ceramic capacitor - wikipedia, the free encyclopedia

Ceramic capacitor

Ceramic capacitors

From Wikipedia, the free encyclopedia

In electronics ceramic capacitor is a capacitor constructed of alternating layers of metal and ceramic, with theceramic material acting as the dielectric. The temperature coefficient depends on whether the dielectric is Class 1 orClass 2. A ceramic capacitor (especially the class 2) often has high dissipation factor, high frequency coefficient ofdissipation.

Contents1 Construction2 HF use3 Classes of ceramic capacitors4 Microphony5 Coding6 References

ConstructionA ceramic capacitor is a two-terminal, non-polar device.The classical ceramic capacitor is the "disc capacitor". Thisdevice pre-dates the transistor and was used extensively invacuum-tube equipment (e.g., radio receivers) from about1930 through the 1950s, and in discrete transistorequipment from the 1950s through the 1980s. As of 2007,ceramic disc capacitors are in widespread use in electronic equipment, providing high capacity & small size at lowprice compared to other low value capacitor types.

Ceramic capacitors come in various shapes and styles, including:

disc, resin coated, with through-hole leadsmultilayer rectangular block, surface mountbare leadless disc, sits in a slot in the PCB and is soldered in place, used for UHF applicationstube shape, not popular now

HF useCeramic capacitors are suitable for moderately high-frequency work (into the high hundreds of megahertz range, or,with great care, into the low gigahertz range), as modern ceramic caps are fairly non-inductive compared to theother major classes of capacitors (film and electrolytic). Capacitor technologies with higher self-resonantfrequencies tend to be expensive and esoteric (typically, mica or glass capacitors).

Sample self-resonant frequencies for one set of C0G and one set of X7R ceramic capacitors are:

12/9/2009 Ceramic capacitor - Wikipedia, the free…

en.wikipedia.org/wiki/Ceramic_capacitor 1/4

10pF 100pF 1nF 10nF 100nF 1uF

C0G (Class 1) 1550MHz 460MHz 160MHz 55MHz

X7R (Class 2) 190MHz 56MHz 22MHz 10MHz

Classes of ceramic capacitors

Three classes of ceramic capacitors are commonly available:[1] [2]

Class I capacitors: accurate, temperature-compensating capacitors. They are the most stable over voltage,temperature, and to some extent, frequency. They also have the lowest losses. On the other hand, they have thelowest volumetric efficiency. A typical class I capacitor will have a temperature coefficient of 30ppm/C. This willtypically be fairly linear with temperature. These also allow for high Q filters -- a typical class I capacitor will have adissipation factor of 0.15%. Very high accuracy (~1%) class I capacitors are available (typical ones will be 5% or10%). The highest accuracy class 1 capacitors are designated C0G or NP0

Class II capacitors: better volumetric efficiency, but lower accuracy and stability. A typical class II capacitor maychange capacitance by 15% over a -55C to 85C temperature range. A typical class II capacitor will have adissipation factor of 2.5%. It will have average to poor accuracy (from 10% down to +20/-80%).

Class III capacitors: high volumetric efficiency, but poor accuracy and stability. A typical class III capacitor willchange capacitance by -22% to +56% over a temperature range of 10C-55C. It will have a dissipation factor of4%. It will have fairly poor accuracy (commonly, 20%, or +80/-20%). These are typically used as decoupling or inother power supply applications.

At one point, Class IV capacitors were also available, with worse electrical characteristics than Class III, but evenbetter volumetric efficiency. They are now rather rare and considered obsolete, as modern multilayer ceramics canoffer better performance in a compact package.

These correspond roughly to low K, medium K, and high K. Note that none of the classes are "better" than anyothers -- the relative performance depends on application. Class I capacitors are physically larger than class IIIcapacitors, and for bypassing and other non-filtering applications, the accuracy, stability, and loss factor may beunimportant, while cost and volumetric efficiency may be. As such, Class I capacitors are primarily used in filteringapplications, where the main competition is from film capacitors in low frequency applications, and more esotericcapacitors in RF applications. Class III capacitors are typically used in power supply applications. Traditionally,they had no competition in this niche, as they were limited to small sizes. As ceramic technology has improved,ceramic capacitors are now commonly available in values of up to 100uF, and they are increasingly starting tocompete with electrolytic capacitors, where ceramics offer much better electrical performance at prices that, whilestill much higher than electrolytic, are becoming increasingly reasonable as the technology improves.

MicrophonySome ceramic capacitors are slightly microphonic.

Coding



There is a three digit code printed on a ceramic capacitor specifying its value. The first two digits are the twosignificant figures and the third digit is a base 10 multiplier. The value is given in picofarads (pF). A letter suffixindicates the tolerance[1] (http://staff.bcc.edu/eet/Capacitor_Coding.html) :

C ± 0.25pF M ± 20%

D ± 0.5pF P +100 -0%

J ± 5% Y -20 +50%

K ± 10% Z -20 + 80%

Example: a label of "104K" indicates 10×104 pF = 100,000 pF = 100 nF = 0.1uF ± 10%

There is also an EIA three character code that indicates temperature coefficient. For non-temperature-compensating capacitor, the code consists of three letters. The first character is a letter that gives the low-endoperating temperature. The second is a digit gives the high-end operating temperature. The final letter givescapacitance change over that temperature range:

Letter (low temp) Digit (high temp) Letter (change)

X= -55°C (-67°F) 2= +45°C (+113°F) D= ±3.3%

Y= -30°C (-22°F) 4= +65°C (+149°F) E= ±4.7%

Z= +10°C (+50°F) 5= +85°C (+185°F) F= ±7.5%

6=+105°C (+221°F) P= ±10%

7=+125°C (+257°F) R= ±15%

S= ±22%

T= +22 to -33%

U= +22 to -56%

V= +22 to -82%

For instance, a Z5U capacitor will operate from +10°C to +85°C with a capacitance change of at most +22% to -56%. An X7R capacitor will operate from -55°C to +125°C with a capacitance change of at most ±15%.

Temperature-compensated capacitors use a different EIA code. Here, the first letter gives the significant figure ofthe change in capacitance over temperature in ppm/C. The second character gives the multiplier. The third charactergives the maximum error from that in PPM/C. All ratings are from 25-85C:

Significant Figure Multiplier Tolerance

C: 0.0 0: -1 G: ±30

B: 0.3 1: -10 H: ±60

L: 0.8 2: -100 J: ±120

A: 0.9 3: -1000 K: ±250

M: 1.0 4: +1 L: ±500

P: 1.5 6: +10 M: ±1000



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R: 2.2 7: +100 N: ±2500

S: 3.3 8: +1000

T: 4.7

V: 5.6

U: 7.5

For instance, a C0G will have 0 drift, with an error of ±30PPM/C, while a P3K will have -1500PPM/C drift, witha maximum error of ±250PPM/C.

Note that in addition to the EIA capacitor codes, there are industry capacitor codes and military capacitor codes.

References1. ^ Kemet: Ceramic leaded Capacitors F-3101F 06/05

(http://www.kemet.com/kemet/web/homepage/kechome.nsf/vapubfiles/F3101_goldmax.pdf/$file/F3101_goldmax.pdf)2. ^ Ceramic (http://my.execpc.com/~endlr/ceramic.html)

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