【文章內(nèi)容簡(jiǎn)介】 黃河科技學(xué)院畢業(yè)設(shè)計(jì) (文獻(xiàn)翻譯 ) 第 10 頁 1 source analysis of harassment In small power DC/DC converter, the main interfereing source is electromagic induction noise and nonlinear switch process noise. This is because in the circuit power changing rectifier diodes and power switch tube in work produced in the process of voltage and current leap to change, and through the high frequency transformers, energy storage inductance coil in the circuit and the layout of elements and device itself bring parasitic parameters caused by the interaction between. In ther words, all of the interference of the circuit produced the root of the problem, is the power switch tube and high frequency rectifier diode in quick open circuit process produced in di/dt and dv/dt. So, in the early stages of the circuit design, the circuit of the scheme should consider when the choice to EMC problem. In various conditions mature and allow, for the Lord switch tube shall be designed with soft switch circuit (for example of power in the circuit of widelyheld phase shifting the whole bridge circuit, etc), such not only can greatly reduce the switch tube switching losses, but also to help reduce in the circuit di/dt. And in the choice of switch frequency also is not the better, but should be to select the suitable frequency. Also, the switch tube and high frequency diode and output capacitance of a circuit should as far as possible to small, because small loop inductance is parasitic small. In the switch tube and high frequency diode opened and shut off the moment it will cause a big di/dt, if parasitic inductance big will induction high voltage, formed so a big source of harassment. In addition,o in the high frequency diode shut off the time will be the reverse recovery, this also is a great source of harassment. We must pay attention to weaken it, so as not to affect the normal work of the circuit, and therefore can give high frequency diode string of a small inductance, restrain high frequency diode current reverse recovery. But the inductance can39。t big, because in the high frequency di/dt under very big, will also introduce a harassment, and therefore must be the difference. Another produce electromagic induction noise is main interfereing source of pulse 黃河科技學(xué)院畢業(yè)設(shè)計(jì) (文獻(xiàn)翻譯 ) 第 11頁 transformer. In the flyback type circuit, because the original vice edge winding coupling coefficient is 1, transformer has certain leak Ls feeling. When the switch off, produced by the potential of the LsLsdi/dt can make switch tube drainsource voltage appears between the blunt. This is because the energy on the Lsleakage magic flux can39。t through the transformer coupling to vice edge for release, so this part of the energy with the switch tube parasitic capacitance Cs and input power Vin pose a decay of the LC resonance, in addition to the shutoff voltage forming shut off the voltage spikes. The peak noise is actually pointed pulse, in addition to cause interference outside, the person that weigh likely breakdown switch tube. And it is still a conductive emi, affecting both of transformer39。s primary, still can make interference conduction return to power distribution system, causing the input side of the grid electromagic interference, thus influence o ther electrical equipment safety and economical operation. And switch tube, circuit of pulse transformer also has high frequency di/dt changes, also can to space radiation of the high frequency electromagic wave, interference of other ponents and equipment. Therefore shall also be thinking of high frequency electromagic shielding transformer these off. As for electromagic field, the electric field and magic field ponent weight there always. So, in shielding electromagic field, must to electric and magic fields and to shielding. The mechanism of high frequency electromagic shielding is mainly based on the electromagic wave through the metal screen body produces wave reflection and wave absorption mechanism. The electromagic wave reached a shielded surface, will produce the reflection, the main reason is the electromagic wave impedance and metal shielding body features impedance is not equal, the greater the difference between values, the greater the loss caused by reflection. Reflected wave also and the frequency, the lower the frequency, the more serious reflection. And the electromagic wave through the shield returns in the absorption of produced when loss are mainly by electromagic waves in a shielded rite of the eddy current cause. The vortex induced can produce a magic field offset against the 黃河科技學(xué)院畢業(yè)設(shè)計(jì) (文獻(xiàn)翻譯 ) 第 12 頁 magic field interference, and at the same time, eddy current in shielding inside the body produce heat loss. 2 the design of the electromagic patibility The electromagic patibility design including circuit choose, ponents selection, filtering, shielding, grounding, layout, etc. soft switch technology Select zero voltage switch, and zero current switch resonance technology or other soft switch technology. In the zero resonant converters voltage, power switch on voltage wa