Views:2 Author:Site Editor Publish Time: 2018-03-23 Origin:Site
Electrolytic capacitors are the most suitable for power frequency filtering or bypass or interstage coupling in low-frequency circuits. And the lower the circuit impedance, the more reliable. When the electrolytic capacitor works, it is equivalent to an electrolytic cell, one of which is the electrolyte. Because the resistance of electrolyte is much higher than that of metal electrode, the series equivalent resistance of electrolytic capacitor is larger. Under the condition of DC or low frequency, the equivalent series resistance RS and the equivalent inductance L can be neglected compared with the dielectric insulation resistance ruler RP of the actual capacitor. With the increase of frequency, both the equivalent series resistance RS and the equivalent inductance L will increase. The increase of the equivalent series resistance RS is due to the "skin effect". The equivalent inductance L is caused by a magnetic field proportional to the frequency. In general, with the increase of frequency, the value of capacitive reactance XC decreases and the inductive XL increases, which indicates that XC-XL2 will decrease with the increase of frequency. When the frequency increases to a certain frequency point XC-XL2 = 0, the impedance Z=RS. At this point the capacitor will resonate. This is the resonance point when the capacitor pair presents a pure resistance. When the frequency is higher than the resonant point of the capacitor, the capacitor has actually become an inductance and can not act as a capacitor, so it is required that the use frequency of the general electrolytic capacitor should not exceed 20 kHz. Because the dielectric constant of most materials is affected by the frequency, its capacity will decrease greatly with the increase of the frequency. Therefore, when the frequency exceeds 20 kHz, the allowable AC component is very small and the capacitance loss of the capacitor is very serious. In this case, a high-frequency ceramic or mica capacitor can be chosen as a high frequency channel in parallel. Because of its large capacity, electrolytic capacitor can be used as a low-frequency channel, and its capacity should be more than 100 times of that of high-frequency capacitor. Because most of the characteristics of capacitors are affected by the frequency to some extent, it is required that the frequency should be more than 1 / 2 of the resonant frequency. Excessive use of frequency will not only consume a large amount of energy in the circuit. Moreover, it can cause the inner core of the capacitor to heat up, thus affecting the reliability of the capacitor. General electrolytic capacitors should work below 10 kHz. If the frequency exceeds 10 kHz, the effective capacity will decrease rapidly until the capacitance impedance becomes pure resistance. Generally, in the range of 100 Hz~100kHz, its capacity varies with frequency, the frequency characteristic of solid tantalum capacitor is better than that of liquid tantalum capacitor, and liquid tantalum capacitor is in the range of 1 kHz~3 kHz. The decrease of the capacity with the frequency is 6. When the frequency increases more than 10 kHz, the decrease will be as high as 65%. This is mainly determined by the properties of dielectric materials. If the electrolytic capacitor can not meet the operational requirements, the use of a four-wire electrolytic capacitor or other dielectric capacitors.