PE #53: How to Implement an Isolated PI Compensator using a TL431

[@MarcosAlonsoElectronics]

LTspice files are now available here: github.com/marcosalonsoelectronics/PE-53

[@biswajit681]

I observed in llc resonant converter also same sort of structure.... could you please make closed loop of llc resonant converter and how to select components value

[@MarcosAlonsoElectronics]

Thanks for your suggestion

[@FidegnonFassinou-yb4wv]

Good morning Professor Alonso. Thank you so much for the video and for all the modeling and simulations. Your videos are always very helpful.

[@MarcosAlonsoElectronics]

Thank you!

[@Marcelo98_Nas]

What a sensational class, congratulations to you, your channel is a find. Following here from Brazil. Soon I will try to design a DC/DC converter, I will certainly post some questions here, in my country this information is a little scarce... Thanks in advance for your attention Hugs.

[@MarcosAlonsoElectronics]

Thank you very much for your nice comment

[@sanjayagrawal6143]

Great Video Sir. Many Many thanks for educating us. You are great. Best Regards, Sanjay

[@MarcosAlonsoElectronics]

Thank you so much for your comment!

[@JorgeSilva-em8pf]

Dear M.A. At first momment, I was shocked by the huge opto output capacitance of 1nF, but which make sense due to slow responde of several opto like CNY17/PS2701 atc. I suppose that this is due the miller effect. At first, I can not find an opto manufacturer reliable spice model; some models shows clearly a huge discrepancy among real and the model. So, could you point out where is the reliable opto spice model repository? Thanks in advance.

[@MarcosAlonsoElectronics]

Hello, thanks for your comment. This was just an example. If the opto output capacitance is too small one might need to add an external capacitor in parallel to attain the desired compensator response. Unfortunately I do not have information on opto spice model repositories

[@patrickliew2756]

Hello Dr, why do I need to model Gop(s) at 6:05 and what can I obtain from the bode plot that you explained? Will the different values of frequency affect the system? If so Dr may I ask what is the range of the frequency for the system to be stable?

[@MarcosAlonsoElectronics]

Hello, the response of the optocoupler is essential to find the response of the compensator. As shown at 14:14 the TL431 plus the optocoupler can be modelled as an operational amplifier with the response A'(s) shown in the slide. This response depends on the parameters of the optocoupler as shown in the slide.

[@Cannabic]

Hello Marcos, your videos are really good, top quality and detailed. I wanted to ask you, if you use for the frequency response analysis of a power supply the LTspice function "FRA" ? and if yes, if you could please make a video about that topic?

[@MarcosAlonsoElectronics]

Hi, thanks for your question. FRA is a new feature of LTspice 17.1. I have tried it but I still prefer the old way to do it that I show in video LTspice #6. This way you have better control of everything and you know exactly what you are doing. For info about FRA I recommend this link: ez.analog.com/design-tools-and-calculators/ltspice/w/faqs-docs/18464/generate-a-bode-plot-for-an-smps-in-ltspice-17-1

[@patrickliew2756]

Hello Dr, for the Rd, Vf, and Cop is it depend on the specification of the LED selected or is it a fixed value?

[@MarcosAlonsoElectronics]

Hello, this depends on the type of optocoupler used for the simulation.

[@FidegnonFassinou-yb4wv]

Good afternoon Professor Alonso. Thank you again for all your videos. I have a question which is not directly related to the videos, but it is related to Power Electronics. I am thinking about designing an Isolated four phases interleaved buck converter and I have the following questions: 1. What will happen to the output voltage, the output power, and the stability of the converter if one phase stops working? The whole converter will stop working? 2. What will happen to the output voltage, the output power, and the stability of the converter if two phases stop working? The whole converter will stop working too? Thank you so much for your time in looking into this. Simon

[@MarcosAlonsoElectronics]

Thanks for your question. This is a very interesting topic that I hope to deal with in a future video. Multi-phase converters can operate with several phases deactivated. In fact this is a common technique to improve efficiency. At low output power fewer phases are activated to improve efficiency. As the output power is increased, more phases are activated to get the optimal efficiency. I recommend to you the following document: Multiphase Buck Design From Start to Finish Carmen Parisi, Texas Instruments, App. Report

[@FidegnonFassinou-yb4wv]

@@MarcosAlonsoElectronics Good morning Professor Alonso. Thank you so much for your response and your recommendation. I really appreciate it. Also, thank you for the knowledge you share with us through your videos.

[@biswajit681]

Sir any video coming this week??

[@MarcosAlonsoElectronics]

I have been very busy. I hope you enjoy the last video I uploaded yesterday. Thanks!