A power switching circuit

Abstract

The utility model discloses a power switching circuit, include: first switch tube, second switch tube, first control circuit and second control circuit, first switch tube's first end is coupled with external power, and first switch tube's second end is coupled with power output end, second switch tube's first end is coupled with internal power, and second switch tube's second end is coupled with power output end, first control circuit is used for when the output voltage of external power is greater than or equal to set threshold value, control first switch tube conduction, to make external power to power output end power supply, second control circuit is used for when the output voltage of external power is less than set threshold value, control second switch tube conduction, to make internal power to power output end power supply, wherein, first control circuit and second control circuit are the circuit built by discrete component, the utility model discloses can reduce the cost of power switching circuit.

Description

Technical Field

[0001] This utility model relates to the field of power switching technology, and in particular to a power switching circuit. Background Technology

[0002] With the development of society, electronic products are being used more and more in various fields. In order to ensure the battery life of electronic products, power switching circuits have gradually emerged in electronic products, which has also put forward higher requirements for the design of power switching circuits.

[0003] Traditional power switching circuits monitor the power supply voltage through software and then control the switching transistors to achieve power switching and priority selection. This type of power switching circuit has significant drawbacks, as it requires software development for circuit control and the use of additional control chips. In other words, the cost of this type of power switching circuit is relatively high due to the need for software development for circuit control and the use of additional control chips. Utility Model Content

[0004] This invention provides a power switching circuit that can reduce the cost of power switching circuits.

[0005] This utility model provides a power switching circuit, including: a first switching transistor, a second switching transistor, a first control circuit, and a second control circuit; the first switching transistor has a first terminal, a second terminal, and a control terminal, the first terminal of the first switching transistor is coupled to an external power supply, and the second terminal of the first switching transistor is coupled to a power output terminal; the second switching transistor has a first terminal, a second terminal, and a control terminal, the first terminal of the second switching transistor is coupled to an internal power supply, and the second terminal of the second switching transistor is coupled to a power output terminal; the first control circuit has an input terminal and an output terminal, the input terminal of the first control circuit is coupled to the first terminal of the first switching transistor, and the first control circuit... The output terminal is coupled to the control terminal of the first switching transistor, and is used to control the first switching transistor to conduct when the output voltage of the external power supply is greater than or equal to a set threshold, so that the external power supply supplies power to the power output terminal; the second control circuit has an input terminal and an output terminal, the input terminal of the second control circuit is coupled to the first terminal of the first switching transistor, and the output terminal of the second control circuit is coupled to the control terminal of the second switching transistor, and is used to control the second switching transistor to conduct when the output voltage of the external power supply is less than a set threshold, so that the internal power supply supplies power to the power output terminal; wherein, the first control circuit and the second control circuit are circuits built from discrete components.

[0006] Optionally, the first control circuit includes a first resistor, a second resistor, a third resistor, a first transistor, and a second transistor; the first transistor is a PNP transistor, and the second transistor is an NPN transistor; the first terminal of the first resistor serves as the input terminal of the first control circuit, and the second terminal of the first resistor is coupled to the base of the first transistor; the emitter of the first transistor is coupled to the first terminal of the first switching transistor, and the collector of the first transistor is coupled to the base of the second transistor through the second resistor; the emitter of the second transistor is grounded, and the collector of the second transistor is coupled to the second terminal of the first switching transistor through the third resistor, and serves as the output terminal of the first control circuit.

[0007] Optionally, the system further includes a voltage regulator circuit, which includes a fourth resistor, a fifth resistor, a sixth resistor, and an adjustable Zener diode; the first end of the fourth resistor is coupled to the first end of the sixth resistor and the first end of the first switching transistor, the second end of the fourth resistor is coupled to the first end of the fifth resistor at a first node, and the second end of the fifth resistor is grounded; the cathode of the adjustable Zener diode is coupled to the second end of the sixth resistor and the first end of the first resistor, the anode of the adjustable Zener diode is coupled to the second end of the fifth resistor, and the adjustment terminal of the adjustable Zener diode is coupled to the first node.

[0008] Optionally, the second control circuit includes a seventh resistor, an eighth resistor, a third transistor, and a fourth transistor; the first terminal of the seventh resistor serves as the input terminal of the second control circuit; the third transistor is an NPN transistor, with its base coupled to the second terminal of the seventh resistor, its emitter grounded, and its collector coupled to the base of the fourth transistor; the fourth transistor is an NPN transistor, with its base coupled to the internal power supply through the eighth resistor, its collector serving as the output terminal of the second control circuit, and its emitter grounded.

[0009] Optionally, the second control circuit further includes a ninth resistor, coupled between the control terminal of the second switch and the first terminal of the second switch, for controlling the conduction speed of the second switch.

[0010] Optionally, the power switching circuit further includes a first diode and a first capacitor; the anode of the first diode is coupled to an external power supply, the cathode of the first diode is coupled to the first terminal of the first capacitor and the first terminal of the first switching transistor, and the second terminal of the first capacitor is grounded.

[0011] Optionally, the power switching circuit also includes a USB interface, through which an external power supply is coupled to the anode of the first diode.

[0012] Optionally, the power switching circuit also includes a second capacitor connected between the power output terminal and ground.

[0013] Optionally, both the first and second switching transistors are P-channel MOSFETs.

[0014] Optionally, the internal power source is a battery.

[0015] The power switching circuit provided in this embodiment includes a first switching transistor, a second switching transistor, a first control circuit, and a second control circuit. The first and second control circuits automatically output different drive signals based on the output voltage of the external power supply, thereby controlling the conduction of either the first or second switching transistor to achieve automatic switching between the external and internal power supplies. Furthermore, the first and second control circuits are constructed from discrete components, thus avoiding the need for power management chips and software control found in existing technologies. This power switching circuit achieves input voltage threshold detection and switching control through discrete component design, thereby improving the response speed and intelligence of the switching circuit. Moreover, the entire circuit uses circuit devices for power cut-off, eliminating the need for dedicated control chips, reducing the cost of the power switching circuit, and enhancing its reliability and applicability, making it particularly suitable for portable electronic products such as mobile phones and computers.

[0016] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this utility model, nor is it intended to limit the scope of this utility model. Other features of this utility model will become readily apparent from the following description. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a power switching circuit provided by this utility model;

[0019] Figure 2 This is a schematic diagram of the structure of a first control circuit provided by this utility model;

[0020] Figure 3 This is a schematic diagram of the structure of a second control circuit provided by this utility model;

[0021] Figure 4 This is a schematic diagram of another power switching circuit provided by this utility model. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0023] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this utility model are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this utility model described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0024] In this application, unless otherwise expressly specified and limited, the term "coupled" and similar terms should be interpreted broadly. For example, "coupled" can mean a direct connection or an indirect connection through an intermediate medium, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] Figure 1 This is a schematic diagram of a power switching circuit provided by this utility model. Figure 1 As shown, the power switching circuit 1 includes a first switching transistor Q1, a second switching transistor Q2, a first control circuit 11, and a second control circuit 12.

[0026] The first switching transistor Q1 has a first terminal, a second terminal, and a control terminal. The first terminal of the first switching transistor Q1 is coupled to the external power supply 10, and the second terminal of the first switching transistor Q1 is coupled to the power output terminal Vout.

[0027] The second switch Q2 has a first terminal, a second terminal, and a control terminal. The first terminal of the second switch Q2 is coupled to the internal power supply 20, and the second terminal of the second switch Q2 is coupled to the power output terminal Vout.

[0028] The first control circuit 11 has an input terminal and an output terminal. The input terminal of the first control circuit 11 is coupled to the first terminal of the first switching transistor Q1, and the output terminal of the first control circuit 11 is coupled to the control terminal of the first switching transistor Q1. It is used to control the first switching transistor Q1 to conduct when the output voltage of the external power supply 10 is greater than or equal to a set threshold, so that the external power supply 10 supplies power to the power output terminal Vout.

[0029] The second control circuit 12 has an input terminal and an output terminal. The input terminal of the second control circuit 12 is coupled to the first terminal of the first switching transistor Q1, and the output terminal of the second control circuit 12 is coupled to the control terminal of the second switching transistor Q2. It is used to control the second switching transistor Q2 to conduct when the output voltage of the external power supply 10 is less than a set threshold, so that the internal power supply 20 supplies power to the power output terminal Vout. The first control circuit 11 and the second control circuit 12 are circuits built from discrete components.

[0030] Specifically, in this embodiment, the products using the power switching circuit 1 include at least battery-powered electronic products, such as toys, smart home devices, handheld devices, emergency lights, etc.; and electronic products with dual power supply redundancy backup, such as 24-hour monitoring equipment, security systems, etc.

[0031] The external power supply 10 can be a charger or other DC power source, and can be connected to the power switching circuit 1 via a USB interface, etc. The internal power supply 20 can be a battery, such as a lithium battery, used to provide power when the external power supply is unavailable. The power output terminal Vout is connected to the load, such as the internal circuitry of a mobile phone or computer, to provide a stable voltage.

[0032] Optionally, both the first switch Q1 and the second switch Q2 are P-channel MOSFETs.

[0033] The first control circuit 11 and the second control circuit 12 are circuits built from discrete components. Here, discrete components are a concept relative to integrated circuits. Specifically, in the circuit structure, the first control circuit 11 and the second control circuit 12 are not composed of a single, integrated dedicated control chip (such as a power management integrated circuit PMIC or a microcontroller MCU), but are composed of multiple independent, single-function electronic components connected by wires on a printed circuit board and working together to achieve the required logic control function.

[0034] Specifically, the discrete components constituting the first and second control circuits include, but are not limited to: resistors: used for current limiting, voltage division, pull-up or pull-down; capacitors: used for filtering, decoupling, and delay.

[0035] Transistors: including NPN and PNP types, used for signal amplification and switching control.

[0036] Diodes / Zenith diodes: used for rectification, voltage regulation, and providing voltage references.

[0037] Through a specific combination and circuit connection of the aforementioned discrete components, the first control circuit 11 implements voltage comparison and switching drive functions. It monitors the voltage of the external power supply 10 and outputs a drive signal to turn on the first switch Q1 when the voltage is greater than or equal to a set threshold. Similarly, the second control circuit 12, also through a combination of discrete components, outputs a drive signal to turn on the second switch Q2 when the output voltage of the external power supply 10 is less than a set threshold. The control logic of the entire process is implemented by pure hardware circuitry, requiring no software program or dedicated control chip, resulting in a simple structure, low cost, and rapid response.

[0038] The power switching circuit 1 of this utility model automatically switches the power supply source based on the voltage state of the external power supply 10. The specific working process is as follows:

[0039] When the output voltage of the external power supply 10 is greater than or equal to a set threshold, the first control circuit 11 detects the high-level signal through its input terminal. The first control circuit 11 then sends a turn-on signal to the control terminal of the first switch Q1 through its output terminal. The first switch Q1 turns on, establishing a path between the external power supply 10 and the power output terminal Vout. At this time, the external power supply 10 is responsible for supplying power to the load at the power output terminal Vout. Simultaneously, since the voltage of the external power supply 10 is normal, the second control circuit 12 outputs a turn-off signal, keeping the second switch Q2 in the off state, thereby isolating the internal power supply 20 from the power switching circuit 1.

[0040] When the output voltage of external power supply 10 is less than a set threshold (e.g., external power supply disconnection or voltage drop), the first control circuit 11 detects insufficient output voltage of external power supply 10 and stops outputting a conduction signal at its output terminal, causing the first switch Q1 to turn off. The power supply path from external power supply 10 to the power output terminal Vout is cut off. At the same time, the second control circuit 12 detects that the voltage of external power supply 10 is less than the set threshold and sends a conduction signal to the control terminal of the second switch Q2 through its output terminal. The second switch Q2 turns on, establishing a path between internal power supply 20 and power output terminal Vout. At this time, internal power supply 20 takes over and continues to supply power to the load at power output terminal Vout, realizing automatic and uninterrupted switching of power supply.

[0041] The power switching circuit provided by this utility model includes a first switching transistor, a second switching transistor, a first control circuit, and a second control circuit. The first and second control circuits automatically output different drive signals based on the output voltage of the external power supply, thereby controlling the conduction of either the first or second switching transistor to achieve automatic switching between the external and internal power supplies. Furthermore, the first and second control circuits are constructed from discrete components, thus avoiding the need for power management chips and software control found in existing technologies. This power switching circuit achieves input voltage threshold detection and switching control through discrete component design, thereby improving the response speed and intelligence of the switching circuit. Moreover, the entire circuit uses circuit devices for power cut-off, eliminating the need for dedicated control chips, reducing the cost of the power switching circuit, and enhancing its reliability and applicability, making it particularly suitable for portable electronic products such as mobile phones and computers.

[0042] Figure 2 This is a schematic diagram of the structure of a first control circuit provided by this utility model. Figure 2 As shown, optionally, the first control circuit 11 includes a first resistor R1, a second resistor R2, a third resistor R3, a first transistor T1, and a second transistor T2; the first transistor T1 is a PNP transistor, and the second transistor T2 is an NPN transistor.

[0043] The first end of the first resistor R1 serves as the input terminal of the first control circuit 11, and the second end of the first resistor R1 is coupled to the base of the first transistor T1.

[0044] The emitter of the first transistor T1 is coupled to the first terminal of the first switch Q1, and the collector of the first transistor T1 is coupled to the base of the second transistor T2 through the second resistor R2.

[0045] The emitter of the second transistor T2 is grounded, and the collector of the second transistor T3 is coupled to the second terminal of the first switching transistor T1 through the third resistor R3, and serves as the output terminal of the first control circuit 11.

[0046] Specifically, when the output voltage of the external power supply 10 is greater than or equal to a set threshold, the higher voltage is applied to the base of the first transistor T1 through the first resistor R1. Since the first transistor T1 is a PNP transistor, the first transistor T1 turns on when the base voltage is sufficiently low relative to the emitter voltage.

[0047] After the first transistor T1 is turned on, current flows from its emitter to its collector, and supplies current to the base of the second transistor T2 through the second resistor R2. After the base of the second transistor T2 obtains current, it is saturated and turned on because it is an NPN-type transistor, pulling its collector voltage (i.e., the output terminal of the first control circuit 11) down to a potential close to ground. This output signal close to 0V is sent to the gate of the first switching tube Q1. Since the first switching tube Q1 is a P-channel MOSFET, its gate voltage is much lower than the source voltage (the output voltage of the external power supply), satisfying the turn-on condition of Vgs<Vth, thereby turning on the first switching tube Q1, and the external power supply starts to supply power to the load.

[0048] When the external power supply voltage is less than the set threshold, the voltage applied to the base of the first transistor T1 is insufficient to turn on the first transistor T1. The first transistor T1 remains off, resulting in no current flowing out from its collector, so that the base of the second transistor T2 cannot be driven. The second transistor T2 is thus turned off, and the first control circuit 11 outputs a high-impedance state. The gate of the first switching tube Q1 is pulled up to the source potential through the third resistor R3, so that the gate-source voltage difference Vgs≈0V, the first switching tube Q1 is turned off, cutting off the power supply path of the external power supply 10.

[0049] Wherein, the first resistor R1, the second resistor R2 and the third resistor R3 are all current-limiting resistors. In addition, the third resistor R3 constitutes part of the gate charge discharge path of the first switching tube Q1. Its resistance directly determines the charge-discharge time constant of the gate capacitor of the first switching tube Q1. Specifically, when the first switching tube Q1 needs to be switched from the on state to the off state, its gate charge is mainly discharged through the third resistor R3. By selecting an appropriate resistance value, the third resistor R3 can control the turn-off speed of the first switching tube Q1, avoiding significant voltage overshoot and electromagnetic interference caused by too fast turn-off, thereby optimizing the dynamic switching performance and reliability of the entire circuit.

[0050] Figure 3 is a schematic structural diagram of a second control circuit provided by the present utility model. As shown in Figure 3 , optionally, the second control circuit 12 includes a seventh resistor R7, an eighth resistor R8, a third transistor T3 and a fourth transistor T4.

[0051] The first end of the seventh resistor R7 serves as the input end of the second control circuit 12, the third transistor T3 is an NPN transistor, the base of the third transistor T3 is coupled to the second end of the seventh resistor R7, the emitter of the third transistor T3 is grounded, and the collector of the third transistor T3 is coupled to the base of the fourth transistor T4;

[0052] The fourth transistor T4 is an NPN transistor. The base of the fourth transistor T4 is coupled to the internal power supply 20 through the eighth resistor R8. The collector of the fourth transistor T4 serves as the output terminal of the second control circuit 12, and the emitter of the fourth transistor T4 is grounded.

[0053] The second control circuit 12 also includes a ninth resistor R9, which is coupled between the control terminal of the second switch Q2 and the first terminal of the second switch Q2, and is used to control the conduction speed of the second switch Q2.

[0054] Specifically, when the output voltage of external power supply 10 is greater than or equal to a set threshold, the higher voltage is applied to the base of the third transistor T3 through the seventh resistor R7. The third transistor T3, being an NPN transistor, is saturated and conducts. After the third transistor T3 is turned on, its collector voltage is pulled down to near ground potential. This ground potential is directly applied to the base of the fourth transistor T4, causing T4 to turn off due to insufficient base voltage.

[0055] When the fourth transistor T4 is turned off, its collector (i.e., the output terminal of the second control circuit 12) is in a high-impedance state. At this time, the ninth resistor R9 pulls the gate potential of the second switch Q2 up to a potential close to its source potential (i.e., the output voltage of the internal power supply 20), making the gate-source voltage difference Vgs≈0V, thereby causing the second switch Q2 to turn off and preventing the internal power supply 20 from supplying power to the load.

[0056] When the external power supply voltage is lower than the set threshold or is disconnected, the voltage applied to the base of the third transistor T3 is insufficient, and the third transistor T3 is turned off. After the third transistor T3 is turned off, its collector becomes high. At this time, the internal power supply 10 provides current to the base of the fourth transistor T4 through the eighth resistor R8, causing the fourth transistor T4 to saturate and conduct. After the fourth transistor T4 is turned on, its collector is pulled down to ground potential. This ground potential signal is applied to the gate of the second switch Q2. Since the second switch Q2 is a P-channel MOSFET, its gate voltage is much lower than its source voltage, satisfying the conduction condition, causing the second switch Q2 to conduct, and the internal power supply 20 begins to supply power to the load.

[0057] The ninth resistor R9 also plays a role in controlling the gate charge discharge speed of the second switch Q2 during this process, thereby affecting its switching speed from turn-off to turn-on and avoiding the generation of severe voltage spikes.

[0058] Figure 4 This is a schematic diagram of another power switching circuit provided by this utility model. (See diagram below.) Figure 4 As shown, optionally, the power switching circuit 1 further includes a voltage regulator circuit 13, which includes a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and an adjustable Zener diode U1.

[0059] The first end of the fourth resistor R4 is coupled to the first end of the sixth resistor R6 and the first end of the first switch Q1. The second end of the fourth resistor R4 is coupled to the first end of the fifth resistor R5 at the first node N1. The second end of the fifth resistor R5 is grounded.

[0060] The cathode of the adjustable Zener diode U1 is coupled to the second end of the sixth resistor R6 and the first end of the first resistor R1. The anode of the adjustable Zener diode U1 is coupled to the second end of the fifth resistor R5. The adjustment terminal of the adjustable Zener diode U1 is coupled to the first node N1.

[0061] Specifically, the adjustable Zener diode U1 refers to a precision programmable voltage regulator, such as the common TL431. Internally, it contains a 2.5V reference voltage source, an operational amplifier, and a transistor. Its cathode voltage can be continuously adjusted over a wide range via an external voltage divider resistor, thus achieving a non-fixed, user-defined stable voltage value. It has three terminals: cathode, anode, and reference.

[0062] Among them, the sixth resistor R6 serves as a current-limiting resistor to protect the adjustable Zener diode U1. The voltage divider network formed by the fourth resistor R4 and the fifth resistor R5 is used to detect the external power supply voltage and set the conduction threshold of the adjustable Zener diode U1.

[0063] The working principle of the voltage regulator circuit 13 is based on the feedback regulation characteristics of the adjustable Zener diode U1, and its working process is as follows:

[0064] When the output voltage of external power supply 10 is greater than or equal to the set threshold, the output voltage of external power supply 10 (e.g., 4.3V after 5V is stepped down by a diode) is divided by the fourth resistor R4 and the fifth resistor R5 to generate a sampling voltage VN1 at the first node N1.

[0065] The operational amplifier inside the adjustable Zener diode U1 continuously compares the voltage VN1 at its adjustment terminal (i.e., the first node N1) with the internal 2.5V reference voltage. When VN1 ≥ 2.5V, the internal circuit of the adjustable Zener diode U1 activates, making it conduct between its cathode and anode.

[0066] Once the adjustable Zener diode U1 is turned on, it automatically adjusts its cathode current through a strong negative feedback mechanism to maintain the voltage VN1 at its adjustment terminal constant at 2.5V. At this point, the circuit enters a stable state. According to the voltage divider relationship, VN1 = 2.5V = Vkat [r5 / (r4+r5)]; where Vkat is the cathode voltage of the adjustable Zener diode U1, it can be deduced that the output voltage of the cathode of the adjustable Zener diode U1 is stabilized at:

[0067] Vkat=2.5V (1+r4 / r5).

[0068] Where r4 represents the resistance value of the fourth resistor R4, and r5 represents the resistance value of the fifth resistor R5.

[0069] This stable Vkat is output through the sixth resistor R6 and provided as a valid power signal to the input of the first control circuit 11, triggering subsequent switching actions.

[0070] When the output voltage of external power supply 10 is lower than the set threshold, due to the low input voltage, the voltage divider VN1 at the first node N1 cannot reach the 2.5V reference voltage inside the adjustable Zener diode U1. The adjustable Zener diode U1 remains off, and its cathode has no stable voltage output, exhibiting a high impedance state. The input terminal of the first control circuit 11 cannot receive a valid power signal, causing the system to determine that external power supply 10 has failed and switch to internal power supply 20.

[0071] Optionally, the power switching circuit 1 further includes a first diode D1 and a first capacitor C1. The anode of the first diode D1 is coupled to the external power supply 10, the cathode of the first diode D1 is coupled to the first terminal of the first capacitor C1 and the first terminal of the first switching transistor Q1, and the second terminal of the first capacitor C1 is grounded.

[0072] Specifically, the first diode D1 is connected in series in the input path of the external power supply 10. When the external power supply 10 is normally connected, its voltage is higher than the voltage of the subsequent circuit of the cathode of the first diode D1. The first diode D1 is forward biased and conducts, allowing the external current to flow smoothly into the subsequent circuit to power the system.

[0073] When the external power supply 10 is suddenly disconnected or its voltage momentarily drops below the voltage of the internal power supply 20, without the isolation of the first diode D1, the current from the internal power supply 20 may flow in reverse into the external power supply port. This "reverse flow" current not only wastes electrical energy but may also damage the external power supply equipment or connectors. Due to the unidirectional conductivity of the first diode D1, it is in a reverse bias state at this time, equivalent to a high-resistance state, thus effectively blocking the path of current flowing in reverse from the inside of the circuit into the external power supply 10, protecting the safety of the entire system.

[0074] The first capacitor C1 is a filter capacitor, which further smooths the voltage, reduces glitches and noise, and prevents breakdown of subsequent circuits.

[0075] Optionally, the power switching circuit 1 further includes a second capacitor C2, which is connected between the power output terminal Vout and ground. The second capacitor C2 is used for output filtering and energy storage buffering.

[0076] During an extremely short time window when the external power supply 10 (such as a charger) is disconnected and the internal power supply 20 (such as a battery) has not yet fully taken over, a brief interruption occurs in the power supply path.

[0077] At this time, the electric energy stored in the second capacitor C2 starts to discharge through the load, maintaining the voltage at the power output terminal Vout for a short period of time (usually on the order of tens of milliseconds) so that the load does not stop working, and after lasting for tens of milliseconds, the voltage returns to the power supply voltage of the internal power supply 20.

[0078] Optionally, the power switching circuit 1 further includes a USB interface 14, and the external power supply 10 is coupled to the anode of the first diode D1 through the USB interface 14.

[0079] The working principle thereof will be described in detail below in conjunction with a typical application scenario and specific numerical values (for example: the external power supply 10 is 5.0V input, the internal power supply is a 3.7V lithium battery, and the set threshold is about 3.5V).

[0080] 1. When the external power supply is connected and supplies power normally (external power supply mode)

[0081] Scenario: A 5.0V charger is connected to the USB interface 14.

[0082] The 5.0V voltage is input through the USB interface 14, and after passing through the first diode D1 (producing a voltage drop of about 0.7V), the voltage at the main node of the circuit drops to about 4.3V.

[0083] The first capacitor C1 (for example, 100µF) filters the 4.3V voltage to smooth the surge at the moment of power-on and daily ripples.

[0084] The 4.3V voltage is applied to the voltage stabilizing circuit 13. The fourth resistor R4 and the fifth resistor R5 form a voltage dividing network. When the voltage at the voltage dividing node N1 reaches the internal reference voltage 2.5V of the adjustable voltage stabilizing tube U1, U1 is turned on and enters a voltage stabilizing state. By properly selecting the resistance ratio of R4 and R5, the cathode voltage of the adjustable voltage stabilizing tube U1 is stabilized at 3.5V.

[0085] The 3.5V voltage output from the cathode of the adjustable voltage stabilizing tube U1 is used as a control signal and sent to the base of the first transistor T1 through the first resistor R1. The emitter voltage VE of the first transistor T1 is 4.3V, and the base voltage VB is 3.5V, which satisfies the turn-on condition of VB<VE, so the first transistor T1 is turned on.

[0086] The collector current of the first transistor T1 drives the base of the second transistor T2 through the second resistor R2, so that the second transistor T2 is saturated and turned on. After the second transistor T2 is turned on, its collector voltage (that is, the output terminal of the first control circuit 11) is pulled down to close to 0V.

[0087] This 0V signal is applied to the gate of the first switching transistor Q1. The source of the first switching transistor Q1 is 4.3V and the gate is 0V. The gate-source voltage difference Vgs = -4.3V, which is much smaller than its threshold voltage (e.g. -1.5V). Therefore, the first switching transistor Q1 is turned on, efficiently delivering the 4.3V voltage to the power output terminal Vout.

[0088] Simultaneously, an input voltage of 4.3V is applied to the base of the third transistor T3 through the seventh resistor R7, causing it to saturate and conduct, clamping the base of the fourth transistor T4 at a low level. The fourth transistor T4 remains off. The ninth resistor R9 pulls the gate of the second switching transistor Q2 up to its source potential (battery voltage 3.7V), Vgs≈0V, therefore the second diode Q2 is reliably turned off, isolating the internal battery from the load.

[0089] In this mode, the load is powered by a stable 4.3V external power supply, and the battery is in standby mode.

[0090] 2. When the external power supply 10 is disconnected or drops (switch to internal power supply mode)

[0091] Scenario: The charger is unplugged.

[0092] When the input voltage disappears, the adjustable Zener diode U1 is cut off due to loss of voltage and no longer outputs 3.5V. The first transistor T1 and the second transistor T2 are also cut off due to loss of bias.

[0093] The first control circuit 11 outputs a high-impedance state. The third resistor R3 pulls the gate of the first switch Q1 up to its source residual potential, Vgs≈0V, and the first switch Q1 is reliably turned off, completely cutting off the external power supply path.

[0094] As the external 4.3V voltage disappears, the voltage applied to the base of the third transistor T3 becomes 0, and the third transistor T3 is cut off. The lithium battery's supply voltage of 3.7V provides current to the base of the fourth transistor T4 through the eighth resistor R8, causing the fourth transistor T4 to saturate and conduct.

[0095] After the fourth transistor T4 turns on, it pulls down the gate of the second switch Q2 to 0V. The source of the second switch Q2 is the lithium battery's supply voltage of 3.7V, and the gate is 0V, so Vgs = -3.7V, which meets the turn-on condition. Therefore, the second switch Q2 turns on. The ninth resistor R9 controls the charging speed of the gate capacitor of the second switch Q2 during this process, optimizing its turn-on waveform.

[0096] At the moment of switching, the electrical energy stored in the second capacitor C2 connected to the power output terminal Vout begins to discharge to the load, maintaining the voltage of the power output terminal Vout for tens of milliseconds to prevent the load from resetting or restarting due to the momentary power failure.

[0097] This buffer time allows time for the response of the second control circuit 12 and for the complete conduction of the second switch Q2. Subsequently, the 3.7V voltage from the lithium battery is stably output to the power output terminal Vout through the conducted second switch Q2, completing the power supply switching. In this mode, the load is powered by the internal 3.7V lithium battery, achieving uninterrupted automatic switching.

[0098] This invention successfully achieves automatic, rapid, and reliable switching between dual power supplies through the coordinated operation of a voltage regulator circuit 13 constructed from discrete components, a first control circuit 11, a second control circuit 12, and an input / output protection / buffer circuit. The entire circuit requires no dedicated control chip or software programming, utilizing common power specifications such as 5.0V USB input and 3.7V lithium battery. It achieves a low-cost, high-reliability power management solution through pure hardware logic, making it particularly suitable for portable electronic devices such as mobile phones and tablets.

[0099] The specific embodiments described above do not constitute a limitation on the scope of protection of this utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A power switching circuit, characterized in that, include: First switching transistor, second switching transistor, first control circuit, and second control circuit; The first switching transistor has a first terminal, a second terminal, and a control terminal. The first terminal of the first switching transistor is coupled to an external power supply, and the second terminal of the first switching transistor is coupled to a power output terminal. The second switching transistor has a first terminal, a second terminal, and a control terminal. The first terminal of the second switching transistor is coupled to an internal power supply, and the second terminal of the second switching transistor is coupled to the power supply output terminal. The first control circuit has an input terminal and an output terminal. The input terminal of the first control circuit is coupled to the first terminal of the first switching transistor, and the output terminal of the first control circuit is coupled to the control terminal of the first switching transistor. It is used to control the first switching transistor to conduct when the output voltage of the external power supply is greater than or equal to a set threshold, so that the external power supply supplies power to the power output terminal. The second control circuit has an input terminal and an output terminal. The input terminal of the second control circuit is coupled to the first terminal of the first switching transistor, and the output terminal of the second control circuit is coupled to the control terminal of the second switching transistor. It is used to control the second switching transistor to conduct when the output voltage of the external power supply is less than the set threshold, so that the internal power supply supplies power to the power output terminal. The first control circuit and the second control circuit are circuits built from discrete components.

2. The power switching circuit according to claim 1, characterized in that, The first control circuit includes a first resistor, a second resistor, a third resistor, a first transistor, and a second transistor; the first transistor is a PNP transistor, and the second transistor is an NPN transistor. The first end of the first resistor serves as the input terminal of the first control circuit, and the second end of the first resistor is coupled to the base of the first transistor. The emitter of the first transistor is coupled to the first terminal of the first switching transistor, and the collector of the first transistor is coupled to the base of the second transistor through the second resistor. The emitter of the second transistor is grounded, and the collector of the second transistor is coupled to the second terminal of the first switching transistor through the third resistor, and serves as the output terminal of the first control circuit.

3. The power switching circuit according to claim 2, characterized in that, It also includes a voltage regulator circuit, which includes a fourth resistor, a fifth resistor, a sixth resistor, and an adjustable Zener diode; The first end of the fourth resistor is coupled to the first end of the sixth resistor and the first end of the first switch transistor; the second end of the fourth resistor is coupled to the first end of the fifth resistor at the first node; and the second end of the fifth resistor is grounded. The cathode of the adjustable Zener diode is coupled to the second end of the sixth resistor and the first end of the first resistor, the anode of the adjustable Zener diode is coupled to the second end of the fifth resistor, and the adjustment terminal of the adjustable Zener diode is coupled to the first node.

4. The power switching circuit according to claim 1, characterized in that, The second control circuit includes a seventh resistor, an eighth resistor, a third transistor, and a fourth transistor; The first terminal of the seventh resistor serves as the input terminal of the second control circuit. The third transistor is an NPN transistor. The base of the third transistor is coupled to the second terminal of the seventh resistor. The emitter of the third transistor is grounded. The collector of the third transistor is coupled to the base of the fourth transistor. The fourth transistor is an NPN transistor. The base of the fourth transistor is coupled to the internal power supply through an eighth resistor. The collector of the fourth transistor serves as the output terminal of the second control circuit, and the emitter of the fourth transistor is grounded.

5. The power switching circuit according to claim 4, characterized in that, The second control circuit also includes a ninth resistor, coupled between the control terminal of the second switch and the first terminal of the second switch, for controlling the conduction speed of the second switch.

6. The power switching circuit according to claim 1, characterized in that, It also includes a first diode and a first capacitor; The anode of the first diode is coupled to the external power supply, the cathode of the first diode is coupled to the first terminal of the first capacitor and the first terminal of the first switching transistor, and the second terminal of the first capacitor is grounded.

7. The power switching circuit according to claim 6, characterized in that, It also includes a USB interface, through which the external power supply is coupled to the anode of the first diode.

8. The power switching circuit according to claim 1, characterized in that, It also includes a second capacitor, which is connected between the power output terminal and ground.

9. The power switching circuit according to claim 1, characterized in that, Both the first and second switching transistors are P-channel MOSFETs.

10. The power switching circuit according to claim 1, characterized in that, The internal power source is a battery.

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