A power supply (or in some cases just a transformer) that is built into the top of a plug is
known as a wall wart, power brick, or just power adapter.
Linear power supply
A simple AC powered linear power supply uses a transformer to convert the voltage from
the wall outlet to a lower voltage. A diode circuit (generally either a single diode or an array of
diodes called a diode bridge but other configurations are possible) then rectifies the AC voltage to
pulsating DC. A capacitor smooths out most of the pulsating of the rectified waveform to give a DC
voltage with some ripple. Finally depending on the requirements of the load a linear regulator may
be used to reduce the voltage to the desired output voltage and remove the majority of the
remaining ripple. It may also provide other features such as current limiting.
Switched-mode power supply
In a switched-mode power supply the incoming power is passed through a transistor and
transformer network that switches on and off thousands to millions of times per second. This means
that a smaller, less expensive, lighter transformer can be used, because the voltage is being made to
alternate faster, and thus a smaller magnetic core can be used.
Switching power supplies can be used as DC to DC converters. In this application, the
power supply is designed to accept a limited range DC input and then output a different DC voltage.
This is particularly useful in portable devices, as well as power distribution in large electronic
equipment. A transformer less switching power supply that outputs a voltage higher than its input
voltage is typically called a boost converter. A transformer less switching power supply that outputs
a voltage lower than its input voltage is typically called a buck converter. These transformer less
switching power supplies use an inductor as the primary circuit element in converting the voltage.
Circuitry is used to pass current through the inductor to store a certain amount of electrical energy
as a magnetic field. The current flow is then stopped, and the magnetic field collapses causing the
stored energy to be released as current again. This is done rapidly (up to millions of times per
second). By carefully metering the amount of energy stored in the inductor, the current released by
the inductor can be regulated thus allowing the output voltage to be tightly regulated. A switching
power supply incorporating a transformer can provide many output voltages simultaneously, and is
typically called a fly back converter. Switching power supplies are typically very efficient if well
designed, and therefore waste very little power as heat. Because of these efficiencies, they are
typically much smaller and lighter than an equivalently rated linear supply.
Power conversion
The term "power supply" is sometimes restricted to those devices that convert some other
form of energy into electricity(such as solar power and fuel cells and generators). A more accurate term for devices that convert one form of electric power into another form of electric
power (such as transformers and linear regulators) is power converter.
Uses in aviation
The most exotic power supplies are used in aviation to enable reliable restarting of stalled
engines.
In jet transports, an engine is restarted from the power produced by the 400 Hz, three-phase AC
generators attached to the shafts of the other engine(s). Most of the starting torque generated by the
engine's motor/generator is provided by the current at the peaks of the AC waveform.
If the aircraft electronics used simple rectifying power supplies, they would use current only
from these peaks, since the diodes conduct only during the voltage peaks where the input voltage is
higher than the output voltage. This could prevent the pilot from restarting an engine in an
emergency.
Therefore, aircraft power supplies take energy evenly from all parts of the AC waveform.
this is done by using a switching power supply technique called "power factor correction" which
creates a balanced current draw over the entire AC waveform.
known as a wall wart, power brick, or just power adapter.
Linear power supply
A simple AC powered linear power supply uses a transformer to convert the voltage from
the wall outlet to a lower voltage. A diode circuit (generally either a single diode or an array of
diodes called a diode bridge but other configurations are possible) then rectifies the AC voltage to
pulsating DC. A capacitor smooths out most of the pulsating of the rectified waveform to give a DC
voltage with some ripple. Finally depending on the requirements of the load a linear regulator may
be used to reduce the voltage to the desired output voltage and remove the majority of the
remaining ripple. It may also provide other features such as current limiting.
Switched-mode power supply
In a switched-mode power supply the incoming power is passed through a transistor and
transformer network that switches on and off thousands to millions of times per second. This means
that a smaller, less expensive, lighter transformer can be used, because the voltage is being made to
alternate faster, and thus a smaller magnetic core can be used.
Switching power supplies can be used as DC to DC converters. In this application, the
power supply is designed to accept a limited range DC input and then output a different DC voltage.
This is particularly useful in portable devices, as well as power distribution in large electronic
equipment. A transformer less switching power supply that outputs a voltage higher than its input
voltage is typically called a boost converter. A transformer less switching power supply that outputs
a voltage lower than its input voltage is typically called a buck converter. These transformer less
switching power supplies use an inductor as the primary circuit element in converting the voltage.
Circuitry is used to pass current through the inductor to store a certain amount of electrical energy
as a magnetic field. The current flow is then stopped, and the magnetic field collapses causing the
stored energy to be released as current again. This is done rapidly (up to millions of times per
second). By carefully metering the amount of energy stored in the inductor, the current released by
the inductor can be regulated thus allowing the output voltage to be tightly regulated. A switching
power supply incorporating a transformer can provide many output voltages simultaneously, and is
typically called a fly back converter. Switching power supplies are typically very efficient if well
designed, and therefore waste very little power as heat. Because of these efficiencies, they are
typically much smaller and lighter than an equivalently rated linear supply.
Power conversion
The term "power supply" is sometimes restricted to those devices that convert some other
form of energy into electricity(such as solar power and fuel cells and generators). A more accurate term for devices that convert one form of electric power into another form of electric
power (such as transformers and linear regulators) is power converter.
Uses in aviation
The most exotic power supplies are used in aviation to enable reliable restarting of stalled
engines.
In jet transports, an engine is restarted from the power produced by the 400 Hz, three-phase AC
generators attached to the shafts of the other engine(s). Most of the starting torque generated by the
engine's motor/generator is provided by the current at the peaks of the AC waveform.
If the aircraft electronics used simple rectifying power supplies, they would use current only
from these peaks, since the diodes conduct only during the voltage peaks where the input voltage is
higher than the output voltage. This could prevent the pilot from restarting an engine in an
emergency.
Therefore, aircraft power supplies take energy evenly from all parts of the AC waveform.
this is done by using a switching power supply technique called "power factor correction" which
creates a balanced current draw over the entire AC waveform.
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