Load between battery and capacitor - Page 1
Forum section: electronics / beginners

author: jacau
author_rank: Contributor
timestamp: November 19, 2021, 09:52:08 am
content: I don't have a specific example for this question but I have read decoupling caps have to be right near the VCC pins on an IC so their placement is easy to understand.But with the larger capacitors, should power from the battery also be behind them from the perspective of the load?If a large cap was at the end of the power line with the load in the middle, would that setup be less that ideal?Thanks

author: Zero999
author_rank: Super Contributor
timestamp: November 19, 2021, 12:56:35 pm
content: Decoupling capacitor should ideally be as close to the load, as possible. The idea is the voltage drop doesn't drop, as the load draw large current pulses. It's true, larger capacitors are normally a little further away from the load, but they should still be as close as possible.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 20, 2021, 06:28:47 pm
content: The issue with bypass caps, is they discharge backwards as well as forwards so watch out for that one.

author: David Hess
author_rank: Super Contributor
timestamp: November 20, 2021, 06:43:03 pm
content: The best location for the bulk decoupling capacitors depends on how power distribution is laid out because it may serve as an AC termination. Usually bulk decoupling capacitors are found at the output of the regulator, where they are also part of the regulator's frequency compensation, and at the power input of each printed circuit board or independent power plane, where they serve as an AC termination. They are sometimes also found as local decoupling between the power distribution on a circuit board and a specific circuit which is susceptible to or or generates noise.Quote from: jacau on November 19, 2021, 09:52:08 amYes.QuoteYes.In both cases, the result is extra lead length which adds to the ESR and ESL of the capacitor. Sometimes you can find circuit layouts where a 4-wire connection is made to the bulk capacitors, as shown below, for exactly this reason. The original much longer capacitor was wired the same way, and the circuit board has two attachment points for each capacitor lead.

author: ogden
author_rank: Super Contributor
timestamp: November 20, 2021, 06:55:21 pm
content: Quote from: Capernicus on November 20, 2021, 06:28:47 pmSorry, but you better explain what you are talking about here.Quote from: jacau on November 19, 2021, 09:52:08 amIt usually depends on impedance of the battery versus it's capacity. For example there are applications which require infrequent high current bursts of load - then bulk storage capacitor (or even supercap) is needed, to avoid requirement for hi-current battery. One example would be - low power sensor which is RF- transmitting it's state few times per day.

author: jacau
author_rank: Contributor
timestamp: November 21, 2021, 05:41:14 am
content: Great, thanks everyone for the information!

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 21, 2021, 08:13:18 am
content: Quote from: ogden on November 20, 2021, 06:55:21 pmIn the case of a ac->dc converter, the smoothing cap will discharge back into the diode bridge. And more, if you want to try out more topologies.

author: Zero999
author_rank: Super Contributor
timestamp: November 22, 2021, 08:15:22 am
content: Quote from: Capernicus on November 21, 2021, 08:13:18 amThe diode bridge doesn't conduct in the reverse direction, so the smoothing capacitor can't discharge back into it.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 22, 2021, 03:20:26 pm
content: If a diode is open, it allows current in both directions as long as the net flow isn't reverse biased.

author: tooki
author_rank: Super Contributor
timestamp: November 22, 2021, 03:36:13 pm
content: Quote from: Capernicus on November 22, 2021, 03:20:26 pmBruh…

author: LaryPant
author_rank: Contributor
timestamp: November 22, 2021, 07:20:40 pm
content: Quote from: Capernicus on November 22, 2021, 03:20:26 pmFor any beginner reading this in the future:The quoted statement is completely wrong!If something isopenin electronics then there is by definition no electrical current flow.It is, however, true that there is current flowing across the p-n junction of an open diode, namely the drift and diffusion currents, which are equal but in opposite direction and the net current is therefore zero. This does NOT mean that electrical current flows through an open diode, but just internal currents which can be explained with semiconductor physics.In circuit theory an open diode means NO current flow!

author: Zero999
author_rank: Super Contributor
timestamp: November 22, 2021, 09:22:41 pm
content: Quote from: Capernicus on November 22, 2021, 03:20:26 pmNo. Look at the diodes. They all point upwards and will be reverse biased by any voltage applied to the output.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 01:14:43 pm
content: I meant the diode being "closed", when its passing current.Here is a Walter Lewin drawing-> (but I added a diode to it.) - its like a H-bridge, except just with resistors.The diode has more current going through it downward, because of the resistance, so then it conducts, but when it conducts itll also allow the reverse current at the same time, so it goes back through the diode as well as forward through.If the diode was upwards - then all current will be stopped in the cross-line, but it will still be blasting through the side channels.

author: Zero999
author_rank: Super Contributor
timestamp: November 23, 2021, 01:34:25 pm
content: Quote from: Capernicus on November 23, 2021, 01:14:43 pmThat's not a bridge rectifier and does not represent one.If you charge up a large capacitor and connect it to the output of a bridge rectifier, + to anode and - to cathode, no current will flow, except a tiny leakage.Look at the schematic I posted above. The cathodes go to the + output and anodes, to the - output, so current can't flow in to the bridge, from the output, using conventional current flow.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 01:50:34 pm
content: Its not supposed to be a bridge rectifier, but its demonstrating a point that if a diode is forward biased, then it is open to conduct in both directions, not just forwards. if its reverse biased, it wont conduct in either direction.So what I'm meaning is to do with ac->dc conversion -> The "smoothing" capacitor might conduct backwards, if the ac power source has opened for conduction the diode for it.

author: Zero999
author_rank: Super Contributor
timestamp: November 23, 2021, 03:00:34 pm
content: Quote from: Capernicus on November 23, 2021, 01:50:34 pmYou're contradicting yourself. A diode can't be forward biased and conduct in the opposite direction. If a diode conducts in both directions, then it's broken.QuoteNo, because the diodes will be reverse biased. The smoothing capacitor will not conduct backwards, as you say. And the last bit "the ac power source has opened for conduction the diode for it." is meaningless.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 03:32:43 pm
content: Take it or leave it, that's what I believe up till now.

author: fourfathom
author_rank: Super Contributor
timestamp: November 23, 2021, 04:27:36 pm
content: Quote from: Capernicus on November 23, 2021, 03:32:43 pmAre you perhaps thinking about a diode biased to pass or block an AC signal? Such as a PIN diode? In this case, yes, a signal can flow "backwards" (source and load can be on either side of the diode), but still, the net current flow is forward when the diode is "on", and when the diode is reverse-biased ("off") there is no current or signal flow (ignoring leakage, parasitic capacitance, etc.)

author: Zero999
author_rank: Super Contributor
timestamp: November 23, 2021, 05:18:06 pm
content: Quote from: Capernicus on November 23, 2021, 03:32:43 pmWell you're belief was mistaken. If there's no load on the rectifier, current only flows into the capacitor, as it charges up, then falls to zero.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 05:28:51 pm
content: My belief isnt mistaken, but yes, it looks like you are correct that it doesnt happen through a diode bridge from the smoothing cap, on my own re-inspection. I hadn't looked at it that hard before, but it looks like one of the diodes conducts, when the other doesnt, and that one that isnt conducting stops the cap from self-discharging behind.But it can happen in different machines than this, there's always the possibility that a bypass cap is going to charge back down the machine as well as in front.It comes up when you have a "multi-rail" when your powering more than one unit off the same battery, it can happen there too, and can just go straight backwards through the diode, given the specific situation.

author: fourfathom
author_rank: Super Contributor
timestamp: November 23, 2021, 06:00:39 pm
content: Quote from: Capernicus on November 23, 2021, 05:28:51 pmCan you please describe this specific situation? Something to do with minority carrier lifetime? Yes, this can allow a small amount of reverse current to *briefly* flow.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 06:14:11 pm
content: Quote from: fourfathom on November 23, 2021, 06:00:39 pmIt can happen on your rail, negative and positive. Maybe there is a way to correctly guard a rail with diodes (I havent thought about it enough yet.), but theres also incorrect ways, which is what I'm talking about.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 23, 2021, 06:21:07 pm
content: Quote from: Capernicus on November 23, 2021, 01:50:34 pmBoth directions but not forward? How many directions does that leave open?Quote from: Capernicus on November 23, 2021, 01:50:34 pmThe only difference between "forward" and "reverse" -biased is the sign of the applied voltage. So you can simplify the whole mumble jumble by stating that a diode only conducts current in one direction.

author: fourfathom
author_rank: Super Contributor
timestamp: November 23, 2021, 06:22:57 pm
content: Quote from: Capernicus on November 23, 2021, 06:14:11 pmThen please describe an incorrect way, where the diode is conducting in the reverse direction. A "rail" is just another node in a circuit. Can you be more specific?

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 07:23:43 pm
content: I mean this...

author: fourfathom
author_rank: Super Contributor
timestamp: November 23, 2021, 07:31:42 pm
content: Quote from: Capernicus on November 23, 2021, 07:23:43 pmI don't see how, the diodes in series with the capacitor will block any discharge current. And those two "2nd rail member" diodes are shorting out the two rails (with a 2-diode voltage drop), so the capacitor actually has about zero volts across it anyway. Let's just say I'm confused by your example.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 07:36:20 pm
content: Just imagine a bit of equal resistance there, and it works fine.Yes, the diodes dont block the discharge current, thats what I meant, If you were putting diodes there to block the discharge current it doesnt work, because the current is going two ways through the diode at the same time.

author: Manul
author_rank: Super Contributor
timestamp: November 23, 2021, 07:45:09 pm
content: Quote from: Capernicus on November 23, 2021, 01:50:34 pmActually Capernicus is quite correct here. When diode is forward biased and it ison, it can conduct both directions in a sense, that it remainsonfor some time after reverse bias voltage is aplied. Practical diode is not ideal, it has forward drop, reverse recovery time, reverse breakdown voltage, capacitance and some other things which we usually don't want, but it's there. Sadly, other statements are seriously messed up.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 07:49:28 pm
content: Quote from: Manul on November 23, 2021, 07:45:09 pmFrom what I looked at it. (That the other poster was kind enough to set up a simulation of, thankyou.) In an ideal sense it looks like the diode behind is left uncharged by the battery when the front diode is charged, so the back diode actually stops this phenomenon I'm talking about in the happenstance of the ac->dc converter.So that gives me an idea. if you use a diode bridge, you can actually separate your rail with it - and it stops cap discharge?

author: Gyro
author_rank: Super Contributor
timestamp: November 23, 2021, 08:43:02 pm
content: Can you please stop posting facebook links, they will become orphaned and useless. If you have images to attach then please attach them to your posts.

author: ogden
author_rank: Super Contributor
timestamp: November 23, 2021, 08:55:36 pm
content: Quote from: fourfathom on November 23, 2021, 07:31:42 pmRight. Electricity and Electronics does not work according to beliefs. You want to know something first before you give lessons to anybody.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 09:07:21 pm
content: One day I'll go and proove this one with prototypin', but I'm always so tired and have plenty of other things to do than continue on with my electronics theory atm.I'm doing programming, mech logic + ceramics, other than this, so I can only do one thing at a time. I'm just about ready to drop unconscious I'm so busy.

author: SL4P
author_rank: Super Contributor
timestamp: November 23, 2021, 09:10:37 pm
content: I’d love to see some of the software you’ve created.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 23, 2021, 10:00:19 pm
content: I haven't got much programming done in a while either, But I did this inverse kinematics for this here little 4 legged spider.And a really wierd one, its cranks connecting to cranks to cranks, for a step up transmission, I've actually improved this design now so It can reverse cycle direction and step down as well as step up.Note I had to compute inverse kinematics all the way down the chain to get that, I'm still yet to print it out to see if it works.Thats programming inside the OPEN-SCAD language, for CAD. But I actually coded OPEN-SCAD in visual studio before I found it existed already, Heres the video to proove it->

author: fourfathom
author_rank: Super Contributor
timestamp: November 23, 2021, 11:20:52 pm
content: Quote from: Manul on November 23, 2021, 07:45:09 pmSure, reverse recovery time, minority carrier lifetime, etc. But these are transient effects and not what I believe Capernicus is talking about, and certainly not effects that will discharge a bulk "smoothing" capacitor. If he is, I wish he would clarify. Sorry, this is making less and less sense.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 24, 2021, 12:04:29 am
content: Quote from: fourfathom on November 23, 2021, 11:20:52 pmYes I dont mean that. I thought it was a possibility that the cap could discharge through the diode bridge because the ac power was activating the diodes, but it turns out another one of the diodes stops the cap discharge separately.

author: fourfathom
author_rank: Super Contributor
timestamp: November 24, 2021, 05:08:24 am
content: Quote from: Capernicus on November 24, 2021, 12:04:29 amI think this "activating the diodes" is the root of the misunderstanding. As long as we aren't considering leakage, capacitance, or minority carrier lifetime, current will not flow "backwards" through a diode regardless of its previous state. However, I think you still believe otherwise.

author: Zero999
author_rank: Super Contributor
timestamp: November 24, 2021, 08:29:13 am
content: Quote from: Capernicus on November 23, 2021, 09:07:21 pmYou seem to have plenty of time to argue the toss. It would be better spend it prototyping, before asking questions.

author: ogden
author_rank: Super Contributor
timestamp: November 25, 2021, 09:15:31 pm
content: Quote from: Capernicus on November 24, 2021, 12:04:29 amIf you got diode property wrong then clearly you would want to learn ALOT before even trying to spread your (clueless) wisdom in "I know it all" style. Oh, and I am not even talking about ridiculous circuit with two series diode short in it...

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 26, 2021, 12:31:03 pm
content: Quote from: ogden on November 25, 2021, 09:15:31 pmMy model of electricity is incomplete and approximate, if yours is too I wont attack in the forumm of saying that it doesnt work most the time anyway, everyone has their little guesses of whats going on, sometimes it works out, sometimes it doesnt, the ending details of what actually happens I think 99% of ppl get it wrong (so u have to do experiments to proove ideas.), so I dont get anything perfect myself either, and I think that's all you need to get your machines up and running, being perfect would be good but its not the end of the world if you get things wrong, as long as u test all your ideas just to make sure of the missing details.

author: tooki
author_rank: Super Contributor
timestamp: November 26, 2021, 12:50:28 pm
content: Quote from: Capernicus on November 26, 2021, 12:31:03 pmThe problem people have with you isn’t your lack of knowledge (because indeed we all started at zero), but your attitude.Despite the fact that your level of knowledge is… limited (and that rather than filling the gaps with “I don’t know”, you’ve filled them with your own hypotheses), you act as though you were an expert, making incorrect proclamations and telling others (whodoknow what they’re talking about) that they’re wrong, when in fact it’syouwho is wrong.Before you start schooling others, you need to:a) expunge your brain of all the answers that you’ve simply made up (as they are not a viable foundation for subsequent learning), andb) learn a LOT more (as in formal learning, not just experimenting and conjecture)

author: fourfathom
author_rank: Super Contributor
timestamp: November 26, 2021, 03:57:36 pm
content: To repeat myself, I think this "activating the diodes" is the root of this particular misunderstanding. Capernicus, please study it a bit more. I think you will find that you have it wrong.

author: Zero999
author_rank: Super Contributor
timestamp: November 26, 2021, 07:05:47 pm
content: Quote from: Capernicus on November 26, 2021, 12:31:03 pmThere are a few people here who understand how diodes work, down to the electron level, but even I know that you're wrong. 99.99% of people here don't get it wrong. Those who do was probably in the minority here.As mentioned above. You need to change your attitude. It's fine to make guesses, but stop acting as though you're certain, when you're just making assumptions.

author: fourfathom
author_rank: Super Contributor
timestamp: November 26, 2021, 07:53:41 pm
content: Quote from: Capernicus on November 26, 2021, 12:31:03 pmThe problem here isn't a missing detail though, but a complete misunderstanding of a fundamental principle. Hey, I had to learn this stuff too.