Bidirectional zero-crossing detection circuit and method

Abstract

The present invention provides a bidirectional zero-crossing detection circuit and method. The detection circuit includes: a positive-to-negative zero-crossing detection module, a negative-to-positive zero-crossing detection module, and an optocoupler module. When the AC signal is at a non-zero-crossing point, the energy storage capacitor is charged, the switch tube is disconnected, and the optocoupler module has no output. When the AC signal is at a zero-crossing point, the energy storage capacitor is discharged, the switch tube is turned on, and the energy of the energy storage capacitor is transferred to the optocoupler module, which turns on and triggers a zero-crossing detection signal. The energy storage capacitor discharge time is different for the positive-to-negative zero-crossing point and the negative-to-positive zero-crossing point. The circuit consists of only a small number of discrete components and an optocoupler, saving PCB space and reducing costs. The zero-crossing detection signal output is a single signal, saving MCU IO resources. The circuit has low power consumption. The direction of the zero-crossing can be determined by the difference in pulse width. The circuit has a wide detection range and high detection accuracy.

Description

Technical Field

[0001] The present invention relates to the field of circuit design, and in particular to a bidirectional zero-crossing detection circuit and method. Background Art

[0002] Many technical fields often detect the zero crossing point of AC power, such as station identification, phase judgment, zero crossing synchronization of communication signals, etc. At present, most of them are unidirectional zero crossing detection circuits, and bidirectional zero crossing circuits are relatively rare, such as Figure 1 This is a commonly used bidirectional zero-crossing circuit. It uses two optocoupler isolation schemes superimposed together. U1 provides the positive zero-crossing, and U2 provides the reverse zero-crossing. The two zero-crossings are combined through a gate circuit. This solution has high power consumption and high cost, and the zero-crossing point is not accurate, which requires software compensation. Figure 2 This is a rectifier plus optocoupler isolation solution. The bridge rectifier rectifies the AC signal and outputs two pulses, one in the positive half-cycle and the other in the negative half-cycle. These are then isolated by an optocoupler and shaped by a transistor. This solution has high power consumption and an inaccurate zero-crossing point, which is far from the actual zero-crossing point. Another common solution is a transformer plus rectifier solution. This solution converts AC220 into low voltage through a transformer, rectifies it through a diode, and shapes the output through a transistor to cross zero. This solution uses a transformer, which is costly and has a large deviation in the zero-crossing point.

[0003] It can be seen that the disadvantages of the above-mentioned existing technical solutions are: high cost, more components requiring more PCB space, high power consumption, and inability to distinguish the direction of zero crossing. Therefore, how to propose a zero-crossing detection circuit and method with a simple circuit structure, low cost, low power consumption, the ability to distinguish the zero-crossing direction, and high detection accuracy has become one of the urgent problems to be solved by those skilled in the art. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a bidirectional zero-crossing detection circuit and method to solve the problems of the prior art such as complex circuits, high power consumption, and inability to distinguish zero-crossing directions.

[0005] To achieve the above-mentioned object and other related objects, the present invention provides a bidirectional zero-crossing detection circuit comprising: a positive-to-negative zero-crossing detection module, a negative-to-positive zero-crossing detection module and an optical coupler module;

[0006] The positive to negative zero-crossing detection module includes: a first diode, a first voltage-stabilizing diode, a first capacitor, a first switching tube and a second resistor; wherein, the cathode of the first voltage-stabilizing diode is connected to the current output end of the AC power supply, and the anode is connected to one end of the first capacitor; the other end of the first capacitor is connected to the cathode of the first diode; the anode of the first diode is connected to the cathode of the first voltage-stabilizing diode; the control end of the first switching tube is connected to the anode of the first diode through the second resistor, and the input end is connected to the cathode of the first diode.

[0007] The negative to positive zero-crossing detection module includes: a second diode, a second voltage-stabilizing diode, a second capacitor, a second switching tube and a fourth resistor; wherein, the anode of the second voltage-stabilizing diode is connected to the anode of the first voltage-stabilizing diode, and the cathode of the second voltage-stabilizing diode is connected to the current input end of the AC power supply; one end of the second capacitor is connected to the anode of the second voltage-stabilizing diode, and the other end is connected to the cathode of the second diode; the anode of the second diode is connected to the cathode of the second voltage-stabilizing diode; the control end of the second switching tube is connected to the anode of the second diode through the fourth resistor, and the input end is connected to the cathode of the second diode.

[0008] The first input end of the optical coupling module is connected to the output ends of the first switching tube and the second switching tube, the second input end is connected to the anode of the second voltage regulator diode, and the first output end outputs a zero-crossing detection signal.

[0009] Optionally, the bidirectional zero-crossing detection circuit also includes a first current limiting module and a second current limiting module, the first current limiting module is connected between the current output end of the AC power supply and the input end of the positive to negative zero-crossing detection module; the second current limiting module is connected between the current input end of the AC power supply and the input end of the positive to negative zero-crossing detection module.

[0010] Optionally, the first current limiting module is a first resistor, and the second current limiting module is a third resistor.

[0011] Optionally, the first switching tube and the second switching tube are triodes.

[0012] Optionally, the optical coupling module includes an optical coupling isolator and a filtering unit.

[0013] Optionally, the first capacitor and the second capacitor have different capacitance values.

[0014] The present invention also provides a bidirectional zero-crossing detection method: when the AC signal is in the positive half cycle, the second voltage-stabilizing diode and the first diode are forward-conducted, the voltage across the first voltage-stabilizing diode is stabilized at the first voltage, and the first capacitor is charged through a loop consisting of an AC power supply-first diode-first capacitor-second voltage-stabilizing diode-AC power supply; the first switch tube is in an off state; when the AC signal is at the zero-crossing point from the positive half cycle to the negative half cycle, the first switch tube is turned on, and the first capacitor is discharged through a loop consisting of the first capacitor-first switch tube-optical coupling module-first capacitor, thereby turning on the optical coupling module and triggering Zero-crossing detection signal output; when the AC signal is in the negative half cycle, the first voltage-stabilizing diode and the second diode are forward-conducted, the voltage across the second voltage-stabilizing diode is stabilized at the second voltage, and the second capacitor is charged through the circuit consisting of the AC power supply-the second diode-the second capacitor-the first voltage-stabilizing diode-the AC power supply; the second switch tube is in the off state; when the AC signal is at the zero-crossing point from the negative half cycle to the positive half cycle, the second switch tube is turned on, and the second capacitor is discharged through the circuit consisting of the second capacitor-the second switch tube-the optocoupler module-the second capacitor, thereby turning on the optocoupler module and triggering the zero-crossing detection signal output.

[0015] Optionally, when the AC signal is in the positive half cycle and the negative half cycle, the charging circuit of the first capacitor and the second capacitor further includes a first current limiting module and a second current limiting module, which are used to limit the current of the charging circuit.

[0016] Optionally, when the AC signal is at a zero-crossing point from the positive half cycle to the negative half cycle and at a zero-crossing point from the negative half cycle to the positive half cycle, the discharge time of the first capacitor and the discharge time of the second capacitor are different.

[0017] As described above, the bidirectional zero-crossing detection circuit and method of the present invention have the following beneficial effects:

[0018] 1. The circuit structure is simple, consisting of only a few discrete components and an optocoupler, thus saving PCB space and reducing costs;

[0019] 2. The zero-crossing detection signal output has only one signal, which can save the MCU's IO resources;

[0020] 3. Low power consumption. Compared with several existing bidirectional zero-crossing solutions, the power consumption is much lower.

[0021] 4. Can detect the direction of zero crossing. If the widths of two zero crossing pulses are inconsistent, the direction of zero crossing can be determined by the difference in pulse widths.

[0022] 5. Wide detection range, it can work normally in the input range of AC176V-AC420V;

[0023] 6. The detection accuracy is high, almost completely consistent with the zero-crossing point. The current test error is on the order of tens of uS. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Shown is a schematic diagram of a bidirectional zero-crossing detection circuit in the prior art;

[0025] Figure 2 Shown is another schematic diagram of a bidirectional zero-crossing detection circuit in the prior art;

[0026] Figure 3 Shown is a block diagram of a bidirectional zero-crossing detection circuit of the present invention;

[0027] Figure 4 Shown is a bidirectional zero-crossing detection circuit diagram of the present invention;

[0028] Figure 5 Shown is a schematic diagram of the simulation output of the bidirectional zero-crossing detection circuit of the present invention.

[0029] Component number description

[0030] 1. First current limiting module

[0031] 2 Positive to negative zero-crossing detection module

[0032] 3 Negative to positive zero-crossing detection module

[0033] 4 Optocoupler Module

[0034] 41 filter units

[0035] 5 Second current limiting module DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0037] See also Figures 3 to 5 It should be noted that the diagrams provided in this embodiment are merely schematic illustrations of the basic concept of the present invention. Therefore, the diagrams only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0038] Example 1

[0039] like Figure 3 and Figure 4As shown, this embodiment provides a bidirectional zero-crossing detection circuit, which includes: a positive-to-negative zero-crossing detection module 2, a negative-to-positive zero-crossing detection module 3, and an optical coupler module 4.

[0040] like Figure 3 As shown, the positive to negative zero-crossing detection module 2 includes: a first diode D1, a first voltage-stabilizing diode VD1, a first capacitor C1, a first switch tube Q1 and a second resistor R2; the cathode of the first voltage-stabilizing diode VD1 is connected to the current output end of the AC power supply, and the anode is connected to one end of the first capacitor C1; the other end of the first capacitor C1 is connected to the cathode of the first diode D1; the anode of the first diode D1 is connected to the cathode of the first voltage-stabilizing diode VD1; the control end of the first switch tube Q1 is connected to the anode of the first diode D1 through the second resistor R2, and the input end is connected to the cathode of the first diode D1.

[0041] like Figure 3 As shown, the negative to positive zero-crossing detection module 3 includes: a second diode D2, a second voltage-stabilizing diode VD2, a second capacitor C2, a second switch tube Q2 and a fourth resistor R4; the anode of the second voltage-stabilizing diode VD2 is connected to the anode of the first voltage-stabilizing diode VD1, and the cathode of the second voltage-stabilizing diode VD2 is connected to the current input terminal of the AC power supply; one end of the second capacitor C2 is connected to the anode of the second voltage-stabilizing diode VD2, and the other end is connected to the cathode of the second diode D2; the anode of the second diode D2 is connected to the cathode of the second voltage-stabilizing diode VD2; the control end of the second switch tube Q2 is connected to the anode of the second diode D2 through the fourth resistor R4, and the input end is connected to the cathode of the second diode D2.

[0042] Specifically, the first switch tube Q1 and the second switch tube Q2 are triodes, corresponding to a first triode and a second triode respectively.

[0043] More specifically, as an example, the first switch tube Q1 and the second switch tube Q2 are PNP transistors, the base of the PNP transistor is the control end of the switch tube, the emitter is the input end of the switch tube, and the collector is the output end of the switch tube.

[0044] It should be noted that the types and models of the first switching tube Q1 and the second switching tube Q2 include but are not limited to the present embodiment, and are not listed one by one here. Any types and models of the first switching tube Q1 and the second switching tube Q2 that can form the discharge circuit of the first capacitor C1 and the second capacitor C2 near the zero crossing point meet the requirements of this invention.

[0045] It should be noted that the function of the first voltage-stabilizing diode VD1 and the second voltage-stabilizing diode VD2 is to provide a stable voltage so that when the AC power supply is in the positive half cycle or the negative half cycle, the voltage across the first diode D1 and the first capacitor C1, and the voltage across the second diode D2 and the second capacitor C2 remain constant.

[0046] Specifically, the first capacitor C1 and the second capacitor C2 have different capacitance values.

[0047] It should be noted that the function of the first capacitor C1 and the second capacitor C2 is to store energy. When the AC power supply is at a non-zero crossing point, the voltage of the first capacitor C1 when fully charged is the reverse stable voltage value of the first voltage-regulating diode VD1 minus the forward voltage drop of the first diode D1, and the voltage of the second capacitor C2 when fully charged is the reverse stable voltage value of the second voltage-regulating diode VD2 minus the forward voltage drop of the second diode D2. When the AC power supply is at a zero crossing point, the first capacitor C1 and the second capacitor C2 discharge by establishing a loop with the optocoupler module 4, triggering the optocoupler module 4 to output a zero-crossing detection signal V0; when the capacitance of the first capacitor C1 and the second capacitor C2 is different, the pulse width of the triggered zero-crossing detection signal V0 is different when the AC signal is at the zero crossing point from the positive half-cycle to the negative half-cycle and at the zero crossing point from the negative half-cycle to the positive half-cycle, so that the two zero-crossing detection points can be distinguished.

[0048] It should be further explained that the capacitance values ​​of the first capacitor C1 and the second capacitor C2 should be selected to ensure that the first capacitor C1 and the second capacitor C2 are fully charged within half a cycle of the positive half cycle or the negative half cycle of the AC power supply, and the specific capacitance value is not limited; any capacitance value of the first capacitor C1 and the second capacitor C2 that can ensure that the first capacitor C1 and the second capacitor C2 can be fully charged within half a cycle of the AC power supply according to actual design requirements and the detection signal pulse width can meet the actual design requirements meets the requirements of this invention.

[0049] like Figure 3 As shown, the optical coupling module 4 includes an optical coupling isolator U1 and a filtering unit 41 .

[0050] Specifically, the optocoupler isolator U1 is mainly used for transmitting the zero-crossing detection signal V0 and isolating strong and weak electricity. The first input end of the optocoupler isolator U1 is connected to the output ends of the first switch tube Q1 and the second switch tube Q2, the second input end is connected to the anode of the second voltage regulator diode VD2, the first output end outputs the zero-crossing detection signal V0, and the second output end is connected to the external power supply VDD.

[0051] More specifically, the filtering unit 41 includes a fifth resistor R5 and a third capacitor C3, one end of the fifth resistor R5 and one end of the third capacitor C3 are connected to the first output end of the optocoupler module 4, and the other end of the fifth resistor R5 and the other end of the third capacitor C3 are both grounded. The filtering unit 41 is used to filter out interference in the zero-crossing detection signal V0.

[0052] Specifically, the bidirectional zero-crossing detection circuit also includes a first current limiting module 1 and a second current limiting module 5, the first current limiting module 1 is connected between the current output end of the AC power supply and the input end of the positive to negative zero-crossing detection module; the second current limiting module 5 is connected between the current input end of the AC power supply and the input end of the positive to negative zero-crossing detection module; the first current limiting module 1 and the second current limiting module 5 are used to limit the current, thereby limiting the power consumption of the entire circuit.

[0053] like Figure 3 As shown, as an example, the first current limiting module 1 is a first resistor R1, and the second current limiting module 5 is a third resistor R3; one end of the first resistor R1 is connected to the current output end of the AC power supply, and the other end is connected to the cathode of the first voltage-stabilizing diode VD1; one end of the third resistor R3 is connected to the current input end of the AC power supply, and the other end is connected to the cathode of the second voltage-stabilizing diode VD2.

[0054] It should be noted that the resistance values ​​of the first resistor R1 and the third resistor R3 are not limited. The larger the resistance value, the smaller the circuit current and the smaller the circuit power consumption. Any resistance value that can meet the design power consumption requirements meets the requirements of this invention.

[0055] Example 2

[0056] This embodiment provides a bidirectional zero-crossing detection method, which is based on the bidirectional zero-crossing detection circuit in the first embodiment.

[0057] When the AC signal is in the positive half cycle, the second Zener diode VD2 and the first diode D1 are forward-conducted, the voltage across the first Zener diode VD1 is stabilized at the first voltage, and the first capacitor C1 is charged through the loop formed by the AC power supply-first resistor R1-first diode D1-first capacitor C1-second Zener diode VD2-third resistor R3-AC power supply; the first switch tube Q1 is in the off state.

[0058] It should be noted that when the AC signal is in the positive half cycle, since the first diode D1 is forward-conducted, the anode voltage of the first diode D1 is higher than the cathode voltage, and the corresponding base voltage of the first transistor Q1 is higher than the emitter voltage. The first transistor Q1 is in the cut-off state, so that the emitter and collector of the first transistor Q1 are disconnected; the voltage of the first capacitor C1 when it is fully charged is the first voltage minus the forward voltage drop of the first diode D1.

[0059] When the AC signal is at the zero-crossing point from the positive half-cycle to the negative half-cycle, the first voltage regulator diode VD1 is forward-conducted, the first switch tube Q1 is turned on, and the first capacitor C1 is discharged through the loop formed by the first capacitor C1-first switch tube Q1-optocoupler isolator U1-first capacitor C1, thereby turning on the optocoupler isolator U1 and triggering the output of the zero-crossing detection signal V0.

[0060] It should be noted that when the AC signal is at the zero-crossing point from the positive half-cycle to the negative half-cycle, the first voltage regulator diode VD1 is forward-conducted, and the emitter voltage of the first transistor Q1 is higher than the base voltage, so that the first transistor Q1 is in a saturation state, thereby making the emitter and collector of the first transistor Q1 conductive.

[0061] When the AC signal is in the negative half cycle, the first Zener diode VD1 and the second diode D2 are forward-conducted, the voltage across the second Zener diode VD2 is stabilized at the second voltage, and the second capacitor C2 is charged through a loop formed by the AC power supply-the third resistor R3-the second diode D2-the second capacitor C2-the first Zener diode VD1-the first resistor R1-the AC power supply; and the second switch tube Q2 is in the off state.

[0062] It should be noted that when the AC signal is in the negative half cycle, since the second diode D2 is forward-conducted, the anode voltage of the second diode D2 is higher than the cathode voltage, and the corresponding base voltage of the second transistor Q2 is higher than the emitter voltage. The second transistor Q2 is in the cut-off state, so that the emitter and collector of the second transistor Q2 are disconnected; the voltage of the second capacitor C2 when it is fully charged is the second voltage value minus the forward voltage drop of the second diode D2.

[0063] When the AC signal is at the zero-crossing point from the negative half-cycle to the positive half-cycle, the second voltage stabilizing diode VD2 is forward-conducted, the second switch tube Q2 is turned on, and the second capacitor C2 is discharged through the loop formed by the second capacitor C2-second switch tube Q2-optocoupler isolator U1-second capacitor C2, thereby turning on the optocoupler isolator U1 and triggering the output of the zero-crossing detection signal V0.

[0064] It should be noted that when the AC signal is at the zero-crossing point from the negative half-cycle to the positive half-cycle, the second voltage regulator diode VD2 is forward-conducted, and the emitter voltage of the second transistor Q2 is higher than the base voltage, so that the second transistor Q2 is in a saturated state, thereby making the emitter and collector of the second transistor Q2 conductive.

[0065] Specifically, when the AC signal is at the zero-crossing point from the positive half-cycle to the negative half-cycle and the zero-crossing point from the negative half-cycle to the positive half-cycle, the discharge time of the first capacitor C1 and the second capacitor C2 are different, so that the pulse width of the triggered zero-crossing detection signal V0 is different, so that the zero-crossing point from the positive half-cycle to the negative half-cycle and the zero-crossing point from the negative half-cycle to the positive half-cycle can be distinguished; the pulse width can be adjusted by the capacitance of the first capacitor C1 and the second capacitor C2.

[0066] It should be noted that when the AC signal is in the positive half cycle and the negative half cycle, the first resistor R1 and the third resistor R3 in the charging circuit of the first capacitor and the second capacitor act as the first current limiting module and the second current limiting module respectively, used to limit the current of the charging circuit.

[0067] like Figure 5 As shown in the figure, it is a simulation timing diagram of the bidirectional zero-crossing detection circuit and method. The second capacitor C2 is greater than the capacitance of the first capacitor C1. As can be seen from the figure, the capacitance of the first capacitor C1 and the second capacitor C2 is different, so the discharge time after the two are turned on is different, the time to maintain the optocoupler on is different, and the pulse width of the zero-crossing detection signal V0 output by the optocoupler is also different. The pulse width of the zero-crossing detection signal V0 from the positive half cycle to the negative half cycle is slightly narrower, and the pulse width of the zero-crossing detection signal from the negative half cycle to the positive half cycle is slightly wider. The two zero-crossing points can be distinguished according to the difference in pulse width. For ease of display, the dotted sine wave is an AC220 signal reduced by a ratio of 89:1, and the solid pulse signal is the zero-crossing output signal of the circuit. It can be seen that the rising edge of the pulse signal and the zero-crossing point are almost completely consistent, and the test error is on the order of tens of uS.

[0068] It should be noted that the bidirectional zero-crossing detection circuit and method can work normally when the input AC power supply is in the range of AC176V-AC420V, and the output zero-crossing detection signal V0 has no difference.

[0069] In summary, the bidirectional zero-crossing detection circuit of the present invention is composed of only a small number of discrete components and an optocoupler, which saves PCB space and reduces costs; the zero-crossing detection signal V0 output is only one signal, which can save MCU IO resources; low power consumption, compared with several existing bidirectional zero-crossing schemes, the power consumption is much lower, it only needs to ensure that the energy storage capacitor is fully charged within half a cycle, and the energy storage capacitor has a very small capacitance, so the current limiting resistor can be selected to have a relatively large resistance value, which only requires a very small consumption of about 47mW. If the pulse width is reduced, the consumption is even lower; it can detect bidirectional zero crossings, and if the pulse widths of two zero crossings are inconsistent, the direction of the zero crossing can be determined by the difference in pulse widths; the detection range is wide, and it can work normally in the AC176V-AC420V input range, and the output zero-crossing detection signal V0 has no difference; the detection accuracy is high, almost completely consistent with the zero crossing point, and the test error is on the order of tens of uS. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial utilization value.

[0070] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A bidirectional zero-crossing detection circuit, characterized in that: The bidirectional zero-crossing detection circuit includes: a positive to negative zero-crossing detection module, a negative to positive zero-crossing detection module and an optical coupler module; The positive to negative zero-crossing detection module includes: a first diode, a first voltage-stabilizing diode, a first capacitor, a first switch tube and a second resistor; The cathode of the first voltage-stabilizing diode is connected to the current output terminal of the AC power supply, and the anode is connected to one end of the first capacitor; the other end of the first capacitor is connected to the cathode of the first diode; the anode of the first diode is connected to the cathode of the first voltage-stabilizing diode; the control end of the first switching tube is connected to the anode of the first diode through the second resistor, and the input end is connected to the cathode of the first diode; The negative to positive zero-crossing detection module includes: a second diode, a second voltage stabilizing diode, a second capacitor, a second switch tube and a fourth resistor; The anode of the second Zener diode is connected to the anode of the first Zener diode, and the cathode of the second Zener diode is connected to the current input terminal of the AC power supply; one end of the second capacitor is connected to the anode of the second Zener diode, and the other end is connected to the cathode of the second diode; the anode of the second diode is connected to the cathode of the second Zener diode; the control end of the second switch tube is connected to the anode of the second diode through the fourth resistor, and the input end is connected to the cathode of the second diode; The first input end of the optical coupling module is connected to the output ends of the first switching tube and the second switching tube, the second input end is connected to the anode of the second voltage stabilizing diode, and the first output end outputs a zero-crossing detection signal; The first capacitor and the second capacitor have different capacitance values; The optical coupling module includes an optical coupling isolator and a filtering unit.

2. The bidirectional zero-crossing detection circuit according to claim 1, wherein: The bidirectional zero-crossing detection circuit also includes a first current limiting module and a second current limiting module, wherein the first current limiting module is connected between the current output end of the AC power supply and the input end of the positive-to-negative zero-crossing detection module; and the second current limiting module is connected between the current input end of the AC power supply and the input end of the negative-to-positive zero-crossing detection module.

3. The bidirectional zero-crossing detection circuit according to claim 2, wherein: The first current limiting module is a first resistor, and the second current limiting module is a third resistor.

4. The bidirectional zero-crossing detection circuit according to claim 1, wherein: The first switching tube and the second switching tube are triodes.

5. A bidirectional zero-crossing detection method, based on the bidirectional zero-crossing detection circuit according to any one of claims 1 to 4, characterized in that: When the AC signal is in the positive half cycle, the second Zener diode and the first diode are forward-conducted, the voltage across the first Zener diode is stabilized at the first voltage, and the first capacitor is charged through a loop formed by the AC power supply - the first diode - the first capacitor - the second Zener diode - the AC power supply; and the first switch is in the off state. When the AC signal is at the zero-crossing point from the positive half-cycle to the negative half-cycle, the first switch tube is turned on, and the first capacitor is discharged through the loop formed by the first capacitor-first switch tube-optocoupler module-first capacitor, thereby turning on the optocoupler module and triggering the output of the zero-crossing detection signal; When the AC signal is in the negative half cycle, the first Zener diode and the second diode are forward-conducted, the voltage across the second Zener diode is stabilized at the second voltage, and the second capacitor is charged through a loop formed by the AC power supply - the second diode - the second capacitor - the first Zener diode - the AC power supply; the second switch is in the off state; When the AC signal is at the zero-crossing point from the negative half-cycle to the positive half-cycle, the second switch tube is turned on, and the second capacitor is discharged through the loop formed by the second capacitor-second switch tube-optocoupler module-second capacitor, thereby turning on the optocoupler module and triggering the zero-crossing detection signal output.

6. The bidirectional zero-crossing detection method according to claim 5, wherein: When the AC signal is in the positive half cycle and the negative half cycle, the charging circuit of the first capacitor and the second capacitor further includes a first current limiting module and a second current limiting module, which are used to limit the current of the charging circuit.

7. The bidirectional zero-crossing detection method according to any one of claims 5 to 6, characterized in that: When the AC signal is at the zero-crossing point from the positive half cycle to the negative half cycle and at the zero-crossing point from the negative half cycle to the positive half cycle, the discharge time of the first capacitor and the second capacitor are different.

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