CN115882580A

CN115882580A - Power supply switching system and dual-power supply equipment

Info

Publication number: CN115882580A
Application number: CN202111157127.0A
Authority: CN
Inventors: 饶志建; 陈正海
Original assignee: Jinka Water Technology Co ltd
Current assignee: Jinka Water Technology Co ltd
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2023-03-31

Abstract

The application provides a power supply switching system and dual power supply equipment. The system and apparatus includes: a power switching circuit; the power supply switching circuit is provided with a first input end, a second input end and an output end, the first input end is connected with a first power supply, the second input end is connected with a second power supply, and the output end of the power supply switching circuit is connected with the second input end and the load circuit; wherein, power supply switching circuit includes: a first switch; the input pole of the first switch is connected to the first input end, the output pole of the first switch is connected to the output end, and the control pole of the first switch is connected with the input pole of the first switch, the second input end and the ground. This application adopts the electronic components design of basis to build power supply switching circuit, utilizes hardware automatic switch-over mode to carry out the autonomic selection of dual supply, need not software participation control, has realized dual supply power's fast switch-over, has fail safe nature.

Description

Power supply switching system and dual-power supply equipment

Technical Field

The application relates to an electronic circuit technology, in particular to a power supply switching system and a dual-power supply device.

Background

In industrial products, such as industrial flowmeters, data collectors, transmitters and the like, two power supplies, namely a lithium battery and an external direct-current power supply, are commonly used for supplying power, so that the product has the maintenance convenience of lithium battery power supply, and the external direct-current power supply can be preferentially used for supplying power when the external direct-current power supply is connected.

At present, some power supply schemes that adopt the diode to carry out the parallel connection to the dual supply of dual supply power supply product, establish ties between every power and load and set up the diode promptly, utilize outside DC power supply voltage to be higher than the voltage difference of lithium cell voltage for the diode that the lithium cell corresponds when inserting outside DC power supply is cut off, and the diode that outside DC power supply corresponds switches on, realizes the demand of preferred outside DC power supply. Some adopt software control dual supply's switching, utilize corresponding switch circuit and the IO mouth of main control unit promptly, realize the power supply selection of lithium cell and external DC power supply.

However, the above diode control scheme has a potential safety hazard caused by diode breakdown, and the software control scheme has a potential safety hazard caused by slow software response speed, so that the switching power supply of the dual power supplies cannot be safely and reliably realized.

Disclosure of Invention

The application provides a power supply switching system and dual power supply equipment, makes dual power supply switching power supply safe and reliable.

In a first aspect, the present application provides a power switching system, comprising: a power switching circuit; the power supply switching circuit is provided with a first input end, a second input end and an output end, the first input end is connected with a first power supply, the second input end is connected with a second power supply, and the output end of the power supply switching circuit is connected with the second input end and the load circuit; wherein, power supply switching circuit includes: a first switch; the input pole of the first switch is connected to the first input end, the output pole of the first switch is connected to the output end, and the control pole of the first switch is connected with the input pole of the first switch, the second input end and the ground.

This application adopts the electronic components design of basis to build power supply switching circuit, utilizes hardware automatic switch-over mode to carry out the autonomic selection of dual supply, need not software participation control, has realized dual supply power's fast switch-over, has fail safe nature.

Furthermore, a TVS tube is arranged between the control pole of the first switch and the input pole of the first switch; the first end of the TVS tube is connected with the input pole of the first switch, and the second end of the TVS tube is connected with the control pole of the first switch.

The TVS tube arranged between the input pole and the output pole of the first switch is used for protecting the first switch, so that breakdown damage is avoided, and the safety and reliability of the power supply switching circuit are further improved.

Further, a first resistor is arranged between the control electrode of the first switch and the ground; one end of the first resistor is connected with the second input end and the control electrode of the first switch, and the other end of the first resistor is grounded.

The first resistor arranged between the control electrode of the first switch and the ground plays a role in limiting current, the first switch is protected, the first switch is prevented from being burnt out due to overlarge current, and the safety and reliability of the power supply switching circuit are further improved.

Furthermore, a first diode is arranged between the second input end and the output end; the anode of the first diode is connected with the second input end, and the cathode of the first diode is connected with the output end.

The first diode is arranged between the second input end and the output end, and the backflow prevention effect is achieved. When only the first power supply supplies power, the current of the first power supply is prevented from flowing to the second power supply, and unnecessary energy loss is avoided.

Furthermore, a second switch is arranged between the second input end and the output end; the input pole of the second switch is connected with the second input end, the output pole of the second switch is connected with the output end, and the control pole of the second switch is connected with one end of the second resistor; the other end of the second resistor is connected with a control electrode of a third switch, an input electrode of the third switch is connected with a control electrode of the first switch, and an output electrode of the third switch is grounded;

the power switching circuit further includes: the fourth switch, the inverter circuit, the first divider resistor and the second divider resistor; a control electrode of the fourth switch is connected with the second input end, an input electrode of the fourth switch is connected with an input node of the inverter circuit and one end of the first divider resistor, and an output electrode of the fourth switch is connected with one end of the second divider resistor; the other end of the second voltage-dividing resistor is grounded, and the other end of the first voltage-dividing resistor is connected with the input electrode of the first switch and a power supply node of the inverter circuit; the output node of the inverter circuit is connected to the control electrode of the third switch.

The second switch, the third switch, the fourth switch, the inverter circuit and the divider resistor are matched with each other to influence the disconnection and the conduction of the second switch, so that the second power supply is preferentially selected to supply power when the first power supply and the second power supply power simultaneously.

Further, a third resistor is arranged between the output node of the inverter circuit and the control electrode of the third switch; one end of the third resistor is connected with an output node of the inverter circuit, and the other end of the third resistor is connected with a control electrode of the third switch.

The third resistor plays a role in limiting current, so that the third switch is prevented from being burnt out, and the circuit is protected.

Further, a fourth resistor is arranged between the second input end and the control electrode of the fourth switch; one end of the fourth resistor is connected with the second input end and one end of the first capacitor, the other end of the fourth resistor is connected with the control electrode of the fourth switch, and the other end of the first capacitor is grounded.

The fourth resistor plays a role in limiting current, and the fourth switch is prevented from being burnt out, so that the circuit is protected. The first capacitor is a filter capacitor and is used for filtering interference of the first power supply, preventing false triggering and improving the stability of the power supply voltage.

Further, a second diode is arranged between the output electrode and the output end of the second switch; the anode of the second diode is connected with the output electrode of the second switch, and the cathode of the second diode is connected with the output end.

The second diode is arranged at the position close to the output end, backflow prevention is achieved, unnecessary energy loss and device loss are avoided, and the circuit is protected.

Further, the inverter circuit includes: a pull-up switch and a pull-down switch; the input pole of the pull-up switch is used as a power supply node of the inverter circuit; the output pole of the pull-up switch is connected with the input pole of the pull-down switch and is used as the output node of the inverter circuit; the output electrode of the pull-down switch is grounded; and the control electrode of the pull-up switch is connected with the control electrode of the pull-down switch and used as an input node of the inverter circuit.

The pull-up switch and the pull-down switch are matched with the first voltage-dividing resistor and the second voltage-dividing resistor, so that the pull-up switch and the pull-down switch are switched on or off, the switching on or off of the second switch is influenced, and the independent selection of double power supplies is realized.

Further, the power supply switching system further includes: a current-limiting anti-reverse circuit between the first power supply and the first input terminal; the current-limiting anti-reverse circuit includes: the current limiting resistor, the filter capacitor, the fifth switch and the grounding resistor; one end of the current-limiting resistor is connected with the first power supply, and the other end of the current-limiting resistor is connected with the first end of the filter capacitor and the input electrode of the fifth switch; the second end of the filter capacitor is grounded; the output pole of the fifth switch is connected with the first input end, the control pole of the fifth switch is connected with one end of the grounding resistor, and the other end of the grounding resistor is connected with the second end of the filter capacitor.

The current-limiting anti-reverse circuit is used for protecting the safety of the first power supply and protecting the safety of the rear-end circuit.

Further, the filter capacitor includes: and the parallel capacitor is formed by the first filter capacitor and the second filter capacitor.

The two capacitors connected in parallel are adopted, and the effect of reducing the equivalent resistance is achieved.

Furthermore, a backflow prevention circuit is arranged between the output electrode and the output end of the first switch, the first end of the backflow prevention circuit is connected with the output electrode of the first switch, and the second end of the backflow prevention circuit is connected with the output end.

The backflow prevention circuit plays a role in protecting the circuit.

Further, the backflow prevention circuit comprises: a sixth switch; the input pole of the sixth switch is used as the first end of the backflow prevention circuit and is connected with the output pole of the first switch; the output electrode of the sixth switch is used as the second end of the backflow prevention circuit and is connected with the output end; and the control electrode of the sixth switch is connected with the control electrode of the first switch.

The sixth switch in the backflow prevention circuit prevents the second power supply current from flowing to the first power supply when the second power supply supplies power, and avoids unnecessary energy loss.

Further, the power switching circuit further includes: a second capacitor; one end of the second capacitor is connected with the output electrode of the first switch, and the other end of the second capacitor is connected with the control electrode of the first switch.

The second capacitor is a filter capacitor, so that power supply interference is filtered, and false triggering is avoided.

Further, the power supply switching system further includes: a load capacitance; one end of the load capacitor is connected with the output end of the power supply switching circuit, and the other end of the load capacitor is grounded.

The load capacitor is a filter capacitor, and the stability of the output voltage is ensured.

In a second aspect, the present application provides a dual power supply apparatus comprising the power switching system of the first aspect.

The application provides a power supply switching system and dual power supply unit includes: a power switching circuit; the power supply switching circuit is provided with a first input end, a second input end and an output end, the first input end is connected with a first power supply, the second input end is connected with a second power supply, and the output end of the power supply switching circuit is connected with the second input end and the load circuit; wherein, power supply switching circuit includes: a first switch; the input pole of the first switch is connected to the first input end, the output pole of the first switch is connected to the output end, and the control pole of the first switch is connected with the input pole of the first switch, the second input end and the ground. This application adopts the electronic components design of basis to build power supply switching circuit, utilizes hardware automatic switch-over mode to carry out the autonomic selection of dual supply, need not software participation control, has realized dual supply power's fast switch-over, has fail safe nature.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.

FIG. 1a is a circuit diagram of a typical dual power supply scheme;

FIG. 1b is a circuit diagram of another exemplary dual power supply scheme;

FIGS. 2a and 2b illustrate an exemplary application scenario of a power switching system;

fig. 3 is a schematic structural diagram of a power switching system provided in the present application;

fig. 4 is a circuit diagram of a first switch in the power switching system provided in the present application;

fig. 5 is a circuit diagram of a TVS transistor in the power switching system provided in the present application;

FIG. 6 is a circuit diagram of a first resistor in the power switching system provided in the present application;

FIG. 7 is a circuit diagram of a first diode in the power switching system provided in the present application;

fig. 8 is a circuit diagram of a power switching system provided in the present application;

FIG. 9 is a circuit diagram of another power switching system provided herein;

fig. 10 is a circuit diagram of an inverter circuit in the power switching system provided in the present application;

FIG. 11 is a schematic diagram of another power switching system provided in the present application;

FIG. 12 is a circuit diagram of a current limiting anti-kickback circuit in the power switching system provided by the present application;

fig. 13 is a schematic structural diagram of another power switching system provided in the present application;

FIG. 14 is a circuit diagram of another power switching system provided in the present application;

fig. 15 is a circuit diagram of another power switching system provided in the present application.

With the above figures, there are shown specific embodiments of the present application, which will be described in more detail below. These drawings and written description are not intended to limit the scope of the inventive concepts in any manner, but rather to illustrate the inventive concepts to those skilled in the art by reference to specific embodiments.

Detailed Description

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

The terms referred to in this application are explained first:

dual power supply: the dual power sources are different in power source (such as different regional substations), and are independent from each other, and after one power source is powered off, the second power source cannot be powered off at the same time.

TVS tube: a Transient Voltage Super (TVS) is a high performance protection device in the form of a diode. When two poles of the TVS tube are impacted by reverse transient high energy, the TVS tube can change the high impedance between the two poles into low impedance at the speed of 10 minus 12 th power second, absorb the surge power of thousands of watts, clamp the voltage between the two poles (the measure of limiting the potential of a certain point to a specified potential, is an overvoltage protection technology) to a preset value, and effectively protect precise components in an electronic circuit from being damaged by various surge pulses.

At present, the application field of using dual power supply is more and more extensive, especially in industrial products to get the common application. The industrial products supporting the dual power supply comprise an industrial flowmeter, a data collector, a transmitter and the like. The following dual power supplies take a battery as an example and an external power supply as an example, wherein the battery takes a lithium battery as an example, and the external power supply takes commercial power as an example.

The dual-power supply product supports free switching between lithium battery power supply and external direct-current power supply, widens the application scene of the product, and enables the product to have the maintenance convenience of lithium battery power supply. In addition, in the external power supply mode, the dual power supply product also has corresponding peripheral functions that are not possessed by a pure lithium battery power supply product (low power consumption requirement), for example, high-power peripheral functions such as outputting a 4-20mA signal and outputting a pulse, and the like, so that the dual power supply becomes a development trend of industrial electronic products.

The traditional power supply scheme design of the dual-power supply product has two types. The first scheme is as follows: a double-power scheme that a diode is adopted to connect a lithium battery and an external power supply in parallel; the second scheme is as follows: and the double-power scheme is characterized in that the power supply of the lithium battery and the external power supply is switched and controlled by adopting software.

It should be noted that the diode itself has a certain forward voltage drop, also called turn-on voltage. The diode also has unidirectional conductivity. The working principle is as follows: the diode is loaded with forward voltage at two ends, and when the forward voltage is smaller than the conduction voltage, the diode is not conducted, and a tiny current still passes through the diode in the forward direction in an actual electronic device, which is related to the preparation process of the diode. A forward voltage is applied across the diode and when the forward voltage is greater than the turn-on voltage, the diode turns on. When a negative voltage is applied to the two ends of the diode, the diode is cut off, and a small current flows in the reverse direction (also called reverse leakage current) in the actual diode of the electronic device, which is related to the preparation process of the diode. When the negative voltage exceeds a certain value, the diode will be broken down and lose one-way conductivity.

Fig. 1a is a circuit diagram of a typical dual power supply scheme, corresponding to the first scheme. As shown in fig. 1a, a diode D3 is connected in series between the output terminal of the lithium battery and the load circuit, the anode thereof is connected to the output terminal of the lithium battery, and the cathode thereof is connected to the load circuit; the diode D4 is connected in series between the output terminal of the external power supply and the load circuit, and has its anode connected to the output terminal of the external power supply and its cathode connected to the load circuit. The circuit has the following action processes: when the external power supply does not supply power and only the lithium battery supplies power, the diode D5 is in a conducting state, and the diode D4 is in a stopping state, namely the lithium battery supplies power for the load circuit; when the external power supply supplies power, the diode D4 is in a conducting state, and since the voltage of the external power supply is higher than the output voltage of the lithium battery, the diode D5 is in a blocking state, that is, the external power supply supplies power to the load circuit. The switching power supply of the lithium battery and the external power supply is realized by utilizing the unidirectional conductivity of the diode.

The first solution described above has the following problems: and (1) potential safety hazards exist. When an external power supply and a lithium battery exist at the same time, the lithium battery and the external power supply are both connected with a rear-end load circuit, if the external power supply is higher than the voltage of the lithium battery, reverse leakage current exists in the diode D5, and when the diode D5 has a short-circuit fault, the lithium battery can be reversely charged, so that the risk of explosion exists; if the two voltages are close, the lithium battery also supplies power when external electricity exists, and the service life of the lithium battery is influenced. And (2) unstable power supply. When only a lithium battery is used for supplying power, due to the fact that inherent forward voltage drop voltage exists in the diode, the voltage of the lithium battery is reduced after the voltage of the lithium battery passes through the diode D5, the voltage drop is increased when the current value flowing through the lithium battery is larger, and the normal work of a load circuit at the rear end is influenced.

Fig. 1b is a circuit diagram of another typical dual power supply scheme, corresponding to the second scheme. As shown in fig. 1b, the power supply switching function between the lithium battery and the external power supply is realized by using a software control mode and matching with a corresponding switch circuit, and the power supply switching function between the lithium battery and the external power supply is realized mainly by a basic electronic device, namely a PMOS transistor Q9, a diode D6, a diode D7, a triode Q10, a resistor R9, a resistor R10, a resistor R11 and a resistor R12, and by matching with the I/O control of a main control chip. Wherein, the EXD-PWR-INT is an I/O port with an interrupt input function in the main control chip; the EXD-PWR-CTL is a common I/O port in the main control chip.

On the basis of software control, when an external power supply is electrified, the external power supply enters the EXD-PWR-INT through the rising edges generated by the voltage dividing resistor R10 and the voltage dividing resistor R11; when the external power supply is powered off, the falling edge generated after passing through the voltage dividing resistor R10 and the voltage dividing resistor R11 enters the EXD-PWR-INT. Based on this, the action process of above-mentioned circuit is: when the external power supply does not supply power, the EXD-PWR-CTL is set to be in a high level, the PMOS tube Q9 is conducted, and then the lithium battery supplies power. When an external power supply is powered on, the EXD-PWR-INT identifies the rising edge of the power-on process, the EXD-PWR-CTL is controlled to be set to be at a low level, the PMOS tube Q9 is switched off, and the external power supply supplies power at the moment; when the external power supply is powered off, the EXD-PWR-INT identifies the falling edge in the power-off process, the EXD-PWR-CTL is controlled to be set to be at a high level, the PMOS tube Q9 is conducted, and at the moment, the lithium battery supplies power.

The second solution described above has the following problems: and (1) potential safety hazards exist. The scheme is realized based on software control, and comprises a power-on detection process, a power-off detection process and a logic control process, so that the response speed is low, and further, the whole system is possibly in a power-off state, and data loss is caused. When software is in error or is stuck, the power supply switching function is lost, the states of all the switch circuits are not controllable, and potential safety hazards are easily caused. And (2) unstable power supply. Depending on the working stability of the software, the power supply switching function is lost when the software is jammed and runs BUG, so that the power supply is disordered.

The application provides a power supply switching system, which aims to solve the technical problems in the prior art.

First, an exemplary application scenario of the present application will be described.

Fig. 2a and 2b are application scenarios of an exemplary power switching system. As shown in fig. 2a and fig. 2b, the dual power supply device refers to a device having two power supplies, and specifically may be an industrial application device such as an industrial flow meter, a data collector, and a transmitter. The two power sources of the dual power supply device need to be independent of each other, that is, after one power source is powered off, the second power source is not powered off at the same time, and a battery and commercial power are taken as examples in fig. 2a and fig. 2 b. A power switching system is arranged in the dual power supply device, and the power switching system is simplified into a double-side switch circuit in fig. 2a and 2 b. The double-side switch circuit is connected with functional parts of the dual-power supply equipment, and a power supply is selected to be a commercial power or a battery through the circuit.

When the utility power fails to supply power, for example, the power grid fails or the utility power is actively disconnected for maintenance and repair, the circuit is controlled by the power switching system, so that the battery supplies power to the functional components, as shown in fig. 2 a. When the commercial power is used for supplying power, the circuit is controlled by the power supply switching system, and the commercial power is switched to supply power for the functional component, as shown in fig. 2 b. It can be understood that the application does not limit the dual power supplies, and as long as two power supplies are mutually independent, under the premise of no fault, the power is not cut off at the same time. The application does not limit the dual-power supply equipment, and only needs to adopt dual power supplies.

Based on the above application background, the technical solutions of the present application and how to solve the above technical problems will be described in detail with specific embodiments below. These several specific embodiments may be combined with each other below, and details of the same or similar concepts or processes may not be repeated in some embodiments. Embodiments of the present application will be described below with reference to the accompanying drawings.

Fig. 3 is a schematic structural diagram of a power switching system provided in the present application, and as shown in fig. 3, the power switching system provided in the present application includes: a power switching circuit; the power supply switching circuit is provided with a first input end, a second input end and an output end, the first input end is connected with a first power supply, the second input end is connected with a second power supply, and the output end of the power supply switching circuit is connected with the second input end and the load circuit; wherein, power supply switching circuit includes: a first switch Q2; the input pole of the first switch Q2 is connected to the first input end, the output pole of the first switch Q2 is connected to the output end, and the control pole of the first switch Q2 is connected with the input pole of the first switch, the second input end and the ground.

The first power supply and the second power supply are used for providing electric energy, and the electric energy can be from a battery, can also be used for generating power for an engine, and can also be used as commercial power. The source of the power supply is not limited, and as long as the first power supply and the second power supply are mutually independent, the first power supply and the second power supply cannot supply power at the same time. In the following description, the first power source is a lithium battery, and the second power source is a commercial power.

The load circuit is a circuit which needs a power supply to provide electric energy to maintain the self function, and includes but is not limited to a main control chip, a power supply chip and the like, and may also include functional components of a dual power supply device, such as a display, a warning light and the like.

Specifically, the first switch may be a PMOS transistor. Fig. 4 is a circuit diagram of a first switch in the power switching system provided in the present application, and referring to fig. 4, the first switch Q2 is a positive PMOS transistor, and the PMOS transistor includes a source, a gate, and a drain. The positive connection refers to the source input current and the drain output current of the PMOS tube. The source electrode is equivalent to the input electrode of the first switch Q2 and is connected with the first input end; the grid electrode is equivalent to the control electrode of the first switch Q2, is connected with the input electrode and the second input end of the first switch, and is grounded; the drain corresponds to the output electrode of the first switch Q2 and is connected to the output terminal.

The action process of the first switch Q2 is as follows: when the source voltage is higher than the grid voltage and the voltage difference exceeds the conducting voltage, the source and the drain of the PMOS are conducted; otherwise, the source and drain of the PMOS are cut off. As shown in fig. 4, the first power source is inputted to the source of the first switch Q2 at a high level, and when the second power source does not supply power, since the gate of the first switch Q2 is grounded and is in a low level state, the source voltage is higher than the gate voltage, the first switch Q2 is turned on, and the first power source can supply power to the load circuit; when the second power supply supplies power, the gate of the first switch Q2 is at a high level in cooperation with other circuits (not shown in fig. 4), and the voltage difference between the source voltage and the gate voltage is not enough to turn on the first switch Q2, so that the first power supply cannot supply power to the load circuit, and the second power supply supplies power to the load circuit.

In one example, a TVS tube is disposed between the control electrode of the first switch Q2 and the input electrode of the first switch Q2; the first end of the TVS tube is connected with the input pole of the first switch Q2, and the second end of the TVS tube is connected with the control pole of the first switch Q2.

Specifically, fig. 5 is a circuit diagram of a TVS transistor in the power switching system provided by the present application, and as shown in fig. 5, a TVS transistor D1 is connected between a gate and a source of a first switch Q2, so as to protect the first switch Q2, avoid breakdown damage, and improve the safety of the power switching circuit.

In one example, a first resistor R7 is provided between the control electrode of the first switch Q2 and ground; one end of the first resistor R7 is connected with the second input end and the control electrode of the first switch Q2, and the other end of the first resistor R7 is grounded.

Specifically, fig. 6 is a circuit diagram of the first resistor in the power switching system provided by the present application, and the first resistor R7 is disposed between the control electrode of the first switch Q2 and the ground, so as to play a role of limiting a current, avoid the first switch Q2 from being burnt by an excessive current, and improve the safety of the power switching circuit.

On the basis of the above example, a first diode D2 is provided between the second input terminal and the output terminal; the anode of the first diode D2 is connected with the second input end, and the cathode of the first diode D2 is connected with the output end.

Specifically, fig. 7 is a circuit diagram of a first diode in the power switching system provided by the present application, and the first diode D2 disposed between the second input end and the output end plays a role of preventing backflow. When only the first power supply supplies power, the first power supply current can be prevented from flowing to the second power supply, and unnecessary energy loss is avoided.

The above for turning on or off the first switch Q2 mainly depends on the voltage difference of the dual power sources, and the dual power source switching scheme lacks reliability. The present application thus provides another power switching system circuit in which a circuit for controlling the first switch Q2 to be turned on or off is designed to achieve the reliability of dual power switching. This circuit is described below.

In one example, a second switch Q8 is provided between the second input terminal and the output terminal; an input pole of the second switch Q8 is connected with a second input end, an output pole of the second switch Q8 is connected with an output end, and a control pole of the second switch Q8 is connected with one end of the second resistor R8; the other end of the second resistor R8 is connected to a control electrode of the third switch Q7, an input electrode of the third switch Q7 is connected to a control electrode of the first switch Q2, and an output electrode of the third switch Q7 is grounded. The second resistor R8 plays a role in limiting current and protects the second switch Q8.

The power switching circuit further includes: the fourth switch Q6, the inverter circuit, the first voltage-dividing resistor R3 and the second voltage-dividing resistor R5; a control electrode of the fourth switch Q6 is connected to the second input end, an input electrode of the fourth switch Q6 is connected to an input node of the inverter circuit and one end of the first voltage-dividing resistor R3, and an output electrode of the fourth switch Q6 is connected to one end of the second voltage-dividing resistor R5. The other end of the second voltage-dividing resistor R5 is grounded, and the other end of the first voltage-dividing resistor R3 is connected with the input electrode of the first switch Q2 and the power supply node of the inverter circuit. The output node of the inverter circuit is connected to the gate of the third switch Q7.

The second switch Q8, the third switch Q7 and the fourth switch Q6 are electronic components playing a role of switching, and may be an NMOS transistor, a PMOS transistor, an NPN triode, a PNP triode, or the like.

For example, fig. 8 is a circuit diagram of a power switching system provided in the present application. Specifically, the second switch Q8 may be a PMOS transistor, the third switch Q7 may be an NPN transistor, and the fourth switch Q6 may be an NPN transistor.

The source electrode of the PMOS tube is the input electrode of the second switch Q8; the drain electrode of the PMOS tube is the output electrode of the second switch Q8; the gate of the PMOS transistor is the control electrode of the second switch Q8. The base electrodes of the NPN triodes are the control electrodes of the third switch Q7 and the fourth switch Q6, the collector electrodes of the NPN triodes are the input electrodes of the third switch Q7 and the fourth switch Q6, and the emitter electrodes of the NPN triodes are the output electrodes of the third switch Q7 and the fourth switch Q6.

It should be noted that, the transistor has an amplifying function and a switching function in the circuit, and the switching function of the transistor is mainly utilized in the present application. Therefore, the operating principle of the NPN transistor is as follows: when the voltage loaded at the two ends of the base electrode and the emitting electrode of the triode is greater than the conduction voltage of the PN junction, and when the current of the base electrode is increased to a certain degree, the current of the collector electrode is not increased along with the increase of the current of the base electrode, but is not changed much nearby a certain value, at the moment, the triode loses the current amplification effect, the voltage between the collector electrode and the emitting electrode is very small, and the conduction state between the collector electrode and the emitting electrode is equivalent to the conduction state of a switch, namely the conduction state of the triode.

Specifically, the switching action of the third switch Q7 will be described as an example. When the base of the third switch Q7 is at a high level, the emitter is grounded (i.e., at a low level), so that the third switch Q7 is in a conducting state. The collector is therefore in a low state and hence the gate of the first switch Q2 is in a low state. At this time, if the first power supply provides a high level state for the source of the first switch Q2, and the source voltage is greater than the gate voltage, the first switch Q2 is turned on, and the first power supply can supply power to the load circuit.

Conversely, when the base of the third switch Q7 is low, the third switch Q7 is off. The voltage of the gate of the first switch Q2 is the voltage of the voltage provided by the first power supply after passing through the TVS tube D1, and because the voltage division of the TVS tube D1 is very small and can be ignored, the gate voltage and the source voltage of the first switch Q2 are substantially the same, the first switch Q2 is turned off, and the first power supply cannot supply power to the load circuit.

In order to protect each part of the device during actual use, a protection circuit needs to be further added on the basis of the above example. Fig. 9 is a circuit diagram of another power switching system provided in the present application, in which some electronic devices are added on the basis of fig. 8 to protect the whole circuit. The concrete protection measures are as follows:

(1) Protection of the third switch Q7: a third resistor R4 is arranged between the output node of the inverter circuit and the control electrode of the third switch Q7; one end of the third resistor R4 is connected to an output node of the inverter circuit, and the other end of the third resistor R4 is connected to a control electrode of the third switch Q7. Specifically, the third resistor R4 plays a role in limiting current, so as to avoid burning out the third switch Q7 and protect the circuit.

(2) Protection of the fourth switch Q6: a fourth resistor R6 is arranged between the second input end and the control electrode of the fourth switch Q6; one end of a fourth resistor R6 is connected with the second input end and one end of the first capacitor C5, the other end of the fourth resistor R6 is connected with the control electrode of the fourth switch Q6, and the other end of the first capacitor C5 is grounded. The fourth resistor R6 plays a role in limiting current, the fourth switch Q6 is prevented from being burnt out, and the circuit is protected. In addition, first electric capacity C5 is filter capacitor for the interference of filtering first power, prevents the spurious triggering, promotes mains voltage stability.

(3) Protection of the second power supply: a second diode D3 is arranged between the output electrode and the output end of the second switch Q8; the anode of the second diode D3 is connected to the output terminal of the second switch Q8, and the cathode of the second diode D3 is connected to the output terminal.

The second diode D3 shown in fig. 9 and the first diode D2 shown in fig. 7 both make the circuit conduct in one direction, play a role of preventing backflow, and are disposed at a position close to the output end to better protect the front end circuit. On one hand, when only the first power supply supplies power, the current of the first power supply is prevented from flowing to the second power supply, and unnecessary energy loss is avoided; on the other hand, when electronic components in a backward flowing way are prevented, energy loss or component damage is avoided.

On the basis of the above-mentioned power supply switching system example shown in fig. 9, fig. 10 is a circuit diagram of an inverter circuit in the power supply switching system provided by the present application. The inverter circuit includes: a pull-up switch Q4 and a pull-down switch Q5; the input pole of the pull-up switch Q4 is used as a power supply node of the inverter circuit; the output pole of the pull-up switch Q4 is connected with the input pole of the pull-down switch Q5 and is used as the output node of the inverter circuit; the output pole of the pull-down switch Q5 is grounded; a control electrode of the pull-up switch Q4 is connected to a control electrode of the pull-down switch Q5 as an input node of the inverter circuit.

As shown in fig. 10, the pull-up switch Q4 is exemplified by an NPN-type transistor, and the pull-down switch Q5 is exemplified by a PNP-type transistor. When the first power supply supplies power and the second power supply is powered off, two ends of the fourth resistor R6 are at low level, so that the fourth switch Q6 is in a cut-off state; the first voltage dividing resistor R3 is connected with a first power supply, so that two ends of the first voltage dividing resistor R3 are at high level, and bases of the pull-up switch Q4 and the pull-down switch Q5 are at high level; the collector of the pull-up switch Q4 is connected to the first power supply, so that the pull-down switch Q4 is turned on; the collector of the pull-down switch Q5 is grounded, so the pull-down switch Q5 is cut off; since the switch Q4 is turned on next, the emitter of the switch Q4 is at a high level next, the third switch Q7 is turned on, the gate of the first switch Q2 is at a low level, the first switch Q2 is turned on, and the first power supply can supply power to the load circuit; the gate of the second switch Q8 is also high, the second switch Q8 is turned off, and the second power supply and the load circuit are disconnected.

When the second power supply is powered on, two ends of the fourth resistor R6 are at high level, so that the fourth switch Q6 is conducted; the base voltages of the pull-up switch Q4 and the pull-down switch Q5 are the same; by adjusting the resistance values of the first voltage-dividing resistor R3 and the second voltage-dividing resistor R5, the base voltage is lower than the turn-on voltage, so that the pull-up switch Q4 is turned off, and the pull-down switch Q5 is turned on; because the pull-down switch Q5 is turned on, the base of the third switch Q7 is at a low level, the third switch Q7 is turned off, the voltage of the gate of the first switch Q2 is the voltage of the voltage provided by the first power supply after passing through the TVS tube D1, and because the voltage division of the TVS tube D1 is very small and can be ignored, the gate voltage and the source voltage of the first switch Q2 are substantially the same, the first switch Q2 is turned off, and the first power supply cannot supply power to the load circuit; the gate of the second switch Q8 is low, the second switch Q8 is turned on, and the second power supply replaces the first power supply to supply power to the load circuit.

The arrangement realizes the quick response of the double power supplies and the requirement that the second power supply is preferentially selected to supply power when the double power supplies are electrified.

In one example, to protect the first power supply, the power supply switching system further comprises: a current limiting anti-kickback circuit is located between the first power supply and the first input terminal.

Fig. 11 is a schematic structural diagram of another power switching system provided in the present application. The current-limiting anti-reverse circuit can protect the safety of the first power supply and the safety of the rear end circuit. Taking a lithium battery as an example, the current-limiting anti-reverse circuit acts on the output end of the lithium battery to prevent the reverse connection of the positive electrode and the negative electrode of the lithium battery, prevent the second power supply from reversely charging the lithium battery, limit the reverse charging current of the battery and avoid the explosion of the lithium battery.

Specifically, the current-limiting anti-reverse circuit includes: the current limiting resistor R1, the filter capacitor, the fifth switch Q1 and the grounding resistor R2; one end of the current-limiting resistor R1 is connected with a first power supply, and the other end of the current-limiting resistor R1 is connected with the first end of the filter capacitor and the input electrode of the fifth switch Q1; the second end of the filter capacitor is grounded; an output electrode of the fifth switch Q1 is connected with the first input end, a control electrode of the fifth switch Q1 is connected with one end of a grounding resistor R2, and the other end of the grounding resistor R2 is connected with the second end of the filter capacitor.

The fifth switch Q1 is an electronic component having a switching function. The current limiting resistor R1 functions to limit the value of current flowing through the entire circuit. The filter capacitor plays a role in filtering, and the stability of the voltage of the lithium battery is ensured.

Further, the filter capacitor includes: and the parallel capacitor is formed by a first filter capacitor C2 and a second filter capacitor C3. And the two capacitors connected in parallel are adopted, so that the equivalent resistance of the filter circuit is further reduced.

Fig. 12 is a circuit diagram of a current-limiting anti-reverse circuit in the power switching system provided in the present application, wherein the fifth switch Q1 takes a PMOS transistor as an example. When the first power supply supplies power and the second power supply is powered off, current provided by the first power supply enters the current-limiting anti-reverse circuit, passes through the current-limiting resistor R1, the first filter capacitor C2 and the second filter capacitor C3, and enters the drain electrode of the fifth switch Q1. The voltage of the first power source is turned on through the body diode of the fifth switch Q1 so that the source voltage of the fifth switch Q1 is approximately equal to the lithium battery voltage. The source voltage of the fifth switch Q1 is slightly lower than the drain voltage due to the inherent conduction voltage drop of the body diode.

The gate of the fifth switch Q1 is grounded through a ground resistor R2, and the gate voltage is at zero level. Since the gate voltage of the fifth switch Q1 is lower than the source voltage and the voltage difference reaches the turn-on voltage of the fifth switch Q1, the fifth switch Q1 is turned on. After the fifth switch Q1 is turned on, the current no longer passes through its body diode, but from the drain to the source. The equivalent impedance between the drain and the source is in milliohm level, so that the first power voltage is connected to the back-end circuit without large voltage loss after passing through the fifth switch Q1.

When the positive electrode and the negative electrode of the first power supply are plugged reversely, the fifth switch Q1 is not conducted, a reverse-prevention power supply protection mechanism is provided, and the safety of the rear-end circuit and the safety of the lithium battery are protected.

In one example, in order to protect the power supply, a backflow prevention circuit is arranged between the output electrode and the output end of the first switch Q2, a first end of the backflow prevention circuit is connected with the output electrode of the first switch Q2, and a second end of the backflow prevention circuit is connected with the output end. Fig. 13 is a schematic structural diagram of another power switching system provided in the present application, in which the backflow prevention circuit is mainly used for preventing a current from flowing backward, and preventing a lithium battery current from entering an external circuit when a lithium battery supplies power; when the external power supply supplies power, the current of the external power supply is prevented from flowing backwards and entering the lithium battery, unnecessary energy loss is avoided, and safety accidents are prevented.

Further, the backflow prevention circuit comprises: a sixth switch Q3; an input electrode of the sixth switch Q3 is used as a first end of the backflow prevention circuit and is connected with an output electrode of the first switch Q2; the output electrode of the sixth switch Q3 is used as the second end of the backflow prevention circuit and is connected with the output end; the control electrode of the sixth switch Q3 is connected to the control electrode of the first switch Q2. The sixth switch Q3 prevents the second power supply current from flowing to the first power supply when the second power supply supplies power, thereby avoiding unnecessary energy loss.

Further, the power switching circuit provided by the present application further includes: a second capacitor C1; one end of the second capacitor C1 is connected to the output electrode of the first switch Q2, and the other end of the second capacitor C1 is connected to the control electrode of the first switch Q2. The second capacitor is a filter capacitor, so that power supply interference is filtered, and false triggering is avoided.

Further, the power switching system provided by the present application further includes: a load capacitor C4; one end of the load capacitor C4 is connected with the output end of the power supply switching circuit, and the other end of the load capacitor C4 is grounded. The load capacitor is a filter capacitor, and the stability of the output voltage is ensured.

For example, fig. 14 is a circuit diagram of another power switching system provided in the present application. The first power source is a lithium battery, and the second power source is a commercial power. With reference to fig. 14, a description will be given of an operation principle of implementing fast switching of the power supply and an implementation process of related functions.

(1) In the first case: when only a lithium battery is present for power. When the lithium battery is used for supplying power, an external power is not connected into the circuit, the lithium battery firstly enters the current-limiting anti-reverse circuit, the lithium battery is connected into the circuit through the current-limiting resistor R1, the first filter capacitor C2 and the second filter capacitor C3, the current-limiting resistor R1 plays a role in limiting the current value flowing through the whole circuit, the first filter capacitor C2 and the second filter capacitor C3 play a role in filtering, and the voltage stability of the lithium battery is guaranteed.

The voltage of the lithium battery is conducted through a body diode of the fifth switch Q1, so that the voltage of a source electrode of the fifth switch Q1 is approximately equal to the voltage of the lithium battery (the body diode has conduction voltage drop), a grid electrode of the fifth switch Q1 is grounded through a grounding resistor R2, the voltage of the grid electrode of the fifth switch Q1 is at a zero level, the voltage of the grid electrode source of the fifth switch Q1 is at a negative voltage and reaches the conduction voltage of the fifth switch Q1, so that the fifth switch Q1 is conducted, the current is not conducted through the body diode of the fifth switch Q1 but from a drain electrode of the fifth switch Q1 to the source electrode, and the equivalent impedance between the drain electrode and the source electrode is in a milliohm level, so that the voltage of the lithium battery cannot have large voltage loss after passing through the fifth switch Q1 and is accessed into a rear-end circuit, the fifth switch Q1 further has an anti-reverse power supply protection mechanism, when the positive electrode and the negative electrode of the lithium battery are plugged, the fifth switch Q1 is not conducted, and the safety of the rear-end circuit and the lithium battery is protected.

The lithium battery voltage acts on the source electrode of the first switch Q2 after passing through the current-limiting anti-reverse circuit, the source electrode voltage of the first switch Q2 is similar to the lithium battery voltage, at the moment, the commercial power is not connected, the commercial power network is in a low level, the levels at the two ends of the fourth resistor R6 are in a low level, and the fourth switch Q6 is cut off. One end of the first voltage dividing resistor R3 is connected to the source of the first switch Q2 and the collector of the pull-up switch Q4, and the other end is connected to the base of the pull-up switch Q4 and the base of the pull-down switch Q5, at this time, the base voltage is forward biased, so that the pull-up switch Q4 is turned on, and the pull-down switch Q5 is turned off. The emitter of the pull-up switch Q4 is at a high level, which is applied to the base of the third switch Q7, and the base of the third switch Q7 is forward biased and in a conducting state.

The third switch Q7 is conducted, and the collector of the third switch Q7 is connected with the grid of the first switch Q2, so that the grid of the first switch Q2 is connected with the ground to be at zero level, the source voltage of the first switch Q2 is at high level, the grid-source voltage of the first switch Q2 is at negative pressure and reaches the conducting voltage of the first switch Q2, and the first switch Q2 is conducted; meanwhile, the grid-source voltage of the PMOS tube of the second switch Q8 is zero level and does not reach the turn-on voltage of the second switch Q8, so that the second switch Q8 is cut off; at this time, the gate voltage of the sixth switch Q3 is at a zero level, and the source voltage of the sixth switch Q3 is at a high level (the voltage value is from the drain to the source through the body diode), so the sixth switch Q3 is also turned on; at this moment, the voltage of the lithium battery supplies power for the load circuit after passing through the output load capacitor C4, wherein the second capacitor C1 is a filter capacitor, so that power interference is filtered, and misconduction is avoided.

When the lithium battery exists independently for power supply, the states of the switching devices are as follows: the fifth switch Q1 is conducted, the first switch Q2 is conducted, and the sixth switch Q3 is conducted; the second switch Q8 is off; the fourth switch Q6 is turned off, the pull-down switch Q5 is turned off, the pull-up switch Q4 is turned on, and the third switch Q7 is turned on.

(2) In the second case: when both mains and lithium batteries are present. After the voltage of the lithium battery passes through the current-limiting anti-reverse circuit, the voltage acts on a source electrode of the first switch Q2, at the moment, mains supply is connected into the circuit, two ends of the fourth resistor R6 are in a high level, the fourth switch Q6 is in a conducting state, base electrodes of the pull-up switch Q4 and the pull-down switch Q5 are connected to the same level point, the voltage value of the source electrode of the first switch Q2 acts on base electrodes of the pull-up switch Q4 and the pull-down switch Q5 through the first voltage-dividing resistor R3 and the second voltage-dividing resistor R5 in a voltage dividing mode, resistance values of the first voltage-dividing resistor R3 and the second voltage-dividing resistor R5 are adjusted and designed to enable the base electrode voltage to be lower than conducting voltage, at the moment, the pull-up switch Q4 is cut off, the pull-down switch Q5 is conducted, after the pull-down switch Q5 is conducted, the base electrode level of the third switch Q7 is in a zero level, the third switch Q7 is cut off, the grid electrode voltage of the first switch Q2 is lower than the source electrode voltage, the conducting condition of the first switch Q2 is not met, the first switch Q2 is cut off, and a path between the lithium battery and the load circuit is cut off.

The source voltage of the second switch Q8 is high level, and the drain voltage is low level; meanwhile, the gate-source voltage of the second switch Q8 is a negative voltage and reaches its turn-on voltage, and the second switch Q8 is turned on. The mains supply acts on the load circuit through the second diode D3 and the load capacitor C4, at the moment, the sixth switch Q3 is in a cut-off state, and the body diode of the sixth switch plays a role in preventing backflow.

When the lithium battery and the mains supply exist at the same time, the states of the switching devices are as follows: the fifth switch Q1 is turned on, the first switch Q2 is turned off, and the sixth switch Q3 is turned off; the second switch Q8 is turned on; the fourth switch Q6 is switched on, the pull-down switch Q5 is switched on, the pull-up switch Q4 is switched off, and the third switch Q7 is switched off; similarly, when the commercial power is changed from high level to low level, the commercial power is automatically switched to the lithium battery for power supply, and the specific steps are the same as those in the first case.

The circuit scheme shown in fig. 14 can be applied to the occasions where the power supply needs to be quickly switched and responded, when the requirement of quick switching of the power supply does not exist, the quick switching circuit can be removed on the basis of the circuit scheme, the automatic switching function of dual power supply can also be achieved, meanwhile, the circuit scheme has the corresponding power supply protection mechanisms of reverse connection prevention, current limiting, reverse flow prevention and the like and the beneficial effects of low voltage loss, and the specific circuit diagram is realized as shown in fig. 15.

Fig. 15 is a circuit diagram of another power switching system provided in the present application, which is formed by combining the current-limiting anti-reverse circuit shown in fig. 12 and a reverse-flow prevention device on the basis of fig. 6. The current-limiting reverse-prevention circuit specifically comprises a current-limiting reverse-prevention circuit, a switching circuit, a reverse-flow-prevention circuit and a load circuit. As shown in fig. 15, the switching circuit is composed of a TVS transistor D1, a first switch Q2, and a first resistor R7; the current-limiting anti-reverse circuit consists of a current-limiting resistor R1, a grounding resistor R2, a first filter capacitor C2, a second filter capacitor C3 and a fifth switch Q1; the backflow prevention circuit consists of a sixth switch Q3 and a first diode D2; the load circuit includes a load capacitor C4. The operation principle of switching the power supply and the implementation process of the related functions will be described with reference to fig. 15.

(1) In the first case: when only a lithium battery is present to supply power. The fifth switch Q1, the first switch Q2 and the sixth switch Q3 are conducted, and the terminal voltage of the lithium battery is transmitted to a load circuit through the load capacitor C4 after small loss.

After the lithium battery is subjected to current limiting through the current limiting resistor R1, the voltage of the lithium battery is loaded at the drain end of the fifth switch Q1 after being filtered by the first filter capacitor C2 and the second filter capacitor C3, and then is transmitted to the source electrode of the fifth switch Q1 through the body diode of the fifth switch Q1, and the voltage of the source electrode is approximately equal to the voltage of the lithium battery. The gate of the fifth switch Q1 is at zero level due to the presence of the pull-down ground resistor R2. The gate-source voltage of the fifth switch Q1 reaches its turn-on voltage threshold, so the fifth switch Q1 is turned on.

After the fifth switch Q1 is turned on, the voltage of the lithium battery is loaded at the source terminal of the first switch Q2, and at this time, the commercial power is not supplied, so the grid of the first switch Q2 is grounded to zero level through the first resistor R7, the grid-source voltage of the first switch Q2 reaches its turn-on voltage threshold, so the first switch Q2 is turned on; the turn-on process of the sixth switch Q3 is the same as the turn-on process of the fifth switch Q1. Sixth switch Q3 has prevents the function of preventing flowing backward, prevents that the lithium cell from being reverse charged, and first diode D2 prevents that the energy from producing the unnecessary loss for preventing that lithium cell electric current flows backward to outer electric circuit in, TVS pipe D1 damages for preventing that first switch Q2 from puncturing.

(2) In the second case: when both mains and lithium batteries are present. The fifth switch Q1 is conducted, the first switch Q2 and the sixth switch Q3 are cut off, the lithium battery is disconnected with the load circuit, and the load circuit is powered by external electricity.

When the mains supply exists, the grid voltage of the first switch Q2 and the grid voltage of the sixth switch Q3 are the mains supply voltage, and the external voltage is larger than the lithium battery voltage, so that the grid source voltage of the first switch Q2 and the grid source voltage of the sixth switch Q3 are lower than the conducting voltage threshold value, and the first switch Q2 and the sixth switch Q3 are cut off. At this time, the external power supplies power to the load circuit through the first diode D2 and the load capacitor C4, and the sixth switch Q3 has an anti-reverse-charging function, so that the external power is prevented from reversely charging the lithium battery.

The application provides a dual power supply device, which comprises the power supply switching system. Other technical features are the same as those of the power switching system and can achieve the same technical effects, and are not described in detail herein.

Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.

It will be understood that the present application is not limited to the precise arrangements that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims

1. A power switching system, comprising: a power switching circuit;

the power supply switching circuit is provided with a first input end, a second input end and an output end, the first input end is connected with a first power supply, the second input end is connected with a second power supply, and the output end of the power supply switching circuit is connected with the second input end and a load circuit;

wherein the power switching circuit comprises: a first switch; the input pole of the first switch is connected to the first input end, the output pole of the first switch is connected to the output end, and the control pole of the first switch is connected with the input pole of the first switch, the second input end and the ground.

2. The system of claim 1, wherein a TVS tube is disposed between the control pole of the first switch and the input pole of the first switch; the first end of the TVS tube is connected with the input pole of the first switch, and the second end of the TVS tube is connected with the control pole of the first switch.

3. The system of claim 1, wherein a first resistor is disposed between the control pole of the first switch and ground;

one end of the first resistor is connected with the second input end and the control electrode of the first switch, and the other end of the first resistor is grounded.

4. The system of claim 2, wherein a first diode is disposed between the second input terminal and the output terminal;

the anode of the first diode is connected with the second input end, and the cathode of the first diode is connected with the output end.

5. The system of claim 1, wherein a second switch is disposed between the second input and the output; an input pole of the second switch is connected with the second input end, an output pole of the second switch is connected with the output end, and a control pole of the second switch is connected with one end of a second resistor; the other end of the second resistor is connected with a control electrode of a third switch, an input electrode of the third switch is connected with a control electrode of the first switch, and an output electrode of the third switch is grounded;

the power switching circuit further includes: the fourth switch, the inverter circuit, the first divider resistor and the second divider resistor; a control electrode of a fourth switch is connected with the second input end, an input electrode of the fourth switch is connected with an input node of the inverter circuit and one end of the first voltage-dividing resistor, and an output electrode of the fourth switch is connected with one end of the second voltage-dividing resistor; the other end of the second voltage-dividing resistor is grounded, and the other end of the first voltage-dividing resistor is connected with the input electrode of the first switch and the power supply node of the inverter circuit; an output node of the inverter circuit is connected to a control electrode of the third switch.

6. The system of claim 5, wherein a third resistor is disposed between the output node of the inverter circuit and the gate of the third switch;

one end of the third resistor is connected with an output node of the inverter circuit, and the other end of the third resistor is connected with a control electrode of the third switch.

7. The system of claim 5, wherein a fourth resistor is disposed between the second input and the gate of the fourth switch;

one end of the fourth resistor is connected with the second input end and one end of the first capacitor, the other end of the fourth resistor is connected with a control electrode of the fourth switch, and the other end of the first capacitor is grounded.

8. The system of claim 5, wherein a second diode is disposed between the output pole of the second switch and the output terminal;

and the anode of the second diode is connected with the output electrode of the second switch, and the cathode of the second diode is connected with the output end.

9. The system of claim 5, wherein the inverting circuit comprises: a pull-up switch and a pull-down switch;

the input pole of the pull-up switch is used as a power supply node of the inverter circuit; the output pole of the pull-up switch is connected with the input pole of the pull-down switch and is used as the output node of the phase-inverting circuit; the output pole of the pull-down switch is grounded; and the control electrode of the pull-up switch is connected with the control electrode of the pull-down switch and is used as an input node of the inverter circuit.

10. The system of claim 1, wherein the power switching system further comprises: a current limiting anti-reverse circuit between the first power supply and the first input terminal;

the current-limiting anti-reverse circuit comprises: the current limiting resistor, the filter capacitor, the fifth switch and the grounding resistor; one end of the current-limiting resistor is connected with the first power supply, and the other end of the current-limiting resistor is connected with the first end of the filter capacitor and the input electrode of the fifth switch; the second end of the filter capacitor is grounded; the output electrode of the fifth switch is connected with the first input end, the control electrode of the fifth switch is connected with one end of the grounding resistor, and the other end of the grounding resistor is connected with the second end of the filter capacitor.

11. The system of claim 10, wherein the filter capacitor comprises: and the parallel capacitor is formed by the first filter capacitor and the second filter capacitor.

12. The system of claim 1, wherein a backflow prevention circuit is disposed between the output electrode of the first switch and the output end, a first end of the backflow prevention circuit is connected to the output electrode of the first switch, and a second end of the backflow prevention circuit is connected to the output end.

13. The system of claim 12, wherein the back-flow prevention circuit comprises: a sixth switch;

the input pole of the sixth switch is used as the first end of the backflow prevention circuit and is connected with the output pole of the first switch; the output electrode of the sixth switch is used as the second end of the backflow prevention circuit and is connected with the output end; and the control electrode of the sixth switch is connected with the control electrode of the first switch.

14. The system of claim 1, wherein the power switching circuit further comprises: a second capacitor;

one end of the second capacitor is connected with the output electrode of the first switch, and the other end of the second capacitor is connected with the control electrode of the first switch.

15. The system of any one of claims 1-14, wherein the power switching system further comprises: a load capacitance;

one end of the load capacitor is connected with the output end of the power supply switching circuit, and the other end of the load capacitor is grounded.

16. A dual power supply apparatus comprising the power switching system of any one of claims 1-15.