Trimmer Capacitor

 

What are trimmer capacitors? Trimmer capacitors are variable capacitors which serve the purpose of initial calibration of equipment during manufacturing or servicing. They are not intended for end-user interaction. Trimmer capacitors are almost always mounted directly on the PCB (Printed Circuit Board), so the user does not have access to them, and set during manufacturing using a small screwdriver. Due to their nature, trimmer capacitors are cheaper than full sized variable capacitors and rated for many fewer adjustments. Trimmer capacitors are used to initially set oscillator frequency values, latencies, rise and fall times and other variables in a circuit. Should the values drift over time, these trimmer capacitors allow repairmen to re-calibrate equipment when needed. There are two types of trimmer capacitors: air trimmer capacitor and ceramic trimmer capacitor. Trimmer capacitor definition A trimmer capacitor is a variable capacitor used for initial calibration and recalibration of equipment. It is commonly mounted directly on a PCB and accessed only by professional repairmen, not the end-user. Characteristics Voltage rating, capacitance range, polarity Trimmer capacitors can be rated for voltages up to 300 volts, although voltage ratings of up to 100 volts are much more common. Since trim caps are variable capacitors, they come in a capacitance range rather than a single capacitance value. The minimum capacitance is usually between 0.5 pF and 10 pF, while the maximum capacitance is usually between 1 pF and 120 pF. The actual capacitance value can be varied between the minimum and maximum capacitance values for a given trimmer capacitor, but it can never be set to zero. It is worth noting that trimmer capacitors are not polarized. Tolerances and accuracy Trimmer capacitors do not boast a good capacitance value tolerance. Sometimes, the tolerances can be as high as -0 to +100%. This means that a trimmer [… read more]

Mica Capacitor

 
Mica Capacitor

What are mica capacitors? Mica is a group of natural minerals. Silver mica capacitors are capacitors which use mica as the dielectric. There are two types of mica capacitors: clamped mica capacitors and silver mica capacitors. Clamped mica capacitors are now considered obsolete due to their inferior characteristics. Silver mica capacitors are used instead. They are made by sandwiching mica sheets coated with metal on both sides. This assembly is then encased in epoxy in order to protect it from the environment. Mica capacitors are generally used when the design calls for stable, reliable capacitors of relatively small values. They are low-loss capacitors, which allow them to be used at high frequencies, and their value does not change much over time. Mica minerals are very stable electrically, chemically and mechanically. Because of its specific crystalline structure binding, it has a typical layered structure. This makes it possible to manufacture thin sheets in the order of 0.025-0.125 mm. The most commonly used are muscovite and phlogopite mica. The first has better electrical properties, while the second has a higher temperature resistance. Mica is delved in India, Central Africa and South America. The high variation in raw material composition leads to high cost needed for inspection and sorting. Mica doesn’t react with most acids, water, oil and solvents. Mica capacitor definition Silver mica capacitors use mica as the dielectric. They have great high-frequency properties due to low resistive and inductive losses, and are very stable over time. Characteristics Precision and tolerances The minimum tolerance for silver mica capacitor values can be as low as ±1%. This is much better than practically all other types of capacitors. In comparison, certain ceramic capacitors can have tolerances of up to ±20%. Stability Mica capacitors are very stable and very accurate. Their capacitance changes little over [… read more]

Polymer Capacitor

 

What are polymer capacitors? Polymer capacitors are capacitors which use conductive polymers as the electrolyte. They use solid polymer electrolytes instead of liquid or gel electrolytes that are found in ordinary electrolytic capacitors. By using solid electrolyte, the electrolyte drying is completely avoided. Electrolyte drying is one the factors that limit the lifetime of ordinary electrolytic capacitors. There are several types of polymer capacitors, including aluminium polymer capacitors, polymerized organic semiconductors and conductive polymer capacitors. In most cases, polymer capacitors can be used as direct replacements for electrolytic capacitors, as long as the maximum rated voltage is not exceeded. The maximum rated voltage of solid polymer capacitors is lower than the maximum voltage of classical electrolytic capacitors: usually up to 35 volts, although some polymer capacitors are made with maximum operating voltages of up to 100 volts DC. Polymer capacitors have a number of qualities superior to ordinary electrolyte capacitors: longer lifetime, higher maximum working temperature, better stability, lower equivalent series resistance (ESR) and a much safer failure mode. These qualities come at a price of lower maximum voltage rating and a narrower capacitance range, as well as a higher cost compared to wet electrolyte capacitors. This type of capacitor is not that new: production started in the 1980s and since then, they have been used in many applications including server motherboards and computer graphic accelerator cards. Polymer capacitor definition A polymer capacitor is a capacitor which uses solid polymers as the electrolyte. They have a number of superior qualities including a safer failure mode, lower losses and a longer lifetime than electrolytic capacitors. Characteristics Equivalent series resistance Compared to ordinary electrolytic capacitors, polymer capacitors have a lower equivalent series resistance. This allows polymer capacitors to withstand higher ripple currents during normal operation. A ripple current is the AC component [… read more]

Film Capacitor

 
Film Capacitor

What are film capacitors? Film capacitors are capacitors which use a thin plastic film as the dielectric. This film is made extremely thin using a sophisticated film drawing process. Once the film is manufactured, it may be metallized or left untreated, depending on the needed properties of the capacitor. Electrodes are then added and the assembly is mounted into a case which protects it from environmental factors. They are used in many applications because of their stability, low inductance and low cost. There are many types of film capacitors, including polyester film, metallized film, polypropylene film, PTFE film and polystyrene film. The core difference between these capacitor types is the material used as the dielectric, and the proper dielectric must be chosen according to the application. PTFE film capacitors, for example, are heat-resistant and used in aerospace and military technology, while metallized polyester film capacitors are used in applications that require long term stability at a relatively low. Cheaper plastics are used if cost is a bigger concern than performance. Film capacitor definition A film capacitor is a capacitor that uses a thin plastic film as the dielectric. They are relatively cheap, stable over time and have low self-inductance and ESR, while some film capacitors can withstand large reactive power values. Characteristics Film capacitors are widely used because of their superior characteristics. This capacitor type is not polarized, which makes them suitable for AC signal and power use.  Film capacitors can be made with very high precision capacitance values, and they retain that value longer than other capacitor types. This means that the aging process is generally slower than in other capacitor types, such as the electrolytic capacitor. Film capacitors have a long shelf and service life, and are very reliable, with a very low average failure rate. They have [… read more]

Supercapacitor

 

What are supercapacitors? Supercapacitors are electronic devices which are used to store extremely large amounts of electrical charge. They are also known as double-layer capacitors or ultracapacitors. Instead of using a conventional dielectric, supercapacitors use two mechanisms to store electrical energy: double-layer capacitance and pseudocapacitance. Double layer capacitance is electrostatic in origin, while pseudocapacitance is electrochemical, which means that supercapacitors combine the workings of normal capacitors with the workings of an ordinary battery. Capacitances achieved using this technology can be as high as 12000 F. In comparison, the self-capacitance of the entire planet Earth is only about 710 µF, more than 15 million times less than the capacitance of a supercapacitor. While an ordinary electrostatic capacitor may have a high maximum operating voltage, the typical maximum charge voltage of a supercapacitor lies between 2.5 and 2.7 volts. Supercapacitors are polar devices, meaning they have to be connected to the circuit the right way, just like electrolyte capacitors. The electrical properties of these devices, especially their fast charge and discharge times, are very interesting for some applications, where supercapacitors may completely replace batteries. Supercapacitor definition A supercapacitor is a specially designed capacitor which has a very large capacitance. Supercapacitors combine the properties of capacitors and batteries into one device. Characteristics Charge time Supercapacitors have charge and discharge times comparable to those of ordinary capacitors. It is possible to achieve high charge and discharge currents due to their low internal resistance. Batteries usually take up to several hours to reach a fully charged state – a good example is a cell phone battery, while supercapacitors can be brought to the same charge state in less than two minutes. Specific power The specific power of a battery or supercapacitor is a measure used to compare different technologies in terms of maximum power output [… read more]

Tantalum Capacitor

 
Tantalum Capacitor

What are tantalum capacitors? Tantalum capacitors are a subtype of electrolytic capacitors. They are made of tantalum metal which acts as an anode, covered by a layer of oxide which acts as the dielectric, surrounded by a conductive cathode. The use of tantalum allows for a very thin dielectric layer. This results in a higher capacitance value per volume, superior frequency characteristics compared to many other types of capacitors and excellent stability over time. Tantalum capacitors are generally polarized, which means that they may only be connected to a DC supply observing the correct terminal polarity. The downside to using tantalum capacitors is their unfavorable failure mode which may lead to thermal runaway, fires and small explosions, but this can be prevented through the use of external failsafe devices such as current limiters or thermal fuses. Technology advances allow tantalum capacitors to be used in a wide variety of circuits, often found in laptops, automotive industry, cell phones and others, most often in the form of surface mounted devices (SMD). These surface mount tantalum capacitors claim much less space on the printed circuit board and allow for greater packing densities. Tantalum capacitor definition Tantalum capacitors are electrolytic capacitors which use tantalum metal for the anode. They are polarized capacitors with superior frequency and stability characteristics. Characteristics General characteristics Tantalum capacitors are made with capacitance values ranging from 1nF all the way to 72mF and they are much smaller in size than aluminum electrolytic capacitors of the same capacitance. The voltage rating for tantalum capacitors varies from 2V to more than 500V.  They have an equivalent series resistance (ESR) ten times smaller than the ESR of aluminum electrolytic capacitors, which allows for larger currents to pass through the capacitor with less heat generated. Tantalum capacitors are very stable over time and [… read more]

Electrolytic Capacitor

 
Electrolytic Capacitor

What are electrolytic capacitors? An electrolytic capacitor is a type of capacitor that uses an electrolyte to achieve a larger capacitance than other capacitor types. An electrolyte is a liquid or gel containing a high concentration of ions. Almost all electrolytic capacitors are polarized, which means that the voltage on the positive terminal must always be greater than the voltage on the negative terminal. The benefit of large capacitance in electrolytic capacitors comes with several drawbacks as well. Among these drawbacks are large leakage currents, value tolerances, equivalent series resistance and a limited lifetime. Electrolytic capacitors can be either wet-electrolyte or solid polymer. They are commonly made of tantalum or aluminum, although other materials may be used. Supercapacitors are a special subtype of electrolytic capacitors, also called double-layer electrolytic capacitors, with capacitances of hundreds and thousands of farads.  This article will be based on aluminum electrolytic capacitors. These have a typical capacitance between 1µF to 47mF and an operating voltage of up to a few hundred volts DC. Aluminum electrolytic capacitors are found in many applications such as power supplies, computer motherboards and many domestic appliances. Since they are polarized, they may be used only in DC circuits. Electrolytic capacitor definition An electrolytic capacitor is a polarized capacitor which uses an electrolyte to achieve a larger capacitance than other capacitor types. Reading the capacitance value In the case of through-hole capacitors, the capacitance value as well as the maximum rated voltage is printed on the enclosure. A capacitor that has “4.7μF 25V“ printed on it has a nominal capacitance value of 4.7μF and a maximum voltage rating of 25 volts, which is never to be exceeded. In the case of SMD (surface mounted) electrolytic capacitors, there are two basic marking types. The first one clearly states the value in microfarads [… read more]

Ceramic Capacitor

 
Ceramic Capacitor

What are ceramic capacitors? A ceramic capacitor uses a ceramic material as the dielectric. Ceramics were one of the first materials to be used in the producion of capacitors, as it was a known insulator. Many geometries were used in ceramic capacitors, of which some, like ceramic tubular capacitors and barrier layer capacitors are obsolete today due to their size, parasitic effects or electrical characteristics. The types of ceramic capacitors most often used in modern electronics are the multi-layer ceramic capacitor, otherwise named ceramic multi-layer chip capacitor (MLCC) and the ceramic disc capacitor. MLCCs are the most produced capacitors with a quantity of approximately 1000 billion devices per year. They are made in SMD (surface-mounted) technology and are widely used due to their small size. Ceramic capacitors are usually made with very small capacitance values, typically between 1nF and 1µF, although values up to 100µF are possible. Ceramic capacitors are also very small in size and have a low maximum rated voltage. They are not polarized, which means that they may be safely connected to an AC source. Ceramic capacitors have a great frequency response due to low parasitic effects such as resistance or inductance. Ceramic capacitor definition A ceramic capacitor is a capacitor which uses a ceramic material as the dielectric. The two most common types are multi-layer ceramic capacitors and ceramic disc capacitors. Characteristics Precision and tolerances There are two classes of ceramic capacitors available today: class 1 and class 2. Class 1 ceramic capacitors are used where high stability and low losses are required. They are very accurate and the capacitance value is stable in regard to applied voltage, temperature and frequency. The NP0 series of capacitors has a capacitance thermal stability of  ±0.54% within the total temperature range of -55 to +125 °C. Tolerances of the nominal capacitance [… read more]

Air Capacitor

 
Air Capacitor

What are air capacitors? Air capacitors are capacitors which use air as their dielectric. The simplest air capacitors are made of two conductive plates separated by an air gap. Air capacitors can be made in a variable or fixed capacitance form. Fixed capacitance air capacitors are rarely used since there are many other types with superior characteristics. Variable air capacitors are used more often because of their simple construction. They are usually made of two sets of semicircular metal plates separated by air gaps. One set is fixed and the other is attached to a shaft which allows the user to rotate the assembly, therefore changing the capacitance as needed. The larger the overlap between the two sets of plates, the higher the capacitance. The maximum capacitance state is achieved when the overlap between the two sets of plates is highest, while the lowest capacitance state is achieved when there is no overlap. Variable air capacitors are used in circumstances where the capacitance needs to be varied. They are sometimes used in resonant circuits, such as radio tuners, frequency mixers or antenna impedance matching applications. Another use for variable capacitors is while prototyping an electronic circuit design. Sometimes, it is simply easier to find the appropriate capacitor value by trial and error instead of calculating it exactly. Air capacitor definition Air capacitors are capacitors which use air as the dielectric medium located between conductive plates. Characteristics The dielectric constant value of a material is a measure of the amount of electrical energy stored in a material for a given voltage. Since capacitors are devices used to store electrical energy, higher dielectric constants are favorable. However, the dielectric value of air is approximately that of vacuum, which is the lowest dielectric constant possible for a material and equals εo = 8.854 * 10-12 [… read more]