CIRCUIT ARRANGEMENT, LIGHTING ARRANGEMENT AND METHOD

Abstract

Circuit arrangement (100) for compensating the temperature dependence of a light source (150, 250), comprising: a voltage input (101, 201) which is coupled to an input (151) of the light source (150, 250), a voltage-controlled switching element (102, 202) having a load input (103), a load output (104) and a control input (105), wherein the load input (103) of the voltage-controlled switching element (102, 202) is coupled to an output (152) of the light source (150, 250), a control voltage source (106, 206) having a voltage output coupled to the control input (105) of the voltage-controlled switching element (102, 202), which outputs a constant control voltage (107, 207) in an active state, and a ground terminal (108, 208), wherein the load output (104) of the voltage-controlled switching element (102, 202) is coupled to the ground terminal (108, 208), wherein the voltage-controlled switching element (102, 202) is dimensioned such that a temperature dependence of the voltage-controlled switching element (102, 202) compensates for the temperature dependence of the light source (150, 250), wherein the voltage-controlled switching element (102, 202) comprises an NPN transistor (215) and a base resistor (209) arranged between the base terminal of the NPN transistor (215) and the voltage output of the control voltage source (106, 206), and an emitter resistor (210) arranged between the emitter terminal of the NPN transistor (215) and the ground terminal (108, 208), the NPN transistor has an internal base-emitter diode with a negative temperature coefficient wherein the base resistor (209) and the emitter resistor (210) are designed such that upon a temperature-dependent reduction of a base-emitter voltage of the NPN transistor (215), the voltage across the emitter resistor (210) increases, and wherein the emitter resistance (210) is dimensioned based on an expected self-heating of the light source (150, 250) and a current increase necessary to compensate for the expected self-heating.

Description

Technical area

[0001] The present invention relates to a circuit arrangement for compensating the temperature dependence of a light source. Furthermore, the present invention relates to a lighting arrangement and a corresponding method. State of the art

[0002] The present invention will be described below primarily in connection with lighting units in vehicles. However, it is understood that this invention can be used in any other application in which electrical lighting is used.

[0003] WO 99 / 39 319 A2 shows an illuminated advertisement with a series connection of LEDs.

[0004] DE 100 13 216 A1 describes a power supply for LEDs for lighting purposes.

[0005] Modern vehicles offer users increasingly extensive options for adjusting vehicle lighting or customizing it to their liking. Such lighting systems are marketed under the name "ambient lighting," or "ambient light," or similar.

[0006] At the same time, energy consumption in vehicles must be continuously reduced in order to comply with increasingly strict emissions regulations. Consequently, modern vehicles use LED light sources with significantly lower energy consumption than conventional light bulbs. However, the brightness of an LED fluctuates depending on its temperature, for example. During operation, the brightness of an LED will therefore fluctuate due to its own heating.

[0007] NTCs can be used to compensate for the reduction in LED luminous intensity due to self-heating. As they heat up, the resistance of NTCs decreases, allowing for a higher current at the same voltage. Ideally, this keeps the LED's luminous intensity constant. However, such an arrangement can only be used with constant input voltages, which is not the case in typical automotive systems.

[0008] To protect the LEDs from overheating, a diode can also be connected in parallel to the base-emitter path of a transistor located in the diode's load path. The diode should heat up in the same way as the transistor's base-emitter diode, causing the forward voltage of both diodes to change equally. This ensures that the emitter voltage level remains constant, and thus the current through the transistor is also kept constant. However, the transistor's self-heating causes other parameters to change, and the expected effect of the additional diode is rendered ineffective if the transistor cannot be cooled sufficiently. Description of the invention

[0009] An object of the invention is therefore to provide an improved control of an LED-based light source.

[0010] The object is achieved by the subject matter of the independent claims. Advantageous developments of the invention are specified in the dependent claims, the description, and the accompanying figures.

[0011] A circuit arrangement according to the invention for compensating the temperature dependence of a light source has a voltage input coupled to an input of the light source. Furthermore, the circuit arrangement has a voltage-controlled switching element having a load input, a load output, and a control input, wherein the load input of the voltage-controlled switching element is coupled to an output of the light source. The circuit arrangement further has a control voltage source having a voltage output coupled to the control input of the voltage-controlled switching element, which outputs a constant or approximately constant control voltage in an active, i.e., switched-on, state.Finally, the circuit arrangement has a ground terminal, wherein the load output of the voltage-controlled switching element is coupled to the ground terminal, and wherein the voltage-controlled switching element is dimensioned such that a temperature dependence of the voltage-controlled switching element compensates for the temperature dependence of the light source.

[0012] A lighting arrangement according to the invention comprises a circuit arrangement according to the invention, a light source which is coupled to the circuit arrangement, and a control device which is designed to provide a control voltage at the control input of the voltage-controlled switching element.

[0013] A method according to the invention for compensating for the temperature dependence of a light source comprises the following steps: supplying an input of the light source with an input voltage, controlling the current through the light source with a voltage-controlled switching element which has a load input, a load output and a control input, wherein the load input of the voltage-controlled switching element is coupled to an output of the light source and the load output is coupled to a ground terminal, and providing a constant control voltage in an active state at the control input of the voltage-controlled switching element, wherein the voltage-controlled switching element is dimensioned such that a temperature dependence of the voltage-controlled switching element compensates for the temperature dependence of the light source.

[0014] The present invention is based on the realization that temperature compensation, for example, of an LED light source using conventional circuitry is very complex. Temperature compensation in this context means that the luminous intensity, i.e., the brightness, of the light emitted by the LED light source remains constant or approximately constant even when the temperature of the LED light source changes, or that the temperature-dependent change in luminous intensity is at least counteracted.

[0015] The present invention further utilizes the knowledge that a second temperature-dependent component is introduced into the circuit with a switching element which is provided for switching the light source on or off.

[0016] The present invention therefore provides that the circuit with the light source and the switching element is dimensioned such that the temperature dependence of the light source and the temperature dependence of the switching element compensate each other.

[0017] LED light sources typically exhibit a negative temperature coefficient with respect to the luminous intensity of the emitted light. This means that as the light source heats up, the luminous intensity of the light emitted by the LED light source decreases.

[0018] Switching elements, such as transistor-based circuits, can, with appropriate design, exhibit a positive temperature coefficient with respect to the current flowing through the circuit. This means that the current flowing through the circuit increases as the switching element heats up.

[0019] However, if a higher current flows through an LED light source, the luminous intensity of the light emitted by the LED light source also increases. Consequently, the temperature dependence of the LED light source can be compensated for with an appropriately dimensioned switching element.

[0020] The present invention therefore makes it possible to control an LED light source in such a way that it emits light with an at least approximately constant luminous intensity even when the temperature increases, without the need to provide additional switching elements in the circuit.

[0021] Furthermore, the constant control voltage limits the current flow through the switching element. Overheating protection is thus already incorporated into the circuit.

[0022] The present circuit arrangement is therefore particularly suitable for use in limited space. However, due to its very simple and thus relatively uncomplicated design, the present invention can also be used advantageously in any other application.

[0023] Further, particularly advantageous embodiments and developments of the invention emerge from the dependent claims and the following description, whereby the features of various embodiments can be combined to form new embodiments. In particular, the independent claims of one claim category can also be developed analogously to the dependent claims of another claim category.

[0024] In one embodiment, the light source and the voltage-controlled switching element can be thermally coupled such that during operation of the circuit arrangement, the temperature changes in the light source and the voltage-controlled switching element have at least the same sign.

[0025] In order to compensate for the change in the luminous intensity of the light emitted by the light source, it is necessary that the switching element is exposed to the same or similar temperature changes as the light source.

[0026] A temperature change in the light source should therefore be reflected in the switching element with at least the same sign. If the light source heats up, the switching element also heats up. If the light source cools down, the switching element also cools down.

[0027] Such thermal coupling can be achieved, for example, by arranging the light source near the switching element. For example, the two components can be arranged on a common circuit board. In particular, the two components can be arranged as close to each other as possible or desired on the common circuit board and, for example, connected with common pads, for example, between the light source output and the power input of the switching element.

[0028] Thermal coupling can also be improved with a suitable housing. The thermal behavior of the circuit arrangement can be simulated, adjusted, or optimized, for example, during the circuit design phase.

[0029] The voltage-controlled switching element comprises an NPN transistor and a base resistor arranged between the base terminal of the NPN transistor and the voltage output of the control voltage source, as well as an emitter resistor arranged between the emitter terminal of the NPN transistor and the ground terminal. The base resistor and the emitter resistor are designed such that when the base-emitter voltage of the NPN transistor decreases with temperature, the voltage across the emitter resistor increases.

[0030] The NPN transistor has an internal base-emitter diode. This base-emitter diode has a negative temperature coefficient. As the temperature rises, the base-emitter voltage of the NPN transistor decreases. However, if a lower voltage drops across the base-emitter path of the NPN transistor at a constant control voltage, a higher voltage drops across the emitter resistor, and the current through the emitter resistor increases.

[0031] The emitter resistor can now be dimensioned such that the increase in current through the emitter resistor with increasing temperature roughly corresponds to the current required to compensate for the decreasing luminous intensity of the light emitted by the LED light source. The increasing current thus counteracts the decreasing luminous intensity. It is understood that the varying luminous intensity of the LED light source may not be fully compensated, but counteracting this already results in a significant reduction in visible luminous intensity fluctuations.

[0032] The emitter resistance is dimensioned based on the expected self-heating of the light source and the current increase required to compensate for the expected self-heating.

[0033] The expected self-heating of the light source can be calculated based on the light source's power dissipation and its thermal resistance. The power dissipation results from the light source's forward voltage and the current required to achieve the desired luminous intensity. For LED light sources, the forward voltage and required current can be found in the datasheet.

[0034] For example, assume that an LED light source has a forward voltage V F_LED of 3 V and a current I LED of 50 mA are required. The power loss is then PLED:=ILED*VF_LED=0.15W

[0035] The self-heating of the LED light source at room temperature can be calculated as: TLED:=23°C+Rth_LED*PLED=64.25°C

[0036] Based on the self-heating and the reduction in light intensity due to heating of the LED light source (see the datasheet), the current change can be calculated.

[0037] The reduction in light intensity due to heating can, for example, be ΔI Licht := -0.15 % / K. The required current increase is therefore: ΔILED:=|ΔILight*TLED|=9.637%

[0038] For the NPN transistor, the reduction in the base-emitter voltage can also be calculated. It is assumed here that the temperature T T of the transistor approximately at the temperature T LED corresponds to the LED light source, TT∼TLED.

[0039] The temperature-dependent voltage change of the NPN transistor can be taken from the data sheet and can be, for example, ΔU BE := -2.129 mV / K.

[0040] The reduction of the base-emitter voltage is therefore: ΔU:=|ΔUBE*TT|=0.113V

[0041] This results in the optimal voltage drop across the emitter resistor being URE:=ΔU / ΔILED=1.171 V

[0042] The value of the emitter resistance is thus RRE:=URE / ILED=23.416 Ω

[0043] In one embodiment, the base resistor may be sized based on a gain factor, the voltage drop across the emitter resistor, and a desired current through the light source.

[0044] The voltage drop across the base resistor results from the control voltage V S minus the base-emitter voltage and the voltage drop across the emitter resistor to URB:=VS−URE−UBE=1.159 V

[0045] The control voltage V S can be, for example, 3 V + / - 0.3 V. U BEcan be found, for example, in the datasheet of the NPN transistor. Generally, the greater the voltage drop across the base resistor, the stronger the compensation effect. However, the voltage drop should at least correspond to the possible fluctuations in the control voltage, for example, + / - 0.3 V, plus a margin of, for example, 50%.

[0046] The maximum base resistance is therefore RB_max:=URB / (ILED / hFE_min)=3.941 kΩ

[0047] Where h FE_min represents the minimum current amplification factor of the NPN transistor. The base resistance can also be chosen smaller, allowing the transistor to safely saturate. Short character description

[0048] An advantageous embodiment of the invention is explained below with reference to the accompanying figures. They show: Fig. 1 is a block diagram of an embodiment of a circuit arrangement according to the present invention; Fig. 2 is a schematic diagram of an embodiment of a lighting arrangement according to the present invention; Fig. 3 is a flowchart of an embodiment of a method according to the present invention; Fig. 4 is a diagram of temperatures in an embodiment of a lighting arrangement according to the present invention; Fig. 5 is a diagram of the current change of an exemplary switching element for use with the present invention; Fig. Figure 6 is a graph of luminous intensity versus current of an exemplary light source for use with the present invention; Fig. 7 is a graph of the luminous intensity variation as a function of temperature of an exemplary light source for use with the present invention; and Fig. 8 is a diagram of the voltages in an embodiment of a lighting arrangement according to the present invention.

[0049] The figures are merely schematic representations and serve only to illustrate the invention. Identical or equivalent elements are provided with the same reference numerals throughout. Detailed description

[0050] Fig. 1 shows an embodiment of a circuit arrangement 100. The circuit arrangement 100 has a voltage input 101 coupled to an input 151 of a light source 150. The voltage input 101 further has a voltage-controlled switching element 102, whose load input 103 is coupled to the output 152 of the light source 150. The load output 104 of the voltage-controlled switching element 102 is coupled to a ground terminal 108. Finally, the circuit arrangement 100 has a control voltage source 106 coupled to the control input 105 of the voltage-controlled switching element 102.

[0051] The circuit arrangement 100 can be coupled, for example, to a vehicle's electrical system via the voltage input 101 and the ground connection 108. Vehicle electrical systems are typically operated with a voltage of 12 V or 14 V, although significant voltage fluctuations are possible, and other voltages, such as 42 or 48 V, can also be used.

[0052] The control voltage source 106 generates a constant control voltage 107 from the voltage at the voltage input 101 when the light source 150 is to be switched on. It is understood that the control voltage source 106 itself can be controlled, for example, via a push-button or digitally, for example, via a vehicle bus, such as a LIN bus or a CAN bus.

[0053] The constant control voltage 107 controls the voltage-controlled switching element 102 in such a way that it enables a current flow between the output 152 of the light source 150 and the ground terminal 108. Typically, the voltage-controlled switching element 102 is fully controlled, i.e., operated in saturation. This minimizes the losses at the voltage-controlled switching element 102.

[0054] During operation, it is unavoidable that both the light source 150 and the voltage-controlled switching element 102 heat up when the light source 150 is switched on. Structural measures can ensure that the light source 150 and the voltage-controlled switching element 102 heat up approximately equally. For example, the light source 150 and the voltage-controlled switching element 102 can be arranged very close to each other so that the thermal coupling between the light source 150 and the voltage-controlled switching element 102 is as great as possible.

[0055] If the light source 150 and the voltage-controlled switching element 102 heat up to approximately the same level, the temperature-dependent changes in these elements can be used to compensate for each other. "Compensation" here means stabilizing the brightness of the light source 150, i.e., at least reducing its fluctuations.

[0056] For this purpose, the voltage-controlled switching element 102 can be dimensioned such that the temperature dependence of the voltage-controlled switching element 102 increases the current flow when the temperature dependence of the light source 150 causes the luminous intensity of the emitted light to decrease. This can be achieved, for example, by appropriately dimensioning the base and emitter resistors in the voltage-controlled switching element 102.

[0057] Fig. Figure 2 shows a schematic circuit diagram of a lighting arrangement 200. In the lighting arrangement 200, the circuit arrangement is not separately labeled. Rather, only the individual components of the circuit arrangement are shown.

[0058] The lighting arrangement 200 has a voltage input 201 coupled to an input of the control voltage source 206. The voltage input 201 is further coupled to the cathode of a green LED 211, a red LED 212, and a blue LED 213, as well as to a limiting resistor 214. Not shown are other possible filter elements that can smooth or filter the voltage provided by the vehicle electrical system, particularly in a vehicle.

[0059] The anodes of the green LED 211, the red LED 212, and the blue LED 213 are each coupled to a control input of the control voltage source 206. The green LED 211, the red LED 212, and the blue LED 213 are provided merely as examples and illustrate that the control voltage source 206 can also control other light sources in addition to the light source 250.

[0060] The green LED 211, the red LED 212, and the blue LED 213 are LEDs whose power consumption is so low that the control voltage source 206 can drive them directly or absorb the current flowing through the respective LEDs 211, 212, and 213. For example, the LEDs 211, 212, and 213 can be operated with a current of less than 40 mA. Furthermore, the LEDs 211, 212, and 213 can also be dimmed, for example, using PWM control, thus mixing different light colors.

[0061] The light source 250 is controlled via a control output of the control voltage source 206, via which the constant control voltage 207 is provided. The constant control voltage 207 can, for example, be 3 V + / - 0.3 V. Constant therefore means constant within specified limits.

[0062] In the lighting arrangement 200, the light source 250 is coupled to the voltage input 201 via the limiting resistor 214. The limiting resistor 214 is optional and can limit the current through the light source 250 such that, for example, it only begins to illuminate above a predetermined supply voltage at the voltage input 201. The limiting resistor 214 can, for example, have a value of 39 ohms and thus limit the current through the light source 250 such that it only begins to illuminate above a supply voltage of approximately 8 V.

[0063] The light source 250 itself is an LED 217, which is additionally provided with an ESD protection element 218 to prevent the LED 217 from being destroyed by static discharges. The voltage-controlled switching element 202 of the lighting arrangement 200 has an NPN transistor 215. A base resistor 209 is arranged between the base terminal, i.e., the control input, of the NPN transistor 215 and the control output of the control voltage source 206, and an emitter resistor 210 is arranged between the emitter terminal, i.e., the load output, of the NPN transistor 215 and the ground terminal 208. The LED 217 of the light source 250 is arranged between the limiting resistor 214 and the collector input of the NPN transistor 215.

[0064] The base resistor 209 and the emitter resistor 210 are now dimensioned such that the change in the base-emitter voltage 216 in the NPN transistor 215 leads to an increase in the voltage across the emitter resistor 210. Increasing the voltage across the emitter resistor 210 simultaneously increases the current through the emitter resistor 210 and thus the current through the light source 250. With appropriate dimensioning, this increase in current compensates for the loss of brightness of the LED 217.

[0065] For the lighting arrangement 200, the dimensions can be as follows: The emitter resistor 210 may be dimensioned based on an expected self-heating of the light source 250 and a current increase necessary to compensate for the expected self-heating.

[0066] The expected self-heating of the light source 250 can be calculated from the power loss P LED the light source 250 and its thermal resistance Rth_LED Calculate the power loss P LED results from the forward voltage V F_LED the light source 250 and the current I required for the desired luminous intensity LED . For LED light sources 250, the forward voltage V F_LED and the required current I LED can be found in the data sheet.

[0067] The light source 250 can provide a forward voltage V F_LED of 3 V and a current I LED of 50 mA. The power loss P LED then results in PLED:=ILED*VF_LED=0.15W

[0068] The self-heating T LED of the LED light source 250 at 23 degrees room temperature can be calculated as: TLED:=23K+Rrh_LED*PLED=64.25K

[0069] Based on the self-heating and the reduction in light intensity or the loss of intensity due to heating of the LED light source 250 (see the data sheet), the current change ΔI LED The amount of light needed to compensate for the loss of luminous intensity can be calculated. The reduction in luminous intensity due to heating can be found in the data sheet and, for example, ΔI Licht := -0.15 % / K. The required current increase is therefore: ΔILED:=|ΔILight*TLED|=9.637%

[0070] The reduction in the base-emitter voltage can also be calculated for the NPN transistor 215. It is assumed here that the temperature T T of the transistor approximately at the temperature T LED the LED light source 250 corresponds, T T ∼ T LED .

[0071] The temperature-dependent voltage change of the NPN transistor 215 can be taken from the data sheet and can be, for example, ΔU BE := -2.129 mV / K.

[0072] The reduction in the base-emitter voltage for the temperature change given above is therefore: ΔU:=|ΔUBE*TT|=0.113V

[0073] This results in the optimal voltage drop across the emitter resistor 210 being URE:=ΔU / ΔILED=1.171V

[0074] The value of the emitter resistor 210 is thus RRE:=URE / ILED=23.416Ω

[0075] The base resistor 209 can be selected based on a gain factor of the NPN transistor 215, the voltage drop across the emitter resistor 210 and a desired current I LED through the light source 250. The voltage drop across the base resistor 209 results from the constant control voltage 207, here V S= 3 V + / - 0.3 V, minus the base-emitter voltage 216, here U BE , and the voltage drop across the emitter resistor 210 to URB:=VS−URE−UBE=1.159V

[0076] U BE can be found, for example, in the datasheet of the NPN transistor 215. Generally, the smaller the voltage drop across the base resistor 209, the stronger the compensation effect of the voltage-controlled switching element 202. However, the voltage drop should at least correspond to the possible fluctuations of the constant control voltage 207 plus a reserve of, for example, 50%, in this case 0.3 V + 0.15 V.

[0077] The maximum base resistance 209 is therefore RB_max:=URB / (ILED / hFE_min)=3.941kΩ

[0078] Where h FE_minrepresents the minimum current amplification factor of the NPN transistor 215. The base resistor 209 can also be chosen smaller, so that the NPN transistor 215 can go into saturation.

[0079] For ease of understanding, the following description of the process-based Fig. 3 the reference symbols for the Fig. Keep 1, 2 and 4 - 8 as reference.

[0080] Fig. 3 shows a flowchart of a method for compensating the temperature dependence of a light source 150, 250.

[0081] In a first supply step S1, the method comprises supplying an input 151 of the light source 150, 250 with an input voltage. This can be provided, for example, by a vehicle electrical system.

[0082] Furthermore, in a second control step S2, the current through the light source 150, 250 is controlled using a voltage-controlled switching element 102, 202, which has a load input 103, a load output 104, and a control input 105. The load input 103 of the voltage-controlled switching element 102, 202 is coupled to an output 152 of the light source 150, 250, and the load output 104 is coupled to a ground terminal 108, 208.

[0083] Finally, in a third step S3 of providing, a constant control voltage 107, 207 is provided in an active state, i.e. when the light source 150, 250 is switched on, at the control input 105 of the voltage-controlled switching element 102, 202.

[0084] The voltage-controlled switching element 102, 202 is dimensioned such that a temperature dependence of the voltage-controlled switching element 102, 202 compensates for the temperature dependence of the light source 150, 250.

[0085] In order to be able to carry out the compensation as a function of the temperature of the light source 150, 250, the light source 150, 250 and the voltage-controlled switching element 102, 202 can be thermally coupled to one another in such a way that, during operation, the temperature changes in the light source 150, 250 and in the voltage-controlled switching element 102, 202 have at least the same sign.

[0086] In the voltage-controlled switching element 102, 202, an NPN transistor 215 and a base resistor 209 arranged between the base terminal of the NPN transistor 215 and the voltage output of the control voltage source 106, 206, as well as an emitter resistor 210 arranged between the emitter terminal of the NPN transistor 215 and the ground terminal 108, 208, can be provided. The base resistor 209 and the emitter resistor 210 are the components that can be designed such that, upon a temperature-dependent reduction in the base-emitter voltage of the NPN transistor 215, the voltage across the emitter resistor 210 increases. As already explained above, this increase in the voltage across the emitter resistor 210 leads to an increased current flow through the emitter resistor 210 and thus also through the light source 250.

[0087] The emitter resistor 210 can be dimensioned based on the expected self-heating of the light source 150, 250 and the current increase required to compensate for the expected self-heating. The base resistor 209 can be dimensioned based on a gain factor, the voltage drop across the emitter resistor 210, and a desired current through the light source 150, 250. To avoid repetition, reference is made here to the explanations for Fig. 1 and Fig. 2.

[0088] Fig. 4 shows a diagram of temperatures as they may occur in a lighting arrangement according to the present invention, for example in the lighting arrangement 200.

[0089] Temperature curve 400 shows the temperature of the NPN transistor, temperature curve 401 shows the temperature of the light source, temperature curve 402 shows the temperature of the control voltage source. Temperature curve 403 shows the temperature near the light source, temperature curve 404 shows the temperature near the transistor, and temperature curve 405 shows the ambient temperature.

[0090] In Fig. 4 it can be clearly seen that, for example, in the lighting arrangement 200 of the Fig. 2, a very high thermal coupling is possible between the light source 250 and the NPN transistor 215. For this purpose, they can be arranged together on a circuit board and in a common housing, for example.

[0091] Fig. Figure 5 shows a diagram of the current change 500, 501, 502 for three exemplary switching elements for use with the present invention. The diagram shows the current through the emitter resistor of the circuit, which, for example, Fig. 2 for the switching element 202. The coefficient of the current change can be taken, for example, from the data sheet of the respective transistor, for example, the NPN transistor 215, or derived from the curve for the base-emitter voltage versus the collector-emitter current at different temperatures.

[0092] It can be seen that between switching on at a room temperature of 23 degrees Celsius and the steady state at 65 degrees Celsius, there is a fluctuation in the output current of 8% for curve 500, 8.51% for curve 501, and 6.38% for curve 502. These values can vary depending on the design of the switching elements and the selection of the individual components, especially the NPN transistors. (Note that – for example – temperatures are always given in degrees Celsius.)

[0093] Fig. Figure 6 shows a graph of luminous intensity 600 versus current for an exemplary LED for use with the present invention. Fig. In the circuit shown in Figure 2, the LED 217 is nominally operated at 50 mA. A fluctuation of approximately 8%, as shown in Fig. 5 for different switching elements, this would mean a change in current of approximately 4 mA.

[0094] The diagram of the Fig. 6 shows that the luminous intensity 600 of the LED would increase by about 5 - 6%.

[0095] Fig. 7 shows a diagram of the change in luminous intensity 700 as a function of temperature for the Fig. 6. The diagram shows that increasing the temperature to 65 degrees would reduce the luminous intensity by approximately 5%.

[0096] The current increase through the switching element is so large that the loss of light intensity is compensated.

[0097] Fig. Figure 8 shows a diagram of the voltages in an embodiment of a lighting arrangement according to the present invention.

[0098] The voltages 800, 803 represent the voltage across the base resistor 209 of the Fig. 2. The voltages 801, 804 represent the base-emitter voltage 216 and the voltages 802, 805 represent the voltage across the emitter resistor 210.

[0099] It can be seen that before self-heating, the base-emitter voltage 801 is higher than the base-emitter voltage 804 after self-heating. The same applies to the voltages 800 and 803 across the base resistor 209. At the same time, the base-emitter voltage 805 after self-heating increases significantly compared to the base-emitter voltage 802 before self-heating. This increase in the base-emitter voltage 805 is also the cause of the increased current flow.

[0100] Since the devices and methods described in detail above are exemplary embodiments, they can be modified widely by those skilled in the art without departing from the scope of the invention. In particular, the mechanical arrangements and the relative dimensions of the individual elements are merely exemplary. LIST OF REFERENCE SYMBOLS 100 circuit arrangement 200 lighting arrangement 101, 201 Voltage input 102, 202 voltage-controlled switching element 103 Load input 104 Load output 105 Control input 106, 206 Control voltage source 107, 207 constant control voltage 108, 208 ground connection 209 Base resistance 210 Emitter resistance 211 green LED 212 red LEDs 213 blue LEDs 214 Limiting resistor 215 NPN transistor 216 Base-emitter voltage 217 LED 218 ESD protective element 150, 250 light source 151 Light source input 152 Output of the light source 400, 401, 402, 403, 404, 405 temperature 500, 501, 502 electricity 600, 700 light intensity 800, 801, 802, 803, 804, 805 voltage S1 - S3 process steps

Claims

[1] Circuit arrangement (100) for compensating the temperature dependence of a light source (150, 250), comprising: a voltage input (101, 201) which is coupled to an input (151) of the light source (150, 250), a voltage-controlled switching element (102, 202) having a load input (103), a load output (104) and a control input (105), wherein the load input (103) of the voltage-controlled switching element (102, 202) is coupled to an output (152) of the light source (150, 250), a control voltage source (106, 206) having a voltage output coupled to the control input (105) of the voltage-controlled switching element (102, 202), which outputs a constant control voltage (107, 207) in an active state, and a ground terminal (108, 208), wherein the load output (104) of the voltage-controlled switching element (102, 202) is coupled to the ground terminal (108, 208), wherein the voltage-controlled switching element (102, 202) is dimensioned such that a temperature dependence of the voltage-controlled switching element (102, 202) compensates for the temperature dependence of the light source (150, 250), wherein the voltage-controlled switching element (102, 202) comprises an NPN transistor (215) and a base resistor (209) arranged between the base terminal of the NPN transistor (215) and the voltage output of the control voltage source (106, 206), and an emitter resistor (210) arranged between the emitter terminal of the NPN transistor (215) and the ground terminal (108, 208), the NPN transistor has an internal base-emitter diode with a negative temperature coefficient wherein the base resistor (209) and the emitter resistor (210) are designed such that upon a temperature-dependent reduction of a base-emitter voltage of the NPN transistor (215), the voltage across the emitter resistor (210) increases, and wherein the emitter resistance (210) is dimensioned based on an expected self-heating of the light source (150, 250) and a current increase necessary to compensate for the expected self-heating. [2] Circuit arrangement (100) according to claim 1, wherein the light source (150, 250) and the voltage-controlled switching element (102, 202) are thermally coupled such that during operation of the circuit arrangement (100) the temperature changes in the light source (150, 250) and the voltage-controlled switching element (102, 202) have at least the same sign. [3] Circuit arrangement (100) according to claim 1 or 2, wherein the base resistor (209) is dimensioned based on a gain factor of the NPN transistor (215), the voltage drop across the emitter resistor (210) and a desired current through the light source (150, 250). [4] Lighting arrangement (200) with a circuit arrangement (100) according to one of claims 1 to 3, a light source (150, 250) coupled to the circuit arrangement (100), and a control device which is designed to control the control voltage source (106, 206). [5] A method for compensating the temperature dependence of a light source (150, 250), the method comprising the following steps: Supplying (S1) an input (151) of the light source (150, 250) with an input voltage, Controlling (S2) the current through the light source (150, 250) with a voltage-controlled switching element (102, 202) having a load input (103), a load output (104) and a control input (105), wherein the load input (103) of the voltage-controlled switching element (102, 202) is coupled to an output (152) of the light source (150, 250) and the load output (104) is coupled to a ground connection (108, 208), and Providing (S3) a constant control voltage (107, 207) in an active state at the control input (105) of the voltage-controlled switching element (102, 202), wherein the voltage-controlled switching element (102, 202) is dimensioned such that a temperature dependence of the voltage-controlled switching element (102, 202) compensates for the temperature dependence of the light source (150, 250), wherein an NPN transistor (215) and a base resistor (209) arranged between the base terminal of the NPN transistor (215) and the voltage output of the control voltage source (106, 206) and an emitter resistor (210) arranged between the emitter terminal of the NPN transistor (215) and the ground terminal (108, 208) are provided in the voltage-controlled switching element (102, 202), in the NPN transistor a base-emitter diode with a negative temperature coefficient is provided, wherein the base resistor (209) and the emitter resistor (210) are designed such that upon a temperature-dependent reduction of a base-emitter voltage of the NPN transistor (215), the voltage across the emitter resistor (210) increases, and wherein the emitter resistance (210) is dimensioned based on an expected self-heating of the light source (150, 250) and a current increase necessary to compensate for the expected self-heating. [6] Method according to claim 5, wherein the light source (150, 250) and the voltage-controlled switching element (102, 202) are thermally coupled such that, during operation, the temperature changes in the light source (150, 250) and the voltage-controlled switching element (102, 202) have at least the same sign. [7] The method of claim 5 or 6, wherein the base resistor (209) is dimensioned based on a gain factor of the NPN transistor (215), the voltage drop across the emitter resistor (210) and a desired current through the light source (150, 250).

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