gods.

author: prasimix
author_rank: Unknown
timestamp: June 09, 2020, 10:13:34 am
content: I totally agree with that. My next question was just supposed to be: is there any DIY LISN schematics to recommend? They have a little monster in the labNSLK 8128(see below) although I also believe that a more modest version can serve the purpose quite fine.Together with some entry level spectrum analyzer he would not be in total darkness believing that everything in the lab would go as it should.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 09, 2020, 10:45:21 am
content: prasimix,I have sent you a PM regarding the DIY LISN.Regards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: June 09, 2020, 10:50:38 am
content: Great, already replied

author: TimNJ
author_rank: Super Contributor
timestamp: June 09, 2020, 05:28:54 pm
content: Rules-of-thumb for conducted emissions:150-500KHz -> Differential mode noise500KHz-30MHz -> Common-mode noiseIt's just a rule-of-thumb. It's possible to have DM noise in the CM range and vice versa.I would try a MnZn ferrite common-mode choke on the inputs/output of your DIB power module, maybe something from Coilcraft's CMT line. You can try a lossy ferrite cable core, maybe try a core made from Fair-Rite 31 material.The LRS-150F looks like a pretty old school design. I'm not sure if it actually is, but newer designs using quasi-resonant flyback or resonant LLC may have lower EMI. Obviously, it's not guaranteed, but may be worth thinking about if you are still having a hard time.LRS-150F certainly takes the cake for cost. It's pretty massive as far as 150W open frame power supplies go at about 6" x 4". EPP-200 is 140W, 4" x 2" and uses an LLC topology. Personally, I think topology is probably not your biggest concern, but just a thought.

author: prasimix
author_rank: Unknown
timestamp: June 09, 2020, 06:06:25 pm
content: Thanks @TimNJ for you input and mentioned Rules-of-thumb. Currently my main concern is not supplying DIB power modules but IRM-10 and powering of the MCU module. But, yes from other side, trying to attenuate noise generated by IRM-10, added AC filter affects IRM-10 + LRS-150F combination even without DIB power module connected. I need to see first what happens when I disconnect GND from PE on the MCU module.You are completely right that LRS-150F is not silent, and for that reason I added a CM choke (RN112-4-02-0M7) to the input of the power module to reduce the input noise to some reasonable extent.

author: jkostb
author_rank: Regular Contributor
timestamp: June 09, 2020, 06:27:27 pm
content: Regarding:@trobbins I'm not sure I really need low galvanic resistance from GND to PE, but I could put some Ferrite bead for the test, or just separate it with HV caps (e.g. 1 to 4n7) to collect spikes when connecting a USB cable from a PC.Please note that a PE connection to chassis is usually done for safety (e.g. if your product must comply with low voltage directive). From EMC point of view it is totally ineffective, because the wiring has too much inductance. If you make a connection between PE and GND (=chassis) because of safety then I would certainly not recommend inserting a ferrite bead. Another thing which you have take into account is that shield of the USB cable is probably also connected to PE (unless you use a laptop). So the metal housing of the MCU can be indirectly connected to PE through a USB cable attached to a desktop computer. If I look at you diagram you have several modules. If these modules all have the same reference (=GND in your diagram) then you must ensure that all these modules are properly bonded (=low impedance path). Safety grounding should be bonded only at one point to your system reference.For debugging of your conducted emission issue you need to understand how the currents flow and if the problem is caused by common mode or differential currents. I suspect that the problem in your case is caused by combination of both. The high frequency components are probably common mode. You can verify this with a current clamp and a spectrum analyzer. Note that you are looking for currents in microampere range!

author: prasimix
author_rank: Unknown
timestamp: June 09, 2020, 08:33:17 pm
content: We have not yet reached the LVD test, as they want me to pass EMC (conductive and radiated emissions) first.I don't know if they will require that the GND of the MCU module must be connected to the PE or it can remain floating just as is the case with the GND on all power modules. This is intentionally done so that their power outputs can be connected in series or parallel as needed.

author: prasimix
author_rank: Unknown
timestamp: June 17, 2020, 05:13:48 pm
content: I was in the lab again today and we made new measurements.1. For start I tried the AUX-PS which has both Mean Well IRM-10 converters for +5 V and +12 V installed andwithouta connected MCU module:2. The next thing I tried was to connect two Mean Well LRS converters to which BB3 power modules (DCP and DCM) are connected (without load attached). MCU module was still disconnected:3. For the next measurement I replaced the AUX-PS module with another on which the IRM-10 +12 V module was removed. LRS converters were not connected, nor the MCU module. I also added a filter (100 nF X2 + 2 x 0.7 mH + 2 x 2.2 nF Y2). That looked great:4. Next I connected the MCU module but on which the PE isnot connectedto the GND like last time. This time it also looks very good:5. Unfortunately adding back LRS converters with connected BB3 power modules creates a problem again and we have breaking the limit in a wide range from 150 kHz to almost 1 MHz:6. The situation is no better with the load connected to the outputs of the power modules:It turns out that the problem is with LRS converters and complex loads such as BB3 modules that have switching power pre-regulators at the input stage. I think now I will really have to get a spectrum analyzer and make a LISN (for which I have already got a schematic!) to continue testing outside the lab.The question is whether I need to deal with the filter at the AC input or maybe better the filter at the DC input of the power module switching pre-regulator.

author: jkostb
author_rank: Regular Contributor
timestamp: June 17, 2020, 10:04:37 pm
content: You always need to insert the filter close to the source. From your experiments it is clear that the problem is caused by the load of the MeanWell LRS module ( DIB module). During a conducted emission test you measure the noise voltage between Line and PE and Phase and PE. Both voltages have to be below the limits. You can derive the currents easily from these voltages by divding the peak valus by 50Ohm. So you can investigate this problem further by use of a current probe (e.g. Fisher F-33-1) and LISN. First you need to figure out whether the problem is caused by common mode or differential mode currents. Note that the Meanwell LRS module has a functional earth, which means that the PE line is internally connected to the DC- output.In your measurements I observe peaks between 150-200Khz. These are most probably direct from the switching power supply. The peaks between 300-400Khz are probably harmonics of the switching frequency of the SMPS. So the noise currents are probably differential noise currents (to be confirmed with current clamp) and I would start adding capacitors between DC+ and DC- just after the Meanwell LRS module. Since module has 48V output, I would use polyesther caps. You can increase the filtering by inserting inductors in the DC+ and DC- lines(only if required). Be careful with inductors with ferrite cores, because these can saturate.Then you can look with current probe whether it reduces the noise currents. Given that the frequency is <1Mhz adding bypass caps combined with inductors (if required) is probably sufficient. Common mode currents are usually much higher in frequency.You also need to investigate the routing of wiring. Don't run input and output wiring close to each other. Hope this helps.

author: trobbins
author_rank: Frequent Contributor
timestamp: June 18, 2020, 02:37:00 am
content: prasimix, what 'is' the DIB power module - both looking in to its power input terminals, and if it has any other external connections, and its loading profile?

author: prasimix
author_rank: Unknown
timestamp: June 18, 2020, 07:58:20 am
content: Many thanks @jkostb and @trobbins. Please find below simplified wiring diagram of DIB DCP405 module connected to LRS converter.Mean well has PE input but it is not connected to the DCout- for sure, e.g. output is "floating" otherwise I would not be able to combine the power module outputs in series.

author: jkostb
author_rank: Regular Contributor
timestamp: June 18, 2020, 05:26:55 pm
content: I see in the block diagram of DIB module a common mode choke. I have looked at specs of this choke and this choke has maximum attenuation around 150Khz (depending on load current). You have a peak in conducted emission diagram also around 150Khz. So this confirms that your problem is not caused by common mode currents. So I don't think that you will solve the problem by adding more common mode chokes. Problem is most likely caused by differential noise currents from the switching power pre-regulator. What is the switching frequency of this module? If you have a near field magnetic probe you can connect it to a spectrum analyzer and look whether you also observe peaks around 150Khz. If this is the case I would increase the input bypass capacitor to this module.Note that C1 (10nF) is not effective around 150Khz. because it has an impedance of 100Ohm at 150Khz. So try adding bigger capacitor (e.g. 10uF) over the + and - input lines after the common mode choke. Do you know what the input capacitor value is of the switcher? You also have to examine the board layout. This input capacitor needs to be located in such a way that the critical current loop is small!

author: prasimix
author_rank: Unknown
timestamp: June 21, 2020, 02:36:08 pm
content: Please let me know how did you realize that max. attenuation for the used RN-112 is at 150 kHz? This is its frequency characteristic:Switching frequency in this case was about 220 kHz. Currently I have the following capacitors on pre-regulator input connected in parallel: 3 x 4u7 X7R + EEEFK1H470P (47u elco).

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 21, 2020, 05:46:16 pm
content: Hi,Let me add a few things to the discussion.Reference:https://www.schaffner.com/fileadmin/media/downloads/application_note/Schaffner_AN_CISPR17_Measurements_E8.pdfThis talks about the issue with filters measured in a 50/ 50environment and then used in a 0.1100environment.0.1100is correct for Differential Mode emissions. The LISN inputs are in series.0.125is correct for Common Mode emissions because the LISNs are in parallel for CM inputs.Inductor ModelHere is the curve from the datasheet:From the datasheet we know:The nominal inductance is 700uHThe Rdc = 24mFrom the curve we know that the SRF is around 3MHzWe can calculate parallel capacitance as 10pFWe need to add a parallel resistance to set the maximum attenuation, at resonance, to be 32dB in the 50test circuit:If I run the model and plot V(vin)/V(vout) I can get the attenuation of the CM choke per CISPR 17 in a 5050test circuit:Given the simplicity of the model, this is pretty close to the datasheet.Application CircuitThe CM choke forms a filter with the Y caps. The X cap connects the two lines in parallel, so the Y capacitors are considered in parallel.If we believe Schaffner, and accept that noise source is 0.1and you trust me that a pair of LISNs presents 25to CM signals.Then the application circuit can be modeled:The result from running the model shows how the CM choke works with the Y-caps to create an effective filter:Y-cap locationThe location of the Y-caps depends on if you are stopping emissions or improving immunity.In a power supply, normally the plan is to reduce emissions, so the Y-caps should be located on the input of the power supply, the mains side of the CM choke.Here are the modelling results showing the impact of having the Y-caps on the wrong side:In the diagram of the DCP405 the Y-caps are on the wrong side of the CM choke.Regards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: June 22, 2020, 07:14:03 am
content: You're completely right. Usually in a power supply, normally the plan is to reduce emissions. However I put that filter in the first place to prevent the emission in the other direction: from Mean Well (that is power supply, too) to the power module. Of course back then I didn’t think about the consequences of why I now have trouble passing conductive emissions tests.This is what the output of a power module powered from Mean Well without a filter looks like:... or with filter that has Y-caps on the "wrong side":

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 22, 2020, 12:11:13 pm
content: Hi,You can split the Y caps, to make a PI filter and put some on each side of the CM choke.Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: June 22, 2020, 12:58:46 pm
content: I will definitely try this when I finish building LISN and get a spectrum analyzer.

author: jkostb
author_rank: Regular Contributor
timestamp: June 22, 2020, 05:08:31 pm
content: Besides splitting the caps i.e. making a pi filter I would also advise to look at you input bypass caps of preregulator module. You use 3 ceramic caps of 4.7uF. Please note that the capacity of ceramic caps drop under DC voltage. You can easily loose > 50% depending on package size. For this reason you see combination of ceramic caps and polyester caps. Polyester caps don't suffer from capacity drop under DC voltage but have higher ESR, but much lower than an electrolytical cap. As you probably know a Buck converter draws a discontinuous input current. The input ripple current is for this reason supplied from the input bypass caps. Insufficient input bypass caps or using wrong type can increase differential mode noise currents and can be a root cause for conducted emission fail! I think that the peaks at 220Khz are really caused by differential moide noise currents. You can easily do the math. Common mode noise currents are usually caused by parasitic capacitance e.g. parasitic capacitance between heat sink and metal housing. But these parasitic capacitances are usually in order of 100pF. The impedance of 100pF at 220Khz is 7.2Kohm, which is too high for common mode noise currents. So my advise is try also to use a polyester cap at input when experimenting and look whether this helps.

author: trobbins
author_rank: Frequent Contributor
timestamp: June 23, 2020, 12:13:33 am
content: If you are using the DPC405 power module, then a quick view of the schematic for the pre-reg shows a buck regulator with I suggest extremely low bulk input supply capacitance. You may want to clarify for yourself how much input supply ripple is being generated (I couldn't easily identify that from the github info, and note that ripple and noise of the output seemed to be the only priority being designed for), and look closely at how that could be modified. One thought is that you have chosen a poor product to integrate for your application.

author: prasimix
author_rank: Unknown
timestamp: June 23, 2020, 06:07:10 am
content: Yes, ripple and noise of the output was not just the only priority but the only thing I thought was important. When I finally managed to get to the lab I see that taking care of the input ripple is also important, something I’ve only read about before. So I need to get a spectrum analyzer as soon as possible and build a LISN that I can proceed with real corrections and not just speculation.

author: prasimix
author_rank: Unknown
timestamp: July 16, 2020, 09:43:17 am
content: I return to the topic. In the meantime I got the Siglent SVA1015X and built LISN thanks to @Jay_Diddy_B who gave me the schematic and referred me to its design discussedhere. LISN has 10 dB attenuator on its outputs. I used a ready made extruded box for which I made a front and rear panel to make construction easier. This is actually the second and wrong revision of the PCB which is 10mm shorter because I misinterpreted the dimensions of the box. If these 10 mm are added, a filter up to 6 A as well as a PCB AC power switch can be installed. Maybe I'll do it once in the future. In this case I had to shorten the box by 10 mmEDIT: Please note that LISN shown above is not open source.

author: prasimix
author_rank: Unknown
timestamp: July 16, 2020, 10:14:52 am
content: The first thing I tried was to get measurements comparable to those from the lab where the Keysight EMI receiver and other LISN are used. I can’t say I’ve made it, but what I’ve achieved is to see the difference for different configurations. For the beginning I lowered the limit lines by 10 dB because like I said LISN has attenuator at the output.I also discovered too late that I hadn’t collected enough measurements while I was in the lab, as well as that some had insufficiently clear names so I’m no longer sure what they referred to.I decided to start with the measurements from scratch by adding component by component. On Siglent I have the EMI filter turned on, used Quasi Peak detection with dwell time at 108.1 us (because I see it was set that way on Keysight), RBW is 9 kHz.Measurement 1: AUX-PS module with two Mean Well IRM converters, no load (no MCU module or Mean Well LRS connected):Measurement 2: AUX-PS module with two Mean Well IRM converters, no load (no MCU module) with 2 x Mean Well LRS connected without load (i.e. no power modules):This combination already seems to be causing problems. If I wrote an accurate comment on the measurement in the lab then it matches, i.e. my first problem is that the combination of the two types of Mean Well converter generates the problem. Lab measurement is shown inpost #16.Measurement #3: AUX-PS module with two Mean Well IRM converters, no load (no MCU module) with 2 x Mean Well LRS connected withresistive load. Situation is not better:

author: prasimix
author_rank: Unknown
timestamp: July 16, 2020, 10:51:28 am
content: Measurement #4: AUX-PS module with two Mean Well IRM converters without 2 x Mean Well LRS but with MCU module connected:Measurement #5: AUX-PS module with two Mean Well IRM converters without 2 x Mean Well LRS with MCU module connected this time with added filter on the AC input (Xin=330n, 2x5 mH, Xout=100n, Yout=2x4n7):Measurement #6: AUX-PS module with two Mean Well IRM converters with MCU module connected with added filter on the AC input (Xin=330n, 2x5 mH, Xout=100n, Yout=2x4n7) and 2 x Mean Well LRS without load. I'm not sure if that is good enough. It is below quasi-peak limit (blue line), but still above average limit (cyan):

author: prasimix
author_rank: Unknown
timestamp: July 16, 2020, 05:03:45 pm
content: It seems that real difference can be measured only when filter is added on the AC input, i.e. before filters built in Mean well LRS converters. More measurements follows.Measurement #7: AUX-PS module with two Mean Well IRM converters, with MCU module connected, with 2 x Mean Well LRS, added filter on the AC input (Xin=330n,2x5 mH, Xout=100n, Yout=2x4n7), DCP405 without load connected:Measurement #8:same as above but with DCP405, Iout=max (5 A):I currently only have a common mode filter with twice the inductance at hand and with it the situation looks better.Measurement #9:AUX-PS module with two Mean Well IRM converters, with MCU module connected, with 2 x Mean Well LRS connected, added filter on the AC input (2x10 mH, Xout=100n, Yout=2x2n2), DCP405 without load connected:Measurement #10:same as above but with DCP405, Iout=max (5 A):I plan to get and test a few more common mode filters with an inductance of 15 to 20 mH before going to the lab. I believe that should help.

author: poorchava
author_rank: Super Contributor
timestamp: July 16, 2020, 09:29:22 pm
content: I recall a similar situation with RSP-2000 power supply (1200W, 12V). It had perfect results with ohmic load, and then all hell was breaking loose when we loaded it with basically a huge 8-phase step down converter (which was well engineered and was generating relatively little EMI when powered from a battery). The noise source was impossible to track down with NF probes.In the end what worked was the exactly right magical combination of Y caps between different grounds in the system and a custom CM choke that passed all 3 mains lines (L,N,PE).What we suspect was happening was that noise was being radiated from the internals of the supply and coupled to some other traces/planes that acted as antennas. It took several months to squish emissions enough that it passed the industrial limits.

author: prasimix
author_rank: Unknown
timestamp: August 06, 2020, 06:06:08 am
content: Relatively speaking I made a real progress some time ago after experimenting with different additional filter connected at the AC input. Once again this is situation with default setup without filter:... and now with filter:Now I have to confirm this results in the lab.

author: prasimix
author_rank: Unknown
timestamp: August 06, 2020, 04:42:48 pm
content: It seems to me that I will not be able to continue testing with the selected filter for the simple reason that the CM choke overheats too much. I overlooked that it was rated for just 1 AThe CM choke in question is WE 750314978 and works almost magically, nothing like it in that inductance range (up to 20 mH) filters so well. I don’t know what the trick is, maybe in its high leakage inductance? This is its specification and how it is connected to get results from previous post:

author: jkostb
author_rank: Regular Contributor
timestamp: August 06, 2020, 05:51:41 pm
content: Wurth does has common mode chokes for higher currents. Have you looked at WE-CMBNC series. For example 7448030333 2.5A rated current. You can find a diagram with insertion loss. Frequency range matches with your measurements above. I don't know whether damping is sufficient for your applicationhttps://www.we-online.de/katalog/en/WE-CMBNC?#744803033

author: TimNJ
author_rank: Super Contributor
timestamp: August 06, 2020, 05:52:55 pm
content: The Wurth choke sems to have a pretty typical leakage inductance for a common-mode choke. 300uH (min) /10mH (typ) = 3% leakage inductance ratio...I think most CMCs are in the range of ~5%, though it can vary considerably with bifilar vs sectional wound. In this case, it's clearly sectional wound with large separation between the windings, so very well may have higher leakage inductance than 300uH.If that hypothesis is true (that a high leakage inductance is helpful), then that indicates a largely differential-mode issue. It's very convenient to use the leakage inductance of a CMC to achieve adequate DM filtering, but in some cases, you might need a dedicated DM choke. Powdered iron, Sendust, or High-Flux core types is probably what's needed to maintain decent inductance at high current.

author: prasimix
author_rank: Unknown
timestamp: August 06, 2020, 06:44:24 pm
content: Quote from: jkostb on August 06, 2020, 05:51:41 pmActually I did, the following one: 7448030417 that has a much higher inductance (17 mH) and rated for 4 A, but still has a minor effect. I tried few others with inductance about 10 mH but again without notable effect, that is strange.

author: prasimix
author_rank: Unknown
timestamp: August 06, 2020, 06:52:08 pm
content: Quote from: TimNJ on August 06, 2020, 05:52:55 pmYes, it’s one of two planned steps: to add a dedicated DM choke or to take the Mean Well IRM-10 modules out and try something else e.g. RECOM. Cui Inc. has interesting and price attractive modules but it is stated on Mouser that products are available only to OEM/EMS Customers and are not shipped to consumers in the EU.

author: prasimix
author_rank: Unknown
timestamp: August 07, 2020, 04:02:53 pm
content: I continued experimenting today by introducing DM choke. First usable case is shown below.Without load connected on the power modules I got the following:... and with max. load on two channels it looks like this (I'm on the edge ofaveragelimit, but still belowquasi-peaklimit):Second usable case include even larger CM choke, 2x11 mH and smaller DM choke (220 uH):Without connected load:... and with max. load on two channels:It seems that DM of about 200 uH and CM of 2x3.3 mH or more is needed. Also X2 on the input has to be 330 nF or more.I need to find now suitable CM choke rated for 4 A or more since used one is for 2 A only. Another thing that is possible worth trying is two CM filters in series with different characteristics that their leakage inductance is big enough for DM suppression.A new challenge is to put two chokes (DM+CM or maybe two CM) on the PCB without increasing its dimensions a lot.

author: TimNJ
author_rank: Super Contributor
timestamp: August 07, 2020, 07:25:29 pm
content: Try putting the choke between two X-caps as Pi filter. Generally, for the same total capacitance (L-C vs. C-L-C) you can get much more attenuation with a Pi filter.See the below simulation. I've added modest parasitic series inductance and resistance to each element. Using a Pi filter can get you more attenuationoryou can get the "same" attenuation as a L-C with smaller components

author: prasimix
author_rank: Unknown
timestamp: August 07, 2020, 08:30:18 pm
content: Excellent suggestion, many thanks! I tried to split existing 430n into two 220n as shown below:New measurement without load:... and with max. load:The final result is comparable with 3 times larger CM choke!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 07, 2020, 08:34:30 pm
content: Hi,You might want to build a DM/CM Separator as I described in this thread:https://www.eevblog.com/forum/projects/diy-dm-cm-seperator-for-emc-lisn-mate/msg3117396/#msg3117396If you know if the emissions are CM or DM that you can add the appropriate filtering.I went to alot of trouble to optimize the performance. But if you just built one, you should get most of the benefits even if the result isn't 100% accurate.Regards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: August 07, 2020, 08:47:42 pm
content: Quote from: Jay_Diddy_B on August 07, 2020, 08:34:30 pmThanks Jay_Diddy_B, I followed that topic, indeed. However, I haven't done anything about it yet because what is left open is what with the cores. Where to get them?BTW, I tried to treat this issue as CM only and DM only, applying chokes that address one or another mode. But it seems that both of them are very prominent and need to be handled.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 07, 2020, 09:03:20 pm
content: Quote from: prasimix on July 16, 2020, 09:43:17 amThat LISN looks great! I may have to build one myself at some point.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 07, 2020, 11:29:41 pm
content: Quote from: prasimix on August 07, 2020, 08:47:42 pmHi,The cores I used the prototype are hard to get. There is a minimum order quantity.I have tried a core that I obtained from a P0354NL common mode choke in one of the two locations. This core is too small for one of the locations.I have also received some ferrite cores that are sold by Digikey. I will test these in the near future.Regards,Jay_Diddy_B

author: prasimix
author_rank: Unknown
timestamp: September 06, 2020, 10:17:33 am
content: Hi all, just to summarize this topic, because a few days ago I passed the conducted emission testing. This of course required adding an AC input filter in front of all Mean Well modules so the scheme now looks like this:Worst case scenario with the max. load in the lab looks like this:Probably the peak around 20 MHz could be ironed out, however this is also passing and I am currently having other problems since I found out that my MCU module is doing a serious problem with conducted emission for which I will open a new topic.Thanks to everyone for the assistance, especially @Jay_Diddy_B who gave me the LISN schematics.

author: Kean
author_rank: Unknown
timestamp: September 06, 2020, 02:46:34 pm
content: Good work!Any way to modify the original power board on the Crowd Supply units?Maybe with a daughter board holding the filter components and some track cutting.Not sure if there is enough space to safely fit it...

author: prasimix
author_rank: Unknown
timestamp: September 06, 2020, 03:05:27 pm
content: Hm, highly unlikely. That was my first approach for test lab, but when I realized that both CM and DM choke is required I gave up and make another revision. The new challenge was to put everything together in the existing PCB dimensions and possibly the same budget. In the end, I succeeded in that by throwing out the triacs and their drivers and heat sink and putting relays, which are used on the BP3C backplane as well. So the audit that passed the conducted emission test now looks like this:Even this revision isn’t necessarily the last one, because I don’t know how the people in charge of LVD testing will like it. For now, the latest AUX-PS module allows a passing of the EMI conducted emission for the entire BB3 chassis.I will follow up on CE testing in the main BB3 thread soon.