開(kai)(kai)(kai)關(guan)(guan)電(dian)(dian)源就(jiu)是(shi)采用(yong)功率半導體器件(jian)(jian)(jian)作(zuo)為(wei)開(kai)(kai)(kai)關(guan)(guan)元(yuan)件(jian)(jian)(jian),通(tong)(tong)過周期性(xing)通(tong)(tong)斷開(kai)(kai)(kai)關(guan)(guan),控制開(kai)(kai)(kai)關(guan)(guan)元(yuan)件(jian)(jian)(jian)的占空(kong)比來(lai)調整(zheng)輸出(chu)電(dian)(dian)壓。開(kai)(kai)(kai)關(guan)(guan)元(yuan)件(jian)(jian)(jian)以一定的時(shi)間間隔重(zhong)復(fu)地(di)接通(tong)(tong)和斷開(kai)(kai)(kai),在開(kai)(kai)(kai)關(guan)(guan)元(yuan)件(jian)(jian)(jian)接通(tong)(tong)時(shi)輸入電(dian)(dian)源Vi通(tong)(tong)過開(kai)(kai)(kai)關(guan)(guan)S和濾波(bo)電(dian)(dian)路(lu)向(xiang)負載(zai)RL提供(gong)能量,當(dang)開(kai)(kai)(kai)關(guan)(guan)S斷開(kai)(kai)(kai)時(shi),電(dian)(dian)路(lu)中(zhong)的儲(chu)能裝置(L1、C2、二極管D組(zu)成的電(dian)(dian)路(lu))向(xiang)負載(zai)RL釋放在開(kai)(kai)(kai)關(guan)(guan)接通(tong)(tong)時(shi)所儲(chu)存的能量,使負載(zai)得到連續(xu)而穩定的能量。
VO=TON/T*Vi;
VO 為負載兩端的(de)電壓平均值;TON 為開(kai)關每次(ci)接(jie)通(tong)的(de)時間;T 為開(kai)關通(tong)斷(duan)的(de)工作(zuo)周(zhou)期;
由(you)式可知,改變(bian)開關接通時(shi)間(jian)和工作(zuo)(zuo)周期的比(bi)(bi)例(li)(li),VO間(jian)電(dian)壓平均值也隨之改變(bian),因此(ci),隨著負載及(ji)輸入電(dian)源電(dian)壓的變(bian)化自動調(diao)整TON和T的比(bi)(bi)例(li)(li)便使(shi)輸出電(dian)壓VO維(wei)持(chi)不變(bian)。改變(bian)接通時(shi)間(jian)TON和工作(zuo)(zuo)周期比(bi)(bi)例(li)(li)亦即改變(bian)脈(mo)沖的占(zhan)空比(bi)(bi),這種方法稱為“時(shi)間(jian)比(bi)(bi)率控制”(TimeRationControl,縮寫為TRC)。
按TRC控(kong)制原理(li),有三種方式:
(1)脈(mo)沖寬度(du)調制(PulseWithModulation,縮寫為PWM):開關周期恒定,通過改(gai)變脈(mo)沖寬度(du)來改(gai)變占空比的方式。
(2)脈沖(chong)頻(pin)率調制(PulseFrequencyModulation,縮寫為PFM):導通脈沖(chong)寬(kuan)度恒定,通過改(gai)變(bian)開(kai)關工作頻(pin)率來改(gai)變(bian)占(zhan)空比的方(fang)式。
(3)混(hun)合(he)調制:導通脈沖(chong)寬度和開關工作頻率均不固定(ding),彼此都能改變的(de)方(fang)式,它是(shi)以上二種方(fang)式的(de)混(hun)合(he)。