Help a newb understand capacitors?

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#1
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Hey everyone,

I'm just beginning with electronics and I'm still a bit confused on exactly how a capacitor is used. I keep reading that they can be used to clean up noise and provide for quick pulses of current. Can anyone explain exactly how and when I should be integrating capacitors into my circuits?

Thanks!

Ben

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Quote:

Can anyone explain exactly how and when

Probably not, as they are used for many different purposes. If someone tried to write the "All uses of capacitors" document it would be a saunting task. What toy could do is search this aite for "decoupling" (and variant "de-coupling"). Aslo "coupling capacitor", and go for "supply", "filter" also. Then do the same on Google, and Wikipedia.

In order to use capacitors you must understand what they do electronically/physically. Wikipedia will teach you some of it, and other Internet finds will help to.

What you also should do is get yourself a good book on electronics. Being more precise about "good" is tougher though as it depends on both your ambition, and your previous knowledge in eg physics. If you really want to buy a book that probably stays with you for a long time and does good service then look for "The Art of Electronics" by Horowitz & Hill. Not cheap, but worth its price and more.

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You might as well have asked: How to use water?
The properties of capacitors makes it suitable for a lot of different purposes.
The most common in digital electronics is to keep signals clean by letting the capacitor "suck up" the differences in voltage, keeping the voltage at a steady level.
In analog electronics the properties of capacitors will block DC and let AC pass through. This will be useful in a lot of ways.
Different capacitor-values will take different time to "charge" and can therefore be used to create filter circuits blocking AC-signal below certain frequencies and letting other frequencies through.
There must be tons of information about capacitors on internet...
Try this for a start
http://en.wikipedia.org/wiki/Cap...

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Like I said, I've been reading about them - and yes, I understand it's a very broad question. What I'm trying to do is fill in the blanks. You pointed me to Wikipedia; so quoting an excerpt from the article:

Quote:

Energy storage

A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory.)

.

How would I apply this in a circuit? How much voltage/current will be supplied from the capacitor? How long will it last?

The problem is that every article I'm reading has great information/theory on the general usage of capacitors but doesn't really touch on any real-world applications to help me understand.

Thanks for your help everyone, I'm new to this so its a little hard to ask the right questions.

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Why not get some capacitors and see what happens?

Leon

Leon Heller G1HSM

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http://www.stanford.edu/class/ee...

The very first hit on google with "capacitor usage". Go down, and look at the examples...

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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uidzer0 wrote:
Can anyone explain exactly how and when I should be integrating capacitors into my circuits?
Whenever the circuit you're building shows them in the schematic =)

If you're simply interfacing IC's, you'll likely find application notes that show the recommended circuit for the IC. It should list any required capacitors and maybe even explain why they're there.

If you're adding other blocks to your design, then you should be able to find (read "google") circuits of that type and find myriads of info on what capacitors might be required where and why.

If you're trying to design your own circuit, then either you're probably doing something that someone else has already done (see previous paragraph) or you should know enough about the circuit you're designing to already know where the capacitors should be and why.

If you're just asking "Hey, I read that there's these neat capacitor things, where should I stick them?", then you're basically saying "Hey, I read that there's this neat sticky stuff called duct tape. Where do I stick it?". They've got their uses, and in any particular application, it's easy to see why it's there, but describing all the places you could think of to use it would take forever.

you're probably better off learning about a specific application than about capacitors in general. Start with power supply bypassing and learn about those. Googling "power supply bypass capacitor tutorial" found a few pages.

After than, maybe learn about RC filters or RC oscillators, or coupling, to name a few.

Clancy _________________ Step 1: RTFM Step 2: RTFF (Forums) Step 3: RTFG (Google) Step 4: Post

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You might want to try asking santa/satan for the latest Radio Shack xx-in-one electronics kit.

Try Wikipedia as well.

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Quote:
How would I apply this in a circuit? How much voltage/current will be supplied from the capacitor? How long will it last?

The problem is that every article I'm reading has great information/theory on the general usage of capacitors but doesn't really touch on any real-world applications to help me understand.


Try googling for Super Cap and you will find some real-world examples.
Datasheet for them will tell you how much can be stored.

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But he wants the integrating capacitors... the kind that you use in the feedback loop of the opamp to change square waves into triangle waves....

Imagecraft compiler user

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Because a picture is worth a thousand words, I will try to explain capacitor usage graphically :)

Attachment(s): 

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Thanks everyone, you've all been very helpful. With any luck I'll get my first AVR in the mail today :mrgreen:

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Capacitors are funny devices, in that they try to keep the voltage constant, while sucking up the excess as current. Inductors do the opposite, trying to maintain the current flow by sucking up voltage.

Place a capacitor in a DC circuit and it'll act as a short circuit for a very short period of time, gradually leading to completely open circuit when charged. Since current always follows the path of least-resistance, placing then in a circuit means that they'll charge up, then try to maintain a steady voltage (absorbing noise or spikes, hence their use as decoupling for digital circuits).

Large capacitors on a DC line will usually have both a bleed resistor (slowly dischanging the capacitor over a long period of time (like in TVs, for safety) as well as a resistor to limit the rush of in-current into the capacitor, to prevent it from blowing up the power supply.

Capacitors act as short circuits to AC voltages, over a specified frequency range. That makes them ideal for use in amplifiers, coupling one part to another. They block out DC but pass the AC, which means that any DC offset to an audio signal from an amplifier stage is removed when the amplified signal is fed to the next stage.

Capacitors also take a time to charge up, and so can be used with a resistor to make simple oscillators.

You'll also find circuits exploiting capacitor's ability to only allow certain AC frequencies, to act as a filter.

- Dean :twisted:

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abcminiuser wrote:

You'll also find circuits exploiting capacitor's ability to only allow certain AC frequencies, to act as a filter.

- Dean :twisted:

That's a little confusing, Dean; capacitors aren't sensitive to 'certain' AC frequencies. Instead, perhaps we should say that their changing impedance (strictly, reactance) to differing frequency signals can be used to build filters.

Neil

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well, they have quite a few uses... as has been said.

they are often used to help crystals oscillate, for that really you should check your uCs datasheet.

another use is to smooth power supplies, usually power supplies will be quite noisy, and could spike or drop below what they should.

i think the best analogy is to think of a capacitor as a bucket with a hole in it that will only let water flow out at a certain rate, so that any spikes wont get through, or if the power drops out for a (very) tiny amount of time keeping the uC powered.

to be honest, your best option would be to buy a "selection box" (box with various amounts of different value capacitors) of tantalum capacitors if you are experimenting.

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There's caps in analog circuits where they are used for 'frequency dependent resistors' in filters, and dc blocking in interstage coupling. Then there's caps in digital circuits where they are mostly used as little distributed 5V batteries near all the chips that suck big slurps of current.

Imagecraft compiler user

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bobgardner: Weren't caps used in digital stuff also as "derivators"? You know, you have a signal, say, square, 50:50, and you need only to get a "needle" at the start.?

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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That's a 'differentiator'... using RC circuits to detect edges is a cheap trick and temperature sensitive... not best practice

Imagecraft compiler user

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Reading the original TOPIC post, I never would have thought this would have turned into such a great thread..

John

Just some guy

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Quote:

think the best analogy is to think of a capacitor as a bucket with a hole in it that will only let water flow out at a certain rate, so that any spikes wont get through, or if the power drops out for a (very) tiny amount of time keeping the uC powered.

I would rather go with a barrel with one pipe at either end, and a rubber membrane in the middle.

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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Hello,

In his book, PRACTICAL ELECTRONICS FOR INVENTORS, Paul Scherz uses a groovy water analogy (he also uses similar analogies to explain the operating principles of many semiconductor devices). I have never before seen someone go to such lengths to simplify explanations.

John

Just some guy

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I think the water analogy is definitely the most common one used when it comes to describing voltage, current, resistors, capacitors, transistors, etc.

I know it helped me out when I first started to figure it all out =)

Clancy _________________ Step 1: RTFM Step 2: RTFF (Forums) Step 3: RTFG (Google) Step 4: Post