Electrolytic capacitor is one of the essential components of almost all switching power supplies, so I will talk about it today. If you know something about the switching power supply, or have repaired the switching power supply, you will know that on the high-voltage side of the circuit, the electrolytic capacitor is eye-catching and plays a huge role, which determines the purity of the power supply and is also a vulnerable component. Today, I will talk about some characteristics of the electrolytic capacitor and matters needing attention in maintenance and replacement in combination with the actual situation.
The electrolytic capacitor used in switching power supply is mainly used for filtering and purifying the circuit. Many switching power supplies connect two capacitors in series between the direct current coming out of the rectifier bridge, as shown in the figure. This is the main function of filtering, and almost all the knowledge points of electrolytic capacitor are included in this place. I will start with this point and explain it.
First, it is filtered in parallel in the DC circuit, reflecting its characteristics of passing AC but blocking DC. If the DC circuit is not blocked, it will be too short-circuited and explode directly. Passing AC and blocking DC is actually the commonality of all capacitors, so I won't talk about it here.
Secondly, because it is used behind the rectifier bridge of switching power supply, it is a pulsating DC circuit with very low frequency, not a high-frequency occasion, which shows that the electrolytic capacitor is used in low-frequency occasions. If you often contact the circuit, you will know that the electrolytic capacitor will not be used in high-frequency circuits, which is also its application limitation.
Thirdly, these two capacitors are connected in series and connected in parallel behind the rectifier bridge. The rectified rectifier bridge should produce about 310 volts of DC, while the rated voltage of the two capacitors connected in series on the diagram is 200 volts, which shows a problem. The capacitors connected in series can distribute voltage like resistors, but the capacity of the capacitors is getting smaller and smaller, which means that two capacitors with a capacity of 220uF are used after being connected in series, and its capacity is equivalent to 110uF, and vice versa.
Fourthly, from the way that the two capacitors on the switching power supply are connected in series first and then in parallel, we can make a deeper understanding. After the rectifier block is rectified, the power supply is divided into positive and negative points, and the electrolytic capacitor used behind it is also divided into positive and negative points. Since there are positive and negative points here, the electrolytic capacitor cannot be used wrongly or reversed, otherwise, it will explode directly after the reverse connection is electrified, which is very dangerous.
Fifth, the fourth item is to replace the electrolytic capacitor when repairing the switching power supply. In the welding process, besides paying attention to the polarity, it should be fast, because the electrolytic capacitor contains electrolyte. Don't let the soldering iron destroy the sealing performance at high temperature, resulting in liquid leakage during use, which will affect performance and life.
