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1、反激变换器的例子Analysis of basic waveforms 基本波形分析The analysis of the basic waveforms will be done on a simulated example of a flyback converter operating in discontinuous conduction mode. Typical drain-source voltage waveform of the primary side switch is shown in Fig. 16.在电感电流断续模式下运营的反激变换器的典型一次侧漏源极开关电压波形见
2、图。Fig. 16 Typical drain-source voltage of the MOSFET in a flyback图反激变换器的典型漏源极电压These drain-source voltage waveforms can be theoretically distinguished into typical elements. Different physical phenomena influence the waveform at given time interval. Fig. 17 and Tab. 4 demonstrate the main elements o
3、f the voltage waveform. The superposition of all these elements results in a typical drain-source voltage shown in Fig. 16.这些漏源极电压波形能用典型的理论来描述。各个时间段有不同物理现象影响这些波形。图和平台描述了电压波形的重要原理。把这些原理准时序整合呈现出图所示的典型漏源极电压。Fig. 17 Main elements of the drain-source voltage图漏源极电压的重要原理原理：开通期间的电压下降过程原理：在开通期间因寄生震荡产生的电流尖刺原理
4、：关断期间的电压上升原理：缓冲电路的钳位电压原理：钳位过程结束后重要由场效应晶体管输出电容和变压器漏感引起的寄生振荡原理：磁芯存储磁能释放完毕后重要由场效应晶体管输出电容和变压器电感引起的寄生振荡原理：反激变换器释放磁能期间的反射电压原理：与直流母线电压等幅的重要方波Tab. 4 Main elements of the drain-source voltage平台漏源极电压的重要原理The spectrum of the whole drain-source waveform (Fig. 16) is presented in Fig. 18.图所示的漏源极电压呈现的电磁干扰频谱见图。Fig
5、. 18 Spectrum of the drain-source voltage (as shown in Fig. 16)图图所示的漏源极电压呈现的电磁干扰频谱The spectra of the main elements of the drain-source voltage can be found in Fig. 20. Fig. 19 is exactly the same as Fig. 17 and has been repeated here for better under-standing.图描述了漏源极电压重要原理产生的电磁干扰频谱。为便于理解，将图映射成图。Fig.
6、 19 Main elements of the drain-source voltage (repeated, same as Fig. 17)图漏源极电压的重要原理（对的反复图）Fig. 20 Spectra of the main elements of the drain-source voltage图漏源极电压重要原理产生的电磁干扰频谱This method allows associating certain parts of the spectrum with their root causes, i.e. the peak at 20 MHz in the spectrum o
7、f the drain-source voltage is caused by the parasitic oscillation due to the output capacitance of the MOSFET and the leakage inductance of the transformer.这种措施可以拟定电磁干扰频谱中某些频点的来源，也就是说漏源极电压产生的电磁干扰频谱中的兆赫兹峰点是钳位过程结束后重要由场效应晶体管输出电容和变压器漏感引起的寄生振荡产生的。The analysis of the drain current of the primary switch wi
8、ll be done in the same way. Fig. 21 demonstrates a typical drain current in a DCM flyback.对一次侧开关的漏极电流进行分析采用相似的措施。图展示出一种工作于电感电流断续模式反激变换器的典型漏极电流。Fig. 21 Typical drain current in a flyback图反激变换器的典型漏极电流This waveform can be presented as a superposition of the following elements (Fig. 22 and Tab. 5). The
9、superposition of all these elements results in a typical drain current shown in Fig. 21.这个波形可以被看作是下列原理的叠加（图和平台）。所有这些波形的叠加整合成果变成图所示的典型漏极电流。Fig. 22 Main elements of the drain current图漏极电流的重要原理原理：漏极电流的重要三角波形原理：在开关开通期间因寄生分布电容引起的电流尖刺原理：钳位过程结束后重要由场效应晶体管输出电容和变压器漏感引起的寄生振荡原理：磁芯存储磁能释放完毕后重要由场效应晶体管输出电容和变压器电感引起的
10、寄生振荡Tab. 5 Main elements of the drain current平台漏极电流的重要原理The spectrum of the whole drain current waveform (Fig. 21) is presented in Fig. 23.所有漏极电流波形产生的电磁干扰频谱（图）呈目前图。Fig. 23 Spectrum of the drain current (as shown in Fig. 22)图漏极电流产生的电磁干扰频谱（与图相似）The spectra of the main elements of the drain current can
11、 be found in Fig. 25. Fig. 24 is exactly the same as Fig. 22 and has been repeated for better understanding.漏极电流重要原理产生的电磁干扰频谱见图。图和图相似。Fig. 24 Main elements of the drain current图漏极电流的重要原理Fig. 25 Spectra of the main elements of the drain current图漏极电流重要原理产生的电磁干扰频谱As in case of drain-source voltage this
12、 method allows to associate the elements of the drain current waveform with its contribution to the whole spectrum. For example, the peak at 20 MHz in the spectrum is caused by the parasitic oscillation due to the output capacitance of the MOSFET and the leakage inductance of the transformer.就象漏源极电压
13、的例子那样，用这种措施也可以找出漏极电流的哪一部分对电磁干扰频谱产生影响。举例阐明，兆赫兹的峰点是钳位过程结束后重要由场效应晶体管输出电容和变压器漏感引起的寄生振荡产生的。This method of separating the waveform in time domain into its main elements helps to find out what part of the spectrum in frequency domain caused by what related physical phenomena. The separation into main eleme
14、nts should be done in respect of reasonable events in the power circuit like on and off slopes, oscillations, clamping, snubbering, reflected voltage, etc.这种在时域里对重要原理进行拆分的措施有助于找出产生电磁干扰频段的干扰源。这种离析重要原理的手法有助于合理审视电源电路里诸如变化速率、振荡、钳位、缓冲、反射电压等过程。In this flyback example only the primary switch has been analy
15、zed as active source of electrical noise. There are also others, like secondary side diodes or synchronous rectifier, control IC (especially its gate drive), etc. In order to obtain more complete analysis all these interference sources have to be analyzed.在这个反激变换器里只对一次侧开关进行电磁噪声产生的分析。但是尚有其她的部分，象二次侧的二极管或同步整流器、控制集成电路（特别是它们的栅极驱动）等等。按顺序分析将获得更完善的有关这些电磁干扰源的解析。However, it is impossible to predict the conducted EMI spectrum using this approach due to the fact, that only interference sour
