EEVblog #859 - Bypass Capacitor Tutorial

Everything you need to know about bypass capacitors.
How do they work?
Why use them at all?
Why put multiple ones in parallel?
What effect does package type have on performance?
Are there any traps?
Dave measures some bypass capacitors with an impedance analyser to confirm the whiteboard theory and shows the complexities involved.

Reverse geometry packages:
Low inductance chip capacitors:

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[Fluxtrance]

Nearly 6 years later and this video helped me tremendously with understanding how to implement bypass capacitors properly in a circuit of my own. Thank you!

[matthewcook]

You should write a book containing all of this practical info. With the amount of times I have heard your "a trap for young players" slogan I think you could easily put together some sort of primer without even thinking about it. A Dave Jones book with practical "rule-of-thumb" ideas for electronics engineering would become a great reference material.

[robinbreslin]

When I remember my Uni studies, the voices of my lecturers voices always come to mind. Now, when I put in any bypass capacitors my inner monologue will be telling me how to do it in a surprised sounding Aussie accent. Love it.

[MikeSims]

"Let's go old school with 5V - none of this 3.3v rubbish" - YOU JUST WON MY LOYALTY WITH THAT ONE STATEMENT - LOL!

[burgerdogs]

Hi Dave. Great video... Just a few minor comments to add from a guy who's done allot of EMC work on PCBs. The inductive reactance of the different value capacitors but in 0805, 0603 and 0402 packages, generally follow rather close and similar upward curve due to similar package inductance. Also as you accurately noted, the parallel resonances can be problematic. Henry Ott's EMC book (chapter 11) provides an in depth analysis of this, and often multiple of the same value cap will outperform other configurations. However, sometimes, notches are desired at certain frequencies (for example for RF tx/rx applications), in which case, mulitple differing values will be recommended in the datasheet. Another option (suitable for some situations) is adding small ferrites between cap stages. Clearly this has to be done with a solid understanding of the di/dt requirements of the circuit at hand. I hope that this was helpful.

[jettrom]

You’ve saved my future PCB designs. Bypass capacitors weren’t very intuitive until you explained things so clearly with this video. You’re a great instructor, thank you so much

[u]

Back in my early career we called these caps, decoupling caps. I was responsible for an engineering change to add a decoupling cap to one particular chip on a cpu pcb. The fix cured a major problem. Back then we used oscilloscopes to chase the chip noise which lead to adding additional caps to the chips on the cpu pcb.

[mariusbogdan]

Very good video! I agree with you! I'm already 70 years old, I can't stop this profession. (It's also my hobby) I also worked as a sound engineer and I also worked with impulse technology (analog video) circuits. Most young colleagues do not understand this problem of ubiquitous inductance. I wish you more success and good health from Hungary.

[doublebassballz]

Videos with your kids and mailbags might be the big earners on the channel, but I really appreciate your tutorial content Dave. Its what first brought me to the channel.

[bernym]

This explanation took me back 55 years to when I was an apprentice and studying general engineering on day release at the local technical college. Our tutor explained in depth the mathematics of inductive capacitive resonant circuits but we never got into any practical applications. You explained it very clearly. Thank you.

[jonathanallen]

I’m not sure if anyone has mentioned this in the comments but the impedance from the model around time 12:30 is actually: Z_cap = ESR -jXc + jXL . The magnitude is: |Z_cap| = sqrt( ESR^2 + (XL-Xc)^2 ).

Great explanation of bypass capacitors Dave.

[womble]

Really interesting I'm just a casual hobbyist but I really like the way you make a complicated subject easy to understand

[kushlanfernando]

I don't know how you do this but I get everything you say, you are a better lecturer than from a campus, really love the way you explain and cool. Awesome, no words to describe my happiness now. Good luck with your future work

[anthonycalia]

I have watched this video multiple times over the last few years. It is by far the best presentation of this topic I have seen. Thanks

[vincentrobinette]

This was a great demonstration! Suggestion: pair some of the capacitors with other capacitors of the same value, except, use a 1 Ohm resistor, to suppress the resonance caused by stray inductance between capacitors, as well as the inductance inherent to the capacitors themselves. Much the way a shock absorber damps the resonance caused by spring rates(inductance) and mass(capacitance) in an automobile suspension.
I have run into problems like these, designing switch mode power supplies, as well as class "D" audio amplifiers. Keeping the high speed switching noise from the huge output transistors out of the sensitive pre-amp circuitry is the trickiest thing of all. You absolutely DON'T want to see those high frequency ringing pulses on the supply rails! Op Amps don't have the bandwidth to chase those high harmonics away. I do a lot of resistance-capacitance snubbing.

[hacksaw]

Just had a much younger engineer ask me about why and how decoupling caps are used. I gave him some of the the basic theory of this that I knew, but will be forwarding your video on, which has way more more info that should be known. Great stuff, thanks!!

[subramaniamchandrasekar]

You are a very good teacher. You have all the Patience, dedication, focus, simple and detail and a big heart to share knowledge. Regards

[sabamacx]

This is really great, Dave. Would love to see much of this content on the channel rather than endless teardowns.

[LazerLord]

Liking and adding to favorites immediately. This will undoubtedly be very useful information.

[jolynnathan]

Thank you very much for this video! It’s remarkable how you explain advanced things, so that even I (who doesn’t have much knowledge about electronics at all) can understand it easily. And it’s also very entertaining to watch your videos!