What is the role ofelectrolyticcapacitorsin switching power supplies?
The role of electrolytic capacitors in switching power supplies are: bypass, decoupling, filtering, energy storage.
1, bypass capacitors are energy storage devices that provide energy to the local device, which can even out the output of the regulator and reduce the load demand. Like a small rechargeable battery, bypass capacitors can be charged and discharged to the device.
2, decoupling: specifically refers to the removal of noise on the chip power tube pin, the noise is generated by the chip itself work. Configuration decoupling capacitors can be suppressed due to load changes in the noise generated by the printed circuit board is a conventional practice of reliability design.
3, filtering: capacitors convert voltage variations into current changes, the higher the frequency, the greater the peak current, thus buffering the voltage. Filtering is the process of charging, discharging.
Electrolytic capacitor is a kind of capacitor, metal foil for the positive pole (aluminium or tantalum), and the positive pole close to the metal oxide film (aluminium oxide or tantalum pentoxide) is the dielectric, the cathode by the conductive material, electrolyte (electrolyte can be liquid or solid) and other materials together, because the electrolyte is the main part of the cathode, electrolytic capacitor is therefore named. At the same time electrolytic capacitors positive and negative can not be connected to the wrong. Aluminium electrolytic capacitors can be divided into four categories: leaded aluminium electrolytic capacitors; bullhorn aluminium electrolytic capacitors; bolted aluminium electrolytic capacitors; solid state aluminium electrolytic capacitors.
Cautions
1, because electrolytic capacitors have positive and negative polarity, so when used in the circuit can not be inverted connection: in the power supply circuit.
In the power supply circuit, the positive pole of the electrolytic capacitor is connected to the output terminal of the power supply when outputting positive voltage, and the negative pole is connected to the ground. When outputting negative voltage, the negative terminal is connected to the output terminal, and the positive terminal 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, on the one hand, causing the power supply output voltage fluctuations, on the other hand, it is equivalent to a resistor, easy to heat up. When the reverse voltage exceeds a certain value, the reverse leakage resistance of the capacitor will become very small, so that shortly after power-on, the capacitor may be damaged due to overheating and cracking.
2, added to the electrolytic capacitor voltage can not exceed the permissible operating voltage, in the design of the actual circuit should be based on the specific circumstances to leave a certain margin. In the design of regulated power supply filter capacitors, if the AC power supply voltage of 220V, the transformer secondary side of the rectifier voltage up to 22V, this time the choice of 25V electrolytic capacitors can generally meet the requirements. However, if the AC power supply voltage fluctuations and may rise to more than 250V, it is best to choose more than 30V electrolytic capacitors.
3, electrolytic capacitors in the circuit should not be close to high-power heating elements, in order to prevent the electrolyte from heat to accelerate the drying.
4, for positive and negative polarity of the signal filtering, can take two electrolytic capacitors with the same polarity in series, as a non-polar capacitor.
