Basic knowledge of capacitors

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1. Classification and function of capacitors Capacitance (Electric capacity) consists of two metal poles with an insulating material (dielectric) sandwiched between them. Due to different insulating materials, the types of capacitors are also different.: 　　 　　 According to structure, it can be divided into: Fixed capacitor, variable capacitor, trimmer capacitor. 　　 According to media materials, it can be divided into: Gas dielectric capacitors, liquid dielectric capacitors, inorganic solid dielectric capacitors, organic solid dielectric capacitors, electrolytic capacitors. 　　 Divided according to polarity: There are polarized capacitors and non-polarized capacitors. The most common one we see is electrolytic capacitors. 　　 Capacitors have the function of blocking DC current and passing AC current in the circuit, so they are often used for inter-stage coupling, filtering, decoupling, bypass and signal tuning. 2. Symbols of capacitors The symbols of capacitors are also divided into domestic standard representation and international electronic symbol representation, but the capacitor symbols are similar in domestic and international representations. The only difference is that in polar capacitors, the domestic one is a horizontal line under an empty basket, while the international one is an ordinary capacitor plus a "+" symbol to represent the positive electrode. 　　 　　3. The unit of capacitance and the basic unit of resistance are: F (farad), in addition to μF (microfarad), pF (picofarad), and another less used unit, that is: nF (), because the capacity of the capacitor F is very large, so what we see are generally the units of μF, nF, and pF, not the unit of F. 　　The specific conversions between them are as follows: 　　 　　1F＝1000000μF 1μF=1000nF=1000000pF 5. Voltage resistance unit of capacitor: V (volt) Each capacitor has its withstand voltage value, which is one of the important parameters of the capacitor. The nominal withstand voltage value of ordinary non-polar capacitors is: 63V, 100V, 160V, 250V, 400V, 600V, 1000V, etc. The withstand voltage of polar capacitors is relatively lower than that of non-polar capacitors. The general nominal withstand voltage is: 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 220V, 400V, etc. 　　 　　6. Types of capacitors There are many types of capacitors, which can be divided into: Non-polar variable capacitors, non-polar fixed capacitors, polar capacitors, etc. can be divided into: CBB capacitors (polyethylene), polyester capacitors, ceramic capacitors, mica capacitors, monolithic capacitors, electrolytic capacitors, tantalum capacitors, etc. The following table shows the advantages and disadvantages of various capacitors: 　　 　　Advantages and Disadvantages of Various Capacitors Polarity Name Production Advantages and Disadvantages Non-inductive CBB capacitor 2 layers of polypropylene plastic and 2 layers of metal foil are alternately mixed and then * * Become. Non-inductive, good high-frequency characteristics, small size and not suitable for large capacity, relatively high price, and poor heat resistance. 　　CBB-free capacitor 2 layers of polyethylene plastic and 2 layers of metal foil are alternately mixed and then * * Become. Yes, the rest is the same as above. 　　Ceramic-free capacitors are made of thin ceramic wafers coated with silver metal films on both sides. Small size, high voltage resistance, low price, high frequency (one type is a high-frequency capacitor) Fragile! Low-capacity mica-free capacitors coated with two layers of metal films on mica sheets are easy to produce and have low technical content. Large volume, small capacity, (almost useless) Monolithic capacitors are smaller in volume than CBB, and others are the same as CBB. Inductive electrolytic capacitors have two aluminum strips and two layers of insulating films stacked on each other, and then immersed in the electrolyte (acidic synthetic solution) after being bundled. Large capacity. High frequency characteristics are not good. 　　Tantalum capacitors use metal tantalum as the positive electrode, and metal is sprayed outside the electrolyte as the negative electrode. Good stability, large capacity, and good high-frequency characteristics. The cost is high. (Generally used in key places) Table 1 7. Nominal and identification methods of capacitors Since the volume of capacitors is larger than that of resistors, the direct nominal method is generally used. If the number is 0.001, then it represents 0.001uF = 1nF. If it is 10n, then it is 10nF. Similarly, 100p is 100pF. 　　 　　Direct representation without units: Expressed by 1 to 4 digits, the capacity unit is pF, such as 350 is 350pF, 3 is 3pF, 0.5 is 0.5pF. Color code representation: Along the direction of the capacitor lead, use different colors to represent different numbers. The first and second rings represent the capacitance, and the third color represents the number of zeros after the significant digit (unit is pF). Color meaning: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Purple=7, Gray=8, White=9. 　　 　　 Capacitor identification: Look at the nominal name on it. Generally, the capacity and positive and negative poles are marked. The length of the pins is also used to distinguish the positive and negative poles. Long pins are positive and short pins are negative.