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teach you how to choose switching power supply capacitors?

Source:AdminAuthor:WPOWER Addtime:2020-06-01 Click:
  Editors of power adapter manufacturers teach you how to choose switching power supply capacitors? The switching power supply capacitor can be used to reduce ripple and absorb the noise generated by the switching regulator. It can also be used for post-stage voltage regulation to improve the stability and transient response of the device. No ripple noise or residual jitter should appear in the power supply output. These circuits often use tantalum capacitors to reduce ripple, but tantalum capacitors may be affected by the noise of the switching regulator and produce unsafe transients.
 
To ensure reliable operation, the rated voltage of the tantalum capacitor must be reduced. For example, the D-type tantalum capacitor rated at 10uF / 35V, the operating voltage should be reduced to 17V, if used to filter ripple at the power input, the 35V rated tantalum capacitor can work reliably on the voltage rail up to 17V. The high-voltage power bus system is generally difficult to achieve the target of 50% reduction in rated voltage. This situation limits the use of tantalum capacitors for applications with voltage rails greater than 28V. At present, because tantalum capacitors need to be derated, the only feasible method for high-voltage filtering applications is to use electrolytic capacitors with larger volume and lead wires instead of tantalum capacitors.
1. New tantalum capacitors:
In order to solve the problem of lowering the rated voltage, Vishay's R & D department has developed a new series of SMD solid tantalum capacitors with higher rated voltage levels, rated voltages up to 75WVDC. The application of 50V rated voltage capacitors in 28V and higher voltage rails has caused design People's concerns, and the use of Vishay's new 63V and 75V tantalum capacitors can achieve industry-recognized safety indicators with a 50% reduction in rated voltage. The dielectric forming is thinner and more consistent, so that the rated voltage of the SMD solid tantalum capacitor can reach 75V, thus achieving a technical breakthrough to increase the rated voltage. Several processes have been improved in the forming process: the mechanical stress concentration generated during the forming process is reduced, the local overheat of the electrolyte during the capacitor forming process is reduced, and the consistency of the electrolyte concentration and purity during the dielectric forming process is improved. The rated voltage of the new capacitor T97 series reaches 75V, and the 83 series reaches 63V.
2. Wireless inductive coupling charging:
A large number of inductive chargers use flyback converters. Inductive charging provides charging power for medical device batteries. At the same time, inductive chargers are also used in a large number of portable devices (such as toothbrushes). Reducing the size of rechargeable batteries helps reduce the size of implantable medical devices that use wireless inductive charging circuits. The wireless induction charger can safely charge the small film (such as Cymbet EnerChip) rechargeable energy storage device installed on the device. The inductive charger uses the working principle of parallel LC (inductor, capacitor) resonant energy storage circuit. Figure 1 shows Cymbet's CBC-eva l-11 RF induction charger evaluation kit.
Vishay 595D series 1000uF tantalum capacitors are used as C5 capacitors in the Cymbet receiving circuit board to provide pulse current for loads such as radio transmission. This induction charger has good isolation between input and output, which is an important requirement for medical equipment. In some inductive charger applications with higher voltages, high-voltage stable capacitors need to be used as resonant capacitors. Since the primary coil of the inductive charger needs to be driven by AC voltage, the capacitance must be adjusted accordingly. Inductive chargers need to have high breakdown voltage (VBD) performance. At the same time, some applications also need to protect against high voltage arc discharge. In order to avoid arc discharge, the circuit board is generally covered with a protective coating, or by reasonably arranging the layout of components to achieve the effect of isolating the high-voltage side from other parts of the circuit board, etc. But this method often requires a lot of circuit board space, because high-voltage circuits usually use large lead-through-hole capacitors.
3. High-voltage arc protection capacitor solution:
To solve this problem, Vishay introduced a series of HVArc (high voltage arc) protection MLCC (multilayer chip ceramic capacitors), which can prevent arc discharge and save space. These new devices have maximum capacity within a higher voltage rating, and have improved voltage breakdown tolerance. High-voltage arc discharge will cause an open circuit 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 protective capacitor can absorb all the energy, therefore, this capacitor can work normally under high voltage, at least before reaching the high voltage breakdown limit, will not produce destructive arc discharge.
The VBD distribution of the HVArc protective capacitor is controlled by the unique design adopted by the device, and the VBD can reach 3kV or more. This product uses NPO and X7R dielectric.
4. New non-magnetic capacitor for MRI:
Capacitors and other electronic components used in magnetic resonance imaging (MRI) equipment or in peripheral circuits need to be shielded or packaged outside the MRI. The capacitor's dielectric, electrode material, or termination material may contain iron or magnetic materials. In order to improve the image resolution, the magnetic field level of the MRI system continues to increase, and the capacitance used in the MRI room will cause magnetic field distortion. Therefore, there is a need 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 structure to meet the requirements of eliminating magnetization. Non-magnetic structure can use X7R and NPO dielectric. The external dimensions are 0402 to 1812, which meets the EIA specifications. Vishay also used special capacitor sorting equipment in the final test to ensure that all non-magnetic capacitors can meet the technical requirements.       

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