WO2013102548A1

WO2013102548A1 - Led driving circuit and illumination device including the same

Info

Publication number: WO2013102548A1
Application number: PCT/EP2012/075746
Authority: WO
Inventors: Hui JIA; Yaping Liu; Middel TJACO; Xuewei Dai
Original assignee: Osram Gmbh
Priority date: 2012-01-06
Filing date: 2012-12-17
Publication date: 2013-07-11
Also published as: CN103200727A

Abstract

The present invention discloses a LED driving circuit and an illumination device including the same, the LED driving circuit including: a power factor correction circuit configured to correct a power factor of a circuit; one or more LED loads; a feedback circuit configured to provide a feedback signal regarding the one or more LED loads to a power factor correction controller; and a power factor correction controller configured to control the power factor correction circuit based on the feedback signal provided by the feedback circuit so as to keep an output of the power factor correction circuit constant. According to the technical solution of the invention, it is possible to implement driving of the LED illumination device while obtaining a high power factor value with a relatively simple circuit structure and a low cost, and to achieve stable luminous intensity.

Description

LED DRIVING CIRCUIT AND ILLUMINATION DEVICE INCLUDING THE SAME

Field of the Invention

The present invention relates to a light emitting diode (LED) driving circuit and an illumination device including the same, and particularly, to a LED driving circuit and an illu- mination device including the same which are capable of achieving a high power factor (PF) value and stable luminous intensity with a simple circuit structure and a low cost.

Background of the Invention

In recent years, the light emitting diode (LED) has been widely used in the illumination device due to its characteristics such as high luminous efficiency, long lifetime, high brightness, energy saving, environmental friendliness as well as robust and durable. However, more and more harmonics have been injected into the power system due to the use of traditional LED driving circuit utilizing a switching power supply, resulting in increasingly serious harmonic pollution in the power grid, thus influencing power supply quality of the power grid and use safety for the user. The active power fac- tor correction (APFC) technology is an effective approach to increase the power factor of electronic appliance, reduce pollution of the power grid and depress influence of the harmonics. Therefore, nowadays, "green power grid" and "green illumination" are advocated, thus the active power factor correction technology has become a focus of research.

In the prior art, the conventional active power factor correction circuit includes a boost, a buck, a buck-boost, a forward and a flyback power factor correction circuits. In the field of LED illumination, an existing implementing scheme of the LED driver is usually constituted by an active power factor correction circuit and a specialized driving circuit, which is very complex and has a high cost, and further there may exist a problem of flicker.

Summary of the Invention

The brief summary of the invention will be given below to provide basic understanding of some aspects of the invention. However, it shall be appreciated that this summary is neither exhaustively descriptive of the invention nor intended to define essential or important components or the scope of the invention but is merely for the purpose of presenting some concepts of the invention in a simplified form and hereby acts as a preamble of more detailed descriptions which will be presented later.

Therefore, in view of the foregoing circumstances, an object of the invention is to provide a LED driving circuit capable of implementing power factor correction while maintaining stable luminous intensity. Such a LED driving circuit can increase a power factor value of the circuit without separately providing a specialized driving circuit or a power factor correction circuit, thus the circuit implementation is rela- tively simple and the cost is significantly reduced. Furthermore, monitoring of a load output is added in this LED driving circuit, thus the power factor correction circuit can be adjusted correspondingly in accordance with the state of the load output so as to keep the output of the circuit constant, so that flicker of LED illumination device can be eliminated and comfort on use is enhanced for the user.

According to an embodiment of the invention, there is pro- vided a LED driving circuit, including: a power factor correction circuit configured to correct a power factor of a circuit; one or more LED loads; a feedback circuit configured to provide a feedback signal regarding the one or more LED loads to a power factor correction controller; and a power factor correction controller configured to control the power factor correction circuit based on the feedback signal provided by the feedback circuit so as to keep an output of the power factor correction circuit constant.

According to a preferred embodiment of the invention, the feedback circuit may include: a signal detection module configured to detect a signal regarding the one or more LED loads; and a signal conversion module configured to convert the detected signal to be the feedback signal .

According to a preferred embodiment of the invention, the power factor correction circuit may be a boost power factor correction circuit.

According to a preferred embodiment of the invention, the one or more LED loads may be connected in series between an input terminal and an output terminal of the power factor correction circuit.

According to a preferred embodiment of the invention, the one or more LED loads may be connected in series between an output terminal of the power factor correction circuit and the ground.

According to a preferred embodiment of the invention, the feedback circuit may further include a resistor connected between the one or more LED loads and the signal conversion module to power the signal conversion module using electric energy from the one or more LED loads.

According to another embodiment of the invention, there is also provided an illumination device including the foregoing LED driving circuit.

Brief Description of the Drawings

The invention can be better understood with reference to the detailed description given below in conjunction with the accompanying drawings, throughout which identical or like reference signs denote identical or like components and together with which the following detailed description is incorporated into and forms a part of the specification and serves to fur- ther illustrate the preferred embodiments of the invention and to explain the principle and advantages of the invention. In the drawings :

Fig. 1 is a block diagram illustrating functional configuration of a LED driving circuit according to an embodiment of the invention;

Fig.2 is a block diagram illustrating functional configuration of a feedback circuit in Fig. 1; and

Fig. 3 is a circuit diagram illustrating specific implementation of the LED driving circuit according to an embodiment of the invention.

Detailed Description of the Invention

Exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. For the sake of clarity and conciseness, not all the features of practical implementations are described in the specification. However, it is to be appreciated that numerous implementation-specific decisions shall be made during developing any of such practical implementations so as to achieve the developer's specific goals, for example, to comply with system- and business-related constraining conditions which will vary from one implementation to another. Moreover, it shall also be appreciated that such a development effort might be very complex and time-consuming but may simply be a routine task for those skilled in the art benefiting from this dis- closure.

It shall further be noted that only those device structures and/or process steps closely relevant to the solutions of the invention are illustrated in the drawings while other details less relevant to the invention are omitted so as not to ob- scure the invention due to those unnecessary details.

The preferred embodiments of the invention will be described with reference to Figs. 1-3 below.

First, the functional block diagram of the LED driving circuit according to the embodiment of the invention will be de- scribed with reference to Fig. 1. As shown in Fig. 1, the LED driving circuit may include a power factor correction circuit 101, one or more LED loads 102, a feedback circuit 103 and a power factor correction controller 104.

Specifically, the power factor correction circuit 101 may be configured to correct a power factor of a circuit. The power factor correction circuit 101 may be a well-known boost power factor correction circuit in the prior art, but the invention is not limited thereto, and those skilled in the art may choose different types of power factor correction circuits as required, e.g., a buck, buck-boost, forward or flyback power factor correction circuit, and to correspondingly change connections and directions between respective circuit components in accordance with principles of the invention, thus realizing corresponding technical effects.

Preferably, one or more LED loads 102 may be connected in series between an input terminal and an output terminal of the power factor correction circuit, or may be connected in se- ries between the output terminal of the power factor correction circuit and the ground potential. Particularly, the connection manner of the LED loads 102 depends on the type of the power factor correction circuit, for example, in case of the boost power factor correction circuit, the anode terminal of the LED load is connected to the output terminal of the power factor correction circuit while the cathode terminal of the LED load is connected to the input terminal of the power factor correction circuit since the output voltage of the power factor correction circuit is higher than the input voltage thereof.

The feedback circuit 103 may be configured to provide a feedback signal regarding the one or more LED loads 102 to the power factor correction controller 104. The feedback signal may be a current or voltage signal regarding the load output.

The power factor correction controller 104 may be configured to control the power factor correction circuit 101 based on the feedback signal provided by the feedback circuit 103 so as to keep the output of the power factor correction circuit 101 constant, so that the LED loads 102 may illuminate at a constant brightness, the phenomenon such as flicker or the like is eliminated, and comfort on use is enhanced for the user .

The functional configuration of the feedback circuit 103 will be described in detail with reference to Fig. 2 below.

As shown in Fig. 2, the feedback circuit 103 may include a signal detection module 201 and a signal conversion module 202.

Specifically, the signal detection module 201 may be config- ured to detect a signal regarding one or more LED loads. The signal may be a current or voltage signal regarding the load output . The signal conversion module 202 may be configured to convert the current or voltage signal regarding the one or more LED loads detected by the signal detection module 201 to be the feedback signal usable by the power factor correction con- troller.

Preferably, the feedback circuit 103 may further include a resistor 203 which may be connected between the one or more LED loads and the signal conversion module 202 to power the signal conversion module 202 using electric energy from the load output. This design simplifies the power supply of the signal conversion module and is easy to implement, thus further reducing the cost.

Next, specific exemplary implementation of the LED driving circuit according to a preferred embodiment of the invention will be described in detail with reference to Fig. 3. It is to be noted that the following implementation of the circuit is merely exemplary, those skilled in the art may readily make various modifications, changes and variations to the following exemplary implementation as required according to the concepts and ideas of the invention.

As indicated by the dashed frame in Fig. 3, a boost power factor correction circuit U4 is constituted by an inductor LI, a diode Dl and a switching element Ql . The boost power factor correction circuit U4 has a well-known circuit struc- ture which will not be described in detail anymore herein. Particularly, the switching element Ql may be a metal oxide semiconductor field effect transistor (MOSFET) , an isolated gate bipolar transistor (IGBT) , a bipolar junction transistor (BJT) or the like which will not be limited herein. Prefera- bly, the boost power factor correction circuit U4 increases an input DC voltage to 400V (which is a typical output voltage value of the power factor correction circuit used for LED driving) for example. Moreover, as compared with other types of power factor correction circuits, the boost power factor correction circuit has advantages of easy regulation, easy driving of the switching element and high PF value.

One or more LED loads are connected between the input termi- nal and the output terminal of the power factor correction circuit, that is, between the input point 1 and the output point 2, as shown in FIG. 3. In this preferred embodiment, the voltage at the output point 2 is higher than that at the input point 1 since this power factor correction circuit is a boost circuit, thus the anode terminal of the LED is connected to the output point 2 while the cathode terminal is connected to the input point 1. Since there is always a voltage drop between the output point 2 and the input point 1, it is easy to implement driving for the LED load, and thus it is possible to drive the LED load without providing an additional driving circuit, while achieving correction for the power factor and thereby simplifying the circuit structure. Furthermore, such connection configuration of the LED load further implements voltage clamping between the input termi- nal and the output terminal of the power factor correction circuit (i.e., between point 1 and point 2), and thus facilitating stabilization of the voltage at the output point 2.

Alternatively, one or more LED loads may also be connected between the output point 2 of the power factor correction circuit and the ground.

In this preferred embodiment, the feedback circuit may be constituted by a signal detection module U3 , a signal conversion module Ul and a resistor R2.

Specifically, the output current of the LED load may be de- tected by the resistor Rl , and the current signal may be provided to the signal detection module U3. As an example, the signal detection module U3 may be implemented by LMV431. The resistor Rl is a sampling resistor for the current output from the load, thus a constant current can be realized by using LMV431, so that detection for the load output is more accurate .

It is to be understood that LMV431 mentioned herein is merely an exemplary implementation of the signal detection module without limitation, those skilled in the art may alternatively adopt other electronic devices as long as they can detect load signal .

The signal conversion module Ul may be realized by an optical couple device herein, which converts the load output current signal detected by the LMV431 to be a corresponding feedback signal and provides the converted feedback signal to the power factor correction controller U2.

It is to be understood that the signal conversion module implemented by the optical couple device is merely exemplary, those skilled in the art may also adopt other electronic devices as long as they can realize signal conversion function.

Further, in this embodiment, as shown in Fig. 3, the resistor R2 is connected between a point 8 between a plurality of LED loads and the optical couple device and powers the optical couple device with the electric energy from the load output, thereby simplifying power supply manner for the optical couple device and making the circuit implementation easier.

The power factor correction controller U2 may control the switching element Ql to turn on or off in accordance with the received feedback signal, thus regulating voltage at the output point 2 to remain at 400V for example, so that stable luminous intensity of the LED may be obtained and the flicker phenomenon of the LED may be eliminated.

According to the above embodiments, the LED driving circuit integrates the functions of power factor correction and LED driving in the same circuit, thus it is possible to implement driving of the LED illumination device while obtaining a high PF value with a simple circuit structure and a low cost, and to control the switching element of the power factor correc- tion circuit to turn on or off by the power factor correction controller based on the signal regarding states of the load provided by the feedback circuit, so as to keep the output of the power factor correction circuit constant, eliminate flicker phenomenon of the illumination device and improve user's experience.

Although specific implementation of the LED driving circuit according to the preferred embodiments of the invention has been described above in combination with Fig.3, it is to be understood that the circuit structure as shown in Fig. 3 and electronic components used in this circuit are only exemplary without limitation, and those skilled in the art may make various variations and alternations to the above circuit structure according to the principles taught by the invention as required.

Further, it is to be noted that the above series functions and devices may also be implemented through software and/or firmware. In case of being implemented through software and/or firmware, a program constituting the software is installed into a computer which is capable of executing various functions when installed with various programs from storage medium or network.

Those skilled in the art should understand that changes and modifications may be made to the invention in addition to the specific description set forth herein without departing from the scope of the invention. All such changes and modifications obvious to those skilled in the art are considered to fall within the spirit and scope of the invention. It is to be understood that all these changes and modifications are included in the invention. The invention also individually or collectively includes all the steps and features recited or indicated in the specification as well as any and all combinations of any two or more of the steps or features.

Claims

Patent claims

1. A light emitting diode (LED) driving circuit, comprising :

a power factor correction circuit configured to correct a power factor of a circuit; one or more LED loads; a feedback circuit configured to provide a feedback signal regarding the one or more LED loads to a power factor correction controller; and a power factor correction controller configured to control the power factor correction circuit based on the feedback signal provided by the feedback circuit so as to keep an output of the power factor correction circuit constant .

2. The LED driving circuit according to claim 1, wherein the feedback circuit comprises:

a signal detection module configured to detect a signal regarding the one or more LED loads; and a signal conversion module configured to convert the detected signal to be the feedback signal .

3. The LED driving circuit according to claim 1, wherein the power factor correction circuit is a boost power factor correction circuit.

4. The LED driving circuit according to claim 1, wherein the one or more LED loads are connected in series between an input terminal and an output terminal of the power factor correction circuit.

5. The LED driving circuit according to claim 1, wherein the one or more LED loads are connected in series between an output terminal of the power factor correction circuit and the ground.

6. The LED driving circuit according to claim 2, wherein the feedback circuit further comprises:

a resistor connected between the one or more LED loads and the signal conversion module to power the signal conversion module with electric energy from the one or more LED loads .

7. An illumination device comprising the LED driving circuit according to any one of claims 1-6.