An electromagnetic induction heating circuit

Abstract

This invention belongs to the field of electromagnetic induction heating technology, specifically relating to an electromagnetic induction heating circuit. This invention precisely controls the turn-on timing of IGBT2 through a delay circuit, ensuring the resonant circuit only turns on after the voltage at point A reaches a preset clamping value. This achieves stable clamping of the node voltage, effectively preventing overvoltage surges and improving system reliability. The frequency modulation circuit, connected to capacitor C1, forms a two-stage resonant frequency adjustable circuit, enabling rapid frequency switching and fine adjustment according to operating conditions, enhancing the circuit's adaptability to different heating loads. The buffer circuit shares the overshoot voltage when capacitor C2 is charging, reducing transient stress across C2 and significantly extending the lifespan of the large-capacity resonant capacitor. By connecting an NTC thermistor RT in series in the power supply path, surge current is effectively suppressed at circuit startup, providing initial current limiting protection for capacitors C1 and C2 and other components, improving component reliability.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic induction heating technology, and specifically relates to an electromagnetic induction heating circuit. Background Technology

[0002] Electromagnetic induction heating technology is a heating method based on the principle of electromagnetic induction. It converts electrical energy into heat energy by inducing eddy currents in a conductor using the resistance heating effect. This technology has advantages such as fast heating speed, high efficiency, strong controllability, energy saving and environmental protection, and is widely used in metal processing, heat treatment, smelting and household appliances.

[0003] In the existing technology, common electromagnetic induction heating circuits mostly adopt full-bridge, half-bridge or push-pull structures, and use high-frequency switching devices (such as MOSFETs and IGBTs) to build a resonant circuit. The high-frequency current generated by the resonance forms a strong electromagnetic field on the heating load, thereby achieving the heating purpose.

[0004] However, in practical applications, in some circuit structures, the resonant frequency is determined by fixed capacitors and inductors, making it difficult to dynamically adjust according to the actual application scenario. This results in poor system adaptability. During circuit operation, high-frequency resonance may cause a sudden rise in node voltage. Without an effective clamping mechanism, it can easily cause overvoltage damage to key components, affecting system reliability. Due to the frequent alternation of resonant current, the energy pressure of some capacitors increases significantly during the resonance process. Without an effective buffering mechanism, it is easy to cause breakdown or aging failure. Summary of the Invention

[0005] The purpose of this invention is to provide an electromagnetic induction heating circuit that can effectively improve the safety, stability and lifespan of the entire machine.

[0006] The specific technical solution adopted by this invention is as follows:

[0007] An electromagnetic induction heating circuit includes:

[0008] The main resonant circuit includes an insulated gate bipolar transistor (IGBT1), a capacitor C1, and a coil disk L. The collector (C) of the IGBT1 is connected to one end of the capacitor C1 and one end of the coil disk L. The emitter (E) of the IGBT1 is grounded, and the other end of the capacitor C1 is connected to the other end of the coil disk L.

[0009] A voltage clamping circuit, comprising an insulated gate bipolar transistor (IGBT2), a diode D1, and a capacitor C2. The emitter (E) of the IGBT2 is connected to the anode of the diode D1 and the collector (C) of the IGBT1. The collector (C) of the IGBT2 is connected to the cathode of the diode D1 and one end of the capacitor C2. The other end of the capacitor C2 is connected to the other end of the capacitor C1.

[0010] The delay circuit is connected to the gate (G) of the insulated gate bipolar transistor (IGBT2) and is used to control the delayed conduction of the IGBT2 to stabilize the clamping voltage.

[0011] The frequency modulation circuit is connected to capacitor C1 and is used to adjust the resonant frequency.

[0012] A buffer circuit is connected in parallel with capacitor C2 to reduce the energy stress on capacitor C2.

[0013] The protection module is connected to capacitors C1 and C2, the frequency modulation circuit, and the buffer circuit to buffer the power supply current.

[0014] In a preferred embodiment, the delay circuit includes a resistor R1 and a capacitor C3, one end of the resistor R1 is connected to one end of the capacitor C3 and the gate (G) of the insulated gate bipolar transistor (IGBT2), and the other end of the capacitor C3 is grounded.

[0015] In a preferred embodiment, the frequency modulation circuit includes an insulated gate bipolar transistor (IGBT3) and a variable capacitor C4. The collector (C) terminal of the IGBT3 is connected to the other end of the capacitor C1, the emitter (E) terminal of the IGBT3 is connected to one end of the variable capacitor C4, and the other end of the variable capacitor C4 is connected to one end of the capacitor C1.

[0016] In a preferred embodiment, the variable capacitor C4 is smaller than the capacitor C1.

[0017] In a preferred embodiment, the buffer circuit includes a diode D2, a capacitor C5, and a resistor R2. The positive terminal of the diode D2 is connected to one end of the capacitor C2, the negative terminal of the diode D2 is connected to one end of the capacitor C5 and one end of the resistor R2, and the other end of the capacitor C5 is connected to the other end of the resistor R2 and the other end of the capacitor C2.

[0018] In a preferred embodiment, the protection module includes an NTC thermistor RT, one end of which is connected to the other end of capacitor C2, and the other end of the NTC thermistor RT is connected to the power supply VIN.

[0019] In a preferred embodiment, capacitor C2 is larger than capacitor C1.

[0020] The technical effects achieved by this invention are as follows:

[0021] This invention precisely controls the turn-on timing of IGBT2 through a delay circuit, ensuring that the resonant circuit turns on only after the voltage at point A reaches a preset clamping value. This achieves stable clamping of the node voltage, effectively preventing overvoltage surges and improving system reliability.

[0022] In this invention, the frequency modulation circuit and capacitor C1 are connected to form a two-stage resonant frequency that can be adjusted, enabling rapid switching and fine adjustment of the frequency according to the operating conditions, thereby enhancing the circuit's adaptability to different heating loads.

[0023] In this invention, the buffer circuit shares the overshoot voltage when capacitor C2 is charging, reduces the transient stress across C2, and significantly extends the service life of the large-capacity resonant capacitor.

[0024] This invention, by connecting an NTC thermistor RT in series in the power supply path, can effectively suppress surge current at the moment of circuit startup, provide initial current limiting protection for capacitors C1, C2 and other components, improve component reliability and reduce maintenance costs. Attached Figure Description

[0025] Figure 1 This is a circuit diagram provided by the present invention. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0028] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in a preferred embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments.

[0029] Furthermore, the present invention will be described in detail with reference to the schematic diagrams. When describing the embodiments of the present invention in detail, the schematic diagrams are merely examples for ease of explanation and should not limit the scope of protection of the present invention.

[0030] Please see the appendix Figure 1 As shown, an electromagnetic induction heating circuit is provided, comprising:

[0031] The main resonant circuit includes an insulated gate bipolar transistor (IGBT1), a capacitor C1, and a coil disk L. The collector (C) of the IGBT1 is connected to one end of the capacitor C1 and one end of the coil disk L. The emitter (E) of the IGBT1 is grounded, and the other end of the capacitor C1 is connected to the other end of the coil disk L.

[0032] A voltage clamping circuit, comprising an insulated gate bipolar transistor (IGBT2), a diode D1, and a capacitor C2. The emitter (E) of the IGBT2 is connected to the anode of the diode D1 and the collector (C) of the IGBT1. The collector (C) of the IGBT2 is connected to the cathode of the diode D1 and one end of the capacitor C2. The other end of the capacitor C2 is connected to the other end of the capacitor C1.

[0033] The delay circuit is connected to the gate (G) of the insulated gate bipolar transistor (IGBT2) and is used to control the delayed conduction of the IGBT2 to stabilize the clamping voltage.

[0034] The frequency modulation circuit is connected to capacitor C1 and is used to adjust the resonant frequency.

[0035] A buffer circuit is connected in parallel with capacitor C2 to reduce the energy stress on capacitor C2.

[0036] The protection module is connected to capacitors C1 and C2, the frequency modulation circuit, and the buffer circuit to buffer the power supply current.

[0037] It should be noted that capacitor C2 is larger than capacitor C1. Generally, in conventional circuits, the capacitance of capacitor C2 is greater than that of capacitor C1. However, in practice, in this circuit, the capacitance of capacitor C2 is much larger than that of capacitor C1.

[0038] It is worth mentioning that it is also connected to peripheral circuits such as synchronous detection and drive control in existing electromagnetic induction heating circuit technology. The protection module is connected in series between the power supply VIN and capacitors C1 and C2, frequency modulation circuit and buffer circuit, which will not be described in detail here.

[0039] As mentioned above, when the entire circuit is powered, the protection module will buffer the power supply current.

[0040] When the external drive control circuit controls the insulated gate bipolar transistor IGBT1 to turn off, capacitor C1 and coil L resonate, and the voltage at point A (i.e., the voltage between the collector of the insulated gate bipolar transistor IGBT1 and capacitor C1) increases. When the voltage at point A exceeds VIN, diode D1 conducts. At this time, capacitor C2 is charged through diode D1. Because capacitor C2 is much larger than capacitor C1, capacitor C2 has a large absorption capacity, and the voltage at point A will be clamped near K*VIN, where K is generally 1.2 to 2 times.

[0041] During the charging process of capacitor C2, the voltage will gradually increase. When it reaches the working voltage of the buffer circuit, the buffer circuit will be activated, which will share the energy of capacitor C2 and extend the service life of capacitor C2.

[0042] When the voltage at point A is clamped at K*VIN, the external drive control circuit supplies power to the delay circuit. When the voltage of the delay circuit causes the insulated gate bipolar transistor IGBT2 to conduct, the coil L and capacitor C2 resonate. Because capacitor C2 is much larger than capacitor C1, the voltage at point A will slowly decrease, but will remain basically near K*VIN.

[0043] When the external drive control circuit controls the insulated gate bipolar transistor IGBT2 to turn off, the coil L and capacitor C1 resonate, and the voltage at point A begins to drop rapidly. When it drops to zero, the insulated gate bipolar transistor IGBT1 is turned on again, completing one control cycle. That is, the complete timing sequence of controlling the insulated gate bipolar transistor IGBT1 to turn off → controlling the insulated gate bipolar transistor IGBT2 to turn on → controlling the insulated gate bipolar transistor IGBT2 to turn off → controlling the insulated gate bipolar transistor IGBT1 to turn on again achieves fixed frequency operation, voltage clamping and power adjustment.

[0044] When it is necessary to change the resonant frequency, the external drive control circuit controls the frequency modulation circuit to work and change the resonant frequency.

[0045] In a preferred embodiment, the delay circuit includes a resistor R1 and a capacitor C3. One end of the resistor R1 is connected to one end of the capacitor C3 and the gate (G) of the insulated gate bipolar transistor (IGBT2), and the other end of the capacitor C3 is grounded.

[0046] As described above, when the peripheral drive control circuit supplies power to resistor R1, it charges capacitor C3 through resistor R1. The gate voltage of the insulated gate bipolar transistor IGBT2 will gradually increase. When it reaches the operating voltage, the insulated gate bipolar transistor IGBT2 will turn on. Through this delay control, the clamping voltage is more accurate and the clamping voltage is stabilized.

[0047] In a preferred embodiment, the frequency modulation circuit includes an insulated gate bipolar transistor (IGBT3) and a variable capacitor C4. The collector (C) terminal of the IGBT3 is connected to the other end of the capacitor C1, the emitter (E) terminal of the IGBT3 is connected to one end of the variable capacitor C4, and the other end of the variable capacitor C4 is connected to one end of the capacitor C1.

[0048] It is worth mentioning that the variable capacitor C4 is smaller than the capacitor C1 to avoid drastic changes in the resonant frequency.

[0049] As described above, when the IGBT3 is off, the capacitor controlling the resonant frequency is capacitor C1. When the IGBT3 is on, the capacitor controlling the resonant frequency is capacitor C1 plus a variable capacitor C4, which lowers the frequency. This allows for two-stage resonant frequency adjustment. The connection between the frequency modulation circuit and capacitor C1 can be designed according to specific application requirements. To increase the frequency, when the IGBT3 is off, the capacitor controlling the resonant frequency is capacitor C1. When the IGBT3 is on, the variable capacitor C4 is connected in series with capacitor C1 to reduce the capacitance value controlling the resonant frequency, thereby increasing the frequency. The appropriate frequency modulation circuit can be designed according to specific application requirements, which will not be elaborated further here.

[0050] In a preferred embodiment, the buffer circuit includes a diode D2, a capacitor C5, and a resistor R2. The positive terminal of the diode D2 is connected to one end of the capacitor C2, the negative terminal of the diode D2 is connected to one end of the capacitor C5 and one end of the resistor R2, and the other end of the capacitor C5 is connected to the other end of the resistor R2 and the other end of the capacitor C2.

[0051] As described above, when capacitor C2 is charged, the voltage at the positive terminal of diode D2 will gradually increase. When the operating voltage is reached, diode D2 conducts, absorbing excess voltage through capacitor C5 and resistor R2 to protect capacitor C2 and prevent overcharging of capacitor C2.

[0052] In a preferred embodiment, the protection module includes an NTC thermistor RT, one end of which is connected to the other end of capacitor C2, and the other end of the NTC thermistor RT is connected to the power supply VIN.

[0053] As mentioned above, power is supplied during the startup circuit. When an excessive startup current passes through the NTC thermistor RT in series, the temperature of the NTC thermistor RT will gradually increase, but its resistance will gradually decrease, in order to limit the excessive startup current and protect the electronic components.

[0054] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. An electromagnetic induction heating circuit, characterized in that, include: The main resonant circuit includes an insulated gate bipolar transistor (IGBT1), a capacitor C1, and a coil disk L. The collector (C) of the IGBT1 is connected to one end of the capacitor C1 and one end of the coil disk L. The emitter (E) of the IGBT1 is grounded, and the other end of the capacitor C1 is connected to the other end of the coil disk L. A voltage clamping circuit, comprising an insulated gate bipolar transistor (IGBT2), a diode D1, and a capacitor C2. The emitter (E) of the IGBT2 is connected to the anode of the diode D1 and the collector (C) of the IGBT1. The collector (C) of the IGBT2 is connected to the cathode of the diode D1 and one end of the capacitor C2. The other end of the capacitor C2 is connected to the other end of the capacitor C1. The delay circuit is connected to the gate (G) of the insulated gate bipolar transistor (IGBT2) and is used to control the delayed conduction of the IGBT2 and stabilize the clamping voltage. The delay circuit includes a resistor R1 and a capacitor C3. One end of the resistor R1 is connected to one end of the capacitor C3 and the gate (G) of the IGBT2, and the other end of the capacitor C3 is grounded. The frequency modulation circuit is connected to capacitor C1 and is used to adjust the resonant frequency. The frequency modulation circuit includes an insulated gate bipolar transistor (IGBT3) and a variable capacitor C4. The collector (C) of the IGBT3 is connected to the other end of the capacitor C1, the emitter (E) of the IGBT3 is connected to one end of the variable capacitor C4, and the other end of the variable capacitor C4 is connected to one end of the capacitor C1. A buffer circuit is connected in parallel with capacitor C2 to reduce the energy stress on capacitor C2. The buffer circuit includes diode D2, capacitor C5 and resistor R2. The positive terminal of diode D2 is connected to one end of capacitor C2, the negative terminal of diode D2 is connected to one end of capacitor C5 and one end of resistor R2, and the other end of capacitor C5 is connected to the other end of resistor R2 and the other end of capacitor C2. The protection module is connected to capacitors C1 and C2, the frequency modulation circuit, and the buffer circuit to buffer the power supply current. The protection module includes an NTC thermistor RT, one end of which is connected to the other end of capacitor C2, and the other end of the NTC thermistor RT is connected to the power supply VIN.

2. The electromagnetic induction heating circuit according to claim 1, characterized in that, The variable capacitor C4 is smaller than the capacitor C1.

3. The electromagnetic induction heating circuit according to claim 1, characterized in that, Capacitor C2 is greater than capacitor C1.

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