High efficiency automotive DC/DC power supply design

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Lazányi János Gyula
Department of Measurement and Information Systems

Nowadays switch mode power supplies (DC/DC converters) are more emphasised in the automotive industry, due to special consumers (LED-strings, BLDC motors) are appearing in vehicles, moreover dissipation reduction is still serious challenge for engineers. Because of beneficial traits, like higher efficiency and controllable output of switch mode power supplies, this kind of DC/DC converters are perfect to achieve the goals of automotive engineers.

The aim of this thesis is to give a detailed overview about the main DC/DC converter topologies and the methods of their operation. Furthermore I explain resonant converters, the design difficulties of switch mode power supplies and the possible control strategies and structures. In addition I provide considerations how to decrease dissipation in a switch mode power supply, furthermore in this chapter I introduce the operation and dissipation calculus of switching elements (MOSFETs) in detail.

After the detailed theoretical explanation I describe the design of a DEMO step down converter, including proper part selection, schematic and PCB design. In this part of my thesis I present a MATLAB-SIMULINK model of this converter, which shows the operation of the designed power supply with voltage mode control. Moreover I review the used TMS320F28035 microcontroller.

I write about the embedded software developing phase of the design in detail, take into consideration of the control structures. I have implemented voltage mode control (VMC) in my DEMO step-down converter and explain the validation of a switch mode power supply, like proper measuring of output voltage ripple, response to load transient or determination of efficiency.

With this DEMO converter I would like to demonstrate the beneficial properties of DC/DC converters and give a detailed description of the developing process. In conclusion, I developed a step-down converter, which is fit for the requirements of an automotive hardware and fulfils the predefined specifications.


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