AT14316U1 - Driver circuit for LEDs - Google Patents

Abstract

The invention relates to a driver circuit (1) for lighting means, in particular for one or more LEDs, comprising: - a circuit (2) which can be supplied with voltage (Vdc) and clocked by means of at least one switch (LS, HS), which supplies one - a control circuit for controlling the lamp current having a regulator (10), the controller (10) depending on a feedback signal (Im), which reflects the current through the lighting means, and a signal (ILS), which represents a setpoint for the luminous flux, generates a manipulated variable (ASF) for controlling the luminous flux, - a PWM modulator (11) for modulating the manipulated variable (ASF) with a PWM signal ,

Description

description

DRIVER SWITCHING FOR LEDS

In particular, the present invention relates to a control circuit and a converter for the operation of at least one light source, e.g. a driver circuit for the operation of at least one LED, and a corresponding method for operating a lighting means.

A driver circuit for operating LEDs is basically known from the prior art. Such a driver circuit is powered by an electrical supply source, and includes a resonant circuit, such as a resonant circuit. an LLC converter, which is responsible for transmitting power via a galvanic barrier from a primary side to a secondary side of the galvanic barrier. The purpose of this transfer of electrical energy is to provide power to a secondary-connected LED track.

The invention is based on such an LLC topology, e.g. a half-bridge inverter with the following resonant circuit comprises. The resonant circuit feeds a Über¬trager, starting from the secondary side in turn an LED section can be supplied.

However, it is known from the prior art, for the constant control of the LED current, to detect the current through the primary side of the transformer as the actual value of the LED current. However, this measurement is subject to the uncertainty of the magnetization current whose exact size is not determined in this topology.

There is a known correction of this measurement is that on the Sekundärsei¬te the voltage across the LED track is measured and, optionally with other measurements wie such. the temperature is sent from a secondary side microcontroller via the SELV barrier to the microcontroller on the primary side. This microcontroller thus corrects the primary current measurement by this correction contribution, which is calculated using empirical, e.g. in a look-up table of stored measurements from the secondary-side LED voltage measurement. Finally, via an ASIC, the microcontroller controls the frequency of the half-bridge as a function of the current and voltage measurements. The disadvantage here is that the look-up table for determining the correction value can only approximately determine the correct correction contribution. In addition, the solution is relatively expensive with respect to the components, in particular to overcome the SELV barrier.

In such a driver circuit, a dimming of the LED track by kurzmündigem switching off the high-frequency timing of the switch of the half-bridge. This is achieved by a low-frequency PWM modulation. However, it is problematic here that the levels of PWM modulation are limited. The resolution of the stages of PWM modulation, e.g. 7-bit causes so-called dithering, i. the frequency of the LLC converter can not be controlled precisely enough. Consequently, the desired LED current and thus the desired brightness can only be approximately adjusted.

The invention is based on the technical problem of specifying a control circuit or driver circuit for operating light sources, in particular LEDs, in which a nominal value for the brightness is better implemented.

This problem underlying the invention is now solved by the combination of the features of the independent claims. The dependent claims further advantageously form the central idea of the invention.

According to a first aspect of the invention, a driving circuit for illuminants is provided, in particular for one or more LEDs. The driver circuit comprises a voltage-supplyable circuit clocked by at least one switch which feeds a resonant circuit for supplying power to the lighting means. The driver circuit further comprises a control circuit for controlling the luminous flux, comprising a regulator. The controller generates a manipulated variable for the regulation of the luminous flux in

Dependence on a return signal representing the current through the lighting means and on a signal representing a set value for the lighting means current. The driver circuit comprises a PWM modulator for modulating the manipulated variable with a PWM signal.

Preferably, the control circuit is activated continuously and in particular in the Ausschalt¬zeitDauern the PWM signal. The modulation of the manipulated variable by the PWM signal preferably results in the control circuit being activated continuously and in particular also in the off-time periods of the PWM signal.

Preferably, the control loop has a time constant which is slower than the duration of a period of the PWM modulation.

Preferably, the time constant of the control loop is much slower than the time duration of a period of the PWM modulation, e.g. at least 5 times slower, especially between 5 and 10 times slower.

Preferably, the driver circuit has a low pass filter for filtering the return signal. Thus, the controller sets the manipulated variable depending on the low-pass filtered feedback signal.

Preferably, the time constant of the low-pass filter is slower than the duration of a period of the PWM modulation.

The time constant of the control loop may thereby be slower than the duration of a period of the PWM modulation that the time constant of the low-pass filtering by the low-pass filter is slower than the duration of a period of the PWM modulation.

Preferably, the time constant of the control algorithm implemented in the controller is slower than the duration of a period of the PWM modulation.

The time constant of the control loop may thereby be slower than the duration of a period of the PWM modulation that the time constant of the control algorithm implemented in the control algorithm is slower than the duration of a period of the PWM modulation.

Preferably, the PWM modulation due to the slow time constant, in particular due to the slowdown by the low-pass filter, nichtausregelbar by the control circuit.

Preferably, the driver circuit comprises a PWM dimming unit for setting a duty ratio for the PWM modulation depending on a dimming command. DB). The sampling ratio is preferably set independently of feedback variables, in particular from the area of the driver circuit.

In this case, the PWM modulation can be done in particular open-loop. That the PWM signal is modulated on the manipulated variable only by control and not by regulation. In other words, the PWM modulation takes place without feedback.

Preferably, the driver circuit has an amplitude dimming unit for Festle¬gung the setpoint for the lamp current in response to the dimming command.

In this case, the setpoint can be set independently of the set duty cycle for the PWM modulation.

Preferably, in a first dimming range of the dimming command, the duty cycle for the PWM modulation is 100%. lies. Preferably, in a second dimming range, the duty cycle is decreased stepwise or continuously (continuously or quasi-continuously, in a digital embodiment).

Preferably, a cascade control is provided. The first control circuit comprising the regulator for regulating the luminous flux is nested with a second control circuit comprising a further regulator. The second loop may have a faster time constant than the first loop. The second control circuit can in particular serve to regulate a residual ripple of the voltage.

Preferably, the driver circuit has an over-carrier following the resonant circuit for transmitting electrical energy from a primary winding coupled to the resonant circuit to a secondary winding from which the illuminants are powered.

Preferably, the feedback signal indirectly reflects the luminous flux, in which it is inductively coupled out on the secondary side of the transformer.

Preferably, the driver circuit comprises a driver for outputting, based on the PWM modulated manipulated variable, at least one on / off drive signal for controlling the at least one switch of the clocked circuit.

Preferably, the manipulated variable is the frequency and / or the duty cycle of Steue¬rung the at least one switch of the clocked circuit again.

According to a further aspect of the invention, a control unit for operating a drive circuit for lighting means, in particular for one or more LEDs, is provided. The control unit comprises an input for a return signal representing the current through the lighting means. The control unit comprises a control circuit for regulating the luminous flux, comprising a regulator. The controller generates a control signal for the regulation of the luminous flux as a function of the feedback signal and of a signal representing a setpoint value for the luminous flux. The control unit comprises a PWM modulator for modulating the manipulated variable with a PWM signal.

Preferably, the control unit is in the form of an integrated circuit, in particular ASIC or microcontroller or a hybrid version thereof.

According to a further aspect of the invention, a method for controlling the current by means of lamps, in particular by one or more LEDs, is provided. A return signal representing the current through the lamps is tapped off. Depending on the feedback signal and on a signal representative of a setpoint for the luminous flux, a manipulated variable for the regulation of the luminous flux is generated. A PWM signal is modulated onto the manipulated variable.

The aspects mentioned above with respect to the driver circuit are also applicable to the control unit and to the method.

The invention thus preferably proposes that the PWM signal does not temporarily switch off the control loop or modulate the entire half-bridge driver, but rather the output signal of the half-bridge control loop.

Preferably, a control of the LED current by changing the frequency of the half-bridge drive is present. This control loop runs constantly, ie also in the off-time periods of the PWM modulation. This control has a time constant which is clearly slower than the frequency / duration of the PWM modulation.

In a preferred embodiment, the targeted 'slowdown' is accomplished by low pass filtering the feedback signal before the comparator with the desired signal. However, this time constant can also be self-implemented after the comparator or in the control algorithm.

Overall, there is preferably a type of combined PWM / AM dimming. However, since the actual value signal is low-pass filtered and the control loop is continuously active, the LED current remains substantially constant over a period of PWM modulation, resulting in improved color continuity of the LED path.

In the following, the invention will also be described with reference to the figures.

Fig. 1 shows schematically the structure of a driver circuit according to the invention for

Supply of lighting means, in particular for the supply of LEDs or an LED track, FIG. 2 shows an alternative embodiment of the driver circuit according to the invention, FIG. 3 shows an alternative embodiment of the driver circuit according to the invention, [0041] FIG 4 shows an alternative embodiment of the detection of the current through the LEDs in the driver circuit according to the invention, [0042] FIG. 5 shows the influence of a dimming value on parameters of the control according to the invention, and [0043] FIG. 6 shows a further embodiment of a driver circuit according to FIG present

Invention.

In Fig. 1, an embodiment of a driver circuit 1 for the supply of lighting means is shown, in particular in the form of an LED converter for the supply of LEDsbzw. an LED track.

The input voltage Vdc is preferably a rectified, and possibly filtered, AC voltage or mains voltage.

Preferably, this rectified mains voltage is supplied to a converter in the form of, for example, a power factor correction circuit (not shown) before supplying the driver circuit 1. The input voltage Vdc in this case is an approximately constant bus voltage optionally having a residual ripple. In the embodiment of FIG. 1, the input voltage Vdc has an amplitude of 400V. The input voltage may also be called bus voltage or intermediate circuit voltage. Alternatively, the input voltage Vdc can also be a DC voltage or a constant voltage, such as a DC voltage. a battery voltage.

On the input side, a switching regulator is provided in the driver circuit 1, which is fed by the input voltage Vdc. In particular, the input voltage Vdc supplies a clocked circuit or inverter, e.g. may be 2ausgestaltet in the form of a half-bridge circuit. The half-bridge circuit 2 shown has a lower potential switch LS and a higher-potential switch HS. According to the invention, the inverter 2 has at least one switch. As an inverter with a switch, e.g. a flyback converter (not shown) may be provided.

The series-connected switches LS, HS of the half-bridge circuit 2 can be used as transistors, e.g. FET or MOSFET be configured. The switches LS, HS are controlled by respective control signals S / LS, S / HS from a half-bridge driver 12 of a control unit ST. The switches LS, HS are preferably switched on and off alternately by the control signals S / LS, S / HS and by the half-bridge driver 12. The mean value of the current through the LEDs can be adjusted by changing the drive frequency ASF of the switches LS, HS, and / or by changing the duty cycle of the drive. The lower potential switch LS is connected to a primary side ground. At the half-bridge circuit 2, the input voltage Vdc is applied.

Between the two switches LS, HS, i. at the midpoint of the half-bridge circuit 2, a resonant circuit 3 in the form of e.g. connected to a series resonant circuit. Alternatively, according to the invention, a parallel resonant circuit can also be connected at the midpoint of the half-bridge circuit 2. The resonant circuit 3 shown in Fig. 1 is designed as a series resonant circuit and includes inductance and capacitance elements. Specifically, between the primary side ground and the center of the half-bridge circuit 2 is a series circuit comprising a first coil Lr, a second coil La, and a capacitor Cr. Reson¬ nanzkreis 3 is referred to in this case as LLC resonant circuit. The coil Lr and the capacitor Cr preferably form an LC resonant circuit and are referred to as a resonant coil and a resonant capacitor.

The second coil La connected in series with the coil Lr and the capacitor Cr is preferably the primary winding of a transformer T serving as a transformer for galvanic

Separation serves. The transformer T is an example of a galvanic barrier, which is shown in FIG. 1 as a Safety Extra Low Voltage (SELV) barrier. The transformer T collectively forms a galvanic barrier between a primary side having the primary winding La and a secondary side having the secondary winding Lb of the transformer T. In Fig. 1, the transformer T is shown as an ideal transformer, the primary winding of the real transformer T having a leakage inductance and a main inductance for guiding the magnetizing current.

The secondary winding Lb of the transformer T has a tapping, in particular a center tap, this center tap can serve as a secondary ground mass. Alternatively, the secondary winding Lb can consist of two separate windings, in which case the center point of these separate windings corresponds to the center tap.

A terminal of the secondary winding Lb is ver¬bunden with a first detection winding L1, and the other terminal of the secondary winding Lb with a second detection winding LT. The first detection winding L1 and the second detection winding LT are preferably identical. Preferably, the respective number of turns nL1_sec, nL1'_sec of the sense coils L1, LT are equal. In series with the first detection winding L1, a first diode D1 is connected. In series with the second detection winding LT, a second diode DT is connected. The detection windings L1, LT are connected to the anode of the diodes D1, DT.

The respective cathodes of the diodes D1, DT are brought together, so that these diodes D1, DT form a rectifier circuit 4. In operation, an AC current, that is, flows through the secondary winding Lb of the transistor T preferably. an alternating current. Depending on the direction of this alternating current, a current flows through the first diode D1 or through the second diode DT. At the output of the rectifier circuit 4, i. at the connection point of the diodes D1, DT, thus flows a rectified current. The rectifier is also referred to as the center rectifier.

The rectifier circuit 4 supplies on the output side a storage capacitor C2. This storage capacitor C2 is preferably connected between the connection point of the diodes D1, DT and the center tap of the secondary winding Lb. As storage capacitor C2, an electrolytic capacitor can preferably be used because of its comparatively high capacity. The secondary-side current through the detection windings L1, LT is thus rectified first by the rectifier circuit 4 for operating the LEDs, and then preferably filtered or low-pass filtered.

Parallel to the storage capacitor C2, the bulbs, preferably LEDs oreine LED track, are connected. The driver circuit 1 accordingly has two output terminals K1, K2 for connecting the LEDs. In Fig. 1, the illustrated LED should be representative of one or more LEDs. Preferably, the LED circuit operated by the driver circuit 1 may comprise a series connection of a plurality of LEDs. Alternatively, parallel-arranged LEDs or a combination of parallel and series-connected LEDs can also be supplied.

At the output of the rectifier circuit 4 or of the storage capacitor C2, further components may be provided for filtering. By way of example, a coil L2 is shown in FIG. This coil L2 may preferably be arranged in series with the LEDs, this series circuit being connected in parallel with the capacitor C2. The coil L2 is preferably connected between the output terminal K1, on the one hand, and the connection point of the diodes D1, DT, on the other hand. Between the two output terminals K1, K2, the driver circuit can also have a further storage or filter capacitor C3. A resistor R3 can additionally be provided between the output terminal K2 and the center tap of the secondary winding Lb.

The detection windings L1, LT are connected to a primary-side winding L1 " coupled.

The alternating current flowing through the secondary winding Lb of the transistor T is thus converted from the secondary-side detection windings L1, LT into a winding L1 " flowing primary-side current transformed. These three windings L1, LT, L1 " form a detection transformer or a preferably isolated detection Über¬tragers T1. The current through the primary-side winding L1 " gives the current through the secondary windings L1, LT, i. also the current through the LEDs, again. At least in time, the current through the primary-side winding L1 " a representation of the average of the current through the LEDs. Of course, the ratio of the number of turns of the corre sponding primary and secondary windings to one another must be taken into account. Preferably, the number of turns nLT'prim, nL1_sec, nLT sec of the primary and secondary side detection windings L1 ", L1, LT are the same.

In this case, the secondary winding Lb, on the one hand, and the detection windings L1, LT, on the other hand, are preferably designed as separate windings. That the secondary winding Lb and the sense windings L1, LT form two separate transformers. This is in particular due to the requirement that the sense transformer L1, LT, L1 " is designed as a current transformer. In particular, the windings of the detection transformer are designed to enable the loss-free detection of the secondary-side alternating current. By suitable choice of the windings, the detection transformer L1, LT, L1 " have the lowest possible impedance.

The alternating current through the detection windings L1, LT generates an alternating current in the coupled primary side detection winding L1 ". An evaluation circuit 6 is connected to the primary side detection winding L1 " connected to generate a measured value Im for the current through the LEDs. This measurement value Im is fed back to the control circuit ST. On the basis of the obtained feedback value Im, the control circuit ST generates the control signals S / LS, S / HS for the switches LS, HS. Starting from the actual value Im, the control circuit ST performs a current control to a desired setpoint value ILS, in which the half-bridge circuit 2 is clocked accordingly.

The evaluation circuit 6 serves in principle to evaluate the information supplied by the detection winding L1 "information about the current through the LEDs and then returned to the control circuit ST. On the secondary side, therefore, inductive current is decoupled from the signal reproducing the secondary side and transferred to the primary side, where it is rectified, averaged and then supplied to the control circuit ST. The detection winding L1 " is connected to a rectifier 5 for this purpose. The rectifier 5 may be e.g. in the form of a full-bridge rectifier having four diodes (not shown) be configured.

At the output of the rectifier 5, a resistor or shunt Resistor is again connected, which reflects the current through the secondary side and through the LEDs. After a low-pass filtering by a low-pass filter LPF, the actual value signal Im of the LED current Control circuit ST returned. The low pass filter LPF may be e.g. be designed as an RC element with a resistor and a capacitor, wherein the capacitor is preferably connected in parallel to the filtered signal Im. This filtered actual value Im represents the mean value of the LED current. The analog average actual value Im of the LED current is preferably converted by an analog-to-digital converter ADC into a digital actual value. The analog-to-digital converter ADC is preferably configured as a 12-bit converter.

The measured actual value Im of the LED current is subtracted from the control unit ST a setpoint value for the LED current ILS. The control unit ST comprises means such as e.g. a comparator 9 for comparing the set value ILS and the actual value Im, or for forming the difference of these values. This results in a control difference RDF for controlling the current through the LEDs.

Meanwhile, the target value ILS for the LED current may be set internally by the control unit ST. Alternatively, a dimming command B as shown in Fig. 1 may be externally given. For example, For example, the control unit ST may be connected to a line to access it

In particular, this line may be a data line or a data bus for data transmission between the control unit ST and an external communication unit (not shown). The data transmission can take place analogously or preferably digitally by means of a protocol for the control of photometric operating devices. As a protocol, e.g. DALI (Digital Addressable Lighting Interface) or DSI (Digital Serial Interface). The received dimming command B is converted or converted by an amplitude dimming unit 8 into the desired value ILS. The amplitude dimming unit 8 preferably generates a set value SIL in digital form, e.g. as a 12-bit value.

The control difference RDF is supplied to a controller 10, in which a Regelalgorith¬mus is implemented for the control of the LED current. The regulator 10 is preferably designed as a digital regulator and can be used e.g. be configured in the form of a PI controller. Depending on the supplied control difference RDF, the controller generates a control variable, by means of which the half-bridge driver 12 is activated. For example, the control frequency ASF, the switch LS, HS, and / or the pulse duty factor of the control of the switches LS, HS can be provided as a manipulated variable. In this case, the switches LS, HS of the half-bridge 2 are switched to high-frequency, typically in a frequency range of about 10 kHz. The drive frequency ASF is alsotypically higher than 10 kHz and can e.g. up to a few MHz.

The control unit ST comprises in parallel with the amplitude dimming unit 8 for setting the set value ILS for the LED current in response to the dimming command B, a PWM dimming unit 8 '. This PWM dimming unit 8 'serves to convert the received dimming command B into a duty cycle TVH for PWM modulation (pulse width modulation). The frequency of the PWM modulation is low-frequency compared with the drive frequency ASF, typically in the range of 100-1000 Hz. The duty cycle TVH is fed to a PWM modulator 11.

The PWM modulator 11 receives on the input side, on the one hand, the value of the duty cycle TVH for the PWM modulation and, on the other hand, the manipulated variable ASF or a signal representing this setting variable.

The duty cycle TVH is preferably dependent only on the dimming command B and in particular not on the setpoint ILS. In the PWM dimming unit 8 ', a look-up table may be provided in which a suitable duty ratio TVH is stored for different dimming commands B.

The duty cycle TVH affects the PWM modulation by the PWM modulator 11, but not the current regulation by the controller 10. In other words, the controller 10 receives as input only the set value ILS for the LED current and not the duty cycle TVH. Thus, the controller 10 is also not turned off during a turn-off period of the PWM modulation.

Thus, there is a kind of combined PWM / AM dimming, wherein the PWM dimming is done by modulating the PWM signal through the PWM modulator 11 and the AM dimming or amplitude dimming by controlling the amplitude the LED current is made by the regulator 10. Since, however, the actual value signal Im is low-pass filtered and the control loop is continuously active, the LED current in the switch-on periods is higher than in the case of a true AM / PWM dimming, where the control is switched off in a switch-off period of the PWM modulation. Thus, the LED current remains substantially constant except for a sawtooth ripple, resulting in improved color continuity of the LED path.

According to the invention, the control loop of the LED current is selected, for example, between 5 and 10 times slower than the low-frequency PWM modulation of the inverter 2. This PWM modulation is superimposed on the high-frequency operation of the half-bridge inverter for dimming the LED path.

According to the invention, the signal representing the LED current is so low-pass filtered or averaged that the time constant is substantially slower than the frequency of the PWM signal.

Signal.

The controller topology according to the invention is now that the control loop with the actual value signal, low-pass filtered LED current 'and the manipulated variable .Frequency of the half-bridge inverter' is continuously activated, ie in particular in the OFF period of the PWM signal.

The PWM signal, which thus stops the operation of the half-bridge in the switch-off periods, is applied to the output of the control algorithm. The control loop is unable to correct the PWM modulation due to the slowdown due to the low-pass filtering of the feedback signal.

In the embodiment of Fig. 1, the low-pass filter LPF is provided outside the control unit ST.

Preferably, the low-pass filter is designed analogously. Alternatively, the low-pass filter may also be connected within the control unit ST. For example, For example, the low-pass filter LPF may be an analog-to-digital converter ADC, in which case the low-pass filter is implemented digitally. In this case, the low-pass filter may be interconnected either between the analog-to-digital converter ADC and the comparator 9, or between the comparator 9 and the controller 10.

FIG. 2 shows an alternative embodiment for the secondary side of the driver circuit. In particular, an alternative design of the rectification of the secondary-side current is shown in this FIG.

As in the embodiment of FIG. 1, the detection winding L1 is connected in series with the secondary winding Lb, which in contrast to the embodiment of FIG. 1 is designed as a single winding without center tap. The current through the secondary winding Lb is fed to a rectifier circuit 20, which is thus coupled on the input side to the secondary winding Lb or to the series circuit of the secondary winding Lb and the detection winding L1. The rectifier circuit 20 is designed as a bridge rectifier or full-bridge rectifier with four diodes (not shown).

The circuit at the output of the rectifier circuit 20 again corresponds to the circuit at the output of the rectifier circuit 4 shown in FIG. 1. The two output terminals of the rectifier circuit 20 are in particular connected to the storage capacitor C 2. The LEDs can be connected to terminals K1, K2.

FIG. 3 shows a further alternative embodiment for the secondary side of the driver circuit. In particular, in this Fig. 3, another alternative construction of the rectification of the secondary current is shown.

Similar to Fig. 2, the detection winding L1 is connected in series with the secondary winding Lb. The terminal of the secondary winding Lb, which is not connected to the detection winding L1, is connected to two diodes 30, 31, respectively. The secondary winding Lb is connected to the anode of the first diode 30 and to the cathode of the second diode 31. A first storage capacitor C30 is connected between the cathode of the first diode 30 and the Erfas¬sungswicklung L1. A second storage capacitor C31 is connected between the anode of the second diode 31 and the detection winding L1. The diodes D30, D31 form a rectifier circuit 30 which corresponds to the rectifier circuit 4 of FIG. Depending on the direction of flow of the current flowing through the secondary winding Lb, the first or the second diode D30, D31 blocks. The storage capacitors C30, C31 are preferably the same and correspond to the storage capacitor C2 shown in FIG.

Fig. 4 shows an alternative embodiment of the detection of the current through the LEDs in the driver circuit according to the invention.

While in the embodiments of Figs. 1 to 3 the secondary-side current is fed back to the primary side via a detection transformer T1, the embodiment of FIG. 4 dispenses with the detection transformer T1 and thus with the secondary-side detection winding or secondary-side detection windings Lb. A shunt connected in series with the LEDs or Measuring resistor Rshunt is used here for current measurement.

At the measuring resistor Rshunt a signal is tapped, which reflects the current through the LEDs. This signal is preferably low pass filtered, e.g. by an RC element consisting of a capacitor C40 and a resistor R40. Namely, the tapped signal may be used to charge the capacitor C40 serving as an example of implementing an integration of the current.

The charging voltage of the capacitor C40 is supplied to a secondary-side control unit ST2 as a signal provided to the LEDs. The secondary control unit ST2, which is thus arranged on the secondary side of the transformer T, comprises an analog-to-digital converter 40 for converting the measurement signal indigitale data. The analog-to-digital converter 40 is preferably designed as a 12-bit converter. This digital data is e.g. is fed back to the primary side of the transformer 7 via an optocoupler 41 via the SELV barrier. Alternatively to the optocoupler 41, e.g. a digital isolator, e.g. ADUM digital isolator. In particular, the digital data representing current through the LEDs are returned to the primary-side control unit ST, which in turn drives the half-bridge circuit 2 on the one hand by these fed-back actual values of the LED current and on the other hand by the current setpoint ILS or by the dimming command B.

FIG. 5 shows an embodiment for dimming by the amplitude dimming unit 8 and the PWM dimming unit 8.

Preferably, the LED path is now dimmed as follows: From dimming value 100% to a specific dimming value range DWB of, for example, 35%, the LED current is reduced continuously. Here, the duty cycle TVH preferably remains at 100%, so that the PWM modulator 11 has no influence on the manipulated variable.

From a certain dimming value DWB of, for example, 35%, the duty cycle of the PWM modulation is then set to less than 100%. That between this threshold DWB of 35% and a lower threshold USW of e.g. 1%, the duty cycle TVH is reduced in steps. In the PWM dimming unit 8, e.g. stored in a look-up table Korres¬pondenz between dimming value B and duty cycle TVH. The duty cycle TVH remains constant for a specific dimming range. For example, in the dimming range DWB - USW (35% -x%) the duty cycle is the value y% etc., s. Fig. 5.

Thus, if a dimming value below the dimming value DWB, for example, below 35% is specified, a linearly decreasing setpoint for the LED current is fed to the controller. At the same time starting from this dimming value, the duty cycle of the PWM modulator at 100% starting is reduced.

The dimming value specification signal B is thus converted, on the one hand, into a variable PWM duty cycle, and, on the other hand, fed to the control algorithm as a continuously decreasing desired value for the time-averaged LED current. The PWM duty cycle and setpoint preferably do not affect. Rather, both values are preferably dependent only on the dimming value B. This can be seen in FIG. 5, in which the setpoint value ILS decreases linearly with the dimming value B. On the other hand, the duty ratio TVH gradually decreases with the dimming value B, preferably from the dimming value DWB, for example 35%.

The PWM modulation is thus modulated open loop. The continuously running controller 10 tries to correct this type of interference, however, this regulation is tight limits due to the low-pass filtering, for example, the actual value signal. Fig. 5 shows how the controller 10 attempts to control the PWM modulation in which the controller 10 attempts to average the LED current to the value ILED_R.

Thus, the setpoint value ILS for the current regulator 10 is continuously reduced. However, the current through the LEDs remains substantially constant in the on periods of the PWM signal, except for a small sawtooth ripple. However, this ripple is not present in the time course, but considered in continuous dimming, since each controller tries in the constantly shortening on stronger dimming on-time, to constantly control the average value of the current.

Fig. 6 shows another embodiment of a driver circuit according to the present invention.

The driver circuit 60 of FIG. 6 is fundamentally based on the structure of FIG. 1. As the actual value ILED__act, the secondary-side LED current is measured, as shown in FIG. Similar to Fig. 1, the actual value is subtracted from the set value ILS by a comparator 61 and a controller 62, e.g. in the form of a P, PI or PID controller supplied. The output of the regulator 62 is fed to a second comparator 63. Alternatively, to measure the LED current, the feedback topology of Figure 1 may be used with the sense transformer T1.

An actual value for the current through the LLC resonant circuit, or for the current through the coil Lr, the primary winding La or through the capacitor Cr, is measured.

In particular, the primary side alternating current is passed through the LLC resonant circuit of e.g. a diode D60 rectified. The rectified current value is then low pass filtered by an RC element 64, i. averaged, and converted by an analog-to-digital converter 65 into a digital actual value, preferably into a 12-bit value.

The measured actual value of the primary-side current is subtracted from the output of the regulator 62 and supplied to the controller 10. The output of regulator 10 is applied to PWM modulator 11 and half-bridge driver 12 as in FIG.

As explained in the beginning, the input voltage Vdc may be of e.g. 400 V have a Restwel¬ligkeit. When rectifying a mains voltage results in particular a residual ripple of 100 Hz.

The first control loop with the regulator 62 preferably refers to a slow control of the LED current. As a result, e.g. the influence of the temperature, in particular the influence of the ambient temperature on the LEDs, can be compensated.

The second nested control loop with the controller 64, on the other hand, implements a faster algorithm, e.g. to correct the residual ripple of the input voltage Vdc.

The interleaving of the two control circuits or by the cascade control therefore gives even faster compensation options in addition to the relatively slow current control loop. For example, the effect of the 100 Hz ripple in the bus voltage can be detected and compensated.

Advantageously, the PWM modulation according to the invention can be used to limit the maximum switching frequency of the LLC resonant circuit.

With the PWM modulation according to the invention, a better efficiency of the Konver¬ters or the LLC resonant circuit can be achieved.

The PWM modulation according to the invention can be used in combination or as an alternative to amplitude dimming without the need for additional circuitry.

When the PWM modulation according to the invention is used, color shifts are avoided, in particular in the range of low dimming values. This is because the regulator 10 controls a higher LED current. This is e.g. 5, where a current ILED_R is regulated, which is significantly higher than the desired value ILS, so that the color shifts occurring at low current values can be avoided according to the invention.

The low resolution of the PWM modulation is compensated by the control of the mean value of the LED current.

Claims (19)

Claims 1. Driver circuit (1) for illuminants, in particular for one or more LEDs aufwei¬send: - a voltage (Vdc) and supplied by means of at least one switch (LS, HS) clocked circuit (2), one for supplying the A current-serving resonant circuit (3), a control circuit for controlling the luminous flux comprising a regulator (10), the regulator (10) being dependent on a feedback signal (Im) representing the current through the luminous means and a signal ( ILS), which represents a setpoint for the luminous flux, generates a manipulated variable (ASF) for controlling the luminous flux, - a PWM modulator (11) for modulating the manipulated variable (ASF) with a PWM signal. 2. Driver circuit (1) according to claim 1, wherein the modulating of the manipulated variable (ASF) by the PWM signal results in that the control circuit is activated continuously and in particular also in the turn-off periods of the PWM signal. 3. Driver circuit (1) according to one of the preceding claims, wherein the control circuit has a time constant which is slower than the time duration of a period of the PWM Modulati¬on. A driver circuit (1) according to claim 3, wherein the time constant of the control loop is substantially slower than the duration of a period of the PWM modulation, e.g. at least 5 times slower, especially between 5 and 10 times slower. 5. driver circuit (1) according to one of the preceding claims, comprising a low-pass filter (LPF) for filtering the feedback signal (Im), so that the controller (10) depending on the low-pass filtered feedback signal (Im) adjusts the manipulated variable (ASF). The driver circuit (1) according to claim 5, wherein the time constant of the low-pass filter (LPF) is slower than the period of one period of the PWM modulation. 7. Driver circuit (1) according to one of the preceding claims, wherein the time constant of the controller (10) implemented control algorithm is slower than the duration of a Perio¬de the PWM modulation. 8. Driver circuit (1) according to one of claims 3 to 7, wherein due to the slow time constant, in particular due to the slowing down by the low-pass filter (LPF) in a driver circuit (1) according to one of claims 5 to 6, the PWM modulation by the Control loop is not ausregelbar. 9. driver circuit (1) according to any one of the preceding claims, comprising a PWM dimming unit (8 ') for setting a duty cycle (TVH) for the PWM modulation abhän¬gig of a dimming command (B), wherein the duty cycle (TVH) preferably independent of feedback variables insbeson¬dere from the range of the driver circuit (1) is set. A driver circuit (1) according to claim 9, comprising an amplitude dimming unit (8) for setting the lamp current set point (ILS) in response to the dimming command (B). 11. driver circuit (1) according to claim 10, wherein in a first dimming range (100% -DWB) of the dimming command (B) the duty cycle (TVH) for the PWM modulation is 100%, and in one second dimming range (DWB-USW), the duty cycle (TVH) is preferably stu¬fenweise reduced. 12. driver circuit (1) according to one of the preceding claims, wherein the first control circuit auf¬weisend the regulator (10) for controlling the luminous flux with a second Regel¬kreis having another controller (64) is interleaved, wherein the second control loop a faster time constant than the first Regel¬kreis, and for regulating a ripple of the voltage (Vdc) is used. 13. Driver circuit (1) according to one of the preceding claims, comprising a transformer (T) following the resonant circuit (3) for transmitting electrical energy from a primary winding (La) coupled to the resonant circuit (3) to a secondary winding (Lb), starting from which the bulbs are supplied with power. 14. Driver circuit (1) according to one of the preceding claims, wherein the feedback signal (Im) indirectly reproduces the luminous flux, in which it is inductively coupled on the secondary side of the transformer (T). 15. Driver circuit (1) according to one of the preceding claims, comprising a driver (12) for outputting, based on the PWM-modulated manipulated variable, at least one on / off control signal (S / LS, S / HS) for the control of the at least one Switch (LS, HS) of the clocked circuit (2). 16. Driver circuit (1) according to one of the preceding claims, wherein the manipulated variable (ASF) the frequency and / or the duty cycle of the control of the at least one switch (LS, HS) of the clocked circuit (2) reflects. 17. Control unit (ST) for operating a driver circuit (1) for lighting means, in particular for one or more LEDs, comprising: - an input for a current through the lighting means reproducing feedback signal (Im), - having a control circuit for controlling the luminous flux a controller (10), wherein the controller (10) generates a manipulated variable (ASF) for the regulation of the luminous flux, depending on the feedback signal (Im) and a signal (ILS) representing a setpoint value for the luminous flux, a PWM modulator (11) for modulating the manipulated variable (ASF) with a PWM signal 18. Control unit (ST) according to claim 17 in the form of an integrated circuit, in particular ASIC or microcontroller or a hybrid version thereof. 19. A method for controlling the current through lamps, in particular by one or more LEDs, in which - a current through the light emitting means reproducing return signal (Im) is tapped, - depending on the feedback signal (Im) and one, a target value for the lamp current output signal (ILS) a control variable (ASF) is generated for the regulation of the illuminant current, - a PWM signal is modulated onto the manipulated variable (ASF). 4 sheets of drawings