Driver circuit for light sources, in particular LEDs, LED modules and luminaires, each with such a circuit, and corresponding method

Abstract

Driver circuit (1, 20) for light sources, in particular LEDs, comprising: - a circuit (2) clocked by means of at least one switch (FET1, FET2), such as an inverter in the form of a half-bridge circuit, which feeds a resonant circuit (3), - a transformer (L2) following the resonant circuit (3), from whose secondary winding (L2b) the light sources can be supplied, and - a control circuit (ST) that clocks the switches (FET1, FET2) of the clocked circuit (2), wherein the control circuit (ST) receives an actual signal (ILED_PRIM) that indirectly reflects the current through the light source, which is inductively coupled out on the secondary side (L2 / 2) of the transformer (L2), the control circuit (ST) is designed to: - to regulate the current through the light sources, to clock at least one switch (FET1, FET2) of the clocked circuit (2) depending on the actual signal (ILED_PRIM), and / or - to detect a fault condition following the secondary winding (L2b) of the transformer (L2) and / or the light source based on the actual signal (ILED_PRIM) and depending on this output a fault signal and / or change the control of the clocked circuit (2).

Description

[0001] The present invention relates to a converter for the operation of at least one light source, in particular a driver circuit for the operation of at least one LED.

[0002] Driver circuits for operating LEDs are generally known from the prior art. Such a driver circuit is powered by an electrical supply and includes a resonant circuit, such as an LLC converter, which is responsible for transferring current from a primary side to a secondary side of a galvanic block via a galvanic barrier. The purpose of this transfer of electrical energy is to supply power to an LED array connected on the secondary side.

[0003] For example, document US 2009 / 0219007A1 provides a transformer comprising a first winding and a second winding connected to a primary magnetic flux. Additionally, the transformer includes a third winding connected to a magnetic leakage flux, which is connected to only one of the first and second windings.

[0004] Furthermore, document WO 2010 / 124 311 A1 relates to a driver circuit for an LED, consisting of a connection for a supply voltage, a filter circuit, a rectifier and an intermediate storage element, an isolated switching regulator circuit with at least one switch and a transformer, to whose output at least one LED is connected, wherein a unidirectional decoupling element is present between the rectifier and the intermediate storage element, wherein a capacitor is coupled to the node between the rectifier and the unidirectional decoupling element, the capacitor being coupled with its second terminal to the LED current or the transformer.

[0005] Furthermore, document DE 10 2012 007 449 A1 describes an LLC resonant converter for a light source. This converter has a primary-side circuit and a galvanically isolated secondary-side circuit. During operation of the LLC resonant converter, a first and a second switch of a half-bridge circuit, to which an LLC resonant circuit of the primary-side circuit is connected, are switched in a clocked manner. A voltage is detected in the primary-side circuit. This voltage is processed to obtain information about an output voltage of the secondary-side circuit. It is known that such a resonant circuit or driver circuit is operated as a constant-current converter. For this purpose, a control loop for regulating the LED current can be provided, whereby an actual value of the LED current can be measured on the secondary side of the galvanic isolation.This actual value measurement must, however, be fed back to a primary-side control circuit in order to control the driver circuit accordingly. A disadvantage of this design is that feeding the actual value of the LED current back to the primary-side control circuit requires galvanic isolation and therefore an optocoupler.

[0006] Therefore, prior art attempts have already been made to eliminate the need for secondary-side measurement of the LED current and to indirectly determine the current value via the current on the primary side of the transformer. Based on this feedback value, current control is performed by changing a corresponding switch in a half-bridge circuit of the driver circuit.

[0007] However, even these designs are unsatisfactory. This primary-side measurement has the disadvantage that it doesn't directly reflect the LED current, but rather includes the variable component of the magnetizing current on the primary side. This component is variable and depends primarily on the LED voltage, which in turn depends, for example, on the number of LEDs. A fixed compensation of the magnetizing current is therefore not possible. Instead, compensation requires a direct measurement of the LED voltage, which, however, necessitates an analog-to-digital converter and feedback via an optocoupler to the control circuit on the primary side.

[0008] The invention is based on the technical problem of providing a circuit or LED converter for operating an LED system and a corresponding operating method, in which the primary-side control can be improved and, in particular, the aforementioned disadvantages can be eliminated.

[0009] This problem underlying the invention is now solved by combining the features of the independent claims. The dependent claims advantageously further develop the central idea of ​​the invention.

[0010] The basic idea of ​​the invention is to indirectly bring about a secondary-side transformer-based detection of the LED current by means of a transformer-based coupling in the area of ​​the secondary side, in particular between the secondary side of the transformer and the rectification.

[0011] According to a first aspect of the invention, a driver circuit for light sources, in particular LEDs, is provided. The driver circuit comprises a circuit switched by means of at least one switch, such as an inverter in the form of a half-bridge circuit, which feeds a resonant circuit. The driver circuit includes a transformer following the resonant circuit, from whose secondary winding the light sources can be supplied. The driver circuit includes a control circuit that switches the switches of the switched circuit.

[0012] The control circuit receives a feedback signal that indirectly reflects the current through the light sources and is inductively coupled out on the secondary side of the transformer.

[0013] The control circuit is designed to control the current through the light sources by pulsing at least one switch of the pulsed circuit depending on the actual signal.

[0014] Alternatively or additionally, the control circuit is designed to detect a fault condition following the secondary winding of the transformer - i.e., a fault condition on the secondary side of the transformer - and / or the light source based on the actual signal, and depending on this, to output a fault signal and / or change the control of the clocked circuit.

[0015] According to a further aspect of the invention, an LED module is provided, comprising such a driver circuit and at least one LED section supplied by the driver circuit, which has at least one LED.

[0016] According to another aspect of the invention, a luminaire, such as an LED luminaire, is provided. The luminaire includes such a driver circuit. The luminaire further includes an upstream rectifier for rectifying a mains voltage, and a DC / DC converter, e.g., in the form of a power factor correction circuit, for supplying the driver circuit from the rectified mains voltage.

[0017] According to a further aspect of the invention, a method is provided for regulating the current through a lighting circuit using a driver circuit. The driver circuit comprises a circuit, for example a half-bridge circuit, which feeds a resonant circuit and is clocked by at least one switch. The driver circuit includes a transformer following the resonant circuit, from whose secondary winding the lighting elements are supplied. The driver circuit further comprises a control circuit that clocks the switches of the clocked circuit.

[0018] The control circuit receives a signal that indirectly reflects the current through the light sources and is inductively coupled out on the secondary side of the transformer.

[0019] The control circuit regulates the current through the light sources according to this actual signal by clocking the clocked circuit depending on the actual signal.

[0020] Alternatively or additionally, the control circuit uses the actual signal to detect a fault condition on the secondary side of the transformer and / or a fault condition of the light source. Depending on this, the control circuit outputs an error signal and / or modifies the control of the clocked circuit.

[0021] Preferably, the secondary winding of the transformer feeds a rectifier circuit and the actual signal is coupled out before rectification.

[0022] Preferably, the rectifier circuit is designed as a full-bridge rectifier or center-tap rectifier.

[0023] Preferably, the driver circuit comprises a sensing transformer with at least one sensing winding connected on the secondary side of the transformer for inductive coupling of the actual signal.

[0024] Preferably, a sensing winding is provided on the secondary side of the transformer if the rectifier circuit is designed as a full-bridge rectifier. Two sensing windings are provided on the secondary side of the transformer if the rectifier circuit is designed as a center-tap rectifier.

[0025] Preferably, the actual signal is supplied to the control circuit via an evaluation circuit.

[0026] Preferably, the evaluation circuit includes a rectifier.

[0027] Preferably, the evaluation circuit is designed such that one or both polarities of the inductively coupled actual signal are supplied to the control circuit.

[0028] Preferably, the control circuit controls the switches of the clocked circuit without galvanic isolation.

[0029] Preferably, the control circuit is an ASIC or a microcontroller.

[0030] Preferably, no signal is fed back to the control circuit from the primary side of the transformer, i.e., the side of the transformer facing the clocked circuit.

[0031] In summary, the invention relates to a driver circuit or an LED driver in which, for example, a so-called LLC resonant circuit is used. A half-bridge circuit feeds a resonant circuit, which, via galvanic isolation in the form of, for example, a transformer and a rectifier circuit, supplies the LED section. According to the invention, no buck converter (DC / DC converter) or other switched-mode converter is provided on the secondary side of the transformer.

[0032] Different circuit topologies are provided, since according to the invention there are different possibilities to tap into the secondary winding of the transformer and to supply this rectified voltage to the LED section.

[0033] The general aim of the embodiments according to the invention is to have as few feedback connections as possible from the secondary side to the control circuit on the primary side, with potential separation, and to avoid costly optocouplers.

[0034] The transformer-based output and the specific evaluation of this transformer-based AC signal according to the invention can be carried out in different ways. According to the invention, it is important that a signal is transformed and, if necessary, processed on the secondary side of the transformer and fed to the primary-side control circuit, which in turn clocks the power switches of the half-bridge. Thus, the control loop is closed.

[0035] The invention is further described below with regard to the figures. Fig. Figure 1 schematically shows the structure of a driver circuit according to the invention for supplying a LED section, Fig. Figure 2 shows a further embodiment of a driver circuit according to the invention for supplying a LED section, Fig. Figure 3 shows a first embodiment of an evaluation circuit for feeding back an actual signal, Fig. Figure 4 shows a further embodiment of an evaluation circuit according to the invention, and Fig. Figure 5 shows another embodiment of an evaluation circuit according to the invention for feeding back the actual signal.

[0036] Fig. Figure 1 shows an embodiment of a driver circuit 1 for supplying light sources, in particular in the form of an LED converter for supplying LEDs or an LED section.

[0037] The driver circuit 1 is powered by an input voltage Vdc. The input voltage Vdc is preferably a rectified, and optionally filtered, AC voltage or mains voltage. Preferably, this rectified mains voltage is fed to a converter, for example, a power factor correction circuit (not shown), before it supplies the driver circuit 1. In this case, the input voltage Vdc is an approximately constant bus voltage, optionally exhibiting ripple. Alternatively, the input voltage Vdc can also be a DC voltage or a constant voltage, such as a battery voltage.

[0038] On the input side, the driver circuit 1 includes a switching regulator which is supplied by the input voltage Vdc. The input voltage Vdc supplies, in particular, a switched-mode circuit or an inverter, which can be configured, for example, as a half-bridge circuit 2. The half-bridge circuit 2 shown has a lower-potential switch FET2 and a higher-potential switch FET1. According to the invention, the inverter 2 has at least one switch. For example, a flyback converter (not shown) can be provided as the inverter with one switch.

[0039] The two switches FET1 and FET2 of half-bridge circuit 2 can be implemented as transistors, e.g., FETs or MOSFETs. Switches FET1 and FET2 are controlled by their respective control signals HS and LS from a control circuit ST. The switch with the lower potential, FET2, is connected to a primary ground, GND_PRIM. The input voltage Vdc is applied to half-bridge circuit 2.

[0040] At the midpoint of the half-bridge circuit 2, i.e., between the two switches FET1 and FET2, a resonant circuit 3, for example in the form of a series resonant circuit, is connected. Alternatively, according to the invention, a parallel resonant circuit can also be connected at the midpoint of the half-bridge circuit 2. The one described in Fig. The resonant circuit 3 shown in Figure 1 is designed as a series resonant circuit and comprises inductor and capacitance elements. Specifically, a series connection between the primary-side ground GND_PRIM and the center point of the half-bridge circuit 2 includes a first coil L1, a second coil L2a, and a capacitor C1. In this case, the resonant circuit 3 is referred to as an LLC resonant circuit. The capacitor C1 and the coil L1 preferably form an LC resonant circuit.

[0041] The second coil L2a is preferably the primary winding of a transformer L2, which serves as a galvanic isolation device. The transformer L2 is an example of a galvanic blocking device. Fig. Figure 1 shows the transformer L2 as an ideal transformer, where the primary winding of the real transformer L2 may have a leakage inductance and a main inductance for carrying the magnetizing current.

[0042] The transformer L2 forms a galvanic barrier 5 between a primary side L2 / 1 having the primary winding L2a and a secondary side L2 / 2 having the secondary winding L2b of the transformer L2.

[0043] This secondary winding L2b of the transformer L2 is fed to a rectifier 4, which in the exemplary embodiment of the Fig. 1 is designed as a bridge rectifier or full bridge rectifier with four switched diodes D1, D2, D3, D4. This design with the four diodes D1, D2, D3, D4 is an example of a passive rectifier. Alternatively, the rectifier can be designed as an active rectifier, in particular with switches, e.g. in the form of MOSFETs.

[0044] The full-bridge rectifier feeds a storage capacitor C2 from a secondary-side ground GND_SEC on its output side. Due to its comparatively high capacitance, an electrolytic capacitor can preferably be used as storage capacitor C2.

[0045] The light sources, preferably LEDs or an LED strip, are connected in parallel to the storage capacitor C2. Fig. The LED shown in Figure 1 is intended to be representative of one or more LEDs. Preferably, the LED array driven by the driver circuit 1 can have several LEDs connected in series. Alternatively, LEDs arranged in parallel or a combination of LEDs connected in parallel and in series can also be driven.

[0046] Additional filtering components may be provided at the output of rectifier circuit 4 or the storage capacitor C2. An example of this is shown in Fig. Figure 1 shows a coil L3. This coil L3 is arranged in series with the LEDs, with this series circuit being connected in parallel with capacitor C2.

[0047] During operation, an AC current preferably flows through the secondary winding L2b of transistor L2. According to the invention, it is now proposed to transform this alternating current into a primary-side current via a sensing winding CTR1 provided on the secondary side L2 / 2. For this purpose, this sensing winding CTR1 is coupled to a primary-side sensing winding CTR3.

[0048] The secondary-side sensing winding CTR1 is arranged in series with the secondary winding L2b of the transformer L2. Preferably, the sensing winding CTR1 is connected between the secondary winding L2b and the rectifier circuit 4, i.e., between a terminal of the secondary winding L2b and an input terminal of the rectifier circuit 4.

[0049] According to a preferred embodiment, the secondary winding L2b and the sensing winding CTR1 are configured as separate windings. That is, the secondary winding L2b and the sensing winding CTR1 form two separate transformers. This is particularly necessary because the sensing transformer CTR1, CTR3 is designed as a current transformer. The windings of the sensing transformer CTR1, CTR3 are specifically designed to enable the most lossless possible detection of the secondary-side alternating current. By appropriately selecting the windings, the current-configured sensing transformer CTR1, CTR3 can exhibit the lowest possible impedance.

[0050] The current through the sensing winding CTR1 reflects the current through the LEDs. If the optional storage capacitor C2 is not included in driver circuit 1, the current through the sensing winding CTR1 actually flows through the LEDs. When the filtering capacitor C2 is connected, the electrical energy it temporarily stores is released back to the load, i.e., the LEDs. Whether with or without storage capacitor C2, the average LED current remains the same, and the sensing winding CTR1 reflects the LED current.

[0051] The alternating current through the sensing winding CTR1 generates a corresponding alternating current in the primary-side sensing winding CTR3. An evaluation circuit 30 is connected to the primary-side sensing winding CTR3 to generate a measured value ILED_PRIM for the current through the LEDs. This measured value ILED_PRIM is fed back to the control circuit ST. Based on the received feedback value, the control circuit ST generates the control signals HS, LS for the switches FET1, FET2, which are alternately switched on and off. Starting from the actual value ILED_PRIM, the control circuit ST performs current regulation to a desired setpoint by clocking the half-bridge circuit 2 accordingly.

[0052] The exemplary embodiment of the Fig. The evaluation circuit 30 used is described below in connection with Fig. 3 explained in more detail.

[0053] Fig. Figure 2 shows another embodiment of a driver circuit 20 for light sources such as LEDs.

[0054] The driver circuit 20 basically corresponds to the one in Fig. The driver circuit 1 shown in 1 comprises the half-bridge circuit 2 and the resonant circuit 3. This is in the exemplary embodiment of the Fig. 1 the driver circuit 20 differs, however, in the design of the transformer and the rectifier circuit 24.

[0055] The secondary winding L2b of the transformer L2 has a tap, specifically a center tap. This center tap forms a potential of the output voltage of the rectifier circuit 24, namely the secondary-side ground GND_SEC.

[0056] One terminal of the secondary winding L2b is connected to the anode of a first diode D1', and the other terminal of the secondary winding L2b is connected to the anode of a second diode D2'. The respective cathodes of diodes D1' and D2' are connected together and form the other output potential of the rectifier circuit 24, which is preferably connected to the storage capacitor C2. This rectifier 24 can be called a center-tap rectifier.

[0057] In contrast to the exemplary embodiment of the Fig. Two secondary-side sensing windings, CTR1' and CTR2', are now required to ensure correct detection of the alternating current on the secondary side L2 / 2. Depending on the direction of the alternating current, a current will flow through either the first or the second diode, D1' or D2'. Therefore, to completely detect the current through the LEDs, the first sensing winding, CTR1', is connected in series with the first diode, D1', and the second sensing winding, CTR2', is connected in series with the second diode, D2'.

[0058] As in Fig. As shown in Figure 2, the two secondary-side sensing windings CTR1' and CTR2' are coupled to the primary-side sensing winding CTR3. Regardless of the design of the driver circuit according to the exemplary embodiment of the Fig. 1 or the Fig. 2 results in the same total current at the primary-side detection winding CTR3.

[0059] Similar to in Fig. 1 The sensing transformer formed by the windings CTR1', CTR2', CTR3 is designed as a current transformer. Preferably, the sensing windings CTR1', CTR2' are also designed separately from transformer L2.

[0060] Compare to the embodiment of the Fig. 2 are involved in the design according to Fig. One more diode is required – the four diodes D1, D2, D3, D4 compared to two diodes D1', D2'. However, driver circuit 1 includes a single secondary-side sensing winding CTR1, compared to the two windings CTR1', CTR2' of driver circuit 20 with center tap.

[0061] Fig. Figure 3 shows an embodiment of the evaluation circuit 30, as it is used in the driver circuits 1, 20 of the Fig. 1, Fig. 2 occurs.

[0062] The evaluation circuit 30 serves, in principle, to evaluate and process the information about the current through the LEDs supplied by the sensing winding CTR3 and then feed it back to the control circuit ST. To determine the value of the current through the secondary side L2 / 2, the control circuit ST should, in particular, take into account the ratio of the number of turns of the windings CTR1, CTR3 or CTR1', CTR2', CTR3, whereby in the exemplary embodiment the Fig. 2 the number of turns of the secondary-side detection windings CTR1', CTR2' are preferably equal.

[0063] In parallel with the detection winding CTR3, two series circuits are connected, each consisting of a diode DR1, DR2 and a resistor or measuring resistor Rb1, Rb2. Resistors Rb1, Rb2 are each connected to the primary ground GND_PRIM. One diode DR2 is connected with its anode to a terminal of the detection winding CTR3, and the other diode DR1 is connected with its cathode to the same terminal. The diodes DR1, DR2, and the corresponding series circuits, are connected in antiparallel.

[0064] The evaluation circuit 30 is designed in such a way that only one half-wave of the current detected by the detection winding CTR3 is evaluated and fed back to the control circuit ST.

[0065] Preferably, the current through the LEDs is evaluated via the voltage across one of the resistors Rb1, Rb2. In the embodiment of the Fig. 3. The voltage across resistor Rb2 is taken into account. Alternatively, the voltage across the other resistor Rb1 could also be considered.

[0066] As in Fig. As shown in Figure 3, the voltage representing the LED current is fed to an RC circuit. This RC circuit consists of a resistor Rlp and a capacitor Clp and serves to low-pass filter the measured voltage across resistor Rb2. Thus, an average value of the current through the LEDs is fed back to the control circuit ST. This RC circuit is optional, so the voltage across resistor Rb2 can also be used as the feedback value ILED_PRIM.

[0067] Fig. Figure 4 shows another embodiment of the evaluation circuit 40. This evaluation circuit 40 can be used, for example, in the Fig. 1 and Fig. 2. Replace the evaluation circuit 30.

[0068] The only difference from the embodiment according to Fig. 3 here is the omission of resistor Rb1, whose voltage in Fig. 3 is not measured.

[0069] The operation of the evaluation circuit 40 is therefore similar, in that only one half-wave of the current detected by the detection winding CTR3 is evaluated and forwarded to the control circuit ST as the actual signal ILED_PRIM.

[0070] In evaluation circuit 40, one component – ​​resistor RB1 – is therefore omitted. However, this embodiment is different compared to... Fig. 3. This is also disadvantageous, as both half-waves are not loaded symmetrically.

[0071] In Fig. However, both half-waves of the circuit are advantageously loaded symmetrically by the resistors Rb1 and Rb2, particularly if both resistors Rb1 and Rb2 have the same electrical resistance. The resulting symmetrical loading of the current through the secondary side, and thus through the resonant circuit 3, is advantageous for the proper operation of the driver circuit.

[0072] Fig. Figure 5 shows another embodiment of the evaluation circuit 50, which is also used with a driver circuit 1, 20 according to Fig. 1 or Fig. 2 can be used.

[0073] In contrast to the Fig. 3 and Fig. 4. Both half-waves are evaluated here. Accordingly, the detection winding CTR3 is connected to a full-bridge rectifier 51, which preferably consists of four diodes DR1', DR2', DR3', DR4'. Thus, both the positive and negative half-waves of the alternating current are passed through or rectified by the rectifier 51 via the winding CTR3.

[0074] At the output of the full-bridge rectifier 51, a resistor or measuring resistor Rb is connected, which indicates the current through the secondary side and through the LEDs. After optional low-pass filtering by the RC network Rlp, Clp, the actual signal ILED_PRIM is fed back to the control circuit.

[0075] Advantageously, both half-waves of the alternating current are evaluated in evaluation circuit 50. The main advantage is that the LED current measurement is now more accurate and that there is a linear relationship between the LED current and the feedback parameter ILED_PRIM. The uncertainty associated with a potentially variable magnetizing current is therefore eliminated in evaluation circuit 50.

[0076] A disadvantage of the solution with the full-bridge rectifier 51 is that, with regard to the components used, it is also the most expensive embodiment of the Fig. The three evaluation circuits shown in 3-5.

[0077] For example, the detection transformer can have a turns ratio of 1:60. The in Fig.The 3-5 resistors Rb1, Rb2, Rb used to evaluate the alternating current have, for example, a value of 60 ohms. For low-pass filtering, the resistor Rlp and the capacitor Clp have, for example, values ​​of 130 ohms and 220 nF respectively.

[0078] Preferably, no further measurement signal from the primary side of the resonant circuit 3 is supplied to the control circuit ST on the primary side L2 / 1, and in particular preferably no measurement signal representing the current through the half-bridge circuit 2. Specifically, no measuring resistor is connected in series with the primary winding L2a or in series with the resonant circuit 3.

[0079] In addition to or as an alternative to regulating the current through the LEDs, certain fault conditions can also be detected via the aforementioned measurement of the actual signal ILED_PRIM. In particular, the fault condition "no load" can be determined, in which case no current flows on the secondary side L2 / 2. For example, this fault condition could mean that there is no load or no LEDs present, or that the LEDs or the LED circuit are defective.

[0080] Based on the current signal ILED_PRIM, the control circuit can detect a fault condition on the secondary side L2 / 2 of transformer L2 and / or a fault condition of the light source or LEDs. Depending on this, the control circuit ST can output a fault signal and forward it, for example, to a central monitoring unit (not shown). Depending on such fault conditions, the control circuit ST can also modify the control of the inverter or half-bridge 2.

Claims

[1] Driver circuit (1, 20) for lighting means, in particular LEDs, comprising: - a circuit (2) clocked by at least one switch (FET1, FET2), such as an inverter in the form of a half-bridge circuit, which feeds a resonant circuit (3), - a transformer (L2) following the resonant circuit (3), from whose secondary winding (L2b) the lamps can be supplied, and - a control circuit (ST) which clocks the switches (FET1, FET2) of the clocked circuit (2), wherein an actual signal (ILED_PRIM) indirectly representing the current through the lamps is fed back to the control circuit (ST), which is inductively coupled out on the secondary side (L2 / 2) of the transformer (L2), wherein the control circuit (ST) is designed to: - to control the current through the lighting means by clocking at least one switch (FET1, FET2) of the clocked circuit (2) depending on the actual signal (ILED_PRIM), and / or - to detect an error condition following the secondary winding (L2b) of the transformer (L2) and / or the lighting means based on the actual signal (ILED_PRIM) and, depending thereon, to output an error signal and / or to change the control of the clocked circuit (2). [2] Driver circuit according to claim 1, wherein the secondary winding (L2b) of the transformer (L2) feeds a rectifier circuit (4, 24) and the actual signal (ILED_PRIM) is coupled out before rectification. [3] Driver circuit according to claim 2, wherein the rectifier circuit is designed as a full-bridge rectifier (4) or center-point rectifier (24). [4] Driver circuit according to one of the preceding claims, comprising a detection transformer with at least one detection winding (CTR1, CTR1', CTR2') connected on the secondary side of the transformer (L2) for inductively coupling out the actual signal. [5] Driver circuit according to claims 4 and 3, wherein a detection winding (CTR1) is provided on the secondary side of the transformer (L2) when the rectifier circuit is designed as a full-bridge rectifier (4), and two detection windings (CTR1', CTR2') are provided when the rectifier circuit is designed as a center-point rectifier (24). [6] Driver circuit according to one of the preceding claims, in which the actual signal is supplied to the control circuit (ST) via an evaluation circuit (30, 40, 50). [7] Driver circuit according to claim 6, wherein the evaluation circuit (30, 40, 50) comprises a rectifier. [8] Driver circuit according to claim 6 or 7, wherein the evaluation circuit (30, 40, 50) is designed such that one or both polarities of the inductively coupled actual signal are fed to the control circuit (ST). [9] Driver circuit according to one of the preceding claims, in which the control circuit (ST) controls the switches (FET1, FET2) of the clocked circuit (2) without galvanic isolation. [10] Driver circuit according to one of the preceding claims, wherein the control circuit (ST) is an ASIC or a microcontroller. [11] Driver circuit according to one of the preceding claims, in which no signal is fed back to the control circuit (ST) from the primary side (L2 / 1) of the transformer (L2), i.e. the side of the transformer (L2) facing the clocked circuit (2). [12] LED module, comprising a driver circuit (1, 20) according to one of the preceding claims and at least one LED path supplied by the driver circuit (1, 20) which has at least one LED. [13] Luminaire, in particular LED luminaire, comprising a driver circuit (1, 20) according to one of claims 1 to 11 and an upstream rectifier for rectifying a mains voltage and a DC / DC converter, e.g. in the form of a power factor correction circuit, for supplying the driver circuit (1, 20) from the rectified mains voltage. [14] Method for regulating the current through a lighting circuit, using a driver circuit (1, 20) comprising: - a circuit (2) clocked by at least one switch (FET1, FET2), for example a half-bridge circuit, which feeds a resonant circuit (3), - a transformer (L2) following the resonant circuit (3), from whose secondary winding (L2b) the lamps are supplied, and - a control circuit (ST) which clocks the switches (FET1, FET2) of the clocked circuit (2), wherein an actual signal (ILED_PRIM) indirectly reflecting the current through the lamps is fed back to the control circuit (ST), which is inductively coupled out on the secondary side (L2 / 2) of the transformer (L2), wherein the control circuit (ST) regulates the current through the lamps by clocking the clocked circuit (2) depending on the actual signal (ILED_PRIM). [15] Method for regulating the current through a lighting circuit, using a driver circuit (1, 20) comprising: - a circuit (2) clocked by at least one switch (FET1, FET2), for example a half-bridge circuit, which feeds a resonant circuit (3), - a transformer (L2) following the resonant circuit (3), from whose secondary winding (L2b) the lamps are supplied, and - a control circuit (ST) which clocks the switches (FET1, FET2) of the clocked circuit (2), wherein an actual signal (ILED_PRIM) indirectly reflecting the current through the lamps is fed back to the control circuit (ST), which is inductively coupled out on the secondary side (L2 / 2) of the transformer (L2), wherein the control circuit (ST) detects an error condition following the secondary winding (L2b) of the transformer (L2) and / or the lighting means on the basis of the actual signal (ILED_PRIM), and, depending thereon, outputs an error signal and / or changes the control of the clocked circuit (2).

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