CN103700484A - Method for designing auxiliary winding of switching power supply high-frequency transformer to inhibit common-mode electromagnetic interference (EMI) - Google Patents

Abstract

The invention discloses a method for designing an auxiliary winding of a switching power supply high-frequency transformer to inhibit common-mode electromagnetic interference (EMI). According to the method, by a measure of reasonably designing an anti-phase auxiliary winding on the primary side of the transformer, the common-mode conducted EMI of a switching power supply is inhibited in high performance. The anti-phase auxiliary winding connected in parallel with a primary winding of the transformer is designed according to a zero equipotential line theory, an electric field generated by the anti-phase auxiliary winding eliminates common-mode noise voltage of primary and secondary windings, and common-mode conducted EMI noise caused by a coupling capacitor between the primary winding and the secondary winding of the transformer is effectively inhibited. According to the method, the common-mode conducted EMI noise is effectively inhibited, the loss of the switching power supply for the transformer is effectively reduced, the volume of the power supply can be greatly reduced and the energy conversion efficiency is improved.

Description

The auxiliary Winding Design method of switch power high-frequency transformer that suppresses common mode EMI

Technical field

The invention belongs to switching mode power supply transformer design field, be specifically related to a kind of auxiliary Winding Design method of switch power high-frequency transformer that suppresses common mode EMI.

Background technology

Along with the switching frequency of Switching Power Supply improves constantly, EMI inhibition problem becomes a very large challenge of design efficient switch power supply.Utilize high frequency transformer technology to suppress common mode EMI noise and can save passive in switching power circuit and active EMI inhibition circuit, cpable of lowering power loss, reduces power supply physical size, improves the efficiency of Switching Power Supply.

The high frequency transformer technology of existing inhibition common mode EMI noise has: adopt and reduce the parasitic coupling capacitance technology inhibition common mode EMI noise of transformer main winding to secondary winding, but this can produce larger leakage inductance on the one hand, can cause on the other hand transformer conversion efficiency to reduce; Employing is once and add shunt capacitance technology between secondary side and suppress common mode EMI noise, the applicable capacitor of this technology can be subject to the restriction of safety standard, enough low impedance can not be provided simultaneously, allow all CM noise currents that filter distributes along this flow path; Faraday shield technology, this Technology Need is integrated into conductive plate on transformer and shunts noise current, because CM noise current circulation path is more, wayward, this technology does not have general validity, and screen correctly installation could meet safety requirements.

The high frequency transformer method that the present invention suppresses common mode EMI unlike other reducing parasitic capacitance, shunt capacitance be provided, make an effort in the shielding that is not easy to implement, but according to zero equipotential lineation opinion, a kind of auxiliary Winding Design method of high frequency transformer of brand-new inhibition common mode EMI has been proposed.The designed high frequency transformer of the present invention has overcome tradition and has utilized high frequency transformer technology to suppress the shortcoming of common mode EMI, at transformer primary side, designs an anti-phase auxiliary winding, suppresses the common mode noise current that between winding and secondary winding, coupling capacitance causes.Anti-phase auxiliary winding produces a reverse potential on armature winding, ideally, the switch electromotive force of secondary winding can be reduced to zero, and making the common mode EMI electric current by transformer one, two sides is zero.

Summary of the invention

The object of this invention is to provide a kind of auxiliary Winding Design method of switch power high-frequency transformer that suppresses common mode EMI, adopt the zero equipotential line Theoretical Design anti-phase auxiliary winding in parallel with transformer first side winding, make transformer totally present equipotential.The method can significantly be cut down common mode EMI noise, substitutes traditional passive EMI low pass filter completely, has solved the engineering problems such as inhibition common mode EMI switch power high-frequency transformer leakage inductance increases, shunt capacitance is difficult for design, effective shielding is difficult to carry out.Also can make the Switching Power Supply loss at this transformer place effectively reduce, can significantly reduce power volume, improve energy conversion efficiency simultaneously.

The technical solution adopted in the present invention is that a kind of switch power high-frequency transformer that suppresses common mode EMI is assisted Winding Design method, specifically according to following steps, implements:

Step 1: search the databook of inverse-excitation type switch power-supply transformer, find out transformer first and second umber of turn N _p, N _sand the coupling capacitance C between transformer first and second side winding _pS; If there is no C in databook _pS, with LCR bridge measurement C more than 30M _pS; If the transformer of existing Switching Power Supply does not have databook, with mensuration, obtain N _p, N _sand C _pS;

Step 2: at the anti-phase auxiliary winding N of the pre-coiling of Circuit Fault on Secondary Transformer winding outermost gapless _pcircle, is connected in parallel in first side winding;

Step 3: survey the coupling capacitance C between anti-phase winding and secondary winding with LCR electric bridge more than 30M _aS;

Step 4: calculate the number of turn N that needs coiling according to the relation between the Transformer Winding number of turn and coupling capacitance _a;

Step 5: adjusting the anti-phase auxiliary umber of turn of transformer is the number of turn N calculating in step 4 _a, according to calculating the corresponding increase of the number of turn or reducing the number of turn of anti-phase auxiliary winding;

Step 6: again survey the coupling capacitance C ' between anti-phase and secondary winding _aS, method of measurement is for adopting LCR bridge measurement coupling capacitance C ' more than 30MHz _aS;

Step 7: calculate N ' according to the formula in step 4 _a;

Step 8: the anti-phase umber of turn N calculating in comparison step 4 and step 7 _aand N ' _a, because umber of turn is integer, minimum value equals 1, if the absolute value of both differences is less than 1, illustrates that anti-phase Winding Design meets equilibrium condition; If the absolute value of both differences is greater than 1, illustrate that anti-phase Winding Design does not meet equilibrium condition, by its coupling capacitance of space change of adjusting between anti-phase auxiliary winding and secondary winding, it is proofreaied and correct, be back to step 5 pair anti-phase auxiliary umber of turn and adjust.

Feature of the present invention is also,

Step 4 wherein is specifically implemented according to following steps:

If N _p>N _s, be step-down transformer, the noise voltage U of a winding P _pthan the noise voltage U of secondary winding S _slarger, anti-phase auxiliary winding A should have same phase with secondary winding S, meets equipotential equilibrium condition:

U _P（C _PS）-U _S（C _PS+C _AS）-U _A（C _AS）=0

Wherein $U_P=\frac{N_P}{N_S}\left(U_S\right)=\frac{N_P}{N_A}\left(U_A\right);$

$\stackrel{\·}{\·\·}{U}_P\left(C_{\mathrm{PS}}\right)-U_P\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})-U_P\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)=0$

$\stackrel{\·}{\·\·}{C}_{\mathrm{PS}}=\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})+\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)$

$\stackrel{\·}{\·\·}{C}_{\mathrm{AS}}=\frac{N_P-N_S}{N_A+N_S}{C}_{\mathrm{PS}}$

$\stackrel{\·}{\·\·}{N}_A=\frac{C_{\mathrm{PS}}}{C_{\mathrm{AS}}}\×(N_P-N_S)-N_S;$

If N _p<N _s, be step-up transformer, the noise voltage U of secondary winding S _sthan the noise voltage U of a winding P _pgreatly, anti-phase auxiliary winding A and a winding P have same phase, meet equipotential equilibrium condition:

U _S（C _PS+C _AS）-U _P（C _PS）-U _A（C _AS）=0

Wherein $U_P=\frac{N_P}{N_S}\left(U_S\right)=\frac{N_P}{N_A}\left(U_A\right);$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{U}_P\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})-U_P\left(C_{\mathrm{PS}}\right)-U_P\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)=0$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})=C_{\mathrm{PS}}+\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{C}_{\mathrm{AS}}=\frac{N_S-N_P}{N_A-N_S}{C}_{\mathrm{PS}}$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{N}_A=\frac{C_{\mathrm{PS}}}{C_{\mathrm{AS}}}\&times;(N_S-N_P)+N_S.$

The invention has the beneficial effects as follows, the inventive method is compared advantage with existing using method and is, utilizes the transformer with anti-phase auxiliary winding of zero equipotential line Theoretical Construction, by eliminating the noise voltage of first and second winding, effectively suppresses common mode EMI noise.Due to the anti-phase auxiliary winding increasing high-current carrying not, so anti-phase auxiliary winding winding diameter is very little, cost is very low.Due to anti-phase auxiliary winding the outer felt of transformer around, so that winding method is implemented is simple, easy to adjust.The most useful effect is not have for one the traditional existing high frequency transformer that suppresses common mode EMI function, can reequip by the method, and such method makes existing high frequency transformer have the ability that suppresses common mode EMI.With the high frequency transformer of the method design, can make place Switching Power Supply volume reduce with 1/8 under power situation, totally save cost approximately 1/6.

Accompanying drawing explanation

Fig. 1 is the auxiliary Winding Design method flow diagram of switch power high-frequency transformer that the present invention suppresses common mode EMI;

Fig. 2 is the winding method cutaway view of the present invention's switch power high-frequency transformer of suppressing common mode EMI, wherein (a), for the present invention suppresses the winding method cutaway view of the Switching Power Supply high frequency voltage descending transformer of common mode EMI, (b) suppresses the winding method cutaway view of the Switching Power Supply high-frequency step-up transformer of common mode EMI for the present invention.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

The present invention suppresses the auxiliary Winding Design method of switch power high-frequency transformer of common mode EMI, as shown in Figure 1, specifically according to following steps, implements:

Step 1: search the databook of this inverse-excitation type switch power-supply transformer, find out transformer first and second umber of turn N _p, N _sand the coupling capacitance C between transformer first and second side winding _pS.If there is no C in databook _pS, with LCR bridge measurement C more than 30M _pS.If the transformer of existing Switching Power Supply does not have databook, with mensuration, obtain N _p, N _sand C _pS.

Step 2: at the anti-phase auxiliary winding N of the pre-coiling of Circuit Fault on Secondary Transformer winding outermost gapless _pcircle, is connected in parallel in first side winding.Winding method is shown in switch power high-frequency transformer winding method cutaway view (Fig. 2), wherein, if N _p>N _s, be step-down transformer, according to the coiling of Fig. 2 (a) mode, if N _p<N _s, be step-up transformer, according to the coiling of Fig. 2 (b) mode.

Step 3: survey the coupling capacitance C between anti-phase winding and secondary winding with LCR electric bridge more than 30M _aS.

Step 4: as formula (3) and (6), calculate the number of turn N that needs coiling according to the relation between the Transformer Winding number of turn and coupling capacitance _a.Step-down transformer is used (6) with (3), step-up transformer.

If N _p>N _s, be step-down transformer, the noise voltage U of a winding P _pthan the noise voltage U of secondary winding S _slarger, anti-phase auxiliary winding A should have same phase with secondary winding S, meets equipotential equilibrium condition:

U _P（C _PS）-U _S（C _PS+C _AS）-U _A（C _AS）=0 （1）

Wherein $U_P=\frac{N_P}{N_S}\left(U_S\right)=\frac{N_P}{N_A}\left(U_A\right).$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{U}_P\left(C_{\mathrm{PS}}\right)-U_P\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})-U_P\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)=0$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{C}_{\mathrm{PS}}=\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})+\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{C}_{\mathrm{AS}}=\frac{N_P-N_S}{N_A+N_S}{C}_{\mathrm{PS}}---\left(2\right)$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{N}_A=\frac{C_{\mathrm{PS}}}{C_{\mathrm{AS}}}\&times;(N_P-N_S)-N_S---\left(3\right)$

If N _p<N _s, be step-up transformer, the noise voltage U of secondary winding S _sthan the noise voltage U of a winding P _pgreatly, anti-phase auxiliary winding A and a winding P have same phase, meet equipotential equilibrium condition:

U _S（C _PS+C _AS）-U _P（C _PS）-U _A（C _AS）=0 （4）

Wherein $U_P=\frac{N_P}{N_S}\left(U_S\right)=\frac{N_P}{N_A}\left(U_A\right).$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{U}_P\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})-U_P\left(C_{\mathrm{PS}}\right)-U_P\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)=0$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})=C_{\mathrm{PS}}+\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{C}_{\mathrm{AS}}=\frac{N_S-N_P}{N_A-N_S}{C}_{\mathrm{PS}}---\left(5\right)$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{N}_A=\frac{C_{\mathrm{PS}}}{C_{\mathrm{AS}}}\&times;(N_S-N_P)+N_S---\left(6\right)$

Step 5: adjusting the anti-phase auxiliary umber of turn of transformer is the number of turn N calculating in step 4 _a.According to calculating the corresponding increase of the number of turn or reducing the number of turn of anti-phase auxiliary winding.

Step 6: again survey the coupling capacitance C ' between anti-phase and secondary winding _aS.Method of measurement is identical with method of measurement in step 3, adopts LCR bridge measurement coupling capacitance C ' more than 30MHz _aS.

Step 7: calculate N ' according to the relation between umber of turn and coupling capacitance _a, computing formula is suc as formula (3) or (6), and step-down transformer is used (6) with (3), step-up transformer.

Step 8: the anti-phase umber of turn N calculating in comparison step 4 and step 7 _aand N ' _a, because umber of turn is integer, minimum value equals 1, if the absolute value of both differences is less than 1, illustrates that anti-phase Winding Design meets equilibrium condition; If the absolute value of both differences is greater than 1, illustrate that anti-phase Winding Design does not meet equilibrium condition, by its coupling capacitance of space change of adjusting between anti-phase auxiliary winding and secondary winding, it is proofreaied and correct.Being back to step 5 pair anti-phase auxiliary umber of turn adjusts.

Claims (2)

1. the auxiliary Winding Design method of switch power high-frequency transformer that suppresses common mode EMI, is characterized in that, specifically according to following steps, implements:

Step 1: search the databook of inverse-excitation type switch power-supply transformer, find out transformer first and second umber of turn N _p, N _sand the coupling capacitance C between transformer first and second side winding _pS; If there is no C in databook _pS, with LCR bridge measurement C more than 30M _pS; If the transformer of existing Switching Power Supply does not have databook, with mensuration, obtain N _p, N _sand C _pS;

Step 2: at the anti-phase auxiliary winding N of the pre-coiling of Circuit Fault on Secondary Transformer winding outermost gapless _pcircle, is connected in parallel in first side winding;

Step 3: survey the coupling capacitance C between anti-phase winding and secondary winding with LCR electric bridge more than 30M _aS;

Step 4: calculate the number of turn N that needs coiling according to the relation between the Transformer Winding number of turn and coupling capacitance _a;

Step 5: adjusting the anti-phase auxiliary umber of turn of transformer is the number of turn N calculating in step 4 _a, according to calculating the corresponding increase of the number of turn or reducing the number of turn of anti-phase auxiliary winding;

Step 6: again survey the coupling capacitance C ' between anti-phase and secondary winding _aS, method of measurement is for adopting LCR bridge measurement coupling capacitance C ' more than 30MHz _aS;

Step 7: calculate N ' according to the formula in step 4 _a;

Step 8: the anti-phase umber of turn N calculating in comparison step 4 and step 7 _aand N ' _a, because umber of turn is integer, minimum value equals 1, if the absolute value of both differences is less than 1, illustrates that anti-phase Winding Design meets equilibrium condition; If the absolute value of both differences is greater than 1, illustrate that anti-phase Winding Design does not meet equilibrium condition, by its coupling capacitance of space change of adjusting between anti-phase auxiliary winding and secondary winding, it is proofreaied and correct, be back to step 5 pair anti-phase auxiliary umber of turn and adjust.

2. the auxiliary Winding Design method of the switch power high-frequency transformer of inhibition common mode EMI according to claim 1, is characterized in that, described step 4 is specifically implemented according to following steps:

If N _p>N _s, be step-down transformer, the noise voltage U of a winding P _pthan the noise voltage U of secondary winding S _slarger, anti-phase auxiliary winding A should have same phase with secondary winding S, meets equipotential equilibrium condition:

U _P（C _PS）-U _S（C _PS+C _AS）-U _A（C _AS）=0

Wherein $U_P=\frac{N_P}{N_S}\left(U_S\right)=\frac{N_P}{N_A}\left(U_A\right);$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{U}_P\left(C_{\mathrm{PS}}\right)-U_P\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})-U_P\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)=0$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{C}_{\mathrm{PS}}=\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})+\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{C}_{\mathrm{AS}}=\frac{N_P-N_S}{N_A+N_S}{C}_{\mathrm{PS}}$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{N}_A=\frac{C_{\mathrm{PS}}}{C_{\mathrm{AS}}}\&times;(N_P-N_S)-N_S;$

If N _p<N _s, be step-up transformer, the noise voltage U of secondary winding S _sthan the noise voltage U of a winding P _pgreatly, anti-phase auxiliary winding A and a winding P have same phase, meet equipotential equilibrium condition:

U _S（C _PS+C _AS）-U _P（C _PS）-U _A（C _AS）=0

Wherein $U_P=\frac{N_P}{N_S}\left(U_S\right)=\frac{N_P}{N_A}\left(U_A\right);$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{U}_P\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})-U_P\left(C_{\mathrm{PS}}\right)-U_P\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)=0$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}\frac{N_S}{N_P}(C_{\mathrm{PS}}+C_{\mathrm{AS}})=C_{\mathrm{PS}}+\frac{N_A}{N_P}\left(C_{\mathrm{AS}}\right)$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{C}_{\mathrm{AS}}=\frac{N_S-N_P}{N_A-N_S}{C}_{\mathrm{PS}}$

$\stackrel{\&CenterDot;}{\&CenterDot;\&CenterDot;}{N}_A=\frac{C_{\mathrm{PS}}}{C_{\mathrm{AS}}}\&times;(N_S-N_P)+N_S.$

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