Abstract:
The present invention discloses a switching regulator, and a control circuit and method for controlling a switching regulator. The switching regulator includes a power stage driven by a driver voltage outputted from a driver circuit. The present invention detects an input current to generate an input current detection signal, and adjusts an operation voltage supplied to the driver circuit according to the input current detection signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a switching regulator, and a control circuit and method for controlling a switching regulator. Particularly, it relates to such switching regulator, control circuit, and control method which adjust the level of a pulse width modulation (PWM) signal according to an input current. 
         [0003]    2. Description of Related Art 
         [0004]      FIG. 1  shows a schematic diagram of a prior art switching regulator. As shown in the figure, a PWM controller  11  outputs a PWM signal for controlling at least one power transistor in a power stage  12  through a driver circuit  15 , to convert an input voltage Vin to an output voltage Vout. The driver circuit  15  outputs a driver signal whose high level is determined by the operation voltage Vd of the driver circuit  15 . A feedback circuit  13  generates a feedback signal related to the output voltage, and inputs the feedback signal to the PWM controller  11  to generate the PWM signal. The power stage  12  may be a synchronous or asynchronous buck, boost, inverting or buck-boost converter as shown in  FIGS. 2A-2J . 
         [0005]    When a load circuit is in light load condition, i.e., the current required by the load circuit is low, if the power transistor still operates in a normal mode, it will result in higher power loss (including switching loss and conduction loss). Therefore, a prior art method is proposed which dynamically adjusts the gate driving voltage of the power transistor to reduce the power loss. More specifically, the prior art method detects an output current Iout to generate an output current detection signal, and inputs the output current detection signal to the PWM controller  11 . When the output current Tout is relatively low, which means that the load circuit is in light load condition, the PWM controller  11  reduces the operation voltage Vd of the driver circuit  15 , such that the power transistor in the power stage  12  operates according to the loading condition at the output terminal to reduce the power loss. 
         [0006]    The aforementioned prior art which detects the output current and adjusts the operation voltage Vd of the driver circuit  15  accordingly is disclosed in, e.g., U.S. Pat. No. 7,265,601, U.S. Pat. No. 7,345,463, and U.S. Pat. No. 7,615,940. 
         [0007]    However, when the switching regulator is a multi-phase switching regulator having multiple power stages and corresponding PWM controllers, it becomes very complicated to obtain the output current detection signal because there are multiple output current paths. In this case, it often requires a very large circuit area for multi-path output current detection, and the signal processing is also very complicated. 
         [0008]    In view of the foregoing, the present invention provides a switching regulator, and a control circuit and method for controlling a switching regulator, which adjust the level of the PWM signal to optimize the operation of the power transistor by detecting the input current. 
       SUMMARY OF THE INVENTION 
       [0009]    The first objective of the present invention is to provide a switching regulator. 
         [0010]    The second objective of the present invention is to provide a control circuit for controlling a switching regulator. 
         [0011]    The third objective of the present invention is to provide a control method for controlling a switching regulator. 
         [0012]    To achieve the objective mentioned above, from one perspective, the present invention provides a switching regulator, comprising: a driver circuit, for receiving a PWM signal and generating a driver signal, the driver circuit determining high level of the driver signal according to an operation voltage; a power stage, switching at least one power transistor to convert an input voltage to an output voltage according to the driver signal; an input current detection circuit, coupled between the power stage and the input voltage, for detecting an input current and generating an input current detection signal; a feedback circuit, generating a feedback signal according to the output voltage; and a PWM controller, generating the PWM signal according to the feedback signal, and adjusting the operation voltage according to the input current detection signal. 
         [0013]    From another perspective, the present invention provides a switching regulator control circuit, for generating a PWM signal for switching at least one power transistor in a power stage through a driver circuit to convert an input voltage to an output voltage, wherein the driver circuit determines high level of a driver signal outputted from the driver circuit according to an operation voltage, the switching regulator control circuit comprising: an input current detection circuit, coupled between the power stage and the input voltage, for detecting an input current and generating an input current detection signal; and a PWM controller, generating the PWM signal according to a feedback signal related to the output voltage, and adjusting the operation voltage according to the input current detection signal. 
         [0014]    In the aforementioned switching regulator or switching regulator control circuit, the PWM controller preferably includes: a PWM signal generator, coupled to the feedback circuit, for generating the PWM signal according to the feedback signal; and a driver voltage adjustment circuit, coupled to the input current detection circuit, for determining the operation voltage according to the input current detection signal. 
         [0015]    The driver voltage adjustment circuit preferably includes a circuit which can provide more than two different voltages, such as a selection circuit, a linear regulator with adjustable reference voltage, or a variable multifold charge pump circuit with variable output to input voltage ratio. 
         [0016]    The aforementioned switching regulator may be a multi-phase switching regulator. 
         [0017]    From another perspective, the present invention provides a control method for controlling a switching regulator, the switching regulator switching at least one power transistor in a power stage according to a PWM signal by a driver circuit to convert an input voltage to an output voltage, and obtaining a feedback signal according to the output voltage, wherein the driver circuit determines high level of a driver signal outputted from the driver circuit according to an operation voltage, the control method comprising: generating an input current detection signal according to an input current; generating the PWM signal according to the feedback signal; and adjusting the operation voltage according to the input current detection signal. 
         [0018]    In the aforementioned control method, the step of adjusting the operation voltage according to the input current detection signal preferably includes: comparing the input current detection signal with a reference voltage; and determining the operation voltage, or a reference voltage of a linear regulator circuit, or the output to input voltage ratio of a variable multifold charge pump circuit, according to the comparison result. 
         [0019]    The objectives, technical details, features, and effects of the present invention will be better understood with regard to the detailed description of the embodiments below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows a schematic diagram of a prior art switching regulator. 
           [0021]      FIGS. 2A-2J  show synchronous and asynchronous buck, boost, inverting and buck-boost converters. 
           [0022]      FIG. 3  shows an embodiment of the basic structure of the present invention. 
           [0023]      FIG. 4  shows another embodiment of the present invention. 
           [0024]      FIG. 5  shows an embodiment of the present invention with more hardware details. 
           [0025]      FIG. 6  illustrates the conversion efficiency of different input currents at two different driving voltages. 
           [0026]      FIGS. 7 and 8  show two embodiments of the driver voltage adjustment circuit  112 . 
           [0027]      FIG. 9  shows an embodiment of a multi-phase switching regulator according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]      FIG. 3  shows an embodiment of the basic structure of the present invention. As shown in the figure, a PWM controller  11  outputs a PWM signal which controls at least one power transistor in a power stage  12  through a driver circuit  15 , to convert an input voltage Vin to an output voltage Vout. The driver circuit  15  outputs a driver signal whose high level (i.e., the driving voltage of the power transistor) is determined by the operation voltage Vd of the driver circuit  15 . A feedback circuit  13  generates a feedback signal related to the output voltage, and inputs the feedback signal to the PWM controller  11  to generate the PWM signal. The power stage  12  may be a synchronous or asynchronous buck, boost, inverting or buck-boost converter as shown in  FIGS. 2A-2J . Different from the prior art, the switching regulator of the present invention detects an input current Iin by an input current detection circuit  14  to generate an input current detection signal, and inputs the input current detection signal to the PWM controller  11 . The PWM controller  11  adjusts the operation voltage Vd of the driver circuit  15  according to the input current detection signal, such that the power transistor in the power stage  12  operates in an optimized condition to reduce power loss. When the load circuit is in light load condition, i.e., the output current is low, the input current Iin will correspondingly drop. Therefore by detecting the input current Iin, the present invention can dynamically adjust the operation voltage Vd to reduce the power loss. Furthermore, an advantage of the present invention over the prior art is that, the present invention can be embodied with a simpler hardware circuit in a multi-phase switching regulator. 
         [0029]      FIG. 4  shows a more specific embodiment of the present invention. As shown in the figure, the PWM controller  11  includes a PWM signal generator  111 , which is coupled to the feedback circuit  13 , for generating the PWM signal according to the feedback signal and sending the PWM signal to the driver circuit  15 ; and a driver voltage adjustment circuit  112  which is coupled to the input current detection circuit  14 , for dynamically adjusting the operation voltage Vd according to the input current detection signal. In this embodiment, the driver voltage adjustment circuit  112  receives the input voltage Vin and converts it to the operation voltage Vd, wherein the conversion ratio of the input voltage Vin to the operation voltage Vd is determined by the input current detection signal. 
         [0030]      FIG. 5  shows another embodiment of the present invention, which illustrates more specific details. As shown in the figure, the power stage  12  is (for example but not limited to) a buck converter as shown in  FIG. 2A , which includes an upper power transistor  121 , a lower power transistor  122 , and an inductor L. The correlation of the input power and the output power is: 
         [0000]        V in* I in= V out* I out*η
 
         [0000]    Wherein η is the conversion efficiency. From the equation, it can be understood that the input current Iin also relates to the load, so the detection of the input current Iin can be used as a reference for adjusting the gate driving voltage of the power transistor to optimize the operation of the power transistor. 
         [0031]    Still referring to  FIG. 5 , the feedback circuit  13  includes two resistors R 1  and R 2  connected in series. One end of the resistor R 1  is coupled to the output voltage Vout, and one end of the resistor R 2  is coupled to ground. In other words, the resistors R 1  and R 2  form a voltage dividend circuit which samples the output voltage Vout by the resistor R 2 . The input current detection circuit  14  includes a resistor R 3  and an error amplifier  141 , for detecting the input current Iin, and generating the input current detection signal. 
         [0032]    The PWM controller  11  includes the PWM signal generator  111  and the driver voltage adjustment circuit  112 . As shown in the figure, the PWM signal generator  111  includes an error amplifier  1111  and a comparator  1112 . The error amplifier  1111  is coupled to the feedback circuit  13  to receive the feedback signal, and compares the feedback signal with a reference signal Vref 1 . The output of the error amplifier  1111  is inputted to the comparator  1112 . The comparator  1112  receives the output from the error amplifier  1111 , and compares it with a ramp signal to generate the PWM signal. 
         [0033]    The driver voltage adjustment circuit  112  includes a comparator  1121 , a selection circuit  1122 , an error amplifier  1123 , a transistor  1124 , and resistors R 4  and R 5 . In the driver voltage adjustment circuit  112 , the error amplifier  1123 , the transistor  1124 , and the resistors R 4  and R 5  form a linear regulator which generates the operation voltage Vd and supplies it to the driver circuit  15 . The comparator  1121  receives the input current detection signal from the input current detection circuit  14 , and compares the input current detection signal with a reference signal Vref 2 . The comparison result of the comparator  1121  determines whether the selection circuit  1122  selects the voltage signal V 1  or V 2  as the reference signal to be inputted to the error amplifier  1123 . The error amplifier  1123  controls the control terminal of the transistor  1124  according to the comparison between its two inputs, i.e., the voltage across the resistor R 5  and the reference voltage V 1  or V 2 , and generates different operation voltages Vd at the output terminal of the linear regulator as the reference voltages are different. The operation voltage Vd is inputted to an upper driver gate  151  and a lower driver gate  152  to drive the upper power transistor  121  and the lower power transistor  122 . If the number of the power transistors in the power stage  12  is different (for example, an asynchronous buck convertor has only one power transistor), the number of the driver gates in the driver circuit  15  should be modified accordingly. 
         [0034]      FIG. 6  illustrates the conversion efficiency of different input currents at different driving voltages. In this example, when the input current is lower than 1.1 A, if the driving voltage is switched from 12V to 8V, the conversion efficiency will be better. The present invention can achieve this. 
         [0035]    In the aforementioned embodiments, the reference voltage of the linear regulator is determined by the input current detection signal; the operation voltage Vd is the output of the linear regulator; and the regulator input voltage of the linear regulator is the input voltage Vin. However, the regulator input voltage of the linear regulator does not have to be the input voltage Vin, but can be any voltage instead. In fact, it suffices as long as the driver voltage adjustment circuit  112  can provide two different voltages as options for the operation voltage Vd, and the operation voltage Vd is switchable according to the input current detection signal. For example as shown in  FIG. 7 , the driver voltage adjustment circuit  112  may include the comparator  1121  and the selection circuit  1122  wherein the selection circuit  1122  determines whether the voltage V 1  or V 2  is provided as the operation voltage Vd according to the output of the comparator  1121 . For another example, as shown in  FIG. 8 , the driver voltage adjustment circuit  112  may include the comparator  1121  and a variable multifold charge pump circuit  1125 , wherein the selection circuit  1122  determines the output-to-input ratio of the variable multifold charge pump circuit  1125  according to the output of the comparator  1121  (the ratio of the charge pump output voltage to the charge pump input voltage does not have to be larger than 1, nor does it have to be an integer), and the output of the variable multifold charge pump circuit  1125  is provided as the operation voltage Vd. Those skilled in this art can readily conceive variations and modifications of the driver voltage adjustment circuit  112  within the spirit of the present invention, which should be interpreted to fall within the scope of the appended claims. 
         [0036]      FIG. 9  shows an embodiment of a multi-phase switching regulator according to the present invention. As shown in the figure, the multi-phase switching regulator includes multiple PWM controllers  11  and multiple corresponding power stages  12 . This embodiment shows that one input current detection signal generated by one input current detection circuit  14  is inputted to every PWM controller  11 , that is, only one input current detection circuit  14  is enough. Compared to the prior art which needs multiple output current detection circuits, the present invention simplifies the circuit design and saves the circuitry area. 
         [0037]    The present invention has been described in considerable detail with reference to certain preferred embodiments thereof. It should be understood that the description is for illustrative purpose, not for limiting the scope of the present invention. Those skilled in this art can readily conceive variations and modifications within the spirit of the present invention. For example, a device which does not substantially influence the primary function of a signal can be inserted between any two devices in the shown embodiments, such as a switch or the like. For another example, the positive and negative input terminals of the error amplifiers or comparators are interchangeable, with corresponding amendment of the circuits processing these signals. In view of the foregoing, the spirit of the present invention should cover all such and other modifications and variations, which should be interpreted to fall within the scope of the following claims and their equivalents.