No-load detection circuit and microwave oven

Abstract

The utility model provides a no-load detection circuit and a microwave oven. The circuit comprises an MCU, a control module and an infrared geminate transistor module. The MCU is respectively connected with one end of the control module and one end of the infrared geminate transistor module; the other end of the infrared geminate transistor module is arranged on the inner side wall of the microwave oven; the MCU and the control module are arranged on a circuit board in the microwave oven; n groups of infrared geminate transistor modules are arranged, and n is a positive integer; one ends of the n groups of infrared geminate transistor modules are respectively connected with corresponding pins of the MCU, and the other ends of the n groups of infrared geminate transistor modules are respectively arranged on the inner side walls of the corresponding side surfaces of the microwave oven; according to the no-load detection circuit and the microwave oven provided by the utility model, the structure of the detection circuit can be simplified, the cost of the circuit can be reduced, and on the premise of avoiding increasing standby power consumption, the food detection range of the microwave oven can be expanded, the detection sensitivity can be improved, and accurate detection on different types of food can be realized; and the service life of the microwave oven can be prolonged.

Description

Technical Field

[0001] This utility model relates to the field of microwave oven technology, and more specifically, to an unloaded detection circuit and a microwave oven. Background Technology

[0002] With the rapid development of technology, the safety of smart appliances has become a crucial concern for users. Traditional microwave ovens lack a detection mechanism to check if food is inside the cavity, leading to empty-load operation, excessive magnetron heating, and a significantly reduced magnetron lifespan, thus affecting the oven's quality. This is especially true for commercial microwave ovens with high power and frequent use, which are prone to running empty even without food, further impacting their lifespan. Therefore, researching ways to optimize the internal circuitry of microwave ovens to improve safety and extend their lifespan is of great significance.

[0003] Currently, existing methods for detecting microwave ovens operating without load include determining whether the microwave oven is unloaded by measuring the incident and reflected power of the microwave source (see patent CN106322452B), and first driving the microwave oven's turntable to rotate for a first time using the microwave oven's motor shaft; then stopping the turntable drive after the first time and detecting the first number of rotations of the microwave oven's motor shaft due to the turntable's inertia within a first inertial time; and determining whether the microwave oven is unloaded based on the first number of rotations and a first predetermined number of rotations (see patent CN107327878B). However, both methods, whether measuring incident and reflected power or counting the first rotations of the turntable within the inertial time, increase standby power consumption, and both detection methods are relatively complex, leading to higher detection costs.

[0004] Patent CN104362922B discloses a control device and method for a transformer in a microwave oven, including a door detection module for outputting an opening command when the microwave oven door is opened according to a user's instruction; and a zero-crossing detection module for detecting the input mains power and outputting a zero-crossing signal. The zero-crossing detection module 2 includes an optocoupler 201 and a first resistor R1. The first input terminal of the optocoupler 201 is connected to the live wire L of the mains power, the second input terminal is connected to the neutral wire N of the mains power, and the first output terminal is grounded (GND). One end of the first resistor R1 is connected to the second output terminal of the optocoupler 201, and the other end, the output terminal ZERO, is connected to a control module 5 to output a zero-crossing signal to the control module 5. The first resistor R1 is used for output current limiting. While the optocoupler 201 can isolate high-voltage and low-voltage circuits, it cannot detect whether the microwave oven is unloaded. Utility Model Content

[0005] In view of this, the present invention aims to propose an idle-load detection circuit and a microwave oven to solve the problems of existing technologies, such as the fact that traditional microwave ovens do not detect whether there is food in the cavity when starting up, which easily leads to a serious shortening of the magnetron life of microwave ovens that are running idle, and the fact that existing microwave ovens use the detection of microwave incident power and reflected power to determine whether the microwave oven is idle, which is relatively complex and costly. The present invention simplifies the structure of the detection circuit, reduces the cost of the circuit, expands the detection range of the microwave oven for food without increasing standby power consumption, improves the detection sensitivity, and enables accurate detection of different types of food; it also extends the service life of the microwave oven.

[0006] To achieve the above objectives, the technical solution of this utility model is implemented as follows:

[0007] This utility model relates to an unloaded detection circuit and a microwave oven. The unloaded detection circuit includes an MCU, a control module, and an infrared photodiode module. The MCU is connected to one end of both the control module and the infrared photodiode module. The other end of the infrared photodiode module is disposed on the inner wall of the microwave oven. Both the MCU and the control module are disposed on a circuit board inside the microwave oven. There are n groups of infrared photodiode modules, where n is a positive integer. One end of each of the n groups of infrared photodiode modules is connected to a corresponding pin of the MCU, and the other end of each of the n groups of infrared photodiode modules is disposed on the inner wall of the corresponding side of the microwave oven.

[0008] Furthermore, the MCU includes m pins, where m is a positive integer and m ≥ 2n + 1.

[0009] Furthermore, the control module is an infrared power control module.

[0010] Furthermore, the control module includes a control module one, a transistor Q, and a control module two; one end of the control module one is connected to the MCU, and the other end of the control module one is connected to the base and emitter of the transistor Q and the first power supply VCC respectively; the collector of the transistor Q is grounded through the control module two.

[0011] Furthermore, the control module includes a first resistor R1 and a second resistor R2; one end of the first resistor R1 is electrically connected to the first power supply VCC and the emitter of the transistor Q, the other end of the first resistor R1 is electrically connected to one end of the second resistor R2 and the base of the transistor Q, and the other end of the second resistor R2 is electrically connected to the MCU.

[0012] Furthermore, the control module includes a third resistor R3 and a first capacitor C1; one end of the third resistor R3 is electrically connected to the collector of transistor Q, the second power supply VCC-OUT, and one end of the first capacitor C1, respectively, and the other end of the third resistor R3 is connected in parallel with the other end of the first capacitor C1 and then grounded.

[0013] Furthermore, the infrared pair module includes an infrared emitting LED and an infrared receiving PT, which are arranged side by side on the inner wall of any one of the top, rear, left, or right sides of the microwave oven; the infrared receiving PT is connected to the MCU.

[0014] Furthermore, n=3, and the three sets of infrared pair modules are respectively denoted as pair module one, pair module two, and pair module three. Pair module one, pair module two, and pair module three are respectively set on the inner side wall of different sides of the microwave oven.

[0015] Furthermore, the transistor module includes a fourth resistor R4, a transmitting transistor LED1, a receiving transistor PT1, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, and a second capacitor C2. One end of the fourth resistor R4 is electrically connected to the second power supply VCC-OUT, and the other end of the fourth resistor R4 is grounded through the transmitting transistor LED1. One end of the receiving transistor PT1 is electrically connected to one end of the fifth resistor R5, the sixth resistor R6, and the seventh resistor R7, respectively. The other ends of the fifth resistor R5 and the sixth resistor R6 are electrically connected to the MCU pin SW1 and the second power supply VCC-OUT, respectively. The other end of the seventh resistor R7 is connected to the MCU pin FB1 and one end of the second capacitor C2, respectively. The other ends of the receiving transistor PT1 and the second capacitor C2 are connected to ground in parallel.

[0016] A microwave oven includes the aforementioned no-load detection circuit, the circuit being disposed within the microwave oven.

[0017] Compared with the prior art, the no-load detection circuit and microwave oven described in this utility model have the following advantages:

[0018] By configuring the circuit inside the microwave oven, the structure of the detection circuit can be simplified, the cost of the circuit can be reduced, the detection range of the microwave oven can be expanded and the detection sensitivity can be improved without increasing standby power consumption, so as to achieve accurate detection of different types of food; it can also improve the safety of microwave oven use, reduce the overheating damage of the magnetron under no-load conditions, and thus extend the service life of microwave oven. Attached Figure Description

[0019] The accompanying drawings, which constitute a part of this utility model, are used to provide a further understanding of the utility model. The illustrative embodiments and descriptions of the utility model are used to explain the utility model and do not constitute an undue limitation of the utility model. In the drawings:

[0020] Figure 1 This is a schematic diagram of the overall circuit principle.

[0021] Figure 2 This is a schematic diagram showing the selectable areas for the placement of each infrared photodiode module inside the microwave oven.

[0022] Explanation of reference numerals in the attached diagram: 1. MCU; 2. Control module; 21. Control module 1; 22. Control module 2; 3. Infrared pair module; 31. Pair module 1; 32. Pair module 2; 33. Pair module 3. Detailed Implementation

[0023] The inventive concepts of this disclosure will be described below using terminology commonly used by those skilled in the art to convey the essence of their work to others skilled in the art. However, these inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0025] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0026] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] This embodiment is for a microwave oven. Similar to a conventional microwave oven, the overall structure consists of a cavity, a door, and a magnetron.

[0028] To address the shortcomings of existing microwave ovens, such as the lack of food detection during startup leading to shortened magnetron lifespan and the complexity and cost of current empty-load detection methods (e.g., relying on microwave incident and reflected power), this embodiment proposes an empty-load detection circuit and microwave oven. The empty-load detection circuit includes an MCU1, a control module 2, and an infrared photodiode module 3. The MCU1 is connected to one end of both the control module 2 and the infrared photodiode module 3. The other end of the infrared photodiode module 3 is mounted on the inner wall of the microwave oven. Both the MCU1 and the control module 2 are mounted on a circuit board inside the microwave oven. There are n groups of infrared photodiode modules 3, where n is a positive integer. Specifically, one end of each of the n groups of infrared photodiode modules 3 is connected to a corresponding pin of the MCU1, and the other end of each group is mounted on the inner wall of the corresponding side of the microwave oven. In this embodiment, the value of n can be varied according to the size of the microwave oven cavity to cover a larger food placement area.

[0029] By configuring the circuit inside the microwave oven, the structure of the detection circuit can be simplified, the cost of the circuit can be reduced, the detection range of the microwave oven can be expanded and the detection sensitivity can be improved without increasing standby power consumption, so as to achieve accurate detection of different types of food; it can also improve the safety of microwave oven use, reduce the overheating damage of the magnetron under no-load conditions, and thus extend the service life of microwave oven.

[0030] MCU1 includes m pins, where m is a positive integer and m ≥ 2n + 1. Preferably, when n = 3, that is, the infrared phototransistor modules 3 are configured in three groups. In this case, MCU1 includes pins POWER, SW1, FB1, SW2, FB2, SW3, and FB3. One end of each of the pins POWER, SW1, FB1, SW2, FB2, SW3, and FB3 is located on MCU1. The other end of the POWER pin is connected to the control module 2, and the other ends of the pairs of pins SW1 and FB1, SW2 and FB2, and SW3 and FB3 are respectively connected to the corresponding infrared phototransistor modules 3.

[0031] By coordinating the pins on MCU1, information from different modules can be received and fed back separately, which helps to avoid interference in the transmission of data and improves the overall stability of the circuit structure.

[0032] Control module 2 is an infrared power supply control module. Control module 2 includes control module 21, transistor Q, and control module 22. One end of control module 21 is connected to MCU1, and the other end of control module 21 is connected to the base and emitter of transistor Q and the first power supply VCC, respectively; the collector of transistor Q is grounded through control module 22.

[0033] By controlling module 21, transistor Q, and module 22, the circuit structure can be simplified. The setting of module 21 enables the anti-misoperation function of control module 2, and the setting of module 22 enables anti-interference. The combination of the two can effectively improve the operational stability and safety of control module 2.

[0034] The control module 21 includes a first resistor R1 and a second resistor R2. One end of the first resistor R1 is electrically connected to the first power supply VCC and the emitter of the transistor Q, respectively. The other end of the first resistor R1 is electrically connected to one end of the second resistor R2 and the base of the transistor Q, respectively. The other end of the second resistor R2 is electrically connected to the POWER pin of MCU1.

[0035] By setting the first resistor R1, the threshold voltage of the drive signal can be raised when Q is cut off, preventing interference from causing false start-up. In addition, by setting the first resistor R1 and the second resistor R2 together, the control module 21 can be protected, improving the operational reliability of the control module 21.

[0036] The control module 22 includes a third resistor R3 and a first capacitor C1. One end of the third resistor R3 is electrically connected to the collector of transistor Q, the second power supply VCC-OUT, and one end of the first capacitor C1, respectively. The other end of the third resistor R3 is connected in parallel with the other end of the first capacitor C1 and then grounded.

[0037] The first capacitor R3 is configured to discharge the first capacitor C1 when the infrared power supply is turned off. Furthermore, the first capacitor C1 is configured to filter the second power supply VCC_OUT, improving the circuit's anti-interference capability.

[0038] The infrared photodiode module 3 includes an infrared emitting LED and an infrared receiving PT, forming a set of infrared photodiode modules 3. The infrared emitting LED and the infrared receiving PT are arranged side-by-side on the inner wall of any one of the top, rear, left, or right sides of the microwave oven; the infrared receiving PT is connected to the MCU1. A certain gap exists between the infrared emitting LED and the infrared receiving PT to avoid crosstalk between them, which could cause false detections and improve the anti-interference capability of the infrared photodiode module 3. The infrared emitting LED and the infrared receiving PT are arranged side-by-side on the lower part of any one of the rear, left, or right sides of the microwave oven to facilitate more accurate measurement of the presence of food inside the microwave oven cavity and to improve the efficiency of food detection. Furthermore, the detection ends of the infrared emitting LED and the infrared receiving PT are oriented away from the inner wall of the microwave oven.

[0039] By using n sets of infrared photodiode modules 3, with the infrared emitting LED and infrared receiving PT of each module mounted side-by-side on the corresponding inner wall of the microwave oven, the infrared emission and reception feedback function of the infrared photodiode modules 3 can be activated before the microwave oven is started. If food is placed in the cavity, the voltage value returned by the infrared receiving PT is low; if no food is placed in the cavity, the voltage value returned by the infrared receiving PT is high. Based on this characteristic, the MCU1 can detect whether food is placed in the microwave oven. If no food is placed, pressing the start button will trigger an alarm, and the microwave oven will not run until food is placed in it. This setup of n sets of infrared photodiode modules 3 allows for convenient coverage of more food placement locations; effectively improves the accuracy of the circuit's detection of whether food is placed in the microwave oven; enhances the flexibility of the circuit design; and increases the sensitivity of the circuit detection, enabling accurate detection of different types of food.

[0040] When n=3, three sets of infrared pair modules 3 are configured. These three sets of infrared pair modules 3 are respectively installed on the inner wall of one or more corresponding positions on one or more of the following sides of the microwave oven: lower rear, lower left, lower right, and top. Specifically, the three sets of infrared pair modules 3 are designated as pair module 1 31, pair module 2 32, and pair module 33. Each of these modules is installed on the inner wall of a different side of the microwave oven. The detection ends of each of these modules are oriented away from the inner wall of the corresponding side of the microwave oven.

[0041] By placing three sets of infrared phototransistor modules 3 sequentially inside the microwave oven cavity along the inner side towards the center, it is possible to accurately detect food even when it is placed in different positions. Furthermore, the arrangement of multiple sets of infrared phototransistor modules 3 enables comprehensive detection of the food placement area inside the microwave oven cavity, improving the accuracy and reliability of the detection.

[0042] Specifically, module 31 includes a fourth resistor R4, a transmitting diode LED1, a receiving diode PT1, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, and a second capacitor C2. One end of the fourth resistor R4 is electrically connected to the second power supply VCC-OUT, and the other end of the fourth resistor R4 is grounded through the transmitting diode LED1. One end of the receiving diode PT1 is electrically connected to one end of each of the fifth, sixth, and seventh resistors R5 and R6, respectively. The other ends of the fifth and sixth resistors R6 are electrically connected to pin SW1 of MCU1 and the second power supply VCC-OUT, respectively. The other end of the seventh resistor R7 is connected to pin FB1 of MCU1 and one end of the second capacitor C2, and the other ends of the receiving diode PT1 and the second capacitor C2 are connected to ground in parallel.

[0043] The transistor module 32 includes an eighth resistor R8, a transmitting diode LED2, a receiving diode PT2, a ninth resistor R9, a first zero resistor R10, a first first resistor R11, and a third capacitor C3. One end of the eighth resistor R8 is electrically connected to the second power supply VCC-OUT, and the other end of the eighth resistor R8 is connected to ground through the transmitting diode LED2. One end of the receiving diode PT2 is electrically connected to one end of the ninth resistor R9, the first zero resistor R10, and the first first resistor R11, respectively. The other ends of the ninth resistor R9 and the first zero resistor R10 are electrically connected to pin SW2 of MCU1 and the second power supply VCC-OUT, respectively. The other end of the first first resistor R11 is connected to pin FB2 of MCU1 and one end of the third capacitor C3, respectively. The other ends of the receiving diode PT2 and the third capacitor C3 are connected to ground in parallel.

[0044] The three-transistor module 33 includes a first two resistor R12, a transmitting three-transistor LED3, a receiving three-transistor PT3, a first three resistor R13, a first four resistor R14, a first five resistor R15, and a fourth capacitor C4. One end of the first two resistor R12 is electrically connected to the second power supply VCC-OUT, and the other end of the first two resistor R12 is grounded through the transmitting three-transistor LED3. One end of the receiving three-transistor PT3 is electrically connected to one end of the first three resistor R13, the first four resistor R14, and the first five resistor R15, respectively. The other ends of the first three resistor R13 and the first four resistor R14 are electrically connected to pin SW3 of MCU1 and the second power supply VCC-OUT, respectively. The other end of the first five resistor R15 is connected to pin FB3 of MCU1 and one end of the fourth capacitor C4, respectively. The other ends of the receiving three-transistor PT3 and the fourth capacitor C4 are connected to ground in parallel. Among them, the transmitting one-transistor LED1, the transmitting two-transistor LED2, and the transmitting three-transistor LED3 are all infrared emitting LEDs. The receiver tubes PT1, PT2, and PT3 are all infrared receiver tubes (PTs).

[0045] Working principle:

[0046] When the microwave oven is powered on and the user activates the microwave function, the POWER signal on the MCU1 pin goes low, and current flows through R2, causing Q to be in the on state. The collector of Q will have a second power supply VCC_OUT with a voltage close to the first power supply +VCC. C1 is used to filter VCC_OUT to improve anti-interference capability. R1 is used to raise the drive signal voltage threshold when Q is off to prevent interference from causing false activation. R3 is used to discharge C1 when the infrared power supply is turned off.

[0047] The voltage of VCC_OUT causes LED1 in transistor module 31 with current-limiting resistor R4 to emit infrared light, LED2 in transistor module 32 with current-limiting resistor R8 to emit infrared light, and LED3 in transistor module 33 with current-limiting resistor R12 to emit infrared light.

[0048] In module 31, if food is placed in front of the receiving tube PT1, PT1 will receive more infrared radiation from LED1, resulting in a larger collector-emitter current flowing through PT1. This leads to a higher voltage division across resistor R6, resulting in a lower voltage at pin C of PT1. This pin C voltage signal enters the RC filter circuit composed of R7 and C2, outputting the FB1 voltage signal to the AD port of MCU1 for detection. MCU1 will then detect the lower FB1 voltage value. Conversely, if no food is placed in front of the infrared receiving tube PT1, PT1 will receive less infrared radiation from LED1, resulting in a smaller current flowing through PT1. This leads to a lower voltage division across resistor R6, resulting in a higher voltage at pin C of PT1. This pin C voltage signal enters the RC filter circuit composed of R7 and C2, outputting the FB1 voltage signal to the AD port of MCU1 for detection. MCU1 will then detect the higher FB1 voltage value. Therefore, based on the FB1 voltage value, it can be determined whether food is placed in front of the module. Among them, pin SW1 is the control signal pin of the processor output, which outputs a high level or high impedance to control the selection or shutdown of R5 and adjust the voltage value of pin C of PT1. It can be used to adjust the voltage threshold for whether food is placed on it, and adapt to more types of food.

[0049] Similarly, the second-phase module 32 and the third-phase module 33 also determine whether there is food placed in front based on the voltage values ​​of FB2 and FB3.

[0050] When the user operates the microwave heating function, if any one of the voltage signals FB1, FB2, and FB3 is lower than the voltage threshold for food placement, it can be determined that there is food in the cavity. In this case, the microwave oven will start microwave operation and turn off the infrared photodiode power supply. If all the voltage signals FB1, FB2, and FB3 are higher than the voltage threshold for food placement, it can be determined that there is no food in the cavity. In this case, the user will be prompted to place food and the microwave operation will not be started.

[0051] Additionally, when there is no user operation of the heating function or after the presence or absence of food is detected, the POWER signal of MCU1 outputs a high level, causing Q to be in the cutoff state and turning off the power supply of the infrared phototransistor module 3.

[0052] By controlling the power supply of the infrared photodiode module 3 as described in this application, it is possible to achieve power off the infrared photodiode module 3 without increasing standby power consumption, and to extend its lifespan by turning off the power after detecting the presence of food. Furthermore, the MCU1 includes selectable threshold adjustment switch pins SW1, SW2, and SW3 to facilitate the detection of different types of food. In addition, the circuit design in this application allows for better placement of the microwave oven during empty-load heating by identifying the presence of food in the cavity, thus extending the microwave oven's lifespan. Moreover, the use of multiple sets of infrared photodiode modules 3 ensures a wide detection coverage, even detecting food placed off-center.

[0053] A microwave oven includes the aforementioned no-load detection circuit, the circuit being disposed within the microwave oven.

[0054] The installation method of each component in the microwave oven makes the assembly of the circuit simple. In addition, the infrared photodiode module 3 can be placed on the lower side, lower rear, or top of the cavity to meet the detection requirements, which also makes it easy to realize the detection of food by the circuit.

[0055] In this utility model, any microwave oven may include the no-load detection circuit structure described in this embodiment. In addition to the relevant structures and assembly relationships of the control module 2 and infrared pair module 3 provided in this embodiment, the microwave oven also includes conventional components such as the oven cavity, oven door, and magnetron. Since these are all prior art, they will not be described in detail here.

[0056] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A no-load detection circuit, characterized in that, It includes an MCU (1), a control module (2), and an infrared pair module (3); the MCU (1) is connected to one end of the control module (2) and the infrared pair module (3) respectively; the other end of the infrared pair module (3) is set on the inner wall of the microwave oven; the MCU (1) and the control module (2) are both set on the circuit board inside the microwave oven; there are n groups of infrared pair modules (3), where n is a positive integer; one end of each of the n groups of infrared pair modules (3) is connected to the corresponding pin of the MCU (1), and the other end of each of the n groups of infrared pair modules (3) is set on the inner wall of the corresponding side of the microwave oven.

2. The no-load detection circuit according to claim 1, characterized in that, The MCU (1) includes m pins, where m is a positive integer and m ≥ 2n + 1.

3. The no-load detection circuit according to claim 1, characterized in that, The control module (2) is an infrared power control module.

4. The no-load detection circuit according to claim 1, characterized in that, The control module (2) includes a control module (21), a transistor Q, and a control module (22). One end of the control module (21) is connected to the MCU (1), and the other end of the control module (21) is connected to the base and emitter of the transistor Q and the first power supply VCC, respectively. The collector of the transistor Q is grounded through the control module (22).

5. The no-load detection circuit according to claim 4, characterized in that, The control module (21) includes a first resistor R1 and a second resistor R2; one end of the first resistor R1 is electrically connected to the first power supply VCC and the emitter of the transistor Q, the other end of the first resistor R1 is electrically connected to one end of the second resistor R2 and the base of the transistor Q, and the other end of the second resistor R2 is electrically connected to the MCU (1).

6. The no-load detection circuit according to claim 4, characterized in that, The control module (22) includes a third resistor R3 and a first capacitor C1; one end of the third resistor R3 is electrically connected to the collector of the transistor Q, the second power supply VCC-OUT, and one end of the first capacitor C1, respectively, and the other end of the third resistor R3 is connected in parallel with the other end of the first capacitor C1 and then grounded.

7. The no-load detection circuit according to claim 1, characterized in that, The infrared pair module (3) includes an infrared emitting tube LED and an infrared receiving tube PT. The infrared emitting tube LED and the infrared receiving tube PT are arranged side by side on the inner wall of any one of the top, rear, left and right sides of the microwave oven; the infrared receiving tube PT is connected to the MCU (1).

8. The no-load detection circuit according to claim 7, characterized in that, The n=3, the three sets of infrared pair modules (3) are respectively referred to as pair module one (31), pair module two (32) and pair module three (33), and pair module one (31), pair module two (32) and pair module three (33) are respectively set on the inner side wall of different sides of the microwave oven.

9. The no-load detection circuit according to claim 8, characterized in that, The transistor module (31) includes a fourth resistor R4, a transmitting transistor LED1, a receiving transistor PT1, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, and a second capacitor C2; one end of the fourth resistor R4 is electrically connected to the second power supply VCC-OUT, and the other end of the fourth resistor R4 is grounded through the transmitting transistor LED1; one end of the receiving transistor PT1 is electrically connected to one end of the fifth resistor R5, the sixth resistor R6, and the seventh resistor R7 respectively, and the other ends of the fifth resistor R5 and the sixth resistor R6 are electrically connected to the pin SW1 of the MCU (1) and the second power supply VCC-OUT respectively; the other end of the seventh resistor R7 is connected to the pin FB1 of the MCU (1) and one end of the second capacitor C2 respectively, and the other ends of the receiving transistor PT1 and the second capacitor C2 are connected to ground in parallel.

10. A microwave oven, characterized in that, The microwave oven includes an unload detection circuit according to any one of claims 1-9, the circuit being disposed inside the microwave oven.

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