Capacitor in switching power supply
In electronic medical equipment, high-precision control and adjustment of the power supply is required to support the device to perform each function. AC and DC power supplies are widely used in these occasions. Switching power supplies are used to control these power supplies. Due to their significant advantages, switching power supplies have become standard power supplies for most electronic products.
The 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, a D-type tantalum capacitor rated at 10uF / 35V, the operating voltage should be reduced to 17V. If used to filter ripple at the input of the power supply, a 35V rated tantalum capacitor can work reliably on a voltage rail up to 17V.
High-voltage power bus systems generally have difficulty meeting the target of a 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 larger and leaded electrolytic capacitors instead of tantalum capacitors.
New tantalum capacitor
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. In the forming process, multiple processes have been improved: 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.
Wireless inductively coupled 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 tiny thin 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-EVAL-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 pulsed 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, high voltage arc discharge protection is also required in certain applications. In order to avoid arc discharge, the circuit board is generally covered with a protective coating, or the layout of components can be reasonably arranged 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.
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 the maximum capacity within a higher voltage rating and improve the 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 parts. 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 above. This product uses NPO and X7R dielectric.
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 ferrous 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 MLCC uses 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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