CN101093235A - System for measuring internal impedance of noise source of switching power supply EMI based on Hilbert transform and current probe, and measuration method - Google Patents

Abstract

An internal impedance measurement system of switch power-supply EMI noise source based on Hibert transform and current probe comprises line-impedance stable network, common mode/difference mode impedance test module, signal generator and frequency spectrum analyzer. It is featured as inputting power supply wire directly to impedance stable network then inputting to switch power supply and load for forming a complete power supply loop through common mode/different mode impedance test module. The method for measuring said internal impedance is also disclosed.

Description

Switch power source EMI noise origin internal impedance test system and assay method based on Hilbert conversion and current probe

Technical field

What the present invention relates to is system and the assay method that conduction electromagnetic interference (EMI) noise source internal impedance is tested, for conduction EMI Noise Suppression is that the design of electromagnetic interface filter provides the prerequisite basis, belong to the electromagnetic compatibility device design and technical field.

Background technology

Electromagnetic interface filter is the effective measures that suppress electromagnetic interference (EMI), but at present both at home and abroad when carrying out the electromagnetic interface filter design, in advance and do not know the internal interference source and the impedance of noise source, often ignore the internal impedance of noise source during design, carried out a kind of general electromagnetic interface filter design.Because the internal impedance of each noise source is also inequality, and the matching relationship between interference source impedance and the filter impedance directly has influence on the filter effect of wave filter, therefore, estimates that accurately the Switching Power Supply internal driving has significance for effective inhibition of electromagnetic interference (EMI).

Summary of the invention

The objective of the invention is at the resistance matching problem of electromagnetic interface filter in the above-mentioned electromagnetic compatibility and switch power source EMI noise origin internal impedance test system and the assay method based on Hilbert conversion and the current probe that propose, it can provide perfect and economical and practical noise source test solution for enterprise and product design slip-stick artist.The present invention both can satisfy the general requirement of noise source modeling, and the reality test is compared with notional result, can provide the good premise condition for the design of next step electromagnetic interface filter, effective inhibition of EMI noise again simultaneously.

The present invention is based on the switch power source EMI noise origin internal impedance test system of Hilbert conversion and current probe, constitute by line impedence stabilizing network (LISN), common mode, signal generator and spectrum analyzer; The power lead of coming from electrical network is directly inputted to the line impedence stabilizing network (LISN), by common mode impedance measuring module, then is input in Switching Power Supply (SMPS) and the load, constitutes a whole piece electric power loop; Signal generator provides an input signal for common mode, then by spectrum analyzer the response signal in this module is detected.

In electric power loop, the effect of line impedence stabilizing network (LISN) is for Switching Power Supply provides power supply, and the noise of insulating power supply side enters test loop simultaneously, also the noise of isolating switch power generation, prevent to pollute electrical network, and the stable impedance of one 50 Ω is provided for test loop.Common mode is used for the internal impedance of measuring switch power supply, and Switching Power Supply is a Devices to test.

Described common code impedance test module is made up of a pair of common mode choke, two electric capacity and two current probes, and one of them is pouring-in current probe, and one is detection formula current probe; Two electric capacity are connected on respectively between L-E, the N-E.Power lead L, the N, the E that come from electrical network are directly inputted to the line impedence stabilizing network, and output terminal L, N are input to Switching Power Supply by a pair of common mode choke, and output E line is directly inputted to Switching Power Supply, and two electric capacity are connected on respectively between L-E, the N-E.Two leads that two electric capacity link to each other with the E line penetrate two current probes, and pouring-in current probe connects signal generator, detect the formula current probe and connect spectrum analyzer, and the DC side output of Switching Power Supply connects load.Read the reading that detects on the examination current probe by inserting blocked impedance, short circuit, three kinds of states of Switching Power Supply operate as normal in the circuit, and the internal impedance of Switching Power Supply is calculated according to the Hilbert algorithm.

For making the internal driving Z of this test circuit _InCan repeat to measure and keep constant as far as possible, this two capacitor fixing is on printed circuit board (PCB), and the pouring-in simultaneously and formula of detection current probe is also fixed its position on circuit board; Between printing board PCB and testing apparatus for short-term is connected, to reduce the ghost effect that the lead layout causes.The test of this stationkeeping, in case after its advantage is the circuit calibration, the test circuit internal driving Z that records _InNot only be applicable to the common mode test, equally also be applicable to the differential mode test, can improve the speed of test greatly.

Described differential mode impedance test module is made up of two differential mode choking coils, two electric capacity and two current probes; Power lead L, the N, the E that come from electrical network are directly inputted to the line impedence stabilizing network, and the L of output, N line are input to Switching Power Supply by 1 differential mode choking coil respectively, and output E line is directly inputted to Switching Power Supply, and two electric capacity also are connected between the L-N; Two leads that two electric capacity link to each other with the E line penetrate two current probes, and pouring-in current probe connects signal generator, detect the formula current probe and connect spectrum analyzer, and the DC side output of Switching Power Supply connects load.

The present invention is based on the noise source of switch power supply EMI internal impedance assay method of Hilbert conversion and current probe, its determination step is as follows:

Step 1: at first SMPS is removed from main circuit,, insert a blocked impedance R with L and N line short circuit _Std, the short circuit point of this impedance one termination L and N line, another termination E line; Main circuit center line impedance stable network no power, the output frequency of conditioning signal generator is got some spots in Conducted Electromagnetic compatibility test standard 10K-30MHz scope, read the reading on the corresponding frequency spectrum instrument respectively, record frequency spectrograph reading A1;

Step 2: with R _StdRemove, and with the short circuit point of L and N line and the short circuit of E line, main circuit center line impedance stable network no power, the output frequency of conditioning signal generator, corresponding with Frequency point in the above-mentioned steps 1, record frequency spectrograph reading A2;

Step 3: in the SMPS line attachment, open main circuit power, the output frequency of conditioning signal generator, corresponding with Frequency point in the above-mentioned steps 1, record frequency spectrograph reading A3;

Step 4: the internal impedance in switching power supply noise source is calculated with the Hilbert converter technique.

Because V _SigAnd Z _SigBe respectively the output voltage and the internal impedance of signal generator, I _pBe the input current of pouring-in current probe, L _p, L _wWith M be respectively the self-induction and the mutual inductance of primary side, secondary side.V _wBe pouring-in current probe input voltage signal, I _wIt is the electric current that pouring-in current probe is inducted in the loop.Then:

V _sig＝(Z _sig+jwL _p)I _p-jwMI _w (1)

V _w＝-jwMI _p+jwL _wI _w (2)

From (1), (2) formula with I _pCancellation:

V _W＝V _M1-Z _M1I _w (3)

Here, Z _M1=-[jwL _w+ ((wM) ²/ Z _Sig+ jwL _p)], V _M1=-(jwM/ (Z _Sig+ jwL _p)) V _SigFormula (3) shows that pouring-in current probe can be used the voltage source V of equivalence _M1With voltage source internal impedance Z _M1Replace.Z _M2Be the mutual inductance that exists owing to the formula of detection current probe, Zc is the mutual impedance that circuit self exists, and Zx is impedance to be measured.So can get:

V _M1＝(Z _M1+Z _M2+Z _C+Z _x)I _w (4)

Make Z _In=Z _M1+ Z _M2+ Z _C, then formula (4) becomes:

W _M1＝(Z _in+Z _x)I _w (5)

By formula (5), unknown impedance Z _xCan represent with following formula:

$Z_x=\frac{V_{M1}}{I_w}-Z_{\mathrm{in}}---\left(6\right)$

The electric current I of passing through in the detection formula current probe _wDetermine by following formula

$I_w=\frac{V_{p2}}{Z_{T2}}---\left(7\right)$

Here V _P2Be the measured voltage of detection formula current probe, Z _T2It is the transfer impedance after this probe calibration.

With V _M1=-(jwM/ (Z _Sig+ jwL _p)) V _Sig(7) in the substitution (6)

$Z_x=\left(\frac{-\mathrm{jw}{\mathrm{MV}}_{\mathrm{sig}}}{Z_{\mathrm{sig}}+\mathrm{jw}{L}_p}\right)\frac{Z_{T2}}{V_{p2}}-Z_{\mathrm{in}}---\left(8\right)$

Make K=(jwMZ _T2/ (Z _Sig+ jwL _p)), formula (8) can be reduced to:

$Z_x=\frac{{\mathrm{KV}}_{\mathrm{sig}}}{V_{p2}}-Z_{\mathrm{in}}---\left(9\right)$

Holding signal generator output V _SigConstant, KV for a given frequency _SigIt is a fixing coefficient.If the precision resister R of a known resistance is arranged _Std＞＞| Z _In|, and replace Z with this resistance _X, fixed coefficient KV then _SigCan obtain by following formula:

${\mathrm{KV}}_{\mathrm{sig}}\≈R_{\mathrm{std}}{V}_{p2}{|}_{Z_x=R_{\mathrm{std}}}---\left(10\right)$

Survey Z _In, with Z _XShort circuit,

$Z_{\mathrm{in}}=\frac{{\mathrm{KV}}_{\mathrm{sig}}}{V_{p2}{|}_{Z_x=0}}=\frac{R_{\mathrm{std}}{V}_{p2}{|}_{Z_x=R_{\mathrm{std}}}}{V_{p2}{|}_{Z_x=0}}---\left(11\right)$

With Switching Power Supply place in circuit and opening power, then the internal impedance of Switching Power Supply is at last:

$Z_x=\frac{{\mathrm{KV}}_{\mathrm{sig}}}{V_{p2}{|}_{Z_x=\mathrm{SMPS}}}-Z_{\mathrm{in}}=\frac{R_{\mathrm{std}}{V}_{p2}{|}_{Z_x=R_{\mathrm{std}}}}{V_{p2}{|}_{Z_x=\mathrm{SMPS}}}-Z_{\mathrm{in}}---\left(12\right)$

After obtaining the amplitude information of impedance, the Hilbert conversion is applied to the noise source impedance phase extracts:

At first the noise source internal impedance is considered as a reversible cause and effect systems stabilisation, is the system function of minimum phase system, because it has following feature: 1. impedance network is made of passive device, and there is energy consumption, so be systems stabilisation: 2. impedance network is physically realizable, so be causal system; When the 3. input of impedance network, output variable exchange, its inverse system also is physically realizable.

Secondly, utilize the Hilbert conversion can set up the transformational relation of modulus of impedance and phase place.Because satisfy the system function of causality condition, its real part and imaginary part satisfy the Hilbert transformation relation, thus impedance z (ω)=| z (ω) | e ^{J θ (ω)}As the system function of causal system, can set up the dependence of its real part and imaginary part with the Hilbert conversion.Moreover, if z (ω) taken the logarithm

$\tilde{z}\left(\mathrm{\ω}\right)=\ln \left(z\left(\mathrm{\ω}\right)\right)=\ln \left(\right|z\left(\mathrm{\ω}\right)\left|\right)+j\·\mathrm{\θ}\left(\mathrm{\ω}\right)---\left(13\right)$

Be that condition of minimum phase can draw system by the z of system (ω) so Be the conclusion of causal system, therefore,

Real part ln (| z (ω) |) and imaginary part θ (ω) between also satisfy the Hilbert transformation relation:

$\mathrm{\θ}\left(\mathrm{\ω}\right)=-\frac{1}{\mathrm{\π}}\·\ln \left(\right|z\left(\mathrm{\ω}\right)\left|\right)*\frac{1}{\mathrm{\ω}}=-\frac{1}{\mathrm{\π}}{\∫}_{-\∞}^{\∞}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}---\left(14\right)$

At last, (14) formula of pressing is carried out the analysis of numerical evaluation to θ (ω) and is achieved as follows.The numerical evaluation condition is: for | ω |＜ω _m, the mould of minimum phase system z (ω) | z (ω) | obtain by measuring.Calculate being analyzed as follows of θ (ω) by (14) formula:

$\mathrm{\θ}\left(\mathrm{\ω}\right)=-\frac{1}{\mathrm{\π}}{\∫}_{-\∞}^{\∞}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}$

$=-\frac{1}{\mathrm{\π}}{\∫}_{-\∞}^{-{\mathrm{\ω}}_m}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}-\frac{1}{\mathrm{\π}}{\∫}_{-{\mathrm{\ω}}_m}^{\mathrm{\ω}-\mathrm{\Δ}}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}-\frac{1}{\mathrm{\π}}{\∫}_{\mathrm{\ω}-\mathrm{\Δ}}^{\mathrm{\ω}+\mathrm{\Δ}}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}$

$-\frac{1}{\mathrm{\π}}{\∫}_{\mathrm{\ω}+\mathrm{\Δ}}^{{\mathrm{\ω}}_m}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}-\frac{1}{\mathrm{\π}}{\∫}_{{\mathrm{\ω}}_m}^{\∞}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}$

Wherein, Δ is a little positive number.

(15) integrand of the 3rd integration has a singular point at ξ=ω place in the formula, about this integration, because

${\∫}_{\mathrm{\ω}-\mathrm{\Δ}}^{\mathrm{\ω}+\mathrm{\Δ}}\frac{1}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}=-{\∫}_{-\mathrm{\Δ}}^{\mathrm{\Δ}}\frac{1}{{\mathrm{\ξ}}_1}{\mathrm{d\ξ}}_1=0---\left(16\right)$

So

$-\frac{1}{\mathrm{\π}}{\∫}_{\mathrm{\ω}-\mathrm{\Δ}}^{\mathrm{\ω}+\mathrm{\Δ}}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}=-\frac{1}{\mathrm{\π}}{\∫}_{\mathrm{\ω}-\mathrm{\Δ}}^{\mathrm{\ω}+\mathrm{\Δ}}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}-\frac{\ln \left(\right|z\left(\mathrm{\ω}\right)\left|\right)}{\mathrm{\π}}{\∫}_{\mathrm{\ω}-\mathrm{\Δ}}^{\mathrm{\ω}+\mathrm{\Δ}}\frac{1}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}$

$=-\frac{1}{\mathrm{\π}}{\∫}_{\mathrm{\ω}-\mathrm{\Δ}}^{\mathrm{\ω}+\mathrm{\Δ}}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)-\ln \left(\right|z\left(\mathrm{\ω}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}---\left(17\right)$

Common ln (| z (ξ) |) be continuous function, the integrand in the following formula $\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)-\ln \left(\right|z\left(\mathrm{\ω}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}$ No longer include singular point at ξ=ω place, therefore

$\underset{\mathrm{\Δ}\→0}{\lim }-\frac{1}{\mathrm{\π}}{\∫}_{\mathrm{\ω}-\mathrm{\Δ}}^{\mathrm{\ω}+\mathrm{\Δ}}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}=\underset{\mathrm{\Δ}\→0}{\lim }-\frac{1}{\mathrm{\π}}{\∫}_{\mathrm{\ω}-\mathrm{\Δ}}^{\mathrm{\ω}+\mathrm{\Δ}}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)-\ln \left(\right|z\left(\mathrm{\ω}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}=0---\left(18\right)$

Promptly in Δ → 0 o'clock, the 3rd integration in (15) formula is 0.

At last, for the passive impedance network that has power consumption, its modulus of impedance | z (ξ) | satisfy

$\underset{\left|\mathrm{\ξ}\right|\→\∞}{\lim }\left|z\left(\mathrm{\ξ}\right)\right|=c{\left|\mathrm{\ξ}\right|}^p---\left(19\right)$

C wherein, p is a constant, so the integrand of the 1st and 5 integration in (15) formula has following characteristic

$\underset{\left|\mathrm{\ξ}\right|\→\∞}{\lim }\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}=0---\left(20\right)$

Therefore work as ω _mWhen enough big, the 1st and 5 integral in (15) formula can be ignored.

So the numerical evaluation formula (15) of θ (ω) can be reduced at last:

$\mathrm{\θ}\left(\mathrm{\ω}\right)=-\frac{1}{\mathrm{\π}}{\∫}_{-{\mathrm{\ω}}_m}^{\mathrm{\ω}-\mathrm{\Δ}}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}-\frac{1}{\mathrm{\π}}{\∫}_{\mathrm{\ω}+\mathrm{\Δ}}^{{\mathrm{\ω}}_m}\frac{\ln \left(\right|z\left(\mathrm{\ξ}\right)\left|\right)}{\mathrm{\ω}-\mathrm{\ξ}}\mathrm{d\ξ}---\left(21\right)$

In a word, the Hilbert conversion can be used for the phase extraction of EMI noise source impedance, promptly utilizes the modulus of impedance that records | z (ω) | and, calculate the phase-frequency characteristic θ (ω) that obtains impedance according to (16) formula.

The inventive method, the detection formula current probe reading that obtains under normal impedance, short circuit and three kinds of situations of operate as normal by circuit only just can calculate the value of noise source impedance to be measured.By this method of testing, not only can determine the internal impedance value amplitude information of noise source, can also obtain the phase information of internal impedance by the Hilbert conversion, thereby can judge the character of internal impedance, that draw internal impedance and be capacitive or perception, further the design for electromagnetic interface filter provides prerequisite, promptly satisfies the impedance matching property of wave filter when Design of Filter, thereby effectively electromagnetic interference (EMI) is suppressed, make it to satisfy the EMC standard.

Description of drawings

Fig. 1 is the switch power source EMI noise origin internal impedance test system structured flowchart that the present invention is based on Hilbert conversion and current probe;

Fig. 2 is switch power source EMI noise origin internal impedance test system (common mode internal impedance) circuit diagram that the present invention is based on Hilbert conversion and current probe;

Fig. 3 is switch power source EMI noise origin internal impedance test system (differential mode internal impedance) circuit diagram that the present invention is based on Hilbert conversion and current probe;

Fig. 4 is a noise source internal impedance test flow chart;

Fig. 5 is a noise source common mode internal impedance test curve;

Fig. 6 is a noise source differential mode internal impedance test curve.

Embodiment

Embodiment 1,

As depicted in figs. 1 and 2, based on the switch power source EMI noise origin internal impedance test system of Hilbert conversion and current probe, constitute by line impedence stabilizing network (LISN), common code impedance test module, signal generator and spectrum analyzer; The power lead of coming from electrical network is directly inputted to the line impedence stabilizing network (LISN), measures module by common code impedance, then is input in Switching Power Supply (SMPS) and the load, constitutes a whole piece electric power loop; Signal generator provides an input signal for the common code impedance test module, then by spectrum analyzer the response signal in this module is detected.

In electric power loop, the effect of line impedence stabilizing network (LISN) is for Switching Power Supply provides power supply, and the noise of insulating power supply side enters test loop simultaneously, also the noise of isolating switch power generation, prevent to pollute electrical network, and the stable impedance of one 50 Ω is provided for test loop.The common code impedance test module is used for the internal impedance of measuring switch power supply, and Switching Power Supply is a Devices to test.

Described common code impedance test module is made up of a pair of common mode choke, two electric capacity and two current probes, and one of them is pouring-in current probe, and one is detection formula current probe; Two electric capacity are connected on respectively between L-E, the N-E.Power lead L, the N, the E that come from electrical network are directly inputted to the line impedence stabilizing network, and output terminal L, N are input to Switching Power Supply by a pair of common mode choke, and output E line is directly inputted to Switching Power Supply, and two electric capacity are connected on respectively between L-E, the N-E.Two leads that two electric capacity link to each other with the E line penetrate two current probes, and pouring-in current probe connects signal generator, detect the formula current probe and connect spectrum analyzer, and the DC side output of Switching Power Supply connects load.Read the reading that detects on the examination current probe by inserting blocked impedance, short circuit, three kinds of states of Switching Power Supply operate as normal in the circuit, and the internal impedance of Switching Power Supply is calculated according to the Hilbert algorithm.For making the internal driving Z of this test circuit _InCan repeat to measure and keep constant as far as possible, this two capacitor fixing is on printed circuit board (PCB), and the pouring-in simultaneously and formula of detection current probe is also fixed its position on circuit board; Between printing board PCB and testing apparatus for short-term is connected, to reduce the ghost effect that the lead layout causes.The test of this stationkeeping, in case after its advantage is the circuit calibration, the test circuit internal driving Z that records _In, can improve the speed of test greatly.

Embodiment 2,

As shown in figures 1 and 3, based on the switch power source EMI noise origin internal impedance test system of Hilbert conversion and current probe, constitute by line impedence stabilizing network (LISN), differential mode impedance test module, signal generator and spectrum analyzer; The power lead of coming from electrical network is directly inputted to the line impedence stabilizing network (LISN), by differential mode impedance measuring module, then is input in Switching Power Supply (SMPS) and the load, constitutes a whole piece electric power loop; Signal generator provides an input signal for the differential mode impedance test module, then by spectrum analyzer the response signal in this module is detected.In electric power loop, the differential mode impedance test module is used for the internal impedance of measuring switch power supply.

Described differential mode impedance test module is made up of two differential mode choking coils, two electric capacity and two current probes; Power lead L, the N, the E that come from electrical network are directly inputted to the line impedence stabilizing network, and the L of output, N line are input to Switching Power Supply by 1 differential mode choking coil respectively, and output E line is directly inputted to Switching Power Supply, and two electric capacity also are connected between the L-N; Two leads that two electric capacity link to each other with the E line penetrate two current probes, and pouring-in current probe connects signal generator, detect the formula current probe and connect spectrum analyzer, and the DC side output of Switching Power Supply connects load.

Embodiment 3,

With certain commercial Switching Power Supply is example, test, experimental provision as shown in Figure 1, be under the situation that connects normal impedance, short circuit and Switching Power Supply operate as normal at circuit respectively and test, test for switching power supply noise source internal impedance, main branch common mode, two kinds of situations of differential mode are tested, and both of these case removes impedance test module and has any different, and method of testing and step all are consistent.Its determination step is as follows:

Step 1: at first SMPS is removed from main circuit,, insert a blocked impedance R with L and N line short circuit _Std, the short circuit point of this impedance one termination L and N line, another termination E line; Main circuit center line impedance stable network no power, the output frequency of conditioning signal generator is got some spots in Conducted Electromagnetic compatibility test standard 10K-30MHz scope, read the reading on the corresponding frequency spectrum instrument respectively, record frequency spectrograph reading A1;

Step 2: with R _StdRemove, and with the short circuit point of L and N line and the short circuit of E line, main circuit center line impedance stable network no power, the output frequency of conditioning signal generator, corresponding with Frequency point in the above-mentioned steps 1, record frequency spectrograph reading A2;

Step 3: in the SMPS line attachment, open main circuit power, the output frequency of conditioning signal generator, corresponding with Frequency point in the above-mentioned steps 1, record frequency spectrograph reading A3;

Step 4: the internal impedance in switching power supply noise source is calculated with the Hilbert converter technique.

Obtain a result shown in Fig. 5,6.As can be seen from the figure the common mode internal impedance of noise source reduces along with increasing of frequency, is capacitive, through fitting, can obtain the common mode internal impedance and be made of the resistance of one 1.2 Ω and the capacitances in series of a 450pF.The differential mode internal impedance increases along with increasing of frequency, is perception, through fitting, can obtain the differential mode internal impedance and be made of the resistance of one 15 Ω and the inductance series connection of a 1.8uH.

After the common mode internal impedance of learning Switching Power Supply, just can carry out corresponding Design of Filter.Write out the transport function of wave filter according to noise source internal impedance, loaded impedance (known) and filter construction, secondly determine wave filter the cutoff frequency point, insert the maximum differential loss that loss, passband allow, calculate the value of each components and parts of wave filter at last.

Because the size of noise source impedance is the important evidence of Design of Filter, has only the impedance matching of working as during design, its filtering characteristic of performance of wave filter ability maximal efficiency.Otherwise, if internal impedance the unknown of noise source when carrying out the electromagnetic interface filter design, will be made as the internal impedance of noise source a general value (for example 50 Ω), and carry out a kind of design of universal filter.Because the type of each noise source is diversified, when adopting general electromagnetic interface filter, the problem of impedance mismatching will inevitably appear, and filter insertion loss is reduced, frequency is drifted about; Heavy then wave filter is amplified noise signal.So, various different types of noise source internal impedance is tested, as corresponding Design of Filter basis, can greatly improve the filtering characteristic of wave filter, save financial cost.

Claims (5)

1, a kind of switch power source EMI noise origin internal impedance test system based on Hilbert conversion and current probe is made of line impedence stabilizing network, common mode, signal generator and spectrum analyzer; It is characterized in that: power lead is directly inputted in the line impedence stabilizing network, by common mode impedance measuring module, then is input in Switching Power Supply and the load, constitutes a whole piece electric power loop; Signal generator provides an input signal for common mode, then by spectrum analyzer the response signal in this module is detected.

2, the switch power source EMI noise origin internal impedance test system based on Hilbert conversion and current probe according to claim 1, it is characterized in that: adopt the common code impedance test module, described common code impedance test module is made up of a pair of common mode choke, two electric capacity and two current probes, one of them is pouring-in current probe, and one is detection formula current probe; Two electric capacity are connected on respectively between L-E, the N-E; L, the N line of the output of line impedence stabilizing network are input to Switching Power Supply by a pair of common mode choke, and the output E line of line impedence stabilizing network is directly inputted to Switching Power Supply; Two leads that two electric capacity link to each other with the E line penetrate two current probes, and pouring-in current probe connects signal generator, detect the formula current probe and connect spectrum analyzer, and the DC side output of Switching Power Supply connects load.

3, the switch power source EMI noise origin internal impedance test system based on Hilbert conversion and current probe according to claim 1, it is characterized in that: adopt the differential mode impedance test module, described differential mode impedance test module is made up of two differential mode choking coils, two electric capacity and two current probes; L, the N line of the output of line impedence stabilizing network are input to Switching Power Supply by 1 differential mode choking coil respectively, and the output E line of line impedence stabilizing network is directly inputted to Switching Power Supply, and two electric capacity also are connected between the L-N; Two leads that two electric capacity link to each other with the E line penetrate two current probes, and pouring-in current probe connects signal generator, detect the formula current probe and connect spectrum analyzer, and the DC side output of Switching Power Supply connects load.

4, according to claim 1,2 or 3 described switch power source EMI noise origin internal impedance test systems, it is characterized in that: the phase information that obtains impedance by the Hilbert converter technique based on Hilbert conversion and current probe.

5, based on the noise source of switch power supply EMI internal impedance assay method of Hilbert conversion and current probe, its determination step is as follows:

Step 1: at first SMPS is removed from main circuit,, insert a blocked impedance Rstd, the short circuit point of this impedance one termination L and N line, another termination E line with L and N line short circuit; Main circuit center line impedance stable network no power, the output frequency of conditioning signal generator is got some spots in Conducted Electromagnetic compatibility test standard 10K-30MHz scope, read the reading on the corresponding frequency spectrum instrument respectively, record frequency spectrograph reading A1;

Step 2: Rstd is removed, and with the short circuit point of L and N line and the short circuit of E line, main circuit center line impedance stable network no power, the output frequency of conditioning signal generator, corresponding with Frequency point in the above-mentioned steps 1, record frequency spectrograph reading A2;

Step 3: in the SMPS line attachment, open main circuit power, the output frequency of conditioning signal generator, corresponding with Frequency point in the above-mentioned steps 1, record frequency spectrograph reading A3;

Step 4: the internal impedance in switching power supply noise source is calculated with the Hilbert converter technique.

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