Method for safety-relevant detection of the voltage drop across a light source in a vehicle

Abstract

Method for determining the voltage drop (VLED) across a light source, in particular across one or more light-emitting diodes, in a vehicle, - wherein the light source is supplied with electrical energy from an operating voltage line (VA) via a light source power source (ISLED) and - wherein the light source has a first connection and a second connection, which is hereinafter referred to as the light source output (VB) and - wherein the first connection of the light source is connected to the operating voltage line (VA) and - wherein the lamp output (VB) is connected via the lamp power source (ISLED) to a reference voltage line (GND), comprising the steps: - Reducing the voltage between the operating voltage line (VA) and a reference potential line by a first factor α1 to a first reduced voltage component (VKA); - Reducing the voltage between the lamp output (VB) and the reference potential line by a second factor α2 to a second reduced voltage component (VKB), - where, in normal operation, the first factor α1 is essentially equal in magnitude to the second factor α2; - Comparison of a sum of the second reduced voltage component (VKB) and a feedback voltage component on the one hand with the first reduced voltage component (VKA) on the other hand and formation of the feedback voltage component depending on the result of this comparison in such a way that the voltage value of the said sum of the second reduced voltage component (VKB) and the feedback voltage component is equal to the voltage value of the first reduced voltage component (VKA); - Generation of an output voltage (Vout) or other suitable output signal depending on the value of the feedback voltage component, - wherein the value of the output voltage (Vout) or other suitable output signal represents or can represent a measure of the voltage drop (VLED) across the light source; - Leaving the normal operating state and entering a test state; - Modification of the first reduced voltage component (VKA) depending on a first enable signal (ENA) and / or the second reduced voltage component (VKB) depending on a second enable signal (ENB); - Recording the value of the output voltage (Vout) or the value of the other suitable output signal as a test value and comparing this test value with an expected value range and concluding that a fault exists if the test value is substantially outside the expected value range; - Terminating the modification of the first reduced voltage component (VKA) and / or the modification of the second reduced voltage component (VKB) and exiting the test state and returning to the normal operating state when the test value is substantially within the expected value range.

Description

Field of invention

[0001] The invention relates to a device for detecting the voltage drop across a light source, in particular one or more light-emitting diodes, in a vehicle. General Introduction

[0002] Today, virtually all automobiles use LEDs for lighting and signaling purposes. In many applications, such as, but not limited to, turn signals, brake lights, and taillights, the LEDs' function as light sources is safety-critical. An important parameter for monitoring the correct operation of LEDs is the voltage drop across the LED, the LED string, or the interconnection of multiple LEDs. An LED string preferably comprises several LEDs connected in series. Measuring the voltage drop across the LED or LED string is also necessary to maintain a constant color temperature of the LED's emission and to compensate for aging of the LED or LED string.For this purpose, the potential of the battery voltage line is to be measured and the difference to the potential of the lamp output (VB) determined. The value of this difference is to be output as the voltage difference between the electrical output potential at an output (Vout) and the reference potential of a reference potential line (GND).

[0003] The electric current (ILED) through the light-emitting diodes (LEDs) is limited by a current source (ISLED). This current source (ISLED) is typically a transistor current source. Preferably, this current source (ISLED) is implemented using an N-channel MOS transistor whose source is connected to a reference potential (GND) at ground potential and whose gate is connected to a reference voltage, for example, in a current mirror configuration. The problem arises because the anode of the LED or LED array is typically connected more or less directly to the battery voltage line (VA), which is essentially at approximately battery potential. In automobiles, the battery voltage (Vbat) can typically fluctuate between 24V and 4V between the potential of the battery voltage line (VA) and the reference potential of the ground line (GND).If all components of the circuit are to be housed in a micro-integrated circuit, then components of the circuit must be able to be at a potential of 24V relative to the reference potential, and other components of the circuit must be able to be at the same potential as the reference potential line.

[0004] To detect the anode potential of the light-emitting diode (LED) or LED string and the cathode potential of the light-emitting diode (LED) or LED string, these inputs of the monitoring circuit must be fixed at 24V.

[0005] The monitoring circuit detects the voltage drop across the light-emitting diode (LED) or the LED string and outputs the value of this voltage difference as a potential value of an output voltage (Vout) against the reference potential.

[0006] State-of-the-art circuits typically comprise four electronic components that are voltage-resistant up to 24V. The voltage rating requirement for these components, which are typically transistors, increases their chip area requirement and thus the product's cost.

[0007] In this context, the document presented here refers in particular to the following documents: The datasheet “BURR-BROWN Products from TEXAS INSTRUMENTS INC.: INA117, High Common-Mode Voltage DIFFERENCE AMPLIFIER. USA, 2000. - Company publication. https: / / www.ti.com / lit / gpn / ina117” describes a (quote) “High-Common-Mode Voltage Difference Amplifier”. Here, the term “high voltage” refers to the amplifier's potential overload capacity or breakdown strength.

[0008] DE 10 2006 033 233 A1 discloses a method and a circuit arrangement for operating a light-emitting diode. DE 10 2010 002 081 A1 discloses an operating circuit for a light-emitting diode system with one light-emitting diode. Task

[0009] The proposal therefore aims to create a solution that avoids the aforementioned disadvantages of the prior art and offers further advantages. It proposes a circuit that enables the detection of the voltage drop across the light-emitting diode (LED) or LED string in the elevated voltage range (typically 24V).

[0010] This problem is solved by a method according to claim 1. Solution to the task

[0011] The solution to the problem is explained with the help of the figure.

[0012] By means of a first voltage divider, the potential of the operating voltage line (VA) is reduced to the potential of a first voltage divider output line (KA).

[0013] By means of a second voltage divider, the potential of the lamp output (VB) is reduced to the potential of a second voltage divider output line (KB).

[0014] A differential amplifier, which in the example of the Fig. 1. A transconductance amplifier (OTA) detects the voltage difference between the potential of the first voltage divider output line (KA) and the potential of the second voltage divider output line (KB).

[0015] The charging current (Itr) generated by the transconductance amplifier (OTA) recharges the parasitic capacitance of a first differential pair transistor (MPE). The first differential pair transistor (MPE) acts as a current source, injecting an additional compensation current (I) into the node of the second voltage divider output line (KB). This increases the voltage drop across the second resistor (RB1) of the second voltage divider. With appropriate dimensioning, the transconductance amplifier (OTA) regulates the value of this additional compensation current (I) until the potential of the node of the second voltage divider output line (KB) is approximately equal to the potential of the node of the first voltage divider output line (KA). A second differential pair transistor (MPF) also acts as a current source. Its source terminal is connected to another positive supply voltage line (V5).The voltage between the potential of the other positive supply voltage line and the reference potential of the reference potential line (GND) is typically smaller in magnitude than the magnitude of the voltage difference between the value of the potential of the battery voltage line (VA) and the value of the reference potential of the reference potential line (GND).

[0016] The second differential pair transistor (MPF) is preferably implemented with the same orientation as the first differential pair transistor (MPE). Preferably, the first differential pair transistor (MPE) and the second differential pair transistor (MPF) are matched. This allows the second differential pair transistor (MPF) to act as a current source, injecting a current into an output resistance (RCI) that is typically directly proportional to the compensation current (I).

[0017] This compensation current (I) is proportional to the voltage drop across the light-emitting diode (LED) or LED string. Therefore, the output voltage (Vout) is proportional to the voltage drop across the LED or LED string.

[0018] In the example of the Fig. 1 The first voltage divider includes a first resistor (RA0) of the first voltage divider and a second resistor (RA1) of the first voltage divider.

[0019] In the example of the Fig. 1 the second voltage divider includes a first resistor (RB0) of the second voltage divider and a second resistor (RB1) of the second voltage divider.

[0020] The first terminal of the first resistor (RA0) of the first voltage divider is connected to the battery voltage line (VA), which is also connected to the anode contact of the light-emitting diode (LED) or the light-emitting diode string.

[0021] The first terminal of the first resistor (RB0) of the second voltage divider is connected to the lamp output (VB), which is also connected to the cathode contact of the light-emitting diode (LED) or LED string and to the first terminal of the lamp power source (ISLED). The second terminal of the lamp power source (ISLED) is preferably connected to a reference potential.

[0022] The second terminal of the first resistor (RA0) of the first voltage divider is directly or indirectly connected to the first voltage divider output line (KA), which is also connected to the positive input (+) of the transconductance amplifier (OTA) and to the first terminal of the second resistor (RA1) of the first voltage divider.

[0023] The second terminal of the first resistor (RB0) of the second voltage divider is directly or indirectly connected to the second voltage divider output line (KB), which is also connected to the negative input (-) of the transconductance amplifier (OTA) and to the first terminal of the second resistor (RB1) of the second voltage divider, and into which the first differential pair transistor (MPE) feeds the additional compensation current (I).

[0024] The first terminal of the second resistor (RA1) of the first voltage divider is connected to the first voltage divider output line (KA).

[0025] The first terminal of the second resistor (RB1) of the second voltage divider is connected to the second voltage divider output line (KB).

[0026] The second terminal of the second resistor (RA1) of the first voltage divider is connected to the reference potential line (GND).

[0027] The second terminal of the second resistor (RB1) of the second voltage divider is connected to the reference potential line (GND).

[0028] In the example of the Fig. In the first voltage divider consisting of the first resistor (RA0) and the second resistor (RA1) of the first voltage divider, a first switching transistor (MNA) is inserted, which, when switched off by means of the first enable signal (ENA), ensures that the potential of the first voltage divider output line (KA) is pulled against the reference potential of the reference potential line (GND) by the second resistor (RA1) of the first voltage divider.

[0029] In the example of the Fig. In the second voltage divider consisting of the first resistor (RB0) and the second resistor (RB1) of the second voltage divider, a second switching transistor (MNB) is inserted, which, when switched off by means of the second enable signal (ENB), ensures that the potential of the second voltage divider output line (KB) is pulled against the reference potential of the reference potential line (GND) through the second resistor (RB1) of the second voltage divider.

[0030] The function of the circuit can be checked using the first enable signal (ENA) and the second enable signal (ENB).

[0031] The proposed device for detecting the voltage drop across a light source, in particular one or more light-emitting diodes (LEDs), in a vehicle preferably comprises at least one operating voltage line (VA), a reference potential line (GND), a light source output (VB), a first voltage divider output line (KA), a second voltage divider output line (KB), a reference node (Kref), a light source, in particular comprising one or more LEDs, a light source current source (ISLED), a first voltage divider, a second voltage divider, a first differential pair transistor (MPE), a second differential pair transistor (MPF), a further positive supply voltage line (V5), and an output resistor (RCI). The light source comprises a first terminal and a second terminal. The light source current source (ISLED) has a first terminal and a second terminal.The first voltage divider comprises a first terminal, a second terminal, and an output. The second voltage divider has a first terminal, a second terminal, and an output. The first differential pair transistor (MPE) preferably has a drain terminal, a source terminal, and a control contact. The second differential pair transistor (MPF) preferably has a drain terminal, a source terminal, and a control contact. The output resistor (RCI) has a first terminal and a second terminal. The first terminal of the lamp is connected to the supply voltage line (VA). The second terminal of the lamp is connected to the lamp output (VB). The first terminal of the lamp power source (ISLED) is connected to the lamp output (VB). The second terminal of the lamp power source (ISLED) is connected to the reference ground (GND).The first terminal of the first voltage divider is connected to the supply voltage line (VA). The second terminal of the first voltage divider is connected to the reference ground line (GND). The output of the first voltage divider is connected to the first voltage divider output line (KA). The first terminal of the second voltage divider is connected to the lamp output (VB). The second terminal of the second voltage divider is connected to the reference ground line (GND). The output of the second voltage divider is connected to the second voltage divider output line (KB). The positive input (+) of the transconductance amplifier (OTA) is connected to the first voltage divider output line (KA). The negative input (-) of the transconductance amplifier (OTA) is connected to the second voltage divider output line (KB). One output of the transconductance amplifier (OTA) is connected to the reference node (Kref).The control contact of the first differential pair transistor (MPE) is connected to the reference node (Kref). The control contact of the second differential pair transistor (MPF) is connected to the reference node (Kref). The source terminal of the first differential pair transistor (MPE) is connected to the second positive supply voltage line (V5). The source terminal of the second differential pair transistor (MPF) is connected to the second positive supply voltage line (V5). The drain terminal of the first differential pair transistor (MPE) is connected to the second voltage divider output line (KB). The drain terminal of the second differential pair transistor (MPF) is connected to the first terminal of the output resistor (RCI). The second terminal of the output resistor (RCI) is connected to the ground (GND) line.The value of the output voltage (Vout) between the first terminal of the output resistor (RCI) and the second terminal of the output resistor (RCI) is then proportional to the value of the voltage between the first terminal of the light source and the second terminal of the light source.

[0032] The device described above thus performs a method for determining the voltage drop (VLED) across a light source, in particular across one or more light-emitting diodes, in a vehicle. In the following method description, it can be assumed that the method steps can be executed in parallel, at least temporarily. Words such as "then" or "afterwards" in the context of the following method description are to be interpreted as indicating a causal sequence. The delays are likely to be difficult to measure, so the causal interpretation is preferable to the temporal interpretation of such time-related terms.The basic assumption of the method is that the light source is supplied with electrical energy from an operating voltage line (VA) via a light source power source (ISLED), that the light source has a first connection and a second connection, which is hereinafter referred to as the light source output (VB), that the first connection of the light source is connected to the operating voltage line (VA), and that the light source output (VB) is connected to a reference voltage line (GND) via the light source power source (ISLED).According to this prior art circuit topology, the process begins with a first reduction of the voltage between the operating voltage line (VA) and a reference potential line by a first factor α1 to a first reduced voltage component (VKA), and a second reduction of the voltage between the lamp output (VB) and the reference potential line by a second factor α2 to a second reduced voltage component (VKB). In normal operation, the first factor α1 is preferably essentially equal in magnitude to the second factor α2. These two steps are implemented by the first voltage divider and the second voltage divider in the example of... Fig. 1. In a causally subsequent step, a comparison is made between the sum of the first reduced voltage component (VKA) and a feedback voltage component on the one hand, and the second reduced voltage component (VKB) on the other, and the feedback voltage component is calculated based on the result of this comparison. This step is carried out in the example of the Fig. 1. This is performed by the transconductance amplifier (OTA). The comparison is preferably carried out such that the voltage value of the sum of the second reduced voltage component (VKB) and the feedback voltage component is equal to the voltage value of the first reduced voltage component (VKA). This closes the control loop. In the example of the Fig. 1. The summation to enable feedback from the second reduced voltage component (VKB) and the feedback voltage component is carried out by summing corresponding currents in the node of the second voltage divider output line (KB).

[0033] To generate the output signal, an output voltage (Vout) or another suitable output signal is then causally generated subsequently, depending on the value of the feedback voltage component. In the example of the Fig. 1 This is achieved by the second differential pair transistor (MPF) in conjunction with the first differential pair transistor (MPE).

[0034] Typically, the value of the output voltage (Vout) or the value of another suitable output signal represents a measure of the voltage drop (VLED) across the light source. This can be acquired in subsequent stages, for example, by an analog-to-digital converter (ADC) not shown. A microcomputer can then evaluate this acquired value and, for example, infer a fault condition of the light source or, particularly in conjunction with other measured values, especially by applying sensor fusion methods, conclude that the light source is functioning correctly. Sensor fusion methods can also be used in conjunction with such other measured values ​​to detect a fault condition of the light source or other system components of the vehicle. At this point, reference should be made to the book by Wolfgang Koch, "Tracking and Sensor Data Fusion: Methodological Framework and Selected Applications," Springer; 7th edition.The methods of sensor fusion are described in, for example, the publications "F: Statistical Sensor Fusion" (October 2013, ISBN-10: 3642392709) and "F: Statistical Sensor Fusion" (Student Literature AB, June 8, 2018, ISBN-10: 9144127243). Other measured values ​​that can be used for fusion include, for example, measurement parameters of the LED current source (ISLED), such as the current through the LED current source (ISLED), the voltage drop across the LED current source (ISLED), the temperature of the LED current source (ISLED), or the operating voltage value in terms of the potential difference between the operating voltage line (VA) and the reference potential of the ground line (GND). For example, voltage measuring devices correspond to these measurement parameters, current measuring devices to current measuring devices, and temperature measuring devices to temperature measuring devices, etc.

[0035] However, it is possible that the device itself is faulty or that the method is being executed incorrectly. Therefore, a method for verifying a device that performs a method as described above during operation is proposed here. For the purpose of verifying the verification device proposed here, it is suggested that, in a first step, the device leaves its normal operating state and enters a test state. In this test state, the first reduced voltage component (VKA) is preferably modified, at least partially, depending on the said first enable signal (ENA), and / or the second reduced voltage component (VKB) is modified, preferably depending on the said second enable signal (ENB). This results in a predictably different value of the output voltage (Vout) or a predictably different value of the other suitable output signal.Preferably, this deviation in the output voltage (Vout) or the deviation in the value of the other suitable output signal is detected as a test value. A reference value is then determined by comparing this test value with an expected value range. Preferably, a fault is identified if the test value lies substantially outside the expected value range. The detection of the deviation in the output voltage (Vout) or the deviation in the value of the other suitable output signal as a test value is preferably performed by the aforementioned analog-to-digital converter (not shown), which preferably transmits its measured values, corresponding to the test values, to the aforementioned microcomputer via a data bus. The microcomputer then preferably compares these test values ​​with a respective expected value range and determines corresponding reference values.If one or more test values ​​are substantially outside the expected range, the microcomputer concludes that a fault condition exists. In the case of a potential fault condition, the microcomputer preferably signals this to a higher-level system and / or initiates appropriate measures. If the test value(s) are substantially within the expected range, the modification of the first reduced voltage component (VKA) and / or the modification of the second reduced voltage component (VKB) is preferably terminated, the test state is exited, and the system returns to normal operating conditions.

[0036] The procedure can also be described as follows: causally, after leaving the normal operating state and entering a test state, a modification of the first factor α1 and / or the second factor α2 occurs in a predetermined manner. The subsequent causally related acquisition of the output voltage (Vout) value or the value of the other suitable output signal as a test value, and the comparison of this test value with an expected value range, then allows conclusions to be drawn about a fault if the test value lies substantially outside the expected value range, and about proper operation if the test value lies substantially within the expected value range.Following this test, the modification of the first factor α1 and / or the second factor α2 is preferably terminated and the test state is exited, and the system returns to normal operating conditions if the test value is essentially within the expected value range. Advantage

[0037] The proposed device and method, at least in some implementations, enable the monitoring of the lamp's correct function during operation and the monitoring device itself to function correctly, while reducing the number of transistors requiring increased voltage withstand capability compared to the prior art. However, the advantages are not limited to this. List of reference symbols and abbreviations ENA first enable signal; ENB second enable signal; GND reference potential line; I additional power; ILED electric current through the light-emitting diode; ISLED light source power source; Itr charging current; KA first voltage divider output line; KB second voltage divider output line; Kref reference node; LED (light-emitting diode) or LED string or interconnection of several LEDs; MNA first switching transistor; MNB second switching transistor; MPE first differential pair transistor. The first differential pair transistor is typically a P-channel MOS transistor; MPF second differential pair transistor. The second differential pair transistor is typically a P-channel MOS transistor; OTA Transconductance Amplifier. The transconductance amplifier is used here as an example comparator. Theoretically, however, it can be replaced by an operational amplifier. Instead of the value of the charging current (Itr) for the parasitic capacitances of the control inputs of the first differential pair transistor (MPE) and the second differential pair transistor (MPF), the output potential of the operational amplifier is then used, referenced to the ground potential of the reference line (GND). To eliminate the resulting dependence on the potential of the other positive supply voltage line (V5) relative to the reference potential, this output voltage must then be converted to an output voltage that is referenced to the potential of the other positive supply voltage line (V5) and no longer to the reference potential of the ground line (GND).Typically, this conversion involves a voltage-to-current conversion followed by a current-to-voltage conversion. Therefore, the direct use of a transconductance amplifier is more advantageous, as it is less complex. However, for the purposes of this document, the use of an operational amplifier is considered functionally equivalent to a transconductance amplifier in terms of its feedback from the load. RA0 first resistor of the first voltage divider; RA1 second resistor of the first voltage divider; RB0 first resistor of the second voltage divider; RB1 second resistor of the second voltage divider; RCI output resistance; V5 further positive supply voltage line; VA operating voltage line; VB light bulb output; VKA first reduced voltage component; VKB second reduced voltage component; VLED voltage drop across the light source. The voltage drop across the light source is preferably the potential difference between the potential of the operating voltage line (VA) on the one hand and the potential of the light source output (VB) on the other; Vout output voltage; List of cited works Wolfgang Koch, “Tracking and Sensor Data Fusion: Methodological Framework and Selected Applications,” Springer; October 7, 2013, ISBN-10: 3642392709, Gustafsson, “F: Statistical Sensor Fusion”, Studentlitteratur AB, June 8, 2018, ISBN-10: 9144127243

Claims

[1] Method for determining the voltage drop (VLED) across a light source, in particular across one or more light-emitting diodes, in a vehicle, - wherein the light source is supplied with electrical energy from an operating voltage line (VA) via a light source power source (ISLED) and - wherein the light source has a first connection and a second connection, which is hereinafter referred to as the light source output (VB) and - wherein the first connection of the light source is connected to the operating voltage line (VA) and - wherein the lamp output (VB) is connected via the lamp power source (ISLED) to a reference voltage line (GND), comprising the steps: - Reducing the voltage between the operating voltage line (VA) and a reference potential line by a first factor α1 to a first reduced voltage component (VKA); - Reducing the voltage between the lamp output (VB) and the reference potential line by a second factor α2 to a second reduced voltage component (VKB), - where, in normal operation, the first factor α1 is essentially equal in magnitude to the second factor α2; - Comparison of a sum of the second reduced voltage component (VKB) and a feedback voltage component on the one hand with the first reduced voltage component (VKA) on the other hand and formation of the feedback voltage component depending on the result of this comparison in such a way that the voltage value of the said sum of the second reduced voltage component (VKB) and the feedback voltage component is equal to the voltage value of the first reduced voltage component (VKA); - Generation of an output voltage (Vout) or other suitable output signal depending on the value of the feedback voltage component, - wherein the value of the output voltage (Vout) or other suitable output signal represents or can represent a measure of the voltage drop (VLED) across the light source; - Leaving the normal operating state and entering a test state; - Modification of the first reduced voltage component (VKA) depending on a first enable signal (ENA) and / or the second reduced voltage component (VKB) depending on a second enable signal (ENB); - Recording the value of the output voltage (Vout) or the value of the other suitable output signal as a test value and comparing this test value with an expected value range and concluding that a fault exists if the test value is substantially outside the expected value range; - Terminating the modification of the first reduced voltage component (VKA) and / or the modification of the second reduced voltage component (VKB) and exiting the test state and returning to the normal operating state when the test value is substantially within the expected value range. [2] A method for checking a device performing a method according to claim 1 in operation, comprising the steps - Leaving the normal operating state and entering a test state; - Modification of the first factor α1 and / or the second factor α2; - Recording the value of the output voltage (Vout) or the value of the other suitable output signal as a test value and comparing this test value with an expected value range and concluding that a fault exists if the test value is substantially outside the expected value range; - Terminating the modification of the first factor α1 and / or the second factor α2 and exiting the test state and returning to the normal operating state when the test value is substantially within the expected value range.

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