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LED Power Engineer Must Have Common Sense – (Capacitance Knowledge)

05 Februarie 2018

Electrolytic capacitor

Characteristics of capacitance (septum)

Capacitor is a container for storing electric charge. It is composed of two pieces of metal, which is close to the plate, and the middle is separated by the insulation material. According to the insulation material, can be made into a variety of capacitors. Such as: Mica, ceramic, paper, electrolytic capacitor. In the construction, it is also divided into fixed capacitor and variable capacitor. The capacitor has a great effect on the DC resistance, that is, the capacitor has a DC effect. Capacitors for alternating current resistance is affected by the influence of the frequency of the alternating current, i.e., the same capacity of capacitors of different frequency alternating current presents different capacitance. Why are these phenomena? This is because the capacitor is dependent on its charge and discharge function to work, the power switch S is not on the. Two sheet metal plates and other common metal plates are not charged. When the switch S is closed, the free electrons on the positive plate of the capacitor are attracted by the power supply and push it to the negative plate. Since there is an insulating material between the two plates of the capacitor, the free electrons that are running from the positive plate are piled up on the negative plate. Because the electronic positive plate decreases with positive, negative plate was gradually increased and the negatively charged electron.

There is a potential difference between the two plates of the capacitor. When the potential difference is equal to the supply voltage, the charging of the capacitor is stopped. At this point, if the power is cut off, the capacitor is still able to maintain the charge voltage. If we connect the two plates with a wire, the electronic will pass through the wire and return to the positive plate. The capacitor is back to the neutral state, and the wire is not current. Add in the two plates of a capacitor AC high frequency, increase in the number of charging and discharging the capacitor; charging and discharging current is enhanced; that is, capacitors for high frequency alternating current inhibition decreases, small capacitance, vice capacitor of low frequency alternating current capacitance. For the same frequency of alternating current. The capacity of the capacitor capacitance is larger, smaller, smaller capacity, greater capacitance.

Parameters and classification of capacitors

In electronic products, capacitors are essential electronic devices, which acts as a smoothing filter, the power supply decoupling, the bypass of AC signals, and the AC coupling of AC signals in electronic devices. Because of the type and structure of the capacitor is more, we need not only to understand the performance of various types of capacitors and general characteristics, but also to understand the advantages and disadvantages of various components in a given application, as well as mechanical or environmental constraints, etc.. Here will be the main parameters of the capacitor and its application to do a simple description.

1. Nominal capacity (R C). Capacitance value of capacitor. The capacitance of mica and ceramic dielectric capacitors is low (about 5000pF below); the capacitor in paper, plastic, and some ceramic medium is in the middle (about 0.005uF~1.0uF); the capacity of the electrolytic capacitor is large. This is a rough classification method.

2. Category temperature range. The ambient temperature range for which the capacitor is designed for continuous operation. The range depends on the temperature limit of the corresponding category, such as the upper limit of the category, the lower temperature, the temperature of the lower temperature, the highest temperature of the rated voltage.

3. Rated voltage (R U). At any temperature between the lower and lower temperature and the nominal temperature, the maximum DC voltage or the maximum AC voltage or pulse voltage of the capacitor can be applied continuously. The capacitor used in high electric field and time, must pay attention to the effects of corona. Corona is generated by the presence of voids between the dielectric/electrode layer, which can cause the dielectric breakdown of the capacitor in addition to the parasitic signals that cause damage to the device. Under AC or pulsating conditions, corona is especially prone to occur. For all capacitors, the use of the DC voltage and AC peak voltage should be guaranteed and not exceed the rated voltage of the capacitor.

4. Loss tangent (TG Delta). In the sinusoidal voltage and frequency regulation, reactive power loss of power divided by the capacitor for loss tangent. In practical application, the capacitor is not a pure capacitance, inside there is the equivalent resistance, its simplified equivalent circuit as shown in the figure shown. For electronic equipment, rs, the smaller the better, this requires little power loss, the included angle and capacitance of the power to small.

5. Temperature characteristics of 5 capacitors. It is usually expressed as a percentage of the capacitance of the reference temperature at 20.

6. Service life. The service life of the capacitor decreases with the increase of the temperature. The main reason is that the temperature accelerates the chemical reaction and causes the medium to be degraded with time.

7. Insulation resistance. As the temperature rises, the temperature rises, so the insulation resistance will be reduced. Capacitor includes two kinds of fixed capacitor and variable capacitor. The fixed capacitor can be divided into the mica capacitor, ceramic capacitor, paper / plastic film capacitor according to the dielectric material.

Category and symbol of capacitance

There are also many types of capacitors, in order to distinguish, and also commonly used to express a number of Latin letters of capacitance. The first letter of the C said the capacitor, the second letters of the material, the third letter after the shape, structure, etc.
Identification of polarity of electrolytic capacitor
Do not know the polarity of electrolysis

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