Electronic Switches - SMPS and snubbers (1/2)

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  • Опубліковано 30 вер 2024
  • #200 In this video I start looking at the slightly different challenges associated with switches when the electronic type is used. To have a clear use case, I analyze the Buck type SMPS and look at where and why problems occur.
    Related content:
    SMPS switches 1/2: • Electronic Switches - ...
    SMPS switches 2/2: • Electronic Switches - ...
    Mechanical switch protections 1/2: • Switch Contact Protect...
    Mechanical switch protections 2/2: • Switch Contact Protect...
    Further reading:
    fscdn.rohm.com...
    fscdn.rohm.com...
    www.analog.com...
    Special Thanks to all my supporters on Patreon!
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  • Наука та технологія

КОМЕНТАРІ • 52

  • @m1geo
    @m1geo Рік тому +9

    Nice video Fesz! Keen to see the practical measurements and testing! 👌

  • @hedleyfurio
    @hedleyfurio Рік тому +9

    Another superb video - I hope in your " other life " you are an educator , you have an excellent way of presenting material - a rare gift 💪, as at university one is often on the calculus treadmill and dealing with abstract concepts, so it often takes companies at least 2 years to get interns to be productive.

    • @Golkun1
      @Golkun1 8 місяців тому

      Exactly my thinking when watching his videos. 👍 If he is a teacher in an university, his students can be proud to have him.

  • @adrienferreira4666
    @adrienferreira4666 Рік тому +5

    It seems to be your 200th video 🎉

    • @FesZElectronics
      @FesZElectronics  Рік тому +3

      I didn't even notice, but I guess you are right :D

  • @urosborovic6409
    @urosborovic6409 Рік тому +3

    Excellent video as per FesZ standard. Clearly dissecting the problem from the definition all the way to possible solutions. Just I would like to add a small comment that the current spike during the turn-on event of the High Side MOSFET is not only due to the stored energy in the MOSFET's output capacitance, but highly probably due to Reverse Recovery mechanism of the Low Side MOSFET's body diode. I don't know, however, if you would touch on that in your second part on this topic. As a final remark, although ignoring this parasitic diode effect, you didn't lose generality on the guidelines for the RC snubber design which are spot on. Keep it up!

  • @adrienferreira4666
    @adrienferreira4666 Рік тому +3

    High quality content. Really informative. Thank you very much.

  • @udhayakumara4033
    @udhayakumara4033 Рік тому +1

    UA-cam has millions of videos, but i don't see a single video for a complete practical (line powered) flyback SMPS design with explanation.
    Why no one has the courage to make one? How difficult it is? If anyone has such video link please share here, but from my knowledge no one makes a video about proper flyback converter😢

    • @Graham_Wideman
      @Graham_Wideman Рік тому

      Three thumbs up for this topic. Particularly the magnetics.

  • @wearethewatt2950
    @wearethewatt2950 Рік тому +1

    Nice video as usual. One note (if it hasnt been mentioned in the comments yet): your comment regarding the contribution of the low side free wheeling diode was not correct. It is actually important to consider and can be a major contributor to ringing after the low to high transition. It is the reverse recovery charge that causes a very high current spike, depending on the implementation. The already conducting high side switch needs to discharge it, before the output even can start rising. The intrinsic MOSFET diode usually has a high Qrr. Higher voltage FETs tend to get even worse. It helps to add a Schottky, but only if it manages to take over most of the current (which is peak inductor current, to make things worse). I use to choose the low side MOSFET to have an as low Qrr as possible. Your ringing waveform looks like you do not have an extra Schootky, as ringing is quite asymmetrical.

  • @adrianvonino2574
    @adrianvonino2574 Рік тому +1

    Super, multumesc pt video !
    Pe mine ma intereseaza orice subiect din categoria SMPS, asa ca la mai mare 😊

  • @louco2
    @louco2 Рік тому +1

    Master class!

  • @biswajit681
    @biswajit681 Рік тому +2

    Could you please make video on current mode buck converter and it's advantages/Disadvantages and how it's better than voltage mode buck converter

    • @FesZElectronics
      @FesZElectronics  Рік тому +7

      I will try to cover the control strategies - current mode and voltage mode at some point; not sure when though

    • @Graham_Wideman
      @Graham_Wideman Рік тому

      @@FesZElectronics We are tremendously fortunate to have you covering the range of topics that you do. If you need any encouragement, I too would eagerly watch current mode vs voltage mode.

  • @Clark-Mills
    @Clark-Mills Рік тому +1

    Thank you, very informative. Appreciated.

  • @ango5421
    @ango5421 Рік тому +1

    I always like your videos. Technical concepts explained in clear manner.

  • @PowerofKnowledgeForAll
    @PowerofKnowledgeForAll Рік тому +1

    Happy 200th!🥳🎉 Excuse this late comment, but i am always backlogged in viewing my subscribed channels. At any rate, yet another excellent video with a lot of new fascinating details i need to learn.
    However, i have a hard time understanding why the forward voltage of the diode would cause a negative voltage (5:20). Do you have any other video that dives deeper into this weird phenomenon?

    • @FesZElectronics
      @FesZElectronics  Рік тому +1

      Well, the diode is placed with anode to GND, and cathode to Switching node; when it is conducting, the cathode is at a voltage potential ~0.5V lower than the anode (exact voltage will be diode type and current dependent). As long as the GND (anode) is 0V, then the cathode (switching node) will be at a negative voltage - the exact value being the forward voltage drop.

    • @PowerofKnowledgeForAll
      @PowerofKnowledgeForAll Рік тому

      @@FesZElectronics I feel like my electronic major has missed something fundamental here... Please let me dumb it down further...
      If we froze time at a moment the diode is conducting, and i use a multimeter, negative lead connected to GND and positive lead to the other side of the diode, would the multimeter show a negative voltage?
      If your answer is yes, then i REALLY need to sue my teacher.....

    • @FesZElectronics
      @FesZElectronics  Рік тому +1

      Lets consider a different example, you have a 10V supply, that drives a resistor trough a diode (diode has the anode towards the positive terminal of the supply, and cathode towards the resistor A -|>|- K); this way the diode is forward biased, and you get a current trough the resistor; to keep numbers simple, lets say the forward voltage is 1V, so the resistor has 9V on it; coming back to the diode, the anode is at 10V, the cathode at 9v, the the cathode is at a lower potential than the anode by 1v; Coming back to the smps circuit, if the diode is forward biased, and the anode is at 0V, the cathode needs to be at a negative voltage; This negative point can also be seen in the simulation at 6:23 ; for short periods when no switch is conducting, the switching node goes negative - that is when the diode is conducting.

    • @PowerofKnowledgeForAll
      @PowerofKnowledgeForAll Рік тому

      I think im starting to get it, but now my head hurts 😅

  • @yousy9629
    @yousy9629 25 днів тому

    Can you please make a video regarding TVS diodes

  • @davidjmstewart
    @davidjmstewart 3 місяці тому

    At 4:48 you introduced a diode across SW2 to ensure current is always flowing through the inductor. How does the diode achieve this? Its anode is at ground so the only way for it to conduct is if Vs2 < -0.6V rigbt? Why is that node swinging below ground when it wasn't before (the only change is that you introduced the delay).
    Is it that with the delay, the left hand side of the inductor would be floating for a short period of time, changing its voltage to try and keep current flowing, and the diode now allows current to flow from ground, and into the inductor?

    • @FesZElectronics
      @FesZElectronics  3 місяці тому

      The inductor current in a buck converter will always flow from the switching node towards the output; when the high side switch is on, the inductor behaves like a load, getting charged with current, so the left side is at a higher voltage potential than the right side; when the high side switch is off, current still flows either trough the diode or the low side switch, an this time the inductor behaves like a battery - it is producing a voltage which is inverted to when it was behaving like a load - so the left side is at a lower voltage potential than the right; if the low side is an ideal switch, then that side of the inductor is at 0V; if its a real switch (with non-zero voltage drop) or a diode, the switching node goes negative - this is how the diode is being polarized.

  • @d614gakadoug9
    @d614gakadoug9 Рік тому

    I'm less than two minutes in and I see someone probing a node with lots of high frequency content with no ground lead on the scope probe .... annnnnd I'm out. That probing technique is so astoundingly bad that I doubt the ability of this person to do anything correctly.

    • @FesZElectronics
      @FesZElectronics  Рік тому +1

      :) look a bit closer, you might see the probe tip ground spring

  • @troy6882
    @troy6882 Рік тому

    😃😄😁😆😅 5 Smile's ever had that in a older relay makes a humming noise some flybacks will help in high frequency and current not in mine unfortunately mainly for that diodes reason😁. Helps fantastic if you want 4 voltage regulator working as the material adds a block to that 5v reg and needs pulling all working to a amp at 32v great for a dynamo ....

  • @olivierconet7995
    @olivierconet7995 Рік тому

    Very well explained, thanks.
    I encountered this precise situation on a buck SMPS. The product was in its final version and the EMC testing revealed a terrible mountain of noise in the 100 MHz range. We found that a combination of schottky diode parasitic few nH inductance coupled with a capacitor was the source of ringing. Changing the diode reference only changed the ringing frequency. Finally, a RC snubber was the solution, without degrading the power supply performances. The cost was a PCB re-design 😭, lost time and the commercial team very angry 😡

  • @wombatau
    @wombatau 4 місяці тому

    Very good lighting

  • @SignalEdgeSolutions
    @SignalEdgeSolutions Рік тому

    In the video you mentioned it is not easy to measure the series resistance to determine the Q, that is not accurate. A simple 2-port impedance measurement can be done to determine the Q very easily. We do this measurement all quite often. We have published multiple papers and app notes on this topic.

    • @FesZElectronics
      @FesZElectronics  Рік тому

      Maybe you can share the names of some of the App notes or papers (but not links - youtube usually hides comments with links)
      Anyway, my point was that the resistance is not just trace resistance, its also in the switches and the decoupling capacitor; you will need to keep one switch on, the other off, and then the other way around to get a proper measurement, as I guess you already detailed in your work; it can be done, but its not as easy as measuring the stray capacitance and inductance :D
      The method for measuring L/C that I will try out in part 2 is to measure the ringing frequency with and without some known added capacitance.

    • @SignalEdgeSolutions
      @SignalEdgeSolutions Рік тому

      @@FesZElectronics Sure, you can find multiple app notes about 2-port impedance measurements on the publication page of our website. Also I would steer you to the Signal Integrity Journal where lots of our peers have publications on measuring the Q using the 2-port shunt through impedance measurement.

  • @fpgaguru2102
    @fpgaguru2102 Рік тому

    Your probe is not properly grounded during the measurement.

    • @FesZElectronics
      @FesZElectronics  Рік тому

      How would you propose doing it differently? As another viewer pointed out, it was not clearly highlighted in the video, but I did use a ground tip spring on the probe; do you suggest a better ground is needed?

    • @fpgaguru2102
      @fpgaguru2102 Рік тому

      @@FesZElectronics could be the circuit board design issue, low cost PSU usually uses 2 layer PCB

    • @FesZElectronics
      @FesZElectronics  Рік тому +1

      The board its self is something I made a while back, and it has some intentional issues; I did things this way to be able to better highlight possible problems and solutions. It was never supposed to be perfect :D

  • @cesarcantoral6100
    @cesarcantoral6100 Рік тому

    “Simulation”……things tend to change in real-life circuits ….,lol

    • @Graham_Wideman
      @Graham_Wideman Рік тому

      If real life is different from the simulation, then the simulation doesn't reflect the real life circuit. FesZ takes steps to remedy that by adding in the parasitics explicitly to the simulation. The next video will show the proof in the pudding!

  • @tannerbass7146
    @tannerbass7146 Рік тому

    I was literally just searching for this. How did you know!!??

    • @FesZElectronics
      @FesZElectronics  Рік тому +2

      I have a 6th sense :D I hope you found it helpful!

    • @Graham_Wideman
      @Graham_Wideman Рік тому

      @@FesZElectronics You are making a joke, but it's uncanny how you do this! Hahaha!

  • @SignalProduct-be2js
    @SignalProduct-be2js Рік тому

    12:05 - Here looks like we are referring to parasitics... worth mentioning just to make traces shorter from Buck IC to MOSFET's drain... which will decrease parasitics inductance..

    • @Graham_Wideman
      @Graham_Wideman Рік тому

      Right, at 12:05 he's discussing the parasitics that he explicitly drew on the diagram at 9:30.

    • @SignalProduct-be2js
      @SignalProduct-be2js Рік тому

      @@Graham_Widemanyep, but would be helpful to mention to make high-current traces shorter

    • @FesZElectronics
      @FesZElectronics  Рік тому

      Indeed I am talking about the parasitic inductance, but formed between the input capacitor and the 2 switches (mosfet+mosfet or mosfet+diode); this was not linked to the driving signal - if that is what you mean by traces from the buck IC...

    • @Graham_Wideman
      @Graham_Wideman Рік тому

      @@SignalProduct-be2js I'm sure that will be one of the topics of the second part of this series of videos.

  • @CarlVanWormerAE7GD
    @CarlVanWormerAE7GD Рік тому

    I'm concerned that much of the ringing (at 1:40) may be caused by your probing technique. The scope ground is not referenced to the measurement point (on the board), so there is a lot of inductance in series with the scope probing point. A local (on board) ground should show much less ringing, and even better results can be obtained with alternate scope probe connections (without the standard 6-inch scope ground lead).

    • @FesZElectronics
      @FesZElectronics  Рік тому +1

      Maybe it was not pointed out, but I am using the short ground connection - the probe tip spring ground thingy; its visible at 1:37 . I am not using an alligator clip or anything longer...

    • @CarlVanWormerAE7GD
      @CarlVanWormerAE7GD Рік тому

      @@FesZElectronics - Oh, I see it now if I look carefully. Have you ever made a video about the importance of this detail of measurements? Since we both know of the importance, and since it is difficult to see (especially in a small-window video), you may want to consider mentioning it at times when it is important. Otherwise, people may continue to use the scope probe tip measurements and relying on scope-grounds back through power supply wiring. Many hours have been wasted troubleshooting scop-ground induced ringing that was not really there.
      Keep up the good work!
      Thanks,
      Carl

    • @FesZElectronics
      @FesZElectronics  Рік тому

      I will try to point it out more clearly in the future, thanks for the suggestion!

  • @cuntyfinger110
    @cuntyfinger110 11 місяців тому +1

    Thank you very much for your excellent presentation. Much appreciated!