電子電路要正常工作，可調直流電源必不可少，并且電源性能對電路、電子儀器和電子設備的使用壽命、使用性能等影響很大，尤其在帶有感性負載的電路和設備(如電(dian)(dian)(dian)機)中(zhong)，對電(dian)(dian)(dian)源(yuan)的(de)性(xing)能要求更高(gao)。在很(hen)多應(ying)(ying)用直流(liu)電(dian)(dian)(dian)機的(de)場合中(zhong)，要求為(wei)電(dian)(dian)(dian)機驅動電(dian)(dian)(dian)路(lu)(lu)提供1個其(qi)輸(shu)出能從(cong)0 V開始連續可(ke)(ke)調(0～24 V)的(de)直流(liu)電(dian)(dian)(dian)源(yuan)，并且要求電(dian)(dian)(dian)源(yuan)有保護功能。實際上就是要求設計一(yi)個具有足夠調壓(ya)范(fan)圍和帶(dai)負載(zai)能力(li)的(de)直流(liu)穩壓(ya)電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)路(lu)(lu)。該電(dian)(dian)(dian)路(lu)(lu)的(de)設計關鍵在于(yu)穩壓(ya)電(dian)(dian)(dian)路(lu)(lu)的(de)設計，其(qi)要求是輸(shu)出電(dian)(dian)(dian)壓(ya)從(cong)0 V開始連續可(ke)(ke)調；所選(xuan)器(qi)件和電(dian)(dian)(dian)路(lu)(lu)必須(xu)達到在較寬范(fan)圍內(nei)輸(shu)出電(dian)(dian)(dian)壓(ya)可(ke)(ke)調；輸(shu)出電(dian)(dian)(dian)壓(ya)應(ying)(ying)能夠適應(ying)(ying)所帶(dai)負載(zai)的(de)啟(qi)動性(xing)能。此外，電(dian)(dian)(dian)路(lu)(lu)還必須(xu)簡單可(ke)(ke)靠，能夠輸(shu)出足夠大的(de)電(dian)(dian)(dian)流(liu)。

可調直流電源電路的(de)設計符合上述要(yao)求的(de)電源電路的(de)設計方法有很多種(zhong)，比較簡(jian)單(dan)的(de)有3種(zhong)：

晶體管(guan)(guan)串(chuan)聯式直流(liu)穩(wen)壓(ya)(ya)(ya)電(dian)(dian)路(lu)。電(dian)(dian)路(lu)框圖(tu)如(ru)圖(tu)1所示，該電(dian)(dian)路(lu)中，輸(shu)出(chu)(chu)(chu)電(dian)(dian)壓(ya)(ya)(ya)UO經取樣(yang)電(dian)(dian)路(lu)取樣(yang)后得(de)到取樣(yang)電(dian)(dian)壓(ya)(ya)(ya)，取樣(yang)電(dian)(dian)壓(ya)(ya)(ya)與(yu)基準電(dian)(dian)壓(ya)(ya)(ya)進(jin)行比較得(de)到誤差(cha)電(dian)(dian)壓(ya)(ya)(ya)，該誤差(cha)電(dian)(dian)壓(ya)(ya)(ya)對(dui)調(diao)(diao)整(zheng)管(guan)(guan)的(de)(de)工作狀態進(jin)行調(diao)(diao)整(zheng)，從(cong)而(er)使輸(shu)出(chu)(chu)(chu)電(dian)(dian)壓(ya)(ya)(ya)發(fa)(fa)生變(bian)化(hua)，該變(bian)化(hua)與(yu)由于(yu)供電(dian)(dian)電(dian)(dian)壓(ya)(ya)(ya)UI發(fa)(fa)生變(bian)化(hua)引(yin)起的(de)(de)輸(shu)出(chu)(chu)(chu)電(dian)(dian)壓(ya)(ya)(ya)的(de)(de)變(bian)化(hua)正好相反，從(cong)而(er)保證輸(shu)出(chu)(chu)(chu)電(dian)(dian)壓(ya)(ya)(ya)UO為恒(heng)定值(zhi)(穩(wen)壓(ya)(ya)(ya)值(zhi))。因輸(shu)出(chu)(chu)(chu)電(dian)(dian)壓(ya)(ya)(ya)要求從(cong)0 V起實現連續可(ke)調(diao)(diao)，因此要在基準電(dian)(dian)壓(ya)(ya)(ya)處設(she)計輔助電(dian)(dian)源(yuan)，用于(yu)控(kong)制輸(shu)出(chu)(chu)(chu)電(dian)(dian)壓(ya)(ya)(ya)能夠從(cong)0 V開始調(diao)(diao)節。