Switching power supply uses ceramic capacitors and film capacitors

Engineers should be aware that the 60% life of the switching power supply is controlled by the capacitor, so the capacitor used in the switching power supply requires long life, small size, high operating frequency and high temperature resistance. Ceramic capacitors and film capacitors commonly used in switching power supply circuits, this article will explain for you.

ceramic capacitor:

Ceramic capacitors have strong insulation and high insulation resistance. They can be used in high-voltage circuits and have good heat resistance. Ceramic materials have a wide temperature coefficient range and can produce capacitors with different temperature coefficients to suit different applications. The loss tangent of ceramic capacitors has little relationship with frequency, and can be widely used in high-frequency circuits of switching power supplies. The capacitance of ceramic capacitors is relatively small, generally only a few picofarads to a few microfarads. Ceramic capacitors are generally in the form of a pellet, a cylinder or a laminate. Low mechanical strength and easy breakage are disadvantages of ceramic capacitors.

Film capacitors:

Film capacitors are made of materials such as polystyrene, polytetrafluoroethylene, polypropylene or polycarbonate. Film capacitors are classified into two types: polar organic thin films and non-polar organic thin film capacitors. Polar organic film capacitors have the advantages of large capacitance to volume ratio, high temperature resistance and high voltage strength. Non-polar organic film capacitors have the advantages of small loss tangent, large insulation resistance, small dielectric absorption coefficient, and negative temperature coefficient. If a single metal film is uniformly coated on one surface of an organic film and laminated to form a capacitor, it is called a metallized organic film capacitor. The film capacitor has a cylindrical shape, a flat shape, a laminated block shape, and the like. In the film capacitor product model, C represents a capacitor, and B represents polystyrene. It is small in size, light in weight, and has a "self-healing" function.

Film capacitors include six kinds of film capacitors such as polystyrene capacitors, polytetrafluoroethylene capacitors, polypropylene capacitors, polyester capacitors, and polycarbonate capacitors. Polystyrene film capacitors have the following characteristics:

1. Wide pressure range, from 30V to 15KV. The working voltage of ordinary polystyrene capacitor is 100V, and the working voltage of high voltage polystyrene capacitor can reach 10KV~15KV;

2. High insulation resistance, generally greater than or equal to 100000000000 ohms, so the leakage current is small, it can be kept for 95 hours after charging for 1000 hours, and the low-quality capacitor is allowed to stand for 200 hours after charging, and its charge is All released;

3. The tangent value of the loss angle is large, and it is not suitable to use a metallized polypropylene capacitor in a high frequency circuit;

4. The capacitor has a wide capacity range and can produce capacitors of 100PF~100UF;

5. The capacitor has high precision and can produce high precision capacitors of 0.3%~0.1%;

6. The temperature coefficient is small, the performance is stable, acid and alkali resistance, moisture resistance, etc., pay attention to the withstand voltage value and capacitance when using;