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Introduction and basic characteristics of aluminum Electrolytic capacitor

2019-07-23

Background:CapacitorIt is one of the three major passive electronic components (resistors, capacitors, and inductors), occupying an important position in the electronic component industry. It is an essential basic electronic component in electronic circuits. Among the electronic components used in the entire machine, capacitors are the most widely used and used, accounting for approximately 40% of the total electronic component usage.

According to the different manufacturing materials of capacitors, they can be divided into: Ceramic capacitor, Aluminum electrolytic capacitor, tantalum capacitors, film capacitors, etc. Among them, the market share of Ceramic capacitor is 43%, ranking first. Ceramic capacitor uses ceramics with high dielectric constant as the medium, which has the advantages of good stability, high insulation, high voltage resistance, etc., but its capacitance is small, and is easy to be broken down by pulse voltage, which is suitable for precision tuned high-frequency oscillation circuits.

Aluminum Electrolytic capacitorThe market share reached 34%, ranking second.Aluminum electrolytic capacitorThe advantages are that: the electrical capacity per unit volume is tens to hundreds times higher than the Ceramic capacitor; Can achieve tens of thousands μ F or even a few f of ultra-high rated rated capacity; The price has an overwhelming advantage over Ceramic capacitor. However, there are issues such as leakage and poor stability, which are suitable for power filtering or low-frequency circuits.

Tantalum capacitors and film capacitors account for 12% and 8% of the market respectively. Tantalum capacitors are mainly used to replace Aluminum electrolytic capacitor in circuits with high requirements, while film capacitors are mainly used for circuit compensation in radio recorders, electronic instruments and other circuits.

Performance characteristics of aluminum Electrolytic capacitor:

(1) The capacitance per unit volume is particularly large, that is, the specific capacity is very high. When the working voltage is lower, this characteristic becomes more prominent, making it particularly suitable for miniaturization,

(2) During the working process of capacitors, the ability to automatically repair or isolate defects in the oxide film enables the oxide film medium to be reinforced and restored to its original insulation capacity at any time, without continuous cumulative damage. This performance is called self-healing characteristic

(3) Having a single conductivity, also known as "polarity". When applying, the circuit should be connected in the positive and negative directions of the power supply. The anode (positive pole) of the capacitor should be connected to the "+" pole of the power supply, and the cathode (negative pole) should be connected to the "1" pole of the power supply. If the connection is incorrect, not only will the capacitor not work, but also the leakage current is large. In a short period of time, the core will heat up, damage the oxide film, and then fail and damage

(4) There is a certain upper limit value for the working voltage. For example, the maximum working voltage of a single Aluminum electrolytic capacitor is generally 600V. Even if it is possible to further increase the upper limit in the future, the potential is limited. However, this shortcoming is not important for matching transistors or integrated circuits

(5) Poor insulation performance. The insulation performance is generally indicated by the leakage current. It can be said that the Electrolytic capacitor is the worst of all types of capacitors. For example, the leakage current of Aluminum electrolytic capacitor with high voltage and large capacitance can reach more than 1mA, and the corresponding insulation resistance is still less than 1M Ω.

In practical application, if the price of the product is further considered, the price of Aluminum electrolytic capacitor is cheap, and its application in consumer electronic products is more attractive

Electrical performance parameters of Electrolytic capacitor:

The parameters characterizing the electrical performance of capacitors include four basic parameters: nominal capacitance, loss tangent, rated voltage and insulation resistance. The parameters of Electrolytic capacitor are no exception. However, due to its performance characteristics, there are some restrictions on specific values, or the allowable error of deviation from the nominal value is relaxed, or the name of the parameter is changed. The most obvious is to replace the "insulation resistance" parameter with the "leakage current" parameter, The following are the explanations:

1. Nominal capacitance and allowable deviation

The selection of values is determined according to the preferred number of E6 series, with a total of 6 numbers as the nominal value series, that is, the values of 1.0, 1.5, 2.2, 3.3, 4.7, 6.8 or above are multiplied by 10, 100 or 1000, etc. The six values of E6 series are about Geometric progression, and the common ratio is aboutThe allowable deviation is ± 20%

2. Loss angle tangent (tg δ)

In the AC circuit, the actual capacitor must consume a small part of useful signal power. Under the sine voltage of the specified frequency, the ratio of the active power consumed to the reactive power is called the loss tangent, and its value is about 0.01 to 0.20. It depends on the type of Electrolytic capacitor, the size of electric capacity, the level of rated voltage, and is closely related to temperature and frequency. Sometimes expressed as a percentage.

3. Leakage current

This parameter represents the insulation quality of Electrolytic capacitor and is equivalent to the insulation resistance parameter of other types of capacitors. Since the leakage current value of Electrolytic capacitor is closely related to its electrical capacity and applied voltage (not greater than rated voltage), the allowable maximum value should be less than I=KCU (K is a constant). And the magnitude of leakage current is related to the ambient temperature, so temperature changes should be strictly controlled during measurement. Generally, when the temperature increases by 10 ℃, the measured value may increase exponentially.

4. Rated voltage

The series of values that represent the highest DC operating voltage that can be applied to a capacitor within a specified ambient temperature range are called rated voltage. Although rated voltage is not a measurement parameter for capacitors, it is generally stipulated that the operating voltage applied to the capacitor should be lower than the rated voltage value. Reducing the applied voltage often has a significant effect on improving the service life of the product, The later introduction of the lifespan formula can be more intuitive to see.