Abstract:
The present invention discloses a dynamic voltage adjustment device for dynamically adjusting an output voltage of a power transmission system which generates the output voltage according to a feedback signal and a reference signal and transmits the output voltage to a remote load via a transmission line to generate a load current. The dynamic voltage adjustment device comprises a first signal terminal, for receiving a first signal corresponding to a forward transmission voltage drop of the transmission line; a second signal terminal, for receiving a second signal corresponding to a reverse transmission voltage drop of the transmission line; a third signal terminal for receiving a reference voltage; a feedback circuit, for generating a feedback signal according to the first signal; and a adder circuit, for generating the reference signal according to the second signal and the reference voltage.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a dynamic voltage adjustment device and related power transmission system, and more particularly, to a dynamic voltage adjustment device and related power transmission system capable of ensuring a voltage difference across a remote load being stable when transmitting electricity to the remote load. 
         [0003]    2. Description of the Prior Art 
         [0004]    Generally, a power system transmits electricity to a remote load via a medium such as a transmission line (e.g. a coaxial cable and a conducting line). However, realistic transmission lines have different non-ideal transmission impedances resulting in different transmission voltage drops when transmitting currents to the remote load through the transmission lines. The different transmission voltage drops may cause the remote load damaged or operated unstably. 
         [0005]    Pleases refer to  FIG. 1 , which is a schematic diagram of a conventional power transmission system  10 . The power transmission system  10  comprises a power converter  100 , a transmission line  102 , a load  104  and a feedback circuit  106 . The power transmission system  10  is utilized for transmitting an output voltage VOUT generated by the power converter  100  to the load  104  through the transmission line  102 . The power converter  100  comprises an error amplifier  108  and a power conversion unit  110 . The power converter  100  utilizes the error amplifier  108  for comparing a difference between a reference voltage VREF and a feedback signal FB from the feedback circuit  106 , such that the power conversion unit  110  generates the stable output voltage VOUT. The transmission line  102  comprises a forward transmission line LINE 1  and a reverse transmission line LINE 2 , which are respectively utilized for a forward transmission from the power converter  100  to the load  104  and a reverse transmission from the load  104  to the power converter  100 . The feedback circuit  106  consists of resistors R 1 , R 2  and divides the voltage of the output voltage VOUT to acquire the feedback signal FB, i.e. 
         [0000]    
       
         
           
             FB 
             = 
             
               
                 ( 
                 
                   
                     R 
                      
                     
                         
                     
                      
                     2 
                   
                   
                     R 
                      
                     
                         
                     
                      
                     1 
                   
                 
                 ) 
               
               × 
               
                 VOUT 
                 . 
               
             
           
         
       
     
         [0006]    When the power converter  100  starts providing the output voltage VOUT to the load  104 , a load current I_LOAD is generated on the forward transmission line LINE 1  and the reverse transmission line LINE 2 . Since the forward transmission line LINE 1  and the reverse transmission line LINE 2  respectively have a forward transmission line resistance R_LINE 1  and a reverse transmission line resistance R_LINE 2 , a forward voltage difference ΔV 1 =I_LOAD*R_LINE 1  and a reverse voltage difference ΔV 2 =I_LOAD*R_LINE 2  are respectively generated when the load current I_LOAD flows on the forward transmission line LINE 1  and the reverse transmission line LINE 2 . In other words, a voltage drop equal to the forward voltage difference ΔV 1  is generated when the load current I_LOAD flows from the power converter  100  to load  104 , and a voltage drop equal to the reverse voltage difference ΔV 2  is generated when the load current I_LOAD feedbacks from the load  104  to the power converter  100 . Therefore, a load output voltage LOAD_VOUT acquired by the load  104  equals subtracting the forward voltage difference ΔV 1  from the output voltage VOUT of the power converter  100 , i.e. LOAD_VOUT=VOUT−ΔV 1 . Similarly, a load ground voltage LOAD_GND of a ground of the load  104  is the reverse voltage difference ΔV 2  higher than a ground voltage GND of a ground of the power converter  100 , i.e. LOAD_GND=GND+ΔV 2 . Therefore, at a moment of a start or an end of supplying power, the load  104  would suffer a voltage difference equal to forward voltage difference ΔV 1  plus reverse voltage difference ΔV 2 . The instantaneous glitch may damage the power transmission system  10 . 
         [0007]    Since a feedback point samples the output voltage VOUT close to the power converter  100  in the power transmission system  10 , the output voltage VOUT is a function of a difference between the reference voltage VREF and the feedback signal FB, i.e. VOUT=f(VREF−FB). Since the reference voltage VREF is a constant value and the feedback signal FB only includes information of the output voltage VOUT, the power transmission system  10  cannot acquire information of voltage difference ΔV 1 , ΔV 2  generated by the load current I_LOAD flowing through the transmission line  102  and cannot accordingly adjust the output voltage VOUT of the power converter  100 , such that the voltage difference ΔV 1 +ΔV 2  generated at the load  104  cannot be adjusted. 
         [0008]    Please refer to  FIG. 2 , which is a schematic diagram of related signals when the power transmission system  10  operates. As shown in  FIG. 2 , at the moments the power transmission system  10  starts and ends providing the output load current I_LOAD to the load  104 , the output voltage VOUT of the power converter  100  respectively rises and falls slightly, but the error amplifier  108  immediately senses the variation of the output voltage VOUT and recovers the output voltage VOUT to a former voltage level via a feedback mechanism. As shown in  FIG. 2 , during the power transmission system  10  outputting the load current I_LOAD, a voltage drop between the load output voltage LOAD_VOUT of the load  104  and the output voltage VOUT equals the forward voltage difference ΔV 1 , and a voltage drop between the load ground voltage LOAD_GND of the load  104  and the ground voltage GND of the power converter  100  equals the reverse voltage difference ΔV 2 . Therefore, the voltage difference across the load  104  equals a difference between the load output voltage LOAD_VOUT and the load ground voltage LOAD_GND, i.e. LOAD_VOUT−LOAD_GND. Therefore, as can be seen from  FIG. 2 , the load  104  suffers a voltage difference ΔV 1 +ΔV 2  at the moments the power transmission system  10  starts and ends outputting the load current I_LOAD, which may cause the load  104  damaged. Thus, resistance of the transmission line  102  causes the power converter  100  incapable of controlling the load  104  to receive a stable voltage via the negative feedback mechanism. As a result, the load  104  would receive a voltage difference related to the resistance of the transmission line  102  and may be damaged by the voltage difference. 
         [0009]    Therefore, for the power transmission system, how to avoid the load generating the voltage difference due to the resistance of the transmission line and allow the load to receive a stable voltage becomes a goal in the industry. 
       SUMMARY OF THE INVENTION 
       [0010]    Therefore, the present invention provides a dynamic adjustment device and related power transmission system for ensuring the voltage difference across the remote load being stable when transmitting electricity to the remote load. 
         [0011]    The present invention discloses a dynamic voltage adjustment device, for dynamically adjusting an output voltage of a power transmission system which generates the output voltage according to a feedback signal and a reference signal and transmits the output voltage to a remote load via a transmission line to generate a load current. The dynamic voltage adjustment device comprises a first signal terminal, for receiving a first signal of a forward transmission voltage drop corresponding to the transmission line; a second signal terminal, for receiving a second signal of a reverse transmission voltage drop corresponding to the transmission line; a third signal terminal, for receiving a reference voltage; a feedback circuit, coupled to the first signal terminal, for generating the feedback signal according to the first signal; and an adder circuit, for generating the reference signal according to the second signal and the reference voltage. 
         [0012]    The present invention further discloses a power transmission system. The power transmission system comprises a remote load; a transmission line, for transmitting an output voltage to the remote load to generate a load current; a power converter, for generating the output voltage according to a feedback signal and a reference signal; and a dynamic voltage adjustment device, comprising a first signal terminal, for receiving a first signal of a forward transmission voltage drop corresponding to the transmission line; a second signal terminal, for receiving a second signal of reverse transmission voltage drop corresponding to the transmission line; a third signal terminal, for receiving a reference voltage; a feedback circuit, coupled to the first signal terminal, for generating the feedback signal according to the first signal; and an adder circuit, for generating the reference signal according to the second signal and the reference voltage. 
         [0013]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic diagram of a conventional power transmission system. 
           [0015]      FIG. 2  is a schematic diagram of related signals when the power transmission system shown in  FIG. 1  operates. 
           [0016]      FIG. 3  is a schematic diagram of a power transmission system according to an embodiment of the present invention. 
           [0017]      FIG. 4  is a schematic diagram of related signals when the power transmission system shown in  FIG. 3  operates. 
           [0018]      FIG. 5  is a schematic diagram of a power transmission system according to an embodiment of the present invention. 
           [0019]      FIG. 6  is a schematic diagram of a power transmission system according to an embodiment of the present invention. 
           [0020]      FIG. 7A-7D  are detailed schematic diagram of an adder circuit of the power transmission system shown in  FIG. 3  according to different embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Please refer to  FIG. 3 , which is a schematic diagram of a power transmission system  30  according to an embodiment of the present invention. The power transmission system  30  comprises a power converter  300 , a transmission line  302 , a load  304  and a dynamic voltage adjustment device  305 . Operating principles and architectures of the power converter  300 , the transmission line  302  and the load  304  are similar to those of the power converter  100 , the transmission line  102  and the load  104 ; thus, the same component symbols are used. The difference between the power transmission system  30  and the power transmission system  10  is that the power transmission system  30  adds the dynamic voltage adjustment device  305 . The dynamic voltage adjustment device  305  respectively samples a load output voltage LOAD_VOUT and a load ground voltage LOAD_GND of the load  304  to dynamically adjust a reference voltage of the power converter  300  according to different transmission voltage drops generated on the transmission line  302  when the power transmission system  30  outputs the different load current I_LOAD, so as to control the voltage difference across the load  304  to stay stable and to avoid the unstable voltage difference causes the load  304  damaged. 
         [0022]    In detail, as shown in  FIG. 3 , the dynamic voltage adjustment device  305  comprises a feedback circuit  306  and an adder circuit  307 . The operating principle and architecture of the feedback circuit  306  are similar to those of the feedback circuit  106  shown in  FIG. 1 ; thus, the same component symbols are used. However, different from the feedback circuit  106  which samples the output voltage VOUT close to the power converter  100 , the feedback circuit  306  samples the load output voltage LOAD_VOUT close to the load  304  to generate a feedback signal FB′ to the power converter  300 . The adder circuit  307  receives the original constant value reference voltage VREF of the power converter  300 , the ground voltage GND of the power converter  300  and the load ground voltage LOAD_GND of the load  304 , to generate a dynamic reference voltage VREF′ to the power converter  300 . The load output voltage LOAD_VOUT sampled by the feedback circuit  306  and the load ground voltage LOAD_GND received by the adder circuit  307  are respectively corresponding to the forward voltage difference ΔV 1  and the reverse voltage difference ΔV 2 , wherein the forward voltage difference ΔV 1  and the reverse voltage difference ΔV 2  are respectively generated on the forward transmission line LINE 1  and the reverse transmission line LINE 2  of the transmission line  302  when the power converter provides the load current I_LOAD to the load  304 . In the prior art, a voltage difference is generated across the load  104  of the power transmission system  10  due to the transmission resistance of the transmission line  102  and may damage the load  104 . In comparison, the dynamic voltage adjustment device  305  of the power transmission system  30  dynamically adjusts the reference voltage of the power converter  300  according to the transmission voltage difference corresponding to the transmission line  302 , to control the voltage difference across the load  304  to stay stable and to avoid the load  304  being damaged. 
         [0023]    Furthermore, the following explains operations of the dynamic voltage adjustment device  305  to keep the voltage difference across the load  304  stable. Since a voltage drop from the output voltage VOUT to the load output voltage LOAD_VOUT is the forward voltage difference ΔV 1  (i.e. LOAD_VOUT=VOUT−ΔV 1 ), the feedback signal FB′ generated by the feedback circuit  306  comprises the information corresponding to the forward voltage difference ΔV 1  of the transmission line  302  and can be expressed as: 
         [0000]    
       
         
           
             
               FB 
               ′ 
             
             = 
             
               
                 ( 
                 
                   
                     R 
                      
                     
                         
                     
                      
                     2 
                   
                   
                     R 
                      
                     
                         
                     
                      
                     1 
                   
                 
                 ) 
               
               × 
               
                 ( 
                 
                   VOUT 
                   - 
                   
                     ΔV 
                      
                     
                         
                     
                      
                     1 
                   
                 
                 ) 
               
             
           
         
       
     
         [0024]    In addition, since a voltage drop from the load ground voltage LOAD_GND to the ground voltage GND of the power converter  300  is the reverse voltage difference ΔV 2  (i.e. GND=LOAD_GND−ΔV 2 ), the adder circuit  307  can obtain the reverse voltage difference ΔV 2  via the load ground voltage LOAD_GND and the ground voltage GND. For example, the adder circuit  307  can obtain the reverse voltage difference ΔV 2 =LOAD_GND-GND via simple addition and subtraction operations. Next, the adder circuit  307  generates the dynamic reference voltage VREF′ via the reference voltage VREF and the reverse voltage difference ΔV 2  for the power converter  300 , e.g. the adder circuit  307  obtains the dynamic reference voltage VREF′=VREF+ΔV 2  via simple additions and subtractions. 
         [0025]    Next, similar to the power converter  100 , an error amplifier  308  of the power converter  300  compares the difference between the dynamic reference voltage VREF′ generated by the adder circuit  307  and the feedback signal FB′ outputted from the feedback circuit  306 , to control a power conversion unit  310  of the power converter  300  to generate the corresponding output voltage VOUT. Since the feedback point of the power converter  300  is changed to the load output voltage LOAD_VOUT close to the load  304 , the negative feedback mechanism of the power transmission system  30  keeps stability of the load output voltage LOAD_VOUT, and the voltage difference between the load output voltage LOAD_VOUT and the load ground voltage LOAD_GND is a function of the difference between the dynamic reference voltage VREF′ and the feedback signal FB′. The function can be conducted as: 
         [0000]    
       
         
           
             
               LOAD_VOUT 
               - 
               LOAD_GND 
             
             = 
             
               
                 f 
                  
                 
                   ( 
                   
                     
                       VREF 
                       ′ 
                     
                     - 
                     
                       FB 
                       ′ 
                     
                   
                   ) 
                 
               
               = 
               
                 
                   f 
                    
                   
                     ( 
                     
                       VREF 
                       + 
                       LOAD_GND 
                       - 
                       
                         FB 
                         ′ 
                       
                     
                     ) 
                   
                 
                 = 
                 
                   
                     f 
                      
                     
                       [ 
                       
                         VREF 
                         + 
                         
                           ΔV 
                            
                           
                               
                           
                            
                           2 
                         
                         - 
                         
                           
                             ( 
                             
                               
                                 R 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               
                                 R 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                             ) 
                           
                           × 
                           
                             ( 
                             
                               VOUT 
                               - 
                               
                                 ΔV 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                             ) 
                           
                         
                       
                       ] 
                     
                   
                   = 
                   
                     
                       f 
                        
                       
                         [ 
                         
                           VREF 
                           - 
                           
                             
                               ( 
                               
                                 
                                   R 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                                 
                                   R 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                               ) 
                             
                             × 
                             VOUT 
                           
                           + 
                           
                             ( 
                             
                               
                                 ΔV 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               + 
                               
                                 
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     1 
                                   
                                 
                                  
                                 ΔV 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                             ) 
                           
                         
                         ] 
                       
                     
                     = 
                     
                       f 
                        
                       
                         ( 
                         
                           VREF 
                           + 
                           
                             ( 
                             
                               
                                 ΔV 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               + 
                               
                                 
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     1 
                                   
                                 
                                  
                                 ΔV 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                             ) 
                           
                           - 
                           FB 
                         
                         ) 
                       
                     
                   
                 
               
             
           
         
       
     
         [0026]    As can be seen from the above function, a voltage offset ERROR_V exists between the voltage difference across the load  104  (i.e. LOAD_VOUT−LOAD_GND) and the output voltage VOUT, and can be expressed as: 
         [0000]    
       
         
           
             ERROR_V 
             = 
             
               ΔV2 
               + 
               
                 
                   
                     R 
                      
                     
                         
                     
                      
                     2 
                   
                   
                     R 
                      
                     
                         
                     
                      
                     1 
                   
                 
                  
                 ΔV 
                  
                 
                     
                 
                  
                 1 
               
             
           
         
       
     
         [0027]    As a result, the voltage offset ERROR_V can be the forward voltage difference ΔV 1  plus the reverse voltage difference ΔV 2  through selecting suitable resistance of the resistors R 1 , R 2  of the feedback circuit  306 . In other words, in order to keep the load output voltage LOAD_VOUT stable, the negative feedback mechanism of the power transmission system  30  forces the power converter  300  to additionally output a voltage ΔV 1 +ΔV 2  when providing the load current I_LOAD, to compensate the forward voltage difference ΔV 1  and the reverse voltage difference ΔV 2  generated by the load current I_LOAD flowing through the transmission line  302 . 
         [0028]    Please refer to  FIG. 4 , which is a schematic diagram of related signals when the power transmission system  30  operates. As shown in  FIG. 4 , at the moments the power transmission system  30  starts and ends outputting the load current I_LOAD to the load  304 , the voltage difference across the load  304  (i.e. LOAD_VOUT−LOAD_GND) respectively reduces and increases slightly, and the error amplifier  308  immediately senses the variation and adjusts the voltage difference across the load  304  back to the former level via the negative feedback mechanism. As shown in  FIG. 4 , during the power transmission system  30  outputting the load current I_LOAD, the power transmission system  30  additionally outputs the output voltage VOUT with a voltage ΔV 1 +ΔV 2  for compensating the forward voltage difference ΔV 1  and the reverse voltage difference ΔV 2  generated by the load current I_LOAD flowing through the transmission line  302 . After the load current I_LOAD flows to the load  104  through the forward transmission line R_LINE 1  of the transmission line  302 , the forward voltage difference ΔV 1  is generated between the output voltage VOUT and the load output voltage LOAD_VOUT; thus, the load output voltage LOAD_VOUT is greater than the output voltage VOUT by the additional compensated value ΔV 2 . Since the load ground voltage LOAD_GND of the load  304  is greater than the ground voltage GND by the reverse voltage difference ΔV 2 , the voltage difference across the load  304  (i.e. LOAD_VOUT−LOAD_GND) can be stable after the load output voltage LOAD_VOUT substrates the load ground voltage LOAD_GND. In comparison, the load  104  of the power transmission system  10  has the voltage difference related to the resistance of the transmission line  102 , and the voltage difference may cause the load  104  damaged. 
         [0029]    Therefore, the objective of the dynamic voltage adjustment device  305  shown in  FIG. 3  is dynamically adjusting the reference voltage of the voltage converter  300  via respectively sampling the voltages across the load  304 , such that the output voltage of the power converter  300  has a function of the voltage difference of the transmission line  302 , and the voltage difference across the load  304  can stay stable. Note that, the dynamic voltage adjustment device  305  shown in  FIG. 3  is not limited for a specific type of power converter but for devices such as power converters, voltage regulators and power supplies. Those skilled in the art can reasonably adjust the dynamic voltage adjustment device  305  according to different applications and requirements. For example, in another embodiment, the feedback circuit  306  can be included in the power converter  300 . Furthermore, in another embodiment, as long as the adder circuit  307  can generate the signal corresponding to the voltage difference of the transmission line  302  for the power converter  300 , the adder circuit  307  also can be implemented by other circuitry. 
         [0030]    For example, please refer to  FIG. 5  and  FIG. 6 , which are schematic diagrams of power transmission systems which reasonably adjust the dynamic voltage adjustment device  305  according to embodiments of the present invention for applying to difference types of power converter. In detail,  FIG. 5  is a schematic diagram of a power transmission system  50  according to an embodiment of the present invention. The power transmission system  50  comprises a power converter  500 , a transmission line  502 , a load  504  and a dynamic voltage adjustment device  505 . The dynamic voltage adjustment device  505  comprises the feedback circuit  306  and the adder circuit  307  shown in  FIG. 3 . Operating principles and architectures of the transmission line  502 , the load  504  and the dynamic voltage adjustment device  505  are substantially the same as those of the transmission line  302 , the load  304  and the dynamic voltage adjustment device  305  of the power transmission system  30  shown in  FIG. 3 ; therefore, the same component symbols are used. The power converter  500  is a switching buck converter, which converts an input voltage VIN to a lower output voltage VOUT. The power converter  500  comprises an error amplifier  508  and a power conversion unit  510 . The error amplifier  508  is similar to the error amplifier  308  and can generate an error result ER. The power conversion unit  510  comprises a comparator  512  and a power stage circuit  514 . The comparator  512  compares a difference between the error result ER generated by the error amplifier  508  and a triangular wave TRG, to generate driving signals VDRV, VDRV_B for the power stage circuit  514 , wherein the driving signal VDRV, VDRV_B have a specific duty cycle and are reverse to each other. The power stage circuit  514  comprises a high-side switch N 1 , a low-side switch N 2 , an inductor L and a capacitor C. The power stage circuit  514  switches connections between the input voltage VIN or the ground and inductor L according to the driving signals VDRV, VDRV_B, so as to convert the input voltage VIN to the suitable output voltage VOUT via the effect of the inductor L and the capacitor C. The dynamic voltage adjustment device  505  is similar to the dynamic voltage adjustment device  305 , which can dynamically adjust a reference voltage of the dynamic voltage adjustment device  505  according to the different transmission voltage drops generated on the transmission line  502 , to control the voltage difference across the load  504  to be stable. The detailed operations can be referred to the above, and is not described herein for simplicity. 
         [0031]    Please refer to  FIG. 6 , which is a schematic diagram of a power transmission system  60  according to an embodiment of the present invention. The power transmission system  60  comprises a power converter  600 , a transmission line  602 , a load  604  and a dynamic voltage adjustment device  605 . The dynamic voltage adjustment device  605  comprises the feedback circuit  306  and the adder circuit  307  shown in  FIG. 3 . Operating principles and the architectures of the transmission line  602 , the load  604  and the dynamic voltage adjustment device  605  are substantially the same as those of the transmission line  302 , the load  304  and the dynamic voltage adjustment device  305  of the power transmission system  30 ; therefore, the same component symbols are used. The power converter  600  is a Low-Dropout (LDO) linear power converter, which converts an input voltage VIN to a lower output voltage VOUT. The operations of the power converter  60  are well-known to those skilled in the art, and are not described herein for simplicity. 
         [0032]    Please continue to refer  FIGS. 7A-7D , which are schematic diagrams of different embodiments of the adder circuit  307  shown in  FIG. 3 , wherein the embodiments respectively utilizes one to three operational amplifiers for implementing the adder circuit  307 , and the operation methods of the embodiments are well-known to those skilled in the art and are not described herein for simplicity. The adder circuit  307  can receive the original constant value reference voltage VREF of the power converter  300 , the ground voltage GND of the power converter  300 , and the load ground voltage LOAD_GND of load  304 , to generate the dynamic reference voltage VREF′ to the power converter  300 . Note that, as long as the adder circuit  307  can acquire the reverse voltage difference ΔV 2  via the load ground voltage LOAD_GND and the ground voltage GND and can accordingly generate the dynamic reference voltage VREF′ to the power converter  300 , the adder circuit  307  also can be implemented by different circuitry and is not limited to perform simple operations of addition and subtraction. 
         [0033]    Noticeably, the spirit of the present invention is to directly sample the load output voltage but not to sample the output voltage. Therefore, the resistance voltage difference generated by the load current flows on the transmission line can be acquired, and the output voltage of the power converter can be dynamically adjusted such that the output voltage of the power converter has a function of the resistance voltage difference. Therefore, the output voltage can be dynamically adjusted corresponding to different resistance voltage differences under different load currents, to ensure the load can receive stable voltage. According to different applications, those skilled in the art can accordingly observe appropriate modifications and alternations. For example, the power transmission system of the present invention is not limited for switching power converters or linear power converters, but for different power converters, such as voltage regulators and power supplies, or any other applications needed to ensure the voltage of remote load staying stable. Furthermore, the resistances of the resistor R 1 , R 2  of the feedback circuit  306  can be appropriately selected, such that the power converter  300  additionally outputs different output voltages VOUT to compensate the voltage difference of the transmission line  302 . 
         [0034]    To sum up, different from the conventional technologies which sample the output voltage as a feedback signal, the dynamic voltage adjustment device of the present invention samples voltages across the load, and thus the reference voltage of the power converter can be dynamically adjusted according to different transmission voltage drops of the transmission line, so as to control the voltage difference across the load to stay stable and to avoid the load being damaged. 
         [0035]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.