Patent Document

FIELD  
       [0001]     The present disclosure relates to a method and apparatus for switching regulation, and more particularly to a method and apparatus for switching regulation capable of quick feedback from load.  
       BACKGROUND  
       [0002]     Recently, energy-saving has been actively promoted in terms of environmental measure. For portable electronic equipment using battery, such as a mobile phone, a digital camera, a PDA (portable digital assistant), a notebook computer, a portable multimedia player (for example, MP3 player, optical disc player, etc.), and so on, it is desirable to have a longer battery life. Such portable equipment commonly employs a switching regulator in power system because a compact and high efficiency power system can be obtained using the switching regulator.  
         [0003]     A conventional switching regulator generally includes a feedback circuit to stabilize output voltage. In the feedback circuit, an ON/OFF circuit is controlled by changing an input pulse width applied to the ON/OFF circuit. The conventional switching regulator includes an oscillation circuit and a comparator which outputs a control signal to control the oscillation circuit. The comparator compares an output voltage of an error-AMP (amplifier) with a reference voltage.  
         [0004]     For example, if the control signal from the comparator outputs is H (high), the oscillation circuit oscillates with a high frequency. If the control signal from the comparator outputs is L (low), the oscillation circuit oscillates with a low frequency which is lower frequency than the high frequency. The operation of the switching regulator will be described more specifically.  
         [0005]      FIG. 1  illustrates a conventional switching regulator  100 . The switching regulator  100  includes a triangular-pulse generator  10 , a first and second reference voltage circuits  11  and  14 , bleeder resistances, an error-AMP  12 , a comparator  13  and a PWM (pulse width modulation) comparator  15 .  
         [0006]     The error-AMP  12  inputs an output voltage Vout of the switching regulator  100 , which is applied to a load as a load voltage, and a reference voltage Vref 1  of the first reference voltage circuit  11 . The error-AMP  12  outputs a voltage difference between these two voltages. The comparator  13  inputs the voltage difference and a second reference voltage Vref 2  of the second reference voltage circuit  14 . The comparator  13  judges whether the difference voltage is higher than the reference voltage Vref 2  of the second reference voltage circuit  14 .  
         [0007]     The PWM comparator  15  outputs a control signal by comparing an output signal of the triangular-pulse generator  10  with the output voltage of the error-AMP  12 . The output signal of the triangular-pulse generator  10  is a triangular wave.  
         [0008]      FIG. 2  illustrates waveforms showing the operation of the switching regulator  100 . The output voltage of the error-AMP  12 , ERROR AMP OUTPUT, is being changed by comparing the output voltage of the error-AMP  12  with the triangular wave output from the triangular-pulse generator  10 . As a result, the output pulse width of the PWM comparator  15  is controlled. An ON or OFF time of a switching transistor arranged next to the switching regulator  100  is controlled for a corresponding time to the output pulse width of the PWM comparator  15 .  
         [0009]     In some switching regulators which do not employ a current control mode, a feedback loop from the output of the switching regulator may include a time lag. The feedback speed may not be fast enough to control due to the time lag. The feedback voltage may move to higher or lower voltage than an expected voltage and may not be adjusted to a desired feed back voltage. As a result, the switching regulator may oscillate unintentionally.  
         [0010]     Even if a switching regulator employs a current control mode and if a duty cycle of the switching regulator exceeds 50%, a slope compensation circuit may be required. The slop compensation circuit makes a slower rising edge of the output voltage of the switching regulator to avoid a destruction of transistor. However, using the slope compensation circuit, the switching regulator may be larger and complicated.  
       SUMMARY  
       [0011]     This patent specification describes a novel switching regulator which includes a first amplifier configured to amplify a voltage difference between a voltage proportional to an output voltage of a switching regulator and a first reference voltage, a current detector configured to detect a current proportional to an output current of the switching regulator, a second amplifier configured to amplify an output signal from the current detector, a first converter configured to convert an output voltage of the first amplifier to a first current signal, a second converter configured to convert an output voltage of the second amplifier to a second current signal, an oscillator configured to oscillate with rectangular pulses and a controller configured to modulate an oscillation signal of the oscillator in accordance with the first and second current signals output from the first and second converters.  
         [0012]     This patent specification further describes a novel switching regulator which further includes an inverter arranged in the controller and configured to input the oscillation signal of the oscillator and a current source connected to the inverter and configured to control a current of the inverter in accordance with the first and second output signals of converters.  
         [0013]     Further, this patent specification describes a novel method of controlling a switching regulator which includes steps of amplifying a difference voltage between a voltage proportional to an output voltage of a switching regulator and a first reference voltage by a first amplifier, detecting a current proportional to an output current of the switching regulator, amplifying the detected current by a second amplifier, outputting the output signal amplified by the second amplifier to a controller, controlling an oscillator by a comparison result of an output signal of the first amplifier with a second reference voltage, inputting an oscillation signal of the oscillator and the output signal of the first and second amplifiers to a controller, comparing a controlled voltage of the oscillation signal based on the output signals from the first and second amplifiers with a third reference voltage and outputting a drive current to drive by controlling a duty cycle of the drive current based on the feedback voltage of the load voltage and a feedback current corresponding to the load current. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0015]      FIG. 1  illustrates a conventional switching regulator;  
         [0016]      FIG. 2  illustrates waveforms showing the operation of the switching regulator;  
         [0017]      FIG. 3  illustrates an example of a basic configuration of a switching regulator circuit according to an exemplary embodiment of the present disclosure;  
         [0018]      FIG. 4  illustrates circuit blocks of a PWM controller shown in  FIG. 3 , in more detail;  
         [0019]      FIG. 5  illustrates operation waveforms of the switching regulator circuit shown in  FIG. 3 ;  
         [0020]      FIG. 6  illustrates a boost DC/DC converter which includes the switching regulator as an example of the application of the switching regulator;  
         [0021]      FIG. 7  illustrates a switching regulator according to another exemplary embodiment;  
         [0022]      FIG. 8  illustrates waveforms at each terminal of the PWM controller shown in  FIG. 7 ; and  
         [0023]      FIG. 9  illustrates a detailed block diagram of the PWM controller shown in  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring how to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to  FIG. 3 , a switching regulator according to exemplary embodiments are described.  
         [0025]      FIG. 3  illustrates an example of a basic configuration of a switching regulator circuit  200  according to an exemplary embodiment of the present disclosure.  FIG. 4  illustrates circuit blocks of a PWM controller  16  shown in  FIG. 3  in more detail.  
         [0026]     The switching regulator circuit  200  includes two reference voltage circuits  11  and  14 , bleeder resistances, an error-AMP  12 , a comparator  13  similar to the conventional switching regulator. Further, the switching regulator circuit  200  includes a ring oscillator  10 A and the PWM controller  16  instead of the triangular-pulse generator  10  and the PWM comparator  15 . The ring oscillator  10 A includes constant current inverters to oscillate with rectangular pulses. The PWM controller  16  includes a voltage-current converter circuit  18 , an inverter  21 , a capacitor  19 , a current source  22 , a third reference voltage (Vref 3 ) circuit  23 , a comparator  24  and an AND circuit  25  as shown in  FIG. 4 .  
         [0027]     Similar to the conventional switching regulator, the error-AMP  12  inputs an output voltage Vout of the switching regulator and an output voltage of the bleeder resistances and outputs a difference voltage between these two voltages. The comparator  13  inputs the output signal of the error-AMP  12  and a second reference voltage Vref 2  of the second reference voltage circuit  14  and judges whether the output signal of the error-AMP  12  is higher than the output voltage Vref 2  of the second reference voltage circuit  14 .  
         [0028]     The output signal of the error-AMP  12  controls a current source  22  arranged in the PWM controller  16  via a voltage-current transfer circuit  18  as shown in  FIG. 4 . Further, the output signal of the error-AMP  12  controls an ON time of a switching transistor arranged outside the switching regulator circuit  200 . The comparator  13  changes an oscillation frequency of the ring oscillator  10 A based on a comparing result of the output signal of the error-AMP  12  with the reference voltage Vref 2 .  
         [0029]     The output signal of the ring oscillator  10 A is inverted by the inverter  21 . The current of the inverter  21  is determined by the current source  22  which is controlled by the output signal of the error-AMP  12 . A delay time is generated by the current of the inverter  21  and the capacitor  19  which is arranged between the output of the inverter  21  and a power terminal.  
         [0030]      FIG. 5  illustrates operation waveforms of the switching regulator circuit  200  of  FIG. 3 . In  FIG. 5 , the output waveform of the ring oscillator  10 A is illustrated. The output waveform of the ring oscillator  10 A is changed from a narrower width pulse to a wider width pulse due to a change of a load. More specifically, the output signal of the error AMP  12 , indicated by ERROR AMP OUTPUT, is increased from a low voltage to a high voltage with respect to the reference voltage Vref 2  in  FIG. 5  while the load is changed from heavier to lighter.  
         [0031]     A waveform of the output signal of the inverter  21  is illustrated as INVERTER OUTPUT in  FIG. 5  while the output voltage of the inverter  21  is high gradually. During a time period the output voltage of the error AMP  12  is lower than the reference voltage Vref 2 , the ring oscillator  10 A generates a rectangular pulse with a constant cycle time. During a time period the output voltage of the error AMP  12  is higher than the reference voltage Vref 2 , the ring oscillator  10 A outputs pulses with longer high time. The inverter  21  outputs pulses having longer cycle time in accordance with the output pulses of the ring oscillator  10 A.  
         [0032]     A waveform of the output voltage of the comparator  24 , COMPARATOR  2  OUTPUT, is illustrated in  FIG. 5 , and is based on comparison of the output voltage of the inverter  21 , INVERTER OUTPUT, to a reference voltage Vref 3 . The reference voltage, Vref 3 , is set to be lower value (approximately 0.5 v) than a supply voltage of the ring oscillator  10 A and the inverter  21 . The output signal of the PWM controller  16  is the output signal of the AND circuit  25  which performs AND calculation with the output of the comparator  24  and the output signal of the ring oscillator  10 A.  
         [0033]      FIG. 6  illustrates a boost DC/DC converter  300  which includes a switching regulator as an example of the application of the switching regulator. The boost DC/DC converter  300  includes a power input terminal Vin, a bleeder resistor  8 , a switching transistor  9 , a first reference voltage generator  11 , a first error AMP  12 , a current detection circuit  13 A, a second error AMP  17 , a PWM controller  36  and a gate drive circuit  15 A.  
         [0034]     The power input terminal Vin inputs a power supply. The bleeder resistor  8  is connected to a load LOAD in parallel. The first error AMP  12  amplifies a difference voltages between a divisional voltage from the bleeder resistor which is proportional to a load voltage, Vout, and a first reference voltage, Vref 1 . The current detection circuit  13 A detects a current which flows through the switching transistor  9  and depends on a load current.  
         [0035]     The second error AMP  17  amplifies an output signal of the current detection circuit  13 A. The gate drive circuit  15 A drives the switching transistor  9 . The PWM controller  36  is a current-control type controller which converts a voltage to a current and modulates an oscillation signal from the oscillation circuit based on the converted current value. The load may be a compact equipment with a battery as a power source, in the exemplary embodiment.  
         [0036]     The boost DC/DC converter  300  includes a first and second feedback circuits. The first feedback circuit is formed by the first error AMP  12  and the PWM controller  36  and the second feedback circuit is formed by the switching transistor  9  and the PWM controller  36 .  
         [0037]     To detect a change of the load voltage, Vout, it is more effective to directly detect the current flow of the switching transistor  9  which is reflected to the load current. Namely, the change of the load can be detected more quickly and in more precise by a detection of an output signal of the second error AMP  17  in comparison with a detection of an output signal of the first error AMP  12 .  
         [0038]     The boost DC/DC converter  300  can instantly detect the voltage change of the load by employing this double feedback control. Namely, it is possible to accelerate a rising speed of the load voltage quickly when the load voltage is decreasing and to slow a falling speed of the load voltage when the load voltage is increasing. It is difficult to control to make the load voltage falling in a short time only by the first error AMP  12  due to time lag.  
         [0039]     The feedback voltage goes higher or lower than a predetermined voltage because of a control timing shift. If an unstable condition has been continued for a certain period, the boost DC/DC converter  300  may begin to oscillate due to this over swing.  
         [0040]     In the switching regulator according to an exemplary embodiment, the current of the switching transistor  9  which is controlled by the gate drive circuit  15 A is being sensed. The sensed signal is amplified by the second error AMP  17 . The PWM controller  36  controls the duty of the control signal for the gate drive circuit  15 A. As a result, it is possible to avoid the oscillation due to the change of the load condition by this feedback.  
         [0041]      FIG. 7  illustrates a switching regulator  400  according to another exemplary embodiment. The switching regulator  400  includes a gate drive circuit  15 A, a NMOS driver transistor  9 , a mirror transistor  19 , a resistor  29 , a second error AMP  17 , a PWM controller  36 , a first reference voltage source  11 , a first error AMP  12 , a second reference voltage source  14 , a comparator  13  and a ring oscillator (OSC)  10 A.  
         [0042]     In  FIG. 7 , the output signal of the PWM controller  36  is input to the gate drive circuit  15 A. The NMOS driver transistor  9  is driven by the gate drive circuit  15 A and the mirror transistor  19  is connected in parallel to the NMOS driver transistor  9 . The comparator  13  compares an output signal of the first error AMP  12  and the second reference voltage Vref 2  of the second reference voltage circuit  14 .  
         [0043]     A current of the NMOS driver transistor  9  is detected by the mirror transistor  19  and the resistor  29  connected to a source of the mirror transistor  19  as a voltage of the resistor  29 . The detected current is amplified by the second error AMP  17  and is output to the PWM controller  36 . Thus, the current detection circuit is formed of the mirror transistor  19  and the resistor  29 .  
         [0044]     The first error AMP  12  amplifies the difference voltage between the load voltage Vout and the first reference voltage circuit  11 . The comparator  13  compares the output voltage of the error AMP  12  with the reference voltage of the second reference voltage circuit  14  and outputs a control signal to control the ring OSC  10 A.  
         [0045]      FIG. 8  illustrates waveforms at each terminal of the PWM controller  36 .  FIG. 9  illustrates a detailed block diagram of the PWM controller  36  of  FIG. 8 . When the load capacity is increased, the current of the NMOS driver transistor  9  in  FIG. 7  is increased. The resistor  29  generates a voltage corresponding to the increase of the current of the NMOS driver transistor  9 . The second error AMP  17  detects the voltage of the resistor  29  as a voltage signal. The second error AMP  17  amplifies the voltage signal of the resistor  29 .  
         [0046]     Referring to  FIG. 9 , the output signal from the second error AMP  17  is input to a current source  22  through a voltage-to-current converter  18 . As described in  FIG. 7 , the first error AMP  12  amplifies the difference voltage between the load voltage Vout and the first reference voltage of the first reference circuit  11 . The output signal from the first error AMP  12  is also input to the current source  22  through a voltage-to-current converter  28  as shown in  FIG. 9 . The current source  22  controls a current of the inverter  21 .  
         [0047]     Furthermore, the oscillation signal is controlled by adjusting the current of the inverter  21  and by comparing the output of the inverter  21  with a third reference voltage Vref 3  of a third reference voltage circuit  23 . As a result, a duty of the switching operation of the switching regulator  400  is controlled.  
         [0048]     The waveforms of the exemplary embodiment will be discussed referring to  FIG. 8  comparing to the waveforms of the conventional basic circuit shown in  FIG. 5 . In the waveforms of the basic circuit  FIG. 5 , the current source  22  of the PWM controller  16  outputs a current signal corresponding to pulses of the ring oscillator  10 A when the output voltage of the error AMP  12  is low and the output voltage of the inverter  21 , INVERTER OUTPUT, is higher than the third reference voltage Vref 3 .  
         [0049]     The current source  22  of the PWM controller  16  outputs a narrower pulse than the pulse width of the ring oscillator  10 A while the output voltage of the error AMP  12  is higher. Similar control is performed in the exemplary embodiment of  FIG. 8 , but, the PWM controller  36  is also controlled by the output signal of the second error AMP  17 .  
         [0050]      FIG. 5  illustrates that the output signal of the error AMP  12  is changing from a lower voltage to a higher voltage. However,  FIG. 8  illustrates that the output signal of the error AMP  12  is changing from a higher voltage to a lower voltage.  
         [0051]     In  FIG. 5 , two output signals i.e., the output signal of the ring oscillator  10 A (RING OSCILLTOR OUTPUT) and the output signal of the first error AMP  12  (ERROR AMP OUTPUT) are referred. However, in  FIG. 8 , three voltages i.e., the output signal of the ring oscillator  10 A (RING OSCILLTOR OUTPUT) and the output signals of the first and second error AMPs  12  and  17 , (ERROR AMP OUTPUT, CURRENT AMP OUTPUT) are referred. Thus, the output signal of the switching regulator  400  is controlled by the effect of the second error AMP  17  additionally.  
         [0052]     When the load capacity is being increased, the current of the NMOS driver transistor is increased in accordance with the increase of the load current and the output signal of second error AMP  17  is becoming higher. The output signal of the first error AMP  12  is shifting from a higher voltage to a lower voltage as shown by a notation “a” in  FIG. 8 .  
         [0053]     Further, the output signal of the second error AMP  17  is increased at each pulse as shown by a notation “b” in  FIG. 8 . At a time period shown by the notation “b”, the output pulse width of the PWM controller  36  is made narrower gradually and the duty cycle is becoming smaller. A part of the output signal of the inverter  21  at corresponding portion shown by “b” in  FIG. 8  is lower than the output voltage of the reference voltage circuit  23  as referred to the waveforms INVERTER OUTPUT and REFERENCE VOLTAGE (Vref 3 ). For the time period, the pulse width of the high level of the PWM controller  36  is shorten.  
         [0054]     When the load capacity becomes lighter, the current of the NMOS driver transistor becomes smaller and the output signal of the second error AMP  17  becomes lower. In this condition, the output pulse width of the PWM controller  36  is depended on the output signal of the first error AMP  12 .  
         [0055]     As described, the current source  22  outputs the current signal corresponding to pulses of the ring oscillator  10 A when the output voltage of the first error AMP  12  is low and the output voltage of the inverter  21  is higher than the third reference voltage Vref 3 . The current source  22  outputs a narrower pulse than the pulse width of the ring oscillator  10 A when the output voltage of first error AMP  12  is higher. Meanwhile, when the load capacity becomes lighter, the output voltage of the second error AMP  17  begins to fall. The output pulse width of the PWM controller  36  is made wider at each pulse of the ring oscillator  10 A. Thus the output pulse width of the PWM controller  36  is controlled.  
         [0056]     In the exemplary embodiment of the switching regulator, the current of the switching transistor is detected and the detected current is amplified by the second error AMP  17 . The output signal of the second error AMP  17  is input to the PWM controller  36 . In parallel, the difference voltage between the load voltage and the first reference voltage is amplified by the first error AMP  12 . The comparator  13  compares the output voltage of the first error AMP  12  and the second reference voltage and outputs a control signal to control the ring oscillator  10 A.  
         [0057]     The PWM controller  36  inputs the output voltage of the first and second error AMPs  12  and  17  and the output signal of the ring oscillator  10 A. The duty cycle of the switching regulator is controlled by the signal of the ring oscillator  10 A based on the feedback voltage of the load voltage and the feedback current in accordance with the load current.  
         [0058]     The comparator  24  compares the controlled output signal of the ring oscillator  10 A with the reference voltage (Vref 3 ). The AND gate  25  outputs a control signal to drive the switching transistor based on the output signal of the comparator  24  and the output signal of the ring oscillator  10 A.  
         [0059]     The switching regulator of the present disclosure can be used in any of a number of manners. For example, as should be apparent from this disclosure, the switching regulator of this disclosure can be employed in portable electronic devices which use a battery as a power source.  
         [0060]     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein. For example, elements and/or features of different examples and illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.  
         [0061]     This patent specification is based on Japanese patent application, No. 2005-281758 filed on Sep. 28, 2005 in the Japan Patent Office, the entire contents of which are incorporated by reference herein.

Technology Category: h