DE102017207956A1 - Safety circuit for a light source - Google Patents

Abstract

Safety circuit (200) for a modulably switchable light source (12), - with a current limiter (140), which is arranged in the current path to the light source (12) and configured such that a current (IB) flowing to the illumination (12) has a current limit ( Ilimit), with a current measuring circuit (105) for detecting a current (IB) flowing to the lighting (12), with a triggering circuit (2) which is designed such that, starting from the current determined in the current measuring circuit (105) ( IB) a medium Strombzw. Current signal formed and a shutdown signal is generated when the average Strombzw. the current signal exceeds a maximum average current, wherein the tripping circuit (2) is connected to an input (EN) of the current limiter (140), and the current limiter (140) is configured such that when the tripping signal is present at the input (EN) of the current limiter (140) the current path for lighting (12) is interrupted.

Description

Systems for three-dimensional image acquisition are known from the prior art, which work with the aid of active illumination. These include so-called time-of-flight (TOF) or transit time measurement systems. These use amplitude-modulated or pulsed illumination to illuminate the three-dimensional scene to be detected.

In particular, all 3D camera systems are included with the time of flight measuring system or the time of flight camera, which acquire transit time information from the phase shift of an emitted and received radiation. As 3D camera or PMD camera in particular so-called photonic mixer detectors (PMD) are suitable, as for example in the DE 197 04 496 A1 are described.

The accuracy and reliability of the distance measurement depends, among other things, on the quality of the receiver and the light source. With a high light energy in particular larger distances can be included in the distance measurement. The quality of the light modulation also influences the accuracy of the distance measurement.

Various regulations for a light source are known from the prior art. In a pure voltage control, it is disadvantageous that this control is typically very sensitive to parameters of the light source (series resistance, threshold voltage) and the duty cycles of the control.

The object of the invention is to ensure safety under all foreseeable error cases, including, above all, a faulty operating mode or a hardware defect that occurred after the final test.

It is advantageous according to the invention a safety circuit for securing a modulated operated lighting proposed in accordance with the independent claim.

Advantageously, a safety circuit is provided for a modulably switchable light source, with a current limiter, which is arranged in the current path to the light source and designed such that a current flowing for illumination current can not exceed a current limit,
with a current measuring circuit for detecting a current flowing for illumination,
with a triggering circuit which is designed such that, starting from the current determined in the current measuring circuit, a mean current or current signal is formed and a shutdown signal is generated when the average current or the current signal exceeds a maximum average current
wherein the trigger circuit is connected to an input of the current limiter, and the current limiter is configured such that when the Ausschaltsignal applied to the input of the current limiter of the current path is interrupted for illumination.

This procedure has the advantage that the illumination is safeguarded with regard to several critical variables, namely a threat to eye safety due to excessive output powers and, secondly, a risk due to excessive radiation exposure.

In a further embodiment, it is advantageous if the triggering circuit has a low-pass filter and a comparator,
and the current measuring circuit is connected to the comparator via the low-pass filter,
wherein the low-pass filter is configured such that an average current signal is present at an input of the comparator,
- Wherein the comparator is configured such that the average current signal is compared with a limit value corresponding to a maximum permissible average current, wherein when exceeding this limit value, a shutdown signal is forwarded to the input of the current limiter.

In a further embodiment, it is provided to realize the current measuring circuit with a measuring resistor and a differential amplifier,
wherein the measuring resistor is arranged in the current path for illumination and the differential amplifier forwards a drop across the measuring resistor voltage as a current signal to the comparator.

It is also advantageous if the current limiter has a time monitoring in such a way that the current supply is interrupted in the case of a current that is applied to the current limit for longer than a time limit.

Likewise, it is advantageous to design an illumination module for a light runtime camera with an aforementioned safety circuit, as well as to configure the light transit time camera system accordingly. The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawings.

Show it

1 schematically a light transit time camera system,

2 schematically a phase measurement principle,

3 Limits of radiated strips against measuring rate for different installation situations,

4a a limitation of the peak current at individual peaks,

4b a limitation of the peak current with respect to constant light

4c a version with dynamically adjusted switch-off time,

4d a version with current limiting,

5a a limitation of the average current with regard to constant light,

5b a limitation of the average current in terms of continuous modulation,

6 a concept of power monitoring of lighting,

7 an embodiment with a current measurement in front of a DC link,

8th an embodiment with a current measurement between the DC link and the lighting,

9 an example in which the current is limited by the lighting,

10 a circuit for operating a lighting with a safety circuit with current limiter,

11 a detailed embodiment of the circuit according to 10 .

12 a circuit for operating a lighting with a safety circuit with circuit breaker,

13 a circuit according to 12 with an additional low pass.

In the following description of the preferred embodiments, like reference characters designate like or similar components.

The solution according to the invention can be used, in particular, for a light transit time camera system 100 as it is in 1 is shown schematically, are used. The 1 shows a measurement situation for an optical distance measurement with a light runtime camera 20 , as for example from the DE 197 04 496 A1 is known.

The light transit time camera system 100 comprises a transmitting unit or a lighting module 10 with a lighting 12 and associated beam shaping optics 15 as well as a receiving unit or light runtime camera 20 with a receiving optics 25 and a light transit time sensor 22 ,

The light transit time sensor 22 has at least one time-of-flight pixel, preferably also a pixel array, and is designed in particular as a PMD sensor. The receiving optics 25 typically consists of improving the imaging characteristics of multiple optical elements. The beam shaping optics 15 the transmitting unit 10 may be formed for example as a reflector or lens optics. In a very simple embodiment, if necessary, optical elements can also be dispensed with both on the receiving side and on the transmitting side.

The measurement principle of this arrangement is essentially based on the fact that, based on the phase shift of the emitted and received light, the transit time and thus the distance covered by the received light can be determined. For this purpose, the light source 12 and the light transit time sensor 22 via a modulator 30 together with a specific modulation signal M ₀ with a base phase position φ ₀ applied. In the example shown is also between the modulator 30 and the light source 12 a phase shifter 35 provided with the base phase φ _{0 of} the modulation signal M _{0 of} the light source 12 can be moved by defined phase positions φ _var . For typical phase measurements, phase positions of φ _var = 0 °, 90 °, 180 °, 270 ° are preferably used.

The light source transmits according to the set modulation signal 12 an intensity-modulated signal S _p1 with the first phase position p1 or p1 = φ ₀ + φ _var . This signal S _p1 or the electromagnetic radiation is in the illustrated case of an object 40 reflects and hits due to the distance traveled corresponding phase-shifted Δφ (t _L ) with a second phase position p2 = φ ₀ + φ _var + Δφ (t _L ) as a received signal S _p2 on the light transit time sensor 22 , In the time of flight sensor 22 the modulation signal M _{o is} mixed with the received signal S _p2 , wherein the phase shift or the object distance d is determined from the resulting signal.

Furthermore, the system has a modulation control unit 27 on, the phase position φ _var the modulation signal M ₀ changed depending on the present measurement task and / or a frequency oscillator 38 sets the modulation frequency.

As illumination source or light source 12 are preferably infrared light emitting diodes or - Laser diodes. Of course, other radiation sources in other frequency ranges are conceivable, in particular, light sources in the visible frequency range are also considered.

The basic principle of phase measurement is schematically in 2 shown. The upper curve shows the time profile of the modulation signal M ₀ with the illumination 12 and the light transit time sensor 22 be controlled. The object 40 Reflected light impinges on the light transit time sensor as received signal S _{p2 in} accordance with its light transit time t _L phase-shifted Δφ (t _L ) 22 , The light transit time sensor 22 collects the photonically generated charges q over several modulation periods in the phase position of the modulation signal M ₀ in a first accumulation gate Ga and in a 180 ° shifted phase position M ₀ + 180 ° in a second accumulation Gb. From the ratio of the charges qa, qb collected in the first and second gate Ga, Gb, the phase shift Δφ (t _L ) and thus a distance d of the object can be determined.

Basically, it is advantageous to obtain signals with a high signal-to-noise ratio, in that it is an effort, if possible and useful to provide the highest possible output power. However, the performance can not be so high that no eye or skin safety is given.

Appropriate limit values are known from the relevant standards and legal regulations. In 3 are schematically and exemplarily applied power limits for accessible radiation as a function of the measuring rate. The upper curve shows the progression of the limit values for an installation situation, in which the eye safety is to be considered and the lower curve a course of the limit values for an installation situation, with which the skin safety is to be considered.

As in 3 It can be seen that the permissible accessible radiation can be limited to very different values depending on the installation situation and measuring rate.

The subject matter of the invention is a safety circuit which, depending on the installation situation of the radiation source, can be tuned in such a way that the permissible output power can be optimally utilized at different measuring rates, if this is necessary.

Eye safety can usually be maintained if peak power is avoided and monitored. For example, the electricity may be used for lighting 12 do not exceed a maximum peak _current I _{Peak_max} and / or a maximum current I _{max may} only be present for a maximum time t _max . In 4a This situation is illustrated schematically by means of a modulated emitted light signal of a lighting for a light transit time camera system. The first exceeding of the current limit I _max is very short and is below a time limit or a turn-off time t _max , but exceeds the maximum peak _current I _{Peak_max} and thus leads to a shutdown. As an alternative to switching off the current can also be down-regulated or controlled to a value below the maximum current I _{max in} order to avoid a false shutdown.

The second exceeding of the current limit I _max does not exceed the limit value of the peak _current I _{Peak_max} and initially does not lead to a shutdown, but then exceeds the turn-off time t _max , which then leads to a shutdown.

4b shows a variant in which already in the normal modulation mode, the current pulses exceed the current limit I _max but remain temporally below the turn-off time t _max and the maximum peak _current I _{Peak_max} . If a current pulse exceeds the switch-off time t _max , this is done as already in 4a explained to a shutdown.

4c shows an embodiment in which the turn-off time t _max shortens with increasing current intensity I _B. Currents I _B below the maximum current level I _max are not critical and are not a turn-off time t _max subjected. When the maximum current intensity I _{max is} exceeded, the switch-off times for increasing currents I _{B, 1} <I _{B, 2} <I _{B, 3} accordingly behave as follows: t _{max, 1} > t _{max, 2} > t _{max, 3} . In such a case, it is not absolutely necessary to separately monitor the peak _current I _{Peak_max} since the safety circuit can be designed such that the disconnection takes place very rapidly at these high currents. Such shortening of the turn-off times can be realized by suitable choice of a low-pass filter, in particular a suitable dimensioning of an RC element.

4d shows a variant in which the current I _B can not exceed a predetermined current _limit I _limit due to circuitry interpretations in an error case. Depending on the application, the current _limit I _limit can be identical to the maximum current I _B , but the current _limit I _limit can also be set below the maximum current I _B.

In such a circuit, an operation may be provided in which the modulation can be maximum up to a current _limit I _limit . If the modulation takes place directly at the current _limit I _limit , the circuit is sensitive to an exceeding of the switch-off time t _max , via which a switch-off then occurs is initiated, according to the last in 4d shown modulation signal.

On the other hand, if the modulation amplitude lies below this current _limit I _limit , on the other hand, exceeding the switch-off time t _max does not lead to a shutdown. Whether such a situation is safety critical is monitored according to the invention by a further safety circuit.

überwacht werden. In 5 ist ein entsprechender Sachverhalt schematisch dargestellt. Während der Strom I_B zu keiner Zeit den maximalen Stromgrenzwert I_max überschreitet, steigt der mittlere Strom

aufgrund eines fehlerhaften, konstanten Lichtsignals immer weiter an und übersteigt letztendlich einen Grenzwert für den mittleren Strom

und führt so zu eine Abschaltung der Beleuchtung.Depending on the installation situation and operating mode, long-term irradiation powers P can also be regarded as critical. Such radiant powers can, for example, a mean maximum current

be monitored. In 5 a corresponding fact is shown schematically. While the current I _B at no time exceeds the maximum current limit I _max , the average current increases

due to a faulty, constant light signal continues to increase and ultimately exceeds a limit for the average current

and thus leads to a shutdown of the lighting.

nicht übersteigt, steigt der mittlere I Strom bei einer kontinuierlichen Modulation immer weiter an. Bei Erreichen der kritischen mittleren Stromgrenze

wird die Beleuchtung 12 abgeschaltet.Likewise it can be like in 5b shown, a permissible irradiation power can be exceeded by the modulation is no longer in modulation intervals, but in a faulty, continuous modulation. While in the interval mode, the average current I a normal value

does not exceed, the middle one rises I Current continues to increase with continuous modulation. Upon reaching the critical mean current limit

will the lighting 12 off.

The basic idea of the safety circuit according to the invention is to limit the current through a light source (laser or LED) so that various defects or incorrect settings can not lead to an unacceptably high power, so that the eye safety and skin safety for all considered time constants is given without the legitimate To limit operating points.

The safety circuit includes two interconnected triggering mechanisms that cover different error cases. A first trigger circuit 1 responds very quickly to excessive currents (s. 4a -C) in order to limit or switch them off to permissible values within a few μs in the event of an error (eg in the event of a failure of the modulation switch), while a second trigger circuit 2 the mean value (s. 5a , b) monitored to switch off when permissible values are exceeded. The averaging is weighted such that the permissible limit value of the optical output power, for example of the KL1, is IEC60825-1: 2014 in no case exceeded, but not restricted more than is necessary due to circuitry limitations (tolerances, design-related limitation of the time constants). One possible concept of power monitoring of lighting is in 6 shown.

There are already some safety concepts for lasers. However, because of the special waveforms that are used as a light source for TOF cameras when using laser modules, these solutions appear problematic. In the following, some aspects of basically known solutions will be discussed.

Example fuses: Due to the specific requirements (comparatively high pulse power with low mean value), reliable fuse dimensioning is not possible, since the comparatively large tolerances of the characteristic I ² T value make sufficiently fast shutdown with simultaneously high operational reliability impossible

Example PTC: Due to their design, these switching elements are so sluggish that they are switched off too late, so that the permissible output power is exceeded for a short time. In addition, the high tolerances and the temperature dependence require an extremely conservative design Occurrence of a greatly increased output power can be avoided, however, the mean can still be unacceptably high, also precise current regulator can cause additional losses.

Monitor diode example: A separate monitor diode allows the emitted optical power to be measured directly and compared to a setpoint. However, these monitor diodes are not easily integrable in all technologies (VCSEL, LEDs) and must also be calibrated.

The safety circuit according to the invention should cover at least three different error cases:
First, failure of the modulation, constant light with high power (s. 4a -C): Due to a disturbance, the light source may no longer be modulated high-frequency, but, for example, be constantly switched on. As a result, the optical power over a long time can assume a value that is above the regularly occurring and tolerated peak power. For such a power, which is only a few nanoseconds in normal operation, the allowable limit is exceeded after a few microseconds, so that the shutdown or limitation must be done very quickly.

The cause of such a modulation failure may be hardware defects or an incorrect configuration of the light transit time sensor.

Second, too high output power (s. 4a , c): The output power is too high, although the lighting is otherwise normal. Cause could be here a very unfavorable tolerance position or a defective power supply.

Third, too long turn-on time (s. 5a . 5b ): The lighting is working correctly but is turned on too long. The cause could be an incorrect configuration or a failure of the control logic.

By a suitable dimensioning of in 6 illustrated safety circuit 200 the aforementioned error cases can be reliably detected and shut down or limited.

In particular, reliable detection of the third fault (too long turn-on time) requires a special tuning, since the allowable power that can be radiated strongly depends on predetermined parameters, for example on the measuring rate and the measuring time, as well as on the installation situation.

In an embodiment according to 7 is the safety circuit 200 between the voltage source 130 on one side and to arrange the driver circuit with DC link on the other side. In this embodiment, it is necessary that not only the second trigger circuit 2 for the second and third error case (too high average current) are equipped with a low pass, but also the trigger circuit 1 for the first error case (failure of the modulation, constant light with too high power), because otherwise at the first trip circuit 1 to false tripping occurs when charging the capacitor in the DC link for the first time. The tuning of the turn-off times for the first trip circuit 1 can also limit the dimensioning of the DC link.

To prevent a restart after a single trip, the triggering mechanism of the switch can be pulse-controlled. Alternatively, in another embodiment, the output signal of the triggering mechanisms may be coupled to the input to achieve latched latching by appropriate coupling.

In a further embodiment according to 8th it is intended to arrange the safety circuit between the DC link and the lighting (laser / LED driver). Such an arrangement has the advantage that the first triggering circuit 1 No filtering is required here, so that the difficult tuning with regard to the DC link is eliminated and there are no restrictions for the DC link.

In an embodiment according to 9 can the trigger circuit 1 be replaced by a limiting constant current source or by a current limiter for the first error case (failure modulation). In this case, the fault is not ensured by switching off, but by limiting it to safe values.

This embodiment has the advantage that, on the one hand, the safety circuit can be arranged in terms of circuitry before the intermediate circuit and, on the other hand, there are no restrictions on the dimensioning of the intermediate circuit.

Depending on the dimensioning of the current limiter, it is also possible to prevent permanent operation under constant current conditions, for example by adding an additional switch-off after a defined time.

10 shows by way of example a circuit for the modulated operation of a lighting 12 with a possible embodiment of a security circuit according to the invention 200 as they are in principle 9 is proposed. About a voltage source 130 becomes a supply voltage U _V for the operation of a light source 12 provided and the light source 12 flowing current I _B by means of a current measuring circuit 105 detected. A modulator 30 represents a modulation signal M ₀ for the light transit time sensor 22 and the lighting or light source 12 ready. To perform the phase measurement is a phase shifter 35 provided, the phase angle of the modulation signal M ₀ for the light source 12 appropriately shifts. Equally effective, of course, the phase angle of the sensor 22 be moved. With this variable modulation signal M _V is in the illustrated case, a switch S in the current path of the light source 12 connected. Parallel to the light source 12 and the switch S, a capacitor C1 is provided.

As already in 9 mentioned, the first trigger circuit 1 as current limiter 140 trains and in the current path of lighting 12 arranged. The current limiter 140 is designed so that the current I _B maximum increase to the level of the current _limit I _limit and can not exceed. Furthermore, the current limiter 140 Preferably configured such that at a current that is applied to the current _limit I _{limit for} more than a limit switch-off time t _{max_limit} , as in 4d already shown, the power supply is interrupted. Possibly. can this shutdown time t _{max_ limit can} also be monitored by another circuit.

anliegt, das einem mittleren Strom

zur Beleuchtung 12 entspricht. Übersteigt das mittlere Stromsignal

einen Grenzwert

des Komparators 120, erzeugt der Komparator 120 ein Ausschaltsignal und leitet dieses an einen Eingang EN der Strombegrenzung 140 weiter. Liegt an diesem Eingang EN ein Ausschaltsignal an, wird die Stromzufuhr in Richtung Beleuchtung 12 unterbrochen.The second trigger circuit 2 is as a comparator 120 formed with an upstream low pass TP2. Starting from a via a current measuring circuit 105 provided current signal S (I _B ), the low-pass filter TP2 is dimensioned so that at the comparator 120 a middle current signal

is attached to a medium current

for lighting 12 equivalent. Exceeds the average current signal

a limit

of the comparator 120 , the comparator generates 120 a switch-off signal and passes this to an input EN of the current limit 140 further. If a switch-off signal is present at this input EN, the power supply will be in the direction of lighting 12 interrupted.

nicht überschritten wird.The current limit 140 thus secures two maximum values, on the one hand exceeding a maximum allowable current I _max is ensured by the current I _B maximum due to the current limit only up to the current _limit I _limit but never can exceed this limit and the other is via the connected comparator 120 ensured that a medium maximum current

is not exceeded.

The current limit 140 thus serves both the protection against high pulse power due to possible hardware defects on a Stromlimitierung and also acts as a circuit breaker.

Further, the comparator 120 preferably designed with a self-holding, so that when outputting a turn-off this signal is maintained. For safety reasons, latching is preferably only canceled when the device is restarted.

The low-pass filter can be dimensioned such that, depending on the pulse repetition frequency in the relevant region, either pulse energy limitation, a mean value limitation or a mixed form of both takes place, whereby protection against all inadmissible operating points is ensured.

11 shows an example of a possible embodiment of the circuit according to 10 , The current measurement 105 is here for example with a measuring resistor R1 in the current path for lighting 12 whose current-related voltage drop _{.DELTA.U I_B} via a differential _amplifier 110 is detected and as a current signal S (I _B ) to the comparator 120 via the low-pass filter TP2, which is designed here as an RC element, R2, C2, is passed on.

12 shows a further variant in which, in contrast to the procedure according to 10 and 11 the current I _B not by a current limiter 140 is limited, but over a circuit breaker 145 a shutdown is provided if limits are exceeded.

bzw. Stromsignals

Die zweite Auslöseschaltung 2 entspricht der in 10 und 11 gezeigten Schaltung, mit einem als RC-Glied R2, C2 ausgebildeten Tiefpass TP2 und einem Komparator 120 zur Überwachung Die Auslöseschaltungen 1, 2 geben jeweils ein Ausschaltsignal aus sobald eines der Stromsignal seinen jeweiligen Grenzwert überschreitet.The circuit breaker 145 interrupts the flow of current to lighting 12 , once at an input of the circuit breaker 145 a shutdown signal is applied. To generate the shutdown signals are two trigger circuits 1 . 2 intended. With a first trigger circuit 1 consisting of a comparator 125 to monitor the for lighting 12 flowing current I _B and current signal S (I _B ) and with a second trigger circuit 2 for monitoring the average current

or current signal

The second trigger circuit 2 corresponds to the in 10 and 11 shown circuit, formed as a RC element R2, C2 low-pass filter TP2 and a comparator 120 for monitoring The tripping circuits 1 . 2 each output a switch-off signal as soon as one of the current signal exceeds its respective limit.

The outputs of the two comparators 120 . 125 are on an OR comparator 150 guided. Once a shutdown signal of a comparator 120 . 125 at the comparator 150 is applied, a corresponding shutdown signal to the circuit breaker 145 passed and the power supply towards lighting 12 interrupted.

The first comparator is preferred 125 in the first trigger circuit 1 so designed or selected that a system-related, inherent time constant of the comparator is sufficiently short to reliably protect high peak currents can. Due to the system, it is also advantageous that the switch-off time t _max shortens with increasing current intensity I _B. Thus, it is advantageous that at very high peak currents, the turn-off time t _{max is} very short.

Furthermore, the circuit is according to 11 On the other hand, the capacitor C1.1 is modified to be parallel to the illumination 12 and switch S is arranged very small, so that at startup due to the flowing charging currents of the second comparator 125 not appealing. The otherwise usual high capacity is in this embodiment directly to the voltage source 130 positioned, here marked C1.2.

As in the previous example, both comparators 120 . 125 configured with a latch, so that when outputting a switch-off this signal is held.

13 shows a further embodiment of the circuit according to 12 in the case of the lighting 12 and the switch S again a large Capacitance C1 is arranged. So that the charging current does not trigger the first comparator 125 leads, is this comparator 125 a first low-pass filter TP1 in the form of a first RC element R3, C3 upstream. However, this first RC element has a much lower time constant than the second before the second comparator 120 switched RC element R2, C2 on. This first RC element R3, C3 is designed such that the current flowing in the direction of the lighting capacitor C1 current does not lead to the automatic interruption of the power supply. However, the time constant of the first RC element R3, C3 must be short enough to switch off when the maximum current I _{max is} exceeded after the switch-off time t _max .

Again, the comparators 120 . 125 designed with a self-retention.

The aforementioned circuits are of course not limited to the illustrated embodiments. In particular, the current measurements 105 or even the low passes are realized in a different way. For example, so-called "switched capacitor filters" are also conceivable as low-pass filters.

LIST OF REFERENCE NUMBERS

• 1 first trigger circuit,
• 2 second trigger circuit,
• 10 lighting module
• 12 Lighting, light source
• 15 Beam shaping optics
• 20 Time of flight camera
• 22 Transit Time Sensor
• 25 optics,
• 27 Modulation controller,
• 30 modulator
• 35 phase shifter
• 38 Frequency oscillator,
• 100 Time of flight camera system
• 105 Current sensing circuit,
• 110 Differential amplifier
• 120 first comparator
• 125 second comparator,
• 130 Voltage source,
• 140 current limiter,
• 145 Circuit Breaker,
• 150 Comparator, or circuit
• 200 safety circuit
• TP1 first low-pass filter,
• TP2 second low-pass filter
• I _B electricity for lighting,
• 
  medium current for lighting
• I _max maximum current, current limit,
• I _{peak_max} maximum peak _current ,
• I _limit current _limit ,
• 
  Limit mean current,
• t _max switch off time, time limit

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19704496 A1 [0002, 0032]

Cited non-patent literature

• IEC60825-1: 2014 [0054]

Claims (6)

Safety circuit ( 200 ) for a modulated switchable light source ( 12 ), - with a current limiter ( 140 ), which is in the current path to the light source ( 12 ) is arranged and designed such that a for lighting ( 12 ) flowing current (I _B ) can not exceed a current _limit (I _limit ), with a current measuring circuit ( 105 ) for detecting a light ( 12 ) flowing current (I _B ), with a trigger circuit ( 2 ) which is designed in such a way that, starting from that in the current measuring circuit ( 105 ) determined current (I _B ) a mean current

or current signal

formed and a shutdown signal is generated when the average current

or the current signal

a maximum average current

exceeds the trigger circuit ( 2 ) with an input (EN) of the current limiter ( 140 ), and the current limiter ( 140 ) is designed such that when concern of the switch-off signal at the input (EN) of the current limiter ( 140 ) the lighting path ( 12 ) is interrupted. Safety circuit ( 200 ) according to claim 1, wherein the triggering circuit ( 2 ) a low pass (TP2) and a comparator ( 120 ), and the current measuring circuit ( 105 ) over the low pass (TP2) with the comparator ( 120 ), wherein the low-pass filter (TP2) is designed such that at an input of the comparator ( 120 ) a mean current signal

- the comparator ( 120 ) is configured such that the average current signal

with a limit corresponding to a maximum allowable average current

When this limit value is exceeded, a shutdown signal is sent to the input (EN) of the current limiter (FIG. 140 ) is passed on. Safety circuit ( 200 ) according to one of the preceding claims, in which the current measuring circuit comprises a measuring resistor (R1) and a differential amplifier ( 110 ), wherein the measuring resistor (R1) in the current path for lighting ( 12 ) and the differential amplifier ( 110 ) via the measuring resistor (R1) falling voltage ( _{.DELTA.U I_B} ) as a current signal (S (I _B )) to the comparator ( 120 ). Safety circuit ( 200 ) according to one of the preceding claims, in which the current limiter ( 140 ) has a time monitoring in such a way that at a current (I _B ), which is applied to the current _limit (I _limit ) longer than a time limit (t _max ), the power supply is interrupted. Lighting module ( 10 ) with a safety circuit ( 200 ) according to one of the preceding claims. Time of Flight Camera System ( 100 ) with a lighting module ( 10 ) according to claim 5.

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