Safety protection circuit for dc / dc converter, dc / dc converter and electric vehicle

Abstract

The utility model relates to power conversion technical field especially relates to a kind of safety protection circuit for DC / DC converter, DC / DC converter and electric vehicle, wherein, the safety protection circuit for DC / DC converter, the DC / DC converter includes high voltage input end, low voltage output end and power conversion module;The input end of the power conversion module is connected with the high voltage input end;The output end of the power conversion module is connected with the low voltage output end;It further includes fusing device, and the fusing device is connected in series between the output of the power conversion module and low voltage output end.Such protection circuit is safe by fusing device.

Description

Technical Field

[0001] This utility model relates to the field of power conversion technology, and in particular to a safety protection circuit for a DC / DC converter, a DC / DC converter, and an electric vehicle. Background Technology

[0002] DC-DC converters are key power supply components in systems such as electric vehicles and communication equipment. In applications such as electric two-wheelers, their core function is to convert the high-voltage DC power (such as 48V, 60V, or 72V) from the power battery pack into stable low-voltage DC power of 12V / 6-10A, etc., to power low-voltage electrical appliances such as vehicle lights, instruments, and controllers.

[0003] To ensure reliability, existing DC / DC converters generally integrate functions such as input overvoltage / undervoltage protection, output overcurrent protection, and output short-circuit protection. However, existing technology has a fatal safety blind spot: when the high-voltage input terminal of the DC / DC converter is accidentally short-circuited to the low-voltage output terminal due to insulation damage, wiring harness friction, or other reasons, the high-voltage current will bypass the internal power conversion module and control unit and be directly applied to the low-voltage circuit.

[0004] Output filter capacitors in low-voltage circuits (typically electrolytic capacitors rated at 16V-35V) can break down, bulge, or even explode due to instantaneous exposure to voltages far exceeding their rated values. Simultaneously, the massive short-circuit current can burn out all connected low-voltage loads (such as lights and instruments) and wiring harnesses, easily igniting a vehicle fire. Existing protection circuits are completely ineffective against this type of fault because the fault point is outside their detection range.

[0005] Therefore, there is an urgent need in this field for an effective, reliable, and cost-effective security protection solution for this specific failure mode. Utility Model Content

[0006] The purpose of this invention is to provide a safety protection circuit for DC / DC converters, DC / DC converters, and electric vehicles, in order to solve the problem of component damage and fire risk caused by accidental short circuit from the high-voltage input terminal to the low-voltage output terminal in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: Firstly, this utility model provides a safety protection circuit for a DC / DC converter, the DC / DC converter including a high-voltage input terminal, a low-voltage output terminal, and a power conversion module; the input terminal of the power conversion module is connected to the high-voltage input terminal, and its output terminal is connected to the low-voltage output terminal. The core of this safety protection circuit is that it also includes a fuse, which is connected in series between the output of the power conversion module and the low-voltage output terminal.

[0008] Preferably, the low-voltage output terminal includes an output filter capacitor; the fuse is disposed between the output of the power conversion module and the output filter capacitor.

[0009] Preferably, the fuse is a disposable fuse.

[0010] Preferably, the fuse is a resettable fuse.

[0011] Preferably, the fuse has preset rated voltage, rated current, and breaking capacity. The rated voltage is higher than the normal maximum output voltage of the DC / DC converter; the rated current is higher than the maximum continuous output current of the DC / DC converter; and the breaking capacity is configured to fuse when a short-circuit current is generated from the maximum voltage at the high-voltage input terminal.

[0012] Preferably, the power conversion module includes an output rectifier element, and the fuse is connected in series at the output terminal of the output rectifier element.

[0013] Furthermore, the power conversion module is a flyback converter, and the output rectifier element is an output rectifier diode.

[0014] Preferably, the power conversion module is a step-down converter, the power conversion module includes an energy storage inductor, and the fuse is connected in series at the output terminal of the energy storage inductor.

[0015] Secondly, the present invention provides a DC / DC converter that includes the safety protection circuit described in any one of the first aspects above.

[0016] Thirdly, this utility model provides an electric vehicle that includes the DC / DC converter described in the second aspect above.

[0017] Compared with the prior art, the beneficial effects of this utility model include: Highly targeted: It precisely solves the fatal fault mode of "short circuit from high voltage input to low voltage output" that existing technologies cannot protect against, filling a safety gap.

[0018] High reliability: As a passive mechanical protection element, the fuse operates decisively and reliably, unaffected by control circuit failures.

[0019] Rapid response: For huge short-circuit currents, the fuse can melt quickly within milliseconds, cutting off the circuit before components and wiring harnesses are damaged.

[0020] Low cost: The added components cost very little, yet can greatly enhance the safety value and reliability of the product.

[0021] Simple to implement: No complex circuits or software algorithms are required; simply add a fuse to the existing PCB layout. Easy to manufacture and maintain. Attached Figure Description

[0022] The above and other objects, features, and advantages of this application will become more apparent from the more detailed description of the embodiments of this application in conjunction with the accompanying drawings. The drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same components or steps.

[0023] Figure 1 This is a schematic diagram of the structure of a safety protection circuit for a DC / DC converter provided in one embodiment of this application.

[0024] Figure 2 This is a schematic diagram of the structure of a safety protection circuit for a DC / DC converter provided in another embodiment of this application.

[0025] Figure 3 This is a schematic diagram of the structure of a safety protection circuit for a DC / DC converter provided in another embodiment of this application.

[0026] Figure label: 1-High voltage input terminal, 2-Power conversion module, 3-Fuse device, 4-Low voltage output terminal. Detailed Implementation

[0027] The technical solution of this utility model will now be clearly and completely described with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection of this utility model.

[0028] Please refer to Figure 1. This embodiment provides a safety protection circuit for a DC / DC converter. The DC / DC converter includes a high-voltage input terminal 1, a low-voltage output terminal 4, and a power conversion module 2. The input terminal of the power conversion module 2 is connected to the high-voltage input terminal 1 and is used to receive high-voltage DC power provided by the power battery pack. The output terminal of the power conversion module is connected to the low-voltage output terminal 4 and is used to convert the high-voltage DC power into low-voltage DC power to power the lamps and instruments connected to the low-voltage output terminal.

[0029] In the solution provided in this application, the safety protection circuit includes a fuse 3, which is a slow-breaking type one-time fuse with a rated voltage of 32V, a rated current of 15A, and a breaking capacity of 500A. It is connected in series between the output of the power conversion module and the low-voltage output terminal.

[0030] When the 72V line at the high-voltage input terminal short-circuits to the 12V line at the low-voltage output terminal due to insulation failure, the fault current (approximately 144A, calculated from the 72V voltage and the equivalent resistance of the low-voltage circuit) will flow through the fuse. Since the fault current is much greater than the fuse's rated current of 15A, the fuse will quickly melt within 5ms, cutting off the path from the power conversion module output to the low-voltage output terminal. This prevents the fault current from damaging the downstream load and wiring harness at the low-voltage output terminal, and also prevents high-voltage electricity from being directly applied to low-voltage components, thus preventing a fire.

[0031] The core of the above solution is the series connection of a fuse between the output of the power conversion module and the entire low-voltage output terminal. This location is crucial to this invention; it places the fuse on the inevitable path of the high-voltage fault current. When a high-voltage short circuit accidentally reaches the low-voltage output terminal, the massive fault current will immediately flow through the fuse and activate it, thereby fundamentally cutting off the continuous flow of the fault current and protecting all components on the low-voltage side. This solution has a simple structure but precisely solves a specific safety problem that has long been neglected in existing technologies.

[0032] Furthermore, the low-voltage output terminal includes an output filter capacitor, and the location of the fuse is precisely defined as "between the output of the power conversion module and the output filter capacitor." The output filter capacitor is the most vulnerable and easily exploded component on the entire low-voltage side. This claim directly targets this core hazardous component for protection, ensuring that in the event of a fault, the fuse can cut off the circuit before the high voltage reaches the output filter capacitor, achieving the most direct and effective protection.

[0033] In some embodiments, the fuse is a one-time fuse (FS). A one-time fuse is a passive protection device that contains a molten metal (such as a copper or silver alloy), which conducts electricity when working normally, and breaks the circuit when a fault occurs due to Joule heating. Once broken, it cannot be restored on its own and requires replacement with a new component to restore the circuit function.

[0034] One-time fuses are characterized by fast operating speed (milliseconds), strong breaking capacity (capable of interrupting short-circuit currents of hundreds of amperes), extremely low cost (a few cents to a few yuan), and immunity to electromagnetic interference. They are suitable for scenarios requiring high reliability and where manual maintenance is permissible after a fault, such as electric two-wheelers (high-frequency use, requiring professional repair after a fault). The one-time fuse is still connected in series between the power conversion module output and the low-voltage output terminal (or the output filter capacitor), only the component type is limited to a one-time structure.

[0035] In some embodiments, the fuse is a resettable fuse. A resettable fuse typically refers to a polymer positive temperature coefficient (PPTC) device, whose core structure is a polymer matrix filled with conductive particles. Under normal operation, it exhibits a low resistance state (milliohms). In the event of a fault, the temperature rises, causing a polymer phase transition and the conductive particle network to break, resulting in a sudden increase in resistance to the kiloohm level to limit the current. Once the fault is cleared and the temperature decreases, the resistance automatically returns to its low resistance state without requiring component replacement.

[0036] Resettable fuses feature self-recovery after a fault and require no manual maintenance, making them suitable for scenarios with high maintenance convenience requirements and where faults are often transient, such as short-distance electric two-wheelers for home use (faults may be caused by temporary metal debris connections, and power can be restored automatically after the fault). The resettable fuse is connected in series between the power conversion module output and the low-voltage output terminal (or the output filter capacitor), with only the component type limited to a resettable structure. In this way, the "fuse device" provides a second feasible solution, complementing the one-time fuse solution, covering the usage needs of different scenarios, while solving the maintenance cost problem of "replacing after a fault" with one-time fuses, thus improving user convenience.

[0037] Specifically, the fuse has a preset rated voltage, rated current, and breaking capacity; wherein, the rated voltage is higher than the normal maximum output voltage of the DC / DC converter; the rated current is higher than the maximum continuous output current of the DC / DC converter; and the breaking capacity is used to interrupt the short-circuit current generated by the maximum voltage from the high-voltage input terminal.

[0038] Rated voltage: The highest voltage that the fuse can withstand for a long period of time. It must be higher than the normal maximum output voltage of the DC / DC converter (e.g., in a 12V output system, the rated voltage of the fuse is ≥32V) to avoid damage to the fuse due to voltage stress during normal operation.

[0039] Rated current: The maximum current that the fuse can conduct for a long time without melting must be higher than the maximum continuous output current of the DC / DC converter (e.g., in a 10A output converter, the rated current of the fuse is ≥12A) to ensure that it will not melt accidentally under full load or load surge.

[0040] Breaking capacity: The maximum short-circuit current that the fuse can safely cut off under rated voltage must be able to cut off the short-circuit current (usually several hundred amperes) formed at the low-voltage output terminal by the maximum voltage at the high-voltage input terminal (such as 72V), so as to avoid secondary accidents such as arcing and component explosion caused by the inability to cut off the current when the fuse is broken.

[0041] By defining three core parameters of the fuse device, the problem of "parameter mismatch leading to protection failure or malfunction" is solved—ensuring that the fuse device "does not malfunction" during normal operation and "can reliably disconnect" during faults, providing parameter basis for the practical application of the fuse device in claims 1-4 and ensuring the effectiveness of the protection function.

[0042] Parameter requirements are the basis for the functioning of fuse devices. If the rated voltage is insufficient, the fuse device may break down during normal operation; if the rated current is insufficient, the normal load current will cause false melting; if the breaking capacity is insufficient, it will be unable to cut off large currents during faults, all of which will lead to protection failure. Therefore, this claim is a key limitation on the performance of the fuse device.

[0043] It should be noted that the core of this application is the design of the fuse device; the selection of other components is not limited. For details, please refer to [reference needed]. Figure 2 and Figure 3 .

[0044] Furthermore, the power conversion module includes an output rectifier element, and the fuse is connected in series at the output terminal of the output rectifier element. The function of the "output rectifier element" is to convert the AC or pulsating DC generated during the power conversion process into smooth DC. Common types are rectifier diodes and synchronous rectifier MOSFETs, such as the output rectifier diode in a flyback converter. The energy transfer path inside the power conversion module is "high voltage input → power switch → energy storage element (such as transformer, inductor) → output rectifier element → output terminal". The fuse is connected in series at the output terminal of the output rectifier element (i.e., the negative / drain terminal of the output rectifier element is connected to one end of the fuse, and the other end of the fuse is connected to the low-voltage output terminal), forming a path of "output rectifier element → fuse → low-voltage output terminal".

[0045] The output rectifier element is the "last stage of energy conversion" in the power conversion module. Placing the fuse at its output ensures that all current output from the power conversion module (including normal current and fault current) flows through the fuse. Regardless of whether the fault occurs in the external wiring harness or inside the module (such as an inter-turn short circuit in the transformer), the fault current will flow through the output rectifier element to the fuse, ensuring that the protection action covers both "external fault" and "internal fault" scenarios, thus expanding the protection range. This solution is applicable to power conversion topologies that include output rectifier elements, such as flyback, forward, and bridge rectifier DC / DC converters, providing a unified protection element layout scheme for DC / DC converters with different topologies. In some embodiments, the power conversion module is a flyback converter, and the output rectifier element is an output rectifier diode.

[0046] The specific topology of the power conversion module is defined as a "flyback converter" (a common isolated DC / DC topology that achieves input-output isolation through a high-frequency transformer, suitable for electric two-wheeled vehicle scenarios with high safety requirements). At the same time, the specific type of the output rectifier element is defined as an "output rectifier diode" (the core rectifier component on the secondary side of the flyback converter, which rectifies the AC current induced on the secondary side of the transformer into DC current). The secondary circuit path of a flyback converter is "transformer secondary winding → output rectifier diode → fuse → output filter capacitor → low-voltage output terminal". The anode of the output rectifier diode is connected to the transformer secondary winding, the cathode is connected to one end of the fuse, and the other end of the fuse is connected to the positive terminal of the output filter capacitor. This configuration, tailored to the topology characteristics of the flyback converter, clarifies the specific form of the output rectifier element and the location of the fuse, resolving the problem of "unclear protection element layout under different topologies." A flyback converter fault may originate from an inter-turn short circuit between the transformer primary and secondary windings (equivalent to a high-voltage input short circuit to the low-voltage output). In this case, the fault current flows through the transformer secondary winding and the output rectifier diode to the fuse. After the fuse blows, it cuts off the circuit, protecting subsequent components and ensuring the effectiveness of the protection function under the flyback topology.

[0047] In some embodiments, the power conversion module is a step-down converter, the power conversion module includes an energy storage inductor, and the fuse is connected in series at the output terminal of the energy storage inductor.

[0048] The "step-down converter" is a non-isolated DC / DC topology that uses an energy storage inductor to step down the voltage. It has a simple structure, high efficiency, and is widely used in electric two-wheelers.

[0049] The main circuit path of a buck converter is "high voltage input terminal → power switch → energy storage inductor → fuse → output filter capacitor → low voltage output terminal". One end of the energy storage inductor is connected to the power switch / freewheeling diode, and the other end is directly connected to one end of the fuse. The other end of the fuse is connected to the positive terminal of the output filter capacitor. Given the topology characteristics of the buck converter, the energy storage inductor is the "core node for energy transfer." During normal operation, current flows to the output terminal through the energy storage inductor. During a fault, the fault current also flows to the output terminal through the energy storage inductor. Connecting the fuse in series at the output terminal of the energy storage inductor ensures that both normal and fault currents flow through the fuse, thus not affecting normal energy transfer and quickly cutting off the path during a fault, solving the protection layout problem in buck converter topologies.

[0050] This application also provides a DC / DC converter adapted to electric two-wheeled vehicles, which integrates the safety protection circuit provided in the above embodiments. Specifically, the DC / DC converter includes input positive and negative terminals (VIN+, VIN-), a power conversion module, a control unit, and output positive and negative terminals (VOUT+, VOUT-). The core of the safety protection circuit lies in connecting a fuse (FS) in series in the low-voltage output circuit on the printed circuit board (PCB) inside the DC / DC converter. The fuse (i.e., the fuse device) is preferably installed after the power conversion module and before the output filter capacitor (C_out). More specifically, it is connected in series between the rear end of the output rectifier element and the positive terminal of the output filter capacitor.

[0051] Specifically, the solution provided in this application addresses the problem of a DC / DC converter's input high-voltage power supply (VIN+) accidentally short-circuiting to its output low-voltage circuit (VOUT+) due to insulation damage, wiring harness friction, accidental impact, or other reasons. Therefore, in order to ensure that the fuse can be used on the short-circuited circuit, the fuse is positioned as close as possible to the low-voltage output terminal.

[0052] The selection parameters for fuses are crucial and must meet the following conditions: 1. Rated voltage: Must be higher than the maximum output voltage of the DC / DC converter (e.g., for a 12V system, select a fuse with a rated voltage of 32V or higher).

[0053] 2. Rated current: slightly higher than the maximum continuous output current of the DC / DC converter (for example, a 10A converter can be equipped with a 12A or 15A slow-blow fuse) to ensure that it will not blow accidentally during normal operation and can withstand short-term surge currents (such as motor starting current).

[0054] 3. Breaking capacity: It must have sufficient breaking capacity to safely cut off the potentially huge short-circuit current from the high-voltage power battery.

[0055] When a fault occurs where the high voltage at the input (VIN+) short-circuits to the output (VOUT+), the high voltage is applied directly to the fuse (FS) and the output filter capacitor (C_out) through the short-circuit point. Because the fault current is enormous and far exceeds the rated current of the fuse (FS), the fuse (FS) will melt rapidly in a very short time (usually milliseconds), thus physically and completely cutting off the current path from the fault point to the downstream low-voltage load.

[0056] After the fuse blows, the following key protections are achieved: 1. Protect the output filter capacitor: Cut off the current to the capacitor, preventing the capacitor from exploding due to overvoltage. 2. Protect low-voltage loads and wiring harnesses: Cuts off the current to all low-voltage electrical appliances such as lamps and instruments, preventing them from burning out due to overcurrent or overvoltage. 3. Curb the development of faults: Limit the impact of faults to a very small area inside the DC / DC converter (i.e., the fuse itself), effectively preventing the occurrence of "car burnout" accidents. With this configuration, the solution provided in this application has the following advantages: 1. Highly targeted: It precisely addresses fatal failure modes that existing protection solutions cannot cover, filling security gaps. 2. High reliability: The fuse is a passive mechanical protection element that does not require external power supply, is not affected by control circuit failure, and operates resolutely and reliably. 3. Rapid response: For such huge short-circuit currents, the fuse melts very quickly, cutting off the circuit before components and wiring harnesses are damaged. 4. Low cost: The added fuse components have extremely low cost, hardly increasing the material cost of the product, but greatly enhancing its safety value. 5. Simple implementation: No complex circuits or software algorithms are required. Simply add a fuse holder and fuse to the existing PCB layout. It is easy to produce and maintain. This application also provides an electric vehicle that includes the aforementioned DC / DC converter.

[0057] Specifically, this embodiment provides an electric vehicle, including a power battery pack, low-voltage electrical appliances, and the DC / DC converter described in Embodiment 5; wherein, the power battery pack is a 72V / 20Ah lithium battery pack, and its output terminal is connected to the high-voltage input terminal (VIN+, VIN-) of the DC / DC converter; the low-voltage electrical appliances include LED headlights, an LCD instrument panel, and a turn horn, with a total power ≤120W, and their input terminals are connected to the low-voltage output terminal (VOUT+, VOUT-) of the DC / DC converter.

[0058] The power supply logic of this electric two-wheeler is as follows: the power battery pack outputs 72V high voltage to the DC / DC converter, which converts it to 12V low voltage to power low voltage electrical appliances; when the DC / DC converter experiences a "high voltage input to low voltage output short circuit" fault, its internal fuse (FS) quickly blows, cutting off the fault path, preventing low voltage electrical appliances from burning out and the power battery pack from overcurrent, preventing fire accidents, and improving the driving safety of the electric two-wheeler.

[0059] Actual testing showed that when the electric two-wheeler simulated a "high-voltage input short circuit to low-voltage output" fault, the average fusing time of the fuse (FS) was 4.2ms, which is much faster than the breakdown time of the output filter capacitor (C_out) (about 20ms) and the burn-out time of the low-voltage electrical appliances (about 15ms). This can 100% prevent capacitor explosion and load damage, and the protection effect is reliable.

[0060] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A safety protection circuit for a DC / DC converter, the DC / DC converter comprising a high-voltage input terminal, a low-voltage output terminal, and a power conversion module; the input terminal of the power conversion module is connected to the high-voltage input terminal; the output terminal of the power conversion module is connected to the low-voltage output terminal; characterized in that, Also includes: Fuses The fuse is connected in series between the output and the low-voltage output terminal of the power conversion module.

2. The safety protection circuit for a DC / DC converter according to claim 1, characterized in that, The low-voltage output terminal includes: an output filter capacitor; The fuse is located between the output of the power conversion module and the output filter capacitor.

3. The safety protection circuit for a DC / DC converter according to claim 1, characterized in that, The fuse is a disposable fuse.

4. The safety protection circuit for a DC / DC converter according to claim 1, characterized in that, The fuse is a resettable fuse.

5. The safety protection circuit for a DC / DC converter according to claim 1, characterized in that, The fuse has a preset rated voltage, rated current and breaking capacity; The rated voltage is higher than the normal maximum output voltage of the DC / DC converter; The rated current is higher than the maximum continuous output current of the DC / DC converter; The breaking capacity is used to interrupt the short-circuit current generated by the maximum voltage from the high-voltage input terminal.

6. The safety protection circuit for a DC / DC converter according to claim 1, characterized in that, The power conversion module includes an output rectifier element, and the fuse is connected in series at the output terminal of the output rectifier element.

7. The safety protection circuit for a DC / DC converter according to claim 6, characterized in that, The power conversion module is a flyback converter, and the output rectifier element is an output rectifier diode.

8. The safety protection circuit for a DC / DC converter according to claim 1, characterized in that, The power conversion module is a step-down converter, and the power conversion module includes an energy storage inductor. The fuse is connected in series at the output terminal of the energy storage inductor.

9. A DC / DC converter, characterized in that, Includes a safety protection circuit for a DC / DC converter as described in any one of claims 1 to 8.

10. An electric vehicle, characterized in that, Includes the DC / DC converter as described in claim 9.

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