EP3064037A1

EP3064037A1 - Circuit assembly for operating at least a first and a second cascade of leds

Info

Publication number: EP3064037A1
Application number: EP14792400.5A
Authority: EP
Inventors: Andreas Seider
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2013-10-31
Filing date: 2014-09-24
Publication date: 2016-09-07
Also published as: JP2016535406A; KR20160079075A; US20160262234A1; DE102013222226B3; CN105684553A; WO2015062790A1

Abstract

The invention relates to a circuit assembly for operating at least a first and a second cascade of LEDs. The LED cascades have a different number of LEDs. The LED cascades are operated in alternation by means of a suitable control logic, the operation being adapted to the instantaneous value of the rectified alternating supply voltage. The LED cascades are associated with LED units (LE1, LE2, LE3), wherein each LED unit (LE1, LE2, LE3) comprises a control device for controlling the particular LED cascade. The LED units (LE1, LE2, LE3) are coupled in series between the two input connections (703, 704), wherein the input connections (703, 704) are formed by the output of a rectifier (702). A linear controller (12) is provided in series with the LED cascades, which linear controller is controlled via a voltage divider (R1, R2, R3, D5, D6), which is coupled between the two input connections (703, 704). For adaptation to different alternating supply voltages, a switching device is associated with at least the highest LED cascade (LE1), which switching device is designed to connect all LEDs (LED1 to LED 28) of the LED cascade (LE1) in series in a first state and to connect a first half of LEDs (LED1 to LED14) of the LED cascade (LE1) in parallel with a second half of LEDs (LED15 to LED28) of the LED cascade (LE1) in a second state.

Description

description

Circuit arrangement for operating at least a first and a second cascade of LEDs

Technical area

The present invention relates to a circuit ^arrangement for operating at least a first and a second cascade of LEDs comprising an input ei ^¬ nem first and a second input terminal for Kop ^¬ PelN with a rectified AC supply voltage, a linear regulator having an input and a first higher up and a second lower LED unit, wherein the first LED unit comprises the first cascade of LEDs and the second LED unit comprises the second cascade of LEDs.

State of the art

A generic circuit arrangement is known from DE 29 25 692 AI. It is known to feed cascades of LEDs, each comprising a plurality of LEDs, via a rectifier from an AC voltage network. However, this leads to a strong light modulation, a so-called "flicker", and an energy-inefficient use of the LEDs For higher performance classes, this approach continues to lead to problems with normative specifications in terms of power factor and harmonics.

From DE 20 2013 000 064 Ul, the successive Überbrü ^¬ ckung the LED cascade the voltage of the half-wave of the following are known, and is connected in series to the LED cascade a linear regier with sinusoidal current control. From EP 2519080 A2 (Fig. 4), the series connection of several LED cascades known to a power source, where ^¬ advertising at the LEDs within each LED cascade with a switching device in series or in parallel to, dependent on the voltage the half-wave.

From DE 10 2012 006 315 AI (Fig. 4), the series connection of several LED cascades with a current source is known, wherein the LED cascades are connected and bridged with a switching device in series or in parallel, depending on the voltage of the half-wave.

From US 2010/0134018 AI (Fig. 4-5B), the successive bridging of the LEDs following the voltage of the half-wave is known, wherein in series with the LED cascades a linear regulator with sinusoidal current control is connected, the control input via a voltage divider with the rectified AC voltage is coupled.

From EP 2645816 Al (Fig. 6), the successive transfer ^¬ bridging the LED cascade the voltage of the half-wave following known, in series with the LED cascade a Li is connected near regulator, wherein the LEDs capacitors connected in parallel are and wherein decoupling diodes are provided in series with the LEDs, so that the capaci ^¬ tors when discharging the LEDs are not discharged.

Presentation of the invention

The object of the present invention is to develop a generic circuit arrangement for operating at least one first and one second cascade of LEDs such that a more efficient operation of the LEDs is made possible. This object is achieved by a circuit arrangement having the features of patent claim 1.

The present invention is based on the realization that the efficiency and thus the efficiency of a genus processing circuit arrangement according increased as well as the requirements can be met with regard to the power factor when a voltage divider is provided, which is between the first and the second input terminal gekop ^¬ pelt, wherein the tap of the voltage divider is coupled to the input of a linear regulator coupled serially to the LED cascades. By this measure, a current consumption of the circuit arrangement can be made dependent on the respective phase position of the rectified AC supply voltage. Each LED unit comprises a first diode serially coupled to the respective LED cascade, this first diode serving as a blocking diode. The coupling point of the first diode and the respective LED cascade represents a first node, wherein the not coupled to the first diode terminal of the LED cascade represents a second node, wherein the not coupled to the LED cascade terminal of the first diode has a third Represents node. Each LED unit further has the Se ^¬ rienschaltung a first capacitor and a second diode which is coupled between the third and the second node, wherein the coupling point of the first Kon ^¬ capacitor with the second diode is a fourth node. Each LED unit also has a first and a second electronic switch each having a control electrode, a reference electrode and a working electrode, wherein the control electrode of the first electronic switch is coupled to a fifth node, wherein the reference electrode of the first electronic switch is coupled to the fourth node, wherein the working electrode of the first electronic switch is coupled to the control electrode of the second electronic ^¬ rule switch, wherein the reference electrode of the second electronic switch is coupled to the third node, wherein the working electrode of the second electronic switch is coupled to the second node. As explained in more detail below, the prerequisite can be created in this way to turn the different LED cascades depending on the instantaneous value of the rectified supply change ^¬ voltage on or off. In this case, only individual ones of the LED cascades or even several LED cascades can be in operation simultaneously. For this purpose, the third node of the highest LED-unit is coupled to the first input terminal, said second bone ^¬ th the lowermost LED unit is so coupled to the linear regulator, the linear regulator serially connected between the second node of the lowermost LED Unit and the second input terminal is coupled. The third node of each LED unit, which is not the highest LED unit, is coupled to the second node of the next higher LED unit.

Since the respective first electronic switch is switched by Vari ^¬ ation of the potential at the reference electrode, a suitably chosen direct voltage to be applied to their control electrode. Therefore, according to the invention the fifth node of all LED units coupled to a DC power source.

Furthermore, the highest LED cascade is associated with at least a switching device, which is designed to switch in a first state, all the LEDs of the LED cascade in series and in a second state a first Hälf ^¬ te of LEDs of the LED cascade of a second half LEDs of the LED cascade to be switched in parallel. This measure takes into account the fact that when a generic circuit arrangement, which is designed, for example, for an AC supply voltage of 200 V, is operated on an AC supply voltage of 100 V, the luminous flux drops to a very small value without further measures. This can occur, for example when a designed for the European market circuit arrangement with an example as ^¬ as usual in Japan mains operated. As a result, the LEDs of the various LED cascades partially no longer light up. This results in an unacceptable inhomogeneity of the luminance.

Conversely, a circuit arrangement designed for a supply from a 100 V network can not be operated on a 200 V network, since the input power thereby increases very greatly. The efficiency (lm / W) of the whole system would be very poor. Furthermore, it is Ge driving ^¬ that the electronic components of the circuit arrangement, here, the LEDs are, in particular to be mentioned to be destroyed in the shortest time ^¬ nerhalb. To address this problem, previously generic circuit arrangements have been operated necessarily with an external electronic ballast with a wide-range input. On the one hand, however, these are expensive and, on the other hand, severely limit the luminaire design.

By the measure according to the invention, the voltage drop across an LED cascade, the so-called strand voltage, can be adapted to the actual ^alternating voltage present. This can be reliably avoided an undesirable inhomogeneity in luminance, poor efficiency and a destruction or premature Old ^¬ tion of components of the circuit.

In a preferred embodiment, the lower end of the first half of LEDs of at least the highest LED cascade represents a sixth node, and the higher end of the second half of LEDs of the highest LED cascade represents a seventh node, the switching device comprising first, second, and second LEDs a third switch, wherein the first switch is coupled between the sixth and seventh nodes, the second switch coupled between the first and seventh nodes, and wherein the third switch is coupled between the sixth and second nodes. This makes it particularly easy to halve the strand voltages according to a halving of the input voltage. The two sub-strings of the highest LED cascade are connected in parallel by the switching device at the higher input voltage in series and at the lower input voltage. It may be provided that only the highest located LED cascade is associated with a switching device, but it may also be provided that at least one further LED cascade, preferably of each LED cascade, a corresponding switching device is assigned.

The voltage divider preferably comprises a switch and at least one first and one second ohmic resistance, the switch being designed and arranged to separate the second ohmic resistance from the first ohmic resistance in a first state and the first and the second ohmic resistance in a second state To connect the resistor in parallel. This switch is used to adjust the current value accordingly, so that at half the AC supply voltage of twice the current through the LED cascade (s) flows to achieve a constant light ^¬ performance.

In a preferred embodiment, the circuit arrangement further comprises a control device which is designed and arranged to detect the amplitude of the voltage applied to the input, wherein the control device is further designed, the at least one switch device and the switch of the voltage divider in dependence of the detected amplitude of the An ^¬ gear applied voltage to control. In this way, the switching of the strings or the current setpoint does not have to be performed manually. Accordingly, the control device includes an input voltage detection ^¬ with a corresponding automatic switching. This is preferably realized using a Schmitt trigger and a MOSFET circuit. In this connection, the control device is preferably designed in a first state, which is correlated to a voltage at the input in a first voltage range, to control at least one switching device such that the corresponding LEDs are connected in series and the switch of the voltage divider of the ^¬ art to control that the second ohmic resistance is abge ^¬ separates, and in a second state, which is correlated with a voltage at the input in a second voltage range, wherein the second voltage range klei ^¬ nere voltages are assigned as the first voltage ^{¬ range} , the at least to drive a switching device such that the first half of the LEDs of the second half is connected in parallel, and to control the switch of the voltage divider such that the second ohm ^¬ cal resistance is connected in parallel with the first ohmic resistance.

In a preferred embodiment, the turn-on durations of the respective LED cascades during operation of the circuit arrangement in the second state are reduced in order to provide a total LED power of the circuit arrangement which substantially corresponds to that in the first state. In this way, an overload of LEDs can be prevented, as will be explained in more detail below.

It has proved to be advantageous if the LED units each comprise a different number of LEDs. In this way, the possibility is basically created to make an adjustment of the LED string voltage to the instantaneous value of the rectified supply AC voltage. It can be provided that each higher LED unit comprises twice the number of LEDs as the next lower LED unit. In this way, a particularly uniform adaptation to the rectified AC supply voltage can be made.

In particular, in a variant in which only the highest-level LED cascade is associated with a switching device, it has proved to be advantageous if the number of LED units is not constructed binary. In this way, however, an adequate electrical performance can be realized, but the cost and assembly costs for the lower than the highest LED cascade LED cascades due to the saving of the corresponding switching devices is reduced. In one embodiment, three LED units, the first LED unit may comprise, for example, LEDs 26, the second LED unit and the eight drit ^¬ te LED unit four.

In this context, the switch-on durations of the LEDs located below the highest-lying LED cascade are preferably periodically reduced. In this way, an overload of these lower-lying LED cascades can be reliably avoided.

In the case of the LED units in which a switching device is provided, the first half of LEDs is preferably a first capacitor and the second half of LEDs a second capacitor connected in parallel. This be ^¬ then meets at least the LED unit with the highest-lying LED cascade ^according to the invention. In this way, even with serial operation light modulations and Flicker phenomena are reduced. Particularly preferably, each further LED unit also comprises at least one second capacitor, which is connected in parallel to the respective LED cascade. In this way, the LEDs of the further LED cascades from the respective second capacitor can be supplied in the phases in which the LEDs of the respective cascade are not supplied directly from the rectified AC supply voltage, either because the rectified supply AC voltage is less than the sum of the flux voltages of the respective LED cascade is, or it is, because another LED cascade is active and the respective LED cascade is just shorted. This results in a further reduction of the light modulation, so that flicker phenomena can hardly be perceived by the human eye.

In order to enable a particularly high efficiency of a erfindungsge ^¬ MAESSEN circuit arrangement, the DC voltage source is realized in that the AC voltage occurring during operation of the circuit arrangement at the second node of the lowest-lying LED unit is used to generate a DC voltage. In this way, no separate auxiliary voltage for the generation ^¬ supply the potential at the fifth node must be provided, for example, using a coupled with the rectifier output buck converter; Rather, a particularly sent selected exchange clamping ^¬ voltage signal is utilized within the circuit arrangement in the present case. As the inventors of the present invention have recognized, the alternating voltage occurring at the second node of the lowest-lying LED unit is particularly suitable. Since this is virtually continuously present at the second node regardless of the instantaneous value of the AC supply voltage, it is permanently available, ie also independent of the instantaneous value of the AC supply voltage, for supplying the fifth node. The auxiliary voltage present has produced single ^¬ Lich a low ripple, and therefore very small capacities can be used compared to other auxiliary power supplies. It is very simple and compact. Moreover, it is also inexpensive for this reason. Particularly advantageous is the fact that a power is taken for the auxiliary voltage supply, which would otherwise have been converted into power loss in the linear regulator. Thus, no additional power dissipation is created by the auxiliary voltage supply, whereby the efficiency of the circuit arrangement is optimized. This not only results in low cost of a circuit ^arrangement according to the invention, but also in a small size. Preferably, each LED unit further comprises a third diode coupled between the fifth node and the control electrode of the respective first electronic switch. This third diode serves to protect the control ^¬ electrode of the respective first electronic switch. In accordance with voltage-resistant design of the first electronic switch, these third diodes can be omitted.

Particularly preferably, the DC voltage source ei ^¬ ne charge pump whose input is coupled to the second node of the lowest-lying LED unit and their ^{output ¬} coupled to the fifth node of all LED units is. By using a charge pump, a DC voltage for supplying the fifth node of all LED units can be obtained particularly easily from the alternating voltage occurring at the second node of the lowest-lying LED unit. The charge pump preferably comprises the series connection of a half-wave rectifier and a voltage limiting device. This makes it possible to provide a voltage supply for the fifth node which reliably lies below a predefinable threshold value. By this measure, a particularly low ripple of the auxiliary voltage can be provided.

In a preferred embodiment, the DC voltage source comprises the series connection of a resistor and a fourth diode, which is coupled between the second node of the lowest LED unit and the fifth node of all LED units, and the parallel connection of a third capacitor and a Zener diode, the zwi ^¬ the fifth node of all LED units and the second input terminal is coupled.

In this connection, the resistor which is connected in series with the fourth diode may be designed as a fixed ohmic resistor. This is preferred if the circuit arrangement does not have to be dimmable. However, if a dimming option is to be provided, the resistor which is connected in series with the fourth diode is designed as a variable resistor for realizing a regulating device of the charge pump. It is preferable if this control device is adapted to the charge pump to control the voltage at the fifth bone ^¬ ten to a predeterminable value. Take this into account into account that the voltage drop across the linear regulator chip ^¬ voltage, that is, in the present case the voltage at the second node of the lowermost LED unit in Phase or Phasenabschnittdimmung corresponds to an asymmetrical sawtooth signal having dropout. By providing a control apparatus in the charge pump that is also supplied in this case the third Kon ^¬ capacitor with sufficient current to provide a substantially con- stant predetermined voltage at five ^¬ th node of all the LED units is ensured.

Preferably, the control device of the charge pump is designed as an inverting voltage regulator. In this case, the voltage regulator has a third and a fourth electronic switch, each having a control electrode, a working electrode and a reference electrode, wherein the control electrode of the third electronic switch is coupled to the anode of the zener diode, with its reference electrode to the second input terminal and its working electrode the control electrode of the fourth electronic switch, wherein the Steuerelekt ^¬ rode of the fourth electronic switch is further ge ^¬ coupled through a resistor with its working electrode, which in turn is coupled to the cathode of the fourth diode, wherein the reference electrode of the fourth electronic switch having is coupled to the fifth node of all LED units. In this constellation, the third electronic switch measures the current through the zener diode. If no current flow through the Zener diode can be detected, then the voltage at the third capacitor is too low. In the absence of current flow through the zener diode, the third electronic switch becomes non-conductive and in turn as a result of acting as a pull-up resistor ohmic resistance between the working electrode and the control electrode of the fourth electronic switch turned on. In this way, a flow of current from the second node of the lowest LED unit to the third capacitor and thus the fifth node of all LED units is made possible.

Preference is given to the other, a Kondensa ^¬ gate coupled between the control electrodes of the third and fourth electronic switch on the one hand and the second input terminal. This serves to filter out cracks, tines and the like, and therefore makes the arrangement less susceptible to interference.

Furthermore, a regulating device for regulating the current through the linear regulator can be provided, the input of the regulating device being coupled to the fifth node and the output of the regulating device to the input of the linear regulator. Such Regelvorrich ^¬ tion allows, for example, a regulation of the current through the at least one LED unit as a function of temperature.

Particularly preferred such Regelvorrich ^¬ tung comprises a fifth electronic switch having a control electrode, a reference electrode and a working electrode, and a voltage divider having at least ei ^¬ nem ohmic resistor and a NTC-resistor, the voltage divider between the fifth node and the second input terminal is coupled, wherein the Ab ^{¬ handle of} the voltage divider is coupled to the control electrode of the fifth electronic switch, wherein the Reference electrode of the fifth electronic switch is coupled to the second input terminal, wherein the working electrode of the fifth electronic switch is coupled to the input of the linear regulator. When heating of the circuit arrangement, therefore, the voltage causing it to become increasingly conductive ge ^¬ turns increases on the control electrode of the third electronic switch. As a result, the voltage at the input of the linear regulator is correspondingly reduced. In this way, the current through the linear ^¬ regulator is also reduced and thus the converted by the LED units power. In addition to a temperature control, this measure also provides a Temperaturabschal ^¬ tion when a predetermined maximum temperature is exceeded.

Further preferred embodiments emerge from the subclaims.

Short description of the drawing (s)

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

1 shows a schematic representation of a first embodiment of a circuit ^¬ arrangement according to the invention;

Fig. 2 is a schematic representation of a second exemplary embodiment of a circuit arrangement according to the invention ^¬; Figure 3 shows the time profile of the voltages at various nodes of the circuit arrangement of Figure 2 in operation with a first supply ^¬ AC voltage..; and Fig. 4 shows the time course of the voltages at different nodes of the circuit arrangement of Fig. 2 when operating with a second supply ^¬ AC voltage, which is half as large as the AC supply voltage used in Fig. 3. 5 is a schematic representation of an alternative to a partial region of the circuit arrangement shown schematically in FIG. 1;

6 shows a schematic representation of a further alternative to a partial region of the circuit arrangement shown schematically in FIG.

Preferred embodiment of the invention

Fig. 1 shows a schematic representation of an embodiment of an inventive Schaltungsanord ^¬ tion. An AC line voltage 701 is connected through a rectifier 702 to two nodes 703 and 704. The node 703 is connected to a node 759 via the ohmic resistor Rl. The node 759 is coupled via the series circuit of two diodes D5, D6 and a resistor R3 to the node 704, the Ka ^¬ Thode of the diodes D5, D6 points in the direction of the node 704th The ohmic resistors Rl, R2, the diodes D5, D6 and the ohmic resistor R3 form a Spannungsstei ^¬ ler, whose tap represents the node 759. The ohm see resistor R3 is a switch S4 a resistor R2 parallel switchable.

The circuit arrangement further comprises a linear regulator 12, which includes two NPN transistors Ql, Q2 in a Darlington arrangement, and a resistor R5 which is serially referred to the Darlington stage Ql, Q2 ge ^¬ is coupled. The base of transistor Q2 represents the control terminal of linear regulator 12 and is coupled to node 759. Between the nodes 703 and 704, a series circuit of present three LED units LEI LE2, LE3 and egg ^¬ nem linear regulator 12 is coupled. The structure of an LED unit is shown below using the example of the LED unit LE3, wherein the structure of the LED units LEI and LE2 is substantially identical, differs only by the number of the respective LEDs and the resulting dimensioning of the components.

The LED unit LE3 comprises the LEDs LED43 to LED48, thus 6 LEDs, which are connected in series with one another and form an LED cascade. Serial to the LED diode D33 is coupled to cascade a, wherein the coupling point of the diode D33 and the LED cascade a node N31 Represents ^¬. The terminal of the LED cascade not coupled to the diode D33 represents a node N32. The terminal of the diode D33 not coupled to the LED cascade represents a third node N33. An optional capacitor C33 may be coupled in parallel with the LED cascade. Between the node N33 and the node N32 is the series connection of a capacitor C32 and a diode D32 coupled, wherein the coupling point of the capacitor C32 with the diode D32 is a node N34.

The LED unit LE3 further comprises two electronic switches Q31 and B31, wherein the control electrode of the switch Q31 is coupled to a node N5 via the series connection of a diode D31 and an ohmic resistor R31. The reference electrode of the switch Q31 is coupled to the node N34, while its Arbeitsselekt ^¬ rode via a resistor R32 to the control electrode of the switch B31 is coupled. The reference ^¬ electrode of the switch B31 is gekop ^¬ pelt to the node N32, whereas its working electrode is coupled to node N33.

In the present embodiment, the switch B31 is implemented as a Darlington stage and includes the Transis ^¬ factors Q32, Q33 and the ohmic resistors R33 and R34. However, instead of the Darlington stage, a single transistor could also be provided.

The LED units LE2, LEI have a comparable structure, but each have a different number of LEDs. Thus, the LED unit LE2 comprises the LEDs LED29 to LED42, ie 14 LEDs. The LED unit LEI comprises the LEDs LED1 to LED28, which means 28 LEDs. The LEDs are before Trains t ^¬ as dual-core LEDs each having two PN junctions executed.

The second node of the lowest LED unit, here the node N32, is coupled to the working electrode of the linear regulator 12, while the third node N13 of the highest LED unit LEI is coupled to the node 703. Between node N5 and the linear regulator ler 12 is coupled to an auxiliary voltage source 14, which will be discussed in more detail below.

By way of example, the circuit shown in Figure 1 ^¬ arrangement, the following components and dimensions on. Rl 200 kQ, R2 1.5 kQ, R3 1.5 kQ, R5 10 Ω, RH 100 kQ, R21 500 kQ, R31 10 kQ , R12 500 kQ, R22 20 kQ, R32 10 kQ. R13 = R23 = R33 = R43 10 kQ, R14 = R24 = R34 = R44 1 kQ, C12 = 470 nf, C13 = C14 = 47 nf, C22 = 2 yf, C32 = 4 yf, C23 = 100 yf, C33 = 220 yf, R4 = 3 kQ, C2 = 10 yf.

The capacitors C13, C14, C23 and C33 are comparatively large dimensioned ^¬ and serve as a buffer capacitor for the LEDs of the respective LED cascade. In this case, it is advantageous that these capacitors only have to be designed for the voltage drop across the corresponding LED cascade and thus not for the full magnitude of the mains AC voltage VI. Accordingly, these con ^¬ capacitors can be made smaller and thus space-saving. The diodes Dil, D21, D32, are optional and can be ^¬ saves, if the transistors QU, Q21 and Q31 are designed to be resistant to voltage.

Within the voltage divider, the diodes D5 and D6 serve to compensate for the base-emitter voltage of the transistors Q1 and Q2. The across ohmic resistor R3 from ^¬ falling voltage is therefore substantially equal to the voltage dropped across the ohmic resistor R5. The current through the resistor R5 is therefore semi-sinusoidal ^¬ shaped. It follows that the current through the circuit follows the input voltage, resulting in a good power factor and low EMC interference.

By dimensioning the circuit arrangement shown in Fig. 1 can be achieved that the transistor Bll is operated at a switching frequency of about 100 Hz. A possibly due to this switching frequency perceptible flicker is prevented by the associated buffer capacitors C13 and C14. The transistor B21 operates with a switching frequency of about 200 Hz and the switch B31 with a switching frequency of about 400 Hz.

The combination of the capacitor C12 and the diode D12 constitutes a peak detector for the LED unit LEI. Accordingly, the capacitor C22 and the diode D22 provide a peak detector for the LED unit LE2 and the capacitor C32 and the diode D32 a peak value detector for the LED unit LE3.

The transistors QU, Q21 and Q31 act as Komparato- ren. The operation will be described by way of example to the hand ^¬ lowermost LED unit LE3. The resistor R32 is designed in combination with the capacitor C32 so that the capacitor C32 is only slightly discharged during the longest expected switch-on of the switch B31. The voltage source 14 provides a voltage offset as a minimum voltage, for example in the amount of 6 V, which should not be undershot in the case of the switch Q1, Q2 of the linear regulator 12. The transistor Q31 compares the voltage 6 V with the voltage at the node N34. If the switch B31 turns on, the LEDs LED43 to LED48 are bypassed, that is short-circuited. This also shifts the working points the remaining control units for the LEDs of the LE2 and LEI LED units.

About how the Darge ^¬ presented in Fig. 1 circuit arrangement will first be considered in a state in which the switches S12, S13, S22, S23, S32, S33 non-conductive while the switches Sil, are turned S21 and S31. The switches Sil, S12 and S13 form ei ^¬ ne switching device SV1, the switches S21, S22 and S23, a switching device SV2 and switches S31, S32 and S33, a switching device SV3. A control device 20 initially remains unconsidered.

As a switch-hereinafter the beginning of a half cycle of the AC voltage source 701 angenom ^¬ men. It is further assumed that all switches of the LED units, ie, the switch QU, Bll, Q21, B21, Q31, B31, are conductive and all capacitors loaded (inserted ^¬ schwungener state). The forward voltage of an LED is assumed to be 3V, that of a diode to 0.7V.

As a result of the switched-on switches, the instantaneous output voltage of the rectifier 702 at the node 703 is also present at the point N32. The nodes N32 and N33 are at the same potential, since the switches Q32 and B31 were lei ^¬ tend assumed. The voltage provided by the auxiliary voltage source 14 to the node N5 is assumed to be 6 V in the exemplary embodiment.

The capacitor C32 is charged at the beginning of the half cycle from the previous cycle to +18 volts. These 21 V result from 6 times the forward voltage of diodes LED43 to LED48, with each forward voltage, as mentioned above, of 3V Is accepted. This results in a potential of -18V at node N34.

The node N5 is charged by the auxiliary power source 14 to 6V. This results in a current flow through the diode D31, the resistor R31 and the transistor Q31. The transistor Q31 is conductive, since at its base a potential of about 6 V is applied, at its emitter, a potential of about minus 18 V. The fact that the Transis ^¬ gate Q31 is conductive, and the switch B31 is conductive. Accordingly, the current flows past the LED of the LED unit LE3 cascade, that is, the LED cascade is shorted ^¬ closed and not supplied with current. By convention, the switches B21 and Bll are conductive, so that the LED cascades of the LED units LEI and LE2 are not energized. This situation represents the starting point of a half-wave of the rectified mains AC voltage VI.

As the half-wave progresses, the potential of the half-wave increases. Due to the increasing potential at node 759, linear regulator 12 begins to become gradually conductive.

As long as switches Q31 and B31 are conductive, the potential at node N33 is equal to the potential at node N32. As the half-wave continues, the potential at node N33 increases until the potential at node N34 is about 5.3 V (potential at node N5 minus the forward voltage of diode D31). At this time, the base-emitter voltage of the transistor Q31 becomes 0V. By dropping 18V across the capacitor C32, this is the case when the potential at the node N32 is 26.3V. Go to this point, the scarf ^¬ ter Q31 and B31 in the off state, that is, the potentials at the nodes N33 and N32 are decoupled. The potential at the node N33 remains at 26.3 V. Since the linear regulator 12 wants to maintain the current flow through the ohmic resistor R5 in accordance with the specification of the voltage divider due to a corresponding control by the voltage divider, the linear regulator 12 is switched to an increasingly conductive state Potential at node N32 decreases until the setpoint current is set. This is the case when the voltage at node N32 has dropped to 4.6V. This value follows from the potential at node N33, which, as shown above, after switching off the switches Q31 and B31, is 26.3 V minus 7 times the diode forward voltage of 3 V, minus 0.7 V for the forward voltage the diode D33. This creates the condition that the current flows through the LED cascade of the LED unit LE3, which is why this cascade lights up from this time (if the optional capacitor C33 is missing, if it is available, its charge must be considered).

In the further course, the half wave continues to increase, where ^¬ continues to increase due to the potential at the node N33. Via the conductive LEDs LED43 to LED48, the potential at the node N32 thus also increases. The voltage difference between the potential at node N33 and node N32 is 26.3V - 4.6V = 21.7V. Capacitor C22 is charged to 14 x 3V = 42V (14 times the forward voltage of diodes LED29 to LED42). If the half-wave rises to 26.7 V, these 26.7 V are present at the node N23, since all overlying switches QU and Bll are turned on. The voltage at node N24 is therefore 26.7V - 42V = -15.3V. Since the voltage at node N5 is still 6V, switches Q21 and B21 are conductive. As the half-wave continues to increase, the potential at node N23 and thus the potential at node N24 increases. When the potential at node N24 has reached 5.3V (potential at node N5 of 6V minus base-emitter voltage of switch Q21), switch Q21, and thus switch B21, goes to the off-state. As the input voltage continues to increase, the potential at node N23 continues to increase until 47.3V is reached (5.3V at node N24 plus 14 by 3V). This is the time from which the current begins to flow via the LED cascade LED29 to LED42 of the LED unit LE2. With ei ^¬ ner input voltage of 47.3 V thus fall 14 times 3 V plus 0.7 V (14 times the forward voltage of the LEDs LED29 to LED42 and the forward voltage of the diode D23), so that the potential at the node N22 only 4, 6V is. Since node N22 corresponds to node N23, the potential at node N23 is only 4.6 V. The potential at node N24 is therefore 4.6 V minus 21.0 V (corresponding to the potential at node N23) the voltage across capacitor C22 drops equal to minus 16.4 V. Thus, the voltage difference between node N5 and node N24 -22 is 4V, causing transistor Q21, and thus switch B21, to turn on again. In this way, the LED cascade LED43 to LED48 of the LED unit LE3 again short-circuit ^¬ sen, that is, it is no longer energized. In the same way, the LED cascades of the LED unit LEI are energized.

When the half-wave has exceeded its maximum, sets the reverse effect, that is nacheinan ^¬ the LED cascades of the LED units LEI, LE2 and LE3 switched according to the above order until at a phase angle of 180 ° again all LED Cascades are bridged (Bll to B31 conductive) and a new half ^¬ wave begins.

The following statements relate to a particularly advantageous realization for providing the potential at the node N5.

Usually, a buck converter is used for the provision of an auxiliary ^¬ voltage, which is coupled to the output of the rectifier. According to the invention, however, the voltage drop at the linear regulator 12, that is to say the voltage at the node N32, is used to generate an auxiliary voltage for the node N5. Due to the binary According to the LED cascades, the linear regulator 12 can pick up a sawtooth-like voltage that fluctuates between 0 and 26.7 V until all LED cascades are switched on. If all LED cascades are activated, the linear regulator drops a voltage resulting from the difference between the input voltage and the sum of the voltages dropping across the LED cascade. Since the voltage peaks of this sawtooth voltage are temporally well distributed within a half-wave, this sawtooth voltage may be used to generate an auxiliary voltage ^¬ by means of an RC element R4, C2 and the rectifier and Zener diode D3, D2. This auxiliary voltage has only a small ripple, so compared to at ^¬ their auxiliary power supplies very small capacity can be used. It is very simple and compact. Moreover, it is also inexpensive for this reason. Particularly advantageous is the fact that for the auxiliary voltage supply a current is taken, which would otherwise have been converted in the linear regulator 12 in power loss. Consequently, according to the invention, a parasitic power is used to generate the auxiliary voltage at the node N5. Thus, by the auxiliary voltage supply no additional loss ^¬ performance, the efficiency of the circuit is optimized.

For the further mode of operation of the circuit arrangement taking into account the switching devices SV1, SV2 and SV3 as well as the control device 20:

The controller 20 is coupled between the terminals 703 and 704 and configured to detect the amplitude of the rectified AC supply voltage. In dependence of the detected voltage, the STEU ^¬ ervorrichtung 20 controls the switches Sil, S12, S13, S21, S22, S23, S31, S32 and S33. For example, if the control device detects a voltage of 200 V at the input, it controls the switches as follows: S12, S13, S22, S23, S32, S33 nonconductive and Sil, S21, S31 conducting. Moreover, the control device 20 controls the switch S4, so that it is non-conductive at the specified voltage range. All LEDs of the LED unit are LEI would take through the described Schaltungsmaß- ge ^¬ switches in series. The same applies to the LEDs of the LED unit LE2 and the LED unit LE3.

If the control device 20 determines that the voltage at the output of the rectifier is in the range in a second voltage that is lower than the first voltage ^¬ area, that is the voltage, for example 100 V be ^¬ wears, it controls the switches as follows : S12, S13, S22, S23, S32, S33 conductive and Sil, S21 and S31 non-conductive. Moreover, the switch S4 is turned on.

By virtue of this measure, a first half of the LED unit LEI comprising the LEDs LED1 to LED14 is now connected in parallel to a second half of the LED unit which comprises the LEDs LED15 to LED28. The same applies to the LED unit LE2: Here, the LEDs LED28 to LED35 are the LEDs LED36 to LED42 connected in parallel by the said switch position. In the case of the LED unit LE3, the series connection of the LEDs LED43 to LED 45 of the series connection of the LEDs LED46 to LED 48 is connected in parallel. As a result of the fact that the switch S4 is turned on, twice the current can flow through the respectively active LED units LE1, LE2 and / or LE3 (as compared with the state in which the switch S4 is switched nonconductive).

In the embodiment of a circuit arrangement according to the invention shown in FIG. 2, only the LED unit LEI has a switching device SV1. In contrast to FIG. 1, furthermore, the numbers of LEDs in the respective LED units are changed. For example, the LED unit LEI comprises the LEDs LED1 to LED26, that is to say 26 LEDs, the LED unit LE2 the LEDs LED27 to LED34, ie eight LEDs, and the LED unit LE3 the LEDs LED35 to LED38, ie four LEDs. The illustrated, non-binary fitting of the LED units LEI, LE2 and LE3 with LEDs makes it possible, even if, as shown, only the LED unit LEI comprises a switching device SV1, to realize an adequate electrical performance characteristic. Fig. 3 shows in this context the time course of the voltages at the nodes 703, N12, N22 and N32 when operating with a Eingangsvorsorgungswechselspannung of 200 V. As already mentioned, here are the LEDs of the LED unit LEI by appropriate control of the switching device SV1 connected in series. In the Fig. 3 is entered into the respective closed areas, which LED unit is responsible for the respective voltage drop, that is turned on. Fig. 4 shows the time course of the corresponding quantities, however, during operation of the circuit arrangement of Figure 2 with an AC supply voltage of 100 V. In the case of realization of the LEDs by double-core LEDs results thus for the example illustrated in Figure 2 execution ^¬ example the following situation..:

LED Unit LEI has 52 serial PN junctions operating at 200V and two parallel strings of 26 serial PN junctions operating at 100V; Strand 2 has 16 serially connected PN junctions; and strand 3, eight serially connected PN junctions.

In the 100 V mode, the position of the switch S4 causes the linear regulator 12 to be switched to double current, so that the appropriate rated current for the double parallel connection of 26 LEDs of the string 1 is set. However, this could overload strands 2 and 3. Therefore it can be provided to reduce their periodically recurring on-duration accordingly.

As a result, the overall LED power remains constant even in 100 V mode, as measured by the 200 V mode.

The flux voltages of the strands 1 and 2 are deliberately chosen by the corresponding number of LEDs so that the third strand in the mains voltage maximum (90 °) is no longer switched on. State 8 and 9 from the above table is not achieved. This prevents overloading of the LEDs in the third strand. A shortening of the on-duration of the string 2 can be achieved by releasing the string 1 earlier in the 100 V mode and remaining active for longer than in the 200 V mode, and by setting the phase-in phase of the string 2 significantly shorter than the mains voltage maximum in 200V mode. Both are achieved in that the resulting flux voltage of the strand 1 is selected by ent ^{¬ appropriate} insertion with LEDs less than twice the forward voltage of strand 2. Fig. 5 shows an alternative embodiment of the auxiliary voltage supply 14. This further comprises a control device 16th for regulating the current through the linear regulator 12. The input of the regulating device 16 is coupled to the node N5, the output to the control electrode of the switch Q2. The control device 16 comprises a transistor Q3 and a voltage divider, the ohmic resistors R7 and R9 and a NTC resistor to ^¬ sums. The tap of the voltage divider is coupled to the STEU ^¬ erelektrode of the transistor Q3. The collector of transistor Q3 is coupled to the control electrode of the switching ^¬ ters Q2.

Once the temperature of the circuit rises, the transistor Q3 is turned increasingly conductive which ^¬ increasingly passes through the switch Ql in the blocking state. As a result, the current through the resistor R5 decreases, whereby the power converted in the LEDs is reduced. If the temperature is so high that the switch Q3 is fully turned on, a Tempe ^¬ raturabschaltung the circuit arrangement is realized. The control device 16 is operated by means of the auxiliary voltage at the node N5. In Fig. 5, moreover, an inrush current delay is shown, which comprises the diode D8 and the parallel circuit of the capacitor C7 and the ohmic resistor R6. This will cause the voltage at the base of transistor Q2 to increase slowly until capacitor C7 has charged to its peak value. This results in the advantage that no inadmissibly high power dissipation in the transistor Ql occurs at the moment of switch-on. Likewise, it makes it possible to operate several modules on a home fuse without them tripping on switch-on.

In a preferred embodiment, R9 is 500 Ω, the NTC resistor is 47kΩ, R7 is 500Ω, R4 is 10kQ, C2 is 10f, C7 is 10f and R6 is 200kQ. FIG. 6 shows a schematic representation of a further alternative of a subregion of the circuit ^arrangement according to the invention shown in FIG. 1. In this embodiment, the ohmic resistor R4, see FIG. 1, is designed as a variable resistor, whereby a regulation of the voltage at the node N5 is provided. As a result, the circuit arrangement for dimmer operation can be used. In the case of phase-angle and phase-section dimmers, there is in part no longer sufficient voltage available at the linear regulator 12 in order to maintain the auxiliary voltage at the node N5. To exclude this, the ohmic resistance R4 would have to be chosen relatively small for the auxiliary voltage supply. This would have negative effects on the circuit ^¬ efficiency and EMC performance. In the exemplary embodiment illustrated in FIG. 6, therefore, an inverting voltage regulator is realized in the charge pump 14, which, in addition to the dimmability, makes possible a higher efficiency of the circuit arrangement. The voltage regulator comprises two electronic switches Q4, Q5, each having a control electrode, a Arbeitselekt ^¬ rode and a reference electrode. The control electrode of the switch Q4 is gekop ^¬ pelt to the anode of Zener diode D2, its reference electrode to the reference potential, lying upstream the second input terminal 704, and its Ar ^¬ beitselektrode to the control electrode of the switch Q5. The control electrode of the switch Q5 is coupled via a pull-up resistor RIO to its working electrode, which in turn is coupled to the cathode of the diode D3. His reference electrode is gekop pelt ^¬ to the node N5. To improve the susceptibility of the scarf ^¬ tion arrangement, a capacitor Cl is provided, which is coupled between the control electrodes of the switches Q4 and Q5 and the reference potential. How it works: The switch Q4 measures the current through the Zener diode D2, and then, when the Zener diode D2 does not conduct, the voltage across the capacitor C2 is too small. Because no current flows through the zener diode D2, the switch Q4 becomes nonconductive. Q5, when the voltage at its collector is higher than at the emitter as a result of the pull-up resistor R4 durchgeschal ^¬ tet and thus supplies the capacitor C2 with ^{Ladsträ ¬} like. Accordingly, the switch Q5 turns on when the circuit on the series regulator 12 is greater than the sum of the forward voltage of the diode D3, the base-emitter Voltage of the switch Q5 and the voltage at the capacitor C2.

If the voltage across the capacitor C2 is sufficiently large, Q4 becomes conductive and thus pulls charge carriers away from the base of the switch Q5.

In this way, even with an asymmetrical, sawtooth-shaped voltage at the series regulator 12, as is the case with phase-angle and phase-segment dimming, a constant voltage is provided at the node N5.

In a preferred embodiment, RIO is 1kQ and Cl is 200nF.

As is obvious to the skilled person, the invention can also be implemented with a different number of LED units, with different numbers of LEDs, or other AC supply voltages ^¬.

Claims

claims

A circuit arrangement for operating at least a first and a second cascade of LEDs, comprising: an input having a first and a second input terminal (703, 704) for coupling to a rectified supply alternating voltage;

a linear regulator (12) having an input; and at least a first higher level (LE2) and a second lower level LED unit (LE3), wherein the first LED unit (LE2) the first cascade of LEDs (LED29 to LED42) and the second LED unit (LE3) the second cascade from LEDs (LED43 to LED48);

a voltage divider (Rl, R2, R3, D5, D6) coupled between the first and second input terminals (703, 703), the tap (759) of the voltage divider (R1, R2, R3, D5, D6) having coupled to the input of the linear regulator (12); wherein each LED unit (LE3, LE2) further comprises:

- A first diode (D33, D23), which is serially coupled to the respective LED cascade (LED29 to LED42, LED43 to LED48), wherein the coupling ^¬ point of the first diode (D33, D23) and the ^¬ respective LED Cascade (LED28 to LED42, LED43 to LED48) represents a first node (N31, N21), wherein the not coupled to the first diode (D33, D23) terminal of the LED cascade (LED29 to LED42, LED43 to LED48) has a second Node (N32, N22), which does not match the LED cascade (LED29 to LED42, LED43 to LED48) coupled connection of the first diode (D33, D23) represents a third node (N33, N23);

the series connection of a first capacitor (C32, C22) and a second diode (D32, D22), which is coupled between the third (N33, N23) and the second node (N32, N22), wherein the coupling point of the first capacitor ( C32, C22) with the second diode (D32, D22) represents a fourth node (N34, N24); and

- A first (Q31, Q21) and a second electronic switch (B31, B21) each having a control electrode, a reference electrode and a working electrode, wherein the control electrode of the first electronic switch (Q31, Q21) coupled to a fifth node (N5) , wherein the reference electrode of the first electronic switch (Q31, Q21) to the fourth node (N34, N24) is coupled, wherein the Arbeitselek ^¬ trode of the first electronic switch (Q31, Q21) (the control electrode of the second elekt ^¬ tronic switch B31, B21) is coupled, wherein the reference electrode of the second electronic ^¬ rule switch (B31, B21) is coupled to the third bone ^¬ th (N33, N23), said working ^¬ electrode of the second electronic switch (B31, B21) with the second node (N32, N22) is coupled;

wherein the third node (N23) of the highest LED unit (LE2) is coupled to the first input terminal (703), the second node (N32) of the lowest LED unit (LE3) being coupled to the linear regulator (12), that the line arcontroller (12) serially coupled between the second node (N32) of the lowest LED unit (LE3) and the second input terminal (704);

wherein the third node (N33) of a respective LED unit (LE3), which is not the highest LED unit, is coupled to the second node of the next higher LED unit; wherein the fifth node (N5) of all the LED units (LE3, LE2) to a DC voltage source (14) are coupled ^¬ ge;

wherein at least the highest-level LED cascade is associated with a switching device (SV2) which is designed to switch in series in a first state all LEDs of the LED cascade in series and in a second state a first half of LEDs of the LED cascade of a second half of LEDs of the LED cascade in parallel.

Circuit arrangement according to Claim 1,

characterized,

the lower end of the first half of LEDs of at least the highest LED cascade (LE2) represents a sixth node (N26) and the higher end of the second half of LEDs of the highest LED cascade represents a seventh node (N27),

wherein the switching device (SV2) comprises a first (S21), a second (S22) and a third switch (S23),

wherein the first switch (S21) is coupled between the sixth (N26) and the seventh node (N27), where ^¬ in the second switch (S22) between the first (N21) and the seventh node (N27), and wherein the third switch (S23) is coupled between the sixth (N66) and the second node (N22).

Circuit arrangement according to one of Claims 1 or 2, characterized

in that at least one further LED cascade (LE2, LE3), preferably each LED cascade (LE2, LE3), is associated with a corresponding switching device (SV1, SV3).

Circuit arrangement according to one of the preceding claims,

characterized,

in that the voltage divider (R1, R2, R3, D5, D6) comprises a switch (S4) and at least a first (R3) and a second ohmic resistance (R2), the switch being designed and arranged, in a first state the second ohmic resistor from the first ohmic resistance separate and in a second state, the first and the second ohmic resistance in parallel.

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

characterized,

in that it further comprises a control device (20) which is designed and arranged to detect the amplitude of the voltage present at the input, wherein the control device (20) is furthermore designed to operate the at least one switching device and the ^{switch of} the voltage divider ( R1, R2, R3, D5, D6) in Ab- dependence of the detected amplitude of the voltage applied to the input.

6. Circuit arrangement according to claim 5,

characterized,

that the control device (20) is designed

in a first state, which is correlated with a voltage at the input in a first voltage range, the at least one switching device so on ^¬ zusteuern that the corresponding LEDs are connected in series, and the switch of the voltage divider (Rl, R2, R3, D5, D6) in such a way that the second ohmic resistor is disconnected,

and a second state, which is correlated to a voltage at the input in a second voltage range, wherein the second voltage range smaller voltages are assigned as the first Spannungsbe ^¬ rich, the driving at least one switching device such that the first half of the LEDs of the two ^¬ th Half is connected in parallel, and the switch of the voltage divider (Rl, R2, R3, D5, D6) such ^¬ control that the second ohmic resistance is connected in parallel with the first ohmic resistance.

7. Circuit arrangement according to claim 6,

characterized,

that the duty cycles of the respective LED cascades are reduced during operation of the circuit arrangement in the second state, to provide a LED total power of the sound ^¬ processing arrangement, which substantially corresponds to that in the first state.

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

characterized,

that the LED units (LE3, LE2) each have a different number of LEDs (LED43 to LED48, LED28 to

LED42).

9. Circuit arrangement according to claim 8,

characterized,

that each higher LED unit (LE2) contains twice the number of LEDs (LED28 to LED42) as the next lower LED unit (LE3).

10. Circuit arrangement according to claim 8 with reference to one of claims 1 or 2 and 4 to 7,

characterized,

that only the highest LED cascade (LEI) is associated with a switching device (SV1), wherein the number of LEDs of the LED units (LEI, LE2, LE3) is not constructed binary.

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

characterized,

in that the DC voltage source (14) is realized in that the alternating voltage occurring during operation of the circuit arrangement at the second node (N32) of the lowest-lying LED unit (LE3) generates a voltage

DC voltage is used. Circuit arrangement according to one of the preceding claims,

characterized,

in that the first half of LEDs of at least the highest-lying LED cascade, a first capacitor (C13) and the second half of LEDs of at least the highest-lying LED cascade, a second capacitor (C14) are connected in parallel.

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

characterized,

in that each LED unit (LE3, LE2) further comprises a third diode (D31, D21) coupled between the fifth node (N5) and the control electrode of the respective first electronic switch (Q31, Q21).

Circuit arrangement according to one of the preceding claims,

characterized,

in that the DC voltage source (14) comprises a charge pump whose input is coupled to the second node (N32) of the lowest-lying LED unit (LE3) and whose output is coupled to the fifth node (N5) of all LED units (LE3, LE2) ,

Circuit arrangement according to Claim 14,

characterized,

that the charge pump device, the series connection of an A ^¬ weggleichrichters (D3) and a voltage limiting comprises (D2). - l -

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

characterized,

in that the DC voltage source (14) is connected in series with an ohmic resistor (R4) and a fourth resistor

Diode (D3) that covers between the second node

(N32) of the lowest-lying LED unit (LE3) and the fifth node (N5) of all LED units (LE3, LE2) is coupled, and the parallel connection of a third capacitor (C2) and a Zener diode (D2), the between ^¬ rule the fifth node (N5) of all LED units

(LE3, LE2) and the second input terminal (704) is ge ^¬ coupled.

17. Circuit arrangement according to claim 16,

characterized,

that the resistance which is connected in Se rie ^¬ the fourth diode (D3) is formed as a fixed ohmic resistor (R4).

18. Circuit arrangement according to claim 16,

characterized,

that is formed as a variable resistor from ^¬ for realizing a control apparatus of the charge pump of the resistor which is connected in series with the fourth diode (D3). 19. Circuit arrangement according to claim 18,

characterized,

in that the regulating device of the charge pump is designed to regulate the voltage at the fifth node (N5) to a predeterminable value.

20. Circuit arrangement according to one of claims 18 or 19,

characterized,

the regulating device of the charge pump is designed as an inverting voltage regulator.

Circuit arrangement according to one of Claims 18 to 20,

characterized,

that the regulating device of the charge pump comprises a drit ^¬ th (Q4) and a fourth electronic switch (Q5) each having a control electrode, a working ^¬ electrode and a reference electrode, the control electrode of the third electronic switch (Q4) connected to the anode of the Zener diode ( D2) is coupled, its reference electrode with the second inlet connection (704) and its working electrode with the STEU ^¬ erelektrode of the fourth electronic switch (Q5), wherein the control electrode of the fourth electronic switch (Q5) further includes a resistor (RIO) is coupled to its working electrode, which is in turn coupled to the cathode of the fourth diode (D3), wherein the reference electrode of the fourth electronic switch (Q5) to the fifth node (N5) of all LED units (LE3, LE2) is coupled. 22. Circuit arrangement according to claim 21,

characterized,

in that a capacitor (Cl) is coupled between the control electrodes of the third (Q4) and the fourth electronic switch (Q5) on the one hand and the second input terminal (704) on the other hand. Circuit arrangement according to one of the preceding claims,

characterized,

in that a regulating device (16) for regulating the current through the linear regulator (12) is provided, wherein the input of the regulating device (16) is coupled to the fifth node (N5) and the output of the regulating device (16) to the input of the linear regulator (12). 24. Circuit arrangement according to claim 23,

characterized,

in that the regulating device (16) comprises:

a fifth electronic switch (Q3) having a control electrode, a reference electrode and ei ^¬ ner working electrode; and

a voltage divider (Rl, R2, R3, D5, D6) with at least one ohmic resistor (R7, R9) and egg ^¬ nem NTC resistor (NTC), wherein the voltage divider (Rl, R2, R3, D5, D6) between the fifth node (N5) and the second input terminal (704) gekop ^¬ pelt;

wherein the tap of the voltage divider (Rl, R2, R3, D5, D6) is coupled to the control electrode of the fifth electronic ^¬ rule switch (Q3), wherein the reference ^¬ electrode of the fifth electronic switch (Q3) to the second input terminal (704) is coupled, wherein the working electrode of the fifth electronic switch (Q3) is coupled to the input of the linear regulator (12).