How do electrolytic capacitors function in switching power supplies?
The functions of electrolytic capacitors in switching power supplies are: bypass, decoupling, filtering, and energy storage.
1. The bypass capacitor is an energy storage device that provides energy for local devices. It can equalize the output of the voltage regulator and reduce the load demand. Like a small rechargeable battery, the bypass capacitor can be charged and discharged to the device.
2. Decoupling: specifically refers to the removal of noise on the power supply pins of the chip, which is generated by the chip itself. Configuring decoupling capacitors can suppress the noise generated by load changes, which is a common practice in the reliability design of printed circuit boards.
3. Filtering: Capacitors convert voltage changes into current changes. The higher the frequency, the greater the peak current, thus buffering the voltage. Filtering is the process of charging and discharging.
Electrolytic capacitor is a kind of capacitor, the metal foil is the positive electrode (aluminum or tantalum), the oxide film (aluminum oxide or tantalum pentoxide) close to the metal is the dielectric, the cathode is made of conductive material, electrolyte (the electrolyte can be liquid or Solid) and other materials, because the electrolyte is the main part of the cathode, so the name of the electrolytic capacitor. At the same time, the positive and negative of the electrolytic capacitor cannot be connected incorrectly. Aluminum electrolytic capacitors can be divided into four categories: lead-type aluminum electrolytic capacitors; horn-type aluminum electrolytic capacitors; bolt-type aluminum electrolytic capacitors; solid aluminum electrolytic capacitors.
Precautions
1. Since the electrolytic capacitor has positive and negative polarity, it cannot be connected upside down when used in the circuit: in the power circuit,
When outputting a positive voltage, the positive pole of the electrolytic capacitor is connected to the output terminal of the power supply, and the negative pole is grounded. When outputting a negative voltage, the negative pole is connected to the output terminal, and the positive pole is grounded.
When the polarity of the filter capacitor in the power supply circuit is reversed, the filter effect of the capacitor is greatly reduced, which causes fluctuations in the output voltage of the power supply on the one hand, and acts as a resistor on the other hand, which is prone to heat. When the reverse voltage exceeds a certain value, the reverse leakage resistance of the capacitor will become very small, so that the capacitor may burst and be damaged due to overheating soon after it is powered on.
2. The voltage applied to both ends of the electrolytic capacitor should not exceed its allowable working voltage, and a certain margin should be left according to the actual situation when designing the actual circuit. When designing the filter capacitor of the regulated power supply, if the AC power supply voltage is 220V, the rectified 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 voltage fluctuates greatly and may rise above 250V, it is best to choose an electrolytic capacitor with a withstand voltage above 30V.
3. Electrolytic capacitors should not be placed close to high-power heating elements in the circuit to prevent the electrolyte from drying up quickly due to heat.
4. For the filtering of signals with positive and negative polarity, two electrolytic capacitors with the same polarity can be connected in series and used as a non-polar capacitor.
