EEVblog 1406 - DC Circuit Transients Fundamentals
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- เผยแพร่เมื่อ 11 ก.ค. 2021
- The conclusion of the DC circuit fundmentals tutorial series.
How a capacitor and inductor works, parallel and series configurations, exponential rise and decay, time constants, and basic differential calculus. Energy storage in capacitors and inductors and how a collapsing inductor magnetic field can be both a problem and a benefit.
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#ElectronicsCreators #Tutorial #Fundamentals - วิทยาศาสตร์และเทคโนโลยี
Thanks Dave, these fundamentals taught me a lot. More please!!
50 years ago an old chap who encouraged me used to say "remember, two things that can catch you unawares are back emf and charged capacitors!"
Taking a screenshot of this comment
Ohh, I do remember that capacitor!
not nearly 50 years ago i heard: if anything in your electronics goes towards infinity it certainly smokes
I was told we call it theory because it's the best idea at the moment.
That was 1976 , still the same : )
Yep... BIG TIME!
One of my first screwups in electronics was unplugging an energized stepper motor. The collapsing field fried the motor driver. Those hundreds-of-dollars lessons stick.
That's why "dangers of back EMF" is the next video in the series! (although having seen that it pointed here, I came for my chalkboard lesson first.)
Oh my God , I am not gonna lie , I have a test on circuits and networks in 2 days
Thanks Dave !
Brilliant, can't get enough of these theory chats. (:
Thank you!
Had a cooling fan hooked up to my Raspberry Pi and when I unplugged the power it fried the TVS. It looks like nothing else got damaged but a lesson about inductance was learned that day.
One of the most important concepts ever presented to me was to think of time zero in a circuit.. and then it starts. Before the circuit comes to operational stasis, it it a mess of inrush currents, charging up elements and even heating. Transient analysis is critical. Same at shut down, collapsing fields and discharging. Everything must be accounted for, not just steady state.
Not only is inrush current a problem charging DC filter caps, so is the haversine wave after a bridge rectifier. Because the cap can never charge to the very peak voltage of the haversine, every time the voltage approaches the peak voltage, the capacitor is a very low impedance load for a very short time period. To eliminate this cyclic but very brief short circuit a current limit device should be used between a rectifier and filter cap..this is where inductors are quite handy. This is trivial with most 'small' circuits, but in large amplifiers, cap banks in the range of tens to hundreds of thousands of uF are quite common, and haversine peak charging currents can easily destroy a large transformer over time. Another solution is to use a mosFET in series between the rectifier and cap bank.. driven by a threshold detector to have very low R below most of the haversine voltage wave, and to start having higher R above a threshold point selected to be near, just below, peak voltage.
The 63.2% comes from 1-exp(-1) (%), which is the voltage factor at t = T = RC, ie the % of total voltage at the first time constant.
O man, so good to see you again in the fundamentals...you taught me a lot ...
At age 14 I built a circuit to shock my friends, with a 9V battery, momentary switch, and large inductor. Convince them to hold on to the wire, then let go of the switch. I was not popular as a teen.
I did the same. What was truly shocking was the number of people who would actually do that despite it obviously being a trick! There's truly one born every minute...
I scored a beefy cap from an old radio. Intentionally prolonged the leads, charged it up and threw it at somebody with words "CATCH"....I was not popular either.
@@robandsharonseddon-smith5216 It's because they're curious and not pussies.
Oh didn't we all :) IIRC I used a transformer to up-transform the voltage. But the part about getting unpopular, well, some meaner buddy of mine grabbed the contraption and went around school to find volunteers, so he was the one drawing the ire. Worked for me ^^ It's weird how this trick worked so frequently. "Look, I'm giving it electricity and it's not too bad at all!" :D
"What is the capacitance between the Earth and the moon?"
Physicists: 1.29284E-21 farads!
EEs: Zero. It's zero.
Astronomer: Is that at the Moons apogee and perigee?
@@philipandrew1626 That's zero and ZERO, respectively.
Bullshit. 10^-21 is not that small, any capacitance between the two is probably too small to be worth calculating, probably e-50 or less. And that value probably changes wildly.
@G E T R E K T 905 Yea, well, when we talk physical limits, what we're talking about is so ridiculously small, that -21 is still close to real world things physicists have seen. I want to be as far away from that as possible. And how the hell can you attach a constant number that. If the sun so much as to do a sneeze, the value changes by a few orders.
man of culture..!
You've left me with a .5M of dust on the floor and tangled in cobwebs. I got my EE degree almost 45 yr ago when I went into engineering SW development; haven't chased electrons in WAY too long. A refreshing review... maybe a "new" hobby re-emerging (if I can find my breadboards and the drawer storage box with all my components and supplies in my storage unit). Thanks.
Got my inductor lesson from the flyback transformer on a color TV. Unforgettable lesson.
And charged up caps in TV sets can be just complementary lesson to it.I should know - Did my own research, where I unintentionally and regretfullly served as test subject.
@@blitzwing1 The shock was painful. The sudden change in position (from standing at the bench to landing on my backside) somewhat moreso, though. The worst pain, however, was the humiliation of my high school shop teacher laughing hysterically across the room for several minutes. Fortunately, it wasn't memorable enough for him to earn me a nickname that stuck.
I was a fool to take an ITT Tech course back in the 80's to get an EET cert for WAY too money. I wish we had instructors like you back then. You explanation was much more clear and concise.
this is a lifesaver! I will have my electronics exam 3 days from now, and the hardest thing for me to understand from my classes was capacitors and inductors.
this was the exact video I've been wanting and needing for a long time, but I couldn't put my finger on it. Thanks.
Love these fundamental videos a lot :D
Very good video here, Dave! Knowledge like this is what makes a good engineer. Keep up the good work.
Circuit transients is what was transitory in my mind always. Quite stabilizing now,....Thanks for awesome videos!!!
Excellent tutorial on LC Transient behavior, much more useful practical knowledge than my EE professors who start out with all the physics and you lose touch with the practical application in circuit design. Thanks for taking the time to produce these videos, so useful.
Nice video - going back to your roots. Good job Dave!
Great video series Dave, real stuff! Thanks 👍
Thanks Dave! Great review!
Just repaired a ups that used sizable inductors to create a 800v dc bus. Biggest inductors I've seen in a boost converter so far.
these fundamentals are a great refresher Dave..about time ya got back to being useful and not just waffling on all the time! :P thanks mate
one of the better times his waffling adds more content. than uh... just repeating again and again.
Excellent presentation !!
Great video lesson! Hope to see more like these ones
Brilliant, my electronics knowledge is now expanded, thank you.
Please keep doing these fundamentals videos. The more I go forward in my education the more I find the need for falling back on fundamentals to understand.
I hope you can make videos on wireless communication fundamentals and signal fundamentals. Topics on communication engineering please.
Good information. This was review for me, but I always like to refresh my memory. I worked on high voltage dc-dc converters in my previous job. This theory came into play on a daily basis. When I saw your initial series caps, I was thinking, “you’re going to need some balancing resistors.” I wasn’t going go bring it up, since you were describing the ideal theoretical concepts, but I was glad to see you mentioned it. Another thing I learned on the job is HV MLCC caps lose most (like 75%) of their capacitance at their rated voltage. I learned about the back emf diodes protection back in my military training, but I don’t think they teach that well in college. Most BSEEs I’ve worked with design relay drives without it.
Interesting to note that the only case of a capacitor storing a charge without any voltage source connected for an inductor is an MRI machine with its superconducting magnet that forever has (or at least until someone hits the red button) current going round and round to make the magnetic field.
I worked with someone who wanted to turn on the light in the MRI electrical room and hit the red button.
Issue with doing that has mainly to do with the coolant eventually getting too warm and gets vented. Fortunately that takes days.
Thanks for making this!
I have had not time to watch this channel during the last 4 years, but now the news cycle is a bit slower than it used to be. I'm ready
Very useful video, thanks much ! Alan Wolke also has some excellent videos on LC series and parallel circuits and diode snubbers for relay coils.
What you call big "T" is Tau in my books. I like these videos. Really takes me back. Thank you Stan Graff, wherever you are. My old proff.
Yes, I forgot to mention Tau
Great material. Thank you.
In two movies you gave me more knowledge than 6 years of a school.
I love your channel Dave. Plus you're freaking hilarious. Keep it up. Greetings from Canada.
I'm looking forward to the follow-up transformer lecture. We deal with a lot of primary measurement CTs in protective relaying in electric power transmission (nameplate ratings on the order of 3200A:5A [N=240]), and inadvertently open-circuiting the secondary of one of those under load gives an impressive, and potentially fatal, demonstration of Lenz's law.
Great class, thank you.
Haha, awesome getting the Fonz involved with electronics.
This one was remarkably informative. Please make a video on LC oscillations. Will be of great help 🙏🏼🙏🏼.
Salvaged components from an old VCR.. was amazed with how many inductors was used right through the board.. the board seems to present a quality that just preceded the move to smd.. lots of good pots etc.. Made me wonder what are the practical uses of inductors...someone liked them.. I did some googling out of curiosity and found articles that seem to suggest that some desighners avoid them... and listed some practical applications and explanations... still enjoying it...
Great stuff.
Masterclass. Nice and easy.
Right over my head, but Thankyou, I'll be probably googling this in 10 years time :)
Dave is doing the semi-math-heavy version here, it's not for everyone.
Ohhhh DC transients! Waiting for someone to really explain this for a while!
nice calculator you have there. Seems to also change with the passing of time!
Very informative!
Very cool how you explained L times di over dt ....
Thank you for talking about the Physics ......
I love fundamentals friday on mondays!
I look forward to the transformers video, and hope you do a piece of choosing inducers and how to size them for the current, likewise how to choose/design transformers for AC circuits and how much voltage they can handle
Some SMPS also includes NTC series resistors to limit current inrush. As it gets hot the resistance decays creating a soft start effect. (Sorry for my english. Hello from México).
Loved it!!
9:32 - "not that electron current flow rubbish" 😂
In my Electrical theory class, the professor asked for conventional flow textbooks. The nimrods at the bookstore ordered the electron flow version. There wasn't a single lecture where he didn't squeeze in a gripe or a jibe.
Holy smokes! I got a like from Dave! Thanks dude!
In electronics class conventional current was king, why make it harder than it needs to be...
Then in physics class, you now have the right and left hand rules as well as velocity vector and magnetic orientation, that's before you even consider curle and variation in field geometry..
It was once so blissful to be so nieve haha :-D
Dave isn't DC "AC with infinitely long wavelength"? xD
AC fanboy ALERT!
surely AC is just DC with terrible ripple?
You will need fourier analyzis to find out.
Until the heat death of the universe, all electric fields are AC.
Nikola Tesla has entered the room.
I hope there will be also videos about AC (for the practical reason like building power supplies, using 3 faze motors or safeyetc.)
What's really interesting and new to me, is that if you have series caps of different Farad ratings, they should end up with different voltages across them.
Well it's not super useful most of the time, since you cant just draw current from it, or use it as a reference, and so on.
This does come into play when you power stuff with a Capacitive Dropper on AC though. The "dropper" capacitor has a small value and gets a lot of voltage, and any (electrolytic) capacitors after the rectifier can have a large value and get a low voltage, even if you dont use any Zener diodes.
Been in electronics the whole adult life (and some before). Now that I am semi-retired, electronics math theory like this still makes my brain hurt. lol
What area of electronics are you in? Were you a design or testing troubleshoot engineer or repair technician or production or anything else? I find engineering education very theory focused compared to technician courses.
Yes Dave, move this to a new blog. I will subscribe.
Grasias x los videos sige adelante compartiendo
One of my favourite channels. The other is Fran Lab . You should get together sometime it would be truly awesome.
Thanks.
I am going to use RC timer on microcontroller because some time it do funny thing when I power it on.
Good day,
Like the videos, thank you,
Jean-François
Hello Dave, I love your videos. Your knowledge has helped a lot. I have a request, can you please make a video about finding the loop stability when we are creating a discrete linear voltage regulator using OPAMP and a BJT? I have tried a lot but I can't seem to find a way to find out the stability and the gain and phase margins.
I was so hoping to see demos of charge-discharge...
Great video. I feel like I come away with a much better understanding.
Thinking about the earth and the moon in this context still makes my head hurt tho lol
9:45 Or, or, or you use your left hand, for the proper current flow, that is, the electron flow, and you also get the direction of the magnetic field ;)
Yes but then you start mixing them up. "Which again uses the right-hand rule?"
@@danman32 You only mix them up if you're not used to use electron current flow.
2:30 an even more fun question would be, what is the _elastance_ between Earth and the moon. That would trip a few people up for sure.
Why did you feature different calculators throughout the video ? Thanks a lot for this video !
Just to add some tidbits about Inductance, that is why start and stopping of high power electric motors like in an industrial settings is its own science by itself to not fry the motor and the electronic driving it or popping all fuses.
If I only had Dave back in 1971. I might have made something of myself.
There actually are practical inductors with true zero DC resistance, superconducting magnets. The coils in those magnets are usually a complete short circuit (closed current loop). In order to charge them up they open up the loop, connect a power supply across the gap, slowly ramp up the current until the desired magnetic field is reached, and then close the loop again and disconnect the power supply. As long as the coil is kept at a low temperature so that superconductivity is maintained the magnetic field will stay and the current will keep flowing (without any voltage no less!) indefinitely.
Fun fact: In practice they don't actually physically open the loop, they just heat up a small section of superconductor to above the critical temperature so that it becomes resistive. Because the resistance of the coil is zero in steady state all the current will flow through the coil and nothing through the resistive section, so the resistive section essentially acts like an open circuit even though it's a conductor (Other fun fact: the windings in a superconductive magnet are usually electrically insulated against each other with copper. During superconductive operation no current will flow through the copper, but in case of an unexpected loss of superconductivity - for example cooling failure - the copper will short out the coil and limit the voltage spike generated by the inductive kick). Kirchhoff's laws become funny when R becomes zero.
Oh yeah, AC next I realy struggle with that....cheers.
OK, I'll fall for it, whats the calculator that pops up at 5:28?
Here is a fun experiment: wind an inductor (5 turns for example) on a ferrite core. Measure the inductance. Wind another 5 turns (on the opposite side and in the same direction) and connect them in parallel. Is the total inductance half of initial 5 turn inductance?
this reminds me why i didn't take electronics engineering back in college. ahh good times
So, Laplace transforms (S-domain analysis) next?
I still dont understand laplace transforms but i havent even taken calculus yet. AC steady state is as far as ive gotten
Noone understands Laplace, hence wolfram alpha
Should probably wait for halloween with such horror tales?
Who would have thought that Joe Mangle would know so much bout leccy. 👍
I wanted to make a four layer capacitor to function as a single component dc transformer. The two outer plates can function as the "primary" and the two inner plates could function as the "secondary" and if you increase the surface area of the primary or secondary you can alter the voltage .....
and things are getting interesting... fast forward to advance players..
I always understood Transients to mean the unexpected effects, like stray capacitance and Inductance due to pcb track or proximity etc?
159uf is the capacitance between the Earth and the Moon. Google is a wonderful thing.
Just some fun with a transformer: get a friend to hold on to the secondary and use a AA on the primary for a shocking good time.
Love the tshirt, where did you get it?
About 63.2% the initial voltage rise rate will be dominated by DC resistance (series R and capacitor ESR), right? So the RC constant is the ratio of DC characteristics (initial circuit state) to the reactive characteristics (changing state), is it? But capacitor ESR is not strictly linked to charge capacity so 63.2% could change, is that not right?
Bit stuck Dave in that Lock down. Stay safe mate.
What is the ESR of the earth-moon capacitor? ;)
so how would you design a simple circuit to limit the inrush current? In a battery operated device for example, when you plug the battery in, if you have a large bypass capacitor as a first component (for purpose of noise reduction for example) it will spark the terminal and have lots of inrush current I would think.
@2:35 I calculated C = 1000 x 8.9E-12 x 4.7E7 / 300E3 ≈ 1.4µF (roughly)
Considering only the moon surface, both electrodes as an approximation.
Does that make sense? I mean... really?
Energy of a capacitor (1/2)cv^2, Energy of an inductor (1/2)Li^2, energy of a moving object (1/2)mu^2, energy of an elastic medium (1/2)kdx^2. Nature if wonderful. :D :D :D
Fantastic video Dave, comprehensive introduction to LC charging/discharging principles, gave me those nostalgic high school memories :-)
Once physics gets involved and 2D circuits become 3D fields everything gets thrown into the air, still extraordinarily fascinating, but well outside the scope of electronics. Magneto-Hydrodynamics is where it's at!
Oh man, I'm going to have to use my confuser more often.
I wonder one thing. The magnetic field is caused only by flowing current. At the beginning non-charged inductor blocks current completely. So how it can build his magnetic field if there is no flowing current?
I'm a complete amatuer with no formal training so I apologize if this makes no sense but at 18:30 when you mention the in rush current being larger due to no charge on the capacitor, is that why you get a pop when plugging in audio gear?
The AC transient looks just like an audio signal and gets amplified and turned into sound.
Could be, depends on the circuit design
I seem to remember the time constant is Tau?
Oh Dave, you missed a golden comedy opportunity right at the end to show you checking everything you just said in "Electricity for Dummies" ;)
I always thought of RC as Radio Controlled and LC as LIGHT SABER CONTROLLED! 😆
20:25
Interesting value of e.....
Capacitance from Earth to moon is cca 0.2F or 200mF
36.8% Hmm 0.368 is 1/e that can't be a coincidence.
Well, he found the number T by putting a slope line in the beginning, so we need to find a derivative at t=0.
Derivative of Ve^(-t/T) = -Ve^(-t/T) /T
Plug in t=0 and you get
-V/T.
That's the slope of the line, and we know that it is equal to V when t=0. So, the equation for the line is V - tV/T. The line crosses the time axis when tV/T = V or in other words when t=T.
Plug that into the original function Ve(-t/T) and we get
Ve(-T/T) = Ve(-1)
What's that as a percentage of V?
It is Ve^(-1) / V = e^(-1) = 0.368 = 36.8%