In any electronic products or projects there is always a source of power for the system to work. This is called a power supply. The source of this power can come from different sources like the mains AC voltage, a battery or even from a renewable power source like a solar panel wind turbine or fuel cell to name just a few. The most common source of power is usually the mains AC, with this power, we need a transformer to convert the 220V 50Hz mains or the 120V 60Hz if you are living in the United States of America to a lower voltage required by the electronic circuit, this can be typically between 6V and 12V when 5V regulated DC is needed. In this article we are going to design a simple 5V DC power supply using the 7805 voltage regulator.