Protective circuit for an electronic fuse for a motor vehicle, electronic fuse, and method for operating an electronic fuse

Abstract

The invention relates to a protective circuit (24) for an electronic fuse (14) for a motor vehicle (10), the protective circuit (24) being formed in parallel with the electronic fuse (14) in an electrical network (12), and the protective circuit (24) having at least a relief switch (28) and a relief impedor (30). The invention also relates to an electronic fuse (14) and to a method for operating an electronic fuse (14).

Description

[0001] Protective circuit for an electronic fuse for a motor vehicle, electronic fuse and method for operating an electronic fuse

[0002] The following invention relates to a protective circuit for an electronic fuse for a motor vehicle. Furthermore, the invention relates to an electronic fuse and a method for operating an electronic fuse.

[0003] Switching off a so-called electronic fuse while a current is flowing leads to high voltages. Appropriate protection circuits are therefore required, especially for the component protection of the MOSFET, which is often provided as an electronic fuse. Common protection circuits include bidirectional parallel TVS diodes, active clamping or avalanche methods, unidirectional freewheeling diodes, or unidirectional TVS diodes.

[0004] EP 3 022 432 B1 relates to an electronic switch in motor vehicles, comprising a switching network. Furthermore, the subject matter relates to a system with an electrical switch and a method for controlling such an electrical switch.

[0005] DE 102007 026 165 A1 relates to a switching device for electrically connecting a plurality of consumers of a motor vehicle to at least one electrical energy source, wherein the switching device has at least one electric motor-driven switch, wherein the switch has a plurality of switching positions and, in the different switching positions, different consumers can be connected to or separated from at least one energy source individually, together or in predetermined groups.

[0006] The object of the present invention is to provide a protective circuit, an electronic fuse, and a method for operating an electronic fuse, by means of which improved operation of an electronic fuse can be realized. This object is achieved by a protective circuit, an electronic fuse, and a method for operating an electronic fuse according to the independent patent claims. Advantageous embodiments are specified in the subclaims.

[0007] One aspect of the invention relates to a protective circuit for an electronic fuse for a motor vehicle. It is provided that the protective circuit is configured in parallel with the electronic fuse in an electrical network, wherein the protective circuit comprises at least one relief switch and a relief impedance.

[0008] In particular, unlike fuses, electronic fuses can interrupt fault currents, such as short circuits, multiple times. The fault current must be allowed to flow freely during the interruption to prevent destructive voltages from occurring in the vehicle electrical system. To achieve this, electronic fuses utilize freewheeling diodes or the avalanche effect of the corresponding MOSFETs, for example. However, the avalanche effect in particular must not be overstressed.

[0009] Due to the high clamping voltage of the avalanche effect, the energy loss is very high, leading to a sharp and rapid temperature rise. Power semiconductors have datasheet specifications for avalanche characteristics and are rated with a maximum number of pulses, which is also referred to as single-pulse avalanche and repetitive avalanche. Exceeding the repetitive avalanche energy must be avoided to ensure repeated turn-off of the semiconductor switch.

[0010] In particular, in the event of a fault in an electrical network, after the current is switched off, it would freewheel via the avalanche effect of the electronic fuse and an external freewheeling diode. The power loss when using the avalanche is much higher than with the freewheeling diode, particularly due to the resulting voltage of approximately 32 to 40 volts with the avalanche effect compared to 0.6 to 1 volt with the freewheeling diode.

[0011] According to the invention, for example, when an overcurrent value is reached, the electronic fuse is opened and a parallel discharge switch is closed simultaneously. As a result, the fault current on the low-impedance discharge switch commutates to the discharge impedance.

[0012] After the current is switched off, the current stored in the line is immediately commutated to the equivalent impedance. The freewheeling diode is now subjected to a higher energy input. However, due to the lower forward voltage, the load is comparatively low and does not require a significant adjustment of the component's dimensions. After a defined time or after a criterion, such as a specified voltage or current, is reached, the discharge switch is opened again.

[0013] The discharge impedance can be implemented in the same power distribution board as the electronic fuse to be discharged. The capacitive load requires a minimum capacitance according to the law of conservation of energy as follows:

[0014] EL = 1 / 2 LA l 2 = E C = 1 / 2CU 2

[0015] In particular, this allows for reduced avalanche energy, which increases the component life of the electronic fuse. Furthermore, a reduced design of the protective circuit can be realized. Furthermore, centering of the protective circuit can be achieved. The proposed discharge switches, together with the discharge impedance, can be used for multiple electronic fuses in a power distribution system, so that, in particular, separate TVS diodes are not necessary for each fuse. Furthermore, an increased ASIL qualification can be achieved with a redundant discharge switch. Furthermore, the use of the protection concept for other overvoltage pulses in the vehicle electrical system, such as load dump, can also be enabled.

[0016] According to an advantageous embodiment, the discharge switch is designed as an electronic switch. For example, the discharge switch can essentially be designed as a MOSFET. This allows for a simple discharge switch to be provided.

[0017] In particular, it is intended that the electronic switch be designed as a MOSFET. MOSFETs, in particular, are already established electronic switches in the state of the art, which are easy to use and have a correspondingly long service life. It is also advantageous if the relief impedance is designed as a capacitance. In particular, the formula:

[0018] EL = 1 / 2 LA l 2 = E C = 1 / 2CU 2The magnitude of the relief impedance must be provided. Here, L represents the inductance, I the current, C the capacitance, and U the voltage to determine the energy E. Thus, freewheeling can be achieved via the relief impedance.

[0019] It has also proven advantageous if the discharge switch is arranged in series with the discharge impedance. In particular, this allows the discharge impedance to absorb the corresponding current within the electrical network when the discharge switch is closed.

[0020] It has also proven advantageous if the discharge switch is designed to close when a predetermined current value is exceeded. In other words, when the current value within the electrical network is exceeded, the electronic fuse opens, allowing the current to flow through the discharge switch, particularly the closed discharge switch. This allows for improved operation of the protective circuit.

[0021] It is also advantageous if the switching device has a precharging circuit for negatively precharging the relief impedance. In particular, this makes it possible to provide a voltage doubler, which is preferably a "negative bias", which aims to negatively precharge the capacitive load. This results in a reduction in the required capacitance. This can therefore lead to a reduction in the required capacitance for a comparatively four-fold relief, for example, particularly compared to a simple connection of the switched capacitor. In corresponding variants, for example, only two unidirectional MOSFETs may be required, which can also be found in a common package. When using a preferred variant, care must be taken to select the appropriate resistance value. Furthermore, in different variants, the circuit can be implemented using two FI bridges.Thus, a corresponding precharging circuit can be provided in a simple manner. It is further advantageous if the precharging circuit comprises at least one bidirectional parallel TVS diode and / or a unidirectional freewheeling diode and / or an ohmic resistor. Thus, simple electronic components can be used to provide the precharging circuit accordingly.

[0022] A further aspect of the invention relates to an electronic fuse for a motor vehicle with at least one protective circuit according to the previous aspect.

[0023] Furthermore, the invention therefore also relates to an electrical network for a motor vehicle with an electronic fuse according to the preceding aspect.

[0024] Furthermore, the invention also relates to a motor vehicle with an electrical network according to the preceding aspect.

[0025] Yet another aspect of the invention relates to a method for operating an electronic fuse according to the preceding aspect. A current within the electrical network is detected, and the electronic fuse is opened when the current exceeds a predetermined current threshold. The discharge switch is then closed when the current threshold is exceeded.

[0026] Advantageous embodiments of the protective circuit are considered to be advantageous embodiments of the electronic fuse, the electrical network, the motor vehicle, and the method. The protective circuit, the electronic fuse, the electrical network, and the motor vehicle have specific features for this purpose, enabling the corresponding method steps to be carried out.

[0027] Further features of the invention emerge from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective specified combination, but also in other combinations or on their own.

[0028] The invention will now be explained in more detail using a preferred embodiment and with reference to the drawings. In the drawings: Fig. 1 is a schematic side view of an embodiment of a

[0029] Motor vehicle with an embodiment of an electrical network with an embodiment of an electronic fuse;

[0030] Fig. 2 is a schematic block diagram according to an embodiment of an electrical network; and

[0031] Fig. 3 is a schematic block diagram according to an embodiment of a

[0032] Protection circuit.

[0033] In the figures, identical or functionally identical elements are provided with the same reference numerals.

[0034] Fig. 1 shows a schematic side view of an embodiment of a motor vehicle 10. The motor vehicle 10 has, in particular, an electrical network 12, for example in the form of an on-board electrical system. The on-board electrical system 12 has at least one electronic fuse 14.

[0035] Fig. 2 shows a schematic block diagram according to an embodiment of the electrical system 12. In particular, the electronic fuse 14 is shown in more detail.

[0036] The electrical system 12 has a consumer 16 and a battery 18.

[0037] Furthermore, a line A and a line B are shown. Line A is formed between the battery 18 and the electronic fuse 14, and line B is formed between the electronic fuse 14 and the load 16. The electrical lines A and B are shown in this figure with their properties as ohmic resistance and parasitic inductance.

[0038] In the present exemplary embodiment, the electronic fuse 14 has, in particular, a switching element 20, which is designed, in particular, as a MOSFET. A freewheeling diode 22 is also shown. Furthermore, Fig. 2 shows that the electronic fuse 14 has a protective circuit 24. In particular, a ground 26 is also shown in the electrical system 12. According to an embodiment of the invention, it is provided that the protective circuit 24 is designed in parallel with the electronic fuse 14 or with the switching element 20, wherein the protective circuit 24 has at least one relief switch 28 and a relief impedance 30. The relief switch 28 can be designed as an electronic switch, in particular as a MOSFET. Furthermore, it is shown that the relief impedance 30 is designed as a capacitor. The relief switch 28 is arranged, in particular, in series with the relief impedance 30.

[0039] In particular, it is provided that the relief switch 28 is designed to close when a predetermined current value is exceeded.

[0040] In particular, Fig. 2 shows that when an overcurrent value of, for example, 400 amperes is reached, the electronic fuse 14, in particular the switching element 20, is opened and simultaneously the parallel discharge switch 28 is closed. As a result, the fault current commutates from line A to the low-impedance discharge switch 28 into the discharge impedance 30.

[0041] After the current is switched off, the current stored in line A is immediately recommutated into the discharge impedance 30. The freewheeling diode 22 is now loaded with a higher energy input from line B. However, due to the lower forward voltage and the lower energy quantity in line B, the load is comparatively low and does not lead to a significant adjustment of the component dimensioning. After a defined time or after a criterion, such as voltage or current, is reached, the discharge switch 28 is opened again, and the discharge capacitance is discharged. The discharge impedance 30 is implemented in the same power distribution board as the electronic fuse 14 to be discharged. The capacitive load requires a minimum capacitance according to the law of conservation of energy:

[0042] EL = 1 / 2 LA l 2 = E C = 1 / 2CU 2

[0043] Fig. 2 shows that, for example, the protective circuit 24 can be implemented in the electronic fuse 14, for example in a housing of the electronic fuse 14. Alternatively, these can also be formed separately from one another. Fig. 3 shows a schematic block diagram according to an embodiment of a pre-charging circuit 32 for negatively pre-charging the relief impedance 30. In particular, it can be provided that the pre-charging circuit 32 has at least one bidirectional parallel TVS diode Zsi and / or a unidirectional freewheeling diode Zs2 and / or an ohmic resistor Zss. The negative pre-charging circuit 32 could also be implemented using power electronics, for example with a full bridge.

[0044] In particular, a voltage doubler, also known as negative bias, can be described with the goal of negatively precharging the capacitive load. This results in a reduction of the required capacitance by, for example, a quarter.

[0045] For example, it can be provided that the discharge impedance 30 is precharged via the battery 18, with a switch Z1 and Z2 closed and a switch Z3 and Z4 open. The discharge effect is achieved in particular by charging the capacitance with the starting voltage subtracted from the mains voltage, with Z1 and Z2 open and Z3 and Z4 closed.

[0046] In a first variant, it can be provided that the switches Z1 and Z2 are designed with a parallel TVS diode Zsi, and the switches Z3, Z4 are also designed as switches with a parallel TVS diode Zsi. The switches can be MOSFETs, for example. Another variant can be that the switches Z1 and Z2 are designed as

[0047] The switches Z1 and Z2 are designed as an ohmic resistor Zss, and the switches Z3 and Z4 are designed with a bidirectional parallel TVS diode Zsi. Yet another variant offers the switches Z1 and Z2 as an ohmic resistor Zss, and the switches Z3 and Z4 are designed with a unidirectional freewheeling diode Zs2 or as an avalanche. Furthermore, a fourth variant offers the switches Z1, Z2, Z3, and Z4 with parallel unidirectional freewheeling diodes Zs2 or avalanche.

[0048] In particular, the relief capacitance 30 is precharged to the voltage -UMains. With the help of the impedances or switching elements Z1, Z2, the capacitance is negatively precharged. When the relief effect occurs, as soon as a fault current shutdown of the "parallel" electronic fuse 14 to be relieved occurs, Z1 and Z2 are opened and Z3 and Z4 are closed simultaneously to provide the relief effect. The relief circuit can be deactivated when, for example, the switching state is returned to the initial state. This can occur after a timeout such as 100 psec, 500 psec, or 1 msec, or after the measured current flowing in the relief impedance has fallen below a defined threshold.

[0049] In particular, the third variant mentioned above requires only two unidirectional MOSFETs, which can also be used in a single package. When using a variant with an ohmic resistance Zss, careful selection of the resistance value is important; for example, 30 kΩ allows for power dissipation to be limited to below 10 mW and results in a charging time of 10 minutes with a capacitance of 2 pF. In variants 1 and 4, the switch can be implemented using two H-bridge components Z1, Z4 and Z2, Z3.

[0050] Reference symbols

[0051] 10 motor vehicle

[0052] 12 electrical network

[0053] 14 electronic fuse

[0054] 16 consumers

[0055] 18 Battery

[0056] 20 switching element

[0057] 22 Freewheeling diode

[0058] 24 protective circuit

[0059] 26 Mass

[0060] 28 relief switches

[0061] 30 Relief impedance

[0062] 32 Precharge circuit

[0063] Z1 switch

[0064] Z2 switch

[0065] Z3 switch

[0066] Z4 switch

[0067] Zsi bidirectional parallel TVS diode

[0068] Zs2 unidirectional freewheeling diode

[0069] Zs3 Ohm resistance

[0070] A line

[0071] B Line

Claims

Patent claims 1. A protective circuit (24) for an electronic fuse (14) for a motor vehicle (10), wherein the protective circuit (24) is formed parallel to the electronic fuse (14) in an electrical network (12), wherein the protective circuit (24) has at least one relief switch (28) and a relief impedance (30).

2. Protective circuit (14) according to claim 1, characterized in that the relief switch (28) is designed as an electronic switch.

3. Protection circuit (14) according to claim 1 or 2, characterized in that the electronic switch is designed as a MOSFET.

4. Protection circuit (14) according to one of the preceding claims, characterized in that the relief impedance (30) is designed as a capacitor.

5. Protection circuit (14) according to one of the preceding claims, characterized in that the relief switch (28) is arranged in series with the relief impedance (30).

6. Protection circuit (14) according to one of the preceding claims, characterized in that the relief switch (28) is designed to close when a predetermined current value is exceeded.

7. Protection circuit (14) according to one of the preceding claims, characterized in that the protection circuit (24) has a precharging circuit (32) for negatively precharging the relief impedance (30).

8. Protection circuit (24) according to claim 7, characterized in that the pre-charging circuit (32) has at least one bidirectional parallel TVS diode (Zsi) and / or a unidirectional freewheeling diode (Zs2) and / or an ohmic resistor (Zss).

9. Electronic fuse (14) for a motor vehicle (10) with at least one protective circuit (24) according to one of claims 1 to 8.

10. A method for operating an electronic fuse (14) according to claim 9, comprising the steps: Detecting a current within the electrical network (12); Opening the electronic fuse (14) when the current exceeds a predetermined current threshold; and closing the relief switch (28) when the current threshold is exceeded.

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