1:01:35 Why does the Y cap reduce noise? Many thanks to Robert and Min for producing this video, very informative. So just to add to the Y cap discussion -- I don't think Ming quite spelled out the cause of the noise in the first place. The noise is common mode on the secondary side of the transformer -- ie: the noise voltage is not between the two output leads, rather it's a voltage on both output leads relative to ground, or more locally, relative to the primary side, say the input side negative rail. This noise almost certainly comes from the primary side switching voltage applied to the primary winding which is capacitively coupling to the secondary secondary. Ie: along with acting like a transformer, the two windings also act like the two plates of a capacitor. (Between primary and secondary, transformers often have a layer of conductive tape which is grounded, to block the primary-to-secondary capacitance, but either not in this case, or it's not effective.) The primary switching is at some significant frequency like 100kHz, and being square pulses, there are many harmonics. The amplitude of those pulses is 170V (for 120VAC line) or 340V (for 240V line), so it doesn't take much inter-winding capacitance to impart that noise to the secondary side, which initially had no other path to ground or to any ground-connected path. So adding that Y cap provides that path -- essentially forming a capacitive voltage divider, with the transformer capacitance as the upper leg, and the new Y cap as the lower leg. So long as the new Y cap has much lower reactance than the transformer interwinding capacitive reactance, there will be significant reduction in the RF on the secondary. But this comes at at the cost of increased line-frequency"leakage" owing to the Y cap not connecting to ground, but rather to the negative side of the full-wave rectifier bridge. (as noted in the video).
If you look at some data sheets for isolated supply modules (Traco, Mean Well ,ect...) they show the circuit used to pass EMC. It's basically what was added to this product to pass the requirement, that's if the original positive DC Y cap was left in place. They have a common mode choke followed by a LC filter on the input, with Y caps between positive DC rails and the grounds. The tip about high capacitor values increasing leakage current is exactly why I watch these videos, I learn something new every time. That circuit is wild, it's as though the engineer looked at the datasheet "simplified block diagram" and thought it was all it needed? lol Application notes were NOT referenced for sure, it's kinda blowing my mind the IC is surviving the voltage spike on the switching node. I'm not a hardware expert, light years away from a SMPS expert, yet even I know this is missing more than a few components. Seeing stuff like this gives me some sense of reassurance, I lose sleep worrying about something I missed in a design for years after they have been in service.
Great movie! Hope the EMC movie series continues! An interesting topic for the next episodes would be solving problems related to reducing the impact on EFT (Burst, Surge) and ESD. Thx.
EFT is a big headache. I can manage to do better design for surge, but not for EFT. No one talking about it and one protection circuit works with one PCB design may not work with another PCB.
Very nice video! So practical and intuitive explanations for everyone. Should be also interesting to see the effect of a clamping diode and snubber on primary side and secondary side, maybe also in a time domain!
Great video! Thx. I was wondering why there is no RCD clamp on the switch node of primary side (drain), and no RC snubber on the diode? Those should be major noise sources.
The CM NOISE source is the current driven through primary to secondary parasitic capacitance due to switching Imagine the Mosfet drain is swinging between 400v and 0 And there is a capacitance from the drain to the secondary side (parasitic) so a current will go through that capacitance this current can only return through earth If we connect a return path from secondary to a cold point (non switching point) this current will mostly return to its source, so will not go to earth and its return loop will be very short so no radiation This return path is done by Y2 CAP
I'm confused with the quarter wave antenna calculation part (14:53). If I use 40MHz to calculate lambda, I will get 7.5m. Then 7.5/4 is 1.875m. I'm confused as to where 0.5m fits in. Kindly clarify..
Thanks a lot for the video. Please, can you suggest the name of the "Thick book talking about the antennas with complicated physics" that you talked about here 18:10
Get a calibrated noise source or make a pwm generator .... get it tested by good spectrum analyser.......... use that calibrated source to calibrated SDR(software define radio or FFT section of oscilloscope!
Hello Robert, please make a video with the EMI filter design method shown in the book 'EMI Filter Design - ByRichard Lee Ozenbaugh, Timothy M. Pullen' on chapter 19.4 EMI Filter Design Example. Its specifically for Switch Mode Power Supplies. I'd love to see this method work for first designs.
thanks for good video but i couldnt understand where is the huge radio transmitter's signals in last measurement on 1:13:20. it is mentioned and seen in first measurement which is mentioned at 10:45. if they are not seen, it means spectrum analyzer dont work well or the antenna didnt connected well.
Why does he mention the .5m from the v=λf formula ?? How does he get 40Mhz? Even going backwards Speed of light (m/s) / 1/f (s) = so the seconds cancel out, and you're left with meters. 300,000,000m/s / 0.000000025/4 = 1.875m which is the cable length. So why is he talking about the quarter wavelength being .5 meters?
![PURPEECH - นี่ฉันเองคนที่... (It's me) [Official MV]](http://i.ytimg.com/vi/NuhHd0hOOg8/mqdefault.jpg)
1:01:35 Why does the Y cap reduce noise? Many thanks to Robert and Min for producing this video, very informative. So just to add to the Y cap discussion -- I don't think Ming quite spelled out the cause of the noise in the first place. The noise is common mode on the secondary side of the transformer -- ie: the noise voltage is not between the two output leads, rather it's a voltage on both output leads relative to ground, or more locally, relative to the primary side, say the input side negative rail. This noise almost certainly comes from the primary side switching voltage applied to the primary winding which is capacitively coupling to the secondary secondary. Ie: along with acting like a transformer, the two windings also act like the two plates of a capacitor. (Between primary and secondary, transformers often have a layer of conductive tape which is grounded, to block the primary-to-secondary capacitance, but either not in this case, or it's not effective.)
The primary switching is at some significant frequency like 100kHz, and being square pulses, there are many harmonics. The amplitude of those pulses is 170V (for 120VAC line) or 340V (for 240V line), so it doesn't take much inter-winding capacitance to impart that noise to the secondary side, which initially had no other path to ground or to any ground-connected path.
So adding that Y cap provides that path -- essentially forming a capacitive voltage divider, with the transformer capacitance as the upper leg, and the new Y cap as the lower leg. So long as the new Y cap has much lower reactance than the transformer interwinding capacitive reactance, there will be significant reduction in the RF on the secondary. But this comes at at the cost of increased line-frequency"leakage" owing to the Y cap not connecting to ground, but rather to the negative side of the full-wave rectifier bridge. (as noted in the video).
That's a great explanation Graham, I totally agree. I need to copy your comments and put them on my notes. Many thanks
If you look at some data sheets for isolated supply modules (Traco, Mean Well ,ect...) they show the circuit used to pass EMC. It's basically what was added to this product to pass the requirement, that's if the original positive DC Y cap was left in place. They have a common mode choke followed by a LC filter on the input, with Y caps between positive DC rails and the grounds. The tip about high capacitor values increasing leakage current is exactly why I watch these videos, I learn something new every time. That circuit is wild, it's as though the engineer looked at the datasheet "simplified block diagram" and thought it was all it needed? lol Application notes were NOT referenced for sure, it's kinda blowing my mind the IC is surviving the voltage spike on the switching node. I'm not a hardware expert, light years away from a SMPS expert, yet even I know this is missing more than a few components. Seeing stuff like this gives me some sense of reassurance, I lose sleep worrying about something I missed in a design for years after they have been in service.
Great movie! Hope the EMC movie series continues! An interesting topic for the next episodes would be solving problems related to reducing the impact on EFT (Burst, Surge) and ESD. Thx.
I'm interested in EFT and ESD too!
EFT is a big headache. I can manage to do better design for surge, but not for EFT.
No one talking about it and one protection circuit works with one PCB design may not work with another PCB.
I had to watch it in stallments, but this video was GREAT! Very clear, very practical, and down-to-earth for most of us. Thank you, Robert!!
Very nice video! So practical and intuitive explanations for everyone. Should be also interesting to see the effect of a clamping diode and snubber on primary side and secondary side, maybe also in a time domain!
yeah, if I had space on the board, I would have added a snubber circuit.
Thank you for such a simple explanation of this complicated topic!
Nice video and explanation. For future videos: how to design EMI filters for SMPS, how to place components, shielding and route, and damping.
Great video! Thx.
I was wondering why there is no RCD clamp on the switch node of primary side (drain), and no RC snubber on the diode? Those should be major noise sources.
Well, if they want to make profit, surely they need to find a way of cutting cost, that's the problem with volume production.
Excellent video for EMC, very useful tips for EMC. Really appreciate Robert and Min's sharing, great work !
Brilliant stuff from Min and Robert, another really great presentation full of useful information. Thanks to you both!
The CM NOISE source is the current driven through primary to secondary parasitic capacitance due to switching
Imagine the Mosfet drain is swinging between 400v and 0
And there is a capacitance from the drain to the secondary side (parasitic) so a current will go through that capacitance this current can only return through earth
If we connect a return path from secondary to a cold point (non switching point) this current will mostly return to its source, so will not go to earth and its return loop will be very short so no radiation
This return path is done by Y2 CAP
ThankYou Min and Robert, this was super interesting. Have nice week. /br, from norway
A Tekbox TEM Cell and tent were the best investments I made to my EMC testing kit.
Thank you Robert for this interview! Super helpful
Love this video and also the other ones from you two!
more videos from you i see, more i like your channel.
Excellent
thank you Min! very well done!
Can you do a video about Radiated susceptible test. It's always been mystical.
I'm confused with the quarter wave antenna calculation part (14:53). If I use 40MHz to calculate lambda, I will get 7.5m. Then 7.5/4 is 1.875m. I'm confused as to where 0.5m fits in. Kindly clarify..
I think maybe your calculation is right...
Let me get popcorn 😂🍿!
Great video ! Thank you for share this content
Awesome!! Thank you so very much!!!
Thanks a lot for the video. Please, can you suggest the name of the "Thick book talking about the antennas with complicated physics" that you talked about here 18:10
Great video!
How can you make a board that passes EMC without being an export on the subject ? Is following guidelines enough for you Robert ?
Great, thank you
Get a calibrated noise source or make a pwm generator .... get it tested by good spectrum analyser.......... use that calibrated source to calibrated SDR(software define radio or FFT section of oscilloscope!
Hello Robert, please make a video with the EMI filter design method shown in the book 'EMI Filter Design - ByRichard Lee Ozenbaugh, Timothy M. Pullen' on chapter 19.4 EMI Filter Design Example. Its specifically for Switch Mode Power Supplies. I'd love to see this method work for first designs.
I like Min
thanks for good video but i couldnt understand where is the huge radio transmitter's signals in last measurement on 1:13:20. it is mentioned and seen in first measurement which is mentioned at 10:45. if they are not seen, it means spectrum analyzer dont work well or the antenna didnt connected well.
Looks to me that Min is not showing that frequencies on the display
Wow! Min really is an EMC crack!
Why does he mention the .5m from the v=λf formula ?? How does he get 40Mhz?
Even going backwards
Speed of light (m/s) / 1/f (s) = so the seconds cancel out, and you're left with meters.
300,000,000m/s / 0.000000025/4 = 1.875m which is the cable length.
So why is he talking about the quarter wavelength being .5 meters?
how to do active emi filter instead of passive emi filter on power supply 500W upto 3000W with gold grade
I approve.
47 minutes in, the concept of y-capacitors is wrong, you don't have an earth so there is no CM reduction. Maybe input-output returns?
Good video but painful to watch as the host kept interrupting his guest Ming, please let the man talk!!
Do you understand Russian ?
it is made in china!!!!!