Circuit for providing an alternative ground path for a ground connection point as required

Abstract

The invention relates to a circuit (1) for providing an alternative ground path (5) for a ground connection point (10) as required in a situation in which a normal ground path (4) is interrupted, wherein, when the normal ground path (4) is intact, the alternative ground path (5) is blocked by two MOSFETs T1, T2 (2) connected in opposition, wherein the circuit (1) is configured to monitor a potential between the normal ground path (4) and the alternative ground path (5) and to open the MOSFETs T1, T2 (2) connected in opposition and to release the alternative ground path if a potential between the normal ground path (4) and the alternative ground path (5) exceeds a threshold value.

Description

[0001] Description

[0002] title

[0003] Circuit for providing an alternative ground path for a ground connection point as required

[0004] State of the art

[0005] Smaller sensor modules usually require little power and are therefore installed fully redundantly if this is required for safety reasons. There are also sensors with pre-evaluation of the data or with a redundant sensor design. If you want to build these fully redundantly, you also need a redundant power supply. This means that two (redundant) voltage sources and two (redundant) ground connections are required to ensure a fully redundant design of the respective sensor.

[0006] Disclosure of the invention

[0007] The following describes a novel circuit that allows for redundant grounding and meets a common technical requirement in automotive electronics. This problem is solved by the invention according to the features of the independent claim. Further advantageous embodiments are specified in the dependent claims as well as in the description and, in particular, in the description of the figures. It should be noted that those skilled in the art can combine the individual features in a technologically expedient manner and thus arrive at further embodiments of the invention.

[0008] What is to be described here is a circuit for providing an alternative ground path for a ground connection point as needed in a situation in which a normal ground path is interrupted, wherein the alternative ground path is blocked by two oppositely connected MOSFETs T1, T2 when the normal ground path is intact, wherein the circuit is configured to monitor a potential between the normal ground path and the alternative ground path and to open the oppositely connected MOSFETs T1, T2 and to release the alternative ground path when a potential between the normal ground path and the alternative ground path exceeds a threshold value.

[0009] A ground path here refers to an electrical connection to a ground, which can be provided with the described circuit. It can happen that a ground path is interrupted, for example because a connecting wire between the ground and the circuit has not been connected or has come loose. The circuit described here is intended to provide a solution to this problem. The simplest solution would be a direct connection between two ground paths. The two ground paths would then be short-circuited with each other. Such a setup could give rise to new difficulties, particularly because compensating currents could then flow arbitrarily between the two ground paths at any time. For this reason, the circuit described is intended to propose a solution by which an alternative ground path is only provided when a normal ground path is interrupted.

[0010] A ground connection point is a circuit terminal to which components requiring grounding (a ground connection) can be connected. From the perspective of the ground connection point, the circuit provides a ground, or earth, and it is not clear whether the ground is currently being provided via the normal ground path or the alternate ground path.

[0011] The circuit can be used, for example, in a control unit or a sensor to provide an earth / ground for the control unit or sensor or for electronic circuits of the control unit or sensor.

[0012] The circuit meets the following requirements in particular:

[0013] 1) Because the circuit allows an alternative (second or additional) ground path to be fed into a control unit, this should not lead to any additional emissions or sensitivities in the EMC (electromagnetic compatibility).

[0014] 2) Automotive manufacturers generally require the possibility of ground offsets. A ground offset means that an expected reference voltage (e.g., zero volts) of an ECU has shifted. Therefore, if the same signal voltage is measured relative to different reference voltages, different readings will be obtained. These must not lead to high ground equalization currents. The connection technology and circuitry must be able to withstand the resulting equalization currents without causing damage.

[0015] 3) The circuit should cause little voltage drop.

[0016] 4) The circuit should have a defined hysteresis for the case of an incomplete ground break. In particular, the circuit should not contribute to the creation of an oscillating circuit in which oscillations of ground currents could occur. Ground break here refers to a situation in which the ground is no longer connected to the control unit.

[0017] 5) The circuit should also be diagnosable.

[0018] The circuit described here makes it possible to provide an alternative ground path as an alternative to a normal ground path, which largely meets the requirements mentioned.

[0019] Requirement 2), for example, would require the admissibility of a ground offset of + / -3 volts at a control unit input. Voltage differences or voltage uncertainties of just + / -3 volts can generate significant electrical currents. A connector resistance of, for example, 0.05 ohms could result in compensating currents of up to 30 amps. For this reason, it is important that the alternative ground path and the normal ground path are separated from each other when the normal ground path is intact. This is achieved in the circuit described here with the MOFSETs T1 and T2, which separate the alternative ground path from the ground connection point when the normal ground path is intact.

[0020] Requirement 1) would also lead to difficulties if the normal ground path and the alternative ground path were directly connected, since equalising currents could occur which could also affect the electronics connected to the circuit (sensors and control units) via the ground connection point.

[0021] These two requirements 1) and 2) are solved in the circuit described here by having a normal ground path and only in the event of a fault, when a potential occurs between the normal ground path and the alternative ground path, is the connection to the alternative ground path established.

[0022] Requirements 3) and 2) are met by arranging the MOFSETs in opposite circuitry. The MOSFETs are preferably n-channel MOSFETs in a back-to-back structure. A MOSFET has an accompanying electrical property of an on-resistance (RDS).on) which is usually quite small and additionally a parasitic Shottky diode. The parasitic Shottky diode is a property that results from the structure of a MOSFET in most designs, in particular because the bulk region is connected to the source terminal. From an electrical point of view, the parasitic diode is connected in parallel to the actual transistor. Therefore, a single MOSFET would lead to compensating currents in the positive ground offset of the second ground terminal and might be destroyed in the process. For this reason, in the circuit described here, two oppositely connected MOSFETs T1, T2 are arranged in the alternative ground path, which together block the alternative ground path. The parasitic Shottky diodes of the MOSFETs are also oppositely aligned due to this arrangement, so that a current flow between the alternative ground path and the ground connection point via the parasitic Shottky diodes is reliably prevented.

[0023] It is particularly preferred if, in order to open the oppositely connected MOSFETs T1, T2, a voltage must be applied to the gates of the oppositely connected MOSFETs T1, T2, wherein the circuit has a diagnostic connection which is connected to the gates of the oppositely connected MOSFETs T1, T2, such that it can be measured at the diagnostic connection whether and at which point the voltage at the gates can be measured. This diagnostic connection also fulfills requirement 5) because, in the event of a fault, gate voltage is provided to the MOSFETs T1, T2. This gate voltage can be provided via a diagnostic connection to a control computer, which analyzes the gate voltage and, if necessary, generates a DTC (defect trouble code).

[0024] It is preferred if the circuit comprises a transistor T3 whose base is connected to the normal ground path and whose emitter is connected to the alternative ground path, wherein the transistor T3 is configured to monitor a potential between the normal ground path and the alternative ground path and to open when a potential between the normal ground path and the alternative ground path exceeds a threshold value.

[0025] The threshold is preferably defined such that, if the threshold is exceeded, it can be assumed that the normal ground path is interrupted. The threshold is preferably defined such that potential fluctuations at the normal ground path and the alternative ground path, which can typically occur without an interruption of the normal ground path, do not yet cause the alternative ground path to open.

[0026] The base-emitter voltage of transistor T3 contributes to providing hysteresis in the event of incomplete grounding (requirement 4).

[0027] It is further preferred if the circuit has a transistor T4 whose base is connected to a voltage supply terminal and whose emitter is connected to the alternative ground path, wherein the transistor T4 is kept open by the voltage applied to the voltage supply terminal as long as the transistor T3 is closed, wherein by opening the transistor T3 the voltage applied to the base of the transistor T4 is discharged, so that the transistor T4 closes.

[0028] It is also preferred if a battery voltage VBAT is applied to the power supply terminal, via which the circuit is supplied with voltage. The described circuit is supplied with power via the power supply terminal and a power supply connected to it (e.g., a battery with a battery voltage VBAT). The described circuit from the supply terminal to the ground paths preferably has a very high electrical resistance, which ensures that the circuit's power consumption is low or acceptable.

[0029] It is also preferred if the base of the two oppositely connected MOSFETs T1, T2 is connected to the collector of the transistor T4, so that when the transistor T4 is open, the base of the two oppositely connected MOSFETs T1, T2 is connected to the alternative ground path, so that no potential or voltage is applied to the base of the two oppositely connected MOSFETs T1, T2 and the oppositely connected MOSFETs T1, T2 are closed.

[0030] It is further preferred if a first supply current path and a second supply current path exist from the supply connection to the alternative ground path, wherein the base of the two oppositely connected MOSFETs T1, T2 only border on the second supply current path, wherein the first supply current path is enabled when the transistor T4 is open, wherein an electrical resistor R4 in the second supply current path prevents a potential from being applied to the base of the two oppositely connected MOSFETs T1, T2 when the first supply current path is enabled.

[0031] Furthermore, it is preferred if the first supply current path and the second supply current path, starting from the supply terminal, both initially run through a resistor R3, which limits a current flow from the supply terminal to the alternative ground path.

[0032] Furthermore, it is preferred if the first supply current path runs through a resistor R3 and the transistor T4 and the second supply current path runs through the resistor R3 and the resistor R4, wherein a ratio of the resistors R3 and R4 is selected such that when the transistor T4 and the first supply current path are closed, a sufficient voltage is applied to the base of the two oppositely connected MOSFETs T1, T2 connected to the second supply current path between the resistor R3 and the resistor R4 in order to open the oppositely connected MOSFETs T1, T2 and to release the alternative ground path.

[0033] Furthermore, it is preferred if a collector of the transistor T3 is connected to the supply terminal via a resistor R2.

[0034] It is also preferred if the base of the transistor T3 is connected to the supply terminal via a resistor R6.

[0035] It is further preferred if a resistor R5 is connected between the base of the transistor T3 and the normal ground path.

[0036] The invention and the technical context of the invention are explained in more detail below with reference to the figures. The figures show preferred embodiments to which the invention is not limited. It should be noted that the figures, and in particular the proportions depicted in the figures, are only schematic. It shows:

[0037] Fig. 1 : the described circuit.

[0038] Figure 1 shows the described circuit 1 without any additional ESD measures that may be provided. ESD measures include, for example, small protective capacitors to protect the two gates of MOSFETs T1 and T2.

[0039] The described circuit 1 connects the ground connection point 10 in a normal case (without fault) with the normal ground path 4 and releases the alternative ground path 5 via the MOSFETs T1 and T2 2 in the event of a fault.

[0040] The core of the described circuit 1 are the two channel MOSFETs 2 and transistors T1 and T2, which act as switches. The MOSFETs 2 and transistors T1 and T2 each have a parasitic diode 3. For this reason, they are connected in an opposite circuit 6. These are connected in opposite directions to block both voltage directions when closed. A fuse resistor R1 is also provided. This has a high resistance and prevents excessive currents from occurring if unforeseen and unspecified voltage spikes destroy the MOSFETs 2.

[0041] The normal ground path 4 is the connection to GND_0. Therefore, the chassis ground and all other electronic grounds are directly connected. The alternative ground path 5 for fault conditions is GND_1. The switches or MOSFETs 2 and resistor R1 connect GND_0 and GND_1 in the event of a fault.

[0042] MOSFETs 2 are controlled via transistors T3 and T4, which should be designed as normal NPN transistors. Normally, GND_0 and GND_1 are at a similar potential, so the emitter-base voltage UBE,T3 of T3 is < 0.5 V and this transistor is blocked. For this to happen, resistor R5 must be significantly smaller than resistor R6. The total resistance R5+R6 should be high enough to meet the customer's quiescent current requirement. Transistor T4, on the other hand, has the full battery voltage applied to the emitter base as the emitter-base voltage UBE,T4 and is conductive. The battery voltage VBAT is supplied to the circuit at supply terminal 7. Therefore, the gate voltage Ucate at transistors T1 and T2 is 0. The line to GND_1, alternative ground path 5 for the case of a fault, is blocked.

[0043] In the event of a fault, GND_0 is disconnected from the normal ground path 4. This causes transistor T3 to conduct via R6 and the base. T4 now blocks, and the gates receive full battery voltage, and the alternative ground path 5 for the fault situation, to GND_1, is conductive.

[0044] Starting from the supply connection 7, the circuit offers a first supply current path 8 and a second supply current path 9 to the alternative ground path 5. The first supply current path 8 leads through resistor R3 and the transistor T4. The second supply current path 9 leads through the resistor R3 and the resistor R4, with the gates of the MOSFETs T1, T2 2 being connected between the resistors R3 and R4. When the transistor T4 is open, the potential of the alternative ground path 5 is present between the resistor R3 and the transistor T4 and thus also at the gates of the MOSFETs T1, T2 2, and the MOSFETs T1, T2 2 are closed. When the transistor T4 is closed, the current flows via the second supply current path 9 and thus via the resistors R3 and R4. The voltage at the gates of the MOSFETs T1, T2 2 is adjusted according to the ratio R3 to R4.

[0045] The diagnostic capability is provided by the gate voltage UGATE, which can be tapped at a diagnostic connection point 11 by a diagnostic device (not shown here).

Claims

Claims 1. Circuit (1) for providing an alternative ground path (5) for a ground connection point (10) as needed in a situation in which a normal ground path (4) is interrupted, wherein the alternative ground path (5) is blocked by two oppositely connected MOSFETs T1, T2 (2) when the normal ground path (4) is intact, wherein the circuit 1 is set up to monitor a potential between the normal ground path (4) and the alternative ground path (5) and to open the oppositely connected MOSFETs T1, T2 (2) and to release the alternative ground path when a potential between the normal ground path (4) and the alternative ground path (5) exceeds a threshold value.

2. Circuit (1) according to claim 1, wherein in order to open the oppositely connected MOSFETs T1, T2 (2) a voltage must be applied to the gates of the oppositely connected MOSFETs T1, T2 (2), wherein the circuit (1) has a diagnostic connection (11) which is connected to the gates of the oppositely connected MOSFETs T1, T2 (2), so that it can be measured at the diagnostic connection (11) whether and at which the voltage at the gates can be measured.

3. Circuit according to claim 1 or 2, wherein the circuit comprises a transistor T3 whose base is connected to the normal ground path (4) and whose emitter is connected to the alternative ground path (5), wherein the transistor T3 is configured to monitor a potential between the normal ground path (4) and the alternative ground path (5) and to open when a potential between the normal ground path (4) and the alternative ground path (5) exceeds a threshold value.

4. Circuit (1) according to claim 3, wherein the circuit comprises a transistor T4, the base of which is connected to a voltage supply terminal (7) and the emitter of which is connected to the alternative ground path (5), wherein the transistor T4 is kept open by the voltage applied to the voltage supply terminal (7) as long as the transistor T3 is closed, wherein by opening the transistor T3 the voltage applied to the base of the transistor T4 is dissipated, so that the transistor T4 closes.

5. Circuit (1) according to claim 4, wherein a battery voltage VBAT is applied to the voltage supply terminal (7) via which the circuit is supplied with voltage.

6. Circuit (1) according to claim 4 or 5, wherein the base of the two oppositely connected MOSFETs T1, T2 (2) is connected to the collector of the transistor T4, so that when the transistor T4 is open, the base of the two oppositely connected MOSFETs T1, T2 (2) is connected to the alternative ground path (5), so that no potential is applied to the base of the two oppositely connected MOSFETs T1, T2 (2) and the oppositely connected MOSFETs T1, T2 (2) are closed.

7. Circuit (1) according to one of claims 4 to 6, wherein a first supply current path (8) and a second supply current path (9) exist from the supply connection (7) to the alternative ground path (5), wherein the base of the two oppositely connected MOSFETs T1, T2 (2) are only connected to the second supply current path (9), wherein the first supply current path (8) is enabled when the transistor T4 is open, wherein an electrical resistor R4 in the second supply current path (9) prevents a potential from being applied to the base of the two oppositely connected MOSFETs T1, T2 (2) when the first supply current path (8) is enabled.

8. Circuit (1) according to claim 7, wherein the first supply current path (8) and the second supply current path (9) starting from the supply terminal (7) both initially run through a resistor R3 which limits a current outflow from the supply terminal (7) to the alternative ground path (5).

9. Circuit (1) according to claim 8, wherein the first supply current path (8) runs through a resistor R3 and the transistor T4 and the second supply current path (9) runs through the resistor R3 and the resistor R4, wherein a ratio of the resistors R3 and R4 is selected such that when the transistor T4 and the first supply current path (8) are closed at the point between the resistor R3 and the resistor R4 a sufficient voltage is applied to the base of the two oppositely connected MOSFETs T1, T2 (2) connected to the second supply current path (9) in order to open the oppositely connected MOSFETs T1, T2 (2) and to release the alternative ground path (5).

10. Circuit (1) according to one of claims 3 to 9, wherein a collector of the transistor T3 is connected to the supply terminal (7) via a resistor R2.

11. Circuit (1) according to claim 10, wherein the base of the transistor T3 is connected to the supply terminal (7) via a resistor R6.

12. Circuit (1) according to one of claims 3 to 11, wherein a resistor R5 is connected between the base of the transistor T3 and the normal ground path.

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