一個只使用低壓元件並達到最高92%轉換效率的無周期空乏區間混合式升降壓轉換器

Abstract

現在有許多的攜帶性的電子產品輸出在幾百毫瓦消耗功率並使用鋰電池供電。因此，升降壓直流電壓轉換器需求日益增加，其中，四開關非反向電感式的升降壓直流電壓轉換器因為其低功耗與大範圍輸入電壓操作區間而受到歡迎。 在鋰電池的應用中，由於鋰電池的輸出電壓會隨著時間而降低，因此，後端的直流電壓轉換器需同時具備升降壓的功能，才能穩定輸出電壓給晶片中的其他子電路。在四開關非反向電感式的升降壓直流電壓轉換器中，分為升壓模式、降壓模式與升降壓模式。在這三種操作模式中，升降壓模式會產生最多的導通損耗和切換損失。因此，很多研究致力於取代掉傳統的升降壓模式，只單純使用升壓與降壓兩種模式。但是在實際應用中，升壓和降壓模式因為最大和最小週期限制，無法運作在極端充放電週期下，所以產生了一個週期空乏區的區間。 本論文透過提出一種混合式無週期空乏區區間的升降壓轉換器架構並且只使用低電壓元件，來解決輸入電壓和輸出電壓相近時的低效率問題。此新架構利用電容結合傳統電感式降壓轉換器來達到升壓的效果並克服了週期空乏區的區間問題並操作在兩種模式下。同時，比起四開關非反向升降壓轉換器的升壓模式和升降壓模式的不連續輸出電流，新的架構的輸出電流連續，不但可以降低平均電感電流值，同時控制設計系統也相對較為簡單，不須考慮三種模式切換的補償設計。 此晶片透過台積電0.18μm 1P6M High Voltage Mixed Signal CMOS製程實現，並且只使用五伏低壓元件。依據實驗結果的波型展示，本晶片在兩種模式下，輸入電壓在四點二伏到二點八伏的區間中均可如預期操作，使輸出電壓穩定在三點三伏特。且負載電流範圍從20毫安培(mA)到300毫安培(mA)，最高效率在負載為60毫安培(mA)時為92.44%。儘管在量測時，有些設計時未考量到的非預期問題產生，但是結果顯示這個架構依舊可以成功達到解決週期空乏區的區間的問題。

Nowadays, many portable electronic devices with power consumption in the range of several hundred milliwatts are powered by lithium batteries. As a result, there is a growing demand for buck-boost DC-DC converters, with the Non-Inverting Buck-Boost Converter (NIBBC) gaining popularity due to its low power consumption and wide input voltage operating range. In the application of lithium batteries, the output voltage tends to decrease over time. Therefore, the DC-DC converter at the backend needs to have both boost and buck-boost capabilities to stabilize the output voltage for other subcircuits within the chip. In the NIBBC, there are three operating modes: boost mode, buck mode, and boost-buck mode. Among these, the boost-buck mode has the highest conduction loss and switching loss due to the operation. Consequently, many research efforts aim to replace the boost-buck mode and use only boost and buck modes. However, boost and buck modes cannot operate in extreme duty cycles in practice due to maximum and minimum duty cycle limitations, creating a dead-zone issue. This thesis addresses the poor efficiency when input voltage and output voltage are close by proposing a Dead-Zone-Free Hybrid Buck-Boost Converter using only low-voltage devices. This architecture combines an extra flying capacitor with the conventional buck converter to replace the capability of the boost converter, which conquers the dead-zone issue and only operates in two modes. Compared to the discontinuous output current in the boost and buck-boost modes of the NIBBC, the proposed architecture provides a continuous output current. This not only reduces the average inductor current but also simplifies control system design, eliminating the need for compensation designs related to three modes. This chip was implemented in the TSMC 0.18μm 1P6M High Voltage Mixed Signal CMOS process and only used low-voltage devices. According to experimental results, the waveform shows that this chip operates as expected under two modes, with the input voltages ranging from 2.8 V to 4.2 V and 3.3V output voltage. The output loading current ranges from 20mA to 300mA, with the highest efficiency reaching 92.44% at a 60mA output loading current. Despite encountering unexpected problems during the measurement, it is noteworthy that the proposed architecture successfully eliminates the dead-zone issue.