Transcript Power supply - WordPress.com

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 wellregulated 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
Self-propelled electric plant
Mobile electric plant
Primary sources of electric supply are Devices in which the electric power is
produced by transformation of five types of unelectric energy
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
In modern terms the transformers of mechanical energy are most widespread.
There are Electrical generators of direct and alternating current.
Converted energy is chemical
Battery
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 mechanical
Electric generators AC and DC
Wave power plant
Wind power plants
Тепловые электростанции
Гидроэлектростанции
Converted energy is solar
Solar power stations
Converted energy is nuclear
Nuclear power stations
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.
AC
IN
Transformer
Rectifier
Smoothing filter
load
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.
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.
A rectifier is an electrical device that converts alternating current (AC) to direct
current (DC), a process known as rectification.
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