Analysis and design of a DCM Flyback converter: A primer 

Best Flyback converter explanation video on the internet till now . Thank you Professor Dr. Ben-Yaakov for creating all these Power electronics educational videos.

My one regret is that my college professors were not so interested in conveying such practical, easily understandable information. I think your style and depth of knowledge is wonderful, as is your willingness to share. Thank you, Dr. Ben-Yaakov.

Truly grateful that you keep producing these videos!

Thank you, Dr. Ben-Yaakov! This knowledge has been a critical stepping stone in the overall re-design of our EE senior project.

Great video! Perfect teaching skills.

Thank you for your sharing Dr. Ben-Yaakov. 谢谢您！

Great introduction to the Flyback. I found also very useful the practical approach given to the presentation. Thank you for sharing your knowledge with us.

Thank you so very much! I'm making a BCM flyback myself and this is a great help!

I am an electronician and I admit that you explain wonderfully well. The teachers I had dreaded switching power supplies. Relatively complex concepts have become simple thanks to you.

شكرآ جزيلا على هذا الفيديو المفيد جدآ. تحياتي لك من تركيا.

Enourmously information-packed videos!

Thank you very much Dr. Yaakov!

Thank you. I learned a lot. This was much better understanding then just throwing a coil and controller on a board 👍

Awesome professor！I learned a lot from your video, thank you!

Thank you prof. for these lectures in English,I'm taking power converter course and my prof. suggested us to watch your lectures to get more clarity and I agree to him, these lectures definitely provide good clarity of the concepts.

I totally agree with Ken Coffman!! Thank you Dr. Yaakov

I thought I knew this - but I was missing a few things - this really is great stuff !

Oh thanks a lot professor. I'm going to watch it

Thank you sir. this video help me in designing fly-back.

Thank You so much sir for this wonderful video

Thanks Professor Ben, I have to design an 80W isolated power supply for IGBT gate drivers. This video is very useful.

Great video, thank you professor

Beautiful!

Very good video , Thanks a lot .

Very Nice Video Sir. Grateful to you for imparting such knowledge to us. Best Regards, Sanjay

Nicely explaination.

Very nice!

Thanks Prof. !!

Thank you

very good

When the switch is opened up in the primary circuit and the magnetic field around the primary inductor collapses, what becomes of the Back EMF spike? Obviously the large Back EMF spike will be coupled over onto the secondary inductor. However, I guess my question is, is the fact that this coupling the Back EMF spike into the secondary's coil - eliminate the need for the traditional 'snubber' circuit or 'snubber' diode across the primary inductor that is traditionally used to 'catch' and 'handle' the large Back EMF spike? Thank you kindly for an excellent explanation - this is a new circuit to me. EDIT: and then the question was answered later in your video - thank you!

Hello! Good explanation! I`d like to add about a self-oscillating flyback converters with two transistors (like in a cheap mobile charger). These converters very dependents on a transformer , feedback winding turn ratio, there may be over-voltages or avalanche damage - because there is not any gate driver. The stability of this type of converter is not good enough - there is a hysteresis in feedback loop. I have an experience with this type of flyback converter - I only want to share my small experience ))) .Maybe I am not right - but integrated circuits with gate drivers and protection much increase reliability of a flyback converter .

Hi Professor, This is really great content. Please consider creating a video on a comparison of all major derived converters. Thanks

Thanks for uploading, please make a video on closed-loop design of buck-boost converters.Thanks.

Nicely explained. One suggestion is to add a working example or link to someone going through the process of applying the principles presented.

Thank you Sam for the video; it was incredibly helpful. I'd like to know if the support material is available. Your work is greatly appreciated, please keep up with this valuable content. Thanks once more!

could you please make video about the feedback and PWM circuitry that controls the switching in any flyback converter?

A great video as always. what happens if we run the flyback converter (or even other DC-DC converters) without load? I see that all analysis are based on the fact that there is an output (load) current and load resistor appears in some of the equations like here. what happens if there is no load? after the capacitor is charged, the diode will never conduct. Will the energy stored in the core be dissipated by heating up the core? If we add the feedback and PWM circuitry, will it even start if there is no load?

Dear Mr Yaakov, I think that at 10mn, the fs frequency is missing in the peak current relationship when you are expressing the power. Thank you for this sharing

Very nice video. Typically DCM transformer core is smaller than CCM core!

Excellent video as usual professor! One question tho @6:50, if energy = power x time, then shouldn't we have P = (1/2)*[(Ipk)^2]*Lm*fsw ? (fsw - switching frequency) And then after algebraic manipulation we will have P = [1/(2*Lm)] * (Vin*ton)^2*fsw ? Thank you!

Hello Ben, it's nice presentation but @9.38 there is a missed T (fclk) in P formula like this: P=Ipk*Ipk*Lm /2*Tm without T we speak energy as previosly you mentioned

thank for the video, I want to know why you are using the average current in the calculation of the clamp current and not the RMS value. because we always use the RMS value in our calculation 18:52

Very nice presentation Schmuel. Are you planning a separate lecture for active clamp operation ? Also can you post lecture on phase shift converter ?

Thank you for this wonderful explanation. Query: Wouldn’t it be more efficient to utilize the back EMF of the secondary coil by dumping it into a capacitor which could then be used to drive the primary circuit? In theory you might be able to double the output of the power by using the resonant frequency, where the voltage peaks are maximized, and instead of dumping that power into a resistor, which turns it into wasted heat energy, you could use it to drive the primary coil or even dump it into a load? Just a thought…

Hi Mr Yaakov, I want to have two output for my application ( eg: +-5V). So, is there any difference in procedure of calculation? thanks a lot!

Dear Professor Yaakov, in calculating power P in the primary, it seems you have considered ton = 1/2 T and if so, P = 2 IPK^2 Lm * fs. In other words, 2 in the denominator should go to the numerator. And P as you know is the peak power. Thanks

Hi Sir , At 16:47 you were saying that time constant for the RC circuit should be larger than fs -> Hence basically in passive clamp you are not settling the RC circuit charge and discharge ; Is the passive clamp circuit just for passing those inductor (LC) undamped oscillations?

Can the peak current also be calculated the following way? Ipk= ton*Vin/Lm? Because the leakage current should be the same as the current through the coupled inductor, right? greetings Nick

Sir I had one question regarding the practical design of the flyback converter that I have seen in most of smps circuits. Sir there is a cermaic capacitor (1nf to 50nf) connected in parallel with the mosfet (drain-source). First I used to think it acts as a snubber during turn off of the mosfet, but soon realized that there should aslo be a snubber resistace in series with it to limit the discharging current, which is not present. I do not understand the reason behind it, as it will stress the current through the mosfet when it will turn on. Thanks.

Hello sir, If possible, could you please throw some light or make a video on flyback operation when Vout< nVin. I am confused about its operation in that region. I found through simulations that, for Vout< n Vin, even if its designed for DCM, it shows CCM operation. Once it crosses that threshold it shows DCM operation. I am working on capacitor charging application. It would be also helpful, if you could include how parasitic capacitance play an important role in the maximum voltage the converter could reach?. If its not possible, recommendations of good reference books would be big help. Thanks a lot.

Dear professor, thanks for your excellent video. There is one thing bothering me for a while: the DCM flyback converter looks like a 1st order system with a single pole and a single zero as you illustrated. Why compensation is needed? As far as I know a 1st order system is always stable.

hi , how a buck or boost or flyback converter ic supply its own circuit ? I mean I always see an internal voltage regulator inside every diagram of these chips but if it get the current from the source directly it is not efficient

2 questions. I have looked at a few abstracts. On some they use the reflected voltage to calculate n and on others they use the vin over out. Which is correct? Also if Bmax is specified by the core and it is not exceeded in the calculations then why do we need the air gap. I understand that the gap changes the slope of the BH curve but is it required in all cases. Thank you

If I have a flyback converter already operating in BCM, how do I send it to CCM or DCM without changing my input and output voltages? Just by changing duty cycle or also the inductor value must be changed?

Hello sir! Its indeed an enlightening video. I have one doubt though, the clamp capacitor is initially charged to the clamp voltage during turn on of the switch. when the switch is turned off and when the switch voltage exceeds the clamp voltage , the diode is turned on and leakage energy has new path. My doubt is through which path the clamp capacitor is initially charged, as the diode is reverse biased. Could you please throw some light ? also in 20.35 you have mentioned ideally the switch voltage goes to zero when the current ceases in secondary. but shouldn't the switch voltage be equal to Vin ? Thank you.

Hello! Thank you very much for your lecture! Very good content! I Have question about formula for P = Ipk^2*Lm/2, because P is power, so may be right formula would be Ipk^2 * Lm* Fsw/2? So we need to product your formula to Fsw(switching frequency) ? I mean content on 6:50 min. Or I misunderstand something... Thank you!

Hi, is there a way to reduce the resonance which happens after the switch go off?

Hi, Dr. Ben-Yaakov. What drawing tool are you using for this presentation? it looks really clear and simple like Texas Instrument's datasheets.

Wow professor.. wicked videos. At 25:00 on this video you mention how you could look at the graph/poles and determine the output could be controlled using just a simple Type 2 / PI control. What concept/basis did you use to be able to determine PI vs PID (for example)? I've long forgotten my math, but more or less followed you to that point! :) Thanks for the education!

@8:10 Dr. Sam: If ton is higher, Duty cycle will be higher, that means peak current will be higher ( RMS will be higher) for variable switching frequency (boundary mode) as well as fixed freq DCM mode converter. Ipeak and L are inversely proportional. Or may be I am missing something here?

Hi , is Lm the mutual inductance or primary coil inductance ?

(Lm . Ip^2)/2 is the energy equation. Power equation must be multiplied with switching frequency. Am i right? Where as through out the video energy equation is mentioned as power.... If I'm right...

Hi Sir, you are a great professor in making complex concepts easy. I need your favor. I am a junior research engineer. I am trying to develop a flyback converter just for understanding purposes. Our goal is something different. Flyback have following specs: Np=30T, Ns=2500T, fs=34kHz, D=47%, Vin=20V, RL=1Meg. Leakage Inductance Llk=200 uH. The Core is UU Core of MnZn Material having Effective Core area of Ae=191mm^2. Both primary and Secondary Windings are wound on separate legs. Primary Winding is of Single Copper Conductor of AWG=25. The issue which I am facing is that during ON Time (Ton), the inductor current doesn't increase linearly rather it oscillates and it seems that there are sinusoidal oscillations which are superimposed on the linearly Increasing Inductor Current. Due to this reason Output Voltage is much smaller in amplitude than the theoretical one. can you Plz explain the reason and Phenomenon which causes inductor current Oscillating. and also how can we solve that problem. Any helpful Information will be Appreciated. A Rough Plot of Primary Current During Ton is attached herewith: drive.google.com/file/d/1HHPh5b1vHrkywzdQzuXvkwrtDxF-Ipu2/view?usp=sharing

is this [L1 = ( A*N^2*m/l )] the equition to find the indactans in the flyback converter??

prof.could you tel me how i can choose the value of Lm ?

Thanks...I understand that you chose to use your referenced equation to solve...however...let's assume a buck converter simulation...would it not be easier to assume that one brings the inductor to full magnetic field and then at that point the charging circuit is disconnected...what ever the duty cycle time to do that...no more, no less. Then at that point in time...the problem now is simplified to that of the load circuit supplied by the flyback energy (Current source) imparted by the collapsing magnetic field...the problem then becomes much easier to conceive as well as approximate...and most likely also to simulate.

Why the stored energy inside choke should not be 1/2*Lm*Iavg instead of peak current? what if the current shape not be triangular in general not here

What do you mean by offline and online application ?

DCM Flybacks use a smaller core size then comparable CCM Flybacks or Forward Converters...

The secondary inductor should be formed as Lm/n^2, am I right?

what do you mean by Lm??

can we use same method for CCM ??

how can i choose the value of the Capacitor?

Dear Mr Yaakov, I love the way you explain electronic. I would like to point up the pole frequency. Based on your explanation this is 1/2*PI*C*(R+Rc) but the real frequency for the pole is 1/PI*C*(R+Rc). Could you explain this inconsistency? Thanks

excuse this sample just is is theory in action problem is not simple.please in action fasten circuit an show to us .thank you

Can this flyback model exchange energy 2 way sir? I plan to use it to balance the voltage between two 15V sources