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About Power Supplies
Power supplies or power supply units (PSU) are devices
that provide electrical power for electronic components. Power supplies
receive power from a source such as a battery or wall socket. It then
provides power to the electronic device. PSUs can be integrated into
the device or externally attached. Power supplies are necessary to the
operation of just about every electrical device. However, the energy
efficiency of PSUs tends to be fairly low.
Power supply manufacturers offer different style and feature choices.
Some of the PSU styles include board, cabinet, desktop, module, open
frame, enclosed, rack mount and wall mount. Some of the display choices
available are digital numerical displays, analog visual indicators and
graphic or video displays. Some of the various features include adjustable
voltage, adjustable frequency, computer interface, fan cooled, integral
heatsink and overcurrent protection. Other features are as follows: overvoltage
protection, power factor correction, pure sine output, remote on/off
switch, short circuit protection and water cooling. When looking at power
supply manufacturers, consider some of these specifications: the number
of outputs, DC output voltage, DC output power, AC output voltage, AC
output frequency and apparent power.
One of the most common applications for power supply manufacturers is
electrical power for computers. This vital component is a metal box typically
located in a corner of the case of a PC. The power supply unit also contains
the power-cord receptacle and the cooling fan and is usually visible
from the back of a system. PSUs use switcher technology to convert AC
input to lower DC voltages, so they are commonly referred to as switching
power supplies. The voltages commonly supplied are 3.3 and 5 volts, which
are used by digital circuits, and 12 volts, which run motors in disk
drives and fans. In order for the power button to work when the PC is
off, the power supplies have a circuit that supplies 5 volts, called “standby
voltage” or VSB.
There are three types of uninterruptible power supplies (UPS). An offline
UPS is basically a standby system that provides battery power to equipment
when the main power supplies fall below a set limit. These power supplies
do not cost much and are recommended for home office use. A line interactive
UPS is similar to an offline UPS in that it switches to battery mode
during a blackout. However, this UPS actually boosts the main power supply
when it falls, using a regulator. These power supplies are ideal for
corporate applications. The highest level of protection for an electrical
device is an on-line UPS unit that converts AC to DC and then back to
AC to supply critical power loads. These UPS units, often referred to
as double conversions, contain an automatic bypass to ensure continuous
power supplies during a short-term overload or UPS failure. On-line UPS
systems are perfect for critical loads and sensitive equipment, such
as medical technology.
Featured
Articles
http://www.dranetz-bmi.com/pdf/detectPqProblems.pdf
http://www.hardwaresecrets.com/article/370
Types of Power Supplies
- converts power from an AC input, such as a wall outlet, into DC current.
- are units that provide power
to an electronic device by converting AC current, such as that which
comes from a wall outlet, to DC current at the proper voltage.
- control the output current for alterations
in load, line and ambient temperature and time within particular limits.
- control the output voltage in load,
line, ambient temperature and drift resulting from changes over time
- are used to increase or decrease the voltage level
of DC electrical power, because, unlike AC, DC cannot be changed using
a transformer.
- ,
such as linear power supplies, switching power supplies, DC/DC converters
and high voltage power supplies,
receive
an input power and output the required form of DC power.
- are utilized at higher levels in static
applications, due to their weight. Ferroresonant power supplies are
effective only when the line frequency is extremely stable, as they
are sensitive to changes of input AC frequencies.
- , a special type of transducer,
are simply electrical currents that convert periodic signals into their
digital
or analog
equivalents. The most common frequency converters are frequency-to-digital
and frequency-to-DC converters.
- are power switching circuits consisting of
two transistors and two capacitors. Half bridge converters function
in
similar fashion to full bridge converters.
- are capable of providing hundreds or
thousands of volts from one or more DC outputs, using linear technology.
Some
high voltage power supplies have adjustable local or computer interface
outputs and are used in specialized applications, including telecommunications,
video technology and medical equipment.
- change DC current to AC current and may be mechanical
(e.g. motor), ferroresonant and solid state.
- have a bulky steel or iron laminate transformer
that acts as a safety barrier for the low voltage output from the
AC input and reduces that input to a much lower voltage. The AC
output is then rectified by two or four diodes, and electrical converters
change the output into low voltage DC, which is regulated into
the
required output voltage by dropping the difference in voltage across
the shunt regulator.
- are comprised of a number of separate subsections,
such as power, input and filter modules.
- operate directly off the AC line. Off-line
power supplies do not use a power transformer before the process
of rectification and filtering.
- have a high open loop gain regulator,
for which passive components can be used to program. The
regulator acts
like an operational amplifier.
- converts DC current to AC current.
- are electrical components containing sets of diodes that
change AC into DC.
- rectify and smooth AC voltage using diodes
and capacitors, resulting in a high voltage DC, which
in turn is converted by a small ferrite transformer and FETs or transistors
into a safe,
low voltage, high frequency voltage. Another set of diodes,
capacitors and inductors convert that DC voltage into the required
voltage,
the corrections of which are done by adjusting the pulse
width
of the high
frequency waveform.
- are power supply units that continue
to provide power during the loss of AC input power,
which is achieved through a back up battery and a DC/AC inverter or
DC/DC converter.
A stand alone UPS unit is external to the equipment
being
powered,
while a battery back up UPS is implanted in the equipment.
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