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Questions tagged [capacitor]

A fundamental electronic component that stores energy in an electric field, commonly used in filtering applications.

178
votes
16answers
148k 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 ...
89
votes
6answers
27k views

Are tantalum capacitors safe for use in new designs?

I've heard it suggested that "solid tantalum" capacitors are dangerous and may cause fire, may fail short circuit and are fatally sensitive to even very short over voltage spikes. Are tantalum ...
67
votes
6answers
32k views

Ceramic caps vs electrolytic. What are the tangible differences in use?

A quick google around and all I seem to be able to find are people talking about the physics & the chemistry of the capacitors but not how this affects choosing which to use. Avoiding talking ...
65
votes
14answers
25k views

My understanding of RC circuits is broken

I asked a relatively simple question. Unfortunately, the answers provoke far more questions! :-( It seems that I don't actually understand RC circuits at all. In particular, why there's an R in there....
64
votes
11answers
49k 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 ...
58
votes
9answers
208k 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, ...
55
votes
5answers
9k 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 to ...
51
votes
8answers
42k 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 ...
50
votes
4answers
55k 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 ...
49
votes
4answers
78k 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 to ...
43
votes
5answers
10k views

Why do 1 pF capacitors exist?

What kind of uses do engineers find for 1 pF or lower-value capacitors? This is the kind of value one gets with two bits of wire close to each other or two tracks.
42
votes
8answers
13k 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, ...
40
votes
9answers
89k 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 ...
36
votes
2answers
6k views

How did this capacitor survive having a nail driven through it?

How did this metal film 1 uF 630 VDC polystyrene capacitor survive having a nail driven through it while under a voltage of 122 VAC? It is part of UL testing for potential X or Y grade capacitors, ...
35
votes
2answers
2k 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, ...
34
votes
2answers
2k views

Cross section of ceramic capacitors

I am trying to make a fault analysis of a bunch of ceramic capacitors. Short description of the application: 10 220 µF ceramic capacitors 1210 package are placed in parallel with a 3.6 V battery. A ...
33
votes
5answers
6k views

Why is the unit for capacitance so large?

Most capacitors are in the µF, nF and pF range. I know there are some special ones that go that high, but at the time faraday was around, and the unit was named after him, they didn't have such a ...
33
votes
9answers
18k views

Organizing electronic parts? [closed]

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 ...
32
votes
6answers
28k 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.
31
votes
4answers
41k 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 ...
29
votes
5answers
22k views

How does a capacitor smooth energy?

I'm trying to wrap my mind around how capacitors work. I understand they store a charge and generally understand how but I don't understand how using them "smoothes" the flow of the charge. Doesn't, ...
29
votes
8answers
24k 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?
29
votes
2answers
57k views

Purpose of the diode and capacitor in this motor circuit

I'm hooking up a small DC motor to an arduino using an NPN transistor using the following diagrams I found online: The circuit works, and I'm successfully able to make the motor run. Now, I'm ...
29
votes
4answers
15k 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??? [...
27
votes
8answers
30k views

Why does a capacitor block DC and not AC? [duplicate]

If someone can explain why a capacitor blocks DC, but not AC, with some math, I will understand all of that much better. I know that there are picture animations illustrating this, but I really want ...
27
votes
1answer
4k views

What effect does selecting the wrong load capacitance for a crystal have?

I've seen questions such as this one and this one that talk about selecting capacitors that, in series, match up as closely as possible to the load capacitance of the crystal. What effect does ...
26
votes
6answers
23k 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 ...
26
votes
8answers
48k views

Why put a resistor in series with signal line?

A lot of times in circuits I see a resistor placed in series in a signal line and sometimes even in series with an MCU's VDD line. Is the intention of this to smooth out noise in the line? How is this ...
26
votes
3answers
4k views

Why do they crimp capacitor leads?

Most manufacturers produces crimped and straight lead pairs of their capacitors which has exactly same capacitance and voltage rating. Why do they bother crimping the leads? What advantage does it ...
26
votes
6answers
30k views

How to find the ESR of a capacitor

I am building a power supply circuit, and the switching regulator (L4963) calls for a low-ESR output capacitor. The capacitor in question is C3 of the evaluation board circuit. What does "low" mean? ...
26
votes
3answers
1k views

Why are resistors tolerances relative instead of absolute?

Every resistor has a tolerance, this provides the user with an idea of the accuracy of the product. This tolerance is represented by a percentage. This means: a big value resistor will be less ...
26
votes
5answers
2k views

Capacitor Gaining Voltage Over Time?

I recently bought two 3300uf 100v capacitors and have connected them in parallel. I charge them up to 100v and discharge them. I then hook up a multimeter and notice the voltage going up very slowly, ...
26
votes
2answers
2k views

Is a bleeder resistor on a small circuit mandatory at the decoupling capacitors?

I have this basic circuit with an MSP430 (The outputs go to LEDs) I have noticed a strange (to me, not saying much though) circumstance. In this circuit, I always have to wait around 20 seconds or ...
25
votes
9answers
33k 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 ...
25
votes
3answers
18k views

Where did the value of 0.1uF for bypass capacitors come from?

Nearly everyone recommends 0.1uF for bypass capacitors. Why this value? I assume there is no harm to using larger values so is it merely a "sensible minimum"? And if so why do people go for the ...
24
votes
10answers
87k 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 ...
24
votes
4answers
65k views

Ceramic capacitors: how to read 2-digit markings?

Related question: Ceramic capacitors: how to read 3-digit markings? I have some ceramic capacitors with a 2-digit marking. How to read them? Do the colored markings at the top mean anything? Image ...
23
votes
7answers
64k views

Inductor vs a capacitor

I'm 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 stores ...
23
votes
3answers
54k views

AC to DC without transformer. How does this thing work?

I disassembled a Chinese-made flashlight and found they use just capacitors to bring down the voltage instead of a transformer. They are using it to charge small lead-acid battery. My question is how ...
23
votes
6answers
9k 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 a ...
22
votes
9answers
4k views

Measure voltage with no current

Suppose I have a capacitor and I want to observe its charge decay over time. How can I do that without affecting its discharge rate through measurement? AFAIK a typical voltmeter runs current ...
21
votes
5answers
3k views

Normal capacitor vs. audio capacitor

I'm building a power supply for old Schoeps CMT30F microphones. Standard condenser mic are 48V-powered nowadays, but these are 60s/70s Schoeps mic from RadioFrance/ORTF, customized at that time to be -...
21
votes
2answers
4k views

What is an “XY” rated safety capacitor, exactly?

Please help me understand this. In a prominent, 480v, 6kW AC servo drive, across three input phases, three 22mm "XY" class 10nF caps are placed for EMI suppression. Also, from these three phases, ...
21
votes
2answers
68k 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 ...
20
votes
4answers
82k 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 ...
20
votes
3answers
15k views

Why does the LM1117 data sheet specifically specify tantalum capacitors?

I'm planning on using an LM1117 to regulate 5 V to 3.3 V. Looking at (any of the several) data sheets for the LM1117, they recommend 10 µF tantalum capacitors between input and ground ...
20
votes
2answers
28k views

How do I decide what capacitor to use in a circuit?

I am using a voltage regulator, and to get cleaner power, the datasheet recommends using a 0.33uF capacitor. However, it doesn't say what type it wants. Stupidly, I ...
20
votes
2answers
3k views

Why would you stack a resistor and capacitor on top of each other?

I've inherited an charge amplifier/shaping circuit from my predecessor. When he wanted to make a low-pass filter with current-to-voltage conversion, he had a standard circuit like: simulate this ...
19
votes
3answers
1k views

Energy in capacitors - loss?

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 ...
19
votes
4answers
24k views

How diodes protect H-bridge DC motor driver?

I don't really understand how these diodes in this circuit and similar circuits (like driving a relay circuit) protects the controller circuit from the energy stored by the inductance of the coil. I ...