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(如電機)中，對電源的性能要求更高。在很多應用直流電機的場合中，要求為電機驅動電路提供1個其輸出能從0 V開始連續可調(0～24 V)的直流電源，并且要求電源有保護功能。實際上就是要求設計一個具有足夠調壓范圍和帶負載能力的直流穩壓電源電路。該電路的設計關鍵在于穩壓電路的設計，其要求是輸出電壓從0 V開始連續可調；所選器件和電路必須達到在較寬范圍內輸出電壓可調；輸出電壓應能夠適應所帶負載的啟動性能。此外，電路還必須簡單可靠，能夠輸出足夠大的電流。

可調直流電源電路的設計符合上述要求的電源電路的設計方法有很多種，比較簡單的有3種：

晶體管串聯式(shi)直流(liu)穩(wen)壓(ya)(ya)(ya)(ya)電(dian)(dian)(dian)路(lu)。電(dian)(dian)(dian)路(lu)框圖如圖1所(suo)示(shi)，該電(dian)(dian)(dian)路(lu)中，輸(shu)出(chu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)UO經取樣(yang)電(dian)(dian)(dian)路(lu)取樣(yang)后得到(dao)取樣(yang)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)，取樣(yang)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)與(yu)基準電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)進行比較(jiao)得到(dao)誤差電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)，該誤差電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)對調(diao)整(zheng)管的工作狀態進行調(diao)整(zheng)，從(cong)而(er)使輸(shu)出(chu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)發生(sheng)變(bian)(bian)化(hua)，該變(bian)(bian)化(hua)與(yu)由于(yu)供電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)UI發生(sheng)變(bian)(bian)化(hua)引起的輸(shu)出(chu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)的變(bian)(bian)化(hua)正好(hao)相(xiang)反，從(cong)而(er)保證(zheng)輸(shu)出(chu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)UO為恒定(ding)值(zhi)(穩(wen)壓(ya)(ya)(ya)(ya)值(zhi))。因(yin)輸(shu)出(chu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)要求從(cong)0 V起實現連續可調(diao)，因(yin)此要在基準電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)處設(she)計輔助電(dian)(dian)(dian)源，用于(yu)控制輸(shu)出(chu)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)能夠從(cong)0 V開(kai)始(shi)調(diao)節。