Troubleshooting Buck converter output spikes: Based on a real story

[@ArifKhan-bp9zx]

I use to think there's no great KZbin guys who explains everything and in details.. but after this channel, I can say there's no good enough audiance for great Channels like this one.. 😢

[@sambenyaakov]

It is the quality that counts, not the quantity🙂 Thanks.

[@mxzhang8836]

This is a very practical topic. Thanks for doing this professor!

[@sambenyaakov]

Thanks

[@xhp74]

Thank you! I am working on a project ( that is failing!) I have been looking at a lot of your videos and they are helping me understand better what is going on. Not there yet but please don't stop. (65Mhz oscillation EMI Nightmare!)

[@sambenyaakov]

Thanks for comment. Happy that the videos help.

[@samratpushpesh7363]

Another Fantastic explanation with practical example by Prof. Sam. Thank you sir

[@sambenyaakov]

Thanks

[@SuperHal2k]

Uniquie hands-on experince, Thank you Professor

[@sambenyaakov]

Thanks

[@DineshKumar-wv1uq]

Feeling grateful. Many thanks Professor!

[@sambenyaakov]

Thanks

[@JadeHare1]

Great video professor, simply explained but deep insight on it!

[@sambenyaakov]

Thanks

[@hamidk4772]

Outstanding Job.

[@sambenyaakov]

Thanks Hamid

[@Sergey2236]

Thanks for interesting video. It would be nice to see also the PCB

[@sambenyaakov]

Thanks. Indeed, I should have. Next time😊

[@bm830810]

Hi Sam, many thanks again for sharing your knowledge with us, what do you think about dissipating the spike in an RC instead of blocking it?

[@sambenyaakov]

Interesting idea considering the very high frequency of spike. Never tried it.

[@argcargv]

There seems to be an interesting tradeoff here. Slowing the switching speed creates dissipation in the switch, whereas the ferrite bead dissipates high frequency energy in the filter. I presume the bead is a more precise approach to add dissipation in the filter as this will be narrowly focused only on the high frequency components of the noise, whereas adding dissipation by slowing down the switch is a much more broadband filter.

[@sambenyaakov]

The added dissipation by bead is indeed minor.

[@argcargv]

@@sambenyaakov so could a more efficient way to slow down the switch be to place a bead on the drain instead of limiting the current to the gate? It seems such an approach would also work, but I am not sure of the tradeoffs.

[@jpedrosc98]

Thank you, professor! For higher currents converters (i.e. >20 A), is there a better alternative to the ferrite beads? Using another inductor wouldn't result in the same problem?

[@sambenyaakov]

You can use an inductor but may have to damp the network by putting a resistor across the inductor.

[@livingstonbrown6826]

Thanks much professor. If this was a regular pwm controller, which one of the output capacitors would we place the feedback resistor for output voltage regulation?

[@sambenyaakov]

It is better to connect to the second one but this may mess up the control by adding a phase leg so usually one prefers to connect to the first one. The penalty is a voltage drop.

[@TheDefpom]

Very interesting, thank you.

[@sambenyaakov]

Thanks

[@ezranoam]

Thanks for sharing, very interesting

[@sambenyaakov]

Toda. Shanna Tova😊

[@ezranoam]

@@sambenyaakov שנה טובה שמואל, תודה על הכל

[@Dc_tech386]

I design my first buck converter while back but every mosfet or igbt I use just a load of 100watt spike kill the fet and fet was 580 watt so it was not overloaded and I use 20v ziner and 10k resistor in series with to the boostrap gate and 200v Shockley diodes in parallel with the inductor and capacitor 1000nf and 300ohm resistor in series to the mosfets source and all the spikes drop to on 100 millivolt and I draw 60 amperage a 16 volt and igbt get warm and circuit work very efficient

[@sambenyaakov]

Thanks for sharing

[@billimew7496]

Great Lecture Prof, However, what would your suggestion about power level for this IC. Since its need external swiches doesnot it will increase the footprint ? recently i have seen for high step down, there is a new no-opto flyback converter. Can you suggest about which converter is better for high to low voltage conversion. Just for an example this IC input range is 5-75 and adjustable output voltage. However, for high gain ratio around 10 (Vin =50 V, and Vo= 5). Do you recommend this buck topology or flyback or other topology. can you if possible name some good IC for high voltage gain conversion application.

[@sambenyaakov]

Constant on time with frequency adjustment ids great for high step down, With an external switch one can reach 5A output easily.

[@billimew7496]

@@sambenyaakov Thanks a lot prof. Can you share any related document as well.

[@sambenyaakov]

@@billimew7496 Look up application notes and data sheets of TI on this subject.

[@factorpotencia]

These spikes will be also present in the input?, When the MOSFET in ON?

[@sambenyaakov]

Indeed

[@dannyphilossof1140]

Instead of dc filtering as shown, why not put the bead in series with the main inductor? In order to lower emi

[@sambenyaakov]

Never tried it. I would guess that the losses will be very high

[@avin6602]

Thank you! there is a chance you have a video explained why putting the probe and its ground on the same point is a common measurement?

[@sambenyaakov]

See kzbin.info/www/bejne/m5KkpKGEoK-Zhrs

[@mohammadhassanzade6893]

so great thank you professor can we use ferrite bead in series with RG (for smooth turn on or off mosfet) and use RC snubber in mid point of two switch in synchronous buck converter( for more output current about 20A or above) for reduce output spikes ?

[@sambenyaakov]

No matter how you slow the gate, losses will increase. Although some manufacturers promote the use of FB in the gate path (for GaN mosfets). I have found that this may promote oscillations.

[@mohammadhassanzade6893]

​@@sambenyaakov i think too bcz increase inductance phenomena in gate may be made oscillation with input capacitance in gate what is your opinion about add RC snubber in mid point of synchornous buck converter ?

[@joelcarvalho6817]

Thank you professor! Is it practical to design a 2400W buck converter with 300V input and 80V output?

[@sambenyaakov]

With 30A inductor current, it would be better to consider an interleaved topology

[@joelcarvalho6817]

@@sambenyaakov Thank you for your advice

[@wordsoccer747]

Dear professor, have you considered seeing the difference by adding ferrite bead in the frequency domain?

[@sambenyaakov]

Not in this case, but this could help.

[@isacdaimary9908]

Sir Please make a video on output capacitor selection. As far as ESR is concerned I saw people combining Aluminium Electrolyte with MLCC capacitor, but while I tried to do the same in my Lab, I failed miserably to combine a good capacitor value.

[@sambenyaakov]

Have you seen: kzbin.info/www/bejne/mWrYpYSAp8ZsqrM kzbin.info/www/bejne/Z6Gap2unjreHbZI kzbin.info/www/bejne/b5fQiIejq7yoqsk

[@dr_davo]

Would you be interesting in collaborating in the future? I'm a PhD student that makes EE videos on my channel. I deal with buck/boost/ buck-boost topologies fairly often and have some cool video ideas.

[@sambenyaakov]

What type of cooperation you have in mind? You can respond to [e-mail].

[@mikemarachov3230]

As always. Thank you :)

[@sambenyaakov]

👍

[@anthonywilliams4572]

I have a 600w high power dc-dc step down buck converter once I connect power input the converter gets heated up without connecting any load what's the likely problem please help

[@sambenyaakov]

Check the gate drive for overshoot in some other malfunctions

[@marcinszajner2924]

Rezonans converters like full bridge could have same source of interference? I mean during dead time.

[@sambenyaakov]

Indeed.

[@ats89117]

Interesting and useful video. And based on a true story! Very Hollywood! But possibly edited to make it more interesting. ;-) But seriously, You chose a very high frequency ferrite bead with maximum impedance at 3.4 GHz and got very good results. Suppose you had chosen a more run of the mill ferrite bead with maximum impedance at around 100 MHz. I ask this because you've achieved a much better result than I've usually obtained by using the same type of T filter with a ferrite bead between two output capacitors. Maybe the higher frequency ferrite bead is the way to go for this type of transient filter?

[@sambenyaakov]

True story only the names have been changed to protect the innocent😊 yes, since the spikes are of HF content, HF bead is useful.

[@ritzayrton4649]

Whoaaaa ur the best

[@sambenyaakov]

Thanks

[@tamaseduard5145]

👍👍👍💖👍👍👍

[@sambenyaakov]

👍🙏