Induction hob device

Abstract

The invention relates to an induction hob device (10a; 10b) comprising: at least one heating inductor (12a); a detection unit (20a) for measuring properties of an induction load of the heating inductor (12a); and at least one switching unit (22a) which is designed to establish an electrically conductive connection between the heating inductor (12a) and the detection unit (20a) for a detection mode and to disconnect said connection for a heating mode. In order to improve efficiency, according to invention the switching unit (20a) has two MOSFETs (24a, 26a) which form a bidirectional switch for establishing and disconnecting the electrically conductive connection between the heating inductor (12a) and the detection unit (20a).

Description

[0001] Induction hob device

[0002] The invention relates to an induction hob device according to the preamble of claim 1.

[0003] Induction hobs with heating inductors and a detection unit for measuring properties of an induction load of the heating inductor, for example, for pan detection, are already known from the prior art. In many cases, the heating inductors are used as sensors, so a connection between one of the heating inductors and the detection unit, which may include a Colpitts oscillator, for example, must be established for detection operation and disconnected for heating operation, with each of the heating inductors being connected to the detection unit in turn.To establish and separate the connections between heating inductors and detection unit, commercially available multiplexers have been used up to now. However, in addition to their comparatively high cost, they have the disadvantage that they are only available with a number of channels corresponding to a power of 2, for example with 2 or 4 or 8 or 16 channels, which means that the number of channels often does not correspond to the number of heating inductors present and efficiency is reduced.

[0004] The object of the invention is, in particular but not limited to, to provide a generic device with improved properties in terms of efficiency. This object is achieved according to the invention by the features of claim 1, while advantageous embodiments and further developments of the invention can be found in the subclaims.

[0005] The invention relates to an induction hob device comprising at least one heating inductor, a detection unit for measuring properties of an induction load of the heating inductor, and at least one switching unit designed to establish an electrically conductive connection between the heating inductor and the detection unit for detection operation and to break it for heating operation. It is proposed that the switching unit comprise two MOSFETs forming a bidirectional switch for establishing and breaking the electrically conductive connection between the heating inductor and the detection unit.

[0006] Such a configuration advantageously provides an induction hob device with improved efficiency properties. In particular, commercially available multiplexers can be replaced by discrete components of the induction hob device, thereby improving cost efficiency. At the same time, increased flexibility is also achieved because a number of switching units can be precisely adapted to a number of heating inductors to be used as inductive sensors. Furthermore, the use of MOSFETs, which form a bidirectional switch for establishing and breaking the electrically conductive connection between the heating inductor and the detection unit, has the advantage that MOSFETs have low on-resistances, whereby the influence of the additional electrical resistances of the MOSFETs on an oscillation range of the detection unit can be kept to a minimum.Furthermore, MOSFETs advantageously have low parasitic capacitances, which allows noise coupling from the high-voltage side, which is formed by the inverters and the heating inductors, to the low-voltage side, where the detection unit is located, to be kept to a minimum.

[0007] The induction hob device is designed as a part, in particular as a subassembly, of an induction hob. The induction hob device can also comprise the entire induction hob. The induction hob device comprises at least one heating inductor, which, in heating mode, provides energy in the form of an alternating electromagnetic field to at least one object, in particular to a cooking utensil. The induction hob device could have at least two, in particular at least three, advantageously at least four, particularly advantageously at least five, preferably at least eight, and particularly preferably several heating inductors, each of which could inductively provide energy in heating mode, in particular to a single object or to at least two or more objects. At least some of the heating inductors could be arranged in close proximity to one another, for example in a row and / or in the form of a matrix.The induction hob device can comprise an inverter unit with at least two inverter switching elements for supplying power to the at least one heating inductor. Alternatively, the inverter unit can also be part of an induction hob having the induction hob device. The inverter switching elements of the inverter unit can be designed as semiconductor switching elements, in particular as transistors, for example as a metal oxide semiconductor field-effect transistor (MOSFET) or an organic field-effect transistor (OFET), advantageously as a bipolar transistor with preferably an insulated gate electrode (IGBT).

[0008] The detection unit is provided for measuring properties of an induction load of the heating inductor, for example, and without limitation, for measuring the presence of an object, in particular a cooking utensil or a foreign metal object, above the heating inductor and / or for measuring a degree of coverage of the heating inductor by the object and / or for measuring material properties of the object and / or the like. Preferably, the detection unit has at least one oscillator, for example a Colpitts oscillator, preferably a Clapp oscillator, which is provided for applying a high-frequency detection signal, in particular with a frequency between 50 kHz and 100 MHz, preferably with a frequency of at least 0.8 MHz and at most 2 MHz, to the heating inductor during detection operation.

[0009] The switching unit is designed to establish the electrically conductive connection between the heating inductor and the detection unit for detection operation and to separate it for heating operation. For this purpose, it comprises two MOSFETs that form the bidirectional switch. In addition to the MOSFETs, the switching unit may comprise further elements, for example, further semiconductor switching elements and / or capacitors and / or electrical resistors and / or the like.

[0010] In this document, numerals such as "first" and "second," which precede certain terms, serve only to distinguish between objects and / or to associate objects with one another and do not imply a total number and / or ranking of the objects. In particular, a "second object" does not necessarily imply the presence of a "first object." "Intended" should be understood to mean specially programmed, designed, and / or equipped. The fact that an object is intended for a specific function should be understood to mean that the object fulfills and / or performs this specific function in at least one application and / or operating state.

[0011] It is further proposed that the MOSFETs be electrically connected in series and arranged in a common source configuration. This advantageously enables a particularly simple design of the switching unit and thus further increases efficiency. Alternatively, the MOSFETs could be electrically connected in series and arranged in a common drain configuration. Alternatively, it would also be conceivable for one of the MOSFETs to be designed as an n-channel MOSFET and one of the MOSFETs as a p-channel MOSFET, and for these to be arranged electrically parallel to one another and in a common source configuration.

[0012] At least one or both of the MOSFETs in the switching unit could therefore be designed as p-channel MOSFETs. However, in an advantageous embodiment, it is proposed that the MOSFETs are each designed as n-channel MOSFETs. Such a design can further improve efficiency. Firstly, n-channel MOSFETs are significantly more widely used in a wide variety of applications than p-channel MOSFETs and are therefore also more cost-effective and available on the market from various manufacturers with the characteristics desired for use in the induction hob device. Secondly, n-channel MOSFETs have lower on-resistances and lower parasitic capacitances than p-channel MOSFETs, which enables particularly reliable and trouble-free operation of the induction hob device.

[0013] Furthermore, it is proposed that the switching unit have at least one capacitor, which is electrically conductively connected to the source terminals and gate terminals of the two MOSFETs. Such a configuration can advantageously further increase flexibility. In particular, voltages of the high-frequency detection signals provided by the detection unit during detection operation can have amplitudes that are higher than a value of a supply voltage provided by a voltage source of the switching unit.At the same time, however, average values ​​of the voltages of the high-frequency detection signals can be below the difference between the supply voltage and a required threshold voltage for activating the MOSFETs of the switching unit, in order to always ensure a sufficient gate-source voltage at the MOSFETs during detection operation, which is greater than the threshold voltage, so that the MOSFETs always remain active during detection operation. Furthermore, it is proposed that the capacitor have a capacitance of at least 470 pF and at most 4.7 nF. This allows the aforementioned advantages of the capacitor to be achieved particularly reliably for the preferred frequency range of the high-frequency detection signal provided by the detection unit in detection operation, of at least 0.8 MHz and at most 2 MHz.

[0014] It is further proposed that the switching unit have a voltage source for providing a supply voltage which corresponds at least to a required threshold voltage for activating the MOSFETs. This can advantageously further improve efficiency. In particular, a simplified structure can be enabled. The switching unit can be arranged on a circuit board, for example. It is also proposed that the switching unit have at least one semiconductor switching element for activating and deactivating the MOSFETs by means of the voltage source and a control terminal for applying a control signal to the semiconductor switching element. Such a configuration can advantageously enable particularly reliable and rapid switching of the switching unit for establishing and breaking the electrically conductive connection between the heating inductor and the detection unit.Preferably, the semiconductor switching element is connected to the respective gate terminals of the MOSFETs and to an output of the voltage source. The semiconductor switching element can be designed as a field-effect transistor, for example as a MOSFET, in particular as an n-channel MOSFET or as a p-channel MOSFET. Alternatively, the semiconductor switching element can be designed as a bipolar transistor, in particular as an NPN bipolar transistor or as a PNP bipolar transistor. It is also conceivable for the switching unit to have two or more interconnected semiconductor switching elements for activating and deactivating the MOSFETs by means of the voltage source. The semiconductor switching elements could, for example, be arranged in an amplifier circuit to amplify the supply voltage of the voltage source.Furthermore, it is proposed that the switching unit have at least two electrical resistors that are connected to the voltage source and form a voltage divider. This can advantageously further improve flexibility. In addition, operational reliability can advantageously be increased. If the switching unit has at least two electrical resistors that are connected to the voltage source and form a voltage divider, the supply voltage provided by the voltage source can exceed a maximum permissible gate-source voltage of the MOSFETs of the switching unit without damaging them. For example, the voltage source can be provided to provide a DC voltage of 24 volts as the supply voltage, and the maximum permissible gate-source voltage of the MOSFETs can be 8 volts, for example.If the switching unit has at least two electrical resistors connected to the voltage source and forming the voltage divider, a suitable arrangement and selection of the values ​​of the electrical resistors can ensure that no voltage drop greater than 8 volts occurs between the gate terminals and the source terminals of the MOSFETs, despite the higher supply voltage. Preferably, a first electrical resistor of the switching unit is arranged electrically in series with the voltage source, and a second electrical resistor is arranged electrically in parallel with the voltage source. Preferably, the second electrical resistor is electrically conductively connected to the source terminals and the gate terminals of the two MOSFETs.

[0015] It is further proposed that the induction hob device have at least one further heating inductor and at least one further switching unit, which is designed at least substantially identically to the switching unit and is provided to establish an electrically conductive connection between the further heating inductor and the detection unit for a detection operation and to separate it for a heating operation. Such a configuration can advantageously further improve efficiency. In particular, it can enable properties of induction loads of the heating inductor and of the at least one further heating inductor to be measured by means of a single detection unit. The induction hob device preferably has a number of switching units which corresponds to a number of heating inductors that are to be used simultaneously as inductive sensors.Furthermore, it is proposed that the induction hob device comprise a control unit designed to activate the switching unit and the further switching unit at temporally separate intervals. This advantageously enables reliable and accurate detection. In particular, it can be ensured that the detection unit is electrically connected to only one of the heating inductors during detection mode.For example, the control unit may be provided to activate the switching unit in a first interval to establish the electrically conductive connection between the heating inductor and the detection unit and, in a subsequent second interval, to deactivate the switching unit and activate the further switching unit to separate the electrically conductive connection between the heating inductor and the detection unit and to establish an electrically conductive connection between the further heating inductor and the detection unit.The control unit can be provided to control the switching unit with inverting logic, wherein the control unit is then provided to permanently apply a control signal to the control terminal of the switching unit during heating operation in order to set the voltage source to a reference potential by means of the semiconductor switching element so that, during heating operation, the required threshold voltage for activation does not drop between the gate terminals and the source terminals of the MOSFETs and these remain non-conductive. During detection operation, when controlling the switching unit with inverting logic, the control unit is provided to interrupt the control signal at the control terminal in order to activate the MOSFETs. Alternatively, the control unit could also be provided to control the switching unit with non-inverting logic.Preferably, the control unit is designed to control all switching units of the induction hob device in the same way.

[0016] Furthermore, it is proposed that the control unit include a shift register. This allows for further improved efficiency, as the number of signals required to control the switching units can be reduced. The shift register is provided for controlling the switching units of the induction hob device. For example, the induction hob device could have a total of four heating inductors and four switching units, and in this case, the shift register could have three inputs and four outputs, with each of the outputs being connected to a respective control input of the switching units, thus allowing the four switching units to be controlled with a total of three signals at the three inputs of the shift register.

[0017] In an alternative advantageous embodiment, it is proposed that the control unit comprise a binary decoder. Such a configuration can further improve efficiency, since the number of signals for controlling the switching units can be further reduced. The binary decoder is provided for controlling the switching units of the induction hob device.

[0018] For example, the induction hob device could have a total of four heating inductors and four switching units, and the binary decoder could in this case have two binary inputs and four analog outputs, each of the outputs being connected to a control input of the switching units, so that the four switching units can be controlled with a total of two binary signals at the binary inputs of the binary decoder.

[0019] The invention further relates to an induction hob with at least one induction hob device according to one of the previously described embodiments. Such an induction hob is characterized in particular by its advantageous properties with regard to increased efficiency, which can be achieved by the induction hob device.

[0020] The induction hob device is not intended to be limited to the application and embodiment described above. In particular, the induction hob device may have a number of individual elements, components, and units that differs from the number stated herein to fulfill a functionality described herein.

[0021] Further advantages will become apparent from the following description of the drawings. The drawings illustrate two embodiments of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also conveniently consider the features individually and combine them into useful further combinations. They show:

[0022] Fig. 1 shows an induction hob with an induction hob device in a schematic representation,

[0023] Fig. 2 is a schematic electrical diagram of a part of the induction hob device with a heating inductor, a detection unit and a switching unit comprising two MOSFETs forming a bidirectional switch for establishing and breaking an electrically conductive connection between the heating inductor and the detection unit,

[0024] Fig. 3 two schematic diagrams showing a time course of a gate-source voltage of the MOSFETs and an output voltage of the switching unit,

[0025] Fig. 4 is a further schematic electrical circuit diagram of a part of the induction hob device with the switching unit, a further switching unit and a control unit,

[0026] Fig. 5 is a schematic diagram of a shift register of the control unit and

[0027] Fig. 6 shows a further embodiment of an induction hob device with a control unit which comprises a binary decoder.

[0028] Figure 1 shows a schematic representation of an induction hob 60a. The induction hob 60a has an induction hob device 10a. The induction hob device 10a comprises at least one heating inductor 12a. In the present case, the induction hob device 10a comprises the heating inductor 12a and three further heating inductors 14a, 16a, 18a. The heating inductors 12a, 14a, 16a, 18a are arranged below a hob plate 62a of the induction hob 60a and are intended to provide energy in the form of an alternating electromagnetic field to at least one object (not shown), for example, a cooking utensil, on the hob plate 62a during heating operation. The induction hob device 10a is not limited to the number of four heating inductors 12a, 14a, 16a, 18a, but could alternatively have any number of heating inductors 12a, 14a, 16a, 18a greater than or equal to one without departing from the scope of the present invention.The induction hob device 10a comprises a detection unit 20a. The detection unit 20a is provided for measuring properties of an induction load of the heating inductor 12a, for example, the presence of cooking utensils above the heating inductor 12a and / or a degree of coverage of the heating inductor 12a and / or a material of the cooking utensil and / or the like. In a detection mode, the heating inductor 12a functions as an inductive sensor and is electrically connected to the detection unit 20a. The detection unit 20a comprises an oscillator (not shown), which can be designed, for example, as a Colpitts oscillator or a Clapp oscillator or the like. The detection unit 20a is provided in the present case to apply a high-frequency detection signal with a frequency between 0.8 MHz and 2 MHz to the heating inductor 12a in the detection mode.The detection unit 20a is also provided in the present case for measuring properties of induction loads of the further heating inductors 14a, 16a, 18a, which can be electrically connected to the detection unit 20a for a respective detection operation and function as inductive sensors.

[0029] Figure 2 shows a schematic electrical circuit diagram of a portion of the induction hob device 10a. The induction hob device 10a comprises at least one switching unit 22a. The switching unit 22a is provided to establish an electrically conductive connection between the heating inductor 12a and the detection unit 20a for detection operation and to break it for heating operation. The switching unit 22a has two MOSFETs 24a, 26a. The MOSFETs 24a, 26a form a bidirectional switch for establishing and breaking the electrically conductive connection between the heating inductor 12a and the detection unit 20a. In this case, the MOSFETs 24a, 26a are each designed as n-channel MOSFETs. The MOSFETs 24a, 26a have essentially identical characteristics, which differ from each other at most within the scope of usual manufacturing tolerances.

[0030] MOSFET 24a has a source terminal 30a, a gate terminal 34a, and a drain terminal 64a. Similarly, MOSFET 26a has a source terminal 32a, a gate terminal 36a, and a drain terminal 66a. In this case, MOSFETs 24a, 26a are electrically connected in series and arranged in a common source configuration. Source terminal 30a of MOSFET 24a is connected to a source terminal 32a of MOSFET 26a. MOSFET 24a has a body diode 68a, which is forward-biased from source terminal 30a to a drain terminal 64a of MOSFET 24a. Likewise, MOSFET 26a includes a body diode 70a connected in a forward direction from source terminal 32a to a drain terminal 66a of MOSFET 24a. Drain terminal 64a of MOSFET 24a is connected to detection unit 20a. Induction cooktop device 10a includes a capacitor 58a.The drain terminal 66a of the MOSFET 26a is connected to the capacitor 58a.

[0031] The capacitor 58a is connected to the heating inductor 12a. In heating mode, the heating inductor 12a is operated by an inverter unit 74a of the induction cooktop device 10a and supplied with energy via high-frequency alternating current signals in a frequency range between 10 kHz and 50 kHz. The capacitor 58a is provided to filter the high-frequency alternating current signals of the inverter unit 74a in heating mode and thus prevent them from reaching the detection unit 20a. The capacitance of the capacitor 58a is selected such that the capacitor 58a has a high capacitive reactance for the frequencies of the alternating current signals of the inverter unit 74a.The capacitance of capacitor 58a, on the other hand, is selected such that capacitor 58a has a low capacitive reactance for the frequencies of the high-frequency detection signals of detection unit 20a, allowing the detection signals to pass through capacitor 58a during detection mode. During detection mode, MOSFETs 24a, 26a are conductive, allowing the detection signals to flow from detection unit 20a via MOSFETs 24a, 26a and capacitor 58a to heating inductor 12a, and from heating inductor 12a via capacitor 58a and MOSFETs 24a, 26a back to detection unit 20a.

[0032] The switching unit 22a has a voltage source 38a. The voltage source 38a is intended to provide a supply voltage (not shown) which corresponds at least to a required threshold voltage 40a (see Figure 3) for activating the MOSFETs 24a, 26a.

[0033] The switching unit 22a has at least one semiconductor switching element 42a for activating and deactivating the MOSFETs 24a, 26a using the voltage source 38a. In the present case, the semiconductor switching element 42a is also designed as a MOSFET. Alternatively, however, other types of semiconductor switching elements, such as bipolar transistors, for activating and deactivating the MOSFETs 24a, 26a using the voltage source 38a would also be conceivable. The switching unit 22a further has a control terminal 44a for applying a control signal to the semiconductor switching element 42a. The control terminal 44a is designed in the present case as a gate terminal of the semiconductor switching element 42a.

[0034] The induction hob device 10a has a control unit 52a. The control unit 52a is provided for controlling the switching unit 22a and, for this purpose, is connected to the control terminal 44a of the switching unit 22a. In the present case, the control unit 52a is provided for controlling the switching unit 22a using inverting logic. In an operating state of the induction hob device 10a, the voltage source 38a permanently provides the supply voltage. The control unit 52a is provided for permanently applying a control signal to the control terminal 44a of the switching unit 22a during the heating operation of the heating inductor 12a, so that the semiconductor switching element 42a is conductive.In the heating mode, the voltage source 38a is therefore connected to a reference potential via the semiconductor switching element 42a, so that between the gate terminal 34a and the source terminal 30a of the MOSFET 24a and between the gate terminal 36a and the source terminal 32a of the MOSFET 26a, no gate-source voltage 76a (see Figure 3) drops that exceeds the required threshold voltage 40a (see Figure 3) for activating the MOSFETs 24a, 26a, and the MOSFETs 24a, 26a are therefore non-conductive in the heating mode.

[0035] The control unit 52a is designed not to apply a control signal to the control terminal 44a of the switching unit 22a for detection operation. As soon as no control signal is present at the control terminal 44a of the switching unit 22a, the semiconductor switching element 42a becomes non-conductive, and a portion of the supply voltage provided by the voltage source 38a drops between the gate terminal 34a and the source terminal 30a of the MOSFET 24a and between the gate terminal 36a and the source terminal 32a of the MOSFET 26a, so that the gate-source voltage 76a exceeds the required threshold voltage 40a, the drain-source paths of the MOSFETs 24a, 26a become conductive, and the electrically conductive connection between the detection unit 20a and the heating inductor 12a is established.

[0036] The switching unit 22a has at least one capacitor 28a, in this case exactly one. The capacitor 28a is electrically connected to the source terminals 30a, 32a and the gate terminals 34a, 36a of the two MOSFETs 24a, 26a. In this case, the capacitor 28a has a capacitance of at least 470 pF and at most 4.7 nF. Due to the presence of the capacitor 28a, voltages of the high-frequency detection signals provided by the detection unit 20a during detection operation can have amplitudes that are higher than a value of a supply voltage provided by the voltage source 38a.At the same time, however, average values ​​of the voltages of the high-frequency detection signals can be below the difference between the supply voltage and the threshold voltage 40a in order to always ensure a gate-source voltage 76a that is greater than the threshold voltage 40a during detection operation, so that the MOSFETs 24a, 24a always remain active during detection operation. This is achieved by the capacitor 28a having a capacitance of at least 470 pF and at most 4.7 nF, which is selected such that the capacitor 28a has a low capacitive reactance for the frequencies of the high-frequency detection signals of the detection unit 20a and therefore behaves like a short circuit for this frequency.

[0037] The switching unit 22a has at least two electrical resistors 46a, 48a. The electrical resistors 46a, 48a are connected to the voltage source 38a. One electrical resistor 46a is electrically arranged in series with the voltage source 38a. One electrical resistor 48a is electrically arranged in parallel with the voltage source 38a. The electrical resistors 46a, 48a form a voltage divider. By appropriately selecting the values ​​of the electrical resistors 46a, 48a, it can be ensured that a maximum permissible gate-source voltage 76a between the gate terminal 34a and the source terminal 30a of the MOSFET 24a and between the gate terminal 36a and the source terminal 32a of the MOSFET 26a is not exceeded.

[0038] Figure 3 shows two schematic diagrams illustrating a time profile of the gate-source voltage 76a of the MOSFETs 24a, 26a and an output voltage 78a of the switching unit 22a. A voltage in volts is plotted on an ordinate 80a of a lower diagram in Figure 3. A time in milliseconds is plotted on an abscissa 82a of the lower diagram. A voltage in volts is also plotted on an ordinate 84a of an upper diagram in Figure 3. The time in milliseconds is plotted on an abscissa 86a of the upper diagram. The lower diagram shows the time profile of the gate-source voltage 76a. The upper diagram shows the time profile of the output voltage 78a. The lower diagram shows the threshold voltage 40a, which in this case is 1.4 V, for example.As soon as the gate-source voltage 76a exceeds the threshold voltage 40a, the drain-source paths of the MOSFETs 24a, 26a become conductive, so that the output voltage 78a is present at an output 88a (see Figure 4) of the switching unit 22a. As soon as the gate-source voltage 76a falls below the threshold voltage 40a, the drain-source paths of the MOSFETs 24a, 26a become non-conductive, so that the output voltage 78a is no longer present at the output of the switching unit 22a. The characteristics of the MOSFETs 24a, 26a are selected such that they have a negligibly low minimum contact resistance (RDSON) in the conducting state, so that the output voltage 78a during detection operation essentially corresponds to the voltage of the high-frequency detection signals provided by the detection unit 20a.In the non-conductive state of the MOSFETs 24a, 26a, the contact resistances are in the mega-ohm range, so that during heating operation no output voltage 78a is present at the output 88a of the switching unit 22a.

[0039] Figure 4 shows a further schematic electrical circuit diagram of a portion of the induction hob device 10a. The induction hob device 10a has at least one further switching unit 50a. The further switching unit 50a is configured at least substantially identically to the switching unit 22a. The further switching unit 50a is provided to establish an electrically conductive connection between the further heating inductor 14a (see Figure 1) and the detection unit 20a (see Figures 1 and 2) for detection operation and to separate them for heating operation. In the present case, the induction hob device 10a has a switching unit for each of the heating inductors 12a, 14a, 16a, 18a, whereby, for the sake of simplicity, only the switching unit 22a and the further switching unit 50a are shown in Figure 4.

[0040] The control unit 52a is designed to activate the switching unit 22a and the further switching unit 50a at temporally separate intervals. This ensures that the detection unit 20a is electrically connected to only one of the heating inductors 12a, 14a at a time during detection operation. An input 90a is shown in Figure 4. The detection unit 20a is connected to the switching unit 22a and the further switching unit 50a via the input 88a. The switching unit 22a is connected to the heating inductor 12a (see Figures 1 and 2) via the output 88a. The further switching unit 50a is connected to the further inductor 14a via a further output 92a.

[0041] In this case, the control unit 52a has a shift register 54a. Figure 5 shows a schematic circuit diagram of the shift register 54a of the control unit 52a. The basic functionality of shift registers is known to those skilled in the art and is therefore not described in detail. The shift register 54a has three inputs 94a, 96a, 98a, namely an enable input 94a, a data input 96a, and a clock input 98a. The shift register 54a also has four outputs 100a, 102a, 104a, 106a. One output 100a is connected to the control terminal 44a of the switching unit 22a (see Figures 2 and 4). One output 102a is connected to a further control terminal 108a of the further switching unit 50a (see Figure 4).Each of the outputs 104a, 106a is connected to a control terminal (not shown) of a further switching unit (not shown) for establishing and breaking an electrically conductive connection between one of the further heating inductors 16a, 18a (see Figure 1) and the detection unit 20a (see Figures 1 and 2). A clock pulse is specified via the clock input 98a, with which the control unit 52a switches the switching units 22a, 52a. For example, at the start of operation of the induction hob device 10a, an active signal can be stored in each data memory of the shift register 54a, so that a control signal is present at each of the outputs 100a, 102a, 104a, 106a and the semiconductor switching element 42a (cf. Figure 2) and further semiconductor switching elements of the further switching units 50a are each conductive and the connections between the detection unit 20a (cf. Figure 2) and the heating inductors 12a, 14a, 16a, 18a (cf.Figure 1). The control unit 52a is provided to apply an inactive signal to the data input 96a to start the detection operation of the heating element 12a. As soon as a new rising edge of a clock signal arrives at the clock input 98a, the values ​​in the data memories of the shift register 54a shift. In a first data memory, which is provided for the output 100a, the value is thereby shifted from the active signal to the inactive signal from the data input 96a. In a second data memory, which is provided for the output 102a, the value is shifted from the previous active signal to the active signal of the first data memory. In a third data memory, which is provided for the output 104a, the value is shifted from the previous active signal to the active signal of the second data memory.In a fourth data memory, which is provided for output 102a, the value shifts from the previous active signal to the active signal of the third data memory. To activate the detection mode for the heating inductor 12a, the control unit 52a is provided to apply an activation signal to the enable input 94a. As soon as the activation signal is present, the shift of the values ​​in the data memories takes effect, so that no control signal is present at the output 100a and the semiconductor switching element 42a (see Figure 2) becomes non-conductive, whereby the MOSFETs 24a, 26a of the switching unit 22a become conductive and the connection between the heating inductor 12a and the detection unit 20a is established. Meanwhile, a control signal continues to be present at the outputs 102a, 104, 106a, so that the further switching units 52a are closed and there is no connection between the further heating inductors 14a, 16a, 18a and the detection unit 20a.The control unit 52a is provided to apply an active signal to the data input 96a to end the detection operation of the heating element 12a and to start the detection operation of the further heating element 14a. As soon as a new rising edge of a clock signal arrives at the clock input 98a, the values ​​in the data memories of the shift register 54a shift again, so that the inactive signal is now shifted from the first data memory to the second data memory, and a control signal is again present at the output 100a and no control signal is present at the output 102a, so that the switching unit 22a disconnects the connection between the heating inductor 12a and the detection unit 20a, and the further switching unit 52a establishes the connection between the further heating inductor 14a and the detection unit 20a. This process can be repeated accordingly for the outputs 104a, 106a.By means of the shift register 54a, the number of signals that must be provided by the control unit 52a for controlling the switching units 22a, 52a can be reduced from four to three, namely to the signals at the inputs 94a, 96a, 98a of the shift register.

[0042] Figure 6 shows a further embodiment of the invention. The following descriptions are essentially limited to the differences between the embodiments, whereby reference can be made to the description of the embodiment in Figures 1 to 5 with regard to identical components, features and functions. To distinguish the embodiments, the letter a in the reference numerals of the embodiment in Figures 1 to 5 has been replaced by the letter b in the reference numerals of the embodiment in Figure 6. With regard to components with the same designation, in particular with regard to components with the same reference numerals, reference can also be made to the drawings and / or the description of the embodiment in Figures 1 to 5.

[0043] Figure 6 shows a further embodiment of an induction hob device 10b. The induction hob device 10b differs from the induction hob device 10a of the previous embodiment essentially with regard to the configuration of a control unit 52b for controlling switching units (not shown) of the induction hob device 10b. Regarding the features of the induction hob device 10b, with the exception of the control unit 52b, reference can be made to the above description of the induction hob device 10a. In contrast to the control unit 52a of the previous embodiment, the control unit 52b of the induction hob device 10b does not have a shift register. Instead, the control unit 52b has a binary decoder 56b. In the present case, the binary decoder 56b is designed as a 2 to 4 binary decoder. The binary decoder 56b has a first binary input 110b and a second binary input 112b.The binary decoder 56b, in turn, has four outputs 100b, 102b, 104b, 106b, each of which is connected to a control terminal of a switching unit (not shown) of the induction hob device 10b. To control the switching units of the induction hob device 10b, the control unit 52b successively applies binary signals to the binary inputs 110b, 112b according to the following table:

[0044] The binary decoder 56b decodes the binary signals at the binary inputs 110b, 112b in a manner known to those skilled in the art, and the truth values ​​specified in the table are obtained at the outputs 100b, 102b, 104b, 106b, so that the switching unit and the further switching units (not shown) of the induction hob device 10b are activated one after the other at temporally separated intervals.

[0045] Reference symbol

[0046] 10 Induction hob device

[0047] 12 Heating inductor

[0048] 14 additional heating inductors

[0049] 16 additional heating inductors

[0050] 18 additional heating inductors

[0051] 20 detection units

[0052] 22 Switching unit

[0053] 24 MOSFET

[0054] 26 MOSFET

[0055] 28 Capacitor

[0056] 30 Source connection

[0057] 32 Source connection

[0058] 34 Gate connection

[0059] 36 Gate connection

[0060] 38 Voltage source

[0061] 40 threshold voltage

[0062] 42 semiconductor switching element

[0063] 44 Control connection

[0064] 46 electrical resistance

[0065] 48 electrical resistance

[0066] 50 additional switching units

[0067] 52 Control unit

[0068] 54 shift registers

[0069] 56 binary decoders

[0070] 58 Capacitor

[0071] 60 induction hob

[0072] 62 hob plate

[0073] 64 Drain connection Drain connection Body diode Body diode Reference potential Inverter unit

[0074] Gate-source voltage Output voltage Ordinate

[0075] Abscissa Ordinate Abscissa Output Input Additional output Enable input Data input Clock input Output Output

[0076] Output Output additional control connection binary input binary input

Claims

Claims 1. Induction hob device (10a; 10b) with at least one heating inductor (12a), with a detection unit (20a) for measuring properties of an induction load of the heating inductor (12a) and with at least one switching unit (22a) which is provided to establish an electrically conductive connection between the heating inductor (12a) and the detection unit (20a) for a detection operation and to separate it for a heating operation, characterized in that the switching unit (22a) has two MOSFETs (24a, 26a) which form a bidirectional switch for establishing and separating the electrically conductive connection between the heating inductor (12a) and the detection unit (20a).

2. Induction hob device (10a; 10b) according to claim 1, characterized in that the MOSFETs (24a, 26a) are electrically connected in series with one another and arranged in a common source configuration.

3. Induction hob device (10a; 10b) according to claim 1 or 2, characterized in that the MOSFETs (24a, 26a) are each designed as n-channel MOSFETs.

4. Induction hob device (10a; 10b) according to one of the preceding claims, characterized in that the switching unit (22a) has at least one capacitor (28a) which is electrically conductively connected to source terminals (30a, 32a) and gate terminals (34a, 36a) of the two MOSFETs (24a, 26a).

5. Induction hob device (10a; 10b) according to claim 4, characterized in that the capacitor (28a) has a capacitance of at least 470 pF and at most 4.7 nF.

6. Induction hob device (10a; 10b) according to one of the preceding claims, characterized in that the switching unit (22a) has a voltage source (38a) for providing a supply voltage which corresponds at least to a required threshold voltage (40a) for activating the MOSFETs (24a, 26a).

7. Induction hob device (10a; 10b) according to claim 6, characterized in that the switching unit (22a) has at least one semiconductor switching element (42a) for activating and deactivating the MOSFETs (24a, 26a) by means of the voltage source (38a) and a control terminal (44a) for applying a control signal to the semiconductor switching element (42a).

8. Induction hob device (10a; 10b) according to claim 6 or 7, characterized in that the switching unit (22a) has at least two electrical resistors (46a, 48a) which are connected to the voltage source (38a) and form a voltage divider.

9. Induction hob device (10a; 10b) according to one of the preceding claims, characterized by at least one further heating inductor (14a, 16a, 18a) and at least one further switching unit (50a), which is designed at least substantially identically to the switching unit (22a) and is intended to establish an electrically conductive connection between the further heating inductor (14a, 16a, 18a) and the detection unit (20a) for a detection operation and to separate it for a heating operation.

10. Induction hob device (10a; 10b) according to claim 9, characterized by a control unit (52a; 52b) which is provided to activate the switching unit (22a) and the further switching unit (50a) at intervals separated from one another in time.

11. Induction hob device (10a) according to claim 10, characterized in that the control unit (52a) has a shift register (54a).

12. Induction hob device (10b) according to claim 10, characterized in that the control unit (52b) has a binary decoder (56b).

13. Induction hob (60a) with at least one induction hob device (10a; 10b) according to one of the preceding claims.

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