Circuit arrangement for vehicle and electric heater

Abstract

The invention relates to a circuit arrangement (1) for an electric heater, in particular an electric fluid heater (12), for a vehicle, comprising: a connection for providing a voltage, in particular a high voltage, having a first connection pole (HV +) for a first operating voltage potential and a second connection pole (HV-) for a second operating voltage potential; a heating resistor (RH) configured to convert a current flowing through the heating resistor (RH) into heat when a voltage is applied; an electronic switch (S1) connected in series with the heating resistor (RH) between the first connection pole (HV +) and the second connection pole (HV-); a control device (42) connected to the electronic switch (S1) and configured to operate the switch (S1) in a pulsed manner to set the heating power of the electric fluid heater (12); and an input capacitor (C1) connected in parallel with the heating resistor (RH) and the switch (S1) connected in series between the first connection pole (HV +) and the second connection pole (HV-). The heating resistor (RH) includes a first partial resistor (R1) and a second partial resistor (R2) connected in series and defining a center tap (34, 36, 38) therebetween. The circuit arrangement (1) also has an additional capacitor (C2) connected between the center tap and the second connection pole (HV-).

Description

Technical Field

[0001] The present invention relates to a circuit arrangement and an electric heater for a vehicle, and in particular to an electric fluid heater having the circuit arrangement. Background Art

[0002] Known electric heaters for vehicles, in particular electric fluid heaters, can have one or more heating elements, each comprising a heating conductor layer arranged on a support element. The heating conductor layer comprises heating conductor tracks and connection regions for making electrical contact with the heating conductor tracks. The heat required for the heating operation can be generated in the heating conductor tracks of the heating conductor layer by applying a voltage, with the heating conductor layer acting as a heating resistor. The heating power can be set, for example, by pulse operation, in particular by pulse width modulation (PWM), pulse frequency modulation (PFM), constant on-time control (COT), or similar methods known per se.

[0003] Pulsed operation is associated with sudden current and voltage jumps. These can cause line-related disturbances. To meet prevailing EMC compliance requirements, these current and voltage jumps must be filtered out. Otherwise, there is a risk of damage to the circuit arrangement or electronic components of connected devices, unwanted electromagnetic radiation within the relevant frequency range, or the generation of objectionable noise.

[0004] For this purpose, electronic filter components are usually provided in the circuit arrangement in question, for example input capacitors, also called DC link capacitors, or common mode chokes, which each fulfill a certain function and are dimensioned accordingly.

[0005] High-voltage heaters for vehicles, in particular high-voltage fluid heaters, operate, for example, at voltages greater than or equal to 250 volts, for example in the range of 250 to 490 volts in the case of so-called 400 V heaters, and in particular at voltages greater than or equal to 500 volts, greater than or equal to 700 volts, 800 volts, or 1000 volts. This is associated with very high heating powers, such as 5 kW, 8 kW, 10 kW, or even higher. In such cases, the size or variations required for the corresponding high-frequency switching of voltages and currents, such as in the case of input capacitors, already occupy a considerable volume within the control housing of the heating device in question, where space is often a concern. Even more significantly, however, the increased capacity that the input capacitors must provide under these conditions increases the component costs considerably. Consequently, the cost and size of the capacitor components become crucial in the design and production of high-voltage electric heating devices for vehicles. Summary of the Invention

[0006] The invention is therefore based on the object of providing a circuit arrangement for an electric heater, in particular an electric fluid heater, for a vehicle, which circuit arrangement involves less costs than known heaters and also has a space-saving design.

[0007] According to various aspects of the present invention, a circuit arrangement for an electric heater for a vehicle, in particular an electric fluid heater, is provided. The circuit arrangement includes an electrical connection for supplying a voltage, in particular a high voltage, wherein the electrical connection includes a first terminal for a first voltage potential and a second terminal for a second voltage potential (e.g., ground potential). The power supply can be provided, for example, by a vehicle battery at the electrical connection terminals. The voltage provided is a DC voltage.

[0008] Furthermore, the circuit arrangement comprises a heating resistor and an electronic switch, the heating resistor being configured to convert the current flowing through the heating resistor into heat when a voltage is applied, the electronic switch being connected in series with the heating resistor between a first terminal pole and a second terminal pole. The electronic switch can be a power switch, in particular a power MOSFET or an IGBT, etc. Furthermore, the circuit arrangement comprises a control device, which is connected to the electronic switch and is configured to operate the switch in a pulsed manner (for example in a pulse width modulation (PWM) or pulse frequency modulation (PFM) manner) to set the heating power of the electric heater. Other pulse operation methods, such as COT (constant on-time control), etc. are also possible.

[0009] The circuit arrangement also includes an input capacitor connected in parallel with the heating resistor, which is connected in series with the switch and between the first and second terminal poles. This input capacitor serves as a filter capacitor to smooth out voltage jumps caused by the switch, particularly during switching operations. The input capacitor is also referred to as a DC link capacitor.

[0010] A special feature of the present aspect is that, although the heating resistor comprises a first partial resistor and a second partial resistor connected in series and defining a center tap (also indicated as center connection point) between them, the circuit arrangement also has an additional capacitor connected between this center tap and the second terminal pole - that is, in parallel with the second partial resistor but in series with the first partial resistor.

[0011] Thus, the circuit arrangement can provide that the input capacitor, together with the first and second resistor sections or the entire heating resistor, forms a first low-pass filter, and the additional capacitor, together with only the first resistor section of the heating resistor, forms a second low-pass filter, so that the entire circuit arrangement forms a second-order low-pass filter. Due to this configuration, compared to a conventional arrangement that provides only an input capacitor without the additional capacitor described above, for example, the filter's attenuation of 20 dB per decade (frequency) can be amplified to 40 dB.

[0012] However, the decisive factor for the advantages to be achieved is not the attenuation of the amplification, but the possibility of designing the input capacitor to be smaller in terms of its size (dimensions and capacitance) and at the same time meeting the requirements in terms of EMC (electromagnetic compatibility) by adding additional capacitors to the described circuit arrangement.

[0013] In this case, according to an embodiment, the additional capacitor may have a (second) capacitance value that is lower than the corresponding (first) capacitance value of the input capacitor. It has been found that a value that is already several powers of ten lower than in conventional cases is sufficient for the additional capacitor to allow the first capacitance value of the input capacitor to be reduced by, for example, half or more with respect to the same filtering effect (from a specific frequency range) while meeting the same EMC requirements.

[0014] In this case, according to an embodiment, the sum of the two capacitance values ​​is less than one capacitance value according to the conventional case, in each case requiring compliance with EMC requirements. Therefore, given the low requirements for capacitance, the additional cost is low. The same applies to its size. In addition, the additional capacitor can also be attached to the printed circuit board in the usual way, for example using THT technology, so that any additional work involved in assembly remains easy to manage. In contrast, the large input capacitor can be designed to be more advantageous, for example, with only about half the BOM (bill of materials) cost. The same applies to its size, thereby saving considerable space in the housing. Therefore, in general, cost reduction and space saving can be achieved by various aspects of the present invention.

[0015] For example, the first capacitance value of the input capacitor may be at least 10 times, preferably at least 100 times, further preferably at least 1000 times greater than the second capacitance value of the additional capacitor.

[0016] Furthermore, this aspect reduces the edges of voltage pulses, in particular those occurring at the high-side portion of the heating conductor, and thus also reduces the common-mode interference that occurs. This also indirectly allows for a relaxation of the requirements on any common-mode chokes that may be present.

[0017] Furthermore, even if the need for action is recognized, a second-order filter, as implemented in the present case, cannot be simply created with only additional resistors, as might seem obvious at first glance. This is because considerable power loss would occur in this case, meaning that power cannot be utilized. Instead, a portion of the heating resistor is used in conjunction with an additional capacitor to increase the filtering effect or, while maintaining the same filtering effect, to reduce the load on the input capacitor, thereby enabling it to be designed smaller.

[0018] According to a specific embodiment of various aspects of the circuit arrangement, the first and second resistor sections have the same ohmic resistance value. Consequently, the voltage divider in the heating resistor (which is configured for the additional capacitor) is implemented in such a way that the voltage generated at the center tap or center connection point is half the value of the maximum voltage or provided operating voltage. On the one hand, it has been shown that this achieves good (even if not optimal) decoupling of potentially resonant circuit components, while on the other hand, this results in optimal potential for reducing the size of the components associated with the input capacitor.

[0019] However, other ratios between the values ​​of the first and second partial resistors are essentially equally possible, preferably within a ratio range of 1 / 4 to 4, and more preferably within a ratio range of 2 / 3 to 3 / 2. If the center tap or center connection point is moved too far from the high-side end of the entire heating resistor, the additional capacitor becomes almost a simple parallel connection with the input capacitor. Its function is then reduced to an additional contribution to the total capacitance. In contrast, if the center tap or center connection point is moved too far from the low-side end of the entire heating resistor, the additional capacitor loses its function significantly due to the reduced resistance, and its contribution to reducing the size of the input capacitor disappears.

[0020] It should be noted that in the case of circuit arrangements according to the above-described aspects and embodiments, the input capacitor and the additional capacitor each form an electronic component, that is, are implemented as discrete components, for example on a corresponding printed circuit board, or are configured as specifically structured capacitor elements on a corresponding substrate (in the case of a structure formed on a ceramic substrate by thick-film technology), and in particular are not arranged as parasitic structures, for example as housing parts that randomly interact with arranged conductors, which is not always avoidable.

[0021] A further aspect of the present invention provides an electric fluid heater for a vehicle, the electric fluid heater having the circuit arrangement described above.

[0022] In the present context, an electric fluid heater is understood to be a heater in which heat is dissipated to a liquid heat transfer medium flowing through a heat transfer circuit of the heater. The heat transfer medium can in particular be the vehicle's liquid coolant, which transports heat within the vehicle and can dissipate heat at various locations. Alternatively, the fluid heater can also be, for example, a component of a heat pump in the vehicle, so that the heat transfer medium can be, for example, the heat pump's refrigerant. In this case, the refrigerant may only be present under certain conditions, only temporarily, or may never be completely liquid, or may also be partially or completely gaseous. However, this is also understood to refer to a fluid heater.

[0023] The electric fluid heater is intended for use in a vehicle. Vehicles are generally understood to mean all possible mobile vehicles, in particular buses, trucks or utility vehicles, construction machines, aircraft, and watercraft. This also includes vehicles that can be towed and transported by other vehicles, such as construction machines or cranes, as well as trailers, such as caravans.

[0024] The electric fluid heater preferably has a heating power of at least 3 kW, preferably at least 5 kW, further preferably at least 7 kW, for example at least 9 kW. The heating power is preferably less than or equal to 13 kW. The operating voltage at which the vehicle heater operates, i.e. the voltage present between the connection poles of the connector of the circuit arrangement and which can be equal to the on-board voltage of the electrically driven vehicle or the high voltage is greater than or equal to 250 V. For example, a heater referred to as a 400 V heater can generally cover a voltage range of 250 V to 490 V. The present invention also includes higher voltage ranges, for example greater than or equal to 500 V, for example higher than 800 V, 900 V or 1000 V. The resulting value of the ohmic resistance of the heating resistor is, for example, approximately in the range of 10 to 200 ohms.

[0025] The fluid heater comprises at least one heating element and at least one heating conductor layer. The heating conductor layer is arranged on a support element, which can be a ceramic substrate, in particular composed of Al2O3. The heating conductor layer has a heating conductor track in the plane of the heating conductor layer, which can also be curved, and the heating conductor track is defined in the plane of the heating conductor layer by at least one insulating interruption, wherein the heating conductor track forms a heating resistor of the circuit arrangement. In this case, the heating conductor layer and the heating conductor track can be arranged together on a single support element or on two or three different support elements. Preferably, each heating conductor layer or each heating conductor track is applied to its own, separate support element. The heating conductor layer or the heating conductor track can be produced on the heat-conducting ceramic substrate by screen printing methods and thick film technology.

[0026] Furthermore, the fluid heater has a heat exchanger thermally connected to the heating element. The heat converted by the heating resistor is transferred via the ceramic matrix and, if appropriate, the adhesion promoter to the fluid flowing through the heat exchanger.

[0027] This configuration allows for a particularly advantageous use of the circuit arrangement, since the heating resistor configured as a heating conductor track is relatively easily accessible on the base body, so that a voltage divider can be configured at any desired location by means of a tap or connection point (e.g., by means of a bonding conductor), at which an additional capacitor can be implemented as described. For this purpose, there is no need to intervene in the structure of the heating element itself, but rather the two partial resistors can extend directly from both sides of the tap or connection point.

[0028] According to a corresponding embodiment, a heating conductor track extends between a first terminal area and a second terminal area, wherein the heating conductor track is respectively electrically connected to at least one electrical connecting line, which respectively provides an electrical connection to a switch or to one of the two connecting poles. The center tap or connection point is thus located in the section of the heating conductor track between the first terminal area and the second terminal area.

[0029] The center tap or center connection point itself can define a third terminal area, which is connected to an electrical wire, such as the above-mentioned bonding conductor, which provides an electrical connection to an additional capacitor. In a specific embodiment, for this purpose, a third terminal position, which is already provided on the heating element in any case, is used, which is characterized by a locally widened or laterally outwardly protruding surface in the wire. This widened surface position can generally be used to provide an alternative wiring for the same heating element, in which the two strands of wire are operated in parallel on both sides of the terminal position instead of in series with the corresponding voltage. Higher powers can thereby be achieved. If such higher powers are not required, then, according to an embodiment, this center tap or center connection point can instead be used for a voltage divider according to the invention, with an additional capacitor connected thereto. An embodiment is further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be described below through specific embodiments with reference to the accompanying drawings.

[0031] In the attached figure:

[0032] Figure 1 shows a schematic circuit diagram of a circuit arrangement for an electric fluid heater according to a comparative example;

[0033] Figure 2 Shows that Figure 1 Comparative example or Figure 4 A top view of a heating element for use with the illustrated embodiment;

[0034] Figure 3A schematic circuit diagram showing a circuit arrangement for an electric fluid heater according to an alternative comparative example, but using the same Figure 1 The same heating element in

[0035] Figure 4 shows a schematic circuit diagram of a circuit arrangement for an electric fluid heater according to an embodiment;

[0036] Figure 5 Shown Figure 4 Equivalent circuit diagram of the schematic circuit diagram;

[0037] Figure 6 Shown Figure 5 Details of the heating element shown; and

[0038] Figure 7 A simplified diagram of an electric fluid vehicle heater is shown. DETAILED DESCRIPTION

[0039] In the following description of the drawings, the same reference numerals denote the same or corresponding components.

[0040] Figure 1 A schematic circuit diagram of a circuit arrangement 1 for an electric fluid heater according to a comparative example is shown.

[0041] Circuit arrangement 1 has a connection for a high voltage (e.g., 400V or 800V, etc.), comprising a first connection terminal HV+ for the actual operating voltage potential and a second connection terminal HV- for a reference potential or ground potential. Similarly, an ohmic resistor is symbolically represented on the first connection terminal HV+ side, designated as input resistance Re, which reflects, for example, a line resistance or the internal resistance of a vehicle battery. A corresponding impedance may also be included. For simplicity, the push-pull choke, which may optionally be present in the circuit arrangement, has been omitted. This also applies to the remaining figures of the present invention.

[0042] Input capacitor C1 is connected between the two connection poles. This is also called a DC link capacitor and has a filtering function. On the one hand, it smoothes fluctuations in the voltage provided by the vehicle electrical system, and on the other hand, it filters out voltage and current jumps caused by the switching process of switch S1 described below.

[0043] The circuit arrangement 1 also has a heating resistor R connected in parallel with the input capacitor C1. H , which is due to Figure 2 The heating conductor track 20 shown in FIG is formed as will be discussed below. The heating resistor R HConnected in series with switch S1, switch S1 is operated by control device 42 in a pulse width modulation manner to set the desired heating power. Switching transistor S1 may be an IGBT or a power MOSFET, etc. Control device 42 may be connected to an input device (not shown), via which, for example, a target temperature may be set, wherein the input device or control device 42 or another device sets the duty cycle for the pulse width modulation in a known manner according to the temperature at which switch S1 is operated.

[0044] Figure 2 Shows that Figure 1 Comparative Examples (or further described below) Figure 4 1 . The heating element 10 comprises a support element 14 formed as a ceramic base and a heating conductor layer 16 formed thereon. In the illustration, the support element 14 is almost completely covered by the heating conductor layer 16. The heating conductor layer 16 is formed, for example, by screen printing so that it is formed with the aid of appropriately arranged insulation interruptions 22. Figure 1 The heating conductor layer 16 can be formed in a heating conductor layer plane 18 on the support element 14 .

[0045] The support element 14 has a rectangular shape. The heating conductor track 20 is defined by two end points forming a first terminal region 32 and a second terminal region 33. The heating conductor track 20 can be formed from a copper alloy and have a thickness of, for example, 12 μm, without limiting the generality. The two terminal regions 32, 33 can be formed from the same material or supplemented by additional material in order to enable a connection, for example, with a bonding wire or another type of electrical connection line 35. In a third terminal region 34, which is arranged symmetrically in the center of the heating conductor track 20, a contact via an electrical connection line 35 can also be provided, such as Figure 1 In the heating resistor R H By means of electrical connecting lines 35 , which can be bonding wires or bonding conductors, electrical energy can be supplied to the heating conductor tracks 20 , which energy is converted into heat in the heating conductor tracks 20 and dissipated to the support element 14 .

[0046] Electrical connections 35 can connect the terminal areas 32, 33 (and, if appropriate, 34) to connection electronics not shown in the figure. This can be a power supply board, a control unit including power electronics, etc. The switch S1 can be arranged in the area of ​​these connection electronics. Each terminal area 32, 33 (and, if appropriate, 34) can be electrically connected to more than one electrical connection line 35, wherein the number of connection lines can be different between two connection lines. The connection lines 35 run from the terminal areas 32, 33 (and, if appropriate, 34) along Figure 2The heating conductor layer 16 extends in the direction of the connection side on the right in the middle and beyond the edge of the heating conductor layer 16 extending on the connection side. As described, these can all be bonding wires.

[0047] Figure 3 An alternative circuit arrangement 1 according to a comparative example of a modification is shown, which uses the same Figure 2 . In this variant, the two terminal areas 32 and 33 are connected to the first connecting pole HV+ carrying the operating voltage potential, while the third terminal area 34 located in the center of the heating conductor track 20 is connected to the switch S1, and the switch S1 is connected to the second connecting pole HV-. In other respects, Figure 3 The circuit arrangement 1 shown is Figure 1 The circuit arrangement shown is the same. The third terminal area 34 serves as a center tap (center connection point) and enables the heating resistor R H can be divided into two parts, whereby the partial resistances are operated in parallel. Therefore, if the voltage supplied is Figure 1 If the same as Figure 3 The circuit arrangement 1 can achieve a greater heating power. Therefore, Figure 2 The heating element 12 shown allows for flexible use, for example in fluid heaters having different predefined maximum powers, such as 400W or 800W devices.

[0048] Figure 4 A circuit arrangement 1 according to a first embodiment of the present invention is shown. Figure 1 or Figure 3 In the same way, we will avoid repetition here and refer to the above further description. In particular, Figure 4 The circuit arrangement 1 uses the input capacitor C1 as described above, the heating resistor R H , switch S1 and control device 42. In this embodiment, which is not intended to limit the generality of various aspects, Figure 3 The higher-power variants provide a center tap or terminal area 34, for example, for setting up a voltage divider. Because the center tap or terminal area 34 is located in the center of each conductor 20, identical conductor lengths exist between the center tap and the first and second connecting poles, respectively. This results in essentially identical partial resistances R1 and R2 between the center tap and the first and second connecting poles. Consequently, half the operating voltage is present between the center tap or third terminal area 34 and the second connecting pole HV-.

[0049] In particular, however, the additional capacitor C2 is connected between the center tap or third terminal region 34 and the second connecting pole HV-. In this case, the conductor bundle containing the additional capacitor C2 is connected in parallel with the second resistor component R2, which is connected in series with the switch S1.

[0050] The capacitance values ​​of the input capacitor C1 and the additional capacitor C2, which together form a second-order low-pass filter, are matched to each other to achieve a predetermined cut-off frequency and a predetermined damping behavior. If the capacitance of capacitor C1 is significantly greater than the capacitance of additional capacitor C2, then if R represents the total resistance, the cut-off frequency of the first low-pass filter is 1 / (2·π·R·C1) and the cut-off frequency of the second low-pass filter is 2 / (π·R·C2). If the center tap is not located in the center of the heating conductor, the second frequency is scaled accordingly. Thus, the cut-off frequency can be adapted to the desired damping behavior. The predetermined cut-off frequency and the predetermined damping behavior are in accordance with Figure 1 and Figure 3 The same requirements are shown in the comparative example.

[0051] Determining the exact values ​​of capacitance required for the two capacitors C1, C2 in this embodiment is a complex task. However, the result is that, according to Figure 1 or Figure 3 Compared to the capacitance of input capacitor C1 in the comparative example shown, the capacitance of input capacitor C1 can be reduced by at least approximately half, which saves cost and component size. Furthermore, additional capacitor C2 only needs to contribute a capacitance that is ten times smaller than the capacitance of input capacitor C1 to achieve the desired overall filtering effect through interaction.

[0052] Figure 6 A variation of the second embodiment is shown. Figure 4 In contrast to the first exemplary embodiment, the center tap is not provided at the third terminal area 34 provided in the heating element 12, but rather at a first freely located terminal area 36 along the heating conductor track 20, which is positioned in the direction of the second terminal area 33, i.e., in the direction opposite to the technical current flow direction as viewed from the third terminal area 34. Consequently, the first partial resistance R1 is now smaller than the second partial resistance R2. This also allows the center tap to be established by pre-positioning the bonding conductor along the heating conductor track 20.

[0053] Likewise Figure 6 As shown, i.e. by the dashed line and the associated double arrow along the heating conductor track 20 towards the second placement terminal area 38, an optimum ratio of R1 to R2 can be set within the framework of a design during the production of the circuit arrangement 1, which achieves an optimum filtering effect in mutual interaction with the capacitance values ​​of C1 and C2.

[0054] Figure 7A simplified diagram of an electric fluid heater 12 for a vehicle is shown. In addition to the electric heating element 10, the electric fluid heater 12 also includes a fluid heat exchanger 44 and a control unit 46 for controlling the electric heating element 10. According to an embodiment, the electric heating element 10 is arranged on the fluid heat exchanger 44 and the heat generated during the heating operation is transferred by the heating element 10 to the fluid heat exchanger 44. The control unit 46 can include one or more printed circuit boards on which the input capacitor C1, the additional capacitor C2, and the control device 42 are arranged. For this purpose, the control unit 46 is connected to the electric heating element 10 via electrical connecting lines 50. According to a general specific embodiment, which is not limiting in all respects, the heating element 10 can be assigned to another printed circuit board having one or more power switching elements forming the switch S1. The connecting lines 50 connect this printed circuit board to the printed circuit board of the control unit. The connecting lines 50 can be formed as a punched grid. Figure 7 A printed circuit board, not shown separately, having power switching elements can be connected to the heating element via connecting lines 35 . Figure 7 Not shown and for simplicity Figure 7 The other components of the electric vehicle heater 12 that are explicitly shown in FIG. 1 are well known to those skilled in the art and are supplemented by the electric vehicle heater 12 to ensure the functional capabilities of the latter.

[0055] The features of the invention disclosed in the above description, the drawings and the claims may be important for the realization of the invention individually or in any combination.

[0056] Reference Mark List

[0057] 1 Circuit Layout

[0058] 2LISN (Line Impedance Stabilization Network)

[0059] 10 Heating element

[0060] 12 Electric fluid heaters

[0061] 14 Support elements

[0062] 16 Heating conductor layer

[0063] 18 Heating conductor layer plane

[0064] 20 Heating conductor tracks

[0065] 22 Insulation interruption

[0066] 32 First terminal area

[0067] 33 Second terminal area

[0068] 34 Third terminal area

[0069] 35 electrical connection wires

[0070] 36 First free terminal area

[0071] 38 Second free terminal area

[0072] 39 center tap

[0073] 42 Control Device

[0074] 44 Heat Exchanger

[0075] 46 control unit (control board)

[0076] 50 electrical connection wires

[0077] S1 electronic switch

[0078] R H Heating resistor

[0079] R1 first part resistor

[0080] R2 Second part resistor

[0081] Re input resistance (main power supply, battery internal resistance, etc.)

[0082] C1 input capacitor, DC bus capacitor

[0083] C2 additional capacitor

Claims

1. A circuit arrangement (1) for an electric heater for a vehicle, in particular an electric fluid heater (12), comprising: an electrical connection for providing a voltage, in particular a high voltage, wherein the electrical connection has a first connection pole (HV+) for a first voltage potential and a second connection pole (HV−) for a second voltage potential; -Heating resistor (R H ), which is configured to flow through the heating resistor (R H ) current is converted into heat; - Electronic switch (S1) which is connected to the heating resistor (R H ) are connected in series between the first connection electrode (HV+) and the second connection electrode (HV-); - a control device (42) connected to the electronic switch (S1) and configured to operate the switch (S1) in a pulsed manner to set the heating power of the electric fluid heater (12); - Input capacitor (C1) connected in series with the heating resistor (R H ) and the switch (S1) are connected in parallel between the first connection electrode (HV+) and the second connection electrode (HV-), It is characterized by -Heating resistor (R H ) includes a first resistor section (R1) and a second resistor section (R2), the first resistor section (R1) and the second resistor section (R2) being connected in series and defining a center tap (34, 36, 38) therebetween; and The circuit arrangement ( 1 ) further comprises an additional capacitor ( C2 ) connected between the center tap and the second connecting pole (HV−).

2. The circuit arrangement (1) according to claim 1, wherein The input capacitor (C1) forms a first low-pass filter together with the first resistor section (R1) and the second resistor section (R2), and the additional capacitor (C2) forms a second low-pass filter together with the first resistor section (R1), whereby the circuit arrangement as a whole forms a second-order low-pass filter.

3. The circuit arrangement (1) according to claim 1 or 2, wherein The input capacitor (C1) has a first capacitance value and the additional capacitor (C2) has a second capacitance value, wherein the first capacitance value is greater than the second capacitance value.

4. The circuit arrangement (1) according to claim 3, wherein The first capacitance value is at least 10 times greater than the second capacitance value, preferably at least 100 times greater, and more preferably at least 1000 times greater.

5. The circuit arrangement (1) according to any one of claims 1 to 4, wherein The first partial resistor (R1) and the second partial resistor (R2) have the same ohmic resistance value.

6. The circuit arrangement (1) according to any one of claims 1 to 5, wherein The input capacitor (C1) and the additional capacitor (C2) each form an electronic component that is fastened to one or more printed circuit boards.

7. An electric heater, in particular an electric fluid heater (12), comprising: - A circuit arrangement (1) according to any one of claims 1 to 6; - a heating element (10) comprising a support element (14) and a heating conductor layer (16) arranged on the support element (14), the heating conductor layer (16) having a heating conductor track (20) in a heating conductor layer plane (18), the heating conductor track (20) being delimited in the heating conductor layer plane (18) by at least one insulation interruption (22), the heating conductor track (20) forming a heating resistor (R H );and - a heat exchanger (44) thermally connected to the heating element (10).

8. The electric heater (12) according to claim 7, wherein The heating conductor track (20) extends between a first terminal area (32) and a second terminal area (33), wherein the heating conductor track (20) is electrically connected to at least one electrical connection line (35), which is electrically connected to the switch (S1) or one of the two connection poles (HV+). in, The center tap is located in a section between a first terminal region (32) and a second terminal region (33) of the heating conductor track (20).

9. The electric heater (12) according to claim 8, wherein The center tap defines a third terminal area (34), which is connected to an electrical conductor (35) that establishes an electrical connection to the additional capacitor (C2).

10. The electric heater (12) according to any one of claims 7 to 9, wherein The support element (14) is a ceramic base and the heating conductor tracks (20) are wires formed of copper and formed on the support element using thick film technology.

Images