阅读说明：本技术 一种面包烤炉的控制电路 (Control circuit of bread oven ) 是由 谭正兵 于 2021-08-23 设计创作，主要内容包括：本发明公开了一种面包烤炉的控制电路,主要特点是在一级电磁控制开关后面串联二级保护电磁开关,二级保护电磁开关由单片机控制工作；当一级电磁控制开关因主触头粘结或熔焊在一起无法分断时,微控制器发出强行断开指令,通过二级保护驱动控制二级保护电磁开关工作,二级保护电磁开关的常闭火线主触头断开、常开火线主触头闭合,二级保护自举电源得电为二级保护电磁开关提供自保持电流,确保电热装置与市电的火线断开,避免电热装置一直发热工作而产生严重后果,从而达到了安全的保护作用。其优点是,整个控制电路结构科学、新颖、简单、实用,充分利用常见电子元器件的功能,组合成结构巧妙的控制电路,使整个控制电路的成本低,工作安全可靠。(The invention discloses a control circuit of a bread oven, which is mainly characterized in that a secondary protection electromagnetic switch is connected in series behind a primary electromagnetic control switch, and the secondary protection electromagnetic switch is controlled by a single chip microcomputer to work; when the primary electromagnetic control switch cannot be disconnected due to the fact that the main contacts are bonded or welded together, the microcontroller sends a forced disconnection instruction, the secondary protection electromagnetic switch is driven and controlled to work through secondary protection, the normally closed live wire main contact of the secondary protection electromagnetic switch is disconnected, the normally open live wire main contact of the secondary protection electromagnetic switch is closed, the secondary protection bootstrap power supply is electrified to provide self-holding current for the secondary protection electromagnetic switch, the fact that the electric heating device is disconnected with the live wire of the mains supply is guaranteed, the phenomenon that the electric heating device is heated to work all the time and serious consequences are generated is avoided, and therefore the safety protection effect is achieved. The control circuit has the advantages that the whole control circuit is scientific, novel, simple and practical in structure, functions of common electronic components are fully utilized, and the control circuit with an ingenious structure is combined, so that the whole control circuit is low in cost and safe and reliable in work.)

1. The utility model provides a control circuit of bread oven, includes control circuit, characterized by, control circuit includes following functional module circuit:

the microcontroller (1) coordinates and controls the operation of each functional module circuit in the whole control circuit;

the primary control drive (3) is connected with the microcontroller (1);

the primary electromagnetic control switch (5) is connected with the primary control drive (3), the microcontroller (1) controls the switching state of the primary electromagnetic control switch through the primary control drive (3), and a main contact of the primary electromagnetic control switch is connected with commercial power;

the secondary protection drive (4) is connected with the microcontroller (1);

the secondary protection electromagnetic switch (6) is connected with the secondary protection drive (4), the microcontroller (1) controls the switching state of the secondary protection drive (4), and the main contact of the secondary protection electromagnetic switch is connected with the main contact of the primary electromagnetic control switch (5) in series;

and the electric heating device (7) is connected with a main contact of the secondary protection electromagnetic switch (6) in series and forms a current loop with the mains supply.

2. The control circuit of the toaster as claimed in claim 1, wherein said control circuit further comprises the following functional block circuits: and the primary control bootstrap power supply (8) is connected with the electric heating device (7) in series, and the electric heating device (7) is used as a voltage reducer to form a current loop with the mains supply.

3. The control circuit of the toaster as claimed in claim 1 or 2, wherein said control circuit further comprises the following functional block circuits: and the secondary protection bootstrap power supply (9) is connected with the main contact of the primary electromagnetic control switch (5) in series and provides a self-holding bootstrap control power supply for the secondary protection electromagnetic switch (6).

4. The control circuit of the toaster as claimed in claim 3, wherein said control circuit further comprises the following functional block circuits:

the control button (2) is connected with the microcontroller (1) and is used for man-machine interaction;

and the gear shifting circuit (10) is connected with the microcontroller (1) and the primary control drive (3) and is used for power regulation of the bread oven.

5. The control circuit of the toaster according to claim 4, wherein said microcontroller (1) is a single-chip microcomputer (U1);

a power supply pin of the singlechip (U1) is connected with the anode output end of a working power supply (VDD);

the grounding pin of the singlechip (U1) is connected with the public ground;

a third high-frequency filter capacitor (C3) and a fourth discharge resistor (R4) for protecting the single chip microcomputer (U1) are connected in parallel between a power supply pin and a grounding pin of the single chip microcomputer (U1);

a first output pin of the singlechip (U1) controls a primary electromagnetic control switch (5) to work;

a second output pin of the singlechip (U1) controls the starting work of the secondary protection electromagnetic switch (6);

an input pin of the singlechip (U1) is connected with the control button (2).

6. The control circuit of the toaster according to claim 5, wherein said primary electromagnetic control switch (5) is an electromagnetically closed electromagnetic switch (K1);

the primary control drive (3) comprises a first NPN type triode (Q1); one end of a coil of the electromagnetic switch (K1) is connected with the positive electrode output end of the secondary protection bootstrap power supply (9), and the other end of the coil is connected with the c electrode of the first NPN type triode (Q1); the e pole of the first NPN type triode (Q1) is connected with the common ground; the b pole of the first NPN type triode (Q1) is connected with the first output pin of the singlechip (U1) through a twelfth resistor (R12); an output signal short-circuit button (SW3) is connected between a first output pin of the single chip microcomputer (U1) and the common ground; a third freewheeling diode (D3) is connected in parallel with two ends of a coil of the electromagnetic switch (K1); the gear shifting circuit (10) comprises a high-grade potentiometer (WR1), one end of the gear shifting potentiometer (WR1) is connected with the public ground, the other end of the gear shifting potentiometer is connected with a first output pin of the single chip microcomputer (U1), an adjustable end in the middle of the gear shifting potentiometer is connected with a third input pin of the single chip microcomputer (U1), and a first output pin of the single chip microcomputer (U1) is connected with the public ground through a fourth high-frequency filter capacitor (C4).

7. The control circuit of toaster according to claim 6, wherein said secondary protective electromagnetic switch (6) is a relay (K2) closed by electromagnetic control, one end of coil of relay (K2) is connected to common ground, and one end of coil of relay (K2) is used as power connection end;

the secondary protection bootstrap power supply (9) comprises a fifth rectifier diode (D5), the anode of the fifth rectifier diode (D5) is connected with the normally-open live wire main contact of the relay (K2) through a thirteenth current-limiting step-down resistor (R13), and the cathode of the fifth rectifier diode (D5) is connected with the power connection end of the coil of the relay (K2); a fifth energy storage capacitor (C5) is connected in parallel with two ends of a coil of the relay (K2);

the secondary protection driver (4) comprises a second NPN type triode (Q2) and a third PNP type triode (Q3); the e pole of the third PNP type triode (Q3) is connected with the positive pole of the output end (VCC) of the primary control bootstrap power supply (8), the b pole of the third PNP type triode (Q3) is connected with the positive pole of the output end (VCC) of the primary control bootstrap power supply (8) through an eleventh resistor (R11), the c pole of the third PNP type triode (Q3) is connected with the power connection end of the coil of the relay (K2) through a fourth isolation diode (D4), and the c pole of the third PNP type triode (Q3) is connected with the anode of the fourth isolation diode (D4);

a pole b of the third PNP type triode (Q3) is connected with a pole c of the second NPN type triode (Q2) through a tenth resistor (R10), a pole b of the second NPN type triode (Q2) is connected with a second output pin of the single chip microcomputer (U1) through a ninth resistor (R9), and a pole e of the second NPN type triode (Q2) is connected with the common ground; the normally closed live wire main contact input end of the relay (K2) is connected with the live wire main contact output end of the electromagnetic switch (K1).

8. The control circuit of the toaster according to claim 7, wherein said control button (2) comprises a two-way tact button circuit; the first light touch key circuit comprises an eighth resistor (R8), a first light emitting diode (LED1), a first light touch key (SW1) and a sixth resistor (R6) which are sequentially connected in series, the whole series body is connected with the anode output end of a working power supply (VDD) through the eighth resistor (R8) and is connected with the public ground through the sixth resistor (R6), and the series connection position between the first light emitting diode (LED1) and the first light touch key (SW1) is connected with a first input pin of a single chip microcomputer (U1); the second light touch key circuit comprises an eighth resistor (R8), a second light emitting diode (LED2), a second light touch key (SW2) and a seventh resistor (R7) which are sequentially connected in series, the whole series body is connected with the anode output end of a working power supply (VDD) through the eighth resistor (R8) and is connected with the public ground through the seventh resistor (R7), and the series connection position between the second light emitting diode (LED2) and the second light touch key (SW2) is connected with a second input pin of the single chip microcomputer (U1).

9. The control circuit of the toaster oven as claimed in claim 8, wherein said electric heating means (7) is connected at one end to the normally closed main contact of the relay (K2) and at the other end to the common ground, the electric heating means (7) being heating wires (H1-H3), the heating wires (H1-H3) being provided with center taps;

the primary control bootstrap power supply (8) comprises a primary control half-wave rectification circuit, the primary control half-wave rectification circuit comprises a first rectifying diode (D1), the anode of the first rectifying diode (D1) is connected with a middle tap of the heating wires (H1-H3), the cathode of the first rectifying diode (D1) is sequentially connected with a first voltage-reducing current-limiting resistor (R1) and a second resistor (R2) in series, and the serial point between the first voltage-reducing current-limiting resistor (R1) and the second resistor (R2) is connected with the common ground through a first capacitor (C1); the series point between the first resistor (R1) and the second resistor (R2) is the output end (VCC) of the primary control bootstrap power supply (8); a second resistor (R2) is connected to common ground through a zener diode (DZ 1); a third resistor (R3) as a dummy load is connected in parallel to both ends of the zener diode (DZ 1).

Technical Field

The invention relates to the field of food processing, in particular to a bread oven.

Background

The control circuit of the existing automatic toaster generally comprises the following functional module circuits:

the microcontroller coordinately controls the work of each functional module circuit in the whole control circuit;

the primary control drive is connected with the microcontroller;

the primary electromagnetic control switch is connected with the primary control drive, the microcontroller controls the switching state of the primary electromagnetic control switch through the primary control drive, and a main contact of the primary electromagnetic control switch is connected with a mains supply;

and the electric heating device is connected with the main contact of the primary electromagnetic control switch in series and forms a current loop with the mains supply.

The control circuit has a relatively simple structure, but has some potential safety hazards, when the primary electromagnetic control switch fails and the main contacts of the primary electromagnetic control switch are bonded or welded together and cannot be disconnected, the electric heating device can generate heat all the time due to the fact that the power supply cannot be automatically disconnected, serious consequences are generated, bread is burnt if the electric heating device is light, the bread oven is burnt if the electric heating device is heavy, and even the potential fire control hazards exist.

Disclosure of Invention

In order to solve the above-mentioned defects of the control circuit of the prior bread oven, the invention provides a safer and more reliable control circuit of the bread oven.

In order to achieve the purpose, the invention adopts the technical scheme that:

the utility model provides a control circuit of bread oven, includes control circuit, characterized by, control circuit includes following functional module circuit:

the microcontroller coordinately controls the work of each functional module circuit in the whole control circuit;

the primary control drive is connected with the microcontroller;

the primary electromagnetic control switch is connected with the primary control drive, the microcontroller controls the switching state of the primary electromagnetic control switch through the primary control drive, and a main contact of the primary electromagnetic control switch is connected with a mains supply;

the secondary protection drive is connected with the microcontroller;

the secondary protection electromagnetic switch is connected with the secondary protection drive, the microcontroller controls the switching state of the secondary protection drive through the secondary protection drive, and the main contact of the secondary protection electromagnetic switch is connected with the main contact of the primary electromagnetic control switch in series;

and the electric heating device is connected with the main contact of the secondary protection electromagnetic switch in series and forms a current loop with the mains supply.

Further, the control circuit further comprises the following functional module circuits: the first-stage control bootstrap power supply is connected with the electric heating device in series, and the electric heating device is used as a voltage reducer to form a current loop with the mains supply.

Further, the control circuit further comprises the following functional module circuits: and the secondary protection bootstrap power supply is connected in series with the main contact of the primary electromagnetic control switch and provides a self-holding bootstrap control power supply for the secondary protection electromagnetic switch.

Further, the control circuit further comprises the following functional module circuits:

the control button is connected with the microcontroller and is used for man-machine interaction;

and the gear shifting circuit is connected with the microcontroller and the primary control drive and is used for regulating the power of the bread oven.

The working principle of the whole technical scheme is as follows: when the primary electromagnetic control switch cannot be disconnected due to the fact that the main contacts are bonded or welded together, the microcontroller sends a forced disconnection instruction, the secondary protection electromagnetic switch is driven and controlled to work through secondary protection, the normally closed live wire main contact of the secondary protection electromagnetic switch is disconnected, the normally open live wire main contact of the secondary protection electromagnetic switch is closed, the secondary protection bootstrap power supply is electrified to provide self-holding current for the secondary protection electromagnetic switch, the fact that the electric heating device is disconnected with the live wire of the mains supply is guaranteed, the phenomenon that the electric heating device is heated to work all the time and serious consequences are generated is avoided, and therefore the safety protection effect is achieved.

From the above, compared with the prior art, the invention has the following advantages: the control circuit of the bread oven is connected with a secondary protection electromagnetic switch in series on the basis of a primary electromagnetic control switch, so that when the primary electromagnetic control switch cannot be disconnected due to the fact that main contacts are bonded or welded together, a microcontroller sends out a forced disconnection instruction, the secondary protection electromagnetic switch is controlled to work through secondary protection driving, the fact that a live wire of an electric heating device and mains supply is disconnected is guaranteed, the situation that the electric heating device heats and works all the time to generate serious results is avoided, and the safety protection effect is achieved; the whole control circuit is scientific, novel, simple and practical in structure, functions of common electronic components are fully utilized, and the control circuit with an ingenious structure is combined, so that the whole control circuit is low in cost and safe and reliable in work.

Drawings

Fig. 1 is a block circuit diagram of a preferred embodiment of the present invention.

Fig. 2 is a circuit schematic of a preferred embodiment of the present invention.

The main reference numbers: the device comprises a microcontroller 1, a control button 2, a primary control drive 3, a secondary protection drive 4, a primary electromagnetic control switch 5, a secondary protection electromagnetic switch 6, an electric heating device 7, a primary control bootstrap power supply 8, a secondary protection bootstrap power supply 9 and a gear shifting circuit 10.

Detailed Description

The invention and its advantageous technical effects are explained in further detail below with reference to the drawings and preferred embodiments.

It should be noted that descriptions related to "first", "second", etc. in the present invention are used for descriptive purposes only, as a distinction of technical features in the same technical terms, and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the technical features.

Referring to fig. 1, the control circuit of the toaster according to the preferred embodiment of the present invention comprises a control circuit, wherein the control circuit comprises the following functional module circuits:

the microcontroller 1 coordinates and controls the work of each functional module circuit in the whole control circuit;

the primary control drive 3 is connected with the microcontroller 1;

the primary electromagnetic control switch 5 is connected with the primary control drive 3, the microcontroller 1 controls the switching state of the primary electromagnetic control switch through the primary control drive 3, and a main contact of the primary electromagnetic control switch is connected with commercial power;

the secondary protection drive 4 is connected with the microcontroller 1;

the secondary protection electromagnetic switch 6 is connected with the secondary protection drive 4, the microcontroller 1 controls the switching state of the secondary protection drive 4 through the secondary protection drive 4, and the main contact of the secondary protection electromagnetic switch is connected with the main contact of the primary electromagnetic control switch 5 in series;

the electric heating device 7 is connected with a main contact of the secondary protection electromagnetic switch 6 in series and forms a current loop with the mains supply;

the primary control bootstrap power supply 8 is connected with the electric heating device 7 in series, and the electric heating device 7 is used as a voltage reducer to form a current loop with the mains supply;

the secondary protection bootstrap power supply 9 is connected with the main contact of the primary electromagnetic control switch 5 in series and provides a self-holding bootstrap control power supply for the secondary protection electromagnetic switch 6;

the control button 2 is connected with the microcontroller 1 and is used for man-machine interaction;

a gear shifting circuit 10, which is connected with the microcontroller 1 and the primary control drive 3, is used for power regulation of the toaster.

Referring to fig. 2, it is further preferable that the microcontroller 1 is a single chip microcomputer U1;

a power supply pin of the singlechip U1 is connected with the anode output end of a working power supply VDD;

the grounding pin of the singlechip U1 is connected with the public ground;

a third high-frequency filter capacitor C3 and a fourth discharge resistor R4 which are used for protecting the single chip microcomputer U1 are connected in parallel between a power supply pin and a grounding pin of the single chip microcomputer U1;

a first output pin of the singlechip U1 controls the first-level electromagnetic control switch 5 to work;

a second output pin of the singlechip U1 controls the starting work of the secondary protection electromagnetic switch 6;

and an input pin of the singlechip U1 is connected with the control button 2.

With reference to fig. 2, it is further preferred that said primary electromagnetic control switch 5 is an electromagnetic control closed electromagnetic switch K1;

the primary control driver 3 comprises a first NPN type triode Q1; one end of a coil of the electromagnetic switch K1 is connected with the positive electrode output end of the secondary protection bootstrap power supply 9, and the other end of the coil is connected with the c electrode of the first NPN type triode Q1; the e pole of the first NPN type triode Q1 is connected with the common ground; a b pole of the first NPN type triode Q1 is connected with a first output pin of the singlechip U1 through a twelfth resistor R12; an output signal short-circuit button SW3 is connected between a first output pin of the singlechip U1 and the common ground; a third freewheeling diode D3 is connected in parallel with two ends of a coil of the electromagnetic switch K1; the main contact of the electromagnetic switch K1 is respectively connected with the live wire and the zero wire of the commercial power, and the common ground is connected with the zero wire;

the gear shifting circuit 10 comprises a high-grade potentiometer WR1, one end of the gear shifting potentiometer WR1 is connected with the public ground, the other end of the gear shifting potentiometer WR1 is connected with a first output pin of a single chip microcomputer U1, an adjustable end in the middle of the gear shifting potentiometer WR1 is connected with a third input pin of the single chip microcomputer U1, and the first output pin of the single chip microcomputer U1 is connected with the public ground through a fourth high-frequency filter capacitor C4. The singlechip U1 acquires the voltage value of the shift potentiometer WR1 through the third input pin to control the output level of the first output pin of the singlechip U1, so that the on-off time of the first NPN type triode Q1 is controlled.

Referring to fig. 2, it is further preferable that the secondary protection electromagnetic switch 6 is a relay K2 closed by electromagnetic control, one end of the coil of the relay K2 is connected to the common ground, and one end of the coil of the relay K2 is used as a power connection terminal;

the secondary protection bootstrap power supply 9 comprises a fifth rectifier diode D5, the anode of the fifth rectifier diode D5 is connected with the normally-open live wire main contact of the relay K2 through a thirteenth current-limiting step-down resistor R13, and the cathode of the fifth rectifier diode D5 is connected with the power connection end of the coil of the relay K2; a fifth energy storage capacitor is connected in parallel at two ends of a coil of the relay K2

C5; the thirteenth current-limiting voltage-reducing resistor R13 and the coil of the relay K2 form a voltage divider.

The secondary protection driver 4 comprises a second NPN type triode Q2 and a third PNP type triode Q3; the e pole of the third PNP triode Q3 is connected to the positive pole of the output terminal VCC of the primary control bootstrap power supply 8, the b pole of the third PNP triode Q3 is connected to the positive pole of the output terminal VCC of the primary control bootstrap power supply 8 through the eleventh resistor R11, the c pole of the third PNP triode Q3 is connected to the power connection end of the coil of the relay K2 through the fourth isolation diode D4, and the c pole of the third PNP triode Q3 is connected to the anode of the fourth isolation diode D4; the unidirectional conductive characteristic of a fourth isolating diode D4 is utilized to isolate two paths of power supplies connected to a coil of a relay K2;

a pole b of the third PNP triode Q3 is connected to a pole c of the second NPN triode Q2 through a tenth resistor R10, a pole b of the second NPN triode Q2 is connected to a second output pin of the single chip microcomputer U1 through a ninth resistor R9, and a pole e of the second NPN triode Q2 is connected to the common ground; the normally closed live wire main contact input end of the relay K2 is connected with the live wire main contact output end of the electromagnetic switch K1.

Referring to fig. 2, it is further preferable that the control button 2 includes two paths of tact key circuits; the first path of light touch key circuit comprises an eighth resistor R8, a first light emitting diode LED1, a first light touch key SW1 and a sixth resistor R6 which are sequentially connected in series, the whole series body is connected with the positive electrode output end of a working power supply VDD through the eighth resistor R8 and is connected with the public ground through the sixth resistor R6, and the series connection position between the first light emitting diode LED1 and the first light touch key SW1 is connected with a first input pin of a single chip microcomputer U1; the second light touch key circuit comprises an eighth resistor R8, a second light emitting diode LED2, a second light touch key SW2 and a seventh resistor R7 which are sequentially connected in series, the whole series body is connected with the positive electrode output end of a working power supply VDD through the eighth resistor R8 and is connected with the public ground through the seventh resistor R7, and the series connection position between the second light emitting diode LED2 and the second light touch key SW2 is connected with a second input pin of the singlechip U1; the first light-emitting diode LED1 and the second light-emitting diode LED2 are turned on when the first light touch key SW1 and the second light touch key SW2 are pressed, and the prompt effect of effective key connection is achieved.

Referring to fig. 2, it is further preferable that one end of the electric heating device 7 is connected with a normally closed live wire main contact of the relay K2, and the other end is connected with the public ground, the electric heating device 7 is heating wires H1-H3, and the heating wires H1-H3 are provided with middle taps;

the primary control bootstrap power supply 8 comprises a primary control half-wave rectification circuit, the primary control half-wave rectification circuit comprises a first rectification diode D1, the anode of the first rectification diode D1 is connected with the middle taps of the heating wires H1-H3, the cathode of the first rectification diode D1 is sequentially connected with a first voltage-reducing current-limiting resistor R1 and a second resistor R2 in series, and the serial point between the first voltage-reducing current-limiting resistor R1 and the second resistor R2 is connected with the common ground through a first capacitor C1; the series point between the first resistor R1 and the second resistor R2 is the output terminal VCC of the primary control bootstrap power supply 8; the second resistor R2 is connected to common ground through a zener diode DZ 1; a third resistor R3 as a dummy load is connected in parallel across the zener diode DZ 1. The resistance of the electric heating wire is skillfully used as the voltage-reducing current-limiting resistance of the first-stage control half-wave rectification circuit, so that various index parameters of the first voltage-reducing current-limiting resistance R1 are reduced, the heat generation of the circuit is reduced, the service life of the circuit is prolonged, the fault generation of the circuit is reduced, and the effects of energy conservation and environmental protection are achieved.

In the above description, the specific types and parameters of each component selected in the circuit may be matched and adjusted according to actual use conditions, which belongs to the common technology in the prior art, and further, for the contents that are conventionally used in the prior art, such as structures, processes, peripheral circuits such as sensors, and other unnecessary technical features, which belong to the conventional technology, are not described in detail in order to save space. The processing technology, parts and components which are not disclosed are processed according to the conventional technology in the prior art, the common single chip microcomputer with 8 pins can be selected as the single chip microcomputer U1, the use requirement is met, and the additional illustration is omitted for space saving. The specific type of the integrated circuit chip of the singlechip U1 can refer to the technical data description disclosed by the singlechip U1. In the automatic control process, the programmed control program can be burnt in the singlechip U1 to operate, and the work of the circuit is controlled.

The working principle of the invention is as follows: when the electromagnetic switch K1 of the primary electromagnetic control switch 5 is bonded or welded together to be unable to be disconnected, the single chip microcomputer U1 sends a high level signal to the second output pin of the single chip microcomputer U1, the second NPN type triode Q2 is conducted, the b pole of the third PNP type triode Q3 is changed from level to low level, the third PNP type triode Q3 is conducted, the relay K2 is powered on to work, the fourth isolation diode D4 is conducted in the forward direction, the coil of the relay K2 is powered on to act, the normally closed live wire main contact of the relay K2 is disconnected, and the normally open live wire main contact is closed; after the main contact of the normally-open live wire is closed, the secondary protection bootstrap power supply 9 is powered on and carries out half-wave rectification through a fifth rectifier diode D5 to provide self-holding current for the coil of the relay K2, and the self-holding current cannot disappear until the main contact of the electromagnetic switch K1 is disconnected; under the condition that the main contact of the electromagnetic switch K1 is closed, the normally closed live wire main contact of the relay K2 connected with the electromagnetic switch K1 in series is disconnected, so that the live wire of the electric heating device 7 and the commercial power can be disconnected, the serious result caused by the fact that the electric heating device 7 always works by heating is avoided, and the safety protection effect is achieved.

The invention is not limited in any way by the above description and the embodiments, which are disclosed and described above, but the control concept and method of the invention can be implemented or adapted in different ways and also fall within the scope of the claims.