This chapter considers various areas of power device application that are often overlooked, or at best, underestimated. Such areas include parallel and series device utilisation, over-current and overvoltage protection, radio frequency interference (rfi) noise, filtering, and interactive noise effects.
پسورد : 4power
Power resistors (≥1W) are used extensively in power electronic circuits, either as a pure dissipative element, or to provide a current limiting path for charging/discharging currents. These energy transfer paths may be either inductive or non-inductive. Resistors are used for the following non-inductive resistance applications.
پسورد : 4power
All power switching devices attain better switching performance if some form of switching aid circuit, called snubber, is employed. Snubber activation may be either passive or active which involves extra power switches. Only passive snubbers, which are based on passive electrical components, are considered in this chapter, while active snubbers are considered in Chapter 9. Fundamentally, the MOSFET and IGBT do not require switching aid circuits, but circuit imperfections, such as stray inductance and diode recovery, can necessitate the need for some form of switch snubber protection.
پسورد: 4power
There is a vast proliferation of power switching semiconductor devices, each offering various features, attributes, and limitations. The principal device families of concern in the power switching semiconductor range are the diode, transistor, and thyristor. Each family category has numerous different members. The basic characteristics of the three families and a range of their members, both uni-polar and bipolar carrier types, will be presented.
پسورد : 4power
Inversion is the conversion of dc power to ac power at a desired output voltage or current and
frequency. A static semiconductor inverter circuit performs this electrical energy inverting transformation. The terms voltage-fed and current-fed are used in connection with the output from inverter circuits. A voltage-source inverter (VSI) is one in which the dc input voltage is essentially constant and independent of the load current drawn. The inverter specifies the load voltage while the drawn current shape is dictated by the load.
پسورد:4power
Power switching devices are employed for controlling inductive, resistive or capacitive loads. Inductive loads include electrical machines, transformers, solenoids, and relays. High-current in-rush occurs with loads such as incandescent lamps, pulse-forming networks, snubbers, and motors. Incandescent lamps are essentially resistive, but the cold resistive in-rush current during turn-on is 12 to 18 times the steady-state current. This turn-on surge presents special switch-on problems. Capacitive loads, such as fluorescent lighting, also present high-current in-rush at turn-on. Electromechanical loads, such as shakers, present loads that vary between capacitive and inductive over their operating frequency range.
پسورد : 4power
Semiconductor device characteristics and ratings are primarily concerned with electrical and thermal properties. The thermal properties and cooling design aspects are similar for all power switching semiconductor devices. A common, unified thermal design approach is applicable since manufacturers use the concept of a semiconductor device being thermally represented by one virtual junction. This virtual junction is considered as the point source of all losses, which comprise on-state and off-state losses as well as switch-on and switch-off losses and any control input loss.
پسورد : 4power
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