Abstract:
A voltage regulator circuit and a method to control the voltage regulator circuit. The voltage regulator circuit comprising an AC switching regulator, a DC switching regulator, a linear voltage regulator and switches to configure the voltage regulator circuit for improved efficiency across a wide load range.

Description:
RELATED APPLICATION 
     The present application claims priority to U.S. Provisional Application No. 62/079,467, filed on Nov. 13, 2014, which is incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The present invention relates to switching regulators, and more particularly to high efficiency switching regulators. 
     BACKGROUND 
     Switching regulators generally have reduced efficiency at very light loads. However, this is suboptimal for some uses. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a circuit diagram of a voltage regulator circuit, in accordance with one embodiment of the present invention. 
         FIG. 2  is one embodiment of the circuit of  FIG. 1 , configured for medium to high current mode. 
         FIG. 3  is one embodiment of the circuit of  FIG. 1 , configured for Light Load mode. 
         FIG. 4  is one embodiment of the circuit of  FIG. 1 , configured for Ultra Light load mode. 
         FIG. 5  shows one embodiment of the Phase 1 and 2 cycling in Ultra Light Load Mode. 
         FIG. 6  shows one embodiment of time domain waveforms of current and voltage during phase 1 &amp; 2 cycling in Ultra Light Load mode. 
         FIG. 7  shows one embodiment of the efficiency across the different modes and the entire load current range. 
         FIG. 8  is a circuit diagram of a voltage regulator circuit, in accordance with another embodiment of the present invention. 
         FIG. 9  is one embodiment of the circuit of  FIG. 8 , configured for medium to high current mode. 
         FIG. 10  is one embodiment of the circuit of  FIG. 8 , configured for Light Load mode. 
         FIG. 11  is one embodiment of the circuit of  FIG. 8 , configured for Ultra Light load mode. 
     
    
    
     DETAILED DESCRIPTION 
     In a voltage regulator circuit, it is desirable to have high efficiency at very light loads. Embodiments of the present disclosure include a regulator coupled between an AC switching stage and a DC switching stage of a voltage regulator circuit. 
     The following detailed description of embodiments of the invention makes reference to the accompanying drawings in which like references indicate similar elements, showing by way of illustration specific embodiments of practicing the invention. Description of these embodiments is in sufficient detail to enable those skilled in the art to practice the invention. One skilled in the art understands that other embodiments may be utilized and that logical, mechanical, electrical, functional and other changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
       FIG. 1  is a circuit diagram of a voltage regulator circuit, in accordance with one embodiment of the present invention. The voltage regulator includes a plurality of switches which switch in and out an AC switching stage and a DC switching stage, using inductors (LAC, LDC) and a capacitor (CAC). By changing the circuit elements switched into the voltage regulator circuit, the voltage regulator can be optimized for different load levels. The elements that may be active or inactive include an AC switching regulator, a DC switching regulator, and a linear voltage regulator. In one embodiment, the linear voltage regulator is a low drop-out regulator (LDO). 
       FIG. 2  shows one embodiment of the configuration of the circuit of  FIG. 1  for medium to high current load mode. In this case, SW_LL is Open, SW_MHL is Closed, SW_ULL is Open, and the LDO (Or Voltage regulator) is disabled. Switcher AC (SW_AC_HS and SW_AC_LS) is enabled continually and Switcher DC (SW_DC_HS and SW_DC_LS) is enabled continually. 
       FIG. 3  shows one embodiment of the configuration of the circuit in  FIG. 1  for Light Load mode. In this case, SW_LL is Closed, SW_MHL is Open, SW_ULL is Open and the LDO (or voltage regulator) is Disabled. In this case, Switcher AC is enabled continually and Switcher DC is disabled. 
       FIG. 4  shows one embodiment of a configuration of the circuit in  FIG. 1  for Ultra Light load mode. In this case, SW_LL is Open, SW_MHL is Open, SW_ULL is Closed, and LDO (or Voltage regulator) is Enabled. Switcher AC is enabled periodically (by the state machine) and Switcher DC disabled. 
     In one embodiment, a threshold detection circuit (here, two comparators and a state machine) monitors the voltage on the VAC node at the output of the AC switching stage. During Phase 1, Switcher AC (Formed by SW_AC_HS, SW_AC_LS, LAC_CAC) charges VAC from V1 to V2 with an output current corresponding to its maximum efficiency and the Voltage regulator or LDO Regulates the Vout voltage at a reference voltage Vref (not shown in  FIG. 4 ). During Phase 2, Switcher AC is disabled and the Voltage regulator or LDO regulates Vout at Vref and discharges VAC from V2 to V1, to keep the voltage between the predefined limits of V1 and V2. 
       FIG. 5  Shows the Phase 1 and 2 cycling in Ultra Light Load Mode. Operation in Ultra Light Load mode, the system switches between Phase 1, and Phase 2 
     In Phase 1: Switcher AC (Formed by SW_AC_HS, SW_AC_LS, LAC_CAC) charges VAC from V1 to V2 with an output current corresponding to its maximum efficiency. Voltage regulator or LDO Regulates the Vout voltage at Vref. 
     In Phase 2: Switcher AC is disabled, Voltage regulator or LDO regulates Vout at Vref and discharges VAC from V2 to V1. 
       FIG. 6  shows the time domain waveforms of current and voltage during phase 1 &amp; 2 cycling in Ultra Light Load mode. 
       FIG. 7  shows exemplary efficiency across the different modes and the entire load current range. 
     Phase 1 Power Losses for Switcher AC:
 
 Eff _ SW _ AC=I out× V out/( I out× V out+ P _ SW _ AC )
 
 P _ SW _ AC=I out_peak_ eff ×( V 1+ V 2)/2×(1− Eff _ SW _ AC )/ Eff _ SW _ AC  
 
     Assuming: 
     Iout_peak_eff=1 A 
     V1=1V 
     V2=1.2V 
     Eff_SW_AC=80% 
     →P_SW_AC=275 mW 
     Time to Recharge VAC from V1 to V2:
 
 T _recharge= CAC ×( V 2− V 1)/ I out_peak  eff  
 
     Assuming: 
     Iout_peak_eff=1 A 
     V1=1V 
     V2=1.2V 
     CAC=10 uF 
     →T_recharge=2 us 
     Phase 2 Duration:
 
 T _dischage= CAC ×( V 2− V 1)/ I load
         Assuming:
           Iload=20 mA   V1=1V   V2=1.2V   CAC=10 uF   →T_discharge=100 us   
               

     Average Power Dissipated in the Switcher AC During Phase 1 and Phase 2:
 
 P _ SW _ AC=P _ SW _ AC _phase1× T _charge/( T _charge+ T _discharge)
 
     With the Previous Assumption:
 
 P _ SW _ AC= 10.57 mW
 
     Average LDO Dissipation During Phase 1 and 2:
 
 P _ LDO=I Load×( V 2− V 1)/2
 
     With the Previous Assumptions:
 
 P _ LDO= 2 mW
 
     Ultra Light Load Efficiency:
 
Efficiency_ ULL=I _Load× V out/( P _ SW _ AC+P _ LDO+I _Load× V out)
 
     With the Previous Assumptions:
 
Efficiency_ ULL= 20 mA×1V/(10.57 m+2 m+20 m)
 
Efficiency_ ULL= 61.4%
 
       FIG. 8  shows a different embodiment of the invention. The voltage regulator includes a plurality of switches which switch in and out inductors (LAC, LDC) and a capacitor (CAC). By changing the circuit element switched into the voltage regulator circuit, the voltage regulator can be optimized for different load levels. As can be seen, the difference between this configuration and the configuration of  FIG. 1  is that the Vout connects between SW_DC_HS and SW_DC_LS. 
       FIG. 9  shows one embodiment of a configuration of the circuit in  FIG. 8  for medium to high current load mode. In this case, SW_LL is Open, SW_MHL is Closed, SW_ULL is Open, and the LDO (Or Voltage regulator) is disabled. Switcher AC is enabled continually and Switcher DC is enabled continually. 
       FIG. 10  shows one embodiment of a configuration of the circuit in  FIG. 8  for Light Load mode where SW_LL is Closed, SW_MHL is Open, SW_ULL is Open and the LDO (or voltage regulator) is Disabled. In this case, Switcher AC is enabled continually and Switcher DC is disabled. 
       FIG. 11  shows one embodiment of a configuration of the circuit in  FIG. 8  for Ultra Light load mode. In this case, SW_LL is Open, SW_MHL is Open, SW_ULL is Closed, and LDO (or Voltage regulator) is Enabled. Switcher AC is enabled periodically (By the state machine) and Switcher DC disabled. 
     A threshold detection circuit (here, two comparators and a state machine) monitors the voltage on the VAC node at the output of the AC switching stage. During Phase 1, Switcher AC (Formed by SW_AC_HS, SW_AC_LS, LAC_CAC) charges VAC from V1 to V2 with an output current corresponding to its maximum efficiency and the Voltage regulator or LDO Regulates the Vout voltage at Vref. During Phase 2, Switcher AC is disabled and the Voltage regulator or LDO regulates Vout at Vref and discharges VAC from V2 to V1. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.