DE102005042082A1 - Circuit arrangement e.g. for motor vehicle dashboard, has measuring device coupled to LED for measurement of ambience brightness - Google Patents

Abstract

A circuit arrangement incorporating a light-emitting diode (LED) has at least one LED (1) which in normal operation is driven from a supply source (2), and a measurement device (3) coupled to the LED (1) for measurement of ambient brightness by the LED (1) in a measurement operational mode. Independent claims are given for the following. (1) (A) Application of a circuit arrangement in a vehicle (2) (B) A method for controlling a LED.

Description

The The present invention relates to a circuit arrangement with a light-emitting diode, their use and a method of controlling a light emitting diode.

LEDs are also referred to as LED, light-emitting diode. Such LED can economical be produced in integrated semiconductor circuit technology and are characterized inter alia by the fact that a relatively large light output with high efficiency and small dimensions is possible. Furthermore LEDs are often more durable than incandescent lamps.

It may be desirable be to control the brightness of a light emitting diode. This is for example the lighting of fittings or dashboards in motor vehicles the case. This lighting is normally manual by the driver by pressing a potentiometer or similar Device for dimming according to the desired personal needs, but also adjusted according to the ambient brightness.

The Brightness control of a light-emitting diode can be achieved, for example done that the height of the Current is controlled by the LED.

In the document DE 10357776 is a control arrangement indicated with light emitting diode. There is provided for controlling the brightness of the light emitting diode during operation to operate them pulsed. A sigma-delta modulator is used to provide a pulsed signal. By controlling the modulation data stream, a signal is emitted in the time average, which determines the brightness of the light emitting diode. Accordingly, the brightness of the LED can be controlled by a pulse width modulated signal and / or a modulation data stream, wherein gaps in the current occur in both cases.

Should the LED is not manual as described above, but automatic controlled in their brightness, so could be a photosensitive component such as a photoresistor are provided to the Ambient brightness to detect and depending on the light emitting diode in their brightness control.

task The present invention is a circuit arrangement with Light-emitting diode and a method for controlling a light-emitting diode specify the automatic control of the brightness of the LED allow at reduced cost.

According to the invention Task regarding the circuit arrangement by a circuit arrangement with light emitting diode solved with the features of claim 1.

Regarding the The object is achieved by a method for controlling a process Light-emitting diode with the steps according to claim 18 solved.

advantageous Further developments and refinements of the proposed principle are each subject of the dependent Claims.

To the proposed principle are two modes of operation of the light emitting diode provided, namely a normal mode and a measurement mode. In normal mode becomes the LED from a supply source with a supply voltage or supplying a supply current such that they emit light in the visible or even in the non-visible area emitted. In the Measuring mode, however, is the LED with a measuring device coupled, such that a measurement of the ambient brightness with the working as a detector LED takes place.

It the physical effect is exploited, that every light-emitting diode, if it is not actively driven, as a photodiode, therefore as photosensitive component works.

Even though the efficiency of such a light emitting diode in measuring or detector operation is less than a specially provided for performing a light measurement Photodiode or a photoresistor, the physical effect is sufficient nevertheless, to achieve the goal, namely a measure of the ambient brightness to win.

Consequently can with advantage on additional omitted photosensitive components such as photodiodes or photoresistors become. Overall, the brightness control is thus automatic Way depending possible from the ambient brightness according to the proposed principle, without a dedicated photosensitive component as an ambient brightness detector to have to provide.

The Photosensitivity of the LED depends on the color of the LED, that is, the color temperature of their emitted light in the normal mode, from.

Preferably, the measuring device is coupled via a control line to the supply source for controlling the brightness of the light-emitting diode in the Normal operating mode as a function of the measured ambient brightness in the measuring mode.

in this connection The brightness is preferred by controlling the height of a Supply voltage or a supply current of the supply source controlled.

alternative or additionally can additional tax funds such as controllable resistors or transistors in one Current path of the power source and the LED must be switched.

For example in pulsed operation of the LED in the normal mode can it may be advantageous that the control line is not the measuring device coupled directly with the supply source, but rather with a switch connected in series with the supply source or another input for activating or deactivating the supply source.

Prefers a multiplexer is provided, on the one hand with the light emitting diode is firmly connected and this other, switchable with the measuring device or coupled to the supply source. Thus, the light emitting diode in the normal mode for its supply with the supply source connected and preferably in this mode of the measuring device separated. In contrast, in the measuring mode, the light-emitting diode is advantageous connected to the measuring device and preferred in this mode of the supply source disconnected.

alternative the supply source can be permanently connected to the light emitting diode but is designed and / or driven so that they in the measuring mode no power supplies.

As well the measuring device can be firmly connected to the light emitting diode and is designed and / or controlled so that only in the Measuring mode, a measurement and / or evaluation takes place.

Prefers a control device is provided with an input with the measuring device is connected, with a first output, with the supply source is coupled to control the brightness the LED and a second output connected to a control input of the multiplexer is connected for switching between normal mode and measuring mode.

alternative can also be provided different control means, one of which dependent on the measured ambient light, the supply source and / or a supplied from the supply source supply current or a Control supply voltage, and another control means, which for example, depending on an externally specified periodic clock signal switching between normal mode and measuring mode causes.

at pulsed operation of the light emitting diode in the normal mode is the However, providing a common control device therefore particularly advantageous, since thus a synchronization of the switching between normal mode and measuring mode on the one hand and the control pulses for the pulsed operation of the light emitting diode in the normal mode on the other hand possible is.

Of the Multiplexer preferably comprises at least one switch. alternative or additionally can also several switches for be provided different current paths.

Of the or the switches are preferably designed as a semiconductor switch, for example as a single transistor or as a transmission gate with two with respect to their controlled paths of parallel-connected transistors of the complementary conductivity type, So for example, an NPN and a PNP transistor or a P-channel transistor and an N-channel transistor.

The Measuring device is preferred for measuring a photocurrent or set a photo voltage of the LED.

to Measuring the photocurrent, the measuring device can be a means for biasing the LED in the reverse direction include. This is preferred in the measuring mode connected to the LED. Thus, done a reverse bias of the LED, allowing a photocurrent delivers in dependence an incident light. This is a simple way of measurement the ambient brightness possible.

alternative Is it possible, that the light emitting diode is not designed to provide a photocurrent is, but a photo tension. In this case, can on an additional active source be waived.

The Supply source is preferred for a pulsed operation of LED is set in normal mode.

This serves to achieve a higher Efficiency of the LED.

Alternatively or additionally, by adjusting the pulse width or sigma-delta modulation or other measures of this control signal, the brightness of the light-emitting diode in the normal operating mode can be influenced. It is particularly advantageous in this Case that in each case a measurement of the ambient brightness takes place in the gaps of the pulsed operation. Depending on the desired application, the ambient brightness may be measured in every gap or only in every nth gap.

The Measurements of the ambient brightness can also be initiated externally and then just need to be synchronized with the control signal, which between active and inactive phases of pulsed operation the LED switches in normal mode.

Prefers is a sigma-delta converter for controlling the brightness of the light-emitting diode provided in the normal mode and coupled to the light emitting diode.

PWM (pulse width modulation) is also very suitable for control the brightness.

In A preferred development, in addition to the LED further Light emitting diodes provided in the normal mode of a supply source are driven to emit light in the visible or invisible Area.

Of course it is It does not require that any of these other LEDs also to do so is designed in a measuring mode with a measuring device be coupled to measure the ambient brightness. Much more it may be enough for that only one of the multiple light emitting diodes in a measuring mode is operable to measure the ambient brightness. These and all other LEDs can in terms of depending on their brightness This measured ambient brightness be controlled for control their brightness in LED mode or normal operation.

If for example, in matrix form arranged light-emitting diodes, as used primarily in displays find light emitting diodes for Different colors are provided, so it may be advantageous be, that of the light-emitting diodes as a light-emitting diode with measuring operation according to the proposed principle perform, due to their color temperature the highest sensitivity for a light measurement of the Ambient brightness has.

Thereby can without additional Expense the sensitivity of the light measurement can be improved.

LEDs according to the proposed principle are in many applications with Advantage applicable. This includes among other things seven-segment displays, backlighting of displays, Indicator lights on control panels or fittings. All these applications It is common that the brightness of the LEDs in normal operation with advantage then bigger, if the ambient brightness, for example, by incidence of direct or indirect sunlight is high, and lower if due to weak room lighting or darkness a lower illumination or brightness of the Leuchtdi ode or LEDs is sufficient. This is also beneficial in mobile or battery powered applications can be used, as with the proposed principle of power consumption lowered and thus the battery life or the time between charging cycles of a battery can be increased.

The latter meets for example battery powered electronic candles too. These are a means intended to operate the light emitting diode, which is an artificial Flickering and thus the visual impression of a torch or a Candle produced by the viewer.

The Control of the brightness of the light-emitting diode can also be designed that for example at night or when switched off Interior lighting the LED is turned off to power to save.

The Invention will be described below in several embodiments with reference to Drawings closer explained.

It demonstrate:

1 a first embodiment of a circuit arrangement with light-emitting diode according to the proposed principle and

2 A second embodiment of a circuit arrangement with light-emitting diode according to the proposed principle.

1 shows an exemplary embodiment of a circuit arrangement with light emitting diode 1 , The LED is in a normal mode from a supply source 2 driving bar, which is in the present case designed as a power source. A measuring device 3 is with the light emitting diode 1 also coupled and used to measure an ambient brightness by means of the LED in a measurement mode. The measuring device 3 outputs a voltage signal depending on the ambient brightness in the measuring mode. The measuring device 3 is via a control line with the supply source 2 coupled to control the brightness of the light emitting diode in the normal mode depending on the measured ambient brightness in the measuring mode. For this purpose, the control line comprises a control device 4 , The control device 4 has an entrance, with an output of the measuring device 3 is connected and has an output connected to the supply source 2 is coupled to control the brightness of the LED 1 in normal mode. Another tax 5 is with control inputs of switches 6 . 7 connected. A first switch 6 is in a common current path with the supply source 2 and the light emitting diode 1 between a supply voltage connection 8th and a reference potential connection 9 connected.

Another switch 7 is between the anode of the LED 1 and an input of the measuring device 3 educated. The measuring device 3 is designed here as a simple amplifier.

In normal mode is the switch 6 closed and the switch 7 open. The supply source 2 drives a current through the LED 1 that makes them shine.

In a measurement mode, however, the first switch 6 open and the second switch 7 closed. Incident light in the LED causes the generation of a photo voltage, by the measuring device 3 is converted into a measuring signal. Depending on the measurement signal output by the measuring device, the control device controls 4 the supply source 2 , This is done in such a way that the supply source 2 in the normal operating mode, the LED is driven with a current which depends on the ambient brightness measured in the measuring mode.

2 shows the signal waveforms of the control signals φ1, φ2 for driving the switch 6 . 7 , It can be seen that the two switches are never switched on at the same time, but rather are alternately switched on and off. The light-emitting diode 1 is operated pulsed in the normal mode. This serves to increase the efficiency. In the gaps, that is when the switch 6 anyway, is open by the pulsed operation, can be carried out without repercussions and without disadvantages for normal operation, a measurement of the photo voltage by the switch 7 is closed.

Advantageously, non-overlap times are met in which neither the first nor the second switch 6 . 7 closed is.

In other words, the light emitting diode is forward biased by the current I of the supply source 2 when the first switch 6 closed is. The control device 4 controls the current of the supply source, which is designed as a controllable current source, as a function of the measurement of the brightness. The second switch 7 will only be closed when the first switch 6 is open and no active current is driven through the LED. When the switch 6 is open, the LED works as a photodiode and its photo voltage is measured.

In alternative embodiments, the control device 4 and the control means 5 be summarized in a common circuit block. This is particularly advantageous if a synchronization of the control of the switch 6 . 7 Thus, the switching from normal operation in measurement mode with a controller of a pulsed operation, for example, by sigma-delta modulation should be synchronized closer.

3 shows an alternative embodiment of the circuit of 1 , As far as the arrangements after 1 and 3 in their structure, the components used and the advantageous operation match, the description will not be repeated at this point.

In the common current path comprising the supply source 2 , the first switch 6 and the light emitting diode 1 is at 3 in addition a third switch 10 connected. Parallel to the third switch 10 is a series circuit comprising a fourth switch 11 and a reverse voltage source 12 connected. The parallel connection of these two branches is between the cathode of the LED and the reference potential terminal 9 connected. The desk 7 is in turn with a connection between the first switch 6 and the anode of the light emitting diode 1 connected. To the second port of the second switch 7 However, instead of the amplifier 3 from 1 a current measuring device 13 whose output is in turn connected to an input of the control device 4 connected is. The controller supplies the signals φ1, φ2 for controlling the switches 6 . 10 . 7 . 11 so the control means 5 eliminated.

The first switch 6 is switched on and off simultaneously with the third switch in response to the clock signal φ1. The second switch 7 and the fourth switch 11 are also switched in pairs at the same time on and off in response to the second control signal φ2.

In contrast to 1 is at 3 the LED in the measurement mode, so if the second and fourth switch 7 . 11 one and the first and third switches 6 . 10 are turned off, not used as a photodiode for measuring the photo voltage, but as a photodiode in current operation, ie biased with a bias voltage Vr in the reverse direction. This is referred to as reverse biasing in English. In this mode, the diode outputs in response to the reverse bias Vr which is the source 12 gives off, and the incident light due to the ambient brightness, a photocurrent from.

The control device 4 controls the switches 6 . 7 . 10 . 11 from 3 at.

The control signals φ1, φ2 for these switches correspond to those of 2 and are below in 4 located.

Of course, it is within the scope of the invention, the features of the embodiments according to 1 . 3 to combine with one another as desired.

1

led

2

source

3

amplifier

4

control device

5

control means

6

switch

7

switch

8th

Supply potential terminal

9

Reference potential terminal

10

switch

11

switch

12

Reverse voltage source

13

Current measuring device

Claims (21)

Circuit arrangement with light-emitting diode ( 1 ), comprising - at least one light-emitting diode ( 1 ) in a normal mode of operation from a supply source ( 2 ), - a measuring device ( 3 . 13 ) connected to the LED ( 1 ) is coupled to measure an ambient brightness by means of the light emitting diode ( 1 ) in a measuring mode. Circuit arrangement according to claim 1, characterized in that the measuring device ( 3 . 13 ) via a control line with the supply source ( 2 ) is coupled to control the brightness of the light emitting diode ( 1 ) in the normal operating mode as a function of the measured ambient brightness in the measuring mode. Circuit arrangement according to claim 2, characterized in that the measuring device ( 3 . 13 ) is coupled to the supply source via the control line for controlling the brightness by controlling the level of a supply voltage or a supply current of the supply source ( 2 ). Circuit arrangement according to one of claims 1 to 3, characterized in that a multiplexer ( 6 . 7 ) provided with the light emitting diode ( 1 ) and this switchable with the measuring device ( 3 . 13 ) or with the supply source ( 2 ) couples. Circuit arrangement according to claim 4, characterized in that a control device ( 4 ) is provided with an input connected to the measuring device ( 3 . 13 ), with a first output connected to the supply source ( 2 ) is coupled to control the brightness of the light emitting diode ( 1 ) and a second output connected to a control input of the multiplexer ( 6 . 7 ) is connected to switch between normal mode and measurement mode. Circuit arrangement according to Claim 4 or 5, characterized in that the multiplexer ( 6 . 7 ) comprises at least one switch. Circuit arrangement according to Claim 6, characterized in that the switch is a semiconductor switch. Circuit arrangement according to one of claims 1 to 7, characterized in that the measuring device ( 3 . 13 ) for measuring a photocurrent or a photo voltage of the light emitting diode ( 1 ) is set up. Circuit arrangement according to one of claims 1 to 8, characterized in that the measuring device ( 13 ) for measuring the photocurrent a means ( 12 ) for biasing the light emitting diode ( 1 ) in the reverse direction, which in the measuring mode with the light-emitting diode ( 1 ) connected is. Circuit arrangement according to one of claims 1 to 9, characterized in that the supply source ( 2 ) for a pulsed operation of the light emitting diode ( 1 ) is set in the normal mode. Circuit arrangement according to Claims 5 and 10, characterized in that the control device ( 4 ) is arranged to trigger a measurement of the ambient brightness during a gap of the pulsed operation of the light emitting diode. Circuit arrangement according to claim 10 or 11, characterized in that a sigma-delta converter for controlling the brightness of the light emitting diode ( 1 ) is provided in the normal mode and coupled thereto. Circuit arrangement according to one of claims 1 to 12, characterized in that at least one further light-emitting diode is provided, which with the measuring device ( 3 . 13 ) is coupled to control the brightness of the at least one further light-emitting diode in dependence on the measured ambient brightness. Use of a circuit arrangement according to a the claims 1 to 13 as an electronic candle. Use of a circuit arrangement according to a the claims 1 to 13 in a dashboard of a vehicle. Use of a circuit arrangement according to a the claims 1 to 13 in an outdoor lighting device of a vehicle. Use of a circuit arrangement according to a the claims 1 to 13 in a signaling device. Method for controlling a light-emitting diode with the steps: - driving the light-emitting diode ( 1 ) with a supply voltage or a supply current in a normal operating mode, - measuring the ambient brightness by means of the light-emitting diode acting as a detector ( 1 ) in a measuring mode. Method according to Claim 18, characterized by controlling the brightness of the light-emitting diode ( 1 ) in the normal operating mode as a function of the ambient brightness measured in the measuring mode. Method according to Claim 18 or 19, characterized by operating the light-emitting diode ( 1 ) in the normal mode in a pulsed mode. A method according to claim 20, characterized by Carry out measuring ambient brightness in a pulsed mode gap.