Common Faults of Electrolytic Capacitors in Switching Power Supplies
The common faults of electrolytic capacitors include capacity reduction, capacity disappearance, short circuit breakdown, and leakage. The capacity change is caused by the gradual drying of the electrolyte inside the electrolytic capacitor during use or heating (generally speaking, the capacity decreases with high temperature), while breakdown and leakage are generally caused by excessive voltage applied or poor quality of the capacitor itself.
matters needing attention
1. Due to the positive and negative polarity of electrolytic capacitors, they cannot be reversed when used in circuits: in power circuits,
When outputting 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 pole is connected to the output terminal and the positive pole is grounded.
When the polarity of the filtering capacitor in the power circuit is reversed, the filtering effect of the capacitor is greatly reduced, which not only causes fluctuations in the output voltage of the power supply, but also acts as a resistor, 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 be damaged due to overheating shortly after being energized.
2. The voltage applied to both ends of the electrolytic capacitor should not exceed its allowable operating voltage, and a certain margin should be left according to the specific situation when designing the actual circuit. When designing the filtering capacitor for a 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 supply voltage fluctuates greatly and may rise above 250V, it is best to choose electrolytic capacitors with a withstand voltage of 30V or above.
3. Electrolytic capacitors should not be placed near high-power heating elements in circuits to prevent accelerated drying of the electrolyte due to heat.
4. For filtering signals with positive and negative polarities, two electrolytic capacitors with the same polarity can be connected in series and used as a non-polar capacitor.
