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1、電容主要參數的應用,作者:Morriss Su 2019.April,討論目的,1.介紹各參數代表的意義 2.利用參數預估計算所需值,討論主題,電容基本module介紹 電容基本參數介紹 如何應用參數決定電容 其它現象討論,一.電容基本Module介紹,1.REAL Module,2.DC Module,3.AC Module (Z=ESR),Frequency Vs Impedance,二.基本參數介紹,1.LEAKGE CURRENT Leakage current is the residual current which flows through the capacitor afte
2、r the charging time underrated voltage.,2.Dissipation Factor It is a function of the series resistance of the capacitor and the capacitance at low frequency,3.Impedance=Z The formula for impedance is: Z=(R2+(L-1/C ) 2),R: equivalent series resistance of the capacitor L: Inductance mainly due to the
3、leads C: capacitance,4.Maximun current ripple & Voltage ripple The maximum value of the ripple current or ripple voltage which can be applied to the capacitor is only limited by the thermal effect .The ESR and to the square of ripple current (P=ESR lrms2),三.如何應用參數決定電容,1.Output 波形,將V-ripple 分為 DC & A
4、C,實際電路與參數的關係,Leak I,Z,對DC而言,可近似為,Vin Vout 5V,對AC而言( 設 Z=ESR),未裝電容時,Vin Vout 50mV,電容並聯時,Voltage ripple: 50mvx(RC/Load)/Rc+(RD/Load)=33mV,如何選用適合的CAP,1,2,3,例: Output 5V 20A 5/20=0.25=250m 選擇小於10倍ESR的兩個6.3V 58m的CAP,例: 5V V Ripple 為50mV(在C上測到)則Cape的 I Ripple為50mV/58m=0.862mA,4,其他現象討論,為何在高溫時Ripple會較好? 為何同樣的濾波電容前級較後級Ripple Current 高? 為何電容要越接近Output端越好?,作者:Morriss Su,
