Abstract:
A method for driving a plurality of LEDs comprises the steps of: driving the plurality of LEDs according to a series of display signals; synchronously detecting the plurality of LEDs in a display mode for obtaining fault information; and serially outputting the fault information.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a driver circuit and the method thereof, and more particularly, to an LED driver circuit and the method thereof. 
     2. Description of the Related Art 
     Compared to most conventional light emitting devices, LEDs consume less power, have longer lifetime and are more durable. Therefore, most indicator devices nowadays, such as traffic signs and commercial billboards, are implemented by LEDs. However, since a large number of those large indicator devices are placed outdoors, there are various sources of hazard, such as weather, animals colliding with them, or even droppings, that can damage such LED indicator devices. Unfortunately, conventional LED indicator devices seldom exhibit fault detection mechanism. Therefore, when LED indicator device are damaged, the control device, such as a control-end processor, has no knowledge of the location and the number of the damaged LEDs, and only by human eyes can such information be observed. Since the height of many modern LED indicator devices are over tens of meters, it requires maintenance personnel to climb up high to confirm information on the damaged LED indicator device, which is an arduous task and costs a lot of money. 
     To solve the problems mentioned above, a fault detection mechanism can be designed for those LED indicator devices such that a control device is able to obtain the fault information of the damaged LEDs automatically.  FIG. 1  shows a conventional LED driver circuit  100 , which is connected to a control-end processor  200  and serves as the driver for a plurality of LEDs  400 . The LED driver circuit  100  comprises a shift register  110 , a plurality of latches  120 , a plurality of driver units  130 , a plurality of comparators  140 , a plurality of state registers  150  and a state switching circuit  160 , wherein the number of the flip-flops in the shift register  110 , the number of the plurality of latches  120 , the number of the plurality of driver units  130  and the number of the plurality of LEDs  400  are the same. The input signals of the LED driver circuit  100  include an input data, a latch signal, a switch signal and a clock signal. The output signal of the LED driver circuit  100  includes an output data. The input terminal of the LED driver circuit  100  for the input data is connected to the first flip-flop of the shift register  110 . The output terminal of the LED driver circuit  100  for the output data is connected to the last flip-flop of the shift register  110 . 
     The state switching circuit  160  determines the status of the LED driver circuit  100  according to the latch signal and the switch signal. When in a display mode, the LED driver circuit  100  receives display signals from the control-end processor  200 . The received display signals are then serially stored in the shift register  110 . When the storing process of the display signals is completed, the data stored in the shift register  110  is then outputted to and stored in the plurality of latches  120 . The output terminals of the plurality of latches  120  are connected to the plurality of driver units  130  respectively. The plurality of driver units  130  have their output terminals connected to, and accordingly drive, the plurality of LEDs  400 . 
     When in a debug mode, the LED driver circuit  100  receives fault-detecting signals (such as the signals of which the bits are all 0s or all 1s) from the control-end processor  200 . The received fault-detecting signals are then serially stored in the shift register  110 . When the storing process of the fault-detecting signals is complete, the data stored in the shift register  110  is then outputted to and stored in the plurality of latches  120  so as to be the input signal for the plurality of driver units  130 . The input terminals of the plurality of comparators  140  are respectively connected to the output terminals of the plurality of LEDs  400  and a reference voltage. The output signals of the comparators  140  indicate whether the plurality of LEDs  400  are in fault state. The plurality of state registers  150  store the comparison results of the plurality of comparators  140 , and then stores such results to the shift register  110  at a later time such that the results can be outputted and transmitted back to the control-end processor  200 . The control-end processor  200  obtains the fault information of the plurality of LEDs  400  according to the comparison results. For instance, if the fault-detecting signal is a signal of which the bits are all 1s, which should turn on all the plurality of LEDs  400 , and the comparison results contain bits of “0”, then the control-end processor  200  determines that the LEDs  400  at the corresponding locations are faulty. 
       FIG. 2  shows the waveforms of the input and output signals of the LED driver circuit  100 . As shown in  FIG. 2 , the clock signal controls the input operation of the shift register  110 . When in the display mode, the display signals are serially stored into the shift register  110 . At such point, the output signals of the LED driver circuit  100  are redundant data. When the storing process of the display signals is complete, a pulse of the latch signal triggers the data stored in the shift register  110  to be stored into the plurality of latches  120 . The switch signal then switches to low to activate the plurality of driver units  130 , and the plurality of LEDs  400  are driven thereby according to the data stored in the plurality of latches  120 . At such point, the output signal is the display signals. After the state switching circuit  160  switches the mode of the LED driver circuit  100  to the debug mode, the driver circuit  100  is ready for the fault detection of the plurality of LEDs, or is ready to transmit the data stored in the plurality of state registers  150  back to the control-end processor  200 . At such point, the output signal is the fault information. As shown in  FIG. 2 , the modes of the driver circuit  100  further include an exit mode, which serves as an interfacing mode between the display mode and the debug mode. 
     However, the aforesaid prior art needs to be switched between several modes, which heavily increases the control complexity for the control-end processor  200 . Moreover, the addition of the plurality of state registers  150  and the state switching circuit  160  increases the hardware cost. Therefore, there is a need to design a display mechanism, which not only can detect the fault status of the plurality of LEDs synchronously, but also does not increase the hardware cost. 
     SUMMARY OF THE INVENTION 
     The method for driving a module including a plurality of LEDs according to one embodiment of the present invention comprises the steps of: driving the plurality of LEDs according to a series of display signals; synchronously detecting the plurality of LEDs in a display mode for obtaining fault information; and serially outputting the fault information. 
     The LED driving method according to another embodiment of the present invention comprises the steps of: serially inputting a series of display signals to a shift register; storing the data stored in the shift register to a plurality of latches; driving a plurality of LEDs according to the data stored in the plurality of latches; synchronously storing fault information of LEDs to the shift register when the plurality of LEDs display the data stored in the plurality of latches; and serially outputting the fault information to determine the fault status of the plurality of LEDs. 
     The LED driver circuit according to another embodiment of the present invention comprises a shift register, a plurality of latches, a plurality of driver units and a plurality of fault-detecting units. The shift register receives display signals from a control-end processor and transmits fault information to the control-end processor. The plurality of latches secure the output signals from the shift register. The plurality of driver units receive the data stored in the plurality of latches and drive a module comprising a plurality of LEDs. The plurality of fault-detecting units synchronously detect the plurality of LEDs in a display mode for obtaining fault information and store the fault information into the shift register. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objectives and advantages of the present invention will become apparent upon reading the following description and upon referring to the accompanying drawings of which: 
         FIG. 1  shows a conventional LED driver circuit; 
         FIG. 2  shows waveforms of the input and output signals of the LED driver circuit according to one embodiment of the present invention; 
         FIG. 3  shows an LED driving method and the circuit thereof according to one embodiment of the present invention; 
         FIG. 4  shows the flow chart of an LED driving method according to the embodiment of the present invention; and 
         FIG. 5  shows waveforms of the input and output signals of the LED driver circuit according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  shows an LED driving method and the circuit thereof according to one embodiment of the present invention. The LED driver circuit  300  is connected to the control-end processor  200 , and serves as the driver for the plurality of LEDs  400 . The LED driver circuit  300  comprises a shift register  310 , a plurality of latches  320 , a plurality of driver units  330  and a plurality of fault-detecting units  340 , such as comparators, wherein the number of the flip-flops in the shift register  310 , the number of the plurality of latches  320 , the number of the plurality of driver units  330 , the number of the fault-detecting units  340  and the number of the plurality of LEDs  400  are the same. The input signals of the LED driver circuit  300  include an input data, a latch signal, a switch signal and a clock signal. The output signal of the LED driver circuit  300  includes an output data. The input terminal of the LED driver circuit  300  for the input data is connected to the first flip-flop of the shift register  310 . The output terminal of the LED driver circuit  300  for the output data is connected to the last flip-flop of the shift register  310 . 
     The LED driving method according to the embodiment of the present invention comprises only one mode, i.e., the display mode. Therefore, the state switching circuit  160  in the conventional LED driver circuit  100  is not required. When in the display mode, the LED driver circuit  300  receives the display signals from the control-end processor  200 . The received display signals are then serially stored in the shift register  310 . When the storing process of the display signals is completed, the data stored in the shift register  310  is then outputted to and stored in the plurality of latches  320 . The output terminals of the plurality of latches  320  are connected to the plurality of driver units  330 , respectively. The plurality of driver units  330  have their output terminals connected to, and accordingly drive, the plurality of LEDs  400 . The input terminals of the plurality of comparators  340  are respectively connected to the output terminals of the plurality of LEDs  400  and a reference voltage. The output signals of the comparators  340  indicate whether the plurality of LEDs  400  are in fault state. The plurality of comparators  340  can detect two kinds of fault states of the plurality of LEDs  400 , i.e., whether the plurality of LEDs  400  are stuck short or stuck open. For instance, if the display signals stored in the plurality of latches  320  contain a bit of “1”, and the corresponding bit of the output signals of the plurality of comparators  340  is “0”, then the corresponding LED  400  is stuck open. If the display signals stored in the plurality of latches  320  contain a bit of “0”, and the corresponding bit of the output signals of the plurality of comparators  340  is “1”, then the corresponding LED  400  is stuck short. After the plurality of LEDs  400  are driven and activated, the plurality of comparators  340  store the comparison results into the shift register  310  before the next clock signal pulse arrives. The comparison results are then outputted serially from the output terminal of the LED driver circuit  300 . That is, the LED driving method according to the embodiment of the present invention combines fault detection mechanism with the display mode such that the fault information of being stuck short and open is transmitted back to the control-end processor  200  in real time. 
       FIG. 4  shows the flow chart of an LED driving method according to the embodiment of the present invention. In step S 1 , a series of display signals outputted by the control-end processor  200  are stored in the shift register  310 . In step S 2 , the data stored in the shift register  310  is stored into the plurality of latches  320 . In step S 3 , the plurality of LEDs  400  are driven according to the data stored in the plurality of latches  320 . In step S 4 , the fault information of the plurality of LEDs  400  is stored into the shift register  310 . In step S 5 , the LED driver circuit  300  serially outputs the comparison results. 
       FIG. 5  shows the waveforms of the input and output signals of the LED driver circuit  300 . As shown in  FIG. 5 , the clock signal controls the input operation of the shift register  310 . When in display mode, the display signals are serially stored into the shift register  310 . When the storing process of the display signals is completed, a pulse of the latch signal triggers the data stored in the shift register  310  to be stored into the plurality of latches  320 . The switch signal then switches to low to activate the plurality of driver units  330 , and the plurality of LEDs  400  are driven thereby according to the data stored in the plurality of latches  320 . The fault information of the plurality of comparators  340  is stored into the shift register  310  before the next clock signal pulse arrives. At such point, the output signal is the comparison results, i.e., the fault information. As shown in the preceding paragraph, after the LED driver circuit  300  receives the display signals and drives the plurality of LEDs  400 , the fault information of the plurality of LEDs  400  is outputted in real time. Therefore, the plurality of state registers  150  of the conventional LED driver circuit  100  are not required in the LED driver circuit  300 . 
     The control-end processor  200  compares the received fault information to the corresponding display signals to obtain the fault status of the plurality of LEDs  400 . If the display signals are inconsistent with the corresponding fault information, the corresponding LEDs are determined to have been stuck open or short. 
     In conclusion, the LED driving method and the circuit thereof according to embodiments of the present invention combine the fault detection mechanism with the display mode, and therefore the hardware costs can be reduced. On the other hand, the fault information can be transmitted back to the control device in real time, and hence the fault status of the faulty LEDs can be discovered sooner. In addition, the LED driving method and the circuit thereof according to embodiments of the present invention are capable of driving of the plurality of LEDs and detecting stuck open and/or stuck short at the same time. Therefore, the control device does not need to switch between different modes, and hence the control complexity is reduced. 
     The above-described embodiments of the present invention are intended to be illustrative only. Those skilled in the art may devise numerous alternative embodiments without departing from the scope of the following claims.