There are several ways to convert an AC voltage at a wall receptacle into the DC voltage required by a microcontroller. Traditionally, this has been done with a transformer and rectifier circuit. There are also switching power supply solutions, however, in applications that involve providing a DC voltage to only the microcontroller and a few other low-current devices, transformer-based or switcher-based power supplies may not be cost effective. The reason is that the transformers in transformer-based solutions, and the inductor / MOSFET / controller in switch-based solutions, are expensive and take up a considerable amount of space. This is especially true in the appliance market, where the cost and size of the components surrounding the power supply may be significantly less than the cost of the power supply alone. Transformer less power supplies ovide a low-cost alternative to transformer-based and switcher-based power supplies. The two basic types of transformer less power supplies are resistive and capacitive.
In most non-battery applications, the power to the microcontroller is normally supplied using a wall mounted transformer which is then rectified, filtered and regulated. In most applications this method of generating the regulated voltage is cost effective and can be justified. In these instances the cost of the transformer becomes the sizable cost factor in the system. Transformer less power supplies, thus, has a distinct advantage in cost as well as in size. The disadvantages of using a transformer less power supply are: (1) Low current supply and (2) no isolation from the AC line voltage. This project is very much useful where; the efficiency is not given much importance. The main advantage of this project is very low cost components, and small in size. This circuit is not suitable for high current drawing circuits like relay boards.
This project uses regulated 5V, 750mA power supply. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/12V step down transformer.