The article is with stimulating formula switch power source instead exemple, elaborated its to conduct in all mechanism of the generation that the model disturbs, transmission. According to the thought that active node balances noise, put forward a kind of new transformer EMC to devise a method. Pass experimental test and verify, with traditional design methodological photograph is compared, this method is disturbed to conducting electromagnetism (of EMI) control capacity stronger, and the making cost that can reduce transformer and technology are sophisticated degree. The belt that this method applies to other form likewise transformer develop attacks switch power source of the structure.

 

As the development of technology of power semiconductor device, volume of high power of switch power source is compared and efficient character makes the instrument equipment that its wait for each level in modern war, industry and commerce medium get applied extensively, and as clock frequency rise ceaselessly, the electromagnetism compatibility of equipment (the wide attention that EMC) problem causes people. EMC designs the indispensable important segment in already becoming switch power source to develop a design.

 

Conduct electromagnetism to disturb (of EMI) noise restrain initial stage must be developed to try to consider in the product. Normally the circumstance falls, adding filter of outfit power supply cord is to restrain the necessary step that conducts EMI [1] . But, the inductance quantity that the filter that relies on power source to input end merely will come to restrain interference to often can cause the cell in filter increases to increase with capacitance. And the addition that inductance measures makes bulk increases; The accretion of capacitance gets the limitation of standard of leakage current safety. If the other part in circuit is designed appropriate also can complete as similar as filter work. The noise that the article put forward transformer is active node is phasic and dry wind a way, method of this kind of design can reduce the volume of filter of power supply cord not only, still can reduce cost.

 

1, stimulate formula switch power source instead in all model conducted interference

The conduction of electronic equipment what noise interference points to is: Equipment passes power supply cord to conduct the electromagnetism interference that goes in environment of communal electrified wire netting with the form of noise electric current when with power supply electrified wire netting join works. Conducted interference cent is in all modular interference and wrong standard disturb two kinds. In all modular interference electric current is in 0 lines and photograph on-line are phasic and equal; Electric current of the interference that need a standard is in 0 lines and photograph on-line are phasic and contrary. The interference that need a standard is lesser to the contribution of overall conducted interference, and main concentration is carried in noise spectrum low frequency, restrain more easily; In all modular interference is bigger to the contribution of conducted interference, and basically mix at the intermediate frequency of noise spectrum high frequency frequency paragraph. Right in all model the inhibition of conducted interference is electronic equipment the difficulty in conducting EMC to design, also be the mainest task.

 

The node of revulsion of a few voltage exists in the circuit that stimulates formula switch power source instead. Differ with the other electromotive force is relatively steady node in circuit, the high frequency part that the voltage of these node includes high strenth [2] . The node with these voltage very active change calls noise active node. Noise is active node is circuit of switch power source is medium in all model conducted interference source, its action arises at the right stray capacitance in circuit in all ICM of modular noise electric current. And the larger to EMI influence right stray electric capacity in circuit has: The leakage that power switch is in charge of is extremely right the parasitism capacitance Cde of the ground, of transformer advocate edge winding is right the parasitism capacitance Cpa of deputy edge winding; The deputy edge loop of transformer is right the parasitism capacitance Cae of the ground, transformer advocate, the parasitism capacitance Cpc to magnetism core, Cac and transformer magnetism core are opposite deputy edge winding these parasitism capacitance are in the parasitism capacitance Cce of the ground if the graph is shown 1 times,circuit distributings mediumly.

 

Graph 1, in all modular noise electric current is in the coupling way in circuit

 

Graph 1 medium in all the coupling way in circuit basically has ICM of modular electric current 3: From noise source ——The D that power switch is in charge of extremely reach the ground through Cde coupling; Arrive through Cpa coupling from noise source transformer is sub circuit, repass Cae coupling reachs the ground; From transformer before, secondary coil arrives through coupling of Cpc, Cac transformer magnetism core, repass Cce coupling reachs the ground. These 3 kinds of electric current are to form in all modular noise electric current (graph 1 medium black arrowhead is shown) main factor. In all the ground wire circumfluence that modular electric current carries through input of power supply cord, be measured to get by LISN sampling thereby.

 

2, the EMC design that keeps apart transformer

2.1, design of traditional transformer EMC

In all the coupling of modular noise besides be in charge of D through field effect outside this extremely right way, the parasitism electric capacity that switch provides the noise voltage of D pole to pass transformer goes to coupling of noise electric current the loop that winding of transformer deputy edge is in, sub loop is opposite repass the parasitism capacitance coupling of the ground reachs the ground also is in all the way that modular electric current produces. Because this tries,reduce from transformer advocate edge winding delivers deputy edge to circle across block in all modular electric current is a kind of effective EMC design method. Method of traditional transformer EMC design is separator is added between two winding [3] , if pursue,2 are shown.

 

Graph 2, the transformer separator influence to noise electric current

 

The design that metallic separator connects ground wire directly can increase in all modular noise electric current, make EMC function becomes poor. Separator should be the node with the stable potential in circuit, the negative pole of the class before the plan for instance 2 medium separator receive circuit repeatedly is receive a standard very well. Such join can what flow to the earth originally in all modular electric current is effective billabong, the conduction that reduces power supply cord greatly thereby noise projects a level.

 

2.2, node is phasic balance law

In circuit, noise voltage is active node is not onefold. The circuit that analyses with the article is exemple: Except what power switch is in charge of outside D pole, the Uin of other one aspect of the matter of winding of the class before transformer also is voltage of a noise active node, and the D of the metabolic direction of node voltage and field canal extremely voltage situation is opposite. Transformer is so sub the two end of winding are phasic and contrary noise voltage active node. What the graph shows 3 times is to use node after phasic balance law, the coil on transformer framework distributings circumstance.

 

Graph 3, noise electric current is in the coupling circumstance of transformer interior

 

Transformer framework most lining is before the half of class winding coil, with what power switch is in charge of D pole is linked together; The coil of intermediate layer is sub winding; The outerest be before the other in part of class winding, be linked together with node Uin. Because noise electric current basically passes the parasitism capacitance coupling between layer of around class coil, before, hind active node circles the noise with class coil opposite way in couples in layer of inside and outside to be able to make relative to the position major noise electric current offsets each other, reduced final coupling to arrive greatly the intensity of sub noise electric current.

 

The auxiliary power source of circuit of the class before still existing in the circuit of article discussion and sub circuit, they also provide energy by the independent coil that is circled on transformer. This two class assisted the existence of coil to offer additional way to the transmission of noise electric current. Auxiliary coil is to control the power supply of circuit of the design. Although the power of control circuit itself is very little, but their existence increased circuit however the parasitism capacitance to the ground, partook thereby one part in all the job that modular noise reachs the ground from active node coupling. Place these winding however the space that around class winding can increase among the winding of advanced course coil and secondary coil, thereby capacitance of the parasitism between their layer was reduced, noise electric current can be reduced accordingly. Accordingly, transformer circles the final method that formulate to if the graph is shown 4 times,answer. From inside the coil winding outside arriving is ordinal be: Before the half of class winding, half of auxiliary winding, hind the other in part of winding of the class before the other in part of class winding, auxiliary winding is mixed.

 

3, experimental part

Transformer is improved circle a law to be able to pass an experiment to get test and verify to the conducts EMC function to rise effectiveness of switch power source.

 

3.1, experimental method

Experiment according to document [the voltage law in 4] undertakes. Frequency Duan Fan is surrounded for 0.15 ～ 30 MHz; The demodulation means of spectrum analyzer is demodulation of exact peak value; Measure bandwidth to be 9 KHz; Spectrum cross axle (frequency) take logarithm form; The unit of noise signal is DBμV[5] .

 

Graph 4, transformer improves the detail that wind a way

 

3.2, experimental result

Graph the 5 conduction that improve around test sample for transformer design noise spectrum is comparative.

 

Graph 5, the noise spectrum that transformer design improves around

 

Graph 5 medium fluctuation two parallel broken line are international Special Committee on Radio Interference respectively (the demodulation of exact peak value that class of the B in the CISPR22 standard that abbreviation CISPR) issues asks is restricted to be worth peace to all be worth demodulation to be restricted to be worth; And the conduction that the curve is switch power source noise spectrum. From the experiment the result can see: Compare with traditional method photograph, new method is having more outstanding right in all the inhibition of modular noise electric current ability, be in especially intermediate frequency the frequency of 1 ～ 5MHz paragraph. In inferior frequency paragraph, the conducted interference on power supply cord basically needs modular electric current to cause; And be in in high frequency paragraph, in all the main effect since modular electric current. And the means that the article offers is right in all the inhibition of modular electric current is stronger, experiment and theory are accorded with. The frequency in 10 MHz above paragraph, basically decide EMC function by the other parasitism parameter in circuit, not as big as transformer relation.

 

4, last word

The noise in circuit of switch power source is active node is circuit is medium in all modular noise source. Want to reduce the conducted interference level of switch power source, it is to reduce actually in all the intensity of modular electric current, right impedance that increases noise source. In design of traditional segregation type EMC, on the node that separator stabilizes even the potential in receiving circuit (be like: The negative pole of the class before transformer) should go to what ground wire disturbs to EMI to restrain than be being connected directly more effective.

 

The noise in circuit of switch power source is active node is didymous existence normally, between these didymous node phasic and contrary, use this one characteristic phasic balance circles active node the segregation type design with traditional to prep above of EMI low-key effectiveness method. Because do not need to add segregation metal layer, the bulk of transformer and cost can be reduced effectively or reduce.