CN212012175U

CN212012175U - Load power supply circuit

Info

Publication number: CN212012175U
Application number: CN202020504117.4U
Authority: CN
Inventors: 魏开林; 赵建坤; 陈中元
Original assignee: Ninebot Beijing Technology Co Ltd
Current assignee: Ninebot Beijing Technology Co Ltd
Priority date: 2020-04-08
Filing date: 2020-04-08
Publication date: 2020-11-24
Anticipated expiration: 2030-04-08

Abstract

The application discloses load supply circuit, the circuit includes: a power supply, a load and a first branch circuit; the first end of the power supply is connected with the first end of the load, the second end of the load is connected with the first end of the first branch circuit, and the second end of the first branch circuit is connected with the second end of the power supply; the load comprises a capacitor, and the first branch circuit comprises a first switch and at least one Positive Temperature Coefficient (PTC) resistor; under the condition that the first switch is in an on state, the power supply, the first branch circuit and the load form a first loop, the power supply charges a capacitor in the load through the first branch circuit, so that the voltage at two ends of the capacitor reaches a set voltage threshold, and the at least one PTC resistor in the first branch circuit is used for limiting the current of the first loop.

Description

Load power supply circuit

Technical Field

The embodiment of the application relates to the field of circuits, in particular to a load power supply circuit.

Background

In power battery systems, the internal resistance of the battery is generally low, while the load connected to the power battery system generally has a relatively large capacitance; due to the existence of the capacitor in the load, when the power battery system is used for supplying power to the load, after the power battery system is communicated with the load, impact current can occur in a loop formed by the power battery system and the load, and the phenomena of starting, ignition, damage to devices and the like of components in the loop formed by the power battery system and the load are caused.

Disclosure of Invention

In order to solve the above technical problem, an embodiment of the present application provides a load power supply circuit.

The load power supply circuit that this application embodiment provided includes: a power supply, a load and a first branch circuit; the first end of the power supply is connected with the first end of the load, the second end of the load is connected with the first end of the first branch circuit, and the second end of the first branch circuit is connected with the second end of the power supply; the load comprises a capacitor, and the first branch comprises a first switch and at least one Positive Temperature Coefficient (PTC) resistor;

under the condition that the first switch is in an on state, the power supply, the first branch circuit and the load form a first loop, the power supply charges a capacitor in the load through the first branch circuit, so that the voltage at two ends of the capacitor reaches a set voltage threshold, and the at least one PTC resistor in the first branch circuit is used for limiting the current of the first loop.

In an optional embodiment of the present application, the circuit further includes: a second branch in parallel with the first branch; the second branch comprises a second switch;

the second switch is in a switch-on state after the voltage at two ends of the capacitor reaches the set voltage threshold; and under the condition that the second switch is in an on state, the power supply, the second branch circuit and the load form a second loop, and the power supply supplies power to the load through the second branch circuit.

In an optional embodiment of the present application, a total pre-charge energy of the at least one PTC resistor is N times a maximum capacitance energy of a capacitor in the load, and a value of N is greater than 1.

In an optional embodiment of the present application, the value of N ranges from 3 to 20.

In an optional embodiment of the present application, the first branch includes a PTC resistor, and when the first switch is in an on state, if a value of a resistance value of the PTC resistor is an initial resistance value, a current value of the first loop is less than or equal to a rated current of the load.

In an optional embodiment of the present application, when the first branch includes a plurality of PTC resistors, and the first switch is in an on state, if a resistance value of each of the plurality of PTC resistors is a corresponding initial resistance value, a current value of the first loop is less than or equal to a rated current of the load; wherein, a plurality of PTC resistance is the parallel structure.

In an alternative embodiment of the present application, for each of the at least one PTC resistor, the curie point temperature of each PTC resistor is in the range of 80 ℃ to 120 ℃.

In an optional embodiment of the present application, the first branch further includes a diode; the diode is in series with the first switch and the at least one PTC resistor for preventing current of the first loop from flowing from the second end of the power supply to the first end of the power supply.

In an alternative embodiment of the present application, the first branch further comprises a first protection element, and the first protection element is connected in series with the first switch and the at least one PTC resistor;

the first protection element is in an off state when the current of the first loop exceeds a first current threshold; the value of the first current threshold is M1 times of the rated current of the load, and the value of M1 is greater than 1.

In an alternative embodiment of the present application, a second protection element is provided between the first terminal of the power source and the first terminal of the load;

the second protection element is in an off state when the current of the first loop or the second loop exceeds a second current threshold; and the value of the second current threshold is M2 times of the rated current of the load, and the value of M2 is larger than that of M1.

According to the technical scheme of the embodiment of the application, the load power supply circuit is provided, and the circuit comprises: a power supply, a load and a first branch circuit; the first end of the power supply is connected with the first end of the load, the second end of the load is connected with the first end of the first branch circuit, and the second end of the first branch circuit is connected with the second end of the power supply; the load comprises a capacitor, and the first branch circuit comprises a first switch and at least one Positive Temperature Coefficient (PTC) resistor; under the condition that the first switch is in an on state, the power supply, the first branch circuit and the load form a first loop, the power supply charges a capacitor in the load through the first branch circuit, so that the voltage at two ends of the capacitor reaches a set voltage threshold, and the at least one PTC resistor in the first branch circuit is used for limiting the current of the first loop. Therefore, when the power battery system is used for supplying power to a load, after the first switch of the first branch circuit is switched on, and the first loop generates impact current, the temperature of the PTC resistor is rapidly increased due to the fact that the current flowing through the PTC resistor is instantly increased to a large value, and the resistance value of the PTC resistor is also rapidly increased under the condition, so that the impact current in a loop formed by the power battery system and the load is reduced, and negative effects of starting ignition, damage to devices and the like of the components in the loop formed by the power battery system and the load due to the impact current are avoided; in addition, the inherent characteristics of the PTC resistor can effectively and reliably protect the working conditions of overcurrent, overheating and the like generated in the operation process of the circuit, the circuit is simple, the cost is low, and the volume of the pre-charging circuit can be reduced; in addition, the first branch circuit comprising the PTC resistor is used for charging the capacitor in the load, so that the voltage at two ends of the capacitor in the load reaches a set voltage threshold value, the capacitor in the load can be quickly and stably charged, and the situation that the impact current can not occur when the power supply is switched to other branch circuits to supply power to the load can be ensured.

Drawings

Fig. 1 is a first schematic structural diagram of a load power supply circuit according to an embodiment of the present disclosure;

fig. 2 is a schematic structural diagram of a load power supply circuit according to an embodiment of the present disclosure;

fig. 3 is a schematic structural diagram three of a load power supply circuit according to an embodiment of the present application;

fig. 4 is a fourth schematic structural diagram of a load power supply circuit according to an embodiment of the present application.

Detailed Description

So that the manner in which the features and elements of the present embodiments can be understood in detail, a more particular description of the embodiments, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings.

In a power battery system, because the internal resistance of a battery is very small, and a load (such as a motor driver) generally has a large capacitance, when the power battery system is connected with the load and the power battery system is used for supplying power to the load, when a circuit is started, the current of a loop formed between the power battery system and the load can reach hundreds of amperes or even thousands of amperes, a starting ignition phenomenon can occur to a switch or a connector in the loop, and the power battery system, the load and other components in the loop can be damaged.

In order to solve the problems, in the related art, a pre-charging circuit is additionally arranged between a power battery system and a load, the pre-charging circuit comprises a switch element and a fixed resistor, in the early stage of utilizing the power battery system to supply power to the load, a loop between the power battery system and the load is firstly switched on through the switch element in the pre-charging circuit, the current in the loop is limited through the fixed resistor, the power battery system firstly charges a capacitor in the load through the pre-charging circuit, and a main loop is started and the pre-charging circuit is switched off after the voltage of the load rises to a certain degree, so that the impact current generated by directly switching on the main loop is avoided. When the scheme is adopted, the adopted fixed resistor is generally a conventional winding, the resistor is small in pulse power and large in size, and if the special ceramic pulse resistor is adopted, the cost of components is increased; in addition, on the occasion with higher requirement on the reliability of the circuit, an additional overload protection circuit needs to be added to the fixed resistor, so that the cost and the complexity of the circuit are obviously improved; moreover, after the switching element in the pre-charging circuit is broken down, the switching element fails, which can also cause the potential safety hazards of thermal runaway of the battery cell and overheating of components in the circuit, and the safety and the reliability are low.

In order to solve the defects of the above embodiments, a technical solution of the load supply circuit according to the embodiment of the present application is provided.

Fig. 1 is a schematic structural diagram of a load power supply circuit according to an embodiment of the present application, where as shown in fig. 1, the load power supply circuit includes: a power supply 10, a load 11, and a first branch 12; a first end of the power supply 10 is connected to a first end of the load 11, a second end of the load 11 is connected to a first end of the first branch 12, and a second end of the first branch 12 is connected to a second end of the power supply 10; wherein the load 11 includes a capacitor therein, and the first branch 12 includes a first switch 121 and at least one PTC resistor 122;

when the first switch 12 is in the on state, the power supply 10, the first branch 12 and the load 11 form a first loop, the power supply 10 charges a capacitor in the load 11 through the first branch 12 so that a voltage across the capacitor reaches a set voltage threshold, and the at least one PTC resistor 122 in the first branch 12 is used for limiting a current of the first loop.

PTC generally refers to a semiconductor material or a component with a large positive temperature coefficient, and generally, the PTC refers to a positive temperature coefficient thermistor, which is referred to as a PTC resistor in the embodiments of the present application. A PTC resistor is a semiconductor resistor typically having temperature sensitivity, and its resistance value increases stepwise with temperature increase when a certain temperature (i.e., curie point temperature) is exceeded. The PTC resistor can protect the circuit when the current surge is too large and the temperature is too high. When in use, the resistor is connected in series in the circuit, and under the normal condition, the resistance value and the loss are very small, so that the normal work of the circuit is not influenced; however, if an overcurrent (such as a short circuit) occurs, the temperature of the PTC resistor rises due to a large current passing through the PTC resistor, and the resistance value of the PTC resistor rises sharply under the condition that the temperature of the PTC resistor rises, so that the effect of limiting the current in the circuit is achieved, and the damage of components in the circuit is avoided. When the fault is eliminated, the temperature of the PTC resistor automatically drops and is restored to a low-resistance state, so that the PTC resistor is also called a resettable fuse.

In practical applications, the resistance of the load 11 may be generally equivalent to a parallel capacitor and inductor structure, and after the load 11 and the power supply 10 are connected and the load 11 and the power supply 10 form a complete loop, due to the existence of the capacitor in the load 11, a transient impulse current may be generated in the loop.

In the embodiment of the present application, a pre-charge circuit including a PTC resistor is disposed between the power source 10 and the load 11, that is, the first branch 12, and when the power source 10 is used to supply power to the load 11, the first switch 121 in the first branch 12 is turned on first, so that the power source 10, the load 11 and the first branch 12 form a closed first loop. After the first switch 121 in the first branch 12 is turned on, when an impact current is generated in a first circuit formed by the power supply 10, the load 11 and the first branch 12, the temperature of the PTC resistor increases, and based on the inherent temperature protection characteristic of the PTC resistor, the resistance value of the PTC resistor increases significantly with the increase in temperature after the temperature of the PTC resistor increases, so that the impact current in the first circuit is suppressed, components in the first circuit are protected from being damaged, and the safety and reliability of the circuit are improved. In addition, when the load in the circuit is abnormal (such as short circuit, overload, etc.), because the current flowing through the PTC resistor is instantly increased to a large value, the temperature of the PTC resistor is rapidly increased, and the resistance value of the PTC resistor is also rapidly increased due to the inherent temperature protection characteristic of the PTC resistor, so that the current in the circuit is reduced, and the temperature and the current of the circuit are both limited within a safe range.

It should be noted that in the embodiment of the present application, an additional software setting may also be used to protect the circuit, for example, in an implementation manner, when it is determined that the current in the first loop exceeds a certain threshold, the connection between the power supply and the load may be disconnected through software, so as to protect elements in the first loop from being damaged; in another embodiment, the elements in the first circuit can be protected from being damaged by detecting the temperature of the PTC resistor and disconnecting the power supply from the load by software after the temperature of the PTC resistor exceeds a certain temperature threshold.

In the embodiment of the present application, after the first switch 121 is turned on, the power supply 10 first charges the capacitor in the load 11 by using the first branch 12, and since the resistor in the load 11 may be equivalent to a structure of a capacitor and an inductor connected in parallel, it is possible to use whether the voltage across the load 11 reaches the set voltage threshold as a reference for whether to complete charging the capacitor in the load 11 (that is, the voltage across the capacitor reaches the set voltage threshold). According to the method and the device, the first branch circuit 12 is adopted to charge the capacitor in the load 11, so that after the voltages at two ends of the load 11 reach the set voltage threshold value, the second branch circuit 13 is used for supplying power to the load 11, the purpose of rapidly charging the capacitor in the load 11 can be achieved, and the power supply 10 can be switched to the state of supplying power to the load 11 by using the second branch circuit 13, so that impact current cannot be generated in the circuit.

In the embodiment of the present application, the specific value of the set voltage threshold may be determined according to actual conditions, and usually 80% to 90% of the rated voltage of the load 11 is selected as the set voltage threshold, so that the capacitor in the load 11 can be charged quickly, and it can be ensured that no surge current is generated in a loop formed by the power supply 10 and the load 11 after the first branch 12 is disconnected and the load 11 is powered by the second branch.

As shown in fig. 1, in the embodiment of the present application, the circuit further includes: a second branch 13, the second branch 13 being connected in parallel with the first branch 12; the second branch 13 comprises a second switch 131;

wherein the second switch 131 is in an on state after the voltage across the capacitor reaches the set voltage threshold; when the second switch 131 is in the on state, the power source 10, the second branch 13 and the load 11 form a second loop, and the power source 10 supplies power to the load 11 through the second branch 13.

Specifically, in the embodiment of the present application, after the first branch 12 is used to complete charging of the capacitor in the load 11, the voltage across the load 11 (that is, the voltage across the capacitor) reaches the set voltage threshold, and after it is detected that the voltage across the load 11 reaches the set voltage threshold, the second switch 131 in the second branch 13 is turned on, so that the power supply 10, the second branch 13, and the load 11 form a second loop, and power is supplied to the load 11 through the second branch 13. Here, the second circuit is also referred to as a main circuit. Preferably, in the embodiment of the present application, the first branch 12 is turned off (i.e., the first switch 121 is turned off) after the second branch 13 is turned on (i.e., the second switch 131 is turned on).

In the embodiment of the present application, specific types of the first switch 121 and the second switch 131 are not specifically limited, and the types of the first switch 121 and the second switch 131 may be the same or different. Specifically, a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET), a Bipolar Junction Transistor (BJT), a relay, a contactor, or other switching elements may be used as the first switch 121 or the second switch 131 in this embodiment of the application.

In an optional embodiment of the present application, the total pre-charge energy of the at least one PTC resistor is N times of the maximum capacitance energy corresponding to the capacitor in the load 11, and a value of N is greater than 1.

Specifically, in the embodiment of the present application, the capacitor in the load has a corresponding maximum capacitor energy, and for the specific setting of the PTC resistor, the pre-charge energy of the PTC resistor is to be N times of the maximum capacitor energy of the capacitor in the load 11, and when only one PTC resistor is included in the first branch 12, the pre-charge energy of the PTC resistor is N times of the maximum capacitor energy; when the plurality of PTC resistors are included in the first branch 12, the precharge energy of the plurality of PTC resistors should be N times the maximum capacitance energy in the case where the plurality of PTC resistors are connected in parallel. Preferably, the value of N ranges from 3 to 20, that is, the total pre-charge energy of the PTC resistor in the first branch 12 is generally 3 to 20 times the maximum capacitance energy of the capacitor in the load 11.

Here, for a PTC resistor, the pre-charge energy of the PTC resistor may be determined according to the curie point temperature of the PTC resistor, the operating temperature, and the specific heat capacity of the PTC resistor material. For example, in the case where only one PTC resistor is included in the first branch 12, if the PTC resistor has a heat capacity value C (J/° C), a curie point temperature T1, and an operating temperature T2, the pre-charge energy Q of the PTC resistor can be determined by the formula Q ═ C (T1-T2); when the first branch 12 includes a plurality of PTC resistors connected in parallel, the total precharge energy obtained by adding the precharge energy of each of the plurality of PTC resistors to each other is obtained.

In an optional embodiment of the present application, for each PTC resistor of the at least one PTC resistor, the curie point temperature of each PTC resistor is in a range of 80 ℃ to 120 ℃.

In the embodiment of the present application, the curie point temperature is related to the whole loop system formed by the power source 10 and the load 11, and generally, the curie point temperature can be selected to be higher if the PTC resistor is farther from the electric core in the power source 10. The curie point temperature of the PTC resistor selected for use in the embodiments of the present application is typically between 80 ℃ and 120 ℃.

In an optional embodiment of the present application, the first branch 12 includes a PTC resistor, and when the first switch 121 is in an on state, if a value of a resistance value of the PTC resistor is an initial resistance value, a current value of the first loop is less than or equal to a rated current of the load 11.

The initial resistance value of the PTC resistor is also called the zero power resistance value R at 25 DEG C₂₅In the embodiment of the present application, the first branch 12 includes only one PTC resistorIn this case, the selected PTC resistor should ensure that the current in the first loop formed by the power source 10, the first branch 12 and the load 11 does not exceed the rated current of the load 11 when the resistance value of the selected PTC resistor is the initial resistance value.

In an optional embodiment of the present application, when the first branch 12 includes a plurality of PTC resistors, and the first switch 121 is in an on state, if a resistance value of each of the plurality of PTC resistors is a corresponding initial resistance value, a current value of the first loop is less than or equal to a rated current of the load 11; wherein, a plurality of PTC resistance is the parallel structure.

In the embodiment of the present application, under the condition that the first branch 12 includes a plurality of PTC resistors and the plurality of PTC resistors are in a parallel structure, when the selected plurality of PTC resistors need to ensure that the resistance value of each PTC resistor is the corresponding initial resistance value, the current in the first loop formed by the power source 10, the first branch 12 and the load 11 does not exceed the rated current of the load 11, that is, the total resistance after the plurality of PTC resistors are connected in parallel should satisfy that the current value of the first loop is less than or equal to the rated current of the load 11 after the first switch 121 is turned on.

Fig. 2 is a schematic structural diagram of a load power supply circuit according to an embodiment of the present application, and as shown in fig. 2, the first branch 12 further includes a diode 123; the diode 123 is connected in series with the first switch 121 and the at least one PTC resistor for preventing the current of the first loop from flowing from the second terminal of the power supply 10 to the first terminal of the power supply 10.

Specifically, as a preferred embodiment, by providing the diode 123, which is also called a backflow prevention diode, it can be ensured that the current in the first loop does not flow from the second end of the power supply 10 to the first end of the power supply 10 when the first switch 121 is turned on, where the second end of the power supply 10 represents the positive pole of the power supply 10 and the first end of the power supply 10 represents the negative pole of the power supply 10. Here, there is no limitation on the specific position of the diode 123 in the first branch 12.

Fig. 3 is a schematic structural diagram of a load power supply circuit according to an embodiment of the present application, and as shown in fig. 3, the first branch 12 further includes a first protection element 124, and the first protection element 124 is connected in series with the first switch 121 and the at least one PTC resistor 122;

the first protection element 124 is in an off state when the current of the first loop exceeds a first current threshold; the value of the first current threshold is M1 times of the rated current of the load 11, and the value of M1 is greater than 1.

Specifically, the first branch 12 may further include a first protection element 124, the first protection element 124 may be a fuse, the fuse is connected in series in the first branch 12, a fusing current (i.e., a first current threshold) of the fuse is 1.5 to 2 times of a rated current of the load 11, and after a current in a first circuit formed by the power source 10, the first branch 12, and the load 11 exceeds the fusing current, the fuse is opened, so as to protect elements in the first circuit from being burned out.

In one embodiment, a second protection element 14 is provided between the first terminal of the power source 10 and the first terminal of the load 11; as shown in figure 3 of the drawings,

the second protection element 14 is in an off state when the current of the first loop or the second loop exceeds a second current threshold; the value of the second current threshold is M2 times of the rated current of the load 11, and the value of M2 is greater than that of M1.

Specifically, a second protection element 14 may be further disposed in the first loop or the second loop, and the second protection element 14 may also be a fuse, which is disposed between the second end of the power source 10 and the first end of the load 11, and the battery can disconnect the power source 10 from the load 11 after the current in the first loop or the second loop exceeds the second current threshold, no matter whether the battery supplies power to the load 11 through the first branch 12 or the second branch 13. Here, the blowing current (i.e., the second current threshold) of the fuse is also set to be generally 1.5 to 2 times the rated current of the load 11, and the second current threshold is larger than the first current threshold.

Fig. 4 is a schematic structural diagram of a load power supply circuit according to an embodiment of the present disclosure, as shown in fig. 4, B1 is a power supply, a parallel circuit formed by CL and RL represents a load, Q1, D1, parallel PTC resistors (i.e., PTC1, PTC2, and PTC3), and a fuse F1 form a first branch; the switch S1 constitutes a second branch, and a fuse F2 is also provided between the power supply B1 and the load. In the figure, RS is a sampling resistor, and a current value of a current in a loop formed by a power supply and a load can be obtained through the RS.

For the load power supply circuit in fig. 4, when the power supply B1 is used to supply power to the load, the Q1 is first turned on, so that the CL in the load is charged and the RL in the load is supplied through the branch where the PTC resistor is located, after the CL in the load is precharged, the voltage at two ends of the load reaches 80% -90% of the rated voltage of the load, then the S1 is turned on, after the S1 is turned on, the branch where the PTC resistor and the Q1 are located is bypassed, and the battery supplies power to the load through the branch where the S1 is located.

Here, the number of PTC resistors connected in parallel in the first branch is usually not more than 5 in view of the economy of the components in the circuit.

According to the technical scheme of the embodiment of the application, the first branch circuit comprising the PTC resistor is adopted, and based on the inherent temperature protection characteristic of the PTC resistor, when the power battery system is used for supplying power to the load, after the first switch of the first branch circuit is switched on and the first loop generates impact current, the temperature of the PTC resistor is rapidly increased due to the fact that the current flowing through the PTC resistor is instantly increased to a large value, and under the condition, the resistance value of the PTC resistor is rapidly increased, so that the impact current in a loop formed by the power battery system and the load is reduced, and negative effects of starting ignition of components and parts in the loop formed by the power battery system and the load, damage of the components and the like caused by the impact current are avoided; in addition, the inherent characteristics of the PTC resistor can effectively and reliably protect the working conditions of overcurrent, overheating and the like generated in the operation process of the circuit, the circuit is simple, the cost is low, and the volume of the pre-charging circuit can be reduced; in addition, the first branch circuit comprising the PTC resistor is used for charging the capacitor in the load, so that the voltage at two ends of the capacitor in the load reaches a set voltage threshold value, the capacitor in the load can be quickly and stably charged, and the situation that the impact current can not occur when the power supply is switched to other branch circuits to supply power to the load can be ensured.

The technical solutions described in the embodiments of the present application can be arbitrarily combined without conflict.

In the several embodiments provided in the present application, it should be understood that the disclosed circuit may be implemented in other ways. The above described circuit embodiments are merely illustrative, for example, the division of the unit is only a logic function division, and there may be other division ways in actual implementation, such as: multiple units or components may be combined, or may be integrated into another system, or some features may be omitted, or not implemented. In addition, the coupling, direct coupling or communication connection between the components shown or discussed may be through some interfaces, and the indirect coupling or communication connection between the devices or units may be electrical, mechanical or other forms.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed on a plurality of network units; some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, all functional units in the embodiments of the present application may be integrated into one second processing unit, or each unit may be separately regarded as one unit, or two or more units may be integrated into one unit; the integrated unit can be realized in a form of hardware, or in a form of hardware plus a software functional unit.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application.

Claims

1. A load supply circuit, characterized in that the circuit comprises: a power supply, a load and a first branch circuit; the first end of the power supply is connected with the first end of the load, the second end of the load is connected with the first end of the first branch circuit, and the second end of the first branch circuit is connected with the second end of the power supply; the load comprises a capacitor, and the first branch circuit comprises a first switch and at least one Positive Temperature Coefficient (PTC) resistor;

2. The circuit of claim 1, further comprising: a second branch in parallel with the first branch; the second branch comprises a second switch;

3. The circuit of claim 1, wherein the total pre-charge energy of the at least one PTC resistor is N times the maximum capacitive energy of the capacitor in the load, N being greater than 1.

4. The circuit of claim 3, wherein N ranges from 3 to 20.

5. The circuit according to claim 1, wherein when the first branch circuit includes one PTC resistor, and the first switch is in an on state, if a resistance value of the one PTC resistor takes an initial resistance value, a current value of the first loop circuit is less than or equal to a rated current of the load.

6. The circuit according to claim 1, wherein when the first branch circuit includes a plurality of PTC resistors, and the first switch is in an on state, if a resistance value of each of the plurality of PTC resistors is a corresponding initial resistance value, a current value of the first loop circuit is less than or equal to a rated current of the load; wherein, a plurality of PTC resistance is the parallel structure.

7. The circuit of claim 1, wherein for each of the at least one PTC resistor, the curie point temperature of each PTC resistor ranges from 80 ℃ to 120 ℃.

8. The circuit according to any one of claims 1 to 7, further comprising a diode in the first branch; the diode is in series with the first switch and the at least one PTC resistor for preventing current of the first loop from flowing from the second end of the power supply to the first end of the power supply.

9. The circuit according to any one of claims 1 to 7, further comprising a first protection element in the first branch, the first protection element being in series with the first switch and the at least one PTC resistor;

10. The circuit of claim 9, wherein a second protection element is provided between the first terminal of the power source and the first terminal of the load;