POWER SUPPLY:
The input
to the circuit is applied from the regulated power supply. The a.c. input i.e.,
230V from the mains supply is step down by the transformer to 12V and is fed to
a rectifier. The output obtained from the rectifier is a pulsating d.c voltage.
So in order to get a pure d.c voltage, the output voltage from the rectifier is
fed to a filter to remove any a.c components present even after rectification.
Now, this voltage is given to a voltage regulator to obtain a pure constant dc
voltage.
Transformer:
Usually, DC voltages are required to operate various
electronic equipment and these voltages are 5V, 9V or 12V. But these voltages
cannot be obtained directly. Thus the a.c input available at the mains supply
i.e., 230V is to be brought down to the required voltage level. This is done by
a transformer. Thus, a step down transformer is employed to decrease the
voltage to a required level.
Rectifier:
The output
from the transformer is fed to the rectifier. It converts A.C. into pulsating
D.C. The rectifier may be a half wave or a full wave rectifier. In this
project, a bridge rectifier is used because of its merits like good stability
and full wave rectification.
The Bridge rectifier is a
circuit, which converts an ac voltage to dc voltage using both half cycles of
the input ac voltage. The Bridge rectifier circuit is shown in the figure. The
circuit has four diodes connected to form a bridge. The ac input voltage is
applied to the diagonally opposite ends of the bridge. The load resistance is
connected between the other two ends of the bridge.
For the positive half cycle
of the input ac voltage, diodes D1 and D3 conduct, whereas diodes D2 and D4
remain in the OFF state. The conducting diodes will be in series with the load resistance
RL and hence the load
current flows through RL.
For the negative half cycle
of the input ac voltage, diodes D2 and D4 conduct whereas, D1 and D3 remain
OFF. The conducting diodes D2 and D4 will be in series with the load resistance
RL and hence the
current flows through RL in
the same direction as in the previous half cycle. Thus a bi-directional wave is
converted into a unidirectional wave.
Filter:
Capacitive
filter is used in this project. It removes the ripples from the output of
rectifier and smoothens the D.C. Output
received from this filter is constant until the mains voltage and load
is maintained constant. However, if either of the two is varied, D.C. voltage
received at this point changes. Therefore a regulator is applied at the output
stage.
Voltage regulator:
As
the name itself implies, it regulates the input applied to it. A voltage
regulator is an electrical regulator designed to automatically maintain a
constant voltage level. In this project, power supply of 5V and 12V are required.
In order to obtain these voltage levels, 7805 and 7812 voltage regulators are
to be used. The first number 78 represents positive supply and the numbers 05,
12 represent the required output voltage levels. The
L78xx series of three-terminal positive regulators is available in TO-220,
TO-220FP, TO-3, D2PAK and DPAK packages and several fixed output voltages,
making it useful in a wide range of applications. These regulators can provide
local on-card regulation, eliminating the distribution problems associated with
single point regulation. Each type employs internal current limiting, thermal
shut-down and safe area protection, making it essentially indestructible. If
adequate heat sinking is provided, they can deliver over 1 A output current.
Although designed primarily as fixed voltage regulators, these devices can be
used with external components to obtain adjustable voltage and currents.
