EEVblog 1406 - DC Circuit Transients Fundamentals

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

[jtb]

Thanks Dave, these fundamentals taught me a lot. More please!!

[AnalogueGround]

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!"

[jenniferwhitewolf]

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.

[abhijithanilkumar]

Oh my God, I am not gonna lie, I have a test on circuits and networks in 2 days
Thanks Dave !

[senorjp]

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.

[PatrickRigney]

Got my inductor lesson from the flyback transformer on a color TV. Unforgettable lesson.

[KeesHessels]

O man, so good to see you again in the fundamentals...you taught me a lot ...

[kevinshumaker]

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.

[anotheruser]

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.

[rogerzimmermann]

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.

[eldorado]

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.

[YT]

Brilliant, can't get enough of these theory chats. (:
Thank you!

[wakkowarner]

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.

[xl]

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

[timthompson]

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.

[mysockC]

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.

[gregorymccoy]

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.

[therealb]

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.

[WacKEDmaN]

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

[tiagooliveira]

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.