Analysis, Design of a Flyback; part 10 Differential Mode Noise

In this video, I discuss why an input filter is needed in a power supply and discuss what common mode and differential mode inductor do and how to analyze, and simulate its performance in attenuating differential mode noise. Comments, questions, and request for SPICE files can be sent to [e-mail]

[@gkhnglmz1]

Very helpful video series. Thank you Mr. Robert.

[@RobertBolanos]

You are welcome

[@SaeidJabbari]

Thanks Mr.Robert It very useful for me.

[@RobertBolanos]

Thanks for the comment. I am glad you found it usefull.

[@ritulshah92]

Very helpful for understanding!

[@titeman9374]

Alright I will check it

[@hScience100]

Mr Balanos always in top i like your videos and i learn a lot. Starting from 27:00 to the end of the video i did not well understand. why in common mode the flux cancel ? It makes me confusing because the flux is canceled when the flux are opposite and it hapends in differentiel mode. Can you explain me well pls ?

[@ritulshah92]

Do you have videos for feedback loop compensation for SMPS?

[@rohandey5516]

Very helpful video. I have a question, in many AC to DC SMPS schematics I find that they use common mode chokes at the input (after the rectifier) to filter the noise. As per your video you say that common mode inductor will work simply as a wire and not help in filtering. Can you please explain then why common mode chokes are used at the input?

[@RobertBolanos]

Hi Rohan, That is a very good question. That is the next video number 11 that will cover that subject. In short, the common mode is noise generated by the switching Mosfet in the primary and if you have synchronous rectification, you will also have Mosfets in the secondary. These Mosfets are usually tied down to the chassis the drain and chassis develop a capacitance where common mode noise is generated. I will see if I can do the video by the end of the day.

[@RobertBolanos]

Hi Rohan, Just uploaded a video on common mode noise. In the next video, I will show you how to design a common mode filter

[@rohandey5516]

Robert Bolanos Thanks. I saw the video and it helped me understand common mode noise. Your videos are really very informative. So as per my understanding, we would need a common mode and a differential mode filter at the input of a power supply. Is that right? Looking forward for your common mode filter design video :)

[@RobertBolanos]

Rohan Dey Hi Rohan, yes, you are corrent. The input filter should have both a common mode and differential mode inductors. In video 12 I will show how both are implemented/

[@anandparalkar]

Super!

[@adebayooladipo859]

Please Sir, can you recommend any good text book for power electronic design? I really gained a lot from your tutorials.

[@RobertBolanos]

Switching Power Supply Design, 3rd Ed. by Pressmen Switching Power Supplies A - Z Hardcover - July 6, 2006 by Sanjaya Maniktala

[@adebayooladipo859]

Robert Bolanos Thanks so much!!!

[@nikulpanchal6655]

hello sir i wanted to know that , can a common mode and/ or differential mode inductor get saturated and if yes then how to find that they are getting saturated

[@RobertBolanos]

Hi Nikul, Sorry I missed reading you question. The differential mode inductor can be saturated but the common mode can not be saturated. The reason the common mode can not be saturated is because the flux in the inductor will cancel and therefore the DC current will not saturate the common inductor. When you design the inductor, you can use Bsat = (Voltage*Time)/ Effective aread*Nturns). Ty[icaaly, Bsat will be around 0.3Teslas. If you exceed this, you will saturate the core. So when you are design, you the Boperate to about 0.15T. So now you can calculate at what current level will saturate the coil. Lets sat you have have Boperate = 0.15T and Icurent = 10A, then Bsat = 0.3T Isaturate = 20A, The ration is (Bopeate/Icurrent) = (Bsat/Isaturate). I hope this makes sense. Regards, Robert Bolanos

[@nikulpanchal6655]

@@RobertBolanos thank you so much sir for this information