Introduction to AC and DC

We know that battery or cell gives DC (Direct current) with steady voltage.It is used to power electronics application such as Televisions, mobiles etc.
DC has steady waveform, that is a straight line you can observe it in the below graphical diagram.

DC waveform

Whereas AC means Alternating Current, which means it alternately rises and fall from it highest
positive value to its lowest value. Thus it form a sinusoidal wave in the graphical diagram.

AC sinusoidal waveform

Thus it is important to understand between AC and DC, we cannot connect a 12V application directly to the to the AC that is main power supply it can be hazardous, thus depending upon the countries 110V AC or 230V AC is supplied to us for household application.

Production of AC and DC
In a power station, electricity can be made most easily by using a gas or steam turbine or water impeller to drive a generator consisting of a magnet spinning inside a set of coils. The resultant voltage is always "alternating" by virtue of the magnet's rotation you can observe it in the above AC sinusoidal waveform diagram how the voltage rises positive then goes negative. This alternating voltage can be carried around the country via cables far more effectively than direct current because AC can be passed through a transformer and a high voltage can be reduced to a low voltage, suitable for use in homes.
This DC is produced by several procedure such as Transformation, Rectification, etc.

DC Conversion

The electricity arrives at your house is alternating voltage. Electric light bulbs and toasters can operate perfectly from 230 volts AC. Other equipment such as televisions have an internal power supply which converts the 230 volts AC to a low DC voltage for the electronic circuits. How is this done? There are several ways but the simplest is to use a transformer to reduce the voltage to, say 12 volts AC (above figure of DC conversion). This lower voltage can be fed through a "Rectifier" which combines the negative and positive alternating cycles so that only positive cycles emerge.
TO KNOW MORE ABOUT RECTIFIER CLICK HERE

DC waveform of full wave rectifier

This "rectified" voltage is suitable for powering things like filament bulbs and electric trains but it is still no good for electronic circuits. What we need is "regulated DC" which truly simulates the steady voltage you get from a battery (cell). The first step is to connect a large value capacitor to the output of the rectifier. A capacitor acts as a voltage reservoir and has the effect of smoothing the "ripples".

Rectified waveform (smoothing the ripples)

But the output is still not the same as a battery but it's often good enough for charging batteries in mobile phones, but if you connect it to stereo equipment, you will hear the ripple as an annoying background hum. The final step is to pass this "rippling DC" through a regulator unit. This effectively reduces the ripple to leave almost pure "regulated DC" suitable for powering electronics equipment such as stereos.

Regulated DC power supply

A high-quality Regulated Power supply is capable of supplying 1.5 Amps (1,500 milliamps) of current. A rotary switch provides selection of 3, 4.5, 6, 7.5, 9 or 12 volts "regulated d.c." It has a multitude of uses, including speed control for a mini drill, amplifiers, CD players etc.