App note: Using trench technology MOSFETs in hot swap applications

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Safely use trench MOSFETs on hot swap application by determining its operation within its SOA in a limited time, app note from International Rectifier. Link here (PDF)

Hot Swap circuits are used to allow for “Hot Plugging” of circuit boards into back planes. The applications that require such functionality are mission critical, such as servers and communications equipment that must operate continuously. These circuit boards are usually employed in a rack mount system which consists of an array of boards that cannot be powered down. Thus hot swapping allows for a bad board in the array to be replaced without powering down the entire system.

In essence the Hot Swap circuit, which is between the board input rail and the rest of the board’s circuitry, is an inrush current limiter that allows for charging of the bulk capacitance in a controlled manner. Also faults, such as over current and overvoltage are managed by Hot Swap circuits.

App note: Class D audio amplifier performance relationship to MOSFET parameters

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Application note from International Rectifier on MOSFET paremeters to consider when designing a Class D audio amplifier. Link here (PDF)

Class D audio amplifier is a switching amplifier that consists in a pulse width modulator (with switching frequency in order of several hundred kHz), a power bridge circuit and a low pass filter. This type of amplifier has demonstrated to have a very good performance. These include power efficiencies over 90%, THD under 0.01%, and low EMI noise levels that can be achieved with a good amplifier design.

Key factors to achieve high performance levels in the amplifier are the switches in power bridge circuit. Power losses, delay times, and voltage and current transient spikes should be minimized as much as possible in these switches in order to improve amplifier performance. Therefore, switches with low voltage drop, fast on and off switching times and low parasitic inductance are needed in this amplifier.

MOSFET have proved to be the best switch option for this amplifier because of its switching speed. It is a majority carrier device, its switching times are faster in comparison with other devices such as IGBT or BJT, resulting in better amplifier efficiency and linearity.

App note: 12Vac LED Driving without smoothing capacitors

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Application note from Diodes Incorporated on driving 12Vac LED without smoothing capacitors with their Zetex ZXLD1360 LED driver IC and SBR2A40P1 super barrier rectifier. Link here (PDF)

LED based architectural lighting is now coming of age, but there are still some problems to be considered when designing luminaires to be fitted into existing installations.

This Application Note discusses some of the challenges and shows that the omission of the traditional smoothing capacitors has advantages in saving cost, space and PFC problems.

App note: CAN Bus – Common high speed physical layer problems

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App note from Vector on three commonly encountered high speed CAN physical layer problems – bus termination, signal levels, and ground. Link here (PDF)

Determining the exact cause of a CAN problem is not at all simple.

Is the problem in hardware or software? Is the problem on the circuit board or on the CAN network wiring?
Sometimes the problem may not be at the module level – perhaps the cause is up at the system level.

This application note discusses methods used to investigate serveral of the more common CAN Physical Layer problems typically encountered when debugging high-speed CAN.

App note: Through-Hole versus SMD components

App note from Vishay on the advantages of using Through-Hole mounting. Link here (PDF)

Most electronic gadgets are designed to interface with humans, and we humans are very abusive to most electronic devices. We drop them, poke them, open and close them, and in general feed stuff into and out of them.

It is well understood that a through-hole connection to the PCB is mechanically stronger than most surface-mount connections. By comparison, the strength of the bond that holds a surface-mount component to the PCB is limited to the strength of the solder joint that holds it to the surface of the laminate. As parts get smaller, so does the amount of solder and thus the strength of the bond.

App note: Thermal management in surface-mounted resistor applications

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App note from Vishay on PCB thermal management specifically on components like SMD resistors, where if allowed a design change (e.g. change in SMD size or change in more heat tolarant ones) must be implemented in order to squeeze more thermal capability. Link here (PDF)

Thermal management is becoming more important as the density of electronic components in modern printed circuit boards (PCBs), as well as the applied power, continues to increase. Both factors lead to higher temperatures of individual components and of the entire assembly. However, every electrical component in an assembly has to be used within its prescribed operating temperature limits due to its material properties and reliability aspects. In this application note, experimental results are provided in order to prevent overheating of electronic devices such as surface-mount resistors.

App note: Minimizing the temperature dependence of digital potentiometers

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Application notes from NIDEC COPAL Electronics Corp. about digital potentiometer’s temperature dependence. Link here (PDF)

The digital potentiometers (DP) has two temperature dependent parameters, the TC of the end-to-end resistance Rpot and the ratiometric TC. The temperature dependence of the parameters of an analog circuit using a digital potentiometers is reduced if the performance of the circuit is shifted from the TC of the end-to-end resistance of the pot to the ratiometric TC.

App note: Potentiometers and trimmers

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App note from Vishay on variable resistors primer. Link here (PDF)

A potentiometer is a mechanically actuated variable resistor with three terminals. Two of the terminals are linked to the ends of the resistive element and the third is connected to a mobile contact moving over the resistive track. The output voltage becomes a function of the position of this contact. Potentiometer is advised to be used as a voltage divider.

App note: How RF transformers work and how they are measured

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Application note from Mini-Circuits about transformers, this time the RF transformers. Link here (PDF)

RF transformers are widely used in electronic circuits for
* Impedance matching to achieve maximum power transfer and to suppress undesired signal reflection.
* Voltage, current step-up or step-down.
* DC isolation between circuits while affording efficient AC transmission.
* Interfacing between balanced and unbalanced circuits; example: balanced amplifiers.

App note: Transformers

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App note from Mini-Circuits on transformer types and some basics of them. Link here (PDF)

The purpose of this application note is to describe the fundamentals of RF and microwave transformers and to provide guidelines to users in selecting proper transformer to suit their applications. It is limited to core-and-wire and LTCC transformers.