Abstract:
A DC to DC converter including a buck converter, a boost converter, and a control unit, wherein the control unit is arranged to calculate an error voltage of the buck converter Verr_buck based on a feedback output voltage Vout_FB of the DC to DC converter and a reference voltage of the buck converter Vref_buck, and wherein the control unit is arranged to calculate an error voltage of the boost converter Verr_boost based on the feedback output voltage Vout_FB of the DC to DC converter and a reference voltage of the boost converter Vref_boost, wherein the reference voltage of the boost converter Vref_boost is shifted by an offset Voffset as compared to the reference voltage of the buck converter Vref_buck.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a DC to DC converter and a method to operate a DC to DC converter. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the automotive market, DC to DC converters must operate through a wide input voltage range defined by a normal variation of the supplied input voltage as well as by some transient voltages. Such a transient voltage may be, for example, a cranking pulse, i.e., a huge voltage drop that can happen when certain events occur simultaneously, for example, a discharged battery, low temperatures, and the driver attempting to start the car. 
         [0003]    A DC to DC converter may be used to compensate such a cranking pulse and may  additionally provide an adapted voltage level to connected electronic devices. Such a DC to DC converter may transform an input voltage V in  to an output voltage V out , wherein the output voltage V out  may be higher or lower than the input voltage V in . A DC to DC converter capable of regulating an output voltage regardless of the input voltage V in  is called a buck-boost DC to DC converter. The buck-boost DC to DC converter comprises a buck converter that converts an input voltage V in  to a lower output voltage V out  and a boost converter that converts an input voltage V in  to a higher output voltage V out . The buck-boost converter may be called non-inverting when the sign of the input voltage V in  is maintained. 
         [0004]    The buck-boost DC to DC converter has too provide a constant output voltage V out . Therefore, a transition between an operation of the buck converter (buck mode) and an operation of the boost converter (boost mode) is necessary when the input voltage V in  drops from a starting value that is higher than the desired output voltage V out  to a final value that is lower than the desired output voltage level V out . This transition from buck mode to boost mode and vice versa must be managed smoothly and efficiently. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a DC to DC converter and a method to operate a DC to DC converter as described in the accompanying claims. 
         [0006]    Specific embodiments of the invention are set forth in the dependent claims. 
         [0007]    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
           [0009]      FIG. 1  schematically shows a circuit diagram of a first example of a DC to DC converter. 
           [0010]      FIG. 2  schematically shows an example of a cranking pulse. 
           [0011]      FIG. 3  schematically shows a further circuit diagram of a second example of a DC to DC converter. 
           [0012]      FIG. 4  schematically shows a diagram of an example of duty-cycles of a DC to DC converter and a corresponding output voltage V out  of this DC to DC converter as a function of an input voltage V in . 
           [0013]      FIG. 5  schematically shows a diagram of examples of an error voltage of a buck converter V err     —     buck  and a corresponding control signal as a function of time. 
           [0014]      FIG. 6  schematically shows an example of an output signal of an LS control circuit as a function of time. 
           [0015]      FIG. 7  schematically shows a diagram of examples of an input voltage V in  and an output voltage V out  of a DC to DC converter as a function of time. 
           [0016]      FIG. 8  shows a diagram of an example of an output voltage V out  of a DC to DC converter as a function of time. 
           [0017]      FIG. 9  shows a diagram of an example of a PWM signal of a boost converter as a function of time. 
           [0018]      FIG. 10  shows a diagram of an example of an input voltage V in  provided to a DC to DC converter as a function of time. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Because the illustrated embodiments of the present, invention may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention. 
         [0020]    Although the definition of term hereinafter should not be construed as limiting, the term as used are understood to comprise at least the following. 
         [0021]    In the context of this specification, the term “switching element” may be used for any electronic element, for example, a generic switch or a transistor that can be changed in its state between “on” and “off”. 
         [0022]    The term “on” in connection with the switching element may describe the used electronic element in its closed or conducting state. Further, the term “off” in connection with the switching element may describe the used electronic element in its open or isolating state. 
         [0023]    Referring to  FIG. 1 , a circuit diagram of a first example of a DC to DC converter  10  is schematically shown. The DC to DC converter  10  according to  FIG. 1  may comprise a buck converter  12  and a boost converter  14 . The DC to DC converter  10  may be supplied with an input voltage V in . The input voltage V in  may be converted to an output voltage V out  by the DC to DC converter  10 . An output of the DC to DC converter  10  may be connected with a load  46 , and an optional capacitor  44  may be provided parallel to the load  46  as part of the DC to DC converter  10 . A capacity of the capacitor  44  may be chosen with respect to requirements of the load  46 . For example, the capacity may be increased to minimize output voltage ripples. When the input voltage V in  is higher than the desired output voltage V out , the buck converter  12  of the DC to DC converter  10  may be active to reduce the input voltage V in . This operating mode may be called “buck mode”. When the input voltage V in  is lower than the desired output voltage V out , the boost converter  14  of the DC to DC converter  10  may be active to increase the input voltage V in . This operating mode may be called “boost mode”. The functional principals of the buck converter  12  and the boost converter  14  are apparent to a person skilled in the art and will not be explained here in any further detail. Since the DC to DC converter  10  comprises the buck converter  12  and the boost converter  14 , it may be called a buck-boost DC to DC converter. 
         [0024]    In the example of  FIG. 1 , the buck converter  12  may comprise a HS (high side) diode  38 , a HS switching element  30 , and an inductor  42 . The boost converter  14  may comprise a LS (low side) diode  40 , a LS switching element  36 , and the inductor  42 . Thus, the inductor  42  may be commonly used by the buck converter  12  and the boost converter  14 . The HS switching element  30  and the LS switching element  36  may be triggered by a control unit not shown in  FIG. 1 . 
         [0025]    The HS switching element  30  and a LS switching element  36  may be, for example, metal oxide semiconductor field-effect transistors (MOSFETs). However, any other electronic element that is capable of being used as a switching element may be used. Further, it may be possible to replace the HS diode  38  and the LS diode  40  by a different electronic element that may fulfil the same function, for example, an appropriate triggered transistor. The input voltage V in  may be provided by a battery. The DC to DC converter  10  shown in  FIG. 1  may be called non-inverting because it maintains the sign of the input voltage V in . 
         [0026]    Referring now to  FIG. 2 , an example of a cranking pulse is schematically shown as a function of time. The term “cranking pulse” describes a high voltage drop that may occur with a discharged battery when the driver attempts to start up the car. Initially, at a time t 1  the battery voltage V batt  may have its normal value V norm . At a time t 2 , the driver may attempt to start the car. As a result, the battery voltage V batt  may drop to a low value V min  within the short time interval t 3 -t 2  before it returns to V norm  at a time t 4 . However, it is very important to keep any supply voltage provided to automotive electronics connected to the battery at a certain stable voltage level to avoid damage to the electronics and unpredictable data processing. The desired supply voltage for the automotive electronics may lie between V norm  and V min . Thus, it may be necessary to convert the supply voltage provided by the battery with a buck-boost DC to DC converter, wherein a transition between a buck mode and a boost mode is necessary when the supply voltage provided by the battery equals the desired supply voltage for the automotive electronics. This transition must be smooth without any voltage or current peaks at the output of the DC to DC converter. 
         [0027]    Referring to  FIG. 3 , a further circuit diagram of a second example of a DC to DC converter  10  is schematically shown. The DC to DC converter  10  according to  FIG. 2  is a buck-boost converter and comprises a buck converter  12 , a boost converter  14 , and a control unit  16 . The basic set-ups of the buck converter  12  and the boost converter  14  as shown in  FIG. 3  correspond to the buck converter  12  and the boost converter  14  already known from  FIG. 1 . However, the circuits are closed by connecting the LS switching element  36 , the HS diode  38 , and the capacitor  44  to a ground  60 . 
         [0028]    The control unit  16  may be arranged to trigger the HS switching element  30  and the LS switching element  36 . As in  FIG. 1 , the HS switching element  30  and the LS switching element  36  may be MOSFETs. However, the use of different electronic elements as HS switching element  30  and LS switching element  36  are apparent to a person skilled in the art. 
         [0029]    The control unit  16  may comprise a first error amplifier  48 , a second error amplifier  50 , a first comparator  52 , a second comparator  54 , a third comparator  56 , a HS control circuit  26 , a HS driver circuit  28 , a LS control circuit  32 , and a LS driver circuit  34 . Additionally, the control unit  16  may optionally comprise a filter  58 . The first error amplifier  48 , the first comparator  52 , the HS control circuit  26 , and the HS driver circuit  32  may be used to trigger the HS switching element  30 . The second error amplifier  50 , the second comparator  54 , the third comparator  56 , the LS control circuit  32 , and the LS driver circuit  34  may be used to trigger the LS switching element  36 . The functionality of the control unit  16  will be explained in the following. 
         [0030]    A feedback output voltage V out     —     FB  may be provided to the first error amplifier  48  and the second error amplifier  50  of the control unit  16 . The feedback output voltage V out     —     FB  may be, for example, the output voltage V out  of the DC to DC converter  10  scaled by a first resistor  62  and a second resistor  64 . The first error amplifier  48  and the second error amplifier  50  may be, for example, operational amplifiers with a differential input and a single-ended output. The feedback output voltage V out     —     FB  and a reference voltage of the buck converter V ref     —     buck  may be used as input signals for the first error amplifier  48 . The first error amplifier  48  provides an error voltage of the buck converter V err     —     buck  at its output. The output signal of the first error amplifier  48  may be used as a negative feedback signal for the feedback output voltage V out     —     FB  at the appropriate input of the first error amplifier  48 . 
         [0031]    Similarly, the feedback output voltage V out     —     FB  and a reference voltage of the boost converter V ref     —     boost  may be used as differential input signals for the second error amplifier  50 . The second error amplifier  50  provides an error voltage of the boost converter V err     —     boost  based on the differential input signals. The output signal of the second error amplifier  50  may be used as a negative feedback signal for the feedback output voltage V out     —     FB  at the appropriate input of the second error amplifier  50 . Thus, the control unit  16  is arranged to calculate an error voltage of the buck converter V err     —     buck  based on a feedback output voltage V out     —     FB  of the DC to DC converter  10  and a reference voltage of the buck converter V ref     —     buck . Further, the control unit  16  is arranged to calculate an error voltage of the boost converter V err     —     boost  based on the feedback output voltage V out     —     FB  of the DC to DC converter  10  and the reference voltage of the boost converter V ref     —     boost . The reference voltage of the boost converter V ref     —     boost  may be shifted by an offset V offset  as compared to the reference signal of the buck converter V ref     —     buck . The reference voltage of the buck converter V ref     —     buck  may define the desired output voltage V out  of the DC to DC converter  10  when operating in buck mode. Analogously, the reference voltage of the boost converter V ref     —     boost  may define the desired output voltage V out  of the DC to DC converter  10  when operating in boost mode. Due to the offset V offset , the output voltage V out  of the DC to DC converter  10  may change from V ref     —     buck  to V ref     —     boost  when changing from buck mode to boost mode and vice versa. The reference voltage of the buck converter V ref     —     buck  may usually be larger than the reference voltage of the boost converter V ref     —     boost . In this case, the difference between the reference voltage of the buck converter V ref     —     buck  and the reference voltage of the boost converter V ref     —     boost  may generate a hysteresis around the transition between buck mode and boost mode. The hysteresis may avoid quick oscillations of the DC to DC converter  10  between buck mode and boost mode. 
         [0032]    When the input voltage V in  of the DC to DC converter  10  lies between the reference voltage of the buck converter V ref     —     buck  and the reference voltage of the boost converter V ref     —     boost , the HS switching element  30  of the buck converter  12  is always on (i.e., conducting or closed), and the LS switching element  36  is always off (i.e., isolating or open). Therefore, the efficiency of the DC to DC converter  10  is increased because the HS switching element  30  and the LS switching element  36  are not triggered in this region and do not cause switching losses. Additionally, the output voltage V out  of the DC to DC converter  10  may equal its input voltage V in  and input current without additional ripples or peaks. 
         [0033]    The error voltage of the buck converter V err     —     buck  may be provided to the first comparator  52  together with a time-dependent sensing voltage V sens . The time-dependent sensing voltage V sens  may be generated based on a pulsating voltage V pulse  and a further voltage, for example, by adding the pulsating voltage V pulse  to the further voltage. The further voltage may be, for example, a voltage that represents the input current of the DC to DC converter  10 . The DC to DC converter  10  may, for example, operate in a current mode. A current pattern, i.e., a current ramp, may be sensed at the HS switching element  30 . The sensed current pattern may be transformed to a voltage pattern by a resistor, and the resulting voltage pattern that may correspond to the current pattern may be the pulsating voltage V pulse . The pulsating voltage V pulse  may be, for example, a sawtooth voltage or a triangle voltage. The pulsating voltage V pulse  may be called a “slope compensation” that allows for the stability of the DC to DC converter  10  at all possible duty cycles between 0 and 100%. The first comparator  52  may provide a first PWM signal  20  at its output. Thus, the control unit  16  may be arranged to calculate the first PWM signal  20  by comparing the time-dependent sensing voltage V sens  with the error voltage of the buck converter V err     —     buck . The first PWM signal  20  may substantially define a duty-cycle of the buck converter  12 . The shape of the first PWM signal  20  may be, for example, rectangular. The HS control circuit  26  may be used to generate an input signal for the HS driver circuit  28  that may trigger the HS switching element  30  of the buck converter  12 . The first PWM signal  20  and a clock signal  24  may be used as input signals for the HS control circuit  26 . The HS control circuit  26  may be, for example, a flip-flop which has the first PWM signal  20  and the clock signal  24  as input signals. 
         [0034]    A second PWM signal  22  may be provided by the second comparator  54  which has the error voltage of the boost converter V err     —     boost  and the time-dependent sensing voltage V sens  as input signals. Thus, the control unit  16  may be arranged to calculate the second PWM signal  22  by comparing the time-dependent sensing voltage V sens  with the error voltage of the boost converter V err     —     boost . Just like the first PWM signal  20 , the second PWM signal  22  may be, for example, rectangular. The second PWM signal  22  and the clock signal  24  may be used as input signals for the LS control circuit  32  that provides an output signal to a LS driver circuit  34 . The LS driver circuit  34  may trigger the LS switching element  36  of the boost converter  14 . An additional control signal  18  may optionally be provided to the LS control circuit  32 . The LS control circuit  32  may be, for example, a flip-flop. The control unit  16  may be described as a current mode PWM controller when the further voltage represents the input current of the DC to DC controller  10 . 
         [0035]    The control signal  18  may be used as an additional input signal that overwrites an output signal of the LS control circuit  32  which is generated on the basis of the second PWM signal  22  and the clock signal  24 . Thus, the control signal  18  may activate or deactivate (i.e., engage or disengage) the boost converter  14 . The second PWM signal  22  may substantially represent a duty-cycle of the boost converter  14 . In particular, the second PWM signal  22  may define when the LS switching element  36  is in its open state (or conducting) or in its closed state (off of isolating). The control signal  18  may be generated directly or indirectly by the second comparator  54  that uses the error voltage of the buck converter V err     —     buck  and a threshold voltage V out     —     of     —     range  as input signals. The filter  58  may be optionally used for smoothing the generated control signal  18 . 
         [0036]    As mentioned before, the control signal  18  may be used to engage or disengage the boost converter  14 . When the error voltage of the buck converter V err     —     buck  is higher than the threshold voltage V out     —     of     —     range , the boost converter  14  may be engaged. When the error voltage of the buck converter V err     —     buck  is lower than the threshold voltage V out     —     of     —     range , the boost converter  14  may be disengaged. Thus, the control unit  16  may be arranged to calculate the control signal  18  to engage and disengage the boost converter  14  based on the error voltage of the buck converter V err     —     buck . The buck converter  12  is the main operating circuit, and the boost converter  14  can operate as an optional auxiliary circuit when the input voltage V in  of the DC to DC converter  10  is too low. 
         [0037]    The reference voltage of the buck converter V ref     —     buck  may define the desired output voltage V out  of the buck converter  12  in buck mode. Thus, the error voltage of the buck converter V err     —     buck  may decrease when the feedback output voltage V out     —     FB  of the DC to DC converter  10  increases. For example, the error voltage of the buck converter V err     —     buck  may tend to 0 when the feedback output voltage V out     —     FB  of the DC to DC converter  10  is higher than the reference voltage of the buck converter V ref     —     buck , and the error voltage of the buck converter V err     —     buck  may reach an upper peak value of the time-dependent sensing voltage V sens  when the feedback output voltage V out     —     FB  of the DC to DC converter  10  equals the reference voltage of the buck converter V ref     —     buck . In the same way, the error voltage of the-boost converter V err     —     boost  may define the desired output voltage V out  of the boost converter  14  in boost mode, and the error voltage of the boost converter V ref     —     boost  may tend to 0 or fall below a lower peak value of the time-dependent sensing voltage V sens  when the reference voltage of the boost converter V ref     —     boost  equals the feedback output voltage V out     —     FB  of the DC to DC converter  10 . 
         [0038]    The duty-cycle of the buck converter  12  increases when the error voltage of the buck converter V err     —     buck  increases. The threshold voltage V out     —     of     —     range  may be chosen such that the duty-cycle of the buck converter  12  reaches 100 percent before the error voltage of the buck converter V err     —     buck  becomes larger than the threshold voltage V out     —     of     —     range . Additionally, the error voltage of the boost converter V err     —     boost  may be chosen such that the duty-cycle of the boost converter  14  is larger than 0 percent when the boost converter  14  is engaged by the control signal  18 . This means that the LS switching element  36  of the boost converter  14  may be periodically triggered when the boost converter  14  is engaged and that a small variation of the input voltage V in  does not significantly change the duty-cycle when the boost converter is engaged. This may avoid the generation of peaks in the output voltage V out  and the output current during the transition from buck mode to boost mode and vice versa. Thus, the electromagnetic compatibility of the DC to DC converter  10  is good. 
         [0039]    It may be possible to use the control signal  18  as an additional input signal for the HS control circuit  26 . In this case, the control signal  18  may be used as a master signal that overwrites the normal output signal of the HS control circuit  26  generated on the basis of the first PWM signal  20  and the clock signal  24 . Thus, the control signal  18  may be used to permanently set the HS switching element  30  on. This may secure that the buck converter  12  is deactivated when the boost converter is activated. Using the control signal  18  as an additional input signal for the HS control circuit  26  may be useful when the threshold voltage V out     —     of     —     range  is chosen such that the duty-cycle of the buck converter  12  does not reach 100 percent before the error voltage of the buck converter V err     —     buck  becomes larger than the threshold voltage V out     —     of     —     range . 
         [0040]    The DC to DC converter shown in  FIG. 3  may be designed as a system on a die, wherein at least parts of the DC to DC converter, for example, the buck converter  12 , the boost converter  14 , or the control unit  16 , are implemented on a single die. The single die may comprise, for example, a silicon substrate. 
         [0041]    Referring now to  FIG. 4 , a diagram of an example of duty-cycles of a DC to DC converter and a corresponding output voltage V out  of this DC to DC converter is shown as a function of the input voltage V in . The diagram is divided in three different regions as will be explained in the following. It can be seen from  FIG. 4  that the desired output voltage V out  of the buck converter may be about 6.5 volt. In region I, the duty-cycle of the buck converter D buck  increases when the input voltage V in  of the DC to DC converter decreases. For example, the duty-cycle of the buck converter D buck  may reach 100 percent at an input voltage V in  of approximately 6.5 volt (i.e., the desired output voltage of the buck converter in this example). The duty-cycle of the boost converter D boost  is 0 in region I. Therefore, the DC to DC converter is in buck mode. A duty-cycle of the buck converter D buck  of 100 percent means that its HS switching element known from  FIGS. 1 and 3  is permanently on. When the input voltage V in  of the DC to DC converter further decreases, the error voltage of the buck converter V err     —     buck  increases further, but the duty-cycle of the buck converter D buck  has already reached its maximum value. This leads to a decreasing output voltage V out  of the DC to DC converter  10  in region II. The duty-cycle of the boost converter D boost  may reach a value larger than 0 in region II. However, the boost converter may not yet be engaged because the error voltage of the buck converter V err     —     buck  has not yet reached the value of the threshold voltage V out     —     of     —     range  and the DC to DC converter stays in buck mode. The error voltage of the buck converter V err     —     buck  may reach the threshold voltage V out     —     of     —     range  at the beginning of region III, and the buck converter may engage the boost converter by generating the control signal. The DC to DC converter switches to boost mode. 
         [0042]    Due to the appropriate offset V offset  between the reference voltage of the buck converter V ref     —     buck  and the reference voltage of the boost converter V ref     —     boost  in connection with the generation of the control signal, the duty-cycle of the boost converter D boost  does not start with 0 percent when the boost converter is engaged with entrance of region III. However, due to the offset V offset , the output voltage, V out  of the DC to DC converter changes from the reference value of the buck converter V ref     —     buck  to the reference value of the boost converter V ref     —     boost . The buck converter is regulating the output voltage V out  of the DC to DC converter and provides good performance versus load in region I and region II. The boost converter is regulating the output voltage V out  of the DC to DC converter in region III. 
         [0043]    Referring now to  FIG. 5 , a diagram of examples of an error voltage of a buck converter V err     —     buck  and a corresponding control signal  18  is shown as a function of time.  FIGS. 5 ,  6  and  7  share a common time axis. As can be seen, at a time t between 1.1 ms and 1.15 ms, the error voltage of the buck converter V err     —     buck  may reach the threshold voltage of the buck converter V out     —     of     —     range , and a value of the control signal  18  may switch from 0 to 1 volt. In the example of  FIG. 5 , the control signal  18  is shown as a voltage signal. 
         [0044]    Referring now to  FIG. 6 , an example of an output signal of the LS control circuit is shown as a function of time. The buck converter may engage the boost converter when the control signal  18  shown in  FIG. 5  switches from 0 to 1. The output signal of the LS control circuit may periodically change its value according to the second PWM signal for the boost converter. The output signal of the LS control circuit may be used directly or indirectly via a LS driver circuit as a signal for triggering the LS switching element of the boost converter. Thus, the function shown in  FIG. 6  may substantially represent a PWM signal for the boost converter. 
         [0045]    Referring now to  FIG. 7 , an example of an input voltage V in  and an output voltage V out  of a DC to DC converter is shown as a function of time. The input voltage V in  drops from an initial value larger than 7 volt at a time t=1.00 ms to a final value smaller than 6 volt at a time t=1.20 ms. At a time t=1.10 ms, the input voltage V in  intersects the output voltage V out . At this time, the HS switching element of the buck converter may be permanently on, and the buck converter is no longer capable of regulating the output voltage V out  of the DC to DC converter in the case of a further voltage drop. In consequence, the output voltage V out  of the DC to DC converter may decrease as the input voltage V in  of the DC to DC converter decreases. At the same time, as can be seen in  FIG. 5 , the error voltage of the buck converter V err     —     buck  may increase until the control signal  18  switches from 0 to 1, and the boost converter may be engaged by the buck converter. The output voltage V out  of the DC to DC converter becomes stabilised at approximately 6.25 volt by the boost converter. The output voltage V out  of the DC to DC converter may pulsate a little in boost mode. However, there are neither voltage nor current peaks, and the deviation of the output voltage V out  from the reference voltage of the buck converter V ref     —     buck  or from the reference voltage of the boost converter V ref     —     boost  may be less than 5 percent. Thus, the electronic elements of the DC to DC converter and/or of the connected load may be dimensioned small because they are not exposed to unwanted peaks. In particular, transistors used as switching elements in the DC to DC converter may have a lower breakdown voltage. 
         [0046]    Referring now to  FIGS. 8 ,  9 , and  10  which share a common time axis,  FIGS. 8 to 10  show the transition between the development of the input voltage V in  and the corresponding output voltage V out  of the DC to DC converter at the transition from buck mode to boost mode in more detail. As can be seen from  FIG. 9 , the duty-cycle of the boost converter increases with the decrease of the input voltage V in , and the duty-cycle of the boost converter does not start with 0 percent. 
         [0047]    The invention may also be implemented in a computer program for running on a computer system, at least including code portions for performing steps of a method according to the invention when run on a programmable apparatus, such as a computer system or enabling a programmable apparatus to perform functions of a device or system according to the invention. 
         [0048]    A computer program is a list of instructions such as a particular application program and/or an operating system. The computer program may for instance include one or more of: a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system. 
         [0049]    The computer program may be stored internally on computer readable storage medium or transmitted to the computer system via a computer readable transmission medium. All or some of the computer program may be provided on transitory or non-transitory computer readable media permanently, removably or remotely coupled to an information processing system. The computer readable media may include, for example and without limitation, any number of the following: magnetic storage media including disk and tape storage media; optical storage media such as compact disk media (e.g., CD-ROM, CD-R, etc.) and digital video disk storage media; nonvolatile memory storage media including semiconductor-based memory units such as FLASH memory, EEPROM, EPROM, ROM; ferromagnetic digital memories; MRAM; volatile storage media including registers, buffers or caches, main memory, RAM, etc.; and data transmission media including computer networks, point-to-point telecommunication equipment, and carrier wave transmission media, just to name a few. 
         [0050]    A computer process typically includes an executing (running) program or portion of a program, current program values and state information, and the resources used by the operating system to manage the execution of the process. An operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. An operating system processes system data and user input, and responds by allocating and managing tasks and internal system resources as a service to users and programs of the system. 
         [0051]    The computer system may for instance include at least one processing unit, associated memory and a number of input/output (I/O) devices. When executing the computer program, the computer system processes information according to the computer program and produces resultant output information via I/O devices. 
         [0052]    In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. 
         [0053]    For example, the semiconductor substrate described herein can be any semiconductor material or combinations of materials, such as gallium arsenide, silicon germanium, silicon-on-insulator (SOI), silicon, monocrystalline silicon, the like, and combinations of the above. 
         [0054]    The connections as discussed herein may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections. For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connection that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals. 
         [0055]    Although specific conductivity types or polarity of potentials have been described in the examples, it will be appreciated that conductivity types and polarities of potentials may be reversed. 
         [0056]    Each signal described herein may be designed as positive or negative logic. In the case of a negative logic signal, the signal is active low where the logically true state corresponds to a logic level 0. In the case of a positive logic signal, the signal is active high where the logically true state corresponds to a logic level one. Note that any of the signals described herein can be designed as either negative or positive logic signals. Therefore, in alternate embodiments, those signals described as positive logic signals may be implemented as negative logic signals, and those signals described as negative logic signals may be implemented as positive logic signals. 
         [0057]    Furthermore, the terms “assert” or “set” and “negate” (or “deassert” or “clear”) are used herein when referring to the rendering of a signal, status bit, or similar apparatus into its logically true or logically false state, respectively. If the logically true state is a logic level one, the logically false state is a logic level 0. And if the logically true state is a logic level 0, the logically false state is a logic level one. 
         [0058]    Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. For example, the first comparator, HS control circuit, and the HS driver circuit may be replaced by a single HS amplifier circuit triggering the HS switching element directly. 
         [0059]    Any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality. 
         [0060]    Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments. 
         [0061]    Also for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same device. For example, the buck converter, the boost converter, and the control unit may be implemented as a single circuitry. Alternatively, the examples may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner. For example, the buck converter and the boost converter may be implemented on a single integrated circuitry and the control unit may be implemented on a different integrated circuitry. 
         [0062]    Also for example, the examples, or portions thereof, may implemented as soft or code representations of physical circuitry or of logical representations convertible into physical circuitry, such as in a hardware description language of any appropriate type. 
         [0063]    Also, the invention is not limited to physical devices or units implemented in non-programmable hardware but can also be applied in programmable devices or units able to perform the desired device functions by operating in accordance with suitable program code, such as mainframes, minicomputers, servers, workstations, personal computers; notepads, personal digital assistants, electronic games, automotive and other embedded systems, cell phones and various other wireless devices, commonly denoted in this application as ‘computer systems’. 
         [0064]    However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. 
         [0065]    In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein; are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an”. The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.