Abstract:
A driving circuit applied in a display system includes a node, a current control circuit, a protecting circuit and a timing controller, wherein the node is arranged to connect to a lighting element; the current control circuit is coupled to the node and arranged to selectively provide a current to the lighting element according to a Pulse Width Modulation (PWM) signal; the protecting circuit is coupled to the node and arranged to be selectively enabled to limit the voltage of the node according to a control signal to make the voltage of the node maintain a predetermined voltage, wherein the lighting element does not have any current passed through when the voltage of the node maintains the predetermined voltage; and the timing controller is arranged to generate the PWM signal and the control signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a driving circuit applied to a display system, and more particularly, to a driving with a protecting circuit to limit a high voltage surge introduced by parasitic inductance, driving method and associated display system. 
         [0003]    2. Description of the Prior Art 
         [0004]    Refer to  FIG. 1 , which is a diagram illustrating a display system  100  in the prior art. As shown in  FIG. 1 , the display system  100  comprises a plurality of Light-Emitting Diodes (LED) D 1  to D N , a plurality of nodes N 1  to N N , a plurality of transistors M 1  to M N , and a plurality of current sources I 1  and I N , wherein the transistors M 1  to M N  are controlled to be opened or closed by a plurality of Pulse Width Modulation (PWM) signals V en1  to V enN . The states of the transistors M 1  to M N  change between open and close constantly by referring to the PWM signals V en1  to V enN  to make the states of the LEDs D 1  to D N  change between light-on and light-off constantly, and the average luminance of LEDs D 1  to D N  are decided according to the time ratio of light-on state and light-off state of the LEDs D 1  to D N  (i.e. the duty cycles of the PWM signals V en1  to V enN ). 
         [0005]    Refer to  FIG. 2 , which is an ideal waveform illustrating a voltage of the node N 1  and a current of the LED D 1  when the PWM signal V en1  changes to low level from the high level. As shown in  FIG. 2 , when the PWM signal V en1  is on high level (e.g. 3V shown in  FIG. 2 ), the transistor M 1  is conductive to make the LED D 1  have a current and illuminate. In this time, the voltage level of the node N 1  is 0V. Next, when the PWM signal V en1  decreases to 0V from 3V, the current of the LED D 1  decreases to OA due to the transistor M 1  is non-conductive (i.e. the LED D 1  does not illuminate). In this time, the voltage level of the node N 1  equals to a supple voltage V LED  of the LED D 1  (e.g. 5V shown in  FIG. 2 ). 
         [0006]    However, because when the PWM signal V en1  decreases to low level from the high level to close the transistor M 1 , there is a parasitic inductance between the node N 1  and the LED D 1 , therefore, the node N 1  has a very high voltage surge and damages the circuit.  FIG. 3  is a practical waveform illustrates the voltage of the node N 1  and the current of the LED D 1  when the PWM signal V en1  changes to low level from high level. As shown in  FIG. 3 , the PWM signal V en1  decreases to 0V from 3V, the voltage level of the node N 1  suddenly jumps to a level close to 25V, in this way, the adjacent circuit of the node N 1  might be damaged and influences the circuit. In addition, with the increase of the frequency of the PWM signal V en1 , the above-mentioned voltage surge phenomenon might be more serious. 
       SUMMARY OF THE INVENTION 
       [0007]    One of the objectives of the present invention is to provide a driving circuit with a protecting circuit to limit the high voltage surge introduced by parasitic inductance, a driving method and associated display system to solve the above-mentioned problems. 
         [0008]    According to an embodiment of the present invention, a driving circuit applied in a display system comprises a node, a current control circuit, a protecting circuit and a timing controller, wherein the node is connected to a lighting element; the current control circuit is coupled to the node and arranged for selectively providing a current to the lighting element according to a PWN signal; the protecting circuit is coupled to the node and arranged for selectively enabling to limit the voltage of the node according to a control signal to make the voltage of the node maintain a predetermined voltage, wherein when the voltage of the node maintains the predetermined voltage, there is no current passes through the lighting element; and the timing controller is arranged for generating the PWM signal and the control signal. 
         [0009]    According to another embodiment of the present invention, a driving method applied in a display system comprising: providing a driving circuit, wherein the driving circuit comprises a node arranged for connecting to a lighting element, a current control circuit coupled to the node and a protecting circuit coupled to the node; generating a PWM signal to the current control circuit to selectively provide a current to the lighting element generating a control signal to the protecting circuit to selectively enable the protecting circuit to limit the voltage of the node to make the voltage of the node maintain a predetermined voltage, wherein when the voltage of the node maintain a predetermined voltage, there is no current passes through the lighting element. 
         [0010]    According to another embodiment of the present invention, a display system comprises a lighting element and a driving circuit, wherein the driving circuit comprises a node, a current circuit, a protecting circuit and a timing controller, wherein the node is arranged to connect to a lighting element; the current control circuit is coupled to the node and arranged for selectively providing a current to the lighting element according to a PWM signal; the protecting circuit is coupled to the node and arranged for selectively enabling to limit the voltage of the node according to a control signal to make the voltage of the node maintain a predetermined voltage, wherein when the voltage of the node maintains the predetermined voltage, there is no current passes through the lighting element; and the timing controller is arranged for generating the PWM signal and the control signal. 
         [0011]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagram illustrating a display system in the prior art. 
           [0013]      FIG. 2  is an ideal waveform illustrating a voltage of a node N 1  and a current of a LED D 1  when a PWM signal V en1  shown in  FIG. 1  changes to low level from high level. 
           [0014]      FIG. 3  is a practical waveform illustrating the voltage of the node N 1  and the current of the LED D 1  when the PWM signal V en1  shown in  FIG. 1  changes to low level from high level. 
           [0015]      FIG. 4  is a diagram illustrating a display system according to an embodiment of the present invention. 
           [0016]      FIG. 5  is a diagram illustrating an input signal V s1 , an PWN signal V en1  and a control signal V c1  shown in  FIG. 4  according to an embodiment of the present invention. 
           [0017]      FIG. 6  is a practical waveform illustrating the voltage of the node N 1  and the current of the LED D 1  when the PWM signal V en1  shown in  FIG. 4  changes to low level from high level. 
           [0018]      FIG. 7  is a flowchart illustrating a driving method applied in a display system according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should not be interpreted as a close-ended term such as “consist of”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
         [0020]    Refer to  FIG. 4 , which is a diagram illustrating a display system  400  according to an embodiment of the present invention. As shown in  FIG. 4 , the display system  400  comprises a plurality of lighting elements (in this embodiment, the lighting elements are LEDs D 1  to D N ) and a driving circuit  410 , wherein the LEDs D 1  to D N  are coupled to the nodes N 1  to N N  of the driving circuit  410 , respectively. The driving circuit  410  comprises a current control circuit  420 , a protecting circuit  430  and a timing controller  440 , wherein the current control circuit  420  comprises a plurality of transistors M 1  to M N  and a plurality of current sources I 1  to I N , the protecting circuit  430  comprises a plurality of transistors M C1  to M CN , wherein the sources terminals of the plurality of transistors M C1  to M CN  are connected to a supply voltage V LED  of the LEDs D 1  to D N . In addition, in this embodiment, the driving circuit  410  is an independent chip. 
         [0021]    In the operation of the system  400 , first of all, the timing controller  440  receives the input signals V S1  to V SN  from the other elements of the driving circuit  410 , and the timing controller  440  generates the PWN signals V en1  to V enN  and the control signals V c1  to V cN  according to the input signals V S1  to V SN , wherein the PWN signals V en1  to V enN  are arranged for controlling the transistor M 1  to M N  of the current control circuit  420  to be opened or closed, respectively, and the average luminance of the LEDs D 1  to D N  are determined by the time ratio of the open/close states of the transistor M 1  to M N , respectively (i.e. the duty cycles of the PWN signals V en1  to V enN ); and the control signals V c1  to V cN  are arranged for controlling the open/close states of the transistors M C1  to M CN  of the protecting circuit  430  to selectively limit the voltages of the node N 1  to N N . 
         [0022]    More specifically, refer to  FIG. 5 , which is a diagram illustrating the input signal V s1 , the PWN signal V en1  and the control signal V c1  according to an embodiment of the present invention. The first set of the input signal V s1 , the PWN signal V en1  and the control signal V c1  are used to be explained in  FIG. 5 , however, the signals in  FIG. 5  can be applied to other sets of input signal (V c2  to V cN ), PWM signals (V en2  to V enN ) and control signals (V c2  to V cN ). In the embodiment of  FIG. 5 , the timing controller  440  delays the input signal V S1  to generate the PWM signal V en1 , wherein there is a delay Td between the PWM signal V en1  and the input signal V S1 , and the timing controller  440  performs inverting operation to the input signal V S1  to generate the control signal V C1 , in this way, before the PWM signal V en1  decreases to low level from high level (i.e. before the PWM signal V en1  closes the transistor M 1  to stop providing current to the LED D 1 ), the control signal V c1  opens the transistor M c1  in the protecting circuit  430  first, so the transistor M c1  in the protecting circuit  430  can discharge the charge stored in the node N 1  immediately when the node N 1  occurs the high voltage surge shown in  FIG. 3  while the PWM signal V en1  decreasing to low level from high level to limit the voltage of the node N 1  to the supply voltage V LED , so the problem that the high voltage surge damages the circuit in prior art can be avoided. 
         [0023]    In addition, before the PWM signal V en1  increase to high level from low level (i.e. before the PWM signal V en1  opens the transistor M 1  to provide current to the LED D 1 ), the control signal V c1  closes the transistor M c1  first to prevent the protecting circuit from forming another current path and affects the current value passed through the LED D 1 . 
         [0024]    Refer to  FIG. 6 , which is a practical waveform illustrating the voltage of the node N 1  and the current of the LED D 1  when the PWM signal V en1  changes to low level from high level. As shown in  FIG. 6 , when the PWM signal V en1  decreases to 0V from 3V, the voltage level of the node N 1  can only reach 6V most, therefore, comparing with the 25V high voltage surge shown in  FIG. 3 , the display system shown in  FIG. 4  can improve the high voltage surge problem in circuit in the prior art indeed to prevent the circuit from damage. 
         [0025]    In addition, according to the applicant, the architecture of the circuit in the protecting circuit  430  is only an example, not a limitation of the present invention. For example, the nodes of the transistors M C1  to M CN  in the protecting circuit  430  can connect to another predetermined voltage instead of the supply voltage V LED . The predetermined voltage can be designed according to the requirement of the designer as long as the predetermined voltage can prevent the nodes N 1  to N N  from being affected by the high voltage surge, and to make no current pass through the LEDs D 1  to D N , when the transistor M 1  to M N  in the current control circuit  420  close. For example, the above-mentioned predetermined voltage can locate between (V LED −M*Vf) and (V LED +M*Vr), wherein M is the number of LED(s) of each LED string (M=1 in the embodiment of  FIG. 4 ), Vf is a positive bias voltage of the LEDs D 1  to D N  and Vr is a negative bias voltage of the LEDs D 1  to D N . In addition, the protecting circuit  430  is not necessarily to be implemented by the transistors M C1  to M CN . The protecting circuit  430  can be implemented in any other suitable architectures, as long as the protecting circuit  430  can provide a charge released path when the transistors M 1  to M N  in the current control circuit  420  are closed to prevent the nodes N 1  to N N  from high voltage surge, and the node N 1  to N N  can maintain a suitable voltage level. These alternative designs should fall within the scope of the present invention. 
         [0026]    In addition, the description about the timing controller  440  generating the PWM signals V en1  to V enN  and the control signal V c1  to V cN  described above, and the input signal V s1 , the PWM signal V en1  and the control signal V c1  shown in  FIG. 5  are only explanation, not a limitation of the present invention. In other embodiments of the present invention, the timing controller  440  can input the input signals V s1  to V SN  to the current control circuit  420  directly as the PWM signals V en1  to V enN , i.e. the delay Td between the PWM signal V en1  and the input signal V S1  as shown in  FIG. 5  does not exist (i.e. the delay Td is very small). In the other words, the time that the PWM signal V en1  starts to close the transistor M 1  in the current control circuit  420  is very close or equal to the time that the control signal V c1  starts to open the transistor M c1  in the protecting circuit  430 . Additionally, the control V c1  can be generated in other ways to make the enable period Tp of the control signal V c1  shown in  FIG. 5  can be reduced. These alternative designs should fall within the scope of the present invention. 
         [0027]    In addition, the LEDs D 1  to D N  shown in  FIG. 4  are only an explanation. In other embodiments of the present invention, each of the LEDs D 1  to D N  can be replaced with other lighting element or a LED string, wherein each LED string can comprise a plurality of LEDs. These alternative designs should fall within the scope of the present invention. 
         [0028]    Refer to  FIG. 7 , which is a flowchart illustrating a driving method applied in a display system according to an embodiment of the present invention. Refer to  FIG. 4  and  FIG. 7 , the flow is described as follows. 
         [0029]    Step  700 : provide a driving circuit, wherein the driving circuit comprises a node arranged for connecting to a lighting element, a current control circuit coupled to the node and a protecting circuit coupled to the node. 
         [0030]    Step  702 : generate a PWM signal to the current control circuit to selectively provide a current to the lighting element. 
         [0031]    Step  704 : generate a control signal to the protecting circuit to selectively enable the protecting circuit to limit the voltage of the node. 
         [0032]    Briefly summarized, in the driving circuit, the driving method and the associated display system of the present invention, a protecting circuit which can limit the high voltage surge introduced by parasitic inductance is provided. Therefore, by limiting the high voltage surge introduced by parasitic inductance, it can prevent the circuit from damage and does not affect the life of the circuit. 
         [0033]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.