CN209488845U - A kind of electromagnetic heating circuit and device inhibiting electromagnetic interference - Google Patents

Abstract

The utility model discloses a kind of electromagnetic heating circuits and device for inhibiting electromagnetic interference, the electromagnetic heating circuit is connect with power supply line, including main electromagnetic interference suppression module, auxiliary selenoid AF panel module, rectification module, filter module and electromagnetic heating module, the alternation line voltage of input is exported through auxiliary selenoid AF panel module to rectification module, the rectification module exports after alternation line voltage is carried out rectification processing to filter module, alternation line voltage is converted into direct voltage output to electromagnetic heating module and main electromagnetic interference suppression module by the filter module, DC voltage is converted into high-frequency alternating voltage and generates alternating magnetic field by the electromagnetic heating module, the Radiative EMI that the main electromagnetic interference suppression module is used to that electromagnetic heating module to be inhibited to generate, the auxiliary selenoid AF panel module is for inhibiting electromagnetism The Conducted Electromagnetic Interference of heating module, so realize to the electromagnetic interference of electromagnetic interference source carry out inhibit and circuit structure it is simple, at low cost.

Description

A kind of electromagnetic heating circuit and device inhibiting electromagnetic interference

Technical field

The utility model relates to electromagnetic heating technique field, in particular to a kind of electromagnetic heating circuit for inhibiting electromagnetic interference And device.

Background technique

Electromagnetic heater is a kind of device that thermal energy is converted electrical energy into using electromagnetic induction principle, specifically, by electromagnetism The AC rectification of 220V or 380V, 50HZ or 60Hz are become direct current by controller, then direct current is converted into frequency and is The high-frequency high-voltage of 20KHz-40KHz, the high-frequency high-voltage current of high speed variation, which flows through coil, can generate the alternation magnetic of high speed variation , countless small vortex can be generated in metallic object when the magnetic line of force in magnetic field passes through magnetic conductive metal material, make metal material Material itself voluntarily generate heat by high speed, to reach the article in heating metal material barrel.

Common conversion circuit is single tube parallel resonance form, wherein main devices insulated gate bipolar transistor IGBT work Make under high-frequency and high-voltage state, since high-speed switch generates stronger high frequency harassing and wrecking, harassing and wrecking are mainly radiated by power supply line to space, Harm is generated to human health and periphery electric appliance.To lower radiation disturbance, Normal practice is to increase filter in power input, Lower radiation intensity.To reach preferable filter effect, need using multiple filter.Specifically, referring to Fig. 1, main device Part IGBT works under high-frequency and high-voltage state, since high-speed switch generates the harassing and wrecking of strong high-frequency electromagnetic, harassing and wrecking by power supply line to Electricity network conduction is radiated to space, to reduce from electromagnetic disturbance, uses three-level filtering device, the i.e. first order in power input Filter S10, second level filter S20 and third level filter S30, to reduce the electromagnetic disturbance generated by power supply line.I.e. Traditional approach mainly by limiting electromagnetic disturbance transmission path, is needed using multiple filter, due to needing to use Multiple magnetic inductive devices, it is at high cost, volume is big, be not suitable for the demand of the miniaturization of small household appliances volume, slimming.

Thus the prior art could be improved and improve.

Utility model content

Place in view of above-mentioned deficiencies of the prior art, the purpose of this utility model is to provide a kind of inhibition electromagnetic interferences Electromagnetic heating circuit and device have only used level-one common-mode filter, have reduced magnetism by inhibiting to electromagnetic disturbance source The quantity of inductance component, simplifies circuit structure, and filter circuit volume is greatly reduced, and reduces cost, it is small in size to meet small household appliances Type, the demand of slimming.

In order to achieve the above object, the utility model takes following technical scheme:

A kind of electromagnetic heating circuit inhibiting electromagnetic interference, connect with power supply line, including main electromagnetic interference suppression module, Auxiliary selenoid AF panel module, rectification module, filter module and electromagnetic heating module, the alternation line voltage of input is through assisting Electromagnetic interference suppression module is exported to rectification module, and the rectification module carries out the alternation line voltage defeated after rectification processing Out to filter module, the filter module by the alternation line voltage be converted into direct voltage output to electromagnetic heating module and The DC voltage is converted into high-frequency alternating voltage and generates alternation magnetic by main electromagnetic interference suppression module, the electromagnetic heating module , the Radiative EMI that the main electromagnetic interference suppression module is used to that electromagnetic heating module to be inhibited to generate, the auxiliary selenoid AF panel module is used to inhibit the Conducted Electromagnetic Interference of electromagnetic heating module.

In the electromagnetic heating circuit, the electromagnetic heating module includes R-T tube, radiator and resonant element, The R-T tube is used to control the input and disconnection of DC voltage, and the resonant element is used to DC voltage being converted into height Frequency alternating voltage generates alternating magnetic field, and the radiator is for distributing heat caused by R-T tube.

In the electromagnetic heating circuit, the main electromagnetic interference suppression module includes first capacitor, the second capacitor, third Capacitor, the 4th capacitor and the 5th capacitor, one end of the first capacitor connect the one of rectification module, filter module and the 4th capacitor The other end at end, the first capacitor is connect by the second capacitor with one end of third capacitor, the other end of the third capacitor The other end connection radiator of R-T tube, the 4th capacitor is connected, the 5th capacitor is connected in parallel on the resonant switch The both ends of pipe.

In the electromagnetic heating circuit, the auxiliary selenoid AF panel module includes the 6th capacitor, the 7th capacitor, the One end of eight capacitors, first resistor, the first common mode inductance and first switch, the 6th capacitor is connected to the first common mode inductance Between first input end and the second input terminal, one end of the 7th capacitor connects the second output terminal, simultaneously of the first common mode inductance Connect rectification module by first switch, the other end of the 7th capacitor connect the 8th capacitor one end and first resistor one End, the other end of the 8th capacitor connect the second output terminal and rectification unit of the first common mode inductance, the first resistor The ground wire of other end connection alternation alternating current.

In the electromagnetic heating circuit, the resonant element includes inductance coil and the 9th capacitor, the inductance coil One end connect filter module, the other end of the inductance coil connects electromagnetic heating module, and the 9th capacitor is connected in parallel on institute State the both ends of inductance coil.

In the electromagnetic heating circuit, the R-T tube is insulated gate bipolar transistor.

In the electromagnetic heating circuit, the filter module includes the first inductance and the tenth capacitor, first inductance One end connect main electromagnetic interference suppression module and rectification module, the other end connection electromagnetic heating module of first inductance and One end of tenth capacitor, the other end ground connection of the tenth capacitor.

The electromagnetic heating circuit further includes current detection module, and the current detection module includes second resistance, institute The one end for stating second resistance connects main electromagnetic interference suppression module and electromagnetic heating module, the other end connection of the second resistance Rectification module.

The electromagnetic heating circuit further includes protective module, and the protective module includes protective tube and varistor, institute The one end for stating protective tube is connect with the firewire of alternation alternating current, the other end of the protective tube and one end of varistor and auxiliary electricity The connection of magnetic disturbance suppression module, the other end of the varistor and the zero curve of alternation alternating current and auxiliary selenoid AF panel module Connection.

A kind of electromagnetic heater inhibiting electromagnetic interference, including pcb board are provided on the pcb board as described above Electromagnetic heating circuit.

Compared to the prior art, a kind of electromagnetic heating circuit and device inhibiting electromagnetic interference provided by the utility model, The electromagnetic heating circuit is connect with power supply line, including main electromagnetic interference suppression module, auxiliary selenoid AF panel module, rectification The alternation line voltage of module, filter module and electromagnetic heating module, input is exported through auxiliary selenoid AF panel module to whole Flow module, output to filter module, the filter module will after alternation line voltage is carried out rectification processing by the rectification module Alternation line voltage is converted into direct voltage output to electromagnetic heating module and main electromagnetic interference suppression module, the electromagnetic heating DC voltage is converted into high-frequency alternating voltage and generates alternating magnetic field by module, and the main electromagnetic interference suppression module is for inhibiting electricity The Radiative EMI that magnetic heating module generates, the auxiliary selenoid AF panel module are used to inhibit the biography of electromagnetic heating module Conductive magnetic disturbance, so realize to the electromagnetic interference of electromagnetic interference source carry out inhibit and circuit structure it is simple, at low cost.

Detailed description of the invention

Fig. 1 is the circuit diagram of the existing electromagnetic heating circuit for inhibiting electromagnetic interference；

Fig. 2 is the structural block diagram of the electromagnetic heating circuit provided by the utility model for inhibiting electromagnetic interference；

Fig. 3 is the circuit diagram of the electromagnetic heating circuit provided by the utility model for inhibiting electromagnetic interference.

Specific embodiment

The utility model provide it is a kind of inhibit electromagnetic interference electromagnetic heating circuit and device, by electromagnetic disturbance source into Row inhibits, and has only used level-one common-mode filter, has reduced the quantity of magnetic inductive device, has simplified circuit structure, substantially drop Low filter circuit volume reduces cost, meets the needs of miniaturization of small household appliances volume, slimming.

To keep the purpose of this utility model, technical solution and effect clearer, clear, develop simultaneously implementation referring to the drawings The utility model is further described in example.It should be appreciated that specific embodiment described herein is only practical to explain It is novel, it is not used to limit the utility model.

Referring to Fig. 2, the electromagnetic heating circuit provided by the utility model for inhibiting electromagnetic interference, connect with power supply line, Including main electromagnetic interference suppression module 100, auxiliary selenoid AF panel module 200, rectification module 300, filter module 400 and electricity Magnetic heating module 500, the auxiliary selenoid AF panel module 200, rectification module 300, filter module 400 and electromagnetic heating mould Block 500 is sequentially connected, the main electromagnetic interference suppression module 100 and rectification module 300, filter module 400 and electromagnetic heating mould Block 500 connects；The alternation line voltage of input is exported through auxiliary selenoid AF panel module 200 to rectification module 300, described whole Output to filter module 400, the filter module 400 will after the alternation line voltage is carried out rectification processing by flow module 300 The alternation line voltage is converted into direct voltage output to electromagnetic heating module 500 and main electromagnetic interference suppression module 100, institute It states electromagnetic heating module 500 and the DC voltage is converted into high-frequency alternating voltage generation alternating magnetic field, the main electromagnetic interference The Radiative EMI that suppression module 100 is used to that electromagnetic heating module 500 to be inhibited to generate, the auxiliary selenoid AF panel module 200 for inhibiting the Conducted Electromagnetic Interference of electromagnetic heating module 500.

The electromagnetic heating module 500 can generate electromagnetic interference in formation alternating electromagnetic field process for heating, Electromagnetic interference can be interfering by way of conduction with the mode of radiation, therefore the original that the utility model is generated according to electromagnetic interference Cause is mainly used for the electromagnetic interference for inhibiting to conduct through power supply line in mains terminals setting auxiliary selenoid AF panel module 200, together When, main electromagnetic interference module is set around electromagnetic heating module 500 and is mainly used for inhibiting by electromagnetic heating module 500 i.e. electromagnetism The electromagnetic interference propagated in a manner of radiation that interference source generates, the structure of the electromagnetic heating circuit is simple, and can Achieve the effect that inhibit electromagnetic interference well, circuit volume is greatly reduced, reduces cost.

Further, referring to Fig. 3, the electromagnetic heating module 500 includes R-T tube Q1, radiator W and resonance Unit 510, the radiator W are connect with R-T tube Q1, and specifically, the radiator W and R-T tube Q1 pass through tightly Firmware, which is fixedly connected, constitutes an entirety, and the R-T tube Q1 is also connect with resonant element 510；The R-T tube Q1 For controlling the input and disconnection of DC voltage, the resonant element 510 is used to DC voltage being converted into high-frequency alternating voltage Alternating magnetic field is generated, the radiator W is for distributing heat caused by R-T tube Q1.Specifically, pass through resonant switch The on-off of pipe Q1 guarantees the DC voltage input resonant element 510, so that resonant element 510 converts DC voltage Alternating magnetic field is generated in turn at the high-frequency alternating voltage of 20KHz ~ 30KHz, for heating ferromagnetic object.The R-T tube Work is in the state of high-frequency and high-voltage, and since high-speed switch can generate strong high-frequency electromagnetic harassing and wrecking, the electromagnetic disturbance can be through It crosses power supply line to be conducted, while will also pass through and be propagated by way of radiation.Equally, connect with the R-T tube Q1 The radiator W connect can disperse the heat of the generation of the inside in the R-T tube Q1 course of work in time, and then effectively guarantee humorous Vibration switching tube Q1 normally works, and enables electromagnetic heating module 500 that heating is effectively performed.

When it is implemented, the main electromagnetic interference suppression module 100 includes first capacitor C1, the second capacitor C2, third electricity The one end for holding C3, the 4th capacitor C4 and the 5th capacitor C5, the first capacitor C1 connects rectification module 300,400 and of filter module The other end of one end of the 4th capacitor C4, the first capacitor C1 is connect by the second capacitor C2 with one end of third capacitor C3, The emitter of the other end connection R-T tube Q1 of the third capacitor C3, the other end of the 4th capacitor C4 connect heat dissipation One end of device W, the 5th capacitor C5 connect the collector of the R-T tube Q1, and the other end of the 5th capacitor C5 connects Connect the emitter of the R-T tube Q1；The first capacitor C1, the second capacitor C2, third capacitor C3 and the 4th capacitor C4 are whole The loop that an encirclement R-T tube Q1 is formed on body by short-circuit to electromagnetic interference source, and then inhibits the electromagnetic interference The radiation interference in source.Specifically, the radiation interference that the 4th capacitor C4 is used to that radiator W to be inhibited to generate, the 5th capacitor The radiation interference that C5 is used to that R-T tube Q1 to be inhibited to generate.

Preferably, the R-T tube Q1 is insulated gate bipolar transistor, the first capacitor C1, the second capacitor C2, third capacitor C3, the 4th capacitor C4 and the 5th capacitor C5 are ceramic paster formula capacitor, capacitance be 470pF ~ 2.2nF, pressure voltage are 1KV ~ 2KV；In the present embodiment, the first capacitor C1, the second capacitor C2, third capacitor C3, Four capacitor C4 and the 5th capacitor C5 pass through short-circuit electromagnetic interference source, can reduce the intensity for the harassing and wrecking signal that frequency is 1MHz ~ 1GHz, And then achieve the purpose that inhibit electromagnetic interference.

Further, the auxiliary selenoid AF panel module 200 includes the 6th capacitor C6, the 7th capacitor C7, the 8th electricity Hold C8, first resistor R1, the first common mode inductance L1 and first switch, one end of the 6th capacitor C6 is connected to the first common mode electricity Between the first input end and the second input terminal for feeling L1, one end of the 7th capacitor C7 connects the second of the first common mode inductance L1 Output end simultaneously connects rectification module 300 by first switch, and the other end of the 7th capacitor C7 connects the one of the 8th capacitor C8 The one end at end and first resistor R1, the other end of the 8th capacitor C8 connect the second output terminal of the first common mode inductance L1 and whole Flow unit, the ground wire PE of the other end connection alternation alternating current of the first resistor R1.The 6th capacitor C6 and the first common mode electricity Feel L1 and form common-mode filter, the intensity for the harassing and wrecking signal for being 150KHz ~ 1MHz along the frequency of power supply line conduction can be reduced, it is described The intensity for the harassing and wrecking signal that 7th capacitor C7 and the 8th capacitor C8 is 1MHz ~ 30MHz for reducing the frequency conducted along power supply line, The first capacitor C1 is then used to adjust ground wire PE impedance, to reduce the space radiation interference of ground wire PE generation.This is practical new Type is compared with traditional electromagnetic interference suppression circuit, it is only necessary to the first electricity of connection ground wire PE is combined by level-one common-mode filter Hinder R1, can effectively inhibit power supply line conduction electromagnetic interference, simplify circuit structure, reached small size, low cost It is required that.

Preferably, the capacitance of the 7th capacitor C7 and the 8th capacitor C8 is 470pF ~ 2.2nF；Preferably, described First resistor R1 is Chip-R, and resistance value is 470 Ω ~ 4.7K Ω.

Further, the resonant element 510 includes inductance coil L3 and the 9th capacitor C9, the inductance coil L3's One end connects filter module 400, and the other end of the inductance coil L3 connects electromagnetic heating module 500, the 9th capacitor C9 It is connected in parallel on the both ends of the inductance coil L3.The resonant element 510 turns DC voltage when there are the input of DC voltage Change the high-frequency alternating voltage that frequency is 20KHz ~ 30KHz into, and thus high-frequency alternating voltage driving inductance coil L3 generates alternation Electromagnetic field, and then for heating ferromagnetic object.

Preferably, please continue to refer to Fig. 3, the electromagnetic heating circuit further includes drive module 700, the drive module 700 include 3rd resistor R3 and driving circuit 710, and one end of the 3rd resistor R3 connects the insulated gate bipolar transistor The gate pole of Q1, the other end driving circuit 710 of the 3rd resistor R3, the driving circuit 710 are controlled by 3rd resistor R3 The conducting and shutdown of insulated gate bipolar transistor Q1, and then the input of 510 DC voltage of resonant element is controlled, so that electric Feel the electromagnetic field that coil L3 generates alternation, realizes heating ferromagnetic object.Wherein, the 3rd resistor R3 is insulated gate bipolar The driving resistance of transistor Q1.

Further, the filter module 400 includes the first inductance L2 and the tenth capacitor C10, the first inductance L2's One end connects main electromagnetic interference suppression module 100 and rectification module 300, and the other end of the first inductance L2 connects resonant element 510 and the tenth capacitor C10 one end, the tenth capacitor C10 the other end ground connection, pass through the first inductance L2 and the tenth capacitor The pi type filter that C10 is formed exports after alternation city polygonal voltage is converted into DC voltage to resonant element 510, it is ensured that electromagnetism adds The normal work of thermal modules 500.

Further, please continue to refer to Fig. 2, the electromagnetic heating circuit also packet current detection module 600, the electric current inspection The electric current that mould 600 is used to detect insulated gate bipolar transistor Q1 is surveyed, the current detection module 600 includes second resistance R2, One end of the second resistance R2 connects main electromagnetic interference suppression module 100 and electromagnetic heating module 500, the second resistance R2 The other end connect rectification module 300, can detect the electricity of the insulated gate bipolar transistor Q1 by current detection module 600 Flow the overcurrent protection, it can be achieved that insulated gate bipolar transistor Q1.

Further, please continue to refer to Fig. 3, the rectification module 300 includes rectifier bridge, the first input of the rectifier bridge End connection first switch, the cathode output end of the second input end grounding of the rectifier bridge, the rectifier bridge connect second resistance The other end of R2, the cathode output end of the rectifier bridge connect one end and the 4th of one end of first capacitor C1, the first inductance L2 The alternation line voltage of input is filtered by one end of capacitor C4 by rectification module 300, and then guarantees output to filter The stability and validity of the alternation line voltage of wave module 400.

Preferably, the electromagnetic heating circuit further includes protective module 800, and the protective module 800 is described for protecting Electromagnetic heating circuit, the protective module 800 include fuse F1 and varistor RZ, one end of the fuse F1 and alternation The firewire L connection of alternating current, the other end of the fuse F1 connect one end of the 6th capacitor C6, with one end of varistor RZ The first input end of one common mode inductance L1, the other end of the varistor RZ connect the 6th capacitor with the zero curve N of alternation alternating current Second input terminal of the other end of C6 and the first common mode inductance L1；The fuse F1 can break in electromagnetic heating circuit short circuit It opens, electromagnetic heating circuit can be protected from damage, meanwhile, the varistor RZ is connected in parallel on the both ends of the 6th capacitor C6, can It is effectively prevented lightning surge interference.

Based on the electromagnetic heating circuit of above-mentioned inhibition electromagnetic interference, the utility model further correspondingly provides a kind of inhibition electricity The electromagnetic heater of magnetic disturbance, including pcb board, on the pcb board on be provided with the electricity as described above for inhibiting electromagnetic interference Magnetic heater circuit, since the electromagnetic heating circuit above to the inhibition electromagnetic interference is described in detail, details are not described herein again.

In conclusion a kind of electromagnetic heating circuit and device for inhibiting electromagnetic interference provided by the utility model, the electricity Magnetic heater circuit is connect with power supply line, including main electromagnetic interference suppression module, auxiliary selenoid AF panel module, rectification module, The alternation line voltage of filter module and electromagnetic heating module, input is exported through auxiliary selenoid AF panel module to rectification mould Alternation line voltage is carried out after rectification processing output to filter module by block, the rectification module, and the filter module is by alternation Line voltage is converted into direct voltage output to electromagnetic heating module and main electromagnetic interference suppression module, the electromagnetic heating module DC voltage is converted into high-frequency alternating voltage and generates alternating magnetic field, the main electromagnetic interference suppression module is for inhibiting electromagnetism to add The Radiative EMI that thermal modules generate, the auxiliary selenoid AF panel module are used to inhibit the conduction electricity of electromagnetic heating module Magnetic disturbance, so realize to the electromagnetic interference of electromagnetic interference source carry out inhibit and circuit structure it is simple, at low cost.

It is understood that for those of ordinary skills, can with technical solution according to the present utility model and The design of its utility model is subject to equivalent substitution or change, and all these changes or replacement all should belong to appended by the utility model Scope of protection of the claims.

Claims (10)

1. a kind of electromagnetic heating circuit for inhibiting electromagnetic interference, connect, which is characterized in that including main electromagnetic interference with power supply line Suppression module, auxiliary selenoid AF panel module, rectification module, filter module and electromagnetic heating module, the alternation alternating current of input Voltage is exported through auxiliary selenoid AF panel module to rectification module, and the rectification module carries out the alternation line voltage whole To filter module, the alternation line voltage is converted into direct voltage output to electromagnetism by the filter module for output after stream process The DC voltage is converted into high-frequency alternating voltage by heating module and main electromagnetic interference suppression module, the electromagnetic heating module And then alternating magnetic field is generated, the electromagnetic radiation that the main electromagnetic interference suppression module is used to that electromagnetic heating module to be inhibited to generate is dry It disturbs, the auxiliary selenoid AF panel module is used to inhibit the Conducted Electromagnetic Interference of electromagnetic heating module.

2. electromagnetic heating circuit according to claim 1, which is characterized in that the electromagnetic heating module includes resonant switch Pipe, radiator and resonant element, the R-T tube are used to control the input and disconnection of DC voltage, and the resonant element is used Alternating magnetic field is generated in turn in DC voltage is converted into high-frequency alternating voltage, and the radiator is for distributing R-T tube institute The heat of generation.

3. electromagnetic heating circuit according to claim 2, which is characterized in that the main electromagnetic interference suppression module includes the One capacitor, the second capacitor, third capacitor, the 4th capacitor and the 5th capacitor, one end connection rectification module of the first capacitor, filter The other end of one end of wave module and the 4th capacitor, the first capacitor is connect by the second capacitor with one end of third capacitor, The emitter of the other end connection R-T tube of the third capacitor, the other end of the 4th capacitor connect radiator, institute The one end for stating the 5th capacitor connects the collector of the R-T tube, and the other end of the 5th capacitor connects the resonance and opens Close the emitter of pipe.

4. electromagnetic heating circuit according to claim 1, which is characterized in that the auxiliary selenoid AF panel module includes 6th capacitor, the 7th capacitor, the 8th capacitor, first resistor, the first common mode inductance and first switch, one end of the 6th capacitor It is connected between the first input end of the first common mode inductance and the second input terminal, one end of the 7th capacitor connects the first common mode First output end of inductance simultaneously connects rectification module by first switch, and the other end of the 7th capacitor connects the 8th capacitor One end and first resistor one end, the other end of the 8th capacitor connects the second output terminal and rectification of the first common mode inductance Module, the ground wire of the other end connection alternation alternating current of the first resistor.

5. electromagnetic heating circuit according to claim 3, which is characterized in that the resonant element includes inductance coil and Nine capacitors, one end of the inductance coil connect filter module, and the other end of the inductance coil connects electromagnetic heating module, institute State the both ends that the 9th capacitor is connected in parallel on the inductance coil.

6. electromagnetic heating circuit according to claim 3, which is characterized in that the R-T tube is insulated gate bipolar Transistor.

7. electromagnetic heating circuit according to claim 1, which is characterized in that the filter module includes the first inductance and the Ten capacitors, one end of first inductance connect main electromagnetic interference suppression module and rectification module, first inductance it is another One end of end connection electromagnetic heating module and the tenth capacitor, the other end ground connection of the tenth capacitor.

8. electromagnetic heating circuit according to claim 1, which is characterized in that it further include current detection module, the electric current Detection module is used to detect the electric current of R-T tube.

9. electromagnetic heating circuit according to claim 1, which is characterized in that it further include protective module, the protective module For protecting the electromagnetic heating circuit.

10. a kind of electromagnetic heater for inhibiting electromagnetic interference, including pcb board, which is characterized in that be provided on the pcb board Electromagnetic heating circuit as described in any one of claims 1-9.