具雙調變機制且寬負載範圍之高效率高頻切換直流-直流降壓式電源轉換器

Abstract

在現今可攜式電子產品的應用上，高效能和小型的電壓轉換器在提供系統電源上扮演非常重要的角色。為了減少輸出級濾波器的面積，提出高頻切換的直流轉直流降壓轉換器來達到元件整合的功能。 然而，對傳統的電流控制模式之直流轉直流降壓式電源轉換器來說並不適合在高切換頻率下操作，因為系統的電源轉換效率在輕載時會急遽下降以及控制器電路中所使用到的運算放大器會限制電源轉換器整體系統的頻寬。換言之，轉換器在輕載時系統轉換效率的降低不適合商業上的應用與電路頻寬的限制造成在高切換頻率下的不正確操作。為了解決以上提到的問題，雙調變機制在本論文中被提出。 由於雙調變機制的使用，主調節器中的交流漣波偵測器不僅讓電壓轉換器在高切換頻率下能夠正常操作而且能加速系統的暫態響應，而由次調節器製造的跳頻切換脈波能做到減少功率開關元件的切換次數以達到提高系統在輕載時的轉換效率。 本論文中，實現一個雙調變控制機制用來改善電源轉換效率伴隨著輸出電壓漣波小幅的提高；所提出的交流漣波偵測器可以減輕輸出電容上的寄生電阻與寄生電感在高速切換下所產生的切換雜訊。此外，雙調變機制能夠在系統暫態響應時做到加快系統反應時間；且當系統操作在極輕載時，系統操作頻率能維持在一高於音頻之最小值，避免系統產生噪音。實驗結果顯示電源轉換器使用1μH的電感操作在5MHz的切換頻率，輸出電壓為1.8伏特。負載電流在150毫安培與450毫安培間瞬間變換時的反應時間小於3μS；且電源轉換效率在寬負載範圍下可以維持在百分之八十五以上。相較於傳統控制方式，輕載時的轉換效率最高可以改善百分之四十五。

For today’s portable electronic device applications, high performance and compact size voltage regulator plays an important role to provide system power. To reduce the size of output filter, a high switching dc-dc buck converter is presented to achieve high integration. However, the conventional current mode DC-DC buck converter is not suitable for high switching operation, because the system conversion efficiency deceases drastically at light load condition and the operational amplifiers of control circuits restrict system’s bandwidth. That is to say, the drop of the efficiency at light load makes the converter not suitable for commercial application and the limitation of circuit bandwidth causes incorrect operation at a high switching frequency. To solve these issues mentioned above, the dual modulation technique is presented in this thesis. Owing the dual modulation technique, the AC ripple detector in primary modulator not only makes converter operate at a high switching frequency correctly but also speeds up the transient response, and the hopping switching pulse produced by secondary modulator reduces switching times of power switches to raise efficiency at the light load condition. In this thesis, a dual modulation technique to improve power conversion efficiency with minimal increase in output voltage ripple is presented. The worsening switching noise caused by parasitic resistance and inductance due to high-switching operation can also be alleviated by the proposed AC ripple detector. Furthermore, the dual modulation method can speed up the load transient response since the switching frequency can increase to 10 MHz during the transient period. At very light loads, the switching frequency is always kept higher than the acoustic frequency to avoid noisy sound. Experiment results show that the converter operates at 5MHz using a small inductor of 1μH. The load transient response time is shorter than 3μs when load current changes from 150 to 450mA or vice versa. Power efficiency is kept higher than 85% over a wide load current range. Specifically, light efficiency can be raised to about 45% above that of the conventional design.