Patent Publication Number: US-9900940-B2

Title: Light-emitting diode device

Description:
This application claims the benefit of Taiwan application Serial No. 104129505, filed Sep. 7, 2015, the disclosure of which is incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     The disclosure relates in general to a light-emitting diode (LED) device, and more particularly to an LED device capable of controlling a magnitude of a driving current. 
     BACKGROUND 
     A conventional light-emitting diode (LED) module is driven by a driving circuit. Based on the magnitude of the driving current required for driving an LED module, a corresponding driving circuit is selected to work with the LED module. When many LED modules requiring different driving currents are used, different driving circuits for providing the required driving currents need to be designed, not only increasing design and manufacturing costs but also adding extra workload to warehousing management, material assignment and component assembly. 
     Therefore, it has become a prominent task for the industry to provide a new LED device for resolving the above problems. 
     SUMMARY 
     The disclosure is directed to a light-emitting diode (LED) device capable of reducing both the design cost and the manufacturing cast. 
     According to one embodiment, a light-emitting diode (LED) device including an LED module and a driver is provided. The LED module includes a voltage sensing module and an LED. The voltage sensing module is configured to generate a reference voltage. The driver includes a power converting module, a current processing module, a feedback module and a controller module. The power converting module is configured to receive and convert an alternating current (AC) into a driving current for driving the LED to emit a light. The current processing module is configured to convert the driving current into a sensing voltage. The feedback module is configured to compare the sensing voltage with a reference voltage and output a level signal according to a magnitude relationship of the sensing voltage and the reference voltage. The controller module is configured to output a pulse width modulation (PWM) signal to the power converting module according to the level signal. The power converting module is further configured to control the magnitude of the driving current according to the PWM signal. 
     The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment (s). The following description is made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an LED device according to an embodiment of the invention. 
         FIG. 2  is functional diagram of the LED device of  FIG. 1 . 
         FIG. 3  is a curve diagram of driving current according to an embodiment of the invention. 
         FIG. 4  is a diagram of PWM signal according to an embodiment of the invention. 
         FIG. 5  is a diagram of PWM signal according to another embodiment of the invention. 
         FIG. 6  is a circuit diagram of the LED module and the driver of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Refer to  FIGS. 1 and 2 .  FIG. 1  is a cross-sectional view of an LED device  100  according to an embodiment of the invention.  FIG. 2  is functional diagram of the LED device  100  of  FIG. 1 . 
     As indicated in  FIG. 1 , the light-emitting diode (LED) device  100  can be realized by a bulb or an LED tube containing LED bars. The LED device  100  includes an LED module  110  and a driver  120 . The LED module  110  and the driver  120  are two separate elements. That is, the LED module  110  and the driver  120  are not integrated into one element but are manufactured separately. Under such design, the driver  120  can be realized by a switch mode driver. 
     As indicated in  FIG. 2 , the LED module  110  includes a voltage sensing module  111 , a plurality of LEDs  112  and a circuit board  113 . The voltage sensing module  111  and the LEDs  112  are disposed on the circuit board  113  as indicated in  FIG. 1 . The driver  120  can be electrically connected to the circuit board  113  for controlling the voltage sensing module  111  and the LEDs  112  which are disposed on the circuit board  113 . 
     The voltage sensing module  111  is configured to generate a reference voltage V REF . The reference voltage V REF  is determined according to the magnitude of the current required by the LED module  110 . For example, the more the magnitude of the current required by the LED module  110  is, the higher the reference voltage V REF  can be set to. For example, the magnitude of current is larger when the quantity of the LEDs  112  is more. Conversely, the smaller the magnitude of the current required by the LED module  110  is, the lower the reference voltage V REF  can be set to. The driver  120  can provide the driving current I LED  required by the LED module  110  according to the magnitude of the reference voltage V REF . Thus, the same driver  120  can provide different currents required by the LED module  110  and there is no need to design different drivers  120  to provide different currents required by the LED module  110 , not only reducing the design cost and the manufacturing cost of the LED device  100  but also reducing the workload in warehousing management, material assignment and component assembly. 
     The driver  120  includes a power converting module  121 , a current processing module  122 , a feedback module  123  and a controller module  124 . 
     The power converting module  121  is configured to receive an alternating current AC from the power module  10  and further converting the alternating current AC into a direct current driving current I LED . The alternating current AC is provided by such as a mains supply. The driving current I LED  is configured to drive the LEDs  112  to emit a light. The driving current I LED  could be higher or lower than the current required by the LED module  110 . 
     As indicated in  FIG. 3 , a curve diagram of driving current I LED  according to an embodiment of the invention is shown. For example, when the LED device  100  is turned on, the driving current I LED  starts to boost from 0, but the driving current I LED1  at the initial stage is insufficient to provide the current I 0  required by the LED module  110 . Then, the driving current I LED  continues to boost, and may even exceed the current I 0  required by the LED module  110  and reach, for example, a driving current I LED2 . If the driving current I LED  is too small, the LED module  110  will have insufficient brightness. Conversely, if the driving current I LED  is too large, the driving current I LED  may damage the LED module  110 . By using following methods, the driving current I LED  can be boosted or dropped to be basically equivalent to the current I 0  required by the LED module  110 , such that the LED module  110  can provide brightness conformed to the specification of design and at the same time the LED module  110  will not be overloaded. 
     For example, the current processing module  122  converts the driving current I LED  outputted from the power converting module  121  into a sensing voltage V S . Then, the feedback module  123  compares the sensing voltage V S  with a reference voltage V REF  and outputs a level signal P 1  according to a magnitude relationship of the sensing voltage V S  and the reference voltage V REF . Then, the controller module  124  outputs a PWM signal P 2  to the power converting module  121  according to the level signal P 1 . Then, the power converting module  121  controls the magnitude of the driving current I LED  according to PWM signal P 2 . The above procedures can be repeated until the driving current I LED  is basically equivalent to the current I 0 . Detailed descriptions are disclosed below. 
     The current processing module  122  includes a current sensing module  1221  and an amplifier module  1222 . The current sensing module  1221  converts the driving current I LED  into a current signal I S , and the amplifier module  1222  further amplifies the current signal and converts the current signal I S  into a sensing voltage V S . 
     The feedback module  123  compares the sensing voltage V S  with a reference voltage V REF  and outputs a level signal P 1  according to a magnitude relationship of the sensing voltage V S  and the reference voltage V REF . For example, if the reference voltage V REF  is higher than the sensing voltage V S , the level signal P 1  is set as one of a low-level signal and a high-level signal. In an embodiment of the invention, if the reference voltage V REF  is higher than the sensing voltage V S , then the level signal P 1  is at a low level; if the reference voltage V REF  is lower than the sensing voltage V S , then the level signal P 1  is at a high level. 
     Refer to  FIGS. 1 and 4 .  FIG. 4  is a diagram of PWM signal according to an embodiment of the invention. The controller module  124  outputs a PWM signal P 2  to the power converting module  121  according to the level signal P 1 . When the controller module  124  receives a level signal P 1  at a low level (in the present example, this indicates that the reference voltage V REF  is higher than the sensing voltage V S ), this indicates that the driving current I LED  is larger than the current I 0  required by the LED module  110 . As indicated in  FIG. 3 , the driving current I LED1  is smaller than the required current I 0 . Therefore, in  FIG. 4 , the controller module  124  increases the duty cycle W 1  of PWM signal P 2 , for example, from 10% (indicated by dotted lines) to 20% (indicated by solid lines). However, in other embodiments of the invention, the duty cycle W 1  is not limited to the said exemplification. For example, the duty cycle W 1  can be defined as t/T, that is, a ratio of the turn-on time t to the period T. 
     Then, the power converting module  121  controls the magnitude of the driving current I LED  according to the PWM signal P 2 . For example, when the duty cycle W 1  of  FIG. 4  is increased, the power converting module  121  increases the driving current I LED  provided to the LED module  110 , and the driving current I LED  is boosted to I LED1  from I LED1  as indicated in  FIG. 3 . 
     Then, based on the above principles, the driver  120  continues to judge the magnitude of the sensing voltage V S  and the reference voltage V REF , converts the sensing voltage V S  into a corresponding driving current I LED  and further provides the corresponding driving current I LED  to the LED module  110 , such that the driving current I LED  gets closer and closer to the driving current I 0 . 
     Refer to  FIGS. 1 and 5 .  FIG. 5  is a diagram of PWM signal according to another embodiment of the invention is shown. When the controller module  124  receives a level signal P 1  at a high-level (in the present example, this indicates that the reference voltage V REF  is lower than the sensing voltage V S ), this indicates that the driving current I LED  is larger than the current I 0  required by the LED module  110 . As indicated in  FIG. 3 , the driving current I LED2  is larger than the required current I 0 . Therefore, in  FIG. 5 , the controller module  124  decreases the duty cycle W 1  of the PWM signal P 2 , from example, from 70% (indicated by dotted lines) to 60% (indicated by solid lines). However, in other embodiments of the invention, the duty cycle W 1  is not limited to the said exemplification. 
     Then, the power converting module  121  controls the magnitude of the driving current I LED  according to the PWM signal P 2 . For example, since the duty cycle W 1  of  FIG. 5  is decreased, the power converting module  121  decreases the driving current I LED  provided to the LED module  110 , and the driving current I LED  drops to the required current I 0  from the driving current I LED2  as indicated in  FIG. 3 . 
     Then, based on the above principles, the driver  120  continues to judge the magnitude of the sensing voltage V S  and the reference voltage V REF , converts the sensing voltage V S  into a corresponding driving current I LED  and further provides the corresponding driving current I LED  to the LED module  110 , such that the driving current I LED  is within the permissible range of the current I 0  required by the LED module  110 . 
     It can be known from the above disclosure that the duty cycle W 1  of the PWM signal P 2  is proportional to the sensing voltage V S , and the driving current I LED  is proportional to duty cycle W 1 . 
       FIG. 6  is a circuit diagram of the LED module  110  and the driver  120  of  FIG. 1 . The voltage sensing module  111  includes a diode D Z , such as a Zener diode. The reference voltage V REF  is determined according to the reverse voltage of the diode D Z . For example, when the diode D Z  has a reverse voltage of 17 volts (V), the reference voltage V REF  is also about 17 V. Thus, the reference voltage V REF  with different design values can be obtained by selecting the diode D Z  with different reverse voltages. 
     The power converting module  121  includes a rectifier  1211 , a transformer  1212  and a switch  1213 . The rectifier  1211  converts an alternating current AC into a direct current DC. The transformer  1212  changes, for example, drops or boosts the voltage of the direct current DC to a driving voltage V LED . The switch  1213  controls the transformer  1212  to be turned on/off according to the PWM signal P 2 . For example, when the PWM signal P 2  is in an ON state, the switch  1213  controls the transformer  1212  to be turned on; when the PWM signal P 2  is in an OFF state, the switch  1213  controls the transformer  1212  to be turned off. 
     The current sensing module  1221  can be realized by such as a resistor R S . The current signal I S  is a diverted current of the driving current I LED , and the value of the current signal I S  is determined according to the value of the resistor R S . That is, a corresponding current signal I S  can be obtained through the design of the resistor R S . 
     The amplifier module  1222  can be composed of an amplifier  1222   a  and two series-connected resistors R 2  and R 3 . When the current signal I S  flows through the resistor R 3 , a corresponding voltage difference V 3  will be generated. 
     The feedback module  123  can be realized by such as a comparer, which compares the magnitude of the sensing voltage V S  with that of the reference voltage V REF  and accordingly outputs a level signal P 1 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.