EP3518625A1 - Driver circuit for supplying power to one or more leds - Google Patents

Driver circuit for supplying power to one or more leds Download PDF

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Publication number
EP3518625A1
EP3518625A1 EP19153652.3A EP19153652A EP3518625A1 EP 3518625 A1 EP3518625 A1 EP 3518625A1 EP 19153652 A EP19153652 A EP 19153652A EP 3518625 A1 EP3518625 A1 EP 3518625A1
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EP
European Patent Office
Prior art keywords
current
driver circuit
leds
resistor
values
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Granted
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EP19153652.3A
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German (de)
French (fr)
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EP3518625B1 (en
Inventor
Christoph Hofinger
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Siteco GmbH
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Siteco Beleuchtungstechnik GmbH
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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]
    • H05B45/10—Controlling the intensity of the light
    • H05B45/14—Controlling the intensity of the light using electrical feedback from LEDs or from LED modules
    • 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]
    • H05B45/10—Controlling the intensity of the light
    • 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]
    • H05B45/30—Driver circuits
    • H05B45/37—Converter circuits
    • H05B45/3725—Switched mode power supply [SMPS]
    • 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]
    • H05B45/30—Driver circuits
    • H05B45/37—Converter circuits
    • H05B45/3725—Switched mode power supply [SMPS]
    • H05B45/375—Switched mode power supply [SMPS] using buck topology
    • 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]
    • H05B45/30—Driver circuits
    • H05B45/395—Linear regulators
    • 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
    • H05B45/59—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits for reducing or suppressing flicker or glow effects

Definitions

  • the invention relates to a driver circuit for powering one or more LEDs, in particular a driver circuit, which comprises a control to a current value to achieve a desired dimming of the LEDs.
  • An LED is any semiconductor light source to understand, including organic semiconductor light sources, so-called OLEDs to count.
  • the driver circuit of the type mentioned above are typically realized in two different variants.
  • On the one hand there is a pulse width modulation control in which LED current with pulse width modulated signal on and off.
  • On the other hand there is an analogous method in which the current can be regulated without interruption to a desired value.
  • the pulse width modulation method is not considered to be preferred for general lighting, as it may lead to stroboscopic effects, in particular interference of cameras or interference of barcode scanners. In addition, health effects are feared by the stroboscopic effect.
  • FIG. 1 A typical prior art circuit is in FIG. 1 shown.
  • An LED load which may include one or more LEDs, is controlled by an integrated circuit.
  • the integrated circuit has an input CS, to which a measuring resistor R CS is connected to ground. By measuring resistor R CS flows in the on state, the same current flowing through the LED load. The voltage drop across R CS is in the integrated circuit measured and used to control a desired amperage for the LED load in the integrated circuit.
  • a disadvantage of this type of analog current control is that at low current values, the voltage drop across the measuring resistor can be very small. By currents inevitably occurring in the circuit, e.g. resulting from switching transistors, therefore, at low current values, the evaluation of the voltage drop across the current measuring resistor for the control of the current is unusable. Thus, in such an analog current control results in a minimum lower value up to which the current control can be done reliably. One way to get to even smaller current values would be to increase the value of the current sense resistor. However, this has the consequence that the power loss at the resistor at high currents leads to large losses and even thermal problems can occur.
  • the object of the present invention is therefore to provide a driver circuit for powering LEDs, which covers the widest possible current range for achieving a large dimming range and avoids the disadvantages of pulse width modulation.
  • the object is achieved by a driver circuit for the power supply of one or more LEDs according to claim 1.
  • a special feature of the driver circuit of the present invention is that the current measuring resistor is switched to at least two different values, the lower of the two values for measuring the current through the LEDs in a lower current range and the higher of the two values for measuring the current through the LEDs is applied in a higher current range.
  • the current measuring resistor is adapted to the particular current range to be measured, so that the voltage drop across the current measuring resistor assumes an acceptable value, which can be easily processed by the driver circuit. This makes it possible to measure even small currents.
  • the power converted at the current measuring resistor is limited because a lower measuring resistor is selected in the higher current range. This limits the power loss and the resulting thermal problems.
  • the measuring resistor is formed by at least two resistors connected in parallel, of which at least one of the two resistors can be electronically connected or disconnected.
  • the two resistors which together form the current measuring resistor, connected in parallel to each other in the circuit of the LEDs to earth, wherein in one of the two parallel branches, an electronic switch is provided which can be opened or closed.
  • the current measuring resistor is formed either only by one of the two resistors (when the switch is open) or by both resistors connected in parallel (when the switch is closed).
  • two different values for the current measuring resistor can be realized.
  • It can also be provided in parallel more than two resistors.
  • more than just an electronic switch can be provided. It can also be connected in series with each of the resistors connected in parallel with an electronic switch, in which case at least one of the switches is closed during operation of the LED.
  • the electronic connection and disconnection of the at least one resistor by driving a gate of a field effect transistor, FET whose source and drain is connected in series with the resistor.
  • a FET has a very low resistance in the closed state between source and drain, so that the resistance of the field effect transistor itself is negligible.
  • the internal resistance of the FET is largely thermally stable, so that measurement errors are minimized by a changing internal resistance of the FED.
  • the FET can be controlled with a microcontroller.
  • the microcontroller only has to generate a voltage which is to be applied to the gate in order to open or close the FET between source and drain.
  • a circuit is easier to set up and can also be fully realized as an integrated circuit.
  • the maximum of the lower current range corresponds to the minimum of the higher of the two current ranges.
  • the driver circuit when the current to be measured reaches the limit of the two current ranges, it switches the driver circuit reverses the current sensing resistor to correspondingly decrease or increase the voltage drop across the current sensing resistor.
  • the two current ranges may also partially overlap. This prevents frequent switching operations between the current sense resistors if the current to be measured by the LEDs happens to oscillate exactly in the area between the two current ranges. For example, when the maximum of the lower current range is reached, the measuring resistor can be switched over to the lower value and, conversely, switched to the higher value only when the minimum of the higher current range has been reached. This type of hysteresis prevents frequent switching operations from occurring at low current fluctuations around the border between the current ranges, which could manifest as LED flickering.
  • the current measuring resistor may assume at least two values, the lower value between 0.1 ohms and 0.5 ohms and the higher of the two values between 0.9 ohms and 1.7 ohms.
  • the power loss can be limited to a maximum of 0.5 W.
  • the lower current range may include 20 mA to 200 mA and the higher current range may comprise 200 mA to 1 A. It may also be provided that the current ranges also overlap, as previously described, such that, for example, the lower current range comprises a maximum value of 250 mA, while the higher current range comprises a minimum value of 150 mA.
  • the current measuring resistor can also be more than just two values, e.g. three or four values, for three or four current ranges.
  • FIG. 2 An embodiment of a driving circuit for LEDs according to the present invention is shown in FIG FIG. 2 shown. Similar to a driver circuit of the prior art, which in FIG. 1 is shown, an LED load 3, which may be formed by one or more LEDs (only one LED shown in the figures) via a supply voltage which is provided by an integrated circuit 2, driven.
  • the integrated circuit 2 provides a constant current supply through the LED load 3. A constant current can be adjusted (not shown in the figure) to produce a desired dimming of the LED load.
  • the LED load can be switched on and off by the integrated circuit.
  • a field effect transistor 4 is connected to an output GATE of the integrated circuit 2, which connects the LED load 3 to ground when it is closed.
  • a resistor R CS is provided.
  • a second resistor R CS 2 is provided which is connected in parallel with the first resistor R CS and is also connected to ground via a semiconductor switch, eg a field effect transistor 22.
  • a semiconductor switch eg a field effect transistor 22.
  • the field effect transistor 22 is turned on, that is, a conductive connection between drain and source, the resistor R CS 2 is parallel to the resistor R CS , so that the current sense resistor for the integrated circuit 2 is given in total by the parallel connection of R CS and R CS 2 is.
  • the gate of the field effect transistor 22 is applied to an output of a microcontroller 24 and is controlled by this. Further, the microcontroller 24 provides a control voltage which acts on an input LD of the integrated circuit 2 to adjust the supply current through the LED.
  • the microcontroller 24 also serves to set the current for the desired dimming of the LED load.
  • the microcontroller 24 generates a control voltage corresponding to the desired dimming, which is applied to the input LD of the integrated circuit 2, taking into account the current measuring resistor selected via the range changeover by the microcontroller 24.
  • the integrated circuit 2 sets the current through the LED load.
  • any current can be set between 20 mA and 1 A, for example.
  • the microcontroller applies a voltage to the gate of the semiconductor switch provided by the FET 22, so that a drain-to-source connection is turned on.
  • the resistors R CS and R CS 2 are connected in parallel to ground.
  • the parallel circuit of R CS and R CS 2 acts in this circuit state as a measuring resistor for the current control of the LED load.
  • the integrated circuit 2 measures the voltage drop across the parallel connection of the resistors R CS and R CS 2 to control the current through the LEDs to a constant value.
  • the field effect transistor 22 is triggered via the microcontroller 24 in order to open the connection between drain and source.
  • the supply current flows through the LED load 3 only through the resistor R CS , so that in this circuit state of the measuring resistor for determining the current is given only by the resistor R CS .
  • the current measuring resistor is switched over the microcontroller 24 according to a predetermined current range between two values.
  • the lower current range of the measuring resistor is given only by R CS
  • the resistance R CS and R CS 2 can each be 1.2 ohms, so that in the higher current range from 200 mA to 1 ⁇ A effectively only a current measuring resistor of 0.6 ohms is given.
  • the power converted at the measuring resistor power is reduced at higher currents.
  • the electricity is higher Measuring range, the voltage drop is still sufficiently high to allow precise current measurement.
  • the lower current measuring range of the measuring resistance is increased accordingly, for example to 1.2 ohms, so that even at the lower to be measured supply currents still a sufficiently high voltage drop is given for the measuring resistor.
  • a control voltage is also output, which acts on the integrated circuit 12, to compensate for the current measurement correspond to the selected measuring resistor by the corresponding factor.
  • the present invention is not limited to the illustrated circuit of two resistors R CS and R CS 2. It is also possible to connect more than two resistors in parallel, and it is also possible to provide more than just two current ranges for measuring the current.
  • the remaining circuit for LED power supply corresponds to the embodiment in the prior art.
  • the inventive range switching for the measuring resistor can also be implemented simply with existing integrated circuits known from the prior art for an LED power supply.

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

Abstract

Die Erfindung betrifft eine Treiberschaltung zur Stromversorgung von einer oder mehreren LEDs, umfassend eine regelbare Konstantstromquelle zum Anschluss einer oder mehrerer in Reihe geschalteter LEDs, und einen Strommesswiderstand, der in Reihe mit der einen oder den mehreren LEDs geschaltet ist, wobei die Treiberschaltung dazu eingerichtet ist, über einen Spannungsabfall des Strommesswiderstands den Strom durch die eine oder die mehreren LEDs zu bestimmen, um den Strom auf einen vorgegebenen Wert zu regeln, wobei die Treiberschaltung ferner dazu eingerichtet ist, den Strommesswiderstand auf wenigstens zwei verschiedene Werte zu schalten, wobei auf den niedrigeren der beiden Werte zur Messung des Stroms durch die eine oder die mehreren LEDs in einem höheren Strombereich und auf den niedrigeren der beiden Werte für eine Messung des Stroms durch die einen oder die mehreren LEDs in einem niedrigeren Strombereich geschaltet wird.The invention relates to a driver circuit for the power supply of one or more LEDs, comprising a controllable constant current source for connecting one or more series-connected LEDs, and a current measuring resistor, which is connected in series with the one or more LEDs, wherein the driver circuit is arranged to determine, via a voltage drop of the current sense resistor, the current through the one or more LEDs to control the current to a predetermined value, the driver circuit being further configured to switch the current sense resistor to at least two different values of the two values for measuring the current through the one or more LEDs in a higher current range and to the lower of the two values for a measurement of the current through the one or more LEDs in a lower current range.

Description

Die Erfindung betrifft eine Treiberschaltung zur Stromversorgung einer oder mehrerer LEDs, insbesondere eine Treiberschaltung, die eine Regelung auf einen Stromwert zur Erzielung einer gewünschten Dimmung der LEDs umfasst. Unter einer LED ist jede Halbleiterlichtquelle zu verstehen, worunter auch organische Halbleiterlichtquellen, sogenannte OLEDs, zu zählen sind.The invention relates to a driver circuit for powering one or more LEDs, in particular a driver circuit, which comprises a control to a current value to achieve a desired dimming of the LEDs. An LED is any semiconductor light source to understand, including organic semiconductor light sources, so-called OLEDs to count.

Die Treiberschaltung der eingangs genannten Art werden typischerweise in zwei verschiedenen Varianten realisiert. Zum einen gibt es eine Pulsweitenmodulationsansteuerung bei der LED-Strom mit pulsweitenmoduliertem Signal an- und abgeschaltet wird. Zum anderen gibt es ein analoges Verfahren, bei dem der Strom ohne Unterbrechung auf einen gewünschten Wert geregelt werden kann. Das Pulsweitenmodulationsverfahren wird jedoch für Allgemeinbeleuchtung als nicht bevorzugt angesehen, da es zu Stroboskopeffekten, insbesondere Störungen von Kameras oder Störungen von Barcode-Scannern kommen kann. Außerdem werden auch gesundheitliche Auswirkungen durch den Stroboskopeffekt befürchtet.The driver circuit of the type mentioned above are typically realized in two different variants. On the one hand, there is a pulse width modulation control in which LED current with pulse width modulated signal on and off. On the other hand, there is an analogous method in which the current can be regulated without interruption to a desired value. However, the pulse width modulation method is not considered to be preferred for general lighting, as it may lead to stroboscopic effects, in particular interference of cameras or interference of barcode scanners. In addition, health effects are feared by the stroboscopic effect.

Somit ist die analoge Stromregelung bevorzugt. Eine typische Schaltung nach dem Stand der Technik ist in Figur 1 dargestellt. Eine LED-Last, welche eine oder mehrere LEDs umfassen kann, wird durch eine integrierte Schaltung gesteuert. Die integrierte Schaltung weist einen Eingang CS auf, an welcher ein Messwiderstand RCS zur Erde angeschlossen ist. Durch den Messwiderstand RCS fließt im eingeschalteten Zustand der gleiche Strom, welcher durch die LED-Last fließt. Der Spannungsabfall über RCS wird im integrierten Schaltkreis gemessen und zur Regelung einer gewünschten Stromstärke für die LED-Last im integrierten Schaltkreis verwendet.Thus, the analog current control is preferred. A typical prior art circuit is in FIG. 1 shown. An LED load, which may include one or more LEDs, is controlled by an integrated circuit. The integrated circuit has an input CS, to which a measuring resistor R CS is connected to ground. By measuring resistor R CS flows in the on state, the same current flowing through the LED load. The voltage drop across R CS is in the integrated circuit measured and used to control a desired amperage for the LED load in the integrated circuit.

Ein Nachteil dieser Art der analogen Stromregelung ist jedoch, dass bei kleinen Stromwerten der Spannungsabfall am Messwiderstand sehr klein werden kann. Durch Ströme die sich unweigerlich in der Schaltung, z.B. aus Schalttransistoren ergeben, wird demnach bei kleinen Stromwerten die Auswertung des Spannungsabfalls über dem Strommesswiderstand für die Regelung des Stromes unbrauchbar. Somit ergibt sich bei einer derartigen analogen Stromregelung ein minimaler unterer Wert, bis zu dem die Stromregelung zuverlässig erfolgen kann. Eine Möglichkeit, um zu noch kleineren Stromwerten zu gelangen, wäre es, den Wert des Strommesswiderstandes zu erhöhen. Das hat aber zur Folge, dass die Verlustleistung an dem Widerstand bei höheren Strömen zu großen Verlusten führt und sogar thermische Probleme auftreten können.A disadvantage of this type of analog current control, however, is that at low current values, the voltage drop across the measuring resistor can be very small. By currents inevitably occurring in the circuit, e.g. resulting from switching transistors, therefore, at low current values, the evaluation of the voltage drop across the current measuring resistor for the control of the current is unusable. Thus, in such an analog current control results in a minimum lower value up to which the current control can be done reliably. One way to get to even smaller current values would be to increase the value of the current sense resistor. However, this has the consequence that the power loss at the resistor at high currents leads to large losses and even thermal problems can occur.

Eine Regelung auf niedrige Stromwerte war im Stand der Technik demnach nur durch die Regelung nach dem Pulsweitenmodulationsverfahren möglich. Es wurden auch kombinierte Verfahren angewandt, indem in einem unteren Strombereich das Pulsweitenmodulationsverfahren und einem höheren Strombereich die analoge Stromregelung wie vorhergehend beschrieben angewandt wurde, um einen größeren Dimmbereich für LEDs bereitzustellen. Dies hat jedoch wieder den vorhergehend beschriebenen Nachteil des Stroboskopeffekts bei niedrigen Stromwerten.A regulation to low current values was therefore possible in the prior art only by the control according to the pulse width modulation method. Combined methods have also been used by applying, in a lower current range, the pulse width modulation method and a higher current range analog current control as previously described to provide a larger dimming range for LEDs. However, this again has the previously described disadvantage of the stroboscopic effect at low current values.

Aufgabe der vorliegenden Erfindung ist es daher, eine Treiberschaltung zur Stromversorgung von LEDs bereitzustellen, welche einen möglichst weiten Strombereich zur Erzielung eines großen Dimmbereichs abdeckt und die Nachteile einer Pulsweitenmodulation dabei vermeidet.The object of the present invention is therefore to provide a driver circuit for powering LEDs, which covers the widest possible current range for achieving a large dimming range and avoids the disadvantages of pulse width modulation.

Gelöst wird die Aufgabe durch eine Treiberschaltung zur Stromversorgung von einer oder mehreren LEDs gemäß Anspruch 1.The object is achieved by a driver circuit for the power supply of one or more LEDs according to claim 1.

Eine Besonderheit der Treiberschaltung der vorliegenden Erfindung besteht darin, dass der Strommesswiderstand auf wenigstens zwei verschiedene Werte geschaltet wird, wobei der niedrigere der beiden Werte zur Messung des Stroms durch die LEDs in einem niedrigeren Strombereich und der höhere der beiden Werte zur Messung des Stroms durch die LEDs in einem höheren Strombereich angewandt wird. Dadurch wird der Strommesswiderstand an den jeweils zu messenden Strombereich angepasst, so dass der Spannungsabfall über den Strommesswiderstand einen akzeptablen Wert annimmt, welcher von der Treiberschaltung leicht verarbeitet werden kann. Dadurch ist ein Messen auch von kleinen Strömen möglich. Ferner ist die am Strommesswiderstand umgesetzte Leistung begrenzt, weil im höheren Strombereich ein niedrigerer Messwiderstand ausgewählt wird. Dadurch werden die Verlustleistung und die daraus resultierenden thermischen Probleme begrenzt.A special feature of the driver circuit of the present invention is that the current measuring resistor is switched to at least two different values, the lower of the two values for measuring the current through the LEDs in a lower current range and the higher of the two values for measuring the current through the LEDs is applied in a higher current range. As a result, the current measuring resistor is adapted to the particular current range to be measured, so that the voltage drop across the current measuring resistor assumes an acceptable value, which can be easily processed by the driver circuit. This makes it possible to measure even small currents. Furthermore, the power converted at the current measuring resistor is limited because a lower measuring resistor is selected in the higher current range. This limits the power loss and the resulting thermal problems.

Gemäß einer bevorzugten Ausführungsform ist der Messwiderstand durch wenigstens zwei parallel geschaltete Widerstände gebildet, von denen wenigstens einer der beiden Widerstände elektronisch zu- oder abschaltbar ist. Beispielsweise sind die beiden Widerstände, welche zusammen den Strommesswiderstand bilden, parallel zueinander im Stromkreis der LEDs zur Erde geschaltet, wobei in einem der beiden parallelen Zweige ein elektronischer Schalter vorgesehen ist, der geöffnet oder geschlossen werden kann. Dadurch wird der Strommesswiderstand entweder nur durch einen der beiden Widerstände (wenn der Schalter geöffnet ist) oder durch beide parallel geschaltete Widerstände (wenn der Schalter geschlossen ist) gebildet. Dadurch lassen sich zwei verschiedene Werte für den Strommesswiderstand realisieren. Es können auch mehr als nur zwei Widerstände parallel vorgesehen sein. Ferner können auch mehr als nur ein elektronischer Schalter vorgesehen sein. Es kann auch jeder der parallel geschalteten Widerstände mit einem elektronischen Schalter in Reihe geschaltet sein, wobei in diesem Fall wenigstens einer der Schalter beim Betrieb der LED geschlossen ist.According to a preferred embodiment, the measuring resistor is formed by at least two resistors connected in parallel, of which at least one of the two resistors can be electronically connected or disconnected. For example, the two resistors, which together form the current measuring resistor, connected in parallel to each other in the circuit of the LEDs to earth, wherein in one of the two parallel branches, an electronic switch is provided which can be opened or closed. As a result, the current measuring resistor is formed either only by one of the two resistors (when the switch is open) or by both resistors connected in parallel (when the switch is closed). As a result, two different values for the current measuring resistor can be realized. It can also be provided in parallel more than two resistors. Furthermore, more than just an electronic switch can be provided. It can also be connected in series with each of the resistors connected in parallel with an electronic switch, in which case at least one of the switches is closed during operation of the LED.

Gemäß einer bevorzugten Ausführungsform erfolgt die elektronische Zu- und Abschaltung des wenigstens einen Widerstandes durch Ansteuern eines Gates von einem Feldeffekttransistor, FET, dessen Source und Drain in Reihe zu dem Widerstand geschaltet ist. Ein FET hat im geschlossenen Zustand zwischen Source und Drain einen sehr geringen Widerstand, so dass der Widerstand des Feldeffekttransistors selbst vernachlässigbar ist. Insbesondere ist der Innenwiderstand des FET weitgehend thermisch stabil, so dass Messfehler durch einen sich verändernden Innenwiderstand des FED minimiert werden.According to a preferred embodiment, the electronic connection and disconnection of the at least one resistor by driving a gate of a field effect transistor, FET whose source and drain is connected in series with the resistor. A FET has a very low resistance in the closed state between source and drain, so that the resistance of the field effect transistor itself is negligible. In particular, the internal resistance of the FET is largely thermally stable, so that measurement errors are minimized by a changing internal resistance of the FED.

Gemäß einer bevorzugen Ausführungsform kann der FET mit einem Microcontroller angesteuert werden. Der Microcontroller muss bei dieser Ausführungsform lediglich eine Spannung erzeugen, welche an das Gate anzulegen ist, um den FET zwischen Source und Drain zu öffnen bzw. zu schließen. Im Vergleich zu einem elektronischen Schalter, der durch ein Relais gebildet ist, ist eine solche Schaltung einfacher aufzubauen und lässt sich auch vollständig als integrierte Schaltung realisieren.According to a preferred embodiment, the FET can be controlled with a microcontroller. In this embodiment, the microcontroller only has to generate a voltage which is to be applied to the gate in order to open or close the FET between source and drain. Compared to an electronic switch, which is formed by a relay, such a circuit is easier to set up and can also be fully realized as an integrated circuit.

Gemäß einer bevorzugten Ausführungsform entspricht das Maximum des niedrigeren Strombereichs dem Minimum des höheren der beiden Strombereiche. Wenn in dieser Schaltung der zu messende Strom die Grenze der beiden Strombereiche erreicht, schaltet die Treiberschaltung den Strommesswiderstand um, um den Spannungsabfall an dem Strommesswiderstand entsprechend zu verringern bzw. zu erhöhen.According to a preferred embodiment, the maximum of the lower current range corresponds to the minimum of the higher of the two current ranges. In this circuit, when the current to be measured reaches the limit of the two current ranges, it switches the driver circuit reverses the current sensing resistor to correspondingly decrease or increase the voltage drop across the current sensing resistor.

Gemäß einer alternativen Ausführungsform können die beiden Strombereiche jedoch auch teilweise überlappen. Dadurch werden häufige Schaltvorgänge zwischen den Strommesswiderständen verhindert, falls der zu messende Strom durch die LEDs zufällig genau im Bereich zwischen den beiden Strombereichen pendelt. Beispielsweise kann der Messwiderstand beim Erreichen des Maximum des unteren Strombereichs auf den niedrigeren Wert umgeschaltet werden und umgekehrt erst beim Erreichen des Minimum des höheren Strombereichs wieder auf den höheren Wert geschaltet werden. Durch diese Art Hysterese wird verhindert, dass häufige Schaltvorgänge bei geringen Stromschwankungen um die Grenze zwischen den Strombereichen auftreten, die sich als Flackern der LED bemerkbar machen könnten.However, according to an alternative embodiment, the two current ranges may also partially overlap. This prevents frequent switching operations between the current sense resistors if the current to be measured by the LEDs happens to oscillate exactly in the area between the two current ranges. For example, when the maximum of the lower current range is reached, the measuring resistor can be switched over to the lower value and, conversely, switched to the higher value only when the minimum of the higher current range has been reached. This type of hysteresis prevents frequent switching operations from occurring at low current fluctuations around the border between the current ranges, which could manifest as LED flickering.

Gemäß einer bevorzugten Ausführungsform kann der Strommesswiderstand wenigstens zwei Werte annehmen, wobei der niedrigere Wert zwischen 0,1 Ohm und 0,5 Ohm und der höhere der beiden Werte zwischen 0,9 Ohm und 1,7 Ohm liegt. Bei einem Versorgungsstrom, der typischerweise zwischen 20 mA und 1 A beträgt, und bei einem Strommesswiderstand, der bei etwa 200 mA umgeschaltet wird, kann die Verlustleistung auf maximal 0,5 W begrenzt werden.According to a preferred embodiment, the current measuring resistor may assume at least two values, the lower value between 0.1 ohms and 0.5 ohms and the higher of the two values between 0.9 ohms and 1.7 ohms. With a supply current that is typically between 20 mA and 1 A, and with a current measuring resistor that is switched at about 200 mA, the power loss can be limited to a maximum of 0.5 W.

Gemäß einer bevorzugten Ausführungsform kann der niedrigere Strombereich 20 mA bis 200 mA umfassen und der höhere Strombereich 200 mA bis 1 A umfassen. Es kann auch vorgesehen sein, dass die Strombereiche auch überlappen, wie vorhergehend beschrieben, so dass z.B. der niedrigere Strombereich einen Maximalwert von 250 mA umfasst, während der höhere Strombereich einen Minimalwert von 150 mA umfasst.In a preferred embodiment, the lower current range may include 20 mA to 200 mA and the higher current range may comprise 200 mA to 1 A. It may also be provided that the current ranges also overlap, as previously described, such that, for example, the lower current range comprises a maximum value of 250 mA, while the higher current range comprises a minimum value of 150 mA.

Gemäß einer bevorzugten Ausführungsform kann der Strommesswiderstand auch mehr als nur zwei Werte, z.B. drei oder vier Werte, für drei oder vier Strombereiche annehmen.According to a preferred embodiment, the current measuring resistor can also be more than just two values, e.g. three or four values, for three or four current ranges.

Weitere Vorteile und Merkmale der vorliegenden Erfindung werden aus der nachfolgenden Beschreibung einer bevorzugten Ausführungsform, die in Verbindung mit den Figuren gegeben wird, deutlich. In den Figuren ist Folgendes dargestellt:

Figur 1
zeigt eine LED-Treiberschaltung gemäß dem Stand der Technik.
Figur 2
zeigt eine LED-Treiberschaltung gemäß einer Ausführungsform der vorliegenden Erfindung.
Further advantages and features of the present invention will become apparent from the following description of a preferred embodiment given in conjunction with the figures. The figures show the following:
FIG. 1
shows a LED drive circuit according to the prior art.
FIG. 2
shows an LED driving circuit according to an embodiment of the present invention.

Eine Ausführungsform einer Treiberschaltung für LEDs gemäß der vorliegenden Erfindung ist in Figur 2 dargestellt. Ähnlich wie eine Treiberschaltung aus dem Stand der Technik, die in Figur 1 dargestellt ist, wird eine LED-Last 3, welche durch eine oder mehrere LEDs gebildet sein kann (in den Figuren nur eine LED dargestellt) über eine Versorgungsspannung, die von einem integrierten Schaltkreis 2 bereitgestellt wird, angesteuert. Der integrierte Schaltkreis 2 sorgt für eine Konstantstromversorgung durch die LED-Last 3. Ein Konstantstrom lässt sich einstellen (in der Figur nicht dargestellt), um eine gewünschte Dimmung der LED-Last zu erzeugen. Ferner kann die LED-Last durch die integrierte Schaltung ein- und ausgeschaltet werden. Dazu ist an einem Ausgang GATE des integrierten Schaltkreises 2 ein Feldeffektransistor 4 angeschlossen, der die LED-Last 3 mit Erde verbindet, wenn er geschlossen. In diesem Stromkreis ist ein Widerstand RCS vorgesehen. Durch diesen Widerstand RCS fließt daher der gleiche Strom, welcher auch durch die LED-Last 3 fließt. Der Spannungsabfall über den Widerstand RCS wird an einem Eingang CS der integrierten Schaltung 2 gemessen und dient zur Steuerung des Konstantstroms durch die LED. Soweit ist die Schaltung gemäß der vorliegenden Erfindung auch gleich zu der in Figur 1 dargestellten Schaltung nach dem Stand der Technik.An embodiment of a driving circuit for LEDs according to the present invention is shown in FIG FIG. 2 shown. Similar to a driver circuit of the prior art, which in FIG. 1 is shown, an LED load 3, which may be formed by one or more LEDs (only one LED shown in the figures) via a supply voltage which is provided by an integrated circuit 2, driven. The integrated circuit 2 provides a constant current supply through the LED load 3. A constant current can be adjusted (not shown in the figure) to produce a desired dimming of the LED load. Furthermore, the LED load can be switched on and off by the integrated circuit. For this purpose, a field effect transistor 4 is connected to an output GATE of the integrated circuit 2, which connects the LED load 3 to ground when it is closed. In this circuit, a resistor R CS is provided. Through this resistor R CS therefore flows the same current, which also by the LED load 3 flows. The voltage drop across the resistor R CS is measured at an input CS of the integrated circuit 2 and serves to control the constant current through the LED. As far as the circuit according to the present invention is also equal to the in FIG. 1 illustrated circuit according to the prior art.

In der erfindungsgemäßen Schaltung nach Figur 2 ist zusätzlich ein zweiter Widerstand RCS2 vorgesehen, welcher parallel zu dem ersten Widerstand RCS geschaltet ist und über einen Halbleiterschalter, z.B. einen Feldeffekttransistor 22 ebenfalls mit Masse verbunden ist. Wenn der Feldeffekttransistor 22 durchgeschaltet ist, d.h. eine leitende Verbindung zwischen Drain und Source besteht, liegt der Widerstand RCS2 parallel zum Widerstand RCS, so dass der Strommesswiderstand für die integrierte Schaltung 2 insgesamt durch die Parallelschaltung von RCS und RCS2 gegeben ist. Das Gate des Feldeffekttransistors 22 liegt an einem Ausgang eines Microcontrollers 24 an und wird durch diesen gesteuert. Ferner stellt der Microcontroller 24 eine Steuerspannung bereit, die auf einen Eingang LD der integrierten Schaltung 2 wirkt, um den Versorgungsstrom durch die LED einzustellen. Der Microcontroller 24 dient in dieser Ausführungsform auch dazu, den Strom für die gewünschte Dimmung der LED-Last einzustellen. Der Microcontroller 24 erzeugt eine der gewünschten Dimmung entsprechenden Steuerspannung, die an den Eingang LD der integrierten Schaltung 2 anliegt, wobei der über die Bereichsumschaltung vom Microcontroller 24 ausgewählte Strommesswiderstand berücksichtigt wird.In the circuit according to the invention according to FIG. 2 In addition, a second resistor R CS 2 is provided which is connected in parallel with the first resistor R CS and is also connected to ground via a semiconductor switch, eg a field effect transistor 22. When the field effect transistor 22 is turned on, that is, a conductive connection between drain and source, the resistor R CS 2 is parallel to the resistor R CS , so that the current sense resistor for the integrated circuit 2 is given in total by the parallel connection of R CS and R CS 2 is. The gate of the field effect transistor 22 is applied to an output of a microcontroller 24 and is controlled by this. Further, the microcontroller 24 provides a control voltage which acts on an input LD of the integrated circuit 2 to adjust the supply current through the LED. In this embodiment, the microcontroller 24 also serves to set the current for the desired dimming of the LED load. The microcontroller 24 generates a control voltage corresponding to the desired dimming, which is applied to the input LD of the integrated circuit 2, taking into account the current measuring resistor selected via the range changeover by the microcontroller 24.

In Betrieb wird von der integrierten Schaltung 2 der Strom durch die LED-Last eingestellt. Zum Dimmen der LED kann ein beliebiger Strom beispielsweise zwischen 20 mA und 1 A eingestellt werden.In operation, the integrated circuit 2 sets the current through the LED load. For dimming the LED, any current can be set between 20 mA and 1 A, for example.

In einem Strombereich von 200 mA bis 1 A legt der Microcontroller eine Spannung an das Gate des Halbleiterschalters, der durch den FET 22 gegeben ist, an, so dass eine Verbindung von Drain zu Source durchgeschaltet ist. In diesem Schaltungszustand sind die Widerstände RCS und RCS2 parallel zueinander mit Erde verbunden. Die Parallelschaltung aus RCS und RCS2 wirkt in diesem Schaltungszustand als Messwiderstand für die Stromregelung der LED-Last. Der integrierte Schaltkreis 2 misst den Spannungsabfall über die Parallelschaltung der Widerstände RCS und RCS2, um den Strom durch die LEDs auf einen konstanten Wert zu regeln.In a current range of 200 mA to 1 A, the microcontroller applies a voltage to the gate of the semiconductor switch provided by the FET 22, so that a drain-to-source connection is turned on. In this circuit state, the resistors R CS and R CS 2 are connected in parallel to ground. The parallel circuit of R CS and R CS 2 acts in this circuit state as a measuring resistor for the current control of the LED load. The integrated circuit 2 measures the voltage drop across the parallel connection of the resistors R CS and R CS 2 to control the current through the LEDs to a constant value.

Wenn der Strom zur Dimmung der LEDs auf einen geringeren Wert geregelt werden soll, z.B. auf einen Strom in einem Bereich zwischen 20 mA und 200 mA, wird über den Microcontroller 24 der Feldeffekttransistor 22 angesteuert, um die Verbindung zwischen Drain und Source zu öffnen. In diesem Fall fließt der Versorgungsstrom durch die LED-Last 3 nur noch durch den Widerstand RCS, so dass in diesem Schaltungszustand der Messwiderstand zur Bestimmung des Stroms nur durch den Widerstand RCS gegeben ist.If the current for dimming the LEDs is to be regulated to a lower value, for example to a current in a range between 20 mA and 200 mA, the field effect transistor 22 is triggered via the microcontroller 24 in order to open the connection between drain and source. In this case, the supply current flows through the LED load 3 only through the resistor R CS , so that in this circuit state of the measuring resistor for determining the current is given only by the resistor R CS .

Somit wird über den Microcontroller 24 der Strommesswiderstand entsprechend einem vorgegebenen Strombereich zwischen zwei Werte umgeschaltet. Im niedrigeren Strombereich ist der Messwiderstand nur durch RCS gegeben, während für den höheren Strombereich der Messwiderstand durch die Parallelschaltung von RCS und RCS2 gegeben ist entsprechend geringer ist. Beispielsweise kann der Widerstand RCS und RCS2 jeweils 1,2 Ohm betragen, so dass im höheren Strombereich von 200 mA bis 1 µA effektiv nur ein Strommesswiderstand von 0,6 Ohm gegeben ist. Dadurch wird die am Messwiderstand umgesetzte Leistung bei größeren Strömen verringert. Da der Strom aber im höheren Messbereich liegt, ist der Spannungsabfall immer noch ausreichend hoch, um eine präzise Strommessung zu ermöglichen. In dem niedrigeren Strommessbereich wird der Messwiderstand entsprechend erhöht, z.B. auf 1,2 Ohm, so dass auch bei den niedrigeren zu messenden Versorgungsströmen noch ein ausreichend hoher Spannungsabfall für den Messwiderstand gegeben ist.Thus, the current measuring resistor is switched over the microcontroller 24 according to a predetermined current range between two values. In the lower current range of the measuring resistor is given only by R CS , while given for the higher current range of the measuring resistor by the parallel circuit of R CS and R CS 2 is correspondingly lower. For example, the resistance R CS and R CS 2 can each be 1.2 ohms, so that in the higher current range from 200 mA to 1 μA effectively only a current measuring resistor of 0.6 ohms is given. As a result, the power converted at the measuring resistor power is reduced at higher currents. But the electricity is higher Measuring range, the voltage drop is still sufficiently high to allow precise current measurement. In the lower current measuring range of the measuring resistance is increased accordingly, for example to 1.2 ohms, so that even at the lower to be measured supply currents still a sufficiently high voltage drop is given for the measuring resistor.

Über den Microcontroller 24 wird ferner eine Steuerspannung ausgegeben, die auf die integrierte Schaltung 12 einwirkt, um die Strommessung entsprechen den ausgewählten Messwiderstand um den entsprechenden Faktor auszugleichen.Via the microcontroller 24, a control voltage is also output, which acts on the integrated circuit 12, to compensate for the current measurement correspond to the selected measuring resistor by the corresponding factor.

Die vorliegende Erfindung ist nicht auf die dargestellte Schaltung von zwei Widerständen RCS und RCS2 beschränkt. Es können auch mehr als zwei Widerstände parallel geschaltet werden und es können auch mehr als lediglich zwei Strombereiche zur Messung des Stroms vorgesehen sein.The present invention is not limited to the illustrated circuit of two resistors R CS and R CS 2. It is also possible to connect more than two resistors in parallel, and it is also possible to provide more than just two current ranges for measuring the current.

Die übrige Schaltung zur LED-Stromversorgung entspricht der Ausführungsform im Stand der Technik. Dadurch lässt sich die erfindungsgemäße Bereichsumschaltung für den Messwiderstand auch einfach mit vorhandenen aus dem Stand der Technik bekannten integrierten Schaltkreisen für eine LED-Stromversorgung realisieren.The remaining circuit for LED power supply corresponds to the embodiment in the prior art. As a result, the inventive range switching for the measuring resistor can also be implemented simply with existing integrated circuits known from the prior art for an LED power supply.

BEZUGSZEICHENLISTELIST OF REFERENCE NUMBERS

22
integrierter Schaltkreisintegrated circuit
33
LED-LastLED load
44
Halbleiterschalter, z.B. FeldeffekttransistorSemiconductor switches, e.g. Field Effect Transistor
2222
Halbleiterschalter, z.B. FeldeffekttransistorSemiconductor switches, e.g. Field Effect Transistor
2424
Microcontrollermicrocontrollers
RCS, RCS2R CS , R CS 2
StrommesswiderstandCurrent sense resistor

Claims (10)

Treiberschaltung zur Stromversorgung von einer oder mehreren LEDs (3), umfassend eine regelbare Konstantstromquelle zum Anschluss einer oder mehrerer in Reihe geschalteter LEDs (3), und
einen Strommesswiderstand (RCS, RCS2), der in Reihe mit der einen oder den mehreren LEDs geschaltet ist, wobei die Treiberschaltung dazu eingerichtet ist, über einen Spannungsabfall des Strommesswiderstands (RCS, RCS2) den Strom durch die eine oder die mehreren LEDs (3) zu bestimmen, um den Strom auf einen vorgegebenen Wert zu regeln,
dadurch gekennzeichnet, dass die Treiberschaltung ferner dazu eingerichtet ist, den Strommesswiderstand (RCS, RCS2) auf wenigstens zwei verschiedene Werte zu schalten, wobei auf den niedrigeren der beiden Werte zur Messung des Stroms durch die eine oder die mehreren LEDs (3) in einem höheren Strombereich und auf den höheren der beiden Werte für eine Messung des Stroms durch die einen oder die mehreren LEDs (3) in einem niedrigeren Strombereich geschaltet wird.Driver circuit for powering one or more LEDs (3), comprising a controllable constant current source for connecting one or more series-connected LEDs (3), and
a current sensing resistor (R CS , R CS 2) connected in series with the one or more LEDs, the driver circuit being configured to regulate current through one or more of the voltage sensing resistor (R CS , R CS 2) voltage drop determine the plurality of LEDs (3) to regulate the current to a predetermined value,
characterized in that the driver circuit is further adapted to switch the current sense resistor (R CS , R CS 2) to at least two different values, wherein the lower of the two values for measuring the current through the one or more LEDs (3) is switched in a higher current range and to the higher of the two values for a measurement of the current through the one or more LEDs (3) in a lower current range. Treiberschaltung nach Anspruch 1, wobei die Umschaltung des Strommesswiderstands (RCS, RCS2) durch einen Microcontroller (24) gesteuert ist und der Microcontroller ferner eine Steuerspannung bereitstellt, welche die Stromerzeugung an der Konstantstromquelle entsprechend dem ausgewählten Messwiderstand (RCS, RCS2) einstellt.A driver circuit according to claim 1, wherein the switching of the current measurement resistor (R CS, R CS 2) is controlled by a microcontroller (24) and the microcontroller further provides a control voltage which the power generation of the constant current source corresponding to the selected measurement resistor (R CS, R CS 2). Treiberschaltung nach Anspruch 1 oder 2, wobei der Messwiderstand (RCS, RCS2) durch wenigstens zwei parallel geschaltete Widerstände (RCS, RCS2) gebildet ist, von denen wenigstens einer (RCS2) elektronisch zu- oder abschaltbar ist.Driver circuit according to claim 1 or 2, wherein the measuring resistor (R CS , R CS 2) by at least two resistors connected in parallel (R CS , R CS 2) is formed, of which at least one (R CS 2) electronically switched on or off. Treiberschaltung nach Anspruch 3, wobei die elektronische Zu- und Abschaltung des wenigstens einen Widerstands (RCS2) durch ein Ansteuern eines Gates (G) von einem Feldeffekttransistor, FET, (22) erfolgt, dessen Source (S) und Drain (D) in Reihe mit dem Widerstand geschaltet ist.Driver circuit according to claim 3, wherein the electronic connection and disconnection of the at least one resistor (R CS 2) by driving a gate (G) of a field effect transistor, FET, (22), whose source (S) and drain (D) connected in series with the resistor. Treiberschaltung nach Anspruch 4 mit Rückbezug auf Anspruch 2, wobei das Gate (G) des FET (22) durch den Microcontroller (24) angesteuert wird.Driver circuit according to claim 4 with reference to claim 2, wherein the gate (G) of the FET (22) by the microcontroller (24) is driven. Treiberschaltung nach einem der vorhergehenden Ansprüche, wobei ein Maximum des niedrigeren Strombereichs einem Minimum des höheren der beiden Strombereiche entspricht.Driver circuit according to one of the preceding claims, wherein a maximum of the lower current range corresponds to a minimum of the higher of the two current ranges. Treiberschaltung nach einem der Ansprüche 1 bis 5, wobei die beiden Strombereiche teilweise überlappen.Driver circuit according to one of claims 1 to 5, wherein the two current ranges partially overlap. Treiberschaltung nach einem der vorhergehenden Ansprüche, wobei der Strommesswiderstand wenigstens zwei Werte annehmen kann, wobei der niedrigere Wert zwischen 0,1 Ohm und 0,7 Ohm und der höhere Werte zwischen 0,9 Ohm und 1,7 Ohm liegt.Driver circuit according to one of the preceding claims, wherein the current measuring resistor can assume at least two values, wherein the lower value is between 0.1 ohms and 0.7 ohms and the higher values between 0.9 ohms and 1.7 ohms. Treiberschaltung nach einem der vorhergehenden Ansprüche, wobei der niedrigere Strombereich 20 mA bis 200 mA umfasst und der höhere Strombereich 200 mA bis 1 A umfasst.Driver circuit according to one of the preceding claims, wherein the lower current range comprises 20 mA to 200 mA and the higher current range comprises 200 mA to 1 A. Treiberschaltung nach einem der vorhergehenden Ansprüche, wobei der Strommesswiderstand mehr als zwei Werte, insbesondere drei oder vier Werte annimmt, um zwischen mehr als zwei Strombereichen, insbesondere drei oder vier Strombereichen, umzuschalten.Driver circuit according to one of the preceding claims, wherein the current measuring resistor takes more than two values, in particular three or four values, to between switch over more than two current ranges, in particular three or four current ranges.
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