Are my Circuits ILLEGAL to use!
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Date: 2024-08-12
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Comments and reviews: 20
nigeljohnson9820
It is frustrating that so many of the AC /DC switch mode bricks, so useful for mains powered construction projects, require so many external EMC filter components to be fitted.
It can be argued that components such as TVS and MOV are better fitted outside the module, as they are the most likely components to require replacement, next to the mains fuse.
There are also X caps, Y caps, common mode, inrush current limit resistors and differential inductors required, that's a lot of extra components. It would be helpful if these could be purchased as an optional complete kit of parts.
Many EMC problems can be reduced by using a pre approved EMC tested USB PSU or other brick power supply, but there are some projects where an integrated AC/DC supply is an unavoidable requirement, such as where the project is used to switch the main supply to other devices. In this case, it would be helpful if the fully integrated AC/DC module, like that the USB PSUs provides, was available as a PCB mountable module, rather than the main plug topology.
Having a safe and EMC standard building block circuit for the AC/DC converter part of the circuit facilities faster project design, as the DC output can always be post regulated to meet the needs of the rest of the circuit, be it 5 or 3, 3 volts.
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It is frustrating that so many of the AC /DC switch mode bricks, so useful for mains powered construction projects, require so many external EMC filter components to be fitted.
It can be argued that components such as TVS and MOV are better fitted outside the module, as they are the most likely components to require replacement, next to the mains fuse.
There are also X caps, Y caps, common mode, inrush current limit resistors and differential inductors required, that's a lot of extra components. It would be helpful if these could be purchased as an optional complete kit of parts.
Many EMC problems can be reduced by using a pre approved EMC tested USB PSU or other brick power supply, but there are some projects where an integrated AC/DC supply is an unavoidable requirement, such as where the project is used to switch the main supply to other devices. In this case, it would be helpful if the fully integrated AC/DC module, like that the USB PSUs provides, was available as a PCB mountable module, rather than the main plug topology.
Having a safe and EMC standard building block circuit for the AC/DC converter part of the circuit facilities faster project design, as the DC output can always be post regulated to meet the needs of the rest of the circuit, be it 5 or 3, 3 volts.
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greatscott
All measuring equipment for verification of EMI/ EMC
compatibility. have internal filters usually of 6dB b. w. and are switched in & out as the test sweeps across the freq. spectrum.
the filters are different for average, peak, weighted average etc.
But most filter b. w. (6dB) are about 10 kHz wide. and is sampled for about 3-5 seconds before the next freq. step is selected.
Hence some chip designs offer pseudo random pwm freq switching and some offer pwm with dither / & or jitter.
this dither freq. jumps by >(13-19) khz at a (300-500)Hz rate to prevent the instrument's from fully filtering the test freq.
Similarly chips with jitter freq. pwm. / spread spectrum pwm/ pesudo random pwm, cause the pwm osc. freq. to vary by (17-23) kHz. thus the filters cannot fully sample the switch freq. This leads to a lower max. measured value thereby the d. u. t. may clear the tests.
The other option is to design using resonant converters.
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All measuring equipment for verification of EMI/ EMC
compatibility. have internal filters usually of 6dB b. w. and are switched in & out as the test sweeps across the freq. spectrum.
the filters are different for average, peak, weighted average etc.
But most filter b. w. (6dB) are about 10 kHz wide. and is sampled for about 3-5 seconds before the next freq. step is selected.
Hence some chip designs offer pseudo random pwm freq switching and some offer pwm with dither / & or jitter.
this dither freq. jumps by >(13-19) khz at a (300-500)Hz rate to prevent the instrument's from fully filtering the test freq.
Similarly chips with jitter freq. pwm. / spread spectrum pwm/ pesudo random pwm, cause the pwm osc. freq. to vary by (17-23) kHz. thus the filters cannot fully sample the switch freq. This leads to a lower max. measured value thereby the d. u. t. may clear the tests.
The other option is to design using resonant converters.
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Dr_Mario2007
Apparently here in the USA, FCC are obviously strict about RFI and EMI, yet they allow some hobbyists to get away with it, at least up to four or six projects, that's it. I am sure it might be the same elsewhere, you gotta look at RFI / EMI rules for where you live at, they differs somewhat. If you wanna sell the completed boards to somebody else, you definitely want to have a decent oscilloscope so you can rework and / or respin the board once you find out why. It's your responsibility to make sure it doesn't disturb TVs and any other electronics.
If you work with SMD components, it's a bit easier to manage RFI with solderable Faraday cages which phones almost always use. It's kinda recommended to use the shields with DIY RF circuits in order to get the cleanest signals possible as outside RFI and EMI would mess with it making it a bit harder to discern via oscilloscope.
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Apparently here in the USA, FCC are obviously strict about RFI and EMI, yet they allow some hobbyists to get away with it, at least up to four or six projects, that's it. I am sure it might be the same elsewhere, you gotta look at RFI / EMI rules for where you live at, they differs somewhat. If you wanna sell the completed boards to somebody else, you definitely want to have a decent oscilloscope so you can rework and / or respin the board once you find out why. It's your responsibility to make sure it doesn't disturb TVs and any other electronics.
If you work with SMD components, it's a bit easier to manage RFI with solderable Faraday cages which phones almost always use. It's kinda recommended to use the shields with DIY RF circuits in order to get the cleanest signals possible as outside RFI and EMI would mess with it making it a bit harder to discern via oscilloscope.
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bzuidgeest
There are several easy to find videos that explain why your four layer stack choice is a poor choice. Though it is a common default and I admit using it non commercially.
As I understand it, the problem lies with how current actually travels, not by electron movement but by electromagnetism. A voltage coupling to the closest ground. A far superior option is two ground layers in the middle and power and signal on top. That way all high voltages are as closely coupled to ground as possible. I don't understand it all to be honest, but when talking about designing pcb and EMC a very important topic.
I therefore feel it would have been better if you left the last part of. Nothing wrong with admitting failure, but it didn't work and had as I understand it a poor suggestion to designing given the video topic.
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There are several easy to find videos that explain why your four layer stack choice is a poor choice. Though it is a common default and I admit using it non commercially.
As I understand it, the problem lies with how current actually travels, not by electron movement but by electromagnetism. A voltage coupling to the closest ground. A far superior option is two ground layers in the middle and power and signal on top. That way all high voltages are as closely coupled to ground as possible. I don't understand it all to be honest, but when talking about designing pcb and EMC a very important topic.
I therefore feel it would have been better if you left the last part of. Nothing wrong with admitting failure, but it didn't work and had as I understand it a poor suggestion to designing given the video topic.
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sebastiannielsen
You can also shield components and/or parts of circuit board to reduce EMC emissions. Also, even if the board itself doesn't pass, the final products could pass in a suitable grounded metal enclosure.
Im pretty sure you could do a EMC shield board, 2 layer with a top 100% plane and then edge solder connections all around, looking like a postage stamp.
Then mill out bottom of this board so it fits on top of the board you want to protect.
Voila, you have now shielded emissions. This works as long as no component is higher than the thickness of the shielding board, but if a single component is higher, you coukd make a hole in the shield for that component and still have a good shield - as long as the high component is not the radiating culprit.
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You can also shield components and/or parts of circuit board to reduce EMC emissions. Also, even if the board itself doesn't pass, the final products could pass in a suitable grounded metal enclosure.
Im pretty sure you could do a EMC shield board, 2 layer with a top 100% plane and then edge solder connections all around, looking like a postage stamp.
Then mill out bottom of this board so it fits on top of the board you want to protect.
Voila, you have now shielded emissions. This works as long as no component is higher than the thickness of the shielding board, but if a single component is higher, you coukd make a hole in the shield for that component and still have a good shield - as long as the high component is not the radiating culprit.
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greatscott
Any power supply or voltage converter should be placed inside a shielded enclosure to prevent EMC issues. If they have DC outputs, filtering of the outputs should be done to remove any noise on them. You aren't going to make a buck or boost converter that doesn't make EMF noise. Same goes for inverters and rectifiers. There is going to be noise from the circuitry. You can make an enclosure using plastic and conductive paint if weight is a concern, just remember that you need to make electrical contact on all seams of it and to ground it so the EMF is being sent directly to the chassis ground of the circuit of the equipment, vehicle, or building so it is dissipated instead of being passed through the enclosure.
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Any power supply or voltage converter should be placed inside a shielded enclosure to prevent EMC issues. If they have DC outputs, filtering of the outputs should be done to remove any noise on them. You aren't going to make a buck or boost converter that doesn't make EMF noise. Same goes for inverters and rectifiers. There is going to be noise from the circuitry. You can make an enclosure using plastic and conductive paint if weight is a concern, just remember that you need to make electrical contact on all seams of it and to ground it so the EMF is being sent directly to the chassis ground of the circuit of the equipment, vehicle, or building so it is dissipated instead of being passed through the enclosure.
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reverse_engineered
Here's a funny story. The office where I work was using several consumer-grade Wi-Fi routers as access points. We are in a research campus near a company that works with satellites. One day the CRTC (Canada's telecom regulator) showed up with a rather expensive RF spectrometer looking all over our building like they were witching for water. Turns out one of those AP's radios was putting out too much energy into adjacent frequencies and those frequencies happened to be what they were using to communicate with the satellites. Every time they had to turn their dish towards our building, they got a bunch of noise. Just goes to show how important it is to meet EMC requirements!
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Here's a funny story. The office where I work was using several consumer-grade Wi-Fi routers as access points. We are in a research campus near a company that works with satellites. One day the CRTC (Canada's telecom regulator) showed up with a rather expensive RF spectrometer looking all over our building like they were witching for water. Turns out one of those AP's radios was putting out too much energy into adjacent frequencies and those frequencies happened to be what they were using to communicate with the satellites. Every time they had to turn their dish towards our building, they got a bunch of noise. Just goes to show how important it is to meet EMC requirements!
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kennener8446
A couple of comments from an old PSU & EMI guy. Sometimes the worst source of EMI is the gate drive current spike inside the chip (assuming the MOSFETs are integrated, which typically needs to be dealt with at the chip supply pins. Also, a single uF-range cap isn't enough in most applications. I'll use tiny caps in the 330pF-3300pF range as close to the device pins as possible, with larger bulk caps a bit further away where there is more room. Remember, it is the high-frequency edges that matter most when it comes to suppressing EMI, and larger bulk caps don't do a great job at high frequencies.
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A couple of comments from an old PSU & EMI guy. Sometimes the worst source of EMI is the gate drive current spike inside the chip (assuming the MOSFETs are integrated, which typically needs to be dealt with at the chip supply pins. Also, a single uF-range cap isn't enough in most applications. I'll use tiny caps in the 330pF-3300pF range as close to the device pins as possible, with larger bulk caps a bit further away where there is more room. Remember, it is the high-frequency edges that matter most when it comes to suppressing EMI, and larger bulk caps don't do a great job at high frequencies.
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SkyhawkSteve
I spent a number of years on getting my designs to pass EMC requirements, and then spent some years in my employer's EMC lab helping folks test their designs and fix problems. Wurth produced some nice ferrites and other devices for addressing EMC issues. I have to say that Fair-rite makes some nice stuff too. Switching converters are one of the biggest offenders in regards to generating noise, and board designers should follow the converter manufacturer's guidelines (and there are often board layout suggestions. EMC is an interesting and complicated subject, and certainly not intuitive.
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I spent a number of years on getting my designs to pass EMC requirements, and then spent some years in my employer's EMC lab helping folks test their designs and fix problems. Wurth produced some nice ferrites and other devices for addressing EMC issues. I have to say that Fair-rite makes some nice stuff too. Switching converters are one of the biggest offenders in regards to generating noise, and board designers should follow the converter manufacturer's guidelines (and there are often board layout suggestions. EMC is an interesting and complicated subject, and certainly not intuitive.
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jonanon8193
For conducted EMC filtering the capacitor used by the test engineer is ridiculous, it's legs are far too long for MHz frequencies - the common mode chokes did all the work.
To make this pass (in a cheaper smaller way) try putting 10nf caps 0603 or smaller on input and output - they are very good for many cases.
You need to check whether any caps used are any good at the frequencies of interest - bigger is not better as the inductance gets worse - you need an impedance graph over frequency to pick a cap that's any good AT the frequencies where your product exceeded the limit.
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For conducted EMC filtering the capacitor used by the test engineer is ridiculous, it's legs are far too long for MHz frequencies - the common mode chokes did all the work.
To make this pass (in a cheaper smaller way) try putting 10nf caps 0603 or smaller on input and output - they are very good for many cases.
You need to check whether any caps used are any good at the frequencies of interest - bigger is not better as the inductance gets worse - you need an impedance graph over frequency to pick a cap that's any good AT the frequencies where your product exceeded the limit.
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StuffJason437
This reminds me of the interference heard on Ham Radio, caused by some L. E. D bulbs and fluorescent light fixture.
Actually- If you put rj45 connectors on each end of telephone cable then interference can be heard on FM radio between 85. 5Mhz - 87. 7Mhz and this all reminds me of back in the day a simple break in a overhead communications cable resulted in the AM radio's & ham radio's being blasted with noise and not even JPO (Called Ofcom nowadays) knew until someone complained about their landline not working and tired engineer had rectified a break and the noise went away.
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This reminds me of the interference heard on Ham Radio, caused by some L. E. D bulbs and fluorescent light fixture.
Actually- If you put rj45 connectors on each end of telephone cable then interference can be heard on FM radio between 85. 5Mhz - 87. 7Mhz and this all reminds me of back in the day a simple break in a overhead communications cable resulted in the AM radio's & ham radio's being blasted with noise and not even JPO (Called Ofcom nowadays) knew until someone complained about their landline not working and tired engineer had rectified a break and the noise went away.
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tommihommi1
at JLCPCB and similar manufacturers, there's almost no price difference between 4 and 2 layer boards, especially compared to shipping and assembly
so just always start with 4 layers for DIY projects unless it's a super duper simple design.
You make your life layouting easier, it'll work better for EMC as well as general performance, and you can make it fit into the size you want more easily.
The stackups of
PWR/DATA
GND
GND
PWR/DATA
or
PWR/DATA
GND
PWR/DATA
GND
are typical recommendations that work for many applications
reply
at JLCPCB and similar manufacturers, there's almost no price difference between 4 and 2 layer boards, especially compared to shipping and assembly
so just always start with 4 layers for DIY projects unless it's a super duper simple design.
You make your life layouting easier, it'll work better for EMC as well as general performance, and you can make it fit into the size you want more easily.
The stackups of
PWR/DATA
GND
GND
PWR/DATA
or
PWR/DATA
GND
PWR/DATA
GND
are typical recommendations that work for many applications
reply
jonanon8193
You wonder if boards from China are checked for EMC
YOU, the importer have that responsibility.
Even though importers have that responsibility, it's self-regulation (which means no regulation until you are caught.
So you can expect serious products manufactured in large quantity to pass, but lots of small stuff to fail.
Populated PCBs are not final products but components, and so they do not have to pass. When you build a product with them it is YOUR responsibility that the final product you make passes EMC laws.
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You wonder if boards from China are checked for EMC
YOU, the importer have that responsibility.
Even though importers have that responsibility, it's self-regulation (which means no regulation until you are caught.
So you can expect serious products manufactured in large quantity to pass, but lots of small stuff to fail.
Populated PCBs are not final products but components, and so they do not have to pass. When you build a product with them it is YOUR responsibility that the final product you make passes EMC laws.
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Simon_Rafferty
Increasingly it feels like EMC is a lost cause!
I'm a Radio Amateur - and for myself take it very seriously. But over the last decade, the amount of stray, broad band RF noise where I live makes radio reception on HF (160m to 10m) near impossible.
The main culprets where I live seem to be Solar Panel Inverters and broadband internet, roadside boxes.
If high value equipment can be sold, installed & used despite radio interfenernce issues, what hope is there for smaller, cheaper appliances from Asia
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Increasingly it feels like EMC is a lost cause!
I'm a Radio Amateur - and for myself take it very seriously. But over the last decade, the amount of stray, broad band RF noise where I live makes radio reception on HF (160m to 10m) near impossible.
The main culprets where I live seem to be Solar Panel Inverters and broadband internet, roadside boxes.
If high value equipment can be sold, installed & used despite radio interfenernce issues, what hope is there for smaller, cheaper appliances from Asia
reply
aquahood
Qungshan radio is a massive harmonics emitter even when you use the CB band in the air band which is no good. It made it through my customs because it wasn't a Bafang.
Someone suggested that the chipset is really awesome in that radio and that it's a reference design that they just rushed to production so actually it is a prime target for someone who wishes to place the right kind of low and high bass band pass filters and some other types of filters to eliminate the very nasty second 3rd and 4th order harmonics.
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Qungshan radio is a massive harmonics emitter even when you use the CB band in the air band which is no good. It made it through my customs because it wasn't a Bafang.
Someone suggested that the chipset is really awesome in that radio and that it's a reference design that they just rushed to production so actually it is a prime target for someone who wishes to place the right kind of low and high bass band pass filters and some other types of filters to eliminate the very nasty second 3rd and 4th order harmonics.
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laurijuusela8122
Whether these boards fall under EMCD due to being research & development boards is irrelevant. The loophole you mentioned isn't accurate. The manufacturer must evaluate the product based on its intended use and account for any foreseeable misuse. So, even if the manufacturer claims the output shouldn't be loaded, it's still a reasonable misuse scenario that requires EMC evaluation.
There aren't any real loopholesjust poor excuses.
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Whether these boards fall under EMCD due to being research & development boards is irrelevant. The loophole you mentioned isn't accurate. The manufacturer must evaluate the product based on its intended use and account for any foreseeable misuse. So, even if the manufacturer claims the output shouldn't be loaded, it's still a reasonable misuse scenario that requires EMC evaluation.
There aren't any real loopholesjust poor excuses.
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misspotato813
I assume this wouldn't work for every situation given the slight increase in size, but could you wrap the device being affected by interference in tape and then wrap that in a conductive thin sheet of metal, like tin foil, perhaps even connecting the metal to ground Would this work like a super cheap faraday cage EDIT: Actually, I think the problem you are referring to is the device itself interfering with itself, so I'm assuming not.
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I assume this wouldn't work for every situation given the slight increase in size, but could you wrap the device being affected by interference in tape and then wrap that in a conductive thin sheet of metal, like tin foil, perhaps even connecting the metal to ground Would this work like a super cheap faraday cage EDIT: Actually, I think the problem you are referring to is the device itself interfering with itself, so I'm assuming not.
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abishvijayan76
Very informative. Keep it up.
A potential series on covering certification is not at all a bad idea. Will be cool to see how you solve each hurdle.
Whenever there's a DC DC converter, going with atleast a 4 layer board is necessary. We usually go with 4 layer board with 2nd and 3rd layer GND, any left over space on top & bottom will be made as GND pour with via stitching.
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Very informative. Keep it up.
A potential series on covering certification is not at all a bad idea. Will be cool to see how you solve each hurdle.
Whenever there's a DC DC converter, going with atleast a 4 layer board is necessary. We usually go with 4 layer board with 2nd and 3rd layer GND, any left over space on top & bottom will be made as GND pour with via stitching.
reply
a2_zhongbaode718
I learnt something new today! I was designing my own budget smart speaker a few weeks ago, using cheap buck boost which coincidentally was the problem when i was troubleshooting it as my speaker output sounded just like the one in your video what are the chances that i get my answer to why it was happening so soon! Thank you! It was very puzzling why it was behaving so weirdly
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I learnt something new today! I was designing my own budget smart speaker a few weeks ago, using cheap buck boost which coincidentally was the problem when i was troubleshooting it as my speaker output sounded just like the one in your video what are the chances that i get my answer to why it was happening so soon! Thank you! It was very puzzling why it was behaving so weirdly
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reedreamer9518
Reducing EMI from power supplies is an art. Every switcher in my house has some kind of noise suppression. Over the years I've become adept at finding the cheapest and most effective solution. I do this, of course, to minimize noise to my ham radio receivers. The real question is, how to I get my crazy neighbor to let me fix his noisy military grade radio jammer power supply.
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Reducing EMI from power supplies is an art. Every switcher in my house has some kind of noise suppression. Over the years I've become adept at finding the cheapest and most effective solution. I do this, of course, to minimize noise to my ham radio receivers. The real question is, how to I get my crazy neighbor to let me fix his noisy military grade radio jammer power supply.
reply
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