Electronics notes/Capacitors: Difference between revisions

Revision as of 19:32, 29 March 2024

⚠ This is for beginners and very much by a beginner / hobbyist

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.

Some basics and reference: Volts, amps, energy, power · batteries · resistors · transistors · fuses · diodes · capacitors · inductors and transformers · ground

Slightly less basic: amplifier notes · varistors · changing voltage · baluns · frequency generation · Transmission lines · skin effect

And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · · Various wireless · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions

Audio notes: See avnotes

Platform specific

Arduino and AVR notes · (Ethernet)

Microcontroller and computer platforms ··· ESP series notes · STM32 series notes

Less sorted: Ground · device voltage and impedance (+ audio-specific) · electricity and humans · power supply considerations · Common terms, useful basics, soldering · landline phones · pulse modulation · signal reflection · Project boxes · resource metering · SDR · PLL · vacuum tubes · Multimeter notes Unsorted stuff

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·

Intro

Capacitors (regularly abbreviated as caps) take an electrostatic charge, which (ignoring leakage) will remain until discharged.

When you put DC across them, they charge to that voltage. They work as a sort of battery - with tiny capacity, but enough for a number of practical uses.

When you put AC across them, limited charging speed means they work more like frequency-dependent resistors, as in oppose some frequencies more than others, which is why they help build signal conditioning, noise reduction, filtering, and resonant circuits.

Some theory and behaviour

Charging and discharging

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Capacitor marking

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Rating considerations

Voltage

You'll often know the maximum voltage a capacitor will be exposed to, though you may wish to consider your circuit's ripple current, peak current, fault current, possible voltage reversal, and more.

The voltage spec seems a nominal one, in that it can probably handle more, but you may shorten its lifespan, and with significantly more you will make it fail.

Temperature (spec / behaviour)

Dielectrics / types / designs

Electrolytic capacitors (type)

polarized - reverse biasing these will cause an electrochemical reaction in the electrolyte, causing it to heat, expand, vent, and likely short in the process. The common cylinder shape has indentations on the top that will bulge and fold open (a safety feature, and one that makes failed electrolytic caps easy enough to identify)

higher inductance than many other types, so not so useful for high-frequency applications

cheap, so common wherever the frequency or stability limitations are not a problem

often can-shaped, and regularly black, grey, blue, and with a stripe indicating its negative lead

Capacitors with more than ~1µF are regularly electrolytic capacitors because of cost. Other types are also used, but often when electrolytic's polarization or lower stability is a problem.

Plastic film

Variable Capacitor (design)

Adjustable capacitors, often looking similar to potmeters (and frequently like trimpots).

@@ Line 1: / Line 1: @@
 {{electronics notes}}
+===Intro===
 [[Image:Capacitors circuit symbols.png|thumb|198px|right|The symbols used in circuits]]
 '''Capacitors''' (regularly abbreviated as '''cap'''s) take an electrostatic charge, which (ignoring leakage) will remain until discharged.
@@ Line 31: / Line 29: @@
 ===Some theory and behaviour===
 <!--
-Physically, capacitors are two conductive plates separated by a non-conductive region, the dielectric.
+Capacitors are two conductive plates separated by a non-conductive region, the dielectric.
-There are a number of different capacitor designs, varying the dielectric materials, plate shape/area, and more (varying in price, max voltage rating, implicit inductance, and more). {{comment|(The physical makeup is not important in generic use, and even in moderately specific specs you're often looking more at specs)}}
+...and (except for a not-very-efficient-at-all physics class model)
+so tiny that you can't see it.
-While ideal capacitor are almost ''completely'' characterized by their capacitance, real-world aspects means you often sometimes care about further specs.
+There are a number of different capacitor designs,
+varying the dielectric materials,
+plate shape/area,
+and more (varying in price,
+max voltage rating,
+maximum charge,
+implicit inductance,
+and more.
+{{comment|(The physical makeup is not important in generic use, and even in moderately specific specs you're often looking more at specs)}}
+While ideal capacitors are almost ''completely'' characterized by their capacitance,
+real-world aspects means you often sometimes care about further specs.
@@ Line 46: / Line 56: @@
 The SI unit of capacitance, the Farad, indicates the a charge in coloumb (Ampere-seconds) a capacitor will accept for 1 Volt across it.
-One Farad is actually a ''lot''.  Capacitors used in most electronics are in the range of microfarads (10<sup>-6</sup>), nanofarads  (10<sup>-9</sup>), or picofarads (10<sup>-12</sup>).
+One Farad is actually a ''lot''.  Capacitors used in most electronics are in the range of microfarads (10<sup>-6</sup>),
+nanofarads  (10<sup>-9</sup>), or sometimes picofarads (10<sup>-12</sup>).
@@ Line 54: / Line 65: @@
 uF and mF capacitors can be pretty chunky, at few-dozen to line voltages,
 Above one farad we'd call it supercapacitors or ultracapacitors,
-chunky things, and much too large for most resonating/filtering uses.
+and much too large for most resonating/filtering uses.
 At uF at line voltage, or mF at PCB voltage, capacitors start being chunky things, finger-sized and larger.
-Chunkier capacitors are often electrolytic designs, because those are easy/cheap for energy storage, and it usually matters little that they're less precise/efficient.
+supercaps tend to be moderate to large at ''any'' useful voltage.
+Chunkier capacitors are often electrolytic designs, because those are easy/cheap for energy storage,
+and for that use it rarely matters that they are less precise/efficient.
@@ Line 66: / Line 84: @@
 '''Imperfections that deviate from ideal capacitors.'''
-Real-world capacitors (and real-world use of them) deviate from the ideal model. For example:
+Real-world capacitors (and real-world use of them) deviate from the ideal model.
-* capacitors have inductance (varying with design), which matters to how well they can be used in high-frequency applications
+For example:
+* real capacitors have inductance (varying with design), which matters to how well they can be used in high-frequency applications
-* capacitors have a small leakage current. It's negligible for many uses, though for battery replacement you'll probably want specific designs that minimize it.
+* real capacitors have a small leakage current. It's negligible for many uses, though for battery replacement you'll probably want specific designs that minimize it.
-* A capacitor '''can have polarity''', which is a result of some specific designs. Polarity means that one lead should always be positive relative to the other, and that reverse-biasing it {{comment|(...with more than perhaps a volt (for most capacitors))}} will cause the capacitor to fail.
+* a real capacitor '''can have polarity''', in that one lead should always have a potential larger or equal to the other. Reverse-biasing it {{comment|(...with more than perhaps a volt (for most capacitors))}} will cause the capacitor to fail.
-** in particular, electrolytic capacitors are polarized (but cheap and good for a number of applications). Reverse biasing these with enough voltage will cause an electrochemical reaction in the electrolyte, causing it to heat, expand, vent, and quite possibly short out.
+** in particular, electrolytic capacitors are polarized. Reverse biasing these with enough voltage will cause an electrochemical reaction in the electrolyte, causing it to heat, expand, vent, and quite possibly for the cap to then short out.
 ** For other capacitor designs you may see nothing more than that the capacitor is now shorted, effectively a bit of wire.

Electronics notes/Capacitors: Difference between revisions

Revision as of 19:32, 29 March 2024

Contents

Intro

Some theory and behaviour

Charging and discharging

Capacitor marking

Rating considerations

Voltage

Temperature (spec / behaviour)

Dielectrics / types / designs

Electrolytic capacitors (type)

Ceramic capacitors (type)

Tantalum capacitors (type)

Silver mica capacitors (type)

Plastic film

See also (types)

Variable Capacitor (design)

Specializations

EMI/RFI suppression (spec)

Pulse capacitor

More applied

Gimmick (design)

Bypass capacitor (application)

De-coupling and coupling capacitor (application)

Power supply filtering (application)

Lowpass filter (application)

Signal generator (application)

Capacitive dropper (application)

Motor capacitor (application)

See also

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