A fundamental electronic component that stores energy in an electric field, commonly used in filtering applications.
43
votes
11answers
32k views
What is a decoupling capacitor and how do I know if I need one?
What is a decoupling capacitor (or smoothing capacitor as referred to in the link below)?
How do I know if I need one and if so, what size and where it needs to go?
This question mentions many ...
23
votes
5answers
1k views
What's the use of a decoupling capacitor near a reservoir capacitor?
I've seen some circuits where a decoupling capacitor is used as well as a reservoir capacitor, like this (C4 and C5):
I've read about decoupling capacitors and for me it looks as if they are meant ...
20
votes
4answers
7k views
Can you make a non-polar electrolytic capacitor out of two regular electrolytic capacitors?
There was some discussion on this question
What are some reasons to connect capacitors in series?
What are some reasons to connect capacitors in series?
which I don't see as being conclusively ...
20
votes
3answers
3k views
Can I replace all electrolytic capacitors with ceramic ones?
I am designing the power supply circuit for a system that needs several supplies, my questions are:
Is it possible to replace all electrolytic caps (Mostly 100uF) by ceramic ones? What are the ...
19
votes
6answers
3k views
How to convert AC to DC
I am designing a circuit that needs to output 5VDC @ 1A. I'm trying to use a wall transformer to step the voltage down to 12VAC. The next step is the diode bridge and ripple capacitor.
The ripple ...
19
votes
6answers
922 views
Can we build capacitors on a PCB board?
For the magnitude of nF or µF capacitors, I hope I can build them on a PCB board. The capacitor is like a two metal layer and something between them.
Is this possible?
Not buying the capacitor, ...
17
votes
6answers
4k views
Decoupling capacitors: what size and how many?
Lots of chips nowadays require smoothing capacitors between VCC and GND for proper function. Given that my projects run at all sorts of different voltage and current levels, I was wondering if anyone ...
17
votes
4answers
836 views
Supercap compared to a battery
What is the current state of things when it comes to super capacitors and batteries? Are super caps anywhere near rivalling LiPo's in capacity? I've often heard people talking about super caps as ...
17
votes
2answers
384 views
Should I discard my inventory of old electrolytic capacitors?
I have been doing hobby electronics for more than 10 years, and some of my electrolytic capacitors are easily that age. They seem to work just fine and do not show corrosion or other visible defects, ...
16
votes
7answers
1k views
Why do capacitors lose capacitance in series?
Unlike rechargeable batteries, capacitors have a lower capacitance in series. Why is this and if I charge each cap separately and then put them in series, will it still be a lower capacitance?
16
votes
4answers
4k views
What's the purpose of two capacitors in parallel?
What's the purpose of the two capacitors in parallel on each side of the regulator in
this power supply circuit
I've seen similar setups in other similar circuits and can guess that it's related ...
15
votes
9answers
16k views
Why use capacitors?
Why do you need to store the voltage for some time in a capacitor? I've always assumed circuits to work when you power it on and stop when you power it off.
Why can't the whole circuit be drawn ...
15
votes
8answers
4k views
What are some reasons to connect capacitors in series?
Usually you either combine capacitors in parallel because you want to increase the total capacitance while fitting the components in a certain shape/position, or you just combine capacitors by buying ...
14
votes
4answers
4k views
Do electrolytic capacitors have a limited shelf life?
Do electrolytic capacitors have a limited shelf life? I would like to know for both aluminium and tantalum.
13
votes
10answers
20k views
Blink an LED with just a capacitor?
Is it possible to blink an LED using just a capacitor? (and maybe a resistor).
For example, if I want to LED to blink once every 2 seconds. Is that possible?
I know it can be done with a 555 as well ...
12
votes
6answers
4k views
How to find the ESR of a capacitor
I am building a power supply circuit. The Switching Regulator calls for a low ESR output capacitor.
What does "low" mean? How low?
Also, how do I find or calculate the ESR for a capacitor whose ...
12
votes
8answers
3k views
Organizing electronic parts?
I've got one of these cabinets, which I intend to use for storing electronic components:
It has 24 drawers (each 175 x 69 x 37mm).
Every drawer can be subdivided into up to six compartments by ...
11
votes
4answers
2k views
What is the role of capacitors in DC circuits like motherboard, graphic card etc?
I was just reading in Capacitors in DC Circuits that "Capacitors do not play an important role in DC circuits because it is impossible for a steady current to flow across a capacitor". I think it ...
11
votes
4answers
3k views
“Starter Kit for electronics” - What to buy?
I'm going to buy some things for back to the electronic world.
Starting with an Resistor Assorted Kit.
Need to buy some kits containing the most common capacitors and transistors... what to buy???
...
11
votes
4answers
330 views
Ceramic or Electrolytic caps for a switching buck regulator?
I'm using the LM2734Z, which operates at 3 MHz. I'm using it to step down 4.8V-20V down to 3.3V +/-5%.
Does anyone know if is better to use ceramic capacitors or electrolytic capacitors in this ...
11
votes
1answer
1k views
Why shouldn't electrolytic capacitors be short-circuited?
In the answer to another question, I read that it's bad to short-circuit electrolytic capacitors. Why is that? What happens if I do?
11
votes
5answers
2k views
Frequency dependence of electrolytic capacitors
It's said that electrolytic capacitors behave as inductors at high frequencies, which is why we put small ceramic caps in parallel with them:
Electrolytic, paper, or plastic film
capacitors are ...
11
votes
3answers
7k views
How can I quickly and safely discharge a charged capacitor (small and low voltage; <= 42V)?
I am learning how to use capacitors (ceramic and electrolytic from 1pf - 1000uf) and am trying out various experiments using a breadboard. I am constantly adding/removing things to my layout to see ...
10
votes
9answers
18k views
How does a capacitor block DC?
I am confused with this! How does a capacitor block DC?
I have seen many circuits using capacitors powered by a DC supply. So, if capacitor blocks DC, why should it be used in such circuits?
Also, ...
10
votes
3answers
8k views
When to use Capacitors?
This is probably the dumbest question ever, but I am an electronics nublet.
I understand what capacitors do, and I've been reading beginner Electronics books and such, but I don't quite understand ...
10
votes
4answers
815 views
Can you store energy in an inductor and use it later?
My company uses supercaps to power the device if power is cut. I was wondering if you could do the same thing with an inductor. If you can't, why not?
10
votes
5answers
997 views
Are decoupling caps necessary for analog ICs (e.g. LM339, LM324…)?
Often 100n to 1µF decoupling caps are placed across IC supply lines for digital logic.
For analog circuitry, are decoupling caps necessary when the environment is also shared by microcontrollers and ...
10
votes
1answer
584 views
How can a capacitor in a disposable camera shock you?
The battery in a disposable camera is usually a single 1.5V AA battery. It charges a large capacitor. When the capacitor is fully charged, it will contain a voltage very close to 1.5V correct?
If ...
10
votes
3answers
2k views
Arduino in car: capacitor for extra 3 sec of power
I want to install an Arduino Uno in a car, powered by a consumer 12V->5V car voltage regulator plugged into the lighter socket. The socket is switched, i.e, there's no power when the motor's off. When ...
10
votes
1answer
1k views
Possible causes for AAA battery to explode
Today, the AAA battery in my remote control exploded. The "pop" sound is pretty loud. I've been using this remote control for years, and I'm more inclined to believe that it is the battery issue ...
9
votes
7answers
4k views
Inductor vs a capacitor
Hi am a Trainee electrician and pc hardware enthusiast. I was just wondering why a mixture of inductors and capacitors are used on motherboards? Why not just use capacitor? I thought the inductor ...
9
votes
3answers
404 views
What is the lowest capacitor voltage rating that is safe to use?
I'm using a few Case R tantalum capacitors (10uF 6.3v) as bulk decoupling on the 3.3v power of a 100mbps Ethernet phy. I am also using 0.1uF ceramics closer to the pins.
As usual, I'm terribly ...
9
votes
4answers
734 views
Will a 0402 0.01uF cer cap next to a 0402 0.1uF cer cap have any power decoupling benefits?
I always understood that the point of using smaller caps in parallel was to provide low impedance at higher frequencies than the bigger caps, BECAUSE the higher capacitance caps 'usually' had larger ...
9
votes
4answers
8k views
How do I calculate how fast a capacitor will discharge?
Say I have a 1F capacitor that is charged up to 5V. Then say I connect the cap to a circuit that draws 10 mA of current when operating between 3 and 5 V. What equation would I use to calculate the ...
9
votes
3answers
371 views
energy in capacitors
The energy stored in a capacitor is
$$ U= \dfrac{1}{2} CV^2 $$
So when I have a 1F supercap charged to 1V the energy is 0.5 J. When I connect a second supercap, also 1F in parallel the charge will ...
9
votes
5answers
990 views
What are Y5V or Z5U capacitors good for?
I was thinking decoupling, but you would have to overdimension them because of the high tolerance and temperature stability. And doesn't a 1uF capacitor (instead of 100nF) have the same inductance ...
9
votes
2answers
2k views
Can I swap an electrolytic capacitor with one with a higher voltage?
I wish I knew more about this stuff, but alas I do not. I have a radial lead aluminum electrolytic capacitor (rated 470mF and 25v) that died on me. Can I swap it out with one rated at 35V, or do I ...
9
votes
2answers
1k views
What is an AC voltage rating for a capacitor?
I thought the only thing that mattered was absolute voltage across a capacitor puncturing the dielectric, but there are some that have an AC rating, too. What does this mean? Why does the value ...
8
votes
6answers
904 views
Paper in oil (PIO) capacitors: what is special?
Many audio circuits use PIO capacitors. What are the electrical Characteristics of PIO caps that make them special (i.e. justify the cost)? Which parts of an amplifier circuit benefit most from the ...
8
votes
5answers
292 views
Sourcing parts for Really, Really low frequency filters
I'm doing a project at work that has a couple of esoteric requirements, particularly for a 0.1 Hz (0.07 Hz really, due to part availability limitations) Highpass filter (in the data acquisition ...
8
votes
3answers
380 views
Why are capacitors sold with imbalanced tolerances?
Short version: Some capacitors (and presumably some other components) are sold with imbalanced/asymmetrical tolerances. Why?
Explanation:
Many ceramic capacitors are marked with, for example, +80% ...
8
votes
3answers
322 views
How safe are pre-charged supercaps compared to pre-charged batteries?
How safe is it to transport and sell pre-charged supercaps with a system?
I'm designing a solar-powered system and I'd like to use something like a
Maxwell's BCAP0005 supercap (2.7V, 5F) to store ...
8
votes
5answers
1k views
How to have arduino only turn on when enough power has been collected?
There was recently an article in the Christian Science Monitor about the launch of a cracker-size satellite. The article says that the satellite has, "power storage in capacitors, and switching ...
8
votes
1answer
219 views
How does ESR affect cutoff frequency calculations for capacitors?
I'm interested in estimating the cutoff frequency of a capacitor in a simple RC circuit. Since the capacitor and resistor are in series, can I simply add the ESR value to the resistor value?
For ...
8
votes
3answers
1k views
Voltage ratings of capacitors: ceramic vs electrolytic
Now I know when it comes to electrolytic capacitors it's usually good practice to use a voltage rating 1.5x - 2.5x the maximum rating you ever expect the capacitor to be exposed to, as the lifetime ...
8
votes
4answers
4k views
Various Small capacitors' markings?
Wikipedia explains the basics about the markings of capacitors, here. It lacks many markings most of which confuses me:
Ceramic brown-yellowish cap
104 K5K (small ) --- what is the end "5K"? ...
8
votes
2answers
2k views
Why connect capacitors to motor body?
So I've found a motor circuit which looks like this:
Since many users here believe that my hand-drawn circuit schematics are in fact pictures of flying spaghetti monster, I'll also provide a ...
8
votes
2answers
634 views
ESR and ESL, small package vs large (SMD)
I was wondering if someone could explain why larger package capacitors (1210) are supposed to have more ESL and ESR than a smaller - say 0603 package?
I would imagine the larger package is still ...
7
votes
5answers
2k views
Do capacitors automatically release their energy over time?
Will a capacitor automatically release its energy over time? Or will it stay in there until manually discharged?
So let's say I've had an old computer sitting around for a year and decide to take ...
7
votes
3answers
682 views
Memory backup capacitors: why a capacitor?
Why would an engineer choose a memory backup capacitor instead of any of the types of rechargeable batteries available?
Their energy density seems far poorer, and they can't hold their charge very ...
