An air fryer

Abstract

The application discloses an air fryer, which comprises a shell, a heating device and a heat exchange system, wherein the heat exchange system comprises a fan, an insulation isolation structure arranged in the fan, a fan control circuit electrically connected with the fan and used for receiving MCU control instructions and driving the fan to work according to corresponding instructions, and a driving circuit which is a non-isolated driving circuit and comprises a rectifier filter unit, a driving control unit and an output interface; the output interface is connected with the fan control circuit and provides working power supply for the fan control circuit; there is no electrical isolation element in the power transmission path between an alternating current power supply and the fan; the fan control circuit drives the fan to work according to the MCU instructions, realizes continuous adjustment of the rotating speed of the fan and changes the flow rate and circulation intensity of hot air in the cooking cavity. The air fryer disclosed by the application realizes adjustable fan speed on the basis of low cost.

Description

Technical Field

[0001] This application relates to the field of cooking technology, and more specifically, to an air fryer. Background Technology

[0002] An air fryer, a kitchen appliance that uses high-speed air circulation technology for cooking, works by generating heat through a heating element and using a fan to drive airflow, creating hot air that evenly heats the food inside the cooking chamber. In this system, the fan that drives the airflow and its control system are crucial.

[0003] Currently, there are two main technical solutions for the heat dissipation or hot air circulation fans in air fryers on the market. One is the commonly used shaded-pole motor fan solution. Although this solution is simple in structure and low in cost, its inherent drawback is that it usually does not have speed adjustment function and can only operate at a fixed speed. This results in fixed energy consumption, which is not energy-efficient, constant noise, which cannot meet the needs of quiet cooking, and it cannot flexibly adjust the air volume according to the real-time temperature inside the pot, thus restricting further improvement in cooking effect and energy efficiency.

[0004] Another solution is the isolated drive brushless motor fan solution, which is used to achieve speed regulation. Although this solution solves the speed regulation problem, its drive circuit must include electrical isolation components such as isolation transformers and optocouplers, which significantly increases the cost. It is usually more than ten yuan higher than the shaded pole motor solution. This seriously restricts the popularization and application of this technology in the cost-sensitive home appliance industry.

[0005] Therefore, there is an urgent need in this field for a new technical solution that can achieve intelligent fan speed control while effectively controlling costs. Utility Model Content

[0006] In view of this, this application provides an air fryer that effectively reduces the cost of the air fryer while achieving adjustable fan speed.

[0007] This application provides an air fryer, including a shell, a heating device, and a heat exchange system. The shell has a cooking cavity for holding food inside. The heating device generates heat, and the heat exchange system transfers the heat generated by the heating device to the cooking cavity. The heat exchange system includes: A fan is used to blow the heat generated by the heating device into the cooking cavity. The fan has an internal insulation structure that is configured to enable the fan to withstand a safety withstand voltage test of 1500V and above. A fan control circuit, electrically connected to the fan, is used to receive MCU control commands and drive the fan to operate according to the corresponding commands; and The drive circuit is a non-isolated drive circuit, consisting of a rectifier and filter unit, a drive control unit, and an output interface. The rectifier and filter unit is directly connected to the AC power supply, and its function is to rectify and filter the AC input from the AC power supply, converting it into stable DC power. The drive control unit is directly electrically connected to the output terminal of the rectifier and filter unit, and it includes a switching power supply control chip and a power switching transistor. The switching power supply control chip is responsible for generating output control signals to control the operating state of the power switching transistor. The output interface is connected to the fan control circuit, providing operating power to the fan control circuit. There are no electrical isolation components in the power transmission path between the AC power supply and the fan; the fan control circuit drives the fan to work according to the MCU instructions, so as to continuously adjust the fan speed and change the flow rate and circulation intensity of the hot air in the cooking cavity.

[0008] By adopting the above technical solution, a non-isolated drive circuit is creatively combined with a brushless motor fan with a high-strength insulation structure. By transferring safety requirements from the drive circuit to the fan body, the drive circuit can completely omit expensive electrical isolation components such as isolation transformers and optocouplers. This achieves a significant reduction in cost while ensuring system safety, reducing material costs and assembly complexity, and realizing the practical value of "low cost and small size" while ensuring performance.

[0009] Furthermore, it overcomes the technical limitations of traditional shaded-pole motors that can only operate at a fixed speed, achieving intelligent and continuously adjustable fan speed. The drive control unit adjusts the duty cycle or frequency of the output control signal through a switching power supply control chip, directly controlling the conduction state of the power switching transistor, thereby achieving continuous stepless adjustment of the fan speed (rather than traditional discrete speed adjustment) to adapt to heat load fluctuations caused by changes in the amount of food loaded in the cooking cavity. This feature allows the heat exchange system to precisely match the airflow according to the real-time temperature of the cooking cavity and the type of food: for example, reducing the fan speed during low-temperature cooking to prevent food dehydration, and increasing the fan speed during high-temperature cooking to enhance heat circulation. Compared to traditional fixed or limited speed adjustments, it has higher heat exchange efficiency and more uniform cooking temperature, significantly reducing the problem of localized overheating or underheating of food, and improving the consistency of cooking results.

[0010] Non-isolated drive circuits, lacking the energy losses of isolation components (such as iron and copper losses in transformers), and with the drive control unit reducing conduction losses of power switching transistors through high-frequency switching (frequency regulation) or duty cycle optimization, achieve higher overall energy conversion efficiency compared to traditional isolated drive circuits. Combined with precise fan speed adjustment (avoiding ineffective high-speed operation), this further reduces overall system energy consumption, aligning with energy-saving and environmentally friendly technological trends.

[0011] Therefore, this technical solution, through the synergistic design of "high-pressure resistant insulated fan + non-isolated drive + precise continuous speed regulation", not only solves the safety shortcomings of non-isolated drive, but also retains its advantages of simplified structure and high efficiency. At the same time, through precise speed regulation, it breaks through the performance limitations of traditional heat exchange systems in air fryers, and achieves multi-dimensional optimization of safety, cost, efficiency and cooking effect.

[0012] In some embodiments, the fan is a brushless motor fan, and the insulating isolation structure includes an insulating impregnated varnish layer covering the motor windings and / or stator core of the fan; or, the insulating isolation structure includes an insulating skeleton disposed between the stator core and the motor windings.

[0013] By adopting the above technical solution, a specific, feasible, and mature insulation implementation plan is provided. The insulating impregnation varnish layer can effectively penetrate and fill the winding gap to form overall insulation, while the insulating skeleton physically isolates the winding from the iron core in terms of structure. Both of these methods can reliably enable the fan motor to meet the safety withstand voltage requirements of 1500V and above, providing key safety assurance for the application of non-isolated drive schemes.

[0014] In some implementations, a soft-start capacitor is provided between the feedback pin of the switching power supply control chip and ground. The drive control unit is configured to gradually increase the duty cycle of the output control signal during the initial power-on process through the charging process of the soft-start capacitor, thereby achieving soft start.

[0015] By adopting the above technical solution, the inrush current during the start-up of the fan motor is effectively suppressed, the current stress impact on the power switching transistor and rectifier components is avoided, the reliability and service life of the system are significantly improved, and the false protection action caused by the current overshoot that may occur during startup is eliminated.

[0016] In some implementations, the control electrode of the power switch receives a pulse width modulation signal, its first conducting electrode is connected to the positive output terminal of the rectifier and filter unit, its second conducting electrode is connected to one end of the fan, and the other end of the fan is connected to the negative output terminal of the rectifier and filter unit, thereby forming a series circuit.

[0017] By adopting the above technical solution, the basic power topology of the non-isolated drive circuit is clearly defined. This series circuit structure is simple and efficient. The fan speed can be adjusted by controlling the on and off of a single power switch, which ensures drive efficiency while controlling the number of components and cost to the greatest extent.

[0018] In some implementations, the drive circuit further includes a current sampling resistor connected in series between the power switch and ground; the overcurrent detection pin of the switching power supply control chip is connected to both ends of the current sampling resistor and is configured to shut down the output control signal when the current flowing through the power switch exceeds a preset threshold.

[0019] By adopting the above technical solution, a fast and reliable hardware-level overcurrent protection mechanism is provided, which can respond to overcurrent faults and immediately shut down the output within microseconds, effectively preventing power transistor damage caused by abnormal load or short circuit, and greatly enhancing the safety and robustness of non-isolated drive circuits.

[0020] In some implementations, the drive circuit further includes a current sampling module, which includes a sampling resistor connected in series in the fan power supply circuit for acquiring a sampling signal characterizing the fan current. The voltage signal across the sampling resistor is connected to the ADC sampling pin of the switching power supply control chip. The drive control unit is configured to adjust the output control signal according to the sampling signal to perform constant current control or overcurrent protection on the fan.

[0021] By adopting the above technical solution, precise monitoring of the fan's operating current is achieved, which not only provides more accurate software overcurrent protection, but also enables constant current drive mode, ensuring stable operation of the fan under different load conditions, and provides important current feedback parameters for intelligent speed regulation algorithms.

[0022] In some implementations, the drive circuit further includes a temperature sampling module, which includes a thermistor disposed near the power switch, and the resistance signal of the thermistor is connected to the drive control unit.

[0023] By adopting the above technical solution, real-time monitoring of the temperature of the core power components of the drive circuit is realized, providing a direct basis for the overheat protection of the system. This is an important guarantee for the long-term reliable operation of the non-isolated drive circuit in a compact space.

[0024] In some implementations, the drive control unit is configured to dynamically adjust the duty cycle of the PWM signal output to the fan based on the temperature value fed back by the temperature sampling module, so as to achieve temperature-adaptive speed regulation.

[0025] By adopting the above technical solution, temperature feedback and speed control are creatively combined. When the power transistor temperature rises, the fan speed is automatically increased to enhance heat dissipation, forming an intelligent temperature-speed closed-loop control. This not only optimizes heat dissipation efficiency but also realizes temperature adaptive protection during system operation, further improving the reliability and service life of the product.

[0026] In some implementations, the frequency of the control signal is determined by the internal oscillator of the switching power supply control chip and an external timing resistor connected to its frequency setting pin.

[0027] By adopting the above technical solution, a simple and reliable method for setting the control signal frequency is provided. The switching frequency can be flexibly adjusted by selecting timing resistors with different resistance values, enabling the circuit design to be optimized according to the electrical characteristics of different fan models, thus enhancing the adaptability and flexibility of the solution.

[0028] In some implementations, the power switch is a MOSFET, with its gate connected to the drive pin of the switching power supply control chip, its drain connected to the positive output terminal of the rectifier and filter unit through an inductor, and its source grounded through a current sampling resistor; the fan is connected between the positive output terminal of the rectifier and filter unit and the drain of the power switch.

[0029] In some implementations, the drive circuit also includes a voltage conversion module, which is a DC-DC converter based on a non-isolated BUCK topology, used to convert the rectified and filtered high-voltage DC power into the low-voltage operating power required by the switching power supply control chip.

[0030] By adopting the above technical solution and using a BUCK converter with the same non-isolated architecture to power the control chip, the non-isolated consistency of the entire drive architecture is maintained, further saving costs. At the same time, the stability and reliability of the control power supply are ensured, providing a basic guarantee for the normal operation of the entire non-isolated drive system.

[0031] In summary, this application has at least one of the following beneficial technical effects: 1. By innovatively combining a non-isolated drive circuit with an insulated fan, the system not only meets safety requirements but also achieves stepless speed regulation of the fan without completely eliminating expensive isolation components. This resolves the contradiction between cost and performance in traditional solutions, and significantly reduces costs compared to isolated drive solutions.

[0032] 2. A multi-layered safety protection design is adopted, including hardware overcurrent protection, software intelligent protection and temperature adaptive control, which ensures the high reliability and safety of the non-isolated drive system after eliminating traditional isolation components, and overcomes the safety concerns in this field regarding the application of non-isolated solutions in high-power home appliances.

[0033] 3. The entire drive system has a simple structure and few components, which not only reduces manufacturing costs but also improves system reliability. At the same time, it realizes a number of advanced functions such as intelligent speed regulation, energy saving and noise reduction, and temperature self-adaptation, providing an innovative technical solution for improving the performance and optimizing the cost of air fryer products. Attached Figure Description

[0034] Figure 1 This is a structural schematic diagram of the air fryer's appearance as described in this application; Figure 2 This is the circuit diagram of the drive circuit; Figure 3 This is the circuit diagram of the rectifier and filter unit; Figure 4 This is the circuit diagram of the drive control unit; Figure 5 This is the circuit diagram of integrated chip U5; Figure 6 This is the circuit diagram of the fan drive unit; Figure 7 This is the circuit diagram of the fan unit. Attached image description:

[0036] 1. Housing; 11. Cooking cavity; 12. Functional cavity; 2. Drive circuit; 21. Rectifier and filter unit; 22. Drive control unit; 3. Output interface; 4. Input interface; 5. Fan interface. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the utility model will be further described in detail below with reference to the accompanying drawings. The components of the embodiments of this utility model described and shown in the accompanying drawings can be arranged and designed in various different configurations. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.

[0038] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0039] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0040] In the description of this application, it should be understood that the terms "upper", "lower", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application 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, and therefore should not be construed as a limitation of this application.

[0041] The embodiments of this utility model will now be described in detail with reference to the accompanying drawings. Unless otherwise specified, the features in the following embodiments can be combined with each other.

[0042] Please see Figure 1 This embodiment provides an air fryer, including a shell 1. The shell 1 has a cooking chamber 11 and a functional chamber 12 inside. The cooking chamber 11 is used to hold the food to be cooked. The functional chamber 12 is equipped with a heating device and a heat exchange system. The heating device is a heating tube. The heating device is responsible for generating the heat required for cooking, and the heat exchange system efficiently transfers the heat generated by the heating device to the cooking chamber 11 to ensure that the food is heated evenly.

[0043] Please see Figure 2 The heat exchange system mainly consists of three parts: a fan, a fan control circuit, and a drive circuit. The fan uses a brushless motor with an internal insulation structure. This structure allows the fan to withstand safety withstand voltage tests of 1500V and above, ensuring safe operation. Specifically, the insulation structure can be an insulating impregnated varnish layer covering the motor windings and / or stator core, enhancing electrical isolation performance through impregnation; or it can be an insulating frame placed between the stator core and the motor windings, achieving electrical separation from a physical structural perspective. For those skilled in the art, the fan structure is simple and conventional, easily understood, and will not be described in detail with accompanying drawings.

[0044] The drive circuit 2 is a non-isolated drive circuit, which mainly includes a rectifier and filter unit 21, a drive control unit 22, and an output interface 3. The rectifier and filter unit 21 is directly connected to the AC power supply and is responsible for converting AC power into stable DC power. The drive control unit 22 includes a switching power supply control chip and a power switching transistor and is responsible for generating output control signals. The output interface 3 is connected to the fan control circuit to provide it with operating power.

[0045] Please see Figure 3 Rectifier and filter unit 21: AC power is connected to the circuit through ACL and ACN. It first passes through fuse FUSE1 (3.15A / 250V) to provide overcurrent protection. When an abnormally large current occurs in the circuit, the fuse blows, cutting off the circuit and protecting subsequent components.

[0046] Next, the AC power enters the front-end filter circuit, which consists of CX1 (0.22μF / 275VAC), R1 (680kΩ / 1206), and R2 (680kΩ / 1206). CX1 is a safety capacitor, mainly used to filter out common-mode interference signals. R1 and R2 are discharge resistors, which can quickly release the charge stored on CX1 after the power is disconnected, ensuring circuit safety.

[0047] The alternating current then enters a rectifier bridge composed of BD1 (ABS210), converting it into pulsating direct current. It then passes through a filter circuit consisting of L1 (20mH, UU9.8), EC1 (15μF / 450V), and EC2 (15μF / 450V). L1 is a common-mode inductor, further suppressing electromagnetic interference, while EC1 and EC2 are electrolytic capacitors, smoothing and filtering the pulsating direct current to provide a more stable output for subsequent circuits.

[0048] Please see Figure 4 The drive control unit 22 is based on the switching power supply control chip U1 (KP321BSG) and works in conjunction with components such as the power switching transistor Q11 (10N65 / TO252). The drive control unit 22 includes functional modules such as control signal adjustment, soft start function, overcurrent protection, current sampling, temperature sampling, voltage conversion, and control frequency setting. The output interface 3 provides 24V operating power to the fan control circuit.

[0049] The power switch is a MOSFET (Q11), whose gate (control electrode) is connected to the GATE pin (pin 3) of the switching power supply control chip U1 through resistor R8 to receive the PWM drive signal. The drain (first conducting electrode) of the MOSFET (Q11) is connected to the positive terminal of the rectifier filter unit output (VH_DC high-voltage DC bus) through inductor L2. The source (second conducting electrode) of the MOSFET (Q11) is grounded (GND) through the parallel current sampling resistors R9 and R10.

[0050] Control signal adjustment: The GATE pin of U1 outputs a pulse width modulation signal to control the on and off states of Q11. The first conducting terminal (drain) of Q11 is connected to the positive output terminal of the rectifier-filter unit 21, and the second conducting terminal (source) is connected to one end of the fan. The other end of the fan is connected to the negative output terminal of the rectifier-filter unit 21, forming a series circuit. By adjusting the duty cycle or frequency of the control signal output by U1, the on-time of Q11 can be changed, thereby adjusting the average voltage across the fan and achieving continuous adjustment of the fan speed. For example, increasing the duty cycle increases the on-time of Q11, raises the voltage across the fan, and increases the fan speed; conversely, decreasing the duty cycle decreases the fan speed.

[0051] Soft-start function: A soft-start capacitor C2 is connected between the U1_FB pin of U1 and ground. Initially, C2 begins charging. As charging progresses, the internal circuitry of U1 adjusts the duty cycle of the output control signal according to the voltage change on C2, gradually increasing the fan speed and preventing damage to circuit components from the instantaneous current surge upon power-up. The U1_FB pin is used for soft-start control because it acts as a feedback regulator within the U1 internal circuitry, altering the feedback signal through capacitor charging, thereby adjusting the duty cycle of the control signal.

[0052] Overcurrent protection: A current sampling resistor R9 (0.24Ω / 1W / 0805) is connected in series between the source of Q11 and ground. The U1_CS pin of U1 is connected to both ends of R9. When the current flowing through Q11 exceeds a preset threshold, the voltage across R9 increases, and this voltage signal is transmitted to the internal circuitry of U1 through the U1_CS pin. Upon detecting this voltage change, U1 immediately shuts off the output control signal, protecting Q11 and components such as the fan from overcurrent damage. The U1_CS pin is specifically used to receive the current detection signal so that U1 can respond to overcurrent protection in a timely manner.

[0053] A current sampling resistor R9 is connected in series between the source of the power switch Q11 and ground to obtain a sampling signal characterizing the current flowing through Q11. The voltage signal across R9 is connected to the CS pin of U1. U1 adjusts the output control signal according to this sampling signal to achieve constant current control or overcurrent protection for the fan.

[0054] The specific working process is as follows: When the current flowing through Q11 increases, the voltage across R9 also increases. After the CS pin of U1 detects this voltage change, it compares it with the internally preset current threshold. If the detected current exceeds the set value, U1 will appropriately reduce the duty cycle of the control signal output to the GATE pin, thereby reducing the conduction time of Q11 and reducing the current flowing through Q11 and the fan, ensuring that the fan operates within the safe current range and realizing the overcurrent protection function; at the same time, U1 can dynamically adjust the duty cycle of the control signal according to the sampling signal to maintain the stability of the fan current and achieve the purpose of constant current control.

[0055] Temperature Sampling: A thermistor (not labeled in the diagram, an NTC thermistor) is placed near the power switch Q11. Its resistance changes with temperature. The thermistor's resistance signal is input to U1. Based on the temperature feedback from the thermistor, U1 dynamically adjusts the duty cycle of the PWM signal output to the fan, achieving temperature-adaptive speed control. When the temperature rises, U1 increases the PWM signal duty cycle, increasing the fan speed and improving heat dissipation; when the temperature decreases, it decreases the duty cycle, reducing the fan speed and saving energy.

[0056] Control signal frequency setting: The frequency of the control signal is determined by the internal oscillator of U1 and the external timing resistor R4 connected to its frequency setting pin. By adjusting the resistance value of R4, the frequency of the control signal can be changed, thereby optimizing the fan speed regulation performance and making the fan run more stably and efficiently at different frequencies.

[0057] Voltage Conversion: The voltage conversion module is a DC-DC converter based on a non-isolated BUCK topology. The rectified and filtered high-voltage DC (VH_DC) undergoes a step-down conversion through a circuit consisting of U2 (such as a buck converter chip) and related components (such as inductors, capacitors, diodes, etc.), outputting the low-voltage operating power required by the switching power supply control chip U1. For example, it converts a higher DC voltage to a voltage suitable for the KP321BSG chip's operation, ensuring stable chip operation and guaranteeing the normal operation of the entire drive circuit 2.

[0058] Please see Figures 5-7 The fan control circuit mainly consists of integrated chip U5 (LCP067AH31GSB / SSOP24) and its peripheral components. The functions of each pin of chip U5 are as follows: OPAL_IN, OPAL_UP, etc., are used to receive external PWM signals or other control signals; FCK, FMFU, FMFV, FDA, etc., are drive signal output pins. Fan interface 5 is used to connect the fan, and peripheral components (such as transistors Q2B, Q4B, Q6B, etc.) constitute the drive circuit to amplify the drive signal.

[0059] The fan control circuit operates on the following principle: Control signal input: Chip U5 receives control signals from external sources, such as PWM (Pulse Width Modulation) signals or other control signals input through pins like OPAL_IN and OPAL_UP. These signals are used to adjust the fan speed.

[0060] Drive signal output: The U5 chip generates corresponding drive signals on its output pins (such as FCK, FMFU, FMFV, FDA, etc.) according to the input control signal. These drive signals are then amplified by subsequent drive circuits (such as circuits composed of transistors Q2B, Q4B, Q6B, etc.).

[0061] Fan motor drive: The amplified drive signal is applied to the corresponding windings of the fan motor. By changing the duty cycle of the drive signal (for PWM control), the average current in the motor windings can be adjusted, thereby controlling the motor speed. For example, when it is necessary to increase the fan speed, increasing the duty cycle of the PWM signal increases the energizing time of the motor windings, increases the average current, and speeds up the motor; conversely, decreasing the duty cycle slows down the motor speed.

[0062] Protection Functions: The U5 chip integrates multiple protection functions, such as overcurrent protection and overheat protection. When an abnormal situation is detected, the chip will automatically adjust the output or shut down the drive signal to protect the fan motor and the entire circuit. For example, when the motor current exceeds the set value, the chip will limit the current or cut off the drive signal to prevent the motor from being damaged due to overcurrent.

[0063] Air fryer working process and principle: After rectification and filtering, the alternating current is converted into a stable high-voltage direct current (marked as VH_DC in the diagram). This high-voltage current supplies power to the power circuit and, through a linear voltage regulator circuit consisting of R2, R3, and Zener diode ZD1, provides the required operating voltage (VDD) to the switching power supply control chip U1, ensuring the chip's normal startup and operation.

[0064] The GATE pin (pin 3) of chip U1 outputs a series of PWM square wave signals with fixed frequency but adjustable duty cycle. Duty cycle refers to the proportion of high level (on time) within one cycle.

[0065] The PWM signal output from the GATE pin of U1 drives the gate of MOSFET Q11 through resistor R8. When the PWM is high, Q11 is turned on; when the PWM is low, Q11 is turned off. The function of resistor R8 is to suppress oscillation in the gate circuit and ensure the stability of the switching process.

[0066] When Q11 is turned on: the current path is: VH_DC → fan → Q11 → current sampling resistor R9 / R10 → GND. At this time, current flows through the fan and inductor L2, and L2 stores magnetic energy. The voltage at one end of the fan is pulled down to near the GND level. When Q11 is turned off: Since the current in inductor L2 cannot change abruptly, it will generate an induced electromotive force to maintain current flow. At this time, the current path is: L2 → Fan → D11 (freewheeling) → L2, forming a loop. During this stage, the voltage at the fan end increases due to the freewheeling effect. Average voltage calculation: During a complete switching cycle, the fan generates a pulse voltage with an amplitude close to high-voltage direct current (VH_DC). Duty cycle refers to the proportion of the PWM signal's high-level time within one cycle. The average voltage V_avg is calculated as: V_avg = VH_DC × Duty Cycle. That is, the larger the duty cycle, the higher the average voltage across the fan, and the faster the fan speed; conversely, the smaller the duty cycle, the slower the fan speed.

[0067] High duty cycle → Long Q11 conduction time → High average voltage → Fast fan speed.

[0068] Low duty cycle → Short Q11 conduction time → Low average voltage → Slow fan speed.

[0069] In this way, without the need for bulky and expensive isolation transformers, smooth and continuous regulation of the fan motor voltage can be achieved simply by controlling the switching of a single MOSFET through a chip. Soft start: Upon power-up, chip U1 charges the soft-start capacitor C4 through its CS_FB pin (pin 4). The gradual increase in charging voltage causes the chip to internally limit an initial very small duty cycle, which gradually increases over time to the target value. This avoids the current surge at startup, achieving a smooth start-up.

[0070] Overcurrent protection: The current sampling resistor R9 converts the current flowing through Q11 into a voltage signal and feeds it back to the CS_FB pin of U1. When this voltage exceeds the threshold set internally by the chip, U1 will immediately turn off the GATE output and shut down Q11, achieving fast hardware protection.

[0071] Temperature-adaptive speed control: By monitoring the temperature near power transistor Q11 (e.g., using a thermistor), the main control system can dynamically adjust the target duty cycle. When the temperature is too high, the fan speed is increased to enhance heat dissipation; when the temperature is low, the speed is reduced to save energy and reduce noise.

[0072] Through the design of the above heat exchange system, the air fryer can precisely adjust the fan speed according to actual cooking needs, so as to achieve effective heat transfer and precise temperature control, thereby improving the cooking effect and the reliability of the equipment.

[0073] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments; the embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes, modifications, substitutions, and variations can be made to this utility model without departing from its spirit and scope, and all such changes, modifications, substitutions, and variations fall within the scope of the claimed utility model.

Claims

1. An air fryer, comprising a shell, a heating device, and a heat exchange system, wherein the shell has a cooking cavity for holding food, the heating device generates heat, and the heat exchange system transfers the heat generated by the heating device to the cooking cavity, characterized in that, The heat exchange system includes: A fan is used to blow the heat generated by the heating device into the cooking cavity. The fan has an internal insulation structure that is configured to enable the fan to withstand a safety withstand voltage test of 1500V and above. A fan control circuit, electrically connected to the fan, is used to receive MCU control commands and drive the fan to operate according to the corresponding commands; and The drive circuit is a non-isolated drive circuit, consisting of a rectifier and filter unit, a drive control unit, and an output interface. The rectifier and filter unit is directly connected to the AC power supply, and its function is to rectify and filter the AC input from the AC power supply, converting it into stable DC power. The drive control unit is directly electrically connected to the output terminal of the rectifier and filter unit, and it includes a switching power supply control chip and a power switching transistor. The switching power supply control chip is responsible for generating output control signals to control the operating state of the power switching transistor. The positive terminal of the output interface is connected to the output terminal of the power switching transistor, providing operating power to the fan control circuit. There are no electrical isolation components in the power transmission path between the AC power supply and the fan; the fan control circuit drives the fan to work according to the MCU instructions, so as to continuously adjust the fan speed and change the flow rate and circulation intensity of the hot air in the cooking cavity.

2. The air fryer according to claim 1, characterized in that, The fan is a brushless motor fan, and the insulation structure includes an insulating impregnated varnish layer covering the motor windings and / or stator core of the fan; or, the insulation structure includes an insulating skeleton disposed between the stator core and the motor windings.

3. The air fryer according to claim 1, characterized in that, A soft-start capacitor is provided between the feedback pin of the switching power supply control chip and ground. The drive control unit is configured to gradually increase the duty cycle of the output control signal during the initial power-on process through the charging process of the soft-start capacitor, thereby achieving soft start.

4. The air fryer according to claim 1, characterized in that, The control electrode of the power switch receives a pulse width modulation signal. Its first conducting electrode is connected to the positive output terminal of the rectifier and filter unit, and its second conducting electrode is connected to one end of the fan. The other end of the fan is connected to the negative output terminal of the rectifier and filter unit, thus forming a series circuit.

5. The air fryer according to claim 1 or 4, characterized in that, The driving circuit also includes a current sampling resistor connected in series between the power switch and ground; the overcurrent detection pin of the switching power supply control chip is connected to both ends of the current sampling resistor and is configured to shut down the output control signal when the current flowing through the power switch exceeds a preset threshold.

6. The air fryer according to claim 1, characterized in that, The drive circuit further includes a current sampling module, which includes a sampling resistor connected in series in the fan power supply circuit to obtain a sampling signal characterizing the fan current. The voltage signal across the sampling resistor is connected to the ADC sampling pin of the switching power supply control chip. The drive control unit is configured to adjust the output control signal according to the sampling signal to perform constant current control or overcurrent protection on the fan.

7. The air fryer according to claim 1, characterized in that, The driving circuit also includes a temperature sampling module, which includes a thermistor disposed near the power switching transistor, and the resistance signal of the thermistor is connected to the driving control unit.

8. The air fryer according to claim 7, characterized in that, The drive control unit is configured to dynamically adjust the duty cycle of the PWM signal output to the fan based on the temperature value fed back by the temperature sampling module, so as to achieve temperature-adaptive speed regulation.

9. The air fryer according to claim 1, characterized in that, The frequency of the control signal is determined by the internal oscillator of the switching power supply control chip and the external timing resistor connected to its frequency setting pin.

10. The air fryer according to claim 1, characterized in that, The power switch is a MOSFET, whose gate is connected to the drive pin of the switching power supply control chip, whose drain is connected to the positive output terminal of the rectifier and filter unit through an inductor, and whose source is grounded through a current sampling resistor; the fan is connected between the positive output terminal of the rectifier and filter unit and the drain of the power switch.

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