Zero-crossing detection circuit, device and microwave oven

Abstract

The application relates to a zero-crossing detection circuit, a device and a microwave oven. The zero-crossing detection circuit comprises a rectification module, an output end of the rectification module being used for outputting a full-wave rectification voltage; an optocoupler driving module, the optocoupler driving module comprising a unidirectional conduction device; one end of the unidirectional conduction device being connected to the output end of the rectification module, and being used for outputting a current signal; the other end of the unidirectional conduction device being used for receiving the current signal; an optocoupler isolation module, a positive input end of the optocoupler isolation module being used for being connected to a preset direct current voltage; a negative input end of the optocoupler isolation module being connected to the other end of the unidirectional conduction device; a positive output end of the optocoupler isolation module being used for outputting a zero-crossing signal to indicate that a rear-stage circuit confirms a zero-crossing position; and the value of the preset direct current voltage being determined according to the full-wave rectification voltage, the voltage drop of the unidirectional conduction device, the working voltage of the optocoupler isolation module and the working time of the optocoupler isolation module. The circuit of the application can reduce power consumption in the zero-crossing detection process.

Description

Technical Field

[0001] This application relates to the field of detection circuit technology, and in particular to a zero-crossing detection circuit, device, and microwave oven. Background Technology

[0002] With the development of household appliances, zero-crossing detection circuits are often needed. Zero-crossing detection refers to the detection made by the system when the waveform passes through zero position during the transition from the positive half-cycle to the negative half-cycle in an AC system. At the same time, zero-crossing detection circuits are required to have signal isolation capabilities, low power consumption, and accurate zero-crossing position detection capabilities.

[0003] like Figure 1 The diagram shows a commonly used zero-crossing detection circuit. The AC mains input ACL (AC live wire) and ACN (AC neutral wire) are current-limited by current-limiting resistor R1. Diode D1 then conducts the positive half-cycle voltage signal of the mains voltage. During the positive half-cycle of the mains voltage, optocoupler U5 is lit, the isolated output side is turned on, and the ZeroCross_Signal voltage is pulled low, sent to the MCU (Microcontroller Unit) or subsequent circuitry for processing. Diode D2 clamps the reverse voltage of the optocoupler, ensuring it remains within its safe operating range.

[0004] However, current zero-crossing detection methods or traditional methods suffer from problems such as high power consumption during the detection process. Summary of the Invention

[0005] Therefore, it is necessary to provide a zero-crossing detection circuit, device, and microwave oven that can reduce power consumption to address the aforementioned technical problems.

[0006] To achieve the above objectives, in a first aspect, embodiments of this application provide a zero-crossing detection circuit, including:

[0007] The rectifier module has an input terminal for connecting to the power supply and an output terminal for outputting a full-wave rectified voltage.

[0008] The optocoupler driver module includes a unidirectional conducting device; one end of the unidirectional conducting device is connected to the output terminal of the rectifier module and is used to output a current signal; the other end of the unidirectional conducting device is used to receive a current signal.

[0009] The optocoupler isolation module has a positive input terminal for connecting a preset DC voltage; a negative input terminal for connecting the other end of a unidirectional conducting device; and a positive output terminal for outputting a zero-crossing signal. The zero-crossing signal is used to indicate to the subsequent circuit that the zero-crossing position has been confirmed. The preset DC voltage value is determined based on the full-wave rectified voltage, the voltage drop of the unidirectional conducting device, the operating voltage of the optocoupler isolation module, and the operating time of the optocoupler isolation module.

[0010] In one embodiment, the zero-crossing detection circuit further includes a voltage supply circuit for providing a preset DC voltage; the voltage supply circuit includes:

[0011] A voltage source circuit, the output of which is used to output a preset DC voltage;

[0012] The first polarity capacitor has its positive terminal connected to the output terminal of the voltage source circuit; its negative terminal is used for grounding.

[0013] In one embodiment, the voltage source circuit includes:

[0014] The primary winding of the power frequency transformer is connected to the input terminal of the rectifier module; one end of the secondary winding of the power frequency transformer is used for grounding.

[0015] The first diode, the positive terminal of the first diode is connected to the other end of the secondary winding of the power frequency transformer;

[0016] The second polarity capacitor has its positive terminal connected to the negative terminal of the first diode; the negative terminal of the second polarity capacitor is used for grounding.

[0017] The three-terminal Zener diode has its first terminal connected to the negative terminal of the first diode; its second terminal is grounded; and its third terminal is used to provide a preset DC voltage.

[0018] In one embodiment, the rectifier module includes a rectifier bridge; a first output terminal of the rectifier bridge is connected to the negative terminal of a unidirectional conducting device; and a second output terminal of the rectifier bridge is grounded.

[0019] The zero-crossing detection circuit also includes:

[0020] The third polarity capacitor; the negative terminal of the third polarity capacitor is used for grounding; the third polarity capacitor is used for filtering;

[0021] The second diode; the cathode of the second diode is connected to the anode of the third polarized capacitor; the anode of the second diode is connected to the first output terminal of the rectifier bridge; the second diode is used to maintain the waveform of the full-wave rectified voltage.

[0022] In one embodiment, the voltage source circuit includes:

[0023] The high-frequency transformer has its primary winding's opposite terminal connected to one end of the second diode; the auxiliary winding's opposite terminal is connected to the negative terminal of the first polarized capacitor.

[0024] The third diode has its anode connected to the same terminal of the auxiliary winding; the cathode of the third diode is connected to the anode of the first polarized capacitor to provide a preset DC voltage; the preset DC voltage ranges from 8V to 16V.

[0025] The switching power supply control circuit is connected to the same-name terminal of the primary winding of the high-frequency transformer and the negative terminal of the third diode, respectively.

[0026] The positive terminal of the fourth diode is connected to the corresponding terminal of the secondary winding of the high-frequency transformer.

[0027] The positive terminal of the fourth polarity capacitor is connected to the negative terminal of the fourth diode; the negative terminal of the fourth polarity capacitor is connected to the opposite terminal of the secondary winding of the high-frequency transformer; the opposite terminal of the secondary winding of the high-frequency transformer is also used for grounding.

[0028] In one embodiment, the unidirectional conducting device is a diode.

[0029] In one embodiment, the circuit further includes a current-limiting and voltage-dividing module; the current-limiting and voltage-dividing module is connected to the positive input terminal of the optocoupler isolation module and the negative input terminal of the optocoupler isolation module respectively; the current-limiting and voltage-dividing module is used to connect to a preset DC voltage.

[0030] In one embodiment, the current limiting and voltage dividing module includes:

[0031] A current-limiting resistor is connected at one end to the positive input terminal of the optocoupler isolation module, and the other end of the current-limiting module is used to connect to a preset DC voltage.

[0032] A voltage divider resistor is connected at one end to the positive input terminal of the optocoupler isolation module, and at the other end to the negative input terminal of the optocoupler isolation module.

[0033] In one embodiment, the optocoupler isolation module includes:

[0034] The positive terminal of the LED is connected to one end of the current-limiting resistor; the negative terminal of the LED is connected to the other end of the voltage-dividing resistor.

[0035] A photodiode has its positive terminal connected to the power supply voltage and its negative terminal grounded. The photodiode outputs a zero-crossing signal based on the conduction state of the light-emitting diode.

[0036] Secondly, embodiments of this application provide a zero-crossing detection device, which includes the zero-crossing detection circuit as described above; the device also includes a microprocessor unit connected to the positive output terminal of the optocoupler isolation module, used to obtain the zero-crossing position based on the rising and falling edges of the zero-crossing signal.

[0037] Thirdly, embodiments of this application provide a microwave oven, which includes the zero-crossing detection circuit described above.

[0038] One of the above technical solutions has the following advantages and beneficial effects:

[0039] The zero-crossing detection circuit proposed in this application outputs a full-wave rectified voltage at the output terminal of the rectifier module. One end of the unidirectional conducting device of the optocoupler drive module outputs a current signal to the output terminal of the rectifier module; the other end of the unidirectional conducting device receives the current signal input from the negative input terminal of the optocoupler isolation module; a preset DC voltage is connected to the positive input terminal of the optocoupler isolation module; and a zero-crossing signal is output from the positive output terminal of the optocoupler isolation module to indicate to the subsequent circuit that the zero-crossing position has been confirmed. The value of the preset DC voltage is determined based on the full-wave rectified voltage, the voltage drop of the unidirectional conducting device, the operating voltage of the optocoupler isolation module, and the operating time of the optocoupler isolation module, which can reduce the problem of high power consumption during the detection process of the zero-crossing detection circuit. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of a commonly used zero-crossing detection circuit in one embodiment;

[0042] Figure 2 This is a schematic diagram of the voltage signal of a commonly used zero-crossing detection circuit in one embodiment;

[0043] Figure 3 This is a schematic diagram of a zero-crossing detection circuit in one embodiment;

[0044] Figure 4 This is a schematic diagram of the output voltage waveform of the rectifier module in one embodiment;

[0045] Figure 5 This is a schematic diagram of the voltage signal of the zero-crossing detection circuit in one embodiment;

[0046] Figure 6 This is a schematic diagram of a zero-crossing detection circuit in another embodiment;

[0047] Figure 7 This is a schematic diagram of a zero-crossing detection circuit containing a power frequency transformer in one embodiment;

[0048] Figure 8 This is a schematic diagram of a zero-crossing detection circuit containing a switching power supply control circuit in one embodiment.

[0049] Component labeling: Rectifier module, 310; Optocoupler driver module, 320; Optocoupler isolation module, 330; Current limiting and voltage divider module, 340; Unidirectional conduction device, D1; First polarity capacitor, EC1; Second polarity capacitor, EC2; First polarity capacitor, EC2; Third polarity capacitor, EC3; Fourth polarity capacitor, EC4; First diode, D5; Second diode, D2; Third diode, D3; Fourth diode, D4; Voltage divider resistor, R3; Current limiting resistor, R1; Power frequency transformer, T1; High frequency transformer, T2; Three-terminal Zener diode, U3. Detailed Implementation

[0050] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0052] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another.

[0053] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as “below,” “under,” or “below” will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.

[0054] It should be noted that when one element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediary element. Furthermore, in the following embodiments, "connection" should be understood as "electrical connection," "communication connection," etc., if there is transmission of electrical signals or data between the connected objects.

[0055] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0056] It should be noted that, as Figure 1 The commonly used zero-crossing detection circuit shown has a drawback: the current-limiting resistor R1 consumes a significant amount of power. (Based on an AC voltage of 220V...) AC For example, ignoring the diode voltage drop, since current flows through the current-limiting resistor R1 throughout the entire positive half-cycle, the power dissipation of the current-limiting resistor R1 is approximately U. 2 Half of R, when the current-limiting resistor R1 is 200kΩ, its power consumption is about 0.12W.

[0057] On the other hand, since the aforementioned zero-crossing detection circuit only operates during the positive half-cycle of the mains voltage and after the voltage amplitude reaches a certain value, it will cause a lag or advance in the zero-crossing point, such as... Figure 2 As shown. This distortion between the zero-crossing signal and the true zero-crossing position is difficult to correct or eliminate in other ways.

[0058] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0059] In one embodiment, such as Figure 3 As shown, a zero-crossing detection circuit is provided, including:

[0060] The rectifier module 310 has an input terminal for connecting to a power supply and an output terminal for outputting a full-wave rectified voltage.

[0061] Specifically, the rectifier module 310 performs full-wave rectification on the sinusoidal voltage received at its input (that is, rectifies the negative half-cycle waveform to the upper half-cycle position), and outputs as follows: Figure 4 The full-wave rectified voltage is shown; in some examples, the input terminals of the rectifier module 310 may include pin 1 and pin 2, with pin 1 connected to ACL (AC live wire) and pin 2 connected to ACN (AC neutral wire); the output terminals of the rectifier module 310 may include pin 3 and pin 4; the rectifier module 310 can be a rectifier bridge;

[0062] The optocoupler driving module 320 includes a unidirectional conducting device D1; one end of the unidirectional conducting device D1 is connected to the output terminal of the rectifier module 310 and is used to output a current signal; the other end of the unidirectional conducting device D1 is used to receive a current signal.

[0063] Specifically, the unidirectional conducting device D1 conducts towards the output of the rectifier module 310; in some examples, the unidirectional conducting device D1 can be a diode.

[0064] The optocoupler isolation module 330 has a positive input terminal for connecting a preset DC voltage; a negative input terminal for connecting the other end of the unidirectional conducting device D1; and a positive output terminal for outputting a zero-crossing signal. The zero-crossing signal is used to indicate to the subsequent circuit that the zero-crossing position has been confirmed. The preset DC voltage value is determined based on the full-wave rectified voltage, the voltage drop of the unidirectional conducting device D1, the operating voltage of the optocoupler isolation module 330, and the operating time of the optocoupler isolation module 330.

[0065] Specifically, the optocoupler isolation module 330 is powered by a preset DC voltage (VDD), and the voltage at pin 3 of the rectifier module 310 is lower than VDD-V. F -V D1 Under these conditions, the optocoupler isolation module 330 operates, where VDD is a preset DC voltage, and V... F For the voltage drop of the optocoupler isolation module 330, V D1The voltage drop across the unidirectional conducting device D1 is shown below. The current flow path is VDD, optocoupler isolation module 330, unidirectional conducting device D1, pin 3 of rectifier module 310, and pin 4 of rectifier module 310.

[0066] In some examples, pin 4 of rectifier module 310 is grounded (e.g., PGND, protective ground), meaning the voltage between pins 3 and 4 of rectifier module 310 is lower than VDD-V. F -V D1 In this case, the optocoupler isolation module 330 operates, where V F V is the forward conduction voltage drop of the optocoupler isolation module 330; D1 This is the forward voltage drop of the unidirectional conducting device D1; for example, VDD = 12V, V F =1.3V, V D1 =0.7V, then the voltage between pin 3 and pin 4 of rectifier module 310 is approximately below 10V, which enables optocoupler isolation module 330 to operate.

[0067] Furthermore, with PGND as the reference ground, when the instantaneous voltage value at pin 3 of the rectifier module 310 is less than or equal to the voltage value of VDD, the voltage at the other end of the unidirectional conducting device D1 is greater than or equal to the voltage at one end of the unidirectional conducting device D1 (for example, if the unidirectional conducting device D1 is a diode, the cathode voltage of the diode is lower than that of the anode, satisfying the forward conduction condition), and the current flows through the unidirectional conducting device D1 in the conduction direction; it should be noted that there is a voltage source between PGND and VDD. In some examples, this voltage source is provided by the power frequency transformer or the auxiliary winding of the switching power supply, forming a closed loop of the entire current path;

[0068] Furthermore, when the instantaneous voltage at pin 3 of the rectifier module 310 is greater than the voltage value of VDD, the voltage at the other end of the unidirectional conducting device D1 is less than the voltage at one end of the unidirectional conducting device D1 (for example, if the unidirectional conducting device D1 is a diode, the cathode voltage of the diode is higher than the anode voltage, satisfying the reverse cutoff condition), and no current flows through the unidirectional conducting device D1; furthermore, no current flows through the optocoupler isolation module 330, making the power consumption of the optocoupler isolation module 330 0, that is, the unidirectional conducting device D1 can reduce the power consumption of the optocoupler isolation module 330.

[0069] Furthermore, if the instantaneous voltage at pin 3 of the rectifier module 310 is greater than the voltage value of VDD, it may cause a large reverse voltage to the optocoupler isolation module 330. Considering the worst-case scenario, this will occur when the AC input voltage connected to the input terminal of the rectifier module 310 is at its maximum value (for example, when the AC input voltage is 265V, the peak output voltage of the rectifier module 310 is Vmax≈265*1.4=371V). Since the unidirectional conducting device D1 is not conducting in reverse (for example, the diode is reverse cut off), in this case, the impedance of the unidirectional conducting device D1 is much greater than the impedance of the optocoupler isolation module 330. Most of the voltage drops across the unidirectional conducting device D1, making the reverse voltage of the optocoupler isolation module 330 very low. That is, the unidirectional conducting device D1 can also protect the optocoupler isolation module 330 from being damaged by excessive reverse bias voltage.

[0070] In some examples, since the mains voltage is a sinusoidal AC wave with symmetrical positive and negative half-cycles, when the absolute value of the instantaneous AC voltage is below 10V, the optocoupler isolation module 330 operates. The input signal at the positive input terminal of the optocoupler isolation module 330 is high, and the zero-crossing signal (ZeroCross_Signal) output from the positive output terminal of the optocoupler isolation module 330 is low. For example... Figure 5 As shown, the intersection of the rectified signal and the 10V voltage level is the start or end position of the working area of ​​the optocoupler isolation module 330. The effective working area of ​​the optocoupler isolation module 330 is very narrow and the working time is very short. When the optocoupler isolation module 330 is not in the forward conduction working range of the unidirectional conducting device D1, since the unidirectional conducting device D1 is not conducting in reverse (for example, the diode is reverse biased), no current flows through the zero-crossing detection circuit, and its power consumption is almost 0.

[0071] Furthermore, the real-time value of the alternating current V ac_in =Sin(wt)*V peak Power consumption P = UI = U 2 / R, when under a 220V, 50Hz AC power grid, can be estimated as follows: T ON ≈0.2ms, T OFF ≈9.8ms(T ON and T OFF These represent the working and non-working times of the optocoupler isolation module 330, respectively. The duty cycle of the optocoupler is T. ON / (T ON +T OFF =2%, the power consumption P when the optocoupler is working is less than 120mW (P = U 2 / R≈(VDD-V F -V D1 ) 2 / 1kΩ=(12-1.3-0.7)2 / 1000=0.1W); It should be noted that VDD is estimated as 12V here, and for the sake of simplicity and convenience, T is... ON During this period, the output voltage of rectifier module 310 is considered to be 0V. However, the actual output voltage of rectifier module 310 should vary sinusoidally. Treating it as 0V will overestimate the power consumption of optocoupler isolation module 330. Even with an accurate calculation model, the absolute value of the power consumption of optocoupler isolation module 330 is still very small and does not affect the explanation of the circuit principle and implementation process. Because the duty cycle of optocoupler isolation module 330 is very small, its average power consumption P*D is also very small, where P is the power consumption of optocoupler isolation module 330 during operation, and D is the duty cycle of optocoupler isolation module 330. When optocoupler isolation module 330 is not operating, it does not generate power consumption; this is used to estimate the power consumption of optocoupler isolation module 330 during operation. ON +T OFF The average power consumption during the entire cycle is P*D = 0.12W * 0.02 (0.02 is the duty cycle of the optocoupler isolation module 330) = 0.0024W, which means that the average power consumption of this zero-crossing detection circuit is only about 2.4 milliwatts, which is 2% of the traditional solution, significantly reducing power consumption by 98%.

[0072] In some examples, based on the symmetry of the positive and negative half-cycle signals of the AC power grid, and since the zero-crossing detection circuit also processes the AC signal symmetrically in both positive and negative half-cycles, the start-end position of the output signal of the optocoupler isolation module 330 can also maintain symmetry with the true zero-crossing position. That is, the midpoint between the falling edge and the rising edge of the zero-crossing signal (ZeroCross_Signal) output from the positive output terminal of the optocoupler isolation module 330 is the true zero-crossing position, and it can maintain very good accuracy.

[0073] Furthermore, the edge signals (including rising and falling edges) of the zero-crossing signal can be acquired by subsequent circuitry (e.g., MCU, microcontroller unit), and the time difference between the rising and falling edges near the zero-crossing position can be calculated. Half of this time difference is then used as the compensation value T. OFFSET Use; subtract the compensation value T from the preset zero-crossing delay time. OFFSET This means obtaining the true and precise zero-crossing position. For example, it is necessary to determine the position T after the zero-crossing. DELAY1 The location triggers the operation of a device, at T DELAY1 >T OFFSET In this case, T can be DELAY1 -T OFFSET The difference is used as more precise data to set the timer, which is equivalent to the device setting the timer at T. DELAY1 Based on the earlier T OFFSETThe timing of the triggering is precisely equal to the delay between the zero-crossing position of the zero-crossing signal and the actual zero-crossing position. This processing achieves zero delay, significantly reducing zero-crossing detection error, essentially operating at the actual zero-crossing position. Considering that VDD or other component voltages may drift due to environmental factors, based on the symmetry of the rising and falling edges of the zero-crossing signal with respect to the zero-crossing position, the time T acquired each time... OFFSET It is the most accurate compensation value under the current working environment of the equipment. This value will vary within a certain range, but after compensation, it will be very close to the true zero crossing position.

[0074] The zero-crossing detection circuit proposed in this application embodiment outputs a full-wave rectified voltage at the output terminal of the rectifier module 310. One end of the unidirectional conducting device D1 of the optocoupler drive module 320 outputs a current signal to the output terminal of the rectifier module 310. The other end of the unidirectional conducting device D1 receives the current signal input from the negative input terminal of the optocoupler isolation module 330. A preset DC voltage is connected to the positive input terminal of the optocoupler isolation module 330. The positive output terminal of the optocoupler isolation module 330 outputs a zero-crossing signal to indicate to the subsequent circuit to confirm the zero-crossing position. The value of the preset DC voltage is determined based on the full-wave rectified voltage, the voltage drop of the unidirectional conducting device D1, the operating voltage of the optocoupler isolation module 330, and the operating time of the optocoupler isolation module 330. This can reduce the problem of high power consumption during the detection process of the zero-crossing detection circuit.

[0075] In one embodiment, the circuit further includes a voltage supply circuit for providing a preset DC voltage; the voltage supply circuit includes:

[0076] A voltage source circuit, the output of which is used to output a preset DC voltage;

[0077] The first polarity capacitor EC1 has its positive terminal connected to the output terminal of the voltage source circuit, and its negative terminal used for grounding.

[0078] Specifically, the voltage source circuit can be a circuit including either a power frequency transformer or a switching power supply auxiliary winding, used to provide a voltage source between PGND and VDD; the power frequency transformer or switching power supply auxiliary winding can output a voltage of VDD; in some examples, such as Figure 6 and Figure 7 As shown, the rated parameters of the first polarity capacitor EC1 can be 100μF / 25V.

[0079] In one embodiment, such as Figure 7 As shown, the voltage source circuit includes:

[0080] Power frequency transformer T1, the primary winding of power frequency transformer T1 is connected to the input terminal of rectifier module 310; one end of the secondary winding of power frequency transformer T1 is used for grounding;

[0081] The positive terminal of the first diode D5 is connected to the other end of the secondary winding of the power frequency transformer T1.

[0082] The second polarity capacitor EC2 has its positive terminal connected to the negative terminal of the first diode D5; the negative terminal of the second polarity capacitor EC2 is used for grounding.

[0083] The three-terminal Zener diode U3 has its first terminal connected to the negative terminal of the first diode D5; its second terminal is grounded; and its third terminal is used to provide a preset DC voltage.

[0084] Specifically, one end of the primary winding of the power frequency transformer T1 (e.g., end 1) is connected to pin 1 of the rectifier module 310, and the other end of the primary winding of the power frequency transformer T1 (e.g., end 2) is connected to pin 2 of the rectifier module 310; one end of the secondary winding of the power frequency transformer T1 (e.g., end 4) is used for grounding; the other end of the secondary winding of the power frequency transformer T1 (e.g., end 3) is connected to the positive terminal of the first diode D5; after being stepped down by a certain ratio, the power frequency transformer T1 provides the preset DC voltage VDD required by the zero-crossing detection circuit through voltage regulation;

[0085] In some examples, the output terminals (pins 3 and 4) of the rectifier module 310 are used to connect to a load circuit. This load circuit can be a circuit that does not exhibit significant capacitive or inductive behavior, such as a purely resistive load. If the load circuit is capacitive or inductive, a diode needs to be connected in series between the load circuit and the rectifier module 310. The first diode D5 can be a 1N4007; the second polarity capacitor EC2 can be rated at 100μF / 25V; and the three-terminal Zener diode U3 can be an L7812CV. The secondary winding of the power frequency transformer T1 can be a dual-winding output. One secondary winding of the power frequency transformer T1 includes the aforementioned terminals 3 and 4. Terminal 4 of the power frequency transformer T1 and the second terminal of the three-terminal Zener diode U3 can be connected to PGND, with the reference ground being the same as that of the rectifier module 310. The other secondary winding of the power frequency transformer T1 includes terminals 5 and 6. The voltage source circuit may also include a three-terminal Zener diode U2, a diode D6, and a polarized capacitor EC5. Terminal 5 of the power frequency transformer T1 is connected to the positive terminal of the diode D6, and terminal 6 of the power frequency transformer T1 is used for grounding (e.g., GND). The first terminal of the three-terminal Zener diode U2 is connected to the negative terminal of the diode D6, the second terminal of the three-terminal Zener diode U2 is used for grounding (e.g., GND), and the third terminal of the three-terminal Zener diode U2 is used to provide the supply voltage VCC. The magnitude of the supply voltage VCC can be +5V. The model of the three-terminal Zener diode U2 can be L7805CV.

[0086] In one embodiment, the rectifier module 310 includes a rectifier bridge; the first output terminal of the rectifier bridge is connected to the negative terminal of the unidirectional conducting device D1; the second output terminal of the rectifier bridge is used for grounding.

[0087] The zero-crossing detection circuit also includes:

[0088] The third polarity capacitor EC3; the negative terminal of the third polarity capacitor is used for grounding; the third polarity capacitor EC3 is used for filtering;

[0089] The second diode D2; the negative terminal of the second diode D2 is connected to the positive terminal of the third polarized capacitor EC3; the positive terminal of the second diode D2 is connected to the first output terminal of the rectifier bridge; the second diode D2 is used to maintain the waveform of the full-wave rectified voltage.

[0090] Specifically, the rectifier bridge rectifies the negative half-cycle waveform to the upper half-cycle position. If a filter capacitor (e.g., the third polarity capacitor EC3) is added after the rectifier bridge, the rectifier bridge will output DC power through the filter capacitor. Figure 3 As shown, a second diode D2 is inserted between the rectifier bridge and the third polarity capacitor EC3, allowing the waveform between pin 3 and pin 4 of the rectifier bridge to maintain a pulsating DC waveform, which still exhibits zero-crossing voltage characteristics. In some examples, the rectifier bridge model can be DF10S-F; such as... Figure 6and Figure 7 As shown, the rated parameters of the third polarity capacitor EC3 are 4.7μF / 450V; the second diode D2 can be a 1N4007.

[0091] In one embodiment, such as Figure 8 As shown, the voltage source circuit includes:

[0092] The opposite terminal of the primary winding of high-frequency transformer T2 is connected to one end of the second diode; the opposite terminal of the auxiliary winding of high-frequency transformer T2 is connected to the negative terminal of the first polarity capacitor EC1.

[0093] The positive terminal of the third diode D3 is connected to the same terminal of the auxiliary winding; the negative terminal of the third diode D3 is connected to the positive terminal of the first polarized capacitor EC1 to provide a preset DC voltage; the value of the preset DC voltage ranges from 8V to 16V.

[0094] The switching power supply control circuit is connected to the same-name terminal of the primary winding of the high-frequency transformer T2 and the negative terminal of the third diode D3, respectively.

[0095] The positive terminal of the fourth diode D4 is connected to the same terminal of the secondary winding of the high-frequency transformer T2.

[0096] The positive terminal of the fourth polarity capacitor EC4 is connected to the negative terminal of the fourth polarity diode D4; the negative terminal of the fourth polarity capacitor EC4 is connected to the opposite terminal of the secondary winding of the high-frequency transformer T2; the opposite terminal of the secondary winding of the high-frequency transformer T2 is also used for grounding.

[0097] Specifically, the auxiliary winding of the high-frequency transformer T2 is supplied with a preset DC voltage VDD through the third diode D3, and the voltage source circuit functions as a voltage source externally. In some examples, the rated parameters of the first polarity capacitor EC1 can be 10μF / 16V; the rated parameters of the fourth polarity capacitor EC4 can be 470μF / 16V. The model of the high-frequency transformer T2 can be GAL-TR009.

[0098] In one embodiment, the unidirectional conducting device D1 is a diode.

[0099] Specifically, the positive terminal of the unidirectional conducting device D1 is connected to the negative input terminal of the optocoupler isolation module 330, and the negative terminal of the unidirectional conducting device D1 is connected to pin 3 of the rectifier bridge; in some examples, the unidirectional conducting device D1 can be a diode of type 1N4007.

[0100] In one embodiment, such as Figures 6 to 8As shown, the zero-crossing detection circuit also includes a current-limiting voltage divider module 340; the current-limiting voltage divider module 340 is connected to the positive input terminal of the optocoupler isolation module 330 and the negative input terminal of the optocoupler isolation module 330 respectively; the current-limiting voltage divider module 340 is used to connect to a preset DC voltage.

[0101] Specifically, the current limiting voltage divider module 340 is used to reduce the operating current of the optocoupler isolation module 330 in the zero-crossing detection circuit and to prevent the optocoupler isolation module 330 from being subjected to excessive reverse voltage and breaking down; in some examples, the current limiting voltage divider module 340 includes several resistors.

[0102] In one embodiment, the current limiting and voltage dividing module 340 includes:

[0103] The current limiting resistor R1 is connected at one end to the positive input terminal of the optocoupler isolation module 330, and the other end of the current limiting module is used to connect to a preset DC voltage.

[0104] Voltage divider resistor R3 is connected at one end to the positive input terminal of optocoupler isolation module 330, and at the other end to the negative input terminal of optocoupler isolation module 330.

[0105] Specifically, under the action of the unidirectional conducting device D1, the current-limiting resistor R1, the voltage divider resistor R3, and the optocoupler isolation module 330 only have current flowing through them when the output voltage of the rectifier bridge (the instantaneous value of pin 3 of the rectifier bridge) is lower than the voltage value of VDD. The current flow path is VDD, current-limiting resistor R1, voltage divider resistor R3 / optocoupler isolation module 330, unidirectional conducting device D1, pin 3 of rectifier module 310, and pin 4 of rectifier module 310. VDD is usually between 8 and 16V, but the output voltage of the rectifier bridge will exceed 16V most of the time. This results in the optocoupler isolation module 330 being able to work for a very short time. During non-working time, because the unidirectional conducting device D1 is cut off, no current flows through the current-limiting resistor R1, the voltage divider resistor R3, and the optocoupler isolation module 330. The power consumption of the zero-crossing detection circuit is 0, which makes the average power consumption of the optocoupler isolation module 330 extremely low throughout the entire cycle, while also reducing the power consumption of the current-limiting resistor R1 and the voltage divider resistor R3.

[0106] Furthermore, when the instantaneous voltage at pin 3 of the rectifier bridge is greater than VDD, the unidirectional conducting device D1 does not conduct in reverse. The impedance of the unidirectional conducting device D1 is much greater than the impedance of the current-limiting resistor R1 and the voltage-dividing resistor R3 (parallel to the optocoupler isolation module 330). Most of the voltage drops across the unidirectional conducting device D1, resulting in a very low reverse voltage for the optocoupler isolation module 330. Without the presence of the unidirectional conducting device D1, and disregarding the volt-ampere characteristics of the optocoupler isolation module 330, the optocoupler isolation module 330... The reverse voltage will be Vmax*(R3 / R1+R3)≈337V, which far exceeds the maximum reverse voltage VR of the optocoupler isolation module 330. That is, the unidirectional conducting device D1 can protect the optocoupler isolation module 330 from breakdown due to excessive reverse bias voltage. In some examples, the current limiting resistor R1 can be 1kΩ±5%; the voltage dividing resistor R3 can be 10kΩ±5%; the optocoupler isolation module 330 can be model PC817, with a maximum reverse voltage VR of 6V.

[0107] In one embodiment, the optocoupler isolation module 330 includes:

[0108] The positive terminal of the LED is connected to one end of the current-limiting resistor R1; the negative terminal of the LED is connected to the other end of the voltage-dividing resistor R3.

[0109] A photodiode has its positive terminal connected to the power supply voltage and its negative terminal grounded. The photodiode outputs a zero-crossing signal based on the conduction state of the light-emitting diode.

[0110] It should be noted that the operation of the aforementioned optocoupler isolation module 330 refers to the LED being turned on; the LED is turned on and emits light by receiving the operating voltage of the optocoupler isolation module 330, and the photodiode outputs a corresponding level according to the LED's emission state; in some examples, the optocoupler isolation module 330 can be a PC817; the positive terminal of the photodiode is connected to the supply voltage VCC through the protection resistor R2; the supply voltage VCC connected to the positive terminal of the photodiode can be +5V; the resistance value of the protection resistor R2 can be 1kΩ±5%;

[0111] In one embodiment, a zero-crossing detection device is provided, the device including the zero-crossing detection circuit as described above; the device also includes a microprocessor unit connected to the positive output terminal of the optocoupler isolation module 330, used to obtain the zero-crossing position based on the rising and falling edges of the zero-crossing signal.

[0112] Specifically, the microcontroller unit (MCU) obtains the zero-crossing position based on the rising and falling edges of the zero-crossing signal in the same way as described above.

[0113] In one embodiment, a microwave oven is provided, which includes the zero-crossing detection circuit described above.

[0114] In the description of this specification, the references to terms such as "some embodiments," "other embodiments," "ideal embodiments," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example that are included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0115] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0116] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A zero-crossing detection circuit, characterized in that, include: A rectifier module, wherein the input terminal of the rectifier module is used to connect to a power supply, and the output terminal of the rectifier module is used to output a full-wave rectified voltage; An optocoupler driving module includes a unidirectional conducting device; one end of the unidirectional conducting device is connected to the output terminal of the rectifier module for outputting a current signal; the other end of the unidirectional conducting device is used to receive a current signal. An optocoupler isolation module is provided, wherein the positive input terminal of the optocoupler isolation module is used to connect to a preset DC voltage; the negative input terminal of the optocoupler isolation module is connected to the other end of the unidirectional conducting device; the positive output terminal of the optocoupler isolation module is used to output a zero-crossing signal; and the optocoupler isolation module determines its operating state based on the output voltage of the rectifier module and the preset DC voltage. The subsequent circuit obtains the time difference between the rising edge and the falling edge of the zero-crossing signal based on the rising edge and the falling edge, takes half of the time difference as a compensation value, subtracts the compensation value from the preset zero-crossing delay time, and confirms the zero-crossing position. The value of the preset DC voltage is determined based on the full-wave rectified voltage, the voltage drop of the unidirectional conducting device, the operating voltage of the optocoupler isolation module, and the operating time of the optocoupler isolation module.

2. The zero-crossing detection circuit according to claim 1, characterized in that, The zero-crossing detection circuit also includes a voltage supply circuit for providing the preset DC voltage; The voltage supply circuit includes: A voltage source circuit, wherein the output terminal of the voltage source circuit is used to output the preset DC voltage; A first polarity capacitor, the positive terminal of which is connected to the output terminal of the voltage source circuit; the negative terminal of the first polarity capacitor is used for grounding.

3. The zero-crossing detection circuit according to claim 2, characterized in that, The voltage source circuit includes: A power frequency transformer, wherein the primary winding of the power frequency transformer is connected to the input terminal of the rectifier module; one end of the secondary winding of the power frequency transformer is used for grounding; A first diode, the positive terminal of which is connected to the other end of the secondary winding of the power frequency transformer; A second polarity capacitor, the positive terminal of which is connected to the negative terminal of the first diode; the negative terminal of the second polarity capacitor is used for grounding. A three-terminal Zener diode, wherein the first terminal of the three-terminal Zener diode is connected to the negative terminal of the first diode; the second terminal of the three-terminal Zener diode is grounded; and the third terminal of the three-terminal Zener diode is used to provide the preset DC voltage.

4. The zero-crossing detection circuit according to claim 2, characterized in that, The rectifier module includes a rectifier bridge; the first output terminal of the rectifier bridge is connected to the negative terminal of the unidirectional conducting device; the second output terminal of the rectifier bridge is used for grounding. The zero-crossing detection circuit also includes: A third polarity capacitor; the negative terminal of the third polarity capacitor is used for grounding; the third polarity capacitor is used for filtering; The second diode; the negative terminal of the second diode is connected to the positive terminal of the third polarized capacitor; the positive terminal of the second diode is connected to the first output terminal of the rectifier bridge; the second diode is used to maintain the waveform of the full-wave rectified voltage.

5. The zero-crossing detection circuit according to claim 4, characterized in that, The voltage source circuit includes: A high-frequency transformer, wherein the opposite terminal of the primary winding of the high-frequency transformer is connected to one end of the second diode; and the opposite terminal of the auxiliary winding of the high-frequency transformer is connected to the negative terminal of the first polarized capacitor. The third diode has its anode connected to the same terminal of the auxiliary winding; the cathode of the third diode is connected to the anode of the first polarized capacitor, and is used to provide the preset DC voltage; the value of the preset DC voltage is in the range of 8V to 16V. A switching power supply control circuit is connected to the same-name terminal of the primary winding of the high-frequency transformer and the negative terminal of the third diode, respectively. A fourth diode, the positive terminal of which is connected to the same-name terminal of the secondary winding of the high-frequency transformer; A fourth polarity capacitor, the positive terminal of which is connected to the negative terminal of the fourth diode; the negative terminal of the fourth polarity capacitor is connected to the opposite terminal of the secondary winding of the high-frequency transformer; the opposite terminal of the secondary winding of the high-frequency transformer is also used for grounding.

6. The zero-crossing detection circuit according to claim 1, characterized in that, The unidirectional conducting device is a diode.

7. The zero-crossing detection circuit according to any one of claims 1 to 6, characterized in that, The circuit also includes a current limiting and voltage dividing module; the current limiting and voltage dividing module is connected to the positive input terminal of the optocoupler isolation module and the negative input terminal of the optocoupler isolation module respectively; the current limiting and voltage dividing module is used to connect to the preset DC voltage.

8. The zero-crossing detection circuit according to claim 7, characterized in that, The current limiting and voltage dividing module includes: A current-limiting resistor, one end of which is connected to the positive input terminal of the optocoupler isolation module, and the other end of which is used to connect to the preset DC voltage; A voltage divider resistor is provided, with one end connected to the positive input terminal of the optocoupler isolation module and the other end connected to the negative input terminal of the optocoupler isolation module.

9. The zero-crossing detection circuit according to claim 8, characterized in that, The optocoupler isolation module includes: A light-emitting diode (LED), wherein the positive terminal of the LED is connected to one end of the current-limiting resistor; and the negative terminal of the LED is connected to the other end of the voltage-dividing resistor. A photodiode, wherein the positive terminal of the photodiode is used to connect to the power supply voltage; the negative terminal of the photodiode is used to ground; and the photodiode is used to output the zero-crossing signal according to the conduction state of the light-emitting diode.

10. A zero-crossing detection device, characterized in that, The device includes a zero-crossing detection circuit as described in any one of claims 1 to 9; the device further includes a microprocessor unit connected to the positive output terminal of the optocoupler isolation module, used to obtain the zero-crossing position based on the rising and falling edges of the zero-crossing signal.

11. A microwave oven, characterized in that, The microwave oven includes the zero-crossing detection device as described in claim 10.

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