App note: HVArc Guard® surface-mount capacitors for low-power voltage multiplier applications


Application note on Vishay’s arc resistant SMD capacitors, Link here (PDF)

Voltage multipliers can generate very high voltages due to an inverter circuit that feeds a step-up transformer, which is connected to the multiplier circuit. An example of a typical voltage multiplier, which is simply a circuit comprised of capacitors and diodes that charge and discharge in alternating half cycles of the applied AC voltage. Applications for voltage multipliers include flyback converters, where a high voltage is produced from a low battery or supply voltage in medical X-ray systems, air ionizers, and oscilloscopes, and instrumentation requiring a high-voltage power supply.

When a high voltage potential is applied at > 1000 V, an arc-over between the terminals, or from terminal to case will occur. To eliminate any arc-over, an overcoating can be applied to the board, or additional board layout spacing can be added to isolate the high-voltage section from other sections of the board. Although coatings add cost to the process and the design, they are required in some applications to meet electrical safety standards.

App note: AC film capacitors in connection with the mains


An application note from Vishay about choosing the right filter capacitors that are placed directly on mains. Link here (PDF)

To help reducing emission and increasing the immunity of radio interference, electromagnetic interference suppression film capacitors (EMI capacitors) are playing a major role in all kind of applications. These capacitors are put directly parallel over the mains at the input of the appliances.

Because of the high energy availability and the severe environment of surge voltages and pulses, applications of capacitors in connection with the mains must be chosen carefully. Two kinds of connections and thus two kinds of applications can be distinguished. One is where the capacitor is directly connected in parallel with the mains without any other impedance or circuit protection, and another where the capacitor is connected to the mains in series with another circuitry.

App note: Power MOSFET in high-side operating modes, possible failure modes, and failure signatures


App note from Vishay on high-side MOSFET failures investigation leads to one of the following modes of operation:
(a) High-impedance gate drive
(b) Electro-static discharge (ESD) exposure
(c) Electrical over-stressed (EOS) operation

More on it here (PDF)

Power MOSFET failures in high-side applications can often be attributed to a high-impedance gate drive creating a virtual floating gate, which in turn increases the susceptibility of the MOSFET to failure during system-generated ESD and EOS scenarios.

App note: Power MOSFET Basics: Understanding the Turn-On Process


More to know about MOSFET gate threshold voltages, an application note from Vishay. Link here (PDF)

The question of how to turn on a MOSFET might sound trivial, since ease of switching is a major advantage of field-effect transistors. Unlike bipolar junction transistors, these are majority carrier devices. One does not have to worry about current gain, tailoring the base current to match the extremes of hfe and variable collector currents, or providing negative drives. Since MOSFETs are voltage driven, many users assume that they will turn on when a voltage, equal to or greater than the threshold, is applied to the gate. However, the question of how to turn on a MOSFET or, at a more basic level, what is the minimum voltage that should be applied to the gate, needs reappraisal with more and more converters being controlled digitally. While digital control offers the next level of flexibility and functionality, the DSPs, FPGAs, and other programmable devices with which it is implemented are designed to operate with low supply voltages. It is necessary to boost the final PWM signal to the level required by the MOSFET gate. This is where things begin to go wrong, because of the misconceptions about what really turns on a MOSFET. Many digital designers look at the gate threshold voltage and jump to the conclusion that, just as with their digital logic, the MOSFET will change state as soon as the threshold is crossed.