Talk about electrolytic capacitors we can not understand more about its role
1, the role of filtering: In the power circuit, the rectifier circuit will become a pulsating DC, and in the rectifier circuit after access to a larger capacity electrolytic capacitors, the use of its charge and discharge characteristics (energy storage), so that after rectification Pulsating DC voltage becomes relatively stable DC voltage. In practice, in order to prevent the PCB manufacturing circuit parts of the power supply voltage changes due to changes in the load, so the power output and load the power input is generally connected to dozens of hundreds of micro-electrolytic capacitors. As the large-capacity electrolytic capacitors generally have a certain inductance, the high-frequency and pulse interference signal can not be effectively filtered, so at both ends in parallel with a capacity of 0.001--0.lpF capacitor to filter high frequency And pulse interference.
2, the coupling effect: in the low-frequency signal transmission and amplification process, in order to prevent the two-stage circuit before the static operating point interaction, often using capacitive coupling. In order to prevent the signal in the low-frequency component loss is too large, the general total capacity of the larger electrolytic capacitors.
Next to understand the electrolytic capacitor to determine the method
Electrolytic capacitors are common faults, capacity reduction, capacity loss, breakdown short circuit and leakage, in which the capacity change is due to electrolytic capacitors in the use or placement process of its internal electrolyte gradually dry up, and breakdown and leakage is generally added Of the voltage is too high or poor quality caused by their own. Determine the PCB proofing power supply capacitor is generally the use of multimeter resistance file for measurement. The specific method is: the capacitor two short-circuit discharge, with a multimeter of the black table pen electrolytic capacitor positive pole. Red gauge pen negative (on the pointer multimeter, with a digital multimeter measurement table pen intermodulation), the normal when the needle should be a small direction to the small swing, and then gradually return to infinity. The greater the swing of the stylus or the slower the return, indicating that the larger the capacity of the capacitor, the smaller the capacitance of the capacitor. If the reference pin is no longer changed in the middle, indicating that the capacitor leakage, if the resistance indication is small or zero, it indicates that the capacitor has been short-circuit. Because the multimeter battery voltage is generally very low, so the measurement of low-voltage capacitor when the more accurate, and when the capacitor voltage is high, although the measurement of normal, but with high pressure when there may be leakage or hit Wear phenomenon.
More need to understand the use of electrolytic capacitors precautions
1, electrolytic capacitors due to positive and negative polarity, so the circuit can not be used when the reverse connection. In the power supply circuit, the output positive voltage when the electrolytic capacitor is connected to the power supply output, the negative ground. Output negative voltage when the negative output terminal, positive ground.
When the power supply circuit in the filter capacitor polarity reversed, due to the capacitance of the filtering effect greatly reduced. On the one hand caused the power supply output voltage fluctuations, on the other hand because of reverse power so that this time equivalent to a resistance of the electrolytic capacitor heat. When the reverse voltage exceeds a certain value, the capacitance of the reverse leakage resistance will become very small, so that power work soon, you can make the capacitor due to overheating and burst damage.
2, the voltage applied to both ends of the electrolytic capacitor can not exceed its allowable operating voltage, in the design of the actual circuit should be based on the specific circumstances left a certain margin, in the design of the power supply filter capacitor, if the AC power supply voltage of 220 ~ Transformer secondary rectifier voltage up to 22V, PCB proofing at this time to choose the voltage of 25V electrolytic capacitors generally meet the requirements. However, if the AC power supply voltage fluctuations and may rise to 250V or more, it is best to choose more than 30V voltage electrolytic capacitor.
3, electrolytic capacitors in the circuit should not be close to high-power heating elements, to prevent the heat caused by accelerated drying of the electrolyte.
4, for the positive and negative polarity of the signal filtering, can take two electrolytic capacitors with the polarity of the series method, as a non-polar capacitor.
5, the capacitor shell, auxiliary lead terminal and positive, negative and circuit board must be completely isolated.