太陽能電池板的便攜式充電器是解(jie)決(jue)通信設(she)(she)備(bei)、田間測量儀器等(deng)移(yi)動(dong)式電(dian)(dian)(dian)(dian)子產品供電(dian)(dian)(dian)(dian)問題的最(zui)佳(jia)解(jie)決(jue)方案之(zhi)一(yi)。采用TPS5430 降壓(ya)(ya)電(dian)(dian)(dian)(dian)路(lu)和(he)MAX167 4 升壓(ya)(ya)電(dian)(dian)(dian)(dian)路(lu)，由(you)LM393、ICL7660 等(deng)元件構成的切(qie)換電(dian)(dian)(dian)(dian)路(lu)為(wei)(wei)控制核(he)心，設(she)(she)計具(ju)有自(zi)啟動(dong)功能的電(dian)(dian)(dian)(dian)能收集(ji)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器。充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器能夠根據充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)(ya)的不(bu)同(tong)，自(zi)動(dong)切(qie)換到不(bu)同(tong)的DC-DC 變換電(dian)(dian)(dian)(dian)路(lu)，實現高效、快速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)。測試表明，當充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源內(nei)阻(zu)(zu)Rs為(wei)(wei)100 Ω，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)(ya)Es在10～20 V 范(fan)圍內(nei)，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)動(dong)勢Ec為(wei)(wei)3.6 V、內(nei)阻(zu)(zu)Rc為(wei)(wei)0.1 Ω 時，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流Ic>58 mA，自(zi)動(dong)啟動(dong)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)(ya)為(wei)(wei)3.6 V，電(dian)(dian)(dian)(dian)池放電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流為(wei)(wei)3 mA；而當充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源內(nei)阻(zu)(zu)Rs為(wei)(wei)1 Ω，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)(ya)Es在1.2～3.6 V 范(fan)圍內(nei)時，最(zui)大(da)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流可達(da)256 mA。

　　太陽能的開發及利用在大力提倡發展低碳經濟的時代背景下日益受到矚目。我國光伏產業以每年30%的速度增長， 最近三年全球太陽能電池總產量平均年增長率高達49.8%以上。而通信設備、田間測量儀器等便攜式電子產品的普及使得以太陽能電池板為基礎的便攜式充電裝置倍受青睞，不受地域限制，能夠在傳統充電器無法工作的場合進行應急或可持續充電。目前，充電電池的充電技術主要有電壓負增量控制、時間控制、溫度控制、最高電壓控制技術等。假設充電電池的電壓保持恒定的條件下， 利用LM393、ICL7660等元件構成的切換電路控制， 由TPS5430 降壓電路和MAX167 4 升壓電路組成智能充電器， 由可調直流(liu)電源模擬(ni)當太陽(yang)能電池板的(de)(de)輸(shu)出電壓大范圍變(bian)化時，實(shi)現充(chong)電器的(de)(de)自動(dong)啟動(dong)并盡可能地增大充(chong)電電流(liu)來實(shi)現充(chong)電效率的(de)(de)提高。

　　1 理論分析與計算

　　充電器的測試原理示意圖如圖1 所示。假定太陽能電池板的輸出功率有限，電動勢Es在一定范圍內緩慢變化，監測和控制電路采用間歇工作方式，以降低能耗。可充電池的電動勢Ec恒定為(wei)(wei)3.6 V，內(nei)阻Rc為(wei)(wei)0.1 Ω。

　　直流電源電動勢為Es，電源內阻為Rs，可充電池電動勢為Ec，可充電池內阻為Rc，充電電流為Ic，為防止電流倒灌，在可充電池兩端并聯電阻Rd。理想情況下，充電器的輸入阻抗與電源內阻匹配，此時直流電源輸出功率為，充電器輸出功率為，則效率為。由此可得，當(dang)Rs=100 Ω，Es=10 V 時(shi)(shi)，Ps=0.25 W，Ic>64 mA，η >92.16%；當(dang)Es=20 V 時(shi)(shi)，Ps=1 W，Ic>160 mA，η>57.6%。為了盡可能提(ti)高高電(dian)(dian)(dian)壓(ya)(ya)時(shi)(shi)的充電(dian)(dian)(dian)效(xiao)率(lv)，除選用TPS5430 構成降壓(ya)(ya)電(dian)(dian)(dian)路外，應(ying)盡量降低(di)切換電(dian)(dian)(dian)路的開(kai)關頻(pin)(pin)(pin)率(lv)。電(dian)(dian)(dian)路中主(zhu)(zhu)要功(gong)耗(hao)元件是功(gong)率(lv)場效(xiao)應(ying)管（FET），在低(di)頻(pin)(pin)(pin)情況下，功(gong)率(lv)FET 主(zhu)(zhu)要是傳(chuan)導損(sun)耗(hao)，在高頻(pin)(pin)(pin)情況下，傳(chuan)導損(sun)耗(hao)維持不變，同頻(pin)(pin)(pin)率(lv)有(you)關的損(sun)耗(hao)會增大。較高或較低(di)的開(kai)關頻(pin)(pin)(pin)率(lv)均會使(shi)效(xiao)率(lv)降低(di)，綜合(he)考(kao)慮各因素(su)并結合(he)試驗，測得開(kai)關頻(pin)(pin)(pin)率(lv)為500 kHz 時(shi)(shi)效(xiao)率(lv)為94.35%。

　　2 硬件電路設計

　　充電器硬件電路組成框圖如圖2 所示。充電器由切換電路自動判斷直流電源輸入電壓， 選擇升壓或降壓電路，實現在工作電壓范圍內自動切換， 模擬對充電電池的充電效果。

　　2.1 切換電路設計

　　切換電路用于切換充電器升壓(ya)(ya)工作和降壓(ya)(ya)工作兩種模式。設定(ding)切換的閾(yu)(yu)值電(dian)(dian)壓(ya)(ya)為3.6 V，閾(yu)(yu)值電(dian)(dian)壓(ya)(ya)由可調電(dian)(dian)阻(zu)設定(ding)并可調。充(chong)電(dian)(dian)電(dian)(dian)壓(ya)(ya)超(chao)過閾(yu)(yu)值電(dian)(dian)壓(ya)(ya)時降壓(ya)(ya)電(dian)(dian)路(lu)工作，低于(yu)閾(yu)(yu)值電(dian)(dian)壓(ya)(ya)時升壓(ya)(ya)電(dian)(dian)路(lu)工作。切換電(dian)(dian)路(lu)由場(chang)效應管、電(dian)(dian)壓(ya)(ya)比較器等分(fen)立(li)元件構成，原(yuan)理圖(tu)如(ru)圖(tu)3 所示。

　　圖(tu)3 中， 輸(shu)(shu)入(ru)端(duan)VIN （P1） 接(jie)(jie)充電(dian)(dian)(dian)電(dian)(dian)(dian)源， 輸(shu)(shu)出端(duan)P2 接(jie)(jie)MAX167 4升(sheng)壓(ya)(ya)電(dian)(dian)(dian)路的(de)輸(shu)(shu)入(ru)端(duan)，肖特基二極管VD1用于(yu)防(fang)止電(dian)(dian)(dian)流倒灌(guan)。穩壓(ya)(ya)器(qi)TL431 為電(dian)(dian)(dian)壓(ya)(ya)比(bi)(bi)較(jiao)器(qi)LM393 的(de)負(fu)輸(shu)(shu)入(ru)端(duan)提供參考電(dian)(dian)(dian)壓(ya)(ya)。輸(shu)(shu)入(ru)端(duan)VIN（P1）通過濾波后接(jie)(jie)入(ru)電(dian)(dian)(dian)壓(ya)(ya)比(bi)(bi)較(jiao)器(qi)LM393 的(de)正輸(shu)(shu)入(ru)端(duan)。調(diao)節R_ad可(ke)調(diao)電(dian)(dian)(dian)阻，使(shi)輸(shu)(shu)入(ru)小(xiao)于(yu)3.6 V 時電(dian)(dian)(dian)壓(ya)(ya)比(bi)(bi)較(jiao)器(qi)LM393 輸(shu)(shu)出負(fu)電(dian)(dian)(dian)壓(ya)(ya)，P 溝(gou)道(dao)MOS 管IRLM16402VQ1、VQ2和(he)VQ3導(dao)通，VQ1，VQ2的(de)漏極連接(jie)(jie)升(sheng)壓(ya)(ya)電(dian)(dian)(dian)路， 使(shi)切換電(dian)(dian)(dian)路輸(shu)(shu)入(ru)、輸(shu)(shu)出端(duan)短接(jie)(jie)，使(shi)充電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)接(jie)(jie)至升(sheng)壓(ya)(ya)電(dian)(dian)(dian)路。當輸(shu)(shu)入(ru)大于(yu)3.6 V 時，輸(shu)(shu)出高電(dian)(dian)(dian)平，VQ1、VQ2和(he)VQ3截止，此時MAX167 4升(sheng)壓(ya)(ya)電(dian)(dian)(dian)路無輸(shu)(shu)入(ru)。VD2、VD3的(de)作用是當電(dian)(dian)(dian)壓(ya)(ya)大于(yu)3.6 V 時，LM393的(de)負(fu)電(dian)(dian)(dian)源端(duan)接(jie)(jie)地； 當電(dian)(dian)(dian)壓(ya)(ya)小(xiao)于(yu)5.5 V 時，LM393 負(fu)電(dian)(dian)(dian)源通過VQ3接(jie)(jie)ICL7660 的(de)負(fu)電(dian)(dian)(dian)壓(ya)(ya)輸(shu)(shu)出引(yin)腳。

　　2.2 升壓/降壓電路設計

　　升(sheng)壓(ya)(ya)電(dian)路主要(yao)由升(sheng)壓(ya)(ya)式DC-DC 電(dian)源(yuan)轉換器MAX167 4組成，升(sheng)壓(ya)(ya)后輸出4 V 直接對電(dian)池進行充電(dian)。MAX167 4升(sheng)壓(ya)(ya)電(dian)路如圖(tu)4 所(suo)示。

　　圖4 中， 升壓芯片的儲能電感L1接MAX167 4的LX 引腳，電阻R1、R2和R3構成反饋網絡，將輸出電壓反饋至FB 引腳，芯片內部保持輸出電壓恒定。選取25 μH 電感和680 μF電容組成一階低通濾波器，截止頻率，以削弱(ruo)紋波對輸出電壓的影響。

　　降(jiang)壓(ya)電(dian)(dian)路主要(yao)由(you)降(jiang)壓(ya)DC-DC 轉(zhuan)換(huan)器(qi)TPS5430 組成，降(jiang)壓(ya)后(hou)直接對電(dian)(dian)池進(jin)行充電(dian)(dian)。TPS5430 降(jiang)壓(ya)電(dian)(dian)路如圖5 所(suo)示。

　　經測試，綜合考慮效率因素，選定開關頻率為500 kHz，輸入端的電容C6和C7為旁路電容和降壓濾波電容， 由于轉換器中開關在導通瞬間需要較大電流，通過旁路電容吸收瞬間大電流和濾除高頻噪聲信號使芯片保持穩定工作。電路輸出功率越大，工作頻率越低，對應的電容值也應越大。選取等效串聯電阻阻值低，容值為10 μF 的電解電容。根據芯片數據資料， 輸出端電感L1的取值按公式計(ji)算， 可得(de)所需(xu)的(de)電(dian)(dian)感(gan)值是(shi)15.8 μH，選取(qu)內徑30 mm 的(de)鐵硅鋁磁(ci)(ci)芯(xin)自行繞制的(de)電(dian)(dian)感(gan)值為18 μH，以保證(zheng)在額(e)定的(de)工(gong)作(zuo)狀況下不(bu)會出(chu)現磁(ci)(ci)飽和(he)。電(dian)(dian)阻(zu)R1、R2和(he)R3構成反饋網(wang)絡， 將(jiang)輸(shu)出(chu)電(dian)(dian)壓反饋到芯(xin)片(pian)的(de)VSNS 引腳，該芯(xin)片(pian)自動調(diao)節輸(shu)出(chu)電(dian)(dian)壓，保證(zheng)充電(dian)(dian)器輸(shu)出(chu)端輸(shu)出(chu)電(dian)(dian)壓恒定。

　　3 試驗結果及分析

　　1）電源內(nei)阻Rs=100 Ω，調整Es的大小，使其在10～20 V范圍內(nei)變化(hua)，記錄數據如表1 所示。

　　由(you)表1 可見，在(zai)Es為(wei)10 V 時，實(shi)測(ce)充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)與理論(lun)值存在(zai)5.9 mA 的(de)偏差，充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)低、充電(dian)(dian)(dian)器(qi)的(de)轉換效率(lv)不高可能與芯片的(de)轉換效率(lv)和輸(shu)(shu)入(ru)電(dian)(dian)(dian)壓(ya)(ya)有關(guan)，由(you)TPS5430 的(de)數(shu)據資料可知，在(zai)輸(shu)(shu)入(ru)電(dian)(dian)(dian)壓(ya)(ya)為(wei)10 V 左(zuo)右，輸(shu)(shu)出(chu)電(dian)(dian)(dian)流(liu)(liu)約為(wei)60 mA 時，其(qi)工(gong)作效率(lv)約為(wei)92%。而在(zai)12～20 V 范圍內，實(shi)測(ce)充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)大(da)于理論(lun)計算充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)值。

　　2）逐漸(jian)降低Es，直(zhi)到(dao)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流Ic略(lve)大于0 時，記錄對應(ying)的電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)壓Es，該(gai)電(dian)(dian)(dian)(dian)(dian)壓即(ji)為最低可充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓。為保證準確(que)性，對多個不(bu)同的電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)壓值(zhi)進行(xing)測(ce)試，選取最優3 組(zu)數據(ju)記錄如(ru)表2 所(suo)示。

　　由表2 可(ke)見，當Es下降到3.6 V 時，充(chong)電(dian)電(dian)流為0，充(chong)電(dian)器不能(neng)再對電(dian)池(chi)進行充(chong)電(dian)，故最低可(ke)充(chong)電(dian)電(dian)壓為3.6 V。

　　3）從0 開始逐(zhu)漸升高(gao)Es，Rs為(wei)0.1 Ω；當Es升高(gao)到高(gao)于1.1 V 時，更換Rs為(wei)1 Ω。然后繼續升高(gao)Es，直(zhi)到充電(dian)(dian)電(dian)(dian)流(liu)略大于0，記錄此時的(de)電(dian)(dian)源電(dian)(dian)壓(ya)值，該電(dian)(dian)壓(ya)即為(wei)自動(dong)啟動(dong)充電(dian)(dian)功能的(de)啟動(dong)電(dian)(dian)壓(ya)。為(wei)保證準確性(xing)，對多(duo)個不同的(de)電(dian)(dian)源電(dian)(dian)壓(ya)值進行測試(shi)，選取最優4 組數據記錄如表(biao)3 所示(shi)。

　　由(you)表3 可見，當Es小(xiao)于3.6 V 時(shi)，充電(dian)電(dian)流持續為0，一旦Es上(shang)升(sheng)到3.6 V 后，充電(dian)電(dian)流由(you)0 開始增加，即自動啟動充電(dian)電(dian)壓(ya)為3.6 V。

　　4）Es降(jiang)低到不(bu)能向(xiang)電(dian)池充電(dian)，最(zui)低至0 時，檢測放(fang)電(dian)電(dian)流。為保證準確性，對多個不(bu)同的電(dian)源(yuan)電(dian)壓值進行測試(shi)，選取最(zui)優3 組(zu)數據(ju)記錄(lu)如表4 所示。

　　由表4 可知， 當電(dian)(dian)(dian)源電(dian)(dian)(dian)動勢下降(jiang)到最(zui)低可充電(dian)(dian)(dian)電(dian)(dian)(dian)壓時，電(dian)(dian)(dian)池(chi)開始放電(dian)(dian)(dian)，放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)為3 mA。考慮到放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)受倒灌(guan)電(dian)(dian)(dian)阻Rd影響，改變Rd的大(da)小(xiao)可改變放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)。試驗表明，Rd=15 Ω 時放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)最(zui)小(xiao)。

　　5）接(jie)上電源內阻Rs=1 Ω，調(diao)整Es，使其在1.2～3.6 V 范(fan)圍內變(bian)化。數據記錄如表(biao)5 所示(shi)。

　　由(you)表5 可見，隨著電(dian)(dian)源電(dian)(dian)勢的(de)增加，充(chong)(chong)電(dian)(dian)電(dian)(dian)流也隨著增加，直(zhi)到當Es達到3.2 V 時，充(chong)(chong)電(dian)(dian)電(dian)(dian)流不(bu)再跟隨電(dian)(dian)源電(dian)(dian)勢變(bian)(bian)化(hua)。當電(dian)(dian)源電(dian)(dian)勢為3.2 V 時，充(chong)(chong)電(dian)(dian)電(dian)(dian)流最大，為256 mA。導致充(chong)(chong)電(dian)(dian)電(dian)(dian)流突變(bian)(bian)的(de)原因是升壓(ya)器件MAX1* 在(zai)不(bu)同(tong)輸入電(dian)(dian)壓(ya)下轉換(huan)效率不(bu)同(tong)。由(you)于MAX1* 在(zai)超(chao)過(guo)3 V 電(dian)(dian)壓(ya)下工作時轉換(huan)效率低，所(suo)以(yi)充(chong)(chong)電(dian)(dian)電(dian)(dian)流出現非線性的(de)突變(bian)(bian)。

　　6）當(dang)Es≥1.1 V 時，取Rs =1 Ω；當(dang)Es＜1.1 V 時，取Rs=0.1 Ω。測(ce)量向電池充電的Es，記(ji)錄(lu)數據如表(biao)6 所示。

　　由表6 可知，逐漸降低電源電勢Es時，充電電流也隨著下降。當Es到達0.4 V 時輸出電壓已經在0 V 附近變化，因此能向電池充電的最低Es為0.4 V。

　　4 結論

　　本設計以切換電路為控制核心，控制升壓型電路和降壓型電路對電池進行充電。該充電器輸出電壓能夠恒定在4 V，自動啟動充電功能的Es為3.6 V，Es降低到不能向電池充電時，電池放電電流為3 mA，電路適合由輸出電壓波動較大的太陽能電池板供電的便攜式充電器，且充電效率高于傳統的充電器。