How do electrolytic capacitors function in switching power supplies?
The functions of electrolytic capacitors in switching power supply include bypass, decoupling, filtering, and energy storage.
1. Bypass capacitors are energy storage devices that provide energy to local devices, which can homogenize the output of the voltage regulator and reduce load demand. Just like a small rechargeable battery, the bypass capacitor can be charged and discharged into the device.
2. Decoupling: Refers to the removal of noise on the power supply pins of a chip, which is generated by the chip's own operation. Configuring decoupling capacitors can suppress noise caused by load changes and is a common practice in the reliability design of printed circuit boards.
3. Filtering: Capacitors convert changes in voltage into changes in current. The higher the frequency, the greater the peak current, thus buffering the voltage. Filtering is the process of charging and discharging.
Electrolytic capacitors are a type of capacitor, with a metal foil as the positive electrode (aluminum or tantalum), and an oxide film (aluminum oxide or tantalum pentoxide) that is closely attached to the positive electrode as the dielectric. The cathode is composed of conductive materials, electrolytes (which can be liquid or solid), and other materials. As the electrolyte is the main part of the cathode, electrolytic capacitors are named after it. At the same time, the positive and negative terminals of the electrolytic capacitor must not be connected incorrectly. Aluminum electrolytic capacitors can be divided into four categories: lead type aluminum electrolytic capacitors; Ox horn type aluminum electrolytic capacitor; Bolt type aluminum electrolytic capacitor; Solid state aluminum electrolytic capacitors.
matters needing attention
1. Due to the positive and negative polarity of electrolytic capacitors, they cannot be connected upside down when used in circuits: in power circuits,
When outputting a positive voltage, the positive pole of the electrolytic capacitor is connected to the power output terminal and the negative pole is grounded. When outputting negative voltage, the negative electrode is connected to the output terminal and the positive electrode is grounded.
When the polarity of the filtering capacitor in the power supply circuit is reversed, the filtering effect of the capacitor is greatly reduced, causing fluctuations in the output voltage of the power supply on the one hand and acting as a resistor on the other hand, making it easy to generate heat. When the reverse voltage exceeds a certain value, the reverse leakage resistance of the capacitor will become very small, which may cause the capacitor to explode and damage due to overheating shortly after being powered on.
2. The voltage applied to both ends of the electrolytic capacitor cannot exceed its allowable working voltage, and a certain margin should be reserved according to the specific situation when designing the actual circuit. When designing the filtering capacitor of a regulated power supply, if the AC power supply voltage is 220V, the rectification voltage on the secondary side of the transformer can reach 22V. At this time, choosing an electrolytic capacitor with a withstand voltage of 25V can generally meet the requirements. However, if the AC power supply voltage fluctuates greatly and may rise above 250V, it is best to choose an electrolytic capacitor with a withstand voltage of 30V or above.
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 filtering signals with positive and negative polarity, the method of connecting two electrolytic capacitors in series with the same polarity can be used as a non polar capacitor.
