WO2017198370A1

WO2017198370A1 - Lighting module having fault diagnosis and associated method

Info

Publication number: WO2017198370A1
Application number: PCT/EP2017/056866
Authority: WO
Inventors: Otmar Schlag
Original assignee: Huf Hülsbeck & Fürst Gmbh & Co. Kg
Priority date: 2016-05-19
Filing date: 2017-03-22
Publication date: 2017-11-23
Also published as: DE102016109240A1

Abstract

The invention relates to a lighting module for a motor vehicle, which has at least a first light-emitting diode (5) and a second light-emitting diode (6), which are connected in series and are coupled to a switchable power supply (1). A control and evaluation device (2) is coupled to the power supply and to the light-emitting diodes in order to switch the power supply on and off and to sense a voltage drop across the light-emitting diodes. A delay capacitor (8) is coupled to the power supply (1) in parallel with the first light-emitting diode (5) and in series with the second light-emitting diode (6). The control and evaluation device (2) activates the power supply and senses a first voltage drop u1 across the light-emitting diode group after a first duration t1, which is shorter than a charging duration of the delay capacitor (8). A second voltage drop u2 across the light-emitting diode group is sensed after a second duration t2, which is longer than a charging duration of the delay capacitor (8). A fault diagnosis of the first and the second light-emitting diodes is performed on the basis of the values u1 and u2 and stored comparison values.

Description

Lighting module with fault diagnosis and associated procedure

The invention relates to a lighting module for

Motor vehicles. In particular, the invention relates to a

Light-emitting diode illumination module with a self-diagnostic capability and an associated method.

Lighting modules with a plurality of light emitting diodes (LED) are used in different positions on motor vehicles for

Signal lighting or comfort lighting used.

For example, instruments are in the interior of vehicles or warning devices with backlit displays or

Operating devices designed. There are often several

Light-emitting diodes used in electrical series connection. These series-connected LEDs then form a light-emitting diode group and are powered by a common power source, the LEDs are operated regularly with a constant current.

The forward voltage in the operation of light-emitting diodes is determined in particular by the temperature and other environmental conditions and, of course, by the selection of the LEDs.

Accordingly, the current through such groups of light emitting diodes may vary depending on environmental conditions. A

Diagnosis of the proper function of the LEDs is regularly possible only by determining a voltage drop across the LEDs. Decreases in the face of the operation of the

Light emitting diodes with a constant current, however, the operating voltage due to the ambient conditions, so there may be a case in which a proper diagnosis is no longer possible.

It is an object of the invention to improve the diagnostic capability of lighting modules.

This object is achieved by a lighting module having the features of claim 1 and a method having the features of claim 7.

According to one aspect of the invention, a lighting module for a motor vehicle is provided, which is a Light-emitting diode group having at least a first and a second light-emitting diode. These LEDs are for

Formation of the light-emitting diode group connected in series. A switchable power supply is coupled to the light emitting diode group.

In addition, a control and evaluation device

provided, which is coupled to both the power supply and the light-emitting diode groups. This tax and

Evaluation device is designed to turn on and off the power supply and a voltage drop across the

Capture light-emitting diode group.

Accordingly, voltage taps in front of and behind the

Light-emitting diode group provided which a voltage tap and thus a detection of the voltage drop across the

Enable light-emitting diode group. It should be noted that the light-emitting diode group may be arranged together with other components of an electrical circuit. It is essential that the voltage drop detects the light-emitting diode group such that a determination of the total voltage drop across the light-emitting diode group is possible.

It is inventively provided that in the

Lighting module at least one delay capacitor

is used, which is coupled in parallel to the first light emitting diode and in series with the second light emitting diode to the power supply. This delay capacitor is used, in particular, to delay the current flow through the first light-emitting diode when the power supply is switched on. The capacitor has a capacity which, when the DC voltage is switched on

Power for a period of time during the

Charging the capacitor has a low electrical

Resistor and therefore offers a low-resistance current path parallel to the first light-emitting diode. The in series

switched second LED is on the other hand current flowing through (if it works properly).

In the context of this application, the timing of the play

Charging and discharging of capacitors play an essential role. It is known that a charging behavior of a capacitor depends substantially on its capacity as well as on series connected resistors and electronic components. Accordingly, charging characteristic times can be calculated, with a simple relationship of a

Time constant for loading and unloading in the printout

τ = R x C exists. Where R is a series resistance to the capacitor and C is the capacitance of the capacitor. Since the charging of a capacitor takes place in accordance with an exponential function, it follows that the voltage drop across the capacitor during charging after the lapse of a period of time which corresponds to the simple time constant τ is approximately 63% of that

Final voltage increases, after 2 τ to about 86%, after 3 τ to about 95%.

When discharging, however, the voltage drops after 1 τ to about 37% of the output voltage, after 2 τ to about 13% and after 3 τ to about 5%. According to this theoretical approach, although a capacitor would never fully charge or never fully discharge, this is not the case in practice and irrelevant to this consideration. If in this

Namely application of the charging time of a capacitor is mentioned, so that the technical charge according to the triple time constant meant, so the duration within which a

Capacitor is charged to at least 90%. In the discharge, accordingly, a period of time is meant at which a capacitor has discharged to at least 10% of the fully charged state.

According to the invention, the control and evaluation device of the lighting module is designed so that they

Powering the light-emitting diode group activated and also starts a timer. After a predetermined first

Time tl, measured from the power supply, will cause a voltage drop ul across the light emitting diode group

detected. The first time period t1 is dimensioned such that the delay capacitor is not yet charged within this time period. tl is thus in particular smaller than 3 τ. However, the first time period can also be significantly shorter than the charging time, for example, be a period of time, about the simple time constant τ of the capacitor corresponds, ie a time range within which the capacitor is charged to about 60%. Even significantly lower states of charge can determine the duration tl. It is essential that the capacitor is still discharged so far that the voltage dropping across it remains below the forward voltage of the parallel-connected first light-emitting diode and this is bridged by the delay capacitor within this period. At the time of the first measurement, the voltage which essentially drops across the second diode is detected, since the first diode is bridged by the capacitor.

After a second period t2, measured by the

Activation of the power supply, the voltage drop is detected again via the light-emitting diode group. So it will be

According to the invention again the voltage at the same

Detected voltage taps, but after another

Delay. The second time t2 is sized to be longer than the charge time of the delay capacitor. As described above, this means that the charge of the

Capacitor is largely completed, wherein

For example, the time t2 of the time constant τ or a multiple of the time constant τ of the charging curve of the capacitor is. At this time, the delay capacitor is charged and is non-conductive in view of the applied DC voltage. The parallel-connected first light-emitting diode, on the other hand, is supplied with the increased voltage, which is also applied to the capacitor, and thus permeable.

The now detected voltage u2 thus represents the voltage that drops at the light-emitting diode group, both light-emitting diodes are now permeable (conductive). In this way, therefore, a voltage ul was measured after the time t1, which is to be assigned to the forward voltage of the second light-emitting diode. After the time t2, however, a voltage u2 is measured, which is assigned to the series connection of the two transparent light-emitting diodes.

For evaluation, the first voltage ul in the control and evaluation circuit with an expected and stored Forward voltage of the second LED compared. It should be noted that the forward voltage of the second LED may well be within a predetermined tolerance range, since this is dependent on the ambient conditions. If the comparison results in a voltage value μ1 which is within the expected forward voltage range of the second LED, then the proper function of the second LED becomes

detected. The determined voltage u2 (with fully charged delay capacitor) is the expected

Forward voltage of the two series-connected LEDs, ie the sum of the forward voltage of the first light emitting diode and the second light emitting diode compared. If this voltage value u2 lies in the expected range of the sum of the forward voltages, a proper function of both light-emitting diodes is concluded.

The delay capacitor according to the invention allows the measurement of a single of the LEDs and, in time

delayed, the measurement of the voltage drop across the

Series connection of the LEDs. By an identical

Voltage tap can be differentiated in this way

Analysis of the accuracy of the light-emitting diodes can be determined.

In the context of the invention may additionally in the

Lighting module to be provided further electronic components. In particular, e.g. a reverse polarity protection diode are introduced or an overvoltage protection. Also series resistors will be used in practice. These others

However, components do not change the fundamentals

Design of the lighting module and the claimed structure. If these components are included in the voltage tap, they must be taken into account in the evaluation.

The method according to the invention essentially reproduces the steps described above, wherein in particular a device according to the above representation can also be used. It is a method of testing at least two light-emitting diodes connected in series. For this purpose, a delay capacitor is coupled to a power supply parallel to the first light emitting diode. The delay capacitor is coupled in series with the second LED. Then, according to the invention, the power supply is activated and a time tl to wait, which is shorter than a charging time of

Delay capacitor is. When the time has elapsed, the voltage drop ul is detected via the light-emitting diode group. As soon as a second period t2 (longer than the charging time of the

Capacitor), measured from the activation of the power supply has expired, the voltage drop is measured again, whereby a voltage drop u2 is determined. These values ul and u2 are expected with stored values

Forward voltages of the first and second LEDs

compared. Depending on this comparison will be one

Fault condition of the first and the second light emitting diode

performed .

As described above, the first voltage ul should be in a predetermined variable value range for forward voltages of the second light-emitting diode. On the other hand, the determined voltage u2 should be in the predetermined range of the acceptable sum of forward voltages of the first and second LEDs.

In a further development of the invention

Lighting module, the voltage across the LED group is measured a third time. However, this is after

Performing the second measurement of the voltage u2, after charging the delay capacitor, the power supply off (disabled). After a period of time t3 after this deactivation, in turn, the voltage drop across the light-emitting diode group is detected, whereby a voltage value u3 is determined. The

Time t3 is smaller than the discharge duration of the

Delay capacitor.

The delay capacitor is, as described above, connected in parallel with the first light-emitting diode. Switching off the supply voltage causes the on-state voltage at the second LED to decrease, approximately to 0 V. However, since the time t3 is shorter than the discharge period, the elapse of this period of time has

Delay capacitor still stores a charge amount and has a voltage which is representative of the Forward voltage of the parallel-connected first LED is. Ideally, with successful timing, the measured voltage will largely correspond to the forward voltage of the first LED during operation. The forward voltage of the first

LED is so to speak for a short period of time after switching off the power supply in parallel

Capacitor frozen and can be measured delayed.

In addition to the detected values ul and u2, the value u3 thus offers a possibility of the forward voltage of the first

To measure the LED separately.

According to this scheme, therefore, a timed connection of the power supply and a delayed measurement of two

Voltage values carried out, then there is a shutdown of the power supply and a delayed measurement of another voltage value. From this set of voltage values, a diagnosis of the operating states of the light emitting diodes

be performed.

It is particularly preferred if the delay capacitor has a capacitance between 100 nF and 900 nF. A

Such delay capacitor design is particularly suitable for common LED types with forward voltages in the range of several volts (e.g., 3V to 5V) because it provides optimized timing for performing the described diagnostic method.

In a development of the invention is a second

Capacitor as protective capacitor coupled to the power supply parallel to the LED group. The capacity of the second capacitor is less than the capacity of the

Delay capacitor. The second capacitor can

For example, as protection against static charges parallel to the light-emitting diode group and thus also parallel to

Delay capacitor be switched. Due to the lower capacity ensures that the time constant and thus also load and unload the second capacitor run faster than the delay capacitor. This facilitates the evaluation in the manner described above. It is particularly preferred that the capacitance of the second capacitor is at most 1/10 of the capacity of the delay capacitor. In this way, although the second capacitor provides its protection, it only influences the evaluation of the charging processes and discharging processes of the delay capacitor

slightly.

In one embodiment of the invention is an ohmic

Resistor parallel to the second LED with the

Power supply coupled, wherein the ohmic resistor is coupled in series with the delay capacitor. This design makes it possible to provide a power supply of the first light emitting diode in case of failure of the second light emitting diode.

The invention will now be explained in more detail with reference to the accompanying drawings.

Figure 1 shows a schematic circuit according to a

Embodiment of the invention;

FIG. 2 shows an exemplary voltage curve for faultless light-emitting diodes;

FIG. 3 shows the comparison of different signal profiles with different diode interruptions;

FIG. 4 shows the comparison of a plurality of signal profiles with different diode short circuits.

In FIG. 1, a circuit for forming a lighting module according to a first embodiment of the invention is shown by way of example

Invention shown. A current source 1 is coupled to a control and evaluation device 2. The tax and

Evaluation device 2 can activate and deactivate the current source 1 for the voltage and current supply of the circuit. The control and evaluation device also has two

Voltage taps 3 and 4, via which a voltage drop across the LEDs 5 and 6 can be measured. The control and evaluation circuit includes a circuit which

specified delay times read voltage values at taps 3 and 4.

The LEDs 5 and 6 are as a light-emitting diode group in

Series connected and are powered by a series resistor 7. Parallel to the first light-emitting diode 5 is a Delay capacitor 8 connected. Of the

Delay capacitor 8 is in series with the second

LED 6 switched. In addition, another ohmic resistor 9 is in series with the delay capacitor 8

connected and parallel to the second light-emitting diode. 6

A capacitor 10 is parallel to the entire

Light-emitting diode group connected and serves for protection

electrostatic disturbances.

As merely exemplary values, a resistance of only a few ohms, for example 18 Ω, can be used as resistor 7. The protection capacitor 10 can be realized for example with a capacitor of a capacitance of 10 nF. The delay capacitor 8 has a larger one

Capacitance as the protection capacitor 10, it may e.g. have a capacity of 470 nF. The resistor 9 can be dimensioned with 1 kOhm. The current source 1 supplies a constant current, matched to the light-emitting diodes 5 and 6 used.

In Figure 2, a voltage waveform is shown, which in the inventive method implementation and in the

Commissioning of the sensor module according to the invention between the taps 3 and 4 shows.

The control and evaluation device 2 switches the current source 1 active at the time t = 0. After the actual

Switching operation, the capacitor 8 is charged according to its capacity and the applied voltage, resulting in the

Voltage rise shows. Depending on the capacitance of the capacitor 8, a time t1 is selected so that a voltage ul is detected after elapse of the time tl from the switching time point of the current source 1. This is shown in FIG. In this example, a span of about 10 ys is selected as the time t1, which is an early point of the charging curve of the

Condenser 8 corresponds. At this time, the

Capacitor still a low resistance and voltage drop and bridges the first light-emitting diode 5. The voltage ul can be detected and later compared with the forward voltage of the second light-emitting diode 6, which is already active. After a time t2, the delay capacitor 8 is complete charged and a voltage u2 is measured. For example, in the above exemplary data, this measurement takes place after about 300 to 350 ys.

Already on the basis of these measurements, an evaluation

be made. The charged capacitor 8 blocks the

DC and the voltage u2 should be within

Tolerance limits the forward voltages of the series

switched LEDs 5 and 6 correspond.

However, it is also possible according to a development of the invention that the control and evaluation device 2 according to

After the measurement has been taken, the power supply 1 is switched off again at time t2 and at time t3 (for example after 450 ys at

Shutdown after 350 ys) measures a third voltage u3. After the shutdown, the capacitor 10 discharges within 30 to 40 ys, and the forward voltage at the second light emitting diode 6 returns to about 0V. Then, when measured at time t3, the delay capacitor 8 is still charged almost with the forward voltage of the first light emitting diode 5, and measurement can be made in consideration of the resistor 9 to detect the forward voltage of the first light emitting diode 5. It is essential that the time t3 is within a period of time after the power source 1 is turned off which is less than the discharge time of the delay capacitor (e.g.

less than the time constant of the capacitor 8 below

Consideration of resistors 7 and 9).

FIG. 3 shows exemplary signal curves for several different cases. The curve 20 corresponds to the

Voltage curve, which is measured at a completely intact LED group (corresponding to Figure 2). In this case, therefore, both the first light-emitting diode 5 and the second

LED 6 intact. The voltage values measured at the times t1, t2 and t3 agree with the expected ones

Voltage values match.

The curve 21 shows a case where the circuit in the first light-emitting diode 5 is interrupted. The first light-emitting diode 5 is therefore defective and has an interruption. The second light-emitting diode 6, however, is intact. In this case, it is due of the missing parallel strand to the delay capacitor 8, the capacitor charged more than an intact first light emitting diode 5. While at time tl still a

Measurement result has been achieved, which indicated the accuracy of the second LED 6 is at time t2, the measured voltage above a tolerance value for the sum of the forward voltages of the light emitting diodes 5 and 6. It can be concluded that the first light emitting diode

Has interruption and the second LED is intact. The voltage at time t3 is also above the tolerable range.

If, on the other hand, the first light-emitting diode 5 is intact and the second light-emitting diode 6 has an interruption, a voltage curve according to the line 22 is shown. The voltage rises considerably steeper at the time t 1 and is already there beyond the tolerable range. At time t3, however, the voltage has fallen back into the normal range, so that a conclusion can be drawn about an interruption in the second light-emitting diode 6.

The voltage curve 23, however, shows interruptions in both LEDs, the voltage does not drop back to the expected range at time t3.

The course of the voltages in FIG. 4 shows fault cases in which short circuits occur in the light-emitting diodes.

The curve 25 again shows a voltage curve of an intact light-emitting diode arrangement (the scale has been changed with respect to the preceding figures for reasons of clarity).

The voltage curve 26 indicates a short circuit in the first light-emitting diode 5. In this case, there is no charging of the capacitor, as there is a short circuit parallel to the capacitor. The voltage can be adjusted accordingly

Time t2 does not rise to the expected voltage values. In addition, at time t3, the voltage has decreased much more than in a charged one

Delay capacitor 8 would be expected.

The voltage curve 27 shows an intact first light-emitting diode 5, but a short circuit in the second light-emitting diode 6. Der Capacitor is charged here again, but only to a voltage value such as in the case of the voltage waveform 26. However, the voltage drops back to the expected range at time t3. From this combination of values, the short-circuit in the second light-emitting diode 6 can be deduced. Finally, the curve 28 shows a short circuit in both the first light-emitting diode 5 and the second light-emitting diode 6.

From these examples it is easy to see that the

Measurement of two or three voltage values at given times, which depends on the used electronic

Components are matched, a differentiated analysis of error conditions in LEDs can be made. It suffices if these measurements are made on uniform voltage taps in order to carry out a fault diagnosis in the lighting module by comparison with stored values.

Claims

claims

1. lighting module for a motor vehicle, wherein the lighting module comprises a light-emitting diode group having at least a first (5) and a second light-emitting diode (6), which are connected in series,

wherein the light-emitting diode group with a switchable

Power supply (1) is coupled,

characterized,

that a control and evaluation device (2) with the

Power supply and the light-emitting diode group is coupled, wherein the control and evaluation device is designed to turn the power on and off and a

Detect voltage drop across the light emitting diode group,

a delay capacitor (8) is coupled to the power supply (1) in parallel to the first light-emitting diode (5) and in series with the second light-emitting diode (6),

that the control and evaluation device (2) is designed such that it supplies the power to the

Light emitting diode group activated and after activation after a first time tl, which is shorter than a charging time of the delay capacitor (8), a first

Voltage drop ul across the light-emitting diode group detected and after the activation of the power supply after a second time period t2, which is longer than a charging time of the delay capacitor (8), a second

Voltage drop u2 detected across the light-emitting diode group,

based on the detected values ul and u2 and stored comparison values of expected forward voltages of the first and second light emitting diode performs a fault diagnosis of the first and the second light-emitting diode.

2. Lighting module according to claim 1, wherein the control and evaluation device (2) is designed such that after detection of the second voltage drop u2, the power supply is deactivated and after a third time duration t3 after deactivation, which is less than one

Discharge time of the delay capacitor (8), a third voltage drop u3 on the LED group

recorded, and

based on the detected value u3 and stored

Comparison values of expected forward voltages of the first light emitting diode a fault diagnosis of the first light emitting diode

performs.

3. Lighting module according to one of the preceding

Claims wherein the delay capacitor (8) has a capacitance between 100 nF and 900 nF.

4. Lighting module according to one of the preceding

Claims, wherein a second capacitor (10) as

Protective capacitor is coupled in parallel with the light-emitting diode group to the power supply, wherein the capacitance of the second capacitor is less than the capacity of the

Delay capacitor (8).

5. The lighting module according to claim 4, wherein the capacitance of the second capacitor is at most one tenth of the capacitance of the delay capacitor.

6. Lighting module according to one of the preceding

Claims, wherein an ohmic resistor (9) in series with the delay capacitor and in parallel with the second

LED is coupled to the power supply.

7. A method for testing at least two light-emitting diodes of a lighting device which has at least one first and one second light-emitting diode connected in series, comprising the steps: Coupling a delay capacitor in parallel with the first light emitting diode and in series with the second light emitting diode with a power supply,

Activating the power supply and after elapse of a first time period tl after activation, detecting a first voltage drop ul across the light emitting diode group, wherein tl is shorter than a charging time of the delay capacitor,

Detecting a second voltage drop u2 across the

LED group after expiration of a second period t2 after activation, wherein t2 is longer than a charging time of the delay capacitor, and

Compare the detected values ul and u2 with

stored values of expected forward voltages of the first and second light emitting diode and determining a

Error state of the first and the second LED depending on the comparison.

8. The method of claim 7, wherein after detection of the second voltage drop u2, the power supply is deactivated and

after a third period t3 after deactivation, which is less than a discharge time of the

Delay capacitor is a third voltage drop u3 is detected across the light-emitting diode group, and

based on the detected value u3 and stored

Comparison values of expected forward voltages of the first light-emitting diode, fault diagnosis of the first light-emitting diode

is carried out.