EP1449408B2 - Circuit for an led array - Google Patents

Circuit for an led array Download PDF

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Publication number
EP1449408B2
EP1449408B2 EP02803750A EP02803750A EP1449408B2 EP 1449408 B2 EP1449408 B2 EP 1449408B2 EP 02803750 A EP02803750 A EP 02803750A EP 02803750 A EP02803750 A EP 02803750A EP 1449408 B2 EP1449408 B2 EP 1449408B2
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EP
European Patent Office
Prior art keywords
led
current
regulating
circuit
case
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EP02803750A
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German (de)
French (fr)
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EP1449408B1 (en
EP1449408A1 (en
Inventor
Simon BLÜMEL
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Ams Osram International GmbH
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Osram Opto Semiconductors GmbH
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Priority claimed from DE10242365.2A external-priority patent/DE10242365B4/en
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/40—Details of LED load circuits
    • H05B45/44—Details of LED load circuits with an active control inside an LED matrix
    • H05B45/46—Details of LED load circuits with an active control inside an LED matrix having LEDs disposed in parallel lines
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
    • H05B45/52—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits in a parallel array of LEDs
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
    • H05B45/54—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits in a series array of LEDs
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S362/00—Illumination
    • Y10S362/80—Light emitting diode

Definitions

  • the present invention relates to a circuit arrangement for an LED array, in particular for a light-signaling device, with two or more parallel-connected LED chains, in each of which at least one LED (light emitting diode, light emitting diode) is arranged, wherein at two or more LEDs are connected in series.
  • the anode sides of the LED chains can each be connected to the positive pole of a supply voltage, the cathode sides can be coupled to the negative pole of the supply voltage.
  • a circuit arrangement for a light-emitting diode display with 7-segment elements, in which a compensation circuit is arranged parallel to the 7-segment elements, is off DE 3030058 known. Furthermore, in US 5,939,839 a circuit with a self-regulating power supply for a lighting element described.
  • a variation of the forward voltage of LEDs can on the one hand be production-related.
  • a fine grouping of the LEDs with respect to the Duchlassbeginn is conceivable. This is associated with relatively high costs, as appropriate logistics and warehousing is required.
  • the forward voltage of a LED is temperature-dependent, whereby in turn different temperature dependencies can occur between individual LEDs. A temperature change can therefore lead to a change in the forward voltages.
  • an electrical resistance is connected in series with each LED chain. Overall, this resistance leads to a flatter UI characteristic of the relevant LED chain, so that a certain limitation of the current in the LED chain is achieved.
  • the size of this resistor and thus the voltage dropping therefrom whereby the efficiency of the overall system is deteriorated.
  • a change in the forward voltage of an LED chain can also be caused by the failure of individual LEDs, for example by shorting an LED. This results in a current setting by means of series-connected resistors to a strong redistribution of the currents in the LED chains.
  • the present invention has for its object to provide a circuit arrangement for an LED array of the type mentioned, in which a predetermined distribution of the currents to the individual LED chains as possible, even with different forward voltages or a change in the forward voltages in the individual LED chains largely upright will hold. In particular, even with a short circuit of an LED or the interruption of an LED chain, the predetermined current distribution should remain as unchanged as possible.
  • a circuit arrangement for an LED array two or more parallel LED chains, in each of which at least one LED is arranged, wherein two or more LEDs are connected in series and wherein the anode sides of the LED chains each at the positive pole a supply voltage and the cathode sides are each coupled to the negative pole of the supply voltage provided, wherein in each case a control arrangement for controlling a predetermined current distribution is connected to the individual LED chains in series with each LED chain.
  • control arrangements each comprise a current amplification device for impressing the current into the respective LED chain.
  • the control arrangements each contain a preferably bipolar transistor and an emitter resistor.
  • the current amplifying circuits each have a control input for controlling the current in the associated LED string, the control inputs being connected together, and the current in the associated LED string being adjusted by means of the emitter resistor connected in series with the current amplifier circuit.
  • the collector terminal of the transistor is in each case connected to the cathode side of the associated LED chain, and its emitter terminal can be connected via the emitter resistor to the negative pole of the supply voltage.
  • the base terminals of the transistors are connected together.
  • a drive circuit supplies the base terminals of the transistors with a predetermined current.
  • a series circuit of a diode and a resistor is provided in each case, which is arranged between the respective collector terminal and the respective base terminal of the transistor of the respective control arrangement.
  • the collector terminal of the transistor is connected in each case to the anode side of the associated LED chain and its emitter terminal can be connected via the emitter resistor to the positive pole of the supply voltage, the base terminals of the transistors being connected to one another.
  • LEDs in the invention are to be understood as light emitting diodes of any type, in particular in the form of LED components.
  • a control arrangement in each case a combination of a transistor provided with an emitter resistor, wherein the collector-emitter path or the emitter resistor is connected in series with the - respective LED chain.
  • the base terminals of the transistors which represent the above control inputs, connected to each other and are in operation at the same potential.
  • the emitter resistor is used in particular for adjusting the current distribution to the LED chains.
  • the value of the emitter resistors is in each case inversely proportional to the corresponding emitter current which approximately corresponds to the collector current or the current in the associated LED chain (with the exception of broken LED chains, as will be explained in more detail below).
  • a drive circuit applies a predetermined current to the base terminals of the transistors.
  • separate drive circuits are provided for the individual LED chains.
  • the drive circuit for supplying the base terminals of the transistors with a predetermined current is formed as a series circuit of a diode and a resistor respectively connecting collector and base terminals of the transistors.
  • the diodes ensure that the operating conditions for the transistors are fulfilled and, on the other hand, prevent a redistribution of the currents in the LED chains via the common connection of the base terminals.
  • a change in the forward voltage of an LED chain for example, by a change in temperature or by can be caused by the short circuit of an LED is intercepted by means of the drive circuit by a corresponding change in the associated collector-base voltage, so that the collector current and thus the current in the relevant LED chain does not change or only to a small extent.
  • the forward voltage of the LED chain decreases. This is compensated by means of the associated control arrangement in that the collector-base voltage increases at the associated transistor. Since only the respective base current of the transistors flows through the resistors of the drive circuit, which is typically smaller by a factor of 100 to 250 than the collector current, the resistors can each be dimensioned so that even with a small change in the current through the resistor sufficient high voltage to compensate for the different forward voltages in the individual LED chains at the resistor drops.
  • the fault situation that is opposite to a short circuit of an LED is a failure of an LED that interrupts the LED chain. This can be caused for example by an overload of the LED, so that the LED "burns through”.
  • the voltage between the collector and base of the associated transistor breaks down.
  • the base of the defective-chain transistor is still at the same potential due to the common electrical connection of the transistor base terminals.
  • the transistor of the defective LED chain is thus operated as a diode, wherein the compensation currents required for this flow over the intact LED chains and the connection of the Tranistorbasisan realise.
  • the predetermined by the dimensioning of the emitter resistors current distribution is maintained for the remaining intact LED chains, the currents in the intact LED chains are approximately equal to the respective emitter currents and in turn in each case inversely proportional to the corresponding emitter resistors.
  • the intended current distribution is kept constant even with extreme changes in the forward voltages.
  • the collector currents or the currents in the LED chains typically only fluctuate by a few mA.
  • neither an interruption of an LED chain nor a short circuit in an LED chain leads to the breakdown of the current distribution.
  • a costly grouping of the LED components according to forward voltages is not required.
  • the values of the resistors in the drive circuit in the first embodiment of the invention range between 100 ohms and 1000 ohms. This can be generated by relatively small currents sufficiently high compensation voltages to compensate for different forward voltages of the LED chains.
  • the described embodiment represents an energetically advantageous overall system, especially with longer LED chains.
  • the LED array can be flexibly designed, it being possible to set a predetermined current for each LED chain, in particular without any particular effort. In general, a uniform current distribution will be desired, which is readily feasible by the same emitter resistors.
  • circuit diagram is a plurality of LEDs 2 connected in series to LED chains. Shown are three chains LK1, LK2, LK3, each with four LEDs 2, wherein a circuit arrangement according to the invention may of course also comprise a different number of LEDs in the LED chains or a different number of LED chains. This is illustrated by the dashed lines in the supply voltage lines (see below), the connection of the transistor base connections (see below) and the LED chains. Furthermore, the number and / or the type of LEDs in the individual LED chains can vary from chain to chain.
  • a melting resistor Fu1, Fu2, Fu3 can be connected in series with the LED chains LK1, LK2, LK3.
  • the LED chains LK1, LK2, LK3 are connected on the anode side respectively to the positive pole of a supply voltage U V and on the cathode side in each case to a regulation arrangement RA1, RA2, RA3.
  • the control arrangements RA1, RA2, RA3 each include an NPN transistor T1, T2, T3, whose collector terminal C1, C2, C3 respectively with the cathode side of the associated LED chain LK1, LK2, LK3 or with the optionally interposed melt resistance Fu1, Fu2, Fu3 is connected.
  • the emitter terminal E1, E2, E3 is connected in each case via an emitter resistor R12, R22, R32 to the negative pole of a supply voltage U V.
  • the transistors T1, T2, T3 are designed in the illustrated arrangement as commercial npn transistors. Between the cathode side or the melting resistance of each LED chain and the respective base terminal B1, B2, B3 of the associated transistor T1, T2, T3 is in each case a drive circuit in the form of a series circuit of a diode D1, D2, D3 and an electrical resistor R11, R21, R31 switched.
  • the base terminals B1, B2, B3 of the transistors T1, T2, T3 are connected together.
  • the following description also applies generally to an LED array with N LED strings, where x is between 1 and N.
  • the current Ix which - apart from the respective much lower base current corresponds to the current in the respective LED chain LKx, is regulated so that at the base-emitter path of the associated transistor Tx a voltage of about 0.65 V occurs.
  • the current is adjusted via the transistors T1, T2, T3 so that the voltage dropping across the emitter resistors is approximately 0, 65 V is below the common base potential. Since the voltage between the base and emitter of 0.65V in the transistors T1, T2, T3 is (almost) the same, must to drop at the respective emitter resistors R12, R22, R32, the same voltages.
  • the currents I1, I2, I3 in the LED chains are thus controlled so that the voltages U12, U22, U32 are equal. Overall, this determines the distribution of the currents on the LED chains through the emitter resistors R12, R22, R32, the ratio of the currents being equal to the ratio of the reciprocal emitter resistance values.
  • each of the emitter current which is composed of the associated base and collector current, equated with the collector current, thus neglecting the significantly lower base current compared.
  • all emitter resistors R12, R22, R32 must have the same resistance value.
  • a different energization of the different chains can be realized without special effort by different values for the emitter resistors R12, R22, R32.
  • the energization of the LED chains can be advantageously adapted as required, without further, possibly more complex changes of the circuit are required.
  • a change in the forward voltage of an LED string LKx e.g. by shorting an LED, is intercepted by a corresponding change in the associated collector-base voltage.
  • the setting of the emitter current Ix explained above and thus of the current in the LED chain LKx remains virtually unaffected, so that the collector current or the current in the LED chain does not change or changes only slightly.
  • the power supply of the base inputs B1, B2, B3 of the transistors T1, T2, T3 is in each case by means of a drive circuit in the form of a series circuit of a Diode D1, D2, D3 and a resistor R11, R21, R31 realized.
  • the diodes D1, D2, D3 here have a dual function: On the one hand, they set the operating condition of the transistors T1, T2, T3, i. On the other hand, they suppress cross-currents between the individual LED chains LK1, LK2, LK3, on the other hand they suppress the required voltage at the respective collector-base path Cx-Bx. The latter causes that over the common electrical connection of the transistor bases B1, B2, B3 no current, for example, due to potential differences in the individual LED chains LK1, LK2, LK3, which may be caused because of different forward voltages or a short-circuited LED, from a LED chain can flow into another LED chain.
  • the diodes D1, D2, D3 are dimensioned so that a voltage drops across them, which is sufficient for a stable operating state of the transistors T1, T2, T3.
  • LEDs could also be used here, which can additionally serve as an optical indicator for different forward voltages in the individual chains.
  • resistors R11, R21, R31 Via the electrical resistors R11, R21, R31 flows the base current of the transistors T1, T2, T3, which is typically smaller by a factor of 100 to 250 than the collector current.
  • These resistors R11, R21, R31 are preferably dimensioned so that even a very small change in the base current through the resistor Rx1, for example in the range below 1 mA, causes a sufficiently large change in the voltage across the resistor Rx1, whereby different forward voltages or a change the forward voltages of the individual LED chains LK1, LK2, LK3 are compensated.
  • the resistors R11, R21, R31 preferably have values in the range of 100 ohms to 1000 ohms.
  • the compensation currents for maintaining the voltage at the emitter resistor of the interrupted LED chain also flow via the drive circuits of the remaining chains.
  • the resistors R11, R21, R31 must not necessarily have the same value in principle. For optimum reliability and symmetry of the arrangement, equal resistance values are advantageous.
  • a fuse Fux is connected in series with an LED chain LKx, which additionally prevents excessive current in an LED chain.
  • the fuse will burn and thus switch off the LED string in a defined manner. This will interrupt the LED chain.
  • the fuses Fu1, Fu2, Fu3 can be designed, for example, as a melt resistance. In this case, commercially available melt resistors can be used, which burn out from a defined power and thus permanently interrupt the flow of current.
  • Another advantage of the described embodiment of the invention or of in FIG. 1 illustrated embodiment is that at each LED chain LKx a partial flow is diverted to the scheme. This increases the reliability and stability of the system.
  • the tolerance of the base currents is 2%, so that overall a comparatively high precision of the current distribution is achieved.
  • circuit arrangement according to FIG. 1 Expandable by any number of LED chains in the manner shown.
  • circuit can be constructed in an analogous manner with pnp transistors.
  • a corresponding second embodiment of the invention is in FIG. 2 shown.
  • FIG. 3 A and B shown third embodiment of the invention shows an LED array in a size that is used for example in signaling technology.
  • Corresponding circuits can be used for example for traffic signals such as traffic lights or warning lights or for railway signals.
  • the circuit essentially corresponds FIG. 2 , In contrast, a total of 120 LEDs 2 are connected in parallel in 20 LED chains LK1, ..., LK20 with 6 LEDs each.
  • the currents in the LED chains of the LED array are additionally controlled by a monitoring circuit 4 which is not described in more detail here.
  • the described embodiment of the invention is characterized by a special stability, since in general all LED chains contribute to the current for the regulation. Furthermore, this embodiment has an advantageously high overall efficiency.

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  • Led Devices (AREA)
  • Circuit Arrangement For Electric Light Sources In General (AREA)

Abstract

The invention relates to a circuit for an LED array, comprising at least two parallel LED chains (LK1, LK2, LK3), in which at least one LED (2) is respectively arranged, at least two LEDs (2) being mounted in series. The anode side of the LED chains (LK1, LK2, LK3) can be respectively coupled to the plus pole of a supply voltage (UV) and the cathode side can be respectively coupled to the minus pole of the supply voltage (UV). A regulating device (RA1, RA2, RA3), used to regulate a provided current distribution between the individual LED chains, is respectively mounted in series with each LED chain (LK1, LK2, LK3).

Description

Die vorliegende Erfindung bezieht sich auf eine Schaltungsanordnung für ein LED-Array, insbesondere für eine Lichtsignaleinrichtung, mit zwei oder mehr parallel geschalteten LED-Ketten, in denen jeweils mindestens eine LED (light emitting diode, Lichtemissiondiode) angeordnet ist, wobei bei zwei oder mehr LEDs diese in Serie geschaltet sind. Die Anodenseiten der LED-Ketten sind jeweils an dem Pluspol einer Versorgungsspannung, die Kathodenseiten jeweils an dem Minuspol der Versorgungsspannung ankoppelbar.The present invention relates to a circuit arrangement for an LED array, in particular for a light-signaling device, with two or more parallel-connected LED chains, in each of which at least one LED (light emitting diode, light emitting diode) is arranged, wherein at two or more LEDs are connected in series. The anode sides of the LED chains can each be connected to the positive pole of a supply voltage, the cathode sides can be coupled to the negative pole of the supply voltage.

Bei derartigen LED-Arrays können aufgrund der steilen U-I-Kennlinie von LEDs bereits kleine Änderungen der Durchlassspannung eine große Stromänderung bewirken und so zu einer erheblichen Abweichung der Stromstärke in den einzelnen LED-Ketten des LED-Arrays von einer vorgegebenen Sollstromstärke führen.With LED arrays of this type, due to the steep U-I characteristic curve of LEDs, even small changes in the forward voltage can cause a large current change and thus lead to a considerable deviation of the current intensity in the individual LED strings of the LED array from a predetermined desired current intensity.

Eine Schaltungsanordnung für eine Leuchtdiodenanzeige mit 7-Segment-Elementen, bei der parallel zu den 7-Segment-Elementen eine Ausgleichsschaltung angeordnet ist, ist aus DE 3030058 bekannt. Weiterhin ist in US 5,939,839 eine Schaltung mit einer selbstregulierenden Stromversorgung für ein Beleuchtungselement beschrieben.A circuit arrangement for a light-emitting diode display with 7-segment elements, in which a compensation circuit is arranged parallel to the 7-segment elements, is off DE 3030058 known. Furthermore, in US 5,939,839 a circuit with a self-regulating power supply for a lighting element described.

Eine Variation der Durchlassspannung von LEDs kann einerseits fertigungsbedingt sein. Zur Lösung des oben geschilderten Problems ist eine feine Gruppierung der LEDs hinsichtlich der Duchlassspannung denkbar. Dies ist mit vergleichsweise hohen Kosten verbunden, da eine entsprechende Logistik und Lagerhaltung erforderlich ist.A variation of the forward voltage of LEDs can on the one hand be production-related. To solve the problem described above, a fine grouping of the LEDs with respect to the Duchlassspannung is conceivable. This is associated with relatively high costs, as appropriate logistics and warehousing is required.

Andererseits ist die Durchlassspannung einer LED temperaturabhängig, wobei zwischen einzelnen LEDs wiederum unterschiedliche Temperaturabhängigkeiten auftreten können.
Eine Temperaturänderung kann daher zu einer Änderung der Durchlassspannungen führen. Um einer damit verbundenen Änderung der Stromstärke in den LED-Ketten entgegenzuwirken, ist bei herkömmlichen Schaltungen beispielsweise zu jeder LED-Kette ein elektrischer Widerstand in Serie geschaltet. Dieser Widerstand führt insgesamt zu einer flacheren U-I-Kennlinie der betreffenden LED-Kette, so dass eine gewisse Limitierung des Stroms in der LED-Kette erreicht wird. Mit steigenden Genauigkeitsanforderungen bei der Einhaltung einer vorgegebenen Stromverteilung auf die einzelnen LED-Ketten wächst allerdings die Größe dieses Widerstands und damit die daran abfallende Spannung, wodurch der Wirkungsgrad des Gesamtsystems verschlechtert wird.On the other hand, the forward voltage of a LED is temperature-dependent, whereby in turn different temperature dependencies can occur between individual LEDs.
A temperature change can therefore lead to a change in the forward voltages. In order to counteract an associated change in the current intensity in the LED chains, in conventional circuits, for example, an electrical resistance is connected in series with each LED chain. Overall, this resistance leads to a flatter UI characteristic of the relevant LED chain, so that a certain limitation of the current in the LED chain is achieved. With increasing accuracy requirements in the maintenance of a given power distribution to the individual LED chains, however, the size of this resistor and thus the voltage dropping therefrom, whereby the efficiency of the overall system is deteriorated.

Weiterhin kann eine Veränderung der Durchlassspannung einer LED-Kette auch durch den Ausfall einzelner LEDs, beispielsweise durch Kurzschluss einer LED, hervorgerufen werden. Dies führt bei einer Stromeinstellung mittels seriell geschalteter Widerstände zu einer starken Umverteilung der Ströme in den LED-Ketten.Furthermore, a change in the forward voltage of an LED chain can also be caused by the failure of individual LEDs, for example by shorting an LED. This results in a current setting by means of series-connected resistors to a strong redistribution of the currents in the LED chains.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, eine Schaltungsanordnung für ein LED-Array der genannten Art zu schaffen, bei der eine vorgegebene Verteilung der Ströme auf die einzelnen LED-Ketten auch bei unterschiedlichen Durchlassspannungen oder einer Veränderung der Durchlassspannungen in den einzelnen LED-Ketten möglichst weitgehend aufrechter halten wird. Insbesondere soll auch bei einem Kurzschluss einer LED oder der Unterbrechung einer LED-Kette die vorgegebene Stromverteilung möglichst unverändert bleiben.The present invention has for its object to provide a circuit arrangement for an LED array of the type mentioned, in which a predetermined distribution of the currents to the individual LED chains as possible, even with different forward voltages or a change in the forward voltages in the individual LED chains largely upright will hold. In particular, even with a short circuit of an LED or the interruption of an LED chain, the predetermined current distribution should remain as unchanged as possible.

Diese Aufgabe wird durch eine Schaltungsanordnung gemäß Patentanspruch 1 gelöst. Vorteilhafte Weiterbildungen der Erfindung sind Gegenstand des abhängigen Ansprüche.This object is achieved by a circuit arrangement according to claim 1. Advantageous developments of the invention are the subject of the dependent claims.

Erfindungsgemäß sind bei einer Schaltungsanordnung für ein LED-Array zwei oder mehr parallel geschalteten LED-Ketten, in denen jeweils mindestens eine LED angeordnet ist, wobei bei zwei oder mehr LEDs diese seriell geschaltet sind und wobei die Anodenseiten der LED-Ketten jeweils an dem Pluspol einer Versorgungsspannung und die Kathodenseiten jeweils an dem Minuspol der Versorgungsspannung ankoppelbar sind, vorgesehen, wobei zu jeder LED-Kette jeweils eine Regelungsanordnung zur Regelung einer vorgegebenen Stromverteilung auf die einzelnen LED-Ketten in Serie geschaltet ist.According to the invention, in a circuit arrangement for an LED array, two or more parallel LED chains, in each of which at least one LED is arranged, wherein two or more LEDs are connected in series and wherein the anode sides of the LED chains each at the positive pole a supply voltage and the cathode sides are each coupled to the negative pole of the supply voltage provided, wherein in each case a control arrangement for controlling a predetermined current distribution is connected to the individual LED chains in series with each LED chain.

Hierbei umfassen dabei die Regelungsanordnungen jeweils eine Stromverstärkungsachaltung zur Einprägung des Stroms in die jeweilige LED-Kette.In this case, the control arrangements each comprise a current amplification device for impressing the current into the respective LED chain.

Die Regelungsanordnungen enthalten jeweils einen vorzugsweise bipolaren Transistor und einen Emitterwiderstand. Die Stromverstärkungsschaltungen weisen jeweils einen Regelungseingang zur Regelung des Stroms in der zugehörigen LED-Kette auf, wobei die Regelungseingänge miteinander verbunden sind, und der Strom in der zugehörigen LED-Kette mittels des zu der Stromverstärkerschaltung in Serie geschalteten Emitterwiderstands eingestellt wird. Der Kollektoranschluss des Transistors ist jeweils mit der Kathodenseite der zugehörigen LED-Kette verbunden, und dessen Emitteranschluss jeweils über den Emitterwiderstand mit dem Minuspol der Versorgungsspannung verbindbar. Die Basisanschlüsse der Transistoren sind miteinander verbunden. Jeweils eine Ansteuerschaltung beaufschlagt die Basisanschlüsse der Transistoren mit einem vorbestimmten Strom. Als Ansteuerschaltung ist jeweils eine Serienschaltung einer Diode und eines Widerstands vorgesehen, die zwischen dem jeweiligen Kollektoranschluss und dem jeweiligen Basisanschluss des Transistors der jeweiligen Regelungsanordnung angeordnet ist.The control arrangements each contain a preferably bipolar transistor and an emitter resistor. The current amplifying circuits each have a control input for controlling the current in the associated LED string, the control inputs being connected together, and the current in the associated LED string being adjusted by means of the emitter resistor connected in series with the current amplifier circuit. The collector terminal of the transistor is in each case connected to the cathode side of the associated LED chain, and its emitter terminal can be connected via the emitter resistor to the negative pole of the supply voltage. The base terminals of the transistors are connected together. In each case, a drive circuit supplies the base terminals of the transistors with a predetermined current. As a drive circuit, a series circuit of a diode and a resistor is provided in each case, which is arranged between the respective collector terminal and the respective base terminal of the transistor of the respective control arrangement.

Alternativ ist der Kollektoranschluss des Transistors jeweils mit der Anodenseite der zugehörigen LED-Kette verbunden und dessen Emitteranschluss ist jeweils über den Emitterwiderstand mit dem Pluspol der Versorgungsspannung verbindbar, wobei die Basisanschlüsse der Transistoren miteinander verbunden sind.Alternatively, the collector terminal of the transistor is connected in each case to the anode side of the associated LED chain and its emitter terminal can be connected via the emitter resistor to the positive pole of the supply voltage, the base terminals of the transistors being connected to one another.

Unter LEDs sind bei der Erfindung Lichtemissionadioden jeder Art, insbesondere in Form von LED-Bauelementen, zu verstehen.LEDs in the invention are to be understood as light emitting diodes of any type, in particular in the form of LED components.

Bei einer bevorzugten Ausgestaltung der Erfindung ist als Regelungsanordnung jeweils eine Kombination eines Transistors mit einem Emitterwiderstand vorgesehen, wobei die Kollektor-Emitter-Strecke bzw. der Emitterwiderstand in Serie zu der - jeweiligen LED-Kette geschaltet ist. Besonderes bevorzugt sind dabei die Basisanschlüsse der Transistoren, die die obengenannten Regelungseingänge darstellen, miteinander verbunden und befinden sich im Betrieb auf gleichem Potential.In a preferred embodiment of the invention is a control arrangement in each case a combination of a transistor provided with an emitter resistor, wherein the collector-emitter path or the emitter resistor is connected in series with the - respective LED chain. Particularly preferred are the base terminals of the transistors, which represent the above control inputs, connected to each other and are in operation at the same potential.

Der Emitterwiderstand dient insbesondere zur Einstellung der stromverteilung auf die LED-Ketten. Dabei ist der Wert der Emitterwiderstände jeweils umgekehrt proportional zum entsprechenden Emitterstrom, der näherungsweise dem Kollektorstrom bzw. dem Strom in der zugehörigen LED-Kette entspricht (ausgenommen unterbrochene LED-Ketten, wie im Folgenden noch genauer erläutert wird).The emitter resistor is used in particular for adjusting the current distribution to the LED chains. The value of the emitter resistors is in each case inversely proportional to the corresponding emitter current which approximately corresponds to the collector current or the current in the associated LED chain (with the exception of broken LED chains, as will be explained in more detail below).

Bei der vorliegenden Erfindung beaufschlagt eine Ansteuerschaltung die Basisanschlüsse der Transistoren mit einem vorbestimmten Strom. Bei einer Ausführungsform der Erfindung sind dabei für die einzelnen LED-Ketten jeweils gesonderte Ansteuerschaltungen vorgesehen.In the present invention, a drive circuit applies a predetermined current to the base terminals of the transistors. In one embodiment of the invention, separate drive circuits are provided for the individual LED chains.

Bei der Erfindung ist die die Basisanschlüsse der Transistoren mit einem vorbestimmten Strom beaufschlagende Ansteuerschaltung jeweils als Serienschaltung aus einer Diode und einem widerstand gebildet, die jeweils Kollektor- und Basisanschluss der Transistoren verbindet. Die Dioden stellen einerseits sicher, dass die Betriebsbedingungen für die Transistoren erfüllt sind und verhindern andererseits eine Umverteilung der Ströme in den LED-Ketten über die gemeinsame Verbindung der Basisanschlüsse.In the present invention, the drive circuit for supplying the base terminals of the transistors with a predetermined current is formed as a series circuit of a diode and a resistor respectively connecting collector and base terminals of the transistors. On the one hand, the diodes ensure that the operating conditions for the transistors are fulfilled and, on the other hand, prevent a redistribution of the currents in the LED chains via the common connection of the base terminals.

Eine Veränderung in der Durchlassspannung einer LED-Kette, die beispielsweise durch eine Temperaturänderung oder durch den Kurzschluss einer LED hervorgerufen sein kann, wird mittels der Ansteuerschaltung durch eine entsprechende Veränderung der zugehörigen Kollektor-Basis-Spannung abgefangen, so dass sich der Kollektorstrom und damit der Strom in der betreffenden LED-Kette nicht bzw. nur in geringem Umfang ändert.A change in the forward voltage of an LED chain, for example, by a change in temperature or by can be caused by the short circuit of an LED is intercepted by means of the drive circuit by a corresponding change in the associated collector-base voltage, so that the collector current and thus the current in the relevant LED chain does not change or only to a small extent.

Fällt beispielsweise in einer LED-Kette eine LED durch Kurzschluss aus, so verringert sich die Durchlassspannung der LED-Kette. Dies wird mittels der zugehörigen Regelungsanordnung dadurch kompensiert, dass sich die Kollektor-Basis-Spannung am zugehörigen Transistor erhöht. Da über die Widerstände der Ansteuerschaltung nur der jeweilige Basisstrom der Transistoren fließt, der etwa typischerweise um einen Faktor 100 bis 250 kleiner als der Kollektorstrom ist, können die Widerstände jeweils so dimensioniert werden, dass schon bei einer geringen Änderung des Stroms durch den Widerstand eine ausreichend hohe Spannung zum Ausgleich der unterschiedlichen Durchlassspannungen in den einzelnen LED-Ketten an dem Widerstand abfällt.If, for example, an LED fails due to a short circuit in an LED chain, the forward voltage of the LED chain decreases. This is compensated by means of the associated control arrangement in that the collector-base voltage increases at the associated transistor. Since only the respective base current of the transistors flows through the resistors of the drive circuit, which is typically smaller by a factor of 100 to 250 than the collector current, the resistors can each be dimensioned so that even with a small change in the current through the resistor sufficient high voltage to compensate for the different forward voltages in the individual LED chains at the resistor drops.

Den zu einem Kurzschluss einer LED entgegengesetzten Fehlerfall stellt ein Ausfall einer LED dar, der die LED-Kette unterbricht. Dies kann beispielsweise durch eine Überlastung der LED verursacht sein, so dass die LED "durchbrennt".The fault situation that is opposite to a short circuit of an LED is a failure of an LED that interrupts the LED chain. This can be caused for example by an overload of the LED, so that the LED "burns through".

In der zugehörigen LED-Kette fließt dann kein Strom mehr, die Spannung zwischen Kollektor und Basis des zugehörigen Transistors bricht zusammen. Die Basis des Transistors der defekten Kette liegt aufgrund der gemeinsamen elektrischen Verbindung der Transistorbasisanschlüsse nach wie vor auf demselben Potential. Der Transistor der defekten LED-Kette wird also als Diode betrieben, wobei die hierfür erforderlichen Ausgleichsströme über die intakten LED-Ketten und die Verbindung der Tranistorbasisanschlüsse fließen. Die durch die Dimensionierung der Emitterwiderstände vorgegebene Stromverteilung bleibt für die übrigen intakten LED-Ketten erhalten, wobei die Ströme in den intakten LED-Ketten annähernd gleich den jeweiligen Emitterströmen und wiederum jeweils umgekehrt proportional zu den entsprechenden Emitterwiderständen sind.In the associated LED chain then no more current flows, the voltage between the collector and base of the associated transistor breaks down. The base of the defective-chain transistor is still at the same potential due to the common electrical connection of the transistor base terminals. The transistor of the defective LED chain is thus operated as a diode, wherein the compensation currents required for this flow over the intact LED chains and the connection of the Tranistorbasisanschlüsse. The predetermined by the dimensioning of the emitter resistors current distribution is maintained for the remaining intact LED chains, the currents in the intact LED chains are approximately equal to the respective emitter currents and in turn in each case inversely proportional to the corresponding emitter resistors.

In entsprechender Weise werden auch alle weiteren Betriebs- bzw. Fehler-Zustände bezüglich der Durchlassspannungen der LED-Ketten zwischen den Extremfällen eines Kurzschlusses und einer Unterbrechung einer LED bzw. LED-Kette kompensiert, so dass die Stromverteilung in den LED-Ketten (abgesehen von einer unterbrochenen LED-Kette) weitgehend aufrechterhalten wird.In a corresponding manner, all further operating or fault states with respect to the forward voltages of the LED chains between the extreme cases of a short circuit and an interruption of an LED or LED chain are compensated, so that the current distribution in the LED chains (apart from a broken LED chain) is largely maintained.

Insbesondere wird bei der erfindungsgemäßen Schaltungsanordnung die vorgesehene Stromverteilung auch bei extremen Änderungen der Durchlassspannungen konstant gehalten. Die Kollektorströme bzw. die Ströme in den LED-Ketten schwanken dabei typischerweise nur noch um wenige mA. Vorteilhafterweise führt weder eine Unterbrechung einer LED-Kette noch ein Kurzschluss in einer LED-Kette zum Zusammenbruch der Stromverteilung. Eine kostenträchtige Gruppierung der LED-Bauelemente nach Durchlassspannungen ist nicht erforderlich.In particular, in the circuit arrangement according to the invention, the intended current distribution is kept constant even with extreme changes in the forward voltages. The collector currents or the currents in the LED chains typically only fluctuate by a few mA. Advantageously, neither an interruption of an LED chain nor a short circuit in an LED chain leads to the breakdown of the current distribution. A costly grouping of the LED components according to forward voltages is not required.

Vorzugsweise liegen die Werte der Widerstände in der Ansteuerschaltung bei der ersten Ausführungsform der Erfindung im Bereich zwischen 100 Ohm und 1000 Ohm. Damit können bereits durch relativ kleine Ströme ausreichend hohe Ausgleichsspannungen zur Kompensation unterschiedlicher Durchlassspannungen der LED-Ketten erzeugt werden.Preferably, the values of the resistors in the drive circuit in the first embodiment of the invention range between 100 ohms and 1000 ohms. This can be generated by relatively small currents sufficiently high compensation voltages to compensate for different forward voltages of the LED chains.

Die beschriebene Ausführungsform stellt vor allem bei längeren LED-Ketten ein energetisch vorteilhaftes Gesamtsystem dar.The described embodiment represents an energetically advantageous overall system, especially with longer LED chains.

Weiterhin ist es vorteilhaft, eine seriell zu den LED-Ketten geschaltete Sicherung, zum Beispiel einen Schmelzwiderstand, vorzusehen. Auf diese Weise werden einzelne fehlerhafte LED-Ketten bei zu hohem Strom in der LED-Kette definiert abgeschaltet. Wie oben beschrieben wird auch bei der damit einhergehenden Unterbrechung einer LED-Kette die vorgegebene Stromverteilung in den verbleibenden LED-Ketten aufrechterhalten.Furthermore, it is advantageous to provide a fuse connected in series with the LED chains, for example a melting resistor. In this way, individual faulty LED chains are shut down when the current in the LED string is too high. As described above, the predetermined current distribution in the remaining LED chains is maintained even with the associated interruption of an LED chain.

Da die Ströme in den LED-Ketten umgekehrt proportional zu den jeweiligen Emitterwiderständen sind, ist das LED-Array flexibel ausgestaltbar, wobei insbesondere ohne besonderen Aufwand für jede LED-Kette ein vorgegebener Strom eingestellt werden kann. In der Regel wird eine gleichmäßige Stromverteilung gewünscht sein, was durch gleiche Emitterwiderstände ohne weiteres realisierbar ist.Since the currents in the LED chains are inversely proportional to the respective emitter resistors, the LED array can be flexibly designed, it being possible to set a predetermined current for each LED chain, in particular without any particular effort. In general, a uniform current distribution will be desired, which is readily feasible by the same emitter resistors.

Weitere Vorteile, Weiterbildungen und Ausführungsformen der Erfindung, insbesondere für eine Lichtsignaleinrichtung, ergeben sich aus den im Folgenden unter Bezugnahme auf die Figuren erläuterten Ausführungsbeispielen.Further advantages, developments and embodiments of the invention, in particular for a light-signaling device, emerge from the exemplary embodiments explained below with reference to the figures.

Es zeigen:

Figur 1
einen schematischen Schaltplan eines ersten Ausführungsbeispiels der Erfindung,
Figur 2
einen schematischen Schaltplan eines zweiten Ausführungsbeispiels der Erfindung, und
Figuren 3 A/B
einen schematischen Schaltplan eines dritten Ausführungsbeispiels der Erfindung.
Show it:
FIG. 1
a schematic circuit diagram of a first embodiment of the invention,
FIG. 2
a schematic circuit diagram of a second embodiment of the invention, and
Figures 3 A / B
a schematic circuit diagram of a third embodiment of the invention.

Gleiche oder gleichwirkende Elemente sind in den Figuren mit denselben Bezugszeichen versehen.The same or equivalent elements are provided in the figures with the same reference numerals.

Bei dem in Figur 1 gezeigten Schaltplan ist jeweils eine Mehrzahl von LEDs 2 seriell zu LED-Ketten geschaltet. Dargestellt sind drei Ketten LK1, LK2, LK3 mit je vier LEDs 2, wobei eine erfindungsgemäße Schaltungsanordnung selbstverständlich auch eine andere Anzahl von LEDs in den LED-Ketten oder eine andere Anzahl von LED-Ketten umfassen kann. Dies ist durch die gestrichelten Linien in den Versorgungsspannungsleitungen (s.u.), der Verbindung der Transistorbasisanschlüsse (s.u.) bzw. der LED-Ketten verdeutlicht. Weiterhin kann auch die Anzahl und/oder der Typ der LEDs in den einzelnen LED-Ketten von Kette zu Kette variieren.At the in FIG. 1 shown circuit diagram is a plurality of LEDs 2 connected in series to LED chains. Shown are three chains LK1, LK2, LK3, each with four LEDs 2, wherein a circuit arrangement according to the invention may of course also comprise a different number of LEDs in the LED chains or a different number of LED chains. This is illustrated by the dashed lines in the supply voltage lines (see below), the connection of the transistor base connections (see below) and the LED chains. Furthermore, the number and / or the type of LEDs in the individual LED chains can vary from chain to chain.

Optional kann zu den LED-Ketten LK1, LK2, LK3 ein Schmelzwiderstand Fu1, Fu2, Fu3 in Serie geschaltet sein. Die LED-Ketten LK1, LK2, LK3 sind anodenseitig jeweils mit dem Pluspol einer Versorgungsspannung UV und kathodenseitig jeweils mit einer Regelungsanordnung RA1, RA2, RA3 verbunden.Optionally, a melting resistor Fu1, Fu2, Fu3 can be connected in series with the LED chains LK1, LK2, LK3. The LED chains LK1, LK2, LK3 are connected on the anode side respectively to the positive pole of a supply voltage U V and on the cathode side in each case to a regulation arrangement RA1, RA2, RA3.

Die Regelungsanordnungen RA1, RA2, RA3 umfassen jeweils einen npn-Transistor T1, T2, T3, dessen Kollektoranschluss C1, C2, C3 jeweils mit der Kathodenseite der zugehörigen LED-Kette LK1, LK2, LK3 bzw. mit dem gegebenenfalls dazwischen geschalteten Schmelzwiderstand Fu1, Fu2, Fu3 verbunden ist. Der Emitteranschluss E1, E2, E3 ist jeweils über einen Emitterwiderstand R12, R22, R32 an dem Minuspol einer Versorgungsspannung UV angeschlossen.The control arrangements RA1, RA2, RA3 each include an NPN transistor T1, T2, T3, whose collector terminal C1, C2, C3 respectively with the cathode side of the associated LED chain LK1, LK2, LK3 or with the optionally interposed melt resistance Fu1, Fu2, Fu3 is connected. The emitter terminal E1, E2, E3 is connected in each case via an emitter resistor R12, R22, R32 to the negative pole of a supply voltage U V.

Die Transistoren T1, T2, T3 sind in der dargestellten Anordnung als handelsübliche npn-Transistoren ausgeführt. Zwischen der Kathodenseite bzw. dem Schmelzwiderstand jeder LED-Kette und dem jeweiligen Basisanschluss B1, B2, B3 des zugehörigen Transistors T1, T2, T3 ist jeweils eine Ansteuerschaltung in Form einer Serienschaltung aus einer Diode D1, D2, D3 und einem elektrischen Widerstand R11, R21, R31 geschaltet.The transistors T1, T2, T3 are designed in the illustrated arrangement as commercial npn transistors. Between the cathode side or the melting resistance of each LED chain and the respective base terminal B1, B2, B3 of the associated transistor T1, T2, T3 is in each case a drive circuit in the form of a series circuit of a diode D1, D2, D3 and an electrical resistor R11, R21, R31 switched.

Die Basisanschlüsse B1, B2, B3 der Transistoren T1, T2, T3 sind miteinander verbunden.The base terminals B1, B2, B3 of the transistors T1, T2, T3 are connected together.

Im Betrieb fällt an den Widerständen Rx2 bei einer Bestromung mit der Stromstärke Ix eine Spannung Ux2=Rx2*Ix ab. Der Laufindex x bezeichnet hier und im Folgenden die Nummer der LED-Kette. Im gezeigten Beispiel gilt also für die linke LED-Kette x=1, für die mittlere x=2 und für rechte LED-Kette LK3 x=3. Die folgende Beschreibung gilt auch allgemein für ein LED-Array mit N LED-Ketten, wobei dann x zwischen 1 und N liegt.During operation, a voltage Ux2 = Rx2 * Ix drops across the resistors Rx2 during current application with the current intensity Ix. The running index x designates here and below the number of the LED chain. In the example shown, therefore, x = 1 applies to the left LED chain, x = 2 for the middle LED chain, and LK3 x = 3 for the right-hand LED chain. The following description also applies generally to an LED array with N LED strings, where x is between 1 and N.

Der Strom Ix, der - abgesehen von dem jeweils sehr viel geringeren Basisstrom dem Strom in der jeweiligen LED-Kette LKx entspricht, wird dabei so geregelt, dass an der Basis-Emitter-Strecke des zugehörigen Transistors Tx eine Spannung von ca. 0,65 V auftritt.The current Ix, which - apart from the respective much lower base current corresponds to the current in the respective LED chain LKx, is regulated so that at the base-emitter path of the associated transistor Tx a voltage of about 0.65 V occurs.

Da die Basiseingänge B1, B2, B3 der Transistoren T1, T2, T3 untereinander elektrisch verbunden sind und auf gleichem Potential liegen, wird über die Transistoren T1, T2, T3 der Strom so eingestellt, dass die an den Emitterwiderständen abfallende Spannung ca. 0,65 V unter dem gemeinsamen Basispotential liegt. Da die Spannung zwischen Basis und Emitter von 0,65V bei den Transistoren T1, T2, T3 (nahezu) gleich ist, müssen dazu an den jeweiligen Emitterwiderständen R12, R22, R32 die gleichen Spannungen abfallen. Die Ströme I1, I2, I3 in den LED-Ketten werden damit so geregelt, dass die Spannungen U12, U22, U32 gleich sind. Insgesamt wird damit die Verteilung der Ströme auf die LED-Ketten durch die Emitterwiderstände R12, R22, R32 festgelegt, wobei das Verhältnis der Ströme gleich dem Verhältnis der reziproken Emitterwiderstandswerte ist.Since the base inputs B1, B2, B3 of the transistors T1, T2, T3 are electrically connected to one another and are at the same potential, the current is adjusted via the transistors T1, T2, T3 so that the voltage dropping across the emitter resistors is approximately 0, 65 V is below the common base potential. Since the voltage between the base and emitter of 0.65V in the transistors T1, T2, T3 is (almost) the same, must to drop at the respective emitter resistors R12, R22, R32, the same voltages. The currents I1, I2, I3 in the LED chains are thus controlled so that the voltages U12, U22, U32 are equal. Overall, this determines the distribution of the currents on the LED chains through the emitter resistors R12, R22, R32, the ratio of the currents being equal to the ratio of the reciprocal emitter resistance values.

Bei dieser Betrachtung wurde jeweils der Emitterstrom, der sich aus dem zugehörigen Basis- und Kollektorstrom zusammensetzt, mit dem Kollektorstrom gleichgesetzt, also der im Vergleich wesentlich geringere Basisstrom vernachlässigt.In this regard, each of the emitter current, which is composed of the associated base and collector current, equated with the collector current, thus neglecting the significantly lower base current compared.

Soll ein Gesamtstrom gleichmäßig auf alle LED-Ketten LK1, LK2, LK3 aufgeteilt werden, so müssen alle Emitterwiderstände R12, R22, R32 denselben Widerstandswert aufweisen. Eine unterschiedlichen Bestromung der verschiedenen Ketten kann ohne besonderen Aufwand durch unterschiedliche Werte für die Emitterwiderstände R12, R22, R32 realisiert werden. Damit kann vorteilhafterweise die Bestromung der LED-Ketten je nach Anforderung angepaßt werden, ohne dass weitere, gegebenenfalls aufwändigere Änderungen der Schaltung erforderlich sind.If a total current is to be equally divided among all LED chains LK1, LK2, LK3, all emitter resistors R12, R22, R32 must have the same resistance value. A different energization of the different chains can be realized without special effort by different values for the emitter resistors R12, R22, R32. Thus, the energization of the LED chains can be advantageously adapted as required, without further, possibly more complex changes of the circuit are required.

Eine Veränderung der Durchlassspannung einer LED-Kette LKx, z.B. durch Kurzschluss einer LED, wird durch eine entsprechende Veränderung der zugehörigen Kollektor-Basis-Spannung abgefangen. Die oben erläuterte Einstellung des Emitterstroms Ix und damit des Stroms in der LED-Kette LKx bleibt hiervon nahezu unberührt, so dass dass sich der Kollektorstrom bzw. der Strom in der LED-Kette nicht oder nur geringfügig ändert.A change in the forward voltage of an LED string LKx, e.g. by shorting an LED, is intercepted by a corresponding change in the associated collector-base voltage. The setting of the emitter current Ix explained above and thus of the current in the LED chain LKx remains virtually unaffected, so that the collector current or the current in the LED chain does not change or changes only slightly.

Wird im Extremfall einer Unterbrechung einer LED-Kette LKx der Strom in der LED-Kette bzw. der Kollektorstrom auf Null reduziert, so wird die Spannung Ux2 am zugehörigen Emitterwiderstand Rx1 durch eine entsprechende Änderung des Basisstroms aufrechterhalten. Dies wird über die gemeinsame elektrische Verbindung der Transistorbasisanschlüsse ermöglicht. Die Näherung, dass der Basisstrom gegenüber dem Kollektorstrom vernachlässigt werden kann, gilt in diesem Ausnahmefall nicht mehr.If, in the extreme case of an interruption of an LED chain LKx, the current in the LED chain or the collector current is reduced to zero, the voltage Ux2 at the associated emitter resistor Rx1 is maintained by a corresponding change in the base current. This is made possible by the common electrical connection of the transistor base terminals. The approximation that the base current can be neglected with respect to the collector current no longer applies in this exceptional case.

Die Stromversorgung der Basiseingänge B1, B2, B3 der Transistoren T1, T2, T3 ist jeweils mittels einer Ansteuerschaltung in Form einer Serienschaltung einer Diode D1, D2, D3 und eines Widerstands R11, R21, R31 realisiert.The power supply of the base inputs B1, B2, B3 of the transistors T1, T2, T3 is in each case by means of a drive circuit in the form of a series circuit of a Diode D1, D2, D3 and a resistor R11, R21, R31 realized.

Den Dioden D1, D2, D3 kommt hierbei eine Doppelfunktion zu: Einerseits stellen sie die Betriebsbedingung der Transistoren T1, T2, T3, d.h. die erforderliche Spannung an der jeweiligen Kollektor-Basis-Strecke Cx-Bx sicher, andererseits unterdrücken sie Querströme zwischen den einzelnen LED-Ketten LK1, LK2, LK3. Letzteres bewirkt, dass über die gemeinsame elektrische Verbindung der Transistorbasen B1, B2, B3 kein Strom, beispielsweise aufgrund von Potentialunterschieden in den einzelnen LED-Ketten LK1, LK2, LK3, die etwa wegen unterschiedlicher Durchlassspannungen oder einer kurzgeschlossener LED verursacht sein können, von einer LED-Kette in eine andere LED-Kette fließen kann.The diodes D1, D2, D3 here have a dual function: On the one hand, they set the operating condition of the transistors T1, T2, T3, i. On the other hand, they suppress cross-currents between the individual LED chains LK1, LK2, LK3, on the other hand they suppress the required voltage at the respective collector-base path Cx-Bx. The latter causes that over the common electrical connection of the transistor bases B1, B2, B3 no current, for example, due to potential differences in the individual LED chains LK1, LK2, LK3, which may be caused because of different forward voltages or a short-circuited LED, from a LED chain can flow into another LED chain.

Die Dioden D1, D2, D3 sind so dimensioniert, dass an ihnen eine Spannung abfällt, die für einen stabilen Betriebszustand der Transistoren T1, T2, T3 ausreicht. Beispielsweise könnten hier auch LEDs zum Einsatz kommen, die zusätzlich als optischer Indikator für unterschiedliche Durchlassspannungen in den einzelnen Ketten dienen können.The diodes D1, D2, D3 are dimensioned so that a voltage drops across them, which is sufficient for a stable operating state of the transistors T1, T2, T3. For example, LEDs could also be used here, which can additionally serve as an optical indicator for different forward voltages in the individual chains.

Über die elektrischen Widerstände R11, R21, R31 fließt der Basisstrom der Transistoren T1, T2, T3, der typischerweise um einem Faktor 100 bis 250 kleiner als der Kollektorstrom ist. Diese Widerstände R11, R21, R31 sind vorzugsweise so dimensioniert, dass bereits eine sehr kleine Veränderung des Basisstroms durch den Widerstand Rx1, beispielsweise im Bereich unter 1 mA, eine ausreichend große Änderung der Spannung an dem Widerstand Rx1 bewirkt, wodurch unterschiedliche Durchlassspannungen oder eine Änderung der Durchlassspannungen bei den einzelnen LED-Ketten LK1, LK2, LK3 ausgeglichen werden. Die Widerstände R11, R21, R31 weisen dazu vorzugsweise Werte im Bereich von 100 Ohm bis 1000 Ohm auf.Via the electrical resistors R11, R21, R31 flows the base current of the transistors T1, T2, T3, which is typically smaller by a factor of 100 to 250 than the collector current. These resistors R11, R21, R31 are preferably dimensioned so that even a very small change in the base current through the resistor Rx1, for example in the range below 1 mA, causes a sufficiently large change in the voltage across the resistor Rx1, whereby different forward voltages or a change the forward voltages of the individual LED chains LK1, LK2, LK3 are compensated. The resistors R11, R21, R31 preferably have values in the range of 100 ohms to 1000 ohms.

Bei der Unterbrechung einer LED-Kette fließen über die Ansteuerschaltungen der verbleibenden Ketten auch die Ausgleichströme zur Aufrechterhaltung der Spannung am Emitterwiderstand der unterbrochenen LED-Kette.When the LED chain is interrupted, the compensation currents for maintaining the voltage at the emitter resistor of the interrupted LED chain also flow via the drive circuits of the remaining chains.

Die Widerstände R11, R21, R31 müssen prinzipiell nicht zwangsläufig denselben Wert aufweisen. Für eine optimale Zuverlässigkeit und die Symmetrie der Anordnung sind gleiche Widerstandswerte vorteilhaft.The resistors R11, R21, R31 must not necessarily have the same value in principle. For optimum reliability and symmetry of the arrangement, equal resistance values are advantageous.

Bei der gezeigten Schaltung ist, insbesondere durch die Emitterwiderstände R12, R22, R32, eine ausreichende Stabilität der Schaltung gegenüber fertigungsbedingten Schwankungen der Stromverstärkungsfaktoren, d.h. dem Verhältnis von Kollektorstrom zu Basisstrom, der Transistoren T1, T2, T3 gewährleistet.In the circuit shown, in particular by the emitter resistors R12, R22, R32, sufficient stability of the circuit to manufacturing variations in current amplification factors, i. the ratio of collector current to base current, the transistors T1, T2, T3 guaranteed.

In einer weiteren Variante, die insbesondere bei erhöhten Sicherheitsanforderungen vorteilhaft ist, ist vorzugsweise jeweils eine Sicherung Fux in Serie zu eine LED-Kette LKx geschaltet, welcher zusätzlich einen zu großen Strom in einer LED-Kette unterbindet. Im Fehlerfall, wenn beispielsweise in einer LED-Kette LKx der doppelte Sollstrom fließt, brennt die Sicherung durch und schaltet so die LED-Kette definiert ab. Damit wird die LED-Kette unterbrochen. Wie bereits beschrieben ist es hierbei von Vorteil, dass bei einer solchen Unterbrechung die Stromverteilung in den noch intakten LED-Ketten aufrechterhalten bleibt. Die Sicherungen Fu1, Fu2, Fu3 können zum Beispiel als Schmelzwiderstand ausgeführt sein. Dabei können handelsübliche Schmelzwiderstände eingesetzt werden, die ab einer definierten Leistung durchbrennen und so dauerhaft den Stromfluss unterbrechen.In a further variant, which is advantageous in particular in the case of increased safety requirements, preferably a fuse Fux is connected in series with an LED chain LKx, which additionally prevents excessive current in an LED chain. In the event of a fault, for example, if twice the setpoint current flows in an LED chain LKx, the fuse will burn and thus switch off the LED string in a defined manner. This will interrupt the LED chain. As already described, it is advantageous in this case that the current distribution in the still intact LED chains is maintained during such an interruption. The fuses Fu1, Fu2, Fu3 can be designed, for example, as a melt resistance. In this case, commercially available melt resistors can be used, which burn out from a defined power and thus permanently interrupt the flow of current.

Ein weiterer Vorteil der beschriebenen Ausführungsform der Erfindung bzw. des in Figur 1 dargestellten Ausführungsbeispiels besteht darin, dass bei jeder LED-Kette LKx ein Teilstrom zur Regelung abgezweigt wird. Dadurch wird die Zuverlässigkeit und Stabilität des Systems erhöht. Bei Verwendung von Emitterwiderständen R12, R22, R32 mit 1% Toleranz beträgt die Toleranz der Basisströme 2%, so dass insgesamt eine vergleichsweise hohe Präzision der Stromverteilung erzielt wird.Another advantage of the described embodiment of the invention or of in FIG. 1 illustrated embodiment is that at each LED chain LKx a partial flow is diverted to the scheme. This increases the reliability and stability of the system. When using emitter resistors R12, R22, R32 with 1% tolerance, the tolerance of the base currents is 2%, so that overall a comparatively high precision of the current distribution is achieved.

Wie bereits erläutert ist die Schaltungsanordnung gemäß Figur 1 um eine beliebige Anzahl an LED-Ketten in der dargestellten Weise erweiterbar.As already explained, the circuit arrangement according to FIG FIG. 1 Expandable by any number of LED chains in the manner shown.

Die in Figur 1 gezeigte Schaltung kann in analoger Weise auch mit pnp-Transistoren aufgebaut werden. Ein entsprechendes zweites Ausführungsbeispiel der Erfindung ist in Figur 2 dargestellt. Hierbei sind die Regelungsanordnungen RA1, RA2, RA3 mit den Transistoren T1, T2, T3, den Emitterwiderständen R12, R22, R32 und den Ansteuerschaltungen aus den Widerständen R11, R21, R31 und den Dioden D1, D2, D3 zwischen den Anodenseiten der LED-Ketten LK1, LK2, LK3 und dem Pluspol der Versorgungsspannung UV angeordnet.In the FIG. 1 shown circuit can be constructed in an analogous manner with pnp transistors. A corresponding second embodiment of the invention is in FIG. 2 shown. Here, the control arrangements RA1, RA2, RA3 with the transistors T1, T2, T3, the emitter resistors R12, R22, R32 and the drive circuits of the resistors R11, R21, R31 and the diodes D1, D2, D3 between the anode sides of the LED Chains LK1, LK2, LK3 and the positive pole of the supply voltage U V arranged.

Das in den Figuren 3 A und B gezeigte dritte Ausführungsbeispiel der Erfindung zeigt ein LED-Array in einer Größe, die beispielsweise in der Signaltechnik eingesetzt wird. Entsprechende Schaltungen können zum Beispiel für Verkehrssignale wie Ampeln oder Warnleuchten oder für Bahnsignale verwendet werden.That in the Figures 3 A and B shown third embodiment of the invention shows an LED array in a size that is used for example in signaling technology. Corresponding circuits can be used for example for traffic signals such as traffic lights or warning lights or for railway signals.

Die Schaltung entspricht im wesentlichen Figur 2. Im Unterschied dazu sind insgesamt 120 LEDs 2 in 20 LED-Ketten LK1,...,LK20 mit je 6 LEDs parallel geschaltet. Die Ströme in den LED-Ketten des LED-Arrays werden zusätzlich durch eine hier nicht näher beschriebene Überwachungsschaltung 4 kontrolliert.The circuit essentially corresponds FIG. 2 , In contrast, a total of 120 LEDs 2 are connected in parallel in 20 LED chains LK1, ..., LK20 with 6 LEDs each. The currents in the LED chains of the LED array are additionally controlled by a monitoring circuit 4 which is not described in more detail here.

Bei Arrays dieser Größe ist es von besonderer Bedeutung, einen möglichst hohen Wirkungsgrad zu erzielen. Die eingangs beschriebene Möglichkeit nach dem Stand der Technik, unterschiedliche Durchlassspannungen der LED-Ketten des Arrays mittels rein ohmscher Serienwiderstände zu kompensieren, würde hier zu einer sehr hohen Verlustleistung und in der Folge zu aufwändigen Kühlmaßnahmen führen.For arrays of this size, it is of particular importance to achieve the highest possible efficiency. The above-described possibility according to the prior art to compensate for different forward voltages of the LED chains of the array by means of purely resistive series resistors would lead here to a very high power loss and as a result to complex cooling measures.

Die beschriebene Ausführungsform der Erfindung zeichnet sich durch eine besondere Stabilität aus, da in der Regel alle LED-Ketten zum Strom für die Regelung beitragen. Weiterhin besitzt-diese Ausführungsform einen vorteilhaft hohen Gesamtwirkungsgrad.The described embodiment of the invention is characterized by a special stability, since in general all LED chains contribute to the current for the regulation. Furthermore, this embodiment has an advantageously high overall efficiency.

Claims (5)

  1. Circuit arrangement for an LED array having two or more parallel-connected LED chains (LK1, LK2, LK3), in each of which at least one LED (2) is arranged and, when there are two or more LEDs (2), the latter are connected in series, in which in each case the anode sides of the LED chains (LK1, LK2, LK3) can be coupled to the positive pole of a supply voltage (Uv) and the cathode sides can be coupled to the negative pole of the supply voltage (Uv), wherein a regulating arrangement (RA1, RA2, RA3) for regulating a predetermined current distribution between the individual LED chains (LK1, LK2, LK3) is in each case connected in series with each LED chain (LK1, LK2, LK3), wherein
    the regulating arrangements (RA1, RA2, RA3) in each case comprise a current amplifying circuit for impressing a current into the LED chains (LK1, LK2, LK3) in accordance with the predetermined current distribution, wherein the regulating arrangements (RA1, RA2, RA3) in each case contain a preferably bipolar transistor (T1, T2, T3) and an emitter resistor (R12, R22, R32), and
    the current amplifying circuits in each case have a regulating input for regulating the current in the associated LED chain, the regulating inputs being connected to one another, and the current in the associated LED chain is set by means of the emitter resistor (R12, R22, R32) connected in series with the current amplifier circuit,
    characterized in that
    the collector terminal (C1, C2, C3) of the transistor (T1, T2, T3) is respectively connected to the cathode side of the associated LED chain (LK1, LK2, LK3), and the emitter terminal (E1, E2, E3) of said transistor can respectively be connected via the emitter resistor (R12, R22, R32) to the negative pole of the supply voltage (Uv), the base terminals (B1, B2, B3) of the transistors (T1, T2, T3) being connected to one another, and a drive circuit applying a predetermined current to the base terminals (B1, B2, B3) of the transistors (T1, T2, T3), and a series circuit formed by a diode (D1, D2, D3) and a resistor (R11, R21, R31) is in each case provided as the drive circuit, said series circuit being arranged between the respective collector terminal (C1, C2, C3) and the respective base terminal (B1, B2, B3) of the transistor (T1, T2, T3) of the respective regulating arrangement (RA1, RA2, RA3).
  2. Circuit arrangement for an LED array having two or more parallel-connected LED chains (LK1, LK2, LK3), in each of which at least one LED (2) is arranged and, when there are two or more LEDs (2), the latter are connected in series, in which in each case the anode sides of the LED chains (LK1, LK2, LK3) can be coupled to the positive pole of a supply voltage (Uv) and the cathode sides can be coupled to the negative pole of the supply voltage (Uv), wherein a regulating arrangement (RA1, RA2, RA3) for regulating a predetermined current distribution between the individual LED chains (LK1, LK2, LK3) is in each case connected in series with each LED chain (LK1, LK2, LK3), wherein
    the regulating arrangements (RA1, RA2, RA3) in each case comprise a current amplifying circuit for impressing a current into the LED chains (LK1, LK2, LK3) in accordance with the predetermined current distribution, wherein the regulating arrangements (RA1, RA2, RA3) in each case contain a preferably bipolar transistor (T1, T2, T3) and an emitter resistor (R12, R22, R32), and
    the current amplifying circuits in each case have a regulating input for regulating the current in the associated LED chain, the regulating inputs being connected to one another, and the current in the associated LED chain is set by means of the emitter resistor (R12, R22, R32) connected in series with the current amplifier circuit,
    characterized in that
    the collector terminal (C1, C2, C3) of the transistor (T1, T2, T3) is respectively connected to the anode side of the associated LED chain (LK1, LK2, LK3), and the emitter terminal (E1, E2, E3) of said transistor can respectively be connected via the emitter resistor (R12, R22, R32) to the positive pole of the supply voltage (Uv), the base terminals (B1, B2, B3) of the transistors (T1, T2, T3) being connected to one another, and a drive circuit applying a predetermined current to the base terminals (B1, B2, B3) of the transistors (T1, T2, T3), and a series circuit formed by a diode (D1, D2, D3) and a resistor (R11, R21, R31) is in each case provided as the drive circuit, said series circuit being arranged between the respective collector terminal (C1, C2, C3) and the respective base terminal (B1, B2, B3) of the transistor (T1, T2, T3) of the respective regulating arrangement (RA1, RA2, RA3).
  3. Circuit arrangement for an LED array according to Claim 1 or 2,
    characterized in that
    the values of the emitter resistors (R12, R22, R32) lie between 1 ohm and 100 ohms and are preferably approximately 10 ohms.
  4. Circuit arrangement for an LED array according to one of Claims 1 to 3,
    characterized in that
    a fuse (Fu1, Fu2, Fu3), preferably a fusible resistor, is in each case connected in series with the LED chains (LK1, LK2, LK3).
  5. Circuit arrangement for an LED array according to one of Claims 1 to 4,
    characterized in that
    the LED array is a light signal device.
EP02803750A 2001-11-26 2002-11-26 Circuit for an led array Expired - Lifetime EP1449408B2 (en)

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DE10157645 2001-11-26
DE10157645 2001-11-26
DE10242365.2A DE10242365B4 (en) 2001-11-26 2002-09-12 Circuit arrangement for a LED array
DE10242365 2002-09-12
PCT/DE2002/004329 WO2003047314A1 (en) 2001-11-26 2002-11-26 Circuit for an led array

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JP2005510891A (en) 2005-04-21
DE50210722D1 (en) 2007-09-27
US20050077838A1 (en) 2005-04-14
EP1449408B1 (en) 2007-08-15
WO2003047314A1 (en) 2003-06-05
US7317287B2 (en) 2008-01-08
CN1596560B (en) 2011-04-06
TWI235349B (en) 2005-07-01
JP4488489B2 (en) 2010-06-23
EP1449408A1 (en) 2004-08-25
CN1596560A (en) 2005-03-16

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