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Talking about capacitor eight: the electrical parameters of electrolytic capacitors

     The electrolytic capacitor here mainly refers to the aluminum electrolytic capacitor, and its basic electrical parameters include the following five points:

    1. Capacitance value

     The capacitance value of an electrolytic capacitor depends on the impedance presented when working under AC voltage. Therefore, the capacitance value, that is, the AC capacitance value, changes with the change of the operating frequency, voltage, and measurement method. In the standard JISC 5102, the measurement conditions of the capacitance of aluminum electrolytic capacitors are carried out under the conditions of a frequency of 120Hz, a maximum AC voltage of 0.5Vms, and a DC bias voltage of 1.5~2.0V. It can be concluded that the capacity of aluminum electrolytic capacitors decreases with the frequency.

    2. Loss angle tangent value

     In the equivalent circuit of a capacitor, the ratio of the series equivalent resistance ESR to the capacitive reactance is called the tangent value, where ESR is the value calculated at 120Hz. Obviously, the tangent value increases with the increase of the measurement frequency, and increases with the decrease of the measurement temperature.

    3. Impedance Z
     At a specific frequency, the resistance that blocks the passage of AC current is the so-called impedance (Z). It is closely related to the capacitance value and inductance value in the capacitance equivalent circuit, and it is also related to ESR. The capacitive reactance (XC) of the capacitor gradually decreases as the frequency increases in the low frequency range, and the reactance (XL) drops to the value of ESR when the frequency continues to increase to reach the intermediate frequency range. When the frequency reaches the high frequency range, the inductive reactance (XL) becomes dominant, so the impedance increases as the frequency increases.

   4. Leakage current

   The medium of the capacitor has a great hindrance to DC current. However, since the aluminum oxide film medium is immersed in electrolyte, when a voltage is applied, a very small current called leakage current is generated when the oxide film is reformed and repaired. Generally, the leakage current will increase with the increase of temperature and voltage.

    5. Ripple current and ripple voltage

    In some materials, these two are called "ripple current" and "ripple voltage", which are actually ripple current, ripple voltage. The meaning is the ripple current/voltage value that the capacitor can withstand. They are closely related to ESR, which can be expressed by the following formula: Urms=lrms x R In the formula, Vrms represents the ripple voltage lrms represents the ripple current R represents the ESR of the capacitor

    It can be seen from the above that when the ripple current increases, even when the ESR remains the same, the ripple voltage will increase exponentially. In other words, when the ripple voltage increases, the ripple current also increases, which is why the capacitor is required to have a lower ESR value. After the ripple current is added, the equivalent series resistance (ESR) inside the capacitor causes heat, which affects the use of the container. Generally, the ripple current is proportional to the frequency, so the ripple current is relatively low at low frequencies.  

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