Patent Publication Number: US-2020296812-A1

Title: System, method, and controller for turning on a low-dimming light source rapidly

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a system and method for turning on a low-dimming light source rapidly. More particularly, the invention relates to a system and method for charging the filter capacitor in a light-emitting diode (LED) driving circuit rapidly so that the LED module to be driven can reach its turn-on voltage value within a short time. 
     2. Description of Related Art 
     Nowadays, LEDs have been widely used in various household lighting devices thanks to the advancement of technology, especially the breakthroughs in white LED technology. As a high-performance light source, LEDs have gradually replaced the conventional incandescent lamps and fluorescent lamps and become the mainstream in the lighting market. 
     To enhance the output stability of LEDs, it is common practice to connect a high-capacity capacitor to the output stage of an LED driving circuit. When the light to be output is low-dimming light (i.e., when the output is a low-current one), however, charging the capacitor can be so time-consuming that it takes a very long time to turn on the LED(s) in question; as a result, the user may misjudge the LED(s) as malfunctioning. The aforesaid problem is attributable mainly to the property of the operating voltage of the LED(s). While the capacitor is being charged, and before the voltage of the capacitor reaches the operating voltage of the LED(s), the LED(s) remains in the cut-off state and is therefore unable to emit light because, although supplied with electricity, the LED(s) does not have enough voltage. 
     BRIEF SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide a system for turning on a low-dimming light source rapidly, comprising: an LED driving circuit and a control circuit. The LED driving circuit includes a power source module and an LED module provided at a rear end of the power source module, wherein the LED module is connected to a filter capacitor. The control circuit includes a voltage detection module, a threshold voltage comparison module, and a current control module. The voltage detection module is connected to the filter capacitor through a feedback circuit in order to obtain an operating voltage value of the filter capacitor. The threshold voltage comparison module includes a threshold voltage value that is set according to the LED module and, based on a difference between the operating voltage value of the filter capacitor and the threshold voltage value, output a control signal to the current control module. The current control module is provided between the power source module and the LED module and is configured to be switched to a fast charging mode or a regular output mode according to the control signal and then modulate an output current of the power source module accordingly. 
     Another objective of the present invention is to provide a method for turning on a low-dimming light source rapidly, wherein the method is applied to the foregoing LED driving circuit, comprising: a power source module and an LED module provided at a rear end of the power source module, and the LED module is connected to a filter capacitor. The method includes: obtaining an operating voltage value of the filter capacitor through a control circuit; comparing the operating voltage value with a threshold voltage value by the controller; and switching the controller to a fast charging mode or a regular output mode according to a comparison result, in order for the controller to determine an output current of the power source module accordingly. 
     Still another objective of the present invention is to provide a controller or a plurality of such controllers, wherein the controller(s) is configured to load a program from a storage unit and execute the program so as to perform the above method. 
     Yet another objective of the present invention is to provide a controller for use with an LED driving circuit, wherein the LED driving circuit comprises a power source module and an LED module provided at a rear end of the power source module and connected to a filter capacitor. The controller includes an input end and an output end. The input end is connected to the filter capacitor, in order to obtain an operating voltage of the filter capacitor. When the operating voltage obtained by the input end has yet to reach a threshold voltage value, the output end is switched to a fast charging mode, in which the output end provides a relatively large current output. When the operating voltage obtained by the input end reaches the threshold voltage value, the output end is switched to a regular output mode to provide a relatively stable output, wherein the threshold voltage value is lower than a turn-on voltage value of the LED module. 
     The present invention provides a system and method that can turn on a low-dimming light source rapidly by fast charging the filter capacitor in the light source driving circuit when the light source driving circuit is switched on from the off state. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a block diagram of a system for turning on a low-dimming light source rapidly according to the present invention. 
         FIG. 2  shows the driving voltage of the LED. 
         FIG. 3  is a block diagram of the control circuit implemented as a controller according to the present invention. 
         FIG. 4  is a circuit diagram of the first embodiment of the feedback circuit of the present invention. 
         FIG. 5  is a circuit diagram of the second embodiment of the feedback circuit of the present invention. 
         FIG. 6  is a circuit diagram of the third embodiment of the feedback circuit of the present invention. 
         FIG. 7  is a flowchart of the method for turning on a low-dimming light source rapidly according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The details and technical solution of the present invention are hereunder described with reference to accompanying drawings. For illustrative sake, the accompanying drawings are not drawn to scale. The accompanying drawings and the scale thereof are not restrictive of the present invention. 
     A detailed description of some illustrative embodiments of the present invention is given below. Please refer to  FIG. 1  for a block diagram of a system for turning on a low-dimming light source rapidly according to the invention. 
     The embodiment shown in  FIG. 1  discloses a system  100  for turning on a low-dimming light source rapidly. The system  100  essentially includes an LED driving circuit  10  and a control circuit  20  connected to the LED driving circuit  10 . 
     The LED driving circuit  10  essentially includes a power source module  11  and an LED module  12  provided at the rear end of the power source module  11 . The LED module  12  is connected to a filter capacitor  13 . The filter capacitor  13  is connected in parallel to the LED module  12  and serves to provide a stable bias voltage to the LED module  12  after being charged. 
     The control circuit  20  essentially includes a voltage detection module  21 , a threshold voltage comparison module  22 , and a current control module  23 . To facilitate circuit design, it is feasible to integrate the voltage detection module  21 , the threshold voltage comparison module  22 , and the current control module  23  into a single chip. Alternatively, selected functions of one or more of the modules can be performed by separate chips respectively. The present invention has no limitation on the number of chips used to implement the voltage detection module  21 , the threshold voltage comparison module  22 , and the current control module  23 . The aforesaid chips may include, for example but not limited to, a central processing unit (CPU), a programmable general-purpose or application-specific microprocessor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), other similar devices, or a combination of the above. 
     The voltage detection module  21  is connected to the filter capacitor  13  through a feedback circuit  30  in order to obtain the operating voltage value of the filter capacitor  13 . The design of the feedback circuit  30 , though not a characterizing feature of the present invention, will be described in more detail below with reference to specific embodiments and the accompanying drawings. The voltage detection module  21  may be configured to modulate the operating voltage obtained and to output the modulated voltage to the threshold voltage comparison module  22  at its rear end in order to reduce the power consumption of the load. 
     The threshold voltage comparison module  22  includes a threshold voltage value that is set according to the LED module  12 . The threshold voltage comparison module  22  is connected to the output end of the voltage detection module  21  in order to obtain the operating voltage value of the filter capacitor  13  and, based on the difference between the operating voltage value of the filter capacitor  13  and the threshold voltage value, output a control signal to the current control module  23 . In one embodiment, the threshold voltage comparison module  22  is a comparator whose positive and negative input ends are supplied respectively with the output of the voltage detection module  21  (which output may be the operating voltage value of the filter capacitor  13  as is or a modulated voltage) and the preset threshold voltage value, and which switches its output between high and low according to the comparison result of the two input values. To protect the LED module  12  in this embodiment, referring to  FIG. 2 , it is preferable that the threshold voltage value V th  is slightly lower than the turn-on voltage value (i.e., driving voltage value) V d  of the LED module  12 , the objective being to ensure that the current control module  23  is switched from a fast charging mode to a regular output mode before the operating voltage value of the LED module  12  reaches that required for emitting low-dimming light. The setting of the threshold voltage value V th  depends mainly on the clock performance of the related chip(s) and the charging speed. 
     The current control module  23  is provided between the power source module  11  and the LED module  12  and is configured to be switched to the fast charging mode or the regular output mode according to the control signal and then modulate the output current of the power source module  11  accordingly. In one embodiment, the current control module  23  includes a current setting module  231 , a pulse width modulator (PWM)  232 , and a field-effect transistor (FET)  233  provided between the power source module  11  and the LED module  12 . The current setting module  231 , or more particularly its current outputs corresponding respectively to the activation of the fast charging mode and the activation of the regular output mode, are preset by the chip designer. The pulse width modulator  232  has its output connected to the gate of the field-effect transistor  233  and is configured to modulate the output of the current setting module  231 , in order for the duty cycle or trigger frequency of the modulated pulses to determine the on and off time of the field-effect transistor  233  and consequently the current output by the power source module  11  to the LED module  12 , thereby achieving the objective of current control. 
     In one embodiment, the control circuit  20  is implemented as a single chip (e.g., a controller) or a microprocessor. Please refer to  FIG. 3  for a block diagram of the control circuit implemented as a controller. 
     As shown in  FIG. 3 , the controller  20 A includes at least one input end  21 A (other necessary inputs such as the power source input Vcc are omitted herein for the sake of brevity) and at least one output end  22 A. The input end  21 A is connected to the filter capacitor  13  for the LED module  12 , either directly or indirectly, in order to obtain the operating voltage of the filter capacitor  13 . When the operating voltage obtained by the input end  21 A has yet to reach the threshold voltage value, the output end  22 A is switched to the fast charging mode, in which the output end  22 A provides a relatively large current output. When the operating voltage obtained by the input end  21 A reaches the threshold voltage value, the output end  22 A is switched to the regular output mode to provide a relatively stable output. It should be pointed out that the threshold voltage value is lower than the turn-on voltage value of the LED module  12 , so the controller  20 A is switched from the fast charging mode to the regular output mode before the turn-on voltage value of the LED module  12  is reached. This allows the filter capacitor  13  to complete its charging process and be activated rapidly when the light to be output is low-dimming light. The “relatively large” current output provided by the output end  22 A in the fast charging mode is in relative terms in comparison with the output current in the regular output mode. Similarly, the “relatively stable” output provided by the output end  22 A in the regular output mode is in relative terms in comparison with the output current in the fast charging mode. 
     The following paragraphs describe various embodiments of the feedback circuit  30 . The functional modules and circuits used in conjunction with those embodiments are the same as those illustrated in  FIG. 1  and therefore will not be described repeatedly. Please refer to  FIG. 4  for a circuit diagram of the first embodiment of the feedback circuit of the present invention. 
     In this embodiment, the feedback circuit  30 A uses a pair of inductors to deliver as feedback to the voltage detection module  21  of the control circuit  20  the current output by the power source module  11  to the filter capacitor  13 . More specifically, the feedback circuit  30 A according to this embodiment includes a primary winding  31 A and a secondary winding  32 A. The primary winding  31 A is connected in series to the filter capacitor  13 . The secondary winding  32 A is provided at the input end of the voltage detection module  21  and is coupled to the primary winding  31 A such that the induced electromotive force generated by the primary winding  31 A (i.e., the first inductor) acts on the secondary winding  32 A (i.e., the second inductor). The voltage detection module  21  can obtain the operating voltage value of the filter capacitor  13  by detecting the voltage across the two ends of the secondary winding  32 A or the current flowing through the secondary winding  32 A. 
     In this embodiment, the primary winding  31 A and the secondary winding  32 A in the feedback circuit  30 A can isolate the power source module  11  from the control circuit  20 . The primary winding  31 A also provides noise suppression. 
     Please refer to  FIG. 5  for the second embodiment of the feedback circuit of the present invention. 
     This embodiment provides a feedback circuit  30 B that includes a first circuit  31 B and a second circuit  32 B. The first circuit  31 B is connected to the high-voltage end of the filter capacitor  13  and the high-voltage end of the voltage detection module  21 . The second circuit  32 B is connected to the low-voltage end of the filter capacitor  13  and the low-voltage end of the voltage detection module  21 . In addition, the second circuit  32 B is electrically connected to a ground end  33 B. By connecting the voltage detection module  21  and the filter capacitor  13  to a common ground, the voltage detection module  21  in this embodiment can directly obtain the operating voltage of the filter capacitor  13  as input. 
     Please refer to  FIG. 6  for the third embodiment of the feedback circuit of the present invention. 
     This embodiment provides a feedback circuit  30 C that gives feedback to the voltage detection module  21  without having to connect the voltage detection module  21  and the filter capacitor  13  to a common ground. In terms of circuit configuration, the feedback circuit  30 C includes a first circuit  31 C and a second circuit  32 C. The first circuit  31 C is connected to the high-voltage end of the filter capacitor  13  and the high-voltage end of the voltage detection module  21  and is connected in series to a first load  311 C. The second circuit  32 C is connected to the low-voltage end of the filter capacitor  13  and the low-voltage end of the voltage detection module  21  and is connected in series to a second load  321 C. Thus, the feedback circuit  30 C, which does not connect the voltage detection module  21  and the filter capacitor  13  to a common ground, allows the voltage detection module  21  to obtain the voltage across the two ends of the filter capacitor  13 . 
     The various embodiments described above are only some feasible and preferred ones of the present invention; the scope of the invention is not confined to the contents of those embodiments. 
     The present invention also provides a method for turning on a low-dimming light source rapidly as detailed below with reference to the accompanying drawings. Please refer to  FIG. 7  in conjunction with  FIG. 1  for a flowchart of the method for turning on a low-dimming light source rapidly according to the invention. 
     The embodiment shown in  FIG. 7  discloses a method for turning on a low-dimming light source rapidly, wherein the method is applied to the foregoing LED driving circuit  10 . As stated above, the LED driving circuit  10  includes the power source module  11  and the LED module  12 , which is provided at the rear end of the power source module  11  and is connected to the filter capacitor  13 . The method essentially includes the following steps: 
     Step S 01 : The control circuit  20 , which is configured for obtaining the operating voltage value of the filter capacitor  13 , is provided. 
     Step S 02 : The control circuit  20  compares the operating voltage value with a threshold voltage value, wherein the threshold voltage value is lower than the turn-on voltage value of the LED module  12 . 
     Step S 03 : Based on the comparison result, the control circuit  20  is switched to a fast charging mode or a regular output mode and determines the output current of the power source module  11  accordingly. More specifically, upon detecting that the operating voltage value of the filter capacitor  13  is lower than the threshold voltage value, the control circuit  20  activates the fast charging mode in order for the filter capacitor  13  to be supplied, and thus charged, with a large current; and upon detecting that the operating voltage value of the filter capacitor  13  reaches the threshold voltage value, the control circuit  20  activates the regular output mode in order for the LED module  12  to be supplied with a stable current. 
     The method described above can be carried out by a single programmable controller or a plurality of such controllers, wherein the controller(s) is configured to load a program from a storage unit and execute the program so as to perform steps S 01  to S 03 . The storage unit may be, for example, a non-transitory computer-readable recording medium. 
     In summary of the above, the present invention provides a system and method that can turn on a low-dimming light source rapidly by fast charging the filter capacitor in the light source driving circuit when the light source driving circuit is switched on from the off state. 
     The above is the detailed description of the present invention. However, the above is merely the preferred embodiment of the present invention and cannot be the limitation to the implement scope of the invention, which means the variation and modification according to the present invention may still fall into the scope of the invention.