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；（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(ban)的(de)(de)M0S－FET寄生二極(ji)管(guan)恢復特性不適宜高頻，因此，增(zeng)(zeng)設低耗二極(ji)管(guan)作(zuo)(zuo)為(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)二極(ji)管(guan)，為(wei)(wei)使放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流全部流經二極(ji)管(guan)VD1，在VF2回路(lu)中增(zeng)(zeng)加了逆阻斷(duan)二極(ji)管(guan)VD2．逆阻斷(duan)二極(ji)管(guan)VD2的(de)(de)耐壓大(da)于VD1的(de)(de)正向壓降(jiang)即(ji)可(ke)(ke)，因此，選用肖特基二極(ji)管(guan)（SBD）。另外(wai)，雙(shuang)向延時(shi)元(yuan)件宜采用可(ke)(ke)飽和(he)電(dian)(dian)(dian)(dian)(dian)(dian)抗器，延時(shi)元(yuan)件和(he)YF2的(de)(de)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)共同(tong)決定延時(shi)時(shi)間(jian)，需要較長(chang)延時(shi)時(shi)間(jian)時(shi)，可(ke)(ke)在柵極(ji)增(zeng)(zeng)接電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)。輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)流一減小(xiao)(xiao)，VF1的(de)(de)導通(tong)時(shi)間(jian)就變短。這(zhe)(zhe)導通(tong)時(shi)間(jian)若短于延時(shi)時(shi)間(jian)，則VF1截止后(hou)，VF2導通(tong)，因此，VF1漏極(ji)－源(yuan)極(ji)間(jian)電(dian)(dian)(dian)(dian)(dian)(dian)壓UDS的(de)(de)波形偏離(li)正常波形，功耗也稍增(zeng)(zeng)大(da)。為(wei)(wei)降(jiang)低最(zui)小(xiao)(xiao)輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)流，延時(shi)時(shi)間(jian)要非常短，這(zhe)(zhe)樣，就不能充(chong)分有效(xiao)利用電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)Cr。這(zhe)(zhe)里，作(zuo)(zuo)為(wei)(wei)大(da)致(zhi)目標，最(zui)小(xiao)(xiao)輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)流設定為(wei)(wei)最(zui)大(da)輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)2％～3％。