Introduction to Power Supplies

Electrical power supplies

Power supply is a reference to a source of electrical power. A device or system that supplies electrical or other types of energy to an output load or group of loads is called a power supply unit or PSU

A power supply may include a power distribution system as well as primary or secondary sources of energy such as:

- Conversion of one form of electrical power to another desired form and voltage, typically involving converting alternating current (AC) line voltage to a well-regulated lower-voltage direct current (DC) for electronic devices. Low voltage, low power DC power supply units are commonly integrated with the devices they supply, such as computers and household electronics; for other examples, see switched-mode power supply, linear regulator, rectifier and inverter (electrical).

- Batteries- Chemical fuel cells and other forms of energy storage systems- Solar power- Generators or alternators- Thermonuclear

Classification of electrical supply sources

The sources of electrical supply are classified:by value produced power;by principle of making of electric energy;by external environments.

1. Powerful descriptions of sources electrical supply are estimated on three power-levels, watt: small < 200, middle < 2000, large > 2000.

2. On principle of making of electric energy all sources of electrical supply are divided on two groups: primary and secondary sources of electric feed.

3. On external environments.- movable (autonomous)- stationary

Mobile (autonomous) source of electrical power

Mobile electric plantSelf-propelled electric plant

Energy transformed Transformers of energy in electric

Chemical Accumulators, batteries

Mechanical Electrical generators of direct and alternating current

Thermal thermic electric generator, fuel elements

Sun Sun battery, heliostation

Thermonuclear Nuclear battery

Primary sources of electric supply are Devices in which the electric power is produced by transformation of five types of unelectric energy

In modern terms the transformers of mechanical energy are most widespread. There are Electrical generators of direct and alternating current.

In electricity, a battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy.

Batteries are classified into two broad categories, each type with advantages and disadvantages.

Primary batteries irreversibly (within limits of practicality) transform chemical energy to electrical energy. When the initial supply of reactants is exhausted, energy cannot be readily restored to the battery by electrical means.

Secondary batteries can be recharged; that is, they can have their chemical reactions reversed by supplying electrical energy to the cell, restoring their original composition.

Converted energy is chemical

Battery

Converted energy is mechanical

Electric generators AC and DC

Wave power plant

Wind power plants

Тепловые электростанции

Гидроэлектростанции

Nuclear power stations

Solar power stations

Converted energy is solar

Converted energy is nuclear

A power supply converting AC line voltage to DC power must perform the following functions at high efficiency and at low cost:1. Rectification: Convert the incoming AC line voltage to DC voltage.2. Voltage transformation: Supply the correct DC voltage level(s).3. Filtering: Smooth the ripple of the rectified voltage.4. Regulation: Control the output voltage level to a constant value irrespective of line, load and temperature changes.5. Isolation: Separate electrically the output from the input voltage source.6. Protection: Prevent damaging voltage surges from reaching the output; provide back-up power or shut down during a brown-out.

Electronic devices may look complicated, they are made up of common basic units (‘building blocks’) connected together. The function of each of these units and path of the signals between them can be shown in a block diagram, The block diagram of a simple power supply is shown in Fig.1.

Fig.1 The block diagram of a simple power supply

To understand how the power supply works, it is more important to understand the function of each unit than to know what components are used. This is known as a systems approach to electronics.

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.

Transformer Rectifier Smoothing filterACIN load

In this way, electrical transformers are a passive device which transforms alternating current (otherwise known as "AC") electric energy from one circuit into another through electromagnetic induction. An electrical transformer normally consists of a ferromagnetic core and two or more coils called "windings". A changing current in the primary winding creates an alternating magnetic field in the core. In turn, the core multiplies this field and couples the most of the flux through the secondary transformer windings. This in turn induces alternating voltage or EMF - ElectroMagnetic Field) in each of the secondary coils.

If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the number of turns in the primary (NP) as follows:

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making NS greater than NP, or "stepped down" by making NS less than NP.

The transformer's ability to step AC voltage up or down with ease gives AC an advantage unmatched by DC in the realm of power distribution in figure below. When transmitting electrical power over long distances, it is far more efficient to do so with stepped-up voltages and stepped-down currents (smaller-diameter wire with less resistive power losses), then step the voltage back down and the current back up for industry, business, or consumer use.

Transformers enable efficient long distance high voltage transmission of electric energy.

An ideal power supply would be characterized by supplying a smooth and constant output voltage regardless of variations in the voltage, load current or ambient temperature at 100% conversion efficiency. Figure 2 compares a real power supply to this ideal one and further illustrates some power supply terms.

Fig. 2. Real Power Supply has error compared to Ideal Power Supply

A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification.