Today I am going to make here a 220
Volt AC to 12 Volt DC Power supply.
For that we must be familiar with
the conversion of high voltage AC to low Voltage AC.A transformer is used
for the conversion, which is the combination of two coils mutually coupled
together using a ferrite core, Which is a soft iron core.One coil is of large
numbers of turns with high resistance of small diameter of copper wire, which
is called high voltage coil and another coil is of low resistance ,low number
of turns but with comparatively large diameter of copper wire,which is
called low voltage coil.
TRANSFORMER TEST-
Before using the transformer we
must know which coil's terminals should be connected to mains
or circuitry.It is important since this knowledge would protect your
home wiring as well as protects your transformer from being
burned or damaged.
Now have a multimeter (analog
or digital) with you and set it to ohm measurement,now test each coils
terminals,see that what readings you get.
If you are getting a reading in few
kilo-ohms then it must be the high voltage coil or primary coil.
If you are getting a reading in
only ohms then it must be the low voltage coil or secondary coil.
Also test for the shorting of the
coils by checking the resistance of both the coil is infinite or
not,If not then the transformer is faulty, just change the transformer.
Also test for the coil and core
resistance is infinite or not,If so then be aware that you can get shock if you
don't take care of it.It is recommended that you must change the
transformer in such condition.
BUILDING THE DEVICE-
Here is the list of components-
:: Four 1N4001 diodes
:: one 9-0-9,500mA transformer
:: one LM7812 IC
:: one 470uF,50v Electrolytic
capacitor
:: one 10uF,25v Electrolytic
capacitor
:: one 0.1uF ceramic capacitor
:: wires
:: shoulder and shouldering iron
:: A perforated copper board or a
copper clad board with 5cm By 5cm
dimensions.
:: A 10 cm by 10 cm cardboard
Make a bridge rectifier (see here how
to make bridge rectifier) on the perforated board now take the transformer
secondary or low voltage coil terminals as the rectifier AC input.The 9-0-9 has
three terminals of the low voltage coil,leave the zero potential or common
terminal of the coil and take the other two terminals.Always remember that a
transformer output gives an AC voltage which has no polarity so don't worry of
the connection at the rectifier input,it can be connected at any polarity as
the input to rectifier.
Now the output of the bridge
rectifier is always fluctuating DC, for knowing the polarity test it with the
multimeter.You can also know the polarity by seeing that the same p terminals
connected together will have negative output and vice-versa in the bridge
rectifier.
Now after knowing the polarity,
connect the 470uF capacitor in parallel to the bridge rectifier output.Before
connecting also see the polarity of the electrolytic capacitor and connect with
the same polarity as the bridge output.The black line near the terminal shows
that it is negative terminal.
If the electrolytic Capacitor is
connected with wrong polarity then the capacitor may explode.Also connect
another 10uF electrolytic capacitor in parallel with the 470uF capacitor with
correct polarity.
Now connect the positive terminal
of the capacitor to the input or first terminal of the LM7812 IC and other
terminal to the ground terminal or second/middle terminal of the IC. Now take
the output at third/Output terminal of the IC w.r.t. the ground terminal.For
stability Connect 0.1uF capacitor in parallel to the output terminal and ground
terminal.Take the output across the 0.1uF capacitor.
Now fit all
the circuitry on the cardboard and use it for any electronic
application, Which requires 12v dc and 400mA of current.For high current
applications just add a heat sink to the LM7812 IC.
You can also mount the components
on a copper clad board PCB (See here how to make PCB).
Here are some pics of the Device-
