Wide-voltage AC / DC automatic detection and switching circuit

Abstract

The invention discloses a wide-voltage AC / DC automatic detection and switching circuit which is characterized in that a first output end and a second output end of an AC input interface are respectively connected with a first input end of a detection and switching circuit and a first input end of an AC-DC conversion circuit as well as a second input end of the detection and switching circuit and a second input end of the AC-DC conversion circuit; the output end of the AC-DC conversion circuit is connected with the third input end of the detection and switching control circuit; a first output end and a second output end of the direct current input interface are respectively connected with a fourth input end of the detection and switching control circuit, a first input end of the DC-DC conversion circuit, a fifth input end of the detection and switching control circuit and a second input end of the DC-DC conversion circuit; the output end of the DC-DC conversion circuit is connected with the sixth input end of the detection and switching control circuit. According to the invention, the wide voltage adaptation capability is realized, and intelligent automatic switching can be realized.

Description

Technical Field

[0001] This invention relates to a detection and switching circuit, and more particularly to a wide-voltage AC / DC automatic detection and switching circuit, belonging to the technical field of current detection circuits. Background Technology

[0002] With the diversification of electronic devices, their power supply scenarios are becoming increasingly complex, and power systems with a single input type can no longer meet actual needs. In scenarios such as outdoor work equipment, communication base stations, and emergency power supply devices, it is often necessary to be compatible with both AC mains power and DC power supply methods such as batteries and solar panels, while ensuring the continuity and stability of power supply.

[0003] Existing AC / DC switching circuits have several limitations. First, they have a narrow input voltage adaptation range. Most circuits are only compatible with specific voltage levels of AC (e.g., 220V±10%) or DC (e.g., 12V, 24V) inputs, making it difficult to handle scenarios with wide AC fluctuations of 90-270V (e.g., unstable mains power in remote areas, generator power fluctuations) and DC inputs of various specifications from 5-50V (e.g., different capacity batteries, solar panel output differences). Second, existing switching circuits often rely on manual switching. Even some automatic switching circuits can only perform "present / absent" judgments, lacking priority logic design. When AC power is lost, prolonged power interruptions are likely to occur, failing to meet the needs of equipment with high power supply continuity requirements (e.g., core modules of communication base stations). Finally, switching reliability is insufficient, and existing switching circuit displays also have problems, leading to operator misjudgments. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a wide voltage AC / DC automatic detection and switching circuit, thereby solving at least one of the defects of the prior art.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A wide-voltage AC / DC automatic detection and switching circuit includes an AC input interface, a DC input interface, an AC-DC conversion circuit, a DC-DC conversion circuit, a detection and switching control circuit, and a subsequent output circuit. The first output terminal of the AC input interface is connected to the first input terminal of the detection and switching circuit and the first input terminal of the AC-DC conversion circuit. The second output terminal of the AC input interface is connected to the second input terminal of the detection and switching circuit and the second input terminal of the AC-DC conversion circuit. The output terminal of the AC-DC conversion circuit is connected to the third input terminal of the detection and switching control circuit. The first output terminal of the DC input interface is connected to the fourth input terminal of the detection and switching control circuit and the first input terminal of the DC-DC conversion circuit. The second output terminal of the DC input interface is connected to the fifth input terminal of the detection and switching control circuit and the second input terminal of the DC-DC conversion circuit. The output terminal of the DC-DC conversion circuit is connected to the sixth input terminal of the detection and switching control circuit. The output terminal of the detection and switching control circuit is connected to the subsequent output circuit.

[0006] Furthermore, the AC-DC conversion circuit includes a power interface CN1, a fuse, capacitors Cy1 and Cy2, a varistor Rt1, an EMI filter, a power management chip U1, capacitor C11, inductor L3, capacitors C12, C8, C9, and C10, diode D1, capacitors C14 and C13. Pin 3 of the power interface CN1 is connected to one end of the fuse and serves as the first input terminal of the AC-DC conversion circuit. The other end of the fuse is connected to one end of capacitor Cy1, one end of varistor Rt1, one end of capacitor C1, and the first input terminal of the EMI filter. The other end of capacitor Cy1 and one end of capacitor Cy2 are grounded. Pin 2 of the power interface CN1 is connected to the other end of capacitor Cy2, the other end of varistor Rt1, and the second input terminal of the EMI filter. The first output of the EMI filter is connected to pin 1 of the power management chip, and the second output of the EMI filter is connected to pin 2 of the power management chip. Pin 4 of the power management chip is connected to one end of capacitor C11 and one end of inductor L3. The other end of inductor L3 is connected to one end of capacitor C12, one end of capacitor C8, one end of capacitor C9, one end of capacitor C10, the cathode of diode D1, one end of capacitor C14, and one end of capacitor C13, which serve as the output of the AC-DC conversion circuit to generate a voltage signal VCC1. Pin 3 of the power management chip, the other end of capacitor C11, the other end of capacitor C12, the other end of capacitor C8, the other end of capacitor C9, the other end of capacitor C10, the anode of diode D1, the other end of capacitor C14, and the other end of capacitor C13 are grounded.

[0007] Furthermore, the EMI filter includes a capacitor C1, an inductor L1, a common-mode choke L2, and a capacitor C2. One end of the capacitor C1 is connected to one end of the inductor L1 and serves as the first input terminal of the EMI filter. The other end of the inductor L1 is connected to pin 1 of the common-mode choke L2. The other end of the capacitor C1 is connected to pin 2 of the common-mode choke L2 and serves as the second input terminal of the EMI filter. Pin 4 of the common-mode choke L2 is connected to one end of the capacitor C2 and serves as the first output terminal of the EMI filter. Pin 3 of the common-mode choke L2 is connected to the other end of the capacitor C2 and serves as the second output terminal of the EMI filter.

[0008] Furthermore, the DC-DC conversion circuit includes capacitor C3, capacitor C4, buck power supply chip U2, freewheeling diode D2, freewheeling inductor L4, capacitor C5, capacitor C6, capacitor C7, feedback resistor R1, and feedback resistor R2. One end of capacitor C3 is connected to one end of capacitor C4 and pin 1 of buck power supply chip U2, serving as the first input terminal of the DC-DC conversion circuit. Pin 2 of buck power supply chip U2 is connected to the cathode of freewheeling diode D2 and one end of freewheeling inductor L4. The other end of freewheeling inductor L4 is connected to one end of feedback resistor R2, one end of capacitor C7, and capacitor C5. One end of capacitor C7 is connected to one end of capacitor C6 and serves as the first output terminal of the DC-DC converter circuit to generate the voltage signal VCC2. The other end of feedback resistor R2 is connected to one end of feedback resistor R1. The other end of capacitor C7 is connected to pin 4 of buck power supply chip U2. The other end of capacitor C3 is connected to the other end of capacitor C4, pin 3 of buck power supply chip U2, pin 5 of buck power supply chip U2, the other end of feedback resistor R1, the anode of freewheeling diode D2, the other end of capacitor C5, and the other end of capacitor C6 and serves as the second input terminal and the second output terminal of the DC-DC converter circuit, grounded.

[0009] Furthermore, the detection and switching control circuit includes an AC detection and switching branch and a DC detection and switching branch.

[0010] Furthermore, the AC detection and switching branch includes a current-limiting resistor R3, a light-emitting diode D3, a diode D4, a power relay RELAY1, and an AC output interface P1. One end of the current-limiting resistor R3 is connected to the cathode of diode D4 and pin 1 of power relay RELAY1, and serves as the third input terminal of the detection and switching control circuit, connected to the voltage signal VCC1. The other end of the current-limiting resistor R3 is connected to the anode of light-emitting diode D3. The cathode of light-emitting diode D3, the anode of diode D4, and pin 2 of power relay RELAY1 are grounded. Pin 3 of power relay RELAY1 serves as the first input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY1 is connected to pin 1 of AC output interface P1. Pin 2 of AC output interface P1 serves as the second input terminal of the detection and switching control circuit.

[0011] Further, the AC detection and switching branch includes resistor R10, resistor R11, NTC interface CN2, diode D5, resistor R7, resistor R8, resistor R9, capacitor C18, comparator LM1, resistor R6, capacitor C16, PMOS transistor Q1, current-limiting resistor R3, light-emitting diode D3, diode D4, power relay RELAY1, forced power supply switch K5, and AC output interface P1. One end of resistor R10 is connected to one end of resistor R11, one end of resistor R6, and the source of PMOS transistor Q1, serving as the third input terminal of the detection and switching control circuit, connected to the voltage signal VCC1. The other end of resistor R10 is connected to the other end of resistor R11, pin 2 of NTC interface CN2, the cathode of diode D5, and one end of resistor R7, connected to the reference voltage Vref. The other end of resistor R7 is connected to one end of resistor R8 and pin 3 of comparator LM1. The other end of resistor R8 and the anode of diode D5 are grounded. Pin 1 of NTC interface CN2 is connected to one end of resistor R9 and capacitor C18. One end is connected to pin 2 of comparator LM1. The other end of resistor R9 and the other end of capacitor C18 are grounded. Pin 4 of comparator LM1 is grounded. Pin 8 of comparator LM1 is connected to voltage signal VCC1. Pin 1 of comparator LM1 is connected to the other end of resistor R6, one end of capacitor C16, and the gate of PMOS transistor Q1. The other end of capacitor C16 is grounded. The drain of PMOS transistor Q1 is connected to one end of current-limiting resistor R3, the cathode of diode D4, and pin 1 of power relay RELAY1. The other end of current-limiting resistor R3 is connected to the anode of LED D3. The cathode of LED D3, the anode of diode D4, and pin 2 of power relay RELAY1 are grounded. Pin 3 of power relay RELAY1 is connected to one end of forced power supply switch K5 and serves as the first input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY1 is connected to the other end of forced power supply switch K5 and pin 1 of AC output interface P1. Pin 2 of AC output interface P1 serves as the second input terminal of the detection and switching control circuit.

[0012] Further, the DC detection and switching branch includes capacitor C15, diode D12, relay K2, resistor R4, LED D6, diode D11, power relay RELAY2, DC output interface P2, LED D8, resistor R5, diode D7, and relay K1. One end of resistor R4 is connected to the cathode of diode D11 and pin 1 of power relay RELAY2, serving as the sixth input terminal of the detection and switching control circuit, connected to the voltage signal VCC2. The other end of resistor R4 is connected to the anode of LED D6. The cathode of LED D6 is connected to pin 7 of relay K2. Pin 8 of relay K2 is grounded, connected to the anode of diode D12 and one end of capacitor C15. Pin 6 of relay K2 is grounded. Pin 1 of relay K2 is connected to diode D8. The cathode of diode 12 and the other end of capacitor C15 are connected to the voltage signal VCC1. Pin 5 of relay K2 is connected to the cathode of LED D8, the anode of diode D7, and pin 8 of relay K1. The anode of LED D8 is connected to one end of resistor R5. The other end of resistor R5 is connected to the cathode of diode D7 and pin 1 of relay K1 to the voltage signal VCC1. Pins 3 and 6 of relay K1 are grounded. Pin 7 of relay K1 is connected to the anode of diode D11 and pin 2 of power relay RELAY2. Pin 3 of power relay RELAY2 serves as the fourth input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY2 is connected to pin 1 of DC output interface P2. Pin 2 of DC output interface P2 serves as the fifth input terminal of the detection and switching control circuit.

[0013] Furthermore, the DC detection switching branch includes resistor R16, resistor R17, NTC interface CN3, diode D10, resistor R13, resistor R14, resistor R15, capacitor C19, comparator LM2, resistor R12, capacitor C17, PMOS transistor Q2, capacitor C15, diode D12, relay K2, resistor R4, light-emitting diode D6, diode D11, power relay RELAY2, DC output interface P2, forced power supply switch K6, light-emitting diode D8, resistor R5, diode D7, and relay K1. One end of resistor R16 is connected to one end of resistor R17, one end of resistor R12, and PMOS transistor Q2. The source terminal of the circuit is connected to the voltage signal VCC2 and serves as the sixth input terminal of the detection and switching control circuit. The other end of resistor R16, the other end of resistor R17, pin 2 of NTC interface CN3, the cathode of diode D10, and one end of resistor R13 are connected to the reference voltage Vref. The other end of resistor R13, one end of resistor R14, and pin 3 of comparator LM2 are connected. The other end of resistor R14 and the anode of diode D10 are grounded. Pin 1 of NTC interface CN3 is connected to one end of resistor R15, one end of capacitor C19, and pin 2 of comparator LM2. The other end of resistor R15 and the other end of capacitor C19 are grounded. Pin 1 of comparator LM2 is connected to resistor R... The other end of resistor R4, one end of capacitor C17, and the gate of PMOS transistor Q2 are connected. The other end of capacitor C17 is grounded. The drain of PMOS transistor Q2 is connected to one end of resistor R4, the cathode of diode D11, and pin 1 of power relay RELAY2. The other end of resistor R4 is connected to the anode of LED D6. The cathode of LED D6 is connected to pin 7 of relay K2. Pin 8 of relay K2 is grounded to the anode of diode D12 and one end of capacitor C15. Pin 6 of relay K2 is grounded. Pin 1 of relay K2 is connected to the voltage signal VCC1 via the cathode of diode D12 and the other end of capacitor C15. Pin 5 of relay K2 is connected to the LED. The cathode of diode D8, the anode of diode D7, and pin 8 of relay K1 are connected. The anode of LED D8 is connected to one end of resistor R5. The other end of resistor R5 is connected to the cathode of diode D7 and pin 1 of relay K1 to receive voltage signal VCC1. Pins 3 and 6 of relay K1 are grounded. Pin 7 of relay K1 is connected to the anode of diode D11 and pin 2 of power relay RELAY2. Pin 3 of power relay RELAY2 serves as the fourth input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY2 is connected to pin 1 of DC output interface P2. Pin 2 of DC output interface P2 serves as the fifth input terminal of the detection and switching control circuit.

[0014] Compared with the prior art, the present invention has the following advantages and effects: 1. This invention provides a wide voltage AC / DC automatic detection and switching circuit, which realizes wide voltage adaptability. The AC input is compatible with the global common mains power range of 90-270V, and the DC input is adapted to common DC power sources such as 5-50V batteries and solar panels, making it applicable to a wide range of scenarios. 2. This invention can intelligently and automatically switch between AC and DC power. Through the detection module and logic control, it can automatically identify AC and DC power supply, prioritize AC power supply, and switch to DC power in milliseconds when AC power is lost, without power interruption. 3. This invention has high reliability and a simple circuit structure. By electrically isolating the control circuit from the AC / DC power circuit, it improves anti-interference capability and safety. 4. This invention has strong functional adaptability and provides AC / DC output interfaces, which can supply power to the subsequent AC / DC circuits respectively, without the need for additional conversion equipment; 5. This invention enables status visualization by using LEDs to indicate the AC / DC power supply status, making it easy to judge intuitively; 6. This invention has a temperature detection function. When the temperature is lower than a certain threshold, the output circuit is cut off to ensure the power safety of the downstream load. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a wide-voltage AC / DC automatic detection and switching circuit according to the present invention.

[0016] Figure 2 This is a circuit diagram of the AC-DC conversion circuit of the present invention.

[0017] Figure 3 This is a circuit diagram of the DC-DC conversion circuit of the present invention.

[0018] Figure 4 This is a circuit diagram of the detection and switching control circuit of the present invention.

[0019] Figure 5 This is a circuit diagram of another embodiment of the detection and switching control circuit of the present invention. Detailed Implementation

[0020] To illustrate in detail the technical solutions adopted by the present invention to achieve the intended technical objectives, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Furthermore, the technical means or technical features in the embodiments of the present invention can be replaced without creative effort. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0021] like Figure 1As shown, the present invention provides a wide-voltage AC / DC automatic detection and switching circuit, comprising an AC input interface, a DC input interface, an AC-DC conversion circuit, a DC-DC conversion circuit, a detection and switching control circuit, and a subsequent output circuit. The first output terminal of the AC input interface is connected to the first input terminal of the detection and switching circuit and the first input terminal of the AC-DC conversion circuit. The second output terminal of the AC input interface is connected to the second input terminal of the detection and switching circuit and the second input terminal of the AC-DC conversion circuit. The output terminal of the AC-DC conversion circuit is connected to the third input terminal of the detection and switching control circuit. The first output terminal of the DC input interface is connected to the fourth input terminal of the detection and switching control circuit and the first input terminal of the DC-DC conversion circuit. The second output terminal of the DC input interface is connected to the fifth input terminal of the detection and switching control circuit and the second input terminal of the DC-DC conversion circuit. The output terminal of the DC-DC conversion circuit is connected to the sixth input terminal of the detection and switching control circuit. The output terminal of the detection and switching control circuit is connected to the subsequent output circuit.

[0022] The AC input interface is for receiving AC power in the range of 90-270V. The DC input interface is for receiving DC power in the range of 5-50V.

[0023] like Figure 2As shown, the AC-DC conversion circuit includes a power interface CN1, a fuse, capacitors Cy1 and Cy2, a varistor Rt1, an EMI filter, a power management chip U1, capacitor C11, inductor L3, capacitors C12, C8, C9, and C10, diode D1, capacitors C14 and C13. Pin 3 of the power interface CN1 is connected to one end of the fuse and serves as the first input terminal of the AC-DC conversion circuit. The other end of the fuse is connected to one end of capacitor Cy1, one end of varistor Rt1, one end of capacitor C1, and the first input terminal of the EMI filter. The other end of capacitor Cy1 and one end of capacitor Cy2 are grounded. Pin 2 of the power interface CN1 is connected to the other end of capacitor Cy2, the other end of varistor Rt1, and the second input terminal of the EMI filter. As the second input terminal of the AC-DC conversion circuit, the first output terminal of the EMI filter is connected to pin 1 of the power management chip, the second output terminal of the EMI filter is connected to pin 2 of the power management chip, pin 4 of the power management chip is connected to one end of capacitor C11 and one end of inductor L3, the other end of inductor L3 is connected to one end of capacitor C12, one end of capacitor C8, one end of capacitor C9, one end of capacitor C10, the cathode of diode D1, one end of capacitor C14 and one end of capacitor C13 and serves as the output terminal of the AC-DC conversion circuit to generate voltage signal VCC1, and pin 3 of the power management chip, the other end of capacitor C11, the other end of capacitor C12, the other end of capacitor C8, the other end of capacitor C9, the other end of capacitor C10, the anode of diode D1, the other end of capacitor C14 and the other end of capacitor C13 are grounded.

[0024] The EMI filter includes capacitor C1, inductor L1, common-mode choke L2, and capacitor C2. One end of capacitor C1 is connected to one end of inductor L1 and serves as the first input terminal of the EMI filter. The other end of inductor L1 is connected to pin 1 of common-mode choke L2. The other end of capacitor C1 is connected to pin 2 of common-mode choke L2 and serves as the second input terminal of the EMI filter. Pin 4 of common-mode choke L2 is connected to one end of capacitor C2 and serves as the first output terminal of the EMI filter. Pin 3 of common-mode choke L2 is connected to the other end of capacitor C2 and serves as the second output terminal of the EMI filter.

[0025] The AC-DC conversion circuit, through input protection, EMI filtering, AC-DC conversion, and output filtering and regulation, converts AC mains power into a stable 5V DC voltage to power subsequent circuits. It also features overcurrent and surge protection and electromagnetic interference suppression capabilities, ensuring the safety and stability of the power supply. Power interface CN1 is used to connect to external AC mains power. The mains power passes through a fuse and a varistor Rt1 for overcurrent and surge protection. After electromagnetic interference is suppressed by the EMI filter circuit, it is connected to the U1 chip, which rectifies the wide-range AC voltage into a stable DC voltage. The DC voltage output from U1 is further rectified and filtered to remove ripple, providing a stable DC voltage VCC1 for subsequent detection and switching circuits.

[0026] like Figure 3 As shown, the DC-DC converter circuit includes capacitor C3, capacitor C4, buck converter chip U2, freewheeling diode D2, freewheeling inductor L4, capacitor C5, capacitor C6, capacitor C7, feedback resistor R1, and feedback resistor R2. One end of capacitor C3 is connected to one end of capacitor C4 and pin 1 of buck converter chip U2, serving as the first input terminal of the DC-DC converter circuit. Pin 2 of buck converter chip U2 is connected to the cathode of freewheeling diode D2 and one end of freewheeling inductor L4. The other end of freewheeling inductor L4 is connected to one end of feedback resistor R2, one end of capacitor C7, and one end of capacitor C5. One end of capacitor C6 is connected to the first output terminal of the DC-DC converter circuit to generate voltage signal VCC2. The other end of feedback resistor R2 is connected to one end of feedback resistor R1. The other end of capacitor C7 is connected to pin 4 of buck power supply chip U2. The other end of capacitor C3 is connected to the other end of capacitor C4, pin 3 of buck power supply chip U2, pin 5 of buck power supply chip U2, the other end of feedback resistor R1, the anode of freewheeling diode D2, the other end of capacitor C5, and the other end of capacitor C6, and is grounded as the second input terminal and the second output terminal of the DC-DC converter circuit.

[0027] The DC-DC converter circuit employs a Buck converter topology to convert a wide-range input DC voltage Vin into a lower and more stable DC voltage VCC2 to power subsequent circuits. The DC input is filtered by capacitors C3 and C4 to remove low-frequency and high-frequency ripple in the input voltage Vin before being fed to pins 1 and 3 of chip U2. When the high-frequency switch inside chip U2 is on, the input voltage Vin charges inductor L4 through the switch, storing energy, while diode D2 is reverse-biased and cut off. When the switch is off, inductor L4, due to its inability to change current abruptly, generates a reverse induced electromotive force, causing diode D2 to forward-bias and conduct. The energy stored in the inductor is released to the load and capacitor through D2, maintaining continuous current. The output voltage is filtered by capacitors C5 and C6 to obtain a cleaner DC voltage VCC2. Simultaneously, resistors R1 and R2 sample VCC2 and feed it back to pin 4 of chip U2. U2 adjusts the switching time of the switch based on the feedback signal to achieve stable voltage output over a wide input range.

[0028] The detection and switching control circuit includes an AC detection and switching branch and a DC detection and switching branch.

[0029] like Figure 4 As shown, the AC detection and switching branch includes a current-limiting resistor R3, an LED D3, an LED D4, a power relay RELAY1, and an AC output interface P1. One end of the current-limiting resistor R3 is connected to the cathode of the LED D4 and pin 1 of the power relay RELAY1, serving as the third input terminal of the detection and switching control circuit, connected to the voltage signal VCC1. The other end of the current-limiting resistor R3 is connected to the anode of the LED D3. The cathode of the LED D3, the anode of the LED D4, and pin 2 of the power relay RELAY1 are grounded. Pin 3 of the power relay RELAY1 serves as the first input terminal of the detection and switching control circuit. Pin 4 of the power relay RELAY1 is connected to pin 1 of the AC output interface P1. Pin 2 of the AC output interface P1 serves as the second input terminal of the detection and switching control circuit.

[0030] The AC-L live wire is controlled by the power relay RELAY1. When the AC input is active, VCC1 output from the AC-DC converter energizes the RELAY1 coil, causing its contacts to close and connecting the AC output. The power relay RELAY1 controls the AC output. When the RELAY1 coil is energized, the contacts close, closing the AC power supply AC-L circuit and outputting to the AC output interface P1 of the subsequent output circuit; when the coil is de-energized, the contacts open, cutting off the AC output. The freewheeling diode D4 provides a discharge path for the induced current in the coil, preventing back electromotive force from damaging the drive circuit.

[0031] like Figure 4As shown, the DC detection and switching branch includes capacitor C15, diode D12, relay K2, resistor R4, LED D6, diode D11, power relay RELAY2, DC output interface P2, LED D8, resistor R5, diode D7, and relay K1. One end of resistor R4 is connected to the cathode of diode D11 and pin 1 of power relay RELAY2, serving as the sixth input terminal of the detection and switching control circuit, connected to the voltage signal VCC2. The other end of resistor R4 is connected to the anode of LED D6. The cathode of LED D6 is connected to pin 7 of relay K2. Pin 8 of relay K2 is grounded to the anode of diode D12 and one end of capacitor C15. Pin 6 of relay K2 is grounded. Pin 1 of relay K2 is connected to diode D12. The cathode of the relay and the other end of capacitor C15 are connected to the voltage signal VCC1. Pin 5 of relay K2 is connected to the cathode of LED D8, the anode of diode D7, and pin 8 of relay K1. The anode of LED D8 is connected to one end of resistor R5. The other end of resistor R5 is connected to the cathode of diode D7 and pin 1 of relay K1 to the voltage signal VCC1. Pins 3 and 6 of relay K1 are grounded. Pin 7 of relay K1 is connected to the anode of diode D11 and pin 2 of power relay RELAY2. Pin 3 of power relay RELAY2 serves as the fourth input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY2 is connected to pin 1 of DC output interface P2. Pin 2 of DC output interface P2 serves as the fifth input terminal of the detection and switching control circuit.

[0032] The AC output status is indicated by the on / off state of LED D3. Resistor R3 limits the current flowing through D3 to prevent the indicator light from being damaged by overcurrent. When RELAY1 is energized, VCC1 illuminates LED D3 through resistor R3, indicating "AC output in progress". DC output branch: The DC + positive cable is controlled by power relay RELAY2 to switch the DC output on and off, providing DC power. Power relay RELAY2 controls the switching on and off of the DC output. The principle is similar to RELAY1: when the coil is energized, the contacts close, closing the DC + power supply circuit and outputting to the P2 DC output interface of the subsequent output circuit; when de-energized, the contacts open, cutting off the DC output. The DC indicator circuit consists of voltage signal VCC2, LED D6, current-limiting resistor R4, and relay K2. The on / off state of LED D6 indicates the DC output status. Resistor R4 limits the current flowing through D6 to prevent the indicator light from being damaged by overcurrent. When DC current VCC2 is input, the normally closed contact (6-7) of relay K2 closes, and VCC2 illuminates LED D6 through resistor R4, indicating "DC output in progress". The normally closed contact of relay K1 is connected to the coil power supply circuit of relay RELAY2, the normally closed contact (6-7) of relay K2 is connected to the DC indicator circuit, and the normally open contact (5-6) of relay K2 is connected to the coil circuit of relay K1.

[0033] The detection and switching control circuit adopts an "AC priority, DC backup" logic. Power relay RELAY1 is activated only when the AC input is valid, prioritizing power supply from the AC side P1. Power relay RELAY2 is activated only when the DC input is valid, providing power from the DC side P2. When both AC and DC are input simultaneously, relay RELAY1 is activated, energizing the coil of control relay K2, which in turn controls relay K1 to operate. The normally closed contact of K1 opens, forcing the RELAY2 coil circuit to be in an open state, thus ensuring that the DC output is cut off. The circuit switches the output signal within milliseconds, de-energizing the DC output interface and switching to AC output from the AC side P1.

[0034] In another embodiment of the invention, such as Figure 5As shown, the AC detection and switching branch includes resistor R10, resistor R11, NTC interface CN2, diode D5, resistor R7, resistor R8, resistor R9, capacitor C18, comparator LM1, resistor R6, capacitor C16, PMOS transistor Q1, current-limiting resistor R3, LED D3, diode D4, power relay RELAY1, forced power supply switch K5, and AC output interface P1. One end of resistor R10 is connected to one end of resistor R11, one end of resistor R6, and the source of PMOS transistor Q1, serving as the third input terminal of the detection and switching control circuit, connected to the voltage signal VCC1. The other end of resistor R10 is connected to the other end of resistor R11, pin 2 of NTC interface CN2, the cathode of diode D5, and one end of resistor R7, connecting to the reference voltage Vref. The other end of resistor R7 is connected to one end of resistor R8 and pin 3 of comparator LM1. The other end of resistor R8 and the anode of diode D5 are grounded. Pin 1 of NTC interface CN2 is connected to one end of resistor R9 and one end of capacitor C18. The circuit is connected to pin 2 of comparator LM1, the other end of resistor R9 and the other end of capacitor C18 are grounded, pin 4 of comparator LM1 is grounded, pin 8 of comparator LM1 is connected to voltage signal VCC1, pin 1 of comparator LM1 is connected to the other end of resistor R6, one end of capacitor C16 and the gate of PMOS transistor Q1, the other end of capacitor C16 is grounded, the drain of PMOS transistor Q1 is connected to one end of current limiting resistor R3, the cathode of diode D4 and pin 1 of power relay RELAY1, the other end of current limiting resistor R3 is connected to the anode of LED D3, the cathode of LED D3, the anode of diode D4 and pin 2 of power relay RELAY1 are grounded, pin 3 of power relay RELAY1 is connected to one end of forced power supply switch K5 and serves as the first input terminal of the detection and switching control circuit, pin 4 of power relay RELAY1 is connected to the other end of forced power supply switch K5 and pin 1 of AC output interface P1, and pin 2 of AC output interface P1 serves as the second input terminal of the detection and switching control circuit.

[0035] like Figure 5As shown, the DC detection switching branch includes resistor R16, resistor R17, NTC interface CN3, diode D10, resistor R13, resistor R14, resistor R15, capacitor C19, comparator LM2, resistor R12, capacitor C17, PMOS transistor Q2, capacitor C15, diode D12, relay K2, resistor R4, LED D6, diode D11, power relay RELAY2, DC output interface P2, forced power supply switch K6, LED D8, resistor R5, diode D7, and relay K1. One end of resistor R16 is connected to one end of resistor R17, one end of resistor R12 is connected to the source of PMOS transistor Q2. Connect the voltage signal VCC2 to the sixth input terminal of the detection and switching control circuit. Connect the other end of resistor R16, the other end of resistor R17, pin 2 of NTC interface CN3, the cathode of diode D10, and one end of resistor R13 to the reference voltage Vref. Connect the other end of resistor R13, one end of resistor R14, and pin 3 of comparator LM2. Connect the other end of resistor R14 and the anode of diode D10 to ground. Connect pin 1 of NTC interface CN3, one end of resistor R15, one end of capacitor C19, and pin 2 of comparator LM2. Connect the other end of resistor R15 and the other end of capacitor C19 to ground. Connect pin 1 of comparator LM2 to resistor R12. The other end of the capacitor C17 is connected to the gate of PMOS transistor Q2, and the other end of the capacitor C17 is grounded. The drain of PMOS transistor Q2 is connected to one end of resistor R4, the cathode of diode D11, and pin 1 of power relay RELAY2. The other end of resistor R4 is connected to the anode of LED D6. The cathode of LED D6 is connected to pin 7 of relay K2. Pin 8 of relay K2 is connected to the anode of diode D12 and one end of capacitor C15 and grounded. Pin 6 of relay K2 is grounded. Pin 1 of relay K2 is connected to the cathode of diode D12 and the other end of capacitor C15, and the voltage signal VCC1 is connected to it. Pin 5 of relay K2 is connected to the LED... The cathode of diode D8, the anode of diode D7, and pin 8 of relay K1 are connected. The anode of LED D8 is connected to one end of resistor R5. The other end of resistor R5 is connected to the cathode of diode D7 and pin 1 of relay K1 to receive voltage signal VCC1. Pins 3 and 6 of relay K1 are grounded. Pin 7 of relay K1 is connected to the anode of diode D11 and pin 2 of power relay RELAY2. Pin 3 of power relay RELAY2 serves as the fourth input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY2 is connected to pin 1 of DC output interface P2. Pin 2 of DC output interface P2 serves as the fifth input terminal of the detection and switching control circuit.

[0036] Based on the original circuit, a temperature comparison circuit was added to the front stage of the detection and switching control circuit to more accurately detect the outdoor ambient temperature. When the outdoor ambient temperature is below 0°C, the comparator outputs a high voltage, the coils of relays RELAY1 and RELAY2 are de-energized, and the AC and DC external output circuits are disconnected.

[0037] Taking the AC control loop as an example, the ambient temperature of the circuit is monitored in real time through an NTC thermistor interface. The characteristic of an NTC resistor is that its resistance decreases as temperature increases. This NTC resistor, along with fixed resistors R10, R11, and R9, forms a voltage divider circuit, converting changes in resistance into changes in voltage. When the temperature is below a certain threshold, the generated temperature signal voltage and a fixed reference voltage (Vref) are fed together into the voltage comparator LM393. When the non-inverting input (IN+) voltage of the voltage comparator LM393 is greater than the inverting input (IN-) voltage, it outputs a high-level signal, close to VCC1. At this time, the P-type MOSFET Q1 (AO3401) turns off, the RELAY1 coil is de-energized, and the AC output is disconnected. Similarly, the DC output is also disconnected.

[0038] Two forced power supply switches, K5 and K6, were added to the AC and DC main circuits to force the power supply process of the subsequent circuits, bypassing the automatic control logic.

[0039] This embodiment further improves the system's security and detection accuracy, and is particularly suitable for scenarios such as medical equipment and industrial control that have high requirements for electrical isolation.

[0040] The output circuit includes an independent AC / DC forced power supply switch and an AC / DC power supply output interface to supply power to different downstream loads.

[0041] The working principle of the wide voltage AC / DC automatic detection and switching circuit of the present invention is as follows: 1. When AC power is connected only, it automatically switches to AC power to supply power to the downstream circuit: The DC power VCC1 output from the AC-DC converter circuit controls the relay, energizing the coil of relay RELAY1. AC power AC-L is then activated through contacts 3 and 4 and output externally via interface P1. D4 provides freewheeling protection for the coil of relay RELAY1, and resistor R3 limits the current, illuminating indicator light D3 to indicate AC power supply.

[0042] 2. When only DC power is connected, it automatically switches to DC power to supply power to the subsequent circuits.

[0043] The DC-DC converter output VCC2 control signal activates the relay. VCC2 is connected to relay RELAY2 via D9, and then grounded through relay K1 contact (6-7). Relay RELAY1 coil is energized, and contacts 3 and 4 of relay RELAY1 close, closing the DC+ circuit and outputting DC power externally via interface P2. D11 provides freewheeling protection for relay RELAY2 coil. VCC2 is current-limited by resistor R4 and grounded through DC indicator D6 and relay K2 contact (6-7), illuminating DC indicator D6 and indicating external DC power supply.

[0044] AC priority principle: When both AC and DC are connected simultaneously, the system automatically identifies the AC and DC inputs and prioritizes AC power output; when the AC input is interrupted, it automatically switches to DC output. Details are as follows: When both AC and DC power are connected, AC power is output externally, as detailed in the above section. At this time, the DC power supply circuit needs to be disconnected. Specifically, VCC1 energizes the coil of relay K2, closing its normally open contact (5-6), which in turn energizes the coil of relay K1. The normally closed contact (6-7) of relay K1 then opens, de-energizing the coil of relay RELAY2. Relay RELAY2 contacts open, cutting off the DC+ power supply circuit. Simultaneously, the DC indicator light circuit is disconnected, and the "DC indicator light" goes out.

[0045] When the AC input is undervoltage, overvoltage, or power failure, the input power to relay K2 is cut off. Contacts (5-6) of relay K2 switch from closed to open, causing the coil of relay K1 to lose power. Contacts (6-7) of relay K1 switch from open to closed, energizing the coil of relay RELAY2. This causes the contacts of relay RELAY1 to close, and the DC+ current is closed and output externally via interface P2. Additionally, VCC2, current-limited by resistor R4, is grounded through DC indicator D6 and relay K2 contact (6-7), illuminating DC indicator D6 to indicate external DC power supply.

[0046] After the AC power supply is restored to normal, the AC-DC detection module confirms that the voltage is compliant, and the circuit switches back to AC power supply according to the reverse logic of "Relay RELAY2 disconnects → Relay 1 engages".

[0047] This invention provides a wide-voltage AC / DC automatic detection and switching circuit, achieving wide voltage adaptability. The AC input is compatible with the 90-270V global mains power range, while the DC input is compatible with common DC power sources such as 5-50V batteries and solar panels, making it suitable for a wide range of scenarios. This invention enables intelligent automatic switching, achieving automatic AC / DC identification through a detection module and logic control. AC power is prioritized, and in the event of AC power failure, it switches to DC within milliseconds without power interruption. This invention boasts high reliability and a simple circuit structure. Electrical isolation between the control circuit and the AC / DC power circuit enhances anti-interference capability and safety. This invention offers strong functional adaptability, providing both AC and DC output interfaces for powering subsequent AC / DC circuits without the need for additional conversion equipment. This invention provides status visualization, using LEDs to indicate the AC / DC power supply status for easy and intuitive judgment. This invention also features temperature detection; when the temperature falls below a certain threshold, the output circuit is cut off to ensure the power safety of subsequent loads.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A wide-voltage AC / DC automatic detection and switching circuit, characterized in that: It includes an AC input interface, a DC input interface, an AC-DC conversion circuit, a DC-DC conversion circuit, a detection and switching control circuit, and a subsequent output circuit. The first output terminal of the AC input interface is connected to the first input terminal of the detection and switching circuit and the first input terminal of the AC-DC conversion circuit. The second output terminal of the AC input interface is connected to the second input terminal of the detection and switching circuit and the second input terminal of the AC-DC conversion circuit. The output terminal of the AC-DC conversion circuit is connected to the third input terminal of the detection and switching control circuit. The first output terminal of the DC input interface is connected to the fourth input terminal of the detection and switching control circuit and the first input terminal of the DC-DC conversion circuit. The second output terminal of the DC input interface is connected to the fifth input terminal of the detection and switching control circuit and the second input terminal of the DC-DC conversion circuit. The output terminal of the DC-DC conversion circuit is connected to the sixth input terminal of the detection and switching control circuit. The output terminal of the detection and switching control circuit is connected to the subsequent output circuit.

2. The wide-voltage AC / DC automatic detection and switching circuit according to claim 1, characterized in that: The AC-DC conversion circuit includes a power interface CN1, a fuse, capacitors Cy1 and Cy2, a varistor Rt1, an EMI filter, a power management chip U1, capacitor C11, inductor L3, capacitors C12, C8, C9, and C10, diode D1, capacitors C14 and C13. Pin 3 of the power interface CN1 is connected to one end of the fuse and serves as the first input terminal of the AC-DC conversion circuit. The other end of the fuse is connected to one end of capacitor Cy1, one end of varistor Rt1, one end of capacitor C1, and the first input terminal of the EMI filter. The other end of capacitor Cy1 and one end of capacitor Cy2 are grounded. Pin 2 of the power interface CN1 is connected to the other end of capacitor Cy2, the other end of varistor Rt1, and the second input terminal of the EMI filter. The second input terminal of the AC-DC conversion circuit is connected to the first output terminal of the EMI filter, which is connected to pin 1 of the power management chip. The second output terminal of the EMI filter is connected to pin 2 of the power management chip. Pin 4 of the power management chip is connected to one end of capacitor C11 and one end of inductor L3. The other end of inductor L3 is connected to one end of capacitor C12, one end of capacitor C8, one end of capacitor C9, one end of capacitor C10, the cathode of diode D1, one end of capacitor C14, and one end of capacitor C13, which serve as the output terminal of the AC-DC conversion circuit to generate a voltage signal VCC1. Pin 3 of the power management chip, the other end of capacitor C11, the other end of capacitor C12, the other end of capacitor C8, the other end of capacitor C9, the other end of capacitor C10, the anode of diode D1, the other end of capacitor C14, and the other end of capacitor C13 are grounded.

3. The wide-voltage AC / DC automatic detection and switching circuit according to claim 2, characterized in that: The EMI filter includes capacitor C1, inductor L1, common-mode choke L2, and capacitor C2. One end of capacitor C1 is connected to one end of inductor L1 and serves as the first input terminal of the EMI filter. The other end of inductor L1 is connected to pin 1 of common-mode choke L2. The other end of capacitor C1 is connected to pin 2 of common-mode choke L2 and serves as the second input terminal of the EMI filter. Pin 4 of common-mode choke L2 is connected to one end of capacitor C2 and serves as the first output terminal of the EMI filter. Pin 3 of common-mode choke L2 is connected to the other end of capacitor C2 and serves as the second output terminal of the EMI filter.

4. The wide-voltage AC / DC automatic detection and switching circuit according to claim 1, characterized in that: The DC-DC conversion circuit includes capacitors C3 and C4, a step-down power supply chip U2, a freewheeling diode D2, a freewheeling inductor L4, capacitors C5, C6, and C7, and feedback resistors R1 and R2. One end of capacitor C3 is connected to one end of capacitor C4 and pin 1 of the step-down power supply chip U2, serving as the first input terminal of the DC-DC conversion circuit. Pin 2 of the step-down power supply chip U2 is connected to the cathode of the freewheeling diode D2 and one end of the freewheeling inductor L4. The other end of the freewheeling inductor L4 is connected to one end of the feedback resistor R2, one end of capacitor C7, and one end of capacitor C5. One end of capacitor C6 is connected to the first output terminal of the DC-DC converter circuit to generate voltage signal VCC2. The other end of feedback resistor R2 is connected to one end of feedback resistor R1. The other end of capacitor C7 is connected to pin 4 of buck power supply chip U2. The other end of capacitor C3 is connected to the other end of capacitor C4, pin 3 and pin 5 of buck power supply chip U2, the other end of feedback resistor R1, the anode of freewheeling diode D2, the other end of capacitor C5, and the other end of capacitor C6, and is grounded as the second input terminal and the second output terminal of the DC-DC converter circuit.

5. The wide-voltage AC / DC automatic detection and switching circuit according to claim 1, characterized in that: The detection and switching control circuit includes an AC detection and switching branch and a DC detection and switching branch.

6. The wide-voltage AC / DC automatic detection and switching circuit according to claim 5, characterized in that: The AC detection and switching branch includes a current-limiting resistor R3, a light-emitting diode D3, a diode D4, a power relay RELAY1, and an AC output interface P1. One end of the current-limiting resistor R3 is connected to the cathode of diode D4 and pin 1 of power relay RELAY1, serving as the third input terminal of the detection and switching control circuit and connected to the voltage signal VCC1. The other end of the current-limiting resistor R3 is connected to the anode of light-emitting diode D3. The cathode of light-emitting diode D3, the anode of diode D4, and pin 2 of power relay RELAY1 are grounded. Pin 3 of power relay RELAY1 serves as the first input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY1 is connected to pin 1 of AC output interface P1. Pin 2 of AC output interface P1 serves as the second input terminal of the detection and switching control circuit.

7. The wide-voltage AC / DC automatic detection and switching circuit according to claim 5, characterized in that: The AC detection and switching branch includes resistor R10, resistor R11, NTC interface CN2, diode D5, resistor R7, resistor R8, resistor R9, capacitor C18, comparator LM1, resistor R6, capacitor C16, PMOS transistor Q1, current-limiting resistor R3, light-emitting diode D3, diode D4, power relay RELAY1, forced power supply switch K5, and AC output interface P1. One end of resistor R10 is connected to one end of resistor R11, one end of resistor R6, and the source of PMOS transistor Q1, serving as the third input terminal of the detection and switching control circuit, connected to the voltage signal VCC1. The other end of resistor R10 is connected to the other end of resistor R11, pin 2 of NTC interface CN2, the cathode of diode D5, and one end of resistor R7, connected to the reference voltage Vref. The other end of resistor R7 is connected to one end of resistor R8 and pin 3 of comparator LM1. The other end of resistor R8 and the anode of diode D5 are grounded. Pin 1 of NTC interface CN2 is connected to one end of resistor R9, one end of capacitor C18, and... Pin 2 of comparator LM1 is connected to ground, the other end of resistor R9 and the other end of capacitor C18 are grounded, pin 4 of comparator LM1 is grounded, pin 8 of comparator LM1 is connected to voltage signal VCC1, pin 1 of comparator LM1 is connected to the other end of resistor R6, one end of capacitor C16 and the gate of PMOS transistor Q1, the other end of capacitor C16 is grounded, the drain of PMOS transistor Q1 is connected to one end of current-limiting resistor R3, the cathode of diode D4 and pin 1 of power relay RELAY1, the other end of current-limiting resistor R3 is connected to the anode of LED D3, the cathode of LED D3, the anode of diode D4 and pin 2 of power relay RELAY1 are grounded, pin 3 of power relay RELAY1 is connected to one end of forced power supply switch K5 and serves as the first input terminal of the detection and switching control circuit, pin 4 of power relay RELAY1 is connected to the other end of forced power supply switch K5 and pin 1 of AC output interface P1, and pin 2 of AC output interface P1 serves as the second input terminal of the detection and switching control circuit.

8. The wide-voltage AC / DC automatic detection and switching circuit according to claim 5, characterized in that: The DC detection and switching branch includes capacitor C15, diode D12, relay K2, resistor R4, LED D6, diode D11, power relay RELAY2, DC output interface P2, LED D8, resistor R5, diode D7, and relay K1. One end of resistor R4 is connected to the cathode of diode D11 and pin 1 of power relay RELAY2, serving as the sixth input terminal of the detection and switching control circuit, connected to the voltage signal VCC2. The other end of resistor R4 is connected to the anode of LED D6. The cathode of LED D6 is connected to pin 7 of relay K2. Pin 8 of relay K2 is connected to the anode of diode D12 and one end of capacitor C15, grounded. Pin 6 of relay K2 is grounded. Pin 1 of relay K2 is connected to diode D12... The cathode and the other end of capacitor C15 are connected to the voltage signal VCC1. Pin 5 of relay K2 is connected to the cathode of LED D8, the anode of diode D7, and pin 8 of relay K1. The anode of LED D8 is connected to one end of resistor R5. The other end of resistor R5 is connected to the cathode of diode D7 and pin 1 of relay K1 to the voltage signal VCC1. Pins 3 and 6 of relay K1 are grounded. Pin 7 of relay K1 is connected to the anode of diode D11 and pin 2 of power relay RELAY2. Pin 3 of power relay RELAY2 serves as the fourth input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY2 is connected to pin 1 of DC output interface P2. Pin 2 of DC output interface P2 serves as the fifth input terminal of the detection and switching control circuit.

9. The wide-voltage AC / DC automatic detection and switching circuit according to claim 5, characterized in that: The DC detection switching branch includes resistor R16, resistor R17, NTC interface CN3, diode D10, resistor R13, resistor R14, resistor R15, capacitor C19, comparator LM2, resistor R12, capacitor C17, PMOS transistor Q2, capacitor C15, diode D12, relay K2, resistor R4, LED D6, diode D11, power relay RELAY2, DC output interface P2, forced power supply switch K6, LED D8, resistor R5, diode D7, and relay K1. One end of resistor R16 is connected to one end of resistor R17, one end of resistor R12, and the source of PMOS transistor Q2. Connect the voltage signal VCC2 to the sixth input terminal of the detection and switching control circuit. Connect the other end of resistor R16, the other end of resistor R17, pin 2 of NTC interface CN3, the cathode of diode D10, and one end of resistor R13 to the reference voltage Vref. Connect the other end of resistor R13, one end of resistor R14, and pin 3 of comparator LM2. Connect the other end of resistor R14 and the anode of diode D10 to ground. Connect pin 1 of NTC interface CN3, one end of resistor R15, one end of capacitor C19, and pin 2 of comparator LM2. Connect the other end of resistor R15 and the other end of capacitor C19 to ground. Connect pin 1 of comparator LM2 to resistor R12. The other end of the capacitor C17 is connected to the gate of PMOS transistor Q2, and the other end of the capacitor C17 is grounded. The drain of PMOS transistor Q2 is connected to one end of resistor R4, the cathode of diode D11, and pin 1 of power relay RELAY2. The other end of resistor R4 is connected to the anode of LED D6. The cathode of LED D6 is connected to pin 7 of relay K2. Pin 8 of relay K2 is connected to the anode of diode D12 and one end of capacitor C15 and grounded. Pin 6 of relay K2 is grounded. Pin 1 of relay K2 is connected to the cathode of diode D12 and the other end of capacitor C15, and the voltage signal VCC1 is connected to it. Pin 5 of relay K2 is connected to the LED... The cathode of diode D8, the anode of diode D7, and pin 8 of relay K1 are connected. The anode of LED D8 is connected to one end of resistor R5. The other end of resistor R5 is connected to the cathode of diode D7 and pin 1 of relay K1 to receive voltage signal VCC1. Pins 3 and 6 of relay K1 are grounded. Pin 7 of relay K1 is connected to the anode of diode D11 and pin 2 of power relay RELAY2. Pin 3 of power relay RELAY2 serves as the fourth input terminal of the detection and switching control circuit. Pin 4 of power relay RELAY2 is connected to pin 1 of DC output interface P2. Pin 2 of DC output interface P2 serves as the fifth input terminal of the detection and switching control circuit.

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