• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    An LED circuit arrangement having at least one LED array has a plurality of LED strands connected in parallel, the LED array having a protective circuit which is designed to bridge all LED strands of the array depending on operating parameters of the LED array. The operating parameters are the magnitude of the current flowing through at least one of the LED strings and / or a temperature in the range of the LEDs.
    公开号:AT15252U1
    申请号:TGM425/2013U
    申请日:2013-12-04
    公开日:2017-04-15
    发明作者:Dipl Ing Olariu Cristian
    申请人:Zumtobel Lighting Gmbh；
    IPC主号:
    专利说明:

    description
    LED CIRCUIT ARRANGEMENT AND METHOD FOR OPERATING AN LED CIRCUIT ARRANGEMENT
    The present invention relates to an LED circuit arrangement for operating a plurality of LEDs, preferably by a common operating device. Furthermore, the invention relates to a method for operating a corresponding circuit arrangement.
    LEDs displace in modern lighting technology more and more classic light sources. There are a variety of different LED types available, which differ in terms of their performance and in terms of the emitted light or the color or color temperature. Depending on the field of application of a luminaire in which the LEDs are used, that is, for example, depending on the size of the luminaire, its light exit surface, the optical system used and the like, the use of a few so-called. High-performance LEDs or a plurality of LEDs with low or medium power of advantage.
    The problem in this context, however, is that in comparison to the widely available LEDs required to operate the LEDs LED operating devices are available only to a limited extent, which in turn requires that esp. In the event that a plurality be operated by LEDs with low or medium power, they must be connected in a suitable manner. In practice, LEDs have been used in so-called serial-parallel arrays, as shown schematically in FIGS. 1 and 2.
    In this known from the prior art circuit variant all LEDs are powered by a common operating device 200. A single array 210 consists in each case of a plurality of parallel-connected LED strings 220, in each of which the LEDs 225 are connected in series. In the variant according to FIGS. 1 and 2, therefore, there are, for example, n parallel LED strands 220, each of which has m LEDs 225, so that an array 210 consists altogether of n × m LEDs 225. As further shown in FIG. 1, a plurality of such arrays 210 can also be interconnected in series with one another, wherein the operating device 200 then preferably supplies the overall resulting arrangement with a constant current. A parallel connection of such LED arrays 210 would be possible.
    A serial-parallel LED array 210, as shown in Figures 1 and 2, has certain advantages in terms of ease of construction, the associated low cost and high efficiency achievable despite all. If identical LEDs 225 are used, which have a substantially identical forward voltage, then the current provided by the operating device 200 is equally divided between the individual LED strands 220 with only slight tolerances. The following relationship applies:
    Ibranch corresponds to the current within a single LED strand 220, whereas lbaiiast corresponds to the constant current provided by the operating device 200. For the voltage drop Vf array via the LED array 210, the following relationship also results:
    wherein Vf led corresponds to the forward voltage of the LEDs 225 which, as already mentioned, is preferably approximately the same for each LED 225. The overall performance of the array 210 is determined as follows:
    The circuit arrangement according to the prior art shown in Figures 1 and 2 thus has many advantages in terms of their simple structure and despite all thus achievable high efficiency. However, there is a problem that, in the case of a defect of at least one LED of the corresponding array, the distribution of the current provided by the constant current source is no longer uniform to all the LED strings but instead an imbalance occurs, resulting in large differences in the intensity of the emitted light can lead. Furthermore, there is a risk that the uneven distribution of the current leads to the permissible maximum value of the current or the maximum permissible operating temperature being exceeded in some areas, which may ultimately result in further failures of LEDs and / or defects of other components of the circuit arrangement.
    This situation is shown in Figures 3a and 3b, which show two different types of LED defects.
    Thus, the most frequently occurring defect in LEDs is shown in Figure 3a, in which there is a short circuit of the corresponding LED. In this case, therefore, the LED string 230 having the defective LED 235 effectively has one LED less in comparison with the other LED strings 220. Due to the parallel connection of all LED strings, this has the consequence that the current lbaMast provided by the constant current source 200 is now divided such that a higher current I SC flows through the LED string 230 with the defective LED 235 than through the other strings In particular, this current S sc is also higher than the current lbranch intended for normal operation, which is distributed uniformly over all the LED strings. Furthermore, this imbalance also means that in the other, non-defective LED strings 220, the current lrest is below the normally present current lbranch. So it applies: as well
    On the other hand, another LED defect can lead to the situation illustrated in FIG. 3b, in which the damaged LED 235 leads to an interruption of the corresponding string 230. This therefore drops out completely (1 | NT = 0), so that now the current lbaNast provided by the operating device 200 is distributed to the remaining n-1 LED strands 220, with the result that the resulting current remains of all active lines 220 above the current intended for normal operation:
    As already mentioned, these imbalances in the current flow through the LED strands initially lead to the LEDs 225 of the array 210 emitting light with different brightness or intensity and, accordingly, no more uniform appearance is obtained. More serious, however, is the problem that the at least partially resulting higher currents in the strands can lead to further damage to the still functional LEDs or even other components of the circuit can be damaged.
    Another known problem in the operation of LED circuit arrangements is that they should only be operated within a certain temperature window or allowed. Luminaires with LED light sources often have optics made of plastic material in order to influence the light emitted by the individual LEDs in a suitable manner. For these optics PMMA is preferably used, since this material has very good optical properties with respect to the transmission coefficient and at the same time is UV-resistant. Furthermore, this material is relatively inexpensive and can be brought in a variety of forms in a simple manner. On the other hand, compared to other plastic materials, PMMA can only be used at relatively low maximum temperatures in the range of 90 ° to 95 ° C., since higher temperatures may otherwise damage the optics. This, in turn, means that very close attention must be paid to the prevailing temperatures, with a safety standard, for example, stipulating that under certain circumstances, maximum temperatures in the range between 65 ° and 70 ° C may be achieved.
    Temperature increases in the range of LED light sources can u.a. caused by external factors, such as the use in environments with a relatively high temperature or the failure of the proposed cooling measures of a lamp. However, the LED defects shown in connection with FIGS. 3a and 3b can also lead to current flows which have a negative effect on the temperature in the region of the LED board. However, an increased temperature in turn can not only lead to damage of the optical elements located in the immediate vicinity of the LEDs, but also lead to further LED defects.
    Finally, this means that when operating LEDs, in particular in the case of the serial-parallel arrays described above, care should be taken that, on the one hand, the currents in the different LED strands are within permissible ranges and, on the other hand, temperatures that are too high in the range of LEDs are present.
    The present invention is based on the task to provide a solution for this, which prevents a simple but efficient manner such conditions occur.
    The object is achieved by an LED circuit arrangement with the features of claim 1 and by a method for operating an LED circuit arrangement 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 a protection circuit to the LED array, which is designed to bridge the entire LED array in the event of certain fault conditions. In particular, in this case the protective circuit is designed to decide on the basis of the current flowing through at least one of the LED strings and / or on the basis of a temperature which is present in the region of the LEDs, whether the LED array is bypassed for safety reasons or not.
    According to the present invention, an LED circuit arrangement with at least one LED array is accordingly proposed, which has a plurality of parallel-connected LED strands, wherein the LED array according to the invention comprises a protection circuit which is designed depending on operating parameters of the LED Arrays to bridge all LED strands of the array together, and wherein the operating parameters is the height of the current flowing through at least one of the LED strands and / or a temperature in the range of the LEDs.
    It has been found that the complete bridging of the LED array is the most efficient measure to reliably avoid further damage to the circuit arrangement in the event of an LED defect and / or the occurrence of high operating temperatures. This is the case in particular when, according to the illustration according to FIG. 1, a plurality of similar LED arrays are connected in series with one another since in this case only the defective array is bridged, but the further array remains unaffected by the constant current source supplied power. As will be explained in more detail below with reference to the preferred exemplary embodiments, the solution according to the invention also has the additional advantage that it can be realized relatively simply and inexpensively, but at the same time represents a reliable safeguard against the problems described above.
    Preferably, the protection circuit according to the invention is based on a thyristor-containing shunt, which is activated in the event of detecting certain fault conditions to permanently bridge the LED array. In this case, the thyristor may in particular be part of a so-called clamping circuit (so-called crowbar circuit). Such a clamp circuit is known from the prior art and is hereby used as protection against overvoltage voltages to trigger a fuse which interrupts the power supply of a device. In a modification of this original procedure, the present invention proposes to use such a clamping circuit now for selective bridging defective LED arrays, such that, if necessary, further arrays unaffected by this can continue to be supplied with power.
    Preferably, the protection circuit is designed such that it monitors the current flow through each individual one of the LED strands of the array and bridges the array if, in at least one of the LED strands, the current is above a predetermined limit value. That is, as soon as defects lead to such an imbalance in the power distribution, that at least in an LED string, the allowable limit is exceeded, the array is completely bypassed and thus deactivated.
    Alternatively or additionally, as already mentioned, the protective circuit can also be designed for temperature monitoring. For this purpose, it preferably has at least one temperature sensor which is designed to activate the bridging of the array when a temperature above a predetermined limit value is detected. The temperature sensor can be based in particular on a temperature-dependent resistance (NTC), wherein preferably a plurality of distributed temperature sensors are provided. In the case of a shared use of current monitoring and temperature monitoring, it is provided, in particular, that the components of the current monitoring and the components of the temperature monitoring jointly control a corresponding shunt or thyristor in order to bridge the LED array, if necessary. That is, in both cases of current monitoring and temperature monitoring, certain components can be shared, so that the cost of implementing an efficient safety circuit can be kept very low.
    The invention will be explained in more detail with reference to the accompanying drawings. 1 shows an LED circuit arrangement according to the prior art in which several re-serial-parallel LED arrays are connected in series and supplied by a common operating device; Figure 2 shows the view of a single LED array according to the prior art; Figure 3a by way of example the case of an LED defect, which leads to a short circuit of the corre sponding LED; Figure 3b shows an example of the case of an LED defect, which leads to an interruption of the ent speaking LED string; Figure 4 shows the basic idea of current monitoring in an LED array according to the present invention; FIG. 5 shows a conceivable embodiment of a current monitoring circuit according to the invention; FIG. 6 generally illustrates the idea of temperature monitoring according to the present invention
    Invention and Figure 7 shows a conceivable embodiment of a temperature monitoring circuit according to the invention.
    The procedure according to the invention is therefore based on monitoring the currents present in the LED strings and, alternatively or additionally, on a temperature monitoring in the area of the LEDs.
    With reference to Figure 4, the principle of current monitoring according to the invention and the corresponding protection circuit will be explained in principle. Shown again is an LED array 110, which is supplied by the constant current source 100 with the current Ibaiiast, wherein now in each individual LED strand 120 in series with the respective LEDs 125, a current detector 10 is arranged. These n current detectors 10 each generate an output signal which optionally activates a bridging element, a so-called shunt 50. This shunt 50 is arranged so that it completely bridges the LED array 110.
    The activation of the shunt 50 by the current detectors 10 should then take place when the respectively determined current is above a certain threshold ILim, this threshold is preferably set such that it is slightly higher than that provided for normal operation LED current is, but still below the maximum allowable current value. The outputs of the current detectors 10 are logically linked together in an OR circuit. That is, as soon as at least one of the detectors 10 detects an unacceptably high current value, the shunt 50 is activated and effectively closes the entire LED array 110 short.
    In a circuit arrangement in which a plurality of such LED arrays 110 are provided, then results depending on the interconnection of the arrays 110 with each other, a corresponding effect. In the event that the arrays 110 are connected in series, as shown in FIG. 1, only the corresponding defective array 110 is bridged by the associated shunt 50. By contrast, the further LED arrays 110 are supplied unchanged by the current of the constant current source 100 and thus remain in operation. In contrast, in the case where the arrays 110 are connected in parallel, the corresponding shunt 50 would short-circuit all the arrays 110 together, which means that even in the case of a single impermissible current value, the entire circuit is deactivated. Accordingly, the serial interconnection of the arrays 110 according to FIG. 1 is preferable.
    When bridging the array 110 through the shunt 50 immediately falls the condition that an unacceptably high current was detected by at least one current detector 10 away. Accordingly, the shunt 50 should preferably be configured to permanently maintain the lock-in state after appropriate activation to avoid uncontrolled oscillations of the system. Further, the shunt 50 must, of course, be designed so that it is able to cope with the current flowing completely completely therethrough in the event of a bridging while at the same time consuming as little power as possible. It should therefore preferably have a very low impedance.
    A preferred embodiment of the current protection circuit according to the invention, which fulfills the above requirements, is shown in FIG. The shunt 50 has an essential element as a thyristor DScr, which is controlled by the current detectors 10 described below. These current detectors 10 in turn are formed by a circuit arrangement consisting of a transistor Qpnp and two resistors Rset and Rb, which is connected as already mentioned in series with the LEDs 125 of the respective strand 120. By appropriately dimensioning the resistors Rset and Rb, the threshold from which the thyristor DScr is activated can be set in a suitable manner.
    The resistors Rset and Rb are usually dimensioned such that in a normal operation of the circuit, so if the current of the constant current source 100 is evenly distributed to all LED strands 120, a voltage drop across the resistor Rset is present, just below the Base-emitter voltage VBE of the transistor Qpnp is located. This means that the transistor Qpnp blocks and accordingly the shunt 50 is opened.
    However, now leads to a fault condition that the corresponding current in the LED strand 120 increases, the voltage drop across the resistor Rset will exceed the base-emitter voltage VBE of the transistor Qpnp, which in turn in a switching of the transistor Qpnp results, which then controls the thyristor DScr and thus closes the shunt 50. The thyristor DSCr thus short-circuits the entire LED array 100 and then remains closed as long as current flows through it, even if the corresponding transistors Qpnp of the current detectors 10 immediately block it again, since current is no longer present through the LED strings 120 themselves flows. As can also be seen in FIG. 5, am
    Output of the thyristor DSCr a filter consisting of a parallel resistor RPd and a capacitor Cffl formed to prevent the kurzeitige fluctuations already lead to a triggering of the shunt 50 and thus a shorting of the LED array 110.
    The circuit shown in Figure 5 has proved to be extremely energy efficient, since it requires less than 0.6 V during normal operation, which corresponds to a loss of only 1.6%, for example, in an array with 12 LEDs in series. In the event that the shunt 50 is activated, too little power is consumed, since the voltage drop is typically less than 2V.
    Alternatively or in addition to the current protection circuit just described, the circuit arrangement can also be formed with a temperature protection circuit, which will be explained below with reference to Figures 6 and 7.
    The basic principle here is similar to that of the monitoring circuit according to Figure 4. That is, in this case, a shunt 50 is provided, which is now controlled by temperature detectors 20 and in the case of detecting an impermissibly high temperature, the entire LED array 110 bridged.
    However, compared to current monitoring, it is now not absolutely necessary to individually monitor each LED string 120. Instead, it is sufficient if some temperature sensors or detectors 20 are distributed in the area of the LEDs 125 and here detect the corresponding temperatures. Again, the monitoring circuit is designed such that the shunt 50 bridges the LED array 110 as soon as at least one of the temperature detectors 20 triggers and activates the shunt 50. This in turn should remain permanently activated, even if, after bridging the LED array 110, the temperature detected by the detectors 20 drops again.
    One possibility of realizing this temperature protection circuit is shown in FIG. 7, wherein it can initially be seen that the shunt 50 is designed here in an identical manner as in the case of the temperature monitoring circuit according to FIG. 5. Differences exist only with regard to the realization the temperature detectors 20, two of which are shown in the present case.
    Central components of the temperature detectors 20 are now temperature-dependent resistors Rth (NTCs), which are arranged such that they - as shown by the dotted lines - in thermal contact with the monitored site (for example, a corresponding LED) are. By the resistors Rb, Rd, Rz and Rth a voltage divider is formed, via which a corresponding limit value can be set. The voltage divider divides the voltage set by the Zener diode Dz and drives the transistor Qpnp. It is dimensioned such that in the event that the temperature is within the intended range, the resistance Rth is sufficiently large, with the result that the voltage drop across Rd is below the base-emitter voltage VBe. The transistor Qpnp is closed in this case and the shunt 50 is opened.
    Now increases the temperature, the resistance value Rth drops until finally the base-emitter voltage VBe of the transistor Qpnp is exceeded. The transistor Qpnp opens in this case and drives the thyristor DScr, so that the shunt 50 is closed and thus the LED array 100 is short-circuited. Again, the thyristor DSCr remains activated as long as current flows through it, so that once again oscillating states of the entire circuit arrangement can be avoided. The filter provided in the shunt 50 in turn serves to prevent inadvertent activation of the shunt 50 due to short-term fluctuations.
    Also for the circuit arrangement shown in Figure 7, the advantages described in connection with Figure 5. So there is a very energy-efficient circuit, which can also be realized by relatively few components beyond. Further, since in both cases the shunts are configured in identical ways, it is easily possible to combine the idea of current monitoring and temperature monitoring, using a single shunt driven by both the current detectors and the temperature detectors. This represents a particularly advantageous embodiment, since elements can be used together and, accordingly, the total effort is further reduced.
    Finally, with the aid of the circuit arrangement according to the invention, the occurrence of false states in LED circuits is reliably avoided.
    权利要求:
    Claims (13)
    [1]
    claims
    1. LED circuit arrangement having at least one LED array (110), which has a plurality of parallel-connected LED strings (120), wherein the LED array (110) has a protective circuit, which is designed depending on operating parameters of the LED Arrays (110) to bridge all the LED strands (120) of the array (110), and wherein the operating parameters to the height of the current flowing through at least one of the LED strands (120) and / or a temperature in the range of the LEDs (125).
    [2]
    2. LED circuit arrangement according to claim 1, characterized in that the protective circuit has a shunt (50) which is arranged parallel to all LED strings (120) and at least one current detector (10) and / or at least one temperature detector (20 ) is driven.
    [3]
    3. LED circuit arrangement according to claim 2, characterized in that the shunt (50) has a thyristor (DScr), which is preferably part of a clamping circuit.
    [4]
    4. LED circuit arrangement according to one of the preceding claims, characterized in that the protection circuit monitors the current flow through each of the LED strands (120) and is adapted to bridge the array (110), if at least in one of the LED strands (120) the current is above a predetermined limit.
    [5]
    5. LED circuit arrangement according to one of the preceding claims, characterized in that the protection circuit comprises at least one temperature detector (20) which is adapted to activate upon detection of a temperature above a predetermined limit, the bridging of the array (110).
    [6]
    6. LED circuit arrangement according to claim 5, characterized in that the temperature detector (20) has a temperature-dependent resistor (Rth).
    [7]
    7. LED circuit arrangement according to claim 5 or 6, characterized in that a plurality of distributed temperature detectors (20) are provided.
    [8]
    8. LED circuit arrangement according to one of the preceding claims, characterized in that it comprises a plurality of LED arrays (110), each having its own protection circuit.
    [9]
    9. LED circuit arrangement according to claim 8, characterized in that the LED arrays (110) are connected in series with each other and are supplied by a common power source, preferably by a constant current source (100).
    [10]
    10. A method for operating an LED circuit arrangement having at least one LED array (110) which has a plurality of parallel-connected LED strands (120) wherein, depending on operating parameters of the LED array (110), all the LED strands (120) of the array (110), and wherein the operating parameters are the magnitude of the current flowing through at least one of the LED strings (120) and / or a temperature in the range of the LEDs (125).
    [11]
    A method according to claim 10, characterized in that the current flow through each of the LED strings (120) is monitored and the array (110) is bypassed if at least in one of the LED strings (120) the current is above a predetermined limit ,
    [12]
    12. The method according to claim 10 or 11, characterized in that detected at several positions of the circuit, the temperature and da array (110) is bridged, if at least at one position, the temperature is above a predetermined limit.
    [13]
    13. The method according to any one of claims 10 to 12, characterized in that the circuit arrangement comprises a plurality of LED arrays (110). 4 sheets of drawings
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    引用文献:
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    DE102008044525A1|2008-09-15|2010-04-01|Werner Turck Gmbh & Co. Kg|Lamp, particularly direction indicator light for motor vehicle, comprises strand or multiple strands, where each strand has series resistor as current source and light emitting diodes connected in series|
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    法律状态:
    2018-08-15| MM01| Lapse because of not paying annual fees|Effective date: 20171231 |
    优先权:
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    DE201310221715|DE102013221715A1|2013-10-25|2013-10-25|LED circuit arrangement and method for operating an LED circuit arrangement|
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