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Why does the life of a capacitor decrease over time? What is the secret of ESR?
Capacitors and inductors are essential components in circuits, but they are not ideal components. These components are actually affected by other non-ideal characteristics during operation, especially the equivalent series resistance (ESR). This article will explore how ESR affects capacitor performance and its impact on service life.
Capacitors are often regarded as ideal capacitive components in circuits. In fact, their performance is also affected by many factors, especially under high frequency conditions.
Definition and importance of ESR
In electronic engineering, ESR refers to the total equivalent resistance presented by a capacitor or inductor, because all real components have some degree of energy loss. ESR is usually AC resistance, which can be measured at a specified frequency depending on the application, for example, 100kHz for switching power supplies and 120Hz for linear power supplies.
Understanding changes in ESR is a key metric in evaluating the performance of a capacitor in a circuit.
Design and characteristics of capacitors
The construction of a capacitor affects its ESR. Whether it is a ceramic capacitor or an electrolytic capacitor, the resistance of its metal pins and electrodes as well as losses in the medium will cause changes in ESR. Typically, ceramic capacitors have an ESR between 0.01 and 0.1 ohms, while electrolytic capacitors can be as high as several ohms.
Under high-frequency operation, the ESR of a used electrolytic capacitor will increase over time. This is because the electrolyte inside it will evaporate over time and the oxygen will be consumed. . This process not only affects the performance of the capacitor, it may even cause circuit failure, although the measured capacitance value is still within the allowable range.
This increased ESR over time can lead to overheating and faster aging, thus shortening the life of the capacitor.
The impact of high ESR
High ESR will have many effects on the circuit. In a circuit with high frequency and obvious pulsating current, if the ESR increases, it will cause excessive heat accumulation and further accelerate the aging of components. The design of electrolytic capacitors must consider the impact of this heat. Therefore, many high-quality electrolytic capacitors will have a significantly longer life than ordinary cheap components when used in high-temperature environments for a long time. Even some high-quality capacitors can last thousands of hours at 85°C.
As the demand for capacitor performance increases in the market, many advanced circuit boards have switched to polymer capacitors to replace traditional electrolytic capacitors.
Methods to deal with increased ESR
By selecting appropriate capacitor types, such as "low ESR" capacitors or capacitors that can withstand high temperatures, the impact of increased ESR on the circuit can be effectively reduced. In addition, on-site testing using appropriate measurement tools such as ESR testers can help maintenance personnel identify components with degraded performance early.
Information about ESR can also be obtained in the data sheet of the capacitor, but there is no unified low ESR standard to help consumers make judgments. Therefore, it is crucial for electronic designers to fully understand the main parameters of capacitors and their practical applications.
When trying to achieve ideal circuit performance, ESR is a factor that cannot be ignored, especially in high-frequency response situations.
Conclusion
To sum up, the capacitors we use are inevitably affected by ESR, both in terms of function and physical properties, which is directly related to the life of the component. Understanding and responding to changes in ESR as environmental conditions change and over time is key to designing reliable circuits. So, what other factors do you think might affect component life in your circuit design?
