WO2017186968A1

WO2017186968A1 - Method for controlling an led module

Info

Publication number: WO2017186968A1
Application number: PCT/EP2017/060375
Authority: WO
Inventors: Clemens KUCERA; Frank Lochmann
Original assignee: Tridonic Gmbh & Co Kg
Priority date: 2016-04-29
Filing date: 2017-05-02
Publication date: 2017-11-02
Also published as: EP3449692A1; AT15390U1

Abstract

The invention relates to a method for controlling an LED module by means of a half-bridge circuit with two switches or a full-bridge circuit with four switches, wherein the LED module (EL) is connected in the bridge branch and a diagonal bridge section is activated, wherein a switch (S1, S2) is actively clocked, wherein the LED module has two antiparallel strands, wherein the two antiparallel strands differ in each strand, in particular by a different colour temperature or wavelength of the corresponding LED.

Description

Method for controlling an LED module

The invention relates to a method and a circuit arrangement for operating light sources, in particular a load such as light-emitting diodes (LED), and a lamp. The light source such as a light emitting diode is also referred to as a lamp.

To operate LED lights typically power factor corrected power supplies are used. Since an LED track, in particular a dimmable LED track, is not a constant load, these power supplies are usually regulated. For this purpose, a monitoring of the output voltage or the output current of the power supply is often performed. This output voltage or the output current is used as a controlled variable.

In particular, in an operation of light emitting diodes, it is possible to control light emitting diodes of different colors and to achieve a color mixing by an independent control of the individual colors. Separate circuit arrangements for feeding the individual colors are nowadays used for such independent activation of the individual colors.

The present invention is based on the object to provide a method and a circuit arrangement which ensure safe and trouble-free operation of a variable color LED module. The invention also relates to a lighting system. The object of the invention is also to ensure the current regulation or the power control of an LED module in more detail.

This object is solved by the features of the independent claims. The dependent claims further form the central idea of the invention in a particularly advantageous manner.

A first aspect of the invention relates to a method for controlling, in particular for controlling the current and adjusting the color of an LED module by means of a

Half-bridge circuit with two switches and two

Capacitance or a full bridge circuit with two active half bridges and thus four switches.

In a half-bridge circuit, this is formed by an active half bridge with two clocked switches and a passive half bridge with two capacitors. Since only one active half-bridge is present, this circuit is generally referred to as a half-bridge circuit.

The LED module is interconnected in the bridge branch. The LED module has two antiparallel strands.

A bridge diagonal of the half-bridge circuit or full-bridge circuit is activated, in which a switch is actively clocked and the capacitance lying in the diagonal or, in the case of a full-bridge circuit, a closed (low-frequency clocked) switch Current flow takes over. The feedback variable used for the regulation is a measured actual value representative of the mean value of the lamp current, which is compared with a reference value as the nominal value.

Depending on which bridge diagonal is activated, a current flows through the first leg of the LED module or, alternatively, through the second leg of the LED module. By appropriate adjustment of the time ratio, when a bridge diagonal is activated and thus a current flows through a strand through one of the two LED strands, the color emitted by the LED module can be adjusted. The invention also relates to a color tunable module and more particularly to an LED module which permits color and / or color temperature adjustment.

Color or color temperature adjustment means that the LED module has a number of lamps and in particular at least two LED strands, each having at least one LED with different color or color temperature and in particular emitted light with different spectra, preferably white spectra with different color temperatures , and allows the color and / or color temperature of the light emitted by the module to be adjusted to a mixed color or color temperature. In addition, the inventive allows

Circuit arrangement with the LED module allow dimming, ie a reduction in the brightness of the emitted light, which is typically referred to as percentages, for example, a dimming of 50% means a reduction of the emitted brightness to 50% and a dimming of 95% refers to the fact that the

Brightness is reduced to 5% of maximum brightness. Dimming may preferably be done by inserting a waiting time before the active switch is switched back on, which may be emitted by the LED module

Brightness can be adjusted and / or through

Adjustment of the switch-off time of the active clocked

Switch (in the example of Figure 2 switch Sl) are adaptively adjusted. The latter can be achieved, for example, by adjusting the switch-off threshold for the lamp current.

The invention thus provides a color tunable module according to the independent claims. Further aspects of the invention are the subject of the dependent claims.

In one aspect of the invention, there is provided a color tunable LED module comprising: an LED array having at least two LED strands, each having at least one preferably white LED, the LED strands being connected in an anti-parallel manner and the LED strands emit different spectra, preferably white spectrums of different color temperature, and circuitry that drives the LED array and is configured to output a DC voltage by respectively activating a bridge diagonal between two polarities is switched, wherein the relative activation of the bridge diagonal and thus the duty cycle of the polarities, ie the ratio of the first period of a first polarity compared to the second period of a second polarity, is adjustable. For adjusting the brightness, for example, depending on a dimming signal, can In addition, a third time period are inserted, in which no bridge diagonal is activated. The third period of time can be achieved, for example, by inserting a waiting time before switching the active-clocked switch back on.

The control unit may be a color tuning signal and / or a

Determine Farbtemperaturabstimmsignal and / or a dimming signal from the detected modulation.

The control unit can send at least one control signal to the

Output operating device. It may vary the activation of the bridge diagonal and thus the duty cycle of the at least one polarity based on the particular tuning / dimming signal.

The operating device can activate the

Change bridge diagonal and thus the polarities and their duty ratio based on the at least one control signal.

By inserting a waiting time before switching the active clocked switch back on, the brightness emitted by the LED module can be adjusted.

The LED module can only be connected to the driver circuit by two wires.

The operating device may set the duty cycle of the polarities based on the tuning signal.

The operating device can supply at least the first LED chain when the operating device activates a bridge diagonal and thus switches to a polarity. The operating device can at least the second LED chain supply if the operating device activates the opposite bridge diagonal and thus switches to the opposite polarity.

The operating device may perform dimming of the LED strings by changing the duty cycle of the current turn-on operation of the active-clocked switch. The duty cycle of the current turn-on of the active clocked switch can be reduced according to a dimming signal.

The module may be a flexible band, a strip, a chain or a punctiform device.

The half-bridge circuit has the advantage that compared to the full-bridge circuit can be dispensed with two active-clocked switch and also the required control including the high-side control for the upper of the two switches can be omitted.

Depending on a difference between the actual value and the setpoint, the duty cycle of the current switch-on of the active clocked switch and / or a subsequent switch-on can be set.

In this case, the duty cycle of the active clocked switch can be changed only every n-th switch-on, where n is greater than or equal to 2. The duty cycle of the active clocked switch can be changed, for example, over the time of switching off the active clocked switch as a control variable.

The duty cycle can be achieved by adaptively specifying a turn-off level of a measured one for the lamp current representative sizes are set, wherein when the switch-off level of the active clocked switch is turned off. As a control variable of the current or power control may alternatively or additionally to the timing of the active clocked switch, the level of the

Half-bridge circuit or full bridge circuit supplying DC bus voltage can be used.

The bus voltage can be generated by means of an active PFC circuit, wherein the level of the generated bus voltage is carried out by changing the timing of a switch of the PFC circuit.

As representative of the average value of the lamp current measured actual value can be a sample of the lamp current, preferably measured at half the turn-on time of the active clocked switch.

The representative of the average value of the lamp current actual value can be determined by a continuous measurement of the lamp current (or a representative size).

The continuously measured lamp current may be compared to a reference value, and the actual value representative of the mean value may be the duty cycle of the comparison value over the turn-on period of the active-switched switch.

The duty cycle can be determined using a bidirectional digital counter.

The reference value may be of a predetermined dimming value and / or the measured lamp voltage.

The invention also relates to an integrated circuit, in particular ASIC, which is designed to carry out a method as stated above.

According to the invention is also provided a power or power control of an LED module, the one

Having half-bridge circuit with two switches or a full bridge circuit, wherein the LED module in the bridge branch is interconnected. A control unit activates a bridge diagonal by activating the switch of the bridge diagonal and the diagonal capacitance takes over the current flow, whereby the LED module is supplied with a high-frequency voltage. The control unit is returned a representative of the average value of the lamp current measured actual value, which is compared with a reference value. Depending on a difference between the actual value and the setpoint value, the control unit can set the duty cycle of the current switch-on operation of the actively switched switch and / or a subsequent switch-on operation.

The control unit can change the duty cycle of the active clocked switch only every n-th switch-on, where n is greater than or equal to 2. The control unit may change the duty cycle of the active clocked switch over the time of switching off the active clocked switch as a control variable.

The control unit may adjust the duty cycle by adaptively specifying a turn-off level of a measured one of the Set lamp current representative sizes, the control unit switches off when reaching the switch-off level of the active clocked switch. In addition to controlling the operation of the LED module, the control unit can also control a DC link circuit and receive feedback signals from the DC link circuit, the DC link voltage carrying the DC link circuit

Half-bridge circuit or full bridge circuit supplying DC bus voltage generated.

As an alternative to or in addition to the clocking of the actively-timed switch, the control unit can use the level of the DC bus voltage supplying the half-bridge circuit or full-bridge circuit as the control variable of the current or power control.

To generate the bus voltage, an active PFC circuit may be provided, wherein the control unit carries out the level of the generated bus voltage by changing the timing of a switch of the PFC circuit.

The control unit can be fed back as a measured value representative of the average value of the lamp current, a sample of the lamp current, preferably measured at half the turn-on time of the active clocked switch.

The control unit can continuously measure the lamp current (or a variable representative thereof) for determining the actual value representative of the mean value of the lamp current.

The control circuit may comprise a comparator which supplies the continuously measured lamp current with a Reference value compares and the control circuit used as the representative of the average value, the duty cycle of the output signal of the comparator. The output of the comparator may be fed to a bidirectional digital counter of the control circuit.

The control circuit may set the reference value depending on an externally or internally predetermined dimming value and / or the measured and the control circuit supplied lamp voltage.

Thus, the invention provides a simplified driver for a color tunable LED module, comprising: an LED array having at least two LED strands, each having at least one preferably white LED, the LED strands in connected in an anti-parallel manner and the LED strands different spectra, preferably white spectra with different color temperature, emit, and a circuit that drives the LED array and is configured to output a DC voltage or a direct current by activating respectively a bridge diagonal between two polarities is switched, the relative activation of the bridge diagonal and thus the relative duty cycle of the polarities, ie the ratio of the time period of a first polarity compared to the period of a second polarity, is adjustable. The brightness of the respective LED string can within a activation period of each bridge diagonal by setting the

Duty cycle of the active clocked switch set and adapted. The present invention will be described below with reference to preferred embodiments with reference to the accompanying drawings.

1 shows an inventive operating device for interconnected in a half-bridge LED modules,

FIG. 2 shows in detail a half-bridge circuit for the operation of a lamp and the measurement signals which can be tapped off from it,

FIG. 3 shows the course of activation signals from

a switch of the half bridge and the

Center point voltage UL3 and the lamp current iLamp, Figure 4 shows the structure of a control of

Lamp current,

FIG. 5 shows the time profile of signals of the control of FIG. 4,

Fig. 6 shows a circuit

Fig. 7a shows a first diagram, which

represents time-dependent voltage and current characteristics in the circuit arrangement shown in FIG. 6,

Fig. 7b shows a second diagram, which the

represents time-dependent current profile and switching states in the circuit arrangement shown in FIG. 6 according to a further development,

FIG. 8 shows an operating device according to the invention for LED modules connected in a full bridge, and FIG FIG. 9 shows in detail a full bridge circuit for operating an LED module as well as measuring signals which can be picked up therefrom. Fig. 1 shows an operating device for operating LED modules.

Figures 1 and 2 relate to an embodiment with an active half-bridge, while Figures 6, 8 and 9 show an embodiment with two interconnected as a full bridge half-bridges. Therefore, the majority of the description of Figures 1 and 2 can also be transferred to Figures 6, 8 and 9 (as much of the description of Figures 6, 8 and 9 can be transferred to Figures 1 and 2). In addition, there is essentially provided a control for the two other switches.

On the input side, the operating device has a mains voltage supplied rectifier GR, to which an active power factor correction circuit PFC (Power Factor Correction) adjoins, which acts as a boost converter. The PFC circuit has an inductance 16 in series with a diode D9, wherein the inductance 16 is magnetized upon turning on a switch S6, charging a capacitor C6, and demagnetizing with the switch S6 turned off, so that the capacitor C6 sets a boosted DC voltage Uo having a triangular ripple at the frequency of the timing of the switch S6. Alternatively, the power factor

Correction circuit PFC, for example, by an isolated flyback converter (flyback converter) or by a SEPIC converter are formed. On the output side, the operating device shown in Fig. 1 comprises a half-bridge circuit with two switches Sl and S2 and two capacitors CS3 and CS4 and an LED module EL. A description of the further elements will be given with reference to FIG. 2.

The control unit feedback signals from the range of PFC DC link voltage can be returned, such as. :

the input voltage via a voltage divider ST1,

the current through the inductance 16 by means of a tap AI (or monitoring the voltage across the inductor 16), and

the bus voltage Uo via a voltage divider ST2.

The control unit can adjust the level of the output voltage by clocking the switch S6 and preferably digitally control it by means of the returned bus voltage. The control unit can be fed back feedback signals from the range of the load circuit containing the LED module EL with the half-bridge circuit:

the lamp voltage VLamp by means of a

Voltage divider ST3,

- The lamp current iLamp by means of the shunt Rl (only during the activation of the active clocked switch of each activated

Bridge diagonal), and

the bridge branch current by means of a tap A2 (inductive or by tapping at the midpoint of the switches Sl and S2).

As shown in Fig. 1, the LED module EL has an anti-parallel arrangement of LED. The circuit arrangement shown is particularly for the operation of LED modules with an anti-parallel arrangement of LED suitable, the two antiparallel strands differ in particular by a different color temperature or wavelength of the corresponding LED in each strand. The LEDs of the two antiparallel strands may also differ in their color rendering or their binning class. By appropriate adjustment of the time relationship, when a current flows through the first strand of the LED module EL and when a current flows through the second strand of the LED module EL, the color emitted by the LED module EL can be adjusted.

FIG. 2 shows in detail the half-bridge circuit with the feedback signals:

- By means of a voltage divider, the midpoint voltage

UL3, which is representative of the bridge branch current,

By means of one or more voltage divider the

Lamp voltage Vi _am p based on the voltages Ui and U2, and - by means of the shunt Rl, the lamp current Iiamp.

The circuit arrangement shown in Figure 2 comprises a bridge circuit with an upper and a lower diagonal point 1, 2 and a right diagonal point 3. The left diagonal point can not be clearly identified.

The bridge circuit has four bridge branches 4, 5, 6, 7. The bridge branches 4 and 6 each contain a switch element in the form of a FET. The switch elements are denoted by Sl and S2.

At the diagonal points 1 and 2 of the bridge circuit are the poles of a DC voltage source. The DC voltage source can be supplied to the circuit arrangement via a bus. But it is also possible that the DC voltage is generated in a conventional manner by inverting the mains voltage.

From the diagonal point 3, a branch PZ1 goes out. The branch PZ1 includes in series an LED module EL with an anti-parallel arrangement of LED, wherein the two anti-parallel strands differ in particular by a different color temperature or wavelength of the corresponding LED in each strand, and an inductance L2.

Furthermore, the branch PZ1 has a diode network consisting of four diodes D1, D2, D3 and D6. The diode D1 connects the inductance L2 to the one terminal of the FET S1, namely the one which is not connected to one pole of the DC voltage source. The other terminal of the FET Sl is connected to the positive pole of the DC voltage source. The diode D2 connects the inductor L2 to a terminal of the FET S2, namely to the one which is not connected to one pole of the DC voltage source. The other terminal of the FET S2 is located at the junction of the half-bridge branch 6 with the half-bridge branch 7. The diode D3 connects the not connected to the negative pole of the DC voltage source terminal of the FET S2 to the positive pole of the DC voltage source. The diode D6 connects the not lying on the positive pole of the DC voltage source terminal of the FET Sl with the negative pole of the DC voltage source. The diodes Dl and D2 are poled on passage. The diodes D3 and D6 are poled in the reverse direction. Preferably, a capacitor C2 is connected in parallel with the LED module EL in parallel as a filter or smoothing capacitor. This one can be in Operation smooth the lamp voltage and maintained during the demagnetization of the inductance L2, the lamp voltage. Between the junction of the half-bridge branch 6 with the half-bridge branch 7 and the negative pole of the DC voltage source, a low-impedance shunt Rl is interposed, which, however, serves only for the measurement of currents and has no measurable influence on the voltages in the circuit.

In FIG. 3, waveforms with activated bridge diagonal A / D (in the designation as in FIG. 2) are shown. As can be seen, the switch S1 is actively clocked and switched on between the times T31 and T32 (time duration tcw). As can be seen, the linearly increasing lamp current Ilamp can only be detected during the period toN at the shunt R1, during which the switch S1 is switched on. In the period of switching off the switch Sl, in which the inductance L2 drives the current through the lamp sinking to the lower reversal point on the other hand, the lamp current can not be detected by means of the shunt Rl. The switch-on time of the high-frequency clocked switch (here: switch A or Sl) can be determined by the monitoring of the current flowing through the inductor L2 branch current iL2. For example, it can be monitored whether the branch current iL2 flowing through the inductance L2 has again fallen to zero or whether the inductance L2 has been demagnetized. This can be done by means of a secondary winding at the inductance L2 or by means of a monitoring of the midpoint voltage between the switches Sl and S2. According to the invention, the cut-off time of the actively-clocked switch (in the example of FIG. 2 switch S1) is now made adaptive so that, as a result, the turn-on time duration toN is variable. This can be achieved, for example, by adaptively configuring the switch-off threshold for the lamp current and / or adaptively adjusting the switch-on time duration of the actively clocked switch. The adaptation takes place on the basis of a feedback signal, which is representative of the average value of the lamp current (averaging over one or more switch-on periods of the active clocked switch). By controlling the average value of the lamp current, the lamp current or power regulation is much more accurate.

The mean value of the lamp current can be detected by detecting and evaluating a sample value at the instant t ₀ n / 2, that is to say half the turn-on time duration toN of the actively-timed switch. If this is higher than the desired average value, the turn-on time or the turn-off current threshold can be reduced, in the current order in a subsequent turn-on of the active clocked switch.

In the following, however, an embodiment will be explained, in which the lamp current is continuously detected and returned to the control unit. As shown in FIG. 4, in the control unit the lamp current I iamp is compared by a comparator Kl with a reference value I avg_soii. This reference value I avg_soii thus provides the desired mean value for the lamp current and can, for example, from an external or internal Dimmwertvorgabe and / or the height of the lamp voltage depend. This reference value I _a vg_soii is a measure of the nominal power.

In order to achieve a constant lamp power, the setpoint input for the mean value of the lamp current must be inversely tracked with fluctuating lamp voltage Ulamp, so that the resulting product of lamp current and lamp voltage remains constantly regulated. With constant lamp voltage corresponds of course one

Medium current control exactly one lamp power control.

In order to achieve a constant lamp current, for example, directly the lamp current (the current through the LED module EL) can be measured, or alternatively the lamp current can be determined indirectly. For example, the lamp current can be determined from the lamp power or the power supplied to the LED module EL and the LED module voltage (lamp voltage). The power supplied to the LED module can be determined, for example, from the product of the output voltage of the PFC circuit and current flowing in the full or half-bridge. The lamp current can be formed by dividing the lamp power or the power supplied to the LED module EL by the lamp voltage.

In this embodiment, the purpose of the control is that the duty cycle of the output of the comparator Kl during a turn-on time to _{N of} the active clocked switch is 50%. In the embodiment, for this purpose, the output signal of the comparator is supplied to a digital up / down counter COUNTER, which is clocked by a timer of the control unit (clock signal CNT_CLK). As can be seen in FIG. 5, the counter COUNTER counts in one direction as long as the lamp current Ilamp is below the reference value Iavg_setpoint and in the opposite direction Direction as soon as the lamp current Ilamp exceeds the reference value Iavg_soii. If the actual value of the average value of the lamp current Iiamp exactly corresponds to the reference value input Iavg_soll, the duty cycle of the comparison signal supplied to the counter COUNTER will be 50% and thus at the end of a switch-on time period the counter reading will correspond exactly to its initial level.

Any deviation, however, will lead to a deviation ERROR of the counter end of its initial state. This deviation signal ERROR is fed to a preferably digital regulator REGULATOR, which is also clocked by a timer of the control unit by a signal reg_clk. The regulator REGULATOR implements a control strategy (eg PI controller) and controls a manipulated variable which influences the power of the LED module EL, depending on the input signal ERROR and the control strategy. This manipulated variable may, for example, be one or more of:

- bus voltage,

Adaptive switch-off threshold Ipeak, and / or

- Adaptive switch-on time Ton.

The manipulated variable (s) can be changed in the current switch-on process, in each subsequent switch-on process or in every n-th switch-on process, where n is an integer greater than or equal to 2.

In the example of Figures 4 and 5, either the on period Ton is changed, or the controller REGULATOR changes the reference value of a further comparator K2 the control unit, at whose non-inverted input ^¬ the lamp current Iiamp.

The output signal of the further comparator K2 controls the switching off gate_off of the active clocked one Switch of the activated bridge diagonal.

In the example in FIG. 6, additional capacitors are provided in each case in each of the two anti-parallel LED strings which are connected in parallel only to a part of the LED of a string. These additional capacitors can serve as additional filter elements. In this example, an additional capacitor C3 is arranged to an LED of the first LED string, and an additional C4 to an LED of the second LED string arranged.

The exemplary embodiment shown in FIG. 6 for an operating circuit according to the invention for light sources, in particular an LED path, includes a circuit arrangement which has four controllable switches S1-S4, which are connected in a full bridge. To the full bridge, a DC voltage Uo is applied, which comes from a suitable DC voltage source of the corresponding operating device (also called electronic ballast), in which the circuit arrangement is used. Freewheeling diodes are in each case connected in parallel with the four switches S 1 -S 4, wherein, for the sake of simplicity, only the free-wheeling diode D 1 connected in parallel to the switch S 1 is shown in FIG. The switches S1-S4 used are preferably field-effect transistors which already contain the freewheeling diodes. In the bridge branch of the shown in Fig. 6

Full bridge circuit is arranged to be driven LED module EL. The circuit arrangement shown in Fig. 6 is particularly suitable for the operation of LED modules with an anti-parallel arrangement of LED, wherein the two antiparallel strands differ in particular by a different color temperature or wavelength of the corresponding LED in each strand. The LEDs of the two antiparallel strands of the LED module EL can also differ in their color rendering or their binning class. By appropriate adjustment of the time relationship, when a current flows through the first strand of the LED module EL and when a current flows through the second strand of the LED module EL, the color emitted by the LED module EL can be adjusted. With the bridge branch of the full bridge shown in FIG. 6, a smoothing or filtering circuit is provided which has an inductance L2 and a capacitance C2, these components being connected as shown in FIG. To the full bridge, a resistor Rl is also connected, which serves as a current measuring or shunt resistor.

Below is the normal operation will be explained in more detail, wherein during normal operation, the circuit arrangement according to the invention or full bridge preferably in a so-called. Borderline mode (border operation) or

Discontinuous mode (lopsided operation) is operated. In principle, the two bridge diagonals with the switches S 1 and S 4 or S 2 and S 3 are alternately activated and deactivated and thus the respective switches of the two bridge diagonals alternately or complementary to each other and switched off, wherein also upon activation of the bridge diagonal with the switches Sl and S4, the switch Sl high-frequency alternately turned on and off, while according to the activation of the bridge diagonal with the switches S2 and S3, the controllable switch S2 high-frequency alternately turned on and off. That is, the full bridge is at a relatively low frequency, which may be in the range 80-150 Hz in particular, reversed, while the switch Sl or S2 of each activated bridge diagonal also high-frequency, for example, with a frequency of about 45 kHz, alternately turned on and off. This high-frequency switching on and off of the switch Sl or S2 is carried out by means of a high-frequency pulse width modulated control signal of a corresponding control circuit, which is screened by means of the components consisting of the elements L2 and C2 filter or smoothing circuit, so that on the LED module EL only the linear average of the current flowing over the bridge branch branch current iL2 is applied. With the aid of the pulse-modulated control signal, the current supplied to the LED module EL or else the supplied power can be kept constant, which is particularly important for the operation of LED modules EL.

The low-frequency component of the current supplied to the LED module EL is achieved by switching or reversing the polarity of the two bridge diagonals, i. by switching from Sl and S4 to S2 and S3. About the right bridge branch with the switches S3 and S4, the LED module EL is low frequency applied to the supply voltage Uo or grounded in this case, so that essentially applied to the terminals of the LED module EL only the low-frequency component. Depending on which bridge diagonal is activated, a current flows through the first strand of the LED module EL or alternatively through the second strand of the LED module EL.

By adjusting the time ratio when a bridge diagonal is activated and thus a current flows through a strand through one of the two LED strands, the color emitted by the LED module EL can be adjusted. According to the aforementioned low-frequency borderline mode, the controllable switch S1 or S2 of the respective activated bridge diagonal is closed at a point in time when the branch current i L2 flowing across the inductance L2 has fallen back to zero, preferably when it has reached its minimum. By "minimum" is meant the lower reversal point of the current iL2, although this minimum may well be in the slightly negative current value range. "Closed" means that a control unit in this time range triggers the switching process - the actual closing of the switch, ie its reaching the conductive state usually occurs only when the rising again after the minimum current about once again (this time ascending) zero crossing The monitoring as to whether the branch current iL2 flowing through the inductance L2 has again fallen to zero or whether the inductance L2 has been demagnetized can take place by means of a secondary winding at the inductance L2 or also by monitoring the midpoint voltage between the switches S1 and S2.

To consider the current flow is to be assumed below that initially the bridge diagonal is activated with the switches S2 and S3, while the bridge diagonal is disabled with the switches Sl and S4. That is, the switches S2 and S3 are closed while the switches Sl and S4 are opened. At the moment of closing of the switches S2 and S3, a current iL2 begins to flow through the inductance L2, which increases in accordance with an exponential function, wherein a quasi-linear rise of the current iL2 can be seen in the range of interest here, so that for the sake of simplicity, FIG a linear increase or decrease of electricity iI2 is spoken. By opening the switch S5, this current is interrupted iL2, which - as already mentioned - the switch S2 in particular high-frequency and regardless of the switching state of the switch 53 is alternately opened and closed. The opening of the switch S2 has the consequence that the current iL2, while initially on the freewheeling diode Dl of the open switch Sl in the same direction continues to flow, but decreases continuously and can finally reach a negative value.

This is especially the case until the electrons have been eliminated from the barrier layer of the freewheeling diode Dl. The reaching of this lower reversal point of the current iL2 is monitored and the switch S2 closed again after detecting this lower reversal point, so that the current rises again. That is, that high-frequency switching of the switch S2 occurs whenever the lower reversal point of the current iL2 has been reached. The opening of the switch S2 can be chosen arbitrarily in principle, wherein the time of opening the switch is particularly crucial for the power supply of the LED module EL, so that regulated by appropriately adjusting the opening time, the power or current supplied to the LED or kept constant can be. As a switching criterion for this purpose, for example, the time or the maximum value of the branch current iL2 be used. By the measure that the respective high frequency alternately switched on and off switches Sl and S2 respectively in the lower reversal point of the current iL2, ie in the vicinity of the current value zero, is turned on again, the respective field effect transistor Sl or S2 is protected, ie before Destruction protected, and it can field effect transistors used as switches Sl and S2 are having relatively long Ausräumzeiten for the corresponding freewheeling diode.

This will be explained in more detail below. Before the switch S2 is closed, a voltage is applied to it, which in the present case is approximately 400 volts. When switch S2 is closed, this voltage collapses, i. It drops very rapidly from 400 volts to 0 volts. The special property of a

Field effect transistor, however, is that the current already begins to flow upon activation of the corresponding field effect transistor, before the corresponding voltage has dropped to 0 volts. In this short period of time between the increase of the current flowing through the field effect transistor and the reaching of the voltage 0 volts, a product supplied to the respective field effect transistor is formed by the product of the current and the voltage, which can destroy the field effect transistor. Therefore, it is advantageous to switch the field effect transistor at a lowest possible current flow, in particular in the vicinity of the current value zero.

Furthermore, it should be noted that the current flowing through the inductance L2 current iL2 flows through the free-wheeling diode of Dl when the switch Sl is open and the switch S2 is still open. If the switch S2 is closed and the switch S1 opened, it takes a certain period of time until the electrons could be eliminated from the barrier layer of the freewheeling diode Dl. During this time, the field effect transistor Sl is practically in a conductive state. This means that the field effect transistor S2 during a relatively short period of time to clear the barrier layer of the

Freewheeling diode Dl, which is associated with the field effect transistor Sl, at the full operating voltage Uo, the approx. 400 volts, is applied, which can also lead to the above-described overloading and possibly even destruction of the field effect transistor S2. Due to the previously proposed procedure, namely the switching on of the switch S2 whenever the current iL2 flowing through the inductance L2 has reached a minimum, the effect previously described with reference to the clearing-out time of the switch or field-effect transistor S1 is almost irrelevant, so that for the switches Sl - S4 also field effect transistors can be used, which have relatively long Ausräumzeiten for the associated freewheeling diodes. Although there are already switching elements with very short Ausräumzeiten, such. As the so-called. IGBT (Insulated Gate Bipolar Transistor), but these devices are very expensive. With the help of the present invention can thus be dispensed with the use of such expensive components.

For the procedure described above, it is necessary that the instantaneous value of the current iL2 and the time at which it reaches its reversal point be known. The instantaneous value of the current iL2 can be determined, for example, by measuring the voltage drop across the resistor Rl. The lower reversal point of the current iL2 can be determined, for example, by a voltage tapped off transformer-wise at the coil L2. For this purpose, a winding or coil (not shown in FIG. 6) can be transformer-coupled to the coil L2, which leads to a differentiation of the current iL2 flowing through the coil L2 and thus permits a statement about the reversal point of the current iL2. The normal operation of the circuit arrangement shown in Fig. 6 will be explained below with reference to the diagram shown in Fig. 7, wherein in Fig. 7 time-dependent the course of the Junction between the switches Sl and S2 voltage applied, the lamp voltage ULED and the current flowing through the coil L2 current iL2 is shown. In particular, in Fig. 7a the case is shown that during a first period Tl of the circuit arrangement shown in Fig. 6, the bridge diagonal with the switches S2 and S3 is activated, whereas during a subsequent period T2, the bridge diagonal with the switches Sl and S4 is activated , That is, during the period Tl, the switch S3 is permanently closed, and the switches Sl and S4 are permanently open. Furthermore, the switch S2 is switched on and off in a high frequency alternating manner during this time period T1. From Fig. 7a is particularly apparent that the switch S2 is always closed when the current flowing through the coil L2 current iL2 has reached its lower reversal point, ie its minimum value, so that there is the pulse-like course of the voltage u. The slope of the edges of the current iL2 is determined by the inductance of the coil L2. By changing the peak value of the current iL2, ie the time of opening of the switch S2, the current average value of the current iL2 can be changed and thus the power supplied to the LED module EL and its color temperature can be regulated or kept constant. The high-frequency course of the current iL2 is smoothed by the components L2 and C2, so that the smoothed course of the voltage applied to the LED module EL voltage ULED shown in Fig. 7 results. After the expiration of the period T2, the switches S2 and S3 are permanently opened, and the switch S4 is turned on permanently. Analogously to the switch S2 during the period Tl, the switch S1 is now switched on and off in a high-frequency manner so that the course of the voltages U1 and ULED shown in FIG of current iL2. As has already been mentioned, is switched by means of a control circuit repeatedly between the operating phases during the periods Tl and T2, this Umpolfrequenz in particular in the range 80 - 150 Hz may be, while the high-frequency clock frequency of the switch S2 (during the period TA and of the switch Sl (during the period T2) may be in the range around 45 kHz.

In the control runs after opening the high-frequency switch, the current continues through the freewheeling diode and thereby decreases relatively slowly, when the second switch of the currently activated bridge diagonal remains closed. This leads to a smaller current peak value and accordingly also to a smaller power loss. However, it may happen that at a time when the electrons have been eliminated from the barrier layers of the freewheeling diodes and thus the lower reversal point of the current iL2 has been reached, this has not dropped sufficiently and thus the switches when closing still a high Are exposed to stress. To exclude these loads, which may occur, for example, when bridging the LED module EL, the switches can be controlled according to the diagram in Fig. 7b in a development.

This diagram of Fig. 7b shows the current waveform iL2 and the state of the second and the third switch 2, 3 during the period T. The two other switches are open in this period T. During a first phase x both switches are closed and the current iL2 increases continuously. As with the control just described, during a second phase, x2 is its beginning can be determined by reaching a maximum value of iL2 or by a predetermined duration of xl, the second switch S2 is opened and iI2 decreases slowly. In addition, however, the third switch S3 will now also be opened in a third phase x3 from a predetermined time after the opening of the second switch S2. The current now flows through the two freewheeling diodes of the first and fourth switches and now decreases more than during the second phase x2. This can ensure that iL2 actually reaches a negative value before the barrier layers of the freewheeling diodes are eliminated. When iL2 reaches the lower reversal point, both switches are closed again and the controller returns to the state of the first phase xl. The opening of the third switch S3 - ie the third phase x3 - is omitted, however, if the current iL2 has previously dropped to zero, since in this case no high loads occur when opening switch. Instead, the first phase x is immediately continued and the second switch S2 is opened again. The low-frequency switching between the two bridge diagonals is analogous to the previous embodiment, wherein also here advantageously the current peaks of the current iL2 before and after the switching between the operating phases Tl and T2 can be reduced.

Alternatively, the switch-off time of the high-frequency clocked switch can be determined by the fact that the lamp current reaches a fixed predetermined switch-off threshold. However, this can lead to inaccuracies that the negative current flow range can vary immediately after switching on the switch, which makes the power control inaccurate. In the embodiment of Figures 8 and 9 On the output side, the operating device has a

Full bridge circuit with four switches Sl to S4 (or A to D) on. The inductors LI, L2, the LED module EL and capacitors C1, C2 are connected as shown in FIG.

It is according to the embodiments, a method for controlling a LED module EL means of a half-bridge circuit with two switches or a full bridge circuit with four switches allows, the LED module EL is connected in the bridge branch. The first bridge diagonal is activated by a first switch S1 being actively clocked in a first time interval T1. In a second time period T2, a second switch S2 is actively clocked, thus activating the second bridge diagonal. The LED module EL has two anti-parallel strands, wherein the two anti-parallel strands in particular by a different

Color temperature or wavelength of the corresponding LED in the respective strand differ. Preferably, each active clocked switch Sl or S2 becomes a

Time turned on, when the indirectly or directly detected bridge branch current has subsided to zero, preferably has reached its lower reversal point.

By adjusting the temporal relationship of

Activation of the two bridge diagonals and thus the two time periods Tl and T2 to each other, the color emitted by the LED module EL color can be adjusted.

By inserting a waiting time before switching on the respective active clocked switch Sl or S2, the average current through the LED module EL and thus the by the LED module EL emitted brightness can be adjusted.

The invention also enables a luminaire, comprising an LED module EL and a control gear, wherein the

Operating device a circuit for power or

Power control of an LED module EL has.

The circuit has a half-bridge circuit with two switches Sl and S2 (eg, Figs. 1 and 2) or a

Full bridge circuit with four active switches Sl, S2, S3 and S4 (eg. Fig. 6, 8 and 9) on. The LED module EL is interconnected in the bridge branch. A control unit may activate a first bridge diagonal by

at least a first switch Sl of the bridge diagonally active in a first time period Tl clocks. In a second time period T2, the second bridge diagonal can be activated by at least the second switch S2 being actively clocked. The LED module EL has two antiparallel strands, wherein the two antiparallel strands differ in particular by a different color temperature or wavelength of the corresponding LED in the respective strand.

The respective active clocked switch Sl or S2 can be turned on at a time when the indirectly or directly detected bridge branch current to zero

decayed, preferably has reached its lower reversal point.

By inserting a waiting time before switching on again the respective active clocked switch Sl or S2, the brightness emitted by the LED module EL can be adjusted.

Claims

claims

Method for controlling an LED module by means of a half-bridge circuit with two switches or a full-bridge circuit with four switches, wherein the LED module (EL) in the bridge branch

is switched and a bridge diagonal is activated, in which a switch (Sl, S2) is actively clocked,

wherein the LED module has two antiparallel strands, wherein the two antiparallel strands differ in particular by a different color temperature or wavelength of the corresponding LED in the respective strand.

Method according to claim 1,

wherein the active clocked switch (Sl, S2) is turned on at a time when the

indirectly or directly detected bridge branch current has decayed to zero, preferably has reached its lower reversal point.

Method according to one of the preceding claims, wherein by adjusting the temporal ratio of the activation of the two bridge diagonals

to each other, the color emitted by the LED module can be adjusted.

Method according to one of the preceding claims, wherein by inserting a waiting time before the

Restarting the active clocked switch (Sl, S2) emitted by the LED module

Brightness can be adjusted.

5. The method according to any one of the preceding claims, wherein the duty cycle of the active clocked switch over the time of switching off the active clocked switch as a control variable

is changed.

Method according to one of the preceding claims, wherein the duty cycle by adaptive default, a Ausschaltpegels a measured for the

Lamp current representative sizes is set, which is switched off when the switch-off level of the active clocked switch.

Method according to one of the preceding claims, wherein a current or power control of an LED module takes place,

in which as the control variable of the current or

Power control is alternatively or in addition to the timing of the active clocked switch, the level of the half-bridge circuit or full bridge circuit supplying DC bus voltage is used.

Method according to claim 7,

in which the bus voltage is generated by means of an active PFC circuit, wherein the level of the

generated bus voltage by changing the timing of a switch of the PFC circuit is executed.

Method according to one of the preceding claims, in which a sample of the lamp current, preferably measured at half the turn-on time duration of the actively-timed switch, is used as a measured actual value representative of the average value of the lamp current.

10. The method according to any one of claims 1 to 8,

wherein the representative of the average value of the lamp current actual value is determined by a continuous measurement of the lamp current.

11. The method according to claim 10,

in which the continuously measured lamp current is compared with a reference value and the actual value representative of the mean value is the duty cycle of the comparison value over the switch-on time duration of the actively switched switch.

Method according to claim 11,

in which the reference value depends on a predetermined dimming value and / or the measured lamp voltage.

13. Light, comprising an LED module and a

Operating device

wherein the operating ^{device has} a circuit for current ^¬ or power control of an LED module, wherein the circuit is a half-bridge circuit with two switches (Sl, S2) or a

Full bridge circuit having four active switches (S1, S2, S3, S4),

wherein the LED module is interconnected in the bridge branch,

wherein a control unit activates a bridge diagonal by actively clocking at least one switch (Sl, S2) of the bridge diagonal, the LED module having two antiparallel strands, the two antiparallel strands being characterized in particular by a different color temperature or wavelength of the corresponding LED in the bridge different strand.

14. Luminaire according to claim 13, wherein the active

clocked switch (Sl, S2) is turned on at a time when the indirectly or directly detected bridge branch current has decayed to zero, preferably has reached its lower reversal point.

Luminaire according to claim 14,

in a control unit in addition to a regulation of the operation of the LED module and a

DC link circuit drives and of the

DC link circuit receives feedback signals, the DC link voltage which is the

Half-bridge circuit or full bridge circuit supplying DC bus voltage generated.

Luminaire according to claim 15,

in which an active PFC circuit is provided for generating the DC bus voltage,

wherein the control unit executes the level of the generated bus voltage by changing the timing of a switch of the PFC circuit.

17. Luminaire according to one of claims 13 to 16,

wherein the control circuit is the reference value

depending on an externally or internally preset dimming value and / or the measured and the

Control circuit supplied lamp voltage depends. 18. Lighting system, comprising a plurality of lights, including at least one lamp according to one of claims 13 to 17, wherein the lights are preferably connected by one or more bus lines with each other and / or with a central control unit.