Passive EMI filter based on RC damper
By introducing RC damper structures into the post-stage common mode noise suppression branch and differential mode noise suppression branch of passive EMI filter, the problem of high Q value and 'ring' phenomenon in switching power supply is solved, and the reliability and stability of the filter are improved.
Patent Information
- Application Number
- CN202411625345.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-14
- Publication Date
- 2025-02-28
AI Technical Summary
Existing passive EMI filters are prone to high Q values and ‘ringing’ in switching power supplies, affecting their stability and reliability.
A passive EMI filter based on RC damper is designed. By introducing an RC damper structure into the rear stage common mode noise suppression branch and differential mode noise suppression branch, the oscillation speed of the signal is slowed down and the occurrence of ‘ringing’ phenomenon is reduced.
It effectively reduces the occurrence of ‘ringing’ phenomenon, improves the reliability of the EMI filter, and reduces the quality factor of the bipolar system by introducing zero points.
Smart Images
Figure CN119543861A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of EMI filters, and in particular relates to a passive EMI filter based on an RC damper. Background Art
[0002] The switching power supply realizes efficient energy transfer and conversion through the high-frequency on and off of the switching device. However, when the switching device is turned on and off at high frequency, it will generate a very large current and voltage change rate (dv / dt, di / dt), resulting in the generation of high-frequency electromagnetic interference (EMI). In order to suppress the electromagnetic interference to the normal operation of the switching power supply itself and surrounding equipment, and at the same time limit the external noise signal from entering the switching power supply to ensure the safe and reliable operation of the switching power supply, a passive EMI filter is generally configured at its front end.
[0003] Passive EMI filters are usually composed of multiple LC structures. In switching power supplies, the high Q value of the LC structure and the possible "ringing" phenomenon pose a huge threat to the stability of its normal operation. How to use passive EMI filters to effectively filter out electromagnetic interference signals while weakening or even avoiding the threat it poses to the normal operation of switching power supplies is a problem that needs to be solved urgently. Summary of the invention
[0004] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a passive EMI filter based on an RC damper.
[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:
[0006] A passive EMI filter based on an RC damper comprises a series mode noise suppression branch, a front stage common mode noise suppression branch, a conjugate coil, a rear stage common mode noise suppression branch and a differential mode noise suppression branch which are arranged in sequence from the input end to the output end of the passive EMI filter. The series mode noise suppression branch is used to suppress high frequency differential common mode noise of a conducting line; the front stage common mode noise suppression branch is used to suppress high frequency common mode noise of a conducting line; the conjugate coil is used to suppress common mode noise of a conducting line; the rear stage common mode noise suppression branch is used to suppress low frequency common mode noise of a conducting line by using a structure with an RC damper; the differential mode noise suppression branch is used to suppress low frequency differential mode noise of a conducting line by using a structure with an RC damper; the series mode noise suppression branch, the front stage common mode noise suppression branch, the conjugate coil and the rear stage common mode noise suppression branch form a common mode EMI filter, and the differential mode noise suppression branch forms a differential mode EMI filter.
[0007] Furthermore, the series-mode noise suppression branch includes a series-mode inductor and a series-mode capacitor; the first end of the series-mode inductor is electrically connected to the positive voltage input terminal IN+, the second end of the series-mode inductor is electrically connected to the first end of the series-mode capacitor, the second end of the series-mode capacitor is electrically connected to the negative voltage input terminal IN-, and the second end of the series-mode capacitor is also grounded.
[0008] Furthermore, the front-stage common-mode noise suppression branch includes a first common-mode capacitor and a second common-mode capacitor, the conjugate coil includes two common-mode inductors with the same inductance, the first end of the first common-mode capacitor and the first end of the first common-mode inductor in the conjugate coil are both electrically connected to the first end of the series-mode capacitor, the second end of the first common-mode capacitor is connected to a common ground line, the first end of the second common-mode capacitor and the first end of the second common-mode inductor in the conjugate coil are both electrically connected to the second end of the series-mode capacitor, and the second end of the second common-mode capacitor is connected to the common ground line.
[0009] Furthermore, the post-stage common-mode noise suppression branch includes a third common-mode capacitor, a fourth common-mode capacitor and a common-mode damping resistor; the first end of the third common-mode capacitor is electrically connected to the second end of the second common-mode inductor in the conjugate coil, and the first end of the fourth common-mode capacitor is electrically connected to the second end of the first common-mode inductor in the conjugate coil; the second end of the third common-mode capacitor and the second end of the fourth common-mode capacitor are both electrically connected to the first end of the common-mode damping resistor, and the second end of the common-mode damping resistor is connected to a common ground line.
[0010] Furthermore, the differential mode noise suppression branch includes a differential mode inductor, a first differential mode capacitor, a second differential mode capacitor and a differential mode damping resistor; the first end of the differential mode inductor is electrically connected to the first end of the fourth common mode capacitor, and the second end of the differential mode inductor is electrically connected to the positive voltage output terminal OUT+; the first end of the first differential mode capacitor and the first end of the second differential mode capacitor are both electrically connected to the second end of the differential mode inductor, the second end of the first differential mode capacitor is electrically connected to the first end of the third common mode capacitor, the second end of the second differential mode capacitor is electrically connected to the first end of the differential mode damping resistor, the second end of the differential mode damping resistor is electrically connected to the first end of the third common mode capacitor, and the second end of the differential mode damping resistor is also electrically connected to the negative voltage output terminal OUT-.
[0011] Furthermore, the inductance L of the series mode inductor is SOURSE And the inductance L of the differential mode inductor DM All are μH level; the capacitance of the series mode capacitor C PI , the capacitance of the first differential mode capacitor C X1 and the capacitance of the second differential mode capacitor C X2 The capacitance of the first common-mode capacitor is C Y1, the capacitance of the second common mode capacitor C Y2 、The capacitance of the third common mode capacitor C Y3 and the capacitance of the fourth common mode capacitor C Y4 All are pF level.
[0012] Furthermore, the capacitance C of the first common-mode capacitor is Y1 and the capacitance of the second common mode capacitor C Y2 Satisfy C Y1 =C Y2 ; The capacitance C of the third common mode capacitor Y3 and the capacitance of the fourth common mode capacitor C Y4 Satisfy C Y3 =C Y4 ; The capacitance C of the first differential mode capacitor X1 and the capacitance of the second differential mode capacitor C X2 Satisfies the following relationship:
[0013]
[0014] Furthermore, the capacitance C of the series mode capacitor is PI If the first and second conditions are met,
[0015] The first condition is:
[0016]
[0017] The second condition is:
[0018]
[0019] Among them, F S Indicates the switching frequency of the switching power supply device in kHz.
[0020] Furthermore, the resistance value R of the common mode damping resistor is CM The calculation formula is as follows:
[0021]
[0022] Among them, Q CM Represents the quality factor of the common mode EMI filter; L CM Indicates the inductance of a common-mode inductor in a conjugate coil.
[0023] Furthermore, the resistance value R of the differential mode damping resistor is DM The calculation formula is as follows:
[0024]
[0025] Among them, Q DMRepresents the quality factor of the differential mode EMI filter.
[0026] In the present invention, by introducing the RC damper structure in the post-stage common mode noise suppression branch and the differential mode noise suppression branch, the oscillation speed of the signal can be slowed down, thereby reducing the occurrence of the "ringing" phenomenon and improving the reliability of the EMI filter. In addition, the improved passive EMI filter based on the RC damper of this embodiment can reduce the occurrence of the "ringing" phenomenon while introducing a zero point into the double-pole system to reduce its quality factor. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:
[0028] Figure 1 It is a structural block diagram of an embodiment of a passive EMI filter based on an RC damper of the present invention.
[0029] Figure 2 This is the circuit diagram of a passive EMI filter.
[0030] Figure 3 Schematic diagram of the equivalent structure of a common-mode EMI filter.
[0031] Figure 4 Schematic diagram of the equivalent structure of the differential mode EMI filter.
[0032] Figure 5 This is a CE102 test result diagram of an existing 60W hybrid DC / DC converter with a built-in passive EMI filter.
[0033] Figure 6 This is a diagram showing the CE102 test results after the passive EMI filter of this embodiment is built into a 60W hybrid DC / DC converter.
[0034] The accompanying drawings in the specification are numeraled as follows:
[0035] External power supply device-100; power supply-110; line impedance stabilization network-120; series mode noise suppression branch-200; front stage common mode noise suppression branch-300; rear stage common mode noise suppression branch-400; differential mode noise suppression branch-500; switching power supply device-600;
[0036] Conjugate coil-T1; series mode inductor-L1; differential mode inductor-L2; first common mode capacitor-C1; second common mode capacitor-C2; third common mode capacitor-C3; fourth common mode capacitor-C4; series mode capacitor-C5; first differential mode capacitor-C6; second differential mode capacitor-C7; common mode damping resistor-R1; differential mode damping resistor-R2. DETAILED DESCRIPTION
[0037] The following describes the implementation methods of the present invention through specific examples. The illustrations provided in the following embodiments are only used to schematically illustrate the basic concept of the present invention. The following embodiments and features in the embodiments may be combined with each other without conflict.
[0038] See also Figure 1 , Figure 1 The passive EMI filter based on RC damper of the present invention is a structural block diagram of an embodiment of the present invention. The passive EMI filter based on RC damper of the present embodiment is used to be connected between an external power supply device 100 and a switching power supply device 600, and includes a series mode noise suppression branch 200, a front stage common mode noise suppression branch 300, a conjugate coil T1, a rear stage common mode noise suppression branch 400 and a differential mode noise suppression branch 500 which are sequentially arranged in a direction from an input end of the passive EMI filter (i.e., an end of the passive EMI filter connected to the external power supply device 100) to an output end of the passive EMI filter (i.e., an end of the passive EMI filter connected to the switching power supply device 600).
[0039] The external power supply device 100 generally includes a power supply 110 and a line impedance stabilization network 120 connected to the output end of the power supply 110; the line impedance stabilization network 120 is connected to a series mode noise suppression branch 200, the series mode noise suppression branch 200 is electrically connected to a front-stage common mode noise suppression branch 300, the front-stage common mode noise suppression branch 300 is electrically connected to a conjugate coil T1, the conjugate coil T1 is electrically connected to a rear-stage common mode noise suppression branch 400, and the rear-stage common mode noise suppression branch 400 is electrically connected to a differential mode noise suppression branch 500.
[0040] The common mode noise suppression branch 200 is used to suppress the high-frequency differential common mode noise of the conduction line (i.e., the line between the power supply device and the switching power supply device 600); the front-stage common mode noise suppression branch 300 is used to suppress the high-frequency common mode noise of the conduction line; the conjugate coil T1 is used to suppress the common mode noise of the conduction line; the rear-stage common mode noise suppression branch 400 is used to suppress the low-frequency common mode noise of the conduction line using a structure with an RC damper; the differential mode noise suppression branch 500 is used to suppress the low-frequency differential mode noise of the conduction line using a structure with an RC damper; the common mode noise suppression branch 200, the front-stage common mode noise suppression branch 300, the conjugate coil T1, and the rear-stage common mode noise suppression branch 400 form a common mode EMI filter, and the differential mode noise suppression branch 500 forms a differential mode EMI filter.
[0041] See also Figure 2 The series-mode noise suppression branch 200 includes a series-mode inductor L1 and a series-mode capacitor C5; the first end of the series-mode inductor L1 is electrically connected to the positive voltage input terminal IN+, and the positive voltage input terminal IN+ is used to connect the positive power output terminal of the external power supply device 100. The second end of the series-mode inductor L1 is electrically connected to the first end of the series-mode capacitor C5, and the second end of the series-mode capacitor C5 is grounded. The second end of the series-mode capacitor C5 is also electrically connected to the negative voltage input terminal IN-, and the negative voltage input terminal IN- is used to connect the negative power output terminal of the external power supply device 100. The inductance L of the series-mode inductor L1 is SOURSE The capacitance of the series mode capacitor C5 is C PI is μF level; its noise suppression cutoff frequency f H1 The calculation formula is:
[0042]
[0043] The front-stage common-mode noise suppression branch 300 includes a first common-mode capacitor C1 and a second common-mode capacitor C2, and the conjugate coil T1 includes two common-mode inductors with the same inductance. The first end of the first common-mode capacitor C1 and the first end of the first common-mode inductor in the conjugate coil T1 are both electrically connected to the first end of the series-mode capacitor C5, and the second end of the first common-mode capacitor C1 is connected to the common ground line PE (generally the housing ground of the device). The first end of the second common-mode capacitor C2 and the first end of the second common-mode inductor in the conjugate coil T1 are both electrically connected to the second end of the series-mode capacitor C5, and the second end of the second common-mode capacitor C2 is connected to the common ground line PE. The capacitance C of the first common-mode capacitor C1 is Y1 and the capacitance of the second common mode capacitor C2 Y2 All are pF level. And meet C Y1 =CY2 .
[0044] The post-stage common-mode noise suppression branch 400 includes a third common-mode capacitor C3, a fourth common-mode capacitor C4 and a common-mode damping resistor R1, and the third common-mode capacitor C3, the fourth common-mode capacitor C4 and the common-mode damping resistor R1 are used to form an RC damper in the post-stage common-mode noise suppression branch 400. The first end of the third common-mode capacitor C3 is electrically connected to the second end of the second common-mode inductor in the conjugate coil T1, and the first end of the fourth common-mode capacitor C4 is electrically connected to the second end of the first common-mode inductor in the conjugate coil T1. The second end of the third common-mode capacitor C3 and the second end of the fourth common-mode capacitor C4 are both electrically connected to the first end of the common-mode damping resistor R1, and the second end of the common-mode damping resistor R1 is connected to the common ground line PE. The capacitance C of the third common-mode capacitor C3 is 1.18V. Y3 and the capacitance C of the fourth common mode capacitor C4 Y4 All are pF level and meet C Y3 =C Y4 .
[0045] The differential mode noise suppression branch 500 includes a differential mode inductor L2, a first differential mode capacitor C6, a second differential mode capacitor C7 and a differential mode damping resistor R2, wherein the first differential mode capacitor C6, the second differential mode capacitor C7 and the differential mode damping resistor R2 are used to form an RC damper in the differential mode noise suppression branch 500. The first end of the differential mode inductor L2 is electrically connected to the first end of the fourth common mode capacitor C4, and the second end of the differential mode inductor L2 is electrically connected to the positive voltage output terminal OUT+, and the positive voltage output terminal OUT+ is used to connect the positive power input terminal of the switching power supply device 600. The first end of the first differential mode capacitor C6 and the first end of the second differential mode capacitor C7 are both electrically connected to the second end of the differential mode inductor L2, the second end of the first differential mode capacitor C6 is electrically connected to the first end of the third common mode capacitor C3, and the second end of the second differential mode capacitor C7 is electrically connected to the first end of the differential mode damping resistor R2. The second end of the differential mode damping resistor R2 is electrically connected to the first end of the third common mode capacitor C3, and the second end of the differential mode damping resistor R2 is also electrically connected to the negative voltage output terminal OUT-, and the negative voltage output terminal OUT- is used to connect the negative power input terminal of the switching power supply device 600.
[0046] The inductance L of the differential mode inductor L2 is DM The capacitance of the first differential mode capacitor C6 is C X1 and the capacitance of the second differential mode capacitor C7 X2 The capacitance of the series mode capacitor C5 is C PI The following two conditions need to be met:
[0047] The first condition is:
[0048]
[0049] The second condition is:
[0050]
[0051] Among them, F S represents the switching frequency of the switching power supply device 600, and the unit is kHz.
[0052] The capacitance value of the first differential mode capacitor C6 is C X1 and the capacitance of the second differential mode capacitor C7 X2 Satisfies the following relationship:
[0053]
[0054] like Figure 3 As shown, it is a schematic diagram of a common-mode EMI filter equivalently obtained by adopting the above circuit structure of the series-mode noise suppression branch 200, the front-stage common-mode noise suppression branch 300, the conjugate coil T1 and the rear-stage common-mode noise suppression branch 400. The resistance value of the common-mode damping resistor R1 is R CM The calculation formula is as follows:
[0055]
[0056] Among them, Q CM Indicates the quality factor of the common mode EMI filter; L CM It represents the inductance of a common mode inductor in the conjugate coil T1.
[0057] The insertion loss mathematical model IL of the common mode EMI filter CM (S) is shown in the following formula:
[0058]
[0059] Where S represents the variable of the Laplace function.
[0060] like Figure 4 , which is a schematic diagram of a differential mode EMI filter equivalently obtained after the differential mode noise suppression branch 500 adopts the above circuit structure. The resistance value of the differential mode damping resistor R2 is R DM The calculation formula is as follows:
[0061]
[0062] Among them, Q DM Represents the quality factor of the differential mode EMI filter.
[0063] The insertion loss mathematical model IL of the differential mode EMI filter DM (S) is shown in the following formula:
[0064]
[0065] Since common mode noise is mainly concentrated in the frequency band of 5MHz to 7.5MHz, the cutoff frequency of the EMI filter is designed according to the cutoff frequency of the differential mode EMI filter. cdm As shown below:
[0066]
[0067] Since the passive EMI filter includes multiple π-type filter structures, when the filter structure is applied to a switching circuit, especially when the filter is built into the switching power supply device 600, a "ringing" phenomenon is likely to occur. Figure 5 , which is a CE102 test result diagram of an existing 60W hybrid DC / DC converter with a built-in passive EMI filter. Figure 5 It can be seen that the switching power supply device 600 has a "ringing" phenomenon, and the "ringing" phenomenon will cause damped oscillation, generate strong electromagnetic radiation, and seriously affect the normal operation of the circuit.
[0068] See also Figure 6 , which is a CE102 test result diagram after the passive EMI filter of this embodiment is built into a 60W hybrid DC / DC converter. It can be seen that this embodiment slows down the oscillation speed of the signal by introducing a damping branch (i.e., a circuit branch with an RC damper structure, in this embodiment) to improve the reliability of the EMI filter. In addition, according to the calculation formula of the quality factor Q, it can be seen that by introducing a damping branch, a zero point can be introduced into the double-pole system to reduce its quality factor.
[0069] In this embodiment, by introducing an RC damper structure in the post-stage common-mode noise suppression branch 400 and the differential-mode noise suppression branch 500, the oscillation speed of the signal can be slowed down, thereby reducing the occurrence of the "ringing" phenomenon and improving the reliability of the EMI filter. In addition, the improved passive EMI filter based on the RC damper of this embodiment can reduce the occurrence of the "ringing" phenomenon while introducing a zero point into the double-pole system to reduce its quality factor.
[0070] The above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.
Claims
1. A passive EMI filter based on an RC damper, characterized in that: The invention comprises a series mode noise suppression branch, a front stage common mode noise suppression branch, a conjugate coil, a rear stage common mode noise suppression branch and a differential mode noise suppression branch which are arranged in sequence from the input end of the passive EMI filter to the output end of the passive EMI filter. The series mode noise suppression branch is used to suppress the high frequency differential common mode noise of the conduction line; the front stage common mode noise suppression branch is used to suppress the high frequency common mode noise of the conduction line; the conjugate coil is used to suppress the common mode noise of the conduction line; the rear stage common mode noise suppression branch is used to suppress the low frequency common mode noise of the conduction line by adopting a structure with an RC damper; the differential mode noise suppression branch is used to suppress the low frequency differential mode noise of the conduction line by adopting a structure with an RC damper; the series mode noise suppression branch, the front stage common mode noise suppression branch, the conjugate coil and the rear stage common mode noise suppression branch form a common mode EMI filter, and the differential mode noise suppression branch forms a differential mode EMI filter.
2. The passive EMI filter based on RC damper as claimed in claim 1, characterized in that: The series-mode noise suppression branch includes a series-mode inductor and a series-mode capacitor; the first end of the series-mode inductor is electrically connected to the positive voltage input terminal IN+, the second end of the series-mode inductor is electrically connected to the first end of the series-mode capacitor, the second end of the series-mode capacitor is electrically connected to the negative voltage input terminal IN-, and the second end of the series-mode capacitor is also grounded.
3. The passive EMI filter based on RC damper as claimed in claim 2, characterized in that: The front-stage common-mode noise suppression branch includes a first common-mode capacitor and a second common-mode capacitor, the conjugate coil includes two common-mode inductors with the same inductance, the first end of the first common-mode capacitor and the first end of the first common-mode inductor in the conjugate coil are both electrically connected to the first end of the series-mode capacitor, the second end of the first common-mode capacitor is connected to a common ground line, the first end of the second common-mode capacitor and the first end of the second common-mode inductor in the conjugate coil are both electrically connected to the second end of the series-mode capacitor, and the second end of the second common-mode capacitor is connected to the common ground line.
4. The passive EMI filter based on RC damper as claimed in claim 3, characterized in that: The post-stage common-mode noise suppression branch includes a third common-mode capacitor, a fourth common-mode capacitor and a common-mode damping resistor; the first end of the third common-mode capacitor is electrically connected to the second end of the second common-mode inductor in the conjugate coil, and the first end of the fourth common-mode capacitor is electrically connected to the second end of the first common-mode inductor in the conjugate coil; the second end of the third common-mode capacitor and the second end of the fourth common-mode capacitor are both electrically connected to the first end of the common-mode damping resistor, and the second end of the common-mode damping resistor is connected to a common ground line.
5. The passive EMI filter based on RC damper as claimed in claim 4, characterized in that: The differential mode noise suppression branch includes a differential mode inductor, a first differential mode capacitor, a second differential mode capacitor and a differential mode damping resistor; a first end of the differential mode inductor is electrically connected to a first end of the fourth common mode capacitor, and a second end of the differential mode inductor is electrically connected to a positive voltage output terminal OUT+; The first end of the first differential mode capacitor and the first end of the second differential mode capacitor are both electrically connected to the second end of the differential mode inductor, the second end of the first differential mode capacitor is electrically connected to the first end of the third common mode capacitor, the second end of the second differential mode capacitor is electrically connected to the first end of the differential mode damping resistor, the second end of the differential mode damping resistor is electrically connected to the first end of the third common mode capacitor, and the second end of the differential mode damping resistor is also electrically connected to the negative voltage output terminal OUT-.
6. The passive EMI filter based on RC damper as claimed in claim 5, characterized in that: The inductance L of the series mode inductor SOURSE And the inductance L of the differential mode inductor DM All are μH level; the capacitance of the series mode capacitor C PI , the capacitance of the first differential mode capacitor C X1 and the capacitance of the second differential mode capacitor C X2 The capacitance of the first common-mode capacitor is C Y1 , the capacitance of the second common mode capacitor C Y2 、The capacitance of the third common mode capacitor C Y3 and the capacitance of the fourth common mode capacitor C Y4 All are pF level.
7. The passive EMI filter based on RC damper as claimed in claim 6, characterized in that: The capacitance of the first common mode capacitor is C Y1 and the capacitance of the second common mode capacitor C Y2 Satisfy C Y1 =C Y2 ; The capacitance C of the third common mode capacitor Y3 and the capacitance of the fourth common mode capacitor C Y4 Satisfy C Y3 =C Y4 ; The capacitance C of the first differential mode capacitor X1 and the capacitance of the second differential mode capacitor C X2 Satisfies the following relationship:
8. The passive EMI filter based on RC damper as claimed in claim 6, characterized in that: The capacitance of the series mode capacitor C PI If the first and second conditions are met, The first condition is: The second condition is: Among them, F S Indicates the switching frequency of the switching power supply device in kHz.
9. The passive EMI filter based on RC damper as claimed in claim 6, characterized in that: The resistance of the common mode damping resistor R CM The calculation formula is as follows: Among them, Q CM Indicates the quality factor of the common mode EMI filter; L CM Indicates the inductance of a common-mode inductor in a conjugate coil.
10. The passive EMI filter based on RC damper according to claim 6, characterized in that: The resistance value of the differential mode damping resistor R DM The calculation formula is as follows: Among them, Q DM Represents the quality factor of the differential mode EMI filter.