USB charger and power control circuit for USB charger

Abstract

A USB charger and a power supply control circuit for the USB charger are provided. The power supply control circuit includes: a digital control unit configured to receive a constant voltage control target value and a constant current control target value, generate a constant voltage reference control signal based on the constant voltage control target value, and generate a first code value and a second code value based on the constant voltage control target value and the constant current control target value, respectively; a current-type digital-to-analog converter configured to generate a constant voltage feedback control current for controlling a constant voltage output of the USB charger based on the first code value; a constant voltage setting module configured to generate an output constant voltage reference signal based on the constant voltage reference control signal; a voltage-type digital-to-analog converter configured to generate an output constant current reference signal based on the second code value; and a current compensation unit configured to generate a constant current feedback control current for controlling a constant current output of the USB charger based on the output constant voltage reference signal, the output constant current reference signal, and the output current feedback signal.

Description

Technical Field

[0001] The present invention relates to the field of circuits, and more particularly to a USB charger and a power control circuit for the USB charger. Background Art

[0002] Currently, most mobile electronic devices are charged using single-port or multi-port Universal Serial Bus (USB) chargers based on the fast charging communication protocol. These USB chargers need to support step adjustment of constant voltage or constant current output according to the requirements of the fast charging communication protocol. Summary of the Invention

[0003] A power control circuit for a USB charger according to an embodiment of the present invention includes: a digital control unit configured to receive a constant voltage control target value and a constant current control target value, generate a constant voltage reference control signal based on the constant voltage control target value, and generate a first code value and a second code value based on the constant voltage control target value and the constant current control target value, respectively; a current-type digital-to-analog converter configured to generate a constant voltage feedback control current for controlling a constant voltage output of the USB charger based on the first code value; a constant voltage setting module configured to generate an output constant voltage reference signal based on the constant voltage reference control signal; a voltage-type digital-to-analog converter configured to generate an output constant current reference signal based on the second code value; and a current compensation unit configured to generate a constant current feedback control current for controlling a constant current output of the USB charger based on the output constant voltage reference signal, the output constant current reference signal, and an output current feedback signal representing the output current of the USB charger.

[0004] A USB charger according to an embodiment of the present invention includes one or more of the above-mentioned power control circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the accompanying drawings, in which:

[0006] Figure 1 A schematic block diagram of a conventional single-port USB charger providing constant voltage / constant current output is shown.

[0007] Figure 2 A schematic block diagram of a conventional single-port USB charger providing constant voltage output is shown.

[0008] Figure 3 A schematic block diagram of a traditional multi-port USB charger is shown.

[0009] Figure 4 An exemplary block diagram of a multi-port USB charger according to an embodiment of the present invention is shown.

[0010] Figure 5 Shown Figure 4An example implementation of a current compensation unit is shown.

[0011] Figure 6 An exemplary block diagram of another multi-port USB charger according to an embodiment of the present invention is shown.

[0012] Figure 7 An exemplary block diagram of a single-port USB charger according to an embodiment of the present invention is shown.

[0013] Figure 8 FIG. 4 shows an exemplary block diagram of another multi-port USB charger according to an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement, and improvement of elements, components, and algorithms without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and techniques are not shown to avoid causing unnecessary ambiguity to the present invention.

[0015] Figure 1 The schematic block diagram of a conventional single-port USB charger providing constant voltage / constant current output is shown. Figure 1 In the single-port USB charger 100 shown, the fast charging protocol chip 102 internally generates an output constant voltage / constant current reference signal Vref_cv / Vref_cc and samples the output voltage / current feedback signal vfb / ifb through the VFB / IFB pin. Inside the fast charging protocol chip 102, the feedback compensation operational amplifier CV_EA / CC_EA generates an output constant voltage / constant current compensation signal based on the output constant voltage / constant current reference signal Vref_cv / Vref_cc and the output voltage / current feedback signal vbf / ifb, and drives the optocoupler through the OPTO pin based on the output constant voltage / constant current compensation signal to control the constant voltage / constant current output of the AC-DC (AC / DC) conversion module 104. Here, the fast charging protocol chip 102 has more integrated functions and higher cost, requires more than 10 pins, and is usually implemented in a QFN16 package.

[0016] Figure 2 The schematic block diagram of a conventional single-port USB charger providing constant voltage output is shown. Figure 2In the single-port USB charger 200 shown, the fast charging protocol chip 202 internally generates a fixed voltage output constant voltage reference signal Vref_cv = 1.24v; within the fast charging protocol chip 202, the digital control unit generates a code value corresponding to the constant voltage control target value, and the current-type digital-to-analog converter (DAC) converts the code value corresponding to the constant voltage control target value into a constant voltage feedback control current Ifb_cv and outputs it to the resistor Ru through the VFB pin, thereby changing the voltage divider ratio of the output voltage feedback signal Vfb obtained by the fast charging protocol chip 202 through the VFB pin relative to the output voltage of the AC / DC conversion module 204 (i.e., the output voltage of the single-port USB charger 200). The feedback compensation operational amplifier CV_EA generates an output constant voltage compensation signal based on the output constant voltage reference signal Vref_cv and the output voltage feedback signal Vfb, and drives the optocoupler through the OPTO pin based on the output constant voltage compensation signal to control the constant voltage output of the AC / DC conversion module 204. Here, the pins of the fast charging protocol chip 202 can be reduced to 9, and can be implemented using a lower-cost ESOP8 package. However, because it does not include an additional constant current loop and IFB pin for current loop compensation, it cannot control the constant current output of the AC / DC conversion module 204.

[0017] Figure 3 Figure 2 shows a schematic block diagram of a traditional multi-port USB charger. Figure 3 In the multi-port USB charger 300 shown, the VFB pin of the fast charging protocol chip 302 is connected to the VFB pins of the DC-DC (DC / DC) conversion modules 304-1 and 304-2. Within the fast charging protocol chip 302, the digital control unit generates a code value corresponding to the constant voltage control target value. The current-mode DAC converts the code value corresponding to the constant voltage control target value into a constant voltage feedback control current Ifb_cv and outputs it to the resistor Ru through the VFB pin. This changes the voltage divider ratio of the output voltage feedback signal Vfb obtained by the DC / DC conversion modules 304-1 / 304-2 through the VFB pin sampling relative to the output voltage of the DC / DC conversion modules 304-1 / 304-2, thereby indirectly controlling the constant voltage output of the DC / DC conversion modules 304-1 and 304-2. However, because the DC / DC conversion modules 304-1 and 304-2 already have feedback compensation operational amplifiers CV_EA integrated inside, the fast charging protocol chip 302 cannot control the constant current output of the DC / DC conversion modules 304-1 and 304-2 by adding additional IFB pins and integrating current compensation operational amplifiers internally.

[0018] In view of the above situation, a USB charger and a power control circuit for a USB charger according to an embodiment of the present invention are proposed, wherein the power control circuit can achieve constant voltage / constant current control for the USB charger by reusing the same pin of the fast charging protocol chip.

[0019] Figure 4 FIG. 1 shows an example block diagram of a multi-port USB charger according to an embodiment of the present invention. Figure 4 As shown, the multi-port USB charger 400 includes a fast charging protocol chip 402 and a DC / DC conversion module 404, wherein the fast charging protocol chip 402 includes a power control circuit 1000, and the DC / DC conversion module 404 includes a feedback compensation operational amplifier CV_EA. The power control circuit 1000 controls the constant voltage / constant current output of the DC / DC conversion module 404 by controlling the output voltage / current feedback signal Vfb_cv / Vfb_cc obtained by sampling the VFB pin of the DC / DC conversion module 404 relative to the output voltage of the DC / DC conversion module 404.

[0020] like Figure 4 As shown, the power supply control circuit 1000 includes a digital control unit 1002, a current-mode DAC 1004, a constant voltage setting unit 1006, a voltage-mode DAC 1008, and a current compensation unit 1010, wherein: the digital control unit 1002 is configured to receive a constant voltage control target value and a constant current control target value from an external source (e.g., a CC1 / CC2 / DP / NP control unit), generate a constant voltage reference control signal based on the constant voltage control target value, and generate a first code value and a second code value corresponding to the constant voltage control target value and the constant current control target value, respectively, based on the constant voltage control target value and the constant current control target value; the current-mode DAC 1004 is configured to generate a constant voltage feedback control current Ifb_cv for controlling the constant voltage output of the DC / DC conversion module 404 based on the first code value corresponding to the constant voltage control target value; the constant voltage setting module 1006 is configured to generate an output constant voltage reference signal Vref_cv based on the constant voltage reference control signal; the voltage-mode DAC 1008 is configured to generate an output constant current reference signal Vref_cc based on a second code value corresponding to the constant current control target value. The current compensation unit 1010 is configured to generate a constant current feedback control current Ifb_cc for controlling the constant current output of the DC / DC converter module 404 based on the output constant voltage reference signal Vref_cv, the output constant current reference signal Vref_cc, and the output current feedback signal Vfb_cc representing the output current of the DC / DC converter module 404. The output voltage and output current of the DC / DC converter module 404 are the output voltage and output current of the multi-port USB charger 400 at the USB port corresponding to the DC / DC converter module.

[0021] like Figure 4As shown, the constant voltage feedback control current Ifb_cv and the constant current feedback control current Ifb_cc can be output to the outside of the fast charging protocol chip 402 through the same pin of the fast charging protocol chip 402. Specifically, the constant voltage / constant current feedback control current Ifb_cv / Ifb_cc can be output to the resistor Ru through the VIFB pin of the fast charging protocol chip 402 to change the voltage divider ratio of the output voltage / current feedback signal Vfb_cv / Vfb_cc obtained by the DC / DC conversion module 404 through the VFB pin sampling relative to the output voltage of the DC / DC conversion module 404, thereby indirectly controlling the constant voltage / constant current output of the DC / DC conversion module 404.

[0022] like Figure 4 As shown, in some embodiments, when the output current of the DC / DC conversion module 404 is less than the constant current control target value, the power control circuit 1000 operates in a constant voltage control mode (i.e., controls the constant voltage output of the DC / DC conversion module 404); when the output current of the DC / DC conversion module 404 is greater than or equal to the constant current control target value, the power control circuit 1000 operates in a constant current control mode (i.e., controls the constant current output of the DC / DC conversion module 404).

[0023] It should be noted that the multi-port USB charger 400 actually includes more than one DC / DC converter module 404 and more than one power control circuit 1000 corresponding to each DC / DC converter module 404 (there is typically a one-to-one correspondence between the DC / DC converter module 404 and the power control circuit 1000). For the sake of simplicity and convenience, only one DC / DC converter module 404 and one power control circuit 1000 are shown and described here.

[0024] like Figure 4 As shown, in some embodiments, the constant voltage control process implemented by the power supply control circuit 1000 is as follows: the digital control unit 1002 generates a first code value corresponding to the constant voltage control target value, and the current-type DAC 1004 converts the first code value corresponding to the constant voltage control target value into a constant voltage feedback control current Ifb_cv, and outputs the voltage feedback control current Ifb_cv to the resistor Ru through the VIFB pin to change the voltage divider ratio of the output voltage feedback signal Vfb_cv obtained by the DC / DC conversion module 404 through the VFB pin sampling relative to the output voltage of the DC / DC conversion module 404, thereby indirectly controlling the constant voltage output of the DC / DC conversion module 404.

[0025] like Figure 4As shown, in some embodiments, the digital control unit 1002 can also be configured to generate a third code value corresponding to the difference between the constant-voltage control target update value and the constant-voltage control target value based on the difference between the constant-voltage control target update value and the constant-voltage control target value; the current-type DAC 1004 can also be configured to generate a constant-voltage feedback control current Ifb_cv based on the third code value corresponding to the difference between the constant-voltage control target update value and the constant-voltage control target value. For example, when the DC / DC conversion module 404 operates in a constant voltage output mode and the resistance of the resistor Ru is fixed at 100kohm, when it is necessary to control the output voltage of the DC / DC conversion module 404 from 5V to 20V (that is, the constant voltage control target value is 5V, and the constant voltage control target update value is 20V), the digital control unit 1002 can generate a code value corresponding to the difference ΔV=20V-5V=15V between the constant voltage control target update value and the constant voltage control target value, and the current-type DAC 1004 can convert the code value corresponding to the difference ΔV=15V into a constant voltage feedback control current Ifb_cv=ΔV / Ru=15V / 100kohm=150uA. At this time, the constant voltage feedback control current Ifb_cv flows into the fast charging protocol chip 402 through the VIFB pin. Conversely, when the constant voltage control target update value is less than the constant voltage control target value, the constant voltage feedback control current Ifb_cv flows out of the fast charging protocol chip 402 from the VIFB pin.

[0026] like Figure 4As shown, in some embodiments, the constant current control process implemented by the power control circuit 1000 is as follows: Assuming that the sampling signal Isense of the output current Io of the DC / DC converter module 404 is Isense = Io / k (k is typically a value in the range of 500 to 3000), the output current feedback signal Vfb_cc = Isense*Rcs = (Io*Rcs) / k. When the output current feedback signal Vfb_cc is less than the output constant current reference signal Vref_cc, the output current of the DC / DC converter module 404 is less than the constant current control target value, the constant current control portion of the power control circuit 1000 is inoperative (i.e., the power control circuit 1000 operates in constant voltage control mode), and the constant current feedback control current Ifb_cc = 0. When the output current feedback signal Vfb_cc is greater than or equal to the output constant current reference signal Vref_cc, the output current of the DC / DC conversion module 404 is greater than or equal to the constant current control target value, and the constant current control part in the power control circuit 1000 controls the constant current output of the DC / DC conversion module 404 (that is, the power control circuit 1000 operates in constant current control mode), and the constant current feedback control current Ifb_cc>0. The constant current feedback control current Ifb_cc is output to the outside of the fast charging protocol chip 402 through the VIFB pin to control the constant current output of the DC / DC conversion module 404. Here, a resistor R1 is connected between the VIFB pin of the fast charging protocol chip 402 and the VFB pin of the DC / DC conversion module 404 to reduce the current loop gain, and a capacitor C1 is connected between the VIFB pin of the fast charging protocol chip 402 and the ground to serve as a current loop compensation capacitor. The resistor R1 and the capacitor C1 do not affect the magnitude of the constant current output by the DC / DC conversion module 404.

[0027] like Figure 4As shown, in some embodiments, the digital control unit 1002 can also be configured to generate a fourth code value corresponding to the difference between the constant voltage control target value and the output voltage target value based on the difference between the constant voltage control target value and the output voltage target value, wherein the output voltage target value is the product of the constant current output target value and the output load impedance of the DC / DC conversion module 404; the voltage-type DAC 1008 can also be configured to generate an output constant current reference signal Vref_cc based on the fourth code value corresponding to the difference between the constant voltage control target value and the output voltage target value. For example, assuming that the constant current control target value of the DC / DC conversion module 404 is 3A, and the resistance value of the resistor Ru is fixed at 100kohm; when the output voltage of the DC / DC conversion module 404 is fixed at 20V (that is, the constant voltage control target value is 20V), the output load impedance Rload1 = 20V / 3A = 6.67ohm; when the output load impedance is instantly reduced to Rload2 = 3.33ohm, the output current Io of the DC / DC conversion module 404 = 20V / 3.33ohm = 6A, and the output current Io of the DC / DC conversion module 404 = 20V / 3.33ohm = 6A. The source control circuit 1000 switches from the constant voltage control mode to the constant current control mode; the digital control unit 1002 generates a code value corresponding to the difference between the constant voltage control target value 20V and the output voltage target value Vo=Rload2*3A=10V, so that the constant current feedback control current Ifb_cc=ΔV / Ru=10V / 100kohm=100uA flows out from the VIFB pin of the fast charging protocol chip 402, thereby stabilizing the output voltage of the DC / DC conversion module 404 at 10V and the output current at 3A.

[0028] Figure 5 Shown Figure 4 An example implementation of the current compensation unit is shown in FIG. Figure 5 As shown, in some embodiments, the current compensation unit 1010 is further configured to: generate a voltage compensation indication signal Vcomp_cv using the operational amplifier EA2 and the gain amplifier Gm1 based on the output voltage characterization signal Vin_fb characterizing the output voltage of the DC / DC conversion module 404 and the output constant voltage reference signal Vref_cv; generate a current compensation indication signal Vcomp_cc using the operational amplifier EA1 based on the voltage compensation indication signal Vcomp_cv and the output constant current reference signal Vref_cc; and generate a constant current feedback control current Ifb_cc using the gain amplifier Gm2 based on the current compensation indication signal Vcomp_cc and the output current feedback signal Vfb_cc.

[0029] It should be noted that, in addition to obtaining the output current feedback signal Vfb_cc through the sampling resistor Rcs built into the fast charging protocol chip 402 , the output current feedback signal Vfb_cc can also be obtained through an external detection resistor of the fast charging protocol chip 402 . Figure 6 FIG. 1 shows an example block diagram of another multi-port USB charger according to an embodiment of the present invention. Figure 6 In the multi-port USB charger 600 shown, the output current feedback signal Vfb_cc = Rcs'*Io*Ka, where Rcs' is the resistance of the external detection resistor Rcs' of the fast charging protocol chip 602, Io is the output current of the DC / DC converter module 604, and Ka is the amplification factor of the operational amplifier EA3 inside the fast charging protocol chip 602. The working principle of the power control circuit 1000 in the multi-port USB charger 600 is the same as that in the multi-port USB charger 400, and will not be repeated here. It should be understood that by connecting the detection resistor Rcs' in series between the power output pin (i.e., the VBULK pin) of the DC / DC converter module 604 and ground, the output current feedback signal Vfb_cc can also be obtained through the detection resistor Rcs'.

[0030] Figure 7 An example block diagram of a single-port USB charger according to an embodiment of the present invention is shown. Figure 7 In the illustrated single-port USB charger 700, the power control circuit 1000 may be included in the fast-charge protocol chip 702 and may change the voltage divider ratio of the output voltage / current feedback signal Vfb_cv / Vfb_cc sampled by the fast-charge protocol chip 702 via the VIFB pin relative to the output voltage of the AC / DC converter module 704 (i.e., the output voltage of the single-port USB charger 700). This allows the fast-charge protocol chip 702 to generate an output constant-voltage / constant-current compensation signal based on the output constant-voltage / constant-current reference signal Vref_cv / Vref_cc and the output voltage / current feedback signal Vfb_cv / Vfb_cc. Based on the output constant-voltage / constant-current compensation signal, the power control circuit 1000 drives an optocoupler via the OPTO pin to control the constant-voltage / constant-current output of the AC / DC converter module 704. The operating principle of the power control circuit 1000 in the single-port USB charger 700 is the same as that in the multi-port USB charger 400 and will not be further described here.

[0031] Figure 8 FIG. 1 shows an example block diagram of another multi-port USB charger according to an embodiment of the present invention. Figure 8 In the multi-port USB charger 800 shown, the power control circuit 1000 can be included in the fast charging protocol chip 802, and can change the voltage divider ratio of the output voltage / current feedback signal Vfb_cv / Vfb_cc obtained by the DC / DC conversion module 804-1 / 804-2 through VFB pin sampling relative to the output voltage of the DC / DC conversion module 804-1 / 804-2, thereby indirectly controlling the constant voltage / constant current output of the DC / DC conversion modules 804-1 and 804-2.

[0032] and Figure 3 Compared to the multi-port USB charger 300 shown, Figure 8 The illustrated multi-port USB charger 800 has the following advantages: 1) When USB1 or USB2 is plugged into a terminal device for charging, the corresponding power switch Q1 or Q2 is turned on, and enable signals EN1 and EN2 control the DC / DC converter modules 804-1 and 804-2 to be inoperative. The AC / DC converter module 906 then directly powers the terminal device. This eliminates the power consumption associated with the DC / DC converter modules 804-1 and 804-2, thereby achieving low standby power consumption and high power conversion efficiency (including light-load efficiency, heavy-load efficiency, and average efficiency) for the multi-port USB charger 800. 2) When the total output power of the multi-port USB charger 800 is 65W, the first terminal device plugged into one of the USB ports is powered by the AC / DC conversion module 906 and is therefore allocated an output power of 45W. The other terminal device plugged into the other USB port is powered by the DC / DC conversion module 804-1 / 804-2 and is therefore allocated an output power of 20W. Therefore, the DC / DC conversion modules 804-1 / 804-2 only need to be designed for 20W power (the selection requirements for the power devices related to the DC / DC conversion modules 804-1 and 804-2 are relatively low. On the contrary, Figure 3 The two DC / DC conversion modules 304 - 1 and 304 - 2 in the multi-port USB charger 300 shown need to support an output power of 65 W.

[0033] The present invention may be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithms described in the specific embodiments may be modified without departing from the basic spirit of the present invention. Therefore, the present embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the invention is defined by the appended claims rather than the foregoing description, and all modifications coming within the meaning and scope of equivalents of the claims are intended to be included within the scope of the present invention.

Claims

1. A power control circuit for a USB charger, comprising: a digital control unit configured to receive a constant voltage control target value and a constant current control target value, generate a constant voltage reference control signal based on the constant voltage control target value, and generate a first code value and a second code value based on the constant voltage control target value and the constant current control target value, respectively; a current-type digital-to-analog converter configured to generate a constant-voltage feedback control current for controlling a constant-voltage output of the USB charger based on the first code value; a constant voltage setting module, configured to generate an output constant voltage reference signal based on the constant voltage reference control signal; a voltage-type digital-to-analog converter, configured to generate an output constant-current reference signal based on the second code value; as well as A current compensation unit is configured to generate a constant current feedback control current for controlling the constant current output of the USB charger based on the output constant voltage reference signal, the output constant current reference signal, and an output current feedback signal representing the output current of the USB charger, wherein the output end of the current compensation unit is connected to the output end of the current-type digital-to-analog converter.

2. The power supply control circuit according to claim 1, wherein: The power control circuit is configured to control the constant voltage output of the USB charger when the output current of the USB charger is less than the constant current control target value, and to control the constant current output of the USB charger when the output current of the USB charger is greater than or equal to the constant current control target value.

3. The power control circuit according to claim 1, wherein: The digital control unit is further configured to generate a third code value based on a difference between the constant voltage control target update value and the constant voltage control target value, and The current-type digital-to-analog converter is further configured to generate the constant-voltage feedback control current based on the third code value.

4. The power control circuit according to claim 1, wherein: The digital control unit is further configured to generate a fourth code value based on a difference between the constant voltage control target value and an output voltage target value, wherein the output voltage target value is a product of the constant current output target value and an output load impedance of the USB charger, and The voltage-type digital-to-analog converter is further configured to generate the output constant-current reference signal based on the fourth code value.

5. The power supply control circuit according to claim 1, wherein: The USB charger includes only one AC / DC conversion module. The output voltage and output current of the AC / DC conversion module are the output voltage and output current of the USB charger. The constant voltage or constant current feedback control current is used to control the voltage divider ratio of the output voltage or current feedback signal sampled by the fast charging protocol chip relative to the output voltage of the AC / DC conversion module.

6. The power supply control circuit according to claim 1, wherein: The USB charger includes multiple DC / DC conversion modules. The output voltage and output current of the DC / DC conversion module associated with the power control circuit among the multiple DC / DC conversion modules are the output voltage and output current of the USB charger. The constant voltage or constant current feedback control current is used to control the voltage divider ratio of the output voltage or current feedback signal sampled by the DC / DC conversion module relative to the output voltage of the DC / DC conversion module.

7. The power supply control circuit according to claim 1, wherein: The current compensation unit is further configured to: generating a voltage compensation indication signal using a first operational amplifier and a first gain amplifier based on an output voltage characterizing signal characterizing an output voltage of the USB charger and the output constant voltage reference signal; generating a current compensation indication signal using a second operational amplifier based on the voltage compensation indication signal and the output constant current reference signal; as well as Based on the current compensation indication signal and the output current feedback signal, the constant current feedback control current is generated by using a second gain amplifier.

8. A USB charger comprising one or more power control circuits according to any one of claims 1 to 7.

9. The USB charger as claimed in claim 8, further comprising an AC / DC conversion module. 10 . The USB charger according to claim 9 , further comprising a plurality of DC / DC conversion modules, wherein the number of the DC / DC conversion modules is equal to the number of the power control circuits.

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