Application of Phase Locked Loop Circuit for Ultrasonic Atomizer Driving Circuit

換能器的共振頻率與相位角會隨著溫度高低、負載量多寡、長時間工作……等因素而偏移。共振頻率與相位角飄移會導致換能器無法正確操作在共振頻率上而轉換效率也因此下降。本論文開發一個自動追蹤頻率的功率超音波驅動電路模組並詳細敘述此電路模組每一細部功能電路之設計概念與設計方法。此驅動模組可在輸出大功率的條件下，以幾百千赫茲到數百萬赫茲的驅動信號驅動，擁有高機電的轉換效率，並可以長時間穩定的高效能作動。本實驗室霧化器之超音波驅動電路可驅動500KHz到2.5MHz之換能器，由於本實驗室正在進行超音波霧化加濕技術應用於燃料電池系統的計畫，由實驗發現驅動頻率愈高會造成相位的飄移更加顯著，因此藉由鎖相迴路電路使換能器準確的操作在共振頻率上，鎖相迴路包含電流與電壓的回授訊號、相位偵測器、迴路濾波器和電壓控制震盪器。本論文觀察與討論，增加鎖相迴路電路於超音波霧化器後的表現，增加鎖相迴路於超音波換能器的相位角被控制在0°左右，而沒有加上鎖相迴路的相位角隨著溫度上升也不斷的增加；而有增加鎖相迴路於超音波換能器電功率的轉換效率維持在95%的轉換效率，而未加上鎖相迴路的超音波換能器電功率會隨溫度上升漸漸的降低。Resonating frequency and phase of the ultrasonic transducer may change due to variation of temperature and loading and duration of working, etc. Resonating frequency and phase of the ultrasonic transducer varies so that the output power of the ultrasonic transducer might decrease. The purpose of this paper is to design a high power ultrasonic driving circuit module with dynamic frequency tuning and describes the concepts and manners in detail of each subtle circuit in this circuit module. This module can drive from hundreds of thousands to several millions Hz on the high power condition, and it has high electro-mechanical conversion efficiency. This circuit can drive transducers with resonance frequency between 500KHz to 2MHz. We are going to apply this circuit module to the ultrasonic atomization system. It was observed that the higher the driving frequency will cause the phase of ultrasonic transducer drift is more significant. An ultrasonic transducer is precisely set at resonating frequency by phase locked loop circuit. Phase locked loop circuit consists of the feedback of voltage and current, phase detector, low-pass filter and voltage control oscillator. Besides, we are going to observe and discuss the ultrasonic atomization system with phase locked loop circuit. It was observed that the phase of ultrasonic transducer with phase locked loop circuit can be controlled at about zero degree. Otherwise, the phase of ultrasonic transducer without phase locked loop circuit will increase due to temperature rise. It was observed that the transfer efficiency of ultrasonic transducer with phase locked loop circuit can be maintained 95% conversion efficiency. Otherwise, the transfer efficiency of ultrasonic transducer without phase locked loop circuit will decrease due to temperature rise