AT16340U1 - Clocked converter for dimmable bulbs with dynamically adjustable filter - Google Patents

Abstract

The invention relates to a 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 (VBus), in particular a DC voltage, can be supplied and a by a control unit (SE) clocked first switch (SW), wherein the control unit (SE) is adapted to superimpose the supplied from the clocked converter to the light emitting diode (LED) voltage a PWM signal, which is proportional to a frequency of the clocking of first switch is low frequency, wherein a second switch (SF) is provided, which is adapted to change the filter characteristics of a filter circuit of the clocked converter, the voltage output from the clocked converter to the light emitting means (LED) at an output (A, B ) of the converter, and wherein the control unit (SE) is adapted to activate or deactivate the second switch (SF) older.

Description

description

CLOCKED CONVERTER FOR DIMMABLE LUMINAIRES WITH DYNAMICALLY ADJUSTABLE FILTER 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 lamp , in particular at least one LED or an LED module.

From WO 2014/047668 A2 an operating circuit with a clocked converter for controlling an LED path is known, in which a switch is used to release a current path between a measuring resistor and a low-pass filter during a switch-on period of a PWM signal and otherwise to interrupt.

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

A disadvantage is now that especially at very high powers close to 100% of the nominal power of the lamp, i.e. in particular with a degree of dimming of almost 100%, a relatively high ripple in the supply voltage of the lamp can occur due to the high-frequency switching of the converter switch. There is therefore a risk that an overriding ribbed egg will exceed the load limits of the illuminant and thus damage or destroy the illuminant (or the ribbed egg appears to be visible to the human eye as a fluctuation in the light output). Particularly in the case of converters with differently strong lamp currents / voltages, the resulting maximum current / maximum voltage at the lamp has a very high ripple at a nominal output of almost 100%. On the other hand, there is also the problem that in known filter circuits when a PWM signal is superimposed, the edges of the PWM signal when dimming with low dimming levels, e.g. approx. 1-5%, "smooth out, which ultimately reduces the advantages of PWM dimming. In particular, PWM dimming is used to ensure constant color points of the lamp at low dimming levels.

To solve the above 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 lamps, in particular for an LED section with at least one LED, is provided, the clocked converter being able to be supplied from an electrical supply, in particular a DC voltage, and by a Control unit has clocked first switch, the control unit being set up to superimpose on the voltage 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, a second switch being provided , which is set up to change filter properties of a filter circuit of the clocked converter, which filters the voltage output by the clocked converter to the lamps at an output of the converter, and wherein the control unit is set up 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 on the lamps by the control unit, and the control unit superimposes the PWM signal when the dimming level to be set falls below a threshold value.

The second switch can the filter circuit by switching circuit 1/8 on or off

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[0009] The second switch can change the filter circuit by changing a circuit component, in particular by changing an inductance value, a capacitance value and / or a resistance value.

[0010] The control unit can be supplied with a parameter reflecting the degree of dimming to be set.

The clocked converter can be a DC / DC converter, in particular a buck walker (step-down converter), boost converter (step-up converter), or flyback converter (flyback converter).

If the degree of dimming is above the threshold value, an amplitude modulation signal can be superimposed instead of a PWM signal.

The voltage across the lamps can be detected on a voltage divider and supplied to the control unit as an actual variable for the current dimming level.

[0014] The threshold value for the degree of dimming can correspond to approximately 1% to approximately 55%, preferably 5% to 45%.

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

The filter circuit can be a low-pass filter, an LC filter or a band-pass filter which has a different characteristic, e.g. has a higher cut-off frequency than in the case of the amplitude modulation signal superimposition.

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

In a further aspect, an operating device for light sources, 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:

Fig. 1 is 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 the fact that, for example, a change in the filter properties and preferably by switching a filter element on and off takes place depending on a degree of dimming. In this case, the clocked converter in particular always has a filter whose properties are only changed.

In particular, a control unit SE is provided, which clocks the clocked switch of the clocked converter for dimmable lamps. A dimming level to be set is fed to this control unit, e.g. Via a bus line for lighting equipment, for example a DALI or DSI bus, or a parameter reflecting the degree of dimming.

As shown in Fig. 1, the control unit SE first controls a first switch S _w high frequency. If the switch S _{w is} switched on, ie switched on, the current through the switch S _w can be detected at a measuring resistor R _shunt . This current increases essentially 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 through the coil L _{buck shows} a zigzag-shaped course over time. When the first switch S _{w is switched on} , the current shows a rising edge and when the first switch S _w is switched off there is a falling edge. During the free-running phase, the current through the first switch S _w , which can be embodied 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

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The high-frequency, approximately zigzag-shaped course of the current or voltage, which / which is supplied by the converter to the illuminant LED at terminals A, B, can by the control unit SE, for example by means of a second switch S _PWM in relation to Clocking of the first switch S _w low-frequency pulse width modulation signal (LF PWM, Low Frequent PWM, hereinafter referred to as PWM signal) are superimposed. The current through the coil L _BuC k can drop to zero before _switching on again. This corresponds to the so-called border operation (borderline operating mode). It is also possible to operate the circuit in what is known as discontinuous conduction mode, the first switch S _w not being switched on for a certain period of time after zero crossing, ie after complete demagnetization or discharge of the inductance L _buck , Of course, operation can also take place in non-intermittent operation (continuous conduction mode), in which case the inductance L _{buck is} always charged in such a way that the zero point is not reached.

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

The high-frequency clocking of the first switch S _w is thus combined with a PWM signal of the second switch S _PW m, the frequency of the PWM signal being low-frequency in relation to the frequency of the high-frequency clocking of the first switch S _w . This results in a high-frequency clocking of the first switch S _w , which is interrupted by longer pauses without clocking, these longer pauses being generated by the switch-off phase of the low-frequency-controlled PWM switch S _PW m. The frequency of the high-frequency clocking of the first switch S _w and the second switch S _P WM is preferably matched to one another in order to avoid flickering effects when the illuminant is in operation. One possibility of tuning is that the frequency of the high-frequency clocking of the first switch S _{w is} an integral multiple of the low-frequency clocking of the second switch S _PW m.

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 switch-on ratio for the high-frequency clocking of the first switch S _{w can be set as a} function of an average value of the current / voltage determined by the lamp. Maintaining the current through the lamp (not shown) are carried out at the lighting means by the parallel connection of an optional capacitor C _L ed. In particular, the energy store C _LE d buffers energy in order to feed the illuminant LED when the coil current has dropped to zero.

Alternatively, the setting of the current through / the voltage on the / the illuminant LED can be carried out by a suitable choice of the switch-on time and switch-off time of the first switch S _w . The times can be chosen, for example, such that the first switch S _{w is} switched on when the current falls below a certain minimum reference value and is switched off when the current exceeds a maximum reference value (switch-off threshold value). The minimum reference value can be zero.

Furthermore, the voltage on the lamp LED can be determined by measurement on a voltage divider connected downstream of the lamp (not shown), which is connected in series with the lamp. The voltage across the lamp then results from the

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Difference between a supply voltage V _BUS , from which the clocked converter is fed, and the voltage across the load LED detected at the voltage divider. The control unit SE could also detect the voltage across the illuminant LED, for example, by measuring a voltage across the coil L _buck . This is shown by way of example in FIG. 1, a voltage V _{buck being} detected on a voltage divider which is formed by resistors R1, R2.

A measurement can take place during the switch-off period of the first switch S _w . 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 illuminant LED. The determination and / or the calculations are preferably carried out in the control unit SE. A correction factor can also be included in the calculation of the transmitted power, which 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 for regulating the lamp current / voltage. The switch-on period 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 pulse duty factor of the low-frequency control of the second switch S _PW m 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 over the first switch S _w . The pulse duty factor of the low-frequency PWM control can be set at least in a partial area of the operation of the load, for example at high brightnesses, that is to say with a degree of dimming of for example around 100%, at a duty ratio of 100% or close to this area. Here, the amount of current through the load and thus the brightness of the light emitted by the lamps can be influenced by adapting the switch-off threshold for the first switch S _w and thus via the control variable of the switch-on period T _{on of} the converter.

However, it is also possible that a combined change in both the duty cycle of the low-frequency PWM control of the second switch S _PW m and the adaptation of the switch-off threshold for the first switch S _w can take place at least in a partial area of the operation of the load. As an alternative, only a switch-off threshold of the first switch S _w can be adjusted in a partial area of the operation of the load.

The control unit SE preferably also detects a signal that represents the supply voltage V _BU s. A signal representing a current through a switch S _w (in the on times of the second switch S _w ) can also be detected. The optional capacitor C _LF d, which can be provided in parallel with the load LED, prevents the current through the load from following the course of the current through the coil L _buck . In non-conductive capable connected first switch S _w, of the coil L that is to say in particular during the phase of the demagnetization _buck the current can be maintained through the LED due to the ed between stored in the energy storage C _L energy. A voltage signal V _BU s_sense representing the bus voltage can be detected, for example, on a voltage divider, which is represented in FIG. 1 by resistors R3, R4.

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

The clocked converter shown in FIG. 1 also has a filter, which is shown in FIG. 1 as an LC filter. The filter is realized by the capacitance C _F and the inductance L _F.

As shown in Fig. 1, the circuit has a third switch S _F , which is provided to adaptively change the filter circuit with the LC filter. The control unit

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As already mentioned, SE is supplied with a dim signal Dim, which indicates which degree of dimming is to be set by the control unit SE. A degree of dimming of 100% can correspond, for example, to operation of the illuminant at full brightness, while a degree of dimming of, for example, 1-5% indicates dimming to a very low value and thus operation with greatly reduced brightness. In particular, the control unit SE controls the third switch S _F depending on the dimming signal Dim. In particular, by switching the third switch S _{F to on,} the additional capacitor C _apapt can be connected to the filter circuit, so that a CLC filter circuit consists of the capacitance C _F , the inductance L _F and the further capacitance C _adapt results.

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

Of course, it is also possible for the properties of the filter circuit to be changed adaptively with the degree of dimming by switching on or off or also by adjusting other passive components that determine the filter properties 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 storage capacitor (not shown) that stabilizes the bus voltage and the LED path at the connections A, B. In particular, the Rippei 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 _PW m depending on 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 value can correspond to a dimming level of 1-5%, but also, for example, a dimming level of approximately 50% to 55%. Below this threshold value, ie if a dimming level of less than approx. 1-5% or approx. 50-55% is to be set, a PWM signal is superimposed. At high degrees of dimming, ie in particular at degrees of dimming that are above the threshold value, the voltage on the illuminant is superimposed with an amplitude modulation.

The filter provided for the lamp supply voltage has a different characteristic when dimming by means of PWM modulation, for example a higher cut-off frequency, an amplitude modulation being superimposed at higher dimming degrees and thus amplitude modulation dimming taking place.

The dynamically adjustable filter influences the curve shape of the PWM signal less strongly at lower dimming levels. This is achieved by switching on the filter capacitance C _adapt, for example by switching the capacitance C _adapt off or bridging it at dimming levels below 10% by activating the switch S _{F in} order to avoid a color shift. In the case of larger currents, however, the capacitance C _{adapt is} switched on in order to limit the ripple current to a level specified for the load.

It is to be understood that the filter circuit can also have filters other than the aforementioned LC or CLC filter, and that other elements can be activated or deactivated adaptively by activating or deactivating the switch S _F. It should also be understood that, for example, components of a filter circuit that can be gradually adjusted can also be changed by correspondingly changing their control by the control unit SE, which overall also changes the behavior of the filter circuit.

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

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Claims (11)

Expectations 1. Clocked converter for dimmable lamps (LED), in particular for an LED section with at least one LED, the clocked converter being able to be supplied from an electrical supply (V _B us), in particular a DC voltage, and one by a control unit (SE) has clocked first switch (S _w ), characterized in that the control unit (SE) is set up to superimpose a PWM signal on the voltage supplied by the clocked converter to the illuminants (LED), which is in relation to a Frequency of the clocking of the first switch is low-frequency, and that a second switch (S _F ) is provided, which is set up to change filter properties of a filter circuit of the clocked converter, which the voltage output by the clocked converter to the lamps (LED) filters an output (A, B) of the converter, and that the control unit (SE) is set up to activate the second switch (S _F ) or to d eaktivieren. 2. Clocked converter according to claim 1, characterized in that the control unit (SE) is supplied with a dimming signal (Dirn), in particular via a lighting device bus, which indicates a dimming level to be set on the lamps (LED) by the control unit (LED), and wherein which the control unit (SE) superimposes the PWM signal when the dimming level to be set falls below a predetermined threshold value. 3. Clocked converter according to claim 2, characterized in that an amplitude modulation signal is superimposed on a degree of dimming above the threshold value instead of a PWM signal; and / or that the threshold value for the degree of dimming corresponds to less than 50%, preferably less than 30%. 4. Clocked converter according to one of the preceding claims, characterized in that the second switch (S _F ) the filter circuit by switching on or off circuit components, in particular at least one capacitance (C _F ), and / or an inductance, and / or one Resistance, changed; and / or that 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. 5. Clocked converter according to one of the preceding claims, characterized in that the control unit (SE) is fed a parameter (Dirn) which reflects the dimming level to be set. 6. Clocked converter according to one of the preceding claims, characterized in that the clocked converter is a DC / DC converter, in particular a buck, boost, or flyback converter; and / or that the clocked converter is fed starting from an energy store, in particular a storage capacitor. 7. Clocked converter according to one of the preceding claims, characterized in that the voltage across the illuminants (LED) is detected at a voltage divider and is supplied to the control unit (SE) as the actual variable for the current degree of dimming. 8. Clocked converter according to one of the preceding claims, characterized in that the filter circuit is a low-pass filter or an LC filter or bandpass filter, which has a different characteristic, e.g. has a higher cut-off frequency than in the case of the amplitude modulation signal superimposition. 6.8 AT16 340U1 2019-07-15 Austrian Patent Office 9. Clocked converter according to one of the preceding claims, characterized in that the control unit is designed to superimpose the PWM signal and / or the amplitude modulation signal by actuating a further switch (S _PW m). 10. Control gear for lamps, in particular LEDs, characterized in that the control gear is provided with a clocked converter according to one of the preceding claims. 1 sheet of drawings 7.8 AT16 340U1 2019-07-15 Austrian Patent Office 1.1 Fig. 1 Π.Η 8.8 11¾¾. Austrian patent office