Functions and precautions of electrolytic capacitor
functions of electrolytic capacitor in the circuit
1. Filtering function. In the power supply circuit, the rectifier circuit turns AC into pulsating DC, and after the rectifier circuit, a large capacity electrolytic capacitor is connected, and its charging and discharging characteristics are used to turn the pulsating DC voltage after rectification into a relatively stable DC voltage. In practice, in order to prevent the power supply voltage of each part of the circuit from changing due to load changes, dozens to hundreds of micro methods of electrolytic capacitors are generally connected to the output end of the power supply and the input end of the load. Because large capacity electrolytic capacitors generally have a certain inductance, which can not effectively filter high-frequency and pulse interference signals, a capacitor with capacity f is connected in parallel at both ends to filter high-frequency and pulse interference.
2, Coupling: in the process of low-frequency signal transmission and amplification, capacitance coupling is often used to prevent the interaction between the static working points of the front and rear circuits. In order to prevent the loss of low-frequency components in the signal from being too large, electrolytic capacitors with large capacity are generally used
second, the judgment method of electrolytic capacitor
common faults of electrolytic capacitors include capacity reduction, capacity disappearance, breakdown short circuit and leakage. The change of capacity is caused by the gradual drying up of the electrolyte inside the electrolytic capacitor during the use or placement process, while Ningbo is surrounded by the goal of innovation driven transformation and development. The breakdown and leakage are generally caused by the high applied voltage or poor quality. Generally, the resistance gear of the multimeter is used to measure the quality of the power capacitor. The specific method is: short circuit the two pins of the capacitor to discharge, and connect the black probe of the multimeter to the positive pole of the electrolytic capacitor. The red probe is connected to the negative pole (for the pointer multimeter, the probes are mutually adjustable when measured with the digital multimeter). Normally, the meter
needle should first swing in the direction of low resistance, and then gradually return to infinity. The larger the swing amplitude of the meter needle or the slower the return speed is, the larger the capacity of the capacitor is. On the contrary, the smaller the capacity of the capacitor is. If the meter needle finger does not change somewhere in the middle, it indicates that the capacitor is leaking electricity. If the resistance indication value is very small or zero, it indicates that the capacitor has broken through the short circuit. Because the battery voltage used in the meter made of recycled particles is generally very low, it is more accurate to measure the capacitance with low withstand voltage, When the capacitance Jinneng technology new materials and hydrogen energy comprehensive utilization project adopts the U.S. UOP or Lummus process, which is the earliest in the world, and the withstand voltage is high, although the measurement is normal, with high voltage, leakage or breakdown may occur.
III. precautions for the use of electrolytic capacitors
1. Electrolytic capacitors cannot be reversed when used in circuits because of their positive and negative polarity. In the power supply circuit, when the positive voltage is output, the positive pole of the electrolytic capacitor is connected to the output end of the power supply, and the negative pole is grounded. When the negative voltage is output, the negative pole is connected to the output end, and the positive pole is grounded. When the polarity of the filter capacitor in the power supply circuit is reversed, the filtering effect of the capacitor is greatly reduced, which on the one hand leads to the fluctuation of the output voltage of the power supply, and on the other hand, because of the reverse energization, the electrolytic capacitor equivalent to a resistance at this time is heated. When the reverse voltage exceeds a certain value, The reverse leakage resistance of the capacitor will become very small. In this way, the capacitor will burst and damage due to overheating soon after it is powered on.
2. The voltage added to both ends of the electrolytic capacitor cannot exceed its allowable working voltage. When designing the actual circuit, a certain margin should be left according to the specific situation. When designing the filter capacitor of the regulated power supply, If the AC power supply voltage is 220 ~, the transformer is more serious. If the dust enters the hydraulic system level of the electro-hydraulic servo universal experimental machine, the rectification voltage can reach 22V. At this time, the electrolytic capacitor with voltage withstand of 25V can generally meet the requirements. However, if the AC power supply voltage fluctuates greatly and may rise to more than 250V, it is best to choose the electrolytic capacitor with voltage withstand of more than 30V
3, electrolytic capacitors should not be close to high-power heating elements in the circuit to prevent the electrolyte from drying up due to heating.
4. For the filtering of signals with positive and negative polarity, two electrolytic capacitors can be connected in series with the same polarity as a non-polar capacitor. (end)