Power supply: - Power supply is the essential part of any device or project. We are using microcontroller and LED. These components needs +5V DC supply. So we need a power supply circuit of +5V DC. Power supply circuit includes step down transformer, rectifier circuit, filter circuit and regulator circuit. An indicating component is also attached with the power supply to indicate the power ON condition of power supply unit.
A step down transformer of 12-0-12 V and 750 mA is used to step down the AC power supply. This transformer can provide current up to 750 mA. Our circuit load is below 750 mA. So there will not be any loading effect on transformer. Output of transformer is given to the rectifier circuit. We are using a central tapped full wave rectifier. In this rectifier we are using 1N4007 pn diode to rectify AC voltage. Output of this rectifier is not purely DC. Output of rectifier is rippled DC. So we need some filtering section to rectify this ripples. Output voltage of rectifier can be calculated by :Vout = (Vin * √2)- (Forward voltage drop of diode) 56 | P a g e