DE102015017315B3 - Process for monitoring at least two LED chains with LEDs of different forward voltages - Google Patents

Abstract

Method for monitoring the electrical energy supply of at least one first LED chain (LED1) with n LEDs with a first forward voltage (ULED1) from a first regulated current source (11) with a first nominal current (I10) and at least one second LED chain (LED2) with m LEDs with a second forward voltage (ULED2), which is different from the first forward voltage (ULED1), from a second current source (12) with a second rated current (I20),- - the forward voltages of the various LEDs being different, with the Steps, - generating a first tap potential as a first error detection parameter at a first tap (ERR1), which depends strictly monotonically on the voltage drop across the first LED chain (LED1), by means of a first voltage divider (RS1), - the first tap (ERR1 ) can also take place at the beginning of the first LED chain (LED1) and- the first voltage divider (RS1) of the first LED chain (LED1) being connected in parallel;- generating a second Ab potential as a second error detection parameter at a second tap (ERR2), which is strictly monotonically dependent on the voltage drop across the second LED chain (LED2), by means of a second voltage divider (RS2),- with the second tap (ERR2) possibly also at the beginning of the second LED chain (LED2) and- the second voltage divider (RS2) of the second LED chain (LED2) being connected in parallel;- comparing the voltage difference between the first tap potential and the second tap potential, with a first threshold value and a second threshold different from the first threshold;- signaling whether the voltage difference is between the first and second thresholds.

Description

This invention relates to a method of monitoring at least two strings of LEDs. The associated device is also described. In a chain of LEDs that are to be used in the automotive industry, for manufacturing reasons, LED carriers with only two electrical connections are usually available. As a result, parts of the chain are usually not accessible/measurable for a status assessment of the LED chain. However, such a status determination is necessary for reliable failure detection.

From the DE 10 2011 120 781 A1 a device for monitoring an LED chain is known, which determines a faulty state by means of a temperature measurement and a subsequent comparison with a reference value.

From the prior art is the U.S. 2006 170 287 A1 known. This is one of the possible solutions to measure the health of a single LED string. However, the solution requires an additional connection for each LED chain. the U.S. 2006 170 287 A1 discloses a lighting control circuit for a motor vehicle lighting unit, such as taillights and headlights, which is characterized in that it includes a fault detection device that performs a relative comparison between a voltage applied to all semiconductor light sources and a voltage applied only to a part of the semiconductor light sources is applied to detect a fault in any one of the semiconductor light sources. This is typically understood to mean that the U.S. 2006 170 287 A1 Taps in the respective LED chain, always based on just one chain, are required. As mentioned above, this is not always possible and sensible.

From the U.S. 2007 159 750 A1 an error detection device for a chain of light-emitting diodes is known. In this case, the chain of light-emitting diodes includes a plurality of serially connected LEDs, ie a single chain. This error detection device of US 2007/0 159 750 A1 includes a voltage measuring device that can detect the voltage drop across at least one LED of the LED chain. This voltage is now measured several times and dynamically evaluated over time. On the one hand, this is again a possible solution to the technical problem with the unwanted taps in the LED chain for a single chain. The second is the attempt to detect a fault, for example a single short circuit in an LED, from transient changes in the voltage drop across a part of the LED chain or the LED chain itself. The idea of US 2007/0 159 750 A1 is therefore that the voltage across the LED chain jumps once in the event of an error. This jump in voltage can occur upwards - e.g. in the event of an "open" error - or downwards - e.g. in the event of a partial short-circuit of individual LEDs in the LED chain.

This method has the disadvantage that the assessment of such individual events of the voltage curve of the voltage drop across a part of the LED chain in automotive applications is extremely critical and unreliable in view of the known and typically present interference pulses. This method of US 2007/0 159 750 A1 of the transient evaluation of a voltage simply increases the unreliability with regard to electromagnetic compatibility (passive EMC) with regard to parasitic electromagnetic radiation.

The measurement of several parallel LED chains is not dealt with in either US 2006/0 170 287 A1 or US 2007/0 159 750 A1. The resulting additional possibilities are therefore not taken into account.

Also from the DE 11 2009 005 227 T5 it is known to monitor a single LED chain by comparing it to voltage reference values.

From the EP 0 955 619 A1 the measurement of the voltage drop across the LEDs of two LED chains is known in order to detect faulty LEDs. This method suffers from several disadvantages. On the one hand, a measuring line is required for each LED. On the other hand, the equivalent stresses must be specified precisely.

From the DE 10 2014 107 947 A1 the measurement of a single LED chain by comparing the voltage drop across two LED chain sections of this LED chain is known.

From US 2008 / 0 204 029 A1 (their 3 ) the monitoring of LED chains of the same length is known, whereby the taps for the monitor circuit described there can always be found at the same place within an LED chain.

From US 2012 / 0 200 296 A1 (their 2 ) the comparison of two LED chains of the same length using a differential amplifier is known. However, LED chains of the same length cannot be realized in many applications.

object of the invention

It is the object of the invention to specify a device and a method which, on the one hand, without taps within an LED chain and, on the other hand, by means of an EMC-robust static measurement solution enables a reliable detection of short circuits of individual LEDs within LED chains and/or reductions in the conductance of individual LEDs within several LED chains connected in parallel with LEDs of different forward voltages. This object is achieved with a method according to claim 1.

Description of the invention

The object according to the invention is achieved in that two LED strands are compared with one another. Parts of these different LED chains can also be used as reference voltage sources. The invention is used to monitor at least two different LED strings. So in contrast to U.S. 2006 170 287 A1 not parts of a single LED chain compared with each other, but different LED chains. This makes it possible to use LED chains without taps. According to the invention, a first embodiment of the invention is therefore a device for monitoring the electrical energy supply of at least a first LED chain (LED1) with n LEDs from a first regulated current source (11) with a first nominal current (I ₁₀ ) and at least one second LED chain (LED2) with m LEDs from a second current source (12) with a second rated current (I ₂₀ ). Similar LEDs are preferably used. This is already customary in the state of the art, in particular because the aim is to preferably achieve the same luminous properties. A first forward voltage (U LED1 ) therefore drops at each LED of the first LED chain (LED1) when the first rated current (I ₁₀ ) of the first current source ( ₁₁ ) flows through it. Naturally, the forward voltages of the various LEDs are slightly different in reality. For the purposes of this disclosure, those LEDs should therefore be considered the same which, when supplied with the same nominal current, have a forward voltage that is less than 20%, better less than 10%, better less than 5%, better less than 2%, better less than 1% from the mean value of the forward voltages of the other LEDs of the first and second LED chain (LED1, LED2). The same should apply to the LEDs of the further, second LED chain. Similarly, further LED chains beyond said first two LED chains, e.g. a third, fourth, etc., can be monitored. Further LED chains are then preferably, but not necessarily, different from all other LED chains. In order to be able to supply the LEDs, the first and the second LED chain (LED1, LED2) and the first regulated current source (11) and the second regulated current source (12) are connected to a common node (GND). If there are resistors or other circuit parts between this common node and the connection of the first and/or second current source (11, 12), for example chokes and/or lead resistors, these can be referred to as part of the first or second power source are considered. If necessary, the evaluation circuit must be connected to the common node by a separate reference potential line in order to be able to correctly record the potentials for the evaluation of the LED chains. According to the invention, a first voltage divider (RS1) with a first total resistance (R1) is connected in parallel with the first LED chain (LED) and a second voltage divider (RS2) with a second total resistance (R2) is connected in parallel with the second LED chain. The first total resistance (R1) of the first voltage divider (RS1) is n times the second total resistance (R2) divided by m. These voltage dividers (RS1, RS2) are preferably designed with relatively high impedance so as not to load the current sources. The first voltage divider (RS1) has a first tap (ERR1) in such a way that the voltage (U1) between this first tap (ERR1) and the common node (GND) is k times the first flow voltage

(U _LED1 ) is when the first LED chain (LED1) is traversed by the first rated current (110). The second voltage divider (RS2) analogously has a second tap (ERR2) in such a way that the voltage (U2) between this second tap (ERR2) and the common node (GND) is also k times the second forward voltage (U _LED2 ) is when the second LED chain (LED2) is flowed through by the second rated current (I ₂₀ ). The first tap (ERR1) and the second tap (ERR2) are now connected to an evaluation circuit (AS). A sensible dimensioning is now, for example, such that when the first nominal current flows through the first LED chain, the first tap has approximately the same potential, apart from production fluctuations, as the second tap (ERR2) of the second voltage divider (RS2), when the second rated current flows through the second LED chain (LED2). If this difference is smaller than a specified tolerance band between two threshold values, then all LEDs are OK and not defective. However, if the voltage difference lies outside of this tolerance range, then there is a defect and an evaluation circuit can detect this by comparing it with two threshold values and set an error signal. According to the invention, the evaluation circuit (AS) therefore generates an error signal (FS) as a function of the voltage difference between the first tap (ERR1) and the second tap (ERR2). Of course, instead of the output of a signal, other types of signaling are also conceivable. For example, an error flag can be set in a data bus within the evaluation circuit.

Moreover, it is clear to the person skilled in the art that other divider ratios can be used for the voltage divider if the forward voltages of the LEDs in the chains are different, which the person skilled in the art will typically avoid because of the associated temperature problems. Thus, depending on the application, the voltage dividers can have all divider ratios from 100% down to just over 0%. Integer divider ratios are preferable because of the matching.

In one variant of the invention, when the first nominal current (110) flows through each LED of the first LED chain (LED1), a first forward voltage (U _LED1 ) drops by less than 20% and/or less than 10% and/or less than 5% and/or less than 2% and/or less than 1% from the mean value of the forward voltages of the other LEDs in the first and second LED chains (LED1, LED2). A second forward voltage (LED2) drops at each LED of the second LED chain (LED1) when the second rated current (I ₂₀ ) flows through it, which decreases by less than 20% and/or less than 10% and/or or less than 5% and/or less than 2% and/or less than 1% from the mean value of the forward voltages of the other LEDs in the first and second LED chains (LED1, LED2). Again, the first and the second LED chain (LED1, LED2) and the first regulated current source (11) and the second regulated current source (12) are connected to a common node (GND). Now, however, only the second LED chain has a second voltage divider (RS2) with a second total resistance (R2) connected in parallel. The other LED chain is connected directly to the evaluation circuit (AS). Said second voltage divider (RS2) again has a second tap (ERR2) in such a way that the voltage (U ₂ ) between this second tap (ERR2) and the common node (GND) is n times the first forward voltage (U _LED1 ) is when the second LED chain (LED2) is traversed by the second rated current (I ₂₀ ). The first tap (ERR1) and the second tap (ERR2) are again connected to an evaluation circuit (AS). As before, the evaluation circuit (AS) generates an error signal (FS) and/or sets an error flag and/or changes one depending on the voltage difference between the first tap (ERR1) as the first error detection parameter and the second tap (ERR2) as the second error detection parameter register content.

In a further variant of the invention, the evaluation circuit (AS) generates an error signal (FS) and/or changes the logical content of an error flag and/or changes a register content if the voltage difference between the first tap (ERR1) and the second tap (ERR2 ) deviate from each other by more than 1% and/or by more than 2% and/or by more than 5% and/or by more than 10% and/or by more than 25%.

In a further embodiment of the invention, the evaluation circuit has an associated sub-device according to the invention, which carries out this detection by comparing the voltage potential of the first tap (ERR1) and the voltage potential of the second tap (ERR2) with a first and second threshold value. For this purpose it has, for example, a first comparator (CMP1) with a first input and a third input and a first comparator output. The first comparator (CMP1) is connected to the first input with the first tap (ERR1).

Furthermore, it has a second comparator (CMP2) with a second input and a fourth input and a second comparator output. The second comparator (CMP2) is connected to the second input with the second tap (ERR2). To set the first threshold value, for example, a first offset voltage source (V _ERR1 ), which is part of the sub-device, is connected to the first tap (ERR1) on one side and to the fourth input of the second comparator (CMP2) on the other side. Other constructions that result in a fixed voltage offset between the first tap (ERR1) and the fourth input of the second comparator (CMP2) are conceivable and are to be regarded as the first offset voltage source (V _ERR1 ) for the purposes of this disclosure.

It also has a second offset voltage source (V _ERR2 ), which is connected to the second tap (ERR2) on one side and to the third input on the other side. Other constructions that result in a fixed voltage offset between the second tap (ERR2) and the third input of the first comparator (CMP1) are conceivable and are to be regarded as the second offset voltage source (V _ERR2 ) for the purposes of this disclosure.

In order to now generate the error signal (FS), a logic circuit (LG), preferably an OR gate, is provided. This logic circuit (LG) links the first and second comparator output of the two comparators (CMP1, CMP2) in order to generate an error signal (FS) therefrom and/or set an error flag and/or change a register content.

In a further embodiment of the invention, the device according to the invention has a partial device with a first comparator (CMP1) with a first input and a third input and a first comparator output connected to the first input having the first tap (ERR1). Furthermore, it has a second comparator (CMP2) with a second input and a fourth input and a second comparator output, which is connected to the second input with the second tap (ERR2). As before, it has a first offset voltage source (V _ERR1 ) connected on one side to the first tap (ERR1) and on the other side to the fourth input. As before, this first offset voltage source (V _ERR1 ) serves to represent a first threshold value with which the potential at the first input of the first comparator is compared by the first comparator (CMP1). As a result, the first tap (ERR1) is compared with this first threshold value. In addition, it has a second offset voltage source (V _ERR2 ), which is connected to the second tap (ERR2) on one side and to the third input on the other side. As before, this second offset voltage source (V _ERR2 ) is used to represent a second threshold value with which the potential at the second input of the second comparator is compared by the second comparator (CMP2). As a result, the second tap (ERR2) is compared with this second threshold value. Other implementations are of course possible. In order to generate the necessary output signal, a logic circuit links the first and second comparator output in order to generate an error signal from it and/or to set an error flag and/or to change a register content.

In addition to this device, the invention therefore also includes a method for monitoring the electrical energy supply of at least one first LED chain (LED1) with n LEDs from a first regulated current source (11) with a first rated current (I ₁₀ ) and at least one second LED chain (LED2) with m LEDs from a second current source (12) with a second rated current (I ₂₀ ). The method according to the invention begins with the generation of a first tap potential as a first error detection parameter at a first tap (ERR1). The tapping potential is preferably dependent proportionally on the voltage drop across the first LED chain (LED1). At the very least, however, this dependency should be the strictly monotonic. According to the invention, the preferred first voltage divider (RS1) is used for this purpose, in which case the first tap (ERR1) can optionally also be at the start of the first LED chain (LED1). Secondly, analogously to this, a second tap potential is generated as a second error detection parameter at a second tap (ERR2). Again, proportionality is preferred here. However, this second tap potential should at least depend monotonically on the voltage drop across the second LED chain (LED2). Again, a voltage divider, here the second voltage divider (RS2), is the preferred implementation. Here, too, the second tap (ERR2) can also be at the start of the second LED chain (LED2). In a third step, the voltage difference between the first tap potential and the second tap potential is compared, in particular by an evaluation circuit (AS) and in particular with the formation of a voltage difference signal. In a fourth step, the voltage difference thus determined is compared between the first tap potential and the second Tap potential, in particular in the form of the voltage difference signal, with a first threshold and a second threshold. In order to be able to form a tolerance window, the latter should be different from the first threshold value. This comparison is preferably carried out again by the evaluation circuit (AS). In a fifth step, the comparison result is utilized by the evaluation circuit (AS). This signals whether the voltage difference is between the first and the second threshold value, with the signaling being able to take place in particular by means of an error signal (FS) and/or setting an error flag and/or changing a register content.

In a variant of the method, the first threshold value and the second threshold value deviate by no more than 1% and/or worse by no more than 2% and/or worse by no more than 5% and/or worse by no more than 10% and /or worse by no more than 25% and/or worse by no more than 50% from each other. In this case, the selection of the width of the tolerance window depends on the manufacturing scatter of the forward voltages of the LEDs.

In a further variant of the method, at least one further error detection parameter is recorded by an error detection parameter measuring device. This is preferably a temperature (ϑ ₁ ), which is measured by a temperature measuring device (TM1) and given to the evaluation circuit (AS). At least one threshold value is changed as a function of at least this one further error detection parameter, in particular by at least part of the evaluation circuit (AS).

In a further variant of the method, the error detection parameters are evaluated, in particular by the evaluation circuit, in a fixed time relationship with a switch-on or switch-off signal for the current sources (11, 12). This has the advantage that problems with the supply stability, especially in the switch-on and switch-off phase, do not lead to erroneous error detections.

In a further variant of the method, at least one temperature (ϑ ₁ , ϑ ₂ ), which is thermally related to at least one of the LED chains (LED1, LED2), is detected by means of a temperature measuring device (TM1, TM2) as a further one error detection parameters.

1. a. eine erste und/oder höhere zeitliche Ableitung eines ersten und/oder zweiten und/oder weiteren Fehlererkennungsparameters und/oder
2. b. eine erste und/oder höhere zeitliche Integration eines ersten und/oder zweiten und/oder weiteren Fehlererkennungsparameters und/oder
3. c. eine Differenz und/oder mit reellen Faktoren gewichtete Summe mindestens zweier Fehlererkennungsparameter, insbesondere eine Temperaturdifferenz einer ersten Temperatur (ϑ₁) und einer zweiten Temperatur (ϑ₂).

In a further variant of the method, at least one derived further error detection parameter is derived, in particular by the evaluation circuit (AS), from at least a first and/or second and/or other further error detection parameter. The result of this derivation can be one of the following derived additional error detection parameters:

1. a. a first and/or higher time derivative of a first and/or second and/or further error detection parameter and/or
2. b. a first and/or higher time integration of a first and/or second and/or further error detection parameter and/or
3. c. a difference and/or a sum of at least two error detection parameters weighted with real factors, in particular a temperature difference between a first temperature (ϑ ₁ ) and a second temperature (ϑ ₂ ).

character list

• 1 shows an example of the basic structure of a device according to the invention with a first LED chain with 4 LEDs and a second LED chain with 6 LEDs.
• 2 shows an example of the basic structure of a device according to the invention with a first LED chain with 2 LEDs and a second LED chain with 4 LEDs.
• 3 shows an example of the basic structure of a device according to the invention with a first LED chain with 4 LEDs and a second LED chain with 6 LEDs and a third LED chain with 5 LEDs.
• 4 shows an example of the basic structure of a device according to the invention with a first LED chain with 2 LEDs and a second LED chain with 4 LEDs, further voltages of the LED chains now also being used as references.
• 5 show the 1 with additional temperature measuring devices.
• 6 shows an exemplary comparator circuit according to the invention
• 7 shows an exemplary comparator circuit according to the invention for the crosswise evaluation of two chains with internal taps.
• 8th indicates 5 with the difference that the first tap (ERR1) does not take place via a voltage divider, but directly at the beginning of the first LED chain (LED1).

figure 1

1 shows an example of the basic structure of a device according to the invention with a first LED chain with 4 LEDs and a second LED chain with six LEDs. The first regulated current source (11) feeds the first nominal current (I ₁₀ ) into the first LED chain, which consists of six LEDs connected in series here, for example. The second regulated current source (12) feeds the second nominal current (I ₂₀ ) into the second LED chain, which consists of six LEDs connected in series here, for example. The individual LEDs of an LED chain should preferably be the same in each case. If this is not the case, the evaluation circuit (AS) must take this inequality into account by measuring other parameters (eg the LED temperature using a temperature measuring device). Instead of a single LED, the series-connected LEDs of a single LED chain of the device according to the invention can also be a module of parallel-connected LEDs, which are considered here like an LED in the chain. The only important thing is that the LEDs show approximately the same forward voltage at the first and second nominal current (I ₁₀ , I ₂₀ ). Since the first and second voltage dividers (RS1, RS2) are typically selected with the highest possible resistance, the current from the first current source (11) flows almost completely through the first LED chain (LED1) and the current from the second current source (12) flows almost completely through it the second LED chain (LED2). In this example, the first voltage divider (RS1) divides the voltage that drops across the first LED chain (LED1) down in a ratio of 1:4. In contrast, the second voltage divider (RS2) divides the voltage that drops across the second LED chain (LED2) down in a ratio of 1:6. The voltage at the first tap (ERR1) of the first voltage divider (RS1) thus corresponds approximately to the forward voltage (U _LED1 ), which drops across an LED within the first LED chain (LED1). In this example, the voltage at the second tap (ERR2) of the second voltage divider (RS2) also roughly corresponds to the forward voltage (U _LED2 ), which drops across an LED within the second LED chain (LED2). In this exemplary device, the evaluation circuit (AS) compares the potentials of the first tap (ERR1) and the second tap (ERR2) with one another and uses this to generate the preferably digital error signal (FS). As already mentioned, it may make sense if the evaluation circuit (AS) has a first temperature (ϑ ₁ ) close to the first LED chain (LED1) detected and / or a second temperature (ϑ ₂ ) in the vicinity of the second LED chain (LED2) detected. This shows the 5 . Typically, the forward voltages (U _LED1 , U _LED2 ) should be approximately the same for the respective rated currents (I ₁₀ , I ₂₀ ) of the LEDs in the at least two LED chains (LED1, LED2). In this case, the potentials of the first tap (ERR1) and the second tap (ERR2) should be approximately the same. The evaluation circuit (AS) thus carries out a static method. Differences in the potentials at the two taps are then either due to manufacturing fluctuations and/or temperature differences. The latter can be compensated by correction methods in the evaluation circuit according to the invention. When designing the at least two threshold values within the evaluation circuit (AS), a person skilled in the art will take this into account by means of suitable calculations in order to avoid incorrect error messages or error messages not being triggered. In particular, the threshold values used in the evaluation circuit, which are used to decide whether there is an error, are preferably dependent on one or more temperatures (ϑ ₁ , ϑ ₂ ) measured in the vicinity of the respective LED chain (LED1, LED2). are, and/or modified/adapted depending on their temperature differences. This is typically done using an analog and/or digital polynomial approximation.

figure 2

2 corresponds essentially 1 with the difference that the first LED chain comprises only two LEDs and the associated first voltage divider therefore only reduces the voltage that drops across the first LED chain (LED1) by a factor of 1:2. The second LED chain (LED2) includes four LEDs. The second voltage divider accordingly reduces the voltage drop across the second LED chain (LED2) by a factor of 1:6.

figure 3

3 shows an example device with three LED strings. While the first and the second LED chain of the 1 correspond, the third LED chain (LED3) is supplied with a third rated current (I ₃₀ ) by a regulated third current source (13). A third voltage divider reduces the voltage drop across the third LED chain (LED3) by a factor of 1:5. The potential of the third tap (ERR3) should therefore correspond to that of the first tap (ERR1) and the second tap (ERR2). The evaluation circuit compares these three potentials of the three taps (ERR1, ERR2, ERR3) with at least two threshold values and signals externally via the error signal (FS) if at least one of the three potential differences between these three potentials of the three taps (ERR1, ERR2, ERR3 ) lies outside the tolerance range specified by the two threshold values.

figure 4

4 is equivalent to 2 with the difference that a third tap (ERR3) of a third potential takes place directly in the first LED chain (LED1) and that a fourth tap (ERR4) of a fourth potential takes place directly in the second LED chain (LED1). The evaluation circuit compares these four potentials of the four taps (ERR1, ERR2, ERR3, ERR4) with at least two threshold values and signals externally via the error signal (FS) if at least one of the four potential differences between these four potentials of the four taps (ERR1, ERR2 , ERR3, ERR4) is outside the tolerance range specified by the two threshold values.

figure 5

5 equals to 1 with the difference that it has a first and a second temperature measuring device (TM1, TM2). Here, by way of example, they record a first temperature (θ ₁ ) of the first LED chain (LED1) and a second temperature (θ ₂ ) of the second LED chain (LED2) as additional error detection parameters. The threshold values for the detection of an error now preferably depend on these additional error detection parameters and/or error detection parameters derived therefrom, for example their difference and/or first and/or further time derivatives.

figure 6

6 12 shows the exemplary comparator circuit according to the invention, as explained above.

This exemplary sub-device has, by way of example, a first comparator (CMP1) with a first input and a third input and a first comparator output which is connected to the first input with the first tap (ERR1).

Furthermore, it has a second comparator (CMP2) with a second input and a fourth input and a second comparator output, which is connected to the second input with the second tap (ERR2).

It has a first offset voltage source (V _ERR1 ), which is connected to the first tap (ERR1) on one side and to the fourth input on the other side. As before, this first offset voltage source (V _ERR1 ) is used for Dar setting of a first threshold value with which the potential at the first input of the first comparator is compared by the first comparator (CMP1). As a result, the first tap (ERR1) is compared with this first threshold value. In addition, it has a second offset voltage source (V _ERR2 ), which is connected to the second tap (ERR2) on one side and to the third input on the other side. As before, this second offset voltage source (V _ERR2 ) is used to represent a second threshold value with which the potential at the second input of the second comparator is compared by the second comparator (CMP2). As a result, the second tap (ERR2) is compared with this second threshold value. Other implementations are of course possible. In order to generate the necessary output signal, a logic circuit links the first and second comparator output in order to generate an error signal from it and/or to set an error flag and/or to change a register content.

figure 7

7 is equivalent to 6 with the exemplary difference that the circuit also evaluates taps within the chains crosswise. The corresponding external wiring is shown as an example in 4 Shown.

figure 8

8th indicates 5 with the difference that the first tap (ERR1) does not take place via a voltage divider, but directly at the beginning of the first LED chain (LED1).

Advantages of the Invention

The invention makes it possible to monitor the function of the LEDs in automotive applications such as brake lights, indicators and taillights, etc.

Reference List

AS

evaluation circuit

CMP1

first comparator

CMP2

second comparator

CMP3

third comparator

CMP4

fourth comparator

ERR1

first tap

ERR2

second tap

ERR3

third tap

ERR4

fourth tap

FS

error signal

GND

common node (reference potential)

11

first regulated power source

I10

first rated current that the first current source (11) for the first LED chain (LED1) provides.

I2

second regulated power source

I20

second nominal current, which the second current source (12) for the second LED chain (LED2) provides.

I3

third regulated current source

I30

third rated current that the third current source (13) for the third LED chain (LED3) provides.

LED1

first LED chain

LED2

second LED chain

LED3

third LED chain

LG

logic circuit

R

base resistance

R1

first total resistance of the first voltage divider (RS1)

RS1

first voltage divider with first total resistance (R1)

R2

second total resistance of the second voltage divider (RS2)

RS2

second voltage divider with second total resistance (R2)

R3

third total resistance of the third voltage divider (RS3)

RS3

third voltage divider with third total resistance (R3)

ϑ1

first temperature or first temperature measurement signal measured in the vicinity of the first LED chain (LED1) that represents this first temperature.

ϑ2

second temperature or second temperature measurement signal measured in the vicinity of the second LED chain (LED2) that represents this second temperature.

TM1

first temperature measuring device for measuring the first temperature (ϑ ₁ )

TM2

second temperature measuring device for measuring the second temperature (ϑ ₂ )

U1

Voltage (U1) between this first tap (ERR1) and the common node (GND)

U2

Voltage (U2) between this second tap (ERR2) and the common node (GND)

U3

Voltage (U3) between this third tap (ERR3) and the common node (GND)

ULED1

first forward voltage of the LEDs of the first LED chain (LED1)

ULED2

second forward voltage of the LEDs of the second LED chain (LED2)

ULED3

third forward voltage of the LEDs of the third LED chain (LED3)

LOCK1

first offset voltage source

VERR2

second offset voltage source

VERR3

third offset voltage source

VERR4

fourth offset voltage source

Claims (2)

Method for monitoring the electrical energy supply of at least one first LED chain (LED1) with n LEDs with a first forward voltage (U _LED1 ) from a first regulated current source (11) with a first nominal current (I ₁₀ ) and at least one second LED chain ( LED2) with m LEDs with a second forward voltage (U _LED2 ), which is different from the first forward voltage (U _LED1 ), from a second current source (12) with a second nominal current (I ₂₀ ), - - the forward voltages of the various LEDs are different, with the steps, - generating a first tap potential as a first error detection parameter at a first tap (ERR1), which is strictly monotonically dependent on the voltage drop across the first LED chain (LED1), by means of a first voltage divider (RS1), - where the first tap (ERR1) can optionally also be at the beginning of the first LED chain (LED1) and - the first voltage divider (RS1) of the first LED chain (LED1) being connected in parallel; - Generation of a second tap potential as a second error detection parameter at a second tap (ERR2), which depends strictly monotonically on the voltage drop across the second LED chain (LED2), by means of a second voltage divider (RS2), - the second tap (ERR2) possibly can also take place at the start of the second LED chain (LED2) and - the second voltage divider (RS2) of the second LED chain (LED2) being connected in parallel; - Comparing the voltage difference between the first tap potential and the second tap potential, with a first threshold value and a second threshold value, which is different from the first threshold value; - Signaling whether the voltage difference is between the first and the second threshold value. procedure after claim 1 - The number n of LEDs in the first LED chain (LED1) differs from the number m of LEDs in the second LED chain (LED2).

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