Electrical circuit with a resistive fuse

Abstract

The invention describes an electrical circuit (100), having (i) at least one electrical component (110) and (ii) at least one zero-ohm resistor (120), wherein each of the zero-ohm resistors (120) is connected in series with an associated electrical component (110), wherein each of the zero-ohm resistors (120) is designed to interrupt an electrical connection to the associated electrical component (110) in the event of the associated electrical component (110) malfunctioning.

Description

[0001] Description

[0002] Electrical circuit with a resistor fuse

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to electronic circuits in which zero-ohm resistors are used to secure components.

[0005] BACKGROUND OF THE INVENTION

[0006] Short circuits in electronic components can lead to excessive heat generation and serious damage to the components themselves, the circuits containing them, or the corresponding products. In the worst case, a short circuit can cause the circuit to burn out, thus posing a critical safety risk.

[0007] Short circuits can occur, for example, in ceramic capacitors due to excessive bending stress. Such capacitors are used in EMC filters or in intermediate circuits for inverters and converters. To counteract the risk of short circuits, "open mode" or "soft termination" ceramic capacitors are typically used. However, the former have lower capacitance values ​​for the same design. Furthermore, both types of capacitors are comparatively expensive.

[0008] To counteract the risk of short circuits, fuses can also be installed in a common supply line leading to the power supply source of a circuit. Such a fuse can be implemented, for example, by inserting a soldered spring wire into the power supply line. In the event of a short circuit, the wire desolders, and the spring action opens the line. This prevents the short circuit and the potentially associated burn-up. At the same time, however, the circuit's function is also interrupted. SUMMARY AND EMBODIMENTS

[0009] It is therefore an object of the present disclosure to protect circuits against malfunctions such as short circuits and the associated risks as efficiently and cost-effectively as possible. If possible, the basic function of the circuit should be largely retained even if a malfunction occurs.

[0010] This object is achieved by an electrical circuit according to the independent patent claim. Advantageous embodiments and further developments of the electrical circuit emerge from the dependent claims, the following description, and the drawings.

[0011] According to one aspect of the present disclosure, an electrical circuit is provided comprising: (i) at least one electrical component and (ii) at least one zero-ohm resistor, wherein each of the zero-ohm resistors is connected in series with an associated electrical component of the electrical components. Each of the zero-ohm resistors is configured to interrupt an electrical connection to the associated electrical component in the event of a malfunction of the associated electrical component.

[0012] In the context of the present disclosure, the term “zero-ohm resistor” means in particular an electrical connection element that is physically configured as a resistor, for example as a cylindrical resistor or as an SMD (surface mounted device) resistor. The zero-ohm resistor can be identified as such, for example by means of a single black ring in the case of a cylindrical resistor or with a single or multiple zeros in the case of an SMD resistor. The zero-ohm resistor can be arranged on a printed circuit board to connect conductors of the printed circuit board to one another. According to one embodiment, only a maximum resistance value and / or a maximum power is specified for the zero-ohm resistor, in particular depending on a size and / or design of the zero-ohm resistor.The technical specification may therefore only specify a maximum resistance value for the zero-ohm resistor, not a minimum non-zero resistance value. For example, the maximum resistance value may be 300 mΩ at most, in particular 100 mΩ at most, in particular 50 mΩ at most, and in particular 20 mΩ at most. The actual resistance value may be greater than 0 mΩ.

[0013] According to one embodiment, the value of the zero-ohm resistor, in particular the actual resistance value, is defined by an upper limit and a lower limit. Accordingly, the mean value of the resistance value can be specified as the nominal value and the upper or lower limit as the tolerance of the resistance value. The upper limit can be, for example, 300 mQ, in particular 100 mQ, in particular 50 mQ, in particular 20 mQ. In other words, the zero-ohm resistor can have a resistance value less than or equal to 300 mQ, in particular less than or equal to 100 mQ, in particular less than or equal to 50 mQ, in particular less than or equal to 20 mQ. The resistance value can be greater than 0 mQ. The resistance value can be determined via four-wire measurement or four-conductor measurement. Determining the nominal value of the resistance value can comprise averaging over several measurements.The distribution of the tolerance of the resistance values ​​can be taken into account by taking into account the multiple, in particular the triple, standard deviation.

[0014] According to one embodiment, the zero-ohm resistor is an SMD resistor. The resistor can be manufactured using thick-film or thin-film technology. The resistor can have a ceramic carrier material, for example aluminum oxide. One or more resistance layers can be applied to this carrier material, for example one or more thick-film pastes. The thick-film paste can be printed onto the carrier material and then fired. In the context of the present disclosure, the term “electrical component” means in particular a component of an electrical circuit that is designed for a predetermined function. For example, an electrical component can be or have a capacitor, a coil, a diode, a transistor, or an integrated circuit. The electrical component can be an active or a passive component. The component is preferably a capacitor, in particular a ceramic capacitor.

[0015] According to one embodiment, different types of components are protected by the at least one zero-ohm resistor, in particular by a plurality of zero-ohm resistors. According to an alternative embodiment, the zero-ohm resistors all protect the same type of component, for example, a capacitor, in particular a ceramic capacitor.

[0016] According to one embodiment, the malfunction is a short circuit in the electrical component. If the component is a capacitor, in particular a ceramic capacitor, the short circuit may be caused by a capacitor break due to excessive bending stress on the capacitor.

[0017] With the described electrical circuit, it may be possible to cost-effectively protect one or more electrical components against malfunctions and / or their consequences. The zero-ohm resistors, for example, their performance class, can be adapted to the specific application context. In particular, zero-ohm resistors can be defined as fuse elements such that the functional case, i.e., the proper functioning of the component, under all tolerance conditions to be considered, is sufficiently far removed from the component's fault case at which the zero-ohm resistor fuse would trigger.

[0018] By protecting individual critical components, especially by separately protecting different components, the functionality of the electrical circuit can be at least partially maintained even if one or more of the components fail. Furthermore, zero-ohm resistors, when designed as separate components, can be more easily replaced in the event of a fault than, for example, a damaged conductor on a circuit board. Thus, the use of zero-ohm resistor fuses allows the functionality of the circuit to be ensured particularly efficiently and, if necessary, restored easily and cost-effectively.

[0019] According to one embodiment, the zero-ohm resistor has a resistance value of less than or equal to 50 mΩ, in particular less than or equal to 20 mΩ. Different zero-ohm resistors can have the same or different resistance values. Such resistance values ​​can be in the order of magnitude of conductor connections or solder joints.

[0020] Resistance values ​​of other resistors used in the electrical circuit may be larger than the resistance values ​​of the zero-ohm resistors, in particular by at least a factor of two, five or ten.

[0021] According to one embodiment, during the malfunction, a minimum short-circuit current and / or a minimum short-circuit power specified by the zero-ohm resistor is exceeded. This can lead to an interruption of the electrical connection to the associated component. The minimum short-circuit power can be defined based on the rated power or nominal power of the zero-ohm resistor, for example as a factor greater than one, in particular greater than or equal to two, of the nominal power. According to one embodiment, if the specified minimum short-circuit power and / or the specified minimum short-circuit current are exceeded, the resistance fuse formed by the zero-ohm resistor is triggered. The triggering of the resistance fuse can interrupt the flow of electrical current through the component.

[0022] Such an embodiment can be advantageous because the zero-ohm resistor, in particular its minimum short-circuit current and / or its minimum short-circuit power, can be adapted to the respective application, such as the particular malfunction to be protected. For example, a power class of the zero-ohm resistor can be adapted to the application.

[0023] According to one embodiment, a performance class of the zero-ohm resistor is selected depending on the electrical component and / or the electrical circuit. The zero-ohm resistor can be selected such that, when the electrical component or the electrical circuit is functioning properly, the minimum short-circuit current and / or the minimum short-circuit power is not reached, but in the event of a malfunction, the minimum short-circuit current and / or the minimum short-circuit power is exceeded.

[0024] According to one embodiment, the at least one zero-ohm resistor and the at least one electrical component are arranged on a printed circuit board.

[0025] According to one embodiment, a region of the circuit board that includes at least one of the zero-ohm resistors is overmolded or overmolded with plastic. All zero-ohm resistors can be overmolded or overmolded with plastic. The plastic can be a thermoset or a thermoplastic.

[0026] Such a design can be advantageous because zero-ohm resistance fuses can remain functional even when overmolded. In contrast, conventional fuses, for example, those using a spring wire, no longer trigger reliably when overmolded with plastic. Upon desoldering, the spring action cannot unfold because the spring wire is mechanically fixed by the overmold and therefore cannot jump. This can be circumvented by leaving an unmolded area around the spring wire, but this involves considerable effort. Such an unmolded area is not necessary in the case of zero-ohm resistance fuses.

[0027] According to one embodiment, the zero-ohm resistor comprises a substrate, in particular a ceramic body, and a resistance material applied to the substrate, wherein the zero-ohm resistor is arranged such that the resistance material points toward the circuit board. The resistance material can, for example, be applied to the substrate in a layered manner. The resistance material can be or comprise a resistance paste, for example, an RuO2 paste. The substrate can comprise a ceramic carrier material, for example, aluminum oxide.

[0028] By arranging the zero-ohm resistor with the resistor material facing the circuit board, the tripping time of the zero-ohm resistor fuse can be adjusted. Compared to arranging the zero-ohm resistor with the resistor material facing the mold material, the tripping time can be shortened. In other words, the mass of the overmold can increase the tripping time of the zero-ohm resistor fuse if the resistor material is oriented toward the mold material.

[0029] According to one embodiment, the zero-ohm resistor is a metal film resistor. In the context of the present disclosure, a "metal film resistor" is, in particular, a resistor in which the resistance element is applied as a layer on a carrier. The use of metal film resistors can be advantageous because they can have a low tolerance. The layer can be applied, for example, in the form of a resistance paste, in particular by printing.

[0030] Such an embodiment can be advantageous because in the event of a short circuit, the resistor paste melts, interrupting the electrical connection to the component. The resistor paste can at least partially become gaseous and expand. However, the expansion can be so small that the overmold does not burst or crack.

[0031] According to one embodiment, the electrical circuit comprises at least two zero-ohm resistors, each of the zero-ohm resistors being connected in series with an associated electrical component, the series-connected zero-ohm resistors and associated electrical components being connected in parallel to one another. Such an embodiment can be advantageous because, in the event of a component malfunction, only the affected path fails due to the triggering of the associated resistor fuse, but paths connected in parallel remain intact, thus at least partially preserving the functionality of the circuit. Zero-ohm resistors can be particularly suitable for such an arrangement because they are cost-effective, take up little space, and can be adapted to the respective component, for example with regard to the triggering criterion.

[0032] According to one embodiment, the electrical circuit comprises at least three, in particular at least five, in particular at least ten zero-ohm resistors and at least three, five, or ten associated electrical components, arranged as just described. The more components included, the less significant the malfunction of one of the components is, so that functionality is largely maintained. For example, with twenty identical capacitors connected in parallel, a short circuit results in a capacitance loss of only 5%.

[0033] According to one embodiment, one of the zero-ohm resistors is connected in series with a subcircuit comprising at least two electrical components, wherein the zero-ohm resistor connected in series with the subcircuit is configured to disconnect an electrical connection to the subcircuit in the event of a malfunction of the subcircuit.

[0034] In the context of the present disclosure, the term “subcircuit” means in particular a connected part of the electrical circuit, for example linked by corresponding electrical conductors.

[0035] Because the subcircuit is connected in series with the aforementioned zero-ohm resistor, no current flows through the subcircuit when the zero-ohm resistor fuse blows. In this respect, such a design can be advantageous because, when the resistor fuse blows, the entire subcircuit is disconnected from the current, especially the at least two other components. Thus, only one fuse is required for several electrical components. Furthermore, the frequency response of the electrical circuit can be influenced by jointly protecting several components in a subcircuit.

[0036] According to one embodiment, the zero-ohm resistor connected in series with the subcircuit is arranged in a series branch of the electrical circuit, in particular in a series branch of an intermediate circuit that the electrical circuit has. In the context of the present disclosure, the term "series branch" can be defined in particular via an electrical line that leads away from one voltage pole and is parallel to another electrical line that leads away from another voltage pole. The zero-ohm resistor can be arranged in this electrical line.

[0037] Such an embodiment can be advantageous for improving the high-frequency behavior of the electrical circuit, particularly the intermediate circuit. This can be due, for example, to the fact that the common protection of capacitors with a zero-ohm resistor can reduce inductance and / or shift a resonance point of the electrical circuit.

[0038] According to one embodiment, the additional zero-ohm resistor is arranged in a shunt branch of the electrical circuit, in particular in a shunt branch of an intermediate circuit provided by the electrical circuit. In the context of the present disclosure, the term "shunt branch" can be defined, in particular, as an electrical line connecting two additional electrical lines leading away from a respective voltage pole.

[0039] According to one embodiment, one of the zero-ohm resistors is connected in series with only one electrical component, thus protecting it, or is connected in series with at least two components connected in parallel, thus protecting them. Individual protection is advantageous because in the event of a short circuit, only one component fails, largely maintaining the functionality of the remaining circuit. Joint protection of at least two electrical components connected in parallel is more space- and cost-effective.

[0040] According to one embodiment, the at least one electrical component is a capacitor, in particular a ceramic capacitor. All electrical components can be capacitors. Alternatively, at least one of the electrical components is not a capacitor.

[0041] Such a design can be advantageous because capacitors, especially ceramic capacitors, can be particularly susceptible to short circuits, for example, due to excessive bending stress on the capacitors. For this reason, "open-mode" ceramic capacitors or "soft-termination" ceramic capacitors are often used, but these are expensive. Protecting capacitors with zero-ohm resistor fuses, on the other hand, represents a cost-effective alternative.

[0042] According to one embodiment, the electrical circuit comprises an EMC filter (electromagnetic compatibility), in particular a low-pass filter, or an intermediate circuit for an inverter and / or converter. Such circuits can comprise a plurality of capacitors, in particular ceramic capacitors, which are to be protected against short circuits. According to one embodiment, the electrical circuit is the EMC filter, in particular the low-pass filter, or the intermediate circuit for the inverter and / or converter.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further advantages and advantageous embodiments and developments of the method and the control unit emerge from the following embodiments shown in conjunction with the figures.

[0045] Figure 1 shows an electrical circuit according to a first embodiment of the present disclosure. Figure 2 shows an electrical circuit according to a second embodiment of the present disclosure.

[0046] Identical, similar, or functionally identical elements are provided with the same reference symbols in the figures. In some figures, individual reference symbols may be omitted for clarity. The figures and the relative sizes of the elements depicted in the figures are not to scale. Rather, individual elements may be exaggerated for clarity and / or clarity.

[0047] DETAILED DESCRIPTION OF EMBODIMENTS

[0048] Figure 1 shows an electrical circuit 100 according to a first exemplary embodiment. The electrical circuit 100 has a zero-ohm resistor 120 and three electrical components 110 to be protected, which are connected in parallel and in series with the zero-ohm resistor 120. The components 110 to be protected are capacitors. The zero-ohm resistor is configured to interrupt an electrical connection to the components 110, i.e., to a subcircuit containing the three components 110, in the event of a malfunction of the components 110 to be protected.

[0049] The 120-ohm zero-ohm resistors in this case are 0W SMD (surface-mounted device) resistors. SMD resistors are available in various power classes, e.g., 0.1W (0603 size); 0.125W (0805 size); 0.25W (1206 size). This allows the resistor fuse to be adapted to the functional application—that is, all conditions that occur during operation and should not lead to the fuse blowing.

[0050] Using PR = iRMs 2 *R (Eq. 1) allows the component shape to be selected according to the required maximum power dissipation. Since the resistance value of a 00 resistor is defined as 00, the actual value must be determined using a 4-wire measurement over a statistically significant number of resistors. To achieve the smallest possible resistance tolerance, metal film resistors should be used. Corresponding series of measurements resulted in the following values ​​for 0.1W (0603): 17.5mQ±3.5mQ; for 0.125W (0805): 7mQ±1mQ; and for 0.25W (1206): 14mQ±1mQ.

[0051] To ensure reliability across different batches, we recommend designing the circuit with a higher tolerance assumption (±40%). Furthermore, when using multiple resistor suppliers, the resistance value must be determined for each supplier, which may lead to a widening of the tolerance.

[0052] Now that the resistor 120 has been designed to be safe for the normal functioning of the circuit 100, the short circuit situation, i.e. the tripping of the fuse, must be considered. To do this, the minimum short-circuit current at which the fuse should trip must be determined. This must result in the nominal power of the resistor 120 being exceeded several times (Eq. 1). In addition to the size of the short-circuit power at the resistive fuse, the installation situation (thermal characteristics) of the resistor 120 also affects its tripping behavior, especially in the case of a slow short-circuit current rise. In the case of rapid processes, as is to be expected from the breakage of a ceramic capacitor, the thermal characteristics determined by the installation situation take a back seat. To ensure that this is also the case with over-molded / over-injected circuit boards, the resistor 120 should be installed so that its resistance layer points towards the circuit board.

[0053] Figure 2 shows an electrical circuit 100 according to a second exemplary embodiment. The electrical circuit 100, here an intermediate circuit of an inverter or converter, has ten capacitors 110 connected in parallel. Eight zero-ohm resistors 120 are each connected in series with a single associated capacitor 110. These zero-ohm resistors 120 are configured to interrupt an electrical connection to this capacitor 110 in the event of a malfunction of the associated capacitor 110. However, the other capacitors 110 connected in parallel are not affected, and corresponding electrical connections to these other capacitors 110 connected in parallel remain intact.

[0054] Another zero-ohm resistor 122 is arranged in the longitudinal branch of the intermediate circuit and is connected in series with a subcircuit containing the two capacitors 110 shown on the right in Figure 2. This additional zero-ohm resistor 122 is configured to interrupt a corresponding electrical connection to these capacitors 110 or to the subcircuit in the event of a malfunction of one of the two capacitors 110 mentioned.

[0055] Since such resistive fuses are small and inexpensive, they can be connected in series with respective capacitors 110, as shown in Figure 2. This means that if a capacitor 110 short-circuits, only the affected capacitor 110 itself is lost, which, for example, in an intermediate circuit of twenty identical capacitors 110 connected in parallel, represents a capacitance loss of just 5%, i.e. the function of the converter / inverter is retained. Several capacitors 110 connected in parallel can also be protected by a resistive fuse. Since the series connection of the resistor 120 to the capacitor 110 leads to an increase in the inductance of the respective capacitor branch, some of the capacitors 110, for example in the intermediate circuit, can be protected by a resistive fuse 122 in the series branch, as shown in Figure 2. This can improve the high-frequency behavior of the overall arrangement.

[0056] The invention is not limited to the exemplary embodiments by the description. Rather, the invention encompasses any novel feature and any combination of features, including, in particular, any combination of features in the exemplary embodiments and patent claims. REFERENCE SIGNS

[0057] 100 electronic circuit

[0058] 110 electronic component 120 zero-ohm resistor

[0059] 122 additional zero-ohm resistors

Claims

Patent claims 1. An electrical circuit (100) comprising at least one electrical component (110) and at least one zero-ohm resistor (120), wherein each of the zero-ohm resistors (120) is connected in series with an associated electrical component (110), wherein each of the zero-ohm resistors (120) is configured to interrupt an electrical connection to the associated electrical component (110) in the event of a malfunction of the associated electrical component (110).

2. Electrical circuit (100) according to the preceding claim, wherein during the malfunction a minimum short-circuit current predetermined by the zero-ohm resistor (120) and / or a minimum short-circuit power predetermined by the zero-ohm resistor (120) is exceeded.

3. Electrical circuit (100) according to one of the preceding claims, wherein a power class of the zero-ohm resistor (120) is selected depending on the electrical component (110) and / or the electrical circuit (100).

4. Electrical circuit (100) according to one of the preceding claims, wherein the at least one zero-ohm resistor (120) and the at least one electrical component (110) are arranged on a printed circuit board and a region of the printed circuit board comprising at least one of the zero-ohm resistors (120) is overmolded with plastic.

5. Electrical circuit (100) according to the preceding claim, wherein the zero-ohm resistor (120) comprises a substrate, in particular a ceramic body, and a resistance material which is applied to the substrate, wherein the zero-ohm resistor (120) is arranged such that the resistance material points in the direction of the printed circuit board.

6. Electrical circuit (100) according to one of the preceding claims, wherein the zero-ohm resistor (120) is a metal film resistor.

7. Electrical circuit (100) according to one of the preceding claims, comprising at least two zero-ohm resistors (120), wherein each of the zero-ohm resistors (120) is connected in series with an associated electrical component (110), wherein the series-connected zero-ohm resistors (120) and associated electrical components (110) are connected in parallel to one another.

8. Electrical circuit (100) according to one of the preceding claims, wherein one (122) of the zero-ohm resistors is connected in series with a subcircuit comprising at least two electrical components (110), wherein the zero-ohm resistor (122) connected in series with the subcircuit is configured to disconnect an electrical connection to the subcircuit in the event of a malfunction of the subcircuit.

9. Electrical circuit (100) according to the preceding claim, wherein the electrical circuit (100) is an intermediate circuit and the zero-ohm resistor (122) connected in series with the subcircuit is arranged in a series branch of the intermediate circuit.

10. Electrical circuit (100) according to one of the preceding claims, wherein the at least one electrical component (110) is a capacitor, in particular a ceramic capacitor.

11. Electrical circuit (100) according to one of the preceding claims, comprising an EMC filter, in particular a low-pass filter, or an intermediate circuit for an inverter and / or converter.

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