Patent Application
20090302769
The present invention relates to a circuit arrangement for controlling at least one light source, a use of the circuit arrangement, and a method for controlling at least one light source.
In lighting arrangements, several light sources can be used together, such as a red and a white light emitting diode, abbreviated LED. A use of three light emitting diodes, a red, a green, and a blue light emitting diode, is also often encountered for RGB lighting. Such lighting arrangements are used, for example, as backlighting for a liquid crystal display.
In order to test whether such a lighting arrangement outputs light with a given wavelength characteristic, lighting arrangements typically provide several photodetectors, which each have different filters. In this way, the light of a red LED is measured by means of a photodetector, which is covered with a filter layer that is transparent for red light. Photodetectors covered with corresponding filters are also provided for a green and a blue LED. This allows white balance correction.
The object of the present invention is to provide a circuit arrangement and a method for controlling at least one light source, which can be realized in a cost-efficient and flexible way.
This object is solved with the arrangement of Claim 1 and also with the method according to Claim 23. Improvements and constructions are the subject matter of each of the dependent claims.
According to the invention, a circuit arrangement for controlling at least one light source comprises a photodetector, a sampling means, a control unit, and also a first and a second power-supply source. The sampling means is coupled on the input side to the photodetector and on the output side to the control unit. The first and the second power-supply source are each coupled at one control input to a first and second output, respectively, of the control unit. A first light source can be coupled to the first power-supply source and a second light source can be coupled to the second power-supply source.
A photodetector signal is generated by the photodetector as a function of the light of the first and the second light source and provided to the sampling means. The sampling means is used for the selective sampling of the photodetector signal. A signal provided by the sampling means is fed to the control unit. Control signals, which are fed to the control inputs of the first and the second power-supply source, are provided by the control unit as a function of the signal fed to the control unit. As a function of the control signals, the first power-supply source supplies electrical energy to the first light source that can be coupled, and the second power-supply source supplies electrical energy to the second light source that can be coupled.
Advantageously, the circuit arrangement can be realized in a cost-efficient way, because the first and the second light source are activated successively and a signal for further processing is provided by the sampling means only when one of the two light sources is activated. Thus, a single photodetector is sufficient for determining brightness and/or color or color temperature of the light sources. Advantageously, the photodetector requires no filter. Thus, it is not necessary to adapt a filter located on the photodetector to the changed wavelengths for the use of light sources with wavelengths different from wavelengths of the original light sources. This increases the flexibility of the circuit arrangement.
In one embodiment, the control unit comprises a first filter, which is coupled on the input side to the sampling means. This first filter is coupled on the output side to the first and to the second output of the control unit. Advantageously, noise that could possibly be generated by the sampling means can be reduced by means of the first filter.
The first filter is advantageously connected downstream of the sampling means. This way prevents the photodetector signal generated as a function of the light of the light source being influenced by the photodetector signal generated as a function of the light of the second light source.
In one preferred embodiment, the first filter can be connected on the input side to the sampling means.
In one embodiment, the first filter can be constructed as a hold circuit or as a sample-and-hold circuit. In this embodiment, a value can advantageously be held at one output of the first filter until another input value is fed to the first filter by the next sampling by means of the sampling means and another value is then held on the output of the first filter.
In one improvement, the circuit arrangement comprises a third power-supply source with an output, to which a third light source can be coupled. For control, the third power-supply source is connected to a third output of the control unit. The light of the third light source also generates the photodetector signal, which is sampled selectively, in order to determine the photodetector signal generated by the third light source.
In one embodiment, the first filter is coupled on the output side to the third output of the control unit.
In one improvement, the circuit arrangement has additional power-supply sources, which are each coupled at a control input to another output of the control unit and which each have an output to which another light source can be coupled, whose light also contributes to the photodetector signal.
In one embodiment, the power-supply sources can each comprise a current source and a switch, which are connected to each other in series.
In one embodiment, the circuit arrangement comprises a sequence control, which is connected to a control input of the sampling means and to additional control inputs of the first, the second, and additional power-supply sources. The sequence controller provides a control signal, which controls, in an adjustment phase, the sequence of activation and deactivation of the power-supply sources and the sampling of the photodetector current, so that the brightness values of the light sources are detected and evaluated in a time sequence. The control signal is used for synchronizing the switches in the power-supply sources and in the sampling means. In one improvement, the sequence controller is also coupled to the control unit, so that the control signal can also be fed to the control unit and is used in the control unit for synchronizing the sampling with the further processing of the sampled signals.
The control unit and the control signals provided by it are used for adjusting the brightness of the light sources by adjusting a parameter of the power-supply sources in an operating phase. The parameter can be a current intensity, a pulse duration, and/or a pulse-duty ratio or a pulse density of a current supplied to a light source from the power-supply source coupled to it.
The photodetector can be a photoresistor, a photodiode, or a phototransistor. Preferably, the photodetector is constructed as a photodiode.
In one embodiment, the sampling means comprises a first sampling circuit, whose input is coupled to the photodetector and whose output is coupled to the control unit. In one embodiment, the sampling means comprises a first sampling circuit, whose input is coupled with the photodetector and whose output is coupled with the control unit. In one embodiment, the first sampling circuit is switched to be conductive when exactly one of the three light sources is activated.
In an alternative embodiment, the first sampling circuit is allocated to the first power-supply source. The sampling means comprises a second sampling circuit, which is allocated to the second power-supply source, and also a third sampling circuit, which is allocated to the third power-supply circuit. In the alternative embodiment, the first sampling circuit is switched to be conductive when the first light source is activated. The second and the third sampling circuits are switched to be conductive when the second and the third light source, respectively, are each activated. In the alternative embodiment, the sequence controller can be designed in such a way that it is connected by means of three bus lines to the three power-supply sources and to the three sampling circuits. Thus, via the first bus line, the first power-supply source can be activated and the first sampling circuit can be switched to be conductive. Via the second and third bus line, the second power-supply source can be activated together with the second sampling circuit or the third power-supply source can be activated together with the third sampling circuit.
In one improvement, a time duration, during which one of the sampling circuits is switched to be conductive, is less than a time duration, during which the corresponding power-supply source is activated.
In one embodiment, the control unit comprises a memory, which is designed for storing a sampled value of the photodetector current for each power-supply source or for storing a value derived from this photodetector current. Alternatively, the memory can also be designed to store a value for each power-supply source, which is determined by means of the control unit from the corresponding measurement value of. the photodetector current and a set point.
The control unit can comprise an analog circuit. In one improvement, the control unit can alternatively or additionally comprise a digital circuit. In one embodiment, the control unit can also comprise a microcontroller.
In one embodiment according to the proposed principle, a lighting arrangement comprises the circuit arrangement and also the first and the second light source. The first light source is connected to the first power-supply source and the second light source is connected to the second power-supply source. Such a lighting arrangement can be used in a lamp whose brightness and whose wavelength characteristics are controlled. The lighting arrangement can comprise the third light source, which is connected to the third power-supply source. The control of the power-supply sources can be used for white balance correction of the lighting arrangement. Such a lighting arrangement can be used advantageously for a display, such as a liquid crystal display.
According to the invention, a method for adjusting at least one light source provides the following steps: a first and a second light source are activated successively. A photodetector current, which is allocated to one of the light sources, is measured and sampled. A first and a second power-supply source, which are provided for the first and second light source, respectively, are controlled as a function of the sampled values of the photodetector current.
Advantageously, the measurement can be performed with a single photodetector based on the selective activation of the light sources and the correspondingly allocated sampling.
In one embodiment, the photodetector current, which is allocated to one of the light sources, is measured, sampled, and filtered. In this way, the sampled photodetector current is filtered.
In one embodiment, the activation of the light sources and the sampling and measuring are performed in an adjustment phase. The power-supply sources are controlled in an operating phase. The adjustment phase can be performed at the beginning of the use of the lighting arrangement. The operating phase follows the completion of the adjustment phase. After a given time duration, the system can be switched from the operating phase back into the adjustment phase. Thus, changes that occur in the lighting arrangement due to temperature or component drift can advantageously be compensated by means of the adjustment phases.
A brightness of one of the light sources can be controlled by setting the current output to the light source from the corresponding power-supply source. Alternatively, the brightness that can be recognized by a viewer from one of the light sources can be controlled by means of pulse-width modulation or pulse-density modulation of the current provided by the corresponding power-supply source of the light source. In this way, a color characteristic of the lighting arrangement can be adjusted by means of a current intensity and/or pulse-duty ratio, with which each of the light sources are provided with electrical energy.
The invention will be explained in more detail below using several embodiments with reference to the figures. Components that are identical in function or effect carry identical reference symbols. Insofar as circuit parts or components correspond in their function, their description will not be repeated in each of the following figures.
The lighting arrangement further comprises a first power-supply source 7, which is connected at one output to the first light source 10. The first power-supply source 7 has a switch 81 and a current source 82. The first power-supply source 7 and the first light source 10 form a series circuit, which is connected between a power-supply voltage terminal 9 and the reference-potential terminal 8. The lighting arrangement likewise comprises a second power-supply source 11 and a third power-supply source 13, which are each connected to an output of the second light source 12 and the third light source 14, respectively. The second power-supply source 11 has a switch 83 and a current source 84. Accordingly, the third power-supply source 13 has a switch 85 and a current source 86. The evaluation circuit 33 and thus the control unit 5 are connected at a first, a second, and a third output of the control unit 5 via a bus line to a control terminal of the current source 82 of the first power-supply source 7, to a control terminal of the current source 84 of the second power-supply source 11, and to a control terminal of the current source 86 of the third power-supply source 13. In addition, the lighting arrangement has a sequence controller 16, which is connected on the output side to a control terminal of the switch 81 of the first power-supply source 7, to a control terminal of the switch 83 of the second power-supply source 11, and to a control terminal of the switch 85 of the third power-supply source 13, and to the three sampling circuits 60, 61, 62 of the sampling means 6.
The lighting arrangement is used for backlighting a liquid crystal display 15. The liquid crystal display 15 can have thin-film transistors, abbreviated TFT.
In a first adjustment phase, the sequence controller 16 provides, on the output side, a control signal sync, which is fed to the first power-supply source 7 and also to the first sampling circuit 60. Due to this control signal sync, the first power-supply source 7 and thus the first light source 10 are activated. The light of the first light source 10 falls on the photodetector 2, so that a photodetector signal lin1 is applied to the node between the photodetector 2 and the power-supply circuit 4. The photodetector signal lin1 is amplified by means of the optional preamplifier 4, so that a photodetector signal lin2 is provided at the output of the preamplifier 4. The photodetector signal lin2 is fed on the input side to the first, the second, and the third sampling circuit 60, 61, 62. By means of the control signal sync, the first sampling circuit 60 is switched to be conductive, so that the photodetector signal lin2 is fed to the first filter 30. A signal that can be tapped on the output side at the first filter 30 is fed to the evaluation circuit 33, in which it is compared with a first default value for the first light source 10. The first default value is made available to the evaluation circuit 33 by the set-point generator 54. A value determined as a function of the signal that can be tapped at the first filter 30 and as a function of the first default value is stored in the memory 34. In a second adjustment phase, by means of the control signal sync, the first power-supply source 7 and the first sampling circuit 60 are deactivated and the second power-supply source 11 and thus the second light source 12 and also the second sampling circuit 61 are activated. Light generated by the second light source 12 and incident on the photodiode 2 leads to a photodetector signal lin1 and a photodetector signal lin2 amplified by means of the preamplifier 4. The second sampling circuit 61 is switched to be conductive, so that the photodetector signal lin2 can be fed to the evaluation circuit 33 via the second filter 31. The filtered signal is compared to a set point and a signal derived from the comparison is stored in the memory 34. In a corresponding way, the third power-supply source 13 and thus the third light source 14 and also the third sampling circuit 62 are activated by means of the control signal sync in a third adjustment phase. The light generated by the third light source 14 falls on the photodetector 2 and produces the photodetector signal lin2, which is amplified by means of the preamplifier 4 and which is fed to the third filter 32 via the third sampling circuit 62. As a function of a value on the output of the third filter 32 and a set point made available by the set-point generator 54, a value is formed that is stored in the memory 34.
In one operating phase, control signals are fed from the control unit 5 via the bus line to the control inputs of the current sources 82, 84, 86 of the first, the second, and the third power-supply sources 7, 11, 13, respectively. The control signals can be formed as a function of the values stored in the memory 34. In this way, three values of the photodetector signal are generated based on the selective sampling of the three light sources, wherein these three values are provided to the evaluation circuit 33 after filtering by means of the first, the second, and the third filter 30, 31, 32, so that, in the following operating phase, setting parameters can be fed to the three power-supply sources 7, 11, 13 as a function of the stored values. This advantageously has the effect that the light output from the three light sources 10, 12, 14 corresponds to the default values.
In one alternative embodiment, the preamplifier 4 and the power-supply circuit 3 can be left out, the photodetector 2 then being connected directly between the reference potential terminal 8 and the input of the sampling means 6.
By closing the switch 38, the capacitor 37 is discharged and the integrator 35 is thus reset. If the switch 63 is switched by means of the control signal sync from an open into a closed state, then the capacitor 37 is charged by the photodetector current lin2. A voltage on the output of the integrator 35 is thus proportional to the intensity of the photodetector current lin2 and the adjustable duration, during which the switch 63 is closed. The voltage is further processed by the evaluation circuit 33. Alternatively, the switch 63 can also be closed multiple times for the given time, so that the voltage on the output of the integrator 35 represents an integrated average value of the photodetector current lin2. The switch is controlled by the control signal sync, which is provided by the sequence controller 14. By means of the control signal sync, how many times and for what time duration the switch 63 is closed can be set.
A setting value Vset, which represents a default value for the associated light source, is provided to the voltage source 41. The integrator 35″ thus allows the setting value Vset to be drawn from the photodetector current lin2. Accordingly, a preprocessed signal is already provided at the output of the integrator 35″. The filter is constructed both for integration of the sampled photodetector current lin2 and also for determining a difference of the sampled photodetector current lin2 from the setting value Vset.
According to
The evaluation unit 33′ is connected at one input to the output of the amplifier 36 and at another input to the sequence controller 16. The three power-supply sources 7, 11, 13 are now activated alternately and the three capacitors 37, 44, 46 are charged. The voltage on the three capacitors 37, 44, 46 is thus fed time-shifted to the evaluation circuit 33′ and compared by this to set points provided by the set-point generator 54. The three power-supply sources 7, 11, 13 are controlled in the following operating phase as a function of the comparison results.
Thus, a single amplifier 36 is advantageously sufficient for integration of the photodetector current lin2 with three different values, which occur as a function of the three light sources 10, 12, 14.
In an alternative embodiment, the switch 38 in the integrator 35′″ can be replaced by the capacitor 41 and the two change-over switches 39, 40, as shown at the top right in
In another alternative embodiment of the lighting arrangement 3 according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 020 839.0 | Mar 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/003969 | 5/4/2007 | WO | 00 | 8/11/2009 |
