LED driver circuit and the method thereof

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.

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. 1shows a conventional LED driver circuit100, which is connected to a control-end processor200and serves as the driver for a plurality of LEDs400. The LED driver circuit100comprises a shift register110, a plurality of latches120, a plurality of driver units130, a plurality of comparators140, a plurality of state registers150and a state switching circuit160, wherein the number of the flip-flops in the shift register110, the number of the plurality of latches120, the number of the plurality of driver units130and the number of the plurality of LEDs400are the same. The input signals of the LED driver circuit100include an input data, a latch signal, a switch signal and a clock signal. The output signal of the LED driver circuit100includes an output data. The input terminal of the LED driver circuit100for the input data is connected to the first flip-flop of the shift register110. The output terminal of the LED driver circuit100for the output data is connected to the last flip-flop of the shift register110.

The state switching circuit160determines the status of the LED driver circuit100according to the latch signal and the switch signal. When in a display mode, the LED driver circuit100receives display signals from the control-end processor200. The received display signals are then serially stored in the shift register110. When the storing process of the display signals is completed, the data stored in the shift register110is then outputted to and stored in the plurality of latches120. The output terminals of the plurality of latches120are connected to the plurality of driver units130respectively. The plurality of driver units130have their output terminals connected to, and accordingly drive, the plurality of LEDs400.

When in a debug mode, the LED driver circuit100receives fault-detecting signals (such as the signals of which the bits are all 0s or all 1s) from the control-end processor200. The received fault-detecting signals are then serially stored in the shift register110. When the storing process of the fault-detecting signals is complete, the data stored in the shift register110is then outputted to and stored in the plurality of latches120so as to be the input signal for the plurality of driver units130. The input terminals of the plurality of comparators140are respectively connected to the output terminals of the plurality of LEDs400and a reference voltage. The output signals of the comparators140indicate whether the plurality of LEDs400are in fault state. The plurality of state registers150store the comparison results of the plurality of comparators140, and then stores such results to the shift register110at a later time such that the results can be outputted and transmitted back to the control-end processor200. The control-end processor200obtains the fault information of the plurality of LEDs400according 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 LEDs400, and the comparison results contain bits of “0”, then the control-end processor200determines that the LEDs400at the corresponding locations are faulty.

FIG. 2shows the waveforms of the input and output signals of the LED driver circuit100. As shown inFIG. 2, the clock signal controls the input operation of the shift register110. When in the display mode, the display signals are serially stored into the shift register110. At such point, the output signals of the LED driver circuit100are 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 register110to be stored into the plurality of latches120. The switch signal then switches to low to activate the plurality of driver units130, and the plurality of LEDs400are driven thereby according to the data stored in the plurality of latches120. At such point, the output signal is the display signals. After the state switching circuit160switches the mode of the LED driver circuit100to the debug mode, the driver circuit100is ready for the fault detection of the plurality of LEDs, or is ready to transmit the data stored in the plurality of state registers150back to the control-end processor200. At such point, the output signal is the fault information. As shown inFIG. 2, the modes of the driver circuit100further 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 processor200. Moreover, the addition of the plurality of state registers150and the state switching circuit160increases 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.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3shows an LED driving method and the circuit thereof according to one embodiment of the present invention. The LED driver circuit300is connected to the control-end processor200, and serves as the driver for the plurality of LEDs400. The LED driver circuit300comprises a shift register310, a plurality of latches320, a plurality of driver units330and a plurality of fault-detecting units340, such as comparators, wherein the number of the flip-flops in the shift register310, the number of the plurality of latches320, the number of the plurality of driver units330, the number of the fault-detecting units340and the number of the plurality of LEDs400are the same. The input signals of the LED driver circuit300include an input data, a latch signal, a switch signal and a clock signal. The output signal of the LED driver circuit300includes an output data. The input terminal of the LED driver circuit300for the input data is connected to the first flip-flop of the shift register310. The output terminal of the LED driver circuit300for the output data is connected to the last flip-flop of the shift register310.

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 circuit160in the conventional LED driver circuit100is not required. When in the display mode, the LED driver circuit300receives the display signals from the control-end processor200. The received display signals are then serially stored in the shift register310. When the storing process of the display signals is completed, the data stored in the shift register310is then outputted to and stored in the plurality of latches320. The output terminals of the plurality of latches320are connected to the plurality of driver units330, respectively. The plurality of driver units330have their output terminals connected to, and accordingly drive, the plurality of LEDs400. The input terminals of the plurality of comparators340are respectively connected to the output terminals of the plurality of LEDs400and a reference voltage. The output signals of the comparators340indicate whether the plurality of LEDs400are in fault state. The plurality of comparators340can detect two kinds of fault states of the plurality of LEDs400, i.e., whether the plurality of LEDs400are stuck short or stuck open. For instance, if the display signals stored in the plurality of latches320contain a bit of “1”, and the corresponding bit of the output signals of the plurality of comparators340is “0”, then the corresponding LED400is stuck open. If the display signals stored in the plurality of latches320contain a bit of “0”, and the corresponding bit of the output signals of the plurality of comparators340is “1”, then the corresponding LED400is stuck short. After the plurality of LEDs400are driven and activated, the plurality of comparators340store the comparison results into the shift register310before the next clock signal pulse arrives. The comparison results are then outputted serially from the output terminal of the LED driver circuit300. 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 processor200in real time.

FIG. 4shows the flow chart of an LED driving method according to the embodiment of the present invention. In step S1, a series of display signals outputted by the control-end processor200are stored in the shift register310. In step S2, the data stored in the shift register310is stored into the plurality of latches320. In step S3, the plurality of LEDs400are driven according to the data stored in the plurality of latches320. In step S4, the fault information of the plurality of LEDs400is stored into the shift register310. In step S5, the LED driver circuit300serially outputs the comparison results.

FIG. 5shows the waveforms of the input and output signals of the LED driver circuit300. As shown inFIG. 5, the clock signal controls the input operation of the shift register310. When in display mode, the display signals are serially stored into the shift register310. When the storing process of the display signals is completed, a pulse of the latch signal triggers the data stored in the shift register310to be stored into the plurality of latches320. The switch signal then switches to low to activate the plurality of driver units330, and the plurality of LEDs400are driven thereby according to the data stored in the plurality of latches320. The fault information of the plurality of comparators340is stored into the shift register310before 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 circuit300receives the display signals and drives the plurality of LEDs400, the fault information of the plurality of LEDs400is outputted in real time. Therefore, the plurality of state registers150of the conventional LED driver circuit100are not required in the LED driver circuit300.

The control-end processor200compares the received fault information to the corresponding display signals to obtain the fault status of the plurality of LEDs400. 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.