EMI Filters on Power Supplies: Design & Application Guide

[@oliverer3]

This is one of those topics I seem to always apply to my designs on some level but I've never felt confident in my approach or reasoning so this will hopefully be very helpful!

[@faroghiftekhar4406]

Thank you so much Zack for considering the request and making this great video. This gave me better understanding and hopefully i would be better with power supply design :))

[@zyeborm]

Thanks mate, I'm going to use some of these concepts today on a sensitive automotive part.

[@TheHareidGamer]

Good video! One fascinating thing I have had to learn is if you are making a DC only circuit you have to make sure the EMI filter is compatible with a LISN. Have experienced seriously noisy oscillations from neglecting this in the past!

[@xdZapo]

What do you mean? LISN have AC input right? How will you connect your DC-only circuit to that? And how do you make sure it is compatible?

[@TheHareidGamer]

@@xdZapo You will see some LISN's that advertise being able to take DC input and follow appropriate standards, so its definitely not AC limited. My employer sells some DC products and according to standards they too need to be checked for conducted emissions the same way as an equivalent AC product

[@mahoneytechnologies657]

Great subject to talk about!

[@nomadic_rider42]

Great explanation, thanks.

[@magnuspihl6974]

It would be wise to mention that the Cy capacitor must not be too large due to safety reasons (and regulatory standards).

[@chadkrause6574]

Hi Zach, I have a board I made that I want to sell. What kind of certifications do I need in order to sell a board in the US? FCC/UL/CE, etc? I’m sure it depends on features, but doesn’t a buck-boost DC/DC produce enough noise to qualify for a FCC test requirement? If not, then why do my phone chargers have FCC on them? It’s all so confusing

[@Zachariah-Peterson]

This is a great question and I'll do a video on it. Unfortunately the answer is far too long for a reply on a youtube comment! I'll write a blog on it too. In short the requirement is FCC for sure, and the exact test depends on the features (wireless, battery power, etc.), the power level, and whether it plugs into the wall. UL testing is not a requirement by law, but UL testing should still be considered in many consumer/residential scenarios or in manufacturing, there may be specific codes that require the use of UL compliant products. CE is the European variant of FCC, then there are also CISPR requirements. For example, in the US, the FCC and CISPR 22 regulations are legal requirements on digital systems. Then if you're in the defense world, you have to look at MIL-STD-461 compliance as well.

[@carlatashkadeh5890]

EE is the only engineering subject where you can be 3 years into it and still don’t understand shit 😊

[@AltiumAcademy]

🤣🤣🤣

[@MatiasJHZ]

At first, when you said that if we see low impedance through the sw reg, we can see some peaking, I was like, hey, thats not true, a LC filter with a resistor R, the lower the R, the larger the damping factor. But then I remembered that sw regulators have negative input impedance 😅

[@kevindewinter8235]

Last week i just used an old c14 EMI filter from my atari monitor. Perfect 50.00hz

[@ehsanbahrani8936]

Excellent. Thank you gentle man. Please introduce some software and methode to simulate different types of power supplies. Thank you in advance

[@WinChester_Ltd]

Hi Zach, where can i read some info about different layer stacks? I mean, which one is better to use in specific design. Thanks a lot, you are doing a great job!!!

[@Zachariah-Peterson]

Thank you, I'll write an article on it and post the link here. You can also check out these videos on the other common types of 4-layer PCBs: kzbin.info/www/bejne/mGXRlKZupst0n6M kzbin.info/www/bejne/r2G2aXiOfbFjgLs

[@yetanotherPC]

Hi Zack, could we get a follow-up video using altium spice simulator to more formally design a discrete pi filter? Really interested in seeing the transient response peaking mitigation as well.

[@Zachariah-Peterson]

I've done something like that in the past but it was more about adding LC sections to the output of a regulator and not speciifcally on Pi filter design. Depending on the load and the ESR on the components there may not be any peaking. It all depends!

[@87Spectr]

I'd ask you explain or make video about correct use ground, chassis... what happens if chassis is GND? can I do it?

[@oliverer3]

They already have a video on grounding, there is also an absolutely amazing lecture by Rick Hartley on the main Altium channel as well.

[@Zachariah-Peterson]

Chassis is not intended for use as the ground that completes a circuit with return current. Chassis is normally meant for use as a safety ground to protect against a fault and/or to shield against noise. Here is the grounding video: kzbin.info/www/bejne/Z2q6n4yGnbOCfpI Here is Rick's video: kzbin.info/www/bejne/r4TYho17n6aFhrs

[@sc0or]

3:00 I think it's better to not "match" Cx capacitors (as well as Cy) in a multi stage EMI filter, but rather chose a different capacitance and size to provide a wider range of a filtration

[@ecprosystems8608]

Great . When this topic will be started ?

[@EugeniaSuarez-u2q]

In which situations common mode filtering could be avoid? The examples you are talking about hasn't common mode noise issues so you can avoid and only use PI differential filtering?

[@Zachariah-Peterson]

The simplest explanation is that you don't need common-mode filtering if you do not have a problem with common-mode noise. Sorry if that is not helpful, but the same statement can be made for any instance with a filter. If there is excess common-mode noise coming into a device power input from a cable, then common-mode filtering is needed. Generally when taking in power from an outside source, it is possible that both noise sources are present in the input power so it is worth planning for this.

[@2LukeLOL]

Great video! How come some people also put Y-caps accross the postive terminals of an isolated converter, don't we just need the ones for the isolated grounds?

[@Zachariah-Peterson]

Y-caps are designed to fail open and are normally line-to-ground, so they provide the required capacitance but if they fail they will leave an open circuit and will not create a fault.

[@joeleonard4515]

Great video! I saw the schematics for a design the other day that had one of those higher order filters either side of a switching regulator, so there was a local ground around the regulator isolated by the chokes. Would this cause an EMI issue?

[@Zachariah-Peterson]

It's only an EMI problem if you try to make a big ground pour out of the output side and then route over it. You get radiation at the gap between these two regions.

[@sanjaybatra6593]

Sir I have a confusion: I have a ATMEGA128A based microcontroller board, which control a small AC synchronous motor , 6 RMP through a 5V/5I REALY with fly back diode across relay coil. during switching of motors sometimes create problem (at random times in hours). RTC freeze and LCD display garbage. Is it EMI problem ? ESD? Board is given power through 5V/5I SMPS. Shall I put a LC or pi-filter or "as you said higher order pi-filter" after SMPS ? what should I do ?

[@Zachariah-Peterson]

Sorry but I could not say what the potential problem may be without at least looking at schematics. It could be due to a power problem that is not related to EMI.

[@sanjaybatra6593]

@@Zachariah-Peterson How I can share schematic with you ? As per my observation, schematic is not of much issue. Its due to "BAD" PCB design. when inductive load switched off , it create noise/surge voltage on AC line, which come back to PCB board through SMPS.

[@AnalogDude_]

Would you need such filter for a class ab amplifier fed from 2 x 15V trafo, I'm building. I would like to include it, but don't have spectrum analyzer.

[@Zachariah-Peterson]

The filters I’m describing here are for the input stage on a power supply that would output DC and would be used before any transformer or rectification stage. I think what you want is a filter directly on the input pins, which is not just about EMI. You can put a capacitor on the power pin to provide some filtering. You could also place an LC filter if much more filtering is needed but you might need to dampen it with a small resistor.

[@87Spectr]

I see that for DC you don't use CMC. Does mean that CMC for DC no need (in most cases)?

[@Zachariah-Peterson]

Many times it is not required, but it can be helpful for passing EMC testing. If the two DC regulators are on the same PCB you might not need a CMC for noise filtering. If the DC power is going out over a cable then it is a good idea to include a CMC on the output before the cable.

[@bellamimi2232]

Can you explain what is matching capacitor means, why and how?

[@Zachariah-Peterson]

When I said a matching capacitor, I just mean a capacitor with the same value as the other capacitor forming the pi filter. The reason is for convenience of calculation of the cutoff, but you could use a different capacitor value in each spot.

[@stiven_ph8656]

i use power sequencer on my audio system but no built in emi filter" are emi filter make the speaker quieter?

[@Zachariah-Peterson]

The EMI filter circuits I'm showing here are specifically being used to remove different types of noise (common mode and differential mode) from the input power connection. I can't tell you whether this would make your audio system quieter because there could be many different noise sources in your system, and any one of them could cause the noise you are observing.

[@stiven_ph8656]

@@Zachariah-Peterson are power supply with emi filter safe?

[@87Spectr]

thanks for great video but I think it's better use TVS-diode before filter, not after... can high voltage destroyed capacitor? can high current destoy inductor? we haven't these risks if TVS near connector

[@Zachariah-Peterson]

That unidirectional TVS diode is being used for DC, which is why it is used in between two regulators. I did not include it on the AC input because the unidirectional TVS would create a short circuit in that application. You can use the unidirectional TVS diode after a bridge rectifier, this is the typical location where it would be placed if it was used for circuit protection before a DC/DC converter. Normally on the AC input, there could be some other form of circuit protection, such as a fusible resistor or resettable fuse. In high current instances a circuit breaker or a GDT might be used, it all depends on what the fault withstand requirements are in your scenario.

[@restingroysurong805]

Sir i don't have enough equipment to test ic .I have only multimeter. Please sir help me which option it will help me to diagnose ic with multimeter in voltage mode..when the power supply is on how can I test voltage of ic and where should I put black lead of multimeter to test red lead on ic.please help me sir

[@brentyen3616]

The countdown is epic lol

[@borisjevic6338]

@Altium Academy Thank you for this presentation. In the start, you were mentioning about filtering for 50Hz / 60Hz / 400Hz. Are you able to create a video that will include the different filter models, together with their math and how to do a two or three step filtering for a combined 50 Hz / 60 Hz filter that is a universal filter for multiple regions, and how to calculate the DM and CM chokes for Amps when different regions need either 10A or 16A. Also in regards to the resistor fuse, how can we choose if there is one, a resettable fuse (NTC) for 120V / 240V @ 10A / 16A. All this using just a two layer pcb. Then on a different topic, we can explore the GDT / MOV / TVS for mains supply, using GDT for capturing spikes from the CM /DM chokes, as shown on some of Mitsubishi's literature and video - kzbin.info/www/bejne/eV7Th2pofN-EoJY - @3:20. The video in whole is excellent too. Can you also elaborate on using a GDT in the middle of a bridge rectifier. Will that be only for SMPS or is it useful for after a transformer (240V / 9V) where you use a full bridge rectifier? Thank you.

[@jaken1319]

Can i just put a big ass magnet on my meters magent??