Patent Publication Number: US-2023163685-A1

Title: Buck converter with high power efficiency

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 63/282,209 filed Nov. 23, 2021, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to buck converters. 
     Description of the Related Art 
     A buck converter steps down voltage from an input voltage (supply) to an output voltage (load). It is a class of switched-mode power supply (SMPS), and typically uses an inductor as an energy storage element. 
     In a traditional inductor-based buck converter operating at a high conversion rate (e.g., 4V-to-1V, the dominant power loss is the switching loss (CV 2 F). The high input voltage (e.g., 4V) results in significant switching loss. In addition to the switching loss, the conduction loss (IR 2 ) should also be taken into consideration in the design of a buck converter. 
     A buck converter with high power efficiency is called for. 
     BRIEF SUMMARY OF THE INVENTION 
     A buck converter with high power efficiency is proposed. 
     In an exemplary embodiment, a buck converter converting an input voltage to an output voltage has an inductor, a voltage shift component, and a discharging branch. The inductor is charged and discharged to regulate the output voltage. The voltage shift component shifts the input voltage to a lower level to charge the inductor. The discharging branch is coupled to the inductor when the inductor is discharged. 
     Because of the voltage shift component, the switching loss (CV 2 F) is significantly suppressed by the lower operating voltages supplied to the parasitic capacitors. 
     Because of the discharging branch, the total current on the circuit is suppressed, and the conduction loss (IR 2 ) is significantly suppressed. 
     In an exemplary embodiment, the buck converter has a first switch. When being turned on, the first switch couples the input voltage to a first terminal of the voltage shift component. The voltage shift component has a second terminal coupled to the first terminal of the inductor. The inductor has a second terminal coupled to the output terminal of the buck converter that provides the output voltage. 
     In an exemplary embodiment, the buck converter has a second switch and a third switch. When being turned on, the second switch couples the first terminal of the inductor to ground. When being turned on, the third switch couples the output terminal of the buck converter to the first terminal of the voltage shift component. 
     In an exemplary embodiment, the first switch is turned on in the charging phase of the inductor, and the second switch and the third switch are turned on in the discharging phase of the inductor. 
     In an exemplary embodiment, the voltage shift provided by the voltage shift component to lower the input voltage is set during the discharging phase of the inductor. 
     In an exemplary embodiment, the voltage shift component is a capacitor. 
     In an exemplary embodiment, the output terminal of the buck converter is directly coupled to the capacitor through the third switch during the discharging phase of the inductor. 
     In an exemplary embodiment, during the discharging phase of the inductor, the capacitor is charged to store the output voltage as the voltage shift. 
     In an exemplary embodiment, the buck converter has a voltage shift setting circuit, converting the output voltage of the buck converter to the expected voltage used in charging the capacitor during the discharging phase of the inductor, for the capacitor to provide the voltage shift during the charging phase of the inductor. 
     In an exemplary embodiment, the expected voltage is coupled to the capacitor through the third switch during the discharging phase of the inductor. 
     In an exemplary embodiment, the expected voltage is b times the output voltage, where b is a number. 
     In an exemplary embodiment, the expected voltage is b times the output voltage plus c, where b and c are two numbers. 
     In an exemplary embodiment, the first switch is a p-channel metal oxide semiconductor transistor, and the second switch and the third switch are n-channel metal oxide semiconductor transistors. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG.  1    shows a buck converter  100  in accordance with an exemplary embodiment of the present invention; 
         FIG.  2 A  illustrates the charging phase (Φ1) of the inductor L; 
         FIG.  2 B  illustrates the discharging phase (Φ2) of the inductor L; and 
         FIG.  3    illustrates a buck converter  300  in accordance with another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG.  1    shows a buck converter  100  in accordance with an exemplary embodiment of the present invention. 
     The buck converter  100  converting an input voltage VIN to an output voltage VA has an inductor L, a voltage shift component  102 , and a discharging branch  104 . The inductor L is charged and discharged to regulate the output voltage VA. The voltage shift component  102  shifts the input voltage VIN to a lower level VLX to charge the inductor L. The discharging branch  104  is coupled to the inductor L when the inductor L is discharged. 
     Because of the voltage shift component  102 , the switching loss (CV 2 F) is significantly suppressed by the lower operating voltages supplied to the parasitic capacitors. In  FIG.  1   , the voltage shift component  102  is a capacitor C, which can be replaced by any component capable of voltage shifting. 
     Because of the discharging branch  104 , the total current on the circuit is suppressed, and the conduction loss (IR 2 ) is significantly suppressed. 
     The voltage shift component  102  also suppresses the voltage ripple of VLX, which is suppressed from VIN to (VIN-VA). Therefore, the inductor current ripple is also suppressed, which further suppresses the inductor ACR loss. 
     The details of the buck converter  100  are described in the following paragraphs. 
     As shown, the buck converter  100  has a first switch SW 1 . In the buck converter  100 , the first switch SW 1  is a p-channel metal oxide semiconductor (PMOS) transistor but not limited thereto. When being turned on, the first switch SW 1  couples the input voltage VIN to a first terminal  n C 1  of the voltage shift component  102 . The voltage shift component  102  has a second terminal  n C 2  coupled to a first terminal  n L 1  of the inductor L. The inductor L has a second terminal  n L 2  that is coupled to the output terminal of the buck converter  100  that provides the output voltage VA. 
     The buck converter  100  has a second switch SW 2  and a third switch SW 3 . In the buck converter  100 , the second switch SW 2  and the third switch SW 3  are n-channel metal oxide semiconductor (NMOS) transistors but not limited thereto. When being turned on, the second switch SW 2  couples the first terminal  n L 1  of the inductor L to ground (GND). As for the third switch SW 3 , the turned-on third switch SW 3  couples the output terminal (VA) of the buck converter  100  to the first terminal  n C 1  of the voltage shift component  102 . 
     In an exemplary embodiment, the first switch SW 1  is turned on in a charging phase Φ1 of the inductor L, and the second switch SW 2  and the third switch SW 3  are turned on in a discharging phaseΦ2 of the inductor L. In an exemplary embodiment, when the first switch SW 1  is turned on in the charging phaseΦ1 of the inductor L, the second and third switches SW 2  and SW 3  are turned off. When the second and third switches SW 2  and SW 3  are turned on in the discharging phaseΦ2 of the inductor L, the first switch SW 1  is turned off. 
     During the discharging phase Φ2 of the inductor L, a voltage shift Vcap provided by the voltage shift component  102  to lower the input voltage VIN is set. In this example, the voltage shift Vcap is set to VA during the discharging phase Φ2 of the inductor L. 
       FIG.  2 A  illustrates the charging phase (Φ1) of the inductor L. The first switch SW 1  is turned on (Φ1), and the voltage shift component  102  and the inductor L form a voltage divider between the input terminal (VIN) of the buck converter  100  and the output terminal (VA) of the buck converter  100 . While a voltage VIN is supplied to a parasitic capacitor C 1  at the terminal  nc   1 , a divided voltage (VIN-VA) is supplied to a parasitic capacitor C 2  at the terminal  nc   2 . 
       FIG.  2 B  illustrates the discharging phase (Φ2) of the inductor L. The second and third switches SW 2  and SW 3  are turned on (Φ2), and the current flowing through the inductor L is reduced by the branch current flowing through the turned-on third switch SW 3 . The terminal  nc   1  (having the parasitic capacitor C 1 ) is at the output voltage VA because of the turned-on third switch SW 3 . The terminal  nc   2  (having the parasitic capacitor C 2 ) is at the ground voltage GND because of the turned-on second switch SW 2 . The capacitor C is charged to store the voltage (VA-GND) as the voltage shift Vcap required in the charging phase (Φ1) of the inductor L. 
     In this design, the voltage swing on the parasitic capacitor C 1  is VIN-VA, and the voltage swing on the parasitic capacitor C 2  is (VIN-VA)~GND. The switching loss (CV 2 F) is: 
     
       
         
           
             C 
             1 
             
               
                 
                   
                     VIN-VA 
                   
                 
               
               2 
             
             F 
             + 
             C 
             2 
             
               
                 
                   
                     VIN-VA-GND 
                   
                 
               
               2 
             
             F 
             , 
           
         
       
     
     which is (C1+C2) (VIN-VA). (VIN-VA) 2  is usually much lower than VIN 2 . The switching loss (CV 2 F) is significantly suppressed. 
     For example, when the input voltage VIN is 4V and output voltage VA is 1V, (VIN-VA) 2  is 9, much lower than VIN 2  that is 16. In comparison with the conventional buck converters, the power efficiency of the buck converter  100  is considerably improved by the suppressed switching loss. 
     As for the conduction loss (IR 2 ), it is: 
     
       
         
           
             
               
                 
                   
                     IL 
                     * 
                     D 
                   
                 
               
               2 
             
             * 
             Rp 
             + 
             
               
                 
                   
                     IL 
                     * 
                     
                       
                         1 
                         − 
                         D 
                       
                     
                   
                 
               
               2 
             
             * 
             Rn 
             1 
             + 
             
               
                 Ic 
               
               2 
             
             * 
             Rn 
             2 
             + 
             
               
                 IL 
               
               2 
             
             * 
             RDC 
           
         
       
     
      where IL is the current through the inductor L, D is the duty cycle of the charging/discharging of the inductor L, Ic is the current through the capacitor C, Rp is the parasitic resistor of the first switch SW 1  (a PMOS transistor), Rn1 is the parasitic resistor of the second switch SW 2  (an NMOS transistor), Rn2 is the parasitic resistor of the third switch SW 3  (another NMOS transistor), and RDC is the equivalent resistance of the inductor L. Because of the discharging branch design, the current Ic and IL in the last two terms of the conduction loss function are considerably suppressed, and the conduction loss is significantly suppressed. 
     In this design, the conventional inductor current is divided into the current Ic and the current IL, For example, the current Ic and the current IL each may be just half the conventional inductor current. Thus, the conduction power is recued to (½) 2  + (½) 2 , half the conventional conduction loss. 
     Furthermore, the duty cycle D of the buck converter  100  is discussed in this paragraph. To operate the buck converter  100 , the duty cycle D should be set to VA/(VIN-VA). A conventional buck converter without the voltage divider design usually operates at a duty cycle VA/VIN. For a 4V-to-1V conversion, the duty cycle of the buck converter  100  is ⅓, which results in a better power efficiency than a conventional buck converter with a duty cycle ¼. 
     The power efficiency of the present invention is obviously much better than conventional buck conversion circuits. 
     In the forgoing example, the output terminal (VA) of the buck converter  100  is directly coupled to the capacitor C through the third switch SW 3  during the discharging phase (Φ2) of the inductor L to charge the capacitor C to store the output voltage VA as the voltage shift Vcap required in the charging phase (Φ2) of the inductor L. In some other exemplary embodiments, the capacitor C may be charged to store another voltage as the voltage shift Vcap. 
       FIG.  3    illustrates a buck converter  300  in accordance with another exemplary embodiment of the present invention. 
     The buck converter  300  has a voltage shift setting circuit  302 , converting the output voltage VA of the buck converter  300  to the expected voltage Ve used in charging the capacitor C during the discharging phaseΦ2 of the inductor L. Thus, during the charging phaseΦ1 of the inductor L, the capacitor C provides Ve (=Ve-GND) as the voltage shift Vcap. 
     In an exemplary embodiment, the expected voltage Ve is b times the output voltage VA, where b is a number. Ve=b*VA. For example, b may be 2. 
     In an exemplary embodiment, the expected voltage Ve is b times the output voltage VA plus c, where b and c are two numbers. Ve=b*VA + c. 
     In another exemplary embodiment, the voltage shift setting circuit  302  may generate the expected voltage Ve based on the output voltage VA in a non-linear way. 
     Any circuit generating the expected voltage Ve based on the output voltage VA may be used to implement the voltage shift setting circuit  302 . 
     In the forgoing exemplary embodiments, the voltage shift component is implemented by a capacitor C. Such a buck converter can be named a series cap-inductor buck converter. However, the voltage shift component is not limited the single capacitor C illustrated in the figures. 
     Note that the proposed buck converter does not add too much switches in its circuit. In comparison with other buck converters using a considerable number of switches, the proposed buck converter using the limited number of switches indeed suppresses the switching loss and does not need a complex circuit design. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.