LIGHTING SYSTEM FOR REGULATING VOLTAGE IN VEHICLE HEADLAMP

Abstract

 The present subject matter relates to a lighting system (100, 200, 300, 400) of a vehicle headlamp. The lighting system (100, 200, 300, 400) comprises a lighting module (110) having a plurality of Light Emitting Diodes (LEDs); a driver module (115) electrically connected to the lighting module (110), configured to drive the lighting module (110) and a voltage regulator (105). The voltage regulator (105) provides voltage to the lighting module (110), and includes a voltage resistor circuit (125) having an internal voltage reference node N. Further, the lighting system (100, 200, 300, 400) comprises a controller to dynamically control an output voltage V_out of the voltage regulator (105) by controlling current I_c on the internal voltage reference node (N) in relation to a voltage V_driver across the driver module.

Description

TECHNICAL FIELD

[0001] The present invention relates to a lighting system for a vehicle, and more particularly, to a lighting system for regulating supply voltage to a lighting module of a vehicle headlamp.

STATE OF THE ART

[0002] A lighting system for a vehicle headlamp, for example, rear lamps, generally includes a lighting module having a plurality of Light Emitting Diodes (LEDs), a driver module connected to the lighting module to drive the LEDs, and a voltage regulator electrically connected to the lighting module. The lighting module may include a circuit board, for example, a printed circuit board, having the plurality of LEDs mounted thereon. The driver module drives the LEDs by providing sufficient current to the LEDs based on the application. Further, the constant supply voltage from the voltage regulator is provided to the LEDs. The driver module can be connected either at a cathode end or at an anode end of the lighting module based on the application

[0003] As well known, it is required to supply sufficient voltage, i.e., forward drift voltage, to LEDs to turn on the LEDs, i.e., to guarantee correct LED polarization. At higher temperatures, the voltage drop across the lighting module decreases. Since the supply voltage to the lighting module is constant, the decrease in the voltage drop across the lighting module results in increased power dissipation in the driver module. Whereas, at lower temperatures, there will be higher voltage drop across the driver module and thereby require higher supply voltage to turn on the LEDs. Therefore, it is required to maintain trade-off between the LED polarization and power dissipation in the driver module.

SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide a lighting system that can provide effective trade-off between the LED polarization and power dissipation in a driver module of a lighting system of a vehicle headlamp, for example, rear lamp, by dynamically regulating the supply voltage to a lighting module, i.e., plurality of LEDs of the lighting system.

[0005] Another object of the present invention is to provide a lighting system that can optimize the power dissipation in the driving module of the lighting system.

[0006] Yet another object of the present invention is to improve the thermal performance of the lighting system.

[0007] According to an embodiment of the present invention, there is provided a lighting system for a vehicle headlamp of an automotive vehicle. The lighting system comprises a lighting module having a plurality of Light Emitting Diodes (LEDs); a driver module; and a voltage regulator. The driver module is electrically connected to the lighting module and configured to drive the lighting module, and the voltage regulator provides voltage to the lighting module and includes a resistor circuit having an internal voltage reference node. Further, the lighting system includes a controller to dynamically control an output voltage of the voltage regulator by controlling current on the internal voltage reference node in relation to a voltage across the driver module.

[0008] In an aspect, the voltage regulator is a Low Dropout (LDO) device or a switched-mode power supply.

[0009] In one embodiment, the driver module is electrically connected at a cathode end of the lighting module. In such cases, the driver module is referred as a low side LED driver. In another embodiment, the driver module is electrically connected at a anode end of the lighting module. In such cases, the driver module is referred as a high side LED driver.

[0010] In one embodiment, the lighting system includes a voltage controlled current source to control the current on the internal voltage reference node. In another embodiment, the lighting system includes a transistor resistor circuit connected between the voltage regulator and the lighting module to control the current on the internal voltage reference node. Yet, in another embodiment, the driver module of the lighting system includes an electronic module, for example, a programmable Integrated Circuit (IC) to control the current on the internal voltage reference node.

[0011] In one embodiment, at higher temperatures, the controller is configured to decrease the output voltage of the voltage regulator by injecting the current into the internal voltage reference node.

[0012] In another embodiment, at lower temperatures, the controller is configured to increase the output voltage of the voltage regulator by extracting the current from the internal voltage reference node.

[0013] In one embodiment, the current varies linearly with respect to the voltage across the driver module. In another embodiment, the current varies non-linearly with respect to the voltage across the driver module. Yet, in another embodiment, the relationship between the current and the voltage across the driver module is defined by a polynomial function.

[0014] In accordance with the present subject matter, the output voltage of the voltage regulator is dynamically varied to provide effective trade-off between the LED polarization and the power dissipation in the driver module at different temperatures, thereby the power dissipation in the driver module is optimized at all temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] To complete the description and to provide a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the invention, which should not be construed as restricting the scope of the invention, but only as an example of how the invention can be carried out. The drawings comprise the following characteristics.

Figure 1 shows a schematic circuit diagram of a lighting system of a vehicle headlamp having a low-side LED driver, according to an embodiment of the present invention.

Figure 2 shows a schematic circuit diagram of a lighting system of a vehicle headlamp having a low-side LED driver and a transistor-resistor circuit, according to another embodiment of the present invention.

Figure 3 shows a schematic circuit diagram of a lighting system of a vehicle headlamp having a low-side LED driver having a programmable IC, according to another embodiment of the present invention.

Figure 4 shows a schematic circuit diagram of a lighting system of a vehicle headlamp having a high-side LED driver, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0017] As discussed above, a lighting system for a vehicle headlamp, for example, rear lamps, generally includes a lighting module having a plurality of Light Emitting Diodes (LEDs), a driver module connected to the lighting module to drive the LEDs, and a voltage regulator to provide supply voltage to the lighting module. The driver module can be either a low-side LED driver or a high-side LED driver based on its position in circuit of the lighting system. Constant supply voltage to the lighting module causes increased power dissipation in the driver module at high temperature due to forward voltage drift of the LEDs. On the other hand, to guarantee the correct polarization of LEDs, it is necessary to supply the sufficient voltage to the lighting module.

[0018] The present subject matter relates to dynamically adjusting the output voltage of the voltage regulator, i.e., supply voltage to the lighting module in order to optimize power dissipation in the driver module as well as to ensure correct polarization of LEDs at different temperatures.

[0019] Figure 1 shows a schematic circuit diagram of a lighting system of a vehicle headlamp having a driver module, according to an embodiment of the present invention. Embodiments of the present invention are explained with respect to a rear lamp of a vehicle. However, it should be noted that the present subject matter could also be implemented in frontal headlamps of the vehicle, without any limitation.

[0020] In particular, Figure 1 shows a lighting system 100 of a rear lamp of the vehicle. The lighting system 100 includes a voltage regulator 105, a lighting module 110, and a driver module 115. In an aspect, the voltage regulator 105 includes a DC-DC converter 120 and voltage resistor circuit 125 connected to the DC-DC converter 120. The voltage regulator 105 is configured to receive a battery voltage V_bat as input voltage and provides a regulated output voltage V_out to the lighting module 110. The lighting module 110 is electrically connected to the voltage regulator 105. The lighting module 110 includes a plurality of Light Emitting Diodes (LEDs), and anode end of the lighting module 110 is electrically connected to the voltage regulator 105. As show in the circuit, the driver module 115 is connected to a cathode end of the lighting module 110, and hence referred as a low side LED driver. In this embodiment, hereinafter, the driver module 115 and the low-side LED driver 115 may be used interchangeably.

[0021] The plurality of LEDs are mounted on a circuit board, for example, a Printed Circuit Board (PCB). The driver module 115 is configured to drive the LEDs in the lighting module 110.

[0022] The voltage regulator 105 of the lighting system 100 further includes an internal voltage reference node N with reference voltage V_ref. The voltage regulator 100 is configured to control the reference voltage V_ref at the internal voltage reference node N, and the output voltage V_out of the voltage regulator 105 is defined by resistor values R and R_L of the voltage resistor circuit 125 and current through the voltage resistor circuit 125. The output voltage V_out of the voltage regulator 105 is controlled by controlling the current through the voltage resistor circuit 125. Although, the Figure 1 shows the voltage resistor circuit 125 with two resistors R and R_L, it is understood to a person skilled in the art that the voltage resistor circuit 125 can include more than two resistors.

[0023] In an aspect, the voltage regulator 105 is a Low dropout device or a switched mode power supply. The voltage regulator 105 is configured to provide a sufficient voltage to turn on the LEDs at all temperatures. The minimum voltage required to turn ON the LEDs is referred as a forward drift voltage.

[0024] In general, the low-side LED driver 115 may include any general circuit for supplying a controlled LED driving current to the LEDs of the lighting module 110. In an embodiment, the low-side LED driver 115 includes a circuitry that can work in conjunction with the lighting module 110 to automatically self-adjust the level or magnitude of driving current to increase as the number of LEDs present in the lighting module 110 increases, and to decrease as the number of LEDs present in the lighting module 110 decreases. In general, the low-side LED driver 115 may include a rectifier, a switching device, a controller, a V_cc supply, a resistor divider network, a temperature sensor, and a voltage sensor (not shown in Figures).

[0025] As shown in Figure 1, the circuit of the lighting system 100 further includes a controllable current source 130 either to inject the current into the internal voltage reference node N or to extract the current from the voltage reference node N. In an embodiment, the controllable current source 130 is a voltage controlled current source (VCCS). The magnitude of current I_c to be injected into the voltage reference node N or to be extracted from the internal voltage reference node N of the voltage regulator 105 depends on magnitude of voltage V_driver across the low-side LED driver 115. By injecting/extracting the current into/from the internal voltage reference node N, the output voltage V_out of the voltage regulator 105 can be controlled dynamically. The controller (not shown in the Figures) of the low-side LED driver 115 dynamically controls the output voltage V_out of the voltage regulator 105 by controlling current on the internal voltage reference node N in relation to the voltage V_driver across the low-side LED driver 115.

[0026] The relation between the output voltage V_out of the voltage regulator 105, voltage V_LEDs across the lighting module 110 and the voltage V_driver across the low-side LED driver 115 is defined by a following equation.

[0027] In operation, at higher temperatures, the voltage V_LEDs across the LEDs decreases and therefore the voltage V_driver across the driver increases for the constant supply voltage from the voltage regulator 105. In an aspect, when the voltage V_driver across the low-side LED driver increases beyond a certain limit, the controller of the low-side LED driver 115 drives the controllable current source (VCCS) to inject the current into the internal voltage reference node N so as to optimize the power dissipation in the low-side LED driver 115. When V_LEDs decreases at higher temperatures, the output voltage V_out is controlled in such a way that V_out decreases to reduce or maintain constant voltage V_driver across the low-side LED driver 115. To reduce the output voltage V_out of the voltage regulator 105, the controller drives the controllable current source to inject the current into the internal voltage reference node N of the voltage regulator 105. By reducing or maintaining the constant voltage across the low-side LED driver 115, the power dissipation in the low-side LED driver 115 can be optimized.

[0028] On the other hand, at lower temperatures, the voltage V_LEDs across the LEDs increases and therefore the voltage V_driver across the driver decreases for the constant supply voltage from the voltage regulator 105. In an aspect, when the voltage V_LEDs across the low-side LED driver1 15 decreases, the controller of the low-side LED driver 115 drives the controllable current source to extract the current from the internal voltage reference node N. When V_LEDs increases at lower temperatures, the output voltage V_out is controlled in such a way that V_out increases to increase or maintain constant voltage V_driver across the low-side LED driver 115. To increase the output voltage V_out of the voltage regulator 105, the controller drives the controllable current source to extract the current from the internal voltage reference node N of the voltage regulator 105. Thereby, the power dissipation in the low-side LED driver 115 is optimized as well as the polarization of the LEDs is guaranteed. With the configuration shown in the Figure 1, the current varies linearly with respect to the voltage V_driver across the low-side LED driver 115.

[0029] In another embodiment, the current to be injected into the voltage reference node N or to be extracted from the voltage reference node N can be generated by using a transistor-resistor circuit, as shown in Figure 2. Figure 2 shows a schematic circuit diagram of a lighting system 200 of a vehicle headlamp having a low-side LED driver and a transistor-resistor circuit, according to another embodiment of the present invention. As can be seen from Figure 2, the transistor-resistor circuit 205 is connected between the output of the voltage regulator 105 and the anode end of the lighting module 110. With the configuration shown in the Figure 2, the current varies linearly with respect to the voltage V_driver across the low-side LED driver 115.

[0030] At higher temperatures, to reduce the output voltage V_out of the voltage regulator 105, the controller drives the transistor-resistor circuit 205 to inject the current into the internal voltage reference node N of the voltage regulator 105. By reducing or maintaining the constant voltage across the low-side LED driver 115, the power dissipation in the low-side LED driver 115 can be optimized.

[0031] At lower temperatures, to increase the output voltage V_out of the voltage regulator 105, the controller drives the transitor-resistor circuit 205 to extract the current from the internal voltage reference node N of the voltage regulator 105. Thereby, the power dissipation in the low-side LED driver 115 is optimized as well as the polarization of the LEDs is guaranteed.

[0032] Yet, in another embodiment, the low-side LED driver 115 includes an electronic module, for example, a programmable Integrated circuit (IC) to control the current, to be injected into the voltage reference node or to be extracted from the voltage reference node, in relation to the voltage V_LEDs across the low-side LED driver 115. Figure 3 shows a schematic circuit diagram of a lighting system of a vehicle headlamp having a low-side LED driver having a programmable IC, according to another embodiment of the present invention.

[0033] For example, the IC 305 includes a microprocessor programmed to control the amount of current to be injected or extracted based on sensed voltage or based on sensed temperature. In an example, the microprocessor is loaded with a look-up table including current values for corresponding voltages, and the controller accordingly injects/extracts the current into/from the internal voltage reference node N based on the sensed voltage V_driver across the low-side LED driver 115. In an embodiment, at higher temperatures, the programmable IC 305 is configured to inject the current into the internal voltage reference node N. In another embodiment, at lower temperatures, the programmable IC 305 is configured to extract the current from the internal voltage reference node N. Therefore, at different temperature levels, the power dissipation in the low-side LED driver 115 is optimized as well as the polarization of the LEDs is guaranteed. With the configuration shown in the Figure 3, the current can be varied either linearly or non-linearly with respect to the voltage V_driver across the low-side LED driver. Further, the relationship between the current and the voltage V_LEDs can also be defined by a polynomial function.

[0034] Figure 4 shows a schematic circuit diagram of a lighting system 400 of a vehicle headlamp having a high-side LED driver, according to an embodiment of the present invention. As previously mentioned, the driver module 115 of the lighting system can be positioned at either anode side or cathode side of the lighting module. In the circuit 400 shown in Figure 4, the driver module 115 is positioned at anode side of the lighting module 110, and hence referred as high-side LED driver 115. The circuit 400 shown in the Figure 4 also includes a voltage regulator 105 connected to the high-side LED driver 115, which is connected to the lighting module 110 to drive the LEDs of the lighting module 110.

[0035] The circuit 400 of the Figure 4 also includes a controllable current source to control the output voltage V_out of the voltage regulator 105 based on a voltage V_LEDs across the high-side LED driver 115. The implementation of this embodiment is shown by including a voltage controlled current source (VCCS) to dynamically control the output voltage V_out of the voltage regulator 105. However, in other embodiments, either the transistor-resistor circuit 205 shown in Figure 2 or a programmable IC 305 shown in Figure 3 can also be employed to control the current to be injected/extracted at the internal voltage reference node N in order to dynamically control the output voltage V_out of the voltage regulator 105.

[0036] Thus, by dynamically controlling the output voltage V_out of the voltage regulator 105, the power dissipation in the driver module 115 can be optimized as well as polarization of the LEDs in the lighting module 110 is guaranteed. This results in improved thermal performance of the lighting system 100, 200, 300 and 400.

Claims

1. A lighting system (100, 200,300, 400), comprises:

a lighting module (110) having a plurality of Light Emitting Diodes (LEDs);

a driver module (115) electrically connected to the lighting module (110), and configured to drive the lighting module (110);

a voltage regulator (105) to provide voltage V_out to the lighting module (110) and includes a voltage resistor circuit (125) having an internal voltage reference node N; and

a controller to dynamically control an output voltage V_out of the voltage regulator (105) by controlling current I_c on the internal voltage reference node N in relation to a voltage V_driver across the driver module (115).

2. The lighting system (100, 400) as claimed in claim 1, wherein the lighting system (100, 400) includes a voltage controlled current source (VCCS) to control the current on the internal voltage reference node N.

3. The lighting system (200) as claimed in claim 1, wherein the lighting system (200) includes a transistor resistor circuit (205) connected between the voltage regulator (105) and the lighting module (110) to control the current I_c on the internal voltage reference node N.

4. The lighting system (300) as claimed in claim 1, wherein the driver module (115) includes an electronic module (305) to control the current I_c through the internal voltage reference node N.

5. The lighting system (100, 200,300, 400) as claimed in claims 1 to 4, wherein the controller is configured to decrease the output voltage V_out of the voltage regulator (105) by injecting the current into the internal voltage reference node N.

6. The lighting system (100, 200,300, 400) as claimed in claims 1 to 4, wherein the controller is configured to increase the output voltage V_out of the voltage regulator (105) by extracting the current from the internal voltage reference node N.

7. The lighting system (100, 200,300,400) as claimed in claims 1 to 4, wherein the current varies linearly with the voltage V_driver across the driver module (115).

8. The lighting system (100, 200,300, 400) as claimed in claim 4, wherein the current Ic varies non-linearly with the voltage V_driver across the driver module (115).

9. The lighting system (100, 200,300) as claimed in claim 1, wherein the driver module (115) is a low-side LED driver electrically connected at a cathode end of the lighting module (110).

10. The lighting system (400) as claimed in claim 1, wherein the driver module (115) is a high-side LED driver electrically connected between the voltage regulator (105) and an anode end of the lighting module (110).

11. The lighting system (100, 200,300, 400) as claimed in claim 1, wherein the voltage regulator (105) is a Low Dropout device.

12. The lighting system (100, 200,300, 400) as claimed in claim 1, wherein the voltage regulator (105) is a switched-mode power supply.

Drawing