【正文】 出所需要的 ESR值，該值應確保輸出紋波低于最大的性能指標。 Calculate needed ESR value that will assure that the output ripple will be lower than maximum specification 3. 選擇恰當?shù)碾娙萜?，它（們）應該能承受計算出?rms電流，而 ESR應當與計算值一致或更低。 Select appropriate capacitor(s) to handle the calculated rms current and having calculated ESR or lower 4. 考慮價格、物理尺寸和瞬態(tài)響應等因素。 Factor in price, physical dimensions and transient response 5. 檢查電容所造成的紋波分量（對于足夠高的 Cf來說，往往可以忽略）。 Check the capacitive ponent value of the ripple (usually negligible for high enough Cf) 注： Notes: ? 副邊整流通路應該盡可能對稱，以保證每個開關(guān)周期具有一致的參數(shù)。 The secondary rectification paths should be as symmetrical as possible to assure same parameters for each switching cycle 43 議程 Agenda ? 為何采用 HB LLC 變換器 Why an HB LLC converter ? HB LLC變換器和諧振回路的構(gòu)形 Configurations of the HB LLC converter and a resonant tank ? HB LLC的工作狀態(tài) Operating states of the HB LLC ? HB LLC變換器建模和增益特性 HB LLC converter modeling and gain characteristics ? 原邊電流和諧振電容的參數(shù)確定 Primary currents and resonant cap dimensioning ? 副邊整流設計和輸出電容參數(shù)的確定 Secondary rectification design and output cap dimensioning ? 諧振電感的平衡性 Resonant inductance balance ? 變壓器繞組參數(shù)的確定和變壓器的制作 Transformer winding dimensioning and transformer construction 44 諧振電感的平衡 Resonant Inductance Balance 例 Example :Llk(ps1) = 105 uH Llk(ps2) = 115 uH ?Llk = 10 uH Llk(total) = 100 uH Lm = 600 uH Cs = 33 nF 總的 Ls總是受到變壓器的漏電感的影響。 Total Ls is always affected by the transformer leakage inductance 具有集成漏電感的變壓器屬于特殊情況 ——Ls=Llk Special case for transformer with integrated leakage inductance Ls=Llk 推挽和多輸出應用對漏電感的平衡性十分敏感。 Push pull and mult. output app. are sensitive to the leakage inductance balance 參數(shù) Parameter 測量引腳Measured between Pins 副邊引腳定義Secondary pins configuration Llk(ps1) AB CD短路 short DE開路 open Llk(ps2) AB CD開路 open DE短路 short Llk(total) AB CD短路 short DE短路 short Lm AB CD開路 open DE開 路 open fs1 = kHz fs2 = kHz 5 % 差值 difference 變壓器的漏電感 Transformer leakage inductance 45 諧振電感的平衡性 Resonant Inductance Balance 每個開關(guān)波形的半周期，串連諧振頻率都不同，這造成了原邊和主副邊的電流不平衡性 Series resonant frequency differs for each switching halfcycle that results in primary and mainly secondary current imbalance Time I(D6) I(D3)0A4A8A12A16A 副邊電流的峰值出現(xiàn) 3A的差異 ——各對整流管的功率耗散就不同，而且對于副邊繞組來說，功率耗散也不同 3 A difference in the peak secondary current – the power dissipation is different for each rectifier from pair as well as for the secondary windings. 46 諧振電感的平衡性 Resonant Inductance Balance 在開關(guān)周期的前半周，變換器工作在串連諧振頻率 Fs 之下，而在開關(guān)周期的第二半周，變換器工作在諧振頻率上。 Converter works below series resonant frequency Fs for the one half of the switching cycle and in the Fs for the second half of the switching cycle. Iprimary 47 對于大功率應用而言，將原邊繞組串連起來，并將副邊繞組并聯(lián)起來，是一種有吸引力分方法。這樣的結(jié)構(gòu)有望可以通過對副邊繞組的恰當連接，對變壓器漏電特性的不平衡性形成補償。 For high power app. it is attractive to connect primary windings in series and secondary windings in parallel. There is possibility to pensate transformer leakage imbalance by appropriate connection of the secondary windings: ?Llk_total = 2* ?Llk ?Llk_total = 0 諧振電感的平衡性 Resonant Inductance Balance 48 副邊漏感被反射到原邊，從而提高了總的諧振電感值。具有很高的匝數(shù)比的 LLC 應用處于危險狀態(tài) The secondary leakage inductance is transformed to the primary and increases the total resonant inductance value. Situation bees critical for the LLC applications with high turns ratios. 12 V / 20 A 應用例 application example : Np = 35 turns Llk_s1 = 100 nH Ns = 2 x 2 turns Llk_s2 = 150 nH n = Np/Ns = Ls = 110 uH Lm = 630 uH ?Llk_s = 50 nH HnLLslks ? ??D?D副邊出現(xiàn) 50 nH的差異，就可能造成 Ls出現(xiàn) 14 % 的差異 !!! 50 nH difference on the secondary causes 14 % difference of Ls !!! 諧振電感的平衡性 Resonant Inductance Balance 49 變壓器的構(gòu)造和副邊在布局方面的考慮： Transformer construction and secondary layout considerations: 采用推挽結(jié)構(gòu)時，諧振回路參數(shù)可以在每個開關(guān)周期中發(fā)生變化。這會導致原邊和副邊的電流出現(xiàn)不平衡。 Resonant tank parameters can change each switching half cycle when push pull configuration is used. This can cause the primary and secondary currents imbalance. 對于集成了諧振電感的變壓器而言，必須檢查變壓器的制造商給如何保證漏電感指標。所有短路的副邊繞組是不相關(guān)的。特定的漏電感值可以不同。 For the transformer with integrated resonant inductance, it has to be checked how the transformer manufacturer specifies the leakage inductance. Specification for all secondary windings shorted is irrelevant. The particular leakage inductance values can differ. 將更多的變壓器組合使用，將其原邊繞組串連起來并將其副邊繞組并聯(lián)，則通過恰當?shù)母边吚@組連接可以補償漏電感的不對稱性。 When using more transformers with primary windings in series and secondary windings in parallel the leakage inductance asymmetry can be pensated by appropriate secondary windings connection. 副邊漏電感可以造成采用高變壓器匝數(shù)比的應用中諧振電感出現(xiàn)顯著的不平衡性。在這種情況下， LLC諧振變換器的副邊的布線就有著關(guān)鍵性影響。 Secondary leakage inductance can cause significant resonant inductance imbalance in applications with high transformer turns ratio. Layout on the secondary side of the LLC resonant converter is critical in that case. 諧振電感的平衡性 Resonant Inductance Balance 50 議程 Agenda ? 為何采用 HB LLC 變換器 Why an HB LLC converter ? HB LLC變換器和諧振回路的構(gòu)形 Configurations of the HB LLC converter and a resonant tank ? HB LLC的工作狀態(tài) Operating states of the HB LLC ? HB LLC變換器建模和增益特性 HB LLC converter modeling and gain characteristics ? 原邊電流和諧振電容的參數(shù)確定 Primary currents and resonant cap dimensioning ? 副邊整流設計和輸出電容參數(shù)的確定 Secondary rectification design and output cap dimensioning ? 諧振電感的平衡性 Resonant inductance balance ? 變壓器繞組參數(shù)的確定和變壓器的制作 Transformer winding dimensioning and transformer construction 51 對于 Fop=Fs而言，原邊電流是正弦型的。副邊電流也近乎于正弦形的 —— 磁化電流造成了輕微的失真 The primary current is sinusoidal for Fop=Fs. The secondary current is almost sinusoidal too – there is slight distortion that is given by the magizing current. 變壓器繞組的參數(shù)確定 Transformer W