This project work is on design of a variable power supply. This work makes it possible for someone that wants to run different appliances with one power supply without buying new power supply.  A variable power supply is an electronic device that supplies different level of electric energy to an electrical load. The primary function of a variable power supply is to supply different electrical energy to loads that fall at the same rating limit (1-3amp). In this work, the heart of the project is an arduino, and  an LCD is used to display the value of voltage selected at any time .

 

CHAPTER ONE
1.0 INTRODUCTION
A power supply is an electronic device that supplies electric energy to an electrical load. The primary function of a power supply is to convert one form of electrical energy to another and, as a result, power supplies are sometimes referred to as electric power converters. Some power supplies are discrete, stand-alone devices, whereas others are built into larger devices along with their loads.
Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source. Depending on its design, a power supply may obtain energy from various types of energy sources, including electrical energy transmission systems, energy storage devices such as a batteries and fuel cells, electromechanical systems such as generators and alternators, solar power converters, or another power supply.
All power supplies have a power input, which receives energy from the energy source, and a power output that delivers energy to the load. In most power supplies the power input and output consist of electrical connectors or hardwired circuit connections, though some power supplies employ wireless energy transfer in lieu of galvanic connections for the power input or output. Some power supplies have other types of inputs and outputs as well, for functions such as external monitoring and control.
To obtain a complete circuit for this work, the circuit is mainly composed of the:

• Input transformer:   The input transformer is used to transform the incoming line voltage down to the required level for the power supply. Typically the input transformer provides a step down function. It also isolates the output circuit from the line supply.
• Rectifier:   The power supply rectifier converts the incoming signal from an AC format into raw DC. Either half wave or more commonly full wave rectifiers may be used as they make use of both halves of the incoming AC signal.
• Smoothing:   The raw DC from the rectifier is far from constant falling to zero when the AC waveform crossed the zero axis, and then rising to its peak. The addition of a reservoir capacitor here fills in the troughs in the waveform, enabling the next stage of the power supply to operate. Large value capacitors are normally used within this stage.
• Voltage adjuster:   This stage of the power supply takes the smoothed voltage and uses a variable ic to provide a variable output virtually regardless of the output current and any minor fluctuations in the input level.

1.2                                                   AIM OF THE PROJECT
The aim of any power supply is to provide the required power to the load using an AC supply at the input. But for variable power supply is to design a power supply with one output terminal with variable output voltage, and the output is gotten by turning the voltage adjuster known as the potentiometer. In this work, voltage level is controlled with help of a Potentiometer and voltage value is displayed on Liquid Crystal Display (LCD) which will be driven by an Arduino Nano.

1.3                                           LIMITATION OF THE PROJECT
This device is limited at producing 0 – 30 v output using a 24 volts center tap transformer and the current rating is between 1-3 ampere.

1.4                                         SIGNIFICANCE OF THE PROJECT
This work makes it possible for someone to use one power supply to run different devices of higher or lower voltage rating without considering buying a new or different power supply.

1.5                                          APPLICATION OF THE PROJECT
A variable power supply is a regulator that electricians and electrical project hobbyists use to test the capacity of voltage for any project they may have completed. The power supply is used as a gauge to make sure the piece of work the person has completed is able to withstand certain amounts of voltage and current load. Tests are generally conducted by applying different amounts of voltage to the piece of completed work a little at a time to ensure the stability of the circuit the individual has created. These types of power supplies also are used by hobbyists to power small electronics requiring variable voltage and by tattoo artists to power tattooing guns.
By using such a variable supply of power, the individual is able to spot any temperaments or inconsistencies in the circuit he’s created in a manner that allows for adjustment to be made without having to scrap the entire project. A variable power supply is a useful tool for anyone who has a background with electrical circuitry and components. It also has many uses other than just testing.
In addition to being used to test circuits, this type of power supply may be used by miniature hobbyists as well. For example, such tools are commonly used by those who work with miniature electronic train sets. The power supply can be adjusted to either speed up or slow down the train as it is pushed around the track by the power of the completed circuit.
Another common use for this type of power supply is in the tattoo industry. Variable power supplies are used every day by tattoo artists to adjust the intensity and speed of the motor on their tattoo guns in order to create the desired effect with the particular tattoo needles they are working. For instance, when a tattoo artist is outlining a new piece, the speed of the gun is increased through the power supply so the needle moves faster, creating a more consistent outline. When the artist is shading an area of the skin, the power supply is used to slow down the needle in order to create consistent color coverage within the tattoo.
A variable power supply works by restricting or increasing the voltage delivered to the circuit from the original power source. For instance, when the electronic train hobbyist starts his train on the track, he doesn’t simply flip a switch and turn the train on full blast; rather, he delivers the voltage to the circuit in small increments through the regulated variable power supply until the desired speed of the train is reached. Most common variable power supplies have voltage ranges of 1 to 3 volts up to 20 or 30, and large-scale variable power supplies can range from 6,000 to 20,000 volts, but these types of power supplies are typically only used in industrial settings.

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