Switching circuit for dual power supplies

Abstract

The utility model discloses a switching circuit for dual power supplies, which comprises a first input end, a second input end and an output end, and is characterized in that the first input end is used for being connected with an anode of a main power supply, and the second input end is used for being connected with an anode of an auxiliary power supply; a first resistor, a second resistor and a third resistor, the first resistor and the second resistor are connected in series between a second input end and the first input end, and the third resistor is connected between the first input end and a grounding point; a source electrode of the first MOS tube is connected with the first input end, a grid electrode of the first MOS tube is connected with a grounding point, and a drain electrode of the first MOS tube is connected with the output end; and the source electrode of the second MOS tube is connected with the second input end, the grid electrode of the second MOS tube is connected with the connection point of the first resistor and the second resistor, and the drain electrode of the second MOS tube is connected with the output end. The charging and discharging times of the auxiliary power supply are reduced, so that the service life of the auxiliary power supply is prolonged.

Description

Technical Field

[0001] This utility model relates to the field of power supply, and more specifically, to a switching circuit for a dual power supply including a main power supply and an auxiliary power supply. Background Technology

[0002] The primary application of dual power supplies is in the field of smart IoT. In such applications, the main power supply typically uses an AC / DC converter, while the auxiliary power supply usually uses a lithium battery. The design requirement is to automatically switch to the auxiliary power supply in the event of a main power failure. Utility Model Content

[0003] The inventors of this utility model recognized the urgent need for a switching circuit that uses only the main power supply when it is available, and switches to auxiliary power only when the main power supply is unavailable. To achieve this technical objective, this utility model proposes a switching circuit for dual power supplies, the switching circuit comprising:

[0004] A first input terminal, a second input terminal, and an output terminal are provided, wherein the first input terminal is used to connect to the positive terminal of the main power supply and the second input terminal is used to connect to the positive terminal of the auxiliary power supply.

[0005] A first resistor, a second resistor, and a third resistor, wherein the first resistor and the second resistor are connected in series between the second input terminal and the first input terminal, and the third resistor is connected between the first input terminal and a ground point;

[0006] A first MOSFET, wherein its source is connected to the first input terminal, its gate is connected to ground, and its drain is connected to the output terminal; and

[0007] The second MOSFET has its source connected to the second input terminal, its gate connected to the junction of the first resistor and the second resistor, and its drain connected to the output terminal.

[0008] In the dual power supply switching circuit according to this utility model, a voltage divider circuit composed of three resistors is used, so that when the main power supply is on, the first MOSFET is turned on and the second MOSFET is turned off, so that the main power supply supplies power to the load connected to the output terminal; correspondingly, when the main power supply is off, the first MOSFET is turned off and the second MOSFET is turned on, so that the auxiliary power supply supplies power to the load connected to the output terminal.

[0009] Preferably, in some embodiments of the present invention, the resistance value of the first resistor is smaller than that of the second resistor and larger than that of the third resistor.

[0010] Preferably, in some embodiments of the present invention, the resistance value of the first resistor and the ratio of the resistance value of the first resistor to the resistance value of the third resistor are 2:4:1. More preferably, in some embodiments of the present invention, the resistance value of the first resistor is 20K ohms, the resistance value of the second resistor is 40K ohms, and the resistance value of the third resistor is 10K ohms.

[0011] Preferably, in some embodiments of the present invention, the first MOSFET and the second MOSFET are configured as a single component. More preferably, in some embodiments of the present invention, the first MOSFET and the second MOSFET are configured as an NCE 4953 selection component.

[0012] Preferably, in some embodiments of the present invention, the switching circuit further includes a first diode and a second diode, wherein the first diode is disposed between the first MOSFET and the output terminal, and the second diode is disposed between the second MOSFET and the output terminal. More preferably, in some embodiments of the present invention, the first diode and the second diode are configured as Schottky diodes. More preferably, in some embodiments of the present invention, the Schottky diode is configured as a DSK 24 selection component.

[0013] Preferably, in some embodiments of the present invention, the switching circuit further includes a first capacitor and a second capacitor, which are disposed between the first input terminal and the ground point. More preferably, in some embodiments of the present invention, the switching circuit further includes a third capacitor and a fourth capacitor, which are disposed between the second input terminal and the ground point. More preferably, in some embodiments of the present invention, the switching circuit further includes a fifth capacitor and a sixth capacitor, which are disposed between the output terminal and the ground point.

[0014] In the dual-power supply switching circuit according to this invention, a voltage divider circuit consisting of three resistors is used. This ensures that when the main power supply is on, the first MOSFET is turned on and the second MOSFET is turned off, allowing the main power supply to power the load connected to the output terminal. Conversely, when the main power supply is off, the first MOSFET is turned off and the second MOSFET is turned on, allowing the auxiliary power supply to power the load connected to the output terminal. This reduces the number of charge-discharge cycles of the auxiliary power supply, thereby increasing its lifespan. Attached Figure Description

[0015] The features, advantages, and other aspects of the various embodiments of this utility model will become more apparent from the accompanying drawings and the following detailed description. Several embodiments of this disclosure are shown herein by way of example and not limitation, in the accompanying drawings:

[0016] Figure 1 A switching circuit 100 for dual power supplies according to an embodiment of the present invention is shown; and

[0017] Figure 2 A switching circuit 200 for dual power supplies according to another embodiment of the present invention is shown. Detailed Implementation

[0018] In the following detailed description of preferred embodiments, reference will be made to the accompanying drawings, which form part of this invention. The accompanying drawings illustrate, by way of example, specific embodiments that can implement this invention. The exemplary embodiments are not intended to be exhaustive of all embodiments according to this invention. It will be understood that other embodiments may be utilized, and structural or logical modifications may be made, without departing from the scope of this invention. Therefore, the following detailed description is not restrictive, and the scope of this invention is defined by the appended claims.

[0019] The terms “comprising,” “including,” and similar terms used herein should be understood as open-ended terms, meaning “including / including but not limited to,” implying that other content may also be included. The term “based on” means “at least partially based on.” The term “one embodiment” means “at least one embodiment”; the term “another embodiment” means “at least one additional embodiment,” and so on.

[0020] The switching between main power and auxiliary power is typically achieved using the unidirectional conductivity of Schottky diodes. However, this method has the following problems:

[0021] When the main power supply voltage is greater than the auxiliary power supply voltage, the main power supply operates, and the auxiliary power supply does not work. The forward voltage drop between individual Schottky diodes needs to be ignored here.

[0022] When the voltage of the main power supply equals the voltage of the auxiliary power supply, both the main and auxiliary power supplies operate simultaneously. In this case, the forward voltage drop between individual Schottky diodes should be ignored.

[0023] When the main power supply voltage is lower than the auxiliary power supply voltage, the auxiliary power supply operates, and the main power supply does not work. In this case, the forward voltage drop between individual Schottky diodes should also be ignored.

[0024] When lithium batteries are used as auxiliary power sources, their usage time should be minimized to extend battery life. Ideally, the lithium battery should only begin operating after the main power supply fails. In other words, when both the main and auxiliary power supplies are connected to the circuit, only the main power supply should operate, while the auxiliary power supply should remain inactive.

[0025] For example, in the design of a home access control system, it is convenient to use 220V AC power, while the door sensor's power supply voltage is around 12V. Therefore, a standard 12V AC / DC converter module is selected. Considering the possibility of a power outage causing system failure, a backup power source (lithium battery) is needed. The charging voltage of lithium iron phosphate batteries is 3.6V. Using four batteries in series results in a voltage of 3.6V*4 (four lithium batteries in series). Without four batteries, the lithium batteries may not fully charge, affecting their utilization rate. In this case, the auxiliary power supply voltage is higher than the main power supply voltage.

[0026] The problem needs to be solved when the backup power supply (lithium battery) is higher than the main power supply voltage (DC 12V). When both are connected to the circuit, only the main power supply works and the auxiliary power supply does not work. Moreover, the auxiliary power supply should only work when the main power supply fails.

[0027] This invention proposes a control circuit that automatically switches between main power and auxiliary power supply based on the switching characteristics of a MOSFET. The circuit includes a main power supply from the output (12V) of an AC / DC converter module and an auxiliary power supply from a lithium battery (14.4V). The circuit utilizes a MOSFET control circuit to control the MOSFET's on / off state, thereby fulfilling the power supply requirements of both the main and auxiliary power supplies. More preferably, the circuit prevents reverse current from flowing back to the power input terminal through the unidirectional conductivity of a Schottky diode.

[0028] In summary, the inventors of this utility model recognized the urgent need for a switching circuit that uses only the main power supply when it is available, and switches to auxiliary power supply only when the main power supply is unavailable. To achieve this technical objective, this utility model proposes a switching circuit for dual power supplies, comprising: a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is connected to the positive terminal of the main power supply and the second input terminal is connected to the positive terminal of the auxiliary power supply; a first resistor, a second resistor, and a third resistor, wherein the first resistor and the second resistor are connected in series between the second input terminal and the first input terminal, and the third resistor is connected between the first input terminal and a ground point; a first MOSFET, whose source is connected to the first input terminal, whose gate is connected to the ground point, and whose drain is connected to the output terminal; and a second MOSFET, whose source is connected to the second input terminal, whose gate is connected to the junction of the first resistor and the second resistor, and whose drain is connected to the output terminal.

[0029] Specifically, the following references Figure 1 To describe a dual-power switching circuit 100 according to an embodiment of the present invention, from Figure 1 As can be seen from the above, the dual-power switching circuit 100 proposed according to this utility model includes: a first input terminal 111, a second input terminal 112, and an output terminal 118, wherein the first input terminal 111 is used to connect to the positive terminal of the main power supply and the second input terminal 112 is used to connect to the positive terminal of the auxiliary power supply; a first resistor 113, a second resistor 114, and a third resistor 115, wherein the first resistor 113 and the second resistor 114 are connected in series between the second input terminal 112 and the first input terminal 111, and the third resistor 115 is connected between the first input terminal 111 and a ground point; a first MOSFET 117, whose source S is connected to the first input terminal 111, whose gate G is connected to the ground point, and whose drain D is connected to the output terminal 118; and a second MOSFET 116, whose source S is connected to the second input terminal 112, whose gate G is connected to the connection point of the first resistor 113 and the second resistor 114, and whose drain D is connected to the output terminal 118. It should be noted that... Figure 1The icons representing the intersections of different connecting lines indicate different meanings. Specifically, a small black dot at the intersection indicates that the connecting lines are electrically connected, while the absence of a small black dot at the intersection indicates that the connecting lines are not electrically connected, i.e., electrically insulated. In the dual-power switching circuit 100 according to this utility model, a voltage divider circuit composed of three resistors 113, 114, and 115 is used. This ensures that when the main power supply (electrically connected to the first input terminal 111) is powered, the first MOSFET 117 is turned on and the second MOSFET 116 is turned off, allowing the main power supply to power the load connected to the output terminal 118. Conversely, when the main power supply (electrically connected to the first input terminal 111) is de-energized, the first MOSFET 117 is turned off and the second MOSFET 116 is turned on, allowing the auxiliary power supply (electrically connected to the second input terminal 112) to power the load connected to the output terminal 118.

[0030] Figure 1 The control circuit structure shown is very simple and low in cost. It does not require a microcontroller or software control. Only a small number of resistors are needed to detect the power failure of the main power supply and turn the auxiliary power supply on / off in time, realizing the automatic switching between the main power supply and the auxiliary power supply in the form of hardware circuit.

[0031] As can be seen from the above discussion, the main problem that this utility model needs to solve is how to ensure that only the main power supply works while the auxiliary power supply does not work when the working voltage of the auxiliary power supply (lithium battery, for example, 14.4V) is higher than that of the main power supply (for example, DC 12V) when both are connected to the circuit. The auxiliary power supply only works when the main power supply fails.

[0032] The following will combine Figure 2 To describe another embodiment according to the present invention. Figure 2 A switching circuit 200 for dual power supplies according to another embodiment of the present invention is shown. Here, the inventors of the present invention would like to emphasize that the present invention... Figure 2 The detailed embodiments shown are illustrated in the following description, and the accompanying images are shown in the drawings; R1, R2, R3, R4, C4, C5, C6, C7, C8, C9, U1, D5, D6, etc., described below are component reference numbers in the schematic diagram; the components in this schematic diagram represent components with the same or similar functional parameters.

[0033] from Figure 2 As can be seen from this, the dual-power supply switching circuit 200 proposed according to this utility model includes: a first input terminal (e.g., a connection terminal connected to the main power supply 220), a second input terminal (e.g., a connection terminal connected to the auxiliary power supply 230), and an output terminal 118 (e.g., Vout). Figure 2In this embodiment, the main power supply operates at 12V, while the auxiliary power supply operates at, for example, 14.4V (higher than 12V). Here, as previously described, the first input terminal is connected to the positive terminal of the main power supply 220, and the second input terminal is connected to the positive terminal of the auxiliary power supply 230; a first resistor 213, a second resistor 214, and a third resistor 215 are present, wherein the first resistor 213 and the second resistor 214 are connected in series between the second input terminal and the first input terminal, and the third resistor 215 is connected between the first input terminal and ground; a first MOSFET 217 has its source S connected to the first input terminal, its gate G connected to ground via resistor 219, and its drain D connected to the output terminal 218; and a second MOSFET 216 has its source S connected to the second input terminal, its gate G connected to the junction of the first resistor 213 and the second resistor 214, and its drain D connected to the output terminal 218. It should be noted that... Figure 2 The icons at the intersections of different connecting lines represent different meanings. Specifically, a small black dot at the intersection indicates that the connecting lines are electrically connected, while the absence of a small black dot at the intersection indicates that the connecting lines are not electrically connected, i.e., electrically insulated. In the dual-power switching circuit 200 according to this utility model, a voltage divider circuit composed of three resistors 213, 214, and 215 is used. This ensures that when the main power supply (electrically connected to the first input terminal) is energized, the first MOSFET 217 is turned on and the second MOSFET 216 is turned off, allowing the main power supply to power the load connected to the output terminal 218. Conversely, when the main power supply (electrically connected to the first input terminal) is de-energized, the first MOSFET 217 is turned off and the second MOSFET 216 is turned on, allowing the auxiliary power supply (electrically connected to the second input terminal) to power the load connected to the output terminal 218.

[0034] exist Figure 2 In the illustrated embodiment, the resistance of the first resistor is smaller than that of the second resistor and larger than that of the third resistor. Preferably, the ratio of the resistance of the first resistor to the resistance of the third resistor is 2:4:1. More specifically, the resistance of the first resistor is, for example, 20K ohms, the resistance of the second resistor is, for example, 40K ohms, and the resistance of the third resistor is, for example, 10K ohms.

[0035] Alternatively, in accordance with this utility model Figure 2 In the illustrated embodiment, the first MOSFET 217 and the second MOSFET 216 are configured as a single component U1, where U1 is a P-type MOSFET (two P-channels). More preferably, according to the present invention... Figure 2In the illustrated embodiment, the first MOS transistor 217 and the second MOS transistor 216 are configured as NCE 4953 selection components.

[0036] Preferably, according to the present invention Figure 2 In the illustrated embodiment, the switching circuit 200 further includes a first diode 261 and a second diode 262. The first diode 261 is disposed between the first MOSFET 217 and the output terminal 218, and the second diode 262 is disposed between the second MOSFET 216 and the output terminal 218. More preferably, according to the present invention... Figure 2 In the illustrated embodiment, the first diode 261 and the second diode 262 are configured as Schottky diodes. More preferably, according to the present invention... Figure 2 In the illustrated embodiment, the Schottky diode is configured as a DSK 24 selection component.

[0037] In the actual operation process, when the main power supply X3 changes from being powered off to being powered on, the system power supply mode switches to main power supply X3 working, and auxiliary power supply X4 not working. The principle of this is as follows. When the main power supply X3 (12V) is connected to the system, according to the principle of resistor voltage division, Va = 14.4V, Vc = 12V, and Vb = 13.6V. For MOSFET 217 in main power supply X3, Vgs = Vg1 - Vs1 = 0V - 12V = -12V, and the turn-on voltage of MOSFET Vgs(th)(max) = -3V, so MOSFET 217 in main power supply X3 can be turned on normally; for MOSFET 216 in auxiliary power supply X4, Vgs = Vg2 - Vs2 = Vb - Va = 13.6V - 14.4V = -0.8V, and the minimum voltage difference for MOSFET 216 to turn on is Vgs(th)(min) = -1V, so MOSFET 216 in auxiliary power supply X4 is turned off.

[0038] Based on the above analysis, we can conclude that: Figure 2 The switching circuit in the illustrated embodiment enables that when the main power supply X3 and the auxiliary power supply X4 are connected at the same time, only the main power supply provides power and the auxiliary power supply does not provide power.

[0039] In another scenario, when the main power supply X3 changes from power-on to power-off, the system power supply mode switches to auxiliary power supply X4, and the main power supply X3 stops working. The implementation principle is as follows: When the main power supply X3 (12V) is powered off, according to the resistor voltage divider principle, Va = 14.4V, Vb = 10.28V, and Vc = 2.05V. For the MOSFET 216 of auxiliary power supply X4, Vgs = Vg2 - Vs2 = Vb - Va = 10.28V - 14.4V = -4.12V, and the maximum voltage difference for MOSFET 216 to turn on is Vgs(th)(max) = -3V. Therefore, MOSFET 216 of auxiliary power supply X4 is turned on. When auxiliary power supply X4 is at 14.4V, after the main power supply X3 is powered off, it can automatically switch to auxiliary power supply X4.

[0040] When the auxiliary power supply X4 is a lithium battery, the battery voltage continuously decreases during the power supply process. The discharge termination voltage for a single lithium iron phosphate battery is set to 2.6V. Therefore, the discharge termination voltage of the lithium iron phosphate battery pack formed by four lithium iron phosphate batteries connected in series is 10.4V. Thus, it is sufficient to ensure that the lithium battery voltage can continue to supply power when it reaches 10.4V. When the voltage of the auxiliary power supply X4 drops to 10.4V, according to the principle of resistor voltage division, Va' = 10.4V, Vb' = 7.4V, and Vc' = 1.48V. For the MOSFET 216 of the auxiliary power supply X4, Vgs = Vg2 - Vs2 = Vb' - Va' = 7.4V - 10.4V = -3V. The maximum voltage difference for the MOSFET 216 to turn on is Vgs(th)(max) = -3V. Therefore, the MOSFET 216 of the auxiliary power supply X4 turns on.

[0041] Based on the above analysis, it can be achieved that when the main power supply X3 fails, the auxiliary power supply X4 can operate from a fully charged state (14.4V) to the battery undervoltage protection state (10.4V). When the auxiliary power supply X4 is a lithium battery and the number of cells in series is different, the operating range of the auxiliary power supply can be adjusted by simply adjusting the resistance value.

[0042] The key point of this invention lies in using simple circuit components to build an automatic switching circuit between the main power supply X3 and the auxiliary power supply X4 that meets the requirements. This invention aims to protect the design architecture of this circuit by utilizing the voltage divider between the main power supply X3 and the auxiliary power supply X4 connected to the system to achieve the switching method of the MOSFET switches for the main power supply X3 and the auxiliary power supply X4.

[0043] In addition to the aforementioned automatic switching working principle, preferably, according to this utility model... Figure 2In the illustrated embodiment, the switching circuit 200 further includes a first capacitor 251 and a second capacitor 252, which are disposed between the first input terminal and the ground point. This arrangement allows for a more stable supply voltage of the main power supply X3. More preferably, according to the present invention... Figure 2 In the illustrated embodiment, the switching circuit 200 further includes a third capacitor 253 and a fourth capacitor 254, which are disposed between the second input terminal and the ground point. This arrangement allows for a more stable supply voltage to the auxiliary power supply X4. More preferably, according to the present invention... Figure 2 In the illustrated embodiment, the switching circuit 200 further includes a fifth capacitor 255 and a sixth capacitor 256, which are disposed between the output terminal 218 and the ground point. This arrangement allows for a more stable supply voltage to the output terminal Vout.

[0044] In summary, the dual-power switching circuit according to this invention utilizes a voltage divider circuit composed of three resistors. This ensures that when the main power supply is active, the first MOSFET is turned on and the second MOSFET is turned off, allowing the main power supply to power the load connected to the output terminal. Conversely, when the main power supply is de-energized, the first MOSFET is turned off and the second MOSFET is turned on, allowing the auxiliary power supply to power the load connected to the output terminal. This reduces the number of charge-discharge cycles of the auxiliary power supply, thereby extending its lifespan.

[0045] The above descriptions are merely optional embodiments of this disclosure and are not intended to limit the embodiments of this disclosure. For those skilled in the art, various modifications and variations can be made to the embodiments of this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this disclosure should be included within the protection scope of the embodiments of this disclosure.

[0046] While embodiments of this disclosure have been described with reference to several specific examples, it should be understood that the embodiments of this disclosure are not limited to the specific embodiments disclosed. The embodiments of this disclosure are intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the appended claims is to be interpreted in the broadest possible sense, thereby encompassing all such modifications and equivalent structures and functions.

Claims

1. A switching circuit for dual power supplies, characterized in that, The switching circuit includes: A first input terminal, a second input terminal, and an output terminal are provided, wherein the first input terminal is used to connect to the positive terminal of the main power supply and the second input terminal is used to connect to the positive terminal of the auxiliary power supply. A first resistor, a second resistor, and a third resistor, wherein the first resistor and the second resistor are connected in series between the second input terminal and the first input terminal, and the third resistor is connected between the first input terminal and a ground point; A first MOSFET, wherein its source is connected to the first input terminal, its gate is connected to ground, and its drain is connected to the output terminal; and The second MOSFET has its source connected to the second input terminal, its gate connected to the junction of the first resistor and the second resistor, and its drain connected to the output terminal.

2. The switching circuit according to claim 1, characterized in that, The resistance of the first resistor is smaller than that of the second resistor and larger than that of the third resistor.

3. The switching circuit according to claim 1 or 2, characterized in that, The resistance value of the first resistor and the ratio of the resistance value of the first resistor to the resistance value of the first resistor are 2:4:

1.

4. The switching circuit according to claim 1 or 2, characterized in that, The first resistor has a resistance of 20K ohms, the second resistor has a resistance of 40K ohms, and the third resistor has a resistance of 10K ohms.

5. The switching circuit according to claim 1, characterized in that, The first MOSFET and the second MOSFET are constructed as a single component.

6. The switching circuit according to claim 5, characterized in that, The first MOSFET and the second MOSFET are configured as NCE 4953 selection components.

7. The switching circuit according to claim 1, characterized in that, The switching circuit further includes a first diode and a second diode, wherein the first diode is disposed between the first MOSFET and the output terminal, and the second diode is disposed between the second MOSFET and the output terminal.

8. The switching circuit according to claim 7, characterized in that, The first diode and the second diode are configured as Schottky diodes.

9. The switching circuit according to claim 8, characterized in that, The Schottky diode is configured as a DSK 24 selection component.

10. The switching circuit according to claim 1, characterized in that, The switching circuit further includes a first capacitor and a second capacitor, which are disposed between the first input terminal and the ground point.

11. The switching circuit according to claim 1, characterized in that, The switching circuit further includes a third capacitor and a fourth capacitor, which are disposed between the second input terminal and the ground point.

12. The switching circuit according to claim 1, characterized in that, The switching circuit also includes a fifth capacitor and a sixth capacitor, which are disposed between the output terminal and the ground point.

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