Patent Publication Number: US-2015062978-A1

Title: Circuit for generating reference signal for controlling peak current of converter switch, isolated converter and method for generating reference signal for controlling peak current of converter switch

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of and priority under 35 U.S.C. §119 to Korean Patent Application No. KR 10-2013-0104131, entitled “CIRCUIT FOR GENERATING REFERENCE SIGNAL FOR CONTROLLING PEAK CURRENT OF CONVERTER SWITCH, ISOLATED CONVERTER AND METHOD FOR GENERATING REFERENCE SIGNAL FOR CONTROLLING PEAK CURRENT OF CONVERTER SWITCH,” filed on Aug. 30, 2013, which is hereby incorporated by reference in its entirety into this application. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a circuit for generating a reference signal for controlling a peak current of a converter switch, an isolated converter, and a method for generating a reference signal for controlling a peak current of a converter switch, and more particularly, to a circuit for generating a reference signal for controlling a peak current of a converter switch, an isolated converter, and a method for generating a reference signal for controlling a peak current of a converter switch, which generate a reference signal for controlling a peak current using a dead-zone added signal. 
     2. Description of the Related Art 
     An isolated converter transfers a current from a primary side to a secondary side by a switching operation. When a converter switch, for example, a MOSFET switch is turned on, an inductor current is increased during a turn-on period. When the inductor current is increased to reach a set peak level, the converter switch is turned off. When the converter switch is turned off, the current is transferred to the secondary side. 
     In a flyback or buck-boost converter type LED driver, which operates in DCM or CRM, an LED current is determined by a peak current flowing in a MOSFET, a switching cycle, and a current transfer time to a secondary side. The LED current ILED on the secondary side is a value that varies according to power and load if there is no special control. However, the higher the fluctuations of the LED current on the secondary side, the worse the line regulation and load regulation characteristics. Therefore, it is needed to suppress the secondary-side current fluctuations. 
     When controlling a converter switch from a primary-side sensing voltage, not controlling the converter switch by receiving a secondary-side output, a peak current of the converter switch should be controlled properly to improve a total harmonic distortion (THD) and a power factor (PF). 
     RELATED ART DOCUMENTS 
     
         
         U.S. Patent Publication No. US 2012/0139438 (Jun. 7, 2012) 
         U.S. Pat. No. 7,443,700 (Oct. 28, 2008) 
       
    
     SUMMARY 
     Accordingly, embodiments of the invention have been made to overcome the above-described problems and it is, therefore, an object of the present invention to provide a technology that controls a peak current of a converter switch using primary-side sensing information without sensing and feeding back a secondary-side output in an isolated converter, for example, a technology that controls the peak current of the converter switch by adding a dead-zone to an input voltage signal divided or detected from a primary-side supply voltage and using a signal proportional to the dead-zone added signal. 
     In accordance with an embodiment of the invention, there is provided a circuit for generating a reference signal for controlling a peak current of a converter switch, including a dead-zone generator for forming a dead-zone in an input voltage signal divided from a primary-side supply voltage of an isolated converter, a duty ratio calculator for calculating a duty ratio of energy transfer to a secondary side, and an operator for generating and outputting the reference signal for controlling the peak current of the converter switch from a dead-zone voltage signal having the dead-zone using the duty ratio of energy transfer calculated by the duty ratio calculator. 
     For example, according to at least one embodiment, the circuit for generating a reference signal for controlling a peak current of a converter switch further includes an automatic gain controller (AGC), which controls a gain of the dead-zone voltage signal output from the dead-zone generator to have a predetermined peak value and outputs the gain-controlled signal to the operator. 
     According to at least one embodiment, the operator includes a multiplier for multiplying the duty ratio of energy transfer, which is calculated by the duty ratio calculator, by a predetermined gain to adjust a secondary-side output, and a divider for generating and outputting the reference signal for controlling the peak current by dividing an output signal of the AGC by an output of the multiplier. 
     According to at least one embodiment, the calculator calculates a time of energy transfer with respect to a cycle of a driving signal as the duty ratio of energy transfer by receiving the driving signal for driving a converter switch and the time of energy transfer to the secondary side. 
     According to at least one embodiment, the reference signal for controlling the peak current output from the operator is compared with a primary-side sensing voltage signal, and the driving signal of the converter switch is generated according to the results of the comparison. 
     According to at least one embodiment, the isolated converter is a flyback converter. 
     In accordance with another embodiment of the invention, there is provided an isolated converter including a transformer including a primary-side winding, a secondary-side main winding, and a secondary-side auxiliary winding; a converter switch connected to the primary-side winding and switched to transfer a primary-side supply voltage to a secondary side through the transformer; an energy transfer time detector for detecting a time of energy transfer to the secondary side from the secondary-side auxiliary winding according to the switching of the converter switch; a circuit for generating a reference signal for controlling a peak current of the converter switch according to the embodiment of the invention discussed above; and a control block for generating and outputting a driving signal of the converter switch by comparing a primary-side sensing voltage signal with the reference signal for controlling the peak current generated by the circuit for generating a reference signal. 
     According to at least one embodiment, the circuit for generating a reference signal of the isolated converter further includes an AGC, which controls a gain of the dead-zone voltage signal output from the dead-zone generator to have a predetermined peak value and outputs the gain-controlled signal to the operator. Further, the operator of the circuit for generating a reference signal includes a multiplier for multiplying the duty ratio of energy transfer, which is calculated by the duty ratio calculator, by a predetermined gain to adjust a secondary-side output, and a divider for generating and outputting the reference signal for controlling the peak current by dividing an output signal of the AGC by an output of the multiplier. 
     According to at least one embodiment, the duty ratio calculator of the circuit for generating a reference signal calculates the time of energy transfer with respect to a cycle of the driving signal as an energy transfer duty ratio by receiving the driving signal for driving the converter switch and the time of energy transfer output from the energy transfer time detector. 
     According to at least one embodiment, the controller block includes a comparator for receiving and comparing the primary-side sensing voltage signal and the reference signal for controlling the peak current generated by the circuit for generating a reference signal, an on-time generator for determining an on operation time of the converter switch from a signal output from the secondary-side auxiliary winding, and a flip-flop for outputting the driving signal of the converter switch by receiving an output of the comparator and an output of the on-time generator. 
     According to at least one embodiment, the isolated converter further includes a voltage divider for dividing the primary-side supply voltage to provide the divided input voltage signal to a dead-zone generator, and a secondary output block including a rectifier diode connected to the secondary side of the transformer to rectify a secondary-side output and an output capacitor for charging a DC voltage rectified by the rectifier diode. 
     According to at least one embodiment, the isolated converter is a flyback converter. 
     In accordance with yet another embodiment of the invention, there is provided a method for generating a reference signal for controlling a peak current of a converter switch, which includes the steps of forming a dead-zone in an input voltage signal divided from a primary-side supply voltage of an isolated converter; calculating a duty ratio of energy transfer to a secondary side of the isolated converter; and generating a reference signal for controlling a peak current of a converter switch from a dead-zone voltage signal having the dead-zone using the duty ratio of energy transfer. 
     According to at least one embodiment, the method for generating a reference signal for controlling a peak current of a converter switch further includes a gain control step of generating and outputting the reference signal for controlling the peak current by controlling a gain of the dead-zone voltage signal having the dead-zone to have a predetermined peak value after the step of forming the dead-zone. 
     According to at least one embodiment, the step of generating and outputting the reference signal for controlling the peak current includes the steps of multiplying the duty ratio of energy transfer by a predetermined gain to adjust a secondary-side output, after the step of calculating the duty ratio of energy transfer, and generating the reference signal for controlling the peak current by dividing a gain-controlled output signal in the gain control step by an output in the step of multiplying the predetermined gain. 
     According to at least one embodiment, in the step of calculating the duty ratio of energy transfer, a time of energy transfer with respect to a cycle of a driving signal is calculated as the duty ratio of energy transfer by receiving the driving signal for driving the converter switch and the time of energy transfer to the secondary side. 
     According to at least one embodiment, in another example, the output reference signal for controlling the peak current is compared with a primary-side sensing voltage signal and the driving signal of the converter switch is generated according to the results of the comparison. 
     According to at least one embodiment, in an example, the isolated converter is a flyback converter. 
     Various objects, advantages and features of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other features, aspects, and advantages of the invention are better understood with regard to the following Detailed Description, appended Claims, and accompanying Figures. It is to be noted, however, that the Figures illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention&#39;s scope as it may include other effective embodiments as well. 
         FIG. 1  is a schematic block diagram of a circuit for generating a reference signal for controlling a peak current of a converter switch in accordance with an embodiment of the invention. 
         FIG. 2  is a schematic block diagram of a circuit for generating a reference signal for controlling a peak current of a converter switch in accordance with another embodiment of the invention. 
         FIG. 3  is a view schematically showing an isolated converter in accordance with another embodiment of the invention. 
         FIG. 4   a  is a view showing an energy transfer time according to a CRM operation of an isolated converter in accordance with another embodiment of the invention. 
         FIG. 4   b  is a view showing an energy transfer time according to a DCM operation of an isolated converter in accordance with another embodiment of the invention. 
         FIG. 5   a  is a graph showing a current supply waveform of an AC power supply when applying a comparative example in accordance with another embodiment of the invention. 
         FIG. 5   b  is a graph showing waveforms of an AGC output, a reference signal for controlling a peak current, an LED current, and an input current when applying an embodiment of the invention. 
         FIG. 6  is a graph schematically showing an input voltage signal detected by a voltage divider and a dead-zone voltage signal generated by a dead-zone generator in an embodiment of the invention. 
         FIG. 7  is a flowchart schematically showing a method for generating a reference signal for controlling a peak current of a converter switch in accordance with another embodiment of the invention. 
         FIG. 8  is a flowchart schematically showing a method for generating a reference signal for controlling a peak current of a converter switch in accordance with another embodiment of the invention. 
         FIG. 9  is a graph schematically showing a drain voltage and a MOSFET current in a converter switch of an isolated converter in accordance with another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Advantages and features of the present invention and methods of accomplishing the same will be apparent by referring to embodiments described below in detail in connection with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various different forms. The embodiments are provided only for completing the disclosure of the present invention and for fully representing the scope of the present invention to those skilled in the art. 
     For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. Like reference numerals refer to like elements throughout the specification. 
     Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     First, a circuit for generating a reference signal for controlling a peak current of a converter switch in accordance with an embodiment of the invention will be described in detail with reference to the drawings. At this time, the reference numeral that is not mentioned in the reference drawing may be the reference numeral that represents the same element in another drawing. 
       FIG. 1  is a schematic block diagram of a circuit for generating a reference signal for controlling a peak current of a converter switch in accordance with an embodiment of the invention,  FIG. 2  is a schematic block diagram of a circuit for generating a reference signal for controlling a peak current of a converter switch in accordance with another embodiment of the invention,  FIG. 4   a  is a view showing an energy transfer time according to a CRM operation of an isolated converter in accordance with another embodiment of the invention,  FIG. 4   b  is a view showing an energy transfer time according to a DCM operation of an isolated converter in accordance with another embodiment of the invention,  FIG. 5   a  is a graph showing a current supply waveform of an AC power supply when applying a comparative example in accordance with another embodiment of the invention,  FIG. 5   b  is a graph showing waveforms of an AGC output, a reference signal for controlling a peak current, an LED current, and an input current when applying an embodiment of the invention,  FIG. 6  is a graph schematically showing an input voltage signal detected by a voltage divider and a dead-zone voltage signal generated by a dead-zone generator in an embodiment of the invention, and  FIG. 9  is a graph schematically showing a drain voltage and a MOSFET current in a converter switch of an isolated converter in accordance with another embodiment of the invention. 
     Referring to  FIGS. 1  or/and  2 , a circuit for generating a reference signal for controlling a peak current of a converter switch according to an example includes a dead-zone generator  11 , a duty ratio calculator  15 , and an operator  17 . For example, referring to  FIG. 2 , the circuit for generating a reference signal for controlling a peak current of a converter switch further includes an AGC  13 . 
     Referring to  FIGS. 1  or/and  2 , the dead-zone generator  11  generates a dead-zone voltage signal by forming a dead-zone in an input voltage signal divided or detected from a primary-side supply voltage of an isolated converter. Referring to  FIG. 6 , the input voltage signal divided or detected from the primary-side supply voltage of the isolated converter has a full-wave rectified sine wave form. Through the dead-zone generator  11 , for example, in one cycle of the full-wave rectified sine wave, that is, in an interval of 0˜π, the dead-zone, where the phase has a zero value, is formed in the intervals of 0˜α and π−α˜π. Thus, the dead-zone voltage signal has a shape in which the dead-zone is formed in the intervals of 0˜α and π−α˜π of the full-wave rectified sine wave. For example, referring to  FIG. 3 , the dead-zone generator  11  is connected to a voltage divider  20 , which provides the input voltage signal by dividing the primary-side supply voltage, and forms the dead-zone in the specific intervals, for example, in the intervals of 0˜α and π−α˜π by receiving or detecting the input voltage signal divided by the voltage divider  20 . The dead-zone voltage signal having the dead-zone is used to generate a reference signal VREF for controlling a peak current in the operator  17 , which will be described later, after being output from the dead-zone generator  11 . 
     According to at least one embodiment, the isolated converter is a flyback converter. For example, the flyback converter operates in critical conduction mode (CRM) or discontinuous conduction mode (DCM). Thus, the dead-zone generator  11  forms the dead-zone and outputs the dead-zone voltage signal by receiving the input voltage signal divided from the primary-side supply voltage of the flyback converter, which operates in CRM or DCM. 
     For example, referring to  FIGS. 2  or/and  3 , in an example, the circuit for generating a reference signal for controlling a peak current of a converter switch further includes the AGC  13  between the dead-zone generator  11  and the operator  17 . According to at least one embodiment, the AGC  13  controls a gain of the dead-zone voltage signal output from the dead-zone generator  11  to have a predetermined peak value K1 and outputs the gain-controlled signal to the operator  17 . 
     Meanwhile, referring to  FIGS. 1  or/and  2 , the duty calculator  15  calculates a duty ratio of energy transfer (hereafter, referred to ‘the energy transfer duty ratio’) to a secondary side of the isolated converter. 
     According to at least one embodiment, the duty ratio calculator  15  receives a driving signal for driving a converter switch  50  and a time Tdm of an energy transfer (hereafter, referred to ‘the energy transfer time’) to the secondary side of the isolated converter and calculates the energy transfer time with respect to a cycle of the driving signal, thus, a switching cycle T as the energy transfer duty ratio Tdm/T. According to at least one embodiment, the energy transfer duty ratio Tdm/T means the energy transfer time Tdm to the secondary side with respect to the cycle of the driving signal, that is, the switching cycle T. 
     Next, referring to  FIGS. 1  or/and  2 , the operator  17  generates the reference signal VREF for controlling a peak current of the converter switch  50  from the dead-zone voltage signal having the dead-zone by using the energy transfer duty ratio Tdm/T calculated by the duty ratio calculator  15 . According to at least one embodiment, the dead-zone voltage signal having the dead-zone is derived from the dead-zone generator  11 . Thus, the operator  17  generates the reference signal for generation of the driving signal for controlling the converter switch. 
     For example, referring to  FIG. 2 , in an example, the operator  17  receives the gain-controlled dead-zone voltage signal by the peak value K1 from the AGC  13  and generates the reference signal for controlling the peak current of the converter switch  50  by using the energy transfer duty ratio Tdm/T. 
     Further, referring to  FIG. 2 , in an example, the operator  17  includes a multiplier  171  and a divider  173 . According to at least one embodiment, the multiplier  171  multiplies the energy transfer duty ratio Tdm/T, which is calculated by the duty calculator  15 , by a predetermined gain K2 to adjust a secondary-side output, for example, a current flowing to a secondary-side load  300  of  FIG. 3 . Further, the divider  173  generates and outputs the reference signal for controlling the peak current by dividing the output signal of the AGC  13  by the output of the multiplier  171 . 
     According to at least one embodiment, referring to  FIG. 3 , in an example, the reference signal for controlling the peak current, which is output from the operator  17 , is compared with a primary-side sensing voltage signal in a comparator  31  of a controller block  30 . According to at least one embodiment, the driving signal of the converter switch  50  is generated according to the results of the comparison. 
     Next, the principle of the present invention will be described in detail. For example, the principles of the present invention will be described in detail by taking the case of an isolated converter applied to an LED driver. 
     According to at least one embodiment, an LED current in a flyback or buck-boost converter type LED driver, which operates in DCM or CRM is determined by a peak current Ipk flowing in a converter switch, for example, a MOSFET switch, a switching cycle T, and a current transfer time or an energy transfer time Tdm (demagnetizing time) to a secondary side. At this time, an LED current ILED of the secondary side is as the following Formula (1). 
       ILED= N/ 2· Ipk ·( Tdm/T )  Formula (1):
 
     According to at least one embodiment, Tdm/T is a function of a power supply voltage, for example, a forward voltage drop VF of the LED. Therefore, ILED is a value that varies according to power and load if there is no special control. 
     However, if Ipk is controlled like Ipk∝T/Tdm, it is possible to suppress current fluctuations due to changes in Tdm/T. 
     If a supply voltage of the converter has an unrectified sine wave shape, it is possible to improve a power factor by including phase information of the power supply voltage in Ipk. 
         Ipk ∝ sin(φ)·( T/Tdm )
 
     In  FIG. 6 , a voltage of the converter switch  50 , for example, a MOSFET switch and a current flowing in a MOSFET according to switching of the isolated converter are shown. When the converter switch  50  is turned on, the current flowing in the MOSFET, that is, an inductor current of the transformer is increased during a period of Ton. When the inductor current is increased to reach a set peak level Ipk, the converter switch  50  is turned off. When the converter switch  50  is turned off, the current is transferred to the secondary side during the energy transfer time to the secondary side, that is, during a period of Tdm. When all the energy is transferred to the secondary side, resonance due to parasitic devices (not shown) occurs until the converter switch  50  is turned on again. 
     According to at least one embodiment, a current supplied from an AC power supply of the isolated converter, that is, an AC input current Iin is calculated as the following Formula (2). At this time, ‘T’ is a driving signal cycle or a switching cycle of the converter switch. 
         I in=½· Ipk ·( T on/ T )  Formula (2):
 
     According to at least one embodiment, the input current is calculated on the assumption that a peak current of the converter switch is as the following Formula (3). 
         Ipk=K ·sin(φ)( T/Tdm )  Formula (3):
 
     When calculating the input current using the above peak current formula of the converter switch, Iin=½·Ipk·(Ton/T)=½·K·sin(φ)(Ton/Tdm). 
     Assuming that a peak value of the power supply voltage is Vsup, for example, a forward voltage of the LED is VF, and a ratio of a primary-side winding Np and a secondary-side winding Ns of the transformer is N(=Np/Ns), Ton and Tdm is calculated as the following Formulas (4) and (5), respectively. According to at least one embodiment, the power supply voltage is typically used as a meaning of the primary-side supply voltage but is used as a meaning of an input power supply voltage of a front end of a bridge rectifier of  FIG. 3 . 
         T on= Lm /( Vsup ·sin(φ))· Ipk   Formula (4):
 
         Tdm=Lm /( N·VF )· Ipk   Formula (5):
 
     Therefore, the input current is as the following Formula (6). 
         I in=½· Ipk ( T on/ T )=½· K ·sin(φ)( N·VF )/( Vsup ·sin(φ))=½· K ·( N·VF )/ Vsup   Formula (6):
 
     According to at least one embodiment, if the input current is controlled ideally, the input current is always constant. Of course, the input current is not controlled perfectly like this, and an LED voltage varies according to the current size. At this time, the input current is not perfectly constant, but referring to  FIG. 5   a , the input current has an almost square wave shape and thus is significantly different from a sine wave shape. Thus, THD is reduced, resulting in a reduction in the power factor. 
     According to at least one embodiment, as a result of calculation of the input current on the assumption that the peak current of the converter switch is as the above Formula (3), the input current has an almost square wave shape as shown in  FIG. 5   a , resulting in the reduction in the THD and power factor. 
     According to at least one embodiment, the operation of the circuit for generating a reference signal for controlling a peak current of a converter switch using the dead-zone voltage signal proposed by embodiments of the invention will be described with reference to structures like  FIGS. 2 and 3 . 
     First, referring to  FIG. 6 , in embodiments of the invention, since the isolated converter is driven using the unrectified power supply voltage, the power supply voltage has a full-wave rectified sine wave shape when it is a primary-side supply voltage like a lower graph of  FIG. 6 . 
     Referring to  FIGS. 2 and 3 , for example, if the input voltage signal divided or detected by the voltage divider  20  is Va, the dead-zone voltage signal Va*, which is formed by adding the dead-zone to [0,α], [π−α,π] like the lower graph of  FIG. 6 , is generated. If the dead-zone voltage signal Va* is determined to have the peak value K1 through the AGC  13 , an output voltage Vagc of the AGC  13  is as the following Formula (7). 
     
       
         
           
             
               
                 
                   Vagc 
                   = 
                   
                     K 
                      
                     
                         
                     
                      
                     
                       1 
                       · 
                       
                         
                           
                             Va 
                             * 
                           
                            
                           
                             ( 
                             Φ 
                             ) 
                           
                         
                         
                           MAX 
                            
                           
                             [ 
                             
                               
                                 Va 
                                 * 
                               
                                
                               
                                 ( 
                                 Φ 
                                 ) 
                               
                             
                             ] 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     7 
                     ) 
                   
                 
               
             
           
         
       
     
     MAX[Va*(φ)] means a maximum value of Va*. Vagc is mathematically expressed as the following Formula (8) by including the phase a that determines the dead-zone. 
         Vagc≧ 0,  Vagc=K 1·((1+ A )sin(φ)− A )
 
         Vagc&lt; 0,  Vagc= 0 
       sin(α)= A /(1+ A )  Formula (8):
 
     The reference signal VREF for controlling a peak current that determines the peak current of the converter switch  50  is finally divided by K2*Tdm/T through the operation of the circuit  10  for generating a reference signal for controlling a peak current of a converter switch in  FIGS. 2  and/or  3 . Therefore, VREF has characteristics like the following Formula (9). 
                     Vagc   ≥   0     ,     VREF   =         K                 1       K                 2       ·     (         (     1   +   A     )          sin        (   Φ   )         -   A     )     ·     T     T   dm                   Formula                   (   9   )                   Vagc&lt; 0,  VREF= 0 
       sin(α)= A /(1+ A )
 
     Therefore, the peak current satisfies the following Formula (10). At this time, Rcs is a primary-side sensing resistor that detects the current flowing through the converter switch  50 . 
                     Vagc   ≥   0     ,     Ipk   =         K                 1       K                 2       ·       (         (     1   +   A     )          sin        (   Φ   )         -   A     )     Rcs     ·     T     T   dm                   Formula                   (   10   )                   Vagc&lt; 0,  Ipk= 0 
       sin(α)= A /(1+ A )
 
     The secondary-side current, for example, the LED current ILED in the LED driving converter is calculated as the following Formula (11) using the above Formula (10). 
                     Vagc   ≥   0     ,     ILED   =         N   2     ·   Ipk   ·       T   dm     T       =       N   2     ·       K                 1       K                 2       ·       (         (     1   +   A     )          sin        (   Φ   )         -   A     )     Rcs                   Formula                   (   11   )                   Vagc&lt; 0, ILED=0 
     An LED average current ILED,avg is calculated as the following Formula (12) by integrating the interval of [0,π] from the above Formula (11). At this time, N is a winding ratio of the primary side and the secondary side of the transformer  100 . 
     
       
         
           
             
               
                 
                   ILED 
                   , 
                   
                     avg 
                     = 
                     
                       M 
                       · 
                       
                         N 
                         4 
                       
                       · 
                       
                         1 
                         Rcs 
                       
                     
                   
                   , 
                   
                     M 
                     = 
                     
                       
                         2 
                          
                         
                           [ 
                           
                             
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   A 
                                 
                                 ) 
                               
                                
                               
                                 cos 
                                  
                                 
                                   ( 
                                   
                                     
                                       sin 
                                       
                                         - 
                                         1 
                                       
                                     
                                      
                                     
                                       A 
                                       
                                         1 
                                         + 
                                         A 
                                       
                                     
                                   
                                   ) 
                                 
                               
                             
                             - 
                             
                               A 
                                
                               
                                 ( 
                                 
                                   
                                     π 
                                     2 
                                   
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                           
                           ] 
                         
                       
                       π 
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     12 
                     ) 
                   
                 
               
             
           
         
       
     
     In the above Formula (12), if the angle α that determines the dead-zone is constant, A is constant by the following Formula (13). 
     
       
         
           
             
               
                 
                   A 
                   = 
                   
                     
                       sin 
                        
                       
                           
                       
                        
                       α 
                     
                     
                       1 
                       - 
                       
                         sin 
                          
                         
                             
                         
                          
                         α 
                       
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     13 
                     ) 
                   
                 
               
             
           
         
       
     
     Therefore, M is also a constant value. That is, since the LED average current ILED,avg is determined by constants such as M, N, and Rcs, the LED average current ILED,avg is maintained constant regardless of fluctuations of the power supply voltage and variations of the load to satisfy line regulation and load regulation characteristics. After all, it is possible to satisfy the regulation characteristics in spite of the addition of the dead-zone. 
     Next, a flyback LED driver is shown in  FIG. 3  as an example of the isolated converter that is implemented by the method according to embodiments of the invention. Referring to  FIG. 3 , first, the full-wave rectified Vac signal is converted to Va using division resistors R 1  and R 2  of the voltage divider  20 . The divided or detected input voltage signal Va generates the dead-zone voltage Va* through the dead-zone generator  11 . The dead-zone voltage signal Va* is converted to the signal Vagc having a size of the maximum peak value K1 through the AGC  13 . The cycle of the driving signal or the switching cycle T is obtained from a gate driving signal of the converter switch  50  and the energy transfer time Tdm is obtained from the output of a secondary-side auxiliary winding  103   b  by using an energy transfer time detector  70  so that a signal Tdm/T*K2 is obtained through the duty calculator  15  and the multiplier  171 . The peak current control signal VREF of the converter switch  50  M1 is generated by dividing Vagc and Tdm/T*K2 using the divider  173 . 
     Referring to  FIG. 5   a , a waveform of an AC input current, which is obtained through a simulation from a signal without a dead-zone by applying a comparative example without the dead-zone generator  11  shown in  FIGS. 2 and 3 , is shown. In  FIG. 5   a , since the waveform of the input current is suddenly changed near a zero-cross of the AC power supply, the total harmonic distortion (THD) is not good and the power factor (PF) is reduced. In the simulation, THD is almost 30% and PF is about 0.96. 
     However, as shown in  FIG. 5   b , according to an embodiment of the invention, when generating the reference signal VREF for controlling a peak current by forming the dead-zone, since the current near the zero-cross is almost 0 and gradually increased later, the THD of the input current is greatly improved. 
       FIG. 5   b  shows waveforms obtained from the results of a simulation when generating the reference signal VREF for controlling a peak current from the input voltage signal having the dead-zone according to an embodiment of the present invention. In  FIG. 5   b , the AGC output has the dead-zone, and the reference signal VREF for controlling a peak current also has a low value near the dead-zone. Therefore, the input current is almost 0 near the zero-cross of the power supply voltage Vac and gradually increased later. Therefore, the input current from the AC power supply has a shape similar to a sine wave as shown in  FIG. 5   b . In the simulation according to  FIG. 5   b , it is possible to obtain THD=16.3% and PF=0.98. Thus, it is possible to significantly improve the THD and PF through the control method proposed in an embodiment of the present invention. 
     Next, an isolated converter according to another embodiment of the invention will be described in detail with reference to the drawings. At this time, the circuits for generating a reference signal for controlling a peak current of a converter switch according to the above-described examples of the first aspect and  FIGS. 1 ,  2 ,  4   a ,  4   b ,  5   b  and  6  will be referenced. Thus, repeated descriptions may be omitted. 
       FIG. 3  is a view schematically showing an isolated converter in accordance with another embodiment of the invention. 
     Referring to  FIG. 3 , an isolated converter according to an embodiment of the invention includes a transformer  100 , a converter switch  50 , an energy transfer time detector  70 , a circuit  10  for generating a reference signal for controlling a peak current of a converter switch, and a controller block  30 . Further, referring to  FIG. 3 , in an example, the isolated converter further includes a voltage divider  20 . 
     According to at least one embodiment, the isolated converter is a flyback converter. For example, the flyback converter operates in CRM or DCM. 
     Referring to  FIG. 3 , the transformer  100  of the isolated converter includes a primary-side winding  101 , a secondary-side main winding  103   a , and a secondary-side auxiliary winding  103   b . The transformer  100  transfers a primary-side supply voltage, which is input to the primary-side winding, to the secondary-side main winding  103   a.    
     Next, referring to  FIG. 3 , the converter switch  50  of the isolated converter is connected to the primary-side winding  101  of the transformer  100  to perform a switching operation. At this time, according to the switching operation of the converter switch  50 , the primary-side supply voltage is transferred to a secondary side through the transformer  100 . That is, according to the switching operation of the converter switch  50 , the transformer  100  transfers primary-side energy to the secondary side. At this time, referring to  FIG. 4   a , in case of CRM, an energy transfer time Tdm from the primary side to the secondary side is equal to an off interval of the converter switch  50 . Further, referring to  FIG. 4   b , in case of DCM, the energy transfer time Tdm from the primary side to the secondary side is equal to an interval from an off time of the converter switch  50  to a point that an inductor current of the transformer  100  is ‘0’. 
     Next, referring to  FIG. 3 , the energy transfer time detector  70  detects the energy transfer time Tdm to the secondary side from the secondary-side auxiliary winding  103   b  of the transformer  100  according to the switching of the converter switch  50 . 
     Next, the circuit  10  for generating a reference signal for controlling a peak current of a converter switch is one of the above-described embodiments according to the first aspect of the present invention. For example, referring to  FIGS. 1 ,  2 , or/and  3 , the circuit  10  for generating a reference signal for controlling a peak current of a converter switch according to an example includes a dead-zone generator  11 , a duty ratio calculator  15 , and an operator  17 . 
     According to at least one embodiment, the dead-zone generator  11  squares an input voltage signal divided from the primary-side supply voltage of the isolated converter. For example, referring to  FIGS. 2  or/and  3 , the dead-zone generator  11  receives or detects the input voltage signal divided from the primary-side supply voltage to square the input voltage signal. 
     According to at least one embodiment, the duty ratio calculator  15  calculates an energy transfer duty ratio Tdm/T to the secondary side of the isolated converter. According to at least one embodiment, in an example, the duty ratio calculator  15  of the circuit  10  for generating a reference signal for controlling a peak current of a converter switch receives a driving signal for driving the converter switch  50  and the energy transfer time output from the energy transfer time detector  70  to calculate the energy transfer time with respect to a cycle of the driving signal as the energy transfer duty ratio Tdm/T. 
     In addition, referring to  FIGS. 1 ,  2 , or/and  3 , the operator  17  generates a reference signal for controlling a peak current of the converter switch  50  from a dead-zone voltage signal by using the energy transfer duty ratio Tdm/T calculated by the duty ratio calculator  15 . For example, referring to  FIGS. 2  or/and  3 , the operator  17  receives the gain-controlled dead-zone voltage signal from an AGC  13  and generates the reference signal for controlling the peak current of the converter switch  50  by using the energy transfer duty ratio Tdm/T. For example, referring to  FIGS. 2  or/and  3 , the operator  17  includes a multiplier  171  and a divider  173 . According to at least one embodiment, the multiplier  171  multiplies the energy transfer duty ratio Tdm/T, which is calculated by the duty ratio calculator  15 , by a predetermined gain to adjust a secondary-side output, for example, a current flowing to a secondary-side load  300 . Further, the divider  173  generates and outputs the reference signal for controlling the peak current by dividing the output signal of the AGC  13  by the output of the multiplier  171 . 
     For example, referring to  FIGS. 2  or/and  3 , the circuit  10  for generating a reference signal for controlling a peak current of a converter switch further includes the AGC  13 . At this time, the AGC  13  controls a gain of the dead-zone voltage signal, which is output from the dead-zone generator  11 , to have a predetermined peak value and output the gain-controlled signal to the operator  17 . 
     Next, the controller block  30  will be described in detail with reference to  FIG. 3 . The controller block  30  generates and outputs the driving signal of the converter switch  50  by comparing a primary-side sensing voltage signal and the reference signal for controlling the peak current, which is generated by the circuit  10  for generating a reference signal for controlling a peak current. 
     For example, referring to  FIG. 3 , in an example, the controller block  30  includes a comparator  31 , an on-time generator  33 , and a flip-flop  35 . The comparator  31  of the control block  30  receives and compares the primary-side sensing voltage signal and the reference signal for controlling the peak current, which is generated by the circuit  10  for generating a reference signal for controlling a peak current. Further, the on-time generator  33  determines an on operation time of the converter switch  50  from the signal output from the secondary-side auxiliary winding  103   b . Further, the flip-flop  35  outputs the driving signal of the converter switch  50  by receiving the output of the comparator  31  and the output of the on-time generator  33 . 
     Further, the isolated converter according to at least one embodiment of the invention will be described with reference to  FIG. 3 . According to at least one embodiment, the isolated converter further includes the voltage divider  20 . The voltage divider  20  divides the primary-side supply voltage and provides the divided input voltage signal to the squarer  11 . Further, the isolated converter includes a secondary output block  200  including a rectifier diode  201  and an output capacitor  203 . The rectifier diode  201  of the secondary output block  200  is connected to the secondary side of the transformer  100  to rectify the secondary-side output. The output capacitor  203  charges a DC voltage rectified by the rectifier diode  201 . 
     According to at least one embodiment, referring to  FIG. 3 , when the isolated converter is an LED driving converter, the load  300 , for example, an LED is connected to the secondary output block  200 , specifically to the output capacitor  203 . 
     Next, a method for generating a reference signal for controlling a peak current of a converter switch in accordance with another embodiment of the invention will be described in detail with reference to the drawings. According to at least one embodiment, the circuits for generating a reference signal for controlling a peak current of a converter switch according to the above-described examples of the first aspect and  FIGS. 1 to 6  will be referenced. Thus, repeated descriptions may be omitted. 
       FIG. 7  is a flowchart schematically showing a method for generating a reference signal for controlling a peak current of a converter switch in accordance with another embodiment of the invention, and  FIG. 8  is a flowchart schematically showing a method for generating a reference signal for controlling a peak current of a converter switch in accordance with another embodiment of the invention. 
     Referring to  FIGS. 7  and/or  8 , a method for generating a reference signal for controlling a peak current of a converter switch according to at least one embodiment of the invention includes an input voltage signal square step S 100 , an energy transfer duty ratio calculation step S 300  and S 300 ′, and a peak current control reference signal generation step S 500  and S 500 ′. Further, referring to  FIG. 8 , the method for generating a reference signal for controlling a peak current of a converter switch according to an example further includes a gain control step S 200 . 
     First, referring to  FIGS. 7  and/or  8 , in the input voltage signal square step S 100 , an input voltage signal divided from a primary-side supply voltage of an isolated converter is squared. For example, at this time, the isolated converter a flyback converter. Thus, the method for generating a reference signal for controlling a peak current of a converter switch according to at least one embodiment is applied to a flyback converter. For example, the method for generating a reference signal for controlling a peak current of a converter switch according to at least one embodiment is applied to a flyback converter that operates in CRM or DCM. 
     Further, referring to  FIG. 8 , in an example, the method for generating a reference signal for controlling a peak current of a converter switch according to at least one embodiment of the invention further includes the gain control step S 200  before the peak current control reference signal generation step, specifically before the step S 530  of  FIG. 8  after the input voltage signal square step S 100 . In the gain control step S 200 , a gain of a dead-zone voltage signal is controlled to have a predetermined peak value and the gain-controlled signal is output to the peak current control reference signal generation step S 530 . 
     Next, referring to  FIGS. 7  and/or  8 , in the energy transfer duty ratio calculation step S 300  and S 300 ′, an energy transfer duty ratio Tdm/T to a secondary side of the isolated converter is calculated. 
     For example, in the energy transfer duty ratio calculation step S 300  and S 300 ′, a driving signal for driving a converter switch  50  and an energy transfer time to the secondary side are input and the energy transfer time with respect to a cycle of the driving signal is calculated as the energy transfer duty ratio Tdm/T. At this time, referring to  FIG. 3 , the driving signal for driving the converter switch  50  is a signal output from a controller block  30 , specifically from a flip-flop  35 , and the energy transfer time to the secondary side is obtained from an output signal of a secondary-side auxiliary winding  103   b  through an energy transfer time detector  70 . 
     Continuously, referring to  FIGS. 7  and/or  8 , in the peak current control reference signal generation step S 500  and S 500 ′, a reference signal for controlling a peak current of the converter switch  50  is generated from the dead-zone voltage signal derived in the input voltage signal square step S 100  by using the energy transfer duty ratio Tdm/T calculated in the energy transfer duty ratio calculation step S 300  and S 300 ′. 
     According to at least one embodiment, referring to  FIG. 8 , in an example, the peak current control reference signal generation step S 500 ′ includes a gain multiplication step S 510  and a peak current control reference signal generation step S 530 . According to at least one embodiment, in the gain multiplication step S 510 , after the energy transfer duty ratio calculation step S 300 ′, the energy transfer duty ratio Tdm/T is multiplied by a predetermined gain K2 to adjust a secondary-side output. Thus, as the energy transfer duty ratio Tdm/T is multiplied by the predetermined gain K2 in the gain multiplication step S 510 , the secondary-side output, for example, a current flowing in a secondary-side load  300  of  FIG. 3  is adjusted later. Continuously, referring to  FIG. 8 , in the peak current control reference signal generation step S 530 , the gain-controlled output signal in the gain control step S 200  is divided by the output in the gain multiplication step S 510 , thus, in the step of multiplying a predetermined gain. According to at least one embodiment, the gain-controlled output signal is divided by the output multiplied by the predetermined gain K2 to generate the reference signal for controlling the peak current. 
     For example, at this time, referring to  FIG. 3 , in an example, the reference signal for controlling the peak current, which is output in the peak current control reference signal generation step S 500  and S 500 ′, is compared with a primary-side sensing voltage signal, and the driving signal of the converter switch  50  is generated according to the results of the comparison. At this time, referring to  FIG. 3 , the driving signal of the converter switch  50  is applied to a gate electrode of the converter switch  50  and transferred to a duty ratio calculator  15  at the same time so that the energy transfer duty ratio Tdm/T is calculated through the energy transfer duty ratio calculation step S 300  and S 300 ′. 
     As described above, the above-described embodiments perform control using primary-side sensing information without sensing and feeding back the secondary-side output in the isolated converter, for example, control the current of the converter switch  50  by adding the dead-zone to the input voltage signal divided or detected from the primary-side supply voltage and using the signal proportional to the dead-zone added signal. 
     According to at least one embodiment, for example, the isolated converter is a flyback converter, for example, a flyback converter that operates in CRM or DCM. According to at least one embodiment, the flyback converter is an LED driving converter. In the above-described embodiments of the present invention, it is possible to improve the THD and PF by controlling the current of the converter switch  50  by the signal proportional to the dead-zone voltage signal having the dead-zone using the primary-side sensing information, not the secondary-side sensing information. Further, when applied to the LED driving converter, it is possible to satisfy the line regulation and load regulation characteristics. 
     According to an embodiment of the present invention, it is possible to control the peak current of the converter switch using the primary-side sensing information without sensing and feeding back the secondary-side output in the isolated converter. For example, it is possible to control the peak current of the converter switch by adding the dead-zone to the input voltage signal divided or detected from the primary-side supply voltage and using the signal proportional to the dead-zone added signal. Accordingly, it is possible to improve the THD and the power factor. Further, for example, when applied to the LED driving converter, it is possible to satisfy the line regulation and load regulation characteristics. 
     Further, according to an embodiment of the present invention, it is possible to control the secondary-side average current regardless of the variations of the load and the fluctuations of the power supply voltage by generating the reference signal for controlling the peak current of the converter switch to control the peak current of the converter switch. Accordingly, it is possible to expect the following effects. 
     First, it is possible to improve the line regulation. Thus, it is possible to satisfy the constant secondary-side current, for example, the LED current in spite of the fluctuations of the power supply voltage. Second, it is possible to improve the load regulation. Thus, it is possible to satisfy the constant secondary-side current, for example, the LED current in spite of the changes in the characteristics of the load. Third, it is possible to improve the THD. Thus, it is possible to improve the THD since the input current supplied from the AC power supply has a sine wave shape. Fourth, it is possible to improve the PF. Thus, it is possible to improve the PF since the current supplied from the AC power supply is equal to the phase of the power supply voltage and the harmonics of the current are suppressed. 
     Terms used herein are provided to explain embodiments, not limiting the present invention. Throughout this specification, the singular form includes the plural form unless the context clearly indicates otherwise. When terms “comprises” and/or “comprising” used herein do not preclude existence and addition of another component, step, operation and/or device, in addition to the above-mentioned component, step, operation and/or device. 
     Embodiments of the present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step. 
     The terms and words used in the present specification and claims should not be interpreted as being limited to typical meanings or dictionary definitions, but should be interpreted as having meanings and concepts relevant to the technical scope of the present invention based on the rule according to which an inventor can appropriately define the concept of the term to describe the best method he or she knows for carrying out the invention. 
     The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. 
     The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise. 
     As used herein and in the appended claims, the words “comprise,” “has,” and “include” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps. 
     As used herein, the terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used. Occurrences of the phrase “according to an embodiment” herein do not necessarily all refer to the same embodiment. 
     Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. 
     Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope of the invention. Accordingly, the scope of the present invention should be determined by the following claims and their appropriate legal equivalents.