Learn To Fix EMC Problem Easily And In Your Lab - Troubleshooting Radiated Emissions | Min Zhang

Troubleshooting EMC problem can be done directly in your lab before going into an EMC test house. Practical example in this video - fixing Radiated Emission issue of a Flyback Power supply. Thank you very much Min Zhang.

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Chapters:
00:00 What is this video about
02:27 EMC pre-compliance setup in your lab
12:14 The first steps to try after seeing EMC problems
13:15 Shorter cable and why it influences EMC results
18:44 Adding a ferrite on the cable
23:32 What causes radiation
27:18 Flyback Converter / SMPS (Switching Mode Power Supply)
29:26 Using TEM Cell for EMC troubleshooting
33:04 Benchmark test with TEM Cell
35:02 Improving input capacitors
43:20 Shielding transformer
46:24 Adding Y-capacitors, low voltage capacitors
49:21 Analyzing the power supply circuit
54:30 Finally finding and fixing the source of the EMC problem
57:59 THE BIG FIX
1:06:11 Adding shield again, adding capacitors
1:12:13 The results after the fix
1:13:09 FIXED!

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It is much appreciated. Thank you,
- Robert

[guillepk]

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!!

[Graham_Wideman]

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).

[PakChannel]

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.

[lucabelvederesi]

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!

[SergioFormal]

Wait a minute....this is not EMC! You guys tricked us into HW design and more specifically power supply design. Still, starting with a really bad (=cheap) design helps to show the impact of each "change". Very useful indeed.

[fedulvtubudul]

Thank you for such a simple explanation of this complicated topic!

[linqiang]

Excellent video for EMC, very useful tips for EMC. Really appreciate Robert and Min's sharing, great work !

[carlosdominguez-palacios]

Nice video and explanation. For future videos: how to design EMI filters for SMPS, how to place components, shielding and route, and damping.

[barkingmadd]

Brilliant stuff from Min and Robert, another really great presentation full of useful information. Thanks to you both!

[rajanaqiuddin]

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..

[JohnSmith-iucj]

Love this video and also the other ones from you two!

[zhitailiu]

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.

[rolfts]

ThankYou Min and Robert, this was super interesting. Have nice week. /br, from norway

[mohammedabdeltawab]

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

[dymastro]

Thank you Robert for this interview! Super helpful

[simonbaxter]

A Tekbox TEM Cell and tent were the best investments I made to my EMC testing kit.

[kingofavalon]

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.

[jozefsoucik]

more videos from you i see, more i like your channel.

[plinsburg]

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

[enginstud]

How can you make a board that passes EMC without being an export on the subject ? Is following guidelines enough for you Robert ?