Abstract:
A plurality of switches, an inductor and two capacitors are configured to be a boost-inverting converter. To operate the converter in a boost-inverting mode, a control apparatus and method switch the switches such that the inductor is energized in a first phase, the first capacitor is discharged to produce an inverting voltage in a second phase, and the second capacitor is charged to produce a boost voltage in a third phase. Therefore, the boost-inverting converter has lower peak inductor current and less power loss, and the limitation to the switch design for the boost-inverting converter is relaxed.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is related generally to a boost-inverting converter and, more particularly, to a control apparatus and method for a boost-inverting converter.  
       BACKGROUND OF THE INVENTION  
       [0002]     Recently, a type of power converter, called boost-inverting converter, which combines the boost converter function and the inverting converter function together, has been applied in LCD (Liquid Crystal Display) and CCD (Charge Coupled Device) image devices. For further discussion, an exemplary circuit of a conventional inverting converter  100  is shown in  FIGS. 1A and 1B . In the inverting converter  100 , a switch SW 1  is connected between a capacitor Cout and a node  102 , a switch SW 2  is connected between an input Vin and the node  102 , and an inductor L is connected between the node  102  and ground GND. In the first phase, as shown in  FIG. 1A , the switch SW 1  turns off and the switch SW 2  turns on, and therefore an inductor current I flows from the input Vin to ground GND through the switch SW 2  and inductor L, by which the inductor L is energized. After switching to the second phase, as shown in  FIG. 1B , the switch SW 1  turns on and the switch SW 2  turns off, and therefore the inductor L releases the energy stored thereof and the inductor current I becomes to flow from the capacitor Cout to ground GND through the switch SW 1  and inductor L. As such, the capacitor Cout is discharged and an inverting voltage Vout 1  is produced thereon. On the other hand, a conventional boost converter  200  is shown in  FIGS. 2A and 2B , in which an inductor L is connected between an input Vin and a node  202 , a switch SW 1  is connected between the node  202  and a capacitor Cout, and a switch SW 2  is connected between the node  202  and ground GND. In the first phase, as shown in  FIG. 2A , the switch SW 1  turns off and the switch SW 2  turns on, such that an inductor current I flows from the input Vin to ground GND through the inductor L and switch SW 2  to energize the inductor L. After switching to the second phase, as shown in  FIG. 2B , the switch SW 1  turns on and the switch SW 2  turns off, and therefore the inductor L releases the energy stored thereof and the inductor current I becomes to flow from the input Vin to the capacitor Cout through the inductor L and switch SW 1 . As a result, the capacitor Cout is charged and a boost voltage Vout 2  is produced thereon. By combining the inverting converter  100  and boost converter  200 , as shown in  FIGS. 3A  to  3 C, a conventional boost-inverting converter  300  comprises a switch SW 1  connected between a capacitor Cout 1  and a node  302 , a switch SW 2  connected between an input Vin and the node  302 , an inductor L connected between the node  302  and a node  304 , a switch SW 3  connected between the node  304  and ground GND, and a switch SW 4  connected between the node  304  and a capacitor Cout 2 . When the boost-inverting converter  300  operates in an inverting mode, as shown in  FIG. 3A  for the first phase, the switches SW 1  and SW 4  turn off and the switches SW 2  and SW 3  turn on, such that the inductor L is energized by an inductor current I flowing from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3 . Then the boost-inverting converter  300  is switched from the first phase to the second phase as shown in  FIG. 3B , the switches SW 1  and SW 3  turn on and the switches SW 2  and SW 4  turn off, and therefore the inductor L releases the energy stored thereof and the inductor current I becomes to flow from the capacitor Cout 1  to ground GND through the switch SW 1 , inductor L and switch SW 3 , by which the capacitor Cout 1  is discharged and an inverting voltage Vout 1  is produced thereon. If the boost-inverting converter  300  is to be operated in a boost mode, the inductor L is also energized in the first phase shown in  FIG. 3A . However, the boost-inverting converter  300  is then switched from the first phase to the third phase as shown in  FIG. 3C , by which the switches SW 1  and SW 3  turn off and the switches SW 2  and SW 4  turn on, and therefore the inductor L releases the energy stored thereof and the inductor current I becomes to flow from the input Vin to the capacitor C out 2  through the switch SW 2 , inductor L and switch SW 4 . Therefore, the capacitor Cout 2  is charged and a boost voltage Vout 2  is produced thereon.  
         [0003]     The boost-inverting converter  300  may excellently operate in single mode, either the inverting mode or the boost mode. Nevertheless, it may not be normally operated in a continuous mode, i.e., switched between the inverting mode and boost mode. If it is switched from one mode to another before the inductor L completely releases the energy stored thereof, error operation will occur in the later mode. For this reason, the boost-inverting converter  300  is always operated either in a pure inverting mode or in a pure boost mode, but never a continuous mode. Furthermore, for both the inverting mode and boost mode to be normally operated, the boost-inverting converter  300  is required to allow for a higher peak inductor current than the inverting converter  100  and boost converter  200 . To satisfy such requirement, the switches it employs have more difficult device design and are more expensive, and the power loss when it is operated is greater.  
         [0004]     Therefore, it is desired a control apparatus and method to operate a boost-inverting converter in a continuous mode and to allow the boost-inverting converter to have a lower peak inductor current.  
       SUMMARY OF THE INVENTION  
       [0005]     An object of the present invention is to provide a control apparatus and method capable of operating a boost-inverting converter in a continuous mode.  
         [0006]     Another object of the present invention is to provide a control apparatus and method that allow a boost-inverting converter to have a lower peak inductor current.  
         [0007]     Yet another object of the present invention is to provide a control apparatus and method that may operate a boost-inverting converter in a boost mode, inverting mode and boost-inverting mode.  
         [0008]     In a boost-inverting converter, at least two switches, an inductor and two capacitors are so configured that by switching the switches, the inductor will be energized in a first phase, the first capacitor will be discharged to produce a first output voltage in a second phase, and the second capacitor will be charged to produce a second output voltage in a third phase. To operate the boost-inverting converter, according to the present invention, a control apparatus comprises a first error amplifier to produce a first signal by amplifying a first difference between a first reference signal and a first feedback signal varying with the first output voltage, a second error amplifier to produce a second signal by amplifying a second difference between a second reference signal and a second feedback signal varying with the second output voltage, a combiner to produce a third signal by combining the first signal multiplied with a first parameter and the second signal multiplied with a second parameter, a waveform generator to produce a fourth signal, a first comparator to produce a first control signal by comparing the first signal with the fourth signal, a second comparator to produce a second control signal by comparing the second signal with the fourth signal, a third comparator to produce a third control signal by comparing the third signal with the fourth signal, and a logical circuit to produce a plurality of drive signals based on the three control signals for switching the switches. The first and second parameters have a sum equal to one.  
         [0009]     When operating in a boost-inverting mode, the switches are so switched that the inductor is energized in a first phase, the inductor is relaxed and the first capacitor is discharged to produce an inverting voltage in a second phase, the first capacitor is discharged and the second capacitor is charged to produce a boost voltage in a third phase, and the first capacitor is discharged and the second capacitor stops being charged in a fourth phase.  
         [0010]     Alternatively, when operating in a boost-inverting mode, the switches are so switched that the inductor is energized in a first phase, the inductor is relaxed and the second capacitor is charged to produce a boost voltage in a second phase, the second capacitor is charged and the first capacitor is discharged to produce an inverting voltage in a third phase, and the second capacitor is charged and the first capacitor stops being discharged in a fourth phase.  
         [0011]     According to the present invention, a boost-inverting converter may be operated in an inverting mode, boost mode and boost-inverting mode. Namely, the boost-inverting converter may be normally operated in a continuous mode. Therefore, the peak inductor current is reduced, the switches is easier to design, and the power loss is less. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings; wherein:  
         [0013]      FIG. 1A  shows a conventional inverting converter when the inductor thereof is energized;  
         [0014]      FIG. 1B  shows how the inverting converter of  FIG. 1A  produces an inverting voltage;  
         [0015]      FIG. 2A  shows a conventional boost converter when the inductor thereof is energized;  
         [0016]      FIG. 2B  shows how the boost converter of  FIG. 2A  produces a boost voltage;  
         [0017]      FIG. 3A  shows a conventional boost-inverting converter when the inductor thereof is energized;  
         [0018]      FIG. 3B  shows how the boost-inverting converter of  FIG. 3A  produces an inverting voltage;  
         [0019]      FIG. 3C  shows how the boost-inverting converter of  FIG. 3A  produces a boost voltage;  
         [0020]      FIGS. 4A  to  4 C show a synchronous-boost-synchronous-inverting converter  400  operating in a boost-inverting mode;  
         [0021]      FIG. 5  shows an embodiment for the logical circuit of the converter shown in  FIG. 4 ;  
         [0022]      FIG. 6  is a timing diagram of various signals in the converter of  FIG. 4  when operating in a boost-inverting mode;  
         [0023]      FIGS. 7A  to  7 C show a synchronous-boost-asynchronous-inverting converter operating in a boost-inverting mode;  
         [0024]      FIG. 8  shows an embodiment for the logical circuit of the converter shown in  FIG. 7 ;  
         [0025]      FIGS. 9A  to  9 C show an asynchronous-boost-synchronous-inverting converter operating in a boost-inverting mode;  
         [0026]      FIG. 10  shows an embodiment for the logical circuit of the converter shown in  FIG. 9 ;  
         [0027]      FIGS. 11A  to  11 C show an asynchronous-boost-asynchronous-inverting converter operating in a boost-inverting mode  
         [0028]      FIG. 12  shows an embodiment for the logical circuit of the converter shown in  FIG. 11 ;  
         [0029]      FIG. 13  shows a modification of the converter shown in  FIG. 11 ; and  
         [0030]      FIG. 14  is a timing diagram of various signals in the converter shown in  FIG. 13 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     1. First Embodiment: Synchronous-Boost-Synchronous-Inverting Converter  
       [0031]      FIGS. 4A  to  4 C show a synchronous-boost-synchronous-inverting converter  400  operating in a boost-inverting mode, in which a switch SW 1  is connected between a capacitor Cout 1  and a node  404 , a switch SW 2  is connected between the node  404  and an input connected with a supply voltage Vin, an inductor L is connected between the node  404  and a node  406 , a switch SW 3  is connected between the node  406  and an input connected to ground GND, a switch SW 4  is connected between the node  406  and a capacitor Cout 2 , and a control apparatus  402  produces four drive signals V 1 , V 2 , V 3  and V 4  for switching the four switches SW 1 , SW 2 , SW 3  and SW 4 , respectively, in order to produce an inverting voltage Vout 1  on the capacitor Cout 1  and a boost voltage Vout 2  on the capacitor Cout 2  and determines the maximum duty cycle of each switch SW 1 , SW 2 , SW 3  and SW 4 . In the control apparatus  402 , two resistors R 1  and R 2  are connected in series between the output Vout 1  and a reference signal Vref as a voltage divider to divide the inverting voltage Vout 1  to produce a feedback signal VFB 1  proportional to the inverting voltage Vout 1 , and two resistors R 3  and R 4  are connected in series between the output Vout 2  and ground GND as a voltage divider to divide the boost voltage Vout 2  to produce a feedback signal VFB 2  proportional to the boost voltage Vout 2 . An error amplifier  408  produces an error signal V CB  by amplifying the difference between the feedback signal VFB 2  and reference signal Vref for a comparator  416  to compare with a signal V W  generated by a waveform generator  414  to produce a control signal V B . Similarly, an error amplifier  410  produces an error signal V CI  by amplifying the difference between the feedback signal VFB 1  and a zero threshold for a comparator  420  to compare with the signal V W  to produce a control signal V I . In addition, the error signal V CB  is multiplied by a multiplier  409  with a parameter α, the error signal V CI  is multiplied by a multiplier  411  with a parameter β, and a combiner  412  combines these two products to produce a signal V CA  for a comparator  418  to compare with the signal V W  to produce a control signal V A . In this embodiment, the parameters α and β have a sum equal to one. Based on the control signals V B , V A  and V I , a logical circuit  422  produces the four drive signals V 1 , V 2 , V 3  and V 4  to switch the four switches SW 1 , SW 2 , SW 3  and SW 4 , respectively. Actually, there may be offsets in the error signals V CB  and V CI  for some reasons, for example the presence or absence of load to the converter  400 , and which will cause the inductor L not sufficiently energized. Therefore, the signal V CA  in this embodiment is so produced from the error signals V CB  and V CI  with the multiplications of the parameters α and β to ensure that the inductor L will be sufficiently energized.  
         [0032]      FIG. 5  shows an embodiment for the logical circuit  422  of the converter  400 , in which a NOR gate  424  produces a signal S 1  in response to the control signals V A  and V B  for a non-overlap clock generator  428  to produce the drive signals V 1  and V 2  for switching the switches SW 1  and SW 2 , and an OR gate  426  produces a signal S 2  in response to the control signals V A  and V I  for a non-overlap clock generator  430  to produce the drive signals V 3  and V 4  for switching the switches SW 3  and SW 4 . By use of the non-overlap clock generators  428  and  430 , the duty cycles of the drive signals V 1  and V 2  are prevented from overlapping with each other, i.e., the switches SW 1  and SW 2  will not turn on simultaneously, and the duty cycles of the drive signals V 3  and V 4  are prevented from overlapping with each other, i.e., the switches SW 3  and SW 4  will not turn on simultaneously.  
         [0033]      FIG. 6  is a timing diagram of various signals in the converter  400  when operating in a boost-inverting mode, in which waveform  500  represents the signal V W , waveform  502  represents the error signal V CI , waveform  503  represents the signal V CA , waveform  504  represents the error signal V CB , waveform  506  represents the control signal V I  and the drive signals V 3  and V 4 , waveform  507  represents the control signal V A , waveform  508  represents the control signal V B , waveform  510  represents the drive signals V 1  and V 2 , waveform  512  represents the switching of the switch SW 1 , waveform  514  represents the switching of the switch SW 2 , waveform  516  represents the switching of the switch SW 3 , and waveform  518  represents the switching of the switch SW 4 . In this embodiment, the switches SW 1  and SW 3  are NOMSes and the switches SW 2  and SW 4  are PMOSes; therefore, the drive signals V 1  and V 2  have the same phase and the drive signals V 3  and V 4  have the same phase. In other embodiments, it may not be the case, e.g., the drive signals V 1  and V 2  are inverse to each other in phase and the drive signals V 3  and V 4  are inverse to each other in phase, if the switches SW 1 , SW 2 , SW 3  and SW 4  are different types of MOSes from those in this embodiment.  
         [0034]     With reference to  FIGS. 4A, 5  and  6 , during the period of time T 0  to time T 1 , since the signal V W  provided by the waveform generator  414  is lower than each of the error signals V CI , V CB  and V CA , the control signals V I , V B  and V A  are all at high level, resulting in the drive signals V 1  and V 2  at low level and the drive signals V 3  and V 4  at high level, and by which the switches SW 1  and SW 4  turn off and the switches SW 2  and SW 3  turn on. Accordingly, as shown in  FIG. 4A , the current I flows from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3 , by which the inductor L is energized. In the period between time T 1  and time T 2 , the signal V W  raises up to the level between those of the error signals V CB  and V CA , and therefore, the control signals V I  and V A  are still at high level while the control signal V B  is at low level. Due to the control signal V A  at high level, the switches SW 1  and SW 4  still turn off and the switches SW 2  and SW 3  still turn on, so that the inductor L is still energized.  
         [0035]     With reference to  FIGS. 4B, 5  and  6 , when the converter  400  operates in the period between time T 2  and time T 3 , the signal V W  is higher than the error signals V CB  and V CA , but still lower than the error signal V CI . Hence, the control signal V I  is at high level and the control signals V B  and V A are at low level. Accordingly, the drive signals V 1 , V 2 , V 3  and V 4  are all at high level, and the switches SW 1  and SW 3  turn on while the switches SW 2  and SW 4  turn off. As shown in  FIG. 4B , due to the released energy from the inductor L, the current I flows from the capacitor Cout 1  to ground GND through the switch SW 1 , inductor L and switch SW 3 , and the capacitor Cout 1  is discharged to produce the inverting voltage Vout 1 .  
         [0036]     With reference to  FIGS. 4C, 5  and  6 , in the period between time T 3  and time T 4 , the signal V W  is higher than each of the error signals V CB , V CI  and V CA , and thereby the control signals V B , V I  and V A  are all at low level. Hence, the drive signals V 1  and V 2  are at high level and the drive signals V 3  and V 4  are at low level. Accordingly, the switches SW 1  and SW 4  turn on and the switches SW 2  and SW 3  turn off. As a result, as shown in  FIG. 4C , the current I flows from the capacitor Cout 1  to the capacitor Cout 2  through the switch SW 1 , inductor L and switch SW 4 , and thereby the capacitor Cout 2  is charged to produce the boost voltage Vout 2 . When the current I is less than zero, the switches SW 1  and SW 4  turn off immediately.  
         [0037]     With reference to  FIGS. 4B, 5  and  6  again, when the converter  400  operates in the period from time T 4  to time T 5 , the signal V W  is higher than the error signals V CB  and V CA , but lower than the error signal V CI , and hence the control signal V I  is at high level and the control signals V B  and V A  are at low level, resulting in the drive signals V 1 , V 2 , V 3  and V 4  all at high level. Accordingly, the switches SW 1  and SW 3  turn on and the switches SW 2  and SW 4  turn off, thereby the current I flowing from the capacitor Cout 1  to ground GND through the switch SW 1 , inductor L and switch SW 3  again, as shown in  FIG. 4B , and the capacitor Cout 1  is discharged.  
         [0038]     Referring back to  FIGS. 4A, 5  and  6 , in the period between time T 5  and time T 6 , the signal V W  is lower than the error signals V CI  and V CA , but higher than the error signal V CB . Thus, the control signals V I  and V A  are at high level and the control signal V B  is at low level, and therefore, the drive signals V 1  and V 2  are at low level and the drive signals V 3  and V 4  are at high level. Accordingly, the switches SW 1  and SW 4  turn off and the switches SW 2  and SW 3  turn on, resulting in the current I flowing from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3 , as shown in  FIG. 4A , and the inductor L is energized again.  
       2. Second Embodiment: Synchronous-Boost-Asynchronous-Inverting Converter  
       [0039]      FIGS. 7A  to  7 C show a synchronous-boost-asynchronous-inverting converter  600  operating in a boost-inverting mode, which has a similar configuration to that of the first embodiment converter  400  except that the switch SW 1  between the capacitor Cout 1  and node  404  is replaced by a diode D 1  and accordingly, only three drive signals V 2 , V 3  and V 4  are required for switching the switches SW 2 , SW 3  and SW 4 , respectively. In the control apparatus  402 , the control signals V B , V A  and V I  are produced in the same way as that of the first embodiment converter  400  and again, the control signal V A  is used to ensure that the inductor L will be sufficiently energized. In addition, the drive signals V 2 , V 3  and V 4  produced by the logical circuit  602  are the same as those shown in  FIG. 6 .  
         [0040]     For the logical circuit  602 ,  FIG. 8  shows an embodiment having the same configuration as that of the logical circuit  422  shown in  FIG. 5 , in which a NOR gate  604  produces a signal S 1  in response to the control signals V A  and V B  for a non-overlap clock generator  608  to produce the drive signal V 2  for switching the switch SW 2 , and an OR gate  606  produces a signal S 2  in response to the control signals V A  and V I  for a non-overlap clock generator  610  to produce the drive signals V 3  and V 4  for switching the switches SW 3  and SW 4 . The non-overlap clock generator  610  prevents the duty cycles of the drive signals V 3  and V 4  from overlapping with each other, and thus the switches SW 3  and SW 4  will not turn on simultaneously. In this embodiment, the switch SW 3  is an NMOS and the switch SW 4  is a PMOS, and hence the drive signals V 3  and V 4  have the same phase as shown in  FIG. 6 . In other embodiments, the drive signals V 3  and V 4  may be inverse to the other in phase, if the switches SW 3  and SW 4  are both PMOSes or NMOSes.  
         [0041]     With reference to  FIGS. 6, 7A  and  8 , when the converter  600  operates in the period from time T 0  to time T 1 , the signal V W  is lower than each of the error signals V CI , V CB  and V CA . Hence, the control signals V I , V B  and V A  are all at high level, the drive signal V 2  is at low level, and the drive signals V 3  and V 4  are at high level. Therefore, the switches SW 2  and SW 3  turn on, the switch SW 4  turns off, and as shown in  FIG. 7A , the current I flows from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3 , thereby energizing the inductor L. In the period between time T 1  and time T 2 , the control signals V I  and V A  are still at high level, while the control signal V B  transits to low level. Because of the control signal V A  at high level, the switches SW 2  and SW 3  still turn on and the switch SW 4  still turns off, so that the inductor L is still energized.  
         [0042]     With reference to  FIGS. 6, 7B  and  8 , in the period between time T 2  and time T 3 , the signal V W  is higher than the error signals V CB  and V CA , but lower than the error signal V CI . Hence, the control signal V I  is at high level, the control signals V B  and V A  are at low level, and the drive signals V 2 , V 3  and V 4  are all at high level. The switches SW 2  and SW 4  turn off, the switch SW 3  turns on, the inductor L is relaxed, and the current I flows from the capacitor Cout 1  to ground GND through the diode D 1 , inductor L and switch SW 3  as shown in  FIG. 7B . The capacitor Cout 1  is thus discharged to produce the inverting voltage Vout 1 .  
         [0043]     With reference to  FIGS. 6, 7C  and  8 , when the converter  600  operates in the period between time T 3  and time T 4 , the signal V W  is higher than each of the error signals V CB , V CI  and V CA , and hence the control signals V B , V I  and V A  are all at low level, resulting in the drive signal V 2  at high level and the drive signals V 3  and V 4  at low level. Subsequently, the switches SW 2  and SW 3  turn off and the switch SW 4  turns on, so that as shown in  FIG. 7C , the current I flows from the capacitor Cout 1  to the capacitor Cout 2  through the diode D 1 , inductor L and switch SW 4 , thereby charging the capacitor Cout 2  to produce the boost voltage Vout 2 . When the current I is lower than a zero threshold, the switch SW 4  turns off immediately.  
         [0044]     With reference to  FIGS. 6, 7B  and  8  again, when the converter  600  operates in the period between time T 4  and time T 5 , the signal V W  is higher than the error signals V CB  and V CA , but lower than the error signal V CI . Hence, the control signal V I  is at high level, the control signals V B  and V A  are at low level, and the drive signals V 2 , V 3  and V 4  are all at high level, so that the switches SW 2  and SW 4  turn off, the switch SW 3  turns on, and the current I flows from the capacitor Cout 1  to ground GND through the diode D 1 , inductor L and switch SW 3  as shown in  FIG. 7B , thereby discharging the capacitor Cout 1 .  
         [0045]     With reference to  FIGS. 6, 7A  and  8 , in the period between time T 5  and time T 6 , the signal V W  is lower than the error signals V CI  and V CA , but higher than the error signal V CB . Hence, the control signals V I  and V A  are at high level, the control signal V B  is at low level, the drive signal V 2  is at low level, and the drive signals V 3  and V 4  are at high level. As a result, the switches SW 2  and SW 3  turn on, the switch SW 4  turns off, the current I flows from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3  as shown in  FIG. 7A , and the inductor L is energized again.  
       3. Third Embodiment: Asynchronous-Boost-Synchronous-Inverting Converter  
       [0046]      FIGS. 9A  to  9 C show an asynchronous-boost-synchronous-inverting converter  700  operating in a boost-inverting mode, which has a similar configuration to that of the first embodiment converter  400  except that the switch SW 4  between the capacitor Cout 2  and node  406  is replaced by a diode D 2  and accordingly, only three drive signals V 1 , V 2  and V 3  are required for switching the switches SW 1 , SW 2  and SW 3 , respectively. In the control apparatus  402 , the control signals V B , V A  and V I  are produced in the same way as that of the first embodiment converter  400  and again, the control signal V A is used to ensure that the inductor L will be sufficiently energized. In addition, the drive signals V 1 , V 2  and V 3  produced by the logical circuit  702  are the same as those shown in  FIG. 6 .  
         [0047]     For the logical circuit  702 ,  FIG. 10  shows an embodiment having the same configuration as that of the logical circuit  422  shown in  FIG. 5 , in which a NOR gate  704  produces a signal S 1  in response to the control signals V A  and V B  for a non-overlap clock generator  708  to produce the drive signals V 1  and V 2  for switching the switches SW 1  and SW 2 , and an OR gate  706  produces a signal S 2  in response to the control signals V A  and V I  for a non-overlap clock generator  710  to produce the drive signal V 3  for switching the switch SW 3 . The non-overlap clock generator  708  prevents the duty cycles of the drive signals V 1  and V 2  from overlapping with each other, and thus the switches SW 1  and SW 2  will not turn on simultaneously. In this embodiment, the switch SW 1  is an NMOS and the switch SW 2  is a PMOS, and hence the drive signals V 1  and V 2  have the same phase as shown in  FIG. 6 . In other embodiments, the drive signals V 1  and V 2  may be inverse to the other in phase, if the switches SW 1  and SW 2  are both PMOSes or NMOSes.  
         [0048]     With reference to  FIGS. 6, 9A  and  10 , when the converter  700  operates in the period between time T 0  and time T 1 , the signal V W  generated by the waveform generator  414  is lower than each of the error signals V CI , V CB  and V CA . Hence, the control signals V I , V B  and V A  are all at high level, the drive signals V 1  and V 2  are at low level, the drive signal V 3  is at high level, the switch SW 1  turns off, and the switches SW 2  and SW 3  turn on, so that as shown in  FIG. 9A , the current I flows from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3 , to thereby energize the inductor L. In the period between time T 1  and time T 2 , the control signals V I  and V A  are still at high level, but the control signal V B  is at low level. Because of the control signal V A  at high level, the switch SW 1  still turns off, and the switches SW 2  and SW 3  still turn on, so that the inductor L is still energized.  
         [0049]     With reference to  FIGS. 6, 9B  and  10 , in the period between time T 2  and time T 3 , the signal V W  is higher than the error signals V CB  and V CA , but lower than the error signal V CI . Hence, the control signal V I  is at high level, the control signals V B  and V A  are at low level, the drive signals V 1 , V 2  and V 3  are all at high level, the switches SW 1  and SW 3  turn on, the switch SW 2  turns off, the current I flows from the capacitor Cout 1  to ground GND through the switch SW 1 , inductor L and switch SW 3 , as shown in  FIG. 9B , and the capacitor Cout 1  is discharged to produce the inverting voltage Vout 1 .  
         [0050]     With reference to  FIGS. 6, 9C  and  10 , when the converter  700  operates in the period between time T 3  and time T 4 , the signal V W  is higher than each of the error signals V CB , V CI  and V CA . Hence, the control signals V B , V I  and V A  are all at low level, the drive signals V 1  and V 2  are at high level, the drive signal V 3  is at low level, the switch SW 1  turns on, the switches SW 2  and SW 3  turn off, and the current I flows from the capacitor Cout 1  to the capacitor Cout 2  through the switch SW 1 , inductor L and diode D 2 , as shown in  FIG. 9C , so that the capacitor Cout 2  is charged to produce the boost voltage Vout 2 . When the current I is lower than zero threshold, the switch SW 1  turns off immediately.  
         [0051]     Referring back to  FIGS. 6, 9B  and  10 , when the converter  700  operates in the period between time T 4  and time T 5 , the signal V W  is higher than the error signals V CB  and V CA , but lower than the error signal V CI . Hence, the control signal V I  is at high level, the control signals V B  and V A  are at low level, the drive signals V 1 , V 2  and V 3  are at high level, the switches SW 1  and SW 3  turn on, the switch SW 2  turns off, the current I flows from the capacitor Cout 1  to ground GND through the switch SW 1 , inductor L and switch SW 3 , as shown in  FIG. 9B , and the capacitor Cout 1  is discharged.  
         [0052]     With reference to  FIGS. 6, 9A  and  10  again, when the converter  700  operates in the period between time T 5  and time T 6 , the signal V W  is lower than the error signals V CI  and V CA , but higher than the error signal V CB . Hence, the control signals V I  and V A  are at high level, the control signal V B  is at low level, the drive signals V 1  and V 2  are at low level, the drive signal V 3  is at high level, the switch SW 1  turns off, the switches SW 2  and SW 3  turn on, the current I flows from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3 , as shown in  FIG. 9A , and thereby the inductor L is energized again.  
       4. Fourth Embodiment: Asynchronous-Boost-Asynchronous-Inverting Converter  
       [0053]      FIGS. 11A  to  11 C show an asynchronous-boost-asynchronous-inverting converter  800  operating in a boost-inverting mode, which has a similar configuration to that of the third embodiment converter  700  except that the switch SW 1  between the capacitor Cout 1  and node  404  is also replaced by a diode D 1  and accordingly, only two drive signals V 2  and V 3  are required for switching the switches SW 2  and SW 3 , respectively. In the control apparatus  402 , the control signals V B , V A  and V I  are produced in the same way as that of the first embodiment converter  400  and again, the control signal V A  is used to ensure that the inductor L will be sufficiently energized. In addition, the drive signals V 2  and V 3  produced by the logical circuit  802  are the same as those shown in  FIG. 6 , and for which  FIG. 12  shows an embodiment having the same configuration as that of the logical circuit  422  shown in  FIG. 5 . Namely, the logical circuit  802  has a NOR gate  804  in response to the control signals V A  and V B  to produce a signal S 1 , an OR gate  806  in response to the control signals V A  and V I  to produce a signal S 2 , a non-overlap clock generator  808  in response to the signal S 1  to produce the drive signal V 2  for switching the switch SW 2 , and a non-overlap clock generator  810  in response to the signal S 2  to produce the drive signal V 3  for switching the switch SW 3 .  
         [0054]     With reference to  FIGS. 6, 11A  and  12 , when the converter  800  operates in the period between time T 0  and time T 1 , the signal V W  is lower than each of the error signals V CI , V CB  and V CA . Hence, the control signals V I , V B  and V A  are all at high level, the drive signal V 2  is at low level, the drive signal V 3  is at high level, the switches SW 2  and SW 3  turn on, and the current I flows from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3 , as shown in  FIG. 11A , so that the inductor L is energized. In the period between time T 1  and time T 2 , the control signals V I  and V A  are still at high level, but the control signal V B  transits to low level. Due to the control signal V A  at high level, the switches SW 2  and SW 3  still turn on, so that the inductor L is still energized.  
         [0055]     With reference to  FIGS. 6, 11B  and  12 , in the period between time T 2  and time T 3 , the signal V W  is higher than the error signals V CB  and V CA , but lower than the error signal V CI . Hence, the control signal V I  is at high level, the control signals V B  and V A  are at low level, and the drive signals V 2  and V 3  are at high level, the switch SW 2  turns off, the switch SW 3  turns on, the current I flows from the capacitor Cout 1  to ground GND through the diode D 1 , inductor L and switch SW 3 , as shown in  FIG. 11B , and the capacitor Cout 1  is discharged to produce the inverting voltage Vout 1 .  
         [0056]     With reference to  FIGS. 6, 11C  and  12 , in the period between time T 3  and time T 4 , the signal V W  is higher than each of the error signals V CB , V CI  and V CA . Hence, the control signals V B , V I  and V A  are all at low level, the drive signal V 2  is at high level, the drive signal V 3  is at low level, the switches SW 2  and SW 3  both turn off, and the current I flows from the capacitor Cout 1  to the capacitor Cout 2  through the diode D 1 , inductor L and diode D 2 , as shown in  FIG. 11C , thereby charging the capacitor Cout 2  to produce the boost voltage Vout 2 .  
         [0057]     With reference to  FIGS. 6, 11B  and  12 , when the converter  800  operates in the period between time T 4  and time T 5 , the signal V W  is higher than the error signals V CB  and V CA , but lower than the error signal V CI . Hence, the control signal V I  is at high level, the control signals V B  and V A  are at low level, the drive signals V 2  and V 3  are at high level, the switch SW 2  turns off, the switch SW 3  turns on, the current I flows from the capacitor Cout 1  to ground GND through the diode D 1 , inductor L and switch SW 3  as shown in  FIG. 11B , and the capacitor Cout 1  is discharged.  
         [0058]     With reference to  FIGS. 6, 11A  and  FIG. 12 , when the converter  800  operates in the period between time T 5  and time T 6 , the signal V W  is lower than the error signals V CI  and V CA , but higher than the error signal V CB . Hence, the control signals V I  and V A  are at high level, the control signal V B  is at low level, the drive signal V 2  is at low level, the drive signal V 3  is at high level, the switches SW 2  and SW 3  both turn on, the current I flows from the input Vin to ground GND through the switch SW 2 , inductor L and switch SW 3 , as shown in  FIG. 11A , and the inductor L is thereby energized again.  
         [0059]     As shown in the above embodiments, when a boost-inverting converter of the present invention operates in a boost-inverting mode, the inductor L is energized only once in order to produce an inverting voltage Vout 1  and a boost voltage Vout 2 , and therefore the incomplete energy release problem will not exit any more. On the other hand, for the operations of the above converters  400 ,  500 ,  600 ,  700  and  800  in an inverting mode and in a boost mode, the detail may refer to the description for the conventional boost-inverting converter  300  shown in  FIG. 3 .  
         [0060]     In addition, although the signal V W  produced by the waveform generator  414  in the above embodiment converters  400 ,  500 ,  600 ,  700  and  800  is a triangular waveform for illustration, other types of waveforms such as sawtooth waveform may also applicable in other embodiments.  
         [0061]     Furthermore, the switches may be switched in alternative orders for implementing various operational processes and the signal V W  may be modified to vary with the levels of the error signals V CB , V CA  and V CI , for example in a manner that the signal V W  is generated varying with the drive signals.  
       5. Fifth Embodiment: Alternative Switching Order and Modified Signal V W    
       [0062]     As shown in  FIG. 13 , an asynchronous-boost-asynchronous-inverting converter  900  is a modification of the fourth embodiment converter  800 , in which for the comparators  416 ,  418  and  420  to compare with the error signals V CI , V CB  and V CA  to determine the control signals V B , V A  and V I , a waveform generator  906  produces the signal V W  varying with the drive signals V 2  and V 3 . In the control apparatus  402 , the control signals V B , V A  and V I  are produced in the same way as that of the first embodiment converter  400  and again, the control signal V A  is used to ensure that the inductor L will be sufficiently energized. With an additional oscillator  902  to supply a clock signal CLK, a logical circuit  904  produces the drive signals V 2  and V 3  for switching the switches SW 2  and SW 3 . However, the drive signal V 2  is inverted to switch SW 2 . The switch SW 2  is a PMOS and the switch SW 3  is an NMOS. In addition, a current source I ON  is connected to the output Vout 1 , and a current source I OP  is connected to the output Vout 2 , which represent the load currents at the outputs Vout 1  and Vout 2  of the converter  900 .  
         [0063]      FIG. 14  is a timing diagram of various signals in the converter  900 , in which waveform  910  represents the error signal V CB , waveform  912  represents the error signal V CA , waveform  914  represents the error signal V CI , waveform  916  represents the signal V W , waveform  918  represents the control signal V I , waveform  920  represents the control signal V A , waveform  922  represents the control signal V B , waveform  924  represents the drive signal V 3 , waveform  926  represents the drive signal V 2 , and waveform  928  represents the clock signal CLK. In this embodiment, if the current of the current source I OP  is higher than the current of the current source I ON , the error signal V CB  produced by the error amplifier  408  will be higher than the error signal V CI  produced by the error amplifier  410 . With reference to  FIGS. 13 and 14 , at time T 1 , the clock signal CLK transits from low level to high level, and the drive signals V 2  and V 3  transit to high level accordingly, so that the switches SW 2  and SW 3  turn on to energize the inductor L, and the signal V W  begins to rise up. At time T 2 , the signal V W  is crossing over the error signal V CA , so that the control signal V A  transits from low level to high level, and the drive signal V 3  transits to low level accordingly. Thereby the switch SW 3  turns off, by which the inductor L stops being energized and the capacitor Cout 2  is charged to produce the boost voltage Vout 2 . At time T 3 , the signal V W  reaches the error signal V CB , so that the control signal V B  transits to high level and the drive signal V 2  transits to low level accordingly. As a result, the switch SW 2  turns off, the capacitor Cout 1  is discharged to produce the inverting voltage Vout 1  and the capacitor Cout 2  is charged to produce the boost voltage Vout 2 . At the same time, the signal V W  is reset, and it will rise up again only when the clock signal CLK transits to high level next time.  
         [0064]     In the converter  900 , the level of the error signal V CA  will vary with the load current such that the inductor L will be ensured to be sufficiently energized. Referring to  FIG. 14 , at time T 4 , the current of the current source I OP  increases, the error signal V CB  rises up accordingly, and the error signal V CA  also rises up in follow to the increasing error signal V CB . Hence, the time that the inductor L will be energized is prolonged, so that the inductor L will be sufficiently energized. At time T 5 , the current of the current source I ON  increases, the error signal V CI  rises up accordingly, and the error signal V CA  also rises up in follow to the increasing error signal V CI . Hence, the time that the inductor L will be energized is prolonged, so that the inductor L will be sufficiently energized. This technique is also applicable to a synchronous-boost-synchronous-inverting converter, synchronous-boost-asynchronous-inverting converter, and asynchronous-boost-asynchronous-inverting converter.  
         [0065]     While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.