EMI reduction device and method of DC-DC converter

Abstract

To provide an EMI reduction device and a method of a DC-DC converter.SOLUTION: A DC-DC converter includes: an input voltage end; an output voltage end; a plurality of switching elements for modulating output voltage of the DC-DC converter by adjusting an operation frequency of the ends; and a control end for changing the operation frequency of the switching element based on output voltage of the output end of the DC-DC converter. An EMI reduction device includes a frequency modulation input unit which is connected to the control end and injects a wave modulation frequency which is set according to desired EMI performance based on output voltage of the output voltage end to the operation frequency of the switching element. The EMI reduction device disperses energy concentrated on a prescribed frequency point fc and high frequency harmonics, 2fc and 3fc, for example, to surrounding frequency bands, reduces EMI in each frequency point and can improve EMI performance of the DC-DC converter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to switching power supplies, and more particularly to an apparatus and method for reducing EMI in frequency modulated DC-DC converters. [Background technology]

[0002] A switching power supply is a high-frequency power conversion device that mainly uses power semiconductor devices (such as bipolar transistors, MOSFETs, etc.). The control circuit periodically switches the electronic switching elements "on" and "off," and the power semiconductor devices pulse-modulate the input voltage to achieve the functions of voltage conversion, output voltage regulation, and automatic voltage stabilization. For different switching power supply topologies, pulse width modulation (PWM) and frequency modulation are two commonly used control methods for switching power supplies. High conversion efficiency and low electromagnetic interference (EMI) are required for switching elements.

[0003] Direct switching frequency modulation (DSFM) is known as a mechanism that can effectively reduce the average EMI noise level of a switching power supply using PWM control. However, the EMI noise reduction mechanism (i.e., DSM) that is suitable for PWM-controlled switching power supplies cannot be applied to converters using DSFM. This is because DSM is difficult to match with the requirements of each load, and for example, DSM designed based on light load conditions will cause large oscillations in the output voltage under full load conditions.

[0004] Therefore, there is a need for an effective mechanism suitable for frequency-modulated switching power supplies that can reduce the average EMI noise under various load conditions and reduce the size of the EMI filter. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above-mentioned problems in the conventional technology, and has an object to provide an apparatus and method for reducing EMI in a DC-DC converter that can improve EMI performance. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided an EMI reduction device for a DC-DC converter, the DC-DC converter including an input voltage end, an output voltage end, a plurality of switching elements for modulating an output voltage of the DC-DC converter by adjusting an operating frequency thereof, and a control end for changing an operating frequency of the switching elements according to an output voltage of an output end of the DC-DC converter, the EMI reduction device including a frequency modulation input unit connected to the control end for injecting a wave modulation frequency into the operating frequency, the wave modulation frequency being set according to an output voltage of the output voltage end and in accordance with a desired EMI performance.

[0007] According to the EMI reduction device of the DC-DC converter of the present invention, the frequency modulation input unit injects a wave modulation frequency through the control end. The wave modulation frequency is set according to the output voltage of the output end voltage end and according to the desired EMI performance. In this way, the EMI reduction device of the present invention can disperse the energy concentrated at a certain frequency point fc and its high-frequency harmonics, such as 2fc and 3fc, to the surrounding frequency bands, thereby reducing the EMI at each frequency point. Since the energy is distributed to the baseband of the frequency point (i.e., frequency expansion), the EMI at each frequency point does not exceed the specified limit value for EMI, and the effect of improving the EMI performance can be achieved.

[0008] In addition, in an EMI reduction device for a DC-DC converter according to another embodiment of the present invention, the frequency modulation input unit may include a wave output voltage detection unit for detecting the wave output voltage at the output voltage end of the DC-DC converter as a wave feedback voltage, a wave modulation voltage output unit for outputting a wave modulation voltage according to a wave modulation frequency, and a wave error control unit for receiving a wave error signal between the wave feedback voltage and the wave modulation voltage and outputting a wave modulation frequency to a control end. In the EMI reduction device of the present invention, the wave error control unit adjusts the operating frequency of the switching element so that the actual wave output voltage follows the preset wave modulation voltage. This allows the desired frequency expansion to be achieved.

[0009] In addition, in an EMI reduction device for a DC-DC converter according to another embodiment of the present invention, the frequency modulation input unit may include a wave modulated voltage output unit that outputs a wave modulated voltage according to the wave modulation frequency. The DC-DC converter may have an output voltage detection unit that detects the output voltage at the output voltage terminal and outputs an output feedback voltage according to the output voltage, and an error control unit that receives the sum of the constant reference voltage and the wave modulated voltage and the output feedback voltage and outputs a frequency related to the wave modulation frequency to the control terminal.

[0010] In addition, according to an EMI reduction device for a DC-DC converter according to another embodiment of the present invention, the corresponding relationship between the wave modulation voltage and the wave modulation frequency may be Vmod=Hout_fd*Fsw_d / Gout_f, where Vmod is the wave modulation voltage, Fsw_d is the wave modulation frequency, Gout_f is the transfer function from the output voltage to the operating frequency of the DC-DC converter, and Hout_fd is the transfer function of the output voltage detection unit.

[0011] The DC-DC converter of this embodiment is a feedback control type DC-DC converter, that is, it has a feedback circuit that controls the frequency of a switching element according to the sum of the output voltage (including the DC output voltage and the wavy output voltage) of the DC-DC converter and a constant reference voltage. Therefore, there is no need to provide a separate feedback circuit for controlling the tracking of a preset wavy modulated voltage, and the preset wavy modulated voltage is added to the original feedback control circuit of the DC-DC converter. This allows the device to be shared, and the effects of miniaturization and cost reduction can be achieved.

[0012] In addition, in the EMI reduction device of the DC-DC converter according to another embodiment of the present invention, the wave modulated voltage output unit may include an operational amplifier having a non-inverting input terminal connected to the output terminal via a first resistor and an inverting input terminal connected to the ground terminal via a capacitor and connected to the output terminal via a second resistor, a constant voltage source having one terminal grounded and the other terminal connected to the non-inverting input terminal of the operational amplifier via a third resistor, and a series circuit of a fourth resistor and a second capacitor, having one terminal connected to the wave output voltage detection unit or the output voltage detection unit and the other terminal connected to the connection point between the second resistor and the first capacitor. The wave modulated voltage output unit injects a preset wave modulated voltage into the output voltage terminal side of the DC-DC converter, and the error control unit adjusts the operating frequency of the switching element. This allows the desired frequency expansion to be achieved.

[0013] Also, an EMI reduction device for a DC-DC converter according to another embodiment of the present invention may further include a current detection unit for detecting an output current of the DC-DC converter. A plurality of current sections are set according to the EMI performance of the DC-DC converter, and in at least one current section, a wave modulation frequency is injected into a switching element of the DC-DC converter, and in other current sections other than the at least one current section, a wave modulation frequency is not injected into the switching element of the DC-DC converter. This makes it possible to control the operation of the EMI reduction device based on the actual EMI performance in different operating sections (current sections in this case) of the DC-DC converter. This makes it possible to obtain high EMI performance in the entire operating range of the DC-DC converter.

[0014] In the EMI reduction device for a DC-DC converter according to another embodiment of the present invention, the desired EMI performance may be an average value of EMI.

[0015] Furthermore, according to an EMI reduction device for a DC-DC converter according to another embodiment of the present invention, the DC-DC converter may include a remote type and a non-remote type DC-DC converter. In addition, according to an EMI reduction device for a DC-DC converter according to another embodiment of the present invention, the DC-DC converter may include at least one of an LLC converter, a quasi resonant boost converter, a quasi resonant buck converter, and a quasi resonant flyback converter.

[0016] One aspect of the present invention provides an EMI reduction method for a DC-DC converter, in which an operating frequency of a switching element of the DC-DC converter is adjusted through a control end based on an output voltage of the DC-DC converter. A wave modulation frequency is injected into the operating frequency through the control end. The wave modulation frequency is set based on the output voltage and according to a desired EMI performance. This allows the operating frequency of the switching element of the DC-DC converter to be extended, and the EMI performance to be improved.

[0017] In addition, an EMI reduction device for a DC-DC converter according to another embodiment of the present invention may set an operating period in which EMI needs to be improved according to the EMI performance of the DC-DC converter, inject a wave modulation frequency into a switching element of the DC-DC converter so as to obtain a desired EMI performance in the operating period, and not inject a wave modulation frequency into the switching element of the DC-DC converter outside the operating period. This makes it possible to control the operation of the EMI reduction device based on the actual EMI performance of the DC-DC converter in different operating periods. This makes it possible to obtain high EMI performance in the entire operating range of the DC-DC converter. Effect of the Invention

[0018] The device and method for reducing EMI in a DC-DC converter of the present invention sets the wave modulation frequency based on the output voltage at the output voltage end of the DC-DC converter and in accordance with the desired EMI performance, thereby extending the frequency of the switching elements of the DC-DC converter and achieving better EMI performance. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a functional block diagram illustrating a frequency modulation DC-DC converter. [Diagram 2] 1 is a functional block diagram of a DC-DC converter having a wave error control unit for controlling the wave of an output voltage according to an embodiment of the present invention; [Diagram 3]FIG. 1 is a functional block diagram of a DC-DC converter having an error control unit for controlling an output voltage according to an embodiment of the present invention. [Figure 4] 4 is a diagram illustrating an example of a circuit of the wave modulated voltage output unit illustrated in FIG. 3. [Diagram 5] FIG. 1 is a schematic diagram of an example of a device under test (UUT) that is a conventional LLC converter with output voltage feedback control. [Figure 6] FIG. 6 is a diagram showing the results of an EMI test on the measurement target mechanism of FIG. 5. [Figure 7] FIG. 4 is a diagram showing an example of a wave modulated voltage. [Figure 8] 8 is a diagram showing a wavy voltage generated in a DC output voltage when the wavy modulated voltage shown in FIG. 7 is injected. [Figure 9] FIG. 5 is a diagram showing the results of an EMI test on the measurement target mechanism of FIG. 4. [Figure 10] FIG. 6 is a diagram showing the results of an EMI test of the measurement target mechanism shown in FIG. 5 when the output is 48V / 1000W and 48V / 100W. [Figure 11] 10 is a flowchart for determining whether to activate an EMI reduction device depending on a load current. [Figure 12] 12 is a diagram showing an example in which the function shown in FIG. 11 is further realized in the configuration of the DC-DC converter shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an apparatus and method for reducing EMI in a DC-DC converter according to an embodiment will be described. In the description of each drawing, the same or corresponding elements are denoted by the same reference numerals, and duplicated descriptions may be omitted.

[0021] FIG. 1 is a functional block diagram showing a frequency modulation DC-DC converter. As shown in FIG. 1, the DC-DC converter converts a DC input voltage at an input voltage end into a DC output voltage at an output voltage end, which is different from the input voltage, by adjusting the operating frequency of the switching element of the DC-DC converter through a control end. As described above, there are conventionally two types of control methods for the switching element: adjusting the duty ratio (PWM) and adjusting the frequency (i.e., width modulation and frequency modulation). In a frequency modulation DC-DC converter, the relationship between the DC output voltage and the DC input voltage is adjusted by changing the frequency at which a pulse appears. The frequency modulation DC-DC converter shown in FIG. 1 may be any converter topology used in a frequency modulation switching power supply.

[0022] In switching power supplies, the power consumption of the switching elements can be reduced by operating them at high frequencies, and the conversion efficiency of the power supply can be significantly improved. On the other hand, the switching elements generate a large amount of electromagnetic interference. Therefore, there is a need for an effective mechanism that can reduce EMI noise and reduce the size of the EMI filter, which is suitable for frequency-modulated switching power supplies.

[0023] A DC-DC converter according to an embodiment of the present invention includes an input voltage end, an output voltage end, a number of switching elements for modulating the output voltage of the DC-DC converter by adjusting their operating frequencies, and a control end for changing the operating frequencies of the switching elements according to the voltage at the output end of the DC-DC converter. The EMI reduction device of the present invention includes a frequency modulation input unit connected to the control end for injecting a wave modulation frequency into the operating frequencies of the switching elements. The wave modulation frequency is set according to the output voltage at the output voltage end and according to the desired EMI performance.

[0024] According to the EMI reduction device of the DC-DC converter of the present invention, a wave modulation frequency is injected through the control end by the frequency modulation input unit. The wave modulation frequency is set according to the output voltage of the output end voltage end and according to the desired EMI performance. In this way, the EMI reduction device of the present invention can disperse the energy concentrated at a certain frequency point fc and its high-frequency harmonics, such as 2fc and 3fc, to the surrounding frequency bands, thereby reducing the EMI at each frequency point. Since the energy is distributed to the baseband of the frequency point (i.e., frequency expansion), the EMI at each frequency point does not exceed the specified limit value for EMI, and the effect of improving the EMI performance can be achieved.

[0025] FIG. 2 is a functional block diagram of a DC-DC converter having a wave error control unit for controlling the wave of the output voltage according to an embodiment of the present invention. As shown in FIG. 2, the frequency modulation input unit includes a wave output voltage detection unit 304, a wave modulated voltage output unit, and a wave error control unit 308. The wave output voltage detection unit 304 detects the wave output voltage at the output voltage terminal of the DC-DC converter 302 as a wave feedback voltage 305. The wave modulated voltage output unit outputs a wave modulated voltage 306 according to the wave modulation frequency. The wave error control unit 308 obtains a wave error signal 307 as an input of the wave error control unit 308 by calculating the difference between the wave feedback voltage 305 from the wave output voltage detection unit 304 and the wave modulated voltage 306 from the wave modulated voltage output unit. The error control unit 308 functions as a feedback control unit that makes the actual wave feedback voltage 305 follow the preset wave modulated voltage 306, and outputs a wave modulation frequency 309. The wave modulation frequency 309 is summed with another given frequency signal 311 determined based on the operating conditions of the DC-DC converter and input as a frequency modulation input 310 to the control end of the DC-DC converter 302 .

[0026] In a frequency-modulated DC-DC converter with a constant DC output voltage, the operating frequency of the switching element is almost constant, and the EMI performance at the operating frequency and its high-frequency harmonics is poor. In the DC-DC converter 300 of the present invention, a wave modulation voltage 306 is introduced on the DC output voltage terminal side. The wave error control unit 308 adjusts the operating frequency of the switching element so that the actual wave feedback voltage 305 follows the preset wave modulation voltage 306. This allows the desired frequency expansion to be achieved under each load condition, and the average EMI noise level to be reduced.

[0027] FIG. 3 is a functional block diagram of a DC-DC converter having an error control unit for controlling an output voltage according to an embodiment of the present invention. The DC-DC converter 500 shown in FIG. 3 is a feedback control type DC-DC converter, and includes an output voltage detection unit 404 and an error control unit 408. The output voltage detection unit 404 detects the output voltage 403 at the DC output voltage terminal, and outputs an output feedback voltage 405 according to the output voltage 403. The wave modulation voltage output unit outputs a wave modulation voltage 501 according to a desired wave modulation frequency. The error control unit 408 receives the sum of the constant reference voltage 406 and the wave modulation voltage 501, and the output feedback voltage 405. The error control unit 408 outputs a frequency 409 related to the wave modulation frequency in order to make the output feedback voltage 405 follow the preset wave modulation voltage 501. The frequency 409 related to the wave modulation frequency is summed with another given frequency signal 411 determined based on the operating conditions of the DC-DC converter and input to the control end of the DC-DC converter 500 as a frequency modulation input 410 .

[0028] The following describes the correspondence between Vmod, which is the wave modulation voltage 501, and Fsw_d, which is the wave modulation frequency (desired frequency expansion).

[0029] In the power conversion circuit 402 of the frequency modulation DC-DC converter, the following correspondence exists: Fsw_d=Vout_d*Gout_f (1) Wherein, Vout_d is the DC output voltage fluctuation at the output voltage end of the DC-DC converter due to Fsw_d, and Gout_f is the transfer function from the output voltage to the operating frequency in the frequency modulation DC-DC converter 402.

[0030] In the output voltage detection unit 404, the relationship between Vout_fd, which is a feedback value of the fluctuation of the output voltage due to Fsw_d, and Vout_d, which is a fluctuation value of the DC output voltage due to Fsw_d, is as follows. Vout_d=Vout_fd / Hout_fd (2) Wherein, Hout_fd is the transfer function of the output voltage detection unit 404.

[0031] In this way, the error control unit 408 functions as a feedback control unit that makes the output feedback voltage 405 follow the preset wave modulated voltage 501. Therefore, the following equation is satisfied. Vmod=Vout_fd (3)

[0032] With reference to the above formulas (1) to (3), Here, Vmod is the wave modulation voltage 501, Fsw_d is the wave modulation frequency, Gout_f is the transfer function from the output voltage to the operating frequency in the DC-DC converter 402, and Hout_f is the transfer function of the output voltage detection unit 404.

[0033] In DC-DC converter 500 having the EMI reduction device, as shown in Fig. 2, there is no need to provide a separate feedback circuit for controlling the tracking of a preset wave modulated voltage, and a preset wave modulated voltage 501 is added to the original feedback control circuit of the DC-DC converter (i.e., error control unit 408). This allows devices to be shared, resulting in miniaturization and cost reduction.

[0034] Fig. 4 is a diagram showing a schematic diagram of an example of the circuit of the wave modulated voltage output unit shown in Fig. 3. In Fig. 4, a DC-DC converter 700 having an EMI reduction device is provided with a constant reference voltage 606, a wave feedback voltage 605 from a wave output voltage detection unit 604, and a wave modulated voltage 701 from a wave modulated voltage output unit 702 as inputs to an error control unit 608.

[0035] As shown in Fig. 4, the wave modulation voltage output unit 702 includes an operational amplifier, the non-inverting input terminal of which is connected to the output terminal via a first resistor R6, the inverting input terminal of which is connected to the ground terminal via a first capacitor C3 and to the output terminal via a second resistor R7, a constant voltage source U2, one terminal of which is grounded and the other terminal of which is connected to the non-inverting input terminal of the operational amplifier via a third resistor R5, and a series circuit of a fourth resistor R8 and a second capacitor C4, the one terminal of which is connected to the wave output voltage detection unit 604 and the other terminal of which is connected to the connection point between the second resistor R7 and the first capacitor C3. The wave modulation voltage output unit 702 injects a preset wave modulation voltage 701 into the output terminal side of the DC-DC converter, and thus the error control unit 608 adjusts the operating frequency of the switching element. This achieves a desired frequency expansion under each load condition.

[0036] It should be understood that Fig. 4 is a specific embodiment of the wave modulated voltage output unit according to the present invention. As long as it can realize the function of the wave modulated voltage of the present invention described above (i.e., outputting a wave modulated voltage according to a desired wave modulated frequency), other realization methods, such as a one-chip microcomputer, may also be adopted.

[0037] Fig. 5 is a schematic diagram showing an example of a device under test (UUT) which is a typical LLC converter with output voltage feedback control. The device under test shown in Fig. 5 differs from that shown in Fig. 4 in that a preset wave modulated voltage 701 is injected into the output voltage terminal side by a wave modulated voltage output unit 702 in a DC-DC converter having the EMI reduction device of the present invention shown in Fig. 4.

[0038] The operation modes of the DC-DC converters shown in Figures 4 and 5 are 390VDC input and 48V / 100W output, and the EMI test results are shown in Figures 6 and 9, respectively, according to the EN55032 Class B standard. In the test, a wave voltage with a peak-to-peak value of 50mV as shown in Figure 7, which is generated by the wave modulation voltage output unit 702, is applied as the wave modulation voltage 701 to the DC-DC converter 700 shown in Figure 4. As shown in Figure 8, the wave modulation voltage as shown in Figure 7 generates a wave voltage of 400mV in the DC output voltage. When the fluctuating voltage becomes large, the DC-DC converter adjusts the operating frequency to stabilize the output voltage.

[0039] The limit value and measurement trace of the quasi-peak value and average value are respectively shown in Figure 6. As shown in Figure 6, the measurement result of the DC-DC converter 600 of Figure 5 meets the standard of EN55032 Class B, but according to the product standard of the UUT, the average noise level does not meet the requirement of 3 dB margin at about 182 kHz and about 455 kHz.

[0040] On the other hand, in the DC-DC converter 700 to which the EMI reduction device of the present invention is applied, as shown in Fig. 9, it is observed that the EMI noise spectrum is broadened and the average noise level is reduced by about 4 dB, satisfying the requirement of an average value of -3 dB. This makes it possible to improve the EMI performance without changing the EMI filter. As is clear from the comparison between Fig. 6 and Fig. 9, the EMI device to which the present invention is applied can effectively reduce the average EMI noise of the frequency-modulated DC-DC converter.

[0041] The EMI reduction device of the present invention can be applied to DC-DC converters with any topology and modulation frequency. That is, the DC-DC converters can include isolated and non-isolated DC-DC converters. The DC-DC converters can be any of LLC converters, quasi-resonant boost converters, quasi-resonant buck converters, and quasi-resonant flyback converters.

[0042] The inventor also found that the EMI performance of the DC-DC converter differs depending on the operating section. Figure 10 is a diagram showing the EMI measurement results in different operating conditions of the measurement target mechanism shown in Figure 5. Among them, Figure 10 (a) shows the EMI performance at full load with an output of 48V / 1000W, and Figure 10 (b) shows the EMI performance at small load with an output of 48V / 100W. By comparing Figure 10 (a) with Figure 10 (b), it can be seen that the average EMI performance at a relatively small load, especially in the frequency range of 150k-400k, is close to the average value limit of EN55032 Class B and is significantly worse than the average EMI performance at full load of 48V / 1000W. Therefore, it is considered to operate the EMI reduction device only in the medium-light load operating section where the EMI performance is poor, rather than in the entire operating section.

[0043] FIG. 11 is a flow chart for determining whether to operate the EMI reduction device according to the load current. As shown in FIG. 11, in step S920, the output load current of the frequency modulation DC-DC converter is detected. In step S930, the output load current detected in step S920 is judged, and if the current satisfies the set condition, the process proceeds to step S940, and if the current does not satisfy the set condition, the process proceeds to step S950. In step S940, the EMI reduction device of the present invention is turned on for the frequency modulation DC-DC converter, that is, the wave modulation frequency is injected. In step S950, the EMI reduction device of the present invention is turned off for the frequency modulation DC-DC converter, that is, the wave modulation frequency is not injected. This makes it possible to control the operation of the EMI reduction device based on the actual EMI performance in different operating sections (current sections here) of the DC-DC converter. This makes it possible to obtain high EMI performance in the entire operating range of the DC-DC converter.

[0044] FIG. 12 is a diagram showing an example in which the configuration of the DC-DC converter shown in FIG. 4 is further provided with the functions shown in FIG. 11. In FIG. 12, an output current detection device 802 is provided for detecting the output current. 803 (U2) is for setting a current threshold and dividing the output current. When the detected load current is greater than the set current value of U2, Q1 is turned on, causing the wave voltage generator 702 to stop outputting the wave modulation voltage 701, and not injecting the wave modulation frequency into the frequency modulation LLC converter device 800. When the detected load current is less than the set current value of U2, Q1 is turned off, causing the wave voltage generator 702 to output the wave modulation voltage 701, and injecting the wave modulation frequency into the frequency modulation LLC converter device 800, that is, the frequency modulation input 610 includes the wave modulation frequency, realizing the extension of the operating frequency of the desired switching element, and reducing the average electromagnetic interference (EMI).

[0045] It should be understood that the embodiment of the present disclosure does not limit the specific method of current detection, and may use resistance sampling or a current transformer. The embodiment of the present disclosure also does not limit the preset current threshold and the number of load operation periods (here, two operation periods), and can be determined according to the noise reduction needs of the average EMI.

[0046] The present disclosure also provides an EMI reduction method for a DC-DC converter using the EMI reduction device described in the above embodiment. Note that the EMI reduction method for a DC-DC converter provided by the present invention is a method that applies the EMI reduction device for a DC-DC converter, and can achieve the same technical effects as the embodiment of the EMI reduction device. To avoid duplication, the embodiment of the EMI reduction method will not be described.

[0047] Although the preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. Those skilled in the art may make modifications and changes to the present invention as necessary without departing from the spirit and scope of the present invention, and all of these modifications and changes are included in the scope of the present invention. [Explanation of symbols]

[0048] 300, 302, 402, 500, 700 DC-DC Converters 304 Wave output voltage detection unit (frequency modulation input unit) 308 Wave Error Control Unit (Frequency Modulation Input Unit)

Claims

1. An EMI reduction device for a DC-DC converter, comprising: the DC-DC converter includes an input voltage terminal, an output voltage terminal, a plurality of switching elements that modulate an output voltage of the DC-DC converter by adjusting an operating frequency thereof, and a control terminal that changes an operating frequency of the switching elements based on an output voltage of an output terminal of the DC-DC converter; The EMI reduction device of the DC-DC converter is characterized in that it includes a frequency modulation input unit connected to the control end and injecting a wave modulation frequency set based on the output voltage of the output voltage end and according to a desired EMI performance into the operating frequency.

2. The frequency modulation input unit includes: a wave output voltage detection unit for detecting a wave output voltage at an output voltage terminal of the DC-DC converter as a wave feedback voltage; a wave modulation voltage output unit that outputs a wave modulation voltage according to the wave modulation frequency; a wave error control unit which receives a wave error signal between the wave feedback voltage and the wave modulation voltage, and outputs the wave modulation frequency to the control end; 2. The EMI reducing device for a DC-DC converter according to claim 1, further comprising:

3. the frequency modulation input unit includes a wave modulation voltage output unit that outputs a wave modulation voltage according to the wave modulation frequency; The DC-DC converter comprises: an output voltage detection unit that detects an output voltage at the output voltage terminal and outputs an output feedback voltage according to the output voltage; an error control unit which receives the sum of a constant reference voltage and the wave modulation voltage and the output feedback voltage, and outputs a frequency related to the wave modulation frequency to the control terminal; 2. The EMI reducing device for a DC-DC converter according to claim 1, further comprising:

4. The correspondence relationship between the wave modulation voltage and the wave modulation frequency is as follows: Vmod=Hout_fd*Fsw_d / Gout_f, 4. The EMI reducing device of claim 3, wherein Vmod is the wave modulation voltage, Fsw_d is the wave modulation frequency, Gout_f is a transfer function from the output voltage of the DC-DC converter to the operating frequency, and Hout_fd is a transfer function of the output voltage detection unit.

5. The wave modulation voltage output unit includes: an operational amplifier having a non-inverting input terminal connected to an output terminal via a first resistor, and an inverting input terminal connected to a ground terminal via a first capacitor and to the output terminal via a second resistor; a constant voltage source having one end grounded and the other end connected to the non-inverting input terminal of the operational amplifier via a third resistor; a series circuit of a fourth resistor and a second capacitor, one end of which is connected to the wave output voltage detection unit or the output voltage detection unit, and the other end of which is connected to the connection point between the second resistor and the first capacitor; 4. The EMI reducing device for a DC-DC converter according to claim 2, further comprising:

6. A current detection unit for detecting an output current of the DC-DC converter is further provided. A plurality of current sections are set according to the EMI performance of the DC-DC converter; In at least one current section, the wave modulation frequency is injected into a switching element of the DC-DC converter; 5. An EMI reduction device for a DC-DC converter as described in any one of claims 1 to 4, characterized in that the wave modulation frequency is not injected into a switching element of the DC-DC converter in a current section other than the at least one current section.

7. 5. The EMI reducing device for a DC-DC converter according to claim 1, wherein the desired EMI performance is an average value of EMI.

8. 5. The EMI reducing device for a DC-DC converter according to claim 1, wherein the DC-DC converter includes a remote type and a non-remote type DC-DC converter.

9. 5. The EMI reduction device for a DC-DC converter according to claim 1, wherein the DC-DC converter includes at least one of an LLC converter, a quasi-resonant boost converter, a quasi-resonant buck converter, and a quasi-resonant flyback converter.

10. Adjusting the operating frequency of the switching element of the DC-DC converter through a control terminal according to the output voltage of the DC-DC converter; A method for reducing EMI in a DC-DC converter, comprising: injecting a wave modulation frequency, which is set based on the output voltage and in accordance with a desired EMI performance, into the operating frequency via the control end.

11. Setting an operating period in which EMI needs to be improved according to the EMI performance of the DC-DC converter; injecting the wave modulation frequency into a switching element of the DC-DC converter to obtain a desired EMI performance during the operating interval; 11. The method for reducing EMI in a DC-DC converter according to claim 10, wherein the wave modulation frequency is not injected into the switching element of the DC-DC converter outside the operating section.

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