How to choose capacitors for switching power supplies-EEWORLD

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　　Switching power supplies are used to control these power supplies. Due to their significant advantages, switching power supplies have become the standard power supply for most electronic products. Capacitors can be used to reduce ripple and absorb the noise generated by switching regulators. They can also be used for post-regulation to improve the stability and transient response of the equipment. There should be no ripple noise or residual jitter in the power supply output. Tantalum capacitors are often used in these circuits to reduce ripple, but tantalum capacitors may be affected by the noise of switching regulators and produce unsafe transients.

　　To ensure reliable operation, the rated voltage of tantalum capacitors must be reduced. For example, a D-type tantalum capacitor rated at 10uF/35V should have an operating voltage reduced to 17V. If used to filter ripple at the power input, a 35V rated tantalum capacitor can work reliably on a voltage rail as high as 17V. It

　　is generally difficult for high-voltage power bus systems to achieve a 50% reduction in rated voltage. This situation limits the use of tantalum capacitors for applications with voltage rails greater than 28V. Currently, because tantalum capacitors need to be derated, the only feasible way to use high-voltage filtering applications is to use larger electrolytic capacitors with leads instead of tantalum capacitors.

　　New Tantalum Capacitors

　　To address the issue of reduced rated voltage, Vishay R&D has developed a new series of SMD solid tantalum capacitors with higher rated voltage levels, rated up to 75WVDC. The use of 50V rated voltage capacitors in 28V and higher voltage rails has caused concerns among designers, but with Vishay's new 63V and 75V tantalum capacitors, the industry-recognized safety indicator of a 50% reduction in rated voltage can be achieved. Thinner and more consistent dielectric formation enables SMD solid tantalum capacitors to achieve a rated voltage of 75V, thus achieving a technological breakthrough in increasing rated voltage. Multiple process steps have been improved in the forming process: reducing the concentration of mechanical stress generated during the forming process, reducing local overheating of the electrolyte during the capacitor forming process, and improving the consistency of electrolyte concentration and purity during the dielectric forming process.

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