Introduction
Power supply is an electronic device that supplies electric energy to an electrical load. The
primary function of a power supply is to convert one form of electrical energy to another and,
as a result, power supplies are sometimes referred to as electric power converters. Some power
supplies are discrete, stand-alone devices, whereas others are built into larger devices along
with their loads. Examples of the latter include power supplies found in desktop computers and
consumer electronics devices.
Components
Resistor 10k.
7805 voltage regulator.
LED.
Step down transformer.
Diode 1n4007
Capacitor 10uf.
Circuit diagram
Working
This design is based around 4 main parts. A transformer, bridge rectifier, a smoothing
capacitor and the LM7805 chip which contains a 'linear voltage regulator'. Transformer is
used to convert 220 VAC to 18 VAC. Bridge rectifier is used to convert AC to ripple DC.
Capacitor is used to filter ripples from dc. 7805 voltage regulator is used to regulate voltage
to 5 VDC. LED is used for indication power supply is working or not.
Linear power supply
A linear regulated power supply regulates the output voltage by dropping excess voltage in
a series dissipative component. They use a moderately complex regulator circuit to achieve
very low load and line regulation. Linear regulated power supplies also have very little ripple
and very little output noise. The above power supply is linear power supply.
Switched-mode power supply
In a switched-mode power supply (SMPS), the AC mains input is directly rectified and then
filtered to obtain a DC voltage. The resulting DC voltage is then switched on and off at a high
frequency by electronic switching circuitry, thus producing an AC current that will pass through
a high-frequency transformer or inductor. Switching occurs at a very high frequency (typically
10 kHz — 1 MHz), thereby enabling the use of transformers and filter capacitors that are much
smaller, lighter, and less expensive than those found in linear power supplies operating at
mains frequency. After the inductor or transformer secondary, the high frequency AC is
rectified and filtered to produce the DC output voltage. If the SMPS uses an adequately
insulated high-frequency transformer, the output will be electrically isolated from the mains;
this feature is often essential for safety.
Switched-mode power supplies are usually regulated, and to keep the output voltage constant,
the power supply employs a feedback controller that monitors current drawn by the load. The
switching duty cycle increases as power output requirements increase.
SMPSs often include safety features such as current limiting or a crowbar circuit to help protect
the device and the user from harm. In the event that an abnormal high-current power draw is
detected, the switched-mode supply can assume this is a direct short and will shut itself down
before damage is done. PC power supplies often provide a power good signal to the
motherboard; the absence of this signal prevents operation when abnormal supply voltages are
present.
Some SMPSs have an absolute limit on their minimum current output. They are only able to
output above a certain power level and cannot function below that point. In a no-load condition
the frequency of the power slicing circuit increases to great speed, causing the isolated
transformer to act as a Tesla coil, causing damage due to the resulting very high voltage power
spikes. Switched-mode supplies with protection circuits may briefly turn on but then shut down
when no load has been detected. A very small low-power dummy load such as a ceramic power
resistor or 10-watt light bulb can be attached to the supply to allow it to run with no primary
load attached.
The switch-mode power supplies used in computers have historically had low power factors
and have also been significant sources of line interference (due to induced power line
harmonics and transients). In simple switch-mode power supplies, the input stage may distort
the line voltage waveform, which can adversely affect other loads (and result in poor power
quality for other utility customers), and cause unnecessary heating in wires and distribution
equipment. Furthermore, customers incur higher electric bills when operating lower power
factor loads. To circumvent these problems, some computer switch-mode power supplies
perform power factor correction, and may employ input filters or additional switching stages to
reduce line interference.
Application
used in electronic devices.
