EP3138368A1

EP3138368A1 - Circuit arrangement and method for operating leds

Info

Publication number: EP3138368A1
Application number: EP15721618.5A
Authority: EP
Inventors: Cristian OLARIU
Original assignee: Zumtobel Lighting GmbH Austria
Current assignee: Zumtobel Lighting GmbH Austria
Priority date: 2014-04-30
Filing date: 2015-04-28
Publication date: 2017-03-08
Anticipated expiration: 2035-04-28
Also published as: AT15510U1; DE102014208190A1; WO2015165898A1; EP3138368B1

Abstract

The invention relates to a circuit arrangement having at least one LED assembly (15) and a controller (50) for providing a supply current (I_BALLAST) for the LEDs (17), wherein the LED assembly (15) is assigned an identification element in the form of a current sink (20) which is connected to the controller (50) via a parallel feedback circuit (25), said controller (50) being designed to provide a suitable supply current for the LEDs (17), based on a current flow (I_FEEDBACK) produced via the feedback circuit (25).

Description

Circuit arrangement and method for operating LEDs

The present invention relates to an arrangement for operating a multiplicity of LEDs, which are arranged in LED circuits to be operated with constant current, preferably connected in the context of several so-called series-parallel arrays. Furthermore, the invention relates to a method for operating LEDs. LEDs are replacing more and more classic light sources in modern lighting technology. There are a wide variety of LED types available, which differ in terms of their performance and in terms of color or color temperature of the emitted light. Depending on the field of application of a luminaire in which the LEDs are used, suitably suitable LEDs are used.

For various reasons, not a few are preferred

Instead, high-power LEDs are used, but instead medium or low power LEDs are used, which are interconnected in larger circuit arrangements. On the one hand, such lower power LEDs are significantly cheaper to manufacture, on the other hand, with the help of such

Arrangements better a large-area light output can be achieved, which is a significant advantage in view of the fact that LEDs are substantially point-like light sources. In practice, it has prevailed to arrange LEDs in the above-mentioned serial-parallel arrays, as shown schematically in Figure 1.

FIG. 1 thus shows a circuit variant known from the prior art, in which all the LEDs are supplied by a common operating device 200. A single LED array 210 consists in each case of a plurality of parallel-connected LED strands 220, in which in turn in each case a plurality of LEDs 225 in series

interconnected with each other. According to the illustration of FIG. 1, a plurality of such LED arrays 210 can also be connected in series with each other and then in turn in parallel, wherein the operating device 200 then supplies the resulting overall arrangement with a correspondingly suitable constant current IBALLAST. As already mentioned, a corresponding use of LEDs in the illustrated series-parallel arrays is characterized by the relatively simple construction, the associated low costs and the high efficiency that can nevertheless be achieved thereby. Obviously, the circuit arrangement shown in FIG. 1 and known from the prior art can be modified in many different ways. In particular, the number of LEDs used within a single array and the type of LEDs can be changed. Furthermore, the number of LED arrays can be varied and it can be varied how many of these arrays are connected in series and how many of the resultant LED array strands are in turn arranged in parallel. Depending on the design of the

Circuitry must then provide the operating device 200 a suitable power. The same applies to the case that only a single LED array is supplied by the operating device with power. Again, depending on the number and interconnection of the LEDs used for a required supply current. The circuit arrangement must therefore be designed such that it is ensured that a suitable current for the LEDs is actually provided by the operating device. The following procedures for solving this problem are already known from the prior art. On the one hand, the operating device can already be appropriately parameterized during manufacture or during startup, so that it permanently outputs the appropriate current given at the beginning. However, this then means that an adaptation of the current to changing conditions during the later operation is not possible. An adaptation could, however, be necessary, for example, if individual LED arrays fail and / or defective LED arrays are replaced by new arrays equipped with other LEDs. These situations may affect the overall power required by the LED array and should ideally be considered by the driver, otherwise reliable operation is not guaranteed.

As an alternative to the preprogramming of the operating devices described above, it is also known from the prior art to characterize LED modules which contain the LEDs by means of a resistor which is evaluated by the operating device. The resistor characterizes, for example, the height of the current required by the LED module and allows the operating device, after evaluation of the

Resistor to adjust the amount of output power accordingly.

However, the problem in this context is that the evaluation of the

Resistance can only be done with a relatively low accuracy. Further In this case, only a single LED array can be identified by the operating device and this must assume that the circuit arrangement has a total of completely identical arrays. In particular, however, can not be seen by the operating device, how many LED arrays are available in total and in what way these are interconnected.

Finally, it is also known from the prior art to provide each LED module with a memory element in which information regarding the required supply current is stored digitally. The operating device must then read this memory and adjust the output current based on it.

In this digital readout of the information is indeed compared to

Assessing an identification resistor achieves greater accuracy, but the means to do so are much more complex and costly. Furthermore, once again results in the above-mentioned problem, namely that the

Operating device usually identifies only a single LED module and in turn is not aware of how many LED arrays are interconnected. Incidentally, the above-described problems also arise when the LEDs are connected in a different way than in the parallel-serial arrays shown. Also in this case, it must be ensured that the LEDs are supplied with a suitable current. The present invention is therefore based on the task, a

Operating device, which supplies LED circuit arrangements, able to put in a position to easily output the supplied power to the

to adapt to actual needs of the circuit arrangement. The object is achieved by a circuit arrangement with the features of claim 1 and by a method according to claim 10. Advantageous developments of the invention are the subject of the dependent claims.

The solution according to the invention is based on the idea of assigning an identification element in the form of a so-called current sink to an arrangement of LEDs. This is connected separately from the actual power supply circuit via a parallel so-called feedback circuit with the operating device, so that the operating device can determine the resulting due to the current sink current flow in the feedback circuit. This current flow in turn characterizes the LED arrangement such that the operating device is enabled to provide a suitable

Supply current to provide.

The invention therefore proposes a circuit arrangement for operating LEDs with at least one - preferably series-parallel LED array and an operating device for providing a supply current for the LEDs, wherein the LED array is associated with an identification element in the form of a current sink, which via a Feedback circuit is connected to the operating device, and wherein the operating device is adapted to provide a suitable supply current for the LEDs based on a resulting from the feedback circuit current flow.

Furthermore, a method for operating at least one - preferably serially parallel - LED arrangement is proposed, in which the LED array a

Identification element assigned in the form of a current sink and a

Feedback circuit is connected to an operating device, based on a resulting from the feedback circuit current flow, a suitable supply current for the LEDs is provided. The inventive concept can already be used when using a single series-parallel LED array or a single LED array, but preferably the LED array has multiple LED arrays. In this case, according to a preferred embodiment of the invention, each LED arrangement is a corresponding identification element in the form of a

Current sink assigned, these current sinks are then connected to each other in the feedback loop. This is separate from the

Supply circuit but executed in terms of its structure exactly the same way. That is, the current sinks are connected in the same way, depending on the number of serially or parallel interconnected LED arrangements. This has the advantage that the overall resulting

Current flow in the feedback circuit, in turn, allows a simple conclusion on the supply current required by all LEDs. It is

It is preferably provided that, due to the current sinks, only a very small current flow in the feedback circuit results, which, however, is connected to the actually required current via a known proportionality factor.

Ultimately, therefore, allows the solution of the invention, regardless of the

Interconnection of the LED assemblies with each other in a simple manner the total to determine required power and accordingly to operate the LED array in a suitable manner.

In addition, according to a preferred embodiment, it can also be provided that the current sinks, that is to say the identification elements, not only make it possible to draw conclusions about the required current but also about the required voltage for operating the LEDs.

It can be provided according to a first variant, that each current sink additionally causes a fixed predetermined voltage drop in the feedback circuit. Is this caused by the current sink voltage drop the

Operating device known, it can be determined from the overall over the entire feedback loop resulting voltage drop, how many LED arrays are connected in series with each other.

As an alternative to the procedure described above, it could also be provided that the voltage drop caused by the current sink corresponds to a predetermined integer fraction of the required forward voltage of the LED arrangement. In the event that this gain factor is known to the operating device, then this in turn can provide a suitable supply voltage available. However, it is not possible to deduce the number of LED arrangements connected in series directly here.

Another development of the invention relates to protection measures by which defects of individual LEDs are taken into account in the circuit arrangement. From the prior art, different variants are known to respond to corresponding LED defects. This is necessary because defective LEDs can lead to a strong imbalance in the distribution of the current within the circuitry, which can then propagate the imbalance such that further LEDs are damaged. Various protective mechanisms are therefore known which, upon detection of corresponding defects, either interrupt the current flow through the associated LED arrangement or bridge it.

According to a particularly preferred embodiment of the invention, it is now provided that in the event that such protective mechanisms are provided, they also relate in the same way to the associated identification current sinks. That is, should a protection mechanism, due to a detected LED defect, bypass the associated array or array, it will do so in the same way for the current sink within the feedback loop. Will, however, the Current flow interrupted, so the associated branch is interrupted in the feedback loop. These measures have the consequence that the electricity in the

Feedback circuit automatically adapts to the changed required supply current, if required by protective measures. The operation of the LEDs as a whole is thereby additionally optimized.

The invention will be explained in more detail with reference to the accompanying drawings. Show it:

Figure 1 is a known from the prior art circuit arrangement of a plurality of interconnected parallel-serial LED arrays;

FIG. 2 shows the embodiment according to the invention of a single LED array;

Figure 3 is a total of the invention resulting circuitry for operating a plurality of LEDs;

Figure 4 shows a first advantageous embodiment of the inventive concept;

Figure 5 shows a second advantageous embodiment of the invention

concept;

6 shows a first possibility for the embodiment of an inventive for

Use of coming current sink;

Figure 7 shows a second possibility for the embodiment of the invention

Current sink and

Figure 8 shows a way to further improve the current sink, in the

Temperature effects are taken into account.

Figure 2 shows a first embodiment of a generally provided with the reference numeral 10 LED module, which is designed in accordance with the invention. In this case, the LED module 10 initially contains a series-parallel LED array 15, which is formed from a plurality of LED strands 16 connected in parallel with one another.

Within each LED string 16, a plurality of LEDs 17 are connected in series with one another, ideally the number of LEDs 17 in the strands 16 being identical. The LED module 10 has at the input and the output of the LED array 15 terminals LED + and LED-, which connects to a Supply circuit, which leads to an operating device for powering the LEDs allow.

It should be noted that in the case shown, the invention is described with reference to serial-parallel LED arrays, which - as mentioned - represent a particularly advantageous circuit variant for operating LEDs. However, the concept according to the invention can be used much more generally and can also be used in LED arrangements in which the LEDs are otherwise connected. Depending on the type of LEDs 17 used, the number of LEDs and the number of parallel connected LED strings 16, the module 10 requires a certain constant supply current I _M O _D U _LE and a suitable supply voltage. In a first step, it is provided according to the present invention that the LED module 10 itself allows the operating device to determine the level of the required current.

For this purpose, according to the invention, the LED module 10 has an identification element in the form of a so-called current sink 20, which is connected to the operating device via a so-called feedback circuit. For this purpose, the LED module 10 has two further connections FB + and FB-, which are separated from the terminals for the

Power supply circuit LED + and LED- are formed on. That is, the

Feedback circuit is basically separate but - as described in more detail below - executed parallel to the power supply circuit. The current sink 20 is now designed such that it specifically causes a defined current flow IS _ET in the feedback circuit, wherein ideally the following relationship exists:

IMODULE ⁼ Fe * ISET

In this case, I _M O _D U _LE denotes the current required by the LED array 15 while IS _ET denotes the current flow caused by the current sink 20. Of the

In this case, the proportionality factor Fe must be known to the operating device, so that this after evaluating the resulting by the feedback loop

Current flow knows what amount of current has to be supplied via the supply circuit. For example, the gain factor F _{c could be} 100, so that at a current level of 3mA caused by the current sink, the driver supplies a supply current to the LEDs of 300mA

Provides. The inventive concept brings advantages in particular when the overall arrangement not only has an LED array as shown in FIG. 2, but consists of a plurality of LED arrays, as shown by way of example in FIG.

In this case, a total of n * m LED modules 10, each including an LED array 15, interconnected, this being done in n parallel strands, each having m connected in series LED modules 10.

As FIG. 3 shows, each LED module 10 has the invention

identifying current sink 20, which are now interconnected in a feedback circuit 25, which also leads to the operating device 50 and is here connected to an internal control unit 51. As can be seen in this case, although the feedback circuit 25 is formed separately from the power supply circuit 5, it is executed in parallel or in an identical manner with respect to its structure. That is, the individual current sinks 20 of the LED modules 10 are connected to each other in the same way as is the case for the LED arrays 15. This automatically results in a corresponding total current I _FEEDB AC _K in the feedback circuit 25 which, in turn, corresponds to the total current required by the LED arrangement via the known proportionality factor Fe and is then output by the operating device 50 in a corresponding manner.

This represents a particularly advantageous effect of the solution according to the invention, since the operating device 50 can be adapted directly to the corresponding circuit arrangement and requires no further information. In particular, the topology of the arrangement of the LED modules, ie the manner in which the modules are connected to one another, must not be known to the operating device.

In this case, the LED arrays 15 of the individual LED modules 10 could even

be designed differently. That is, the modules themselves may even each require different supply currents, since this effect automatically also - if the above relationship applies, according to the current flow caused by the current sink is a predetermined fraction of the required current - on the in the feedback loop resulting current flow. Ideally, however, the modules are as similar as possible or even identical, since this usually results in advantages in terms of a uniform light output. The previous considerations related to the magnitude of the current provided by the operating device 50 for the LED modules 10. In addition, however, the concept can also be used to adapt the voltage output by the operating device in a corresponding manner or to identify the number of LED modules 10 connected in series.

In accordance with a first option, it may be provided that the current sink 20 causes a specific voltage drop VS _INK (see FIG. 2), which is fixed and known to the operating device 50. Out of the total resulting

Voltage drop V _FEEDB AC _K via the feedback circuit then the information can be derived how many - in the illustrated embodiment of Figure 3 so m - LED modules 10 are connected in series.

According to a second option, however, the voltage drop VS _{INK could} also represent a fraction of the voltage V _LED dropping across the LED array (see FIG. 2). That means it applies

VSINK = fv * LED In this case, the operating device 50 can automatically reset the total required

Detect voltage for the LED array, but no longer determine how many modules are connected in series. The proportionality factor f _v must of course be known to the operating device 50 in this case. The minimum required voltage VS _{INK of} the current sink can be very low,

especially be kept smaller than 1 volt. Combined with a high

Amplification factor F _c and thus a low current flow through the

Current sink is caused, it follows that the power loss, which is caused by the inventive measures is extremely low. At the same time, however, as described above, significant advantages in terms of

achieved automatic adjustment with respect to the supply current.

As already mentioned, protective mechanisms are known from the prior art which interrupt or bridge the associated array in the event of an LED defect. FIG. 4 shows a first protective mechanism 30 which has a switching element 31 which interrupts the current flow through the entire array 15 in certain situations. This can be the case, for example, if the result is an excessively high current flow due to individual defective LEDs, which possibly leads to another one Damage to all LEDs can cause. As already mentioned are such

Protective mechanisms from the prior art already known.

The interruption of the current flow through the array 15 of course then also affects the height of the total required by the LED array current. In order to be able to take this into account in the procedure according to the invention, it is provided that the current sink 20 of the LED module 10 is treated in the same way by the protective mechanism 30. That is, in the feedback circuit of the current sink 20 is assigned a switch 32, of the

Protective mechanism 30 is driven in an identical manner. So will the

Current flow interrupted by the LED array 15, this is equally true for the branch with the current sink 20th

FIG. 5 shows an alternative protection mechanism 40 which, in the event of a problem being detected by means of a switch 41, shorts or bridges the LED array 15. Also in this case, an identical treatment of the current sink 20 is provided. That is, the feedback circuit has now parallel to the current sink 20, a switch 42 which is the same as the switch 41 is driven by the protective mechanism 40.

In both variants, which could otherwise be combined with each other, therefore, the interruption or bridging of an LED module is automatically taken into account in the feedback circuit and the output of the supply current can be adjusted by the operating device in a corresponding manner. This achieves an even better adaptation of the power supply for the LEDs.

Finally, FIGS. 6 to 8 show three possibilities for configuring the current sink which according to the invention is used to identify the LED array. In this context, however, it should be noted that

Current sinks from the prior art are already known and could be realized in many ways. The following variants represent only a few conceivable examples.

Thus, in the variant according to FIG. 6, a very simple embodiment is formed by two transistors Qi and Q ₂ and two resistors Ri and R ₂ , in which the transistor Q1 causes a predetermined current flow due to the illustrated interconnection. To operate this current sink is a suitable

Preload V _BI AS is required, which can be obtained, for example, that the corresponding terminal to the positive input of the supply circuit for the LED module is connected. In this case, the current sink works so only when the LEDs of the associated LED array are actually supplied with power. With the aid of an optional zener diode D _z , the total resulting voltage drop VS _INK can be increased, for example, the

To improve accuracy in detecting the number of series connected LED modules or to optimize the accuracy of the total required forward voltage for the LEDs. This brings with it advantages, since due to a relatively strong temperature dependent on the base-emitter voltage V _{BE of} the second transistor Q ₂ there is a risk that the forward voltage across the current sink varies too much and accordingly no more accurate detection is possible.

An alternative possibility for designing a current sink is shown in FIG. Again, this is based on the realization or interconnection of two transistors Qi and Q ₂ and two resistors Ri and R ₂ , but now with the help of additional components, in particular the other transistors Q ₃ and Q ₄ and the resistor R _3, the current sink in the position is added to independently create a corresponding bias. In this case, the current sink must actually be connected exclusively to the terminals of the feedback circuit FB + and FB- and a coupling with the power supply circuit for the LEDs is not required. In this case, however, a higher voltage VS _{INK is} required, which can optionally be obtained again with the aid of the zener diode D _z .

As already mentioned, there is the problem that temperature fluctuations can lead to a strong dependence of the base-emitter voltage V _{BE of} the transistor Q ₂ . This could potentially cause current flow through the sink to decrease with increasing temperature, which ultimately means that the power supplied to the LEDs will be reduced as the modules become warmer. Such an effect could even have a corresponding effect

Represent protection mechanism by which the LED power at too high

Temperatures is automatically reduced.

However, if this is not desired, then the temperature dependence can be compensated by the supplement shown in FIG. A temperature-dependent resistor R _TH , which is part of a corresponding resistor network with the resistors R _B AS _E , Rp and Rs, serves to compensate for thermal fluctuations of the base-emitter voltage. This ensures that the supply current remains constant even at higher temperatures. As already mentioned, FIGS. 6 to 8 represent only conceivable variants for realizing a current sink. Of course, these could also be formed elsewhere.

Overall, therefore, with the help of the present invention, the advantage that for the power supply of more complex LED circuits, the corresponding operating device is enabled to automatically adjust the supply current to the corresponding needs of the circuit. In this case, not only failures or bypasses of individual LED arrangements due to defects are automatically taken into account, but also the replacement or replacement of an LED module with a new one, which places different demands on the supply current, is automatically taken into account.

Claims

claims

1. Circuit arrangement with at least one LED arrangement (15) and a

Operating device (50) for providing a supply current (I _B A _LL AS _T ) for the LEDs (IV),

wherein the LED array (15) is associated with an identification element in the form of a current sink (20), which via a parallel feedback circuit (25) with the

Operating device (50) is connected,

and wherein the operating _device (50) is designed to have a suitable current flow on the basis of a current flow (I _FEEDB AC _K ) resulting from the feedback circuit (25)

Supply current for the LEDs (17) to provide.

2. Circuit arrangement according to claim 1,

characterized,

that it has a plurality of LED arrays (15), which via a

Supply circuit (5) are connected to the operating device (50),

wherein each LED array (15) is associated with a respective current sink (20) and the structure of the feedback circuit (5) is identical to that of the supply circuit (25).

3. Circuit arrangement according to claim 1 or 2,

characterized,

a current flow caused by the current sink (20) is proportional to the current required by the associated LED array (15).

4. Circuit arrangement according to one of the preceding claims,

characterized,

in that the operating device (50) is further adapted, depending on one

Voltage drop in the feedback circuit (5) to output a supply voltage for the LEDs.

5. Circuit arrangement according to claim 4,

characterized,

that the current sink (20) causes a fixed predetermined voltage drop (VS _INK ).

6. Circuit arrangement according to claim 4,

characterized, a voltage drop (VSINK) caused by the current sink (20) is proportional to the required forward voltage of the associated LED array (15).

7. Circuit arrangement according to one of the preceding claims,

characterized,

in that the LED arrangement (15) is assigned a protective mechanism (30, 40) which bridges the LED arrangement (15) or interrupts a current flow through the LED arrangement (15) in the event of a recognized fault condition,

the protection mechanism having the same influence on the associated

Current sink (20) decreases.

8. Circuit arrangement according to one of the preceding claims,

characterized,

in that the LEDs of the LED arrangement (15) or LED arrangements (15) are each arranged in the form of a series-parallel array.

9. LED module (10) with an LED arrangement (15) and connections (LED +, LED-) for connecting the module to an operating device (50) for providing a supply current (IBALLAST) for the LEDs (17),

wherein the LED module further comprises an identification element in the form of a current sink (20), which is connectable via additional connections to the operating device (50) to allow them to provide a suitable supply current for the LEDs (17).

10. A method for operating at least one LED arrangement (15) and an operating device (50) for providing a supply current (IBALLAST) for the LEDs (IV),

Operating device (50) is connected,

and on the basis of a through the feedback circuit (25) resulting current flow (IFEEDBACK) a suitable supply current for the LEDs (17) is provided.

1 1. Method according to claim 10,

characterized,

in that the arrangement has a plurality of individual LED arrangements (15) which are connected to the operating device (50) via a supply circuit (5), wherein each LED array (15) is associated with a respective current sink (20) and the structure of the feedback circuit (5) is identical to that of the supply circuit (25).

12. The method according to claim 10 or 1 1,

characterized,

13. The method according to any one of claims 10 to 12,

characterized,

that depending on a voltage drop in the feedback circuit (5) a

Supply voltage for the LEDs is output.

14. The method according to claim 13,

characterized,

15. The method according to claim 13,

characterized,

in that a voltage drop (VS _INK ) caused by the current sink (20) is proportional to the required forward voltage of the associated LED arrangement (15).

16. The method according to any one of claims 10 to 15,

characterized,

the protection mechanism having the same influence on the associated

Current sink (20) decreases.

17. The method according to any one of claims 10 to 16,

characterized,