Aluminum electrolytic capacitors: It is made of aluminum cylinder to do the negative, which is equipped with liquid electrolyte, insert a curved aluminum belt made of positive electrode. Also need to go through the DC voltage treatment, so that the formation of an oxide film on the positive film to do the media. It is characterized by large capacity, but leakage large, poor stability, positive and negative polarity, suitable for power supply filter or low frequency circuit. When used, positive and negative do not reverse. Capacity and rated operating voltage: Aluminum electrolytic capacitor on the body marked with the capacity and pressure, these two parameters is very important, is the most basic content of the choice of capacitance. In the actual capacitor selection, the current changes in the fast pace of the place to use a larger capacity of the capacitor, but not the capacity of the bigger the better, first of all, the capacity increases, the cost and volume may rise, in addition, the larger the capacitor charge current The greater the charging time will be longer. These are the practical application of the selection to be considered. Rated operating voltage: within the specified operating temperature range, the capacitor long-term reliable work, it can withstand the maximum DC voltage. In the AC circuit, pay attention to the maximum value of the AC voltage can not exceed the DC voltage of the capacitor voltage. Commonly used fixed capacitor operating voltage is 6.3V, 10V, 16V, 25V, 50V, 63V, 100V, 250V, 400V, 500V, 630V. Capacitance in the circuit actually bear the voltage can not exceed its pressure value. In the filter circuit, the capacitance of the voltage value should not be less than the AC rms 1.42 times. Also pay attention to a problem is the working voltage margin of the problem, in general, to more than 15%.