问大虾们一个问题:
在反激式中,我们一般用非连续模式,为什么?
非连续模式比连续模式有什么优点?
反激式中的连续和非连续模式
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@ykkj
在输出不变化的情况下,非连续的峰值电流要大一些,工作时开关管输出二极管以及电容产生最大的损耗,变压器也产生最大铜损. 连续状态下原边电感比较大,电流斜率低,损耗较小,但变压器容易饱和,所以一般采取比较折中的办法,按照峰值电流和初始电流3:1设计变压器.
Advantages of discontionuous operation:
1.A small transformer can be used because the average energy is low, use of fewer turns also translates into redused I^2*R losses.
2.Stability is easier to achieve because at frequencies less than one half the switching frequency there is no net inductance reflected to the transformer secondary.and hence no second pole in the input to output transfer function.
3.Output rectifies are operating at Zero current just prior to becoming reverse biased. therefore reverse recovery requirement are not critical for these rectfiers.
4.similarly, the power transsitor turns on to a curen level which is initially zero , so its turn on time is not critical.
5.transsitor turn on to zero current also results in low RFI generation.
Disadvantange
1.Transistor and diode peak current requirement are apporoximately twice.
2.Transformer leakage inductance is high , result in some loss of cross-regulation.
3.High value of ripple current make E cap quite stringent.
1.A small transformer can be used because the average energy is low, use of fewer turns also translates into redused I^2*R losses.
2.Stability is easier to achieve because at frequencies less than one half the switching frequency there is no net inductance reflected to the transformer secondary.and hence no second pole in the input to output transfer function.
3.Output rectifies are operating at Zero current just prior to becoming reverse biased. therefore reverse recovery requirement are not critical for these rectfiers.
4.similarly, the power transsitor turns on to a curen level which is initially zero , so its turn on time is not critical.
5.transsitor turn on to zero current also results in low RFI generation.
Disadvantange
1.Transistor and diode peak current requirement are apporoximately twice.
2.Transformer leakage inductance is high , result in some loss of cross-regulation.
3.High value of ripple current make E cap quite stringent.
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@chenpen
Advantagesofdiscontionuousoperation:1.Asmalltransformercanbeusedbecausetheaverageenergyislow,useoffewerturnsalsotranslatesintoredusedI^2*Rlosses.2.Stabilityiseasiertoachievebecauseatfrequencieslessthanonehalftheswitchingfrequencythereisnonetinductancereflectedtothetransformersecondary.andhencenosecondpoleintheinputtooutputtransferfunction.3.OutputrectifiesareoperatingatZerocurrentjustpriortobecomingreversebiased.thereforereverserecoveryrequirementarenotcriticalfortheserectfiers.4.similarly,thepowertranssitorturnsontoacurenlevelwhichisinitiallyzero,soitsturnontimeisnotcritical.5.transsitorturnontozerocurrentalsoresultsinlowRFIgeneration.Disadvantange1.Transistoranddiodepeakcurrentrequirementareapporoximatelytwice.2.Transformerleakageinductanceishigh,resultinsomelossofcross-regulation.3.HighvalueofripplecurrentmakeEcapquitestringent.
说国语吧,老兄
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