Do-it-Yourself Linear DC Variable Power Supply with Digital Electronic Controller for High Precision Regulated Supply

For an electronic hobbyist, the most important gadget is a good, stable and variable DC Voltage power supply to test their projects. One should shell out huge amount to purchase a decent DC variable power supply. This paper describes a Do-It-Yourself variable DC Linear Power supply, which is cheaper, easy to build, an user interface to set and monitor the voltage & current, includes all the protective circuits including over-current protection, short circuit protection and provision to limit the output current as per the user’s requirement to obtain constant current source commonly used for battery charging. The construction and working of a high precision series pass voltage regulator with NPN transistor based power supply with smart control and monitoring system is explained. The proposed design of the DC linear power supply primarily involves two modules, namely the analog and digital modules. Analog module includes an error amplifier & comparator built around operational amplifiers and a pair of power transistor to regulate the output voltage. The digital controller for power supply is based on PIC16F877 microcontroller. The user interface includes LCD display to indicate real time voltage and current, rotary encoders for course & fine output voltage adjustment and current adjustments, push buttons to cruise through the mode and settings. This proposed prototype also incorporates galvanic isolation, which makes it safer and accountable for the user to use with bench oscilloscopes to diagnose and analyze the faults that arise.