WO2013072111A1

WO2013072111A1 - Damping circuit, led driver and led illuminating system

Info

Publication number: WO2013072111A1
Application number: PCT/EP2012/069022
Authority: WO
Inventors: Zeke WEI; Ningbo KANG; Yan Li; Dan LIN; Fu Peng LI; Michele Menegazzi; Xihe ZHUANG
Original assignee: Osram Gmbh
Priority date: 2011-11-14
Filing date: 2012-09-27
Publication date: 2013-05-23
Also published as: CN103108435B; CN103108435A

Abstract

The present invention relates to a damping circuit (10), used for a driver (100) for inhibiting flickering, comprising a first branch (11) formed by a first capacitor (C1) and a first resistor (R1) serially connected, and at least one damping element (R' ), wherein the first branch (11) is connected with an input voltage terminal (Vin_DC), characterized in that the damping circuit (10) further comprises a recognition control circuit, wherein the recognition control circuit comprises a detection function module and a switch function module, wherein the detection function module collects at least one detection signal representing a voltage change from the input voltage terminal (Vin_DC) to generate a first control signal (S1) recognizing that a dimmer (1) is not connected upstream from the driver (100) and a second control signal (S2) recognizing that the dimmer (1) is connected upstream, or to generate a third control signal (S3) recognizing that the dimmer (1) having reached a predetermined dimming level is connected upstream from the driver (100) or a fourth control signal (S4) recognizing that the dimmer (1) does not reach the predetermined dimming level, and the switch function module controls an operation state of the damping element (R' ) according to the first control signal (S1) or the third control signal (S3) and according to the second control signal (S2) or the fourth control signal (S4). The damping circuit (10) of the present invention has a strong universality and the advantages of high efficiency and energy saving.

Description

Damping Circuit, LED Driver and LED Illuminating System Technical Field

The present invention relates to a damping circuit, an LED driver and an LED illuminating system.

Background Art

In current illuminating devices, especially in LED illuminat- ing devices, an improved design having a dimming function is provided for obtaining luminance adapted to different illumination environments. A prior LED illuminating device installed with a dimmer generally comprises a dimmer 1, LED driver 100 and a load LED 8, wherein the LED driver 100 com- prises a rectifying device 9, a damping circuit 10 and a power converter 7, as shown in Fig. 1. The damping circuit 10 generally comprises a capacitor CI, a resistor Rl and, for instance, a high-power damping element R' . The damping element R' is additionally provided for inhibiting flickering as an LED will be caused to flicker when a dimmer is connected with an LED driver for dimming operation. In such a damping circuit, a main current flows through the high-power damping element R' having a high resistance value or other damping elements. However, as the damping element R' consumes a lot of power, the power of the LED driver will be reduced. For example, a power loss of a driver of 15W can reach 4%. In addition, the service lifetime of electronic elements of the LED driver also will be adversely affected after an electrical energy lost on the damping element R' is converted to heat energy.

In order to improve the power of the LED driver, the power lost on the high-power damping resistor should be reduced; as a result, a dynamic switch is often used. The disadvantage of such method lies in that the dynamic switch used cannot recognize whether the driver is connected with a dimmer, i.e., an operation state of the dimmer cannot be recognized, which thus results in that, when a driver is not connected with the dimmer or the dimmer is not conducted, R' is still in an operation state and further affects an output power of the driver of the illuminating device.

Summary of the Invention

The object of the present invention lies in providing a damp- ing circuit used in an LED driver. The damping circuit can provide a high output power according to different practical requirements, reduces a power loss on a damping device in a non-dimming process, and has a strong universality.

A damping circuit used for a driver for inhibiting flickering is provided in the present invention. The damping circuit comprises a first branch formed by a first capacitor and a first resistor serially connected, and at least one damping element, wherein the first branch is connected with an input voltage terminal, characterized in that the damping circuit further comprises a recognition control circuit, wherein the recognition control circuit comprises a detection function module and a switch function module, wherein the detection function module collects at least one detection signal representing a voltage change from the input voltage terminal to generate a first control signal recognizing that a dimmer is not connected upstream from the driver and a second control signal recognizing that the dimmer is connected upstream, or to generate a third control signal recognizing that the dimmer having reached a predetermined dimming level is connected upstream from the driver or a fourth control signal recognizing that the dimmer does not reach the predetermined dimming level, and the switch function module controls an operation state of the damping element according to the first control signal or the third control signal and according to the second control signal or the fourth control signal . For example, the dimmer having reached the predetermined dimming level may be construed as a non-conductive state of the dimmer, and the dimmer not reaching the predetermined dimming level may be construed as a conductive state of the dimmer.

A start point of the design of the present invention lies in controlling the operation state of the damping element in the damping circuit according to a result of recognizing whether the dimmer is connected upstream from the LED driver by actively collecting the at least one detection signal representing the voltage change from the input voltage terminal . For instance, controlling the operation state of the high- power damping element can prevent the high-power damping element from maintaining an operation state in which energy is consumed. By controlling the damping element configured as an inductor, for example, noises produced during operation of the inductor can be reduced when the dimmer works . An LED driver using such damping circuit is adapted to an illuminating circuit having the dimmer, an illuminating circuit without a dimmer directly controlling a state of the illuminating device, and also adapted to different cases with a leading dimmer and with a trailing dimmer; moreover, the damping device can be controlled according to different applications so as to reduce unnecessary power loss as much as possible, for instance, a driving power of a driver of 15W can be improved by 2% or other performances of the damping circuit can be improved. A further improvement of the present invention lies in not only recognizing whether there is a dimmer but also further recognizing the operation state of the dimmer so as to, for example, turn on the high-power damping element when flickering is practically caused, for further improving the energy- saving effect.

According to a preferred embodiment of the present invention, the damping element is a power resistor, and the switch function module short-circuits the damping element according to the first control signal or the third control signal and turns on the damping element according to the second control signal or the fourth control signal, so that the driving efficiency of the damping circuit is improved and unnecessary power loss is reduced. According to a preferred embodiment of the present invention, the damping element is an inductor, and the switch function module turns on the damping element according to the first control signal or the third control signal and short-circuits the damping element according to the second control signal or the fourth control signal, so that noises produced during op- eration of the inductor are reduced when the dimmer works.

Preferably, the detection function module comprises a first detecting module, the switch function module comprises a first switch module, the first detecting module collects a first detection signal from a first detection signal terminal between the first capacitor and the first resistor to generate the first control signal and the second control signal, and the first switch module controls the operation state of the damping element according to the first control signal and the second control signal. Collecting the first detection signal from the first detection signal terminal between the first capacitor and the first resistor can well reflect voltages applied on the first resis

tor and the power resistor, and can well represent a rate of change of an input voltage rectified so that whether the dimmer is connected or not can be detected.

In order to improve the universality of the damping circuit and realize cooperation with the leading dimmer, the first detecting module comprises a first detecting unit for generating the first control signal and the second control signal recognizing whether the leading dimmer is connected upstream. Preferably, the first detecting unit outputs a low-level signal as the first control signal when the leading dimmer is not connected upstream or outputs a high-level signal as the second control signal when the leading dimmer is connected upstream. As phase-cut dimmer used by different illuminating devices is divided into leading dimmer and trailing dimmer, different detecting units are taken into consideration for the leading dimmer and the trailing dimmer, improving the universality .

According to an exemplary embodiment of the present inven- tion, the first detecting unit comprises a first diode, a second resistor and a third resistor serially connected, and a second capacitor, wherein an Anode of the first diode is connected with the first detection signal terminal, and a Cathode of the first diode is connected with one terminal of the second resistor, the second capacitor is connected in parallel to the second resistor and the third resistor serially connected, a signal terminal of a control signal is provided between the second resistor and the third resistor for inputting the first or second control signal into the first switch module, and the other terminal of the third resistor is connected with a ground potential.

Preferably, the first detecting unit outputs a low-level signal as the first control signal when the leading dimmer is not connected upstream or outputs a high-level signal as the second control signal when the leading dimmer is connected upstream .

According to an exemplary embodiment of the present invention, the first detecting unit comprises a first diode, a second resistor and a third resistor serially connected, and a second capacitor, wherein an Anode of the first diode is connected with the first detection signal terminal, and a Cathode of the first diode is connected with one terminal of the second resistor, the second capacitor is connected in parallel to the second resistor and the third resistor seri- ally connected, a signal terminal of a control signal is provided between the second resistor and the third resistor for inputting the first or second control signal into the first switch module, and the other terminal of the second re- sistor is connected with a ground potential. In cases where the function of detecting simultaneously the leading dimmer and the trailing dimmer is provided, the Anode of the first diode can be indirectly connected with the first detection signal terminal. The first detecting unit can use a small number of elements to precisely generate the first control signal and the second control signal detecting whether the leading dimmer is connected upstream, having the advantages of a low cost and a high detection precision.

Preferably, the first switch module comprises a first switch element. The first switch element preferably is a first transistor, the damping element is connected between a working electrode and a reference electrode of the first transistor, and the reference electrode of the first transistor is connected to a ground potential. The use of the first switch element achieves the direct control on the damping element.

According to a preferred embodiment of the present invention, the first switch module further comprises a first clamping circuit for the first transistor, wherein the first clamping circuit comprises a fourth capacitor and/or a first voltage stabilizing diode connected between a control electrode of the first transistor and the ground potential. The control electrode of the first transistor can be controlled with the first clamping circuit in different situations. In cases where the fourth capacitor is used in the first clamping cir- cuit, a current still can be assured to flow through the power resistor during dimming, serving a certain damping function and preventing light flickering caused by current shake of the dimmer.

Preferably, the first switch module further comprises a sec- ond switch element for controlling on and off of the first switch element according to the first control signal and the second control signal from a signal terminal . The second switch element, operating in cooperation with the first control signal at a low level or the second control signal at a high level, is a second transistor that has a control electrode connected with the signal terminal, a working electrode connected with the control electrode of the first transistor and a reference electrode connected to the ground potential .

According to a preferred embodiment of the present invention, the first switch module further comprises a second clamping circuit for the second transistor, and the second clamping circuit comprises a third capacitor and/or a second voltage stabilizing diode connected between the control electrode of the second transistor and the ground potential. A voltage of the control electrode of the second transistor is controlled with the second clamping circuit.

According to a further preferred embodiment of the present invention, the first switch module further comprises a third voltage stabilizing diode that has one terminal connected with the signal terminal and the other terminal connected with the control electrode of the second transistor. The third voltage stabilizing diode is used for further assuring that the second transistor may be started only when the third voltage stabilizing diode is turned on so as to control a voltage of the control electrode of the second transistor.

According to a preferred embodiment of the present invention, the damping circuit further comprises a second branch connected with the input voltage terminal, the second branch comprises a fifth resistor and a sixth resistor serially connected as dropping resistors, and a control electrode of the first transistor is connected between the fifth resistor and the sixth resistor. A stable high-level voltage can be applied on the first transistor by selecting suitable resis- tance values of the fifth resistor and the sixth resistor, and subsequently, the first control signal and the second control signal exert influences thereon.

According to a preferred embodiment of the present invention, in order to improve the universality of the damping circuit and realize cooperation with the trailing dimmer, a second detecting unit is provided. The second detecting unit comprises a fifth capacitor and a second diode, wherein the fifth capacitor has one terminal connected with the first detection signal terminal, and the other terminal connected with the Anode of the first diode and a Cathode of the second diode, respectively, and an Anode of the second diode is connected with the other terminal of the third resistor. Requirements of the trailing dimmer are also satisfied by using the second detecting unit in combination with the first de- tecting unit. The fifth capacitor, the second diode and the first diode adjust the first detection signal to be at a high level .

According to a preferred embodiment of the present invention, in order to improve the recognition control function of the damping circuit, the detection function module comprises a second detecting module that generates the third control signal recognizing whether the dimmer having reached the predetermined dimming level is connected upstream or the fourth control signal recognizing that the dimmer does not reach the predetermine dimming level. In an exemplary embodiment, the second detecting module is a third branch formed by a seventh resistor and an eighth resistor and connected with the input voltage terminal, and the third control signal or the fourth control signal is output from between the seventh resistor and the eighth resistor, so that a voltage after voltage output division from the voltage input terminal is directly obtained .

Corresponding to this preferred embodiment, the switch func- tion module comprises a second switch module, the first switch module controls on and off of the damping element according to the second control signal, and the second switch module controls the on and off of the damping element according to the third control signal or the fourth control signal . According to a preferred embodiment, the second switch module comprises a third transistor, a fourth transistor, a fourth voltage stabilizing diode and a ninth resistor, wherein the third transistor has a working electrode connected with a reference electrode of the second transistor, and a reference electrode connected with the ground potential, and the fourth transistor has a control electrode connected with the fourth voltage stabilizing diode, and a working electrode connected with a working electrode of the second transistor via the ninth resistor and the working electrode also connected with a control electrode of the third transistor, so that the de- tecting and controlling capabilities of the damping circuit are further improved, improving the illuminating efficiency of the LED driver to which it belongs.

The present invention further relates to a driver and an il- luminating system.

It shall be understood that both the above general description and the following detailed description are for illustrative and explanative purposes in order to provide further description of the claimed present invention. Brief Description of the Drawings

The accompanying drawings constitute a part of the present Description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention and are used to de- scribe the principles of the present invention together with the Description. In the accompanying drawings the same components are represented by the same reference numbers. As shown in the drawings :

Fig. 1 shows a layout of a dimmer and an LED driver in the prior art;

Fig. 2a is a damping circuit of a first exemplary embodiment of the present invention;

Fig. 2b is another example of the application of the damping circuit of the first exemplary embodiment of the present in- vention; Figs. 3a-3b and Figs. 4a-4b are schematic diagrams of non- rectified input voltage waveforms and corresponding voltage waveforms of a control electrode of a first transistor with a leading dimmer and a tailing dimmer respectively in the first exemplary embodiment of the present invention;

Fig. 5a is a damping circuit of a second exemplary embodiment of the present invention;

Fig. 6a shows waveforms of a voltage after rectification at an input voltage terminal, a voltage after rectification at a first detection signal terminal and a current flowing into a damping element at this time, with the leading dimmer in the damping circuit according to the first and second exemplary embodiments of the present invention;

Fig. 6b shows waveform comparison charts of voltages after rectification at the input voltage terminal, without and with the leading dimmer in the damping circuits according to the first and second exemplary embodiments;

Fig. 6c shows a waveform comparison chart of a voltage of a control electrode of the first transistor, without and with the leading dimmer in the damping circuits according to the first and second exemplary embodiments; and

Fig. 7 is a damping circuit of a third exemplary embodiment of the present invention.

Detailed Description of the Embodiments Fig. 2a is a damping circuit 10 of a first exemplary embodiment of the present invention. The damping circuit 10 of the present invention comprises a first capacitor CI, a first resistor Rl and a damping element or a high-power element mainly serving a function of inhibiting flickering, for instance, the high-power damping element in the present exem- plary embodiment is a power resistor. It should be indicated that the first capacitor CI, the first resistor Rl and the power resistor, for example, are the same as that in the prior art and serve a main function of inhibiting flickering.

In the first exemplary embodiment of the present invention, the damping circuit 10 of the present invention further comprises a recognition control circuit. After the recognition control circuit is added, the damping circuit 10 of the present invention has a dimmer recognition function and a corresponding control function performed according to the dimmer recognition function. For example, the damping circuit 10 can control to short-circuit a power resistor when recognizing that a dimmer is not connected upstream from a driver and it can control to enable the power resistor when recognizing that the dimmer is connected upstream from the driver, so that a good energy- saving effect is achieved. Of course, as shown in other embodiments (e.g., Fig. 2b), the damping circuit 10 also can control other damping elements such as an inductor L2. It can control the inductor L2 to be connected when recognizing that the dimmer is not connected upstream from the driver for improving EMI and PF performances, and it can control to short-circuit the inductor L2 when recognizing that the dimmer is connected upstream from the driver, so that noises brought by operation of the inductor L2 are reduced . The recognition control circuit of the damping circuit 10 of the present invention comprises a detection function module and a switch function module. In order to generate a first control signal SI recognizing that a dimmer 1 is not connected upstream from the driver 100 and a second control sig- nal S2 recognizing that the dimmer 1 is connected upstream, the damping circuit 10 comprises a first detecting module 4, and the switch function module comprises a first switch module 5.1. The first detecting module 4 collects at least one detection signal representing a voltage change from an input voltage terminal Vin_DC to generate the first control signal SI recognizing that the dimmer 1 is not connected upstream from the driver 100 and the second control signal S2 recognizing that the dimmer 1 is connected upstream. In this exemplary embodiment, the first detecting module 4 collects a first detection signal from a first detection signal terminal V_Detectorl between the first capacitor CI and the first resistor Rl to generate the first control signal SI and the second control signal S2.

In order to enhance the universality of the damping circuit 10 of the present invention, the first detecting module comprises a first detecting unit 4.1 for generating the first control signal SI and the second control signal S2 recognizing whether the leading dimmer is connected upstream. As shown in Fig. 2a, the first detecting unit 4.1 comprises a first diode Dl, a second resistor R2 and a third resistor R3 serially connected, and a second capacitor C2 , wherein an Anode of the first diode Dl is connected with the first detection signal terminal V_Detectorl, and a Cathode of the first diode Dl is connected with one terminal of the second resis- tor 2, the second capacitor C2 is connected in parallel to the serially connected second resistor R2 and third resistor R3 , a signal terminal V_out of a control signal is provided between the second resistor R2 and the third resistor R3 for inputting the first or second control signal SI, S2 into the first switch module 5.1, and the other terminal of the third resistor R3 is connected with a ground potential. The first diode Dl, the second resistor R2 and the third resistor R3 serially connected, and the second capacitor C2 form the first detecting unit 4.1.

In order to carry out a control process according to the first or second control signal SI, S2, the first switch module 5.1 comprising a first switch element is provided, wherein the first switch element is a first transistor Ql, a damping element R' is connected between a working electrode and a reference electrode of the first transistor Ql, and the reference electrode of the first transistor Ql is connected to the ground potential. The first switch module 5.1 further comprises a second switch element for controlling on and off of the first switch element according to the first control signal SI and the second control signal S2 from the signal terminal V_out . The second switch element is a second transistor Q2 that has a control electrode connected with the signal terminal V_out, a working electrode connected with the control electrode of the first transistor Ql and a reference electrode connected with the ground potential. In this exem- plary embodiment, the first switch module 5.1 further comprises a first clamping circuit for the first transistor Ql, wherein the first clamping circuit comprises a fourth capacitor C4 and/or a first voltage stabilizing diode Dl' connected between the control electrode of the first transistor Ql and the ground potential for controlling a voltage level of the control electrode of the first transistor Ql . The damping circuit 10 of the present invention further comprises a second branch 12 that is different from a first branch 11 and connected with the input voltage terminal Vin_DC. The second branch 12 comprises a fifth resistor R5 and a sixth resistor R6 serially connected as dropping resistors. The control electrode of the first transistor Ql is connected between the fifth resistor R5 and the sixth resistor R6.

In this exemplary embodiment, a symmetrical sine wave voltage (see Fig. 3a) is converted to be one-way sine voltage (curve 1' in Fig. 6a) after adjusted by the rectifying device 9, as a result, in the present embodiment, a voltage value of the first detection signal terminal V_Detectorl detecting a rate or level of a voltage change input into the input voltage terminal Vin_DC is V_Ri,_R- =C1 (Rl+R' ) dv/dt .

It can be seen in conjunction with Fig. 6a that in cases where the leading dimmer is added, a voltage waveform at the input voltage terminal Vin_DC after rectification with the leading dimmer connected in the damping circuit 10 is one-way sine voltage (as shown curve 1' in Fig. 6a, taking a phase cut angle of 90° as an example, and curve 5' shown in Fig. 6b) . After conversion with formula V_R1;R- =C1 (Rl+R' ) dv/dt , it can be seen that the voltage waveform at the first detection signal terminal V_Detectorl is as shown by curve 3' in Fig. 6a. Therefore, the first detecting unit 4.1 generates a high-level signal effecting on the second transistor Q2 to enable the second transistor Q2 to be turned on. As the second transistor Q2 is turned on, a voltage of the control electrode of the first transistor Ql is reduced to be at a low level (see the voltage waveform of the control electrode of the first transistor Ql shown in Fig. 3b, and curve 7' in Fig. 6c) . At this time, the first transistor Ql is disabled, and then a current having a current waveform as shown by curve 11' in Fig. 6a flows through the power resistor R' . In cases where the leading dimmer is connected upstream, a voltage waveform of the input voltage terminal Vin_DC is shown by curve 4' in Fig. 6b, at which time, as a voltage effecting on the first resistor Rl and the power resistor R' , i.e., a voltage on the first detection signal terminal V_Detectorl, is quite low, a quite low dv/dt value is generated. Accordingly, upon voltage detection and voltage division, a level on the third resistor R3 in the first detecting unit 4,1 is quite low and is not sufficient to turn on the second transistor Q2. As the first transistor Ql is con- trolled by the first clamping circuit (which may be considered to be formed by one or two of the fourth capacitor C4 and the first voltage stabilizing diode Dl') and the resistors R5 , R6 in the second branch 12, a stable high-level voltage can be applied on the first transistor Ql by select- ing suitable resistance values of the dropping resistors R5 , R6 (see curve 6' in Fig. 6c) , as a result, the first transistor Ql is turned on, and the power resistor R' is short- circuited .

In order to further enhance the universality of the damping circuit 10 of the present invention, the first detecting module 4 comprise a second detecting unit 4.2 generating, together with the first detecting unit 4.1, the first control signal SI and the second control signal S2 recognizing whether a trailing dimmer is connected upstream. The second detecting unit 4.2 comprises a fifth capacitor C5 and a second diode D2 , wherein the fifth capacitor C5 has one terminal connected with the first detection signal terminal V_Detectorl, and the other terminal connected with the Anode of the first diode Dl and a Cathode of the second diode D2 , respectively, and an Anode of the second diode D2 is con- nected with the other terminal of the third resistor R3. At this time, when the trailing dimmer is connected, a symmetrical sine wave voltage of the trailing dimmer (see Fig. 4a) is converted to one-way sine voltage after adjusted by the rectifying device 9, and a level different from that of the leading dimmer 1 is generated after conversion of a voltage signal from the first detection signal terminal V_Detectorl according to formula V_Ri,_R- =C1 (Rl+R' ) dv/dt , at this time, a voltage signal from the first detection signal terminal V_Detectorl is adjusted to be at a high level using the fifth capacitor C5, the first diode Dl and the second diode D2 for performing corresponding control. A high-level signal effecting on the second transistor Q2 is generated using the first detecting unit 4.1 and the second detecting unit 4.2 to enable the second transistor Q2 to be turned on. As the sec- ond transistor Q2 is turned on, a gate voltage of the first transistor Ql is reduced to a low level (see the voltage waveform of the control electrode of the first transistor Ql shown in Fig. 4b) . At this time, the first transistor Ql is turned off, and therefore, a current flows through the power resistor R' .

Fig. 5a is a damping circuit 10 of a second exemplary embodiment of the present invention. Most of contents in Fig. 5a are the same as that in the first exemplary embodiment in Fig. 2a. Differently, Fig. 5a takes detecting whether a leading dimmer 1 is connected upstream as example to further enrich and perfect the first exemplary embodiment. For exam- pie, in order to further control a voltage of the control electrode of the second transistor Q2 in Fig. 5, the first switch module 5.1 further comprises a second voltage stabilizing diode D2 ' that is connected between the control elec- trode of the second transistor Q2 and the ground potential and forms a second clamping circuit together with the third capacitor C3 that is also connected between the control electrode of the second transistor Q2 and the ground potential. An additional difference is that the first switch module 5.1 further comprises a third voltage stabilizing diode D3 ' that has one terminal connected with the signal terminal V_out and the other terminal connected with the control electrode of the second transistor Q2 for further controlling a voltage of the control electrode of the second transistor Q2. For exam- pie, when the dimmer 1 is not connected, upon voltage detection and division, there is no sufficient voltage to turn on the third voltage stabilizing diode D3 ' and subsequently to turn on the second transistor Q2.

Fig. 6a shows waveforms of a voltage at the input voltage terminal, a voltage at the first detection signal terminal and a current flowing into the damping element at this time, after rectification, with the leading dimmer in the damping circuit of the first and second exemplary embodiments of the present invention; Fig. 6b shows waveform comparison charts of voltages at the input voltage terminal, after rectification, without and with the leading dimmer, in the damping circuits of the first and second exemplary embodiments; and Fig. 6c shows a waveform comparison chart of a voltage of the control electrode of the first transistor, without and with the leading dimmer, in the damping circuits of the first and second exemplary embodiments. Specific concepts of the first and second exemplary embodiments of the present invention can be seen clearly in conjunction with curves 1', 3' and 11' in Fig. 6a, curves 4' and 5' in Fig. 6b, and curves 6' and 7' in Fig. 6c. Fig. 7 is a damping circuit 10 of a third exemplary embodiment of the present invention. The damping circuit 10 of Fig. 7 makes further improvements on the damping circuits of Fig. 5 and Fig. 6. In addition to capability of recognizing whether a dimmer 1 is connected upstream, the damping circuit 10 also can recognize whether the dimmer 1 reaches a predetermined dimming level . The predetermined dimming level can be, for instance, non-conductive state of the dimmer 1, and a non-predetermined dimming level can be conductive state of the dimmer 1. Therefore, the recognition control circuit of the present invention generates a third control signal S3 recognizing whether the dimmer 1 reaching the predetermined dimming level is connected upstream or a fourth control signal S4 recognizing that the dimmer 1 does not reach the predetermined dimming level. A switch function module controls an operation state of the damping element R' according to the third control signal S3 or the fourth control signal S4. Therefore, compared with the first exemplary embodiment and the second exemplary embodiment of the present invention, corresponding detecting module and switch module are added in the third embodiment. In this exemplary embodiment, the detection function module further comprises a second detecting module 6 that generates the third control signal S3 recognizing whether the dimmer 1 having reached the predetermined dimming level is connected upstream or the fourth control signal S4 recognizing that the dimmer 1 does not reach the predetermine dimming level. In this exemplary embodiment, the second detecting module 6 is a third branch formed by a seventh resistor R7 and an eighth resistor R8 connected with the input voltage terminal Vin_DC, and the third control signal S3 or the fourth control signal S4 is output from between the seventh resistor R7 and the eighth resistor R8. Correspondingly, the switch function module further comprises a second switch module 5.2 that comprises a third transistor Q3 , a fourth transistor Q4 , a fourth voltage stabilizing diode D4 ' and a ninth resistor R9, wherein the third transistor Q3 has a working electrode connected with the reference electrode of the second transistor Q2 , and a reference electrode connected with the ground potential, and the fourth transistor Q4 has a control electrode connected with the fourth voltage stabilizing diode D4 ' , a working electrode connected with the working electrode of the second transistor Q2 via the ninth resistor R9, and a working electrode connected with the control electrode of the third transistor Q3.

Next, the working principle and operation process of detecting whether the dimmer 1 reaches the predetermined dimming level in this exemplary embodiment will be explained in detail .

A leading dimmer is taken as an example. If there is a dimmer 1 connected upstream, a level on the third resistor R3 of the first detecting unit 4.1 comprising the first diode Dl, serially connected second resistor R2 and third resistor R3 , and the second capacitor C2 is quite high, the third diode D3 ' is turned on, and a high level is present on the control electrode of the second transistor Q2. When the dimmer 1 reaches the predetermined dimming level, for instance, the dimmer 1 is not turned on, a level on the eighth resistor R8 is quite low, the fourth voltage stabilizing diode D4 ' is not turned on, a level on the working electrode of the fourth transistor Q4 , i.e., a level of the control electrode of the third transistor Q3 , is quite high, the third transistor Q3 and the second transistor Q2 are turned on, and the first transistor Ql is turned off as a level of the control electrode thereof is dropped; when a conduction edge of the dimmer 1 arrives, a level of the eighth resistor R8 increases, the fourth voltage stabilizing diode D4 ' is turned on, the fourth transistor Q4 is turned on and the third transistor Q3 is turned off, the first transistor Ql will be turned on after the fourth capacitor C4 is charged for a period of time. This fixed period can assure that a current still flows through the damping element R' when a rising edge arrives, serving a certain damping function and preventing light flickering caused by current shake of the dimmer 1.

The damping circuit of the present invention can cooperate with converters of different types of the LED driver, for example, it can cooperate with different topologies such as flyback converter and buck converter.

The above is merely preferred embodiments of the present invention but not to limit the present invention. For the person skilled in the art, the present invention may have various alterations and changes. Any alterations, equivalent substitutions, improvements, within the spirit and principle of the present invention, should be covered in the protection scope of the present invention. List of reference signs

I dimmer

S1-S4 first, second, third, fourth control signals

4 first detecting module

4.1 first detecting unit

4.2 second detecting unit

5.1 first switch module

5.2 second switch module

6 second detecting module

7 power converter

8 load LED

9 rectifying device

10 damping circuit

II first branch

12 second branch 100 (LED) driver

V_out signal terminal

V_Detectorl first detection signal terminal

Vin_DC input voltage terminal

R' damping element

Rl , R2 , ...R9 first, second, ...ninth resistors

CI, C2 , ...C5 first, second, ...fifth capacitors

Dl, D2 first, second diodes

Dl', D2', D3', D4' first, second, third and fourth volt age stabilizing diodes

Ql, Q2 , Q3 , Q4 first, second, third and fourth tran sistors

Claims

Patent claims

1. A damping circuit (10), used for a driver (100) for inhibiting flickering, comprising a first branch (11) formed by a first capacitor (CI) and a first resistor (Rl) serially connected, and at least one damping element (R' ) , wherein the first branch (11) is connected with an input voltage terminal (Vin_DC) , characterized in that the damping circuit (10) further comprises a recognition control circuit, wherein the recognition control circuit comprises a detection function module and a switch function module, wherein the detection function module collects at least one detection signal representing a voltage change from the input voltage terminal (Vin_DC) to generate a first control signal (SI) recognizing that a dimmer (1) is not connected upstream from the driver (100) and a second control signal (S2) recognizing that the dimmer (1) is connected upstream, or to generate a third control signal (S3) recognizing that the dimmer (1) having reached a predetermined dimming level is connected upstream from the driver (100) or a fourth control signal (S4) recognizing that the dimmer (1) does not reach the predetermined dimming level, and the switch function module controls an operation state of the damping element (R' ) according to the first control signal (SI) or the third control signal (S3) and according to the second control signal (S2) or the fourth control signal (S4) .

2. The damping circuit (10) according to Claim 1, characterized in that the damping element (R' ) is a power resistor, and the switch function module short-circuits the damping element (R' ) according to the first control signal (SI) or the third control signal (S3) and turns on the damping ele- ment (R' ) according to the second control signal (S2) or the fourth control signal (S4) .

3. The damping circuit (10) according to Claim 1, characterized in that the damping element (R' ) is an inductor, and the switch function module turns on the damping element (R' ) according to the first control signal (SI) or the third control signal (S3) and short-circuits the damping element (R' ) according to the second control signal (S2) or the fourth control signal (S4) .

4. The damping circuit (10) according to any one of Claims 1-3, characterized in that the detection function module comprises a first detecting module (4), the switch function module comprises a first switch module (5.1), the first detecting module (4) collects a first detection signal from a first detection signal terminal (V_Detectorl ) between the first capacitor (CI) and the first resistor (Rl) to generate the first control signal (SI) or the second control signal (S2), and the first switch module (5.1) controls the operation state of the damping element (R' ) according to the first control signal (SI) and the second control signal (S2) .

5. The damping circuit (10) according to Claim 4, characterized in that the first detecting module (4) comprises a first detecting unit (4.1) for generating the first control signal (SI) and the second control signal (S2) recognizing whether a leading dimmer (1) is connected upstream.

6. The damping circuit (10) according to Claim 5, characterized in that the first detecting unit (4.1) outputs a low- level signal as the first control signal (SI) when the lead- ing dimmer (1) is not connected upstream or outputs a high- level signal as the second control signal (S2) when the leading dimmer (1) is connected upstream.

7. The damping circuit (10) according to Claim 6, characterized in that the first detecting unit (4.1) comprises a first diode (Dl) , a second resistor (R2) and a third resistor (R3) serially connected, and a second capacitor (C2), wherein an Anode of the first diode (Dl) is connected with the first detection signal terminal (V_Detectorl ) , and a Cathode of the first diode (Dl) is connected with one terminal of the second resistor (2), the second capacitor (C2) is connected in parallel to the second resistor (R2) and the third resistor (R3) serially connected, a signal terminal (V_out) of a control signal is provided between the second resistor (R2) and the third resistor (R3) for inputting the first or second control signal (SI, S2) into the first switch module (5.1), and the other terminal of the third resistor (R3) is connected with a ground potential .

8. The damping circuit (10) according to Claim 4, characterized in that the first switch module (5.1) comprises a first switch element.

9. The damping circuit (10) according to Claim 8, characterized in that the first switch element is a first transistor (Ql) , the damping element (R' ) is connected between a working electrode and a reference electrode of the first transistor (Ql) , and the reference electrode of the first transistor (Ql) is connected to a ground potential.

10. The damping circuit (10) according to Claim 9, charac- terized in that the first switch module (5.1) further comprises a first clamping circuit for the first transistor (Ql) , wherein the first clamping circuit comprises a fourth capacitor (C4) and/or a first voltage stabilizing diode (Dl') connected between a control electrode of the first transistor (Ql) and the ground potential.

11. The damping circuit (10) according to Claim 8, characterized in that the first switch module (5.1) further comprises a second switch element for controlling on and off of the first switch element according to the first control signal (SI) and the second control signal (S2) from a signal terminal (V_out) .

12. The damping circuit (10) according to Claim 11, characterized in that the second switch element is a second transistor (Q2) that has a control electrode connected with the signal terminal (V_out) , a working electrode connected with the control electrode of the first transistor (Ql) and a reference electrode connected to the ground potential .

13. The damping circuit (10) according to Claim 12, characterized in that the first switch module (5.1) further comprises a second clamping circuit for the second transistor (Q2), and the second clamping circuit comprises a third capacitor (C3) and/or a second voltage stabilizing diode (D2') connected between the control electrode of the second transistor (Q2) and the ground potential.

14. The damping circuit (10) according to Claim 12, characterized in that the first switch module (5.1) further comprises a third voltage stabilizing diode (D3') that has one terminal connected with the signal terminal (V_out) and the other terminal connected with the control electrode of the second transistor (Q2) .

15. The damping circuit (10) according to Claim 7, characterized in that the damping circuit (10) further comprises a second branch (12) connected with the input voltage terminal (Vin_DC) , the second branch (12) comprises a fifth resistor (R5) and a sixth resistor (R6) serially connected as dropping resistors, and a control electrode of the first transistor (Ql) is connected between the fifth resistor (R5) and the sixth resistor (R6) .

16. The damping circuit (10) according to Claim 7, characterized in that the first detecting module (4) comprise a second detecting unit (4.2) generating, together with the first detecting unit (4.1), the first control signal (SI) and the second control signal (S2) for recognizing whether a trailing dimmer (1) is connected upstream.

17. The damping circuit (10) according to Claim 16, characterized in that the second detecting unit (4.2) comprises a fifth capacitor (C5) and a second diode (D2), wherein the fifth capacitor (C5) has one terminal connected with the first detection signal terminal (V_Detectorl ) , and the other terminal connected with the Anode of the first diode (Dl) and a Cathode of the second diode (D2), respectively, and an Anode of the second diode (D2) is connected with the other terminal of the third resistor (R3) .

18. The damping circuit (10) according to any one of Claims 2-17, characterized in that the detection function module further comprises a second detecting module (6) that generates the third control signal (S3) recognizing whether the dimmer (1) having reached the predetermined dimming level is connected upstream or the fourth control signal (S4) recognizing that the dimmer (1) does not reach the predetermine dimming level .

19. The damping circuit (10) according to Claim 18, characterized in that the second detecting module (6) is a third branch formed by a seventh resistor (R7) and an eighth resistor (R8) and connected with the input voltage terminal (Vin_DC) , and the third control signal (S3) or the fourth control signal (S4) is output from between the seventh resistor (R7) and the eighth resistor (R8) .

20. The damping circuit (10) according to Claim 19, characterized in that the switch function module further comprises a second switch module (5.2), the first switch module (5.1) controls the operation state of the damping element (R' ) according to the second control signal (S2), and the second switch module (5.2) controls the operation state of the damping element (R' ) according to the third control signal (S3) or the fourth control signal (S4) .

21. The damping circuit (10) according to Claim 20, characterized in that the second switch module (5.2) comprises a third transistor (Q3), a fourth transistor (Q4), a fourth voltage stabilizing diode (D4') and a ninth resistor (R9) , wherein the third transistor (Q3) has a working electrode connected with a reference electrode of the second transistor (Q2), and a reference electrode connected with the ground potential, and the fourth transistor (Q4) has a control elec- trode connected with the fourth voltage stabilizing diode (D4')# and a working electrode connected with a working electrode of the second transistor (Q2) via the ninth resistor (R9) and connected with a control electrode of the third transistor (Q3) .

22. A driver (100) comprising the damping circuit (10) according to any one of Claims 1-21.

23. An illuminating system comprising the driver (100) according to Claim 22.