Analysis And Design Of A Boost DC-DC Converter

Electronic products need high performance's power supply circuits. At the present time, various high efficiency portable electrical devices such as cell phones are being miniaturized. The more functions there are, the more power losses they dissipate. Thus they require the battery power supply system's size smaller, weight lighter and efficiency higher. To meet these requirements, high efficiency DC-DC switching mode power supply is adopted. There exists a big gap between China's techniques and overseas'. China's DC-DC power supply market is mainly taken up by foreign brands. Consequently, the research about control circuits in DC-DC power supply for driving white LEDs has important significance.Aimed at the single-chip switching mode power supply circuits, which presently have wide applications in portable devices, control circuits applied in a high efficiency boost DC-DC converter for driving white LEDs have been designed in this thesis. The circuit utilizes 1.2MHz current-mode Pulse Width Modulation (PWM) control to allow small input and output capacitors and a small inductor, while reducing the circuit's volume. It drives up to seven white LEDs in series with a constant current to provide display backlighting for one displays in cell phones and other hand-held devices with the input voltage ranging from 2.5V to 10V, and the maximum output voltage is 28V. With LEDs series connected, accurate current regulation for uniform illumination can be obtained. The circuit includes a 30V, low rd sON N-channel MOSFET switch for high efficiency up to 84% and maximum battery life. Compounded with several simple external components, the circuit can construct a white LED driver.The author firstly introduces the developments and investigation significations about DC-DC converters, and then basic principle of the boost PWM DC-DC converter and the basic knowledge of white LEDs. And then, the stability of whole system is analyzed according to the system model, control loop design of whole system are completed, design result is verified with Matlab. In the circuit design chapter, the operation principle of the whole-chip circuit and function of each sub-block circuit are given. Subsequently, operation principles of several sub-blocks designed by author, including bandgap reference, current- sensing circuit as well as PWM control etc, are analyzed. The sub-block and whole-chip simulation results with Cadence indicate that the IC has achieved its function target and the expected electrical characteristics, also have validated the circuit's function. Finally, summary of the thesis is given out. Although there are unavoidable disadvantages of this thesis, it is a worthwhile and valuable experience.