A signal zero-crossing detection circuit and switching power supply

Abstract

This invention discloses a signal zero-crossing detection circuit and a switching power supply. The signal zero-crossing detection circuit includes a signal sampling circuit and a zero-crossing identification circuit. During operation: when the AC signal is a positive half-wave, the signal sampling circuit converts the AC signal into a first set voltage plus an amplitude voltage and outputs it to the zero-crossing identification circuit, which then outputs a low level after identification. When the AC signal is a negative half-wave, the signal sampling circuit converts the AC signal into a first set voltage minus the amplitude voltage and outputs it to the zero-crossing identification circuit, which then outputs a low level after identification. When the AC signal is zero, the signal sampling circuit converts the AC signal into the first set voltage and outputs it to the zero-crossing identification circuit, which then outputs a high level after identification. This invention can accurately identify whether the detected AC signal has crossed zero and outputs a high level when the detected signal crosses zero, serving as an indicator or controlling subsequent circuits.

Description

Technical Field

[0001] This invention relates to power conversion technology, and in particular to a signal zero-crossing detection circuit and a switching power supply. Background Technology

[0002] The magnitude of the input inrush current is a crucial performance indicator for switching power supplies. A smaller input inrush current signifies higher reliability and stronger compatibility. AC / DC switching power supplies (primary power supplies) convert AC power from the mains grid into the required DC power. However, the phase of the mains AC power is not fixed at the moment it is connected to the switching power supply; it can be any phase between 0° and 360°. The largest inrush current is generated when the mains AC power is connected to the switching power supply at 90° or 270° phase (peak voltage point), while the smallest inrush current is generated when the mains AC power is connected to the switching power supply at 0°, 180°, or 360° phase (voltage zero-crossing point). Existing methods for suppressing the input inrush current of switching power supplies include increasing the line impedance (connecting a negative temperature characteristic thermistor in series in the line) and using a microprocessor with external circuitry to achieve zero-phase detection. These existing technologies have the following characteristics:

[0003] Connecting a negative temperature characteristic thermistor in series in the circuit increases the line impedance. This can effectively reduce the input inrush current of the switching power supply, regardless of the phase of the grid connection. However, the long-term series connection of the thermistor will introduce additional power consumption, which will have a significant negative impact on the product's efficiency and temperature rise performance. The higher the power of the product, the more significant the impact. Although a relay solution can be used to allow the thermistor to be briefly connected to the line and then disconnected, the high cost of this solution becomes another limiting factor.

[0004] By using a microprocessor and peripheral circuitry to perform zero-phase detection of the grid voltage, the grid voltage is always near the zero-crossing point when the switching power supply is connected to the grid. This method can effectively reduce the input inrush current without causing additional performance loss, but its disadvantages are high cost and complex circuitry. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a signal zero-crossing detection circuit and a switching power supply that can effectively suppress the input inrush current of the switching power supply. This solution will not have a negative impact on the performance of the switching power supply, and the circuit is simple and inexpensive.

[0006] As a first aspect of the present invention, the technical solution of an embodiment of a signal zero-crossing detection circuit is provided as follows:

[0007] A signal zero-crossing detection circuit is used to detect whether an AC signal crosses zero, wherein the signal zero-crossing detection circuit includes:

[0008] A signal sampling circuit includes a first input terminal, a second input terminal, and an output terminal. The first input terminal and the second input terminal of the signal sampling circuit are used to acquire the AC signal.

[0009] The zero-crossing identification circuit includes an input terminal and an output terminal. The input terminal of the zero-crossing identification circuit is connected to the output terminal of the signal sampling circuit, and the output terminal of the zero-crossing identification circuit is used to output a zero-crossing identification signal.

[0010] During operation of the signal zero-crossing detection circuit:

[0011] When the AC signal is a positive half-wave, the signal sampling circuit converts the AC signal into a first set voltage plus a magnitude voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a low-level zero-crossing identification signal.

[0012] When the AC signal is a negative half-wave, the signal sampling circuit converts the AC signal into the first set voltage minus the amplitude voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a low-level zero-crossing identification signal.

[0013] When the AC signal is zero, the signal sampling circuit converts the AC signal into the first set voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a high-level zero-crossing identification signal.

[0014] Preferably, the signal sampling circuit includes: resistors R1, R2, R3, R4, R5, R6, R7, R8, and operational amplifier U1; one end of resistor R1 is the first input terminal of the signal sampling circuit, the other end of resistor R1 is connected to one end of resistor R2 and one end of resistor R3, one end of resistor R8 is connected to power supply VCC3, and the other ends of resistor R3 and R8 are connected to the non-inverting input terminal of operational amplifier U1; one end of resistor R4 is the second input terminal of the signal sampling circuit, the other end of resistor R4 is connected to one end of resistor R5 and one end of resistor R6, the other end of resistor R6 and one end of resistor R7 are connected to the inverting input terminal of operational amplifier U1, and the other end of resistor R7 is connected together with the output terminal of operational amplifier U1 as the output terminal of the signal sampling circuit; the other ends of resistors R2 and R5 are grounded.

[0015] Furthermore, any one, two, or all of the resistors R2, R5, and R7 are connected in parallel with a capacitor.

[0016] Preferably, the zero-crossing identification circuit includes: operational amplifier U2, operational amplifier U3, transistor Q1, and transistor Q2; the non-inverting input terminals of operational amplifier U2 and operational amplifier U3 are connected together as the input terminals of the zero-crossing identification circuit; the inverting input terminal of operational amplifier U2 is connected to power supply VCC1; the non-inverting input terminal of operational amplifier U3 is connected to power supply VCC2; the output terminal of operational amplifier U2 is connected to the base of transistor Q1; the output terminal of operational amplifier U3 is connected to the base of transistor Q2; the emitter of transistor Q1 is connected to power supply VCC0; the collector of transistor Q1 is connected to the emitter of transistor Q2; and the collector of transistor Q2 is the output terminal of the zero-crossing identification circuit.

[0017] Furthermore, the zero-crossing identification circuit also includes a resistor R9, one end of which is the input terminal of the zero-crossing identification circuit, and the other end of which is connected to both the non-inverting input terminal of operational amplifier U2 and the non-inverting input terminal of operational amplifier U3.

[0018] Furthermore, the zero-crossing identification circuit further includes a resistor R13, which is connected between the output terminal of the operational amplifier U2 and the base of the transistor Q1; and / or the zero-crossing identification circuit further includes a resistor R15, which is connected between the output terminal of the operational amplifier U3 and the base of the transistor Q2.

[0019] Furthermore, the zero-crossing identification circuit further includes a resistor R12 connected between the emitter and base of the transistor Q1; and / or the zero-crossing identification circuit further includes a resistor R14 connected between the emitter and base of the transistor Q2.

[0020] Furthermore, the zero-crossing identification circuit also includes resistors R10 and R11. One end of resistors R10 and R11 are connected in series to the output terminal of operational amplifier U2, and the other end is connected to the output terminal of operational amplifier U3. The connection point of resistors R10 and R11 in series is used to connect to the power supply VCC0.

[0021] A signal zero-crossing detection circuit is used to detect whether an AC signal crosses zero, wherein the signal zero-crossing detection circuit includes:

[0022] A signal sampling circuit includes: resistors R1, R2, R3, R4, R5, R6, R7, and R8; operational amplifier U1; capacitors C1, C2, and C3; one end of resistor R1 is the first input terminal of the signal sampling circuit; the other end of resistor R1 is connected to one end of resistor R2 and one end of resistor R3; one end of resistor R8 is connected to power supply VCC3; the other ends of resistors R3 and R8 are connected to the non-inverting input terminal of operational amplifier U1; one end of resistor R4 is the second input terminal of the signal sampling circuit; the other end of resistor R4... One end of the resistor is connected to one end of resistor R5 and one end of resistor R6. The other end of resistor R6 and one end of resistor R7 are connected to the inverting input of operational amplifier U1. The other end of resistor R7 is connected to the output of operational amplifier U1 as the output of the signal sampling circuit. The other ends of resistor R2 and resistor R5 are grounded. Capacitor C1 is connected in parallel with resistor R2, capacitor C2 is connected in parallel with resistor R5, and a plurality of capacitors C3 are connected in parallel with resistor R7. The first input and second input of the signal sampling circuit are used to acquire the AC signal.

[0023] The zero-crossing identification circuit includes resistors R9, R10, R11, R12, R13, R14, and R15, operational amplifier U2, operational amplifier U3, transistor Q1, and transistor Q2. One end of resistor R9 is the input terminal of the zero-crossing identification circuit, connected to the output terminal of the signal sampling circuit. The other end of resistor R9 is connected to both the non-inverting input terminals of operational amplifier U2 and operational amplifier U3. The inverting input terminal of operational amplifier U2 is connected to power supply VCC1, and the non-inverting input terminal of operational amplifier U3 is connected to power supply VCC2. The output terminal of operational amplifier U2 is connected to one end of resistor R13, and the other end of resistor R13 is connected to the base of transistor Q1. The output terminal of operational amplifier U3 is connected to... One end of resistor R15 is connected to the base of transistor Q2. The emitter of transistor Q1 is connected to the power supply VCC0. The collector of transistor Q1 is connected to the emitter of transistor Q2. The collector of transistor Q2 is the output terminal of the zero-crossing identification circuit, which outputs a zero-crossing identification signal. Resistor R12 is connected between the emitter and base of transistor Q1. Resistor R14 is connected between the emitter and base of transistor Q2. Resistors R10 and R11 are connected in series, with one end connected to the output terminal of operational amplifier U2 and the other end connected to the output terminal of operational amplifier U3. The connection point of resistors R10 and R11 in series is used to connect to the power supply VCC0.

[0024] As a first aspect of the present invention, the technical solution of an embodiment of a signal zero-crossing detection circuit is provided as follows:

[0025] A switching power supply, comprising the signal zero-crossing detection circuit described in any of the first aspects above.

[0026] The working principle of this invention will be analyzed in conjunction with specific embodiments. Compared with the prior art, this invention has the following beneficial effects:

[0027] 1. The signal zero-crossing detection circuit of this invention converts the acquired AC signal in a non-zero state into a voltage after adding / subtracting a first set voltage and a first set voltage when crossing zero. This makes the identification and judgment of the subsequent zero-crossing identification circuit very easy, which helps to simplify the circuit and control logic, thereby improving the reliability of the circuit and reducing the circuit cost.

[0028] 2. The switching power supply of this embodiment of the invention uses the zero-crossing detection circuit of this embodiment of the invention, which can detect the zero-crossing point of the input AC power and control the switching power supply to connect to the power grid when the AC power crosses zero, so as to reduce the input inrush current and will not have a negative impact on other performance of the switching power supply. Attached Figure Description

[0029] Figure 1 This is a schematic block diagram of the signal zero-crossing detection circuit according to the first embodiment of the present invention;

[0030] Figure 2 This is a specific circuit diagram of the signal zero-crossing detection circuit according to the first embodiment of the present invention. Detailed Implementation

[0031] To make the technical solution of the present invention clearer, 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. Those skilled in the art can make other modifications, substitutions, or changes to the present invention without creative effort, and these modifications, substitutions, or changes still fall within the protection scope of the present invention.

[0032] It should be noted that the terms "comprising" and "having" and any variations thereof described in the specification and claims of this application are intended to cover non-exclusive inclusion. For example, including a series of components, unit circuits or control timings is not necessarily limited to those components, unit circuits or control timings that are explicitly listed, but may include components, unit circuits or control timings that are not explicitly listed or that are inherent to these circuits.

[0033] Furthermore, unless otherwise specified, the embodiments and features described in this application may be combined with each other.

[0034] It should be understood that, in the specification and claims, when an element is described as being "connected" to another element, that element may be "directly connected" to that other element or "connected" to that other element through a third element; when a step is described as being connected to another step, that step may be connected directly to that other step or connected to that other step through a third step.

[0035] First Embodiment

[0036] This embodiment provides a signal zero-crossing detection circuit for detecting whether an AC signal has crossed zero. Figure 1 This is a schematic block diagram of the signal zero-crossing detection circuit according to the first embodiment of the present invention; please refer to [link / reference]. Figure 1 The signal zero-crossing detection circuit includes:

[0037] The signal sampling circuit includes a first input terminal, a second input terminal, and an output terminal. The first input terminal and the second input terminal of the signal sampling circuit are used to acquire AC signals.

[0038] The zero-crossing identification circuit includes an input terminal and an output terminal. The input terminal of the zero-crossing identification circuit is connected to the output terminal of the signal sampling circuit, and the output terminal of the zero-crossing identification circuit is used to output the zero-crossing identification signal.

[0039] When the signal zero-crossing detection circuit is in operation:

[0040] When the AC signal is a positive half-wave, the signal sampling circuit converts the AC signal into a first set voltage plus an amplitude voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a low-level zero-crossing identification signal.

[0041] When the AC signal is a negative half-wave, the signal sampling circuit converts the AC signal into a first set voltage minus the amplitude voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a low-level zero-crossing identification signal.

[0042] When the AC signal is zero, the signal sampling circuit converts the AC signal into a first set voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a high-level zero-crossing identification signal.

[0043] Figure 1 The signal zero-crossing detection circuit converts the acquired AC signal in a non-zero state into a voltage equal to or equal to a first set voltage plus / minus an amplitude voltage, and then converts it into the first set voltage when it crosses zero. This makes the subsequent zero-crossing identification circuit very easy to identify and process, which helps to simplify the circuit and control logic, thereby improving the reliability of the circuit and reducing the cost of the circuit.

[0044] Figure 2For a specific circuit diagram of the signal zero-crossing detection circuit of the first embodiment of the present invention, please refer to [link / reference]. Figure 2 :

[0045] The signal sampling circuit includes resistors R1, R2, R3, R4, R5, R6, R7, and R8, and operational amplifier U1. One end of resistor R1 is the first input terminal (signal in+) of the signal sampling circuit. The other end of resistor R1 is connected to one end of resistor R2 and one end of resistor R3. One end of resistor R8 is connected to the power supply VCC3. The other ends of resistor R3 and R8 are connected to the non-inverting input terminal of operational amplifier U1. One end of resistor R4 is the second input terminal (signal in-) of the signal sampling circuit. The other end of resistor R4 is connected to one end of resistor R5 and one end of resistor R6. The other ends of resistor R6 and R7 are connected to the inverting input terminal of operational amplifier U1. The other end of resistor R7 is connected to the output terminal of operational amplifier U1 as the output terminal of the signal sampling circuit. The other ends of resistors R2 and R5 are used for grounding.

[0046] The working principle of the signal sampling circuit is as follows:

[0047] In the signal sampling circuit, the first input terminal signal in+ and the second input terminal signal in- are connected to the input L and N lines of the AC switching power supply, respectively, and GND is the power ground of the switching power supply. Among them, R1=R4, R2=R5, R3=R6, R8=R7; R1 and R4 are much larger than R2, R5, R3, R6, R8, and R7.

[0048] When the AC input is in the positive half-wave, signal in+≈Vac, signal in-≈0, then the voltage at the non-inverting input terminal of op-amp U1 is... The voltage at the inverting input terminal of op-amp U1 The output voltage of op-amp U1 .

[0049] When the AC input is in the negative half-wave, signal in+≈0, signal in-≈Vac, then the voltage at the non-inverting input terminal of op-amp U1 is... Voltage at the inverting input of op-amp U1 The output voltage of op-amp U1 .

[0050] Therefore, the output waveform of the signal sampling circuit, that is, the voltage waveform at the output terminal of operational amplifier U1, is a sine wave with the same phase as the input voltage. Its voltage magnitude is the first set voltage VCC3 plus or minus the amplitude voltage. So, when the input voltage crosses zero, the output voltage of the signal sampling circuit... .

[0051] Furthermore, resistor R2 is connected in parallel with capacitor C1, resistor R5 is connected in parallel with capacitor C2, and resistor R7 is connected in parallel with capacitor C3. The purpose of adding capacitors C1, C2, and C3 is to filter the sampled signal and improve its accuracy.

[0052] Please continue reading Figure 2 The zero-crossing identification circuit includes: operational amplifier U2, operational amplifier U3, transistor Q1, and transistor Q2. The non-inverting input terminals of operational amplifier U2 and operational amplifier U3 are connected together as the input terminals of the zero-crossing identification circuit. The inverting input terminal of operational amplifier U2 is connected to the power supply VCC1, and the non-inverting input terminal of operational amplifier U3 is connected to the power supply VCC2. The output terminal of operational amplifier U2 is connected to the base of transistor Q1, and the output terminal of operational amplifier U3 is connected to the base of transistor Q2. The emitter of transistor Q1 is connected to the power supply VCC0, and the collector of transistor Q1 is connected to the emitter of transistor Q2. The collector of transistor Q2 is the output terminal of the zero-crossing identification circuit.

[0053] The working principle of the zero-crossing identification circuit is as follows:

[0054] The signal sampling circuit outputs a sine wave with the same phase as the input voltage. The voltage magnitude is the first set voltage VCC3 plus or minus the amplitude voltage. The waveform is used as the input signal for the zero-crossing detection circuit, and is connected to the non-inverting input of comparator U2 and the inverting input of comparator U3 respectively, providing a voltage level V to the inverting input of comparator U2. CC1 V CC1 ≈V CC3 But V CC1 Slightly greater than V CC3 Apply a voltage level V to the non-inverting input of comparator U3. CC2 V CC2 ≈V CC3 But V CC2 Slightly less than V CC3 .

[0055] When the AC input is a positive half-wave, that is, when the phase of the input voltage is between 0 and 180°:

[0056]

[0057] When the voltage level at the non-inverting input of comparator U2 is higher than that at the inverting input, the output of comparator U2 is high, and no current flows through the base of transistor Q1, making Q1 cut off. When the voltage level at the inverting input of comparator U3 is higher than that at the non-inverting input, the output of comparator U3 is low, and current flows through the base of transistor Q2, making Q2 turn on. With transistor Q1 cut off and Q2 turned on, the loop from Vcc0 to the output signal is broken, resulting in a low output signal. This prevents the switching power supply from connecting to the mains.

[0058] When the AC input is a negative half-wave, that is, when the phase of the input voltage is between 180° and 360°:

[0059]

[0060] When the voltage level at the inverting input of comparator U2 is higher than that at the non-inverting input, the output of comparator U2 is low, and current flows through the base of transistor Q1, turning Q1 on. When the voltage level at the non-inverting input of comparator U3 is higher than that at the inverting input, the output of comparator U3 is high, and no current flows through the base of transistor Q2, turning Q2 off. With transistor Q1 on and Q2 off, the circuit from Vcc0 to the output signal is broken, resulting in a low output signal. This prevents the switching power supply from connecting to the mains.

[0061] When the AC input is zero, that is, when the input voltage phase is 0° (360°) or 180°:

[0062]

[0063] When VCC1 > Vout1 = VCC3, the inverting input of comparator U2 is at the same level as the non-inverting input, so the output of comparator U2 is low, and current flows through the base of transistor Q1, turning it on. When VCC2 < Vout1 = VCC3, the inverting input of comparator U3 is higher than the non-inverting input, so the output of comparator U3 is low, and current flows through the base of transistor Q2, turning it on. With both transistors Q1 and Q2 conducting, the loop from Vcc0 to the output signal is complete, resulting in a high output signal. This allows the switching power supply to connect to the grid at this time, suppressing inrush current.

[0064] Furthermore, the zero-crossing identification circuit also includes resistor R9. One end of resistor R9 is the input terminal of the zero-crossing identification circuit, and the other end of resistor R9 is connected to both the non-inverting input terminal of operational amplifier U2 and the non-inverting input terminal of operational amplifier U3. The purpose of adding resistor R9 is to achieve impedance matching and avoid distortion during signal transmission.

[0065] Furthermore, the zero-crossing identification circuit also includes a resistor R13, which is connected between the output of operational amplifier U2 and the base of transistor Q1; and / or the zero-crossing identification circuit also includes a resistor R15, which is connected between the output of operational amplifier U3 and the base of transistor Q2. The purpose of adding resistors R13 and R15 is to limit the current and prevent excessive current from damaging transistors Q1 and Q2.

[0066] Furthermore, the zero-crossing identification circuit also includes a resistor R12, which is connected between the emitter and base of transistor Q1; and / or the zero-crossing identification circuit also includes a resistor R14, which is connected between the emitter and base of transistor Q2. The purpose of adding resistors R12 and R14 is also to limit the current and prevent excessive current from damaging transistors Q1 and Q2.

[0067] Furthermore, the zero-crossing identification circuit also includes resistors R10 and R11. Resistors R10 and R11 are connected in series, with one end connected to the output of operational amplifier U2 and the other end connected to the output of operational amplifier U3. The connection point of resistors R10 and R11 in series is used to connect to the power supply VCC0. The purpose of adding resistors R10 and R11 is to provide pull-up resistors for operational amplifier U2, so that the comparator can output valid high and low levels.

[0068] Second Embodiment

[0069] This embodiment provides a switching power supply, including any of the signal zero-crossing detection circuits in the first embodiment.

[0070] The switching power supply in this embodiment uses the zero-crossing detection circuit of the first embodiment, which can detect the zero-crossing point of the input AC power and control the switching power supply to connect to the power grid when the AC power crosses zero, so as to reduce the input inrush current and not have a negative impact on other performance of the switching power supply.

[0071] The above description is only for illustrating the technical solution of the present invention and is not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can make modifications or substitutions to the specific embodiments of the present invention. Any modifications or substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention.

Claims

1. A signal zero-crossing detection circuit for detecting whether an AC signal has crossed zero, characterized in that, The signal zero-crossing detection circuit includes: A signal sampling circuit includes a first input terminal, a second input terminal, and an output terminal. The first input terminal and the second input terminal of the signal sampling circuit are used to acquire the AC signal. The zero-crossing identification circuit includes an input terminal and an output terminal. The input terminal of the zero-crossing identification circuit is connected to the output terminal of the signal sampling circuit, and the output terminal of the zero-crossing identification circuit is used to output a zero-crossing identification signal. During operation of the signal zero-crossing detection circuit: When the AC signal is a positive half-wave, the signal sampling circuit converts the AC signal into a first set voltage plus a magnitude voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a low-level zero-crossing identification signal. When the AC signal is a negative half-wave, the signal sampling circuit converts the AC signal into the first set voltage minus the amplitude voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a low-level zero-crossing identification signal. When the AC signal is zero, the signal sampling circuit converts the AC signal into the first set voltage and outputs it to the zero-crossing identification circuit. After identification and judgment, the zero-crossing identification circuit outputs a high-level zero-crossing identification signal.

2. The signal zero-crossing detection circuit according to claim 1, characterized in that, The signal sampling circuit includes: resistors R1, R2, R3, R4, R5, R6, R7, R8, and operational amplifier U1. One end of resistor R1 is the first input terminal of the signal sampling circuit, and the other end of resistor R1 is connected to one end of resistor R2 and one end of resistor R3. One end of resistor R8 is connected to the power supply VCC3, and the other ends of resistors R3 and R8 are connected to the non-inverting input terminal of operational amplifier U1. One end of resistor R4 is the second input terminal of the signal sampling circuit, and the other end of resistor R4 is connected to one end of resistor R5 and one end of resistor R6. The other ends of resistor R6 and R7 are connected to the inverting input terminal of operational amplifier U1, and the other end of resistor R7 is connected to the output terminal of operational amplifier U1 as the output terminal of the signal sampling circuit. The other ends of resistors R2 and R5 are grounded.

3. The signal zero-crossing detection circuit according to claim 2, characterized in that: A capacitor is connected in parallel with any one, two, or all of the resistors R2, R5, and R7.

4. The signal zero-crossing detection circuit according to claim 1, characterized in that, The zero-crossing identification circuit includes: operational amplifier U2, operational amplifier U3, transistor Q1, and transistor Q2; the non-inverting input terminals of operational amplifier U2 and operational amplifier U3 are connected together as the input terminals of the zero-crossing identification circuit; the inverting input terminal of operational amplifier U2 is connected to power supply VCC1; the non-inverting input terminal of operational amplifier U3 is connected to power supply VCC2; the output terminal of operational amplifier U2 is connected to the base of transistor Q1; the output terminal of operational amplifier U3 is connected to the base of transistor Q2; the emitter of transistor Q1 is connected to power supply VCC0; the collector of transistor Q1 is connected to the emitter of transistor Q2; and the collector of transistor Q2 is the output terminal of the zero-crossing identification circuit.

5. The signal zero-crossing detection circuit according to claim 4, characterized in that: The zero-crossing identification circuit also includes a resistor R9. One end of the resistor R9 is the input terminal of the zero-crossing identification circuit, and the other end of the resistor R9 is connected to both the non-inverting input terminal of the operational amplifier U2 and the non-inverting input terminal of the operational amplifier U3.

6. The signal zero-crossing detection circuit according to claim 4, characterized in that: The zero-crossing identification circuit further includes a resistor R13, which is connected between the output terminal of the operational amplifier U2 and the base of the transistor Q1; and / or the zero-crossing identification circuit further includes a resistor R15, which is connected between the output terminal of the operational amplifier U3 and the base of the transistor Q2.

7. The signal zero-crossing detection circuit according to any one of claims 4 to 6, characterized in that: The zero-crossing identification circuit further includes a resistor R12 connected between the emitter and base of the transistor Q1; and / or the zero-crossing identification circuit further includes a resistor R14 connected between the emitter and base of the transistor Q2.

8. The signal zero-crossing detection circuit according to any one of claims 4 to 6, characterized in that: The zero-crossing identification circuit also includes resistors R10 and R11. One end of resistors R10 and R11 are connected in series to the output terminal of operational amplifier U2, and the other end is connected to the output terminal of operational amplifier U3. The connection point of resistors R10 and R11 in series is used to connect to the power supply VCC0.

9. A signal zero-crossing detection circuit for detecting whether an AC signal has crossed zero, characterized in that, The signal zero-crossing detection circuit includes: A signal sampling circuit includes: resistors R1, R2, R3, R4, R5, R6, R7, and R8; operational amplifier U1; capacitors C1, C2, and C3; one end of resistor R1 is the first input terminal of the signal sampling circuit; the other end of resistor R1 is connected to one end of resistor R2 and one end of resistor R3; one end of resistor R8 is connected to power supply VCC3; the other ends of resistors R3 and R8 are connected to the non-inverting input terminal of operational amplifier U1; one end of resistor R4 is the second input terminal of the signal sampling circuit; the other end of resistor R4... One end of the resistor is connected to one end of resistor R5 and one end of resistor R6. The other end of resistor R6 and one end of resistor R7 are connected to the inverting input of operational amplifier U1. The other end of resistor R7 is connected to the output of operational amplifier U1 as the output of the signal sampling circuit. The other ends of resistor R2 and resistor R5 are grounded. Capacitor C1 is connected in parallel with resistor R2, capacitor C2 is connected in parallel with resistor R5, and a plurality of capacitors C3 are connected in parallel with resistor R7. The first input and second input of the signal sampling circuit are used to acquire the AC signal. The zero-crossing identification circuit includes resistors R9, R10, R11, R12, R13, R14, and R15, operational amplifier U2, operational amplifier U3, transistor Q1, and transistor Q2. One end of resistor R9 is the input terminal of the zero-crossing identification circuit, connected to the output terminal of the signal sampling circuit. The other end of resistor R9 is connected to both the non-inverting input terminals of operational amplifier U2 and operational amplifier U3. The inverting input terminal of operational amplifier U2 is connected to power supply VCC1, and the non-inverting input terminal of operational amplifier U3 is connected to power supply VCC2. The output terminal of operational amplifier U2 is connected to one end of resistor R13, and the other end of resistor R13 is connected to the base of transistor Q1. The output terminal of operational amplifier U3 is connected to... One end of resistor R15 is connected to the base of transistor Q2. The emitter of transistor Q1 is connected to the power supply VCC0. The collector of transistor Q1 is connected to the emitter of transistor Q2. The collector of transistor Q2 is the output terminal of the zero-crossing identification circuit, which outputs a zero-crossing identification signal. Resistor R12 is connected between the emitter and base of transistor Q1. Resistor R14 is connected between the emitter and base of transistor Q2. Resistors R10 and R11 are connected in series, with one end connected to the output terminal of operational amplifier U2 and the other end connected to the output terminal of operational amplifier U3. The connection point of resistors R10 and R11 in series is used to connect to the power supply VCC0.

10. A switching power supply, characterized in that: Includes the signal zero-crossing detection circuit as described in any one of claims 1 to 9.

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