开关电源中的磁性元件

1、安森美半导体 Magnetics in Switched-Mode Power Supplies开关电源中的磁性元件Outline 纲要 Block Diagram of a Typical AC-DC Power Supply 一个典型的交流直流电源的框图 Specification of the Power Supply电源的技术规格 Key Magnetic Elements in a Power Supply电源中的关键磁性元件 Review of Magnetic Concepts磁概念的回顾 Magnetic Materials 磁性材料 Inductors and Transfo

2、rmers电感和变压器References参考文献Block Diagram of an AC-DC Power Supply 交流直流电源框图 Input Filter 输入滤波器 Rectifier 整流器 PFC 功率因数 AC Input 交流 输入 Power Stage原边电源 TransFormer 变压器 Output Circuits 输出电路 DC Outputs (to loads 直流输出 （至负载）Specifications (Abbreviated 技术规格（精简版） 100-Watt Three-Output Power Supply 100 瓦 3 输出电源

3、Input Voltage: 输入电压： Input Current: 输入电流： Input Harmonics: 输入谐波： Hold-up Time: 保持时间： Inrush Current: 浪涌电流：Outputs: 输出： OUTPUT VOLTAGE (V 输出电压 (v 5 3.3 12 90 264 Vac, 47-63 Hz 90264V 交流， 47 63Hz 2 A maximum. 最大 2A 。 Meets IEC1000-3-2 A14 for all load conditions. 在所有负载条件下均符合 IEC1000-3-2 A14。 20 ms min

4、imum. 最少20ms。 40 A peak at 264 V (cold start 在 264V 时 40A 峰值（冷启动） OUTPUT CURRENT (A 输出电流 (v MIN. 最小值 MAX. 最大值 1.5 10 0.3 5 0.3 3 TOTAL REGULATION 总调整率 2.0% 2.0% 2.0% RIPPLE (mV pp 纹波 (mV pp 50 50 100Specifications (cont技术规d格.（接上）Efficiency: 效率： Temperature: 温度： 75% minimum at full load, 120 Vac inpu

5、t 120V 交流输入，满载时最小 75 Operating: See derating curve below工作温度：见下面的降额曲线 Storage储存 100 W -40 oC to +85 oC -40 oC 至 +85 oC 200 LFM FORCED AIR COOLING 80 W 200LFM 强制风冷 NATURAL CONVECTION COOLING 自然对流冷却 50 W 40 W 0 oC 10 oC 20 oC 30 oC 40 oC 50 oC 60 oC 70 oC Temperature Derating温度降额Review of Some Magneti

6、c Concepts磁概念的回顾Units used in the design of magnetic components磁性元件设计中用到的单位 Current and magnetic flux电流和磁通量Characteristics of magnetic materials磁性材料的特点Faraday s Law (the“ transformer equation法拉第定律（” “变压器方程 ”）Flux Direction as a Result of Current FlowRight-Hand Rule右手法则电流流动引起的磁通方向磁通方向右手法则Wrap one s r

7、ight hand around a conductor with thumb pointing in the direction of current flow. Fingers point in the direction of flux lines. 右手握住导体，拇指指向电流流动的方向。四指代表磁力线的方向。Wound Coil Characteristics 线圈特性 flux turns in weber turns = volt secondsSlope = L = inductance (henries磁通匝数以韦伯匝数为单位 =伏特 秒 斜率 L电感（亨利） I curren

8、t in amperes电流以安培为单位 Using volt-seconds and amperes, the wound component can be analyzed easily by circuit engineers using time-domainanalysis. 使用伏特 秒和安培，电路工程师可以方便地使用时域分析法来分析磁性元件。The “ Transformer Equation 变压”器方“程 ” E = 4 B? Ae ? f N (Faraday s Law （法拉第定律） B in tesla, Ae in m2, f in Hz B 的单位是特斯拉， Ae

9、 的单位是 m2 ，f 的单位是 Hz Modern SI units 通用 SI 单位 The saturation flux density, Bmax, determines the maximum volts per turn that can be applied to a given transformer or inductor winding at a given frequency. 饱和磁通密度，即 Bmax，决定了特定变压器或电感绕 组在特定频率下每一匝可以施加的最大电压。Transformer Equation from Faraday从法sLaw拉第定律得出的变压器方

10、程Watch closely, now: 现在，请仔细观察： ? E=N ?t = ?B Ae B ?B ? = B? ? Ae = 2 B ? Ae 1 1 1 ?t = T = ? 2 2 f E ? 1 = = ?2 BAe ? 1 = 4 B ? Ae ? f N ?t 2f Note: This applies to square waves (where ?t = half of the period注.意：该方程适用于方波（ ?t = 半个周期）。An Extremely Important Fact 一个非常重要的定律E ? = = 4 B? Ae ? f N ?tUnless

11、 the flux is changing, there will be no voltage.只有磁通变化才会有感应电压。 If the flux swings back and forth, so will the voltage. 如果磁通往返摆动，电压也会摆动。 In order for there to be a net dc voltage, the flux must be continually increasing为.了得到一个纯直流电压，磁通必须不断增大。 Therefore, our chances of inventing amagnetic rectifier are

12、 ZERO. 因此，我们发明磁整流器的可能性为零。 The average voltage (dc across a winding (neglecting winding resistance is ALWAYS ZERO. This is one of the most useful facts in our bag of tools一.个绕组（忽略绕线电阻）两端的平均电压（直流）总是零。这是最有用的 定律之一。Popular Materials 常用材料 Material 材料 Permeability (relative 磁导率（相对） Bsat Loss 0.1 T, 100 kHz

13、 (tesla损耗 0.1 T, 100 Bsat kHz （特斯 拉） (mW/cm30.5 80 Usage用途 Pow er Transform ers Filter Inductors (gapped PFC Inductors (gapped 电源变压器 滤波 电感（有空隙） PFC 电感（有空隙） EMI Filters (com m on-mode only EMI 滤波器（仅限常用模式） Ferrite 铁氧体 (Mag. Inc. P Ferrite 铁氧体 (Mag. Inc. W Molypermalloy 钼坡莫合金 (Mag. Inc. MPP Sendust铝硅铁

14、(Mag. Inc. Kool-Mu Powdered iron 铁粉 (Micrometals 52 80% Cobalt tape 80%钴带 (Honeywell 2714A 2500 10,000 0.42 250 60 0.75 340 Filter Inductors PFC Inductors滤波电感 PFC 电感 60 1 850 Filter Inductors PFC Inductors滤波电感 PFC 电感 75 1.4 3200 Filter Inductors PFC Inductors 滤波电感 PFC 电感 100,000 0.55 90 Mag. Am ps磁放

15、大器 Note the wide range of permeability and power loss.注意宽范围的磁导率和功耗。Inductors and Transformers电感和变压器 Inductor operation (example: buck regulator 电感工作原理（例如：降压调整器） Conduction modes 导电模式 Continuous mode 连续模式 Critical conduction mode 临界导电模式 Discontinuousmode 不连续模式 The boost regulator升压调整器 Transformer ope

16、ration 变压器工作原理 Flyback converter 反激变换器 Forward converter 正激变换器Inductor Operation 电感工作 v 0 time v Current (i 电流 时间 i 0 Voltage and current are related by: V = L di/dt. 电压和电流的关系为： V = L di/dt 。 Slope of current = V / L. 电流的斜率 = V / L 。 Positive voltage: Current ramps up.正电压：电流斜升。 Negative voltage: Cur

17、rent ramps down.负电压：电流斜降。(Continuous Conduction 降压调整器（连续导电） Inductor current is continuous. 电感电流连续。 Vout is the average of the voltage at its input (V1. Vin = Vout 是其输入电压（ V1）的平均值。 15 V Output voltage is the input voltage times the duty ratio (D of the switch. 输出电压为输入电压乘以开关的占空比（ D）。 When switch in o

18、n, inductor current flows from the battery. 接通时，电感电流从电池流出。When switch is off, it flows through the diode. 断开时，电流流过二极管。 Neglecting losses in the switches and inductor, D is independent of load current忽.略开关和电感中的损耗， D 与负载电流无关。 A characteristic of buck regulators and its derivatives: 降压调整器的特征曲线及其导数： Inp

19、ut current is discontinuous (chopped, and output current is continuous (smooth输.入电流不连续（斩波），输出电流连续 （平滑）。 i1 v1 i2 i3 Vout = 5 V Load (R Buck Regulator 负载（ R） v1 0i1 0 i2 0 i3 0 time 时间(Critical Conduction 降压调整器（临界导电）Inductor current is still continuous,but just“ touches ” zero as the switch turns on电

20、感again电流.仍然是连续的，但在开关再次接通时电流 “达 到”零点。 This is called“critical conduction这被.称为 “”临界导电 ”。 Output voltage is still equal to the input voltage times D. 输出电压仍等于输入电压乘 以 D。 i1 v1 Vin = 15 V i2 i3 Vout = 5 V Load (R 负载（ R） Buck Regulator v1 0 i1 i2 i3 0 time 时间(Discontinuous Conduction 降压调整器（不连续导电） In this c

21、ase, the current in the inductor is zero during part of each period.在这种情况下，电感中的电流在每个周期的一段时间中为零。 Output voltage is still (as always the average of v1输.出电压仍然（始终）是 v1 的平均值。 Output voltage is NOT the input voltage times the duty ratio (D of the switch. 输出电压不是输入电压乘以开关的占 空比（ D）。 While the load current is

22、below the critical value, D varies with load current (while Vout remains constant.当负载电流低于临界值时， D 随着负载 电流而变化（而 Vout 保持不变）。 i1 i1 Vin = 15 V i2 v1 i3 i2 Vout = 5 V Load (R 负载（ R） Buck Regulator v1 0 i1 i2 i3 time 时间Boost Regulator 升压调整器 Output voltage is always greater than (or equal to the input volt

23、age. 输出电压始终大于（或等于）输入电压。 Input current is continuous, and output current is discontinuous (the opposite of a buck regulator输.入电流连续，输出电流不连续（与降压调 整器相反）。 Relationship of the output voltage to the duty ratio, D, is not as simple as in the buck regulator. In the continuousconduction case, it is:输出电压与负荷比（

24、D）的关系不如在降压 调整器中那么简单。在连续导电的情况下： i1 v1 Vin = 5V i2 i3 Vout = 15 V Load (R 负载（ R） Vout = 15 V Vin = 5 V v1 0 i1 0 ? 1 ? Vo = Vin ? ? ? 1- D ? In this example, Vin = 5, 在本例中， Vin = 5， Vout = 15, and D = 2/3. Vout = 15， D = 2/3。 i2 0 i3 0 time 时间Transformer (No Energy Storage变压器（无能量存储） 输入 IN ? OUT输出 Ampe

25、re-turns of all windings sum to zero. 所有绕组的安匝数之和为零。 Right-hand rule applies to the applied current and the resulting flux. The opposite occurs on the output winding. 右手法则适用于所施加的电流和它所产生的磁通。输出绕组上出现相 反的电流。Including Effect of Primary Inductance Transformer Operation 变压器工作原理 包括初级电感的作用 v 0 time 时间 i turns

26、 ratio: 1:2 i2 匝数比 i sec. i1 v sec. Load (R负载（ R） i 0 v sec. 0 i1 i2 0 0 i sec. 0 Transformer is shown as an ideal transformer, with its primary (magnetizing inductance as an inductor in parallel with the primary.变压器看作理想的变压器，它的初级（磁化）电感与初级并联。(Really a Multi-Winding Inductor 反激变压器（实际是多绕组电感） turns rati

27、o: 匝数比 i sec. i pri. 1:2 Vin v pri. 0 v pri. v sec. Vout Load (R 负载（ R） Flyback Transformer v drain 0 Vout v sec. 0 i pri. 0 time 时间 i sec. 0 Here, the primaryinductance is intentionally low, to determine the peak current and hence the stored energy. When the primary switch is turned off, the energy

28、 is delivered to the secondary反.激的初级电感一般很低，用于确定峰值电流和存储的能量。当初级开关断开时， 能量传送到次级。Forward Converter Transformer正激变换变压器i 匝数比 turns ratio: 1:2 i pri. i1i2 i sec. 3 Vin v pri. 0 Vout v sec. Load (R 负载（ R） iRESET v drain 0 1 v sec. 0 i pri.0 i1 0 v node 0 Vout iRESET 0 i2 0 time 时间 i sec. 0 i3 0 Primary induc

29、tance is high, as there is no need for energy storage正.激的初级电感一般很高，因为无需存储能量，是纯粹的变压器。Magnetizing current (i1 flows in the“magnetizing inductance” andcauses core reset (voltage reversal after primary switch turns off磁.化电流（ i1 ）流入“磁化电感 ”，使磁芯在初级开关断开后去磁（电压反向）。References参考文献 1. 2. 3. 4. Dixon, Unitrode (Te

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