Patent Publication Number: US-2019200428-A1

Title: Driving device and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 106145140, filed on Dec. 21, 2017. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a driving device, and more particularly, to a driving device and a driving method thereof that can stop generating a driving signal for a light emitting diode string when detecting that at least one group of the light emitting diode strings among multiple groups of light emitting diode strings is damaged. 
     2. Description of Related Art 
     With the advancement of semiconductor technology, traditional lighting equipments have been gradually replaced by light emitting diodes (LEDs) for generating illumination light sources. Owing to advantages of power saving, long lifetime, small volume and high reliability, the light emitting diodes have become a lighting device that can take both power saving and environmental protection into consideration. 
     In general, during factory processing or assembly, a light emitting diode string is prone to issues of electrostatic discharge (ESD) or electrical over stress (EOS) caused by factors like the assembly environment, which leads to damages on part of the light emitting diode strings before shipment. Moreover, if aforesaid issues occur when a group of light emitting diodes are already assembled onto an lighting equipment, it is difficult for staff members to detect the light emitting diodes one by one because the time consumed by doing so can seriously affect the subsequent production progress. Therefore, finding a way to effectively detect the malfunction light emitting diodes for subsequent maintenance and replacement is the problem to be addressed by persons skilled in the art. 
     SUMMARY OF THE INVENTION 
     The invention provides a driving device and a driving method thereof that can stop generating a driving signal for a light emitting diode string when detecting that at least one of the light emitting diode strings among multiple groups of light emitting diode strings is damaged. 
     The driving device of the invention includes at least one driving signal generator, respectively coupled to at least one light emitting diode string, and respectively generating at least one driving signal to drive the light emitting diode strings, respectively. At least one detection device is coupled to a detection point of the respective light emitting diode string and respectively coupled to the driving signal generators. The respective detection device compares a first detection voltage on the detection point of a corresponding first light emitting diode string with a plurality of second detection voltages on the detection points of a plurality of remaining second light emitting diode strings to generate a detection result. The respective driving signal generator determines whether to stop generating the respective driving signal according to the detection result generated by the corresponding detection device. 
     The driving method of the invention is adapted to drive at least one light emitting diode string, and includes: respectively generating at least one driving signal to drive the light emitting diode strings, respectively, and generating a plurality of detection voltages on a plurality of detection points of the light emitting diode strings; comparing a first detection voltage among the detection voltages with a plurality of remaining second detection voltages among the detection voltages to generate a detection result of the light emitting diode string corresponding to the first detection voltage; and determining whether to stop generating the driving signal of the corresponding light emitting diode string according to the detection result corresponding to the first detection voltage. 
     Based on the above, it is known that, when the driving signal generator transmits the driving signal to one or more light emitting diode strings in the driving device, the light emitting diode strings are prone to damages caused by factors like the assembly environment. When aforesaid situation does occur, the invention can be used to conduct detections on the light emitting diode string by utilizing one or more detection devices and respectively generate the detection voltages at the time. Besides, the detection device further compares the detection voltage of the light emitting diode string under detection with the detection voltages of the remaining light emitting diode strings to generate a detection result. Accordingly, the driving signal generator may be utilized to determine whether to stop transmitting the driving signal to the damaged light emitting diode string according to the detection result. 
     To make the above features and advantages of the disclosure more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram illustrating a driving device according to an embodiment of the invention. 
         FIG. 2A  is a schematic diagram illustrating a detection device of  FIG. 1  according to an embodiment of the invention. 
         FIG. 2B  is a schematic circuit diagram illustrating a voltage subtractor of  FIG. 2A  according to an embodiment of the invention. 
         FIG. 3  is a schematic diagram illustrating a driving device according to another embodiment of the invention. 
         FIG. 4  is a schematic diagram illustrating a switch circuit of  FIG. 3  according to another embodiment of the invention. 
         FIG. 5  illustrates a current-voltage graph of a light emitting diode string according to an embodiment of the invention. 
         FIG. 6  is a flowchart illustrating a driving method of a driving device according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     With reference to  FIG. 1 ,  FIG. 1  is a schematic diagram illustrating a driving device according to an embodiment of the invention. A driving device  100  includes detection devices  110  to  11 N, and driving signal generators  120  to  12 N. The driving device  100  may be coupled to each of light emitting diode strings  130  to  13 N. In the present embodiment, the driving signal generators  120  to  12 N may be respectively coupled to the light emitting diode strings  130  to  13 N and may respectively generate a plurality of driving signals to drive the light emitting diode strings  130  to  13 N, respectively, so as to turn on the light emitting diode strings  130  to  13 N. On the other hand, each of the detection devices  110  to  11 N may be coupled between a detection point of respective one of the light emitting diode strings  130  to  13 N and respective one of the driving signal generators  120  to  12 N so as to generate a detection result by detecting an operating state of each of the light emitting diode strings  130  to  13 N and transmit the detection result to the driving signal generators  120  to  12 N. Here, detection voltages V 1  to VN are provided on the detection points of the light emitting diode strings  130  to  13 N, respectively. The detection devices  110  to  11 N may be used to further determine whether the light emitting diode strings  130  to  13 N are in an abnormal state according to the detection voltages V 1  to VN. It is noted that, the detection devices  110  to  11 N, the driving signal generators  120  to  12 N and the light emitting diode strings  130  to  13 N in the present embodiment (where N is a positive integer) may be one or more, and their numbers thereof are not particularly limited. 
     The following description is described using the light emitting diode string  131  as an example. With reference to  FIG. 1 , in the driving device  100 , the detection device  111  compares a detection voltage V 2  on the detection point of the light emitting diode string  131  with the detection voltages on the detection points of the other light emitting diode strings  130  and  130 N to generate a detection result. Also, the driving signal generator  121  may determine whether to stop generating the driving signal according to the detection result generated by the corresponding detection device  111 . In other words, the driving signal generator  121  may determine whether the light emitting diode string  131  is in the abnormal state according to the detection result generated by the detection device  111 . If the light emitting diode string  131  under detection is in the abnormal state, the light emitting diode string  131  is stopped from being driven so the light emitting diode string  131  is turned off. Conversely, if the light emitting diode string  131  under detection is not in the abnormal state, the light emitting diode string  131  stays being turned on. 
     The detection device  111  obtains the detection result through a comparison performed by subtracting the detection voltage V 2  of the detection point of the light emitting diode string  131  under detection from the detection voltages (V 1  and VN) on the detection points of both the other light emitting diode strings  130  and  130 N. If none of voltage differences obtained by subtracting the detection voltage V 2  from the detection voltages V 1  and VN is greater than a predetermined threshold, it means that the light emitting diode string  131  is not in the abnormal state. Otherwise, if at least one of the differences obtained by subtracting the detection voltage V 2  from the detection voltages V 1  and VN is greater than the predetermined threshold, it means that the light emitting diode string  131  is in the abnormal state. 
     In addition, the detection device  111  may generate a plurality of logic values by detecting whether the voltage differences obtained by subtracting the detection voltage V 2  from the detection voltages V 1  and VN on the detection points of the other light emitting diode strings  130  and  13 N, and perform an OR operation on the logic values to generate the detection result. In other words, when the voltage difference obtained by subtracting the detection voltage V 2  from one detection voltage is greater than the predetermined threshold, the detection device  111  may generate the detection result indicating that the light emitting diode string  131  is abnormal. 
     With reference to  FIG. 2A ,  FIG. 2A  is a schematic diagram illustrating a detection device of  FIG. 1  according to an embodiment of the invention. A detection device  200  includes voltage subtractors  210  and  220  and an operational circuit  230 . Output terminals of the voltage subtractors  210  and  220  may receive the detection voltages V 1  and VN from the light emitting diode strings  130  and  13 N, respectively, and may be used to calculate voltage differences among the detection voltages V 1  and VN and determine whether the voltage differences are greater than a predetermined threshold to generate an output signal. On the other hand, an output terminal of the operational circuit  230  may be coupled to the voltage subtractors  210  and  220  to receive the output signals, and may perform an OR logical operation according to the output signals to generate the corresponding detection result. 
     In the present embodiment, the voltage subtractors  210  and  220  may be the same circuit of a voltage subtractor  300  in  FIG. 2B  of the invention, or may be a voltage subtractor well-known by persons skilled in the art. Detailed operating method of the voltage subtractor  300  in  FIG. 2B  will be described later. 
     On the other hand, the operational circuit  230  may be, for example, an OR gate or a combinational logic circuit constituted by one or more logic gates of any types, but not limited thereto. It should be noted that, the detection device  200  in  FIG. 2A  may be used to realize any one of the driving signal generators  120  to  12 N in  FIG. 1 . It is to be noted that, the following description is also described using the light emitting diode string  131  as an example. 
     Working details regarding the driving device  100  may refer to  FIG. 1  and  FIG. 2A  together. The voltage subtractor  210  may receive the detection voltages V 1  and V 2  from the light emitting diode strings  130  and  131 . The detection device  200  may generate an output signal V 2   a  by subtracting the detection voltage V 2  under detection from the detection voltage V 1  through the voltage subtractor  210 . On the other hand, the voltage subtractor  220  may receive the detection voltages V 2  and VN from the light emitting diode strings  131  and  13 N. The detection device  200  may generate an output signal V 2   b  by subtracting the detection voltage V 2  under detection from the detection voltage VN through the voltage subtractor  220 . It should be noted that, the output terminal of the operational circuit  230  may receive the output signals V 2   a  and V 2   b , and determine whether the light emitting diode string  131  under detection is abnormal according to the output signals V 2   a  and V 2   b  so as to output a corresponding detection result V 2   o.    
     In detail, after the detection device  200  calculates the voltage difference between the detection voltage V 1  and the detection voltage V 2  (e.g., by subtracting the detection voltage V 2  under detection from the detection voltage V 1 ) through the voltage subtractor  210  and calculate the voltage difference between the detection voltage V 2  and the detection voltage VN (e.g., by subtracting the detection voltage V 2  under detection from the detection voltage VN) through the voltage subtractor  220 , if at least one of voltage values of the output signals V 2   a  and V 2   b  is greater than a predetermined threshold, it means that a voltage value of the detection voltage V 2  in the light emitting diode string  131  under detection is different from voltage values of the detection voltages V 1  and VN in the light emitting diode strings  130  and  13 N, and it can be further determined that the light emitting diode string  131  under detection may be in a damaged state. In this case, the operational circuit  230  may generate the detection result V 2   o  indicating that the corresponding light emitting diode  131  is in the abnormal state according to the output signals V 2   a  and V 2   b . In other words, when the driving signal generator  121  receives the detection result V 2   o  indicating that the corresponding light emitting diode string  131  is abnormal, the driving signal generator  121  stops generating the corresponding driving signal so the light emitting diode string  131  under detection is turned off. 
     Conversely, if none of the voltage values of the output signals V 2   a  and V 2   b  is greater than the predetermined threshold, eans that the voltage values of the detection voltage V 2  in the light emitting diode string  131  under detection and the detection voltages V 1  and VN in the light emitting diode strings  130  and  13 N are close to each other. In other words, the light emitting diode string  131  under detection is not in the abnormal state. The driving signal generator  121  may continue to generate the driving signal so the light emitting diode string  131  under detection can stay being turned on. It should be noted that, the predetermined threshold in the present embodiment may be, for example, 0.5V, but not limited thereto. 
     The following description refers to both  FIG. 2A  and  FIG. 2B , where  FIG. 2B  is a schematic circuit diagram illustrating a voltage subtractor of  FIG. 2A  according to an embodiment of the invention. The voltage subtractor  300  includes an operational amplifier  310  and resistors  320  to  350 . Among them, a first terminal of the resistor  320  may receive one of a plurality of detection voltages V 1  to VN (e.g., receive the detection voltage V 1 ), and a second terminal of the resistor  320  may be coupled to a positive input terminal of the operational amplifier  310 . A first terminal of the resistor  330  may receive one of the detection voltages V 1  to VN under detection (e.g., receive the detection voltage V 2 ), and a second terminal of the resistor  330  may be coupled to a negative input terminal of the operation amplifier  310 . In addition, the resistor  340  is serially connected between the second terminal of the resistor  320  and an output terminal of the operational amplifier  310 , and the resistor  350  is serially connected between the second terminal of the resistor  330  and a reference ground terminal GND. Further, the operational amplifier  310  may generate a corresponding output signal Vo according to the received detection voltages V 1  and V 2 . 
     The following description is described using the voltage subtractor  300  with reference to the implementation of the voltage subtractor  210 . In the case as described above, the voltage difference generated by subtracting the detection voltage V 2  from the detection voltage V 1  may be calculated through the voltage subtractor  300 . When resistances of the resistor  320  and the resistor  330  are identical and resistances of the resistor  340  and the resistor  340  are also identical, the output signal Vo of the operational amplifier  310  =(V 1 −V 2 )×Rf/R. However, if the resistances of the resistors  320  to  350  are not identical, it is required to moderately adjust the output signal Vo of the operational amplifier  310  according to the resistances of the resistors  320  to  350 . It should be noted that, the detection voltages V 1  and V 2  in  FIG. 2B  may be any two detection voltages among the detection voltage V 1  to VN in  FIG. 1  without particular limitation. 
     With reference to  FIG. 3 ,  FIG. 3  is a schematic diagram illustrating a driving device according to another embodiment of the invention. A driving device  400  includes detection devices  411  to  413  and driving signal generators  421  to  423 . Here, the driving device  400  may be coupled to light emitting diode strings  431  to  433 , respectively. It should be noted that, the driving signal generators  421  to  423  may include voltage followers  441  to  443 , switch circuits SW 1  to SW 3  and current generators  451  to  453 , respectively. In addition, the light emitting diode strings  431  to  433  may be controlled by a power voltage VLED. 
     In  FIG. 3 , the voltage followers  441  to  443  may include input terminals for receiving a reference voltage Vref, and includes output terminals for generating bias voltages V 1 ′ to V 3 ′. The switch circuits SW 1  to SW 3  may be coupled to the output terminals of the voltage followers  441  to  443  to receive the bias voltages V 1 ′ to V 3 ′, respectively. The switch circuits SW I to SW 3  may determine whether to turn on or off the switch circuits SW 1  to SW 3  according to detection results V 1   o  to V 3   o  outputted by the detection devices  411  to  413 , respectively. Besides, the current generators  451  to  453  may be coupled between respective one of the light emitting diode strings  431  to  433  and respective one of the switch circuits SW 1  to SW 3 . The current generators  451  to  453  further include power amplifiers M 1  to M 3  (formed by transistors) and resistors R 1  to R 3 , respectively. 
     On the other hand, first terminals of the power amplifiers M 1  to M 3  are coupled to the respective one of the light emitting diode strings  431  to  433  to provide the corresponding driving signals, respectively. In addition, control terminals of the power amplifiers M 1  to M 3  may be coupled to the switch circuits SW 1  to SW 3  to receive the bias voltages V 1 ′ to V 3 ′ via the switch circuits SW 1  to SW 3 , respectively. Further, the resistors R 1  to R 3  may be coupled between respective one of the second terminals of the power amplifiers M 1  to M 3  and a reference ground voltage. 
     In the present embodiment, the switch circuits SW 1  to SW 3  may determine whether to provide the bias voltages V 1 ′ to V 3 ′ to the current generators  451  to  453  according to the detection results V 1   o  to V 3   o , respectively. It should be noted that, when respective one of the current generators  451  to  453  receives respective one of the bias voltages V 1 ′ to V 3 ′, respective one of the current generators  451  to  453  may generate the corresponding driving signal according to respective one of the bias voltages V 1 ′ to V 3 ′ to drive respective one of the light emitting diode strings  431  to  433  so respective one of the light emitting diode strings  431  to  433  can be turned on. Conversely, when respective one of the current generators  451  to  453  does not receive respective one of the bias voltages V 1 ′ to V 3 ′, respective one of the current generators  451  to  453  stops generating the corresponding driving signal so respective one of the light emitting diode strings  431  to  433  is turned off. 
     Working details regarding the driving device  400  is described below with reference to the light emitting diode string  432  as an example. In detail, the driving device  400  receives the detection voltages V 1  to V 3  via the output terminal of the detection device  412 , and is configured to calculate voltage differences between the detection voltage V 2  under detection and the detection voltages V 1  and V 3 . If one of said voltage differences is greater than a predetermined threshold (e.g., 0.5V), it means that the voltage value of the detection voltage V 2  in the light emitting diode string  432  under detection is different from the voltage value of one of the detection voltage V 1  and V 3  in the light emitting diode strings  431  and  433 , and it can be further determined that the light emitting diode string  432  may be in the damaged state. In this case, the detection device  412  generates a detection result V 2   o  (e.g., logic high) indicating that the light emitting diode string  432  is abnoiinal. Accordingly, the switch circuit SW 2  is turned on so the voltage value of the bias voltage V 2 ′ is pulled down to be equal to a reference ground voltage AGND. Meanwhile, the power amplifier M 2  is turned off so the current generator circuit  452  stops generating and providing the driving signal to the light emitting diode  432  under detection. In other words, the current generator circuit  452  stops generating the driving signal corresponding to the light emitting diode string  432  according to the detection result V 2   o  generated by the corresponding detection device  412  so the light emitting diode string  432  under detection is turned off 
     Conversely, when none of the voltage differences between the detection voltage V 2  under detection and the detection voltages V 1  and V 3  determined by the detection device  412  is greater than the predetermined threshold, it means that the voltage values of the detection voltage V 2  in the light emitting diode string  432  under detection and the detection voltages V 1  and V 3  in the light emitting diode strings  431  and  433  are close to each other, and it can be further determined that the light emitting diode string  432  is not in the damaged state. In this case, the detection device  412  generates the detection result V 2   o  (e.g., logic low) indicating that the light emitting diode string  432  is normal so the switch circuit SW 2  is turned off to prevent the voltage value of the bias voltage V 2 ′ from being pulled down to be equal to the reference ground voltage AGND. Meanwhile, the power amplifier M 2  may be turned on normally. In other words, the current generator circuit  452  may continue to generate the driving signal for the light emitting diode string  432  according to the detection result V 2   o  generated by the corresponding detection device  412  so the light emitting diode string  432  under detection stays being turned on. 
     In the present embodiment, another implementation for the switch circuits SW 1  to SW 3  is further provided. The following description refers to  FIG. 3  and  FIG. 4  together, where  FIG. 4  is a schematic diagram illustrating a switch circuit of  FIG. 3  according to another embodiment of the invention. A switch circuit  500  includes a first switch SW 4  and a second switch SW 5 . The first switch SW 4  is coupled between a current generator  520  and a reference ground GND, and determines whether to turn on the first switch SW 4  according to the corresponding detection result V 2   o . On the other hand, the second switch SW 5  is coupled between an output terminal of a voltage follower  510  and the first switch SW 4 , and also determines whether to turn on the second switch SW 5  according to the corresponding detection result V 2   o . Here, on/off states of the first switch SW 4  and the second switch SW 5  are opposite. 
     In detail, when the detection result outputted by the detection device corresponding to the switch circuit  500  indicates that the light emitting diode string under detection is in the damaged state, the first switch SW 4  is turned on. Meanwhile, the second switch SW 5  is turned off so the current generator  520  is cut off and the voltage follower  510  stops to operate, and thus the light emitting diode string under detection is turned off Conversely, when the detection result outputted by the detection device corresponding to the switch circuit  500  indicates that the light emitting diode string under detection is not in the damaged state, the first switch SW 4  is turned off. Meanwhile, the second switch SW 5  is turned on so the current generator  520  is turned on and the voltage follower  510  can continue to operate, and thus the light emitting diode string under detection can stay being turned on. 
       FIG. 5  illustrates a current-voltage graph of a light emitting diode string according to an embodiment of the invention. In  FIG. 5 , the horizontal axis represents a voltage state of the light emitting diode string, and the vertical axis represents a current state of the light emitting diode string. Here, the current-voltage graph of the light emitting diode string includes a curve  710  representing the detection result when the light emitting diode string under detection is not in the abnormal state and a curve  720  representing the detection result when the test light emitting diode string is in the abnormal state. It should be noted that, in the present embodiment, driving signals less than a predetermined current are provided to a plurality of light emitting diode strings within a test time interval by utilizing a plurality of driving signal generators in a driving device, so as to detect whether the light emitting diode strings are in the abnormal state. Also, the detection devices generate the corresponding detection results within the test time interval. The predetermined current in the present embodiment may be set according to a current value generated when the light emitting diode string is biased to a threshold voltage Vt (e.g., to be less than the current value generated when the light emitting diode string is biased to the threshold voltage Vt). In the present embodiment, the respective driving signal generator makes the bias voltage received by the corresponding light emitting diode string less than the threshold voltage Vt of the corresponding light emitting diode string within the test time interval. 
       FIG. 6  is a flowchart illustrating a driving method of a driving device according to an embodiment of the invention. In step S 610 , driving signal generators respectively generate a plurality of driving signals to drive light emitting diode strings, respectively, and generate a plurality of detection voltages on a plurality of detection points of the light emitting diode strings. In step S 620 , the detection device compares the detection voltage on the detection point of one specific light emitting diode string with the detection voltages on the detection points of the remaining light emitting diode strings to generate a detection result of the specific light emitting diode string corresponding to the detection voltage. In step S 630 , the respective driving signal generator determines whether to stop generating the driving signal of the specific light emitting diode string according to the detection result corresponding to the detection voltage. 
     Relevant implementation details regarding the steps above have been described in foregoing embodiments and implementations, which are not repeated hereinafter. 
     In summary, according to the embodiments of the invention, when the light emitting diode string is damaged in the driving device, the invention can utilize one or more detection devices to detect the light emitting diode strings and respectively generate the detection voltages at the same time. Besides, the detection device further compares the detection voltage of the light emitting diode string under detection with the detection voltages of the remaining light emitting diode strings to generate a detection result. Accordingly, the driving signal generator may be utilized to determine whether to stop transmitting the driving signal to the damaged light emitting diode string according to the detection result. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.