Capacitor Tutorial Includes:
Capacitor uses Capacitor types Electrolytic capacitor Ceramic capacitor Ceramic vs electrolytic Tantalum capacitor Film capacitors Silver mica capacitor Super capacitor Surface mount capacitors Specifications & parameters How to buy capacitors - hints & tips Capacitor codes & markings Conversion table
Electrolytic and ceramic capacitors are the two most commonly used types of capacitor, both for circuits requiring traditional leaded electronic components as well as for those using surface mount devices.
Electrolytic, or more correctly for the types widely used, the aluminium electrolytic capacitor and the ceramic capacitor both have their advantages and disadvantages.
Selecting the right type of capacitor and using its advantages to the best for each circuit design situation can result in a circuit that performs better, costs less, is more reliable and is smaller in size.
Choosing the right type: electrolytic vs ceramic, and looking at the differences between them is an essential part of any electronic circuit design, but knowing which type to select requires an understanding of the characteristics of both types.
What is an electrolytic capacitor
Electrolytic capacitors are widely used in many electronic circuit designs where they provide higher levels of capacitance.
Strictly speaking the type of capacitor that is often referred to as an electrolytic capacitor is more correctly termed an aluminium electrolytic capacitor as it is based around the use of aluminium foil, an oxide layer and an electrolyte between the two layers of the capacitor.
Tantalum capacitors are also a type of electrolytic capacitor, but they tend to be referred to as tantalum capacitors, so there is not normally any issue with the terminology.
Electrolytic capacitors were originally not available in surface mount packages because of their tolerance of high temperatures during the soldering processes required for surface mount printed circuit boards. Now this issue has been overcome they are available both in leaded and surface mount packages.
Ceramic capacitors use ceramic as the dielectric in the capacitor. They tend to be used for the lower capacitance values, although the technology is advancing and some surprisingly high values can now be obtained.
Within the general category of ceramic capacitors, there are many different types of ceramic available and these offer different levels of performance, and therefore when using ceramic capacitors, the best type of ceramic must be selected. Types such as C0G, X5R, Y5V and the like are available, each having their own advantages.
Particularly for surface mount capacitors, a type known as MLCC - multi-layer ceramic capacitor is available. This has multiple layers of the conductor and the ceramic dielectric, arranged to give a high level of capacitance in a small volume.
Electrolytic vs ceramic capacitors: differences & characteristics
When looking at the two types of capacitor for possible inclusion in a particular position in an electronic circuit design, it is necessary to be able to compare the characteristics of each type, looking at the differences and adb=vantages of each type.
Each type of capacitor: electrolytic and ceramic has its own advantages, and by selecting the right type, the optimum circuit performance can be obtained.
The different sections below give a summary of the performance of both types of capacitor for different parameters and in this way it is possible to compare and contrast ceramic vs electrolytic capacitors.
In some areas the capacitors will perform in very different ways, whereas in others they can be quite similar.
• Capacitance range
The value of a capacitor is a key parameter for any circuit. The value of the capacitor used will determine many performance factors of the overall circuit design. In some cases the value may be critical, in others less so.
|Normally from a few picofarads up to 0.5µF, although technology, especially for surface mount capacitors means that higher values are sometimes available||Normally used for values over 1µF. Top values tend to be a 100µF for surface mount types and up to 1000µF or more for leaded or capacitors with terminals.|
The tolerance of the capacitor is the range over which the capacitor may be from its stated value. For some circuits it is necessary to have an accurate level of capacitance, whereas for others the actual value is not critical.
Understanding the tolerance for the capacitor type chosen can be a key element in deciding which type to chose.
|Some types can have very close tolerance levels, 5% and some are much better, and some may not be as close, dependent upon the actual specific component chosen.||Electrolytic capacitors have a notoriously wide tolerance. Many are specified as +50% - 20%. As they are often used for stage coupling, line decoupling and smoothing applications the tolerance is not normally an issue.|
• Voltage rating
When selecting a capacitor for any function within a circuit, it is necessary to ensure that its working voltage is not exceeded. Often running a capacitor at no more than 2/3 its maximum rating will ensure good reliability. If transients are likely to be experienced, then it is wise to select a capacitor with a working voltage that can tolerate this.
|The rating of ceramic capacitors can go to 1kV and beyond, but these tend to be the disc ceramic types that are leaded and intended for high voltage use. The surface mount components are very much lower because having a lower voltage will reduce their size.||The leaded and types with terminals can have working voltages up to 350V and more, although these tend to be used with vacuum tubes / valves. Leaded types tend to have working voltages 25, 35, 50V, and the SMD varieties less than this because of their intended use and the size restrictions on SMD components.|
|Non-polar: it does not matter which way round the electronic component is placed within a circuit. They can be used on AC as wella s DC signals.||Polarised: electrolytic capacitors have a positive and negative terminal, and they must be placed correctly orientated within a circuit to match the polarisation of the capacitor. If not, then damage can result. This means that cannot be used inth e circuit where the polarity of the voltage across them changes, although if a bias is applied, as in many circuits they can still be used provided the AC signal does not reverse the voltage across the capacitor.|
• Circuit symbol
Although both types of component are both capacitors and as such use the basic schematic symbol, there are slight differences to show the polarity of the electrolytic capacitor.
|The ceramic capacitor uses the basic capacitor circuit symbol.||There are various symbols that are used for the electrolytic type of capacitor which are shown below. They conform to different standards.
• Temperature stability
The temperature stability of a capacitor is the amount by which it varies when the temperature changes. This factor can be very important where the value of the capacitor determines some key parameters of a particular electronics circuit design. It is important where the value of the capacitor determines a key aspect of the circuit design.
For example the temerpature stability is important in circuit designs including oscillators, and filters. Any changes in the value of a capacitor which determines the oscillator frequency, cut-ff frequency etc will have a significant impact on the circuit.
|The temperature stability of a ceramic capacitor will depend upon the actual type of ceramic used. Some ceramic dielectrics give a medium level of temperature stability whereas others are very good. Some even have a negative temperature coefficient (NP0) and can be used for compensating the temperature effects of other components.||Electrolytic capacitors have a poor level of temperature stability and as a result they should not be used in any circuit where the level of their capacitance is important.|
• Package types
The package types and styles are very important. Not only are the electrical characteristics very important, but so too are the physical or mechanical aspects as the electronic components need to be compatible with the size constraints, manufacturing techniques and the like.
Possibly the most important are whether the component needs to be a traditional leaded type, or whether it needs to be a surface mount device.
|Available a leaded types - normally disc ceramic format, and as SMD, surface mount capacitors. Some of the surface mount capacitor versions can be very small.||The electrolytic capacitor is available in both leaded formats as well as surface mount capacitors. Some of the very large value leaded electronic components may use a solder terminal or screw terminal for the connection.|
• Current capability
It is necessary to consider how much current will flow through a capacitor, especially in high current circuits such as power supplies.
Although in many instances such as low power circuits, the current capability is not an issue and is never considered, it is around known high current areas that it needs to be taken into consideration.
|Ceramic capacitors are used for low current situations - they are not able to withstand high levels of current.||Aluminium electrolytic capacitors are often used in power supply smoothing circuits where they need to have a high current capability. However for these applications the ripple current specification needs to be considered as excessive current beyond their specified capability can cause overheating and hence damage or failure.|
• Frequency capability
The frequency capability or response of a capacitor is important because many circuits operate at very high frequencies and it is necessary to select a capacitor that can operate over the frequencies used by the particular electronic circuit design.
|Dependent upon the actual type, package, etc, ceramic capacitors can be used well into the RF portion of the spectrum. Surface mount ceramic capacitors, because of their small size and inherent low inductance, are typically capable of operating into the GHz region and specialist types beyond this.||Electrolytic capacitors are only applicable for lowish frequencies - often below about 100kHz. Because of the electrolytic action of the capacitor, their frequency capability is limited.|
• Equivalent series resistance, ESR
The equivalent series resistance of a capacitor is an important aspect of its overall performance. As the name indicates, it equates to the resistance that exists within the capacitor and it is shown in the equivalent circuit as a series resistor.
ESR tends to manifest itself by affecting different types of circuits in slightly different ways. IN power circuits, the ESR is a resistor that will dissipate heat, and this can have an effect ont he temerpature of the capacitor. In circuits used for RF applications, etc, it will reduce the Q or quality factor of a circuit, and for decoupling situations in an electronic circuit design it will mean that the route to ground for unwanted spikes and ripple, etc has a DC resistor in series making it less effective.
Typically ceramic capacitors have a low ESR and therefore they tend to be very effective in decoupling, coupling situations in electronic circuit designs as well as providing a good level of Q in RF designs.It is often between about 0.01 and 0.1 Ohms.
Electrolytic capacitors tend to have a higher level of ESR compared to ceramic types.
The value of ESR for electrolytic capacitors varies widely according to a variety of factors. One may have an ESR of anywhere between about 0.5 and 30 Ohms dependent upon its intended application, etc. Special low ESR capacitors are available where ESR is of paramount importance.
Reliability is a major issue these days not only for the traditional high reliability arenas such as medical, military and aerospace, but much more these days for consumer and industrial products where long operational life is expected.
|Normally ceramic capacitors are very reliable. In some instances, the surface mount capacitors can crack if the PCB on which they are mounted is flexed, but apart from this they are very good.||Aluminium electrolytic capacitors have a finite lifetime and as such they can often be avoided in some designs - see more below.|
Aluminium electrolytic capacitor reliability & lifetime
Aluminium electrolytic capacitors have a name for poor reliability in some circles. Their performance degrades over time and as a result they are more likely to either fail themselves or cause the circuit to fall outside its operating specification.
The main cause of the degradation in performance is the slow evaporation of the electrolyte, and this issue is made worse at higher temperatures.
This results in lower capacitance level and higher level of effective series resistance (ESR). In fact, as ESR rises, so does any self-heating effect due to ripple currents.
In many circuits using electrolytic capacitors, the value itself does not need to be maintained accurately, and so the effect may pass unnoticed for some while.
However it is necessary to be aware of the problem, especially with equipment that is many years old, and also that where the capacitors may be subject to high current levels.
Under normal operating conditions, electrolytic capacitors can be a very good choice, and their lifetime is likely to considerably exceed that of the overall equipment, so any issues may not arise.
However, if possible, where electrolytic capacitors are used, it is best to keep temperatures low as this will reduce the effects of the electrolyte evaporation.
Choosing between ceramic & electrolytic
The choice between a ceramic and an electrolytic capacitor may not be easy. In some instances both types could perform equally well, but in other circuit functions, one type may be far better than another.
Often ceramic capacitors are used for general coupling and decoupling where values up to around 100nF (0.1µF) are needed. Normally the exact value is not particularly important. For these electronic circuit design situations relatively low tolerance types can be used.
Ceramic capacitors are also available in higher tolerance versions, again, typically up to 0.1µF and they can be used for a variety of requirements where the value of the capacitor is critical, i.e in oscillators, filters, etc.
Where smoothing and high values or capacitance are required for coupling, electrolytic capacitors may be needed. here the values tend not to be critical and the poor tolerance of electrolytic capacitors is not an issue.
Both ceramic and electrolytic capacitors have an important place in the electronic circuit designers toolbox. However it is necessary to look at the differences between them and then to determine the best type for a given position in any circuit.
Knowing the characteristics of each type will enable the best choice to be made when considering the ceramic vs electrolytic capacitor choice.
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