Abstract:
An LED display device providing current correction includes a number of LED modules, a microprocessor, and a storage unit storing a standard voltage value. The correction sequence begins with each of the plurality of LED modules entering a work state in sequence, outputting a feedback voltage indicating work current of one of the LED modules to the microprocessor in sequence, comparing the feedback voltage with the standard voltage, adjusting the current of the LED module if the feedback voltage does not equal the standard voltage.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to LED display devices and, particularly, to an LED display device providing current correction and correction method thereof. 
     2. Description of Related Art 
     Conventional LED display devices include many LEDs, and each LED was produced exactly the same during manufacture, as a result, currents through the LEDs differ even when the LEDs are driven by the same voltage. 
     Therefore, it is desirable to provide an LED display device to overcome the described limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present disclosure should be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a circuit diagram of an LED display device capable of correcting its current, in accordance with an exemplary embodiment. 
         FIG. 2  is a flowchart illustrating a method for correcting current of each LED module of a LED display device, such as, for example, that of  FIG. 1 , in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will now be described in detail, with reference to the accompanying drawings. 
     Referring to  FIG. 1 , an LED display device  1  capable of correcting its current is provided in accordance with an exemplary embodiment. The LED display device  1  includes a microprocessor  10 , a feedback voltage generating module  20 , and a number of LED modules  30 . The microprocessor  10  includes a number of output ports P and a feedback port FB. Each output port P is connected to one LED module  30 , and is used to output a pulse width modulation (PWM) signal to turn the LED module  30  on, when the LED display device enters a correction mode. 
     In the embodiment, the LED modules  30  are connected in parallel between a high potential point Vcc and the feedback voltage generating module  20 . Each LED module  30  includes a control switch K and at least one LED D, and is connected between the high potential point Vcc and the feedback voltage generating module  20  in serial. Each output port P of the microprocessor  10  is connected to one control switch K of one LED module  30 , and outputs the PWM signal to turn on the corresponding control switch K and thus turn on the corresponding LED module  30  when the LED display device  1  enters the correction mode. When the control switch K is turned on, current is generated through the at least one LED D connected to the control switch K which is turned on, and the LED module  30  is turned on and is in a work state, namely, the LED module  30  emits light. The feedback voltage generating module  20  further connects to the feedback port FB, and is used to produce a feedback voltage reflecting the current through the LED module  30  which is turned on. The feedback voltage generating module  20  outputs the feedback voltage to the feedback port FB of the microprocessor  10 . 
     The LED display device  1  further includes a storage unit  40 . The storage unit  40  stores a standard voltage value which reflects a standard current through the LED modules  30 . The microprocessor  10  includes a trigger module  101  and a current correction module  102 . The trigger module  101  produces a trigger signal to trigger the LED display device  1  to enter the correction mode. This can take place periodically, namely the trigger module  101  produces the trigger signal at intervals. The interval can be set by the user or be a system default setting. In other embodiments, the trigger module  101  produces the trigger signal when the LED display device  1  starts to turn on or turn off. In another embodiment, the LED display device  1  further includes a particular key (not shown) for directing the trigger module  101  to produce the trigger signal. 
     The current correction module  102  receives the trigger signal and turns the LED module  30  on in sequence. In detail, the current correction module  102  directs one of the output ports P to output a PWM signal to turn on corresponding control switch K in sequence, and the LED modules  30  are turned on in sequence. When one of the LED modules  30  is turned on, the feedback voltage generating module  20  produces a feedback voltage reflecting the current through the LED module  30 , and outputs the feedback voltage to the feedback port FB of the microprocessor  10 . 
     The current correction module  102  receives the feedback voltage via the feedback port FB and compares the feedback voltage with the standard voltage stored in the storage unit  40 , and corrects the PWM signal output by the corresponding output port P according to the comparison result, thereby correcting the value of the current through the LED module  30  which is turned on. In detail, if the feedback voltage is lower than the standard voltage, the current correction module  102  adjusts the PWM signal of the output port P connected to the LED module  30  which is turned on to increase the current through the LED module  30 . If the feedback voltage exceeds the standard voltage, and the current correction module  102  adjusts the PWM signal to reduce the current through the LED module  30 . In the embodiment, the current correction module  102  increases or reduces the current through the LED module  30  by adjusting the duty cycle of the PWM signal. When the duty cycle of the PWM signal is increased, the current through the LED module  30  is increased, and when the duty cycle of the PWM signal is decreased, the current through the LED module  30  is decreased commensurately. 
     In the embodiment, each control switch K includes a control terminal (not labeled), a first path terminal (not labeled), and a second path terminal (not labeled). The control terminals of the control switches K are respectively connected to the output ports P, and the first path terminal of each control switches is connected to the LED D of the corresponding LED module  30 . The feedback voltage generating module  20  includes a resistor Rs connected between all of the second path terminals and the ground. A terminal T of the resistor Rs is connected to the feedback port FB of the microprocessor  10 . In the embodiment, the control switches K are negative-positive-negative (NPN) bipolar junction transistors (BJTs) Q. A base, an emitter, and a collector of the NPN BJTs Q function as the control terminal, the first path terminal, the second path terminal of the control switches K. 
     As described, when the current correction module  102  receives the trigger signal from the trigger module  101 , the current correction module  102  controls the output ports P to respectively output the PWM signal to turn on the control switches K in sequence. When one of the control switches K is turned on, the high potential point Vcc, the corresponding LED module  30 , the resistor Rs, and the ground form a loop, then there is current flows through the LED module  30 , and the resistor Rs. Therefore, the terminal T of the resistor Rs has a voltage, and the voltage is the feedback voltage reflecting the current through the LED module  30  that is turned on currently. As described, the current correction module  102  receives the feedback voltage via the feedback port FB of the microprocessor  10 , and compares the feedback voltage with the standard voltage and adjusts the PWM signal output by the output port P connected to the LED module  30  which is turned on when the feedback voltage does not equal the standard voltage. 
     Thus, in the embodiment, the LED display device  1  can correct the current through LED modules  30  individually when the LED display device  1  enters the correction mode. 
       FIG. 2  is a flowchart illustrating a method for correcting current of each LED module of a LED display device such as, for example, that of  FIG. 1 . In step S 201 , the trigger module  101  produces a trigger signal to trigger the LED display device  1  to enter a correction mode periodically or when the key is operated. 
     In step S 202 , the current correction module  102  turns on the LED modules  30  in sequence when receiving the trigger signal, namely, the current correction module  102  controls the output ports P to output the PWM signal to turn the control switch K of each LED modules  30  on in sequence. 
     In step S 204 , the current correction module  102  compares the feedback voltage with a standard voltage stored in the storage unit  40 . 
     In step S 205 , the current correction module  102  adjusts the PWM signal output by the output port P connected to the LED module  30  which is turned on when the feedback voltage does not equal the standard voltage. Namely, when the feedback voltage is lower than the standard voltage, the current correction module  102  increases the duty cycle of the PWM signal, and when the feedback voltage exceeds the standard voltage, the current correction module  102  decreases the duty cycle of the PWM signal. 
     It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being exemplary embodiments of the present disclosure.