Patent Publication Number: US-11032881-B2

Title: Controller for controlling light source module

Description:
BACKGROUND 
     In a Light-Emitting Diode (LED) display system such as a Liquid Crystal Display (LCD) TV, a controller is used to control the power of multiple LED strings for back-lighting. Because the controller has a given number of control pins, only a limited number of LED strings can be controlled by one controller. In order to control more LED strings, more controllers are needed, which increases the cost of the system. 
     SUMMARY 
     In embodiments, a controller for controlling a light source module including a first LED array and a second LED array includes a power input terminal, a first power output terminal and a second power output terminal. The power input terminal is operable for receiving electric power from a power converter. The first power output terminal is coupled to the first LED array, and the second power output terminal is coupled to the second LED array. The controller is operable for delivering the electric power to the first LED array via the first power output terminal in a first sequence of discrete time slots, and for delivering the electric power to the second LED array via the second power output terminal in a second sequence of discrete time slots. The first sequence of discrete time slots and the second sequence of discrete time slots are mutually exclusive. 
     In other embodiments, a controller is coupled to a power source and operable for controlling a light source module including a first LED array and a second LED array. Each of the first LED array and the second LED array includes multiple LED strings. The controller includes a switching module and a current regulation module. The switching module is coupled to the first LED array and the second LED array and is operable for alternately delivering power to the first LED array and to the second LED array. In other words, power is delivered to the first LED array (but not to another LED array), and then power is delivered to the second LED array (but not to another LED array), and so on depending on the number of LED arrays, and then the pattern/cycle is repeated. The current regulation module is coupled to the first LED array and the second LED array and is operable for linearly regulating a current of each LED string in the first LED array and a current of each LED string in the second LED array. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of embodiments of the claimed subject matter will become apparent as the following detailed description proceeds, and upon reference to the drawings, wherein like numerals depict like parts, and in which: 
         FIG. 1  shows a light source driving circuit including a controller for controlling a light source module, in accordance with embodiments of the present invention. 
         FIG. 2  shows a light source driving circuit including a controller for controlling a light source module, in accordance with embodiments of the present invention. 
         FIG. 3  shows a timing diagram of a controller for controlling a light source module, in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present invention. While the invention will be described in combination with these embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention. 
       FIG. 1  shows a light source driving circuit  100  including a controller  180  for controlling a light source module, in accordance with embodiments of the present invention. In the example of  FIG. 1 , the light source module includes four LED arrays A 1 , A 2 , A 3  and A 4 , where each LED array includes multiple (e.g., eight) LED strings. This example is used as the basis for the discussion below; however, the invention is not limited to four LED arrays and/or eight LED strings per array. 
     The controller  180  receives electric power from a power converter  120 . The power converter  120  is coupled between the controller  180  and a power source  110 . The controller  180  includes a power input terminal PWIN, a feedback terminal FBOUT, multiple power output terminals PWO 1 -PWO 4  and multiple current sensing terminals ISEN 1 -ISEN 8 . The number of the power output terminals is equal to the number of the LED arrays. The number of the current sensing terminals is equal to the number of the LED strings in each LED array. The controller  180  includes a switching module  130 , a feedback control module  140 , a current regulation module  150  and a decoding module  160 . 
     The power input terminal PWIN is coupled to the power source  110  through the power converter  120  and is operable for receiving electric power from the power converter  120 . The power output terminals PWO 1 -PWO 4  are coupled to the LED arrays A 1 -A 4 , respectively. The controller  180  is operable for delivering the electric power to the LED arrays A 1 -A 4  via the power output terminals PWO 1 -PWO 4  in a first sequence, a second sequence, a third sequence, and a fourth sequence of discrete time slots, respectively. The first, second, third and fourth sequences of discrete time slots are mutually exclusive; that is, they do not overlap in time. 
     More specifically, the switching module  130  includes multiple switches SW 1 -SW 4  that are coupled between the power input terminal PWIN and a corresponding power output terminal. For example, a first switch SW 1  is coupled between the power input terminal PWIN and the first power output terminal PWO 1 , and a second switch SW 2  is coupled between the power input terminal PWIN and the second power output terminal PWO 2 . Referring to  FIG. 3 , the controller  180  is operable for turning on the first switch SW 1  in the first sequence of discrete time slots T 11 , T 12 , T 13 , turning on the second switch SW 2  in the second sequence of discrete time slots T 21 , T 22 , T 23 , turning on the third switch SW 3  in the third sequence of discrete time slots T 31 , T 32 , T 33 , and turning on the fourth switch SW 4  in the fourth sequence of discrete time slots T 41 , T 42 , T 43 . The first, second, third and fourth sequences of discrete time slots are mutually exclusive and are interleaved as shown in the example of  FIG. 3 . 
     With reference back to  FIG. 1 , the current sensing terminals ISEN 1 -ISEN 8  are coupled to the LED arrays A 1 -A 4  for sensing a level of a current of each LED string in the LED arrays A 1 -A 4  in the manner described below. The current regulation module  150  is coupled to the LED arrays A 1 -A 4  via the sensing terminals ISEN 1 -ISEN 8  and is operable for linearly regulating the current of each LED string in the LED arrays A 1 -A 4 , as described further below in the discussion of  FIG. 2 . 
     Continuing with reference to  FIG. 1 , the feedback control module  140  is operable for generating a feedback signal FB based on a power requirement of the light source module to control the power converter  120 , such that the electric power from the power converter can satisfy the power requirement of the light source module. The feedback signal FB is provided to the power converter  120  via the feedback terminal FBOUT. The feedback control module  140  is coupled to the current sensing terminals ISEN 1 -ISEN 8  and generates the feedback signal FB based on the voltages at the current sensing terminals ISEN 1 -ISEN 8 . The voltages at the current sensing terminals ISEN 1 -ISEN 8  can indicate a power requirement of the light source module. More specifically, the feedback control module  140  selects a minimum voltage among the voltages at the current sensing terminals ISEN 1 -ISEN 8  and compares the minimum voltage with a predetermined voltage range to generate the feedback signal FB. The power converter  120 , under control of the feedback signal FB, increases or decreases the electric power such that the minimum voltage is within the predetermined voltage range. 
     The decoding module  160  is operable for receiving a timing signal from a timing controller  190  (e.g., a Micro Controlling Unit) and for generating a switching signal to control the switches SW 1 -SW 4  in the switching module  130  based on the timing signal. The decoding module  160  is further operable for generating multiple control signals to control the current regulation module  150 . Accordingly, multiple current regulation units (shown in  FIG. 2 ) can be independently enabled and disabled by a corresponding control signal. The decoding module  160  can communicate with the timing controller through, for example, a Serial Peripheral Interface (SPI). 
     The LED arrays A 1 -A 4  are configured to receive electric power from power output terminals PWO 1 -PWO 4 , respectively, and share the current sensing terminals ISEN 1 -ISEN 8 . More specifically, the anodes of the LED strings in the first LED array A 1  are connected to a common node N 1 , and the common node N 1  is connected to the first power output terminal PWO 1 . The anodes of the LED strings in the second LED array A 2  are connected to a common node N 2 , and the common node N 2  is connected to the second power output terminal PWO 2 . The anodes of the LED strings in the third LED array A 3  are connected to a common node N 3 , and the common node N 3  is connected to the third power output terminal PWO 3 . The anodes of the LED strings in the fourth LED array A 4  are connected to a common node N 4 , and the common node N 4  is connected to the fourth power output terminal PWO 4 . 
     On the other hand, the cathode of a first LED string in the first LED array A 1 , the cathode of a first LED string in the second LED array A 2 , the cathode of a first LED string in the third LED array A 3  and the cathode of a first LED string in the fourth LED array A 4  are connected to a first common node NC 1 . The common node NC 1  is connected to a current sensing terminal ISEN 1 . Thus, the current sensing terminal ISEN 1  senses the current on each of the first LED strings in each of the LED arrays. Similarly, the cathodes of each of the second LED strings in each LED array are connected to a second common node NC 2  (not shown), which is connected to a current sensing terminal ISEN 2  (not shown), and so on. The cathodes of each of the last (e.g., eighth) LED strings in each LED array are connected to the respective (e.g., eighth) common node NC 8 , which is connected to a current sensing terminal ISEN 8 . 
     In operation, if the switch SW 1  is turned on, then a current flows through the first power output terminal PWO 1 , the common node N 1  to the first LED array A 1 , and then back to the controller  180  through the common nodes NC 1 -NC 8  and the current sensing terminals ISEN 1 -ISEN 8 . If the switch SW 2  is turned on, then a current flows through the second power output terminal PWO 2 , the common node N 2  to the second LED array A 2 , and then back to the controller  180  through the common nodes NC 1 -NC 8  and the current sensing terminals ISEN 1 -ISEN 8 . As such, the configuration of the controller  180  and the structure of the circuit  100  allow the LED arrays A 1 -A 4  to share the same group of current sensing terminals SEN 1 -ISEN 8 . 
       FIG. 2  shows a light source driving circuit  200  including a controller  180  for controlling a light source module, in accordance with embodiments of the present invention.  FIG. 2  shows a detailed view of the internal structure of the controller  180 . The controller  180  includes a switching module  130 , a feedback control module  140 , a current regulation module  150  and a decoding module  160 . 
     The current regulation module  150  includes multiple current regulation units  230 _ 1 - 230 _ 8  coupled to the current sensing terminals ISEN 1 -ISEN 8 , respectively. The current regulation units  230 _ 1 - 230 _ 8  are operable for linearly regulating current of each LED string in the LED arrays A 1 -A 4 , and each current regulation unit is independently and individually enabled and disabled by a corresponding control signal of control signals PWM 1 -PWM 8 . The control signals PWM 1 -PWM 8  can be Pulse Width Modulation (PWM) signals. 
     More specifically, each current regulation unit  230 _ 1 - 230 _ 8  includes a respective amplifier  290 _ 1 - 290 _ 8  coupled to a respective switch Q 1 -Q 8 . Each switch Q 1 -Q 8  is in coupled in series with a corresponding LED string. Each current regulation unit has a similar configuration. Take current regulation unit  230 _ 1  as an example. A non-inverting input of the amplifier  290 _ 1  receives a reference signal ADJ 1  indicative of a target current. An inverting input of the amplifier  290 _ 1  receives a sensing signal IS 1  indicative of a level of a current through the corresponding LED string. The amplifier  290 _ 1  compares the reference signal ADJ 1  with the sensing signal IS 1  to generate an error signal EA 1 , and linearly controls the switch Q 1  with the error signal EA 1  so as to regulate the current of the corresponding LED string so that current is at the target current. The switch Q 1  is controlled linearly means that, instead of either being fully turned on or fully turned off, the switch Q 1  can be partially turned on such that a level of the current flowing through the switch Q 1  can be continuously (non-discretely) and gradually adjusted. 
     The amplifier  290 _ 1  is controlled by a control signal PWM 1 . If the control signal PWM 1  is in a first state (e.g., logic high), then the amplifier  290 _ 1  is enabled and the corresponding LED string is turned on and regulated as described above. If the control signal PWM 1  is in a second state (e.g., logic low), then the amplifier  290 _ 1  is disabled and the corresponding LED string is turned off. 
     In an embodiment, the decoding module  160  includes a SPI decoder  210 , a PWM generator  220 , a digital-analog convertor (DAC)  240 , and a reference selection unit  250 . The SPI decoder  210  receives a timing signal from a timing controller (not shown) and decodes the timing signal. The PWM generator  220  is coupled to the SPI decoder  210  and generates the control signals PWM 1 -PWM 8  based on the timing signal. The DAC  240  is coupled to the SPI decoder and generates reference signals ADJ 1 -ADJ 8 . The reference selection unit  250  selects either the reference signals ADJ 1 -ADJ 8  or a system reference signal SYS_REF that is also generated from the SPI decoder  210 , and supplies the selected signal(s) (e.g., ADJ 1 -ADJ 8  or SYS_REF) to the respective amplifier  290 _ 1 - 290 _ 8 . That is, either the non-inverting input of the amplifier  290 _ 1  receives the signal ADJ 1 , the non-inverting input of the amplifier  290 _ 2  receives the signal ADJ 2 , and so on, or the non-inverting inputs of the amplifiers  290 _ 1 - 290 _ 8  all receive the signal SYS_REF. Furthermore, the decoding module  160  processes the timing signal and provides a switching signal to the switching module  130 . The switching module  130  controls the switches SW 1 -SW 4  with the switching signal to turn on the switches SW 1 -SW 4  in four sequences of discrete time slots that are mutually exclusive. 
     As described above, the present invention includes a controller for controlling a light source module. The controller is operable for alternately delivering electric power to multiple LED arrays, and for regulating the current of each LED string in the LED arrays. The controller enables the LED arrays to share a same group of current sensing terminals of the controller. Advantageously, multiple LED arrays can be controlled by a single controller, and thus the cost of the system is reduced. Moreover, each LED string in the LED arrays can be independently and individually regulated or disabled, which allows flexible and fine (accurate or precise) levels of dimming in a display system. 
     While the foregoing description and drawings represent embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the principles of the present invention as defined in the accompanying claims. One skilled in the art will appreciate that the invention may be used with many modifications of form, structure, arrangement, proportions, materials, elements, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims and their legal equivalents, and not limited to the foregoing description.