Low voltage electromagnetic heating device

Abstract

The application discloses a low-voltage electromagnetic heating device, which comprises a power supply circuit, a control circuit, a voltage-boosting and power-regulating circuit, a resonant heating circuit and a heating coil, and is characterized in that the voltage-boosting and power-regulating circuit comprises at least one transformer, the middle tap of the primary side of the transformer is the power input end, the two end taps of the primary side of the transformer are respectively connected with the drain electrodes of the switch tubes M4 and M5, the source electrodes of the switch tubes M4 and M5 are grounded, the gate electrodes of the switch tubes M4 and M5 are connected with the transistor driving circuit, the secondary side of the transformer is connected with the IGBT circuit through a rectifier bridge and an inductor L2, the power supply end VH is connected with the power supply end VH1 through the inductor L2, and the voltage-boosting and power-regulating circuit is started at low power under the control of a single-chip microcomputer.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic heating, and more specifically, to a low-pressure electromagnetic heating device. Background Technology

[0002] Existing heating devices such as single-tube induction cookers cannot achieve continuous low-power operation. When the duty cycle of the switching tube of the induction cooker is less than a certain value each time it is turned on, the ineffective power applied to the switching tube is too large due to the leakage inductance of the coil. This results in high reverse voltage and high temperature of the switching tube, which can easily cause damage. Summary of the Invention

[0003] The purpose of this invention is to provide a low-voltage electromagnetic heating device that enables continuous low-power operation of an induction cooker through a boost power regulation circuit, thereby overcoming the shortcomings of the prior art.

[0004] A low-voltage electromagnetic heating device includes a power supply circuit, a control circuit, a boost power regulation circuit, a resonant heating circuit, and a heating coil. The boost power regulation circuit includes at least one transformer. The power input terminal is the center tap of the primary side of the transformer. The two taps on the primary side of the transformer are connected to the drains of switching transistors M4 and M5, respectively. The sources of switching transistors M4 and M5 are grounded, and their gates are connected to a transistor drive circuit. The secondary side of the transformer is connected to the resonant heating circuit via a rectifier bridge and inductor L2. The power supply terminal VH is connected to the power supply terminal VH1 via inductor L2. The boost power regulation circuit is controlled by a microcontroller to start at low power.

[0005] When there are two or more transformers, the primary side of each transformer is connected in parallel through a switching transistor, and the secondary side of each transformer is rectified independently or in series before rectification.

[0006] The resonant heating circuit consists of a power transistor and its driving circuit. The resonant heating circuit is connected to the PAO and OPO pins of the control circuit IC3. The input terminal of the driving circuit of the power transistor is connected to the PPG pin of the control circuit IC3 via resistor R71.

[0007] A control method for a low-voltage electromagnetic heating device: when the electromagnetic heating device requires a power output of less than X%, the output voltage of the low-voltage rectifier bridge is changed by the MCU of the control circuit, thereby reducing the input voltage of the resonant heating circuit to less than Va, so that the resonant heating circuit can operate continuously with low output power.

[0008] The value of X is in the range of 40-60.

[0009] The value of Va ranges from 80 to 120.

[0010] The beneficial effects of this invention are as follows:

[0011] 1. By setting up a boost power regulation circuit and a resonant heating circuit, the output power is controlled by these two circuits. When heating at low power (below X% of the nominal power), the control method of directly adjusting the duty cycle through the power transistor is changed. Instead, the MCU changes the output voltage of the rectifier bridge. Since the resonant impedance remains unchanged, the power decreases when the output voltage decreases. This invention avoids the problem of severe overheating of power transistors at low duty cycles, preventing the device from exploding. The circuit ensures that the operating voltage of the power transistor is below 80V, or even below 60V. The power transistor can be an IGBT or a MOSFET.

[0012] 2. This invention overcomes the inherent defect of frequent on / off switching of the switching transistor during low-power heating, thereby eliminating the operating noise caused by frequent start-up. Attached Figure Description

[0013] Figure 1 This is a circuit diagram of the transformer control circuit of the present invention.

[0014] Figure 2 This is a sampling circuit diagram of the present invention.

[0015] Figure 3 This is a microcontroller control circuit diagram for the present invention.

[0016] Figure 4 This is the power supply circuit diagram of the present invention.

[0017] Figure 5 This is a diagram of the boost power regulation circuit of the present invention.

[0018] Figure 6 This is a diagram of the resonant heating circuit of the present invention.

[0019] Figure 7 This is a circuit diagram of another embodiment of the boost power regulation circuit of the present invention.

[0020] Figure 8 This is a simplified schematic diagram of the control circuit of the present invention. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] In the description of this invention, it should be understood that the terms "center," "lateral," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention 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 the invention. Unless otherwise stated, "a plurality of" means two or more.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can be a mechanical connection or an electrical connection; they can be a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] See Figure 1-6 This invention discloses a low-voltage electromagnetic heating device, including a power supply circuit, a control circuit, a boost power regulation circuit, a heating coil, and a sampling circuit. The boost power regulation circuit includes two transformers. The power input terminal is the center tap of the primary side of the transformer. The two taps of the primary side of the transformer are connected to the drains of switching transistors M4 and M5, respectively. The sources of switching transistors M4 and M5 are grounded, and their gates are connected to a transistor drive circuit. The secondary side of the transformer is connected to a resonant heating circuit through a rectifier bridge and inductor L2. The power supply terminal VH is connected to the power supply terminal VH1 through inductor L2. The boost power regulation circuit is controlled by a microcontroller to start at low power. The control circuit includes an MCU module and an IC module. The primary sides of the two transformers are connected in parallel in a modular structure through the switching transistors. The secondary sides of each transformer are rectified independently or in series before rectification.

[0025] The resonant heating circuit consists of a power transistor and its driving circuit. The resonant heating circuit is connected to the PAO and OPO pins of the control circuit IC3. The input terminal of the driving circuit of the power transistor is connected to the PPG pin of the control circuit IC3 via resistor R71.

[0026] In summary, the transformer is controlled by two switching transistors, which change the transformer's polarity. The heating coil is connected to the sampling circuit. See also... Figure 5 The secondary side of transformer T1 is connected to the power supply terminal VH via the P terminal of diode D1, and grounded via diode D3. The N terminal of diode D1 is connected to the power supply terminal VH. The secondary side of transformer T2 is connected to the power supply terminal VH via the P terminal of diode D2, and grounded via diode D4. The N terminal of diode D2 is connected to the power supply terminal VH.

[0027] The P-terminal of diode D1 is connected to the N-terminal of D3. The P-terminals of diodes D3 and D4 are grounded. The power supply terminal VH is grounded through capacitor EC6 and through inductor L2 and capacitor EC7. The power supply terminal VH is connected to the power supply terminal VH1 through inductor L2. The boost power regulation circuit is controlled by the MCU to start at low power.

[0028] See Figure 7 , Figure 7 Another implementation of the boost power regulation circuit is shown, which uses a transformer to achieve step-down power regulation. In this case, the power input terminal is the middle tap of the primary side of the transformer. The two taps of the primary side of the transformer are connected to the drains of switching transistors M4 and M5, respectively. The sources of switching transistors M4 and M5 are grounded, and their gates are connected to the transistor drive circuit. The secondary side of the transformer is connected to the resonant heating circuit through a rectifier bridge and inductor L2.

[0029] See Figure 8 This diagram illustrates the working principle of the low-voltage electromagnetic heating device. When the electromagnetic heating device requires power output below 50%, the MCU in the control circuit outputs a signal to the power module. The power module outputs control signals from ports A and B to adjust the output voltage of the transformer module, thus changing the output voltage of the low-voltage rectifier bridge. Since the resonant impedance formed by the inductor and capacitor after the rectifier bridge does not change with voltage adjustment, when the rectifier bridge output voltage decreases, that is, the input voltage of the power transistor decreases and falls below its safe value, allowing the resonant heating circuit to operate continuously. In the diagram, a represents voltage detection, b represents current detection, and c represents the output voltage control signal.

[0030] All components involved in this invention can be general standard parts or components known to those skilled in the art. Their structures, principles and control methods are known to those skilled in the art through technical manuals or conventional experimental methods.

[0031] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, other low-pressure electromagnetic heating devices obtained by using the same or similar technical features as the above embodiments of the present invention are all within the protection scope of the present invention.

Claims

1. A low-voltage electromagnetic heating device, comprising a power supply circuit, a control circuit, a boost power regulation circuit, a resonant heating circuit, and a heating coil, characterized in that: The boost power regulation circuit includes at least one transformer. The power input terminal is the center tap of the primary side of the transformer. The two taps of the primary side of the transformer are connected to the drains of switching transistors M4 and M5, respectively. The sources of switching transistors M4 and M5 are grounded, and their gates are connected to the transistor drive circuit. The secondary side of the transformer is connected to the resonant heating circuit through a rectifier bridge and inductor L2. The power supply terminal VH is connected to the power supply terminal VH1 through inductor L2. The boost power regulation circuit is controlled by a microcontroller to start at low power.

2. The low-pressure electromagnetic heating device according to claim 1, characterized in that: When there are two or more transformers, the primary side of each transformer is connected in parallel through a switching transistor, and the secondary side of each transformer is rectified independently or in series before rectification.

3. The low-pressure electromagnetic heating device according to claim 1, characterized in that: The resonant heating circuit consists of a power transistor and its driving circuit. The resonant heating circuit is connected to the PAO and OPO pins of the control circuit IC3. The input terminal of the driving circuit of the power transistor is connected to the PPG pin of the control circuit IC3 via resistor R71.

4. The control method for the low-pressure electromagnetic heating device according to claim 1, characterized in that: When the electromagnetic heating device requires a power output of less than X%, the MCU in the control circuit changes the output voltage of the low-voltage rectifier bridge, thereby reducing the input voltage of the resonant heating circuit to less than Va, so that the resonant heating circuit can operate continuously with low output power.

5. The control method for the low-pressure electromagnetic heating device according to claim 4, characterized in that: The value of X is in the range of 40-60.

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