DE102017216902A1 - Device and method for dynamic overload limitation in color temperature dimmable multi-channel LED systems - Google Patents

Abstract

Multi-channel LED system, comprising: - a driver unit (8), (9A), (9B), which is designed for the independent supply of at least two LED output channels (16A), (16B) with a regulated to a desired value Voltage (U_K1), (U_K2) or current (I_K1), (I_K2), wherein the drive unit (8), (9A), (9B) is further configured to control the maximum power of each LED output channel (16A), (16B On the other hand, the sum power of all LED output channels (16A), (16B) on the other hand to limit to predetermined values, and wherein the driver unit (8), (9A), (9B) is adapted to the setpoint of an LED output channel (16B ) if its power (P_K2) is greater than the maximum allowable total power (P_system) minus the power of the other LED output channel (P_K1).

Description

The invention relates to a device and a method in the region of a preferably two-channel LED module, wherein both channels can be controlled separately from each other to achieve a Farbtemperaturdimmen.

Previous devices for two-channel color temperature dimming are mostly LED systems, which have a group of cold white and a group of warm white LED elements usually on a common chip, i. are applied to a single substrate.

Such a device is for example in US 2012038286 disclosed.

Among other things, the device comprises a current driver which generates a first and a second drive current. The first drive current causes the illumination of a first group of LED chips with a first color temperature and brightness (intensity). The second drive current causes the illumination of a second group of LED chips having a second color temperature and second brightness.

In order to homogenize the color matching process, the color different LED groups or elements may also be mixedly arranged on the substrate.

However, said apparatus and method implemented thereby comprises separately controlling both drive currents such that user-desired light results in a selected color temperature at a selected intensity.

Since the driver circuit of this device has, inter alia, a controller, a memory and, apart from the current driver, also a data bus and a sensor interface which has a plurality of CPUs, processors, gates, arrays, hardware logic and memory documents, such a device is also suitable Computer program product provided by the method of color dimming is implemented.

The driver circuit of this device has a circuit arrangement configured to generate drive currents (first and second drive currents) capable of switching both the first and second groups of LEDs from their respective "off" state to to control the state of their maximum intensity.

The driver circuit currently sets the levels of the first and second drive currents on the basis of user input (via an interactive display, keyboard, rotary or slider, etc.) and / or based on sensor-based feedback, which is why this circuit does not represent control in the true sense, but a regulation. The resulting light emitted by the entire LED system is ultimately a combination of color temperature and intensity of light at that color temperature.

However, in US 2012038286 pointed out that the LED system is not limited to two groups of LED chips, but can have any number of LED groups, each with their own individual color temperature and brightness behavior. Necessary is a corresponding number of drive currents (depending on the encapsulation), which must be provided by the driver circuit available.

To generate currents for different intensities and color temperatures of specific LED groups, the control either uses drive current tables stored in a memory or calculates the required values for the respective drive currents on the basis of algebraic equations themselves.

wobei L_K die Intensität des kalten Weißlichtes und Lw die des warmen Weißlichtes sowie T_K und Tw die jeweiligen Farbtemperaturen darstellen die möglicherweise von Sensoren gemessen werden.For example, the mixing color temperature (T _mix ) resulting from the superposition of the light of two LED groups can be determined according to the following equation: $$T_{miscH}=\frac{\left(L_K\cdot T_C+L_W\cdot T_W\right)}{\left(L_C+L_W\right)}$$

where L _{K is} the intensity of the cold white light and Lw that of the warm white light and T _K and Tw are the respective color temperatures that may be measured by sensors.

The difference in color temperature between both groups of LED chips should advantageously be at least 300 Kelvin.

$$I_K=\frac{\text{L}}{\text{K}}\cdot \frac{T-T_W}{T_K-T_W}$$

mit W als eine Konstante der Wirksamkeit (Einheit in Lumen pro Ampere) der warmweißen Gruppe von LED-Chips und K als eine Konstante der Wirksamkeit der kaltweißen Gruppe von LED-Chips bei einer Gesamtlichtleistung L und einer durchschnittlichen Farbtemperatur (Gesamtfarbtemperatur) T.The values of the two impulse currents (I _K and Iw) for the two groups of LED chips (cool white and warm white) are also algebraic $$I_W=\frac{\text{L}}{\text{W}}\cdot \frac{T_K-T}{T_K-T_W}$$

$$I_K=\frac{\text{L}}{\text{K}}\cdot \frac{T-T_W}{T_K-T_W}$$

with W as a constant of effectiveness (unit in lumens per ampere) of the warm white group of LED chips and K as a constant of the efficiency of the cold-white group of LED chips at a total light output L and an average color temperature (total color temperature) T.

The above equations allow the controller to compute all drive currents to achieve a desired (physically possible) color temperature with an equally desired brightness (intensity) and to supply the resulting parameters to the drive current table (color temperature, two intensity levels) to complete them.

The drive current tables, for example, stored in memory during device manufacture, are accessible to the control or the corresponding modules of the driver circuit via the data bus. Or, the drive current tables are stored by the processor by taking information from another device, e.g. is detected via a network connection.

In one possible mode of operation, the drive currents are set to constant currents at predetermined voltage levels. In another possible operating mode, (Activation) defines current amplitudes of the drive currents which are pulsed at a selectable pulse rate.

During operation, the respective drivers receive drive current parameters (e.g., from the controller) and use them to generate the corresponding drive currents.

Device indicators, which measure color temperature and intensity of the light currently emitted by the light source, provide feedback to the driver circuit and form part of the basis for the overall control.

The change in the intensity and / or the color temperature of the light emitted by a light source (LED system eg from two groups) due to user input and / or due to timing indicators, environment indicators and device indicators (also in the context of a physical parameter involved in drift) is generally considered "Dimming" designates.

It should be noted that dimming with, for example, only two LED groups of different color temperature (e.g., cool white and warm white) and intensity is very complex.

It should also be noted that the luminous flux of a white LED (measured in lumens, Im) is proportional to its driving current, the proportionality constant being dependent on the color temperature and assuming that all other factors are equal.

For example, a 6000Kelvin cold white source LED produces light at a rate of 100 lumens per amp, while a 3000K warm white source generates light at only a rate of 70 lumens generated per amp. This inequality must be taken into account when dimming (in particular when calculating the drive currents).

• ◯ Beim PWM-Dimmen wird der LED-Strom in gewisser Weise zerhackt und durch Variation des Tastverhältnisses gesteuert.
• ◯ Beim Analog-Dimmen skaliert der Dimmer die Amplitude des LED-Stromes in konstanter Weise.

When controlling the LED current with a dimmer, it is decisive which type of dimming control is to be implemented. There are essentially two different approaches to dimming: Pulse Width Modulated (PWM) and analog dimming.

• ◯ In PWM dimming, the LED current is somewhat chopped and controlled by varying the duty cycle.
• ◯ With analog dimming, the dimmer scales the amplitude of the LED current in a constant way.

The dimmer can thus reduce the AC power to produce an AC voltage resulting in a reduced (second) drive current.

With two or more dimming channels, analogue dimming is advantageous since several PWM dimming signals generate so-called beat frequencies, ie they can produce beats that cause flickering or audible noise.

Analog dimming, but also to realize PWM dimming is done easily with a buck converter. It is even proposed in the prior art to use a suitable integrated circuit (IC) (see Jon Kraft, "Convert a Buck Regulator into a Smart LED Driver, Including Dimming;" www.analog.com/en/analog-dialogue/articles/convert- a-buck-regulator.html), for example the ADP2384 or the ADP2441 of the company ANALOG DEVICES. A Texas Instruments datasheet suggests dimming with the TPS92075 integrated circuit.

A buck converter is a form of switching DC-DC converter and serves to transfer electrical energy between an input and an output side of galvanically isolated DC voltages. Here is the output voltage U _a always smaller than the amount of input voltage U _e ,

In 1 is a simple variant of a buck converter 1 shown.

A switch 2 is regularly turned on and off by a controller (not shown). Usually, several hundred to several million switching cycles per second occur, which is why this switch 2 usually represents a transistor.

With the switch closed 2 gets electrical energy from U _e (left connected voltage source) to the right connected load 7 (here an LED or an LED system) transfer.

Both the coil 4 (Throttle) and the electrolytic capacitor 6 (ELKO) serve as energy storage and allow a supply of the load 7 in the phases in which the switch 2 is open.

During the switch-on time T _e the load current flows through the coil 4 and by the consumer 7 , here an LED. The diode 3 locks. During the switch-off phase T _a the energy stored in the coil is dissipated: the current through the consumer 7 (LED) and through the resistor 5 continues to flow, but now from the condenser 6 through the diode 3 ,

The switching cycle of the switch 2 can either be set so that the coil current never stops flowing (non-latching operation) because the switch 2 already closed again before the whole in the coil 4 stored energy is completely dissipated.

However, the switching cycle can also be set so that the current during the cycle 'regularly drops to zero and currentless or voltage-free intervals occur (intermittent operation).

In order to be able to precisely control both modes of operation or their transition from both sides, a controller must be used in the design of the circuit, through which all, at least the most important, sometimes rapidly changing parameters (inductance, switching frequency, input voltage, output voltage, flowing current) Output current, output voltage dependence on the duty cycle, etc.) can be taken into account.

In the literature mentioned above, therefore, it is indicated how the respective integrated circuit (IC) for the regulation of the output voltage, in particular for dimming, by a pulse width modulation (PWM) in the latching or non-latching operation or for analog dimming, are connected got to.

Further circuit suggestions for buck converters in this context are currently also available in the chapter under the link www.joretronik.de 6 to find.

The present invention now relates to multi-channel LED modules, in particular two-channel LED modules, which preferably have a cold white and a warm white channel, and which can be controlled separately from each other so that a color dimming can be achieved with a simultaneous brightness dimming , In order to achieve this, a high-precision control of the respective LED current is necessary, the difficulty being essentially that of not exceeding the maximum power which a single channel is allowed to perform during the dimming process, otherwise in current systems, the LED module before overloading is completely shut down (system shut down). Another prior art method of protecting a multichannel dimmable system from electronic overstressing / overloading is a significant power limitation for each channel.

Both approaches are undesirable from the user's point of view, but also from the point of view of the manufacturer, since in a shutdown the feeling is conveyed that the lighting device can not be operated properly or if the color temperature and / or brightness value of the light source is unattainable Imagine having acquired a device with very limited performance.

The invention is therefore based on the object to make for a color temperature and brightness dimmable two- or multi-channel system safety measures by which a maximum caused by dimming emerging Ausstreizen the color temperature and brightness range is no risk to the technical safety of the system.

• 1 zeigt eine einfache Ausfiihrungsform eines Buck-Konverters.
• 2 zeigt das Schaltschema eines Farb- und Helligkeits-dimmbaren Zwei- oder Mehrkanalsystems gemäß der vorliegenden Erfindung.

This object is solved by the features of the independent claim. Advantageous developments of the invention are described in the appended subclaims.

• 1 shows a simple embodiment of a buck converter.
• 2 shows the circuit diagram of a color and brightness dimmable two- or multi-channel system according to the present invention.

The basic idea of the present invention is to provide a dynamic overload limitation in color temperature and / or brightness dimmable two- or multi-channel LED systems which prevents the system from exceeding power in protects individual channels or in all channels and prevents possibly on the environment across damage or even destruction.

A "dimmer" in the most general sense is used to control the (variable) power consumption of (electrically operated) consumers. The type of dimming depends on the type of consumer or on its load characteristics.

If the variable (s) to be changed depends on several possibly interacting interacting parameters, a control may not be sufficient for the dimming process, but a regulation is necessary.

According to the invention, it is now provided in the simplest case between two (for example on a common or adjacent substrate) LED groups of different color temperature (for example, cool white and warm white) to produce a mixed value of the color temperature, but this is brightness given the specification of a defined intensity.

If the dimming is done manually, the user has two interfaces (button with display, knob, slider, etc.): one for setting the color temperature and one for adjusting the brightness at this selected color temperature.

If the dimming is done fully automatically, the system has suitable sensors (for example brightness sensors, color temperature sensors, etc.) which, if necessary, register changes in the lighting conditions of the environment and allow the system to react dimmingly according to its configuration.

In two- or multi-channel systems according to the prior art, any dimming according to the above statements is technically not feasible, since - for safety reasons - the maximum power of each channel, but also the total power of all channels of the entire system must not be exceeded.

This means, for example, that a 50Watt 2-channel system with 25W each may be run on each channel, but if this power is exceeded in just one channel, the system will shut down immediately.

However, it is still of interest in such a 50W 2-channel device to operate a single channel up to 50W without shutting down the system. Such a channel is called a "master channel" in the present invention.

One of the objects of the invention is to implement a current limitation for the second non-master channel (or for further non-master channels). In the following, a two-channel system is considered without restriction of generality.

The "master channel" can be run with a power P_K1 in a range between minimum and maximum power, with its maximum power corresponding to the maximum power P_system of the overall system.

The maximum power of the second channel P_K2 now depends on the load of the first channel. It can only be the admissible total power minus the currently measured power of the first channel: $$P\_\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102017216902A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}2=P\_System-P\_\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="DE102017216902A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}1$$

wobei der Wert für (Dimm-Wert • gewählter Strom) gesetzt wird und der Wert für den Strom des zweiten Kanals U_K2 gemessen werden muss.The power of the first channel P_K1 must be determined technically-physically. As soon as the maximum power of the second channel P_K2 is known, this also leads to a current limitation I _max, which is determined as follows: $$P\_\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102017216902A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}2=U\_\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102017216902A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}2\cdot \left(Dimm-Wert\cdot GewäHlterStrOm\right)$$

where the value for (dimming value • selected current) is set and the value for the current of the second channel U_K2 has to be measured.

Thus applies to the current to be limited $$I_{max}=\left(Dimm-Wert\cdot GewäHlterStrOm\right)=\frac{P\_K2}{U\_\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102017216902A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}2}$$

Since the selected current is a fixed value, only the dimming value has to be limited. $$Dimm-Wert=\frac{P\_K2}{U\_\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102017216902A1\_0009.png"\; state="\{\{state\}\}">K</figure-callout>}2\cdot GewäHlterStrOm}$$

Taking into account a tolerance width of approx. 10% upwards, the maximum current is therefore limited to I _max so as not to exceed the rated output of the system.

If the situation should arise that the remaining maximum permissible power P_System is exceeded by the current power of the second channel P_K2, according to the invention a safety measure comes into force, by which the power of the second channel P_K2 is reduced and, accordingly, the setpoint value of the current for the second Channel I_K2 is reduced.

It must, however, be accepted that this unilateral reduction of electricity alone on channel 2 , without changing the corresponding setpoint on channel 1 , the color coordinate of the system (including an N-channel system) can change.

One measure that prevents this is the recalibration of the current value for the first channel (the master channel) after limiting the current value for the second channel, so that overall reduces the brightness of the system, but the desired color coordinate of the mixed light is maintained.

In summary, the voltage across the second channel U_K2 (the voltage across the second LED path) in the device (system) is measured (in the case of a 2-channel system). This measurement results in the permissible maximum current through the second channel I _max , which in turn can be expressed as a dimming value.

Thus, the power of the first channel P_K1 - the maximum permissible sum power P_System is known - and the voltage across the second channel U_K2 must be detected in order to determine the information of the maximum permissible current I _max in the second channel.

Of course, in a multi-channel system (N-channel system), any Nth channel may be used as the master channel.

A measurement and control circuit for the LED current and the voltage at two LED lines included, as well as the control circuit, which performs an internal maximum power limitation and depending on a LED power determining control variable outputs, in particular the timing of a switch of a clocked LED Converter, is in 2 shown.

2 shows a dimmable 2-channel LED system. On the left side of 2 the preferably software-based part (eg microcontroller) 8 of the system is shown, on the right side the preferably hardware-executed part in the form of 2 LED drivers 9A . 9B each for two LED routes, for example, with a cool white diode 16A in channel 1 and a warm white diode 16B in channel 2 , and each one from a converter 13A . 13B driven, preferably by a buck converter like him in 1 is shown.

Each LED driver unit 9A . 9B also contains two mutually parallel resistance paths, which in turn each with a voltmeter 14A . 14B as well as with a current measuring device 15A . 15B the actual values of the LED-side voltage U_K1, U_K2 and / or the current LED-side current I_K1, I-K2 are measured and the measurement results 17A . 17B . 18A . 18B a control unit 11 eg in the software section 8th be supplied.

The en control unit 11 furthermore, the desired values are supplied 19A . 19B in terms of color temperature and brightness of both channels, for example, on the part of a user who manually from this or via a suitable interface 10 be set or entered. However, the values can - as already mentioned - automatically detected by an external (measuring) sensor and sent to the control unit 11 be passed on automatically as well.

The e control unit 11 thus receives setpoint values for the mixed color of the overall LED system 21 and its brightness as well as the actually applied actual values of currents and voltages of the respective LED paths 16A . 16B (Channels).

Due to the necessary limitation of the voltages or currents in the LEDs - in other words, the unavoidable power limitation of each LED route involved 16A . 16B of the overall system 21 - it is not always possible, that of the interface 10 delivered, eg desired by the user or required by the sensor system, color-brightness pairs to realize. However, the present invention makes it possible to come as close as possible to these set points, either on the part of the color temperature or on the part of their intensity or possibly by a compromise in the form of an acceptable intermediate value.

For this purpose, the e calculates control unit 11 from the actual values 17A . 17B . 18A . 18B and the desired setpoints 19A . 19B possible setpoints 20A . 20B which correspond to the preferences of the user and / or the specifications of the sensor as best as possible.

LIST OF REFERENCE NUMBERS

1

Buck converter (down converter)

2

Switch (transistor)

3

Diode (Schottky, Zener, Transistor, etc.)

4

Throttle (coil)

5

Ohmic resistance

6

ELKO (electrolytic capacitor)

7

LED (LED)

8th

Software part

9A

LED driver unit channel 1

9B

LED driver unit channel 2

10

interface

11

e control unit

12A

Current controller channel 1

12B

Current controller channel 2

13A

Buck converter channel 1

13B

Buck converter channel 2

14A

Voltage measurement channel 1

14B

Voltage measurement channel 2

15A

Current measurement channel 1

15B

Current measurement channel 2

16A

LED track (diode / diodes) cool white

16B

LED track (diode / diodes) warm white

17A

Current actual value channel 1

17B

Current actual value channel 2

18A

Voltage actual value channel 1

18B

Voltage actual value channel 2

19A

e.g. user-defined setpoints channel 1

19B

e.g. user-defined setpoints channel 2

20A

best possible setpoints channel 1

20B

best possible setpoints channel 2

21

LED overall system

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

• US 2012038286 [0003, 0010]

Claims (6)

Multi-channel LED system, comprising: a driver unit (8), (9A), (9B), which is designed for the independent supply of at least two LED output channels (16A), (16B) with a voltage regulated to a desired value (U_K1), (U_K2) or current (I_K1), (I_K2), wherein the drive unit (8), (9A), (9B) is further adapted to the maximum power of each LED output channel (16A), (16B) on the one hand and the total power of all LED On the other hand, to limit the output channels (16A), (16B) to predetermined values, and wherein the drive unit (8), (9A), (9B) is adapted to decrease the setpoint value of an LED output channel (16B) when its power ( P_K2) is greater than the maximum permissible total power (P_System) minus the power of the other LED output channels (P_K1). Multi-channel LED system after Claim 1 , characterized in that the two LED output channels (16A), (16B) are two white light output channels. Multi-channel LED system after Claim 1 or 2 characterized in that the two LED output channels (16A), (16B) are a warm white light output channel and a cold white light output channel. Multi-channel LED system after Claim 1 . 2 or 3 Characterized in that by the change of the target value resulting change in the color coordinate system is compensated by a recalibration by the driving unit (8), (9A), (9B) is adapted to the nominal value of a selected master output channel as far as to reduce that with reduced brightness of the system, the desired color coordinate of the mixed light is maintained. Method for dynamic overload limitation in color temperature dimmable multichannel LED systems, comprising the following steps: Measuring actual values of the current (17A, 17B) and / or the voltage (18A, 18B) on at least two LED output channels (16A, 16B) of defined color temperature and brightness by means of respective LED output channels (16A), (16B) associated driver hardware channels (9A), (9B); - Supplying these actual values (17A, 17B, 18A, 18B) to an e control unit (11) in a software part (8) of the driver unit (8), (9A), (9B) and in particular the respective current actual Values (17A, 17B) are applied to respective current controllers (12A, 12B) associated with a driver hardware channel (9A), (9B); Calculating possible set values (20A, 20B) for color temperature and brightness of the overall system (21) from target values (19A, 19B) supplied by an interface (10) and from the actual values (17A, 17B) of the voltage measurement and Actual values (18A, 18B) of the current measurement by the e control unit (11); - supplying the possible setpoint values (20A, 20B) to the respective current regulators (12A, 12B) and - configuring the respective downconverters (13A, 13B) associated with each driver hardware channel (9A, 9B) by the respective current regulators (12A, 12B) on the basis of the values obtained (20A, 20B, 17A, 17B) such that the Setpoint (20B) of an LED output channel (16B) is reduced when its power (P_K2) is greater than the maximum allowable total power (P_System) minus the power (P_K1) of the other LED output channel (16A). Method according to Claim 5 characterized in that a change in the nominal value resulting change in the color coordinate of the system is compensated by a recalibration by the driver unit (8), (9A), (9B) reduces the setpoint of a selected master output channel so far that at reduced brightness of the system is maintained the desired color coordinate of the mixed light.

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