WO2012000291A1

WO2012000291A1 - Method and device for lowering the electro-magnetic interference of pulse width modulation dimming circuit

Info

Publication number: WO2012000291A1
Application number: PCT/CN2010/079917
Authority: WO
Inventors: 华桂潮; 姚晓莉
Original assignee: 英飞特光电（杭州）有限公司
Priority date: 2010-06-29
Filing date: 2010-12-17
Publication date: 2012-01-05
Also published as: CN102316621A

Abstract

A method and device for lowering the Electro-Magnetic Interference (EMI) of a Pulse Width Modulation (PWM) dimming circuit is disclosed in this invention. The method includes the following steps: the frequency variation range of a PWM dimming control signal is set; the PWM dimming control signal is controlled so as to vary periodically in the frequency variation range. In this way, a light emitting diode (LED) driver operates in the frequency jitter mode of a PWM dimming state; if the EMI is relatively serious at a certain frequency point, the frequency of the PWM dimming control signal varies in a certain range which includes said frequency point, thereby the EMI that concentrates at said frequency point being de-concentrated beside said frequency point, and thus the LED driver is enabled to reach to an EMI standard.

Description

Method and device for reducing electromagnetic interference of pulse width modulation dimming circuit The present application claims to be submitted to the Chinese Patent Office on June 29, 2010, application number 201010213948.7, and the invention name is "a method for reducing EMI of PWM dimming circuit and The priority of the Chinese Patent Application, the entire disclosure of which is incorporated herein by reference.

Technical field

The present invention relates to the field of PWM dimming technology, and in particular, to a method and apparatus for reducing EMI of a PWM dimming circuit.

Background technique

As power electronics bring great convenience to human production and life, electromagnetic compatibility of power electronic devices is challenged because of its working in switching mode. Power electronics often produce severe EMI at work. EMI, through conduction and radiation, severely contaminates the surrounding electromagnetic environment and power system.

The EMI problem generated during the PWM dimming process will be described below with reference to the accompanying drawings.

Referring to Figure la, the figure is a schematic diagram of a prior art PWM dimming LED driver. See Figure lb, which is a waveform diagram of Io in Figure la.

The current Io from the LED driver 101 in Fig. la is the PWM wave, and its waveform is shown in Figure lb. The current output from the LED driver 101 supplies power to the load LED. The average value of Io can be adjusted by adjusting the duty cycle of the PWM dimming control signal that controls the switching transistor S to be turned on and off, thereby adjusting the brightness of the load LED.

Referring to Figure 2a, there is shown a schematic diagram of another PWM dimming LED driver in the prior art. The LED driver includes an LED front-stage constant voltage driving circuit and an LED post-stage constant current driving circuit. The output voltage Va of the LED pre-stage constant voltage driving circuit is an input signal of the n-th LED constant-current driving circuit. Va in Fig. 2a is a PWM signal, and the current Io outputted by the corresponding n LED rear-stage constant current driving circuits is also a PWM signal. See Fig. 2b and Fig. 2c, respectively, waveform diagrams of Va and Io.

Wherein, the LED front-stage constant voltage driving circuit and the LED rear-stage constant current driving circuit are connected in series

S, the PWM dimming control signal controls the on and off of the switch S.

In a PWM dimming LED driver, the PWM voltage or PWM current output by the LED driver contains a large number of higher harmonics in addition to the useful fundamental signal. Due to the presence of higher harmonics, the PWM voltage or PWM current will affect the LED driver, causing it to generate EMI, resulting in LED flooding The actuator does not meet the requirements of the EMI standard.

Summary of the invention

The technical problem to be solved by the present invention is to provide a method and device for reducing the EMI of a PWM dimming circuit, which can reduce the EMI of the PWM dimming circuit and achieve the EMI standard.

The invention provides a method for reducing EMI of a PWM dimming circuit, comprising the steps of: setting a frequency variation range of a PWM dimming control signal;

The PWM dimming control signal is controlled to periodically change within the frequency variation range. Preferably, before the setting the frequency variation range of the PWM dimming control signal, the method further includes: presetting or detecting a center frequency of the PWM dimming control signal of the control switch; the switch tube is connected in series between the LED driver and the LED load Interposed or serially between the LED pre-stage constant voltage driving circuit and the LED after-stage constant current driving circuit;

The setting a frequency variation range of the PWM dimming control signal is specifically: determining, by the center frequency, a frequency variation range of the PWM dimming control signal.

Preferably, the frequency variation range of the PWM dimming control signal is determined by the center frequency, specifically:

Determining, by the center frequency, a frequency variation proportional coefficient of the PWM dimming control signal; wherein a frequency variation range of the PWM dimming control signal is: [(f0-kf0), (f0+kf0)]; wherein k Is a frequency variation proportional coefficient of the PWM dimming control signal; f0 is a center frequency of the PWM dimming control signal.

Preferably, the controlling the PWM dimming control signal periodically changes within the frequency variation range, specifically:

Setting a change period and a frequency change step of the PWM dimming control signal;

Controlling the PWM dimming control signal to start from the set first frequency in each of the change periods, and gradually increasing in the frequency change step to a set second frequency; and then controlling the PWM tone The light control signal starts from the second frequency and gradually decreases in the frequency change step until the first frequency;

Or controlling the PWM dimming control signal to start from the set second frequency in each of the change periods, and gradually decreasing in the frequency change step to a set first frequency; and then controlling the The PWM dimming control signal starts from the first frequency, and gradually increases in the frequency change step. Up to the second frequency;

The first frequency is less than the center frequency, and the second frequency is greater than the center frequency.

Preferably, the controlling the PWM dimming control signal to periodically change during the frequency change period further comprises: controlling a period of time during which the PWM dimming control signal is continuously set at a center frequency.

The present invention also provides a method for reducing EMI of a PWM dimming circuit, comprising the steps of: setting a duty cycle variation range of a PWM dimming control signal;

The PWM dimming control signal is controlled to periodically change within the duty cycle variation range. Preferably, before the setting the duty cycle variation range of the PWM dimming control signal, the method further includes: presetting or detecting a central duty ratio of the PWM dimming control signal of the control switch; the switch tube is connected in series to the LED driver And the LED load or in series with the LED pre-stage constant voltage drive circuit and

LED after the constant current drive circuit;

The setting of the duty ratio of the PWM dimming control signal is specifically: determining, by the center duty ratio, a duty cycle variation range of the PWM dimming control signal.

Preferably, the duty cycle variation range of the PWM dimming control signal is determined by the center duty ratio, specifically:

Determining, by the central duty ratio, a duty cycle variation ratio coefficient of the PWM dimming control signal; wherein a duty cycle variation range of the PWM dimming control signal is: [(D0-kD0), (D0+kD0) Where k is the duty cycle variation ratio coefficient of the PWM dimming control signal; D0 is the center duty ratio of the PWM dimming control signal.

Preferably, the controlling the PWM dimming control signal periodically changes within the duty cycle variation range, specifically:

Setting a change period of the PWM dimming control signal and a duty cycle change step;

Controlling, the PWM dimming control signal starts from the set first duty cycle in each of the change periods, and gradually increases in the duty cycle change step until the set second duty ratio; And then controlling the PWM dimming control signal to start from the second duty cycle, and gradually decreasing the duty cycle change step to the first duty ratio;

Alternatively, controlling the PWM dimming control signal to start from the set second duty cycle in each of the change periods, and gradually decreasing in the duty cycle change step until the set first duty cycle And then controlling the PWM dimming control signal to start from the first duty cycle, with the duty cycle varying step size Gradually rising until the second duty cycle;

The first duty cycle is less than the center duty cycle, and the second duty cycle is greater than the center duty cycle.

Preferably, the controlling the PWM dimming control signal to periodically change during the duty cycle change period further comprises: controlling a time period during which the PWM dimming control signal is continuously set at a center duty ratio.

The present invention also provides an apparatus for reducing EMI of a PWM dimming circuit, comprising: a frequency variation range determining unit and a frequency variation control unit;

The frequency change range determining unit is configured to set a frequency change range of the PWM dimming control signal, and send the frequency change range to the frequency change control unit;

The frequency change control unit is configured to control the PWM dimming control signal to periodically change within the frequency variation range.

Preferably, the method further includes a center frequency setting or detecting unit, configured to preset or detect a center frequency of the PWM dimming control signal of the control switch tube, and send the center frequency to the frequency change range determining unit; Between the LED driver and the LED load or in series between the LED pre-stage constant voltage driving circuit and the LED post-stage constant current driving circuit;

The frequency variation range determining unit sets a frequency variation range of the PWM dimming control signal, specifically, setting a frequency variation range of the PWM dimming control signal according to the center frequency.

Preferably, the frequency variation range determining unit is configured to determine, by the center frequency, a frequency variation range of the PWM dimming control signal, specifically:

Preferably, the frequency change control unit is configured to control the PWM dimming control signal to periodically change within the frequency variation range, specifically:

Controlling the PWM dimming control signal to start from the set first frequency in each of the change periods, and gradually increasing in the frequency change step to a set second frequency; then controlling the The PWM dimming control signal starts from the second frequency and gradually decreases in the frequency change step until the first frequency;

Or controlling the PWM dimming control signal to start from the set second frequency in each of the change periods, and gradually decreasing in the frequency change step to a set first frequency; and then controlling the The PWM dimming control signal starts from the first frequency and gradually increases in the frequency change step until the second frequency;

Preferably, the frequency change control unit is further configured to control a period of time during which the PWM dimming control signal is continuously set at a center frequency.

The present invention also provides an apparatus for reducing EMI of a PWM dimming circuit, comprising: a duty ratio variation range determining unit and a duty ratio change control unit;

The duty ratio variation range determining unit is configured to determine a duty ratio variation range of the PWM dimming control signal, and send the duty ratio variation range to the duty ratio change control unit;

The duty cycle change control unit is configured to control the PWM dimming control signal to periodically change within the duty ratio variation range.

Preferably, the method further includes: a central duty ratio setting or detecting unit, configured to preset or detect a central duty ratio of the PWM dimming control signal of the control switch, and send the central duty ratio to a duty cycle variation range Determining a unit; the switching tube is connected in series between the LED driver and the LED load or in series between the LED pre-stage constant voltage driving circuit and the LED post-stage constant current driving circuit;

The duty ratio variation range determining unit is configured to determine a duty cycle variation range of the PWM dimming control signal by the center duty ratio, specifically: determining the PWM dimming according to the center duty ratio The duty cycle variation range of the control signal.

Preferably, the duty ratio variation range determining unit is configured to determine, by the central duty ratio, a duty cycle variation range of the PWM dimming control signal, specifically:

Determining a duty cycle variation ratio coefficient of the PWM dimming control signal by the center duty ratio; then a duty cycle variation range of the PWM dimming control signal is: [(D0-kD0), (D0+kD0) Where k is the duty cycle variation ratio coefficient of the PWM dimming control signal; D0 is the center duty ratio of the PWM dimming control signal.

Preferably, the duty cycle change control unit is configured to control the PWM dimming control signal at The duty cycle varies periodically within a range of changes, specifically:

Alternatively, controlling the PWM dimming control signal to start from the set second duty cycle in each of the change periods, and gradually decreasing in the duty cycle change step until the set first duty cycle Comparing; then controlling the PWM dimming control signal to start from the first duty cycle, and gradually increasing the duty step by the duty cycle until the second duty ratio;

Preferably, the duty cycle change control unit is further configured to control a period of time during which the PWM dimming control signal is continuously set at a center duty ratio.

Compared with the prior art, the present invention has the following advantages:

The method for reducing the EMI of the PWM dimming circuit provided by the embodiment of the present invention sets the frequency variation range of the PWM dimming control signal, and then controls the PWM dimming control signal to periodically change within the frequency variation range, so that the LED driver operates in the The frequency jitter mode of the PWM dimming state, if the EMI is severe at a certain frequency point, the frequency of the PWM dimming control signal changes within a certain range of the frequency point, so that the EMI concentrated at the frequency point is dispersed. Beside this frequency point, the LED driver meets EMI standards.

DRAWINGS

Figure la is a schematic diagram of a prior art PWM dimming LED driver;

Figure lb is a waveform diagram of Io in Figure la;

2a is a schematic diagram of another PWM dimming LED driver in the prior art; FIG. 2b is a waveform diagram of Va in FIG. 2a;

Figure 2c is a waveform diagram of Io in Figure 2a;

3 is a flow chart of Embodiment 1 of the method provided by the present invention;

4 is a schematic diagram of frequency variation of a PWM dimming control signal provided by the present invention; 5 is a schematic diagram of the frequency provided by the present invention having five frequency points in each variation period T; FIG. 6 is a schematic diagram showing the frequency variation of another PWM dimming control signal provided by the present invention; FIG. 7 is a method implementation of the present invention. Example 2 flowchart;

8 is a schematic diagram showing a duty cycle change of a PWM dimming control signal provided by the present invention;

Figure 9 is a schematic illustration of the duty cycle provided by the present invention with five duty cycle points in each variation period ;;

10 is a schematic diagram of a duty cycle change of another PWM dimming control signal provided by the present invention; FIG. 11 is a structural diagram of Embodiment 1 of the apparatus provided by the present invention;

Figure 12 is a block diagram showing still another embodiment of the apparatus provided by the present invention.

detailed description

In order to enable those skilled in the art to better understand and practice the invention, several basic concepts are described below.

As shown in the PWM dimming control signal in LA, the frequency of the PWM dimming control signal is called the center frequency and is represented by f ₀ ; the duty ratio of the PWM dimming control signal is called the center duty ratio, and D is used. ₀ means.

The method for reducing EMI of a PWM dimming circuit provided by the present invention comprises the steps of: setting a frequency variation range of a PWM dimming control signal; and controlling the PWM dimming control signal to periodically change within the frequency variation range.

The present invention dims the dimming PWM dimming control signal such that the frequency of the PWM dimming control signal varies within a certain range, rather than always outputting the PWM dimming control signal at a constant frequency.

It should be noted that the frequency variation range of the PWM dimming control signal can be directly set or set by the center frequency.

The above described objects, features and advantages of the present invention will become more apparent from the aspects of the appended claims.

Referring to FIG. 3, the figure is a flowchart of Embodiment 1 of a method provided by the present invention.

A method for reducing EMI of a PWM dimming circuit provided by an embodiment of the present invention includes the following steps:

S201: preset or detect a center frequency of a PWM dimming control signal of the control switch tube; the switch tube is connected in series between the LED driver and the LED load or in series with the LED pre-stage constant voltage driving power Between the circuit and the LED after the constant current drive circuit; as shown in Figures la and 2a. It should be noted that the center frequency of the PWM dimming control signal is preset, and is suitable for directly generating a PWM dimming control signal of a preset center frequency when the PWM dimming control signal is generated. The center frequency of the PWM dimming control signal is detected. The PWM dimming control signal is provided by an external device and is not directly generated. Therefore, it is necessary to detect the center frequency of the PWM dimming control signal.

It should be noted that the center frequency of the PWM dimming control signal is not necessarily fixed, and the center frequency of the PWM dimming control signal can be changed, but the frequency of the PWM dimming control signal is a certain period in a certain period of time. value.

S202: determining, by the center frequency, a frequency variation range of the PWM dimming control signal; determining a frequency variation range of the PWM dimming control signal, specifically: when the center frequency is known, setting a required The frequency variation ratio coefficient of the PWM dimming control signal; then the frequency variation range of the PWM dimming control signal is: [(fO-kfO), (fO+kfO)]; wherein k is the PWM dimming control The frequency change proportional coefficient of the signal; f0 is the center frequency of the PWM dimming control signal.

It should be noted that the frequency variation proportional coefficient k may be different in different cases.

S203: Control the PWM dimming control signal to periodically change within the frequency variation range.

In the prior art, the center frequency of the PWM dimming control signal is constant and constant for a certain period of time, and in this embodiment, the PWM dimming control signal is controlled to the current center frequency during this period. Centered, jitter around the center frequency to dissipate EMI.

It should be noted that controlling the PWM dimming control signal to periodically change within the frequency variation range may be continuously changed, and may be discontinuously changed.

In the method for reducing the EMI of the PWM dimming circuit provided by the embodiment, the center frequency of the PWM dimming control signal is preset, or the center frequency of the PWM dimming control signal at the current moment is detected, and the frequency variation range of the PWM dimming control signal is determined. Then controlling the PWM dimming control signal to periodically change within the frequency variation range, so that the LED driver operates in the frequency dither mode of the PWM dimming state, if the EMI is more serious at a certain frequency point, such PWM dimming control signal The frequency changes within a certain range including the frequency point, so that EMI concentrated at the frequency point Disperse to the side of this frequency point, so that the LED driver meets EMI standards.

The method for continuously changing the frequency of the PWM dimming control signal provided by the embodiment of the present invention is described in detail below with reference to the accompanying drawings.

Referring to FIG. 4, the figure is a schematic diagram of frequency variation of a PWM dimming control signal according to an embodiment of the present invention.

Setting the change period of the PWM dimming control signal T and the frequency change step fa;

Controlling the PWM dimming control signal to start from the set first frequency fl in each of the change periods T, and gradually increasing in the frequency change step fa until the set second frequency f(n) As shown in FIG. 4, the change process is fl-f2-f0-f(nl)-f(n); then controlling the PWM dimming control signal starts from the second frequency f(n), The frequency change step fa is gradually decreased until the first frequency fl, as shown in FIG. 4, the change process is f(n)-f(nl)-f0-i2-fl; the first frequency fl is smaller than The center frequency f0 is greater than the center frequency f0.

It should be noted that the change period T is greater than the center period T0 of the PWM dimming control signal. It should be noted that, the frequency change may be: in each of the change periods ,, from the set second frequency f(n), the frequency change step fa is gradually decreased until a set first frequency fl, the change process is f(n)-f(nl)-f0-i2-fl; then controlling the PWM dimming control signal to start from the first frequency f(l) The frequency change step fa is gradually increased until the second frequency f(n), the change process is fl-f2-f0-f(nl)-f(n); the first frequency fl is smaller than the center The frequency f0, the second frequency f(n) is greater than the center frequency f0.

It can be understood that the first frequency and the second frequency can be set according to actual conditions. As shown in Fig. 5, the figure is a schematic diagram of five frequency points in each variation period T.

The frequency of the PWM dimming control signal starts from fl in the change period T, gradually increases to f4 in the same step size, and then gradually decreases from f4 to fl in the same step size, and then cycles through, and the specific change process is : fl-f2-f0-fi-f4-fi-f0-f2-fl. The frequency change period provided by this embodiment is T.

The embodiment of the present invention further provides a method for changing a PWM dimming control signal. When the frequency of the PWM dimming control signal is gradually increased by the above method, and then gradually decreasing, the PWM dimming control signal is controlled to be continuously set at a center frequency. The time period. Referring to FIG. 6, the figure is a schematic diagram of frequency variation of another PWM dimming control signal provided by the present invention.

The frequency variation law shown in FIG. 6 is different from the variation law shown in FIG. 4 in the variation period. The frequency variation process is fl-f2-f0-f3-f4-f3-f0-f2-fl; after the change period T, the time period t1 is continuously set with the center frequency f0, and the frequency change period of the method is T +tl.

In the above embodiment, the EMI of the decentralized LED driver is realized by changing the frequency of the PWM dimming control signal. The following embodiment introduces the EMI of the decentralized LED driver by changing the duty ratio of the PWM dimming control signal, and the principle and the change PWM The frequency of the dimming control signals is the same, so the following embodiment only describes the basic operating principle.

The present invention also provides a method for reducing EMI of a PWM dimming circuit, comprising the steps of: setting a duty cycle variation range of a PWM dimming control signal; controlling the PWM dimming control signal within the duty cycle variation range Change periodically.

The present invention dims the dimming PWM dimming control signal so that the duty cycle of the PWM dimming control signal varies within a certain range, instead of always outputting the PWM dimming with a constant duty cycle. control signal.

It should be noted that the duty cycle variation range of the PWM dimming control signal may be directly set or may be set by the center duty ratio.

Referring to FIG. 7, FIG. 7 is a flowchart of Embodiment 2 of a method provided by the present invention.

The method for reducing the EMI of the PWM dimming circuit provided by the embodiment includes the following steps: S601: preset or detect a central duty ratio of the PWM dimming control signal of the control switch; the switch tube is connected in series between the LED driver and the LED load Interposed or serially between the LED pre-stage constant voltage drive circuit and the LED post-stage constant current drive circuit; as shown in Figures la and 2a.

It should be noted that the center duty ratio of the PWM dimming control signal is preset, and is suitable for directly generating a PWM dimming control signal with a preset center duty ratio when the PWM dimming control signal is generated. The center duty ratio of the PWM dimming control signal is detected. The PWM dimming control signal is input from an external device and is not directly generated. Therefore, it is necessary to detect the center duty ratio of the PWM dimming control signal. It should be noted that the center duty ratio of the PWM dimming control signal is not a fixed value, and the duty ratio of the PWM dimming control signal is changed, but the duty ratio of the PWM dimming control signal is within a certain period of time. A fixed value.

For example, during PWM dimming, the duty cycle of the PWM dimming control signal may be adjusted from 10% to 100%.

S602: Determine a duty cycle variation of the PWM dimming control signal by the center duty ratio Wai

Determining a duty cycle variation range of the PWM dimming control signal, specifically:

In the case where the center duty ratio is known, the duty ratio variation coefficient of the required PWM dimming control signal is set; then the duty cycle variation range of the PWM dimming control signal is: [(D0) -kD0), (DO+kDO)]; where k is a duty cycle variation ratio coefficient of the PWM dimming control signal; DO is a center duty ratio of the PWM dimming control signal.

S603: Control the PWM dimming control signal to periodically change within the duty cycle variation range.

In the prior art, the center duty ratio of the PWM dimming control signal is constant for a certain period of time, and in this embodiment, the PWM dimming control signal is controlled to the current center in this period. The duty cycle is centered and dithers around the center duty cycle to dissipate EMI.

It should be noted that controlling the PWM dimming control signal to periodically change within the duty cycle variation range may be continuously changed, and may be discontinuously changed.

In the method for reducing the EMI of the PWM dimming circuit provided by the embodiment, the central duty ratio of the PWM dimming control signal is preset, or the center duty ratio of the PWM dimming control signal at the current moment is detected, and the PWM dimming control signal is determined. The duty cycle varies, and then controls the PWM dimming control signal to periodically change within the duty cycle variation, thus allowing the LED driver to operate in the duty cycle dither mode of the PWM dimming state, if EMI is at a certain duty cycle The point is more serious, so that the duty ratio of the PWM dimming control signal changes within a certain range including the duty ratio, so that the EMI concentrated at the duty point is dispersed to the side of the duty point. This allows the LED driver to meet EMI standards.

A method for discontinuous change of the duty ratio of the PWM dimming control signal provided by the embodiment of the present invention is described in detail below with reference to the accompanying drawings.

Referring to FIG. 8, the figure shows a duty cycle variation of a PWM dimming control signal according to an embodiment of the present invention.

Setting the change period of the PWM dimming control signal T and the frequency change step size Da;

Controlling, the PWM dimming control signal starts from the set first duty ratio D1 in each of the change periods T, and gradually increases in the duty change step Da until the set second share The space ratio D(n), as shown in Fig. 8, the change process is D1-D2-DO-D(n-1)-D(n); then the PWM is controlled The dimming control signal starts from the second duty ratio D(n), and gradually decreases by the duty cycle change step Da until the first duty ratio D1, as shown in FIG. for

D(n)-D(n-1)- DO-D2-D1; the first duty ratio D1 is smaller than the center duty ratio DO, and the second duty ratio Dn is greater than the center duty ratio D0.

The duty cycle variation may also be: a second duty ratio set from each of the change periods T

Starting at D2, the duty ratio is gradually decreased by the duty ratio change step Da until the first duty ratio D1; the change process is: D(n)-D(n-1)-DO - D2-D1; then starting from the set first duty cycle D1, gradually increasing by the duty cycle change step Da until the set second duty ratio D(n); the change process is D1 -D2- DO- D(n-1)-D(n); the first duty ratio D1 is smaller than the center duty ratio D0, and the second duty ratio Dn is greater than the center duty ratio D0 .

It should be noted that the change period T is greater than the center period T0 of the PWM dimming control signal. It can be understood that the first duty ratio and the second duty ratio can be set according to actual conditions.

As shown in Figure 9, the figure is a schematic diagram of five duty cycle points in each variation period Τ. The duty cycle of the PWM dimming control signal starts from D1 in the change period ,, gradually increases to D4 in the same step size, and then gradually decreases from D4 to D1 in the same step size, and then cyclically, the specific change The process is: D1-D2-D0-D3-D4-D3-D0-D2-D1 The duty cycle variation period provided by this embodiment is Τ.

The embodiment further provides a method for changing the PWM dimming control signal. When the duty ratio of the PWM dimming control signal is gradually increased by the above method, and then gradually decreasing, the PWM dimming control signal is controlled to be centered. The space ratio continues for the set period of time. Referring to FIG. 10, the figure is a schematic diagram of a duty cycle change of another PWM dimming control signal provided by the present invention.

The duty cycle variation rule shown in FIG. 10 is different from the variation rule shown in FIG. 9 in that the duty cycle variation process in the variation period T is D1-D2-D0-D3-D4-D3-D0-D2- D1 ; After the change period T, the duty cycle change period of this method is T+tl o with the time period t1 set continuously by the center duty ratio D0.

Based on the above method for reducing the EMI of the PWM dimming circuit, the present invention also provides a system for reducing the EMI of the PWM dimming circuit. The components thereof will be described in detail below in conjunction with specific embodiments.

The device for reducing EMI of a PWM dimming circuit provided by the invention includes: Fixed unit and frequency change control unit;

Referring to Figure 11, there is shown a block diagram of an embodiment of an apparatus for reducing EMI of a PWM dimming circuit provided by the present invention.

The apparatus for reducing EMI of the PWM dimming circuit provided by the embodiment includes: a center frequency setting or detecting unit 1001, a frequency variation range determining unit 1002, and a frequency variation control unit 1003.

The center frequency setting or detecting unit 1001 is configured to preset or detect the control switch tube

The center frequency of the PWM dimming control signal is sent to the frequency variation range determining unit 1002; the switching tube is connected in series between the LED driver and the LED load or in series with the LED pre-stage constant voltage driving circuit and the LED rear stage constant Between the flow drive circuits; the switch S as shown in Figures la and 2a.

It should be noted that the center frequency of the PWM dimming control signal is preset, and is suitable for directly generating a PWM dimming control signal with a preset center frequency when the PWM dimming control signal is generated. The center frequency of the PWM dimming control signal is detected. The PWM dimming control signal is input from an external device and is not directly generated. Therefore, the center frequency of the PWM dimming control signal needs to be detected.

The frequency variation range determining unit 1002 is configured to determine a frequency variation range of the PWM dimming control signal by the center frequency, and send the frequency variation range to the frequency variation control unit 1003;

The frequency variation range determining unit 1002 determines, by the center frequency, a frequency variation range of the PWM dimming control signal, specifically:

Determining, by the center frequency, a frequency variation proportional coefficient of the PWM dimming control signal; The frequency variation range of the PWM dimming control signal is: [(f0-kf0), (f0+kf0)]; where k is a frequency variation proportional coefficient of the PWM dimming control signal; f0 is the PWM dimming The center frequency of the control signal.

The frequency change control unit 1003 is configured to control the PWM dimming control signal to periodically change within the frequency variation range.

The frequency change control unit 1003 controls the PWM dimming control signal to periodically change within the frequency variation range, specifically:

Controlling the PWM dimming control signal to start from the set first frequency in each of the change periods, and gradually increasing in the frequency change step to a set second frequency; and then controlling the PWM tone The light control signal starts from the second frequency and gradually decreases in the frequency change step until the first frequency; the first frequency is smaller than the center frequency, and the second frequency is greater than the center frequency .

It should be noted that the frequency change control unit 1003 is further configured to control a period of time during which the PWM dimming control signal is continuously set at a center frequency.

The apparatus for reducing the EMI of the PWM dimming circuit provided by the embodiment, presets the center frequency of the PWM dimming control signal, or detects the center frequency of the PWM dimming control signal at the current moment, and determines the frequency variation range of the PWM dimming control signal, Then controlling the PWM dimming control signal to periodically change within the frequency variation range, so that the LED driver operates in the frequency dither mode of the PWM dimming state, if the EMI is more serious at a certain frequency point, such PWM dimming control signal The frequency changes within a certain range that protects the frequency, so that EMI concentrated at that frequency point is dispersed to the side of this frequency point, thereby enabling the LED driver to meet EMI standards.

The invention uses a dithered PWM dimming control signal to dim the light to enable this PWM dimming control The duty cycle of the signal varies within a certain range, rather than always outputting this PWM dimming control signal with a fixed duty cycle.

Referring to Figure 12, there is shown a second structural diagram of an apparatus for reducing EMI of a PWM dimming circuit provided by the present invention.

The apparatus for reducing the EMI of the PWM dimming circuit provided by the embodiment includes: a central duty ratio setting or detecting unit 1101, a duty ratio varying range determining unit 1102, and a duty ratio changing control unit 1103;

The central duty ratio setting or detecting unit 1101 is configured to preset or detect a central duty ratio of a PWM dimming control signal that controls the switch tube, and send the center duty ratio to the duty ratio variation range determining unit 1102. The switch tube is connected in series between the LED driver and the LED load or in series between the LED pre-stage constant voltage drive circuit and the LED post-stage constant current drive circuit; as shown in FIGS. 1a and 2a.

It should be noted that the center duty ratio of the PWM dimming control signal is preset, and is suitable for directly generating a PWM dimming control signal with a preset center duty ratio when the PWM dimming control signal is generated. The center duty ratio of the PWM dimming control signal is detected. The PWM dimming control signal is input from an external device and is not directly generated. Therefore, it is necessary to detect the center duty ratio of the PWM dimming control signal.

The duty ratio variation range determining unit 1102 is configured to determine, by the center duty ratio

a duty cycle variation range of the PWM dimming control signal, the duty cycle variation range is sent to the duty ratio change control unit 1103;

The duty ratio variation range determining unit 1102 determines a duty cycle variation range of the PWM dimming control signal by the center duty ratio, which is specifically:

The duty cycle change control unit 1103 is configured to control the PWM dimming control signal in the The duty cycle varies periodically within a range of variations.

The duty cycle change control unit 1103 controls the PWM dimming control signal to periodically change within the duty ratio variation range, specifically:

Controlling, the PWM dimming control signal starts from the set first duty cycle in each of the change periods, and gradually increases in the duty cycle change step until the set second duty ratio; And then controlling the PWM dimming control signal to start from the second duty ratio, and gradually decreasing the duty cycle to the first duty ratio; the first duty ratio is less than The center duty ratio, the second duty ratio being greater than the center duty ratio.

It should be noted that the duty ratio change control unit 1103 is further configured to control a period of time during which the PWM dimming control signal is continuously set at a center duty ratio.

The device for reducing the EMI of the PWM dimming circuit provided by the embodiment, presets the central duty ratio of the PWM dimming control signal, or detects the center duty ratio of the PWM dimming control signal at the current moment, and determines the PWM dimming control signal. The duty cycle varies, and then controls the PWM dimming control signal to periodically change within the duty cycle variation, thus allowing the LED driver to operate in the duty cycle dither mode of the PWM dimming state, if EMI is at a certain duty cycle The point is more serious, so that the duty ratio of the PWM dimming control signal changes within a certain range including the duty ratio, so that the EMI concentrated at a certain duty point is dispersed to the side of the duty point. , thus enabling the LED driver to meet EMI standards.

The above description is only a preferred embodiment of the invention and is not intended to limit the invention in any way. Although the present invention has been disclosed above in the preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above, or modify the equivalents of equivalent changes without departing from the scope of the technical solutions of the present invention. Example. Therefore, any modification, equivalent changes, and modifications made to the above embodiments in accordance with the technical spirit of the present invention are still within the scope of the technical solutions of the present invention.

Claims

Rights request

A method for reducing EMI of a PWM dimming circuit, comprising the steps of: setting a frequency variation range of a PWM dimming control signal;

The PWM dimming control signal is controlled to periodically change within the frequency variation range.

2. The method of reducing EMI of a PWM dimming circuit according to claim 1, further comprising: presetting or detecting a PWM modulation of the control switch before the setting of the frequency variation range of the PWM dimming control signal a center frequency of the light control signal; the switch tube is connected in series between the LED driver and the LED load or in series between the LED front stage constant voltage driving circuit and the LED rear stage constant current driving circuit;

3. The method of reducing EMI of a PWM dimming circuit according to claim 2, wherein the frequency variation range of the PWM dimming control signal is determined by the center frequency, specifically:

The method of reducing EMI of a PWM dimming circuit according to claim 1, wherein the controlling the PWM dimming control signal periodically changes within the frequency variation range, specifically:

Or controlling the PWM dimming control signal to start from the set second frequency in each of the change periods, and gradually decreasing in the frequency change step to a set first frequency; and then controlling the The PWM dimming control signal starts from the first frequency and gradually increases in the frequency change step until the second frequency; The first frequency is less than the center frequency, and the second frequency is greater than the center frequency.

The method of reducing EMI of a PWM dimming circuit according to claim 4, wherein the controlling the PWM dimming control signal periodically changes during the frequency change period, further comprising: controlling the The PWM dimming control signal continues for a set period of time at the center frequency.

6. A method for reducing EMI of a PWM dimming circuit, comprising the steps of: setting a duty cycle variation range of a PWM dimming control signal;

The PWM dimming control signal is controlled to periodically change within the duty cycle variation range.

The method of reducing the EMI of the PWM dimming circuit according to claim 6, wherein before the setting of the duty ratio of the PWM dimming control signal, the method further comprises: presetting or detecting the control switch The central duty ratio of the PWM dimming control signal; the switching tube is connected in series between the LED driver and the LED load or in series between the LED pre-stage constant voltage driving circuit and the LED post-stage constant current driving circuit;

The method for reducing the EMI of the PWM dimming circuit according to claim 7, wherein the duty ratio of the PWM dimming control signal is determined by the central duty ratio, specifically: The central duty ratio determines a duty cycle variation ratio coefficient of the PWM dimming control signal; then the duty cycle variation range of the PWM dimming control signal is: [(D0-kD0), (D0+kD0)]; Where k is a duty cycle variation ratio coefficient of the PWM dimming control signal; D0 is a center duty ratio of the PWM dimming control signal.

The method of reducing EMI of a PWM dimming circuit according to claim 6, wherein the controlling the PWM dimming control signal periodically changes within the duty cycle variation range, specifically:

Or controlling the PWM dimming control signal from the set second in each of the change periods The duty cycle begins to gradually decrease in the duty cycle change step until the set first duty cycle; then controlling the PWM dimming control signal from the first duty cycle to The duty cycle change step gradually increases until the second duty ratio;

10. The method of reducing EMI of a PWM dimming circuit according to claim 9, wherein the controlling the PWM dimming control signal periodically changes during the duty cycle change period, further comprising: controlling The PWM dimming control signal continues for a set period of time with a center duty ratio.

11. A device for reducing EMI of a PWM dimming circuit, comprising: a frequency variation range determining unit and a frequency variation control unit;

12. The apparatus for reducing EMI of a PWM dimming circuit according to claim 11, further comprising a center frequency setting or detecting unit for presetting or detecting a center frequency of a PWM dimming control signal for controlling the switch tube, Transmitting the center frequency to the frequency variation range determining unit; the switching tube is connected in series between the LED driver and the LED load or in series between the LED pre-stage constant voltage driving circuit and the LED post-stage constant current driving circuit;

The apparatus for reducing EMI of a PWM dimming circuit according to claim 12, wherein the frequency variation range determining unit is configured to determine, by the center frequency, a frequency variation range of the PWM dimming control signal, Specifically:

14. The apparatus for reducing EMI of a PWM dimming circuit according to claim 11, wherein The frequency change control unit is configured to control the PWM dimming control signal to periodically change within the frequency variation range, specifically:

Controlling, the PWM dimming control signal starts from the set first frequency in each of the change periods, and gradually increases in the frequency change step to a set second frequency; and then controls the

The PWM dimming control signal starts from the second frequency and gradually decreases in the frequency change step until the first frequency;

The device for reducing EMI of a PWM dimming circuit according to claim 14, wherein the frequency change control unit is further configured to control a period of time during which the PWM dimming control signal is continuously set at a center frequency.

16. A device for reducing EMI of a PWM dimming circuit, comprising: a duty cycle variation range determining unit and a duty cycle change control unit;

The device for reducing EMI of a PWM dimming circuit according to claim 16, further comprising: a central duty ratio setting or detecting unit, configured to preset or detect a PWM dimming control signal for controlling the switch tube a center duty ratio, the center duty ratio is sent to the duty ratio variation range determining unit; the switch tube is connected in series between the LED driver and the LED load or in series with the LED pre-stage constant voltage driving circuit and the LED after the constant current Between the drive circuits;

The apparatus for reducing EMI of a PWM dimming circuit according to claim 17, wherein the duty ratio variation range determining unit is configured to determine the PWM dimming control signal by the central duty ratio The duty cycle variation range is specifically as follows:

Determining a duty cycle variation ratio coefficient of the PWM dimming control signal by the center duty ratio; then a duty cycle variation range of the PWM dimming control signal is: [(D0-kD0), (DO+kDO Where k is the duty cycle variation factor of the PWM dimming control signal; DO is the center duty cycle of the PWM dimming control signal.

The apparatus for reducing the EMI of the PWM dimming circuit according to claim 16, wherein the duty ratio change control unit is configured to control the PWM dimming control signal to be within the duty cycle variation range. Periodically change, specifically:

The apparatus for reducing EMI of a PWM dimming circuit according to claim 19, wherein the duty ratio change control unit is further configured to control the PWM dimming control signal to continuously set at a center duty ratio Time period.