Ping Shang explains the knowledge of aluminum electrolytic capacitors
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Understanding Aluminum Electrolytic Capacitors
The capacitance of electrolytic capacitors is influenced by the impedance they exhibit when subjected to alternating current (AC) voltage. As a result, the measured capacitance value—often referred to as the AC capacitance—can vary depending on factors such as operating frequency, applied voltage, and the measurement technique used.
According to the Japanese Industrial Standard JIS C 5102, the capacitance of aluminum electrolytic capacitors is typically measured at a frequency of 120 Hz, with a maximum AC voltage of 0.5 Vrms and a DC bias voltage ranging from 1.5 to 2.0 V. Under these standardized conditions, it is well established that the capacitance of an aluminum electrolytic capacitor tends to decrease as the frequency increases. This behavior is due to the inherent characteristics of the dielectric material and the internal structure of the capacitor.
In the equivalent circuit model of an electrolytic capacitor, the ratio of the equivalent series resistance (ESR) to the capacitive reactance (1/ωC) is known as the dissipation factor, or tan δ. The ESR value is usually measured at 120 Hz. As the measurement frequency increases, tan δ also increases, which indicates greater energy loss within the capacitor. Additionally, tan δ tends to rise as the ambient temperature decreases, further affecting the performance of the component.
Impedance (Z) represents the total opposition to the flow of AC current at a specific frequency. It is closely related to both the capacitance and inductance values within the capacitor's equivalent circuit, as well as the ESR. At lower frequencies, the capacitive reactance dominates, while at higher frequencies, the inductive effects become more significant, leading to a change in overall impedance.
Understanding these parameters is crucial for selecting the right electrolytic capacitor for a given application, especially in power supply circuits, audio systems, and other electronic devices where stability and efficiency are important. Proper selection ensures optimal performance and longevity of the components.
By considering the impact of frequency, temperature, and measurement conditions, engineers can make more informed decisions when designing and troubleshooting electronic systems.
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