Electrolytic capacitor is one of the essential electronic components in circuit design, so it is the goal of every engineer to make full use of the advantages of electrolytic capacitor and make it give full play to its maximum effect. So, what should be paid attention to in the selection of electrolytic capacitor in power supply circuit?
First, let's understand the advantages and disadvantages of aluminum electrolytic capacitors:
Advantages: it has the obvious advantages of easy access to large capacity, high withstand voltage and low price. It is commonly used in the input and output filter circuit of power supply.
Disadvantages: fear of high temperature. Because the electrolyte of aluminum electrolytic capacitor is liquid, core heating or high ambient temperature will lead to electrolyte volatilization, and long-term high temperature will lead to electrolyte drying up and failure.
When we are familiar with the characteristics of electrolytic capacitors, we should select suitable aluminum electrolytic capacitors according to the application requirements in power supply circuits:
1. Prevent halogen corrosion
Aluminum electrolytic capacitor is very sensitive to chlorine and bromine. If halogen containing flux, cleaning agent, fixing agent and fumigant are used, halide may invade into the capacitor through the sealing rubber plug, which is very easy to cause capacitor anode corrosion and accelerate capacitor failure after power on. Therefore, the halogen components of relevant sensitive preparations used in the production process must be strictly controlled.
2. Control and periodic activation of storage environment
It is necessary to control the storage environment and time of electrolytic capacitor and power on regularly.
After aluminum electrolysis is stored at high temperature for a long time, the capacitor anodic oxide film and electrolyte will have a chemical reaction, resulting in the decrease of withstand voltage and the increase of leakage current. When the capacitor voltage is close to the rated voltage when suddenly powered on, it may cause overvoltage failure or large leakage flow, resulting in overheating failure.
The corresponding monomer capacitor, especially the high-voltage capacitor, needs to be activated after long-term storage. It is recommended to connect 1K Ω protective resistance in series, gradually pressurize it to the rated voltage and maintain it for about 1 hour, so that the anodic oxide film of the capacitor can be repaired and the leakage current returns to the normal level.
3. Reasonably arrange the devices on the PCB to keep the aluminum electrolytic capacitor away from the heat source.
4. Select solid-state capacitor according to product characteristics.
For example, aluminum solid-state capacitors are used in applications with low voltage and high current output. Aluminum solid-state capacitor has very low ESR and high ripple current bearing capacity, which is very suitable for low-voltage and high current rectification and filtering occasions.