WO2011117024A1 - Method and circuit arrangement for operating a multiplicity of leds - Google Patents

Abstract

The present invention relates to a method for operating a multiplicity of LEDs (LED1, LED2, LED3) on a circuit arrangement having a supply connection for coupling to a supply voltage (V_CC); a reference potential connection for coupling to a reference potential, at least one first parallel circuit of at least one first LED (LED1) and a first short-circuiting switch (KS1) for short-circuiting the at least one first LED (LED1); at least one second parallel circuit of at least one second LED (LED2) and a second short-circuiting switch (KS2) for short-circuiting the at least one second LED (LED2); a current source (I_Q), wherein the series circuit comprising the current source (I_Q), the at least one first and the at least one second parallel circuit is coupled between the supply connection and the reference potential connection; and a control apparatus (10), which comprises at least one first output (A1) for controlling the first short-circuiting switch (KS1); a second output (A2) for controlling the second short-circuiting switch (KS2); and at least one input (St) for supplying at least one first control signal for setting an instantaneous brightness output of the at least one first LED (LED1) and a second control signal for setting an instantaneous brightness output of the at least one second LED (LED2); wherein the instantaneous current (I) from the current source (I_Q) is varied by the control apparatus (10) depending on the instantaneous brightness output to be set for the at least one first LED (LED1) and/or the at least one second LED (LED2). It furthermore relates to a corresponding circuit arrangement for operating a multiplicity of LEDs (LED1, LED2, LED3).

Description

 description

Method and circuit arrangement for operating a plurality of LEDs

Technical area

The present invention relates to a method for operating a plurality of LEDs on a circuit arrangement with a supply terminal for coupling to a supply voltage, a reference potential terminal for coupling to a reference potential, at least a first parallel connection of at least a first LED and a first shorting switch for shorting the at least a first LED, at least one second parallel connection of at least one second LED and a second shorting switch for shorting the at least one second LED, a current source, the series circuit comprising the current source, the at least one first and the at least one second parallel connection between the supply terminal and the reference potential ^¬ alanschluss is coupled, and a control device, the at least one first output for driving the first short-circuit switch, a second output for driving the second short-circuit switch un d comprises at least one input for supplying at least one first control signal for setting an instantaneous brightness output of the at least one first LED and a second control signal for setting a momentary brightness output of the at least one second LED. It also relates to a corresponding circuit arrangement for operating a plurality of LEDs. State of the art

The present invention is an example of so-called AFS (Advanced Forward Lighting system) systems beschrie ^¬ ben, although, as apparent to those skilled in the art can also be used in other areas. In the case of AFS systems, for example, a large number of surface elements of a travel path or an environment with LEDs are to be illuminated differently in terms of time with varying degrees of brightness. Individual surface elements must be ^¬ be lights dimmed while others, for example, functions in Gefahrensitua-, even briefly with particularly high brightness.

It is known to dim LEDs by appropriate control with ^{¬ means of} a PWM (Pulse Width Modulation) signal. In order to set a lower brightness output, the duty cycle, ie the duty cycle, is therefore reduced, in order to set a higher brightness output. Only when the brightness requirement is high, the duty cycle is increased to 100%. In normal operation, therefore, the duty cycle is significantly lower. With the reduction of the duty cycle is accompanied by a reduction of the efficiency of the circuit arrangement.

Presentation of the invention

The object of the present invention is therefore to develop a generic method or a generic circuit arrangement such that an increase in the efficiency is made possible. This object is achieved by a method having the features of patent claim 1 and by a circuit arrangement having the features of patent claim 13. The present invention is based on the recognition that the efficiency of an LED with respect to the momenta ^¬ NEN, the LED current flowing through is lower, the higher the current, the LED is the current flowing through. In the prior art, the LEDs are powered by a power source that continuously supplies a constant current. The brightness output currently to be set is achieved solely by driving the short circuit switch connected in parallel to the LED with a signal which has a duty cycle which leads to the setting of the instantaneous brightness output.

The present invention now goes to the solution of the above-described object, the way to vary the current supplied by the current source instantaneous current. According to the invention, therefore, the instantaneous current of the current source is varied by the control device, specifically as a function of the instantaneous brightness output to be set of the at least one first LED and / or the at least one second LED. By this procedure, operation of the LEDs is possible with the lowest possible current at the highest possible duty cycle. This resul ^¬ advantage in a significantly increased efficiency, and as a result thereof in a lower thermal load on the circuit arrangement. As a result, on the one hand cooling measures can be reduced, on the other hand an increase in the service life of the components involved is thereby achieved.

Although the present invention is fundamentally independent of the fact that the short-circuiting switches are actuated with a PWM signal, it is nevertheless preferred if a first PWM signal is provided at the first output of the control device, which signal comprises a first PWM signal Duty cycle, and at the second output of the control device, a second PWM signal having a second ^{Dy ¬} cycle. Since these signals are coupled to the short-circuit ^¬ switches, the corresponding LED will thus operate with the respective inverse duty cycle.

In a preferred embodiment, the smaller of the at least two duty cycles is first determined on this basis. Subsequently, the smaller of the at least two duty cycles is reduced and the instantaneous current of the current source is lowered in such a way that the at least one LED operated with the smaller duty cycle outputs its brightness which is currently to be set. Finally, the at least one other duty cycle is reduced so that the NE with the at least one other duty cycle betriebe- at least one LED emits its currently adjusted Hel ^¬ ligkeit. By this measure, it is ensured that both LEDs on the one hand deliver their currently set brightness, on the other hand, the LEDs can be operated with a pos ^¬ lichst low power, being turned off on the smaller of the at least two duty cycles, since this is not lowered below 0% can be. The smaller of the two duty cycles is preferred in this case to a duty cycle of not more than 10%, preferably Hoechsmann ^¬ least 5%, more preferably reduced to 0%. This resulted in an advantage to minimize the current flowing through the LED, and accordingly maximizing the effect ^¬ grads of the circuit arrangement.

Preferably, the reduction of the duty cycles and the corresponding reduction of the instantaneous current of the current source takes place stepwise, in particular in predefinable stages. she carried out in particular so that the abge from the LEDs ^¬ added brightness does not change.

To take account of varying brightness requirements, it is preferred if the determining step, that is the step in which the smaller of at least two duty cycle is determined, is repeated at predetermined intervals zeitli ^¬ chen. This will sicherge ^¬ assumed that the LEDs are operated for long periods of time as possible with an optimum ratio of the duty cycle and Momen- tanstrom.

A preferred development of the method according to the invention is characterized in that, moreover, is ^¬ telt ermit whether achievable with the current instantaneous current at a third predetermined duty cycle, in particular a duty cycle of 0%, a brightness output to be set the at least one LED. If the resulting ^¬ nis this determination is "no", is increased according to the invention of the instantaneous current. So, if even a duty cycle of 0% is no longer sufficient for short circuit switches to achieve high brightness output to be set at least one LED, the instantaneous current is again raised. this is a dynamic adjustment of Mo ^¬ mentanstroms, both downwards and upwards, allows the LEDs are thus operated such that on the one hand, the brightness to be set can be realized, on the other hand this is done at the lowest possible Mo ^¬ mentanstrom. ,

Increasing the instantaneous current in egg ^¬ nem step is preferably carried out, wherein the step is chosen such that at a fourth predetermined duty cycle, in particular a Duty cycle of 20%, preferably 0%, the einzu ^¬ alternate brightness output of the at least one LED it is ^¬ targetable. The increase in one step allows ei ^¬ ne rapid response to a momentary brightness requirement, for example, in a dangerous situation. On the other hand, this is performed such that the brightness output to be set is obtained at a lowest possible instantaneous ^¬ current of the current source.

If a time duration in which the maximum instantaneous current flows exceeds a predefinable time duration, the maximum instantaneous current is the rated current of the at least one LED. This ensures that the LED will not be damaged even if it has to emit high brightness over a longer period of time. However, if a time duration in which the maximum instantaneous current flows does not exceed a predefinable time duration, then the maximum instantaneous current can be the maximum pulse current of the at least one LED. As a result, particularly high levels of brightness can be achieved, in particular at certain points, whereby it is again ensured that the LEDs affected thereby and the components of the circuit arrangement are not damaged. Such high brightness have been impossible to achieve in the prior art because the components involved, especially drivers and power source, were not designed to continuously supply the maximum pulse current ^¬ the at least one LED. Only the variation of the current provided by the current source enables the provision of a particularly high current over a short limited period of time. As a result of the above-mentioned increase in instantaneous current, the at least one other duty cycle is advantageously Cycle increased so that at least one LED, the short-circuit switch is operated with the at least one other Dy-Cycle, outputs their currently set brightness. This ensures that all LEDs output their currently set brightness.

While in the preferred embodiments presented above, the aim was to achieve a brightness to be set with the largest possible duty cycle and the lowest possible instantaneous current of the current source, another preferred embodiment of the invention takes into account the fact that, if the instantaneous current already exists, the current source a brightness request occurs that can not be adjusted by means of a ^pre-¬ given duty cycle in this minimum instantaneous current, since it is below.

According to the invention, therefore, it is further provided that it is determined whether a brightness output of the at least one LED to be set can be achieved with the current duty cycle at a minimum instantaneous current of the current source. If this is not the case, since the adjustable at the ge ^¬ genwärtigen duty cycle brightness output Ü is over the adjusted brightness output, it is ^¬-making according to the duty cycle increases, runs the short ^¬ switch the relevant LED. The invention therefore enables an extremely wide dynamic range of the brightness to be emitted by the LEDs, which could not be achieved using the prior art procedure.

Further preferred embodiments emerge from the subclaims. The measures with respect to the inventive method ^¬ presented preferred embodiments and the advantages thereof, apply mutatis mutandis, as applicable, for the inventive S cha 11ung s at or dnung. The corresponding steps are realized by appropriate design of the control device.

Short description of the drawing (s)

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Show it:

1 shows a schematic illustration of an exemplary embodiment of a circuit arrangement according to the invention;

Fig. 2 shows the time course of various signals from

 Fig. 1 in a known from the prior art method;

Fig. 3 shows the time course of various signals from

Fig. 1 of a first embodiment of he ^¬ inventive method; and

Fig. 4 shows the time course of various signals from

 Fig. 1 of a second embodiment of a method according to the invention.

Preferred embodiment of the invention

Fig. 1 shows a schematic representation of an embodiment of an inventive Schaltungsanord ^¬ tion. This includes several LEDs, in this case LED1, LED2, LED3, each LED being a short-circuiting switch in parallel is connected, in this case the LEDl the Kurzschlussschal ^¬ ter KS1, the LED2 of the short-circuit switch KS2 and the LED3 of the short-circuit switch KS3. Although present each short-circuiting switch, only one LED is connected in parallel, can of course each short-circuiting switch, a LED strand a plurality of serially gekop ^¬ pelte LEDs be fully connected in parallel.

A current source I _{Q is} connected in series with these parallel ^circuits , the combination of current source I _Q and the several parallel circuits being coupled between a supply voltage V _C c and a reference potential. The current source I _Q is designed to deliver a rated current Io. The current current provided by the current source I _Q is denoted by I. The current source I _Q preferably comprises a switching regulator and a Freilaufdi ^¬ ode and thus operates at very low losses.

The circuit arrangement further comprises a control device 10, having an input St, to which control signals for setting a momentary brightness output of the LED1, LED2, LED3 are supplied. The individual control signals can be provided serially at the input St. Alternatively, a plurality of such inputs St may be provided. The control device 10 here has three outputs and that an output AI for driving the first short-circuit switch KS1, an off ^¬ gear A2 for driving the second short-circuit switch KS2 A3 and an output for driving the third short-circuit switch KS3. The signals provided at the outputs AI to A3 are each PWM signals, which are characterized by a respective current duty cycle, that is, a current duty cycle. The signal provided at the output signal AI is ^¬ be labeled Sl, the signal provided at the output A2 is connected to S2 and the signal provided at the output A3 is denoted by S3. The duty cycle of the signal Sl is Dl, that of the signal S2 is D2 and that of the signal S3 is D3. The control device 10 also has an output A4, which is gekop ^¬ pelt to a control input of the current source and through which the abgege ^¬ surrounded by the current source I _Q instantaneous current I can be adjusted. Fig. 2 shows a schematic representation of the temporal

Course of the current I, as well as the signals Si, S2 and S3.

In this case, the signal S 1 is complementary to the signal Sl, the

Signal S2 complementary to the signal S2, and the signal S3 complementary to the signal S3. The representation of the signals Si, S2 and S3 has the reason that they dergeben the sequence as ^¬, according to which the respective LED emits light.

In Fig. 2, the circuit arrangement according to the prior art is operated (without connection between the control device 10 and current source I _Q ). The current source I _Q continuously supplies the rated current Io. For example, the duty cycle of the signal Sl is 50%, the duty cycle of the signal S2 is 90% (corresponding to the duty cycle of the signal S2 is 10%), the duty cycle of the signal S3 is 70% (corresponding to the Duty cycle of signal S ₃ 30%)

In the illustration of FIG. 3, the circuit ^arrangement of FIG. 1 is operated according to the method according to the invention. The LEDs should deliver the same brightness in the method of FIG. 2. For this purpose, the control device 10 is adapted to determine the smallest duty cycle of the Sig ^¬ dimensional Sl, S2 and S3 of FIG. 2. This is above the signal Sl (50%). The control device 10 is further designed to reduce the smallest duty cycle, in the present case Sl, as far as possible, that is to say in the present case to 0%. At the same time, the instantaneous current I of the current source I _{Q is} correspondingly lowered, that is to say below IQ / 2, that is to say according to the efficiency characteristics of the LEDs, to less than half of the nominal current Io, which results in the efficiency advantage of the present invention. In the example the typical value is 0.4 * Io.

The duty cycle Si is now 100% to achieve the desired brightness output of the LED1. The duty cycles of the further signals S2, S3 are adapted accordingly. After adjustment, the duty cycle S2 is accordingly

80%, corresponding to the duty cycle of the signal S ₂ 20%, and the duty cycle S3 40%, the duty cycle of the signal S 3 corresponding to 60%.

If the circuit arrangement of Fig. 1 with the signals shown in FIG. 3 is operated, thus giving off the LEDs LED1, LED2, LED3 same brightness as if they are operated in accordance with the Sig ^¬ dimensional of FIG. 2. Thereby, however, that the current I in the procedure of FIG. 3 is only half as high as in the procedure of Fig. 2, ^¬ which the LEDs LED1, LED2, operated in a work area LED3, which is characterized by a higher efficiency as according to the procedure of FIG. 2. The reduction of the duty cycle and the corresponding From ^¬ reduction of the instantaneous current I is the current source I _Q can be done stu ^¬ fenweise, especially in predetermined steps. In order to respond to keitsabgabe instantaneous variations of the desired brightness, the test is whether a re ^¬ production of the instantaneous current I is possible to repeatedly at predefinable time intervals.

If it is determined that at the instantaneous instantaneous current I and a predefinable duty cycle of the signals S1, S2, S3, a brightness output to be set can no longer be achieved, the instantaneous current I is increased again. The increase is preferably such that the smallest duty cycle of the signals Sl, S2, S3 is 0%. The per ^¬ weils other duty cycle will be adjusted accordingly. If it is determined that with the current duty cycle at a minimum instantaneous current I of the current source I _Q a brightness output of at least one LED to be set is no longer achievable, since the brightness ^output which can be set using the present duty cycle lies above the brightness output to be set, the Duty cycles, with which the short circuit of the LEDs are operated, again increased accordingly.

In the control device 10 it can be provided that the above-mentioned checking steps are carried out at predeterminable time intervals or when the control signals at the input St. change. If the brightness emitted by the LEDs is fed to a control circuit, the control device 10 can carry out the set checking step if reason of the control loop results in a change in the control of the short-circuit switch KS1 to KS3.

4 shows the operation of the circuit arrangement of FIG. 1 according to a further exemplary embodiment of the method according to the invention. The single ^¬ sake of simplicity, only the waveform of the instantaneous current I and of the signals Si and S ₂ · The duty cycle of the illustrated

Signal S 3 is 100% during periods Tl and T3. As can be seen from Fig. 4, the Duty Cycles amount of the signals S 1 and S ₂ during the period Tl 60%, of the instantaneous current I corresponds to its face value Io The LEDs LED1 and LED2 give accordingly during the time Tl space ^¬ a average brightness from which a maxi ^¬ male brightness abgege- over a longer period can be ben LED3. At time t a particularly ho ^¬ he brightness output of the LED 1 is desired. This is achieved before ^¬ lying by the fact that the duty cycle of the signal

5 * 1 is raised to 100% during the period T2 and at the same time the instantaneous current I is raised to the maximum pulse current Ip. However, the operation of the circuit ^arrangement with the maximum pulse current I _P is possible only during a time period T _max , without the risk of damage to elements of the circuit arrangement. In the present case, the period T2 is smaller than the period T _max , so that the circuit arrangement can be operated safely with the maximum pulse current I _P.

Since during the period T2 the LED 2 is to emit the same brightness as during the period T 1, the duty cycle of the signal S ₂ in the ratio rated current to maximum learning pulse current, taking into account the efficiency characteristic of the LED2 reduced. At the time t ₂ , operation of the LED 1 is desired again with the brightness as in the period T ₁ . Therefore, in the period T3, the instantaneous current I is lowered again to the nominal current Io, or, if the operation of the LED3 makes this possible, even further.

The duty cycles of the signals Si and S ₂ are again adjusted accordingly ^¬ , that is, the duty cycle of the signal

5 * 1 to deliver the desired brightness in the period T3, the duty cycle of the signal S ₂ back to the duty cycle according to period Tl, if it is desired that the LED2 continuously outputs the same brightness during the periods Tl to T3.

The period T _max may be, for example, between 1 ms and 100 ms, preferably 20 ms.

Claims

claims A method of operating a plurality of LEDs (LED1, LED2, LED3) in a circuit arrangement having a supply port for coupling to a versor ^¬ supply voltage (V _C c); a reference potential terminal for coupling to a reference potential; at least ei ^¬ ner first parallel connection of at least a first LED (LED1) and a first short circuit switch (KS1) for shorting the at least one first LED (LED1); at least one second parallel connection of at least one second LED (LED2) and a second short-circuit switch (KS2) for short-circuiting the at least one second LED (LED2); a power source (IQ), where the series circuit from the power source (IQ), the at least a first and the at least one second parallel connection between the supply terminal and the reference potential terminal is ge ^¬ coupled; and a control device (10), the at least one first output (AI) for driving the first short-circuit switch (KS1); a second ^{output ¬ out} (A2) for driving the second short-circuit switch (KS2); and at least one entrance (St) for supplying at least a first control signal for setting an instantaneous brightness output of the at least one first LED (LED1) and a second control signal for setting a momentary brightness output of the at least one second LED (LED2) comprises; characterized by the following step: Varying the instantaneous current (I) of the current source (I _Q ) by the control device (10) as a function of to be set instantaneous brightness output of the at least one first LED (LED1) and / or the at least one second LED (LED2). Method according to claim 1,  characterized by the following steps:  a) providing a first PWM signal (Sl) having a first duty cycle at the first output (AI) of the control device (10); and b) providing a second PWM signal (S2), which has a second duty cycle, at the second ^{output ¬ out} (A2) of the control device (10). Method according to claim 2,  characterized by the following steps:  c) determining the smaller of the at least two duty cycle; d) reducing the smaller of the at least two duty cycle and lowering the instantaneous current (I) of the current source (I _Q ) such that the at least one LED (LED1, LED2, LED3) whose short-circuiting switch (KS1, KS2, KS3) with the smaller duty cycle is ^{¬ be} driven, their momentarily discontinued Hel ^¬ ligkeit outputs; and e) reducing the at least one other duty cycle such that the at least one LED (LED1, LED2, LED3), the short-circuit switch (KS1, KS2, KS3) with the at least one other duty cycle Betrie ^¬ ben is their currently to set the brightness to be set. 4. The method according to claim 3, characterized, that in step d) the smaller of the two duty cycles is reduced to a duty cycle of at most 10%, preferably at most 5%, more preferably at 0%. Method according to one of claims 3 or 4, characterized, that the reduction of the duty cycle and the entspre ^¬-reaching reduction in the instantaneous current (I) of the Stromquel ^¬ le (I _Q) steps, in particular in predeterminable Stu ^¬ fen occurs. Method according to one of claims 3 to 5, characterized, that step c) is repeated at predeterminable time intervals. Method according to one of claims 2 to 6, characterized by the following steps: f) determining whether (with the current instantaneous current I) at a third predetermined duty cycle, in particular a duty cycle of 0%, a einzustel ^¬ loin brightness output of the at least one LED (LED1, LED2, LED3) is achievable; and g) if the answer to step f) is no:  Increase the instantaneous current (I). Method according to claim 9, characterized, the increase of the instantaneous current (I) takes place in one step, the step being selected that in a fourth predetermined duty cycle, in particular ^¬ sondere a duty cycle of not more than 20%, preferably 0%, the brightness output to be set to the Minim ^¬ least one LED (LED1, LED2, LED3) is achievable. Method according to one of claims 7 or 8,  characterized, in that the maximum instantaneous current (I) is the rated current (Io) of the at least one LED (LED1, LED2, LED3) when a time period in which the maximum instantaneous current (I) flows exceeds a predefinable time duration ( _Tmax ). 10. The method according to any one of claims 7 to 9,  characterized, that the maximum instantaneous current (I) of the maximum pulse ^¬ current (Ip) of the at least one LED (LED1, LED2, LED3), when a period of time in which the maximum instantaneous current (I) flows, a predeterminable time period (T _max) is not exceeds. Method according to one of claims 7 to 10,  characterized by the following step: h) increasing the at least one other duty cycle such that at least one LED (LED1, LED2, LED3), the short-circuit switch (KS1, KS2, KS3) is reacted with the at least one other duty cycle Betrie ^¬ ben, their brightness currently adjusted gives up. 12. The method according to any one of the preceding claims, characterized by the following steps: Determining whether the current duty cycle at a minimum instantaneous current (I) of the current source (I _Q) output a brightness to be set to the min ^¬ least one LED (LED1, LED2, LED3) is achievable; and if the answer to step i) is no, because the adjustable at the current duty cycle Hel ^¬ ligkeit sabgabe is above the adjusted brightness predictions: Increasing the duty cycle with which the at least one LED (LED1, LED2, LED3) is operated, the short circuit ^¬ switch (KS1, KS2, KS3). Circuit arrangement for operating a plurality of LEDs (LED1, LED2, LED3) with  a supply connection for coupling with a Supply voltage (V _C c) a reference potential terminal for coupling with egg ^¬ nem reference potential;  at least a first parallel connection of at least one first LED (LED1) and a first short-circuit switch (KS1) for short-circuiting the at least one first LED (LED1);  at least one second parallel connection of at least one second LED (LED2) and a second short-circuit switch (KS2) for short-circuiting the at least one second LED (LED2); a current source (I _Q ), wherein the series circuit of the current source (I _Q ), the at least one ers ^¬ th and the at least one second parallel ^¬ circuit between the supply terminal and the reference potential terminal is coupled; and a control device (10) comprising:  - At least a first output (AI) for driving the first short-circuit switch (KS1);  - A second output (A2) for driving the second short-circuit switch (KS2); and - At least one input (St) for supplying at least one control signal for adjusting a current brightness of the at least one Ers ^¬ th (LED1) and a momentary brightness of the at least one second LED (LED2); characterized, that the current source (I _Q) a control input for Va ^¬ riieren of her deployable instantaneous current (I), wherein the control device (10) further comprises a third output (A4) coupled to the control input of the current source (I _Q ).