What is DC Power Supply?

All circuits and gadgets and everything that is running on Electrical energy requires some particular Voltage and Current. There are 2 type of electrical powers available, called AC Supply and DC Supply. AC Supply is the one which is available to us from our Home Socket, this is a very high voltage (230v) and coming directly from power plant, no storage. While in India, and in most of the countries, the domestic supply is AC only, most of the electronics circuits (almost all of them!!!) runs only on Pure DC power supply. Now DC is Direct Current and AC is alternating Current, below image might clear some things for you

what is ac and dc supply

AC and DC Waveform

above image shows that DC is a continuously ON and constant value where as AC is continuously varying and changing its value continuously. Electronics circuits require no more than 12v DC and in most cases not more than 5v DC, such small DC voltages are not hazardous to human being and you can touch the source of such small DC supply, but never attempt to touch AC supply at all. Now lets see how this AC is converted to DC for our use.All electronics circuits run on DC Power supply and understanding working of power supply is the main key for running your project. A poor power supply may interfere in lots of different things making the circuit to not work, to hang sometimes, or to fluctuate the proper working. Hence though its little boring to study, its always good to understand what are the DC Power supplies, and what are the sources of good DC power

DC Adapters

Using a very simple and popular electronic component called diode, any AC signal can be converted to DC signal. But before doing this, we have to drop down the 230v AC to somewhat smaller voltage like 12V AC. This is done by using a Step Down Transformer. Step Down Transformer is an AC to AC Converter which can convert a higher AC voltage to smaller AC voltage. After Step Down transformer, a diode based rectifier circuit is used to convert the AC supply to DC Supply.A Typical transformer looks like this

It has 2 coils, one called primary winding and the other called secondary winding. For a typical step down transformer, Primary is the One where we connect the Mains Supply (230v) and secondary is the one where we observe step down voltage(say 12v).You can develop such a small circuit on your own using a circuit like below. After diode based rectifier, we're required to use a Capacitor filter and voltage regulator. A Voltage Regulator like 7805 can give you 5 v of regulated constant DC voltage at the output. There are many variants of voltage regulator like 7805,7809, 7812 and so on. Below is a simple DC power supply Circuit

dc power supply