A primer to resonant DC-DC converters

An intuitive explanation of the basics of resonant converters and elements of their analysis and design - including some aspects of soft switching.

[carmelpule]

Now that I am an old man well above 80, retired from working as an engineer, I have time to ponder and philosophize about my past. Listening to the great details and intricacies and activity inside the various electronic circuits depicted by Sam Ben- Yaakov reminds me of the many heated arguments I had with my linguists and artists and religious " socially emotional" colleagues, who criticized me whenever I described my practical electronic circuits as being, " so nice and beautiful and so poetic and so exact and elegant in their rhythmic, synchronized and phased operations, as if a musical piece was being played, while the currents and voltages, always dance in pairs at different orientations, to the beat of the elements in the circuit, which has its own soul and spirit at every location in the array of connected components. " My learned colleagues always said that one cannot use such emotional language when dealing with silent and unseen electronics activities, where all that one can say about them is, that the circuits are "useful and operational" but not "pretty" and "beautiful" and "poetic". nor " artistic" in their nature. Somehow they were only sensitive to social emotions and not the rhythm of the natural universe!

The use of his frequency to voltage conversion for automatic gain control reminds me of Frequency modulation and how the resonant circuit is used offset, on either side to change frequency to the magnitude to do what one requires with it, but one side is preferable for technical convenience. This FM demodulator circuit is related to the one that was invented by Dudley E. Foster and Stuart William Seeley in 1936. Although it was originally intended as a circuit to provide automatic frequency control, it was more widely used as an FM demodulator, whilst also being able to provide a voltage for automatic frequency control.

In my youth, I used to build my own phase-locked loop to lock two frequencies together, and in my switched servos operating on pulse width positional control, one needed to compare pulses and change the information from phase overlap to voltage with an XOR gate used as a switching or pulse train error detector, to then operate the motors or the variable frequency oscillator.

These last two days, I have got drunk and certainly intoxicated myself with many of San Ben Yaakov videos and their detailed explanations, and I am thinking whether there was any manner in which my past, where my literary, linguists and artistic and religious and political and legal and medical colleagues could ever gain any level of technical sensitivity and selectivity to tune and recognize the souls and spirits existing in our electronic circuits and the music and the beautiful moves, as in this case, obtained by staying off-resonance of a tuned circuit. It is a remarkable human feat associated with developing the sensitivity of feeling for those various voltages, located at different nodes, periodically extending their long arms into the four corners of that full switching bridge and the importance associates with the hesitation and pausing till that natural moment when the inherent rhythm, of the rate of rising of voltages to the switching sequence, is just right to operate any of Q1, Q2, Q3, and Q4. with zero voltage across them. Operating one transistor at a time AT THE RIGHT MOMENT related to the natural rate of change of those various voltage variations seems to obtain the right swinging music to achieve a smoother soothing action in that circuit.
Ben, should know that I compare him with a brilliant musical conductor dealing with the electronic components in a philharmonic orchestra, where he certainly knows what each player in that orchestrating circuit can play. He may only have L, C, R, Voltage and Current sources, a few diodes and transistors of all types, but he can certainly feel the music they play right in his heart. Congratulations on your dedicated efforts in depicting the beauty within the soul and spirit of our electronics. Wish Ben had a larger hall ( whiteboard) to write and play his music on!
To think that it is electronic circuits that are playing this submitted video makes the heart of an old engineer, beat a little faster, but it would leave all my past colleagues cold and unmoved by that idea. Ben Yaakov, Prosit. Now that we are close to Christmas festivities and New Year, I can propose a toast. May you have a good Christmas and a Healthy new year to proceed with your sublime electronic explanations for the good of our young people who need to know the soul and spirit and the rhythms of the gems of engineering in all their brilliant facets. Ben's video is not any different from the contents of the following video

[beforebefore]

Great explanation... very clear and precise... not too fast, not too technical... very good! I learned a lot in this one video, and I've been in electronics for 40 years.

[juliatruchsess]

Wonderful presentation, thank you. Extremely intuitive, immediately getting to the gist of essential aspects without a lot of digression.

[pablogonzalezvizuete]

Really great explanation of the basic conceps of resonant converters.
Obtaining mathematical expressions of the non linear and square wave circuit is very complex. I like that you clarly reasoned how to turn this complex problem into a handful circuit that can be manipulated. Thank you.

[George-ktgy]

Outstanding tutorial, the best so far. Please keep them coming.

[SivarajanAryan]

Thank you Prof. Yaakov you have explained a complex topic in a very easy way to understand....

[hataimti]

Thank you, Prof. Sam for this beautifully explained lecture. Its clear my following doubt:
1) Effect of harmonic content of input square wave
2) Leading vs lagging operating range
3) Why LLC preferred compare to LC

[mubtadiiman]

As a beginner, your lecture open my mind about harmonic wave as you mention 1rst, 3trd, 5th, 7th and so on. Thank a lot Prof. Sam

[krhnetanel]

Simple and intuitive explanation. thanks professor

[my_home_interiors_hyderabad]

Very helpful and natural
Respect from India Sir.

[a]

The first good lecture I found on this topic!

[tolgaozer]

Thanks for your good lesson professor, as an engineer it was very helpful.

[power-max]

14:02 why is a series inductance necessary once you add a transformer? don't transformer primaries already have an inductance that is exploited when building the typical flyback topology converters? I have always thought of a flyback topology as being sort of an extension of a boost converter.

[my_home_interiors_hyderabad]

Sir at 18:06, how Q3 body diode conducts even if voltage on the line and drain of Q3 are at same potential ?

I understood because of lagging nature of circuit the current is starting slow and switching losses are reduced

[emondedead]

Thank you Prof. Sam for the wonderful explanation of the operation. I was wondering how to come up with a new resonant circuit for ZVS or ZCS? Can you please shed some light on that.

[power-max]

I actually built this topology of converter before even knowing what about it "academically"! So I'm happy to learn about it!
I built a Tesla coil with a primary coil in series with a bunch of film capacitors with the primary tuned to the frequency of the secondary, around 300kHz, I got the idea learning that series LC circuit has ZERO impedance at resonance, so to get maximum power transfer, since FET's have very low Rds(on), I should a series LC network and use a phase locked loop (CD4046) to lock on and ram as much current as I possibly can at a given can into the primary and let the voltage at the node between L and C climb unbounded. :)

I am now able to dump over 500W into the secondary with a full bridge, and my FETs don't get too hot :D It still needs lots of work. My PCB layout has issues and my FET's keep dying especially if something causes the circuit to fall out of resonance and switch at a lower frequency. Still trying to identify the root cause. I did observe 1.8x voltage in ringing at 40MHz, which might be the culprit. Also it is strenuous on the capacitor and even my secondary as it heats up noticably. Had to buy the lowest dissipation capacitors I could find on LCSC and put lots of them in series/parallel.

But as of now my biggest limit is really my 48V 7.5A mean-well SMPS that apparently can output 55V at >10A before shutting down due to overcurrent.

[Rajat]

Why do we use a coupling capacitor along with a transformer in the "current driven rectifier" of a resonant LLC converter ?? Could you pls share some thoughts. Thank you

[masoudghazali]

Hi Professor, Thanks for your explanation. where I can find the mathematical proof of the relationship between Re and R l?

[basiqquddusi]

Hello sir! Your video is amazing but I have a little confusion, at 11:20 minutes there are two formulas written for Re and RL, according to my calculations they should be like "R=[(pi^2)/8]Re" & "Re=[8/(pi^2)]R". Please help if I am doing it wrong even a small hint will be of great use.

[xinchen]

Thank you a lot!!! This question bothers me quite a long time but your explanation is quite clear!!!