充電電路的控制吸收電容充放電電路圖
下面給大家介紹一種控制吸收電容充放電的電路圖。
(a)原理電路(lu);
(b)實用電路控制吸收電容充放電的電路圖
來自PWM集成控制器的脈沖使其通/斷工作。為使VF2的通/斷時間與VF1相反,增設雙向延時電路S1。現假設VF1為截止狀態,VF2為導通狀態,吸收電容Cr充電到VF1的漏極-源極間電壓,由此,也吸收加在VF1上的浪涌電壓。在由延時電路確定的延時時間后VF2截止,但這時,Cr兩端電壓等于加在VF1上的電壓,因此,為零電壓和零電流開關器件斷開方式。
二次側二極管VD2的電流降為零,變壓器無勵磁能量。此時一次主繞組N1感應的回掃電壓變為零,以高于C1上電壓進行充電的吸收電容C1對一次主繞組N1反向放電,這樣,放電電流經VF2的寄生二極管(虛線所示)流通。Cr放電開始時,VF2必須截止。由于Cr放電,電容Cr與一次主繞組的電感Lp產生諧振。
若VF2為導通狀態,諧振繼續衰減振蕩,但VF2截止狀態時,電容Cr兩端電壓為零時振蕩停止。若Cr停止諧振,則以VF1和VF2的輸入較小容量電容繼續產生較短周期的諧振。VF1再度導通時,軔小電容放電電流流經VF1本身而消耗掉。VF1導通時,其小容量電容充電的電壓隨導通時間而改變,但Cr兩端電壓降到最低電壓,因此,可以減小Cr產生的損耗。也就是說,即使采用較大容量的電容Cr損耗也不會增大。
一般的(de)M0S-FET寄(ji)生二極(ji)(ji)(ji)管(guan)恢復(fu)特性不適宜(yi)高頻,因此(ci)(ci),增設(she)低耗(hao)二極(ji)(ji)(ji)管(guan)作(zuo)為(wei)電(dian)(dian)(dian)容放電(dian)(dian)(dian)二極(ji)(ji)(ji)管(guan),為(wei)使放電(dian)(dian)(dian)電(dian)(dian)(dian)流全部流經二極(ji)(ji)(ji)管(guan)VD1,在VF2回路中增加了逆(ni)阻(zu)斷(duan)二極(ji)(ji)(ji)管(guan)VD2.逆(ni)阻(zu)斷(duan)二極(ji)(ji)(ji)管(guan)VD2的(de)耐壓(ya)(ya)大(da)于(yu)(yu)VD1的(de)正向壓(ya)(ya)降即可(ke),因此(ci)(ci),選(xuan)用肖特基二極(ji)(ji)(ji)管(guan)(SBD)。另外,雙(shuang)向延(yan)(yan)時(shi)(shi)(shi)元件宜(yi)采用可(ke)飽和(he)電(dian)(dian)(dian)抗(kang)器,延(yan)(yan)時(shi)(shi)(shi)元件和(he)YF2的(de)輸(shu)入電(dian)(dian)(dian)容共同決定延(yan)(yan)時(shi)(shi)(shi)時(shi)(shi)(shi)間(jian)(jian),需要(yao)(yao)較長延(yan)(yan)時(shi)(shi)(shi)時(shi)(shi)(shi)間(jian)(jian)時(shi)(shi)(shi),可(ke)在柵極(ji)(ji)(ji)增接電(dian)(dian)(dian)容。輸(shu)出(chu)電(dian)(dian)(dian)流一減小,VF1的(de)導通(tong)(tong)時(shi)(shi)(shi)間(jian)(jian)就變短。這(zhe)導通(tong)(tong)時(shi)(shi)(shi)間(jian)(jian)若短于(yu)(yu)延(yan)(yan)時(shi)(shi)(shi)時(shi)(shi)(shi)間(jian)(jian),則VF1截止(zhi)后,VF2導通(tong)(tong),因此(ci)(ci),VF1漏極(ji)(ji)(ji)-源極(ji)(ji)(ji)間(jian)(jian)電(dian)(dian)(dian)壓(ya)(ya)UDS的(de)波形偏(pian)離(li)正常(chang)波形,功(gong)耗(hao)也(ye)稍(shao)增大(da)。為(wei)降低最(zui)小輸(shu)出(chu)電(dian)(dian)(dian)流,延(yan)(yan)時(shi)(shi)(shi)時(shi)(shi)(shi)間(jian)(jian)要(yao)(yao)非常(chang)短,這(zhe)樣,就不能充(chong)分有效利用電(dian)(dian)(dian)容Cr。這(zhe)里,作(zuo)為(wei)大(da)致目標(biao),最(zui)小輸(shu)出(chu)電(dian)(dian)(dian)流設(she)定為(wei)最(zui)大(da)輸(shu)出(chu)電(dian)(dian)(dian)流的(de)2%~3%。