Understand the use of electrolytic capacitors
1. Since the electrolytic capacitor has positive and negative polarity, it cannot be reversed when used in the circuit. In the power supply circuit, when the positive voltage is output, the positive pole of the electrolytic capacitor is connected to the output end of the power supply, and the negative pole is grounded. When a negative voltage is output, the negative terminal is connected to the output terminal, and the positive electrode 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, the power supply output voltage fluctuates, and on the other hand, the electrolytic capacitor corresponding to one resistor is heated by the reverse energization. When the reverse voltage exceeds a certain value, the reverse leakage resistance of the capacitor will become small, so that the power supply will work shortly, and the capacitor may be broken due to overheating.
2. The voltage applied to the two ends of the electrolytic capacitor should not exceed the allowable working voltage. When designing the actual circuit, there should be a certain margin according to the specific conditions. When designing the filter capacitor of the regulated power supply, if the AC power supply voltage is 220~ The rectification voltage of the secondary of the transformer can reach 22V. At the time of PCB proofing, the electrolytic capacitor with a withstand voltage of 25V can generally meet the requirements. However, if the AC power supply voltage fluctuates greatly and it is possible to rise above 250V, it is best to select an electrolytic capacitor with a withstand voltage of 30V or higher.
3. The electrolytic capacitor should not be close to the high-power heating element in the circuit to prevent the electrolyte from accelerating due to heat.
4. For the filtering of signals with positive and negative polarity, two electrolytic capacitors can be used in series with the same polarity as a non-polar capacitor.
5. The capacitor case and auxiliary lead-out terminals must be completely isolated from the positive and negative terminals and the circuit board.