Direct current conversion circuit and vehicle-mounted charger

Abstract

The utility model discloses a DC conversion circuit and a vehicle-mounted charger, and relates to the technical field of power conversion, and the DC conversion circuit comprises a boost module which is used for carrying out the boost processing of an input voltage under the condition that the received input voltage is smaller than a preset voltage, and obtaining a target voltage; and the input ends of the power conversion modules are connected in parallel and then connected to the output end of the boosting module, and the power conversion modules are used for carrying out voltage conversion on the target voltage so as to output multiple paths of power supply voltages. According to the invention, through a mode that the pre-stage boost module is combined with the plurality of post-stage power conversion modules, full-power output of the DC conversion circuit under the condition of different input voltages is realized, the DC conversion circuit is applied to a power architecture of a new energy automobile, and full-power output of a vehicle-mounted DC-DC converter under the condition of wide-range input voltages is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power conversion, and particularly relates to a direct current conversion circuit and a vehicle-mounted charger. BACKGROUND

[0002] In the power architecture of a new energy vehicle, in order to adapt to the input voltage platform requirements of different vehicle models, a vehicle-mounted DC-DC converter needs to be able to adapt to a wide input voltage range. However, in the case of a wide range of input voltages, the vehicle-mounted DC-DC converter of a single-stage isolation conversion architecture cannot maintain full power output. Therefore, the problem of how to ensure that the vehicle-mounted DC-DC converter can maintain full power output in the case of a wide range of input voltages needs to be solved. CONTENT OF THE UTILITY MODEL

[0003] The main purpose of the present application is to provide a direct current conversion circuit and a vehicle-mounted charger, which aims to solve the technical problem of how to ensure that the vehicle-mounted DC-DC converter can maintain full power output in the case of a wide range of input voltages.

[0004] To achieve the above-mentioned purpose, the present application provides a direct current conversion circuit, which comprises:

[0005] A boost module, configured to perform boost processing on an input voltage to obtain a target voltage in the case that the received input voltage is less than a preset voltage.

[0006] A plurality of power conversion modules, input ends of the plurality of power conversion modules being connected to an output end of the boost module in parallel, configured to perform voltage conversion on the target voltage to output a plurality of power supply voltages.

[0007] In an embodiment, the power conversion module comprises a symmetric half-bridge unit, a transformer and a rectifier unit connected in sequence.

[0008] In an embodiment, the rectifier unit comprises a full-bridge rectifier circuit or a full-wave rectifier circuit.

[0009] In an embodiment, the symmetric half-bridge unit comprises:

[0010] The symmetric half-bridge unit comprises a first capacitor, a second capacitor, a first switch tube and a second switch tube.

[0011] The first end of the first capacitor and the first end of the first switch tube are connected to form a first input end of a symmetrical half-bridge unit, the first output end of the symmetrical half-bridge unit is connected to the first output end of the boost module, the first end of the second capacitor and the first end of the second switch tube are connected to form a second input end of the symmetrical half-bridge unit, the second output end of the symmetrical half-bridge unit is connected to the second output end of the boost module, the second end of the first capacitor and the second end of the second capacitor are connected to form a first output end of the symmetrical half-bridge unit, the first input end of the transformer, the second end of the first switch tube and the second end of the second switch tube are connected to form a second output end of the symmetrical half-bridge unit, the second input end of the transformer.

[0012] In an embodiment, the rectifying unit is a full-bridge rectifying circuit, and the full-bridge rectifying circuit comprises a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube.

[0013] The first end of the third switch tube and the first end of the fifth switch tube are connected to form a first output end of the full-bridge rectifying circuit, the second end of the third switch tube and the first end of the fourth switch tube are connected to form a first input end of the full-bridge rectifying circuit, the second end of the fifth switch tube and the first end of the sixth switch tube are connected to form a second input end of the full-bridge rectifying circuit, and the second end of the fourth switch tube and the second end of the sixth switch tube are connected to form a second output end of the full-bridge rectifying circuit.

[0014] The transformer comprises a first primary winding and a first secondary winding, the first end and the second end of the first primary winding form a first input end and a second input end of the transformer respectively, the first end of the secondary winding forms a first output end of the transformer connected to the first input end of the full-bridge rectifying circuit, and the second end of the secondary winding forms a second output end of the transformer connected to the second input end of the full-bridge rectifying circuit.

[0015] In an embodiment, the rectifying unit is a full-wave rectifying circuit, and the full-wave rectifying circuit comprises a seventh switch tube and an eighth switch tube.

[0016] The transformer comprises a second primary winding, a second secondary winding and a third secondary winding.

[0017] The two ends of the second primary winding form a first input end and a second input end of the transformer respectively, the first end of the second secondary winding is connected to the first end of the seventh switch tube, the second end of the second secondary winding and the first end of the third secondary winding are connected to form a first output end of the full-wave rectifying circuit, the second end of the third secondary winding is connected to the first end of the eighth switch tube, and the second end of the seventh switch tube and the second end of the eighth switch tube are connected to form a second output end of the full-wave rectifying circuit.

[0018] In an embodiment, the boost module adopts a boost circuit.

[0019] In an embodiment, the direct-current conversion circuit further comprises:

[0020] The control module is connected with the control end of each switch tube in the voltage boosting module and the plurality of power conversion modules, and is used for controlling the on / off time of each switch tube in the voltage boosting module and the plurality of power conversion modules.

[0021] In an embodiment, the direct current conversion circuit further comprises a plurality of loads corresponding to the plurality of power conversion modules, and the plurality of loads are respectively connected to the output end of the corresponding power conversion module.

[0022] The application further provides a vehicle-mounted charger.

[0023] The direct current conversion circuit as described above.

[0024] The one or more technical solutions provided by the application have at least the following technical effects:

[0025] The technical solution of the application can boost the input voltage to obtain a target voltage when the received input voltage is less than a preset voltage through the front-stage voltage boosting module, and can convert the target voltage into a supply voltage through the plurality of rear-stage power conversion modules. When the input voltage of the voltage boosting module is low, the input voltage of the rear-stage power conversion module remains unchanged, so that the rear-stage power conversion module can not be affected by the input voltage of the front-stage voltage boosting module and can maintain full power output. Therefore, the direct current conversion circuit can maintain full power output under different input voltages through the combination of the front-stage voltage boosting module and the plurality of rear-stage power conversion modules, and can be applied to the power architecture of a new energy vehicle to ensure that the vehicle-mounted DC-DC converter can maintain full power output under a wide range of input voltages. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can be obtained from the structures shown in the drawings without creative labor.

[0027] Figure 1 The connection schematic diagram of the direct current conversion circuit provided by the application is shown in FIG. 1.

[0028] Figure 2 The circuit principle diagram of the power conversion module in the direct current conversion circuit provided by the application is shown in FIG. 2.

[0029] Figure 3 The circuit principle diagram of the power conversion module in the direct current conversion circuit provided by the application is shown in FIG. 2.

[0030] The objectives, functional features and advantages of the present application will be further described with reference to the embodiments in combination with the accompanying drawings. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0032] It should be noted that, in the present application, the terms "comprising", "containing" or any other variants thereof are intended to cover non-exclusive containing, so that the device or system comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such device or system. Without more limitation, the elements defined by the statement "comprising" do not exclude the presence of other identical elements in the device or system comprising the element.

[0033] In the present application, unless otherwise explicitly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense, for example, "connection" can be fixed connection, or detachable connection, or integral; can be mechanical connection, or electrical connection; can be direct connection, or indirect connection through an intermediate medium; can be internal connection of two elements or interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0034] In the present application, there are descriptions related to "first", "second" and the like, which are only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first" and "second" can explicitly or implicitly include at least one of the features.

[0035] In the present application, the suffixes such as "module", "component" or "unit" used to represent elements are only for the convenience of description of the present application, and have no specific meaning. Therefore, "module", "component" or "unit" can be used mixedly. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the fact that the technical solutions can be realized by those skilled in the art. When the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the scope of protection claimed by the present application.

[0036] In the power architecture of a new energy vehicle, in order to adapt to the input voltage platform requirements of different vehicle models, a vehicle-mounted DC-DC converter needs to be able to adapt to a wide input voltage range. The vehicle-mounted DC-DC converter usually adopts a single-stage isolation conversion architecture, but the vehicle-mounted DC-DC converter with a single-stage isolation conversion architecture cannot maintain full power output under a wide range of input voltages, and needs to reduce the output power and output voltage in the low-voltage section.

[0037] In addition, with the guidance of the lightweight design requirements and market cost competition pressure of new energy vehicles, the low-voltage storage battery is usually removed in the low-voltage power supply system of a new energy vehicle, and the output of the vehicle-mounted DC-DC converter is used to directly supply power to the low-voltage system. At this time, in order to realize multi-output, it is usually necessary to set up multiple independent DC-DC converters in the power architecture of a new energy vehicle, which is not conducive to the lightweight of the vehicle.

[0038] To solve the above technical problems, the application provides a direct current conversion circuit and a vehicle-mounted charger.

[0039] Please refer to Figure 1 The direct current conversion circuit provided by the application can include:

[0040] A boost module, configured to perform boost processing on the input voltage to obtain a target voltage when the received input voltage is less than a preset voltage;

[0041] A plurality of power conversion modules, the input ends of the plurality of power conversion modules being connected to the output end of the boost module in parallel, configured to perform voltage conversion on the target voltage to output a plurality of power supply voltages.

[0042] It should be noted that the direct current conversion circuit in the vehicle-mounted charger of a new energy vehicle is taken as an example for description. In the vehicle-mounted charger, the input voltage of the direct current conversion circuit is provided by the power battery of the new energy vehicle, and the input voltage of the direct current conversion circuit is different for different new energy vehicles. Therefore, the input voltage of the boost module has a wide range for different new energy electric vehicles. The boost module can perform boost processing on the input voltage to obtain a target voltage when the received input voltage is less than a preset voltage, and does not perform boost processing on the received input voltage when the received input voltage is greater than or equal to the preset voltage, and directly outputs the received input voltage to each power conversion module. The size of the preset voltage is the same as that of the target voltage, and the preset voltage can be determined according to the actual hardware structure of the boost module.

[0043] For example Figure 1As shown, the plurality of power conversion modules can include power conversion modules 1-N, N is greater than or equal to 2, the boost module can output a target voltage through the DC bus, that is, the input ends of the plurality of power conversion modules are connected to the output end of the boost module through the DC bus, wherein the voltage across the bus capacitor Cbus is the target voltage. The power conversion module can convert the target voltage into a power supply voltage required for the operation of the DC load to supply power to the load, so that the power supply voltage can be determined according to the operating voltage of the load connected to the power conversion module, and N can be determined according to the number of loads in the low-voltage system of the new energy vehicle.

[0044] It can be understood that the front-stage boost module can perform boost processing on the output voltage of the low-voltage section power battery to obtain a higher target voltage Vbus, thereby ensuring the input voltage stability of each power conversion module in the rear stage; so that each power conversion module does not need to reduce power or output voltage under different input voltages to ensure the reliability of the DC conversion circuit; and full voltage output and full power output of the DC conversion circuit can be realized within a larger input voltage range.

[0045] In this embodiment, the DC conversion circuit can further include a plurality of loads corresponding to the plurality of power conversion modules, and the plurality of loads are respectively connected to the output ends of the corresponding power conversion modules.

[0046] It should be noted that the power supply voltages output by the plurality of power conversion modules are used to supply power to the plurality of loads one by one. Among them, the output ends of each power conversion module can be connected to the corresponding load, that is, in actual operation, one power conversion module supplies power to one load.

[0047] In this embodiment, the boost module can adopt a Boost circuit.

[0048] It can be understood that the boost module can be implemented through a circuit with a boost function, for example, a bootstrap circuit, a Boost circuit, and a push-pull circuit. Preferably, the boost module is implemented through a Boost circuit.

[0049] In a feasible implementation manner, the power conversion module includes: a symmetric half-bridge unit, a transformer, and a rectifier unit which are electrically connected in sequence.

[0050] It should be noted that the symmetric half-bridge unit can convert the target voltage into an alternating voltage, the transformer can perform voltage transformation processing on the alternating voltage, and the rectifier unit can perform rectification processing on the alternating voltage after voltage transformation to obtain a power supply voltage.

[0051] It can be understood that the number of symmetrical half-bridge units, transformers and rectifier units in the direct current conversion circuit is the same. Among them, the symmetrical half-bridge units in different power conversion modules can be realized by the same circuit, and the rectifier units in different power conversion modules can be realized by the same circuit or different circuits.

[0052] In an example, in the case that the direct current conversion circuit includes two power conversion modules, one of the rectifier units in the two power conversion modules is realized by a full-bridge rectifier circuit and the other is realized by a full-wave rectifier circuit, so that the direct current conversion circuit can supply power to a first load with a relatively high supply voltage and a second load with a relatively low supply voltage at the same time, improving the applicability of the direct current conversion circuit.

[0053] In a feasible implementation, the rectifier unit can include a full-bridge rectifier circuit or a full-wave rectifier circuit.

[0054] It should be noted that the type of rectifier unit in the power conversion module can be determined according to the amplitude of the transformed alternating voltage. In the case that the amplitude of the transformed alternating voltage is relatively high, the full-bridge rectifier circuit can be used to rectify the transformed alternating voltage, and in the case that the amplitude of the transformed alternating voltage is relatively low, the full-wave rectifier circuit can be used to rectify the transformed alternating voltage. Thus, in actual use, the type of corresponding rectifier unit can be set according to the amplitude of the transformed alternating voltage output by each transformer.

[0055] Therefore, the embodiment provides a direct current conversion circuit. The input voltage is boosted by the pre-stage boost module in the case that the received input voltage is less than the preset voltage, and a target voltage is obtained. The target voltage is converted into a supply voltage by the plurality of power conversion modules in the rear stage. In the case that the input voltage of the boost module is low, the input voltage of the power conversion module in the rear stage remains unchanged, so that the power conversion module in the rear stage can not be affected by the input voltage of the boost module in the pre-stage, and the full power output is maintained. Thus, by combining the pre-stage boost module with the plurality of power conversion modules in the rear stage, the direct current conversion circuit can output full power in the case of different input voltages, and is applied to the power architecture of the new energy vehicle, so that the vehicle-mounted DC-DC converter can output full power in the case of a wide range of input voltages.

[0056] Moreover, the direct current conversion circuit of the embodiment is realized by the power conversion module through the symmetrical half-bridge unit, the transformer and the rectifier unit connected in sequence. Compared with setting a plurality of independent DC-DC converters in the power architecture of the new energy vehicle, the power conversion module has a smaller size, is more conducive to the lightweight of the vehicle when applied to the power architecture of the new energy vehicle, improves the power density of the vehicle-mounted DC-DC converter, and reduces the cost of the vehicle.

[0057] In an embodiment, the symmetrical half-bridge unit comprises:

[0058] The symmetrical half-bridge unit comprises a first capacitor C1, a second capacitor C2, a first switch Q1 and a second switch Q2.

[0059] The first end of the first capacitor C1 is connected to the first end of the first switch Q1 to form a first input end of the symmetrical half-bridge unit, the first end of the second capacitor C1 is connected to the first end of the second switch Q2 to form a second input end of the symmetrical half-bridge unit, the second end of the first capacitor C1 is connected to the second end of the second capacitor C2 to form a first output end of the symmetrical half-bridge unit, and the second end of the first switch Q1 is connected to the second end of the second switch Q2 to form a second output end of the symmetrical half-bridge unit.

[0060] It should be noted that, as shown in Figure 2 or Figure 3 The capacitor C1 and the capacitor C2 are connected in series and are connected in parallel with the bus capacitor Cbus to receive the target voltage output by the voltage boosting module. The switch Q1 and the switch Q2 are connected in series and are connected in parallel with the series-connected capacitor C1 and capacitor C2. The connection point of the capacitor C1 and the capacitor C2 forms a first output end of the symmetrical half-bridge unit, and the connection point of the switch Q1 and the switch Q2 forms a second output end of the symmetrical half-bridge unit.

[0061] It can be understood that the switches Q1 and Q2 can be Insulated Gate Bipolar Transistors (IGBT), Metal Oxide Semiconductor Field Effect Transistors (MOSFET) or Silicon Carbide Metal Oxide Semiconductor (SiC MOSFET), and preferably the switches Q1 and Q2 are MOSFETs.

[0062] In an embodiment, the rectifier unit is a full-bridge rectifier circuit, and the full-bridge rectifier circuit comprises a third switch Q3, a fourth switch Q4, a fifth switch Q5 and a sixth switch Q6.

[0063] The first end of the third switch tube Q3 and the first end of the fifth switch tube Q5 are connected together to form a first output end of the full-bridge rectifier circuit, the second end of the third switch tube Q3 and the first end of the fourth switch tube Q4 are connected together to form a first input end of the full-bridge rectifier circuit, the second end of the fifth switch tube Q5 and the first end of the sixth switch tube Q6 are connected together to form a second input end of the full-bridge rectifier circuit, and the second end of the fourth switch tube Q4 and the second end of the sixth switch tube Q6 are connected together to form a second output end of the full-bridge rectifier circuit.

[0064] The transformer T1 includes a first primary winding and a first secondary winding, the first end and the second end of the first primary winding form a first input end and a second input end of the transformer T1 respectively, the first end of the secondary winding forms a first output end of the transformer T1 connected to the first input end of the full-bridge rectifier circuit, and the second end of the secondary winding forms a second output end of the transformer T1 connected to the second input end of the full-bridge rectifier circuit.

[0065] It should be noted that, as shown in Figure 2 in the case of high demand for supply voltage, the power conversion module adopts a symmetric half-bridge + full-bridge rectifier structure, the transformer T1 includes a first primary winding and a first secondary winding, the first primary winding is connected to the symmetric half-bridge unit, and the first secondary winding is connected to the first input end and the second input end of the full-bridge rectifier circuit, the switch tube Q3 and the switch tube Q4 are connected in series in the full-bridge rectifier circuit, and the switch tube Q5 and the switch tube Q6 are connected in parallel to the series connection of the switch tube Q3 and the switch tube Q4, forming a first output end and a second output end of the full-bridge rectifier circuit, the common connection point of the switch tube Q3 and the switch tube Q4 forms a first input end of the full-bridge rectifier circuit, and the common connection point of the switch tube Q5 and the switch tube Q6 forms a second input end of the full-bridge rectifier circuit, the alternating voltage output by the symmetric half-bridge unit is subjected to voltage transformation and rectification to obtain the supply voltage.

[0066] It can be understood that the switch tubes Q3 to Q6 can be IGBT, MOSFET or SiC MOSFET, and preferably the switch tubes Q3 to Q6 are all MOS tubes.

[0067] In a possible implementation, the rectifier unit is a full-wave rectifier circuit, and the full-wave rectifier circuit includes a seventh switch tube Q7 and an eighth switch tube Q8.

[0068] The transformer T2 includes a second primary winding, a second secondary winding and a third secondary winding.

[0069] The two ends of the second primary winding form a first input end and a second input end of the transformer T2 respectively, the first end of the second secondary winding is connected with the first end of the seventh switch tube Q7, the second end of the second secondary winding is connected with the first end of the third secondary winding to form a first output end of the full-wave rectifier circuit, the second end of the third secondary winding is connected with the first end of the eighth switch tube Q8, and the second end of the seventh switch tube Q7 and the second end of the eighth switch tube Q8 are connected to form a second output end of the full-wave rectifier circuit.

[0070] It should be noted that, as shown in Figure 3 In the case of low demand for the supply voltage, when the power conversion module adopts the symmetric half-bridge + full-wave rectification structure, the transformer T2 includes a second primary winding, a second secondary winding and a third secondary winding, the second primary winding is connected with the symmetric half-bridge unit, and the second secondary winding and the third secondary winding are connected with the full-wave rectifier circuit, wherein the second end of the second secondary winding is connected with the first end of the third secondary winding to form a first output end of the full-wave rectifier circuit, the first end of the second secondary winding is connected with the first end of the switch tube Q7, the second end of the third secondary winding is connected with the first end of the switch tube Q8, and the second end of the switch tube Q7 and the second end of the switch tube Q8 are connected to form a second output end of the full-wave rectifier circuit. The alternating voltage output by the symmetric half-bridge unit is subjected to voltage transformation and rectification processing to obtain the supply voltage.

[0071] It can be understood that the switch tubes Q7 and Q8 can be IGBT, MOSFET or SiC MOSFET, and preferably the switch tubes Q7 and Q8 are MOS tubes.

[0072] In a feasible implementation, the direct current conversion circuit can further include:

[0073] The control module is connected with the control end of each switch tube in the voltage boosting module and the plurality of power conversion modules, and is used for controlling the on / off time of each switch tube in the voltage boosting module and the plurality of power conversion modules.

[0074] It should be noted that the control module can determine the turn-on time and turn-off time of each switch tube in the voltage boosting module according to the target voltage and the input voltage, and determine the turn-on time and turn-off time of each switch tube in the corresponding power conversion module according to the target voltage and the supply voltage.

[0075] Specifically, the control module can control the boost module to perform boost processing on the received input voltage according to the target voltage and the input voltage, and control the corresponding power conversion module to perform voltage conversion on the target voltage according to the target voltage and each supply voltage, in a case where it is detected that the input voltage received by the boost module is less than the preset voltage; and control the boost module to directly access each power conversion module with the received input voltage as the target voltage, and control the corresponding power conversion module to perform voltage conversion on the target voltage according to the target voltage and each supply voltage, in a case where it is detected that the input voltage received by the boost module is greater than or equal to the preset voltage. The control module can include a microcontroller or a single-chip microcomputer, etc.

[0076] Thus, the embodiment provides a DC conversion circuit. In a case where a required supply voltage is high, a symmetric half-bridge + full-bridge rectification structure is used to supply power to a load, compared with a sample full-bridge topology for voltage conversion of a target voltage, i.e., the load power supply requirement is met, the stress of MOS tubes in the full-bridge rectification circuit is reduced, the selection difficulty of the MOS tubes in the full-bridge rectification circuit is avoided, and the design cost of the DC conversion circuit is reduced. In a case where a required supply voltage is low, a symmetric half-bridge + full-wave rectification structure is used to supply power to a load, compared with a sample full-bridge topology for rectification of a supply voltage, i.e., the load power supply requirement is met, the number of MOS tubes used in the rectification circuit is reduced, the control complexity of the rectification circuit is simplified, and the cost of the DC conversion circuit is reduced.

[0077] In addition, the embodiment of the application further provides a vehicle-mounted charger. The vehicle-mounted charger can include:

[0078] The DC conversion circuit as described above.

[0079] It should be noted that the specific structure of the DC conversion circuit is referred to the above embodiments. Since the DC conversion circuit uses all the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0080] The above only describes exemplary embodiments of the application, and does not limit the patent scope of the application. Any equivalent structural transformation made by using the content of the specification and drawings, or direct / indirect application in other related technical fields is included in the patent protection scope of the application.

Claims

1. A direct current conversion circuit, characterized by The direct current conversion circuit comprises: a boost module, configured to perform boost processing on the input voltage to obtain a target voltage when the received input voltage is less than a preset voltage; a plurality of power conversion modules, input ends of the plurality of power conversion modules being connected to an output end of the boost module in parallel, configured to perform voltage conversion on the target voltage to output a plurality of power supply voltages.

2. The dc-to-dc conversion circuit of claim 1, wherein, The power conversion module comprises, in sequence, a symmetrical half-bridge unit, a transformer and a rectifier unit.

3. The dc-to-dc conversion circuit of claim 2, wherein, The rectifier unit comprises a full-bridge rectifier circuit or a full-wave rectifier circuit.

4. The dc-to-dc conversion circuit of claim 3, wherein, The symmetrical half-bridge unit comprises: The symmetrical half-bridge unit comprises a first capacitor, a second capacitor, a first switch tube and a second switch tube; a first end of the first capacitor is connected to a first end of the first switch tube to form a first input end of the symmetrical half-bridge unit, a first end of the second capacitor is connected to a first end of the second switch tube to form a second input end of the symmetrical half-bridge unit, a second end of the first capacitor is connected to a second end of the second capacitor to form a first output end of the symmetrical half-bridge unit connected to a first input end of the transformer, and a second end of the first switch tube is connected to a second end of the second switch tube to form a second output end of the symmetrical half-bridge unit connected to a second input end of the transformer.

5. The dc-to-dc conversion circuit of claim 4, wherein, The rectifier unit is a full-bridge rectifier circuit, and the full-bridge rectifier circuit comprises a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube; a first end of the third switch tube is connected to a first end of the fifth switch tube to form a first output end of the full-bridge rectifier circuit, a second end of the third switch tube is connected to a first end of the fourth switch tube to form a first input end of the full-bridge rectifier circuit, a second end of the fifth switch tube is connected to a first end of the sixth switch tube to form a second input end of the full-bridge rectifier circuit, and a second end of the fourth switch tube is connected to a second end of the sixth switch tube to form a second output end of the full-bridge rectifier circuit; The transformer comprises a first primary winding and a first secondary winding, a first end of the first primary winding forms a first input end of the transformer, a second end of the first primary winding forms a second input end of the transformer, a first end of the secondary winding forms a first output end of the transformer connected to the first input end of the full-bridge rectifier circuit, and a second end of the secondary winding forms a second output end of the transformer connected to the second input end of the full-bridge rectifier circuit.

6. The dc-to-dc conversion circuit of claim 4, wherein, The rectifier unit is a full-wave rectifier circuit, and the full-wave rectifier circuit comprises a seventh switch tube and an eighth switch tube; The transformer comprises a second primary winding, a second secondary winding and a third secondary winding. Two ends of the second primary winding respectively constitute a first input end and a second input end of the transformer, a first end of the second secondary winding is connected with a first end of the seventh switch tube, a second end of the second secondary winding is connected with a first end of the third secondary winding to constitute a first output end of the full-wave rectifier circuit, a second end of the third secondary winding is connected with a first end of the eighth switch tube, and a second end of the seventh switch tube and a second end of the eighth switch tube are connected together to constitute a second output end of the full-wave rectifier circuit.

7. The dc-to-dc conversion circuit of claim 1, wherein The boost module adopts a boost circuit.

8. The dc-to-dc conversion circuit according to any one of claims 1 to 7, wherein The direct current conversion circuit further comprises: A control module is connected with control ends of the switch tubes in the boost module and the power conversion modules, and is used for controlling on / off time of the switch tubes in the boost module and the power conversion modules.

9. The dc-to-dc conversion circuit of claim 8, wherein, The direct current conversion circuit further comprises a plurality of loads corresponding to the power conversion modules, and the loads are respectively connected to output ends of the corresponding power conversion modules.

10. An on-board charger, comprising: The vehicle-mounted charger comprises: The direct current conversion circuit according to any one of claims 1 to 9.

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