JPH01181310A - Method for deciding value of line filter component - Google Patents

Abstract

PURPOSE:To improve the attenuation effect against the normal mode noise and to attain small size and light weight by forming a characteristic curve representing the relation of the inductance of each choke coil under a specific condition and obtaining the combination of the inductance of each choke coil. CONSTITUTION:In the determination of leakage inductances (L1e, L2e) of balun type common mode choke coils L1, L2, a straight line giving a minimum value of the inductance L3e is drawn to select a point tangent to a straight line of L1e+L2e=constant or its vicinity point. Furthermore, in the selection of the capacitance of X capacitors Cx0, Cx1, the minimum value of the L2e by giving the L1e or that of the L2e by giving the L1e conversely under the condition of Cx0+Cx1=constant is obtained respectively and the Cx0 or Cx1 or its vicinity is selected. Thus, the line filter with high effect to reduce the normal mode noise and with small size and light weight is obtained.

Description

Detailed Description of the Invention [Purpose of the Invention (Industrial Application Field) The present invention relates to line filter components (choke coils, capacitors, etc.) connected to a switching power supply in order to reduce common mode noise and normal mode noise. )
Concerning how to determine the value of.

(Prior Art) Generally, when a switching power supply is used as a power supply device for electronic equipment, conduction noise is generated, and this noise causes malfunction of the equipment.

Conduction noise includes common mode noise that flows between the power supply line and ground, and normal mode noise that flows between the power supply lines.Generally, a line filter is inserted on the input side of the power supply to reduce the level. A method is being adopted.

This line filter uses a balloon coil (balanced unbalanced transformer) with two sets of windings around a ring-shaped core.
Insert a capacitor between the power supply line on the load side of each coil (hereinafter referred to as an This is known as a Y capacitor.

FIG. 10 is a diagram showing the configuration of a power supply circuit using this type of line filter.

In the figure, 1.1' is an input terminal, 2.2' is an output terminal, G is a ground terminal, Rect is a diode bridge that rectifies alternating current to direct current, and CF is a capacitor that smoothes the rectified output voltage.

In addition, T is a transformer consisting of a primary side coil and a secondary side coil,
Q is a switching transistor, D is a diode that rectifies the induced voltage of the secondary coil of the transformer T, and Co is a capacitor that smoothes the rectified output voltage.

L+, t, 2 are balloon coils, Cx l, cx
2 is the X capacitor connected between the power supply lines, CV+,
CV2 is a Y capacitor connected between the power supply line and ground.

In this circuit, DC output is taken out from the output terminal 3.3' of the secondary coil and supplied to the load. Note that the output terminal 3' is generally grounded to stabilize the operation of the electronic circuit.

By the way, Cc in the figure is a distributed capacitance generated between the primary coil and the secondary coil of the transformer T, and acts to cause common mode noise generated by switching of the transistor Q to flow to the secondary side.

In the figure, the current path of common mode noise is indicated by an arrow.

As mentioned above, conduction noise can be divided into common mode components and normal mode components, but in the circuit shown in Figure 10, each noise component is attenuated by the action of the equivalent circuits shown in Figures 11 and 12, respectively. I'm letting you do it.

FIG. 11 is a diagram showing an equivalent circuit for common mode noise of the circuit shown in FIG. 10.

In the same figure, Ec is the source of common mode noise, R
N is the impedance of the artificial power supply network (hereinafter referred to as LISN) representing the equivalent impedance of the AC power line (
In general, RN=50Ω), and other symbols are the same as in FIG.

For example, most of the common mode noise flowing out via the distributed capacitance Cc is recovered as iC2 by the Y capacitor CV2. Most of the leaked amount is recovered as IC+ by the Y capacitor CV+, and the remaining amount does not flow out as iRN.

Here, in order to reduce the noise components of low-order harmonics, it is necessary to increase the capacity of the Y capacitor CV2, but since the Y capacitor is connected to the ground, it is subject to safety standard restrictions with respect to leakage current.

Therefore, it is necessary to increase the inductance of the balun coil L2 instead of increasing the capacitance of the Y capacitor CV2, but since the balun coil is a parasitic element, the distributed capacitance is large, and high frequency noise passes through the balun coil L2.

In this case, by connecting the balun coil L1 having a small distributed capacitance (also having a small inductance) to the input side of the balun coil L2, high frequency common mode noise can be suppressed.

The inventor of the present invention has previously developed a method for effectively reducing the common mode component by setting L+<L;
7111, US Pat. No. 4,667,173, etc.).

On the other hand, FIG. 12 is a diagram showing an equivalent circuit for normal mode noise of the circuit of FIG. 10.

In the figure, I indicates a switching current which is a source of normal mode noise, and an example of its waveform is shown on the right side. CF is a smoothing capacitor and serves as a supply source for the switching current (■). ESR indicates equivalent series resistance, which is a parasitic element of capacitor CF.

The voltage generated at the ESR is overwhelmingly larger than the voltage generated at the capacitor CF due to the current I at -ffi, but this voltage becomes normal mode noise.

In the figure, Led and Le2 are balloon coils L, , and L, respectively.
This is the leakage inductance of L2, and presents an impedance that is a hindrance to normal mode noise.

Here, RN is the equivalent impedance of LISN.

The noise current generated in the ESR becomes normal mode noise iN that flows backward from the line filter toward the power supply, and most of it is recovered by the X capacitor CX1 as ic x+, but some of it passes through the balloon coil L1. flows backwards from the AC power line to the LIS.
N and is measured as noise.

(Problem to be solved by the invention) By the way, in the conventional line filter mentioned above, the capacitor Cx2 is a smoothing capacitor CF (several 100 μF
), but the capacitor Cx2
The capacitance of the capacitor CF is about 0.1 to 0.5 μF, which is so small that it can be ignored when compared with the capacitance of the capacitor CF.

At this time, the impedance of the capacitor cx2 becomes 11/ωcx21>>SR+1/ωcr) from the fundamental wave of switching to low-order harmonic noise, and does not work effectively to reduce normal mode noise.

The present invention has been made in response to the above-mentioned circumstances, and aims to provide a line filter that has a high attenuation effect on normal mode noise and is small and lightweight.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve this object, the present invention provides choke coils inserted between power lines on the input side and between power lines on the load side, and each choke coil. In determining the values of each component of a line filter including an X capacitor inserted between the power supply lines on the input side of at least one of the choke coils, Assuming that each is inserted in between,
Further, the sum of the capacitances of each X capacitor and the capacitance of one of the X capacitors at which the inductance of the other choke coil is minimum or minimum, assuming that the inductance of one of the choke coils is constant. Under these conditions, the combination of inductances of each choke coil is determined.

(Function) In the present invention, it is assumed that the X capacitor is inserted between the power supply lines on the input side of each of the choke coils. Then, a characteristic curve is created assuming that the sum of the capacitances of the respective X capacitors and the inductance of one of the choke coils are constant. Using this, find the capacitance of one of the X capacitors when the inductance of the other choke coil is minimum or minimum, and create a characteristic curve showing the relationship between the inductances of each choke coil under this condition, Find the inductance combination of each choke coil.

(Example) Hereinafter, details of an example of the present invention will be described based on the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of a line filter obtained by the method of the present invention.

In the same figure, Ll is a balun coil inserted into the power line on the input side, L2 is a balun coil inserted between the power lines on the load side, and Cx1 is an X capacitor inserted between the power lines on the input side of balun coil L2. It is.

CV+ is a Y capacitor connected between the power line on the load side of the balun coil L1 and the ground, CV2 is a Y capacitor connected between the power line on the load side of the balun coil L2 and the ground, and 1.1' is a Y capacitor connected between the power line on the load side of the balun coil L2 and the ground. 2.2' is an input terminal to which a power supply line is connected; 2.2' is an output terminal to which a load is connected; and G is a ground terminal connected to the ground side of the AC power source.

In the circuit of this embodiment, the inductance of the balun coil L2 is larger than the inductance of the balun coil L1, and the capacitance of the Y capacitor CV2 is larger than the inductance of the balun coil L1.
, It is made larger than the capacitance of It.

As can be seen from Figure f41, in the circuit of this embodiment, the X capacitor for suppressing normal mode noise is centrally provided at the intermediate position between the two balloon coils L, L2.

FIG. 2 is a diagram showing the configuration of a circuit to be compared with the circuit of FIG. 1.

In this circuit, an X capacitor CXo is inserted between the power supply lines on the input side of the balun coil L1, and the balun coil L2
An X capacitor Cx1 is inserted between the power supply lines on the input side of the circuit, and the rest is the same as the circuit shown in FIG.

The process of obtaining the circuit shown in FIG. 1 based on the circuit shown in FIG. 2 will be described below.

FIG. 3 is a diagram showing an equivalent circuit for normal mode noise of the circuit of FIG. 2.

In the figure, l indicates a switching current which is a source of normal mode noise. In the figure, CF is a smoothing capacitor and serves as a supply source for the switching current.

Further, RF is an equal series resistor which is a parasitic element of capacitor CF, and CXo and Cx1 are X capacitors connected between power supply lines 1 and 1'.

Lle and L2e are leakage inductances of the balloon coils L1 and L2, respectively, and exhibit impedance so as to become a hindrance to normal mode noise. RN is LI
This is the equivalent impedance of SN.

Also, cN is a bypass filter capacitor that blocks commercial frequency components and passes only measurement noise, and Le and Re are L
The rest of the ISN consists of actance elements and resistance elements that correct impedance in low frequencies.

Note that 3.3' is a terminal for extracting normal mode noise and connecting it to an interference wave strength measuring device, vN is a voltage value of the normal mode noise component, and en is a voltage value of the source noise.

In this circuit, the noise generated in the equal series resistors RF, which are parasitic elements of the capacitor CF, are expressed as Lee, L2 e,
It is attenuated by a filter consisting of Cx o and CX +.

In the circuit shown in FIG. 10 described above, the X capacitor Cx1 is inserted between the power lines on the load side of the balloon coil L1, and the X capacitor Cx2 is inserted between the power lines on the load side of the balloon coil L2. In the circuit shown in Fig. 2, the X capacitor CXo is inserted between the power supply lines on the input side of the balun coil L1, and the X capacitor CX+
It is inserted between the power supply lines on the input side of 2.

If the line filter is configured as shown in Figure 2,
In particular, the effect of reducing normal mode noise is increased, and this is detailed in the patent specification filed by the present inventor on December 15, 1988.

The present invention provides a line filter having the configuration shown in FIG. 2, in which Cx o , Cx 1 , Lle , L2
This article discloses how to select the value of e to achieve miniaturization and weight reduction.

First, the waveform of ■ is set to 50 to 7 (■・20Az S ), and in Fig. 3, Le → 100μH 10Ω in Re RN = 50Ω CM = 0.1μF or less CF = 270μF or less RF = 0.2Ω en = 0. 163V (50k)tz,'ro
n = = 3.75 μS )Vn = 2.118
mV (50k)tz), Cx o CX + = 0.477JF (constant)
The procedure for determining the value of L2e by further setting L 1e =0.2mH will be explained.

In FIG. 3, since RF>>1/ωCF and ω switching frequency, the voltage en of the source noise is en=RF a n
+ na(n)=I2sinθ/nx−(I2I+)X(
1-cosθ)/nπθ b(n) =I+/nyr-I2CO3θ/nx+
(I2-11) sinθ/nyrθθ=2xnδ, δ=
It can be expressed as 0.5E i l1in /E.

Note that 11 and 12 in these equations indicate the current values of the switching current over time, as shown in FIG. 4, and are the values at 1=0 and t=Ton, respectively.

In addition, Eiiiin is the pulse width of the switching current: Ton
= 1/2T (T: period) is the lowest input DC voltage, and pulse width control cannot be performed for inputs lower than this voltage.

Input voltage E i = 280V, E i l1in
= 105V, the voltage e of the source noise at this time
When n is calculated, the fundamental wave (n=1
), e (1) = 0.163 V, e (2) = 0.1365 V for the 2.3rd high frequency, e (3) =
It becomes 0.0983V. When calculating the values of the constituent elements of the filter, if CX (1, Cx +≧0.1 μF Lle, L2e≧0.05 mH), it is understood that it is necessary to calculate only the fundamental wave.

The regulation value is VDE 0871 B level, vn
(1)・2.118m'V (50kHz, 55.5(I
B) Vn (2) = 1.20 mV (100kHz,
61.6dB). Here, e n (1), Vn, (1), Cx o +CX
To calculate Lle by giving + = C'r (=constant) and Lle, do as follows.

In addition, below, the current value, voltage value, etc. of the circuit of Fig. 3 will be explained as follows.
It will be defined and explained as shown in the figure.

First, when IA is sent to RN, VN = 1 (^) x 1/2 RN = 1/2 RNCX
Voltage across o: VCO=RN-jXn Xe, current of Re: iZ = Vco/ (Re + Jxe) = izr
-, J IZi izr = (Rn Re -Xn Xe)/(Re'
+Xe 2)izi = (Rn Xe 10Re Xn
)/(Re ” +Xe 2) CXo electric 'fft: i co= J ωcx o Vco=Xn Yco+
J Rn Yc.

YCO=ωCX.

Current of Lle: 1L1= 1+iZ +1CO iL+ =iL+ r +J iL+ ii L +
r=1+izr+XnYc.

i L 1i =Rn Yco −l Z! Voltage of L1e: VL + =jωL1 e ・it 1 ;V+=ωL
e8,”, VL+2-XL+tL1!+JXL1iL1rC
Voltage of x1: VC+ = VCQ+VL 1 ,', VC+ = Rn −XL 1f L 1! +j
(XL 1i L + r −Xn) Current of CX1: ic 1 = Jca>Cx, −Vc 1 ; YC+
=ωCX + ,', i C+ =-yc 1Vc 1 i+JYC
1i Vc 1 r Current in L2: iL 2 =it + +ic1, °, iL2
=iL2 r 10J iL21it2r=i L +r
+ic1 r iL 21=iL ti+ic1 i ' Voltage of L 2: VL 2=JωL 2e iL 2 ; (a) L
2e=XL2,', VL2=-XL2iL2i+jXL2iL2r source voltage: et :vc++VL2,. ct = etr + j eti e tr = VC1r -XL 2 i L 2 ! et
i=Vc+i+XL2iLzr Divide both sides by Rn for all of the above equations, Rn = 2
Since Vn, it is converted into a relational expression of various quantities per 2Vn. Therefore, (et/2Vn)' = (en/2Vn)
'=r, and to find Lle, we express the unknown number XL2 by , f=iL2r, g=i
L2i.

D=r(f'+g')-(af+bg)"From now on, the source noise voltage en, regulation value vn, CXo, CX1
, Lle is obtained as L2 e =x/ω. Therefore, in the case of cx o +cx 1 =c'r= 0.47 uF, it can be seen that if Lle is 0.2mM, Lle can be obtained by calculation.

At this time, the fundamental wave voltage of the RF source noise is 0, 16
3V, noise voltage regulation value at measurement end RN VDE 087
At the B level of 1, compared to 50, Vn = O, 0O118
It was set as V.

The amount of attenuation of the filter is determined by (0, 16310, 00118), but in order to obtain this amount of attenuation, it is necessary to set Lle to a value as shown in FIG.

In addition, in FIG. 6, Ca is CXa where Lle is the minimum
The value of (= OμF), Cb is CX where Lle is minimum
The value of o (=0.32 μF) is shown.

In order to reduce the size of the filter, it is necessary to make Lle as small as possible, so CX o =Ca=
O,uF.

cx 1 = 0.47 μF-CX o = 0.4
If it is set to 7 μF, L2 e = 0.3mM is sufficient.

In addition, in Fig. 6, Lle is maximum and maximum at cx O+ and Cx o 2, respectively, but Lie//L2
e (series composite value of inductance), COl and L
It shows the series resonance point between le and Cx1.

Next, when Lee is changed in the range of 0.05 m H to 0.6 m H and a characteristic curve of Lle similar to that shown in FIG. 6 is drawn, it becomes as shown in FIG. 7. Here, the minimum value of Lle is cx o
= O, uF%CX + = 0.47 μF. Furthermore, cx o +CX + = 0.68 μ
When calculating similarly for F, Lle becomes Cx o
= OμF%Cx t = 0.68 If the zeroth order is minimized when ttF is increased to Cx o +CX + = IJJF, the point that produces the minimum value of Lle as shown in Figure 7 is cx o = Move to Cb ap 0.5 μF.

Even if cx o + CX + = Ltz F, Lle≦0.2m H Then, Lle is cx o = Ca = OμF is minimum when .

Taking the minimum value of Lle for all cases, L
When a characteristic curve is drawn in relation to le, g, h, 1 are shown in Figure 8.
It becomes as shown in . These curves determine the required t and 2e when Lie is given under the condition that cx o +cx I = constant.

These curves touch at points E and F, where Lle + L2 e = constant straight line a, b, c, and these tangent points give points that minimize the sum of Lle + L2 e. Since the characteristic curves of g, h, and 1 are originally under the condition that Cx o +cx 1 = constant, it can be said that the total amount of X capacitors has been optimized.

Since the tangent points E and F on these curves give the minimum point of the choke coil, it can be said that the inductance has also been optimized.

That is, contact points E and F are points where both the X capacitor and the choke coil are optimized.

Note that the section on one curve is the section that gives the minimum value of Lle in the vicinity of CXo→CX + =1/2 (1, 0, uF). and 1
The part of Lee≦0.26 mH on the curve is CXo=O1Cx + = 1.0. cz L at the point of F
This is the point that gives the minimum value of 2e. These optimal scores, E
, F are all C) jo=o, CX 1 =IlaX, Ll 13
<L2 e.

Finally, the optimal point is CXa=0 The cause of this occurrence will be explained below.

If CXo>0, the circuit state approaches the series resonance state caused by CXo and Le//Lee, so the noise voltage between terminals 1 to 1' becomes slightly higher.

Therefore, in order to suppress this to the regulation value, L2e must be increased.

When the sum of Cx (1+cx 1 becomes large such as 1μF, the reduction effect by concentrating 1μF in CXI and the reduction effect of L-C two-stage type by dividing it into equal parts and providing it in CXO) are as follows. The latter is more dominant.Therefore, as shown in Fig. 7, CXoΦ1/2 (cx o
+Cx 1 ), L2e becomes minimum.

FIG. 9 is a diagram showing an ellipse of an embodiment in which this phenomenon is utilized. This example corresponds to the case where cx o =Cx + and L+ <L2, and the operation is performed in the section shown in FIG.

Assuming that the size of the choke coil is proportional to the amount of energy stored in the choke coil E = 1/2 L = 2 (L: inductance, ■ = power supply current), make the total number of two choke coils the smallest and lightest. In order to do this, E++E2=minimum, that is, Lle+L2e=minimum. Points E and F in FIG. 8 give the minimum and lightest points of the choke coil that satisfy these conditions. In addition, since the calculations are made in FIGS. 6 and 7 with Cx a +cx + constant, under the condition that cx o +Cx i = constant, CXo=O1Ox 1 =IlaX, and Cx o +Cx + = Setting it to 1/2 (lla , becomes a point on i.

In addition, in Figure 3, Lee and L2e are explained as the leakage inductance of a balun type common mode choke coil, but an independent choke coil may be used instead of a balun. Generally, a balun type common mode choke coil has a normal mode inductance. is small, so choke coils may be more advantageous in reducing normal mode noise.

For example, if a switching converter transformer is shielded to reduce the capacitance between the primary and secondary, normal mode noise will become dominant, so in such a case, a choke coil may be used instead of a balun. can be used in the circuits of FIGS. 1 and 9.

In the above explanation, the self-inductance L and the leakage inductance Ll were not clearly distinguished as the inductance of the balun. However, the balun is originally intended to reduce common mode noise, and the self-inductance is useful for this purpose. .

On the other hand, the leakage inductance Le of the balloon is
Helps suppress normal mode noise.

In the above explanation, Le is used to remove normal mode noise.
L is used to remove common mode noise.

In this way, in this embodiment, the choke coils Lee, L2e
To determine the value of L2e, draw a straight line that gives the minimum value of L2e, and select a point tangent to the straight line, where Lle + L2e = constant, or a point near it.

In addition, when selecting the values of the X capacitors Cx o and Cx I, under certain conditions cx o + CX + = Lt (given 3 and L2e, or vice versa, L
2e is given, each minimum value of Lle is determined, and the value of CXa or Cx1 that produces the minimum value or a value in the vicinity thereof is selected.

As a result, it is possible to obtain a line filter that is highly effective in reducing normal mode noise and is compact and lightweight.

Furthermore, in the conventional line filter, the Y capacitor CV2 located at Cx2 acts as an X capacitor for normal mode, which increases the effect of reducing noise at high frequencies.

[Effects of the Invention] As explained above, according to the present invention, it is possible to obtain a small and lightweight line filter that has a high attenuation effect on normal mode noise.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram explaining an embodiment of the present invention, Fig. 2 is a diagram showing the configuration of a circuit to be compared with the circuit in Fig. 1, and Fig. 3 is a diagram showing normal mode noise of the circuit in Fig. 2. 4 is a diagram showing the waveform of the power supply current in the circuit of FIG. 3, FIG. 5 is a diagram showing the definition of current, voltage, etc. in the circuit of FIG. 3, and FIGS. 6 and 7 are diagrams showing an equivalent circuit. The figure shows the inductance of the choke coil when the sum of the capacitances of the X capacitors is kept constant. Figure 8 shows the relationship between the minimum required values of the choke coils t and 2e with respect to the choke coil Lee. Figure 10 shows an example of the configuration of a power supply circuit using a conventional line filter. Figure 11 shows the configuration of another circuit obtained by the present invention. A diagram showing the equivalent circuit of
FIG. 12 is a diagram showing an equivalent circuit for noise in the normal mode of the same circuit. Ll, L2-...Balun coil, cxl, cxl-X
Capacitor, CV +, CV 2...Y capacitor. Applicant Toshiba Corporation Patent Attorney Satoshi Suyama - Figure 1 Figure 2 Figure 412 Figure 7 Figure 8 Figure 90

Claims (1)

[Claims] (1) Consisting of choke coils inserted between the power lines on the input side and between the power lines on the load side, and an X capacitor inserted between the power lines on the input side of at least one of each choke coil. In determining the values of each component of the line filter, it is assumed that the X capacitors are inserted between the power supply lines on the input side of each of the choke coils, and the sum of the capacitances of the X capacitors and the Assuming that the inductance of one of the choke coils is constant, find the capacitance of one of the X capacitors at which the inductance of the other choke coil is minimum or minimum, and under this condition, calculate the inductance of each choke coil. A method for determining values of line filter components, characterized by determining a combination.