Abstract:
A soft switch driving circuit is disclosed for a DC converter, to transform an input voltage into an output voltage. The soft switch driving circuit includes a regulating module for outputting a reference voltage, a first bootstrap circuit for generating a first voltage value according to a DC voltage, a second bootstrap circuit for generating a second voltage value according to the reference voltage, a control module for generating a plurality of control signals according to a control voltage, a switch module having one end coupled to the first bootstrap circuit and another end coupled to the second bootstrap circuit for outputting a voltage signal, and an output circuit connected to the control module and the switch module for transforming the input voltage into the output voltage according to the voltage signal and one of the plurality of controlling signals.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a soft switch driving circuit, and more particularly, to a soft switch driving circuit which utilizes a plurality of bootstrap circuits and a switch module to generate a plurality of driving voltages, so as to transform an input voltage into an output voltage. 
         [0003]    2. Description of the Prior Art 
         [0004]    Generally, DC-DC voltage converters are classified into two groups, one is a buck (step down) converter and the other is a boost (step up) converter. The buck converter can decrease an input DC voltage to a default voltage level, and the boost converter can increase an input DC voltage. With development, both the buck and boost converters are varied and modified to conform to different system architectures and requirements. 
         [0005]    Please refer to  FIG. 1 , which illustrates a conventional schematic diagram of a bootstrap circuit  106  being utilized in a boost/buck converter  10 . The bootstrap circuit  106  includes a bootstrap capacitor C_BS and a diode D_BS. Additionally, the boost/buck converter  10  further includes a driving circuit  100 , an output circuit  102  and a control module  104 . The driving circuit  100  includes transistors Q 1 , Q 2  and driving units DRV_ 1 , DRV_ 2 . The control module  104  generates control signals VCTRL, V_CTRL_B to input to the driving units DRV_ 1 , DRV_ 2 , and to control conducting conditions of the transistors Q 1 , Q 2  in order to output a switch signal to a terminal point Y. The outputting circuit  102  coupled to the terminal point Y includes an inductor L, a capacitor C and feedback resistors R 1 , R 2 . The output circuit  102  utilizes the switch signal and the inductor L to operate a power switch at an output port. The feedback resistors R 1 , R 2  generate a feedback voltage VFB for the control module  104  to generate the control signals V_CTRL, V_CTRL_B. Therefore, the bootstrap circuit  106  operates a charge/discharge process at terminal points X, Y of the bootstrap capacitor C_BS according to the conducting conditions of the transistors Q 1 , Q 2 , and outputs a conducting current passing through the inductor L. Furthermore, the control module  104  determines a switch frequency of the above two conducting conditions to provide a proper voltage/switch-frequency. 
         [0006]    Please refer to  FIG. 2 , which illustrates a schematic diagram of a bootstrap circuit module  200  driving a gate driving circuit  20 . The bootstrap circuit module  200  is a simplified block diagram of the bootstrap circuit  106  and other control circuits thereof in  FIG. 1 . As shown in  FIG. 2 , the gate driving circuit  20  includes an up-bridge switch M 1 , a down-bridge switch M 2 , a parasitic inductor CL, an inductor L, a capacitor C and a controller  202 . The bootstrap circuit module  200  is coupled to the up-bridge switch M 1  to supply different driving voltages to the up-bridge switch M 1 . The parasitic inductor CL is coupled between the up-bridge switch M 1  and the down-bridge switch M 2 . The down-bridge switch M 2  includes a parasitic diode D_body. When the down-bridge switch M 2  and the up-bridge switch M 1  are both turned off, the parasitic diode D_body provides a forward-bias current to provide the inductor L a continuous current. When the bootstrap circuit module  200  drives the up-bridge switch M 1 , the up-bridge switch M 1  provides a larger in-rush current passing through the inductor L to turn off the parasitic diode D_body. During the process of turning off the parasitic diode D_body, a driving current passing through the up-bridge switch M 1  causes a large amount of reverse-bias current passing through the parasitic diode D_body via the parasitic inductor CL to suddenly turn off the parasitic diode D_body. While the parasitic diode D_body is turned off, the large amount of reverse-bias current passing through the parasitic inductor CL disappears. Accordingly, a terminal point PK generates a voltage pulse higher than a voltage of a terminal point Z, which results in a higher in-rush voltage to damage the drain (i.e. the terminal point PK) of the down-bridge switch M 2  due to insufficient voltage blocking capability. During the practical chip design process, the up-bridge switch M 1  is close to the only output pin of the chip to avoid a parasitic inductor (not shown in the figure) of the up-bridge switch M 1  having the same voltage pulse. In this situation, a longer wire of the down-bridge switch M 2  is inevitable, which exaggerates the in-rush current passing through the parasitic inductor CL and elevates a damage probability of the down-bridge switch M 2 . Therefore, it has become an important issue to provide another soft switch driving circuit, which adaptively controls an initial voltage state of the up-bridge switch M 1  to confine the sudden reverse-bias current passing through the parasitic diode D_body of the down-bridge switch M 2  without dramatically changing the original design for the up-bridge switch M 1  and the down-bridge switch M 2 . 
       SUMMARY OF THE INVENTION 
       [0007]    It is therefore an objective of the invention to provide a soft switch driving circuit. 
         [0008]    The present invention discloses a soft switch driving circuit for a DC converter to transform an input voltage into an output voltage including a regulating module for outputting a reference voltage; a first bootstrap circuit for generating a first voltage value according to a DC voltage; a second bootstrap circuit for generating a second voltage value according to the reference voltage; a control module for generating a plurality of control signals according to a control voltage; a switch module having one end coupled to the first bootstrap circuit and another end coupled to the second bootstrap circuit for outputting a voltage signal according to the DC voltage, the first voltage value, the second voltage value and the plurality of control signals; and an output circuit electrically connected to the control module and the switch module for transforming the input voltage into the output voltage according to the voltage signal and one of the plurality of controlling signals. 
         [0009]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates a conventional schematic diagram of a bootstrap circuit being utilized in a boost/buck converter. 
           [0011]      FIG. 2  illustrates a schematic diagram of a bootstrap circuit module driving a gate driving circuit. 
           [0012]      FIG. 3  illustrates a schematic diagram of a soft switch driving circuit according to an embodiment of the invention. 
           [0013]      FIG. 4  illustrates a comparative diagram of the voltage between the invention and the prior art at different terminal points. 
           [0014]      FIG. 5  illustrates a flow chart of the soft switch driving process according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Please refer to  FIG. 3 , which illustrates a schematic diagram of a soft switch driving circuit  3  according to an embodiment of the invention. As shown in  FIG. 3 , the soft switch driving circuit  3  includes a regulating module  30 , a first bootstrap circuit  32 , a second bootstrap circuit  34 , a control module  36 , a switch module  38  and an output circuit  39 . The regulating module  30  includes an operational amplifier OP and division-voltage resistors R 3 , R 4 , and utilizes a voltage source Vref to output a reference voltage V_ref. The first bootstrap circuit  32  includes a diode D 1  and a capacitor C 1 , and the second bootstrap circuit  34  also includes a diode D 2  and a capacitor C 2 . Similar to the bootstrap circuit  106  of the prior art, the first bootstrap circuit  32  utilizes the diode D 1  and the capacitor C 1  to generate a first voltage value BOOT 1  according to a DC voltage VCC, and the second bootstrap circuit  34  utilizes the diode D 2  and the capacitor C 2  to generate a second voltage value BOOT 2  according to the reference voltage V_ref. The switch module  38  includes a first switch unit SW 1 , a second switch unit SW 2 , a third switch unit SW 3 , an elevating unit Mup and a lowering unit Mdown, and the mentioned units are realized by MOS transistors in this embodiment. The control module  36  generates a plurality of control signals according to a control voltage VC. For the users&#39; requirements, the plurality of control signals are inputted to the first switch unit SW 1 , the second switch unit SW 2  and the third switch unit SW 3  to control conducting conditions thereof. The switch module  38  utilizes the elevating unit Mup to couple to the second bootstrap circuit  34 , and the first switch unit SW 1 , the second switch unit SW 2  and the third switch unit SW 3  to couple to the first bootstrap circuit  32  and the control module  36 . The output circuit  39  is similar to the gate driving circuit  20  of the prior art, and includes a bridge switch (i.e. the up-bridge switch M 1  and the down-bridge switch M 2 ), the parasitic inductor CL, the inductor L and the capacitor C. The output circuit  39  is coupled to the control module  36 , i.e. receiving the control signal via the down-bridge switch M 2 , and the switch module  38 , so as to transform the input voltage VIN into the output voltage VOUT. 
         [0016]    Preferably, the soft switch driving circuit  3  of the invention generates a two-stage driving voltage to input to the output circuit  39  via the control module  36  and the switch module  38 , and to avoid a sudden larger voltage directly supplied to the down-bridge switch M 2  inside the output circuit  39 , which results in damage to the down-bridge switch M 2 . In this embodiment, the DC voltage source Vref, such as 1 Volt, is initially inputted to the regulating module  30  to generate the reference voltage V_ref, such as 6 Volts, and then the reference voltage V_ref is inputted to the second bootstrap circuit  34 . Simultaneously, the control module  36  outputs the plurality of control signals to the switch module  38 . At a first predetermined timing, such as from 0 to 10 nanoseconds, the plurality of control signals turn on the first switch unit SW 1  and turn off the second switch unit SW 2 . In this situation, the second voltage value BOOT 2  generated by the second bootstrap circuit  34  charges a terminal point P 1  of the capacitor C 2  from 6 Volts to 18 Volts. Accordingly, another terminal point P 1  of the capacitor C 2  has a voltage change from 0 to 12 Volts. Next, the second voltage value BOOT 2  can sequentially boost/buck the same voltage value, such as 1 Volt, via the elevating unit Mup and the lowering unit Mdown, and inputted to the gate of the up-bridge switch M 1  as the driving voltage. Therefore, during the process of turning on the first switch unit SW 1  and turning off the second switch unit SW 2 , the driving voltage from 6 Volts to 18 Volts is transmitted to the gate of the first switch unit SW 1 , and correspondingly, the voltage from 0 to 12 Volts is transmitted to the source of the first switch unit SW 1 , where a voltage difference of 6 Volts between the gate and the source of the first switch unit SW 1  can conduct the up-bridge switch M 1 . The terminal point PHASE of the parasitic inductor CL has an equivalent voltage to the terminal point P 2  from 0 to 12 Volts. Afterward, at a second predetermined timing, such as from 10 nanoseconds to 20 nanoseconds, the control module  36  utilizes the plurality of control signals to turn off the first switch unit SW 1  and turn on the second switch unit SW 2 . In this situation, the first voltage value BOOT 1  generated by the first bootstrap circuit  32  is inputted to the gate and the source of the up-bridge switch M 1  via the two terminal points P 3 , P 4  of the capacitor C 1 , respectively. The first voltage value BOOT 1  causes the terminal point P 3  to have the voltage from 12 Volts to 24 Volts, and the terminal point P 4  to have the voltage from 0 to 12 Volts, which maintains a voltage difference as 12 Volts between the gate and the source of the up-bridge switch M 1  to make the up-bridge switch M 1  conduct. 
         [0017]    This embodiment focuses on the up-bridge switch M 1  being turned on and the down-bridge switch M 2  being turned off. For the current continuously passing through the inductor L, the parasitic diode D_body of the down-bridge switch M 2  is utilized for generating the forward-bias current, and a reverse-bias current is needed if turning off the parasitic diode D_body. Besides, the reverse-bias current passing through the parasitic inductor CL can further determine a pulse voltage generated at the drain of the down-bridge switch M 2 . If the inductance of the parasitic inductor CL is fixed, the larger the reverse-bias current is, the larger the pulse voltage can be anticipated while turning off the parasitic diode D_body. However, a solution to the above problem can be provided by the soft switch driving circuit  3 . The soft switch driving circuit  3  controls the first switch unit SW 1  and the second switch unit SW 2  serially to be on or off, and accordingly, the second voltage value BOOT 2  and the first voltage value BOOT 1  are supplied to the up-bridge switch M 1  to form a two-stage driving voltage, i.e. two voltage differences are provided sequentially as 6 Volts and 12 Volts, so as to avoid directly driving the up-bridge switch M 1  at a larger voltage. Consequently, the reverse-bias current can be reduced while the parasitic diode D_body is turned off, and the current passing through the parasitic inductor CL can be reduced as well, so as to lower the voltage pulse of the terminal point PK. 
         [0018]    Please refer to  FIG. 4 , which illustrates a comparative diagram of the voltage between the invention and the prior art at different terminal points, where the visual line represents the voltage measured in the prior art excluding the soft switch driving circuit  3  and the solid line represents the voltage measured in the invention including the soft switch driving circuit  3 , and they indicate the voltage of the gate of the up-bridge switch M 1 , the voltage difference between the gate of the up-bridge switch M 1  and the terminal point PHASE, and the voltage of the terminal point PK from top to bottom. As shown in  FIG. 4 , by utilizing the soft switch driving circuit  3  of the invention, since the two-stage driving voltage is supplied to the up-bridge switch M 1 , a gradually increasing slope of the voltage curve is demonstrated to show the voltage difference between the gate of the up-bridge switch M 1  and the terminal point PHASE. Also, the terminal point PK can prevent a larger voltage pulse that occurs in the prior art, as circled in  FIG. 4 , to enhance a protect mechanism of the down-bridge switch M 2 . 
         [0019]    Noticeably, the embodiment of the invention provides an operational process utilizing the soft switch driving circuit  3 , which can be summarized as a soft switch driving process  50 , as shown in  FIG. 5 . The soft switch driving process  50  includes the steps as following: 
         [0020]    Step  500 : Start. 
         [0021]    Step  502 : According to the DC voltage VCC, the first bootstrap circuit  32  generates the first voltage value BOOT 1 . 
         [0022]    Step  504 : According to the reference voltage V_ref generated by the regulating module  30 , the second bootstrap circuit  34  generates the second voltage value BOOT 2 . 
         [0023]    Step  506 : According to the control voltage VC, the control module  36  generates the plurality of control signals. 
         [0024]    Step  508 : According to the plurality of control signals, the conducting conditions of the first switch unit SW 1  and the second switch unit SW 2  of the switch module  38  are determined, and accordingly the first voltage value BOOT 1  or the second voltage value BOOT 2  is supplied to the up-bridge switch M 1 . 
         [0025]    Step  510 : When the first switch unit SW 1  is on and the second switch unit SW 2  is off, the second voltage value BOOT 2  is inputted to the gate and the source of the up-bridge switch M 1  via the elevating unit Mup and the lowering unit Mdown, so as to transform the input voltage VIN into the output voltage VOUT. 
         [0026]    Step  512 : When the first switch unit SW 1  is off and the second switch unit SW 2  is on, the first voltage value BOOT 1  is directly inputted to the gate and the source of the up-bridge switch M 1  to transform the input voltage VIN into the output voltage VOUT. 
         [0027]    Step  514 : End. 
         [0028]    The soft switch driving process  50  can be understood in the related paragraphs of the soft switch driving circuit  3  and in  FIG. 3 , and is not described hereinafter for simplicity. Noticeably, in this embodiment, the soft switch driving process  50  utilizes the step  508  and the step  510  to generate the two-stage driving voltage, i.e. the gate and the source of the up-bridge switch M 1  provide the voltage differences as 6 Volts and 12 Volts, to reduce the larger in-rush current passing through the parasitic inductor CL and avoid the higher pulse voltage at the terminal point PK. Therefore, those skilled in the art can change/modify the soft switch driving circuit  3  of the invention with other additional voltage bulk/boost mechanisms or current increase/reduction mechanisms to drive the up-bridge switch M 1  with a multi-stage driving voltage. It is optional to combine the embodiment of the invention with other comparison circuits to adaptively adjust the driving voltages for the up-bridge switch M 1 , or to drive the up-bridge switch M 1  and the down-bridge switch M 2  respectively or simultaneously in order to avoid the in-rush current passing through the parasitic inductor CL and prevent the pulse voltage, which is also in the scope of the invention. 
         [0029]    In summary, the invention provides a soft switch driving circuit utilizing a plurality of bootstrap circuits, a switch module and a control module to generate a plurality of multi-stage driving voltages for input to an up-bridge switch of an output circuit. Consequently, it provides a smaller in-rush current passing through a parasitic capacitor, and has a gradual slope of a voltage curve at a terminal point, such as the terminal point PK in the embodiment. A protection mechanism of a down-bridge switch of the output circuit is improved, and users have the advantage of dynamically adjusting the driving voltage of the output circuit for different requirements, which also expands product applications. 
         [0030]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.