EP3481143B1 - Heating system for operating a heating element - Google Patents

Description

The present invention relates to a heating system for operating a heating element. The invention also relates to a method for operating a heating element and a kitchen appliance with a heating system.

Heating systems can be used in electrical devices for various applications, such as, for example, in a kitchen appliance for heating a medium in a stirred vessel. The heating system controls a heater, for example in the mixing vessel of the food processor, in such a way that the medium to be heated is heated to preselectable setpoint values.

So are z. B. heating systems are known in which a thick-film heating is used triac-controlled to heat the medium to be heated to the setpoints. The medium temperature, which is calculated, for example, by algorithms and based on the detection of a temperature sensor, can serve as a control variable for a controller of the heating system.

Frequently, alternating current flows through a heating element for reasons of safety and service life. Often, however, such heating systems can only be operated with large switching intervals, for example with a triac control. In particular, the need to reduce interference from flicker has a limiting effect.

With a large switching interval, such as, for example, 4 s in conventional heating systems, regulating the output of the heating element in order to maintain the setpoint values is often technically complex. In particular, a system deviation that is unfavorable for some applications must be accepted. Known heating systems are therefore often complex to manufacture and / or costly and / or too unreliable for certain applications, in particular for use in a kitchen appliance for the at least partially automated preparation of food.

From the DE 44 46 796 A1 a generic heating system is known.

It is therefore an object of the present invention to at least partially remedy the disadvantages mentioned above. In particular, it is an object to propose an improved heating system in which the technical effort is reduced and / or the reliability is improved. In particular, the control deviation should be reduced so that an almost constant heating output can be achieved. A further task can be to reduce the power loss during operation of the heating element, in particular a thick-film heater of a kitchen appliance.

The above object is achieved by a heating system with the features of claim 1, a method with the features of claim 13 and a kitchen appliance with the features of claim 14. Further features and details of the invention emerge from the respective subclaims, the description and the drawings. Features and details that are described in connection with the heating system according to the invention naturally also apply in connection with the method according to the invention and the kitchen appliance according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made to the individual aspects of the invention .

In particular, in the following - unless expressly described otherwise - an electrical connection is both a direct and an indirect connection, ie also via further electrical components, but in particular only if the connection is made in the same circuit or exclusively electrically (ie without galvanic separation).

• einen Lastkreis, welcher zumindest zwei elektronische Schaltelemente, insbesondere Halbleiter-Schaltelemente, mit jeweils einem Steuerungsanschluss und jeweils einem Eingangsanschluss umfasst, wobei vorzugsweise die Schaltelemente antiseriell (im Lastkreis) geschaltet sind, um einen Wechselstrom (des Lastkreises) zum Heizelement zu beeinflussen,
• einen Ansteuerungskreis, um ein elektrisches Ansteuerungssignal zur Ansteuerung der Schaltelemente (insbesondere am jeweiligen Steuerungsanschluss) zu initiieren, wobei vorzugsweise die Schaltelemente auch mit dem Ansteuerungskreis verbunden sind,
• eine Potentialtrennvorrichtung, um den Lastkreis mit dem Ansteuerungskreis zu verbinden und/oder um das Ansteuerungssignal an den Steuerungsanschlüssen (und insbesondere auch an den Eingangsanschlüssen) derart bereitzustellen, insbesondere potentialfrei zu erzeugen, dass ein elektrisches Potential an den Eingangsanschlüssen ein gemeinsames Bezugspotential der Schaltelemente für das Ansteuerungssignal bildet. Hierzu kann die Potentialtrennvorrichtung bspw. sowohl mit den Steuerungsanschlüssen als auch mit den Eingangsanschlüssen elektrisch verbunden sein, um vorzugsweise das Ansteuerungssignal als eine elektrische Spannung zwischen diesen Anschlüssen zu erzeugen.

The above object is achieved in particular by a heating system, in particular a control and / or regulating system, for operating a heating element, in particular in a kitchen appliance, having:

• a load circuit which comprises at least two electronic switching elements, in particular semiconductor switching elements, each with a control connection and an input connection each, the switching elements preferably being connected in antiseries (in the load circuit) in order to influence an alternating current (of the load circuit) to the heating element,
• a control circuit to initiate an electrical control signal to control the switching elements (in particular at the respective control connection), the switching elements preferably also being connected to the control circuit,
• a potential separation device to connect the load circuit to the control circuit and / or to provide the control signal at the control connections (and in particular also at the input connections) in such a way, in particular to generate potential-free, that an electrical potential at the input connections is a common reference potential of the switching elements for the Forms control signal. For this purpose, the potential separation device can be electrically connected, for example, both to the control connections and to the input connections, in order to preferably generate the control signal as an electrical voltage between these connections.

In other words, the input connections can be electrically connected directly and are therefore at a common electrical potential, which can preferably be used as a reference potential for the gate-source voltage. In particular, the common reference potential can thus be a common (and thus the same) electrical potential of the input connections (source connections) of the switching elements. This has the advantage of a simple and reliable circuit structure and possibly that, in a cost-saving manner, only one voltage source is required for switching the switching elements becomes. In particular, the load and control circuit relates to separate switching arrangements which, if necessary, can be electrically connected to one another and / or can also have separate current paths and / or circuits.

It can in particular be provided that a switching frequency of the switching elements for controlling (i.e. also regulating) the heating element greater than 1 kHz or greater than 2 kHz or greater than 5 kHz or greater than 10 kHz or greater than 20 kHz is used. As an alternative or in addition, the switching elements can switch a power of at least 0.5 kW or at least 1 kW. Furthermore, it can be provided that the switching elements are designed as (for example N-channel) MOSFETs (ie metal-oxide-semiconductor field effect transistor) which, for example, have a high switch-on speed (slew rate) and / or a low capacitance at the gate -Connection, so as to reduce circuit losses. For example, the MOSFETs can have a low electrical resistance when switched on between the drain and the source connection in order to reduce the on-state losses.

In particular, it may be necessary that (due to the changing potential at the switching elements) the voltage at the control connection or gate connection is or must always be related to the voltage at the input connection or source connection. In other words, the voltage difference between the input and control connection in the switched-on and in the switched-off state of the switching element must be kept constant, and thus in particular be independent of the voltage between the output connections of the switching elements. This voltage between the output connections varies, for example, during operation between + 330 V and - 330 V. For this purpose, the control connections of the switching elements can be controlled electrically independently of a mains voltage of the heating system (i.e. potential-free), in particular so that the control circuit can be controlled by a control circuit and / or a control device can be controlled, which / which can be on the same (or alternatively on a further) ground potential as the load circuit. In other words, the switching elements can be activated in a potential-free manner. In addition, high-frequency activation of the heating element by the switching elements can offer the possibility of reducing the control deviation of the heating control and thus setting an almost constant heating output.

Provision can therefore preferably be made for the switching elements, in particular MOSFETs, to be actuated in a potential-free and / or high-frequency manner (i.e. above 2 kHz). This also has the advantage that a desired heating output can be set particularly precisely and this heating output also remains constant.

For example, the input connections of the switching elements can be directly electrically connected to one another and / or to a second ground potential and thus be at a common electrical potential (the common reference potential). This common potential can thus be used as the common reference potential for the control signal, i.e. H. For example, to form a gate-source voltage or as a reference point for a potential at the control connection. In this way, the advantage can be achieved that a particularly simple and cost-effective structure is made possible, and in particular only one voltage source is required for switching the switching elements.

In particular, conventionally, due to the operation with the alternating current, there may be a problem that the common reference potential varies. Such a non-constant common reference potential can make the control of the switching elements much more difficult. Therefore, it can be provided according to the invention that the control signal is generated as a potential difference, in particular generated potential-free, preferably so that a control voltage between the control connections and the input connections (i.e. in particular a gate-source voltage for the switching elements) remains at least almost constant. The control voltage or gate-source voltage can have the same level for both control elements and, for example, have a different level when the control elements are switched on than when the switching elements are switched off, but are preferably kept at least almost constant in both cases. For example, the control elements always have the same status in normal operation for heating control, so that the alternating current can always be blocked for both current directions.

According to a further advantage, the heating element can be operated with an electrical power in the range 200 W to 5 kW, in particular 500 W to 3 kW, preferably 800 W to 2 kW, preferably 1 kW to 1.5 kW, and / or the switching elements in each case be designed to switch electrical power in these areas. The heating element is supplied with energy in particular by an electrical voltage, in particular an (possibly high-frequency) alternating voltage, preferably a mains voltage, in a range from 100 V to 400 V, preferably 200 V to 300 V, preferably 230 V to 250 V. Preferred the switching elements are switched in opposite directions (antiserial) in order to block both the positive and the negative half-wave of the voltage for the energy supply (mains voltage) when the switching elements are switched off. In this context, “block” refers in particular to a state in which the flow of current to the heating element is predominantly or completely blocked by the switching elements. For this purpose, the switching elements are preferably connected in series with the heating element and integrated into the load circuit (load circuit). The control circuit (control circuit) and the load circuit are preferably designed separately from one another, so that in particular a current flow from the heating element to the control circuit or from one of the switching elements to the control circuit is prevented.

The different alignment of the switching elements in relation to the current direction is particularly useful in order to block any current direction through the switching elements (from and to the heating element). In particular, a single switching element, which can be implemented as a MOSFET, for example, can only block one current direction. This is related to the structure of the switching elements, which can cause the switching elements to behave in a way that is similar to a parallel connection of a diode in the respective switching elements. This property of the structure is also referred to below as a parasitic diode, and can, for. B. between a carrier material of a switching element and an output connection (drain connection) of this switching element. Usually (especially in the case of MOSFETs) the carrier material (bulk) is connected directly to an input connection (source connection) of the switching element, so that the flow of current can only be prevented in one direction. For example, a current flow from source to drain is possible (with a positive voltage) (whereas the current flow from drain to source is blocked when the switching element is switched off and released when the switching element is switched on). By using at least two switching elements, this problem can be solved reliably and inexpensively.

For certain applications, in particular when switching an alternating voltage and / or when switching at high frequency, the control of the switching elements may not be easy, e.g. B. by a transistor connected to the control terminal. In particular, this can possibly only bring about an adequate blocking of one of the current directions, since with such an activation a potential difference at the switching elements can fluctuate too much. When the heating element is supplied with a mains voltage, the problem arises that the potential at the input connection (source) may not be constant. In particular, if there is a changing voltage at the output connections (drain connections) of the switching elements (changing drain potential), an almost constant potential at the control connection (gate connection) or an almost constant voltage between the control connection and the input connection of the respective Switching elements are guaranteed. In other words, it can be provided that a control voltage of the switching elements (or a potential at the control connection) is always related to the input connection of a respective switching element. In particular, it is provided for this purpose that a voltage between the input connection (source) and the control connection (gate) for the switched-on state and / or for the switched-off state is kept at least almost constant and thus at least essentially independent of a voltage between the output connections the switching elements is. The voltage between the output connections varies, for example (in heating mode) between +330 V and - 330 V.

An average switching frequency of the switching elements which is used in a heating mode to regulate a heating power of the heating element is preferably at least 500 Hz or at least 1 kHz or at least 2 kHz. This has the advantage that the high-frequency control can significantly reduce any deviation in the heating control.

Furthermore, it is optionally possible within the scope of the invention that the load circuit and the control circuit are electrically connected to different grounds (in particular that means that the load circuit is connected to a first ground and the control circuit is connected to a second ground, to which the load circuit is not directly or galvanically connected), preferably a first ground potential (first Ground) is connected to the load circuit, and a second ground potential (second ground) is connected to the control circuit, is preferably electrically connected to the input terminals of the switching elements and / or the potential separation device, and particularly preferably forms the common reference potential. In other words, in particular the switching elements (in particular the respective control connections) can be activated in a potential-free manner, ie preferably (at least almost) independently of the energy supply or mains voltage for the heating element. This enables a particularly precise and reliable control of the switching elements, in particular since an at least almost constant control signal can be guaranteed. In particular, the potential-free control enables the control circuit (i.e. the control circuit for the switching elements) to be operated with the same supply voltage (e.g. the kitchen appliance, in particular mains voltage), in particular with the same ground potential as the load circuit with the Switching elements. For example, a further energy supply for the control circuit can be provided for this purpose, for example an AC / DC converter for electrical isolation in order to supply the control circuit with current. Here, the further energy supply can, for example, provide a further ground (second ground potential) which differs from the ground of the load circuit (first ground potential) and is provided in particular for the control circuit. A simpler and cheaper structure can thus be achieved.

The control signal is preferably implemented as a voltage between the control connection (gate) and the input connection (source), ie a gate-source voltage, or as an (electrical) potential of the control connection (gate potential). In particular, the control signal is kept at least almost constantly at a first level (for the switched-on state of the switching elements) and / or at a second level (for the switched-off state of the switching elements) by using the potential separation device, ie the floating control of the switching elements. The switchover between the first and the second level can take place in that the potential separation device is controlled by a control device, for example by different voltages on the input side of the potential separation device.

A further advantage can be provided that the switching elements are each designed as a transistor, preferably as a field effect transistor, preferably as a MOSFET, so that a current flow between the input terminal and an output terminal of the respective switching element in each case by switching the respective switching elements on the basis of the control signal Direction is influenced, with the control connection of the respective switching elements preferably being electrically connected to the potential separation device for this purpose. This has the particular advantage that such switching elements, in particular MOSFETs, have a high switch-on speed (slew rate) and a low capacitance at the gate connection, so that the switching losses can be significantly reduced. For example, the switching elements are designed as N-channel MOSFETs. In particular, an electrical connection between the control connections and the potential separation device can also be implemented indirectly via further components.

It is also advantageous if the potential separation device comprises a first connection which is electrically (e.g. indirectly, possibly via at least one control element, such as a transistor) connected to the control connections of the switching elements, and a second connection which is electrically ( in particular directly and / or via a second ground) is connected to the input connections of the switching elements in order to preferably generate a potential difference between the first and second connection for the control signal. This enables in particular the generation of a corresponding (source-drain) voltage of the switching elements for fast and reliable switching.

It may optionally be possible for the switching elements to be (at least partially) integrated into the load circuit in such a way that they have different current blocking directions in the load circuit, in particular through a correspondingly different alignment of the switching elements or a parasitic diode (between a carrier material and an output connection ) of the switching elements, so that preferably different half-waves of a supply voltage of the load circuit can be blocked. An alternating voltage for operating the heating element can thus be reliably controlled.

Advantageously, it can be provided in the invention that a control device for heating regulation is provided in order to preferably carry out an electrical activation of the potential separation device for generating the control signal, so that the switching elements can preferably be controlled at high frequency by the control signal, in particular with a switching frequency (in the high-frequency range) above 2 kHz or above 10 kHz or above 20 kHz. For example, the control device (in the load or a control circuit) can be connected to a first ground, preferably to which the load circuit is also connected. In particular, the first ground can differ from a second ground to which the control circuit is connected, the potential separation device preferably performing the potential separation between the load (or control circuit) and the control circuit, and / or a potential of the load circuit or control circuit galvanically to one Disconnects the potential of the control circuit.

It can be advantageous if, within the scope of the invention, the load circuit includes the heating element or can be electrically (detachably) connected to the heating element, the heating element preferably being designed as a thick-film heater and preferably being and / or integrable in a mixing vessel of a kitchen appliance . For example, the heating element can be part of the heating system according to the invention or can be designed separately therefrom. Accordingly, the load circuit can be designed as an open circuit, which is closed by being connected to the heating element. In particular, the heating system and heating element can be designed to be detachably connectable to one another. The heating element can preferably be connected to (electrical) connecting elements which enable a detachable (electrical) connection to (electrical) counter-connecting elements of the heating system. In particular, the heating element can be integrated into a mixing vessel of a kitchen appliance, the mixing vessel being designed, for example, to be detachable and / or integratable in the kitchen appliance. Furthermore, the heating system can be integrated in a stationary part of the kitchen appliance, which, for example, can accommodate the mixing vessel. This enables flexible handling of the heating element and the kitchen appliance.

A further advantage can be provided that the load circuit comprises a voltage source, in particular an alternating voltage source, for providing the alternating current of the load circuit, which is preferably connected electrically (in series) via the switching elements is and / or can be connected to the heating element, in particular to transmit electrical power to the heating element, so that the power transmission can be controlled, in particular switched, by the switching elements as a function of the control signal. This enables the output of the heating element to be controlled reliably and quickly.

Optionally, it can be provided that the potential separation device is electrically connected to the switching elements in such a way that, when a control signal is provided (directly), the potential separation device creates an at least almost constant voltage between the respective control connection, in particular a gate connection, and the respective input connection, in particular a source connection, can be generated, preferably at least almost independently of a polarity of the alternating current and / or of a voltage between output connections of the switching elements in normal operation. This ensures that the heating power is switched reliably even with the negative half-wave.

It may optionally be possible that the control circuit comprises an energy transmitter, preferably its own energy source and / or a switched-mode power supply and / or an AC / DC converter (ie rectifier), in order to preferably provide the power supply for the control circuit, and preferably the potential separation device for generation to supply the control signal with energy. For example, the energy transmitter can be connected to a first ground to which the load circuit is also connected. In particular, the energy transmitter can provide a second mass different therefrom for the control circuit, in particular by implementing a potential separation. This has the advantage that the switching elements can be controlled particularly reliably. AC / DC converters (sometimes also referred to as AC / DC converters) rectifiers that convert alternating current into direct current are preferred.

Furthermore, it is optionally provided that the potential separation device is designed as an optocoupler. This includes, for example, a transmitter, such as a light-emitting diode, and / or a receiver, such as a photodiode. This has the advantage that a trigger signal can be generated reliably in a potential-free manner.

According to a further possibility, it can be provided in the heating system according to the invention that the potential separation device comprises a first separation unit, in particular a first winding, in the control circuit and a second separation unit, in particular a second winding, in the load circuit, preferably through the second separation unit, in particular a second winding , a potential difference can be generated for the control signal as a function of a voltage signal at the first separating unit, preferably the first winding. This represents a further possibility for reliable generation of the control signal.

Particularly preferably, it is conceivable that the input connections are at a common source potential and are preferably connected to the control connections via the potential separation device, in particular so that the control signal can be used to switch off the switching elements in order to avoid both a negative and a positive Half-wave of a voltage supply in the load circuit to block the current flow. This enables reliable operation of the heating element.

• die Potentialtrennvorrichtung und eine Spannungsquelle des Lastkreises sind jeweils direkt mit einem gemeinsamen Massepotential verbunden,
• die Potentialtrennvorrichtung, insbesondere ein (ausgangsseitiger) erster Anschluss der Potentialtrennvorrichtung, ist über wenigstens einen ersten Widerstand und/oder wenigstens einem Kontrollelement mit dem ersten Schaltelement und über wenigstens einen zweiten Widerstand und/oder wenigstens einem (ggf. weiteren) Kontrollelement mit dem zweiten Schaltelement verbunden,
• die Potentialtrennvorrichtung, insbesondere (ausgangsseitig) ein erster Anschluss der Potentialtrennvorrichtung, ist über wenigstens einen dritten Widerstand mit einem Source-Potential der Schaltelemente verbunden, wobei vorzugsweise der dritte Widerstand sehr viel größer als der erste und zweite Widerstand ist.

Another advantage can be achieved within the scope of the invention if at least one of the following arrangements are provided:

• the potential separation device and a voltage source of the load circuit are each directly connected to a common ground potential,
• the potential separation device, in particular a (output-side) first connection of the potential separation device, is connected to the first switching element via at least one first resistor and / or at least one control element and via at least one second resistor and / or at least one (possibly further) control element to the second switching element connected,
• the potential separation device, in particular (on the output side) a first connection of the potential separation device, is connected to a source potential of the switching elements via at least one third resistor, the third resistor preferably being much greater than the first and second resistors.

The invention also generally includes a household appliance, such as. B. a food processor, with the heating system according to the invention for operating a heating element.

• Ansteuern einer mit dem Ansteuerungskreis verbundenen Potentialtrennvorrichtung durch eine Kontrollvorrichtung in Abhängigkeit von einer Ansteuerungsvorgabe, sodass vorzugsweise bei einer ersten Ansteuerungsvorgabe ein erstes Ansteuerungssignal (insbesondere potentialfrei) erzeugt wird, und bei einer zweiten Ansteuerungsvorgabe ein zweites Ansteuerungssignal (insbesondere potentialfrei) erzeugt wird,
• Anlegen des erzeugten Ansteuerungssignals an wenigstens zwei Schaltelemente, sodass vorzugsweise ein Wechselstrom im Lastkreis zum Heizelement für beide Stromrichtungen gesperrt wird, wenn das erzeugte Ansteuerungssignal das erste Ansteuerungssignal ist, und für beide Stromrichtungen freigegeben wird, wenn das erzeugte Ansteuerungssignal das zweite Ansteuerungssignal ist.

The invention also relates to a method for operating a heating element, in particular in a kitchen appliance. In this case, it is preferably provided that a load circuit with the heating element and a control circuit (in particular executed separately from the load circuit) are provided. In particular, the following steps can be carried out, preferably one after the other or in any order, with individual steps also being able to be carried out repeatedly if necessary:

• Activation of a potential separation device connected to the activation circuit by a control device as a function of an activation specification, so that a first activation signal (in particular potential-free) is generated with a first activation specification and a second activation signal (in particular potential-free) is generated with a second activation specification,
• Applying the generated control signal to at least two switching elements, so that an alternating current in the load circuit to the heating element is preferably blocked for both current directions if the generated control signal is the first control signal, and is released for both current directions if the generated control signal is the second control signal.

The method according to the invention thus has the same advantages as have been described in detail with reference to a heating system according to the invention. In addition, the method can be suitable for operating a heating system according to the invention.

For example, the potential separation device can be electrically connected on the input side to a control circuit and / or load circuit, and in particular a control device, and on the output side to the control circuit, and in particular to the switching elements. The connection to the respective switching element can serve to apply the generated control signal by transmitting the control signal to the switching elements via the connection.

It can be provided that an (at least almost constant) voltage is generated as the respective control signal for at least one of the control signals, for example a source-gate voltage for the switching elements. For example, the Control specification can be digitally (temporarily) stored in order to be evaluated by the control device. The control specification is, for example, specific for a target temperature of a medium that is to be heated by the heating element. It is also conceivable that the control specification is implemented as control information which, for example, determines a switching frequency with which the heating element is to be controlled. Furthermore, it may be possible for the control specification to be determined as a function of a detection by a temperature sensor. For example, a first control specification can be first control information (which, for example, indicates blocking of the alternating current) and the second control specification can be second control information (which, for example, indicates enabling of the alternating current).

• wenigstens einem Rührgefäß, welches zumindest ein Heizelement aufweist,
• wenigstens einen Temperatursensor zur Erfassung einer Temperatur am Rührgefäß.

The invention also relates to a food processor for the at least partially automatic preparation of food, with:

• at least one stirred vessel, which has at least one heating element,
• at least one temperature sensor for detecting a temperature on the stirred vessel.

It is particularly conceivable here that a heating system according to the invention is provided in order to carry out a heating regulation of the heating element on the basis of the detected temperature, in particular in order to determine an actuation specification in this way. The kitchen appliance according to the invention thus brings the same advantages as have been described in detail with reference to a heating system according to the invention and / or a method according to the invention. In addition, the kitchen appliance can be suitable to be operated according to a method according to the invention.

It can furthermore be possible in the case of the kitchen appliance according to the invention that scales are provided which can weigh the medium, in particular at least one food present in the mixing vessel. Weight information of the food that is determined in this way can, for example, be displayed to a user of the food processor via a display device such as a display or a touchscreen. Furthermore, it can be conceivable that the recorded temperature of the temperature sensor and / or a set heating power is also displayed on the display device. It may be possible for the heating system to be controlled by the user on a Input device of the food processor, such as the touchscreen, is influenced or activated. This enables very convenient operation of the food processor.

Figur 1

eine Darstellung von Teilen eines erfindungsgemäßen Heizsystems,

Figur 2

eine weitere Darstellung von Teilen eines erfindungsgemäßen Heizsystems,

Figur 3

eine schematische Darstellung von Teilen einer erfindungsgemäßen Küchenmaschine.

Further advantages, features and details of the invention emerge from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination. They show schematically:

Figure 1

a representation of parts of a heating system according to the invention,

Figure 2

a further representation of parts of a heating system according to the invention,

Figure 3

a schematic representation of parts of a food processor according to the invention.

In the following figures, the same reference numerals are used for the same technical features from different exemplary embodiments.

In Fig. 1 parts of a heating system 200 according to the invention are shown schematically. Further serves Fig. 1 to illustrate a method 100 according to the invention. A load circuit 201 and a control circuit 202 are identified, whereby these are preferably circuits with separate grounds and / or (at least approximately) separate galvanic circuits 201, 202. In addition to the control circuit 202, a control circuit can optionally be provided which, for example, comprises the control device 220 and is electrically connected to a potential separation device 270. Alternatively, the control device 220 can also be integrated directly into the load circuit 201. The potential separation device 270 (on the input side, e.g. in the control circuit) and / or the control device 220 and / or the load circuit 201 can be connected to a first ground potential GND (first ground) (as in FIG Fig. 1 is shown as an example). A different second ground potential SGND (second ground which is at least not directly connected to GND) can optionally be connected to a second connection 270.2 of the potential separation device 270 and / or to an input connection 250.3 of two switching elements 250 must be electrically connected (as also in Fig. 2 is shown in more detail). In order to provide a power supply for the control circuit 202, an energy transmitter 280, for example, can be provided which, for example, can provide the second ground potential SGND (this is also shown in more detail in FIG Fig. 2 shown).

The switching elements 250, i. H. a first switching element 250a and a second switching element 250b, which is oriented differently, can each be, for. B. be designed as a transistor or MOSFETs. Due to a respective parasitic diode 250.1, it is necessary to provide both switching elements 250 in an anti-series connection in order to completely block an alternating voltage U or alternating current I of a voltage source 260, in particular alternating voltage source 260 (i.e. in both current directions).

The individual switching elements 250 can have an input connection 250.3 with a source potential S and an output connection 250.4 with a drain potential D and a control connection 250.2 with a control potential G, in particular gate potential G. The potential separation device 270 can have on the output side (on the control circuit 202) in particular at least one first (output) connection 270.1 and the second (output) connection 270.2, which are each connected to the control circuit 202. Further (input) connections can also be provided on the input side, which are connected, for example, on the control device side or on the control circuit side. A first separating unit 270.3 (e.g. first winding 270.3) and on the output side a second separating unit 270.4 (e.g. second winding 270.4) of the potential separation device 270 are also shown by way of example on the input side, which illustrate the galvanic separation can also be an optocoupler or the like, which therefore does not have to have any windings.

The first connection 270.1 of the potential separation device 270 is z. B. via a first resistor R1 and / or via at least one control element 230 with the control connection 250.2 of the first switching element 250a and via a second resistor R2 and / or via at least one (possibly further) control element 230 with the control connection 250.2 of the second switching element 250b electrically connected. Optionally, a third resistor R3 can be provided, which z. B. with a high Resistance is designed to increase the stability of the circuit. The second connection 270.2 of the potential separation device 270 is electrically connected, for example (for example directly and / or via a second ground potential) to the input connections 250.3 of the switching elements 250, ie to the source potential S. In this way, a common reference potential S can be created for the control signal A and / or the control signal A can be applied to the switching elements 250 according to a method 100 according to the invention. In particular, the control signal A (e.g. as gate-source voltage) is used to control the switching elements 250, ie to transfer the switching elements 250 from an open state, in which the flow of a current I in the load circuit 201 is prevented, to a closed state , in which the flow of current is allowed, and / or vice versa. In this way, the heating power of a heating element 210, in particular a thick-film heater 210, in the load circuit 201 can be reliably controlled and / or regulated.

In Fig. 2 is the in Fig. 1 or a similar circuit configuration of a heating system 200 is shown schematically. Here, an energy supply device 290 for the control circuit 202 is shown, which, for example, has a voltage source X1, which z. B. supplies a mains voltage and / or that of the voltage source 260 in Fig. 1 corresponds to. This can, for example, be connected to an energy transmitter 280, which z. B. provides the voltage supply for the control circuit 202 as a rectifier. As a result, a second ground potential SGND can also be provided, which differs from a first ground potential GND of the load circuit 201, that is to say, in particular, is designed to be electrically isolated from it. Furthermore, a first voltage V1 can be provided by this or by the energy transmitter 280, which z. B. is used to operate at least one control element 230. The control element (s) 230 are, for example, a semiconductor switch, for example a transistor or MOSFET, in order to generate the control signal A, in particular at a control potential G of the switching elements 250 a control element 230 is controlled by the potential separation device 270 and / or the first voltage is generated in an electrically isolated manner and / or the switching elements 250 are each connected to the second ground potential SGND. The potential separation device 270 is, for example a second voltage V2 operated, which can be provided by the energy transmitter 280.

The activation signal A generated in a potential-free manner is initiated, for example, by a control device 220, which in particular activates the potential separation device 270. For this purpose, the control device 220 provides, for example, a voltage supply U270 for the potential separation device 270 and / or a control signal KS at an input of the potential separation device 270.

In Fig. 3 a mixing vessel 2 of a food processor 1 is shown schematically. A medium 20 is shown in the stirred vessel 2 with a stirrer 3, the medium 20 being able to be heated by a heating element 210. The heating element 210 is integrated, for example, in a mixing vessel base 2.1, with the heating element 210 then optionally also being able to be designed separately from the kitchen appliance 1. For example, the mixing vessel 2 can be detachably connected to the heating system 200 of the kitchen appliance 1, it also being possible for electrical contacts to be provided for integrating the heating element 210 into the load circuit 201. The activation of the heating element 210 is then controlled, for example, by a control device 220 which, for example, is also connected to the load circuit 201 and / or is integrated into an electronics of the kitchen appliance 1. To regulate the activation of the heating element 210, for example, temperature values can be evaluated by the detection of a temperature sensor 4 by the control device 220, the temperature sensor 4 being integrated, for example, in the stirred vessel.

The above explanation of the embodiments describes the present invention exclusively in the context of examples. Of course, individual features of the embodiments can be freely combined with one another, provided that they are technically sensible, without departing from the scope of the present invention.

List of reference symbols

1

Food processor

2

Stirring vessel

2.1

Mixing vessel bottom

3

Agitator

4th

Temperature sensor

20th

medium

100

Procedure

200

Heating system

201

Load circuit

202

Control circuit

210

Heating element, thick film heating

220

Control device

230

Control element

250

Switching element

250.1

parasitic diode

250.2

Control connection

250.3

Input connector

250.4

Output connector

250a

first switching element

250b

second switching element

260

Voltage source, AC voltage source

270

Potential separation device

270.1

first connection

270.2

second connection

270.3

first winding

270.4

second winding

280

Energy transmitter, energy source, switched-mode power supply

290

Power supply device

A.

Control signal

D.

Drain potential

G

Control potential, gate potential

I.

electric current, alternating current

KS

Control signal

GND

first ground potential

SGND

second ground potential

R1

first resistance

R2

second resistance

R3

third resistance

S.

Source potential, common reference potential

U

tension

U270

Power supply for 270

X1

Power supply, if necessary corresponds to 260

Claims (14)

1. Heating system (200) for operating a heating element (210), in particular in a food processor (1), comprising:

   - a load circuit (201) comprising at least two electronic switching elements (250) each comprising a control terminal (250.2) and a respective input terminal (250.3), wherein the switching elements (250) are anti-serially interconnected to influence an alternating current (I) to the heating element (210),

   - a control circuit (202) to initiate an electric control signal (A) to control the switching elements (250),

   - a potential separating device (270) for providing the control signal (A) at the control terminals (250.2) in such a way that an electric potential at the input terminals (250.3) forms a common reference potential (S) of the switching elements (250) for the control signal (A).
2. Heating system (200) according to claim 1,
   characterized in that
   the load circuit (201) and the control circuit (202) are electrically connected to different grounds, wherein a first ground potential (GND) is connected to the load circuit (201), and a second ground potential (SGND) is connected to the control circuit (202), preferably electrically connected to the input terminals (250.3), and particularly preferably forming the common reference potential (S).
3. Heating system (200) according to claim 1 or 2,
   characterized in that
   the switching elements (250) are each designed as a transistor, preferably as a field-effect transistor, preferably as a MOSFET, so that a current flow between the input terminal (250.3) and an output terminal (250.4) of the respective switching element (250) is influenced in one direction in each case by switching the respective switching elements (250) using the control signal (A), wherein the control terminal (250.2) of the respective switching elements (250) is electrically connected to the potential separating device (270) for switching.
4. Heating system (200) according to any one of the preceding claims,
   characterized in that
   the potential separating device (270) comprises a first terminal (270.1), which is electrically connected to the control terminals (250.2) of the switching elements (250), and a second terminal (270.2), which is electrically connected to the input terminals (250.3) of the switching elements (250), in order to generate a potential difference between the first and second terminals (270.1, 270.2) for the control signal (A).
5. Heating system (200) according to any one of the preceding claims,
   characterized in that
   the switching elements (250) are integrated into the load circuit (201) in such a way that they comprise a current blocking direction in the load circuit (201) which differs from one another, in particular by a corresponding alignment of a parasitic diode (250.1) between a carrier material and an output terminal (250.4) of the switching elements (250), so that different half-waves of a supply voltage of the load circuit (201) can be blocked.
6. Heating system (200) according to any one of the preceding claims,
   characterized in that
   a controlling device (220) for heating regulation is provided in order to carry out electric activation of the potential separating device (270) for a potential-free generation of the control signal (A), so that the switching elements (250) can be controlled at high frequency by the control signal (A), in particular at a switching frequency above 2 kHz.
7. Heating system (200) according to any one of the preceding claims,
   characterized in that
   the load circuit (201) comprises to the heating element (210) or can be connected to the heating element (210), which is designed as a thick-film heater and can preferably be integrated in a stirring vessel (2) of a food processor (1).
8. Heating system (200) according to any one of the preceding claims,
   characterized in that
   the load circuit (201) comprises a voltage source (260), in particular an alternating voltage source (260), for providing the alternating current (I) of the load circuit (201), which can be electrically connected to the heating element (210) via the switching elements (250) in order to transmit electrical power to the heating element (210), so that the power transmission can be controlled, in particular switched, by the switching elements (250) depending on the control signal (A).
9. Heating system (200) according to any one of the preceding claims,
   characterized in that
   the potential separating device (270) is connected to the switching elements (250) in such a way that, when the control signal (A) is provided, an at least almost constant voltage can be generated directly by the potential separating device (270) between the respective control terminal (250.2), in particular a gate terminal, and the respective input terminal (250.3), in particular a source terminal, preferably at least almost independently of a polarity of the alternating current (I) and/or of a voltage between output terminals (250.4) of the switching elements (250) in normal operation.
10. Heating system (200) according to any one of the preceding claims,
    characterized in that
    the control circuit (202) comprises an energy transformer (280), preferably a dedicated energy source (280) and/or a switched-mode power supply (280) and/or an AC/DC converter (280), to provide the current supply to the control circuit (202), and preferably to supply energy to the potential separating device (270) for generating the control signal (A).
11. Heating system (200) according to any one of the preceding claims,
    characterized in that
    the potential separating device (270) is designed as an opto-coupler.
12. Heating system (200) according to any one of the preceding claims,
    characterized in that
    at least one of the following arrangements are provided:

    - the potential separating device (270) and a voltage source (260) of the load circuit (201) are each directly connected to a common ground potential (GND),

    - the potential separation device (270), in particular a first terminal (270.1) of the potential separation device (270), is connected to the first switching element (250a) via at least one first resistor (R1) and to the second switching element (250b) via at least one second resistor (R2),

    - the potential separation device (270), in particular a first terminal (270.1) of the potential separation device (270), is connected to a source potential (S) of the switching elements (250) via at least one third resistor, wherein the third resistor (R3) is very much larger than the first and second resistors (R1, R2).
13. Method for operating a heating element (210), in particular in a food processor (1), wherein a load circuit (201) with the heating element (210) and a control circuit (202) are provided, wherein the following steps are performed:

    - Control of a potential separating device (270) connected to the control circuit (202) by a controlling device (220) depending on a control specification, so that a first control signal (A) is generated potential-free in the case of a first control specification, and a second control signal (A) is generated potential-free in the case of a second control specification,

    - Application of the generated control signal (A) to at least two switching elements (250) so that an alternating current (I) in the load circuit (201) to the heating element (210) is blocked for both current directions when the generated control signal (A) is the first control signal (A) and is enabled for both current directions when the generated control signal (A) is the second control signal (A), wherein a heating system (200) according to any one of the preceding claims is operated.
14. Food processor (1) for at least partially automatic preparation of food, comprising:

    - at least one stirring vessel (2), which comprises at least one heating element (210),

    - at least one temperature sensor (4) for acquiring a temperature at the stirring vessel (2),

    characterized in that
    a heating system (200) according to any one of claims 1 to 12 is provided for performing a heating regulation of the heating element (210) based on the acquired temperature.

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