DE102016202323A1 - Driver circuit and method for driving an LED track - Google Patents

Abstract

The invention relates to driver circuits for driving an LED track (3), comprising at least one LED, comprising a clocked converter (1), which is supplied on the input side with a voltage (Uin) and the output side, an electrical parameter (ILED, Uout) of LED track (3) controls a control unit (2) which is adapted to change the timing of the converter (1) to the electrical parameter (ILED, Uout) of the LED track (3) by means of a feedback quantity (7 ) to a minimum value (Imin, Umin); and the control unit (2) is further configured to gradually below the minimum value (Imin, Umin) of the electrical parameter (ILED, Uout), the clocking of the converter (1) and / or the clocking of a further switching element (S1) of the driver circuit to change, so that after receiving a switching command (6), the electrical parameter (ILED, Uout) of the LED route (3) is initially regulated by means of feedback variable (7) to the minimum value (Imin, Umin) and then without feedback variable (7 ) is gradually regulated in a range below the minimum value (Imin, Umin). The invention further relates to a method for operating lamps, a computer program product, an integrated circuit and a lamp.

Description

The invention relates to the control of a light source, in particular an LED track with at least one LED, with the aid of a clocked converter. The present invention relates in particular to a driver circuit for the operation of at least one light source, for. Example by means of a clocked converter for the operation of at least one LED. The present invention further relates to a method for operating lamps, an integrated circuit and a lamp.

Driver circuits for operating LEDs are generally known from the prior art. Such a driver circuit is powered by an electronic supply source and includes a converter which is responsible for controlling an electrical parameter, in particular a current or a voltage, of the LED route.

From the DE 10 2014 200 437 A1 For example, an LLC converter is known as an exemplary representative of clocked converters that is used to drive an LED track. Here, a half-bridge circuit is clocked by means of a switching signal of a control unit to supply an LLC resonant circuit with an AC voltage. On a secondary side of the LLC resonant circuit, a current is measured through an LED path and fed via, for example, an optocoupler or an alternative data transmission to the control unit on the primary side. The current through the LED path is a control feedback variable in the control loop of the driver circuit. Thus, a control of an electrical parameter using a feedback variable, referred to as feedback control in English.

A clocked converter for a driver circuit can thus be operated as a constant current source. In this case, the timing of the converter is changed so that the electrical parameter of the LED route is controlled. The current through the LED path or the voltage drop across the LED path is detected as an actual value and compared with a desired value in a control unit. The target value is, for example, a dimming value specification.

In today's converters, changing the timing of the converter to regulate the electrical parameter using a feedback quantity is limited to a minimum value of the electrical parameter. The converter is therefore unable to control the electrical parameter over its entire range of values.

If the LED track is to be completely de-energized after receiving an external or internal switch-off command - that is, the electrical parameter is actually down to zero - nowadays the minimum value of the electrical parameter is regulated and then the supply voltage is switched off. This abrupt switching causes jumps in the light power change, for example in the form of flicker and / or lightning effects. This is perceived by the user as disturbing. This applies both for switching off and for switching on the LED track. These abrupt changes in light output are undesirable and should therefore be avoided.

In order to prevent the sudden disappearance or emergence of the light, one could try to further reduce the minimum value. However, due to technical constraints, no recoverable value can be recorded for these cases. In addition, the control of the converter with very small non-realizable pulse widths would be necessary, which would immediately be perceived as a flicker.

It is therefore an object of the present invention to provide a driver circuit for driving an LED track, in which no abrupt changes in light power occur when turning on or off the LED track.

This object is achieved with the drive circuit described in the independent claim 1 and 2. Preferred embodiments are described in the respective dependent claims.

• – Ausgangsanschlüsse zum Versorgen einer LED-Strecke,
• – einen mittels wenigstens einem Schalter getakteten Konverter,
• – eine Steuerschaltung,

die ein Steuersignal zur Taktung des Konverters ausgibt. Die Steuerschaltung ist dabei dazu ausgelegt, bei Erhalt eines Ausschaltbefehls die Taktung des Konverters über einen vorgebebenen Zeitbereich grösser Null stetig ohne Verwendung eines Rückführsignals derart zu verändern, dass die Lichtleistung graduell verringert wird und am Ende des genannten Zeitbereichs Null ist. Diese Verringerung kann ausgehend von einem vorgegeben Mindestwert erfolgen, oberhalb dessen ein gedimmter Betrieb oder ungedimmter Betrieb mit Rückführ-Regelung erfolgt.According to a first aspect of the invention, a clocked LED driver circuit comprises:

• Output terminals for supplying an LED track,
• A converter clocked by means of at least one switch,
• A control circuit,

which outputs a control signal for clocking the converter. The control circuit is designed to, upon receipt of a turn-off, the clocking of the converter over a predetermined time range greater zero continuously without Using a feedback signal to change so that the light output is gradually reduced and is zero at the end of said time range. This reduction can be made starting from a predetermined minimum value, above which a dimmed operation or undimmed operation with feedback control takes place.

Alternatively or additionally, the control circuit can be designed, upon receipt of a switch-on command, to continuously change the clocking of the converter over a predetermined time range greater than zero without the use of a feedback signal such that the light output is gradually increased and has a predetermined minimum value at the end of the mentioned time range, above which a dimmed operation or an undimmed operation with feedback control can take place.

According to a further aspect of the invention, a driver circuit for driving an LED track consisting of at least one LED is provided. The driver circuit has a clocked converter, which is supplied on the input side with a voltage and the output side regulates an electrical parameter of the LED route. A control unit is designed to change the timing of the converter in order to regulate the electrical parameter of the LED path by means of a feedback variable to a minimum value. The control unit is further configured to gradually change below the minimum value of the electrical parameter, the timing of the converter and / or the timing of another switching element of the driver circuit by forward control, so that after receiving a switch-off command, the electrical parameter of the LED route first by means of feedback is controlled to the minimum value and is then controlled without feedback variable in a range below the minimum value to zero.

The driver circuit thus has a control unit which regulates the electrical parameter in a first value range using a feedback variable and regulates it in a second value range without using a feedback variable, preferably this feedback variable. The first value range of the electrical parameter preferably extends from a maximum value to a minimum value. The second value range of the electrical parameter extends from a minimum value to a zero value of the electrical parameter. Due to the configuration of the clocked converter, the minimum value is a value not equal to zero, for example 10 percent of the electrical parameter, preferably 5 percent of the electrical parameter, more preferably 1 percent of the electrical parameter.

The electrical parameter is, for example, the current through the LED track or the voltage across the LED track or the electrical power provided to the LED track.

The Regelrückführgröße is preferably an electrical variable, by means of which the actual value of the electrical parameter of the LED route can be closed. In one application, the control feedback is the sensed current through the LED link. Alternatively or additionally, the control feedback variable is the detected voltage across one of the LED or the LED path. The Regelrückführgröße can thereby by direct measuring directly or indirectly - for example by means of electrical probes or electrical coupling - are detected. The Regelrückführgröße can also be determined from the emitted light power - for example, using a light power sensor.

The clocked converter is a circuit for voltage and / or current conversion as the basis for the power supply of the LED track using a periodically operating electronic switch and at least one energy storage, such as a coil. The clocked converter is, for example, a buck converter or buck converter, which produces a lower DC voltage at the output than at the input. The clocked converter, for example, a boost converter or boost converter, English boost converter, which produce a higher DC voltage at the output than at the input. The clocked converter is, for example, an inverse converter, English Buck Boost, which can produce a higher or a lower DC voltage at the output than at the input, but this is inverted.

The control unit is set up to change the timing of the converter. Under clocking in particular the switching frequency - also referred to as the operating frequency - to understand the on time and / or the off time of the converter. The switching frequency indicates the number of on and off operations of a switching element of the converter per second.

The driver circuit receives a switching command. This is done for example via an interface, in particular via a DALI interface of the control unit of a central control of the lighting system or via a network switch. With this switching command, the LED track should either be switched on or off. In order to prevent a jump in the light power for bridging the second value range, a gradual feedforward control takes place below the minimum value of the electrical parameter. In this case, the control feedback variable is ignored and the electrical parameter is regulated by changing the timing of the converter or by changing the timing of a further switching element in the driver circuit.

Forward control is gradual, which means that the electrical parameter is adjusted stepwise by changing the timing to prevent an abrupt change in light output. Thus, there is no abrupt turn on or off, but a gentle regulation of the electrical parameter in the second value range, which can also be referred to as a "fade-in" or "fade-out". The gradual regulation takes place in particular via a defined Time domain and preferably without human perception of the individual stages of gradual regulation.

The gradual change is then a gradual minimization or a gradual increase in a manipulated variable, for example the clocking of the converter or the timing of the further switching element.

If the LED path is now to be switched off, according to the invention first of all a control of the electrical parameter in the first value range using the control feedback variable to a minimum value of the electrical parameter and directly control of the electrical parameter in the second value range without using the Regelrückführgröße to a value of zero percent of the electrical parameter.

If now the LED track is to be switched on, according to the invention first of all a control of the electrical parameter in the second value range without using the Regelrückführgröße of zero percent of the electrical parameter to the minimum value and then a control of the electrical parameter in the first range of values using the Regelrückführgröße.

Detecting the control feedback variable at low values of the electrical parameter in the second value range has hitherto been too difficult and prone to error, so that regulation in this range simply does not take place in conventional driver circuits. According to the invention, a forward control is applied for the second value range of the electrical parameter in order to prevent an abrupt change in the light output.

The further switching element is in particular no switching element of the converter, but additionally introduced into the driver circuit. The further switching element is, for example, a field-effect transistor, which is operated by the control unit by means of a switching signal. The timing of the further switching signal is changed by means of the control unit in order to regulate the electrical parameter in the second value range, ie below the minimum value of the electrical parameter in feedforward control.

The regulation below the minimum value is not a possible steady state of the LED link that would have to be maintained for any length of time, but a transient process that can be handled as forward control.

In a preferred embodiment, the further switching element is arranged parallel to the LED path, preferably, the further switching element has a further coil connected in series, for example in the form of a storage inductor, which must be made correspondingly large due to the timing of the further switch or by means high switching frequencies must be controllable. In this way, a short-circuit switch is introduced into the driver circuit. Upon reaching the zero value of the electrical parameter, a true turn off the LED track can be effected by the switch is permanently closed.

In an alternative embodiment, the further switching element is arranged in series with the LED path. This series switching element interrupts the supply of the electrical parameter to the LED track and thus causes the on or off. In principle, an LLC resonant circuit is used in a newer generation converter. The LLC resonant circuit is in principle a voltage source with an output capacitance in the nanofarrad range. When a switch is connected in parallel, this leads to undesirable voltage changes in the LED path, which in turn are perceptible as abrupt changes in the light output. Therefore, a switching element is preferably used in series with the LED track, in principle, an anti-glow field effect transistor.

The control unit preferably regulates the electrical parameter by changing the timing of the converter and by means of the feedback variable to 10 percent, preferably 5 percent, more preferably 1 percent, of the maximum electrical parameter as the minimum value. The minimum value is, for example, the minimum dimming value which can be corrected by evaluating the feedback variables. Below this minimum value then the feedforward control is applied.

Preferably, a drive characteristic is stored in the control unit, with which the clocking of the converter and / or the timing of the further switching element of the driver circuit is changed gradually by means of feed forward control below the minimum value of the electrical parameter. For example, the drive characteristic determines the number of steps of the gradual feedforward control. For example, the drive characteristic determines the period of the gradual feedforward control. The drive characteristic defines, for example, the step size of the gradual feedforward control. In this way, different characteristics can be realized in the control unit, whereby the switching on and off can be customized.

Preferably, the drive characteristic is linear. Thus, the timing of the converter or the other switching element is changed so that a linear light power change in the second value range is obtained, so that no abrupt Changes in light output can occur. The linear control characteristic can be obtained, for example, by suitable control by means of a PWM switching signal by linearly shortening the pulse width of the PWM signal until the zero point of the electrical parameter is reached.

Alternatively, the drive characteristic is non-linear, for example logarithmic. Thus, the timing of the converter or the other switching element is changed so that a non-linear light power change in the second value range is obtained. The non-linear control characteristic can be adapted, for example, to human eye behavior, so that in particular the lower values in the second range of values are set more slowly since the human eye is better able to resolve the light change as the LED track becomes darker. The control is thus designed so that the light power change for the eye is harmonious.

Forward control below the minimum value is limited to a period of 0.5 to 3 seconds after receiving the switching command or after reaching the minimum value. Thus, this gradual feed-forward control of the LED track is designed to be perceived by the human eye as the extinction of the LED track or as a slow brightening of the LED track.

Preferably, the switching signal for the switching element of the converter and / or the further switching element is a PWM signal. The timing can now be changed in such a way that the switching frequency is changed and / or the turn-on time and / or the turn-off time. Thus, the timing of the switching elements is modulated with no difference between the different types of modulation.

Preferably, the clocking of the further switching element or the clocking of the converter should have a switching frequency greater than 100 hertz, since a clocking below 100 Hz would be perceived as a flicker of light. In addition, from a topological point of view, the minimum pulse width is limited to 1 microsecond. It is thus possible to gradually control the electrical parameter by varying the number of pulses themselves or the distance of the pulses from each other. At the end of the feedforward control, for example, a switching signal with a pulse having a pulse duration of one microsecond at a switching time (on-time + off-time) of 10 milliseconds is used as the clocking of the converter or as the clocking of the further switching element. This corresponds to 10,000 steps in the feedforward control.

In a preferred embodiment, the converter is an LLC converter. The control unit gradually changes the timing of a half-bridge circuit upon receipt of the switching command by means of feedforward control to change the electric parameter of the LED route. When using an LLC converter, the voltage provided on the output side must be changed over the LED path. However, changing the amplitude of the voltage changes the operating point of the LLC converter. This operating point change is counteracted by gradually changing the timing of the LLC converter. In this way, the operating point frequency is gradually increased when switching off and gradually reduced when switching.

Preferably, a final frequency of, for example, 200 kHz is set so that the feedforward control is completed (or begins) when the switching frequency has been gradually changed to this value. For example, the switching frequency obtained by means of feedback control at the minimum value can be 100 kHz. The switching frequency is then gradually changed to the limit switching frequency of 200 kHz to turn off the LED path. Conversely, even when the lamps are switched on, the limit switching frequency of 200 kHz is first switched on, which is gradually reduced until the minimum value is obtained. The drive change in the control unit of the driver circuit can be enabled by software modification. The software change then affects the changed response to a switching command, such as a DALI ON / OFF command. The switching frequency is controlled so that it is adjustable to the maximum.

Due to the software adaptation, it is now also possible to further correct the difficult-to-obtain minimum value. Thus, for example, a converter, which is in principle aligned for balancing to 1% of the electrical parameter, can now be regulated to a minimum value of 10% by means of feedback variables. Below 10% to 0% of the electrical parameter then the gradual feedforward control takes place.

In a further aspect of the invention, a method for operating light sources, in particular LEDs, is proposed. In this case, an input-side supply of a converter with a voltage first takes place in order to regulate an electrical parameter of the LED path on the output side. Subsequently, changing a clocking of the converter by means of a control unit to regulate the electrical parameter of the LED track by means of a feedback variable to a minimum value. Finally, changing the timing of the converter and / or the timing of another switching element of the driver circuit is done gradually by forward control by the control unit, so after receiving a switching command, the electrical parameter of the LED path is first controlled by means of feedback to the minimum value and is then controlled gradually without feedback in a range below the minimum value.

In a further aspect, a computer program product is proposed which implements a method according to the previous type when running in a computing device.

In a further aspect, an integrated circuit, in particular ASIC or microcontroller or a hybrid version thereof, which is designed to implement a method according to the preceding type is proposed.

In a further aspect, a luminaire, comprising an LED track and a driver circuit according to the previously described manner for driving the LED track with a variable electrical parameter is provided.

The invention or further embodiments and advantages of the invention will be explained in more detail with reference to figures, the figures only describe embodiments of the invention. Identical components in the figures are given the same reference numerals. The figures are not to be considered as true to scale, it can be exaggerated large or exaggerated simplified individual elements of the figures. Show it

1 a first embodiment of a driver circuit according to the invention;

2 A second embodiment of a driver circuit according to the invention;

3 a current-time characteristic of a LED track in classic control and driving according to the invention;

4 A third embodiment of a driver circuit according to the invention;

5 A fourth embodiment of a driver circuit according to the invention;

6 a further current-time characteristic in accordance with the invention control;

7 A fifth embodiment of a driver circuit according to the invention;

8th a voltage-frequency characteristic in inventive driving an LLC converter.

1 shows a first embodiment of a driver circuit according to the invention.

There is a converter 1 configured to receive a voltage U _IN on the input side. The converter 1 has at least one switching element S _K , which by means of a control unit 2 and one from the control unit 2 generated switching signal is clocked. The converter 1 moreover, has at least one memory unit, for example in the form of a coil, so that the converter is to be regarded as a clocked switching regulator. The output side is the converter 1 adapted to an electrical parameter, in particular a current I _LED or an electrical voltage U _out , to an LED track 3 provide. The converter 1 can be the electrical parameter of the LED range 3 regulate by the timing of the switching element S _{K of} the converter 1 from the control unit 2 is changed. This control of the electrical parameter is performed by comparing an actual value of the electrical parameter and a desired value, the control unit 2 for example via a DALI interface 6 provided. The control unit 2 receives the actual value by detecting a feedback variable 7 For example, the current measurement or the voltage measurement.

The LED range 3 is shown here by way of example with an LED. The actual wiring of the LED track 3 is not limited. Thus, both the number and the colors as well as the electrical arrangement in series or in parallel for this LED track 3 vary.

The control unit 2 receives via an interface (not shown) 6 Commands to the LED track 3 to regulate. For example, a DALI interface on the control unit 2 be provided to commands for dimming the LED track 3 to obtain. The dimming takes place from a maximum value of the electrical parameter to a minimum value of the electrical parameter using the feedback variable 7 , ie in a first range of values of the electrical parameter. The minimum value I _min , U _min corresponds to a certain percentage of the electrical parameter.

The converter 1 is designed to set the electrical parameter down to 1% as the minimum value using a feedback variable 7 to regulate. Will now be a switching command to the control unit 2 transmitted, for example, via the DALI interface or a switch of the lighting unit, so the LED track 3 initially regulated to the minimum value I _min , U _min .

Below the minimum value I _min , U _min is the electrical parameter by means of gradual feed forward control, ie without using the Feedback variable 7 regulated. It is provided on the one hand, the timing of the converter 1 to change. On the other hand, by the control unit 2 generates a further switching signal which is provided to a further switching element S ₁ . This further switching element S ₁ is according to 1 in series with the LED track 3 is arranged and controlled by means of a PWM signal. At the end of the control, the switch S ₁ additionally serves to interrupt the power supply to the LED track 3 , The PWM signal is gradually changed in the second value range of the electrical parameter, in particular, the pulse width Ton is gradually reduced and / or the turn-off time T _{off of} the PWM signal is gradually increased, should a turn-off command be received. This is the return size 7 disregarded. Alternatively, a switch-on command via the interface 6 to the control unit 2 in this case the electrical parameter is from 0% to the minimum value without feedback value 7 is regulated by the timing is changed gradually.

In this way, the light output of the LED track will not change abruptly due to a switching command. Due to the gradual change of the electrical parameter up to the actual zero point of the electrical parameter, the LED path is switched off 3 What happens to the eye without flickering or abrupt change in light output.

In 2 a second embodiment of a driver circuit according to the invention is shown. Contrary to the serial connection of the further switching element S ₁ is according to 2 the switch S ₁ parallel to the LED track 3 arranged. This arrangement corresponds to a real short-circuit switch to bypass the supply of the power supply. The converter 1 has a non-negligible output capacity. By arranging the switching element S _{1 in} parallel, current / voltage peaks can occur during switching, which in turn could cause flickering. Therefore, it is advantageous if the switch S _1, a coil L _{S is connected} in series in order to suppress such current / voltage spikes can.

In 3 is a comparison of a current-time curve with traditional control 4 and in the inventive control 5 an LED track 3 shown. In a first range of values 8th between the maximum value I _max and the minimum value I _{min of} the current I _LED as the electrical parameter, the control is carried out using the feedback variable 7 , This scheme in the area 8th is both for driving 4 as well as the control 5 identical.

In a second range of values 9 between the minimum value I _min and the zero value I _{o of} the current I _LED is carried out according to traditional control 4 no regulation. This leads from the time t _x to an abrupt drop of the current I _LED to the zero value I _o . This abrupt drop in current causes a disturbing abrupt change in the light output, which is undesirable.

According to the invention takes place in the second range of values 9 between the minimum value I _min and the zero value I _{o of} the current I _LED , the control takes place 5 by forward control of the current I _LED . In this case, the control characteristic is in accordance with the control 5 linear, that is the gradual change to the regulation of the current I _LED is gradually decreasing. This is achieved, for example, by a linear change in the turn-on time of a PWM signal of the further switching element S ₁ or a linear change in the timing of the converter to change its switching frequency.

As soon as a switch-off command via the interface 6 is obtained, the current I _LED by Regelrückführgröße 7 regulated to the minimum value I _min and then controlled by means of forward control to zero. This forward control can - as in 3 Shown - linearly done to realize the simplest possible control. Alternatively, this regulation can be non-linear, for example in order to realize the fastest possible turn-off, and possibly the eye inertia with darkening light sources 3 exploit.

This control 5 is through the in 1 and 2 allows illustrated driver circuits. In this case, either a further switching element S _{1 is} subjected to a variable PWM signal and / or the timing of the converter 1 itself is varied accordingly. It should be noted that the clock should not fall below a frequency of 100 Hz in order to avoid flickering.

In 4 a third embodiment of a driver circuit according to the invention is shown. Here is the in 2 used driver circuit, so that the further switch S ₁ parallel to the LED track 3 is arranged. In contrast to 2 is the converter 1 shown in detail. This is a buck converter, also known as buck converter or English "buck-converter". The buck converter has a series connection of a converter diode D and the switching element S _K. The converter 1 is supplied by means of an input voltage U _in . Between the anode of the diode D and a first contact of the switch S _K , a converter coil L is arranged as a storage element. At the output of the converter 1 is the LED track 3 arranged. The control unit 2 affects the switching element S _K with a switching signal to provide a constant current I _LED . This current I _LED can by changing the timing of the switch S _K between I _max and I _min under Use of the feedback size 7 be managed. The control unit compares 2 the return size 7 as an actual value with a setpoint value and sets the clocking of the converter 1 one. By clocking is meant both the switching frequency and the turn-on or turn-off time.

Below the minimum value I _min , the regulation of the current I _LED will now be effected by varying the timing of the further switching element S ₁ . The converter 1 So also supplies the current I _min , which now by means of the further switching element S ₁ without feedback 7 is reduced.

The situation is very easy to realize for Buck converters operating in the so-called continuous mode. Here you can easily insert a short-circuit switch S ₁ . This simplicity must be qualified: the switch S _{K of} the Buck converter 1 must be able to supply the _minimum current value I _min to a short circuit, so you can handle very short turn-on times. For discontinuous or boundary-mode systems, there is a risk of visible flicker due to interference between the converter and short circuit frequencies.

In 5 a fourth embodiment of a driver circuit according to the invention is shown. In contrast to 4 is in 5 a series connection of the switch S ₁ used to the in 1 to achieve the benefits discussed.

In 6 is a current-time history for the in 4 and 5 illustrated embodiments of a driver circuit. Here, the switching signal for the further switching element S _{1 is shown} from the time t _x . It can be seen that the further switching element S _{1 is} a PWM signal, which has an increasing turn-off time T ₁ , T ₂ , T ₃ , with the same turn-on time t _on .

In any case of modulation, the minimum occurring frequency must not fall below 100 Hz, otherwise it would be perceived as flickering. On the other hand, a minimum pulse width t _ON of one microsecond from a driver's point of view can not be undershot.

Thus, either the number of pulses t _ON can be reduced or the distance T ₁ , T ₂ , T ₃ between the individual pulses can be changed. In this way, the current I _{LED is} through the LED track 3 stepwise - without using a control feedback variable 7 - reduced. At the end of the gradual control, only a pulse having a pulse width of 1 μs is set at a period of 10 milliseconds as a minimum level. At frequencies above 100 Hz and a minimum pulse width of 1 μs, the current I _LED below the minimum value I _{min can be} reduced or increased in 10000 steps. Assuming that the converter 1 a minimum value of 1% of the electrical parameter can be compensated, with the pulse pauses and corresponding pulse widths of the PWM signal with each step a 0.0001% reduction can be achieved, so that in the first step of 1% of the electrical parameter to 0, 9999% of the electrical parameter is reduced.

Because the control unit 2 has a finite bit width, for example, 12 bits, for example, 4,096 steps as gradual control in the second range of values 9 to be provided.

Thus, in 4.096 steps, from 1% minimum value I _MIN to 0% of the electrical parameter can be dimmed. This is done in a gentle manner so that it is not perceived as an abrupt change in light output. For practical purposes, 100 steps, or a maximum of 1,000 steps, is sufficient because the human eye can not resolve a finer difference in light.

In 7 a fifth embodiment of a driver circuit according to the invention is shown. The converter 1 is shown here as an LLC converter. The mode of operation of an LLC converter is known in principle and should be assumed to be known here. Only to complete it is pointed out that the voltage applied to the input V is _in a DC voltage, which is decomposed by means of a half-bridge circuit into an AC voltage. A resonant circuit - consisting of the elements L _R , L _M , C _R - converts this received AC voltage to an output side provided LED voltage U _out for the LED track 3 , For galvanic separation of the possibly high input voltage, for example, obtained from a mains voltage of 230 volts, a transformer T, consisting of two coils, is provided. The secondary-side coil has a center tap to allow easy rectification.

According to 7 the drive according to the invention is achieved in that the operating point of the LLC converter is changed. The control unit 2 For example, in the form of a microcontroller, drives the half-bridge circuit by a complementary switching signal. This switching signal has a switching frequency. By changing the frequency of the switching signal to the half-bridge circuit, the output voltage U _{out can be} varied, whereby the light output is varied. The smaller the switching frequency, the higher the output voltage and thus the light output at the output of the converter 1 ,

Thus, by changing the switching frequency of the half-bridge, the voltage U _out across the LED path 3 regulated. This regulation takes place up to a minimum value U _{min of} the voltage U _out by means of a control feedback variable 7 , Below the minimum value U _min , the control of the switching frequency of the half-bridge takes place without the feedback variable 7 to avoid an abrupt change in light output.

At LLC converters 1 namely, a short circuit switch S _{1 is} not optimal. The LLC converter is in principle a voltage source with a capacity of a few hundred nanofarrads at the output. Therefore, would rather use a breaker in series with the LED string (principle "anti-glare FET"). Here, however, the losses in normal operation are to be considered. These have the LLC converter 1 usually no intelligent Steurschaltung on the secondary side. Thus, the control of such a switch S _{1 is} difficult or cumbersome, for example, optocouplers could be provided.

An unillustrated approach would be to use an auxiliary winding on the transformer T. It would be conceivable to periodically short an auxiliary winding including a rectifier, thus removing the current I _LED from the LLC converter output. At some point, the voltage U _{out on the} secondary side is too small to go through the LED track 3 to be able to drive a current I _LED . In continuous short-circuit the LLC converter pumps 1 then only reactive power between the resonant capacitor C _r and the leakage inductance L _r back and forth.

For safety reasons (Selv) if necessary, the auxiliary winding would have to be attached to the primary side of the transfer T. This then has a better coupling than the secondary winding and thus possibly reduces the effective leakage inductance L _r . If one were to associate the secondary winding with an additional rectifier and short it periodically, no auxiliary winding would be necessary, the problem with the coupling change and the output capacitors would be easily solved, but again a control over the Selv path is necessary.

An LLC converter 1 is in principle a voltage converter. Large voltage regulation ranges are difficult to handle because zero-voltage operation or zero-current operation is not possible. The regulation of the voltage U _out is thus in the ratio 1 to 2, that is, for example, in the range between U _min = 50 and U _max = 100 volts. If the voltage range is further restricted and it is required that at least as many LEDs be connected to this converter that the voltage is above 80 V, then the current can be set to zero since U _min = 50 V due to the added limit voltages U _cut-off electricity can no longer flow.

As soon as the LED voltage is at least 1/6 above the minimum, around 60 V at minimum value U _min of 50 V, the current I _{LED can be set} to zero.

In 8th a voltage-frequency characteristic for an inventive drive of an LLC converter is shown. Here, the output voltage U _{out is} maximum when the frequency f of the half-bridge circuit is minimum. With increasing frequency f of the switching signal for the half-bridge circuit of the LLC converter 1 the voltage U _out at the output of the converter decreases 1 and thus the light output coming from the LED track 3 is delivered. Also the LLC converter 1 can only up to a minimum value U _{min of} the electrical parameter U _out to operate the LED track 3 by means of feedback size 7 be managed. For this minimum value U _min , an operating frequency f _{1 is} set.

In application of the control according to the invention is now the operating frequency f of the half-bridge circuit of the LLC converter 1 gradually increased so that the output voltage U _out gradually decreases. At a frequency f ₂ , the threshold voltage Ucut _{-off of} the LED track 3 achieved and the LED range 3 goes out completely. The operating frequency f ₂ represents the final frequency, by means of the control unit 2 can be adjusted.

All shown, illustrated and described features can be combined with each other.

LIST OF REFERENCE NUMBERS

1

Clocked converter

2

control unit

3

LED track, LED

4

Traditional control

5

Inventive control

6

Switching command, DALI interface

7

Feedback variable

8th

First value range

9

Second value range

S _k

Switching element of the converter

S ₁

Another switching element

D

converter diode

L

converter coil

L _S

switch coil

T

Transformers of the LLC converter

I _LED

Electricity through the LED track

I _max

Maximum value of the current through the LED track

I _min

Adjustable minimum value of the current through the LED track

f ₁

Operating frequency of the converter at minimum value

f ₂

Operating frequency of the converter at cut-off frequency of the LED

U _out

Voltage across the LED range

U _max

Maximum value of the voltage across the LED track

U _min

Adjustable minimum value of the voltage across the LED track U _min

U _cut-off

Switch-off voltage of the LED track

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014200437 A1 [0003]

Claims (18)

Switched LED driver circuit, comprising: - output terminals for supplying an LED track, - a converter clocked by means of at least one switch, - a control circuit, - which outputs a control signal for clocking the converter, characterized in that the control circuit is adapted to Obtaining a turn-off command to continuously change the timing of the converter over a predetermined time range greater zero without the use of a feedback signal such that the light output is gradually reduced and at the end of said time range is zero. Driver circuit with output terminals for preferably dimmable driving of an LED track ( 3 ) consisting of at least one LED, comprising: a clocked converter ( 1 ), which is supplied on the input side with a voltage (U _in ) and the output side, an electrical parameter (I _LED , U _out ) of the LED track ( 3 ), a control unit ( 2 ), which is adapted to a control signal for timing the converter ( 1 ) to determine the electrical parameter (I _LED , U _out ) of the LED track ( 3 ) in a region above a minimum value (I _min , U _min ) by means of a feedback variable ( 7 ) to regulate; and the control unit ( 2 ) is further adapted, below the minimum value (I _min , U _min ) of the electrical parameter (I _LED , U _out ), the timing of the converter ( 1 ) and / or to gradually change the timing of a further switching element (S ₁ ) of the driver circuit by means of forward control, so that after receiving a switch-off command ( 6 ) the electrical parameter (I _LED , U _out ) of the LED track ( 3 ) first by means of feedback ( 7 ) is controlled to the minimum value (I _min , U _min ) and then without feedback ( 7 ) gradually to zero in a range below the minimum value (I _min , U _min ) with this feedforward control. Driver circuit according to claim 2, wherein the further switching element (S ₁ ) parallel to the LED track ( 3 ) is arranged, preferably wherein the further switching element (S ₁ ) is connected in series with another coil. Driver circuit according to claim 2, wherein the further switching element (S ₁ ) in series with the LED track ( 3 ) is arranged. Driver circuit according to one of claims 2 to 4, wherein the control unit ( 2 ) by changing the timing of the converter ( 1 ) and by means of the return variable ( 7 ) controls the electrical parameter (I _LED , U _out ) to 10 percent, preferably 5 percent, more preferably 1 percent, of the maximum electrical parameter (I _LED , U _out ) as the minimum value (I _min , U _min ). Driver circuit according to one of claims 2 to 4, wherein in the control unit ( 2 ) a drive characteristic is stored, below the minimum value (I _min , U _min ) of the electrical parameter (I _LED , U _out ), the timing of the converter ( 1 ) and / or the timing of the further switching element (S ₁ ) of the driver circuit is gradually changed by means of feed forward control. Driver circuit according to claim 6, wherein the drive characteristic is linear. Driver circuit according to claim 6, wherein the drive characteristic is non-linear, for example logarithmic. Driver circuit according to one of claims 2 to 7, wherein changing the electrical parameter (I _LED , U _out ) below the minimum value (I _min , U _min ) for a period of 0.5 seconds to 3 seconds after receiving the switching command ( 6 ) or after reaching the minimum value (I _min , U _min ) is limited. Driver circuit according to one of claims 2 to 9, wherein the turn-on time and / or the turn-off time of the converter ( 1 ) or the further switching element (S ₁ ) by means of the control unit ( 2 ) is changed gradually. Driver circuit according to one of claims 2 to 10, wherein the timing of the further switching element (S ₁ ) or the clocking of the converter ( 1 ) has a switching frequency greater than 100 hertz. Driver circuit according to one of claims 2 to 11, wherein the timing of the further switching element (S ₁ ) or the clocking of the converter ( 1 ) is changed gradually in one thousand steps, preferably one hundred steps. Driver circuit according to one of claims 2 to 12, wherein the converter ( 1 ) is an LLC converter and the control unit ( 2 ) the timing of a half-bridge circuit after receiving the switching command ( 6 ) gradually changed by forward control. Driver circuit according to claim 13, wherein the switching frequency for the LLC converter ( 1 ) has a fixed final value, for example 200 kilohertz. A driver circuit according to claim 13 or 14, wherein Upon receiving a power down command, the switching frequency of the LLC converter ( 1 ) is gradually increased; and upon receiving a power-on command, the switching frequency of the LLC converter ( 1 ) is gradually reduced. Method for operating light sources, in particular LEDs, comprising the following steps: Supplying a converter on the input side ( 1 ) with a voltage (V _in ) to the output side an electrical parameter (I _LED , U _out ) of the LED track ( 3 ) to regulate; Changing a clocking of the converter ( 1 ) by means of a control unit ( 2 ) to the electrical parameters (I _LED , U _out ) of the LED track ( 3 ) by means of a feedback variable ( 7 ) to a minimum value (I _min , U _min ); and changing the timing of the converter ( 1 ) and / or the timing of another switching element (S ₁ ) of the driver circuit gradually by forward control by the control unit ( 2 ), so that after receiving a switching command, the electrical parameter (I _LED , U _out ) of the LED route ( 3 ) first by means of feedback ( 7 ) is controlled to the minimum value (I _min , U _min ) and then without feedback ( 7 ) is gradually regulated in a range below the minimum value (I _min , U _min ). Integrated circuit, in particular ASIC or microcontroller or a hybrid version thereof, which is designed to implement a method according to claim 16. Luminaire comprising an LED track and a driver circuit according to one of claims 1 to 15 for driving the LED track ( 3 ) with a variable electrical parameter (I _LED , U _out ).

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