摘要
随着信息技术的迅速发展，小功率DC/DC变换器在计算机、通讯等应用场合得到了广泛的使用。为了满足这些场合对更快、更有效的数据处理的要求，其供电电源的要求也在不断提高，具体表现在：更低输出电压、更高输出电流、高功率密度、高效率、快动态响应及高可靠性。
本文针对低压/大电流输出的小功率DC/DC变换器，围绕着变换器的效率问题，分析了同步整流的原理和特点，重点阐述了自驱动同步整流在低功率场合的优势，在分析比较了多种与自驱动同步整流相结合使用的电路拓扑后，指出常规的自驱动同步整流方案限制了与之结合使用的电路拓扑的范围这一局限性，从而给出了一种新颖的单绕组自驱动同步整流方案。
这种新的驱动方案能够使副边的同步整流管在主变绕组电压为零阶段都导通，而且因为一个SR管栅极的放电电荷被用于另一个同步整流管栅极电容的充电，因而大大减小了变换器的损耗。该方案拓宽了自驱动同步整流的应用拓扑范围，特别适用于宽输入电压范围、变压器对称工作的拓扑(如推挽、桥式等)。
绕组间耦合的紧密程度对这种新驱动方案性能的影响很大，在详细分析了这一影响后，本文对变压器绕组的绕制工艺进行了介绍和比较。文中在给出了结合单绕组自驱动方案的对称半桥变换器稳态原理分析、同步整流管损耗分析暨选择原则、同步整流管相关电路的布局设计后，建立了对称半桥变换器的小信号数学模型，分析了电源系统时域性能指标与频域特性之间的联系，在此基础上完成了系统的设计。并进行了必要的仿真。
最后，本文完成了单绕组自驱动同步整流对称半桥变换器的原理样机的制作。给出了实验结果，验证了原理分析及设计的正确性。
With the rapid development of Information Technology, low power DC/DC converter is used widely in computer and communication applications. In order to meet demands for faster and more efficient data processing in these applications, it will require aggressive power management. That is to say, it will require special power supply to provide lower voltages with higher currents and fast transient capabilities, whilst high power density, high efficiency, and high reliability is also desired.
This work presents some research on the corresponding problem of high efficiency low-voltage/high-current output DC/DC converter. The principles and characteristics of Synchronous Rectification(SR) are given, and advantages of Self-Driven SR in low power applications is detailed. Review of several topologies which incorporate Self-Driven SR makes the constrains of conventional Self-Driven SR scheme apparent and thus a new scheme to drive SRs is proposed.
The developed Single-Winding Self-Driven Synchronous Rectification(SWSDSR) scheme works properly in topologies that drive symmetrically the transformer (push-pull, half bridge,...).It allows for maintaining the SRs on even when the voltage in the transformer is zero, which is impossible to do in traditional self-driven approaches. Furthermore, driving losses are very low, since the discharge of one MOSFET is used to charge the other and vice versa. Influence of coupling between transformer windings on the performance of this circuit is analyzed in detail and different winding design is compared.
In this paper, the DC operation principle of SWSDSR half-bridge is analyzed. And power loss analysis of SRs and the layout design related to SRs are very important to the proper design. With a small signal mathematic model of half-bridge converter, the relationship between performance of power supply and frequency domain characteristics of the system is analyzed. Based on the above study and some simulation the system design is completed.
In the end, a prototype is fulfilled , and experimental results verify the analysis and design in this work. Some suggestion is put forward for further research work.
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