Driver circuit and method for operating a dimmable LED section in a dimming range with two zones

Abstract

A driver circuit (TS) for dimmable operation of an LED section (LM) supplied by the driver circuit (TS), wherein the driver circuit (TS) is designed such that the dimming range has at least a first area in which dimming is carried out by changing the amplitude of the LED current, and a second area not overlapping with the first area in which dimming is carried out by PWM modulation of the LED current, wherein the second area is located below and adjacent to the first area, wherein a dimming value at which the transition from the first area to the second area takes place is adjustable, and wherein the driver circuit (TS) recognizes the type of LED section (LM) depending on a coded plug or socket of the LED section (LM) for connection to the driver circuit (TS) in order to set the adjustable dimming value accordingly.

Description

The invention relates to a driver circuit and a method for driving a dimmable illuminant section. In this case, the driver circuit directly or indirectly electrically supplies the luminous means section, in particular an LED section, with at least one LED, and allows a luminous means section connected or connectable to the driver circuit to be dimmed over a dimming range. In the present case, a lighting means section is also to be understood as at least one LED module which, in addition to the lighting means, has further components such as a memory and / or a communication interface. In particular, the illuminant section can also have one or more OLEDs.It is known from the prior art to choose a dimming method for dimming LEDs / OLEDs, which method uses either pulse width modulation (PWM) of the LED current or amplitude modulation (AM), i.e. a change in the amplitude value of the illuminant current. As prior art, WO 2011 / 024101 A1, EP 1 689 212 B1 and DE 198 48 925 B4 are mentioned here by way of example.US 2012 / 0 086 701 A1 describes a method for providing an input signal, which indicates a desired brightness for one or more LEDs, for a first and a second parallel control path. The method further includes performing compensation in at least one of the control paths to increase the efficiency of the one or more LEDs.US 2013 / 0 293 134 A1 describes an LED lighting device that can tone and dim and an LED luminaire including the LED lighting device.DE 10 2011 002 830 A1 describes a method for dimming lighting means operated by means of an operating device. The operating device is in particular converters for at least one LED.DE 10 2008 029 816 A1 describes a circuit for dimming a lamp with lighting units. The circuit comprises a control unit for coupling a brightness and a color temperature as a function of an input signal, wherein the lighting units can be controlled as a function of the input signal by means of the control unit.US 2011 / 0 234 104 A1 describes a load determination device and a lighting device using the same for determining and illuminating a lighting load.WO 2010 / 034 509 A2 describes a method and a measuring device for determining the electrical properties of an OLED.In particular, it is known that at higher dimming levels, i.e. when lighting means are to be operated with a slightly reduced brightness, dimming takes place by means of amplitude modulation until a specific dimming level is reached at which the amplitude is kept constant. A changeover is then made to dimming by means of PWM modulation in order to dim to dimming values below the specific dimming level, i.e. if, for example, a low dimming level is required.It is now problematic that analog dimming, i.e. dimming by means of changing the amplitude value, has effects on the one hand on the color constancy of the lighting means. In particular, a color migration, a color shift, can be caused by the change in amplitude. On the other hand, limits of PWM dimming at low dimming values result in the lowest adjustable duty cycle. Thus, due to the lighting means to be operated, the intended purpose or the environment in systems according to the prior art, different negative properties can become noticeable during dimming, which have an effect in particular on the quality of the light emission.It has now been recognized that the transition point between the analog and the PWM dimming, i.e. the transition dimming value or dimming level at which the dimming is changed to the PWM dimming by means of amplitude change, should advantageously be set depending on the configuration of the lighting means or the specific application purpose. The invention therefore provides a driver circuit having an adjustable transition dimming value. Also disclosed is a method for operating an LED path. The driver circuit and the method are subject matter of the independent claims. Further developments of the invention are the subject of the dependent claims.In a first aspect, there is provided a driver circuit according to claim 1.The driver circuit may adjust the adjustable dimming value depending on the LED route driven by the driver circuit.The driver circuit can have a user interface via which the adjustable dimming value can be adjusted. The adjustable dimming value can be adjustable by a user and / or on the production side.The LED path can alternatively or additionally comprise at least one OLED.The driver circuit can have a sensor interface, in particular for a connection to a photosensor and / or a temperature sensor.The driver circuit can set the adjustable dimming value on the basis of a direct information determined, in particular by retrieving the information from the LED line, for example by accessing a memory, and / or an indirect information determined, in particular by detecting parameters.The driver circuit can record electrical parameters of the LED line and / or environmental parameters as parameters, in particular by means of connectable sensors.The driver circuit can draw conclusions from ascertained information about the type of LED path to be operated and set the adjustable dimming value as a function thereof.The driver circuit can record at least one test dimming curve by means of a connectable sensor, for example by recording emission properties of the LED path over a specific period of time, and determine and set the adjustable dimming value based thereon. The driver circuit can furthermore have an evaluation circuit functionally connected thereto, which serves for evaluating captured data / parameters.The driver circuit may store the at least one detected test dimming curve in a memory operatively connected to the driver circuit.The driver circuit can in particular have a bus interface, preferably a DALI bus interface, and can set the adjustable dimming value as a function of a signal supplied via the bus interface, in particular a bus command.An amplitude value can decrease during dimming by means of amplitude variation toward the adjustable dimming value, and dimming below the adjustable dimming value can be effected by means of PWM modulation, preferably with the smallest amplitude value with respect to the adjustable dimming value and preferably with constant clocking.The driver circuit may communicate with the LED line via a communication interface.The driver circuit can have a memory, in particular a look-up table, in which at least one adjustable dimming value is preferably stored, e.g. in association with information about the LED path and / or parameters, and wherein the driver circuit can set the adjustable dimming value on the basis of the direct and / or indirect information, and can retrieve it in particular from the memory.In a further aspect, a method according to claim 15 is provided.The invention will now also be described with reference to the figures. Figure shows FIG. 1 schematically shows two settings for the adjustable dimming value of a driver circuit according to the invention; FIG. 2 is a schematic diagram of the driver circuit; and FIG. 3 is a schematic second view of the driver circuit.In the following, the dimming of the illuminant section by means of amplitude variation of the illuminant current is also referred to as analog dimming or amplitude dimming, while the dimming by means of pulse width modulation of the illuminant current is also referred to as PWM dimming.The adjustable dimming value or the transition dimming value can be adjusted depending on various criteria.For example, it can be provided that a purely analog dimming takes place at dimming values which are above the transition dimming value, while a pure PWM dimming takes place in the lower region, i.e. below the transition dimming value. Preferably, therefore, no mixing of the two dimming methods takes place in the static state. However, in the case of dynamic dimming, it may occur that the dimming methods overlap, in particular at the transition dimming value or in a limited range around the transition dimming value or for a limited time.For the PWM dimming, in particular the lowest amplitude value with constant clocking can be selected, i.e. the amplitude value which is assumed when amplitude dimming is applied to the transition dimming value (i.e. the amplitude value which results when a dimming value approaches the transition dimming value when dimming with amplitude variation).According to the invention, it is now possible to adjust the transition dimming value on the basis of various factors.One possibility here is to provide a user interface on the driver circuit, for example a controller which is accessible to a user and by means of which the transition dimming value can be established. As a result, the dimming value can also already be set on the production side, for example depending on a customer-specific application.Furthermore, it can be provided that the driver circuit acquires information and, depending on this, adjusts the transition value accordingly during operation or when connecting a lighting means section. For this purpose, the driver circuit can be designed such that it can retrieve information from the illuminant system, for example by access to a memory of the illuminant system, which in particular identifies the type and / or configuration of illuminants. This information is referred to below as direct information, since the driver circuit accesses the illuminant path directly. However, the driver circuit can alternatively or additionally also be designed to indirectly ascertain information and thus to infer the type of connected lighting means or ambient conditions.The driver circuit can thus be configured to record and / or evaluate electrical parameters of the illuminant section. For example, for evaluations, the driver circuit may use an integrated circuit (IC, ASIC) operatively connected to the driver circuit. On the basis of the detected electrical parameters or on the basis of their evaluation, it is possible on the one hand to infer the type / configuration of the illuminant section to be operated. On the other hand, for example, ambient parameters can be detected and included via additionally or alternatively provided sensors, for example temperature or photo sensors. The detected and / or evaluated electrical and / or environment-related parameters are referred to below as indirect information.Depending on the acquired direct or indirect information, the driver circuit can then define the transition dimming value. For this purpose, the driver circuit can also access a memory assigned to it, in which data for setting the transition dimming value are stored. For example, a look-up table and the information can be used to select a transition dimming value associated therewith. Furthermore, at least one function can also be stored in the memory assigned to the driver circuit, so that a transition dimming value is determined functionally as a function of the acquired information.The driver circuit can therefore also have a sensor interface via which it can be connected to a temperature and / or a photosensor in order in particular to record or measure test dimming curves. This can be done, for example, in a configuration phase of the driver circuit or at the factory under conditions simulating those prevailing during later use. This can also allow adaptation to specific lighting means. It can also be provided that the configuration phase is triggered again manually or automatically, for example, in order to achieve an adaptation to changed environmental conditions and / or lighting means. The latter can also result without replacement, for example, on the basis of aging phenomena of the lighting means.Measurements can thus be carried out by the driver circuit in which the driver circuit detects light properties of the illuminant section depending on different dimming values and determines an optimum transition dimming value from the analog dimming to the PWM dimming on the basis of the detected properties or the behavior of the illuminant section.It is thus also possible for the driver circuit to distinguish different lighting means distances on the basis of their electrical properties. Thus, a lighting means section with LED lighting means can be distinguished from a lighting means section with OLED lighting means, since the electrical characteristic values of OLEDs and LEDs are different. Among other things, a color change is more pronounced in analog dimming of OLEDs than in analog dimming of LEDs. In the case of a lighting means section with OLEDs or in the case of operation of a lighting means section with exclusively OLEDs, the transition dimming value is therefore chosen differently than in the case of operation of a lighting means section with exclusively LEDs. The transition dimming value is then higher in OLEDs in particular than when a lighting means section is operated with only LEDs.Furthermore, the adjustable transition dimming value can be adjusted on the basis of a signal / command which is / is supplied to the driver circuit. One possibility here is to specify a dimming value to be set to the driver circuit via its electrical supply, for example by supplying a supply voltage of alternating and / or different polarity, or by an on / off sequence. On the other hand, the signal can also be supplied via a bus interface. For this purpose, a bus interface of the driver circuit can preferably be connected to a DALI or DSI bus.Via the bus interface, the driver circuit can also inform other bus subscribers about the adjusted or adjustable transition dimming value, for example. It is thus possible, for example, for the driver circuit to determine information and data relevant for the setting of the transition dimming value by means of measurements and / or sensory detection. If the transition dimming value is determined by the driver circuit, the driver circuit can transmit this transition dimming value to be set to other driver circuits which, for example, do not have the possibility of detecting / ascertaining the corresponding information or data, that is to say, for example, do not have a sensor interface.In static dimming, it is particularly desirable that the range in which PWM dimming is performed and the range in which amplitude dimming is performed do not overlap, so that there is separation between the two dimming methods.In the case of dynamic dimming, however, it may happen that a mixture of the dimming methods at the adjustable changeover dimming value results for a limited period of time or in a limited range.FIG. 1 shows two examples in which the transition dimming value is changed by the driver circuit. Here, it is shown that the transition dimming value can be set to x % (FIG. 1 on the left) on the one hand or to a higher dimming value y % (FIG. 1 on the right) on the other hand in order to set the regions of dimming by means of PWM modulation (PWM) or amplitude modulation (AM) respectively.Depending on the setting of the adjustable transition dimming value, dimming can also be effected, for example, merely by changing the amplitude or exclusively by means of PWM dimming. This is the case when the transition dimming value is set to zero percent (0%) or a minimum dimming value (e.g. 5%) or to one hundred percent (100%) or a maximum dimming value (e.g. 80%-95%). In the first case, dimming can then take place only by means of amplitude variation, in the second case only by pulse width modulation, or vice versa. As stated, the transition dimming value can be set by a user or based on the connected lighting means.FIG. 2 shows an example of how the driver circuit TS supplies the illuminant path LM on the one hand, but can additionally exchange data D with the illuminant path on the other hand. In particular, the illuminant path has a memory S which contains information about the illuminant path. The driver circuit TS thus directly acquires information about the lamp section LM in order to set the adjustable transition dimming value accordingly. Also shown schematically on the driver circuit is a bus interface bus and a sensor interface Sens, and an optional memory TSS associated with the driver circuit.As an alternative to the memory TSS, the lighting means section LM can also have a coded plug or a coded socket for connection to the driver circuit or to an operating device having the driver circuit, wherein the driver circuit can then recognize the type of lighting means section depending on the plug / socket.In particular, bidirectional communication can take place between the driver circuit TS and the illuminant path LM, such that the driver circuit TS can change or adapt parameters of the illuminant path LM, for example. The communication between driver circuit TS and lamp section LM can naturally be either analog or digital. However, communication via a separate communication interface to driver circuit TS and / or illuminant section LM is not absolutely necessary, since communication via supply V can also take place, for example, by modulation of the supply parameters.A further exemplary embodiment is shown by way of example in FIG. 3, in which the driver circuit TS communicates with the lighting means section only via the supply V. The driver circuit TS has in FIG. 3 a detection circuit / detection circuit which can be provided additionally or alternatively to the already described components of the driver circuit TS. This detection circuit is preferably configured to detect electrical parameters, such as current or voltage parameters or capacitance values, which serve directly or indirectly for the supply V of the illuminant section LM.The detection of the parameters can also take place continuously, so that in the event of a change in the illuminant section, for example due to aging phenomena, and a change in the electrical parameters of the illuminant section LM resulting therefrom, and / or in the event of a change in the environmental parameters, the transition dimming value can be changed.The leakage current can also be measured as an electrical parameter, for example, if OLEDs are used as lighting means of the lighting means section. For example, even in the case of LED lines in which white light LEDs are operated together with LEDs of a different color, for example red LEDs, the adjustable transition dimming value can be set by the driver circuit TS detecting or monitoring saturation of the LEDs and detecting by means of its measurement at which dimming value the colored LEDs are no longer conducting / are no longer active. For this purpose, the driver circuit TS can also use the optional photosensor. The driver circuit can then define the adjustable transition dimming value such that it lies above the dimming value at which the colored LEDs are no longer conducting, so that dimming takes place below this dimming value merely with PWM modulation.Alternatively to PWM modulation, other pulsed modulation types can also be used according to the invention, for example pulse duration modulation or pulse code modulation.

Claims

Driver circuit (TS) for dimming operation, which can be dimmed over a dimming range, of an LED path (LM) which can be supplied by the driver circuit (TS), wherein the driver circuit (TS) is designed such that - the dimming range has at least a first range in which dimming is carried out by means of amplitude variation of the LED current, and a second range which does not overlap the first range, in which dimming is carried out by means of PWM modulation of the LED current, wherein the second range is below adjoining the first range, wherein - a dimming value at which the transition from the first range to the second range takes place can be set, and wherein the driver circuit (TS) recognizes the type of the LED path (LM) depending on a coded plug or a coded socket of the LED path (LM) for connection to the driver circuit (TS), in order to set the adjustable dimming value accordingly.Driver circuit (TS) according to Claim 1, wherein the driver circuit (TS) is configured to set the adjustable dimming value as a function of the LED path (LM) operated by the driver circuit (TS).Driver circuit (TS) according to claim 1 or 2, wherein the driver circuit (TS) has a user interface via which the adjustable dimming value is adjustable.Driver circuit (TS) according to one of the preceding claims, wherein the LED path (LM) alternatively or additionally comprises at least one OLED.Driver circuit (TS) according to one of the preceding claims, wherein the driver circuit (TS) has a sensor interface (Sens), in particular for a connection to a photosensor and / or a temperature sensor.Driver circuit (TS) according to one of the preceding claims, wherein the driver circuit (TS) is configured to set the adjustable dimming value on the basis of a direct information determined, in particular by retrieving the information from the LED line (LM), e.g. by accessing a memory (S), and / or an indirect information determined, in particular by detecting parameters.Driver circuit (TS) according to one of the preceding claims, wherein the driver circuit (TS) is configured to record electrical parameters of the LED line (LM) and / or environmental parameters as parameters, in particular by means of connectable sensors.Driver circuit (TS) according to one of the preceding claims, wherein the driver circuit (TS) is configured to infer the type of the LED line (LM) to be operated from ascertained information and to set the adjustable dimming value as a function thereof.Driver circuit (TS) according to one of the preceding claims, wherein the driver circuit (TS) is configured to record at least one test dimming curve by means of a connectable sensor, e.g. by recording emission properties of the LED line (LM) over a specific period of time, and based thereon to determine and set the adjustable dimming value.Driver circuit (TS) according to one of the preceding claims, wherein the driver circuit (TS) is configured to store the at least one detected test dimming curve in a memory (TSS) functionally connected to the driver circuit (TS).Driver circuit (TS) according to one of the preceding claims, in particular having a bus interface (bus), preferably a DALI bus interface, wherein the driver circuit (TS) is configured to set the adjustable dimming value as a function of a signal supplied via the bus interface (bus), in particular a bus command.Driver circuit (TS) according to one of the preceding claims, wherein an amplitude value decreases towards the adjustable dimming value during dimming by means of amplitude variation, and wherein dimming below the adjustable dimming value takes place by means of PWM modulation, preferably with the smallest amplitude value with respect to the adjustable dimming value and preferably with constant clocking.Driver circuit (TS) according to one of the preceding claims, wherein the driver circuit (TS) is configured to communicate with the LED line (LM), e.g. via a communication interface.Driver circuit (TS) according to one of the preceding claims, wherein the driver circuit (TS) has a memory (TSS), in particular a look-up table, in which at least one adjustable dimming value, for example in association with information about the LED path (LM) and / or parameters, is stored, and wherein the driver circuit (TS) is configured to set the adjustable dimming value on the basis of the direct and / or indirect information, and in particular to call it from the memory (TSS).Method for operating an LED path (LM) which can be supplied by a driver circuit (TS) in a dimmable manner over a dimming range, wherein the driver circuit (TS) carries out dimming by means of amplitude variation of the LED current in a first region of the dimming range, and carries out dimming by means of PWM modulation of the LED current in a second region which does not overlap with the first region, wherein the second region is below adjoining the first region, wherein - a dimming value at which the transition from the first region to the second region takes place can be set, and wherein the driver circuit (TS) recognizes the type of the LED path (LM) depending on a coded plug or a coded socket of the LED path (LM) for connection to the driver circuit (TS), in order to set the adjustable dimming value accordingly.

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