DE102016206772A1 - Clocked converter for dimmable bulbs with dynamically adjustable filter - Google Patents

Abstract

A clocked converter for dimmable lighting means, in particular for an LED track with at least one LED, is provided, wherein the clocked converter can be supplied from an electrical supply, in particular a DC voltage, and has a first switch which is clocked by a control unit, wherein the control unit is adapted to superimpose on the voltage supplied to the lighting means by the clocked converter a PWM signal which is low-frequency relative to a frequency of the clocking of the first switch, wherein a second switch is provided which is arranged to Filter characteristics of a filter circuit of the clocked converter, which filters the voltage output by the clocked converter to the light source voltage at an output of the converter, and wherein the control unit is adapted to activate or deactivate the second switch.

Description

The invention relates to a clocked converter and in particular a DC / DC converter, for example a Buck converter, a boost converter, or a flyback converter, for the operation of a dimmable light source, in particular at least one LED or a LED Module.

From the WO 2014/047668 A2 For example, a switched-clock drive circuit for driving an LED track is known in which a switch serves to enable and otherwise interrupt a current path between a sense resistor and a low-pass filter during a turn-on period of a PWM signal.

According to this prior art signal generated by a high-frequency, clocked switch signal is superimposed in comparison to a low-frequency PWM signal, in particular an operating current / an operating voltage for a light source. By the high-frequency switching of the switch, a ripple is generated, which is supplied to the lamp with the operating current / the operating voltage.

A disadvantage now is that, in particular at very high powers, close to 100% of the rated power of the luminous means, i. in particular with a degree of dimming of almost 100%, can occur by the high-frequency switching of the converter switch, a relatively high ripple in the supply voltage of the lamp. Thus, there is a danger that an over-swinging ripple will exceed the load limits of the bulb and thus damage or destroy the bulb (or the ripple appears detectable to the human eye as a fluctuation in light output). In particular, in converters with different levels of luminous flux / voltages at a rated power of almost 100% of the consequent maximum current / the maximum voltage across the lamp has a very high ripple. On the other hand, the problem still arises that in known filter circuits, when a PWM signal is superimposed, the edges of the PWM signal when dimming with low degrees of dimming, e.g. Approximately 1-5%, "grind", which ultimately reduces the benefits of PWM dimming. In particular, the PWM dimming is used to ensure constant color dots of the light source at low dimming levels.

To solve the above-mentioned problems, the invention provides a device according to the independent claims. Further embodiments of the invention are the subject of the dependent claims.

In a first aspect, a clocked converter for dimmable bulbs, in particular for an LED track with at least one LED, provided, wherein the clocked converter from an electrical supply, in particular a DC voltage, can be supplied and a clocked by a control unit first Switch, wherein the control unit is adapted to superimpose the signal supplied from the clocked converter to the lighting means a PWM signal which is low-frequency in relation to a frequency of the clocking of the first switch, wherein a second switch is provided, the is arranged to change filter characteristics of a filter circuit of the clocked converter, which filters the voltage output by the clocked converter to the lighting means at an output of the converter, and wherein the control unit is adapted to activate or deactivate the second switch.

The control unit can be supplied with a dimming signal, in particular via a lighting device bus, which indicates a dimming level to be set by the control unit at the lamps, and wherein the control unit superimposes the PWM signal if the dimming level to be set falls below a threshold value.

The second switch can change the filter circuit by switching on or off of circuit components, in particular at least one capacitor, an inductor, and / or a resistor.

The second switch may change the filter circuit by changing a circuit component, in particular by varying an inductance value, a capacitance value and / or a resistance value.

The control unit can be supplied with a parameter to be set to reflect the dimming level to be set.

The clocked converter may be a DC / DC converter, in particular a Buckwander (down converter), boost converter (boost converter), or flyback converter (flyback converter).

At a dimming level above the threshold, an amplitude modulation signal may be superposed instead of a PWM signal.

The voltage at the light sources can be detected at a voltage divider and fed to the control unit as an actual variable for the current dimming level.

The threshold for the degree of dimming may be about 1% to about 55%, preferably 5% to 45%.

The clocked converter can be powered starting from an energy store, in particular a storage capacitor.

The filter circuit may be a low-pass filter, an LC filter or a band-pass filter that has a different characteristic, for example, during the PWM signal superposition. a higher cutoff frequency, than in the amplitude modulation signal overlay.

The control unit can superimpose the PWM signal and / or the amplitude modulation signal by activating a further switch.

In a further aspect, an operating device for lighting means, in particular LEDs, is provided with a clocked converter as described above.

The invention will now be described with reference to the figure. It shows:

1 a schematic representation of a circuit arrangement according to the invention.

According to the invention, it is provided that an adaptive filter is used, wherein the adaptivity relates in particular to, for example, a change in the filter properties and preferably by switching on and off of a filter element, depending on a degree of dimming. In particular, the clocked converter thus always has a filter which is only changed in its properties.

In particular, a control unit SE is provided, which clocks the clocked switch of the clocked converter for dimmable bulbs. This control unit is supplied with a dimming level to be set, e.g. via a bus line for lighting means, for example a DALI or DSI bus, or a parameter representing the degree of dimming.

As in 1 shown, the control unit SE first controls a first switch S _W high frequency. If the switch S _{W is} turned on, ie _{turned on,} the current through the switch S _W can be detected at a measuring resistor R _shunt . This current increases substantially linearly during the switch-on phase of the first switch S _W and drops to zero when the first switch S _{W is opened} , ie when it is deactivated. As a result, the current shows a zigzag over time through the coil L _buck. When the first switch S _{W is turned on} , the current shows a rising edge and when the first switch S _W is turned off, a falling edge results. During the freewheeling phase, the current through the first switch S _W , which may be designed in particular as a transistor and in particular as a MOSFET, is therefore zero, before it rises again when the first switch S _{W is switched on} again.

Preferably, the switch S _{W is} turned off when a shutdown threshold, which may be stored in particular in the control unit SE, is reached. Therefore, the time profile of the current through the switch can be detected by the control unit SE at the first switch S _W. Further, for example, the controller may internally include a filter such as a low pass filter to time average the sensed current.

The high-frequency, approximately zigzag course of the current or the voltage which is supplied by the converter to the light emitting diode LED at terminals A, B, by the control unit SE, for example by means of a second switch S _PWM in relation to the timing of the first Switch S _W low-frequency pulse width modulation signal (LF PWM, low-frequency PWM, hereinafter referred to as PWM signal) are superimposed. The current through the coil L _{Buck can} drop to zero before it is switched on again. This corresponds to the so-called limit operation (borderline operating mode). It is also possible to operate the circuit in the so-called discontinuous conduction mode, in which case after reaching the zero crossing, ie after complete demagnetization or discharging of the inductance L _buck, no switching on of the first switch S _W takes place for a certain period of time , Of course, in the non-contiguous operation (continuous conduction mode) operation can take place, in which case the inductance L _{buck is} always charged so that the zero point is not reached.

For example, low-frequency (typically with a frequency in the range of 100-1000 Hz) pulse packets are supplied to the lighting means by the control unit SE with preferably constant average time over time. The current or the voltage within the pulse packet is then superimposed on the above-mentioned high-frequency ripple. The brightness of the light source can now be controlled by the frequency of the pulse packets. For example, the bulbs can be dimmed by increasing the time interval between the pulse packets.

Thus, the high-frequency clocking of the first switch S _{W is combined} with a PWM signal of the second switch S _PWM , wherein the frequency of the PWM signal in relation to the frequency of the high-frequency clocking of the first switch S _{W is} low frequency. This results in a high-frequency clocking of the first switch S _W , which is interrupted by longer pauses without clocking, these longer pauses are generated by the turn-off of the low-frequency driven PWM switch S _PWM . The frequency of the high-frequency clocking of the first switch S _W and of the second switch S _PWM is preferably matched to one another in order to avoid flickering effects during operation of the luminous means. One possibility of tuning is that the frequency of the high-frequency clocking of the first switch S _{W is} a whole-part multiple of the low-frequency clocking of the second switch S _PWM .

In particular, for reasons of color consistency, the amplitude of the ripple should be as low as possible within a pulse packet. Thus, at a fixed predetermined frequency, the turn-on ratio for the high-frequency clocking of the first switch S _W can be set by the lighting means as a function of an average value of the determined current / voltage. The maintenance of the current through the lighting means can be effected by the parallel connection of an optional capacitor C _LED (not shown) to the lighting means. In particular, the energy storage C _LED buffers energy to power the _LED light when the coil current has dropped to zero.

Alternatively, the adjustment of the current may be performed by / to the voltage at the / the LED lamps by a suitable choice of the power is turned ON on and off times of the first switch S _W. The times may, for example, be selected so that the first switch S _{W is} turned on when the current falls below a certain minimum reference value and is turned off when the current exceeds a maximum reference value (Abschaltschwellenwert). The minimum reference value can be zero.

Furthermore, the voltage at the light-emitting means LED can be determined by measurement on a voltage divider (not shown) connected downstream of the light-emitting means, which is connected in series with the light-emitting means. The voltage across the lamp then results from the difference between a supply voltage V _BUS , from which the clocked converter is fed starting, and the voltage detected at the voltage divider across the load LED. The control unit SE could detect the voltage across the light-emitting means LED but also, for example, by means of a measurement of a voltage on the coil L _buck . This is exemplary in 1 in which a voltage V _{buck is} detected at a voltage divider formed by resistors R1, R2.

In this case, a measurement during the turn-off period of the first switch S _W take place. Alternatively, a voltage measurement can also be carried out on a choke winding ZX during the demagnetization phase of the coil L _buck . The current through the load can be determined indirectly by calculating the transmitted power and the detected voltage across the LED light source. The determination and / or the calculations are preferably carried out in the control unit SE. It can also be included in the calculation of the transmitted power, a correction factor that includes, for example, the switching behavior and / or the losses of the converter.

The calculated LED current can thus be used as an actual value variable for a regulation of the luminous flux / the luminous flux. On the one hand, the turn-on time T _{on of} the first switch S _W (converter switch of the Buck converter) can be used as the control variable for the control. Alternatively or additionally, the duty cycle of the low-frequency control of the second switch S _PWM can be used.

If the control variable is the switch-on time T _{on of} the converter, the switch-off threshold for the first switch S _{W of} the control unit can be shifted depending on the mean value of the current across the first switch S _W. The duty cycle of the low-frequency PWM control can be set at least in a partial range of the operation of the load, for example at high brightness, ie at a dimming level of, for example, 100%, at a duty cycle of 100% or close to this range. Here, the height of the current through the load and thus the brightness of the light emitted by the bulbs can be influenced by the adjustment of the switch-off threshold for the first switch S _W and thus on the control variable of the switch-on time T _{on of} the converter.

However, it is also possible that a combined change of both the duty cycle of the low-frequency PWM control of the second switch S _PWM and the adaptation of the switch-off threshold for the first switch S _{W can be effected} at least in a partial region of the operation of the load. Alternatively, only an adaptation of the switch-off threshold of the first switch S _W can take place in a partial region of the operation of the load.

The control unit SE further preferably detects a signal that the supply voltage V _BUS reproduces. A signal representing a current through a switch S _W (in the Einschaltzeitdauern of the second switch S _W) may also be detected. The optional capacitor C _LED , which can be provided in parallel with the load LED, avoids that the current through the load is the course the current through the coil L _buck follows. When the first switch S _W is not capable of conducting a conductive connection, ie, in particular during the phase of demagnetization of the coil L _buck , the current through the LED can be maintained due to the energy temporarily stored in the energy store C _LED . A voltage signal V BUS_Sense reproducing the bus voltage can be _detected , for example, at a voltage divider which is in 1 represented by the resistors R3, R4.

The low-frequency PWM signal need not be generated by the control unit SE itself, but can also be supplied from outside by an externally supplied PWM control signal.

The in 1 Clocked converter shown further has a filter that in 1 is shown as an LC filter. The filter is realized by the capacitance C _F and the inductance L _F.

As in 1 2, the circuit has a third switch S _F , which is provided to adaptively change the filter circuit with the LC filter. As already mentioned, the control unit SE is supplied with a dimming signal Dim which indicates which dimming level is to be set by the control unit SE. In this case, a dimming level of 100%, for example, correspond to operation of the luminous means at full brightness, while a dimming level of, for example, 1-5% indicates dimming to a very low value and thus operation with greatly reduced brightness. In particular, the third switch S _{F can} control the third switch S _{F as a} function of the dimming signal Dim. In particular, the further capacitor C _{apapt of} the filter circuit can be switched on by conductively switching the third switch S _F so that a CLC filter circuit is formed from the capacitance C _F , the inductance L _F and the further capacity C _adapt .

Switching on or switching off the additional filter component C _adapt the filter circuit can also be done by activating or deactivating the switch S _F by a separately provided by the control unit SE control circuit, such as a microcontroller, ASIC, IC, ..., the / to which the dimming information Dim is supplied, or which generates the dimming information Dim on the basis of the supplied parameters (for example voltage values supplied by a motion detector).

Of course, it is also possible that properties of the filter circuit are adaptively changed with the degree of dimming by switching on or off or even an adjustment of other, the filter characteristics of determining passive components by the control unit SE. This can be done, for example, by switching off and / or switching on inductors, capacitors or resistors.

It should be noted that the clocked converter shown relates to the circuit part of an operating device between a bus voltage stabilizing storage capacitor (not shown) and the LED track at the terminals A, B. In particular, the ripple thus occurs at the voltage of the storage capacitor.

As already mentioned, the modulation takes place by means of the PWM control of the second switch S _{PWM as a} function of a dimming level to be set by the control unit. In particular, a threshold value can be stored in the control unit SE. For example, this threshold may correspond to a dimming level of 1-5%, but for example also a dimming level of about 50% to 55%. Below this threshold value, ie when a dimming level of less than approximately 1-5% or approximately 50-55% is to be set, an overlay with a PWM signal takes place. At high dimming levels, ie in particular at dimming levels which are above the threshold value, a superimposition of the voltage on the lighting means takes place with an amplitude modulation.

The filter provided for the lighting supply voltage filter has during dimming by means of the PWM modulation another characteristic, for example, a higher cutoff frequency, at higher dimming levels amplitude modulation is superimposed and thus takes an amplitude modulation dimming.

The dynamically tunable filter lessens the waveform of the PWM signal at lower dimming levels. This is achieved by switching on the filter capacitance C _adapt, for example, in that at dimming levels below 10%, the capacitance C _adapt is switched off or bypassed by the activation of the switch S _{F in} order to avoid a color shift. For larger currents, however, the capacitance C _{adapt is} added to limit the ripple current to a level specified for the load.

It is to be understood that the filter circuit may also comprise filters other than the said LC or CLC filter, and that other elements may be adaptively switched on or off by activating or deactivating the switch S _F. Furthermore, it is to be understood that, for example, also gradually adjustable components of a filter circuit can be changed by a corresponding change in their control by the control unit SE, whereby overall the behavior of the filter circuit is also changed.

Therefore, the filter circuit, in particular as a low-pass filter or a band-pass filter may be provided, which reduces the ripple.

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

• WO 2014/047668 A2 [0002]

Claims (13)

Clocked converter for dimmable lamps (LED), in particular for an LED track with at least one LED, wherein - the clocked converter starting from an electrical supply (V _BUS ), in particular a DC voltage, can be supplied and a by a control unit (SE ) clocked first switch (S _W ), wherein - the control unit (SE) is adapted to superimpose the supplied from the clocked converter to the lighting means (LED) voltage a PWM signal which is proportional to a frequency of the clocking of first switch is low-frequency, - a second switch (S _F ) is provided, which is adapted to change filter characteristics of a filter circuit of the clocked converter, which outputs the output of the clocked converter to the light emitting diode (LED) voltage at an output (A, B) of the converter, and - the control unit (SE) is adapted to activate or deactivate the second switch (S _F ).  Clocked converter according to claim 1, wherein the control unit (SE) a dimming signal (Dim) is supplied, in particular via a Beleuchtungsgerätebus that indicates a to the light sources (LED) by the control unit (LED) dimming level to be set, and wherein the control unit (SE ) superimposes the PWM signal when the dimming level to be set falls below a predetermined threshold.  The clocked converter of claim 2, wherein at a dimming level above the threshold, instead of a PWM signal, an amplitude modulation signal is superimposed.  Clocked converter according to one of claims 2 or 3, wherein the threshold for the degree of dimming below 50%, preferably below 30%. Clocked converter according to one of the preceding claims, wherein the second switch (S _F ) changes the filter circuit by switching on or off of circuit components, in particular at least one capacitance (C _F ), and / or an inductor, and / or a resistor. A clocked converter according to one of the preceding claims, wherein the second switch (S _F ) changes the filter circuit by changing a circuit component, in particular by changing an inductance value, a capacitance value and / or a resistance value.  Clocked converter according to one of the preceding claims, wherein the control unit (SE) is supplied to a set the Dimmgrad setting parameter (Dim).  A clocked converter according to one of the preceding claims, wherein the clocked converter is a DC / DC converter, in particular a buck, boost, or flyback converter.  Clocked converter according to one of the preceding claims, wherein the voltage at the light-emitting means (LED) detected at a voltage divider and the control unit (SE) is supplied as actual size for the current Dimmgrad.  Clocked converter according to one of the preceding claims, wherein the clocked converter, starting from an energy storage, in particular a storage capacitor, is fed.  A clocked converter as claimed in any one of the preceding claims, wherein the filter circuit is a low-pass filter or an LC filter or band-pass filter which, during the PWM signal superposition, has a different characteristic, e.g. a higher cutoff frequency, than in the amplitude modulation signal overlay. Clocked converter according to one of the preceding claims, wherein the control unit is adapted to superimpose the PWM signal and / or the amplitude modulation signal by driving a further switch (S _PWM ).  Operating device for illuminants, in particular LEDs, with a clocked converter according to one of the preceding claims.

Images