問大蝦們一個問題:
在反激式中,我們一般用非連續模式,為什么?
非連續模式比連續模式有什么優點?
反激式中的連續和非連續模式
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@ykkj
在輸出不變化的情況下,非連續的峰值電流要大一些,工作時開關管輸出二極管以及電容產生最大的損耗,變壓器也產生最大銅損. 連續狀態下原邊電感比較大,電流斜率低,損耗較小,但變壓器容易飽和,所以一般采取比較折中的辦法,按照峰值電流和初始電流3:1設計變壓器.
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.
說國語吧,老兄
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