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Thursday, 17 January 2019

Power Supplies Introduction

Power Supplies Introduction: 


For any electronic equipment to function a power supply stage is necessary. The power supply stage provides the different voltages required by the various devices incorporated in the equipment. The electronic equipment requires D.C. power supplies, with varied specifications. The specifications depend on the type of equipment or the instrument. Currents ranging from few microamperes to several hundreds of amperes and voltage from as low as 1.5 V to several kilo volts are required.

In addition steady voltage (DC voltage) is also required to set the level in digital circuits to establish the high level (1 state) differentiating it from the low state (0 state). This voltage level will be dependent on the digital system requirement.

Further control voltages for functioning of several systems in automatic control systems are also required.

Initially use of primary cells (dry cells) and secondary cells (wet batteries / lead acid cells) were used to supply the DC requirement in electronic circuits. The primary cells are of the disposable type; where as the secondary cells are rechargeable. Disposable alkaline cells were used in portable instruments. Nickel Cadmium cells are used when the current requirement is large. They are rechargeable Lithium based primary cells will find their use in miniature equipment. Lithium iodine and lithium sulphur dioxide cells are of the rechargeable type, are used where the current requirements are large.

It is to be noted that the cost of the batteries plays an important role in their use. Mostly disposable types are not economical. Rechargeable types can be used for low power equipment. Solar cells are used in satellites to energize the electronic circuitry. They are also used in miniature equipment like calculators, digital clocks etc, that take minute current for their operation.

The most common method of supplying power to electronic equipment is to use line operated power supply. There are power supplies for low, medium and high power equipment, use rectifier circuits that take the alternating voltage, either from the single phase, three phase or poly phase transformer and work a rectifier circuit designed as per the requirement.

Improvement in the performance of a power supply can be achieved using regulated power supply circuits that work on feed back principle. The present trend is to use a switched mode power supply that has many advantages over the conventional type.

Uninterrupted power supplies are now in use for continuous power supply to electronic equipment.

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