Questions tagged [capacitor]

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

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214 votes
17 answers
182k 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 ...
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128 votes
5 answers
20k views

Why does Samsung include useless capacitors? [closed]

I do component-level repair of tablet mainboards, and I have seen this puzzling situation on two different models of Samsung tablet mainboards so far (SM-T210, SM-T818A). There are ceramic chip ...
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110 votes
6 answers
41k 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 ...
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99 votes
6 answers
73k 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 ...
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89 votes
11 answers
71k 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 ...
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80 votes
9 answers
270k 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, ...
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79 votes
8 answers
73k 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 ...
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74 votes
14 answers
30k 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....
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66 votes
4 answers
102k 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 ...
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65 votes
5 answers
12k 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 ...
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64 votes
4 answers
69k views

Can I replace all electrolytic capacitors with ceramic?

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 ...
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  • 2,567
49 votes
5 answers
14k 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.
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48 votes
11 answers
3k views

How do I improve a simple home-made capacitor?

I was explaining to my son that a capacitor is simply 2 sheets of foil separated by a dielectric and rolled up and he said, "can we make one then?" I'm giving it a go. I used household ...
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46 votes
8 answers
19k 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, ...
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  • 777
45 votes
9 answers
101k 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 ...
43 votes
4 answers
58k 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 ...
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43 votes
5 answers
13k views

Why did Axial Capacitors Fall Out of Use in the Industry?

When inspecting the boards from electronics made in 1980s and earlier, one distinct feature is the extensive use of axial, electrolytic capacitors as power supply filter. Axial ceramic decoupling ...
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43 votes
7 answers
9k 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 ...
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42 votes
3 answers
11k views

Why is the number 63 popular in electronics?

Capacitors have a voltage of 63V (not 60 or 65). Fuses have a value of 63A (not 60 or 65). And there exist more odd values in electronics... Who knows the history of this convention?
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40 votes
8 answers
72k 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 ...
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  • 3,675
39 votes
2 answers
6k 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, ...
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38 votes
2 answers
84k 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 ...
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38 votes
2 answers
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, ...
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36 votes
9 answers
25k 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 ...
35 votes
9 answers
32k 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?
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35 votes
4 answers
33k 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 ...
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  • 1,023
35 votes
6 answers
38k 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.
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35 votes
2 answers
3k 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 ...
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33 votes
2 answers
16k 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, ...
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32 votes
4 answers
109k 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 ...
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31 votes
5 answers
37k 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, ...
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31 votes
10 answers
42k 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 ...
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  • 27.8k
31 votes
1 answer
5k 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 ...
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  • 6,657
29 votes
6 answers
25k 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 ...
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  • 3,212
29 votes
7 answers
77k 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 ...
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  • 3,219
29 votes
9 answers
101k 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 ...
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  • 591
29 votes
2 answers
7k views

What killed these X2 caps?

A few years ago, I designed an MCU-controlled dimmer driving a 150W mains halogen lamp. This is in Western Europe; 50Hz 230VAC. It uses X2-rated capacitors as capacitive droppers for the power supply, ...
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  • 2,328
29 votes
4 answers
16k 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??? [...
29 votes
3 answers
2k 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 ...
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28 votes
3 answers
7k 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 ...
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  • 13.5k
28 votes
7 answers
37k 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? ...
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  • 3,212
28 votes
5 answers
4k 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, ...
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  • 391
27 votes
8 answers
40k 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 ...
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  • 959
27 votes
5 answers
33k views

Why can I put an electrolytic capacitor on AC?

I have seen here and there schematics with electrolytic capacitors put on AC. And this sounds weird to me. Electrolytic capacitors have a polarity, right? If we invert the polarities on DC, bad ...
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  • 1,114
27 votes
3 answers
49k views

Is it possible to use just a capacitor to debounce a button?

I have been wondering: why cannot you just hook up a capacitor to a button to debounce it? I have been figuring out how to reduce the work my microprocessor has to do, but I have very limited space on ...
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26 votes
4 answers
105k 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 ...
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  • 3,675
26 votes
3 answers
19k 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 ...
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26 votes
3 answers
69k 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 ...
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26 votes
6 answers
15k 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 ...
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  • 27.8k
26 votes
2 answers
3k 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 ...
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