不(bu)知道你(ni)是否(fou)和我(wo)(wo)一樣，經常混用充(chong)電(dian)線(xian)，這不(bu)有天當我(wo)(wo)向另一個AI借用他(ta)的(de)平板充(chong)電(dian)線(xian)給我(wo)(wo)的(de)手(shou)機充(chong)電(dian)時，他(ta)義正言辭地拒絕了(le)！

還跟我“科普”道：在非快充模式下，雖然兩種充電線長得一樣，電壓都是5V，但iPhone的充電電流是1A，而iPad卻是2.1A，根據P=UI可得iPhone充電器的功率為5W，而iPad為10.2W。這樣做的后果是既傷iPhone又傷iPad 充電器（過高電流有可能導致關鍵電容擊穿！）。”

嚇死人了，真的嗎？

相信(xin)經常混用充電(dian)線的(de)人為數不(bu)少，看到(dao)這篇標題后，是否會覺(jue)得心頭一緊？其實完全不(bu)用擔心。以上(shang)的(de)“科普知識”的(de)作者大概并不(bu)真(zhen)正(zheng)懂得電(dian)子知識，只是單純依據充電(dian)器的(de)參數，想當然地得出了這樣一個錯誤的(de)結論。

想弄清(qing)楚為什么iPad充(chong)電器可以(yi)為iPhone充(chong)電，得先真正了解充(chong)電器的工作原理。

充電過程是怎樣的？

充電器插(cha)頭一(yi)端插(cha)在(zai)220V交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的插(cha)座(zuo)上，另一(yi)端用(yong)(yong)蘋果專(zhuan)用(yong)(yong)的數(shu)據線接(jie)到iPhone/iPad上。220V交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)先(xian)通過(guo)整(zheng)流(liu)(liu)電(dian)(dian)(dian)路(lu)(lu)變成高壓(ya)(ya)(ya)直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)，再經過(guo)開關管變成高頻高壓(ya)(ya)(ya)脈(mo)沖(chong)，然(ran)后通過(guo)變壓(ya)(ya)(ya)器轉換為低(di)壓(ya)(ya)(ya)（比如(ru)5V）脈(mo)沖(chong)。5V的低(di)壓(ya)(ya)(ya)脈(mo)沖(chong)再經過(guo)一(yi)個整(zheng)流(liu)(liu)、穩壓(ya)(ya)(ya)電(dian)(dian)(dian)路(lu)(lu)，變成5V穩定的直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)。在(zai)從(cong)220V交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)變為5V直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)的整(zheng)個過(guo)程(cheng)中，變壓(ya)(ya)(ya)器、整(zheng)流(liu)(liu)電(dian)(dian)(dian)路(lu)(lu)、穩壓(ya)(ya)(ya)電(dian)(dian)(dian)路(lu)(lu)只是起到一(yi)個改變電(dian)(dian)(dian)能形(xing)態的作(zuo)用(yong)(yong)（從(cong)高壓(ya)(ya)(ya)交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)變為低(di)壓(ya)(ya)(ya)直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)）。

在充電(dian)這件事情上，只有充電(dian)器可是一(yi)巴掌拍不響的。如果穩壓電(dian)路(lu)輸出5V的一(yi)端(duan)（USB接口(kou)）沒有接上iPad或(huo)者iPhone（術語稱為負載），就(jiu)不會(hui)有電(dian)流流過，也就(jiu)不會(hui)消(xiao)耗電(dian)能。

接(jie)上負(fu)(fu)載之(zhi)后，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)才(cai)開始(shi)工(gong)作(zuo)，流(liu)過(guo)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)大小取決(jue)于負(fu)(fu)載的狀態：只要(yao)(yao)在力所能及的范圍(wei)內(nei)，負(fu)(fu)載（也就(jiu)是(shi)iPad或者iPhone）需(xu)要(yao)(yao)多(duo)大的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)就(jiu)提供(gong)多(duo)大的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。如果負(fu)(fu)載需(xu)要(yao)(yao)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)超過(guo)了充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)能夠提供(gong)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)上限，那么充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)就(jiu)會(hui)一直輸(shu)出(chu)這(zhe)個最大的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。這(zhe)是(shi)因為，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)內(nei)部通常會(hui)設計保護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，一旦輸(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)過(guo)大，就(jiu)會(hui)觸發保護機制，暫停電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)輸(shu)出(chu)。

不過(guo)，蘋果公司(si)為了讓旗(qi)下的所(suo)有充電(dian)器(qi)和數碼產品能(neng)夠盡量混用，想(xiang)出了一個奇招(zhao)：

仔細觀(guan)察一下USB接口，你會發現一共有四個窄金屬條，稱(cheng)為四個引(yin)腳。這四個引(yin)腳分別連接5V電源、GND地、D+數據線正信號和(he)D-數據線負信號。

一般兼容USB接口的充電(dian)(dian)器(qi)，D+和(he)D-兩(liang)(liang)個(ge)引腳(jiao)(jiao)是懸空(kong)的，任何設(she)(she)備只(zhi)要插上(shang)這(zhe)(zhe)樣的充電(dian)(dian)器(qi)，就會從5V和(he)GND兩(liang)(liang)個(ge)引腳(jiao)(jiao)獲得電(dian)(dian)能(neng)。而蘋果的充電(dian)(dian)器(qi)則(ze)在D+和(he)D-兩(liang)(liang)個(ge)數據(ju)引腳(jiao)(jiao)上(shang)增加了分(fen)壓電(dian)(dian)阻(zu)，使充電(dian)(dian)的設(she)(she)備能(neng)夠在充電(dian)(dian)時(shi)從這(zhe)(zhe)兩(liang)(liang)條數據(ju)線上(shang)讀(du)到兩(liang)(liang)個(ge)電(dian)(dian)壓。

網絡上的(de)創客經過實踐證明，iPhone或者iPod對應的(de)5V1A充電器，D+上的(de)電壓(ya)(ya)是(shi)2V，D-也是(shi)2V；而iPad使(shi)用的(de)5V2.1A的(de)充電器，D+電壓(ya)(ya)2.7V，D-電壓(ya)(ya)2V。當(dang)iPad或者iPhone接上充電器時，通過這兩個引腳上不同的(de)電壓(ya)(ya)就可以區分當(dang)前使(shi)用的(de)是(shi)哪種充電器，也就能對負載做出相應的(de)調整，從而安全地充電。

呵呵，想蒙充電器……AI笑而不語

用iPad充電(dian)(dian)器給iPhone充電(dian)(dian)，會(hui)怎樣？

iPad和iPhone充電(dian)(dian)(dian)(dian)器(qi)的(de)設計不同是有原因的(de)。iPhone的(de)電(dian)(dian)(dian)(dian)池容量較(jiao)小，只需要1A的(de)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流就能在一個合理的(de)時間內完成充電(dian)(dian)(dian)(dian)。雖然更(geng)大(da)的(de)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流能大(da)幅縮短(duan)充電(dian)(dian)(dian)(dian)時間，但(dan)會(hui)帶來更(geng)大(da)的(de)發熱(re)量，而(er)高溫是鋰(li)電(dian)(dian)(dian)(dian)池壽命縮短(duan)的(de)頭號殺手，所以iPhone充電(dian)(dian)(dian)(dian)器(qi)的(de)最大(da)輸(shu)出(chu)電(dian)(dian)(dian)(dian)流被設計為1A。

iPad的(de)(de)充電器(qi)上標(biao)明了5V 2.1A，指的(de)(de)是iPad的(de)(de)充電器(qi)最(zui)(zui)大(da)只(zhi)(zhi)(zhi)能(neng)輸出(chu)2.1A的(de)(de)電流。當你(ni)用iPad的(de)(de)充電器(qi)給iPhone充電時，雖(sui)然iPad的(de)(de)充電器(qi)最(zui)(zui)大(da)能(neng)夠提供2.1A的(de)(de)電流，但由于iPhone只(zhi)(zhi)(zhi)能(neng)接受(shou)1A的(de)(de)電流，iPad的(de)(de)充電器(qi)也只(zhi)(zhi)(zhi)好遷(qian)就(jiu)它。這就(jiu)好比在4車(che)道的(de)(de)公路上開車(che)，遇到收(shou)(shou)費(fei)站的(de)(de)時候，只(zhi)(zhi)(zhi)有1個收(shou)(shou)費(fei)亭開著(zhu)，那么同時通過收(shou)(shou)費(fei)站的(de)(de)汽車(che)最(zui)(zui)多也就(jiu)只(zhi)(zhi)(zhi)有1輛(liang)。

iPad的電池設計成充電電流為2.1A時充電時間最合適。如果用iPhone的電池充電器給iPad進行(xing)充(chong)電(dian)，由于(yu)iPhone的充(chong)電(dian)器最大只(zhi)能提供1A的電(dian)流輸出，整(zheng)個充(chong)電(dian)的時間會(hui)是原來的2.1倍(bei)左右。由于(yu)蘋果在USB接口數據引腳上耍的小花招(zhao)，iPad知道這是iPhone的充(chong)電(dian)器，也就不會(hui)“要求”超(chao)過(guo)1A的充(chong)電(dian)電(dian)流，并不會(hui)使iPhone充(chong)電(dian)器過(guo)載(zai)而導致損壞。

這(zhe)也好比在公路上，雖(sui)然收(shou)費站里有4個收(shou)費亭(ting)，但(dan)是由于修路的(de)原因，實際通車的(de)車道只(zhi)有1條(tiao)，那么同時通過這(zhe)個收(shou)費站的(de)汽車最多仍然只(zhi)有1輛。

至(zhi)于這條流(liu)言最后提到的(de)(de)(de)，過(guo)高的(de)(de)(de)電(dian)流(liu)可能(neng)導致關(guan)鍵電(dian)容擊(ji)穿(chuan)，完全邏輯(ji)不(bu)通，也(ye)說明了微博作(zuo)者缺乏電(dian)學物理知(zhi)識。電(dian)容的(de)(de)(de)最基本功能(neng)是“通交流(liu)，隔直流(liu)”。充電(dian)器輸出(chu)的(de)(de)(de)是直流(liu)電(dian)，而無論多大的(de)(de)(de)直流(liu)電(dian)流(liu)，都是無法通過(guo)電(dian)容的(de)(de)(de)，并不(bu)能(neng)導致電(dian)容“擊(ji)穿(chuan)”。能(neng)夠擊(ji)穿(chuan)電(dian)容的(de)(de)(de)，是過(guo)高的(de)(de)(de)直流(liu)電(dian)壓，也(ye)就(jiu)是“擊(ji)穿(chuan)電(dian)壓”。

所以說，用iPad充(chong)電器(qi)為(wei)iPhone充(chong)電是(shi)完全可(ke)行的，對(dui)iPhone和(he)充(chong)電器(qi)都不會(hui)有損傷。而iPhone充(chong)電器(qi)為(wei)iPad充(chong)電也可(ke)以，只不過所需的充(chong)電時間更(geng)長(chang)。

話說回(hui)來，如果這樣(yang)交叉充電有危險(xian)的(de)話，以蘋果公司的(de)尿(niao)性……

他們根(gen)本不(bu)會把iPad和iPhone的(de)充電線做成一樣的(de)啊！