DE102016105516B3 - Method for monitoring at least two LED chains of different length using programmable voltage dividers - Google Patents

Abstract

The invention relates to a method for monitoring the electrical power supply of a first LED chain (LED1) with n LEDs from a first regulated current source (I1) with a first rated current (I10) and a second LED chain (LED2) with m LEDs from one second current source (I2) with a second rated current (I20), where n ≠ m applies. The method comprises as a first step the setting of the voltage divider ratio of a programmable voltage divider and the generation of a first tap potential as first error detection parameter at a first tap (ERR1) of the programmable voltage divider and as second step generating a second tap potential as second error detection parameter at a second tap ( ERR2). The tap potentials thus displayed are then compared in a next step with the voltage difference between the first tap potential and the second tap potential. The voltage difference thus determined is then compared with a first threshold value and a second threshold value, which is different from the first threshold value, by an evaluation circuit (AS). The evaluation circuit (AS) then signals whether the voltage difference lies between the first and the second threshold value.

Description

This invention relates to a method for monitoring at least two LED strings. The associated device will also be described. For production reasons, a chain of LEDs which are to be used in the automotive industry usually has LED carriers with only two electrical connections. As a result, parts of the chain are usually unachievable / measurable for a status evaluation of the LED string. For a reliable failure detection, however, such a state determination is necessary. From the DE 10 2011 120 781 A1 a device for monitoring an LED chain is known, which detects a faulty state by means of a temperature measurement and a subsequent comparison with a reference value.

From the prior art is the US 2006 170 287 A1 known. This is one of the possible solutions for measuring the state of a single LED string. However, the solution requires a further connection per LED chain. The US 2006 170 287 A1 discloses a lighting control circuit for a vehicle lighting unit, such as taillights and headlamps, characterized by comprising an error detecting device that makes a relative comparison between a voltage applied to all the semiconductor light sources and a voltage that is applied to only a part of the semiconductor light sources is applied to detect a fault in any of the semiconductor light sources. This is typically understood to mean that US 2006 170 287 A1 Taps in the respective LED chain, always referring to only one chain, requires. As mentioned above, this is not always possible and useful.

From the US 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 comprises a plurality of serially connected LEDSs, ie a single chain. In this case, this error detection device comprises US 2007 159 750 A1 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 evaluated dynamically 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. Secondly, an attempt is made to detect an error case, for example a single short circuit of an LED, from transient changes in the voltage drop across part of the LED chain or the LED chain itself. The idea of US 2007 159 750 A1 is thus that the voltage on the LED chain jumps once in case of an error. This voltage jump can go upwards - z. B. in an "open" error - or down - z. B. in a partial short circuit of individual LEDs of the LED chain - done.

This method has the disadvantage that the evaluation of such individual events 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 existing interference pulses. This method of US 2007 159 750 A1 The transient evaluation of a voltage simply increases the unreliability with regard to electromagnetic compatibility (passive [MV) with regard to parasitic electromagnetic radiation.

The measurement of several parallel LED chains is both in the US 2006 170 287 A1 as well as in the US 2007 159 750 A1 not treated. Therefore, the resulting additional options are not taken into account.

Also from the DE 11 2009 005 227 T5 For example, monitoring of a single LED string is known by comparison with voltage reference values.

From the EP 0 955 619 A1 the measurement of the voltage drop across the LEDs of two LED strings is known in order to detect faulty LEDs. This method has several disadvantages. On the one hand, one measuring lead per LED is required. On the other hand, the reference voltages must be specified precisely.

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

From the US 2008 0 204 029 A1 (whose 3 ) Monitoring the same length LED chains is known, the taps for the monitor circuit described therein are always to be found in the same place within an LED chain.

From the US 2012 0 200 296 A1 (whose 2 ) is the comparison of two equal length LED chains by means of a differential amplifier known. Equally long LED chains can not be realized in many applications.

From the US 2006 0 170 287 A1 and from the DE 10 2010 002 707 A1 In each case a device for monitoring an LED chain with adjustable division ratio is known. In the technical teaching of US 2006 0 170 287 A1 For example, a reference voltage is compared to a tap voltage within the LED string that is generated by a voltage divider.

In the technical teaching of DE 10 2010 002 707 A1 For example, a reference voltage is compared with a tap voltage within the LED string which creates a resistor string as a voltage divider. The resistor chains of US 2006 0 170 287 A1 and the DE 10 2010 002 707 A1 should be saved.

Object of the invention

It is the object of the invention to provide 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 reliable detection of short circuits of individual LEDs within different lengths of LED chains and / or humiliations of the Conductance of individual LEDs within several parallel-connected different lengths LED chains allows. In addition, a device that performs the method to monitor different lengths LED chains can be changed without significant. This object is achieved by a method according to claim 1.

Description of the invention

The object according to the invention is achieved by comparing two LED strands of different lengths. 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 strands. So it will be in contrast to US 2006 170 287 A1 not parts of a single LED chain compared to each other, but different LED chains. This makes it possible to use LED chains without taps. It is thus in a first embodiment to a device for monitoring the electrical power supply at least a first LED chain (LED1) with n LEDs from a first regulated current source (I1) with a first rated current (I ₁₀ ) and at least one second LED Chain (LED2) with m LEDs from a second current source (I2) with a second rated current (I ₂₀ ). Preferably, similar LEDs are used. This is already common practice in the prior art today, since the same luminous properties should preferably be achieved. Therefore, at each LED of the first LED chain (LED1), when it flows through the first rated current (I ₁₀ ) of the first current source (I1), a first _forward voltage (U _LED1 ) _drops . Of course, the flux voltages of the different LEDs are slightly different in reality. As such in the sense of this disclosure, therefore, such LEDs should apply, which have a forward voltage when energized with the same rated current by less than 20%, better less than 10%, better less than 5%, better less than 2%, better less than 1% of 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 other, second LED chain. In a similar manner, further LED strings extending beyond said first two LED strings, for example a third, fourth, etc., may be monitored. Other LED chains are then preferably, but not necessarily, different from all other LED chains. In order to power the LEDs, the first and second LED strings (LED1, LED2) and the first regulated current source (I1) and the second regulated current source (I2) are connected to a common node (GND). Insofar as resistors or other circuit parts should still be located between this common node and the connection of the first and / or second current source (I1, I2), for example, chokes and / or lead resistors, they can be simplified as part of the first or second power source are considered. Possibly. the evaluation circuit must be connected to the common node by a separate reference potential line in order to correctly detect the potentials for the evaluation of the LED chains. The first LED chain (LED) is now a first voltage divider (RS1) with a first total resistance (R1) and the second LED chain, a second voltage divider (RS2) with a second total resistance (R2) connected in parallel. These voltage dividers (RS1, RS2) are preferably integrated in a monolithic integrated circuit, which includes the current sources and the evaluation circuit (AS). Since such monolithic integrated circuits are typically used in different applications with different LED chain lengths between applications and also within the individual application, it makes sense if the first voltage divider (RS1) and the second voltage divider (RS2) are monolithically integrated and then simultaneously are programmable. The variant with non-programmable first voltage divider (RS1) and second voltage divider (RS2), which are already described in the German patent applications, will first be described below DE 10 2015 008 110.1 and DE 10 2015 008 109.8 which are the fullest part of this description. The programming of the voltage dividers is typically carried out in such a way that a data register within the monolithic integrated circuit can be described via a data interface of the monolithic integrated circuit, the part of which is the current sources (I1, I2). Its content then sets the division ratio of the first voltage divider (RS1) and the division ratio of the second voltage divider (RS2). The first total resistance (R1) of the first voltage divider (RS1) is the correct programming of the first voltage divider (RS1) and the second voltage divider (RS2) n times the second total resistance (R2) divided by m. Preferably, these voltage dividers (RS1, RS2) are made relatively high impedance, so as not to burden the power sources. The first voltage divider (RS1) in this case has a first tap (ERR1) in such a way that the voltage (U1) between this first tap (ERR1) and the common node (GND) with correct programming of the first voltage divider (RS1) and second voltage divider (RS2) k times the first _forward voltage (U _LED1 ), when the first LED chain (LED1) from the first rated current (I10) is flowed through. 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) with correct programming of the first voltage divider (RS1) and the second voltage divider (RS2) is also a k-times the second _forward voltage (U _LED2 ), when the second LED chain (LED2) from the second rated current (I ₂₀ ) is flowed through. The first tap (ERR1) and the second tap (ERR2) are now connected to an evaluation circuit (AS). A meaningful dimensioning is now, for example, such that during the flow through the first LED chain with the first rated current with correct programming of the first voltage divider (RS1) and the second voltage divider (RS2) of the first tap (ERR1) in about, except for manufacturing variations, has the same potential as the second tap (ERR2) of the second voltage divider (RS2), when the second LED chain (LED2) flows through the second rated current. If this difference is smaller than a specified tolerance band between two threshold values, all LEDs are in order and not defective. However, if the voltage difference is outside this tolerance band, then there is a defect and an evaluation circuit can detect this by comparison with two threshold values and set an error signal. 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, other signals are conceivable instead of the output of a signal. For example, it is possible to set an error flag in one via a data bus within the evaluation circuit.

Incidentally, it is clear to the person skilled in the art that if necessary different divider ratios can be used for the programmable voltage dividers if the forward voltages of the LEDs in the chains are different, which however is typically avoided by the person skilled in the art due to the associated temperature problems. Thus, depending on the application, the voltage dividers can have all divider ratios of 100% down to just over 0%. Integer divider ratios are preferable due to matching and ease of programmability design.

In a variant of the device, at each LED of the first LED chain (LED1), when it flows through the first rated current (I10), 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% of the average of the forward voltages of the other LEDs of the first and second LED chain (LED1, LED2) is different. In this case, falls on each LED of the second LED chain (LED1) when it flows through the second rated current (I ₂₀ ), a second forward voltage (LED2) 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 average of the forward voltages of the other LEDs of the first and second LED strings (LED1, LED2). Again, the first and second LED strings (LED1, LED2) and the first regulated current source (I1) and the second regulated current source (I2) are connected to a common node (GND). However, only the second LED chain, a second programmable voltage divider (RS2) with a second total resistance (R2) is 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, if the second LED chain (LED2) from the second rated current (I ₂₀ ) flows through. 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) as a function of 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 and / or sets an error flag and / or changes one content tab.

In a further variant of the device, 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 ) differs by more than 1% and / or more than 2% and / or more than 5% and / or more than 10% and / or more than 25%.

In a further embodiment of the device, the evaluation circuit has an associated sub-device, which detects 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 is performed. 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 to 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 to the second tap (ERR2). To set the first threshold, for example, a first offset voltage _source (V _ERR1 ) that is part of the subdevice is connected on one side to the first tap (ERR1) and on the other side to the fourth input of the second comparator (CMP2). 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 considered to be the first offset voltage _source (V _ERR1 ) in the sense of this disclosure.

Furthermore, it has a second offset voltage _source (V _ERR2 ) connected on one side to the second tap (ERR2) and on the other side to the third input. 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 regarded as a second offset voltage _source (V _ERR2 ) in the sense of this disclosure.

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

In a further embodiment, the device has a sub-device with a first comparator (CMP1) having 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). 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 display a first threshold value with which the potential at the first input of the first comparator is compared by the first comparator (CMP1). This compares the first tap (ERR1) with this first threshold. In addition, it has a second offset voltage _source (V _ERR2 ) which is connected on one side to the second tap (ERR2) and on the other side to the third input. As before, this second offset voltage _source (V _ERR2 ) serves 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). This compares the second tap (ERR2) with this second threshold. Other implementations are of course possible. To generate the necessary output signal, a logic circuit couples the first and second comparator outputs to produce an error signal and / or set an error flag and / or change register contents.

In addition to this device, therefore, the invention also includes a method for monitoring the electrical power supply of at least one first LED chain (LED1) with n LEDs from a first regulated current source (I1) with a first rated current (I ₁₀ ) and at least one second LED chain (LED2) with m LEDs from a second current source (I2) with a second rated current (I ₂₀ ). This method is claimed here. The method according to the invention begins with the generation of a first tap potential as the first error detection parameter at a first tap (ERR1). Preferably, the tap potential is proportional to the voltage drop across the first LED string (LED1). At the very least, this dependency should be strictly monotone. According to the invention, the preferred first voltage divider (RS1) is used for this purpose, with the first tap (ERR1) possibly also being able to be made at the beginning of the first LED chain (LED1). The second part of the method is the setting of the voltage divider ratio of the first voltage divider (RS1) as a function of a signal and / or a data word. Third, analogously, a second tap potential is generated as a second error detection parameter at a second tap (ERR2). Again, proportionality is preferred again. However, at least this second tap potential should depend strictly monotone on the voltage drop across the second LED string (LED2). Again a voltage divider, here the second voltage divider (RS2) is the preferred realization. Here, too, the second tap (ERR2) may also take place at the beginning of the second LED chain (LED2). In a third step, the comparison of the voltage difference between the first tap potential and the second tap potential, in particular by an evaluation circuit (AS) and in particular with the formation of a voltage difference signal, follows in one The fourth step is followed by comparing the thus determined voltage difference between the first tap potential and the second tap potential, in particular in the form of the voltage difference signal, with a first threshold value and a second threshold value. The latter should be different from the first threshold in order to form a tolerance window. This comparison is preferably carried out again by the evaluation circuit (AS). In a fifth step, the utilization of the comparison result by the evaluation circuit (AS) takes place. This signals whether the voltage difference lies between the first and the second threshold value, wherein the signaling can be effected in particular by an error signal (FS) and / or the setting of an error flag and / or the changing of a register content.

In a variant of the method, the first threshold value and the second threshold value do not differ by more than 1% and / or inferior by not more than 2% and / or worse by not more than 5% and / or worse by not more than 10% and / or worse by not more than 25% and / or worse by not more than 50%. In this case, the choice of the width of the tolerance window depends on the production spread of the forward voltages of the LEDs.

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

In a further variant of the method, an evaluation of the error detection parameters, in particular by the evaluation circuit, takes place in a fixed temporal relationship with an on or off signal for the current sources (I1, I2). This has the advantage that problems with the supply stability, especially in the switch-on and switch-off do not lead to erroneous error detection.

In a further variant of the method, detection of at least one temperature (θ ₁ , θ ₂ ) which is in thermal operative connection with at least one of the LED chains (LED1, LED2) is carried out by means of a temperature measuring device (TM1, TM2) as another error detection parameters.

• a. eine erste und/oder höhere zeitliche Ableitung eines ersten und/oder zweiten und/oder weiteren Fehlererkennungsparameters und/oder
• b. eine erste und/oder höhere zeitliche Integration eines ersten und/oder zweiten und/oder weiteren Fehlererkennungsparameters und/oder
• 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, in particular by the evaluation circuit (AS), is derived from at least one first and / or second and / or other further error detection parameter. The result of this derivation can be one of the following derived further error detection parameters:

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

Description of the figures

1 shows by way of example the basic structure of a device with a first LED chain with 4 LEDs and a second LED chain with 6 LEDs,

2 shows by way of example the basic structure of a device with a first LED chain with 2 LEDs and a second LED chain with 4 LEDs.

3 shows by way of example the basic structure of a device 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 by way of example the basic structure of a device with a first LED chain with 2 LEDs and a second LED chain with 4 LEDs, now also other voltages of the LED chains are used as references.

5 show the 1 with additional temperature measuring devices.

6 shows an exemplary comparator circuit

7 shows an exemplary comparator circuit for the cross-evaluation of two chains with internal taps.

8th shows 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).

9 shows 2 with the difference that the first and second voltage divider (RS1, RS2) are programmable voltage dividers by a parallel-connected switch chain.

9 shows 9 with the difference that the first and second voltage divider (RS1, RS2) are each designed by an analog multiplexer as a programmable voltage divider.

Fig. 1

1 shows by way of example the basic structure of a device with a first LED chain with 4 LEDs and a second LED chain with six LEDs. The first regulated current source (I1) spits the first rated current (I ₁₀ ) into the first LED chain from here, by way of example, six LEDs connected in series one after the other. The second regulated current source (I2) spits the second nominal current (I1 ₂₀ ) into the second LED chain from here, for example, six LEDs connected in series one after the other. 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 further parameters (eg the LED temperature by means of a temperature measuring device). The LEDs connected in series of a single LED chain of the device may also be a module of parallel-connected LEDs instead of a single LED, which are here regarded as an LED in the chain. It is only important that the LEDs show approximately the same forward voltage at the first and second rated current (I ₁₀ , I ₂₀ ). Since the first and second voltage divider (RS1, RS2) are each typically selected as high impedance as possible, the current of the first current source (I1) flows almost completely through the first LED chain (LED1) and the current of the second current source (I2) almost completely the second LED chain (LED2). In this example, the first voltage divider (RS1) divides the voltage falling across the first LED string (LED1) by a ratio of 1: 4. In contrast, the second voltage divider (RS2) divides the voltage that drops across the second LED chain (LED2) in a ratio of 1: 6. Thus, the voltage at the first tap (ERR1) of the first voltage divider (RS1) corresponds approximately to the _forward voltage (U _LED1 ), which _drops via an LED within the first LED chain (LED1). The voltage at the second tap (ERR2) of the second voltage divider (RS2) in this example also corresponds approximately to the _forward voltage (U _LED2 ), which _drops via an LED within the second LED chain (LED2). The evaluation circuit (AS) compares the potentials of the first tap (ERR1) and the second tap (ERR2) with each other in this exemplary device and produces therefrom the preferably digital error signal (FS). As already mentioned, it may be useful if the evaluation circuit (AS) detects a first temperature (θ ₁ ) in the vicinity of the first LED chain (LED1) and / or a second temperature (θ ₂ ) in the vicinity of the second one LED chain (LED2) detected. This shows the 5 , Typically, the flux voltages (U _LED1 , U _LED2 ) at the respective nominal currents (I ₁₀ , I ₂₀ ) of the LEDs in the at least two LED chains (LED1, LED2) should be approximately the same. In that case, the potentials of the first tap (ERR1) and the second tap (ERR2) should thus be approximately equal. The evaluation circuit (AS) thus performs a static procedure. 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. When designing the at least two threshold values within the evaluation circuit (AS), the person skilled in the art will take this into account by suitable calculation in order to avoid false error messages or non-triggering of error messages. In particular, the threshold values used in the evaluation circuit, which are for the decision that an error occurs, preferably in response to one or more temperatures (θ ₁ , θ ₂ ), which have been measured in the vicinity of the respective LED chain (LED1, LED2) are, and / or modified / adjusted depending on their temperature differences. Typically this is done by an analog and / or digital polynomial approximation.

Fig. 2

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

Fig. 3

3 shows an exemplary device with three LED chains. While the first and the second LED chain the 1 corresponding to the third LED chain (LED3) through a controlled third current source (I3) having a third nominal current (I ₃₀₎ is supplied. A third voltage divider reduces the voltage that drops across the third LED chain (LED3) by a factor of 1: 5. Thus, the potential of the third tap (ERR3) should 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 outwards 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 ) is outside the tolerance range given by the two thresholds.

Fig. 4

4 corresponds to 2 with the difference that a third tap (ERR3) of a third potential occurs directly in the first LED string (LED1) and a fourth tap (ERR4) of a fourth potential occurs directly in the second LED string (LED1). The evaluation circuit compares these four potentials of the four taps (ERR1, ERR2, ERR3, ERR4) with at least two thresholds and signals outwards 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 thresholds.

Fig. 5

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

Fig. 6

6 shows the exemplary comparator circuit, as previously explained.

By way of example, this exemplary sub-device has 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 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 display a first threshold value with which the potential at the first input of the first comparator is compared by the first comparator (CMP1). This compares the first tap (ERR1) with this first threshold. In addition, it has a second offset voltage _source (V _ERR2 ) which is connected on one side to the second tap (ERR2) and on the other side to the third input. As before, this second offset voltage _source (V _ERR2 ) serves 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). This compares the second tap (ERR2) with this second threshold. Other implementations are of course possible. To generate the necessary output signal, a logic circuit couples the first and second comparator outputs to produce an error signal and / or set an error flag and / or change register contents.

Fig. 7

7 corresponds to 6 with the exemplary difference that the circuit additionally evaluates taps within the chains crosswise. The corresponding external interconnection is exemplary in 4 Shown.

Fig. 8

8th shows 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).

Fig. 9

9 essentially corresponds 2 with the difference that the first voltage divider (RS1) is designed as a resistor chain of here by way of example six resistors (R). The upper resistors can be bridged by six switches (S _1,1 to S _1,5 ). These switches (S _1,1 to S _1,5 ) are typically controlled by signal lines which are fed either from a data register of the monolithic integrated circuit or from a logic thereof. The switches (S _1.1 to S _1.5 ) and the resistor chain can be well integrated in a monolithic integrated circuit, which already includes, for example, the current sources (I1, I2) and the evaluation circuit (AS). That for the first voltage divider regarding 9 the same applies analogously to the second voltage divider (RS2). In the example, a first LED string having two LEDs and a second LED string having four LEDs are connected to the exemplary monolithic integrated circuit. Therefore, in the example, the upper four switches (S _1.5 , S _1.4 , S _1.3 S _1.4 ) of the first programmable Voltage divider (RS1) is closed and the upper two switches (S _2.5 , S _2.4 ) of the second programmable voltage divider (RS2) closed. This results in the same effect as in a fixed wiring accordingly 2 ,

Fig. 10

10 essentially corresponds to the 9 with the difference that the first voltage divider (RS1) is again designed as a resistor chain of here six exemplary resistors (R), but now not partially shorted depending on the programming, but now by a first analog multiplexer (MUX1) according to the programmed Value is tapped. The resistors (R) are in this example the 10 in contrast to the previous examples preferably not executed the same, but each adjusted in size so that the correct divider ratios arise. The first analog multiplexer (MUX1) is typically controlled by signal lines fed either from a data register of the monolithic integrated circuit or from a logic thereof. The first analog multiplexer (MUX1) and the resistor chain can be well integrated in a monolithic integrated circuit, which already includes, for example, the current sources (I1, I2) and the evaluation circuit (AS). That for the first voltage divider (RS1) with respect to 10 the same applies analogously to the second voltage divider (RS2).

Advantages of the invention

The invention enables the monitoring of the function of the arranged in different lengths, freely configurable LED chains LEDs in automotive applications such as brake lights, indicators and taillights, etc.

LIST OF REFERENCE NUMBERS

• AS

  evaluation circuit

  CMP 1

  first comparator

  CMP2

  second comparator

  CMP 3

  third comparator

  CMP 4

  fourth comparator

  ERR1

  first tap

  ERR2

  second tap

  ERR3

  third tap

  ERR4

  fourth tap

  IT

  error signal

  GND

  common node (reference potential)

  I1

  first regulated power source

  I ₁₀

  first rated current that provides the first current source (I1) for the first LED string (LED1).

  I2

  second regulated power source

  I ₂₀

  second rated current that provides the second current source (I2) for the second LED string (LED2).

  I3

  third regulated power source

  I ₃₀

  third rated current, which provides the third current source (I3) for the third LED chain (LED3).

  LED1

  first LED chain

  LED2

  second LED chain

  LED3

  third LED chain

  LG

  logic circuit

  MUX1

  first analog multiplexer of the first programmable voltage divider (RS1). The first analog multiplexer in this example, depending on the contents of a data register and / or depending on a logic of the monolithic integrated circuit, the potential of a node of the resistor chain of the first programmable voltage divider (RS1) of resistors (R) as a first tap (ERR1) from ,

  MUX2

  second analog multiplexer of the second programmable voltage divider (RS2). The second analog multiplexer in this example, depending on the contents of a data register and / or depending on a logic of the monolithic integrated circuit, the potential of a node of the resistor chain of the second programmable voltage divider (RS2) from resistors (R) as a second tap (ERR1) from ,

  R

  ground 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) in the vicinity of the first LED chain (LED1) measured first temperature or first temperature measurement signal that represents this first temperature. measured in the vicinity of the second LED chain (LED2) second temperature or second temperature measurement signal that represents this second temperature.

  S _1,1

  first switch of the first programmable voltage divider (RS1). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _1,2

  second switch of the first programmable voltage divider (RS1). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _1,3

  third switch of the first programmable voltage divider (RS1). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _1.4

  fourth switch of the first programmable voltage divider (RS1). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _1.5

  fifth switch of the first programmable voltage divider (RS1). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _2.1

  first switch of the second programmable voltage divider (RS2). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _2,2

  second switch of the second programmable voltage divider (RS2). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _2,3

  third switch of the second programmable voltage divider (RS2). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _2,4

  fourth switch of the second programmable voltage divider (RS2). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  S _2,5

  fifth switch of the second programmable voltage divider (RS2). The switch is typically opened or closed in response to a data register and / or logic of the monolithic integrated circuit.

  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)

  U _LED1

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

  U _LED2

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

  U _LED3

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

  V _ERR1

  first offset voltage source

  V _ERR2

  second offset voltage source

  V _ERR3

  third offset voltage source

  V _ERR4

  fourth offset voltage source

Claims (1)

Method for monitoring the electrical power supply of at least one first LED chain (LED1) with n LEDs from a first regulated current source (I1) with a first rated current (I ₁₀ ) and at least one second LED chain (LED2) with m LEDs from a second one Current source (I2) having a second rated current (I ₂₀ ), wherein min is, with the steps, - generating a first tap potential as a first fault detection parameter at a first tap (ERR1) strictly monotone from the voltage drop across the first LED string ( LED1), by means of a first voltage divider (RS1), wherein the first tap (ERR1) is not at the beginning of the first LED chain (LED1) and - adjusting the voltage divider ratio of the first voltage divider (RS1) in response to a signal or a data word ; Generating a second tap potential as a second fault detection parameter at a second tap (ERR2) which strictly monotonically depends on the voltage drop across the second LED string (LED2), the second tap (ERR2) also at the beginning of the second LED string (LED2 ) can take place; - comparing the voltage difference between the first tap potential and the second tap potential, with a first threshold and a second threshold different from the first threshold; Signaling whether the voltage difference lies between the first and the second threshold value.

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