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16

2022

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08

What are the applications of electrolytic capacitors?

Electrolytic capacitors are used in many industries. Since many readers are not familiar with them, we will take this opportunity to introduce them. If you are interested, please read on; it may be helpful. Although electrolytic capacitors have a wide range of applications, they also involve many aspects of knowledge. First, you should know that electrolytic capacitors are so named because they use an electrolyte as the negative electrode (note the difference between electrolyte and dielectric). Non-polar electrolytic capacitors are commonly used in speaker crossover circuits, TV correction circuits, and single-phase motor starting circuits. In addition to what I have mentioned, there are also polar electrolytic capacitors, which are commonly used in power circuits or medium and low-frequency circuits for power filtering, decoupling, signal coupling, time constant setting, and DC isolation. Of course, as you can see, electrolytic capacitors are generally not used in AC power circuits. When used as filter capacitors in DC power circuits, the anode (positive electrode) should be connected to the positive terminal of the power supply voltage, and the cathode (negative electrode) should be connected to the negative terminal of the power supply voltage. Reversal is not allowed, otherwise, the capacitor will be damaged. Electrolytic capacitors also have good development prospects. For example,

04

2022

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08

How to check non-polar electrolytic capacitors? How to test chip electrolytic capacitors? Let's find out.

Non-polar electrolytic capacitors have a very large capacitance per unit volume, tens to hundreds of times larger than other types of electrolytic capacitors. Its rated capacitance can be very large, easily reaching tens of thousands of f or even several F (but not as large as double-layer capacitors). The inspection of such goods is also important, mainly the infinite constraint. So, how to check the capacitance of a non-polar electrolytic capacitor? The following points: 1. Accurate selection of the multimeter's resistance range Since the capacitance of a non-polar electrolytic capacitor is far greater than that of a typical fixed electrolytic capacitor, an appropriate range should be selected according to the different capacitances. Generally, capacitors between 1-47uf can be measured using the R*1k range, and capacitors greater than 47uf can be measured using the R*100 range. 2. Measuring leakage resistance Connect the red probe of the multimeter to the negative pole and the black probe to the positive pole. At the moment of contact, the multimeter pointer will deflect to the right by a large amount (the same resistance, the larger the capacitance, the greater the swing), then gradually reverse to the left until it stops at a certain position. Then, switch the red and black probes, and the multimeter pointer will repeat the above shaking scene. However, the measured resistance is the reverse leakage resistance of the electrolytic capacitor, which is slightly smaller than the forward leakage resistance

27

2022

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07

Are you familiar with the failure modes and causes of electrolytic capacitors?

Electrolytic capacitors use an aluminum cylinder as the negative electrode, containing a liquid electrolyte, and inserting a bent aluminum strip as the positive electrode. It also requires DC voltage processing to form an oxide film on the anode plate that serves as the dielectric. Its characteristics include large capacitance, large leakage, poor stability, and defined polarity; it is suitable for power filters or low-frequency circuits. Electrolytic capacitors can sometimes malfunction. However, due to differences in materials, structure, manufacturing process, performance, and operating environment among various electrolytic capacitors, the failure mechanisms also vary. Below are some common failure modes of electrolytic capacitors: leakage, explosion, open circuit, breakdown, and deterioration of electrical parameters. 1. Liquid Leakage Leakage is one of the reasons for electrolytic capacitor failure. The working electrolyte of an electrolytic capacitor is acidic. If it spills, it will severely contaminate and corrode other components and the printed circuit board around the electrolytic capacitor. At the same time, inside the electrolytic capacitor, the working electrolyte gradually dries up due to liquid leakage, losing its ability to repair the anodic oxide film dielectric, leading to the breakdown of the electrolytic capacitor or deterioration of electrical parameters, resulting in failure. 2. Explosion Excessive AC component in the electrolytic capacitor's operating voltage, many defects in the oxide film dielectric, or the presence of chloride ions, sulfate radicals, etc., can cause an explosion.

19

2022

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07

What are the causes of electrolytic capacitor explosion? How to select electrolytic capacitors?

There are many reasons for electrolytic capacitor explosion, such as current exceeding the promised ripple current, applied voltage exceeding the operating voltage, reverse voltage, frequent charge and discharge, etc. However, the direct cause is still high temperature. We know that an important parameter of an electrolytic capacitor is its temperature resistance, which refers to the boiling point of the electrolyte inside the capacitor. When the internal temperature of the capacitor reaches the boiling point of the electrolyte, the electrolyte begins to boil, and the internal pressure of the electrolytic capacitor rises. When the pressure exceeds the acceptance limit of the explosion-proof door, explosion will occur. Therefore, temperature is the direct cause of capacitor explosion. The planned service life of an electrolytic capacitor is about 20,000 hours, which is greatly affected by the ambient temperature. The service life of an electrolytic capacitor decreases with increasing temperature. Experiments show that for every 10℃ increase in ambient temperature, the service life of an electrolytic capacitor is halved. The main reason is that the temperature accelerates the chemical reaction, leading to the degradation and failure of the dielectric over time, thus ending the life of the electrolytic capacitor. In order to ensure the stability of the electrolytic capacitor, before plugging in the board, the capacitor must be tested for a long time in a high-temperature environment. Even at 100℃, high-quality capacitors can work for thousands of hours. Together, the life of an electrolytic capacitor we are talking about refers to the electrolytic capacitor

Factors to consider in common-mode inductor design

07

2022

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07

Factors to consider in common-mode inductor design

Many electromagnetic interference (EMI) filters require the use of common-mode inductors. Common-mode inductors exhibit high impedance over a wide frequency range, thus suppressing high-frequency noise generated by high-frequency switching power supplies. Let's explore the factors to consider when designing common-mode inductors.

Working principle of common-mode inductor

01

2022

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07

Working principle of common-mode inductor

The common-mode inductor filtering circuit, where La and Lb are common-mode chokes. The two coils are wound on the same core, having the same number of turns and phase (opposite direction). In this way, when the normal operating current in the circuit can flow through the common-mode inductor, the current generates a reverse-affecting magnetic field in the in-phase wound common-mode inductor, and the effects cancel each other out.

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