EEVblog 1399 - Electronics Fundamentals: Voltage Dividers

Fundamentals video. Voltage dividers, series and parallel resistors, current dividers, a revisit of Norton and Thevenin's theorems, rules of thumbs, and a demonstration of circuit multimeter loading and a trap for young players.
00:00 - Intoduction to voltage dividers
01:33 - Uses of voltage dividers
04:27 - Rules of thumb
06:55 - Calculations
08:57 - Current dividers
10:56 - Let's revisit Thevenin & Nortons Theorems
17:29 - Demonstration of a trap for young players
DC Fundamentals Playlist: • Electronics Tutorial -...
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[@dr_davo]

I teach at a University, and I show your vids to my freshman class. I also make vids for the entire EE curriculum, but in my opinion - having multiple sources of info from places all over the world help students learn way better than pushing to read a single textbook.

[@vgamesx1]

As someone who learned almost everything about electronics from youtube, I can confirm using multiple sources makes a huge difference, whenever I had trouble learning something I found another video on the topic that simplified or explained it in a way I could actually understand, also using analogs how Louis Rossmann likes to explain things can also sometimes help.

[@eebaker699]

@@vgamesx1 couldn't agree more. 😁

[@robbieaussievic]

..... Hollywood would have re-dubbed it, (Like they did with 'Mad max').

[@JoeOlneyGym]

Then again there are books I didn't sell back after the semester was over because I knew the book cover to cover.

[@shrimpkins]

@@robbieaussievic Don't write off the Goose before you see the box going into the hole, mate 😁

[@Fordgpw1942ocalafl]

These are my favorite videos just like the old ones because of you I understand opamps!

[@fiakergulaschsaft]

THIS!

[@bergamt]

Or at least I can pretend to understand op amps well enough to fool most people

[@fiakergulaschsaft]

@@bergamt also this! xD

[@advanceringnewholder]

Same here

[@Erudotic]

I second that!

[@airmann90]

Don't care how simple any of these fundamentals are, I love the 'fun'damental vids.

[@Erudotic]

Me too!

[@bertblankenstein3738]

"Resistance is futile." Ok now that that is out of the way, thank you for another fundamentals video.

[@whitefields5595]

Dave, every day is a school day. Even when you think you know what you need to know there will be new insights from a new teacher. Please keep doing these fundamentals vids.

[@8BitThoughts]

Man, I wish I had a teacher like you in high school.

[@s8wc3]

Right? All high school electronics class is these days is "how to make blinkie LED wowee with arduino".

[@8BitThoughts]

@@s8wc3 Arduino’s didn’t exist when I was in high school 😂

[@s8wc3]

@@8BitThoughts I was the first of the arduino era, the students before me at least got to put together jaycar kits and that kind of stuff, we just sat on the computer...

[@kemonoyama2084]

College too!

[@Jason-wc3fh]

I would be shocked if my high school actually taught something useful like this from back when I was there. They were too busy teaching us useless garbage about religion, history, music, french, and other junk that serves you no purpose in life.

[@amratsingh5206]

EEVblog Fundamentals videos is what I live for. ❤

[@Seiskid]

The 10% 1% 0.1% rule is useful. I've been doing this a long time but hey never thought of this before. Its a winner.

[@hopelessnerd6677]

Even if you think you know something well, watching a refresher like this is always good. You never know what shortcut you might pick up. Thanks Dave!

[@robsdeviceunknown]

I took Computer Electronics back in 1989. LOVED it but ended up going a different route in my career. Now that I'm retired I am getting back into it for fun so these videos will be a life saver. So sorry to those that think this is too basic of info. For me it's astrophysics atm.

[@stevedaenginerd]

Thank you so much for continuing the fundies series! I thought I had a good understanding of these concepts, but now I feel like I have a better and deeper understanding. I feel like I just upgraded my tools! lol

[@thomasesr]

"Anywhere I go, every place I look. All I see is voltage dividers everywhere"

[@EEVblog]

My god, it's full of voltage dividers...

[@Dave_Rice]

All stuff I learned eons ago, but rarely revisit. And you brought a few points out that I had never considered. Thanks for the fundamental videos. Wonderful stuff!

[@jardel_lucca]

Please keep posting these fundamentals videos!

[@JosepsGSX]

Thanks a lot for this back to basics sessions. I'm on the uneducated side, learning electronics as a late hobby, and these lessons are quite helpful and interesting.

[@HaloWolf102]

I've clicked on a few videos on this subject, this is by the far the best explanation of it across those videos. Thank you very much Dave.

[@blward]

Thank you for the fundamentals video! I really appreciate having a good place to direct people for reference.

[@TheEmbeddedHobbyist]

Well done, the meter error due to input impedance is something that gets missed in the KZbin uni class's. I can remember having to work out the affect the meter would have on the reading, then taking the readings and checking to see if the reading was as expected. so you knew the circuit voltage was correct. Avo MK8 great place to start with you measuring kit, you had to know by how far out your reading will be.

[@anuragkondle2269]

Thanks for your videos... Always keep us posted with these basic but important stuff. Efforts appreciated.👍🏻

[@eebaker699]

Great video, thanks. I was experiencing the same readings on my analogue multi meter when testing a voltage divider circuit. This has cleared up many questions.😁

[@thesadhak]

Sir your teaching style is impeccable. Keep up the good work 💯.

[@nathanrussell2158]

Thanks Dave, really appreciate your videos.

[@michaelmccarty4765]

I am an amature who recently dropped the $$ for the "Art of Electronics" (and the lab guide). This was so helpful, thank you!

[@jackevans2386]

15:15 ". . . don't want to piss away power" Love the Aussie vernacular.

[@bradtito3309]

Thanks Dave. Very nice explanation

[@clems6989]

I love these old videos Dave, Just look how the channel (and You) have grown... Great Job !

[@andymouse]

Your 'Fundamentals' stuff is realy enjoyable and useful, please keep 'em coming !....cheers.

[@KrisKustomPaint]

I really appreciate these videos. They've helped me quite a bit. Thank you for making them.

[@LousyPainter]

Learned something very valuable Dave. Thanks!

[@onjofilms]

Been in Electronics since 1982, but always like to see your fundamentals anyway.

[@ChrisHalden007]

Love those "Electronics Fundamentals" episode!!!! Thank you

[@simbozoni]

Thanks Dave, more fundamentals please!

[@brad5947]

Nice, clear explanation, thank you!

[@Sahilkhan-jd5fz]

You are an angel for me from whom I am going to learn a lot. I am obliged to get these free lesson.

[@Basement-Science]

In my opinion learning about voltage dividers early like in schools, you never have any idea what they are even good for and may think they are pointless. That is, unless you come to the wrong conclusion and think you can just power your whole circuit from them. In this video I think you've both shown how they work and simple, practical examples where you encounter them. That's how everything should be taught!

[@jeffm2787]

I had this pretty much nailed down when I was 8, however I think it's a great video and these topics are good for people trying to learn.

[@lynxian-6097]

I'm a new subscriber and I finally got out of bed wanting to kickstart learning more about electronics (im stuck, finding good lectures is hard that i barely understood and lacking materials) It really works, wrote it and did that 10x rule, using that formula it works! My cheap multimeter didn't lie too, learning something like this is already flabbergasting to me already, even though there is a lot more

[@McTroyd]

If I'd had this explanation 30 years ago when I got into electronics, I'd probably be an EE now. In the pre-Internet world, this stuff was all over every book I read, but its fundamental relevance wasn't really explained well. In particular, I never made the link between "load" and "resistance" until a couple years' back. Until this video, I hadn't made the (obvious in hindsight) link that the wiring itself could present a voltage divider. 🤦‍♂️ Thanks much!

[@lasersbee]

Love the Fundamental Videos... Its been a while even though I saw the recent last one.

[@JR-rk5dr]

been a fan since highschool have taken 3 EE classes in uni (ME major) and to be honest your Vids gave me a better understandsing then those 3 semsters of work keep it up make :)

[@00Skyfox]

I always love these fundamentals videos. Thanks!

[@MichaelClark-uw7ex]

Playing with 555 timers and the voltage divider built into them is a great way to understand them. In fact some people say the 555 timer is named for the series of 5k resistors in the built-in voltage divider.

[@jdmccorful]

Good one! Enjoyed.

[@velanvasanth6545]

👏👏👏thanks a lot for teaching technical things...

[@petersage5157]

"Digital? Every ID-10-T can count to 1." I'm glad to see Dave returning to the Electronics Fundamentals videos. The absolute bog-standard jellybean TL072 has famously low input current, but even the most basic distortion pedal designs using 9V batteries and a voltage divider to produce the center voltage reference will typically have two 22K resistors (bypassed with 22-100uF in case of a noisy wall wart supply) *plus* individual ground reference resistors on the order of 220K. This is, again, because the input current is naff all, so the op amp doesn't have to source or sink much current to keep the input referenced to ground at the same voltage as the other input, and the build-out resistors help isolate the amplifier sections. In a multi-stage amplifier, the last thing you want is signal riding a rail from one stage to another, which will happen if an input is tied directly to ground with no current limiting resistor. We also used to see this on valve amplifiers that didn't have adequate decoupling between stages on the B+ rails.

[@juckis]

more fundamentals please, thank you. this vid was great!

[@Oberon4278]

I'm kind of surprised that you managed to go for 24 minutes straight just about voltage dividers, without any fluff, without repeating anything, and everything you covered was relevant and interesting.

[@rádiosantigos1958]

I guess that the impedance trap on the meters loading the circuits is very important when working on tube radios. Nice presentation!

[@10o01semih10o01]

Ahhh, just needed this video for school assignment. Thanks!

[@TheDrunkenMug]

Thanks Dave, verry interesting! 😀 Paul Carlson, down at Mr. Carlsons lab, made several pretty interesting videos in which he sometimes mentions circuit-loading a device under test while using modern test equipment like DSO's and DMM's. Then he goes about explaining how these problems were absent in the past due to having high-impedance VTVM's (vacuum tube volt meter). Interestingly, the second analogue meter you showed (but didn't use) is a FET volt meter. Most of the time these meters are based on the circuit design of the older VTVM's. Especially since Vacuum Tubes act alot like FET's themselves, albeit with allot higher voltages.

[@frankwalsh1379]

i need more fundamentals videos. Thanks dave

[@dhpbear2]

13:45 - Rth can also be found by replacing the voltage source with a short and measuring the resultant resistance: R1 // R2 :)

[@afourtrackmind]

Thanks again Dave

[@Abihef]

This is great. I've been building a lot of devices lately and designing but I keep getting confused at what node to reference, feel like an absolute beginner, somehow I swapped the order In my head recently when I was testing an idea in ltspice and now I keep switching it up in my schematics. The video is only just playing but this timing is great.👌😁😅 Thank you so much.

[@LZ1SSA]

Колега, желая ти много качествени ученици. 🙂

[@kaistutz7067]

awesome! more of that please :)

[@Limeayy]

I remember learning about Voltage Dividers in Automotive ECU's.

[@Nabilphysics]

Thanks dev for your time

[@zyghom]

I learned this in school - it took few months then. Nowadays 25min 20sec including all jokes - amazing ;-)

[@pranjal3727]

The cube and infinitely long series problem sucking my life in school🔥🔥

[@paulmillard1130]

Go for it Dave!

[@datnguyenp]

I never memorized voltage and current divider back in school. I just applied KVL and KCL, which are pretty much the same things

[@mgx9383]

6:40 "Good enough for Australia" "Near enough" That's why you have summer in December. ;)

[@johnanderson9619]

Resistors in series are cool, because they give voltage references. Resistors in parallel are cool because each set of voltage dividers current in parallel, is separate from the others current(s). Each voltage divider in parallel has it's own private current, and the total current is only taxed from the battery directly and separately from the total amount of voltage dividers in parallel in the circuit.

[@pyromen321]

You do such a good job with these whiteboard videos! I imagine it takes a good amount of planning to make these, and your effort really pays off!

[@EEVblog]

Planning? You must be new here :-> My plan constitutes pushing the record button and hoping something sensible comes out.

[@pyromen321]

@@EEVblog, haha I figured that was the typical workflow (for non-whiteboard videos), hence my comment! It’s even more impressive if you just whip out all these great little details off the cuff

[@siddharthmali5841]

Excellent.

[@myetis1990]

voltage dividers are everywhere, even in Dave's youtube channel :)

[@IanScottJohnston]

When I was at school and we started electronics we got the formulas but were were taught exactly how and where they were derived (early 80's).

[@elektron2kim666]

The rule of 2 resistors (of the same value) in parallel giving half is easier to think with by seeing "the extra wire" being added - so the flow got better and both resistors are now inefficient.

[@tdrelectronics766]

Another way to calculate thevenin resistance is short circuit any voltages and open circuit any currents so in your example short circuit the voltages so tthis parallels the 2 10k resistances to give 5K at time 13.57 in the video

[@stevenspmd]

I found this confusing when I started learning electronics; it wasn't until I started thinking of current as marbles in a pipe (i.e one goes in, ones pops out) that the current and the voltage drop/division started to make sense. The same analogy helps explains why a resistor that is only connected on one end has sees a voltage to ground.

[@roseelectronics4582]

You're doing great, Dave. I like you.

[@raymondbyczko]

It finally occurred to me over the years, is that 'shorting' a ckt, introduces a GND between R1 and R2 (in series). And so more current is pushed through R1, given V is constant, possibly damaging R1. So theres a connection between shorting, and voltage dividers.

[@hankdewit7548]

I always thought that the Thevenin impedance was calculated by shorting out the voltage source and "measuring" across the output. In your example we get the same answer as by shorting out the 10V source we end up with two 10k resistors in parallel, making 5k.

[@MatthewSuffidy]

Yes, the way I see it is the resistor tap points define the voltage gradient BUT the load on the taps can mess it up, the more the current vs the larger the resistor network values, the more messed up it will get. Parallel resistors are actual counterproductive because there are more paths for electrons. The whole point of resistors is they are mostly insulators that have only a finite number of paths.

[@Daveyk021]

DVM Input Impedance: Older Flukes (I do not know if modern ones are like this or not): In auto voltage mode, the input resistance was 10Meg ohms, in Manual Voltage range, is was 11Mohms. The high voltage probes only were accurate in manual voltage range mode. It's been too long, it may have been 11/10 megohms.

[@SixTough]

Thanks Dave you're a legend. Can you go depper into voltage versus current dividers? Like what to expect if I use AAA batteries, wall AC or something like a capacitor as a source? Which one will change in terms of practice?

[@robertmckelvey3091]

I had to use a voltage divider on the end of my bridge rectifier after two capacitors it was at 41 volts I dropped it down to 38 v and I hook up my power supply the voltage drops to 2.3 what's going on

[@thomasw6169]

Next in series: What is this resistor thing anyway ? (These basic series are great!)

[@bobwhite137]

Maybe you have this queued up for another time, but since you mentioned Vin on the left and Vout on right as a convention, it's probably worth mentioning that THE most important convention is that positive current flows into the positive terminal of devices. Darn Ben Franklin, he had a fifty fifty shot of getting it right...

[@miguelangelsimonfernandez5498]

Knowing the load (input impedance) is also important, actually paramout, in analog (AVO) voltmeters

[@cellularmitosis2]

Awesome!

[@jaguarpaw1638]

Thank you legend !!!!!!

[@liquidsonly]

I have a green haired troll too, given to me by a very attractive Australian. Sadly she's now back in Australia and I'm in rainy Wales. Oh, about the actual subject, thanks Dave. I used to work at a company that had an engineer did this sort of tutorial for us mere techies. Taught me a lot. I miss that job/place/time/aussie girl.

[@AJMansfield1]

My favorite type of "voltage divider" is the autotransformer. As long as it's the same wire gauge on the entire coil, they technically even work to divide DC (though your efficiency will be criminally bad lol).

[@raymondbyczko]

I like to remember parallel => product over the sum :)

[@sefarkas0]

Don't know where you are going with the series but you may want to present at some point solving the corner to corner resistance of a cube of resistors

[@harleyarmstrong5947]

Hi Dave, Thank you for the fundamentals video! I wanted to ask on the source video, but since you revisit the topic here I thought it would be a good time to ask. Is the thevenin equivalent circuit mainly useful for testing/designing batteries/power supplies since you can model the complex board you are powering with a single resistor, or does it have other uses outside of the implementation of the voltage/current source?

[@robbyxp1]

Very good

[@hansdegroot652]

Thx dave

[@mattb9664]

If only we had KZbin and EEVblog to assist with us 25 years ago through terribly written EE books with pages of errata sheets...

[@gandalf87264]

A young man who was interested in electronics came to me recently and explained to me that he was trying to run a small amplifier in his car on 6 Volts. He had read up on using resistors as voltage dividers and thought that would work, which off course didn't, so I introduced the LM7806 to him. Problem solved 😁

[@evensgrey]

Parallel and series resisters and capacitors have a some of other important uses. Because one of the factors controlling the price an assembly house will charge you for stuffing boards is how many different components are in the BOM, if you can use a combination of more common resistors or capacitors to get some of the values used rarely on your board you may be able to significantly cut your costs (or get the bard into the range of numbers of different components that more houses can handle, which can potentially get you a cheaper price by having more options and thus put you in a better shopping and negotiating position). (This is an engineering decision, so you will need to run the numbers to figure out what the best alternative is.) If you can be sure of the actual distribution of values for your parts ahead of time (which can be difficult, as many suppliers won't give you this kind of detail and only guarantee the parts to be withing the tolerance, not how they distribute in the tolerance) you can use multiple parts to get statistical reduction in the distance from the expected value. (This could be useful for high-frequency circuits where the exact values of parts can be critical but you can't get super-precise parts for some reason, or at least not all the parts at the super-precise values.) You can also use multiple parts to create redundancy if there's likely to be conditions that will cause individual parts to blow but the circuit needs to still operate (perhaps at decreased accuracy, but you still need it to work even if it acts funny). If you put, for example, two pairs or parallel resistors in series, you have the same resistance as any one of them, but you need to have at least two of them fail for the whole resistance array to fail. The circuit won't work properly with one failed, but it won't fail as easily as with only one resister, and there are times when it's better for a circuit to act weird than to just fail. (I'm thinking emergency equipment, where as long as it does something, it's still useful. An emergency pump controller that makes the pump go at the wrong speed is a LOT more useful than one that won't make the pump go at all. An emergency lighting controller that brings the lights to the wrong brightness is far better than one that doesn't make the lights do anything. And so forth.)

[@ShomiTheGreat]

Hey brother, you should totally do an in-depth hybrid model high-frequency BJT analysis for all cases (CC, CE, CB) and comparing those cases. It'd be a lengthy video, but, hey, nobody has explained the analysis properly on yt so far. You could also do the part 2 for FET analysis.

[@magnuswootton6181]

DACs use current division to get consequtive analogue divides just 1 wire each, its the coolest circuit that just uses resistance and natural raw electrical division to work.

[@utsavsapkota2137]

My laptop charger was making arking noise. So I opened it and it seems that the bottom of the pcb locking input dongle is sparking how can I solve this ?

[@johnanderson9619]

Analog to Digital is voltage dividers. With voltage dividers, you can make sleeping circuits. Voltage, Current, and Resistance all play together. Simple.... but very powerful. Resistors are king in the circuit world. imho.

[@dedr4m]

I use knowledge of voltage dividers to "calibrate" sensors on printers (mainly EPSON TMH6000 Version 4) where the voltage divider is for an analog pin input on the micro, the source voltage is off of the IR photo-transistor. Placing a "pull-up" resistor between 10K and 80K ohms fixes an issue/oversight where they sampled an analog voltage and that voltage (or IR-Xsistor) goes out of wack rendering the whole printer unusable.

[@robertlsvejda]

i always go offtrack but resistors in parallel, the rt is always lower than the lowest resistor value . capacitor discharge resistor value 470 ohms, 2k2 x4 ans a 3k3 ohm in parallel = 470. good for high voltage caps. make one , resistors, wire and aligator clip

[@KillerXtreme]

When can I expect to get my Diploma from Uni-Dave?