Tips: Industry insiders explain how to choose capacitors in switching power supply design

To ensure reliable operation, the rated voltage of tantalum capacitors must be reduced. For example, the operating voltage of a D-type tantalum capacitor rated at 10uF/35V should be 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.

High voltage power bus systems generally have difficulty achieving a 50% reduction in rated voltage. This situation limits the use of tantalum capacitors for applications with voltage rails greater than 28V. Currently, due to the need to derate tantalum capacitors, the only viable solution for high voltage filtering applications is to use larger leaded electrolytic capacitors instead of tantalum capacitors.

New Tantalum Capacitors

To solve the problem of reducing the rated voltage, Vishay R&D has developed a new series of SMD solid tantalum capacitors with higher rated voltage levels, with rated voltages up to 75WVDC. The use of 50V rated voltage capacitors in 28V and higher voltage rails has caused concerns among designers, but the use of Vishay's new 63V and 75V tantalum capacitors can achieve an industry-recognized safety indicator of a 50% reduction in rated voltage. Thinner and more consistent dielectric formation enables the rated voltage of SMD solid tantalum capacitors to reach 75V, thus achieving a technological breakthrough in increasing the rated voltage. Improvements have been made to multiple processes 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. The rated voltage of the new capacitor T97 series is 75V, and the 83 series is 63V.

Wireless inductive coupling charging

A large number of inductive chargers use flyback converters. Inductive charging provides charging power for medical device batteries. Inductive chargers are also used in a large number of portable devices (such as toothbrushes).

Reducing the size of rechargeable batteries can help reduce the size of implantable medical devices that use wireless inductive charging circuits. Wireless inductive chargers can safely charge tiny thin-film rechargeable energy storage devices (such as CymbetEnerChip) installed on the device. The inductive charger uses the working principle of a parallel LC (inductor, capacitor) resonant energy storage circuit.

Vishay 595D series 1000uF tantalum capacitors are used as C5 capacitors on the Cymbet receiver circuit board to provide pulse current for loads such as radio transmitters. This inductive charger has good isolation between the input and output, which is an important requirement for medical equipment.

In some higher voltage inductive charger applications, high voltage stable capacitors are required as resonant capacitors. Since the primary coil of the inductive charger needs to be driven by AC voltage, the capacitor must be adjusted accordingly. The inductive charger needs to have high breakdown voltage (VBD) performance. At the same time, protection against high voltage arc discharge is also required in some applications. To avoid arc discharge, the circuit board is generally coated with a protective coating, or the high voltage side is isolated from the rest of the circuit board by properly arranging the component layout. However, this method often requires a lot of circuit board space because high voltage circuits usually use large leaded through-hole capacitors. High Voltage Arc Protection Capacitor Solution

To solve this problem, Vishay has introduced a series of HVArc (high voltage arc) protection MLCC (multilayer ceramic capacitors) that prevent arc discharge while saving space. These new devices have maximum capacity within higher voltage ratings and improved voltage breakdown tolerance. High voltage arc discharge will cause short circuits and may damage other components . Standard high voltage SMD capacitors will eventually fail and short circuit, depending on the number of arc discharges and the problematic part. Vishay HVArc protection capacitors can absorb all energy, so this capacitor can work normally under high voltage, at least before reaching the high voltage breakdown limit, without destructive arc discharge.

The VBD distribution of HVArc protection capacitors is controlled by the unique design of the device, and the VBD can reach 3kV or more. This product uses NPO and X7R dielectrics.

New non-magnetic capacitor for MRI

Capacitors and other electronic components used in the circuits inside or around magnetic resonance imaging (MRI) equipment need to be shielded or packaged outside the MRI room. The capacitors may contain ferrous or magnetic materials in the dielectric, electrode materials, or termination materials. The magnetic field level of MRI systems is constantly increasing to improve image resolution, and the capacitors used in the MRI room will cause magnetic field distortion. Therefore, it is necessary to reduce or completely eliminate the magnetic materials in most capacitors.

The latest series of MLCCs use non-ferrous materials in the electrode and termination structures to meet the requirements of eliminating magnetization. X7R and NPO dielectrics can be used for non-magnetic structures. The outer dimensions are 0402 to 1812, which meet EIA specifications. Vishay also uses dedicated capacitor sorting equipment during final testing to ensure that all non-magnetic capacitors meet technical requirements.