Design And Construction Of A 19V And 5V Dual Power Supply

ABSTRACT

This work is on a dual power supply. A dual power source provides two separate Direct Current (DC) or Alternating Current (AC) voltage outputs. Both are usually electrically isolated from the power supply input by a transformer. The outputs may be electrically isolated from each other as well, depending upon the design. It may be an adjustable power supply or it may provide fixed voltages or currents.

In electrical and electronics engineering, dual power supply are used to supply positive polarity (+Vcc) as well as negative polarity (-Vcc) and ground potential to appliances.

 CHAPTER ONE

1.0                                                          INSTRUCTION

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. Examples of the latter include power supplies found in desktop computers and consumer electronics devices.

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.

Dual power supply units are common equipment in electrical engineering and electronics. They supply positive polarity (+Vcc) as well as negative polarity (-Vcc, not connected to ground!) and ground potential. In particular cases both the positive and negative rails are required for the proper operation of your circuit. For example, some Op-Amps need dual power sources.

A dual output power supply is a power source that provides two separate Direct Current (DC) or Alternating Current (AC) voltage outputs. Both are usually electrically isolated from the power supply input by a transformer. The outputs may be electrically isolated from each other as well, depending upon the design. It may be an adjustable power supply or it may provide fixed voltages or currents. This type of power source is often used by scientists and technicians in laboratories as well as medical and industrial facilities.

If both outputs of a DC dual output power supply are electrically isolated, they can be wired in series or parallel to increase the available voltage or current. Isolated outputs also allow a dual output power supply to drive separate circuits which must not have a common ground connection. If the outputs are not electrically isolated from each other, they will share a common ground. Such a supply may have only three physical connectors, instead of two output and two ground connectors.

Some dual output supplies provide fixed, regulated voltages and currents. In a DC supply, the polarity may be the same or opposite for the two outputs. It may also be selectable with a switch for each output. An AC supply may allow the frequency to be adjusted, or it may be fixed like the voltage.

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.
• Regulator:   This stage of the power supply takes the smoothed voltage and uses a regulator circuit to provide a constant output virtually regardless of the output current and any minor fluctuations in the input level.

1.2                                                   AIM OF THE PROJECT

The aim of this work is to design a power supply that supplies positive polarity (+Vcc) as well as negative polarity (-Vcc) and ground potential with the output rating of 19v and 5v.

1.3                                              PURPOSE OF THE PROJECT

The purpose of This project is to bring a solution to power up most of devices or projects requiring dual (+/-V) power supply.

1.4                                         SIGNIFICANCE OF THE PROJECT

Constant Power

A single–phase circuit, instantaneous power varies sinusoidally. However, a dual power supply ensures constant power supply to a device when one power source fails, which could be as a result of a lot of factors.

Multiplies Supply Frequency

Dual DC power supply mutiplies the the supply frequency by 2.

Increases Power Output

More power is guaranteed whenever a dual DC power supply is engaged, compared to a single power source. Just like supply frequency, it multiplies the power supply by 2.

Pocket-Friendly

A dual DC power supply is less expensive. Dual DC power supply is cheaper than running on a single power supply. It also comes in useful in situations where one needs more power to boost already available amps. The additional power supply doesn’t have to be of a higher wattage as not much loads need to run on it. For instance, the old power can be used to run the fan and pumps and the new DC source can power the motherboard and other components of the desktop computer.

Ease of Installation

Addition of a dual DC power supply to an already existing direct current power supply source is easy and can be completed in less than 20 minutes. For example, once the spot is identified for the second power supply, run a cord out of the case to connect the green pin and any black pin coming from the main power supply to the auxiliary. It is as simple as that.

Constant Power

A rig that uses dual DC power supply is guaranteed with constant and uninterruptible power supply. Again, a desktop computer can receive dual power supply, one for the fan and the second one for the motherboard. This set up ensures that power supply is not compromised whenever a device is switched on due to fluctuation of voltage. An electricity power supply can fluctuate whenever we add a load to it. Fluctuation of electric current is one of the major causes of damage to computer systems

Convenient Temperature

Extra power supply does not change the case temperature as may logically be expected.

User-friendly

Dual power connection makes it easy to switch off the air conditioning device of an ATM machine without interrupting the entire power supply during cold weather conditions and saving up energy in the process.

A dual electric power supply is important for several reasons. Not only does it ensure stable power supply to a device, but it also helps prevent system damage. It allows for multiple usage of power by increasing power output. To put short, it ensures regular direct current power supply. The importance of a dual DC power supply cannot be overemphasized.

1.5                                          APPLICATION OF THE PROJECT

The general application of a dual power supply is as below:

• For this particular project, the 19v part is for charging of laptop while the 5v out terminal is for charging cell phone.

1.6                                                  PROBLEM STATEMENT

The problem of this work is high heat loss, and lower efficiency levels when compared to a switch-mode power supply.

If this device output is regulated, that means it will required heat heatsink for the regulators

1.7                                           LIMITATION OF THE PROJECT

The output of the power supply is limited to 19v and 5v. Dual power supply units are common equipment in electrical engineering and electronics. They supply positive polarity (+Vcc) as well as negative polarity (-Vcc,) and ground potential. In particular cases both the positive and negative rails are required for the proper operation of your circuit.

1.8                                                 SCOPE OF THE PROJECT

The construction of this work involves three steps:

• Firstly, 220V AC is converted into 19V and 5vac by using simple step-down (220V/19V/5v) transformer.
• Secondly, output of this transformer is given to the rectifier circuit, which will convert the ac supply into dc supply. The output of the rectifier circuit that is DC contains the ripples in the output voltage.
• Lastly, the output of the capacitor that is pure DC is given to voltage regulator IC 7819 by IC7919 and IC 7805 by IC7905, which will regulate the output voltage at 19V and -19V DC, +5v and – 5v despite the change in input voltage

1.9                                        PROJECT WORK ORGANIZATION

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this work is on the introduction to a dual power supply. In this chapter, the background, significance, objective limitation and problem dual power supply were discussed.

Chapter two is on literature review of dual power supply. In this chapter, all the literature pertaining to this work was reviewed.

Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.

Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.

Chapter five is on conclusion, recommendation and references.