EP2668822B1 - Actuating a plurality of series-connected luminous elements - Google Patents

Description

The invention relates to a circuit for controlling a plurality of series-connected bulbs.

Basically, it is a problem to use semiconductor light elements, e.g. Light-emitting diodes (LED) or LED systems to operate directly on an electrical power grid, in particular when the semiconductor light elements are dimmable and should have at least approximately a sinusoidal current consumption.

Known approaches use up or down converters to set a supply voltage to the semiconductor light elements. Also, a mesh capacitor is used after the mains rectification to keep the current in the semiconductor light elements at a nearly constant level. Such solutions are not dimmable. Furthermore, the current flow through the semiconductor light-emitting elements is not sinusoidal, which leads to a disadvantageous load or unwanted disturbances of the AC mains.

Another disadvantage is that a circuit without energy storage (filter capacitor) leads to a visible flicker of the connected bulbs. However, the filter capacitor also has the disadvantage that high Umladeströme reduce its life; Thus, the filter capacitor is often the weak point of a circuit for controlling the bulbs.

In the US 2010/308739 A1 and the EP 2 187 706 A2 show lighting devices in which, depending on an applied voltage, the number of active light-emitting diodes is changed.

The object of the invention is to avoid the abovementioned disadvantages and, in particular, to provide a solution for efficiently operating dimmable semiconductor light elements via a mains voltage.

This object is achieved according to the features of the independent claims. Further developments of the invention will become apparent from the dependent claims.

To achieve the object, a circuit according to claim 1 is given.

• bei Unterschreiten eines vorgegebenen Schwellwerts elektrische Energie für einen Teil der Leuchtmittel bereitstellen und
• bei Überschreiten des vorgegebenen Schwellwerts (oder eines weiteren Schwellwerts) über die gleichgerichtete Netzspannung aufgeladen werden.

Thus, the energy storage can advantageously serve as a charge pump and depending on the height of the rectified mains voltage

• provide below a predetermined threshold electrical energy for a portion of the bulbs and
• when the predetermined threshold value (or a further threshold value) is exceeded, they are charged via the rectified mains voltage.

As a result, during the course of a cycle (including, for example, discharging, charging and discharging of the energy store), at least a part of the lighting means is almost without Interruption can emit light. The interruptions are not present or so short that a flickering of the bulbs from the human eye is imperceptible. By working as a charge pump energy storage is thus effectively a perceptible flicker of the bulbs prevented.

It should be noted that the discharge phase in particular comprises only a partial discharge of the energy store (a complete discharge is not necessary and possibly also undesirable). Thus, the charging phase is based on that electrical energy is supplied to the energy storage and the discharge phase is based on that electrical energy is removed from the energy storage.

A development is that the energy store during an initial charging phase over several cycles of the rectified mains voltage is rechargeable.

If the energy store, e.g. a capacitor, initially (nearly) empty, it is charged over several cycles. Thereafter, the cyclic operation is performed around an operating point as described above.

It should be noted that one cycle of a positive half cycle may correspond to the rectified pulsating mains voltage. The frequency of the half-waves (and thus of the cycles) corresponds in particular to twice the frequency of the mains alternating voltage.

In particular, it is a further development that the energy store is connected in series with a current source, in particular a constant current source or a voltage-controlled current source.

This makes it possible to ensure that the energy store provides a suitable current during the discharge phase of the second group of light sources.

It is also a development that the series-connected bulbs are connected in series with a voltage-controlled current source.

The current controlled by the voltage-controlled current source is set or limited by the lighting means (as a function of the number of light-emitting means activated by means of the electronic switches). Furthermore, the charging current of the energy storage can be limited by the voltage-controlled current source, if the voltage-controlled current source, for example, is arranged in series with the parallel circuit of energy storage and lighting.

Furthermore, it is a development that the voltage-controlled current source can be controlled via the rectified mains voltage.

By controlling the voltage-controlled current source by means of, for example sinusoidal-like pulsed rectified mains voltage is achieved that at low voltage values (in which only one lamp or a few lamps are activated) and a correspondingly adapted smaller current flows through the lamps than at high voltage values (in which, for example all bulbs are activated). Thus, the voltage controlled current source provides a current suitable for the currently active number of lamps.

Both the number of active lamps and the current through these lamps is therefore influenced or adjusted by the waveform of the rectified mains voltage. This advantageously leads to an almost sinusoidal current consumption and thus minimizes disturbances that act on the power network starting from the circuit.

In an additional development, the electronic switches and the voltage-controlled current source are arranged together in an integrated circuit.

• wobei der erste Energiespeicher
  • während einer Ladephase anhand der elektronischen Schalter parallel zu der ersten Gruppe von Leuchtmitteln geschaltet ist und
  • während einer Entladephase anhand der elektronischen Schalter parallel zu der zweiten Gruppe von Leuchtmitteln geschaltet ist,
• wobei der zweite Energiespeicher
  • während einer Ladephase anhand der elektronischen Schalter parallel zu der ersten Gruppe von Leuchtmitteln geschaltet ist und
  • während einer Entladephase (z.B. anhand der elektronischen Schalter) parallel zu einer dritten Gruppe von Leuchtmitteln geschaltet ist, wobei die dritte Gruppe von Leuchtmitteln beispielsweise eine Teilmenge der ersten Gruppe von Leuchtmitteln ist.

A next development consists in that a first energy store and a second energy store are provided,

• wherein the first energy store
  • is connected in parallel to the first group of lamps during a charging phase based on the electronic switch and
  • is switched parallel to the second group of lamps during a discharge phase on the basis of the electronic switch,
• wherein the second energy storage
  • is connected in parallel to the first group of lamps during a charging phase based on the electronic switch and
  • during a discharge phase (eg based on the electronic switch) is connected in parallel to a third group of bulbs, wherein the third group of bulbs is for example a subset of the first group of bulbs.

Thus, it is possible to further reduce the flicker by providing another charge pump. In particular, both energy stores during the discharge phase (eg when the rectified mains voltage reaches or falls below a predetermined threshold value) can be activated alternately. This can be done by a corresponding control of electronic switches, which are arranged for example in series with the respective energy storage.

An embodiment is that on the basis of a control unit, a detection and evaluation of the rectified mains voltage takes place and depending on a level of the detected mains voltage more or fewer bulbs can be activated via the electronic switch.

In particular, depending on the height of the rectified mains voltage, different electronic switches are activated. Thus, different electronic switches can be gradually activated via the rectified mains voltage and thus a different number of series-connected lighting means can be activated or deactivated. The course of a pulsating DC voltage can thus be used to activate or deactivate different numbers of the lamps depending on their voltage value.

The electronic switches are arranged parallel to the lighting means. In particular, each electronic switch, when activated, can bridge (or short-circuit) a different number of light sources. It is advantageous if the electronic switches are arranged so that upon activation of a first electronic switch of the bulbs, upon activation of a second electronic switch two of the bulbs, upon activation of a third electronic switch three of the bulbs, etc. are bridged. When the last electronic switch is activated, for example, all but one of the lamps connected in series are bridged.

By a common reference potential of the electronic switch, for example, it is ensured that each of the electronic switches can be activated with the same switching voltage.

An alternative embodiment consists in that, in particular based on the control unit, a dimmable control of the lighting means takes place.

Thus, e.g. by means of a reference voltage that can be changed by a user, a brightness control (dimming) of the series-connected bulbs done.

A next embodiment is that the control unit and the electronic switches are designed to be integrated together in a circuit.

A further development is that the lighting means comprises at least one semiconductor light-emitting element, in particular a group of semiconductor light-emitting elements.

The semiconductor light element can be a light-emitting diode (LED).

One embodiment is that the electronic switches comprise semiconductor switches, in particular transistors, bipolar transistors and / or MOSFETs.

It is also an embodiment that the energy storage comprises a capacitor, an electrolytic capacitor or a battery.

The battery can be a rechargeable battery.

Embodiments of the invention are illustrated and explained below with reference to the drawings.

Fig.1

ein schematisches Schaltbild mit einer Ladungspumpe zum Betrieb mehrerer in Reihe geschalteter Leuchtdioden an einer Netzwechselspannung;

Fig.2

ein schematisches Schaltbild mit zwei Ladungspumpen zum Betrieb mehrerer in Reihe geschalteter Leuchtdioden an einer Netzwechselspannung basierend auf der Darstellung von Fig.1;

Fig.3

eine schematische Schaltungsanordnung mit einer Steuereinheit zur Ansteuerung elektronischer Schalter.

Show it:

Fig.1

a schematic circuit diagram with a charge pump for operating a plurality of series-connected LEDs on an AC line voltage;

Fig.2

a schematic diagram of two charge pumps for operating a plurality of series-connected LEDs to an AC line voltage based on the representation of Fig.1 ;

Figure 3

a schematic circuit arrangement with a control unit for controlling electronic switches.

It is proposed to use one or more charge pumps for operating light bulbs, wherein the at least one charge pump, for example, at the beginning (substantially or preferably) continuously and then cyclically (or iteratively) is charged. In periods in which a value of the mains voltage is small, the energy for the lighting means (in particular a chain or a series connection of semiconductor light elements, eg light-emitting diodes) is made available without significantly distorting or disturbing the power consumption of the power network ,

The bulbs can be operated via a voltage-controlled current source, which can serve as a controlling voltage, for example, a pulsed rectified mains voltage. The (sinusoidal) half-waves of the rectified (pulsating) mains voltage have twice the frequency of the mains alternating voltage (eg 100Hz or 120Hz). This results in a (nearly or substantially) sinusoidal operating current for the operation of the lamps.

The bulbs can be controlled via electronic switches. The electronic switches may be semiconductor switches, e.g. Transistors, bipolar transistors, mosfets, etc. act. Preferably, semiconductor switches can be used with a common reference potential. This simplifies the control of the semiconductor switches. In addition, the semiconductor switches may be integrated with the driving unit (e.g., silicon).

Fig.1 shows a schematic circuit diagram for the operation of several series-connected light-emitting diodes 101 to 109 at an AC line voltage 110th

The AC line voltage 110 is converted via a rectifier 111 in a (pulsating) DC voltage. The DC voltage is connected after the rectifier 110 to the anode of a diode 112 (positive supply voltage) and to the terminal of a current source 121 (ground potential).

The cathode of the diode 112 is connected to a node 113. The node 113 is connected via a series connection of a diode 114 and an (optional) current source 115 to a node 118, wherein the cathode of the diode 114 points in the direction of the node 113.

The light-emitting diodes 101 to 109 are connected in series in the same orientation, wherein the anode of the light-emitting diode 101 is connected to the node 113 and the cathode of the light-emitting diode 109 is connected to a node 119. The current source 121 is arranged between this node 119 and the rectifier 111.

A tap or center tap between the light emitting diodes 104 and 105 is referred to as a node 127. Between the node 127 and the node 118, a diode 120 is arranged, the cathode of which in the direction of the node 118 shows. Between the node 117 and the node 119, a capacitor 117 (eg, configured as an electrolytic capacitor) is disposed.

The node 127 is further connected to the drain terminal of a mosfet 122. The source terminal of the mosfet 122 is connected to the node 119. A tap between the light emitting diodes 105 and 106 is connected to the drain terminal of a mosfet 123. The source terminal of the mosfet 123 is connected to the node 119. A tap between the light emitting diodes 106 and 107 is connected to the drain terminal of a mosfet 124. The source terminal of the mosfet 124 is connected to the node 119. A tap between the light emitting diodes 107 and 108 is connected to the drain terminal of a mosfet 125. The source terminal of the mosfet 125 is connected to the node 119. A tap between the light emitting diodes 108 and 109 is connected to the drain terminal of a mosfet 126. The source terminal of the mosfet 126 is connected to the node 119.

The diodes 112, 114 and 120 may be 1N4004 type diodes. Each light-emitting diode 101 to 109 may be embodied as at least one light-emitting diode or at least one semiconductor light-emitting element. In particular, each light-emitting diode 101 to 109 may comprise a group of light-emitting diodes. A setpoint voltage for a group of light-emitting diodes may in particular correspond to the total voltage by the number of light-emitting diodes per group.

For example, each light emitting diode 101 to 109 correspond to a group of light emitting diodes that require a supply voltage of 35V.

• der Mosfet 126 bei einer Netzspannung in Höhe von 8*35V=280V;
• der Mosfet 125 bei einer Netzspannung in Höhe von 7*35V=245V;
• der Mosfet 124 bei einer Netzspannung in Höhe von 6*35V=210V;
• der Mosfet 123 bei einer Netzspannung in Höhe von 5*35V=175V;
• der Mosfet 123 bei einer Netzspannung in Höhe von 4*35V=140V.

The gate terminals of the MOSFETs 122 to 126 are controlled by a suitable control unit (not in FIG Fig.1 shown; Control unit details: see also Figure 3 ). Thus, the mosfets can be activated depending on the level of the mains voltage, eg

• the Mosfet 126 at a mains voltage of 8 * 35V = 280V;
• the Mosfet 125 at a mains voltage of 7 * 35V = 245V;
• the Mosfet 124 at a mains voltage of 6 * 35V = 210V;
• the Mosfet 123 at a mains voltage of 5 * 35V = 175V;
• the Mosfet 123 at a mains voltage of 4 * 35V = 140V.

If the respective mosfet 122 to 126 is activated (short-circuited), the remaining mosfets are preferably blocked. In the above example, this means that with a mains voltage in a range between approximately 175V and 210V, the MOSFET 123 is turned on, as a result of which the light-emitting diodes 106 to 109 are short-circuited or bridged. Thus, during this period, only the light-emitting diodes 101 to 105 are effectively connected in series and can be operated by the (current) mains voltage. The same applies to the other switching states.

Instead of the mosfets, any electronic switches can be used, e.g. (Bipolar) transistors or similar The electronic switches may be used together with the control unit and / or the power sources e.g. be manufactured based on silicon.

It should be noted that center tap or tap designates a possibility of contacting between two components. This corresponds electrically to a node that may be connected to multiple components.

The capacitor 117 is first over several network periods via a threshold voltage of the four light-emitting diodes 101 to 104 (in the above example: 140V) charged. The charging takes place via the node 127 and the diode 120. The current source 121 also limits the charging current for the capacitor 117. During charging, the MOSFETs 122 to 126 are preferably blocked, ie none of the LEDs 105 to 109 is short-circuited.

In this case, the maximum charge of the capacitor 117 is limited to approximately the voltage which drops across the five light-emitting diodes 105 to 109 (175V in the above example).

When the mains voltage at node 118 drops below a predetermined level (e.g., 165V in the above example), the energy stored in capacitor 117 flows through diode 114 and node 113 into the series connection of the LEDs. In this case, the current flow is limited by the optional existing current source 115. Preferably, in this case, the mosfet 122 is turned on, blocking the remaining mosfets 123 to 126. Thus, the current flows from the node 113 via the light-emitting diodes 101 to 104 and the mosfet 122 to the node 119 and from there further via the current source 121 in the direction of the rectifier 111.

The current source 121 limits the current flowing through the LEDs and the maximum charging current of the capacitor 117.

In this respect, cyclically with twice the frequency of the AC line voltage (the pulsating DC voltage provided by the rectifier 111 has twice the mains frequency), the light-emitting diodes 101 to 109 can be operated, wherein at a mains voltage which is less than a predetermined threshold, the Mosfet 122 is turned on and the light emitting diodes 101 to 104 are supplied by the capacitor 117. The capacitor is recharged as soon as the mains voltage is greater than the predetermined threshold (or greater than a second threshold, which in turn is greater than said threshold); In this case, at least the mosfet 122 is deactivated again (switched off).

Preferably, the circuit may be dimensioned such that at least the light-emitting diodes 101 to 104 are not (or only for a very short period of time) de-energized, independent of the instantaneous voltage value of the pulsed rectified waveform of the mains voltage.

The first charging of the capacitor 117 can take place over several network cycles, since (also) the charging current is limited by the current source 121.

Optionally, the power source 115 can be omitted. The current source 115 may be a constant current source or a voltage controlled current source. In the latter case, the controlling voltage may be provided by the rectified mains voltage.

Preferably, the energy supplied to the capacitor 117 during the charging cycle is above its cyclic discharge energy. Preferably, the charging voltage is greater than the discharge voltage of the capacitor. For example, the charging time may be longer than the discharging time and / or an average value of the charging current for the capacitor 117 may be greater than an average value of its discharging current.

Thus, the voltage on the capacitor 117 may oscillate after a successful charging by one operating point. In the example described here, this voltage can oscillate between four to five times the light-emitting diode voltage, ie between 140V and 175V. Advantageously, the capacitor 117 is designed so that in the illustrated Application, the voltage level of 140V during the discharge cycle is not exceeded.

For example, the recharging of the capacitor 117 occurs when the mains voltage is so high that no Mosfet 122 to 126 is turned on or that only the Mosfet 126 is turned on. In the example described here, this corresponds to recharging the capacitor 117 from a voltage of approximately 280V.

The current source 121 is preferably a voltage-controlled current source, wherein the control voltage can be effected by means of the (rectified) mains voltage (dashed line 116 in FIG Fig.1 ). This ensures that the current through the LEDs or to charge the capacitor (almost) sinusoidal (or similar sinusoidal due to the rectified pulsating sinusoidal-wave signal) and thus does not disturb the power supply or not significantly.

The diodes 112, 114 and 120 may be used as electronic switches, e.g. be realized as transistors, mosfets, etc. In particular, the electronic switches can be designed to be integrated together with the current source 115 and / or the current source 121.

Characterized in that the capacitor 117 "charges" charge in the LEDs, when the rectified mains voltage drops below a predetermined threshold, there is an intensity modulation of the lamps with a frequency which is above twice the mains frequency. Thus, a noticeable flicker of the LEDs is effectively prevented.

The capacitor 117 is in the in Fig.1 presented wiring around a charge pump: The capacitor 117 (after initial charging) becomes dependent charged by the voltage of an input signal for a certain period of time; If the voltage falls below a predetermined level, the capacitor pumps charge into the lamps. Discharging and charging can alternate cyclically, with one cycle being dictated by a sinusoidal half cycle of a rectified AC voltage.

It will be explained below by way of example that it is also possible to provide a plurality of charge pumps for operating the lighting means.

Fig.2 shows a schematic circuit diagram for operating a plurality of series-connected LEDs 101 to 109 at an AC line voltage 110 based on the representation of Fig.1 ,

In addition to the charge pump of Fig.1 comprising the capacitor with current source 115 and associated circuitry has Fig.2 another charge pump on. As a result, the pause times can be further shortened and achieve a brightness impression that appears again continuously.

In contrast to Fig.1 has Fig.2 a capacitor 201 (eg, an electrolytic capacitor) connected in series with a current source 202 and a diode 204, the cathode of the diode 204 being connected to a node 203 corresponding to the tap between the light emitting diode 105 and the light emitting diode 106 , The capacitor 201 is connected at its negative pole to the node 119. A tap between the capacitor 201 and the current source 202 is connected via a diode 205 to the node 127, wherein the anode of the diode 205 points in the direction of the node 127.

The diodes 204, 205 are, for example, the same types as the diodes 112, 114 and 120 (1N4004).

The current source 202 may be a current source which can be switched on or off, in particular a controlled current source.

Analogous to the previous comments Fig.1 The capacitor 201 is charged via the voltage at the node 127 and the diode 205. If the voltage at the node 203 falls below a predetermined voltage, which is smaller than the voltage of the charged capacitor 201, the current source 202 can be switched on and the capacitor 201 feeds energy via the diode 204 into the node 203 and thus supplies the light-emitting diodes 106 to 109 with energy. The charging current for the capacitor 201 is limited by the (voltage-controlled) current source 121 and the current through the light-emitting diodes 106 to 109 is also limited by the (possibly voltage-controlled or constant) current source 202.

Optionally, the power source 202 can be omitted and replaced by an electronic switch that can be controlled by the control unit. For example, with the activation of the mosfet 122 (charge flows from the capacitor 117 into the light emitting diodes 101 to 104 and via the mosfet 122 into the node 119), this electronic switch can also be activated: charge then additionally flows from the capacitor 201 via the node 203 through the light emitting diodes 106 to 109 (all Mosfets 123 to 126 lock). It is also possible for the current source 202 to be switched on or off (or the switch provided instead) and the mosfet 122 to be operated alternately (with the same or different switch-on and / or switch-off periods).

Thus, the supply of the light emitting diodes 106 to 109 through the capacitor 201 in addition to the supply of the light emitting diodes 101 to 104 by the capacitor 117 (see above).

Figure 3 shows a schematic circuit arrangement with a control unit 302 for controlling electronic switches (eg, the gate terminals of in Fig.1 and Fig.2 shown Mosfets 122 to 126).

The light-emitting means 305 are, for example, semiconductor light-emitting elements or groups of semiconductor light-emitting elements which are connected in series with one another. In particular, groups of lamps can each be controlled jointly.

A pulsating DC voltage 301 with twice the frequency of an AC line voltage is supplied to a control unit 302. The control unit may have a processor and / or a (micro) controller which, depending on the course of the pulsating DC voltage 301, drives the electronic switches 303. The switches 303 may be the in Fig.1 and Fig.2 Mosfets shown correspond. In addition, it is possible for the current sources 115 and / or 202 to be switched on and off (see in this regard the switch in the current source 202 in FIG Fig.2 ). In principle, it is also possible to use other electronic switches, for example (bipolar) transistors.

The control unit 302 evaluates the progression of a half-wave of the pulsating DC voltage 301 by activating one or more of the switches 303 as a function of the magnitude of the voltage of the half-wave, so that the lighting means 305 are activated in stages via the switches 303 in a manner adapted to the voltage profile ( In this case, the number of activated lighting means 305 can gradually be increased according to the height of the voltage curve). For this purpose, the half-wave is preferably subdivided into stages or switching thresholds, so that the illuminants 305 are switched on stepwise with increasing voltage, and the illuminants 305 are switched off step by step with decreasing voltage of the half-wave.

Furthermore, the pulsating DC voltage 301 also becomes a voltage-controlled current source 304 (compare: voltage-controlled current source 121 in FIG Fig.1 and Fig.2 ) is supplied, by means of which a current through the lighting means 305 depending on the voltage of the half-wave is provided (in particular limited). Thus, it can be achieved that the current through the lighting means 305 is also substantially in phase with the mains voltage, which has a favorable effect on the power factor and reduces or prevents disturbing influences of the circuit on the power grid.

The control unit 302 also shows (at least) an energy store 306 which, as described here, functions as a charge pump and "charges" charge into the lighting means as a function of the height of the pulsating DC voltage.

The energy storage 306 is shown here as an example as part of the control unit, but may also be designed separately for this. Optionally, in this case, the control unit to control at least one switch for activating the energy storage.

Alternatively, it is possible for the control unit 302 to control the voltage-controlled current source 304.

Other advantages:

The at least one charge pump is charged during the lighting phase of the bulbs; During the time in which the grid power is not available or is not sufficient for the operation of the lighting means, energy is provided by the at least one charge pump for operating the lighting means. The energy storage can be done for example by means of a capacitor or by means of another energy storage.

This solution also has the advantage that the power factor is essentially dependent on the voltage-controlled current source and is also limited by this. This results in a substantially sinusoidal current load on the power grid.

The charge pump may be made discrete or integrated.

In particular, the charge pump may be part of the chain of the lighting means (eg integrated in an LED chain). Implementations in which the charging voltage of the at least one charge pump is higher than its discharge voltage are advantageous; In particular, it is advantageous if more current is supplied during a cyclic charging of the charge pump than during the cyclical discharge of the charge pump. Correspondingly (alternatively or additionally), the cyclic charging of the charge pump may take longer than its cyclical discharge.

LIST OF REFERENCE NUMBERS

101 to 109

Light emitting diode or group of semiconductor light elements

110

AC line voltage

111

rectifier

112

diode

113

node

114

diode

115

Power source (constant current source or voltage controlled current source)

116

Voltage for controlling the voltage-controlled current source

117

capacitor

118

node

119

node

120

diode

121

voltage-controlled current source

122 to 126

electronic switches (n-channel mosfets)

127

node

201

capacitor

202

Power source with electronic switch (activatable, for example, from the control unit)

203

node

204, 205

diodes

301

rectified pulsating mains voltage (double the frequency compared to the mains (alternating) voltage)

302

control unit

303

electronic switches

304

voltage-controlled current source

305

Light source (eg series connection of semiconductor light elements or series circuit of semiconductor light systems, each Semiconductor luminaire system has at least one semiconductor element

306

Energy storage (charge pump), e.g. (Electrolyte) Condenser

Claims (13)

1. Circuit for actuating a plurality of light-emitting means (101-109; 305) which are connected in series,

   - comprising a plurality of electronic switches (122-126; 303), which can be actuated depending on a rectified system voltage (301),

   - wherein the plurality of electronic switches (122-126; 303) are arranged in parallel with at least some of the light-emitting means (105-109),

   - wherein each of the plurality of electronic switches (122-126; 303) short-circuits on activation of in each case at least one of the light-emitting means (105-109; 305) connected in series,

   characterized in that

   - the circuit comprises at least one first energy store (117; 306),

   - which is connected in parallel with a first group of light-emitting means (105-109) during a charge phase by virtue of the electronic switches, and

   - which is connected in parallel with a second group of light-emitting means (101-104) during a discharge phase by virtue of the electronic switches,

   - wherein there is a higher voltage drop across the first group of light-emitting means than across the second group of light-emitting means.
2. Circuit according to the preceding claim, in which the first energy store (117; 201; 306) can be charged during an initial charge phase over a plurality of cycles of the rectified system voltage (301).
3. Circuit according to one of the preceding claims, in which the first energy store (117; 201; 306) is connected in series with a current source (115; 202), in particular a constant current source or a voltage-controlled current source.
4. Circuit according to one of the preceding claims, in which the light-emitting means (101-109; 305) connected in series are connected in series with a voltage-controlled current source (121; 304).
5. Circuit according to Claim 4, in which the voltage-controlled current source (121; 304) is actuable via the rectified system voltage (301).
6. Circuit according to either of Claims 4 and 5, in which the electronic switches (122-126; 303) and the voltage-controlled current source (121; 301) are arranged together in an integrated circuit.
7. Circuit according to one of the preceding claims, comprising a second energy store (201),

   - wherein the second energy store

   - is connected in parallel with the first group of light-emitting means (105-109) during a charge phase by virtue of the electronic switches, and

   - is connected in parallel with a third group of light-emitting means (106-109) during a discharge phase, wherein the third group of light-emitting means is in particular a subset of the first group of light-emitting means (105-109).
8. Circuit according to one of the preceding claims, in which detection and evaluation of the rectified system voltage (301) is performed using a control unit (302) and, depending on a level of the detected system voltage (301), more or fewer light-emitting means (101-109; 305) can be activated via the electronic switches (122-126; 303).
9. Circuit according to Claim 8, in which dimmable actuation of the light-emitting means is performed using the control unit.
10. Circuit according to either of Claims 8 and 9, in which the control unit (302) and the electronic switches (122-126; 303) are integrated together in a circuit.
11. Circuit according to one of the preceding claims, in which the light-emitting means comprises at least one semiconductor light-emitting element, in particular a group of semiconductor light-emitting elements.
12. Circuit according to one of the preceding claims, in which the electronic switches comprise semiconductor switches, in particular transistors, bipolar transistors and/or MOSFETs.
13. Circuit according to one of the preceding claims, in which the energy store comprises a capacitor, an electrolyte capacitor or a battery.

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