An intuitive explanation of the Fly-Buck* converter and comparison to Flyback

[@tseckwr3783]

Professor Sam. I always appreciate your fine analysis videos.

[@sambenyaakov]

Glad to hear it! Thanks

[@josepeeterson6681]

Dear professor, i really appreciate your commitment to teach at your old age!! I still remember watching your videos to understand power factor corrector and it's control circuits a few years ago (2016) when i was working as a power electronics engineer. Your videos helped me to understand how my circuit design was working internally. You videos are one of the best resources of PE. I have recommended your channel to my friends. Now i have switched to machine learning and it's applications to finance because of the latest trend. I am forever grateful for your explanations!! Thank you dear professor. May you live long and continue to be a blessing. 🎉 Shalom. Am yisrael chai!

[@sambenyaakov]

Thank you for the warm words. I appreciate it very much. Comments like yours keep me going. Sorry for losing you to AI. I am trying to harness AI to power electronics. Best wishes for a successful transition. Am Israel chai and and shows it strength.

[@gaozihan4]

Dr. Ben-Yaakov, if you remember I had that comment on FlyBuck below your piggyback Buck vid🤣🤣 We used Flyback with primary control for our 10-kV SiC gate drive power supply and the CM noise of device switching interfered the Flyback feedback and caused faults frequently. Finally we changed to FlyBuck and the problems are gone.

[@sambenyaakov]

You got me there. Forgot your comment. If you have a stable low voltage, I would prefer kzbin.info/www/bejne/r2O4aJiCm6mnopI over Fly-Buck

[@gaozihan4]

​@@sambenyaakov That indeed would work in the case, with a higher current version driver, but the transformers were encapsulated and unable to be changed to center-tapped 🤣

[@RixtronixLAB]

Creative, thanks :)

[@sambenyaakov]

👍🙏

[@ChrisSmith-tc4df]

Have you done a quick analysis of Dr. Slobodan Ćuk’s Hybrid Switching Converter?

[@sambenyaakov]

have you seen kzbin.info/www/bejne/nKW8Z2CnZbWmfac

[@paradox_1729]

Thank you.

[@sambenyaakov]

👍🙏

[@ChrisSmith-tc4df]

Would the fly-buck better accommodate larger input to output ratios?

[@sambenyaakov]

There might be a leakage inductance problem. I would prefer kzbin.info/www/bejne/r2O4aJiCm6mnopI

[@bharatraj32]

Hi Professor, What are the ideal topologies for designing an efficient aux power supply? Flybacks are being utilized in many designs but their efficiency is not so good.

[@sambenyaakov]

I would consider this approach kzbin.info/www/bejne/r2O4aJiCm6mnopI

[@qwaqwa1960]

LTC has been doing primary sensing of isolated outputs for decades, no?

[@sambenyaakov]

Indeed

[@biswajit681]

Hi sir could you please make video on constant voltage constant current controller working.. getting hard time to understand constant current control part

[@sambenyaakov]

You mean like in a battery charger?

[@biswajit681]

@@sambenyaakov yes sir similar like battery charger or supercap charging

[@adamcordingley2572]

When I first heard the name "Fly-Buck" some years ago, I thought TI was implying that it's very similar to a flyback topology, and never really thought too hard about it. When I see now that it's really more like a forward topology, and the energy flow is really not like a flyback. I haven't read TI's paper yet, but what is TI claiming the main advantage of the fly-buck is over a flyback (aside from allegedly smaller magnetics?)? Is it the fact that it allows for primary-side regulation? Maybe that it can be done cheaper/simpler than a flyback? Easier control loop tuning? Interested in what you think on this. I've been a viewer for several years, excellent video as always! - Thanks

[@sambenyaakov]

Thanks for comment and input. Except for the case that primary side control of a Flyback is troublesome (very high common mode noise ) Flyback is in my opinion better. But if a stable low voltages is available then kzbin.info/www/bejne/r2O4aJiCm6mnopI might be the best

[@jontylewis7301]

missed an opportunity to call it a Piggybuck

[@sambenyaakov]

Great👍I am going to adopt it! OK if I will give credit to Jontylewis or let me know your exact name?

[@jontylewis7301]

@@sambenyaakov haha yes its Jonty Lewis

[@biswajit681]

Wow food came out of the oven😅😅 ...

[@sambenyaakov]

👍

[@GoodWill-s8j]

Flyback vs. Flyback 🤣🤯

[@gregorymirsky8707]

Dear Professor Ben-Yaakov. Unfortunately, this schematic arrangement has a few substantial downsides, which limit its implementation. 1. Energy from the primary winding of the inductor is transferred to the secondary winding only by changing current in the primary winding. If there is no current in the primary winding, there would be no voltage in the secondary one. This means the piggyback part of the converter is a current source, while the primary (main) part of the converter is a voltage source. Combination of both under reigning by the same controller is questionable. 2. The primary converter should be loaded fully at any time since otherwise there would be no voltage induced across the secondary winding, and its load will remain deenergized. 3. Even if the primary buck converter is regulated but its load changes within some range, the output voltage would change as the input current requires. 4. Since the whole power supply is intended for a gate driver, whose load changes within a huge range, a set of energy storing capacitors should be used that would keep voltage across the upper gate driver stable. This increases charging time of these capacitors, which is rarely acceptable, especially when supplying upper and lower MOSFETs of a half / full bridge. 5. This circuit arrangement requires operation at a 50% duty cycle and low currents in order to keep the voltages supplying the upper and lower gate drivers equal and timing relationships stable. Otherwise, the gate driver power supply operation would be disrupted. 6. So, there is going to be a substantial cross-talk between the lower converter and the upper one. 7. I am referring here to a gate driver since this is the main implementation of this schematic arrangement per Texas Instruments publications.

[@sambenyaakov]

Hi Gregory, you are wrong. You obviously did nor watch the video carefully. See 9:54 . Perhaps you did not realize that the coupled inductors act as a transformer between the output capacitor and the piggyback load during OFF time.

[@gregorymirsky8707]

@@sambenyaakov Hi professor, contrary - the 9:54 time mark initiated my comment. At 10:18 you are stating that "... all the energy of the primary...", but the primary winding is terminated to a capacitor, which does not create high enough current to be stored by the inductor. Therefore, current in the primary inductor is limited by its inductance and is negligible. LTSpice simulation confirms that. This is why energy stored in the primary inductor is close to zero and cannot be transferred anywhere. The schematic at 10:20, nonetheless, has a substantial load on the primary side, which makes it viable, but the downsides described in my first set of comments still exist.

[@sambenyaakov]

@@gregorymirsky8707 With no load, there are a positive AND negative currents in the primary AND in the output capacitor with a ZERO net current to the capacitor. Run a simulation and see for yourself.