Views:4 Author:Site Editor Publish Time: 2020-06-17 Origin:Site
Aluminum electrolytic capacitors:
It is made of water-absorbing paper impregnated with paste electrolyte sandwiched between two aluminum foils, and a thin oxide film is used as a dielectric capacitor. Because the oxide film has unidirectional conductivity, the electrolytic capacitor has polarity. Large capacity, can withstand large pulsating current. Large capacity error, large leakage current; ordinary is not suitable for high frequency and low temperature applications, should not be used at frequencies above 25kHz. Low frequency bypass, signal coupling, power supply filtering.
Tantalum electrolytic capacitor:
A sintered tantalum block is used as the positive electrode, and solid manganese dioxide is used as the electrolyte. The temperature characteristics, frequency characteristics and reliability are better than ordinary electrolytic capacitors, especially the leakage current is extremely small, the storage is good, the life is long, the capacity error is small, and the volume is small. The maximum capacitance voltage product can be obtained per unit volume. The resistance to pulsating current is poor, and it is easy to be short-circuited if damaged. In ultra-small high-reliability parts.
The structure is similar to paper capacitors, but uses low-loss plastic materials such as polyester and polystyrene as the medium. Good frequency characteristics and low dielectric loss. Can not be made into a large capacity, poor heat resistance. Filter, integration, oscillation, timing circuit.
Ceramic Dielectric Capacitor:
Through-hole or pillar structure ceramic dielectric capacitor, one of its electrodes is the mounting screw. The lead inductance is extremely small, the frequency characteristics are good, the dielectric loss is small, and there is a temperature compensation effect. Can not be made into a large capacity, the vibration will cause the capacity to change. Especially suitable for high frequency bypass.
Monolithic capacitor (multilayer ceramic capacitor):
Several ceramic film blanks are covered with electrode paddle material, and after being laminated, they are wound into an inseparable whole at a time, and the outside is encapsulated with resin. New capacitors with small size, large capacity, high reliability and high temperature resistance, low frequency monolithic capacitors with high dielectric constant also have stable performance, the body is actively small, and the Q value is high. Large capacity error. Noise bypass, filter, integration, oscillation circuit.
Paper dielectric capacitors:
Generally, two aluminum foils are used as electrodes, and a capacitor paper with a thickness of 0.008 to 0.012 mm is wound and wound in the middle. The manufacturing process is simple, the price is cheap, and a large electric capacity can be obtained.
Metallized polypropylene capacitors:
Generally in low-frequency circuits, it cannot be used at frequencies above 3 to 4 MHz. Oil-immersed capacitors have higher withstand voltage than ordinary paper capacitors and good stability. They are suitable for high-voltage circuits.
Trimmer capacitor (semi-variable capacitor):
The capacitance can be adjusted within a small range and can be fixed to a certain capacitance value after adjustment. Porcelain dielectric trimmer capacitors have a high Q value and a small volume. They can usually be divided into two types: tube type and wafer type. The mica and polystyrene media are usually spring-type east, the structure is simple, but the stability is poor. Wire-wound ceramic dielectric fine-tuning capacitors remove the copper wire <external electrode> to change the capacitance, so the capacitance can only be reduced, and it is not suitable for use in occasions that require repeated debugging.
Capacitor ceramic (barium titanate-titania) with high dielectric constant is extruded into a circular tube, disc or disc as a medium, and silver is plated on the ceramic as an electrode by infiltration method. It is divided into two kinds of high-frequency porcelain medium and low-frequency porcelain medium. Capacitors with a small positive capacitance temperature coefficient are used in high-stability oscillation circuits as loop capacitors and matting capacitors. Low-frequency ceramic dielectric capacitors are limited to the use of bypass or DC blocking in circuits with lower operating frequencies, or occasions that do not require high stability and loss (including high frequencies). Such capacitors are not suitable for use in pulse circuits because they are easily broken down by pulse voltage. High frequency ceramic dielectric capacitors are suitable for high frequency circuits.
In terms of structure, it can be divided into foil type and silver type. The silver-type electrode is formed by plating a silver layer directly on the mica sheet by vacuum evaporation or infiltration. Due to the elimination of the air gap, the temperature coefficient is greatly reduced, and the capacitance stability is also higher than that of the foil type. The frequency characteristic is good, the Q value is high, and the temperature coefficient is small. It cannot be made into a large capacity. It is widely used in high-frequency electrical appliances and can be used as a standard capacitor.
Glass glaze capacitor:
It is formed by spraying a special mixture with a concentration suitable for spraying into a thin film, and the medium is sintered with a silver layer electrode to form a "monolithic" structure. Performance is comparable to mica capacitors, can withstand various climatic environments, generally can work at 200 ℃ or higher, rated operating voltage can reach 500V, loss tgδ0.0005～0.008
Capacitors: Electronic components that act as smoothing filters for rectifiers, power supply and decoupling, bypass of AC signals, AC coupling of AC and DC circuits in electronic equipment are called capacitors. Capacitors include fixed capacitors and variable capacitors. Fixed capacitors can be divided into mica capacitors, ceramic capacitors, paper/plastic film capacitors, electrolytic capacitors and glass glazed capacitors according to the dielectric materials used; variable capacitors can also be used It is a glass, air or ceramic medium structure.
The loss of the capacitor has a great relationship with the leakage current and the temperature of the environment.
The detection method of fixed capacitor:
A. Detection of small capacitors below 10pF. Because the capacity of fixed capacitors below 10pF is too small, use a multimeter to measure, only qualitatively check whether there is leakage, internal short circuit or breakdown. When measuring, the multimeter R×10k block can be selected, and the two pins of the capacitor can be arbitrarily connected with two test leads, and the resistance value should be infinite. If the measured resistance value (the pointer swings to the right) is zero, it indicates that the capacitor leakage damage or internal breakdown.
B. Check whether the 10PF～001μF fixed capacitor is charged, and then judge whether it is good or bad. Multimeter selects R×1k block. Both betas of the two transistors are above 100, and the penetration current is small. Can choose 3DG6 and other types of silicon triode to form a composite tube. The red and black test leads of the multimeter are connected to the emitter e and collector c of the composite tube, respectively. Due to the amplification effect of the composite transistor, the charging and discharging process of the measured capacitor is amplified, so that the amplitude of the multimeter pointer swing is increased, which is convenient for observation.
It should be noted that: during the test operation, especially when measuring a small-capacity capacitor, the pins of the capacitor under test must be replaced with the two points A and B repeatedly to see the swing of the multimeter pointer. C For a fixed capacitance above 001μF, the R×10k block of the multimeter can be used to directly test whether the capacitor is charging and whether there is an internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.