發(fā)布時間：2018-05-09 16:31

  本文選題：開關(guān)電源 + 高效率　； 參考：《西安電子科技大學(xué)》2014年碩士論文

【摘要】：LED由于其環(huán)保、節(jié)能、亮度高、發(fā)展空間大等優(yōu)點,正逐漸成為LCD背光光源的理想選擇。在背光LED驅(qū)動方式的發(fā)展過程中,與傳統(tǒng)的電荷泵驅(qū)動方式相比,基于開關(guān)電源的串聯(lián)升壓式驅(qū)動方案更適合當(dāng)今的LCD背光應(yīng)用。首先BOOST架構(gòu)保證了芯片能應(yīng)用在鋰電池供電的低壓系統(tǒng)中,并且輸出電壓可根據(jù)LED串聯(lián)個數(shù)自動調(diào)整,然后恒流式驅(qū)動方式保證了串聯(lián)LED之間亮度的一致性,消除了制造工藝帶來的偏差。而電荷泵由于其輸出電壓固定、并聯(lián)驅(qū)動方式以及有限的帶載能力,導(dǎo)致LED規(guī)模較小,亮度不均勻,只能應(yīng)用在一些低成本、小尺寸的LCD背光應(yīng)用中。本論文以“電源管理類集成電路關(guān)鍵技術(shù)理論研究與設(shè)計”項目為背景,結(jié)合背光LED驅(qū)動的需求,設(shè)計了一款高效率、大功率白光LED驅(qū)動電路XD1420,驅(qū)動類型屬于升壓型開關(guān)電源、恒流式驅(qū)動方式。電路設(shè)計基于某公司的0.18μmBCD工藝,仿真軟件為Cadence、Hspice。XD1420屬于典型的大功率LED驅(qū)動,電流最高可達(dá)350mA,為了增加應(yīng)用的靈活性,LED電流設(shè)計為片外可編程。為了滿足不同尺寸的LCD顯示需要,LED電流可擴展到四個通道。系統(tǒng)的輸出電流最大可達(dá)1.4A,應(yīng)用時只需選擇合適的外圍器件參數(shù)即可保證系統(tǒng)在大范圍負(fù)載內(nèi)正常工作。芯片集成了完善的保護(hù)機制,確保每一個通道有足夠的電壓工作,并且一個通道在發(fā)生故障后會被移除,不會影響其它通道工作。每路電流之間經(jīng)過了精確的匹配,誤差可達(dá)到1%以內(nèi)。四個通道的反饋電壓的校正值隨LED電流可調(diào),有效地避免了固定的校正電壓額外造成的功率損耗,實現(xiàn)了輕載高效,在60mA LED電流應(yīng)用中,效率可達(dá)90%以上。為了滿足控制亮度的一般需求,設(shè)計了模擬調(diào)光和PWM調(diào)光兩種調(diào)光模式,亮度調(diào)節(jié)范圍為最大亮度的0~100%。論文詳細(xì)研究了系統(tǒng)的應(yīng)用方案與電路關(guān)鍵功能的實現(xiàn)。首先研究了系統(tǒng)外圍設(shè)計,討論了器件選擇的依據(jù)并展示出了器件參數(shù)的計算過程;其次對系統(tǒng)環(huán)路的穩(wěn)定性進(jìn)行了分析,基于“平均開關(guān)模型思想”對功率級電路進(jìn)行建模,并對LED負(fù)載進(jìn)行建模以獲得LED的小信號模型,據(jù)此提出了一種補償方法并給出了詳細(xì)的補償步驟和相關(guān)計算,確保了環(huán)路在各種電源輸入及不同負(fù)載情況下的穩(wěn)定性;然后研究了調(diào)光功能的實現(xiàn),分析了PWM調(diào)光對LED電流的影響并提出了改進(jìn)方法;最后針對系統(tǒng)啟動時引入的電流過沖問題,提出了一種改善方法。所有電路模塊均使用Hspice軟件進(jìn)行了仿真驗證,并給出了相關(guān)的仿真波形,仿真結(jié)果證明芯片性能良好。
[Abstract]:Because of its advantages of environmental protection, energy saving, high brightness and large development space, LED is becoming an ideal backlight source for LCD. In the development of backlight LED drive mode, compared with the traditional charge pump drive mode, the series boost drive scheme based on switching power supply is more suitable for the application of LCD backlight nowadays. First, the BOOST architecture ensures that the chip can be used in the low voltage system powered by lithium battery, and the output voltage can be automatically adjusted according to the number of LED series, then the constant current drive ensures the consistency of the brightness between the series LED. The deviation caused by manufacturing process is eliminated. Because of its fixed output voltage, parallel drive mode and limited load capacity, the charge pump can only be used in low cost and small size LCD backlight applications because of its small scale and uneven brightness. In this paper, a high efficiency, high power white light LED drive circuit XD1420 is designed based on the project of "Research and Design of key Technologies of Power Management IC". The driving type belongs to boost switching power supply. Constant current drive mode. The circuit design is based on the 0.18 渭 mBCD process of a company. The simulation software is Cadence Hspice.XD1420, which is a typical high-power LED driver with a maximum current of 350 mA. in order to increase the flexibility of application, the mBCD current is designed as off-chip programmable. LCD current can be extended to four channels in order to meet different sizes of LCD display. The maximum output current of the system can be up to 1.4 A. in application, it is necessary to select appropriate peripheral device parameters to ensure the system to work normally in a wide range of loads. The chip integrates perfect protection mechanism to ensure that each channel has enough voltage to work, and one channel will be removed after failure, which will not affect the operation of other channels. After a precise match between each current, the error can reach less than 1%. The correction value of the feedback voltage of the four channels can be adjusted with the LED current, which can effectively avoid the power loss caused by the fixed correction voltage, and achieve light load and high efficiency. In the application of 60mA LED current, the efficiency can reach more than 90%. In order to meet the general requirement of brightness control, two dimming modes, analog dimming and PWM dimming, are designed. The application scheme of the system and the realization of the key function of the circuit are studied in detail. Firstly, the peripheral design of the system is studied, the basis of device selection is discussed and the calculation process of device parameters is shown. Secondly, the stability of the system loop is analyzed, and the power level circuit is modeled based on the idea of "average switch model". The LED load is modeled to obtain the small signal model of LED. Based on this, a compensation method is proposed and detailed compensation steps and relevant calculations are given to ensure the stability of the loop under various power input and load conditions. Then, the realization of dimming function is studied, the influence of PWM dimming on LED current is analyzed and the improvement method is put forward. All the circuit modules are verified by Hspice software, and the relevant simulation waveforms are given. The simulation results show that the chip has good performance.
【學(xué)位授予單位】：西安電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TM46;TM923.34

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