Selasa, 12 Juli 2011

voltage regulator

Typically, electronic voltage regulators employ a feedback network, where a high-gain amplifier compares a fraction of the load voltage VL/k with a constant reference Vref. Any difference between these two voltages is amplified and used to control a series pass device in a manner whereby this difference is minimized. For an ideal amplifier with zero offset and infinite voltage gain, the difference is reduced to zero and the ideal relationship of Eq. (2) is realized. See also Feedback circuit.

The wide range of applications for electronic voltage regulators has led to the development of these circuits in fully monolothic integrated circuit technology, where all or most of the required circuit components are realized on a single chip of silicon. Offering various output current and voltage ratings, and output voltages of either positive or negative polarity, several commercial regulator integrated circuits are now available to suit the requirements of most applications. The designs of these regulators have matured and have become rather sophisticated. In addition to implementation of the high-gain feedback amplifier, the series pass element, and an accurate voltage reference, all on a single silicon die, built-in protection against overload conditions (such as output short circuits and excessive operating temperature) is now standard. Novel circuit-design, processing, and packaging techniques have been developed and implemented to achieve increased accuracy, temperature stability, efficiency, reliability, and power-handling capability, while reducing package size and cost. See also Integrated circuits.

Voltage regulators are used on distribution feeders to maintain voltage constant, irrespective of changes in either load current or supply voltage. Voltage variations must be minimized for the efficient operation of industrial equipment and for the satisfactory functioning of domestic appliances, television in particular. Voltage is controlled at the system generators, but this alone is inadequate because each generator supplies many feeders of diverse impedance and load characteristics. Regulators are applied either in substations to control voltage on a bus or individual feeder or on the line to reregulate the outlying portions of the system. These regulators are variable autotransformers with the primary connected across the line. The secondary, in which an adjustable voltage is induced, is connected in series with the line to boost or buck the voltage. See also Autotransformer; Electric distribution systems; Electric power substation.

Voltage regulators are used on rotating machines in power generation applications to automatically control the field excitation so as to maintain a desired machine output voltage. Rotating machines, both small (down to 1 kW) and large (up to 1,000,000 kW), are the predominant means of power generation throughout the world, and voltage regulators of varying design and sophistication are employed on most of them. Even ac generators (or alternators) in automotive applications employ voltage regulators utilizing similar principles.

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