Patent Publication Number: US-8981652-B2

Title: Apparatus and method for compensating current deviation

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to Korean Patent Application No. 10-2012-0003354, filed on Jan. 11, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present application relates to an apparatus and method for compensating for a current deviation of a light emitting diode (LED) array connected with a circuit. 
     BACKGROUND 
     A light emitting diode (LED) is preferred and popularized as an environment-friendly product. 
     The LED is manufactured by a semiconductor manufacturing process. Presently, research and development on the LED is being conducted actively. 
     Recently, due to various positive features of the LED, interest in the LED for lighting, having optical characteristics suitable for replacing conventional incandescent bulbs, is increasing. Accordingly, products in which the LED replaces a fluorescent lamp or incandescent bulb in conventional lighting systems are being put on the market. 
     Nowadays, LED lighting systems having brightness comparable to a level of conventional lighting systems are being developed. However, several research projects are still being conducted in many fields including an LED, a package, an optical system including the LED, and an LED control circuit. 
     Additionally, use of a high-output and high-brightness LED is increasing as an external pilot lamp of a car, for safer driving. 
     LED lamps for cars include an LED head lamp (H/L), a rear combination lamp (RCL), a center high mounted stop lamp (CHMSL), a daytime running lamp (DRL), a position lamp, and the like. An LED package mounting the RCL and the DRL occupies a main part. 
     With the increase in use of the LEDs for cars, when a plurality of LEDs is applied, a small number of LEDs are serially connected into strings and a plurality of the strings of LEDs is connected in parallel. 
     When constituting an LED array using the above parallel configuration, a current difference may be generated between respective parallel strings due to a current of the serially connected LEDs. 
     Since the LED is driven by a current, a constant current supply is necessary to maintain constant brightness. 
     Generally, a constant current driving integrated circuit (IC) or a microprocessor is used to achieve a constant current driving circuit. However, such devices may lead to an increase in manufacturing costs. 
     In general LED arrays, although a constant current source is used, a current flowing to each respective string may be different due to a deviation of current (V f ) of the LEDs connected to each of the respective strings. 
     SUMMARY 
     According to an aspect of the present application, there is provided a current deviation compensating circuit. The circuit includes a light emitting diode (LED) array to which a plurality (i.e. two or more) of LEDs are connected. At least one constant current circuit is connected to each respective string of the LED array to compensate for a current deviation among each of the respective strings. 
     The at least one constant current circuit may set a current amount to be applied to each of the respective strings. 
     The at least one constant current circuit may control a power supply so that a current amount to be applied to each of the respective strings is uniform. 
     The respective strings of the at least one LED array are connected in parallel. 
     The at least one constant current circuit may be a constant current circuit driven through an application of external power. 
     The at least one constant current circuit may be an LED driving current circuit. 
     The at least one constant current circuit may compensate for a brightness deviation among each of the respective strings. 
     According to another aspect of the present application, there is provided a current deviation compensating method. The method includes the step of applying a current through a light emitting diode (LED) array to which a plurality (i.e. two or more) LEDs are connected. A current deviation is compensated among respective strings of the LED array using at least one constant current circuit connected to each of the respective strings. 
     The current deviation compensating method may further include the step of setting a current amount to be applied to the respective strings using the at least one constant current circuit. 
     The current deviation compensating method may further include the step of controlling a power supply so that a current amount to be applied to the respective strings is uniform using the at least one constant current circuit. 
     The current deviation compensating method may further include compensating for a brightness deviation among the strings using at least one constant current circuit. 
     Additional advantages and novel features will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The advantages of the present teachings may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed examples discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects, features, and advantages of the present application will become apparent and more readily appreciated from the following description of the examples, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a block diagram illustrating a structure of a current deviation compensating circuit according to an example of the present application; 
         FIG. 2  is a flowchart illustrating a method for compensating for a current deviation according to an example of the present application; and 
         FIGS. 3 and 4  are circuit diagrams illustrating actual examples of a current deviation compensating circuit according to examples of the present application. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings. 
     In the description of the present invention. if detailed descriptions of related disclosed art or configuration are determined to unnecessarily make the subject matter of the present invention obscure, they will be omitted. Terms to be used below are defined based on their functions in the present invention and may vary according to users, user&#39;s intentions, or practices. Therefore, the definitions of the terms should be determined based on the entire specification. 
     Reference will now be made in detail to the examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. 
       FIG. 1  is a block diagram illustrating a structure of a current deviation compensating circuit  100  according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the current deviation compensating circuit  100  may include a light emitting diode (LED) array  110  to which at least one LED is connected, and at least one constant current circuit  120  connected to string(s) of the LED array to compensate for a current deviation of each string. 
     Hereinafter, a method for compensating for the current deviation will be described with reference to  FIG. 2 . 
       FIG. 2  is a flowchart illustrating a method for compensating for a current deviation according to an example of the present application. 
     Referring to  FIG. 2 , the current deviation compensating circuit  100  applies a current through an LED array  110  to which at least one LED is connected, in operation  210 . 
     The current deviation compensating circuit  100  is supplied with a constant current from a constant current supply device (not shown). The constant current is supplied to the LED array  110  so that the at least one LED maintains a constant brightness. 
     According to an aspect of the present application, the constant current supply device generates a constant current control signal in accordance with a driving control signal input to drive a load, and generate a constant current corresponding to the constant current control signal. 
     In general LED arrays, although a constant current source is used, a current flowing in each respective string may be different due to a current deviation among the LEDs connected to each of the respective strings. Accordingly, since a current flowing in each of the respective strings is different in the LED array, brightness of the at least one LED connected to each of the respective strings may also be different. The current deviation compensating circuit  100  may minimize the current deviation among parallel arrays by applying a constant current feedback circuit to the LED array. 
     In operation  220 , the compensating circuit  100  may compensate for the current deviation of each of the respective strings using the at least one constant current circuit  120  connected to each of the respective strings of the LED array. 
     The at least one constant current circuit  120  may set a current amount to be applied to each of the respective strings. 
     The at least one constant current circuit  120  may control the current amount to be uniform. 
     That is, the current deviation compensating circuit  100  may connect a small constant current circuit to each of the respective strings, from which the current deviation may occur, in the LED array connected to a circuit including a constant current source. thereby setting a current amount to be applied to each of the respective strings. Accordingly, a constant current may flow without causing the current deviation. By compensating for the current deviation, the current deviation compensating circuit  100  may accordingly compensate for an error caused by a brightness deviation. 
       FIGS. 3 and 4  illustrate actual examples of a current deviation compensating circuit according to examples of the present application. 
     Referring to  FIG. 3 , at least one LED array  110  may include constant current circuits  330  and  340  driven by external power, to which strings  310  and  320  are connected in parallel, respectively. 
     For example, the constant current circuits  330  and  340  may apply external power of about 5 volts (V) direct current (DC) for driving a circuit, and control a current deviation of the strings  310  and  320 . 
     Referring to  FIG. 4 , the at least one constant current circuit  120  may compensate for the current deviation of strings  410  and  420  using an LED driving current circuit  430 . 
     For example, the at least one constant current circuit  120  may use an LED driving current to drive a circuit. A structure shown in  FIG. 4  may omit a dedicated input line. 
     The at least one constant current circuit  120  may compensate for a brightness deviation of each of the respective strings  410  and  420 . 
     The current deviation compensating apparatus  100  may compensate for the brightness deviation of the LEDs of the LED array by compensating for the deviation of current applied to each of the respective strings. 
     Since the brightness deviation is compensated, the current deviation compensating apparatus  100  may improve quality of products employing LED(s). For example, light distribution performance of a car may be increased. 
     According to the examples of the present application, a deviation of current flowing through each respective string of an LED array may be compensated for. 
     Also, a brightness deviation caused by a voltage applied to each respective string of an LED array may be compensated for. 
     In addition, the current deviation among parallel arrays may be minimized by applying a constant current feedback circuit to the LED array. 
     While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples. and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings.