Characteristics of aluminum electrolytic capacitor in power adapter
Aluminum electrolytic capacitors are components based on electrochemical effects.
Electrolytic capacitor is a medium of capacitor with electrolyte coating polarity, positive and negative points can not be wrong. Capacitance (
, By two metal poles, with insulating material in the middle (Media)Composition.
Electrolytic Capacitor features one: the capacitance per unit volume is very large, dozens to hundreds of times larger than other kinds of capacitance;
Electrolytic Capacitor features two: the rated capacity can be very large, can easily do tens of thousands of μF even a few f (But can not be compared with the electric double layer capacitance);
Electrolytic Capacitor features three: the price has an overwhelming advantage over other types, because the composition of electrolytic capacitor materials are ordinary industrial materials, such as aluminum and so on.
The equipment for manufacturing electrolytic capacitors is also common industrial equipment, which can be produced on a large scale with relatively low cost. Heat has a great influence on the life of capacitors.
The main circuit, the input side and the output side of the power supply equipment each filter uses the aluminum electrolytic capacitor to flow through the ripple current, so the heating of the capacitor itself caused by the ripple current will also affect the service life.
The life of the electrolytic capacitor can be said to be related to its own calorific value and ambient temperature. In the range of slightly more than the highest operating temperature of the capacitor, it is considered that the life of the capacitor is reduced by half for every 10 ℃ rise in component temperature (Arenius's 10-degree rule).
Under several conditions that the temperature of the capacitor's components is kept unchanged at 90℃, the weight reduction of the capacitor is grasped at any time.
However, the weight reduction caused by changing the temperature is more than that caused by adding DC voltage, and the correct reduction of increasing 10 ℃ is twice as much as that of adding voltage.
The main reason affecting the life of electrolytic capacitors is'
Due to the deterioration of the characteristics caused by the reduction of electrolyte, this reason and the aforementioned capacitor life'Halved at 10℃'The statement is very consistent. At ambient temperature and high frequency (80 KHz)
Several conditions for the combination of ripple current values, equivalent series resistance of capacitors, ESR aging changes, at high frequencies (Above 10 KHz)And at low frequencies (1 KHz)The following are very different.
As the self-heating caused by ripple current exceeds 15℃, the ESR under the condition of adding high ripple greatly increases the ESR change on the low frequency side compared with the condition of adding value only current, this indicates that the loss resistance of the oxide film increases. Therefore, the electrostatic capacity is reduced.
In the circuits with low ripple or low ripple, such as the input side filter circuit, the temperature rise caused by the ambient temperature and the heating of the capacitor itself is regarded as the same condition, but I have to think that the life span is not the same.
The following two conclusions are drawn: 1. If the ambient temperature is known, the ambient temperature correction coefficient and frequency coefficient (
Coefficient set according to the frequency characteristic of ESR of capacitor)
Find out the maximum allowable value under this condition, and find out whether the ripple current that may flow through the aluminum electrolytic capacitor is within the allowable value.
2. The actual measurement of the temperature in the power supply equipment and the component temperature caused by the heating of the capacitor itself, and the understanding of the degree of thermal stress are beneficial to the selection of capacitors.
In places where the ambient temperature is high, such as near the heating body, the temperature quota should be raised to a higher level.
As mentioned before, in the case of low frontal ripple, if the current is too large, even if the component temperature is below the allowable temperature, the loss resistance of the oxide film will increase with the passage of time, therefore, I hope to realize the appreciation of temperature caused by self-heating.
In the case of general input capacitors, if it is assumed that the ambient temperature is below 50℃, the temperature appreciation caused by self-heating is 10℃. When the ambient temperature is 50℃-85℃, the temperature caused by self-heating rises below 5℃, based on the component temperature, life is reduced by half for every increase of 10℃.
On the other hand, it is also effective to adopt the method of blowing cooling to reduce the appreciation of temperature. The above data is collected from the network! (
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