Abstract:
A switching regulator for fixing a frequency which includes a power stage circuit, for receiving an input voltage and outputting an output voltage according to an control signal; a reference voltage generator for generating a reference voltage; a comparator for outputting a comparing result according to the output voltage and the reference voltage; a constant-time trigger circuit for outputting the control signal according to the comparing result and a compensating signal; an a frequency compensator for outputting the compensating signal according to the output voltage and a phase signal; wherein the phase signal is corresponding to the magnitude of the voltage across the lower gate switch of the power stage circuit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is related to a switching regulator, and more particularly, to a switching regulator for fixing an operating frequency by controlling a constant-time trigger, according to an output voltage and a phase signal. 
         [0003]    2. Description of the Prior Art 
         [0004]    Power supply devices play an essential role in modern information technology. Among all the power supply devices, a DC-DC switching regulator has been very popular and is mainly used to provide regulated DC power sources to electronic components. Please refer to  FIG. 1 , which illustrates a schematic diagram of a DC-DC switching regulator  10  of the prior art. The DC-DC switching regulator  10  is used to provide power for a load Load 1 , and includes an upper gate switch  100 , a lower gate switch  102 , a constant time trigger circuit  104 , a comparator  106 , an inductor L 1 , a capacitor C 1 , a reference voltage Vref 1  and an inverter INV 1 . The constant time trigger circuit  104  can output a signal pulse with constant time width to control operations of the upper gate switch  100  and the lower gate switch  102 . Every time when the output voltage Vout 1  reaches a level smaller than the reference voltage Vref 1 , the comparator  106  outputs a signal to the constant time trigger circuit  104 , such that the constant time trigger circuit  104  can output the signal pulse, to turn on the upper gate switch  100  and turn off the lower gate switch  102 . Then, the input voltage source Vin 1  starts delivering electric energy to the inductor L 1  and then to the load Load 1  via the upper gate switch  100 . Since the signal pulse outputted from the constant time trigger circuit  104  is with constant time width, the upper gate switch  100  can be turned on for a constant period of time when the output voltage Vout 1  is smaller than the reference voltage Vref 1 . If the output voltage Vout 1  becomes higher than the reference voltage Vref 1  after the constant period of time, the upper gate switch  100  will be turned off for a time interval of indefinite length. When the upper gate switch  100  is turned off, the output voltage of the DC-DC switching regulator  10  starts falling, and only when the output voltage Vout 1  is less than the reference voltage Vref 1 , the upper gate switch  100  will be turned on again. In other words, the DC-DC switching regulator  10  uses a PWM (pulse width modulation) type of control to regulate the power delivery to the load Load 1  by turning on and off the upper gate switch  100 . 
         [0005]    Meanwhile, since the operating period of the PWM signal is the summation of the turn-on time and the turn-off time of the upper gate switch  100 , when the load Load 1  changes, the duty cycle of the PWM signal will be changed accordingly, but since the turn on time of the constant time trigger circuit  104  has been fixed, and only the turn off time can be changed, it implies the operating period (as well as the operating frequency) of the PWM signal will also be changed when the output load changes. As can be seen in the DC-DC switching regulator  10 , there are some components (e.g. inductor L and capacitor C for energy efficiency enhancement and ripple reduction) whose operating characteristics are highly dependent on the operating frequency of the DC-DC switching regulator  10 . If the operating frequency roams in a wide range, it becomes impossible for the designer to optimize the designs of those frequency-sensitive components. In this case, some negative results might be present; for example, in the DC-DC switching regulator  10 , the ripples of the output voltage Vout 1  will become too large for proper operation in some applications. 
         [0006]    Please refer to  FIG. 2 , which illustrates a schematic diagram of a DC-DC switching regulator  20  of the prior art which can fix its operating frequency. The DC-DC switching regulator  20  differs from the DC-DC switching regulator  10  by adding some components for fixing the operating frequency. The DC-DC switching regulator  20  includes an upper gate switch  200 , a lower gate switch  202 , a constant time trigger circuit  204 , a comparator  206 , an inductor L 2 , a capacitor C 2 , a reference voltage Vref 2   a  and an inverter INV 2 . Besides, a frequency fixing circuit  250  is added to the DC-DC switching regulator  20 . The frequency fixing circuit  250  further includes an error amplifier  252 , a compensator  254 , a frequency-to-voltage converter  256  and a voltage reference Vref 2   b.  Noticeably, the constant time trigger circuit  204  also differs from the constant time trigger circuit  104  by adding an extra control input end  204   a.  Since the control input end  204   a  can be utilized to adjust the turn-on time of the constant time trigger circuit  204  for the purpose of frequency fixing, the turn-on time of the constant time trigger circuit  204  is not always fixed. When the frequency tends to change, the constant time trigger circuit  204  can adjust the length of its turn-on time according to the control signals received from the control input end  204   a.  Furthermore, the constant time trigger circuit  204  can combine with the frequency to voltage converter  256 , the error amplifier  252  and the compensator  254  to form a closed loop, to force the output voltage V 256  of the frequency to voltage converter  256  to track the reference voltage Vref 2   b,  such that the frequency (or period) of the PWM signal outputted by the constant time trigger circuit  204  can be fixed. 
         [0007]    However, although the operating frequency of the DC-DC switching regulator  20  can be fixed and let the designer optimize the designs of the frequency sensitive components to reduce the output ripples, the architecture and the related circuit of the DC-DC switching regulator  20  still deserve further investigation - - - to realize the frequency fixing functions, it requires complex circuitry to implement the frequency to voltage converter  256 , the error amplifier  252  and the compensator  254 . In other words, it will take relatively large chip area, and the production cost is still higher than expected. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore a primary objective of the claimed invention to provide a switching regulator which can fix its operating frequency by controlling a constant-time trigger, according to an output voltage and a phase signal. 
         [0009]    The present invention discloses a switching regulator for fixing a frequency, which comprises a power stage circuit, for receiving an input voltage and outputting an output voltage according to an control signal, comprising an upper gate switch, a lower gate switch coupled to the upper gate switch, and an output inductor coupled to the upper gate switch and the lower gate switch; a reference voltage generator for generating a reference voltage; a comparator for outputting a comparing result according to the output voltage and the reference voltage; a constant-time trigger circuit for outputting the control signal according to the comparing result and a compensating signal; and a frequency compensator for outputting the compensating signal according to the output voltage and a phase signal, wherein the phase signal is corresponding to the magnitude of the voltage across the lower gate switch of the power stage circuit. 
         [0010]    The present invention further discloses a frequency compensator for a switching regulator, which comprises a voltage-to-current converter for outputting a converted current according to the phase signal; and a current-to-voltage converter for outputting a compensating signal according to the converted current and the output voltage. 
         [0011]    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 
         [0012]      FIG. 1  illustrates a schematic diagram of a DC-DC switching regulator of the prior art. 
           [0013]      FIG. 2  illustrates a schematic diagram of a DC-DC switching regulator of the prior art which can fix an operating frequency. 
           [0014]      FIG. 3  illustrates a schematic diagram of a DC-DC switching regulator according to an embodiment of the present invention. 
           [0015]      FIG. 4  illustrates a schematic diagram of a circuit of a frequency compensator used in a DC-DC switching regulator according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Please refer to  FIG. 3 , which illustrates a schematic diagram of a DC-DC switching regulator  30  according to an embodiment of the present invention. The DC-DC switching regulator  30  is mainly utilized to provide an output voltage Vout 3  to a load Load 3 , which is denoted as a current source Iout 3 . The DC-DC switching regulator  30  comprises a power stage circuit  32 , a comparator  306 , a reference voltage Vref 3 , an inverter INV 3 , a constant time trigger circuit  304  and a frequency compensator  310 . The power stage circuit  32  comprises an upper gate switch  300 , a lower gate switch  302 , an inductor L 3 , and a capacitor C 3 . The architecture of the DC-DC switching regulator  30  is similar to that of the DC-DC switching regulator  20 , while the frequency compensator  310  of the DC-DC switching regulator  30  controls the constant time trigger circuit  304  according to an inductor current IL 3  of the inductor L 3  and an output voltage Vout 3 , to fix an operating frequency. The control input end  304   a  can be utilized to adjust the turn-on time of the constant time trigger circuit  304  for the purpose of frequency fixing. The working principle of the frequency compensator  310  is introduced as follows. 
         [0017]    In the DC-DC switching regulator  30 , the output voltage Vout 3  can be derived by examining the voltage across the inductor L 3  and can be expressed by the following equation: 
         [0000]    
       
         
           
             
               Vout 
                
               
                   
               
                
               3 
             
             = 
             
               
                 
                   1 
                   Ts 
                 
                 · 
                 
                   
                     ∫ 
                     0 
                     Ton 
                   
                    
                   
                     
                       ( 
                       
                         
                           Vin 
                            
                           
                               
                           
                            
                           3 
                         
                         - 
                         
                           IL 
                            
                           
                               
                           
                            
                           
                             3 
                             · 
                             Rds 
                           
                            
                           
                               
                           
                            
                           1 
                         
                       
                       ) 
                     
                     · 
                     
                        
                       t 
                     
                   
                 
               
               + 
               
                 
                   1 
                   Ts 
                 
                 · 
                 
                   
                     ∫ 
                     Ton 
                     Ts 
                   
                    
                   
                     
                       ( 
                       
                         0 
                         - 
                         
                           IL 
                            
                           
                               
                           
                            
                           
                             3 
                             · 
                             Rds 
                           
                            
                           
                               
                           
                            
                           2 
                         
                       
                       ) 
                     
                     · 
                     
                       
                          
                         t 
                       
                       . 
                     
                   
                 
               
             
           
         
       
     
         [0018]    The symbols Ts, Ton, IL3, Rds1 and Rds2 denote the length of the operation period, the length of the turn-on time of the upper gate switch  300 , the inductor current, the on resistance of the upper gate switch  300  and the on resistance of the lower gate switch  302 , respectively. The first term on the right hand side of the above equation is contributed by the condition when the upper gate switch  300  is on and the lower gate switch  302  is off; meanwhile, the second term on the right hand side is contributed by the condition when the upper gate switch  300  is off and the lower gate switch  302  is on. These two terms determine the magnitude of the output voltage Vout 3 . And, when the input voltage Vin 3 , the output voltage Vout 3  and the inductor current IL 3  are relatively stable, the above equation can be rearranged as the following equation: 
         [0000]        Ts·V out3= T on·( V in3− IL 3· Rds 1)+[0−( Ts−T on)·( IL 3· Rds 2)].
 
         [0019]    By rearranging the above equation, the operation period Ts can be expressed as: 
         [0000]    
       
         
           
             
               
                 
                   Ts 
                   = 
                     
                    
                   
                     Ton 
                     · 
                     
                       
                         
                           Vin 
                            
                           
                               
                           
                            
                           3 
                         
                         + 
                         
                           IL 
                            
                           
                               
                           
                            
                           
                             3 
                             · 
                             
                               ( 
                               
                                 
                                   Rds 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                                 - 
                                 
                                   Rds 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           Vout 
                            
                           
                               
                           
                            
                           3 
                         
                         + 
                         
                           ( 
                           
                             IL 
                              
                             
                                 
                             
                              
                             
                               3 
                               · 
                               Rds 
                             
                              
                             
                                 
                             
                              
                             2 
                           
                           ) 
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     Ton 
                     · 
                     
                       
                         Vin 
                          
                         
                             
                         
                          
                         3 
                       
                       
                         Vout 
                          
                         
                             
                         
                          
                         3 
                       
                     
                     · 
                     
                       
                         1 
                         + 
                         
                           
                             IL 
                              
                             
                                 
                             
                              
                             
                               3 
                               · 
                               
                                 ( 
                                 
                                   
                                     Rds 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                   - 
                                   
                                     Rds 
                                      
                                     
                                         
                                     
                                      
                                     1 
                                   
                                 
                                 ) 
                               
                             
                           
                           
                             Vin 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                       
                       
                         1 
                         + 
                         
                           
                             ( 
                             
                               IL 
                                
                               
                                   
                               
                                
                               
                                 3 
                                 · 
                                 Rds 
                               
                                
                               
                                   
                               
                                
                               2 
                             
                             ) 
                           
                           
                             Vout 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
         [0020]    According to function of the constant time trigger circuit  304 , the length of the turn-on time Ton is determined internally by the output voltage Vout 3  and the input voltage Vin 3 , and the Ton can then be expressed as: 
         [0000]    
       
         
           
             
               Ton 
               = 
               
                 K 
                  
                 
                     
                 
                  
                 
                   1 
                   · 
                   
                     
                       Vout 
                        
                       
                           
                       
                        
                       3 
                     
                     
                       Vin 
                        
                       
                           
                       
                        
                       3 
                     
                   
                 
               
             
             , 
           
         
       
     
         [0000]    where the parameter K 1  is a constant parameter and is decided by the internal circuit of the constant time trigger circuit  304 . Then, the equation for Ts can now be rearranged and expressed as the following equation: 
         [0000]    
       
         
           
             Ts 
             = 
             
               K 
                
               
                   
               
                
               
                 1 
                 · 
                 
                   
                     
                       1 
                       + 
                       
                         
                           IL 
                            
                           
                               
                           
                            
                           
                             3 
                             · 
                             
                               ( 
                               
                                 
                                   Rds 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                                 - 
                                 
                                   Rds 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                               ) 
                             
                           
                         
                         
                           Vin 
                            
                           
                               
                           
                            
                           3 
                         
                       
                     
                     
                       1 
                       + 
                       
                         
                           ( 
                           
                             IL 
                              
                             
                                 
                             
                              
                             
                               3 
                               · 
                               Rds 
                             
                              
                             
                                 
                             
                              
                             2 
                           
                           ) 
                         
                         
                           Vout 
                            
                           
                               
                           
                            
                           3 
                         
                       
                     
                   
                   . 
                 
               
             
           
         
       
     
         [0021]    Typically, the parameter K 1  is equal to 2.5 μsec for a switching regulator operated at 400 KHz. 
         [0022]    By closely examining the above equation, the operating frequency of the DC-DC switching regulator  30  will be changed if the values or the magnitudes of the inductor current IL 3 , the output voltage Vout 3 , the input voltage Vin 3 , the on resistance of the upper gate switch Rds 1  and/or the on resistance of the lower gate switch Rds 2  change, and the stability of the operating frequency of the DC-DC switching regulator will be affected. According to more detailed numerical simulation, the term in the denominator, which is 
         [0000]    
       
         
           
             
               1 
               + 
               
                 
                   ( 
                   
                     IL 
                      
                     
                         
                     
                      
                     
                       3 
                       · 
                       Rds 
                     
                      
                     
                         
                     
                      
                     2 
                   
                   ) 
                 
                 
                   Vout 
                    
                   
                       
                   
                    
                   3 
                 
               
             
             , 
           
         
       
     
         [0000]    of the above equation is the one which is much influential to the stability of the operating frequency. According to the above equation for Ts, if the influence of the term in the denominator can be removed, the operating frequency of the DC-DC switching regulator will be much more stable. 
         [0023]    Therefore, in the present invention, in order to stabilize the operating frequency of the DC-DC switching regulator  30 , the equation to determine the turn-on time can be modified and expressed as follows: 
         [0000]    
       
         
           
             Ton 
             = 
             
               K 
                
               
                   
               
                
               
                 1 
                 · 
                 
                   
                     
                       
                         Vout 
                          
                         
                             
                         
                          
                         3 
                       
                       + 
                       
                         IL 
                          
                         
                             
                         
                          
                         
                           3 
                           · 
                           Rds 
                         
                          
                         
                             
                         
                          
                         2 
                       
                     
                     
                       Vin 
                        
                       
                           
                       
                        
                       3 
                     
                   
                   . 
                 
               
             
           
         
       
     
         [0024]    In the equation above, the term Vout 3 +IL 3 ·Rds 2  in the nominator is used to replace the original nominator (Vout 3 ) in the equation for determining the turn-on time Ton. This is equivalent to increase the output voltage Vout 3  by 
         [0000]    
       
         
           
             1 
             + 
             
               
                 ( 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
                 ) 
               
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
         [0000]    times, such that the Ton Time can also be increased by 
         [0000]    
       
         
           
             1 
             + 
             
               
                 ( 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
                 ) 
               
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
         [0000]    times, then the above equation for the period of operation Ts can be modified as follows: 
         [0000]    
       
         
           
             Ts 
             = 
             
               K 
                
               
                   
               
                
               
                 1 
                 · 
                 
                   
                     [ 
                     
                       1 
                       + 
                       
                         
                           IL 
                            
                           
                               
                           
                            
                           
                             3 
                             · 
                             
                               ( 
                               
                                 
                                   Rds 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                                 - 
                                 
                                   Rds 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                               ) 
                             
                           
                         
                         
                           Vin 
                            
                           
                               
                           
                            
                           3 
                         
                       
                     
                     ] 
                   
                   . 
                 
               
             
           
         
       
     
         [0025]    As can be observed in the above equation, the term in the denominator, 
         [0000]    
       
         
           
             
               1 
               + 
               
                 
                   ( 
                   
                     IL 
                      
                     
                         
                     
                      
                     
                       3 
                       · 
                       Rds 
                     
                      
                     
                         
                     
                      
                     2 
                   
                   ) 
                 
                 
                   Vout 
                    
                   
                       
                   
                    
                   3 
                 
               
             
             , 
           
         
       
     
         [0000]    has been removed, and the operating frequency of the DC-DC switching regulator  30  becomes much more stable. To implement the working principles stated above, the frequency compensator  310  of the present invention is designed to generate the special voltage Vout 3 +IL 3 ·Rds 2 , and the constant time trigger circuit  304  will determine the pulse width of the turn-on time according to the latest equation for Ton. Noticeably, a phase signal PSIG is measured at one end of the inductor L 3  and is equal to the voltage IL 3 ·Rds 2 , which is also the voltage difference across the lower gate switch  302  when the device is on. 
         [0026]    Please refer to  FIG. 4 , which illustrates a schematic diagram of a circuit of the frequency compensator  310  used in the DC-DC switching regulator  30  according to an embodiment of the present invention. The circuit of the frequency compensator  310  illustrated in  FIG. 4  can be utilized to generate the voltage Vout 3 +IL 3 ·Rds 2 , and comprises a voltage-to-current converter  310   a  and a current-to-voltage converter  310   b  . The voltage-to-current converter  310   a  is utilized to convert the voltage level of the phase signal PSIG, which is equal to IL 3 ·Rds 2 , into a converted current I_ 3 . Then, the current-to-voltage converter  310   b  transforms the converted current I_ 3  into a voltage (by a resistor) and generates the sum of the voltage IL 3 ·Rds 2  and the output voltage Vout 3 . 
         [0027]    To detail further, the voltage-to-current converter  310   a  comprises two resistors R 1 , R 2 , a current mirror CM 1 , two current sources CS 1 , CS 2 , and a current switch SW 1 . The current mirror CM 1  comprises two transistors M 1 , M 2  of the same type. Both of the current sources CS 1 , CS 2  can supply the same magnitude of current I_ 1  into the transistors M 1 , M 2 , respectively. The current mirror CM 1  further assures the currents flowing through the transistor M 1  and the transistor M 2  are of the same magnitude. Therefore, if the output current is I_ 3 , then the voltage-to-current converter  310   a  can assure that a current I_ 2  flowing through the resistor R 2  is equal to the current I_ 1  plus the output current I_ 3 . If the phase signal PSIG, which is IL 3 ·Rds 2 , is applied to the input end of the voltage-to-current converter  310   a  , the output current I_ 3  will be proportional to the phase signal IL 3 ·Rds 2 , and can be expressed as follows: 
         [0000]    
       
         
           
             
               
                 I_ 
                  
                 3 
               
               = 
               
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
                 R 
               
             
             , 
           
         
       
     
         [0000]    where R is the resistance of the resistor R 2 . 
         [0028]    Furthermore, the output current I_ 3  of the voltage-to-current converter  310   a  can be fed into the current-to-voltage converter  310   b  . The current-to-voltage converter  310   b  comprises a current mirror CM 2  and a resistor R 3 . The current mirror CM 2  comprises two transistors M 4  and M 5  of the same type. The current mirror CM 2  will duplicate the input current I_ 3  and make the current flowing through the resistor R 3  to be equal to I_ 3 . The current I_ 3  can be converted into a voltage difference by flowing through the resistor R 3 . Since the voltage of the input end of the current-to-voltage converter  310   b  is Vout 3 , the voltage in the output end of the current-to-voltage converter  310   b  can be derived as follows: 
         [0000]    
       
         
           
             
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
               + 
               
                 I_ 
                  
                 
                   3 
                   · 
                   R 
                 
               
             
             = 
             
               
                 
                   Vout 
                    
                   
                       
                   
                    
                   3 
                 
                 + 
                 
                   
                     
                       IL 
                        
                       
                           
                       
                        
                       
                         3 
                         · 
                         Rds 
                       
                        
                       
                           
                       
                        
                       2 
                     
                     R 
                   
                   · 
                   R 
                 
               
               = 
               
                 
                   Vout 
                    
                   
                       
                   
                    
                   3 
                 
                 + 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2. 
                 
               
             
           
         
       
     
         [0029]    As can be observed, the output voltage of the current-to-voltage converter  310   b  as well as the frequency compensator  310  is equal to Vout 3 +IL 3 ·Rds 2 . Therefore, by taking the output voltage Vout 3  and the phase signal IL 3 ·Rds 2  as the inputs of the frequency compensator  310 , the voltage Vout 3 +IL 3 ·Rds 2  can be generated by the circuit illustrated in  FIG. 4 . 
         [0030]    Noticeably, some other voltages which are proportional to Vout 3 +IL 3 ·Rds 2  can also be used to adjust the length of the turn-on time Ton, and the 
         [0000]    
       
         
           
             1 
             + 
             
               
                 ( 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
                 ) 
               
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
         [0000]    term in the denominator can also be removed. People with ordinary knowledge in the art should readily to know there are numerous alterations can be made. For example, a voltage, which is equal to 
         [0000]    
       
         
           
             
               
                 1 
                 3 
               
               · 
               
                 ( 
                 
                   
                     Vout 
                      
                     
                         
                     
                      
                     3 
                   
                   + 
                   
                     IL 
                      
                     
                         
                     
                      
                     
                       3 
                       · 
                       Rds 
                     
                      
                     
                         
                     
                      
                     2 
                   
                 
                 ) 
               
             
             , 
           
         
       
     
         [0000]    can also be applied to remove the denominator, 
         [0000]    
       
         
           
             1 
             + 
             
               
                 
                   ( 
                   
                     IL 
                      
                     
                         
                     
                      
                     
                       3 
                       · 
                       Rds 
                     
                      
                     
                         
                     
                      
                     2 
                   
                   ) 
                 
                 
                   Vout 
                    
                   
                       
                   
                    
                   3 
                 
               
               . 
             
           
         
       
     
         [0000]    To realize this, the circuit in the frequency compensator  310  can be modified by changing the resistance of R 3  from R to R/3, and the input voltage from Vout 3  to 
         [0000]    
       
         
           
             
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
               3 
             
             . 
           
         
       
     
         [0000]    Under this condition, a common voltage divider can be added to generate the voltage 
         [0000]    
       
         
           
             
               Vout 
                
               
                   
               
                
               3 
             
             3 
           
         
       
     
         [0000]    from Vout 3 . By this method, the voltage 
         [0000]    
       
         
           
             
               1 
               3 
             
             · 
             
               ( 
               
                 
                   Vout 
                    
                   
                       
                   
                    
                   3 
                 
                 + 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
               
               ) 
             
           
         
       
     
         [0000]    can be generated to adjust the turn-on time Ton. In this case, the period of operation becomes: 
         [0000]    
       
         
           
             Ts 
             = 
             
               
                 
                   1 
                   3 
                 
                 · 
                 K 
               
                
               
                   
               
                
               
                 1 
                 · 
                 
                   
                     [ 
                     
                       1 
                       + 
                       
                         
                           IL 
                            
                           
                               
                           
                            
                           
                             3 
                             · 
                             
                               ( 
                               
                                 
                                   Rds 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                                 - 
                                 
                                   Rds 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                               ) 
                             
                           
                         
                         
                           Vin 
                            
                           
                               
                           
                            
                           3 
                         
                       
                     
                     ] 
                   
                   . 
                 
               
             
           
         
       
     
         [0031]    It can be observed from the above equation that a constant parameter ⅓ has appeared in the equation, and the internal circuit of the constant time trigger circuit  304  which is related to the parameter K 1 , can be readily modified by the designer to select a proper operating frequency (or period). As stated above in this alternative embodiment of the present invention, the influence of the denominator term, 
         [0000]    
       
         
           
             
               1 
               + 
               
                 
                   ( 
                   
                     IL 
                      
                     
                         
                     
                      
                     
                       3 
                       · 
                       Rds 
                     
                      
                     
                         
                     
                      
                     2 
                   
                   ) 
                 
                 
                   Vout 
                    
                   
                       
                   
                    
                   3 
                 
               
             
             , 
           
         
       
     
         [0000]    can also be removed. 
         [0032]    To sum up, the frequency compensator  310  of the present invention is utilized to generate the special voltage Vout 3 +IL 3 ·Rds 2 , and to increase the output voltage Vout 3  by 
         [0000]    
       
         
           
             1 
             + 
             
               
                 ( 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
                 ) 
               
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
         [0000]    times, such that when the load experiences a sudden change, the turn-on time Ton can be increased by 
         [0000]    
       
         
           
             1 
             + 
             
               
                 ( 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
                 ) 
               
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
         [0000]    times, and the operating frequency can be kept nearly constant. 
         [0033]    Furthermore, in many applications, where both the upper gate switch and the lower gate switch use the same type of power transistors, the on resistance of the lower gate switch Rds 2  is very close to the on resistance of the upper gate switch Rds 1 , then the term 
         [0000]    
       
         
           
             [ 
             
               1 
               + 
               
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     
                       ( 
                       
                         
                           Rds 
                            
                           
                               
                           
                            
                           2 
                         
                         - 
                         
                           Rds 
                            
                           
                               
                           
                            
                           1 
                         
                       
                       ) 
                     
                   
                 
                 
                   Vin 
                    
                   
                       
                   
                    
                   3 
                 
               
             
             ] 
           
         
       
     
         [0000]    in the nominator of the above equation will be very close to 1, and the period of operation Ts will be very close to a constant value. However, even the upper gate switch  300  and the lower gate switch  302  are not of the same type, the operating frequency can be stabilized by increasing the output voltage Vout 3  by 
         [0000]    
       
         
           
             1 
             + 
             
               
                 ( 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
                 ) 
               
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
         [0000]    times, and thus, the present invention can be used to increase the turn-on time Ton by 
         [0000]    
       
         
           
             1 
             + 
             
               
                 ( 
                 
                   IL 
                    
                   
                       
                   
                    
                   
                     3 
                     · 
                     Rds 
                   
                    
                   
                       
                   
                    
                   2 
                 
                 ) 
               
               
                 Vout 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
         [0000]    times. 
         [0034]    Also, noticeably, instead of utilizing the phase signal PSIG to get a voltage signal corresponding to the magnitude of the output current, some alternatives can also be utilized to get the magnitude of the output current (e.g. by using a proprietary sensing resistor in the output current path to sense the magnitude of the current). The present invention can utilize the frequency compensator  310  to replace the phase signal PSIG by any signal which is corresponding to the magnitude of the output current to perform the functions of fixing the operating frequency. 
         [0035]    On the other hand, compared with the DC-DC switching regulator of the prior art, the architecture of the present invention becomes much simpler. The DC-DC switching regulator  20  of the prior art needs to sample the PWM signal generated by the constant time trigger circuit  204 , and if the period of operation is longer than the desired value, the turn-on time Ton is adjusted to fix the operating frequency. To implement the architecture of the prior art, the circuit needs to realize an error integration process; therefore, it will include at least an OTA (operational transconductance amplifier), and a large on-chip capacitor. However, the present invention only needs a compact circuit to decide the summation of the output voltage Vout 3  and the voltage across the lower gate switch  302 . According to experimental results, the present invention spends only about 20% of the chip area of the circuit of the prior art. Also, according to the experiment, the operating frequency can be fixed in a narrow range (with variation less than 10%) for a wide range of load current (3˜10 Amperes), with Rds 1 =9 mini-ohms, and Rds 2 =4 mini-ohms. 
         [0036]    The present invention regulates the operating frequency of the DC-DC switching regulator in a nearly fixed manner, such that the design of the frequency sensitive components of the DC-DC switching regulator becomes much simpler and more effective to reduce the output ripples. The present invention develops a theoretical background for adjusting the turn-on time of the constant time trigger circuit by referring to the output voltage and the voltage across the lower gate switch (phase signal). Meanwhile, the present invention develops a compact circuit to calculate the summation of the output voltage and the phase signal, such that the turn-on time and the operating frequency can be adjusted effectively according to the theory being developed. The experiment done in the lab proves that the theory and the circuit of the present invention are function correct and cost effective. 
         [0037]    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.