Patent Publication Number: US-2023155495-A1

Title: Biphasic dickson switched capacitor converter

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Chinese application serial no. 202111353958.5, filed on Nov. 12, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The present application relates to the field of switching power supply, and particularly relates to a biphasic Dickson switched capacitor converter. 
     Description of Related Art 
     Conventional inductive direct current-direct current (DC-DC) converters (for example, buck, boost, buck-boost, etc.) are widely used in 5G base station, server power supply, and mobile phone motherboard to achieve a conversion between different voltages. However, a conversion efficiency of the conventional inductive converter is generally inefficient due to large switching loss and inductive loss. In some applications, such as 5G communication with high power consumption and mobile phones with high power fast charging, the inductive converter requires higher conversion efficiency. Conventional inductive converters do not meet requirements of the conversion efficiency. 
     Since the energy density of capacitors is higher than that of inductors, the conversion efficiency of switched capacitor converters using capacitors for energy transmission is much higher than that of the inductive DC-DC converter, and the switched capacitor converters are widely used in various high efficiency scenarios. And Dickson switched capacitor converters are widely used because of their low equivalent impedance. 
     As shown in  FIG.  1   , a conventional biphasic Dickson type 4:1 switched capacitor converter includes twelve power transistors (i.e., Q 1 , Q 2 , Q 3 , Q 4 , Q 5 A, Q 5 B, Q 6 A, Q 6 B, Q 7 A, Q 7 B, Q 8 A and Q 8 B), six capacitors (i.e., OA, C 1 B, C 2 A, C 2 B, C 3 A and C 3 B), an input capacitor CIN, an output capacitor COUT and an output load TOUT. In control, the power transistor Q 1 , the power transistor Q 3 , the power transistor Q 5 A, the power transistor Q 7 A, the power transistor Q 6 B and the power transistor Q 8 B are driven by a same control signal, and the power transistor Q 2 , the power transistor Q 4 , the power transistor Q 6 A, the power transistor Q 8 A, the power transistor Q 5 B and the power transistor Q 7 B also are driven by a same control signal. Both control signals are square wave signals with 50% duty ratio, and have a complementary in waveform. The conventional biphasic Dickson 4:1 switched capacitor converter can realize that an output voltage VOUT is a quarter of an input voltage, i.e. VIN=4*VOUT. And voltage differences of the six capacitors are VC 1 A=VC 1 B=VOUT, VC 2 A=VC 2 B=2*VOUT, VC 3 A=VC 3 B=3*VOUT, respectively. 
     Although the conventional biphasic Dickson 4:1 switched capacitor converter do not have switching-off loss and inductive loss, it still needs to overcome two parasitic capacitors Cds and Cgd when the power transistor is turned on, therefore, the two parasitic capacitors have a certain switching-on loss. For high voltage and low current applications, a ratio of switching-on loss is larger due to higher voltage differences of the two capacitors Cds and Cgd, which limits the further improvement of converter efficiency of the conventional biphasic Dickson 4:1 switched capacitor converter. 
     SUMMARY 
     The present application is directed to the above-mentioned problems, and a biphasic switched capacitor converter is proposed, all primary power transistors can turn on at zero voltage by using an auxiliary circuit, thereby reducing switching loss. Furthermore, the biphasic switched capacitor converter is a biphasic N:1 zero voltage switching-on (ZVS) switched capacitor converter. 
     An aspect of the embodiments of the present application provides a biphasic dickson switched capacitor converter, including a first branch, a second branch and an auxiliary circuit, the auxiliary circuit is connected between the first branch and the second branch, the first branch and the second branch are connected in parallel to an output terminal of the biphasic dickson switched capacitor converter, and power transistors of the first branch and the second branch are primary power transistors; the auxiliary circuit is configured to transfer an electric charge or electric charges on one of the first branch and the second branch to another of the first branch and the second branch during a dead time when the primary power transistors are turned off, so that voltage difference between both terminals of each of the primary power transistors become zero to, then the primary power transistors are turned on under a zero voltage respectively. 
     In some embodiments of the present application, the biphasic dickson switched capacitor converter is a biphasic dickson 4:1 switched capacitor converter, the first branch includes a first power transistor, a second power transistor, a fifth power transistor, a sixth power transistor, a seventh power transistor, an eighth power transistor, a first capacitor, a second capacitor and a third capacitor, and the second branch includes a third power transistor, a fourth power transistor, a ninth power transistor, a tenth power transistor, an eleventh power transistor, a twelfth power transistor, a fourth capacitor, a fifth capacitor and a sixth capacitor. 
     A first terminal of the eighth power transistor and a first terminal of the twelfth power transistor are connected as an input terminal of the biphasic dickson switched capacitor converter, the input terminal of the biphasic dickson switched capacitor converter is connected to an external input voltage, a second terminal of the eighth power transistor is connected to a first terminal of the seventh power transistor and a first terminal of the third capacitor respectively, and a second terminal of the twelfth power transistor is connected to a first terminal of the eleventh power transistor and a first terminal of the sixth capacitor respectively. 
     A second terminal of the seventh power transistor is connected to a first terminal of the sixth power transistor and a first terminal of the fifth capacitor respectively, and a second terminal of the eleventh power transistor is connected to a first terminal of the tenth power transistor and a first terminal of the second capacitor respectively. 
     A second terminal of the sixth power transistor is connected to a first terminal of the fifth power transistor and a first terminal of the first capacitor, and a second terminal of the tenth power transistor is connected to a first terminal of the ninth power transistor and a first terminal of the fourth capacitor respectively. 
     A second terminal of the fifth power transistor is connected to a first terminal of the second power transistor, and a second terminal of the ninth power transistor is connected to a first terminal of the third power transistor. 
     A second terminal of the second power transistor is connected to a first terminal of the first power transistor, a second terminal of the first capacitor, a second terminal of the second capacitor and a second terminal of the third capacitor respectively; a second terminal of the third power transistor is connected to a first terminal of the fourth power transistor, a second terminal of the fourth capacitor, a second terminal of the fifth capacitor and a second terminal of the sixth capacitor respectively; and a second terminal of the first power transistor and a second terminal of the fourth power transistor are grounded. 
     The second terminal of the fifth power transistor, the first terminal of the second power transistor, the first terminal of the third power transistor and the second terminal of the ninth power transistor are connected as the output terminal. 
     The first terminal of the first power transistor, the second terminal of the second power transistor, the second terminal of the first capacitor, the second terminal of the second capacitor and the second terminal of the third capacitor are connected as a first node of the first branch, and the second terminal of the third power transistor, the first terminal of the fourth power transistor, the second terminal of the fourth capacitor, the second terminal of the fifth capacitor and the second terminal of the sixth capacitor are connected as a second node of the second branch. 
     In some embodiments of the present application, the auxiliary circuit includes a thirteenth power transistor, a fourteenth power transistor, a fifteenth power transistor, a sixteenth power transistor and an inductor; a first terminal of the thirteenth power transistor is connected to the first node, a second terminal of the thirteenth power transistor is connected to a first terminal of the inductor and a first terminal of the fourteenth power transistor respectively, and a second terminal of the fourteenth power transistor is grounded; and a second terminal of the inductor is connected to a first terminal of the fifteenth power transistor and a first terminal of the sixteenth power transistor respectively, a second terminal of the fifteenth power transistor is grounded, and a second terminal of the sixteenth power transistor is connected to the second node. 
     In some embodiments of the present application, a working sequence of the biphasic dickson switched capacitor converter includes four stages as follows. 
     A first stage: the second power transistor, the fourth power transistor, the sixth power transistor, the eighth power transistor, the ninth power transistor, the eleventh power transistor, the fourteenth power transistor and the sixteenth power transistor are turned on, and remaining power transistors are turned off; the first capacitor, the second capacitor and the third capacitor are in a charging state, the fourth capacitor, the fifth capacitor and the sixth capacitor are in a discharging state, and a current on the inductor is zero. 
     A second stage: the thirteenth power transistor and the sixteenth power transistor are turned on, and remaining power transistors are turned off, the current on the inductor increases and then decreases, and the second stage ends when the current on the inductor decreases to zero. 
     A third stage: the first power transistor, the third power transistor, the fifth power transistor, the seventh power transistor, the tenth power transistor, the twelfth power transistor, the thirteenth power transistor and the fifteenth power transistor are turned on, and remaining power transistors are turned off; the first capacitor, the second capacitor and the third capacitor are in the discharging state, the fourth capacitor, the fifth capacitor and the sixth capacitor are in the charging state, and the current on the inductor is zero. 
     A fourth stage: the thirteenth power transistor and the sixteenth power transistor are turned on, and remaining power transistors are turned off, the current on the inductor increases and then decreases, and the fourth stage ends when the current on the inductor decreases to zero, and returning to the first stage. 
     In some embodiments of the present application, the biphasic dickson switched capacitor converter is biphasic Dickson N:1 switched capacitor converter, and N is an integer greater than or equal to 5. 
     The first branch includes a first power transistor, a second power transistor, N first sub power transistors and N−1 first sub capacitors, and the second branch includes a third power transistor, a fourth power transistor, N second sub power transistor and N−1 second sub capacitors; 
     both terminals of the auxiliary circuit are connected to a first node between the first power transistor and the second power transistor and a second node between the third power transistor and the fourth power transistor respectively. 
     An input terminal of the biphasic dickson switched capacitor converter is connected to the output terminal through the N first sub power transistors and the N−1 second sub capacitors respectively, the N first sub power transistors are connected in turn, and the N−1 second sub capacitors are connected in turn. 
     Two adjacent first sub power transistors form a first sub power transistor pair, two adjacent first sub power transistor pairs include a same first sub power transistor; and two adjacent second sub power transistors form a second sub power transistor pair, two adjacent second sub power transistor pairs include a same second sub power transistor. 
     Any two adjacent first sub power transistor pairs include a first pair of first sub power transistor pair and a second pair of first sub power transistor pair, one of the N−1 first sub capacitors is connected between two first sub power transistors of the first pair of first sub power transistor pair, one of the N−1 second sub capacitors is connected between two first sub power transistors of the second pair of first sub power transistor pair. 
     Any two adjacent second sub power transistor pairs include a first pair of second sub power transistor pair and a second pair of second sub power transistor pair, another of the N−1 first sub capacitors is connected between two second sub power transistors of the first pair of second sub power transistor pair, and another of the N−1 second sub capacitors is connected between two second sub power transistors of the second pair of second sub power transistor pair. 
     One of the N−1 first sub capacitors is connected between two first sub power transistors of a 1-th first sub power transistor pair which is connected the output terminal, and one of the N−1 second sub capacitors is connected between two second sub power transistors of a 1-th second sub power transistor pair which is connected the output terminal. 
     All second terminals of the N−1 first sub capacitors are connected to the first node, and all second terminals of the N−1 second sub capacitors are connected to the second node. 
     In some embodiments of the present application, the thirteenth power transistor, the fourteenth power transistor, the fifteenth power transistor and the sixteenth power transistor are N-type power transistors; or the thirteenth power transistor and the sixteenth power transistor are P-type power transistors, and the fourteenth power transistor and the fifteenth power transistor are N-type power transistors. 
     In some embodiments of the present application, the auxiliary circuit includes a thirteenth power transistor, a sixteenth power transistor, a first diode, a second diode and an inductor; a first terminal of the thirteenth power transistor is connected to the first branch, a second terminal of the thirteenth power transistor is connected to a first terminal of the first diode and a first terminal of the inductor, a second terminal of the first diode is grounded; and a second terminal of the inductor is connected to a first terminal of the second diode and a first terminal of the sixteenth power transistor, a second terminal of the second diode is grounded, and a second terminal of the sixteenth power transistor is connected to the second branch. 
     In some embodiments of the present application, the auxiliary circuit includes a thirteenth power transistor, a sixteenth power transistor and inductor, a first terminal of the thirteenth power transistor is connected to the first branch, a second terminal of the thirteenth power transistor is connected to a first terminal of the inductor, a second terminal of the inductor is connected to a first terminal of the sixteenth power transistor, and a second terminal of the sixteenth power transistor is connected to the second branch. 
     In some embodiments of the present application, the thirteenth power transistor and the sixteenth power transistor are N-type power transistors or P-type power transistors. 
     The above-mentioned control sequence is used in the biphasic switched capacitor converter, of course, the biphasic switched capacitor converter can use other control sequence. 
     The auxiliary circuit are added between two branches at outer side of the biphasic switched capacitor converter, an electric charge or electric charges at a branch can be transferred to another branch by controlling the auxiliary circuit during a dead time when all primary power transistors are turned off, so as to realize zero voltage switching (ZVS) of all primary power transistors and reduce the switching loss. The on-resistance of the auxiliary power transistor is much larger than the on-resistance of the primary power transistor, and the cost is very low. The inductance value of the auxiliary inductor is small and the package size and cost are also very low. Therefore, by adding the auxiliary circuit, the biphasic switched capacitor converter of the embodiments of the present application can significantly reduce the switching loss of a switched capacitor converter, improve efficiency, and has good performance benefits and commercial prospects. 
     To make the aforementioned more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG.  1    is a schematic diagram showing a circuit structure of a conventional biphasic 4:1 switched capacitor converter. 
         FIG.  2    is a schematic diagram showing a circuit structure of a biphasic 4:1 switched capacitor converter of an embodiment of the present application. 
         FIG.  3    is a typical waveform diagram of a biphasic 4:1 switched capacitor converter of an embodiment of the present application. 
         FIG.  4    is an equivalent circuit diagram of a biphasic 4:1 switched-capacitor converter working in Stage 0 of an embodiment of the present application. 
         FIG.  5    is an equivalent circuit diagram of a biphasic 4:1 switched capacitor converter working in Stage 1 of an embodiment of the present application. 
         FIG.  6    is an equivalent circuit diagram of a biphasic 4:1 switched capacitor converter working in Stage 2 of an embodiment of the present application. 
         FIG.  7    is an equivalent circuit diagram of a biphasic 4:1 switched capacitor converter working in Stage 3 of an embodiment of the present application. 
         FIG.  8    is a schematic diagram of a biphasic N:1 switched capacitor converter of an embodiment according to the present application. 
         FIG.  9    is a schematic diagram showing circuit structures of various auxiliary circuits of an embodiment according to the present application. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     To describe the technical solutions in embodiments of the present application more clearly, the following briefly describes the accompanying drawings required for describing the embodiments. It should be noted that, the embodiments of the present application and the features in the different embodiments may be combined with each other under the condition that they do not conflict with each other. 
     As shown in  FIG.  2   , the biphasic 4:1 switched capacitor converter of an embodiment of the present application includes a primary power circuit and an auxiliary circuit. The primary power includes twelve primary power transistors (i.e., a first power transistor Q 1 , a second power transistor Q 2 , a third power transistor Q 3 , a fourth power transistor Q 4 , a fifth power transistor QSA, a ninth power transistor QSB, a sixth power transistor Q 6 A, a tenth power transistor Q 6 B, a seventh power transistor Q 7 A, an eleventh power transistor Q 7 B, an eighth power transistor Q 8 A and a twelfth power transistor Q 8 B),  6  capacitors (i.e., a first capacitor OA, a fourth capacitor C 1 B, a fifth capacitor C 2 A, a second capacitor C 2 B, a third capacitor C 3 A and a sixth capacitor C 3 B), an input capacitor CIN, an output capacitor COUT and an output load TOUT. The auxiliary circuit includes four auxiliary power transistors (i.e., a thirteenth power transistor QX 1 A, a fourteenth power transistor QX 2 A, a sixteenth power transistor QX 1 B and a fifteenth power transistor QX 2 B), and an auxiliary inductor L. 
     The primary power circuit includes a first branch and a second branch, the first branch includes the first power transistor Q 1 , the second power transistor Q 2 , the fifth power transistor QSA, the sixth power transistor Q 6 A, the seventh power transistor Q 7 A, the eighth power transistor Q 8 A, the first capacitor OA, the second capacitor C 2 B and the third capacitor C 3 A, and the second branch includes the third power transistor Q 3 , the fourth power transistor Q 4 , the ninth power transistor QSB, the tenth power transistor Q 6 B, the eleventh power transistor Q 7 B, the twelfth power transistor Q 8 B, the fourth capacitor C 1 B, the fifth capacitor C 2 A and the sixth capacitor C 3 B. 
     A first terminal of the eighth power transistor Q 8 A and a first terminal of the twelfth power transistor Q 8 B are connected as an input terminal of the biphasic dickson switched capacitor converter, the input terminal of the biphasic dickson switched capacitor converter is connected to an external input voltage, a second terminal of the eighth power transistor Q 8 A is connected to a first terminal of the seventh power transistor Q 7 A and a first terminal of the third capacitor C 3 A respectively, and a second terminal of the twelfth power transistor Q 8 B is connected to a first terminal of the eleventh power transistor Q 7 B and a first terminal of the sixth capacitor C 3 B respectively. 
     A second terminal of the seventh power transistor Q 7 A is connected to a first terminal of the sixth power transistor Q 6 A and a first terminal of the fifth capacitor C 2 A respectively, and a second terminal of the eleventh power transistor Q 7 B is connected to a first terminal of the tenth power transistor Q 6 B and a first terminal of the second capacitor C 2 B respectively. 
     A second terminal of the sixth power transistor Q 6 A is connected to a first terminal of the fifth power transistor Q 5 A and a first terminal of the first capacitor OA, and a second terminal of the tenth power transistor Q 6 B is connected to a first terminal of the ninth power transistor Q 5 B and a first terminal of the fourth capacitor C 1 B respectively. 
     A second terminal of the fifth power transistor Q 5 A is connected to a first terminal of the second power transistor Q 2 , and a second terminal of the ninth power transistor Q 5 B is connected to a first terminal of the third power transistor Q 3 . 
     A second terminal of the second power transistor Q 2  is connected to a first terminal of the first power transistor Q 1 , a second terminal of the first capacitor OA, a second terminal of the second capacitor C 2 B and a second terminal of the third capacitor C 3 A respectively; a second terminal of the third power transistor Q 3  is connected to a first terminal of the fourth power transistor Q 4 , a second terminal of the fourth capacitor C 1 B, a second terminal of the fifth capacitor C 2 A and a second terminal of the sixth capacitor C 3 B respectively; and a second terminal of the first power transistor Q 1  and a second terminal of the fourth power transistor Q 4  are grounded. 
     The second terminal of the fifth power transistor Q 5 A, the first terminal of the second power transistor Q 2 , the first terminal of the third power transistor Q 3  and the second terminal of the ninth power transistor Q 5 B are connected as the output terminal. 
     The first terminal of the first power transistor Q 1 , the second terminal of the second power transistor Q 2 , the second terminal of the first capacitor OA, the second terminal of the second capacitor C 2 B and the second terminal of the third capacitor C 3 A are connected as a first node CFLA of the first branch, and the second terminal of the third power transistor Q 3 , the first terminal of the fourth power transistor Q 4 , the second terminal of the fourth capacitor C 1 B, the second terminal of the fifth capacitor C 2 A and the second terminal of the sixth capacitor C 3 B are connected as a second node CFLB of the second branch. 
     The auxiliary circuit includes the thirteenth power transistor QX 1 A, the fourteenth power transistor QX 2 A, the fifteenth power transistor QX 2 B, the sixteenth power transistor QX 1 B and the inductor L. 
     A first terminal of the thirteenth power transistor QX 1 A is connected to the first node CFLA, a second terminal of the thirteenth power transistor QX 1 A is connected to a first terminal of the inductor L and a first terminal of the fourteenth power transistor QX 2 A respectively, and a second terminal of the fourteenth power transistor QX 2 A is grounded. 
     A second terminal of the inductor L is connected to a first terminal of the fifteenth power transistor QX 2 B and a first terminal of the sixteenth power transistor QX 1 B respectively, a second terminal of the fifteenth power transistor QX 2 B is grounded, and a second terminal of the sixteenth power transistor QX 1 B is connected to the second node CFLB. 
     All power transistors in the first branch and the second branch are primary power transistors, and each primary power transistor has a parasitic capacitor. 
     In steady state working conditions, VIN=4*VOUT, VC 1 A=VC 1 B=VOUT, VC 2 A=VC 2 B=2*VOUT, VC 3 A=VC 3 B=3*VOUT. The VIN presents an input voltage, the VOUT presents an output voltage, the VC 1 A presents a voltage difference between both terminals of the first capacitor OA, the VC 2 B presents a voltage difference between both terminals of the second capacitor C 2 B, the VC 3 A presents a voltage difference between both terminals of the third capacitor C 3 A, the VC 1 B presents a voltage difference between both terminals of the fourth capacitor C 1 B, the VC 2 A presents a voltage difference between both terminals of the fifth capacitor C 2 A, and the VC 3 B presents a voltage difference between both terminals of the sixth capacitor C 3 B. 
       FIG.  3    shows a working waveform of the novel biphasic 4:1 switched capacitor converter in one switching cycle. There are four working states in sequence within one working cycle, namely stage 0, stage 1, stage 2 and stage 3. The signal PHA is an original clock signal with a 50% duty ratio, the signal PHB is an inverse signal of the PHA, the signal PHA_DLY is a clock signal obtained by the PHA passing a delay, and the signal PIB_DLY is a clock signal obtained by PHB passing a delay. Signals corresponding to Q 1 , Q 3 , QSA, Q 7 A, Q 6 B and Q 8 B present on-off states of the first power transistor Q 1 , the third power transistor Q 3 , the fifth power transistor QSA, the seventh power transistor Q 7 A, the tenth power transistor Q 6 B and the twelfth power transistor Q 8 B respectively, and signals corresponding to Q 2 , Q 4 , Q 6 A, Q 8 A, Q 5 B, Q 7 B present on-off states of the second power transistor Q 2 , the fourth power transistor Q 4 , the sixth power transistor Q 6 A, the eighth power transistor Q 8 A, the ninth power transistor Q 5 B and the eleventh power transistor Q 7 B respectively. Signals corresponding to QX 1 A, QX 2 A, QX 1 B and QX 2 B present on-off states of the thirteenth power transistor QX 1 A, the fourteenth power transistor QX 2 A, the sixteenth power transistor QX 1 B and the fifteenth power transistor QX 2 B respectively, signals corresponding to CFLA and CFLB present voltage waveforms of the node CFLA and node CFLB respectively, signals corresponding to LXA and LXB present voltage waveforms of the node LXA and node LXB respectively, and a signal corresponding to iL present a current waveform flowing through the inductor L. 
     Stage 0 (t 0 -t 1 ): As shown in  FIG.  4   , in stage 0, the second power transistor Q 2 , the fourth power transistor Q 4 , the sixth power transistor Q 6 A, the eighth power transistor Q 8 A, the ninth power transistor Q 5 B and the eleventh power transistor Q 7 B are turned on, and the first power transistor Q 1 , the third power transistor Q 3 , the fifth power transistor Q 5 A, the seventh power transistor Q 7 A, the tenth power transistor Q 6 B and the twelfth power transistor Q 8 B are turned off. The first capacitor C 1 A, the second capacitor C 2 B and the third capacitor C 3 A are in charging state, and the fourth capacitor C 1 B, the fifth capacitor C 2 A and the sixth capacitor C 3 B are in discharging state. In the auxiliary circuit part, the sixteenth power transistor QX 1 B and the fourteenth power transistor QX 2 A are turned on, and the thirteenth power transistor QX 1 A and the fifteenth power transistor QX 2 B are turned off. In this stage, a voltage of the first node CFLA is equal to the output voltage, a voltage of the second node CFLB is zero, the voltages of the node LXA and node LXB are zero, and a current flowing through the inductor L is zero. 
     Stage 1 (t 1 -t 2 ): As shown in  FIG.  5   , at the moment t 1 , the second power transistor Q 2 , the fourth power transistor Q 4 , the sixth power transistor Q 6 A, the eighth power transistor Q 8 A, the ninth power transistor Q 5 B and the eleventh power transistor Q 7 B are turned off, and the first power transistor Q 1 , the third power transistor Q 3 , the fifth power transistor Q 5 A, the seventh power transistor Q 7 A, the tenth power transistor Q 6 B and the twelfth power transistor Q 8 B maintain turning off, therefore, all twelve primary power transistors are turned off. The first capacitor OA, the fourth capacitor C 1 B, the fifth capacitor C 2 A, the second capacitor C 2 B, the third capacitor C 3 A and the sixth capacitor C 3 B stop charging or discharging and maintain respective current voltage differences. A current of the load is provided by the output capacitor which is in discharging state. The fourteenth power transistor QX 2 A and the fifteenth power transistor QX 2 B are turned off, and thirteenth power transistor QX 1 A and the sixteenth power transistor QX 1 B are turned on. 
     Before the moment t 1 , a voltage of the first node CFLA is VOUT and a voltage of the second node CFLB are zero. From the moment t 1 , the inductor L is connected between the first node CFLA and the second node CFLB, then a parasitic capacitor of the first node CFLA and a parasitic capacitor of the second node CFLB, and the inductor L start to resonate. The voltage of the first node CFLA syntonically decreases, the voltage of the second node CFLB syntonically increases, and the current of the inductor L gradually increases. When the voltage of the first node CFLA and the voltage of the second node CFLB are same, the current through the inductor L reach a positive peak value. Then, the voltage of the first node CFLA maintains decreasing, the voltage of the second node CFLB maintains increasing, and the current of the inductor begins to decrease. At the moment t 2 , the voltage of the first node CFLA resonates to zero, the voltage of the second node CFLB resonates to VOUT, and the current of the inductor L decreases to zero, then the biphasic 4:1 switched capacitor converter enters in stage 2. 
     It can be seen that the electric charges of the first node CFLA can be transferred to the second node CFLB by using the resonance between the inductor and the parasitic capacitors in stage 1. A ZVS condition is thus provided for the first power transistor Q 1 , the third power transistor Q 3 , the fifth power transistor QSA, the seventh power transistor Q 7 A, the tenth power transistor Q 6 B and twelfth power transistor Q 8 B to be turned on in the next stage. 
     Stage 2 (t 2 -t 3 ): As shown in  FIG.  6   , at the moment t 2 , the first power transistor Q 1 , the third power transistor Q 3 , the fifth power transistor QSA, the seventh power transistor Q 7 A, the tenth power transistor Q 6 B and the twelfth power transistor Q 8 B are turned on at zero voltage, and the second power transistor Q 2 , the fourth power transistor Q 4 , the sixth power transistor Q 6 A, the eighth power transistor Q 8 A, the ninth power transistor Q 5 B and the eleventh power transistor Q 7 B maintain turning off. The thirteenth power transistor QX 1 A and the fifteenth power transistor QX 2 B are turned on, and the fourteenth power transistor QX 2 A and the sixteenth power transistor QX 1 B are turned off. The biphasic 4:1 switched capacitor converter enters in the stage 2. The first capacitor OA, the second capacitor C 2 B and third capacitor C 3 A are in discharging state, and the fourth capacitor C 1 B, the fifth capacitor C 2 A and the sixth capacitor C 3 B are in charging state. The voltage of the first node CFLA is zero, the voltage of the second node CFLB is equal to the output voltage, the voltages of the node LXA and node LXB are zero, and the current flowing through the inductor L is zero. 
     Stage 3 (t 3 -t 4 ): As shown in  FIG.  7   , at the moment t 3 , the first power transistor Q 1 , the third power transistor Q 3 , the fifth power transistor Q 5 A, the seventh power transistor Q 7 A, the tenth power transistor Q 6 B and the twelfth power transistor Q 8 B are turned off, and the second power transistor Q 2 , the fourth power transistor Q 4 , the sixth power transistor Q 6 A, the eighth power transistor Q 8 A, the ninth power transistor Q 5 B and the eleventh power transistor Q 7 B maintain turning off, therefore, all twelve primary power transistors are turned off. The first capacitor C 1 A, the second capacitor C 2 B, the third capacitor C 3 A, the fourth capacitor C 1 B, the fifth capacitor C 2 A and the sixth capacitor C 3 B stop charging or discharging and maintain the current voltages respectively. The current of the load is provided by the output capacitor which is in discharging state. The fourteenth power transistor QX 2 A and the fifteenth power transistor QX 2 B are turned off, and the thirteenth power transistor QX 1 A and the sixteenth power transistor QX 1 B are turned on. 
     Before the moment t 3 , the voltage of the first node CFLA is zero and the voltage of the second node CFLB is the output voltage. From the moment t 3 , the inductor L is connected between the first node CFLA and the second node CFLB, then the parasitic capacitor of the first node CFLA, the parasitic capacitor of the second node CFLB and the inductor L start to resonate. The voltage of the first node CFLA syntonically increases, the voltage of the second node CFLB syntonically decreases, and the current of the inductor L gradually increases in negative direction. When the voltage of the first node CFLA and the voltage of the second node CFLB are same, the current through the inductor L reaches a negative peak value. Then, the voltage of the first node CFLA maintains increasing, the voltage of the second node CFLB maintains decreasing, and the current of the inductor L begins to decrease in negative direction. By the moment t 0 , the voltage of the first node CFLA resonates to the output voltage, the voltage of the second node CFLB resonates to zero, and the current of the inductor L decreases to zero. Then the biphasic 4:1 switched capacitor converter returns to the stage 0. 
     It can be seen that the electric charges of the second node CFLB can be transferred to the first node CFLA by using the resonance between inductor L and the parasitic capacitors in stage 3. The ZVS condition is thus provided for the second power transistor Q 2 , the fourth power transistor Q 4 , the sixth power transistor Q 6 A, the eighth power transistor Q 8 A, the ninth power transistor Q 5 B and the eleventh power transistor Q 7 B to be turned on in the next stage. 
     According to the biphasic switched capacitor converter, by controlling the thirteenth power transistor QX 1 A, the fourteenth power transistor QX 2 A, the sixteenth power transistor QX 1 B and the fifteenth power transistor QX 2 B according to the above-mentioned control sequence, the electric charges on the first node CFLA can be transferred to the second node CFLB via the inductor L within the stage 1, and the electric charges on the second node CFLB can be transferred to the first node CFLA via the inductor L within the stage 3, so that the voltage difference of both terminal of each of the first power transistor Q 1 , the second power transistor Q 2 , the third power transistor Q 3 , the fourth power transistor Q 4 , the fifth power transistor QSA, the ninth power transistor Q 5 B, the sixth power transistor Q 6 A, the tenth power transistor Q 6 B, the seventh power transistor Q 7 A, the eleventh power transistor Q 7 B, the eighth power transistor Q 8 A and the twelfth power transistor Q 8 B are zero before these power transistors are turned on respectively, which greatly reduces the switching loss and improves the conversion efficiency of the switched capacitor converter. 
     Based on the biphasic 4:1 switched capacitor converter shown in  FIG.  2   , a biphasic N:1 switched capacitor converter can be realized by adding primary power transistors and capacitors, as shown in  FIG.  8   . An auxiliary circuit of the biphasic N:1 switched capacitor converter of  FIG.  8    is same as the auxiliary circuit as in  FIG.  2   , and a similar control mode can be used in the biphasic N:1 switched capacitor converter to achieve zero voltage switching of all primary power transistors. Wherein N is an integer greater than or equal to 4. When the N=4, the biphasic N:1 switched capacitor converter is the biphasic 4:1 switched capacitor converter as shown in  FIG.  2   . 
     When N is an integer greater than or equal to 5, as shown in  FIG.  8   , the biphasic N:1 switched capacitor converter includes an auxiliary circuit, a first branch and a second branch. 
     The first branch comprises a first power transistor Q 1 , a second power transistor Q 2 , N first sub power transistors and N−1 first sub capacitors, and the second branch comprises a third power transistor Q 3 , a fourth power transistor Q 4 , N second sub power transistor and N−1 second sub capacitors. 
     Both terminals of the auxiliary circuit are respectively connected to a first node CFLA between the first power transistor Q 1  and the second power transistor Q 2  which are connected with each other and a second node CFLB between the third power transistor Q 3  and the fourth power transistor Q 4  which are connected with each other. A circuit structure of the auxiliary circuit of the biphasic N:1 switched capacitor converter of  FIG.  8    is same as that of the biphasic 4:1 switched capacitor converter as shown in  FIG.  2     
     An input terminal of the biphasic dickson switched capacitor converter is connected to an external input voltage, the input terminal is connected to the output terminal of the biphasic dickson switched capacitor converter through the N first sub power transistors and the N−1 second sub capacitors respectively, the N first sub power transistors are connected in turn, and the N−1 second sub capacitors are connected in turn. 
     Any two adjacent first sub power transistors form a first sub power transistor pair, any two adjacent first sub power transistor pairs include a same first sub power transistor; and any two adjacent second sub power transistors form a second sub power transistor pair, any two adjacent second sub power transistor pairs include a same second sub power transistor. 
     Any two adjacent first sub power transistor pairs are configured to connect to a first terminal of a first sub capacitor of the N−1 first sub capacitors and a first terminal of a second sub capacitor of the N−1 second sub capacitors respectively, for example, any two adjacent first sub power transistor pairs include a first pair of first sub power transistor pair and a second pair of first sub power transistor pair, a first terminal of one of the N−1 first sub capacitors is connected between two first sub power transistors of the first pair of first sub power transistor pair, a first terminal of one of the N−1 second sub capacitors is connected between two first sub power transistors of the second pair of first sub power transistor pair. 
     Any two adjacent second sub power transistor pairs are configured to connect to a first terminal of another first sub capacitor of the N−1 first sub capacitors and a first terminal of another second sub capacitor of the N−1 second sub capacitors respectively, for example, any two adjacent second sub power transistor pairs include a first pair of second sub power transistor pair and a second pair of second sub power transistor pair, a first terminal of another of the N−1 first sub capacitors is connected between two second sub power transistors of the first pair of second sub power transistor pair, and a first terminal of another of the N−1 second sub capacitors is connected between two second sub power transistors of the second pair of second sub power transistor pair. 
     The output terminal is connected to a 1-th first sub power transistor pair and a 1-th second sub power transistor pair respectively, a first terminal of one of the N−1 first sub capacitors is connected between two first sub power transistors of the 1-th first sub power transistor pair, and a first terminal of one of the N−1 second sub capacitors is connected between two second sub power transistors of the 1-th second sub power transistor pair. 
     All second terminals of the N−1 first sub capacitors are connected to the first node CFLA, and all second terminals of the N−1 second sub capacitors are connected to the second node CFLB. 
     For example, as shown in  FIG.  8   , the N first sub power transistors include a 1-th first sub power transistor, a 2-th first sub power transistor, . . . , a (N−1)-th first sub power transistor Q(N+3)A and a N-th first sub power transistor Q(N+4)A which are connected with each other in turn, the 1-th first sub power transistor is the fifth power transistor QSA, the 2-th first sub power transistor is the sixth power transistor Q 6 A, the fifth power transistor Q 5 A and the sixth power transistor Q 6 A form a 1-th first sub power transistor pair, the sixth power transistor Q 6 A and a first sub power transistor (no shown in  FIG.  8   ), which is adjacent to the sixth power transistor Q 6 A, form a 2-th first sub power transistor pair, . . . , the (N−1)-th first sub power transistor Q(N+3)A and the N-th first sub power transistor Q(N+4)A form a (N−1)-th first sub power transistor pair. The N−1 first sub capacitors include a 1-th first sub capacitor, a 2-th first sub capacitor, . . . , a (N−2)-th first sub capacitor and a (N−1)-th first sub capacitor, the 1-th first sub capacitor is the first capacitor OA, the 2-th first sub capacitor is the second capacitor C 2 B, when N is an even number, the (N−2)-th first sub capacitor is a first sub capacitor C(N−2)B, and the (N−1) first sub capacitor is a first sub capacitor C(N−1)A, and when N is an odd number, the (N−2)-th first sub capacitor is a first sub capacitor C(N−2)A, and the (N−1) first sub capacitor is a first sub capacitor C(N−1)B. 
     The input terminal of the biphasic dickson switched capacitor converter is connected to the output terminal of the biphasic dickson switched capacitor converter through the N-th first sub power transistor Q(N+4)A, the (N−1)-th first sub power transistor Q(N+3)A, . . . , the 2-th first sub power transistor and the 1-th first sub power transistor respectively. 
     The N second sub power transistors include a 1-th second sub power transistor, a 2-th second sub power transistor, . . . , a (N−1)-th second sub power transistor Q(N+3)B and a N-th second sub power transistor Q(N+4)B which are connected with each other in turn, the 1-th second sub power transistor is the ninth power transistor QSB, the 2-th second sub power transistor is the tenth power transistor Q 6 B, the ninth power transistor Q 5 B and the tenth power transistor Q 6 B form a 1-th second sub power transistor pair, the sixth power transistor Q 6 B and a second sub power transistor (no shown in  FIG.  8   ), which is adjacent to the sixth power transistor Q 6 B, form a 2-th second sub power transistor pair, . . . , the (N−1)-th second sub power transistor Q(N+3)B and the N-th second sub power transistor Q(N+4)B form a (N−1)-th second sub power transistor pair. The N−1 second sub capacitors include a 1-th second sub capacitor, a 2-th second sub capacitor, . . . , a (N−2)-th second sub capacitor and a (N−1)-th second sub capacitor, the 1-th second sub capacitor is the fourth capacitor C 1 B, the 2-th second sub capacitor is the fifth capacitor C 2 B, when N is an even number, the (N−2)-th second sub capacitor is a second sub capacitor C(N−2)A, and the (N−1) second sub capacitor is a second sub capacitor C(N−1)B, and when N is an odd number, the (N−2)-th second sub capacitor is a second sub capacitor C(N−2)B, and the (N−1) second sub capacitor is a second sub capacitor C(N−1)A. 
     The input terminal of the biphasic dickson switched capacitor converter is connected to the output terminal of the biphasic dickson switched capacitor converter through the N-th second sub power transistor Q(N+4)B, the (N−1)-th second sub power transistor Q(N+3)B, . . . , the 2-th second sub power transistor and the 1-th second sub power transistor respectively. 
     The second terminal of the second power transistor Q 2 , second terminals of all the first sub capacitors and the first terminal of the first power transistor Q 1  are connected as a first node CFLA, and the second terminal of the third power transistor Q 3 , second terminals of all the second sub capacitors and the first terminal of the fourth power transistor Q 4  are connected as a second node CFLB. 
     The first terminal of the first capacitor OA is connected between the fifth power transistor Q 5 A and the sixth power transistor Q 6 A of the 1-th first sub power transistor pair, and the first terminal of the second capacitor C 2 B is connected to between the tenth power transistor Q 6 B and the second sub power transistor, which is adjacent to the tenth power transistor Q 6 B, of the 2-th second sub power transistor pair. When the N is an even number, a first terminal of the (N−1)-th first sub capacitor is connected between the (N−1)th first sub power transistor Q(N+3)A and the N-th first sub power transistor Q(N+4)A of the (N−1)-th first sub power transistor pair, and when the N is an odd number, the first terminal of the (N−1)-th first sub capacitor is connected between the (N−1)th second sub power transistor Q(N+3)B and the N-th second sub power transistor Q(N+4)B of the (N−1)-th second sub power transistor pair. 
     The first terminal of the fourth capacitor C 1 B is connected between the ninth power transistor Q 5 B and the tenth power transistor Q 6 B of the 1-th second sub power transistor pair, and the first terminal of the fifth capacitor C 2 A is connected to between the sixth power transistor Q 6 A and the first sub power transistor, which is adjacent to the sixth power transistor Q 6 A, of the 2-th first sub power transistor pair. When the N is an even number, a first terminal of the (N−1)-th second sub capacitor is connected between the (N−1)th second sub power transistor Q(N+3)B and the N-th second sub power transistor Q(N+4)B of the (N−1)-th second sub power transistor pair, and when the N is an odd number, the first terminal of the (N−1)-th second sub capacitor is connected between the (N−1)th first sub power transistor Q(N+3)A and the N-th first sub power transistor Q(N+4)A of the (N−1)-th first sub power transistor pair. 
     In all embodiments of the present application, all the power transistors and all the sub power transistors are switch transistors, for example, P-type transistors or N-type transistors. All the power transistors and all the sub power transistors of the first branch and the second branch are primary power transistors, and each primary power transistor has a parasitic capacitor. 
     The auxiliary circuit shown in  FIG.  2    includes four NMOS and an inductor, and it can be realized that the electric charges at one branch can be transferred to another branch by controlling the auxiliary circuit during the dead time when all the primary power transistors are turned off, so as to realize zero voltage switching of all the primary power transistors and reducing switching loss. Besides the auxiliary circuit of  FIG.  2   , various other types of circuits can also perform the function of the ZVS of all the primary power transistors. For example, a variety of different auxiliary circuits are shown in  FIG.  9   . 
     As shown in  FIG.  9   , the auxiliary circuit includes a thirteenth power transistor, a fourteenth power transistor, an fifteenth power transistor, a sixteenth power transistor and an inductor; a first terminal of the thirteenth power transistor is connected to the first node CFLA of the first branch, a second terminal of the thirteenth power transistor is connected to a first terminal of the fourteenth power transistor and a first terminal of the inductor, and a second terminal of the fourteenth power transistor is grounded; a second terminal of the inductor is connected to a first terminal of the fifteenth power transistor and a first terminal of the sixteenth power transistor, a second terminal of the fifteenth power transistor is grounded, and a second terminal of the sixteenth power transistor is connected to the second node CFLB of the second branch. When the thirteenth power transistor, the fourteenth power transistor, the fifteenth power transistor and the sixteenth power transistor are N-type power transistors, the auxiliary circuit is shown by an auxiliary ZVS circuit A of  FIG.  9   , when the thirteenth power transistor and the sixteenth power transistor are P-type power transistors, and the fourteenth power transistor and the fifteenth power transistor are N-type power transistors, the auxiliary circuit is shown by an auxiliary ZVS circuit D of  FIG.  9     
     According to another embodiment of the present application, as shown in  FIG.  9   , the auxiliary circuit includes a thirteenth power transistor, a sixteenth power transistor, a first diode, a second diode and an inductor; a first terminal of the thirteenth power transistor is connected to the first node CFLA of the first branch, a second terminal of the thirteenth power transistor is connected to a first terminal of the first diode and a first terminal of the inductor, a second terminal of the first diode is grounded, the first terminal of the first diode is a cathode, and the second terminal of the first diode is an anode; a second terminal of the inductor is connected to a first terminal of the second diode and a first terminal of the sixteenth power transistor, a second terminal of the second diode is grounded, the first terminal of the second diode is a cathode, the second terminal of the second diode is an anode, and a second terminal of the sixteenth power transistor is connected to the second node CFLB of the second branch. When the thirteenth power transistor and the sixteenth power transistor are N-type power transistors, the auxiliary circuit is shown by an auxiliary ZVS circuit B of  FIG.  9   , when the thirteenth power transistor and the sixteenth power transistor are P-type power transistors, the auxiliary circuit is shown by an auxiliary ZVS circuit E of  FIG.  9   . 
     According to another embodiment of the present application, as shown in  FIG.  9   , the auxiliary ZVS circuit includes a thirteenth power transistor, a sixteenth power transistor and inductor, a first terminal of the thirteenth power transistor is connected to the first node CFLA of the first branch, a second terminal of the thirteenth power transistor is connected to a first terminal of the inductor, a second terminal of the inductor is connected to a first terminal of the sixteenth power transistor, and a second terminal of the sixteenth power transistor is connected to the second node CFLB of the second branch. When the thirteenth power transistor and the sixteenth power transistor are N-type power transistors, the auxiliary circuit is shown by an auxiliary ZVS circuit C of  FIG.  9   , when the thirteenth power transistor and the sixteenth power transistor are P-type power transistors, the auxiliary circuit is shown by an auxiliary ZVS circuit F of  FIG.  9   . 
     Since the specific implementation modes of the circuit structure are various, and the corresponding control methods are also various, they cannot be exemplified one by one in the present application, after those skilled in the art understand the contents of the present application, various modifications, variations or equivalents of the above described examples may be readily conceived, but still be controlled by the limitations set forth in the claims and any equivalents thereof