Chapter 1 Introduction
This chapter describes the project background, objectives, scopes, methodology, and Summary of the thesis. In the project background, it briefs the description of the buck converter and controller as well as the objectives and the scopes. Lastly, outline of this thesis is given in this chapter.
1.1 Project Background
Direct current to direct current (DC-DC) converters are power electronics circuits that converts direct current (DC) voltage input from one level to another. DC-DC converters are also known as switching converters, switching power supplies or switches. DC-DC converters are important in portable device such as cellular phones and laptops.
Why do we need DC-DC converter? For example, when we want to use a device with low voltage level, if we connected the device such as laptop or charger directly to the rectified supplied from the socket at home, the device might not functioning properly or it might be broken due to over current or overvoltage. Therefore to avoid unnecessary damage to the equipments and devices, we would need to convert the voltage level to suitable voltage level for the equipments to function properly. In this project, the configuration of DC-DC converter chosen for study was buck configuration. Buck converter converts the DC supply voltage to lower DC output voltage level. The buck converter is suitable for low power application due to the low voltage level at the output.
1.2 Project Objectives
The main objective of this project is to design a buck converter to convert the input DC voltage to lower DC output voltage level for low power applications to solve the problem of buck converter. The converter uses switching scheme operates the switches such as MOSFET in Cut-off and saturation region to reduce power loss across the transistor or switch. The output voltage level is then regulated by the control circuit and power circuit to desired output voltage level as in the design specification.
1.3 Project Scopes & Methodology
The scopes of this project are:
- Study the operation of buck converter.
- Study the operation of PWM step down techniques.
- Simulation of buck converter, control circuit and power circuit by using PSpice, Protel DXP 2004 and MATLAB
software’s.
- Simulation of buck converter frequency response using PSpice software.
- Design the buck converter power stage circuit.
- Design the controller and compensator circuit.
- Testing and calibration of the completed buck converter to confirm the actual response with the theoretical
predictions.
- Observation of waveforms from the different Test point of the converter.
The design specification is based on low power applications. The circuit is simulated by using PSpice software to obtain the desired output voltage to giving fix input value.
1.3.1 Methodology
This chapter discusses on methodology and procedures as well as equipments and software’s used in the entire work process. The methodology describes how the flows of the project and procedures topic describes how the project was divided into two phases (Final year project 1 and 2) and the works involved in each phase. The work schedule topic mentioned about the use of Gantt charts for the project schedules and the equipment and software topic describes about the equipments and software’s used when the project was carried out.
Fig1.1 below shows that the first step in this project was to design the circuit components value for buck converter configuration. During this step, the components value was calculated using established equations and formulas. Then models of buck converter and its controller were built and simulated using PSpice, and Protel DXP 2004 software’s. The output voltage and frequency response of the power circuit and control circuit were analyzed and compared with the earlier theoretical predictions
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Fig1.1 Project Methodology
Next, when the simulation results had been confirmed to be approximately the same with the predictions, the power circuit and control circuit are assembled on the PCB. The PCB circuits were built using Protel DXP 2004. The circuits were then printed on the PCB before they undergo the etching process. After the circuits had been etched properly, the hardware’s of buck converter power circuit and its controller 555 Timer on the PCB platforms were obtained. Then the components were placed and soldered on the PCBs to complete the hardware’s of buck converter power circuit and Control Circuit.
Lastly, the hardware’s were tested in the lab to ensure that they function as the desired buck converter in the earlier design process. Any flaws detected on the hardware’s were fixed immediately. Several numbers of tests were carried out during this step in order to make the hardware’s to operate properly and accurately.
1.3.2 Works Schedule
Gantt chart is used to organize works schedules and to simplify the projects outline for project 1 and project 2. Project 1 consists of works plan on designing and simulating the buck converter and control circuit using PSpice software while project 2 works plan emphasizes on constructing the hardware and thesis writing as describe in 1.3.3 procedure shows Fig1.2.
1.3.3 Procedures
The procedures involved in this project are as shown in the Figure-1.2.During final year project (FYP) 1; the works were focused on designing the buck converter control circuit and control Circuit. It was started with choosing a title for the FYP 1, and ends with completed design of the converter’s power stage, first seminar and report on the FYP 1 works. In FYP 2, the works were focused on constructing the hardware’s of buck converter power Circuit and Control circuit it ends with final FYP 2 and the submitting of completed thesis to the supervisor and the faculty.
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Figure1.2 Flow charts showing the works flow
1.3.4 Equipment and Software
The equipment used in this project consists of hardware components and also software program to carry out the circuit simulation. The software’s used for circuit simulation were PSpice, and Protel DXP 2004. A buck converter circuit was simulated using actual components’ value to simulate the output voltage response and compared it with the desired response in the earlier design. During hardware construction phase, Protel DXP 2004 and MATLAB were used to construct the PCB circuits for buck converter power circuit and its controller and to calculate the components’ value for both circuits respectively.
The components used to construct the hardware of buck converter and 555 Timer controllers were capacitors, resistors, inductors, diodes, MOSFET and etc. The values chosen were based on the specifications in the earlier design phase as mentioned in Chapter 4.
1.4 Outline of Thesis
This thesis consists of 5 chapters. In the first chapter, it discusses Methodology and Equipments of project. It gives introduction, background, project objects and scopes. In Chapter 2, literature reviews and theories on power converter and switching converter are discussed & PWM technique and step down operations and switching power losses in MOSFET are discussed while buck converter design, introduction about buck converters, buck design & control scheme and strategies are discussed in chapter 3.
In the chapter 4, Hardware design has included Zero voltages switching resonant converter & also include Zero current Switching resonant converters are discussed in detailed. Chapter 5, Topic covers Implementation & test. it gives the result information of software and hardware which is implemented in PCB along with observation of waveforms & mathematically analysis of Mode of operation. The suggestions and conclusions obtained upon successfully completing this project are given. Finally, the last part in the thesis provides the conclusions, references, Acknowledgement and appendices used in the project as well.
