太陽能電池板的便攜式充電器是解(jie)決(jue)通信設(she)備、田間測量儀器(qi)等移動式電(dian)(dian)(dian)(dian)(dian)(dian)子(zi)產品供電(dian)(dian)(dian)(dian)(dian)(dian)問(wen)題的(de)最佳解(jie)決(jue)方(fang)案之一。采(cai)用TPS5430 降壓(ya)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)和MAX167 4 升壓(ya)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，由LM393、ICL7660 等元件構成的(de)切換電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)為(wei)(wei)控制核(he)心(xin)，設(she)計(ji)具有自(zi)啟動功能的(de)電(dian)(dian)(dian)(dian)(dian)(dian)能收集(ji)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)。充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)能夠根(gen)據充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)不同(tong)，自(zi)動切換到不同(tong)的(de)DC-DC 變換電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，實(shi)現高效、快速充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。測試表(biao)明(ming)，當(dang)(dang)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)內阻Rs為(wei)(wei)100 Ω，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)Es在10～20 V 范(fan)圍(wei)內，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)動勢Ec為(wei)(wei)3.6 V、內阻Rc為(wei)(wei)0.1 Ω 時，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流Ic>58 mA，自(zi)動啟動充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)為(wei)(wei)3.6 V，電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)放電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流為(wei)(wei)3 mA；而當(dang)(dang)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)內阻Rs為(wei)(wei)1 Ω，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)Es在1.2～3.6 V 范(fan)圍(wei)內時，最大充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流可(ke)達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(ke)調直流電(dian)(dian)源模擬當太陽能(neng)(neng)電(dian)(dian)池板的(de)輸出(chu)電(dian)(dian)壓大范圍(wei)變化時，實現(xian)充(chong)電(dian)(dian)器的(de)自動(dong)啟(qi)動(dong)并盡可(ke)能(neng)(neng)地增大充(chong)電(dian)(dian)電(dian)(dian)流來(lai)實現(xian)充(chong)電(dian)(dian)效(xiao)率的(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(dian)動勢Ec恒定為(wei)3.6 V，內阻Rc為(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(ke)得，當(dang)(dang)Rs=100 Ω，Es=10 V 時(shi)(shi)，Ps=0.25 W，Ic>64 mA，η >92.16%；當(dang)(dang)Es=20 V 時(shi)(shi)，Ps=1 W，Ic>160 mA，η>57.6%。為(wei)(wei)了(le)盡可(ke)能提(ti)高高電(dian)(dian)(dian)壓時(shi)(shi)的充電(dian)(dian)(dian)效(xiao)率(lv)，除(chu)選用TPS5430 構成降(jiang)(jiang)壓電(dian)(dian)(dian)路外，應盡量降(jiang)(jiang)低切(qie)換(huan)電(dian)(dian)(dian)路的開(kai)關(guan)頻(pin)率(lv)。電(dian)(dian)(dian)路中主(zhu)要(yao)功(gong)耗(hao)(hao)元件是(shi)功(gong)率(lv)場效(xiao)應管(guan)（FET），在低頻(pin)情況下，功(gong)率(lv)FET 主(zhu)要(yao)是(shi)傳導(dao)(dao)損耗(hao)(hao)，在高頻(pin)情況下，傳導(dao)(dao)損耗(hao)(hao)維持不變(bian)，同頻(pin)率(lv)有關(guan)的損耗(hao)(hao)會(hui)增大。較(jiao)高或較(jiao)低的開(kai)關(guan)頻(pin)率(lv)均會(hui)使效(xiao)率(lv)降(jiang)(jiang)低，綜合考慮各(ge)因素并(bing)結合試(shi)驗(yan)，測得開(kai)關(guan)頻(pin)率(lv)為(wei)(wei)500 kHz 時(shi)(shi)效(xiao)率(lv)為(wei)(wei)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(gong)作和降壓(ya)(ya)工(gong)作兩(liang)種模(mo)式。設定切換的閾(yu)值電(dian)壓(ya)(ya)為3.6 V，閾(yu)值電(dian)壓(ya)(ya)由可(ke)調(diao)電(dian)阻設定并可(ke)調(diao)。充電(dian)電(dian)壓(ya)(ya)超(chao)過閾(yu)值電(dian)壓(ya)(ya)時降壓(ya)(ya)電(dian)路(lu)工(gong)作，低于(yu)閾(yu)值電(dian)壓(ya)(ya)時升壓(ya)(ya)電(dian)路(lu)工(gong)作。切換電(dian)路(lu)由場效應管、電(dian)壓(ya)(ya)比較器等分立元件構成，原理圖如圖3 所示。

　　圖(tu)3 中(zhong)， 輸(shu)(shu)入(ru)(ru)(ru)端VIN （P1） 接(jie)(jie)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源， 輸(shu)(shu)出端P2 接(jie)(jie)MAX167 4升壓(ya)(ya)電(dian)(dian)(dian)路的(de)(de)輸(shu)(shu)入(ru)(ru)(ru)端，肖特基(ji)二極(ji)管(guan)VD1用(yong)于(yu)(yu)(yu)防止電(dian)(dian)(dian)流倒灌。穩壓(ya)(ya)器(qi)TL431 為電(dian)(dian)(dian)壓(ya)(ya)比(bi)較器(qi)LM393 的(de)(de)負(fu)(fu)輸(shu)(shu)入(ru)(ru)(ru)端提供參(can)考電(dian)(dian)(dian)壓(ya)(ya)。輸(shu)(shu)入(ru)(ru)(ru)端VIN（P1）通過(guo)濾波后(hou)接(jie)(jie)入(ru)(ru)(ru)電(dian)(dian)(dian)壓(ya)(ya)比(bi)較器(qi)LM393 的(de)(de)正輸(shu)(shu)入(ru)(ru)(ru)端。調節R_ad可調電(dian)(dian)(dian)阻，使(shi)(shi)輸(shu)(shu)入(ru)(ru)(ru)小(xiao)于(yu)(yu)(yu)3.6 V 時電(dian)(dian)(dian)壓(ya)(ya)比(bi)較器(qi)LM393 輸(shu)(shu)出負(fu)(fu)電(dian)(dian)(dian)壓(ya)(ya)，P 溝道MOS 管(guan)IRLM16402VQ1、VQ2和(he)VQ3導通，VQ1，VQ2的(de)(de)漏極(ji)連接(jie)(jie)升壓(ya)(ya)電(dian)(dian)(dian)路， 使(shi)(shi)切換(huan)電(dian)(dian)(dian)路輸(shu)(shu)入(ru)(ru)(ru)、輸(shu)(shu)出端短接(jie)(jie)，使(shi)(shi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)接(jie)(jie)至升壓(ya)(ya)電(dian)(dian)(dian)路。當輸(shu)(shu)入(ru)(ru)(ru)大(da)于(yu)(yu)(yu)3.6 V 時，輸(shu)(shu)出高電(dian)(dian)(dian)平，VQ1、VQ2和(he)VQ3截(jie)止，此時MAX167 4升壓(ya)(ya)電(dian)(dian)(dian)路無輸(shu)(shu)入(ru)(ru)(ru)。VD2、VD3的(de)(de)作用(yong)是當電(dian)(dian)(dian)壓(ya)(ya)大(da)于(yu)(yu)(yu)3.6 V 時，LM393的(de)(de)負(fu)(fu)電(dian)(dian)(dian)源端接(jie)(jie)地(di)； 當電(dian)(dian)(dian)壓(ya)(ya)小(xiao)于(yu)(yu)(yu)5.5 V 時，LM393 負(fu)(fu)電(dian)(dian)(dian)源通過(guo)VQ3接(jie)(jie)ICL7660 的(de)(de)負(fu)(fu)電(dian)(dian)(dian)壓(ya)(ya)輸(shu)(shu)出引腳。

　　2.2 升壓/降壓電路設計

　　升(sheng)(sheng)壓(ya)電路(lu)主(zhu)要(yao)由升(sheng)(sheng)壓(ya)式(shi)DC-DC 電源轉換器MAX167 4組成，升(sheng)(sheng)壓(ya)后輸出(chu)4 V 直接對電池進(jin)行(xing)充電。MAX167 4升(sheng)(sheng)壓(ya)電路(lu)如圖4 所示。

　　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(yi)削弱紋波對輸(shu)出(chu)電壓的(de)影響。

　　降(jiang)壓電(dian)路主(zhu)要(yao)由降(jiang)壓DC-DC 轉換(huan)器TPS5430 組成，降(jiang)壓后直(zhi)接(jie)對電(dian)池進行充電(dian)。TPS5430 降(jiang)壓電(dian)路如圖5 所示。

　　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(suan)， 可得所需的(de)電(dian)(dian)感值(zhi)是15.8 μH，選(xuan)取(qu)內(nei)徑30 mm 的(de)鐵硅鋁(lv)磁(ci)芯(xin)自(zi)行繞制的(de)電(dian)(dian)感值(zhi)為18 μH，以保(bao)證(zheng)在額定(ding)(ding)的(de)工作狀況下(xia)不會出(chu)(chu)(chu)(chu)現磁(ci)飽和。電(dian)(dian)阻R1、R2和R3構成反饋網(wang)絡(luo)， 將輸(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)壓(ya)反饋到芯(xin)片的(de)VSNS 引腳(jiao)，該芯(xin)片自(zi)動調節(jie)輸(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)壓(ya)，保(bao)證(zheng)充(chong)電(dian)(dian)器輸(shu)出(chu)(chu)(chu)(chu)端輸(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)壓(ya)恒定(ding)(ding)。

　　3 試驗結果及分析

　　1）電源內阻Rs=100 Ω，調整Es的(de)大小，使其在10～20 V范圍內變(bian)化，記錄數據如(ru)表1 所(suo)示(shi)。

　　由(you)表1 可(ke)見(jian)，在(zai)Es為10 V 時，實測(ce)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)與理(li)論值存(cun)在(zai)5.9 mA 的偏差，充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)低、充(chong)(chong)電(dian)(dian)(dian)(dian)器的轉換效(xiao)率不高可(ke)能與芯片的轉換效(xiao)率和輸入電(dian)(dian)(dian)(dian)壓(ya)有關，由(you)TPS5430 的數據(ju)資料可(ke)知，在(zai)輸入電(dian)(dian)(dian)(dian)壓(ya)為10 V 左右，輸出電(dian)(dian)(dian)(dian)流(liu)約為60 mA 時，其工作效(xiao)率約為92%。而在(zai)12～20 V 范圍內(nei)，實測(ce)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)大于理(li)論計算充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)值。

　　2）逐漸降低Es，直到充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流Ic略大(da)于0 時，記(ji)(ji)錄(lu)對(dui)應(ying)的電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓Es，該電(dian)(dian)(dian)(dian)壓即為最(zui)低可(ke)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓。為保(bao)證準(zhun)確性，對(dui)多個不同的電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓值進行測(ce)試(shi)，選(xuan)取最(zui)優3 組數據記(ji)(ji)錄(lu)如表2 所(suo)示。

　　由表2 可(ke)見(jian)，當(dang)Es下降(jiang)到3.6 V 時，充(chong)電(dian)電(dian)流為(wei)0，充(chong)電(dian)器不(bu)能再對電(dian)池進(jin)行充(chong)電(dian)，故最(zui)低可(ke)充(chong)電(dian)電(dian)壓(ya)為(wei)3.6 V。

　　3）從0 開始逐漸(jian)升高Es，Rs為(wei)(wei)0.1 Ω；當(dang)Es升高到高于(yu)1.1 V 時，更換Rs為(wei)(wei)1 Ω。然后繼(ji)續(xu)升高Es，直到充電(dian)(dian)電(dian)(dian)流略大(da)于(yu)0，記(ji)錄此時的電(dian)(dian)源(yuan)電(dian)(dian)壓(ya)值，該(gai)電(dian)(dian)壓(ya)即(ji)為(wei)(wei)自動(dong)啟(qi)動(dong)充電(dian)(dian)功能的啟(qi)動(dong)電(dian)(dian)壓(ya)。為(wei)(wei)保證準(zhun)確性，對多個(ge)不(bu)同的電(dian)(dian)源(yuan)電(dian)(dian)壓(ya)值進(jin)行測試(shi)，選取最優4 組數據記(ji)錄如表3 所示。

　　由(you)表3 可見，當(dang)Es小于3.6 V 時，充(chong)(chong)電(dian)電(dian)流持續(xu)為0，一旦Es上升(sheng)到(dao)3.6 V 后，充(chong)(chong)電(dian)電(dian)流由(you)0 開始(shi)增(zeng)加，即自動(dong)啟(qi)動(dong)充(chong)(chong)電(dian)電(dian)壓為3.6 V。

　　4）Es降低到不能(neng)向電池充電，最低至0 時(shi)，檢測放電電流。為(wei)保證準確性，對多個不同(tong)的(de)電源(yuan)電壓值進行(xing)測試，選取最優3 組數據(ju)記錄如(ru)表4 所示。

　　由表(biao)4 可知， 當電(dian)(dian)源電(dian)(dian)動勢下降到最低可充(chong)電(dian)(dian)電(dian)(dian)壓時，電(dian)(dian)池開始放(fang)(fang)(fang)電(dian)(dian)，放(fang)(fang)(fang)電(dian)(dian)電(dian)(dian)流(liu)為3 mA。考慮到放(fang)(fang)(fang)電(dian)(dian)電(dian)(dian)流(liu)受倒(dao)灌電(dian)(dian)阻Rd影響(xiang)，改變(bian)Rd的大小(xiao)可改變(bian)放(fang)(fang)(fang)電(dian)(dian)電(dian)(dian)流(liu)。試(shi)驗表(biao)明，Rd=15 Ω 時放(fang)(fang)(fang)電(dian)(dian)電(dian)(dian)流(liu)最小(xiao)。

　　5）接上電源(yuan)內阻Rs=1 Ω，調整Es，使其在1.2～3.6 V 范圍內變化。數據(ju)記(ji)錄(lu)如表5 所示。

　　由表5 可見，隨著電(dian)(dian)(dian)源電(dian)(dian)(dian)勢的增加，充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)也隨著增加，直(zhi)到(dao)當(dang)Es達到(dao)3.2 V 時，充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)不(bu)再跟(gen)隨電(dian)(dian)(dian)源電(dian)(dian)(dian)勢變化(hua)。當(dang)電(dian)(dian)(dian)源電(dian)(dian)(dian)勢為3.2 V 時，充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)最大，為256 mA。導(dao)致(zhi)充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)突變的原因是升壓(ya)器件MAX1* 在(zai)不(bu)同輸入(ru)電(dian)(dian)(dian)壓(ya)下轉換效率不(bu)同。由于MAX1* 在(zai)超過3 V 電(dian)(dian)(dian)壓(ya)下工作時轉換效率低(di)，所以(yi)充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)出現(xian)非線性的突變。

　　6）當Es≥1.1 V 時，取(qu)Rs =1 Ω；當Es＜1.1 V 時，取(qu)Rs=0.1 Ω。測量(liang)向電池充(chong)電的Es，記錄數據如表6 所(suo)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。