Protective lighting circuit
The lighting circuit addresses LED failure in parallel branches by using an imbalance detection circuit to maintain main light source intensity and prevent decorative branch interference, ensuring stable lighting.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- VALEO VISION SA
- Filing Date
- 2024-07-03
- Publication Date
- 2026-07-07
Smart Images
Figure 2026522524000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a protective lighting circuit for avoiding chain problems in case of failure of a lighting element. More specifically, it relates to a lighting circuit using LEDs, which has at least two parallel LED branches connected in series.
Background Art
[0002] Light emitting diodes (hereinafter referred to as LEDs) are commonly used for lighting. They can be mounted in series or in parallel, and an LED driver supplies a regulated current or a regulated voltage for supplying power to the LEDs. When an open circuit or a short circuit occurs due to a failure of an LED, the LED driver can monitor the voltage and / or current and adjust the output current or voltage to avoid more serious problems. Depending on the type of LED circuit and the type of LED driver, the LED driver can reduce the current or voltage, or simply switch off.
[0003] For decorative reasons, an LED circuit may include parallel LED branches connected in series to another LED branch, as shown in FIG. 1. In such a configuration, it becomes difficult for the LED driver to adjust the current or voltage to achieve an acceptable degradation mode for lighting. More specifically, when an LED in a parallel branch is open-circuited or short-circuited, all the current will flow through this branch or other parallel branches, resulting in an increase or decrease in the total voltage. Although the LED driver can detect this and reduce the current, in that case, the current in the series branch will be significantly reduced. If the series branch constitutes the main lighting source and the parallel branch is only for decoration, such a reduction in the light quantity is unacceptable.
Summary of the Invention
Means for Solving the Problems
[0004] The present invention provides a lighting circuit in which a first branch of a light-emitting diode (hereinafter referred to as LED) is connected in series with a second branch of an LED having at least two parallel LED branches. Each parallel LED branch has two ends, one of which is connected to a reference voltage. The lighting circuit further includes an imbalance detection circuit and a switch. The imbalance detection circuit is connected to the at least two parallel LED branches and measures the voltage and / or current difference between the parallel LED branches and activates a control signal if a difference is detected. The switch short-circuits the parallel LED branches when the control signal is activated.
[0005] With this configuration, the imbalance detection circuit can be configured to detect LED failures in the second LED branch.
[0006] An advantage is that the lighting circuit can be configured to keep the first LED branch on and switch off the second LED branch based on a detected LED failure.
[0007] According to a particular embodiment, the imbalance detection circuit may include at least two comparators and a control circuit. Each parallel LED branch may include pickup points located at the same position across all parallel LED branches. Each comparator can compare the voltage of one pickup point among at least two parallel LED branches with the voltage of another pickup point among at least two parallel LED branches. The output of the comparator is activated when the voltage of one parallel LED branch is higher than the voltage of another parallel LED branch, and the comparator is connected to each parallel LED branch. The control circuit is connected to the outputs of all comparators and provides a control signal at its output, activating the control signal when one of the comparator outputs is activated.
[0008] To compare currents, each parallel LED branch includes a sense resistor connected in series with the LEDs. The sense resistor has one terminal, corresponding to the end of the parallel LED branch, connected to a reference voltage, and the other terminal of the sense resistor connected to a pickup point.
[0009] To power the imbalance detection circuit and switch with the current flowing through the lighting circuit, each comparator may include a transistor whose base is connected to one pickup point of at least two parallel LED branches, whose emitter is connected to another pickup point of at least two parallel LED branches, and whose collector is connected to the control circuit as the output of the comparator. The sense resistor is determined to provide a voltage higher than the threshold voltage of the transistor in each comparator when the sense resistor is crossed by the current flowing through that parallel LED branch when that parallel LED branch is off.
[0010] The control circuit includes a first transistor and a second transistor, the base of the first transistor connected to the output of all comparators, the emitter of the first transistor connected to one end of at least two parallel LED branches, the collector of the first transistor connected to the base of the second transistor, the emitter of the second transistor connected to a reference voltage at the other end of at least two parallel LED branches, and the collector of the second transistor can be the output of the control circuit.
[0011] To reduce power consumption, the control circuit includes an input resistor connected in series with its input, and the sense resistor has a sufficiently high resistance so that its resistance is negligible compared to the input resistor.
[0012] In the case of a pulsed power supply, the control circuit includes a memory capacitive element connected between the collector of a first transistor and the ends connected to the reference voltages of at least two parallel LED branches, which are charged through the collector of the first transistor and discharged through the base of a second transistor.
[0013] When the lighting circuit is powered by an LED driver using pulse-width modulation (PWM) of current, the memory capacitive element is sized to maintain sufficient voltage at the base of the second transistor to keep the control signal active for at least one PWM cycle.
[0014] To reduce the size of the charging capacitance element, the control circuit includes a discharge resistor connected in series between the collector of the first transistor and the base of the second transistor, and the memory capacitance element is connected to the base of the second transistor through the discharge resistor.
[0015] Preferably, the switch includes a switching transistor whose base is connected to the output of the control circuit, whose emitter is connected to one end of a parallel LED branch, and whose collector is connected to a pickup point of at least two parallel LED branches.
[0016] According to a particular embodiment, the reference voltage is ground. The transistors of each comparator and the second transistor are NPN type transistors, while the first transistor and the switching transistor are PNP type transistors.
[0017] In a specific application to an automotive vehicle, the first LED branch corresponds to the light source for the position lights, and the second LED branch corresponds to the light source for backlighting the logo inside the automotive vehicle.
[0018] Another object of the present invention is an automotive lighting device including a position light and a light source for backlighting a logo mounted on an automobile vehicle. The automotive lighting device includes an LED driver and a lighting circuit according to the present invention, wherein a first LED branch corresponds to a position light and a second LED branch corresponds to a light source for backlighting a logo.
[0019] The present invention also relates to a motor vehicle comprising at least one position light and at least one logo attached near the position light. The motor vehicle includes at least one lighting circuit according to the present invention, wherein a first LED branch is the light source of one position light and a second LED branch is the light source for backlighting the logo.
Brief Description of the Drawings
[0020] [Figure 1] Showing an LED circuit including series and parallel connections of LEDs according to the prior art [Figure 2] Showing an application example of the motor vehicle of the present invention [Figure 3] Showing the LED circuit of FIG. 1 modified according to the present invention [Figure 4] Showing in detail the first embodiment of the present invention [Figure 5] Showing an improvement of the embodiment of FIG. 4 [Figure 6] Showing an improvement of the embodiment of FIG. 5 [Figure 7] Showing another improvement of the embodiment of FIG. 6 [Figure 8] Showing a modification of the embodiment of FIG. 5.
Modes for Carrying Out the Invention
[0021] For the sake of simplicity of the specifications, the same reference signs are used in a plurality of drawings to designate the same or similar elements. Also, elements already described in one drawing are not necessarily described in subsequent drawings.
[0022] As described above, the prior art corresponds to FIG. 1 and is improved by the present invention. FIG. 1 corresponds to an LED arrangement used for lighting and decorative reasons. The LED arrangement includes a first LED branch 20 connected to an LED driver 10, which is connected in series with a second LED branch 30 including two parallel LED branches 30A and 30B. Each of the LED branches 20, 30A, and 30B includes a plurality of LEDs connected in series, as is well known in the art. To adjust the power of the light, the LED driver 10 is preferably an adjusted current source. In an embodiment, the LED driver 10 is preferably an adjusted voltage source.
[0023] In this FIG. 1, the first LED branch 20 constitutes the main light source, and the second LED branch 30 constitutes the decorative light source. The main light source provides more important light than the decorative light source. Therefore, the LED driver 10 adjusts the current to correspond to the optimal current for the first LED branch 20. In the case of an LED failure, the LED driver can adjust the current so that the optimal current for the main light source is continued. In the case of an LED failure where the LED is converted into a short circuit or an open circuit, the LED driver 10 can compensate for the failure or switch off, as is well known in the art.
[0024] The failure of one LED in the first LED branch 20 is automatically compensated by the LED driver. When one LED fails and is converted into a short circuit, the LED driver 10 maintains the nominal current and reduces the voltage. When one LED fails and is converted into an open circuit, the LED driver 10 is switched off, and the LED circuit needs to be replaced or repaired.
[0025] In the event of a failure of one LED in parallel LED branch 30A or 30B, adjustment by the LED driver 10 can be used, but this is not the optimal solution. For example, if one LED in parallel LED branch 30A fails and is converted into a short circuit, the voltage in parallel LED branch 30A will drop instantaneously from the voltage of one LED, causing parallel LED branch 30B to turn off, and the current flowing through parallel LED branch 30A will double. As another example, if one LED in parallel LED branch 30A fails and is converted into an open circuit, the current in parallel LED branch 30A will stop instantaneously, and the current flowing through parallel LED branch 30B will double. Doubling the current in one of the parallel LED branches 30A or 30B will double the decorative light intensity (which is undesirable) and may also exceed the current range of the LEDs in parallel LED branches 30A and 30B, causing the remaining LEDs to be destroyed and increasing the risk of LED fire.
[0026] On the driver side, a failure in an LED within parallel LED branch 30A or 30B can be detected because it is a different voltage / current change than a failure in an LED from the first LED. However, the only adjustment that can be made is to reduce the current supplied by the LED driver 10. Reducing the current automatically reduces the current in the first LED branch 20, lowering the lighting power, which is unacceptable in the application example of the present invention shown in Figure 2.
[0027] Figure 2 shows an automobile vehicle 100 including a position light 110 using LED technology, the light source of the position light being a first LED branch 20. The automobile vehicle 100 includes a logo 120, which is a trademark corresponding to the name of the vehicle or the manufacturer's brand. For decorative reasons, the logo 120 is illuminated when the position light 110 is switched on. For this purpose, the logo 120 is made of a translucent material for backlighting. Since the logo 120 is illuminated simultaneously with the position light 110, the same LED driver 10 is used for economic reasons, and the backlighting of the logo is done by a second LED branch 30 located behind the logo 120. The use of parallel LED branches 30A and 30B is preferable because the illumination of the logo and the position light do not require the same light power. However, in this example, a failure of an LED in the second LED branch 30 must not interrupt or reduce the light generated by the first LED branch 20. The present invention provides a solution that keeps a first LED branch 20 corresponding to a position light in the ON state and switches the second LED branch 30 OFF in the event of an LED failure in the second LED branch 30. This solution is presented in relation to Figure 3. Figure 3 shows an LED arrangement in which an LED driver 10 is connected to the first LED branch 20 connected in series with two parallel LED branches 30A and 30B connected as shown in Figure 1, and further includes an imbalance detection circuit 40 and a switch 50. The imbalance detection circuit 40 is connected to the two parallel LED branches 30A and 30B to measure the voltage difference and / or current difference between the parallel LED branches 30A and 30B. The switch 50 has two terminals for bypassing the parallel LED branches 30A and 30B, respectively, connected to the two ends of the parallel LED branches 30A and 30B, and has a control terminal connected to the output of the detection circuit.
[0028] Typically, when all LEDs are functioning, the currents in the two parallel LED branches are approximately the same, and the voltages at the terminals of each LED or parallel LED branch 30A and 30B are approximately the same. In the event of an LED failure, only one of the two branches 30A and 30B is traversed by current, while the other is blocked. In one embodiment, the imbalance detection circuit 40 is configured to detect whether the currents are approximately the same at two common midpoints of the two parallel LED branches 30A and 30B. In another embodiment, the imbalance detection circuit 40 is configured to detect whether the voltages are approximately the same at two common midpoints of the two parallel LED branches 30A and 30B. In yet another embodiment, the imbalance detection circuit 40 is configured to detect whether both the current and voltages are approximately the same at two common midpoints of the two parallel LED branches 30A and 30B. If the current or voltages are approximately the same, the output of the imbalance detection circuit 40 is inactive, and the switch 50 is open. If the current or voltage is not the same, the output of the imbalance detection circuit 40 is activated, and the switch 50 is closed, bypassing the parallel LED branches 30A and 30B.
[0029] In the event of a failure of one LED in parallel LED branches 30A and 30B, the imbalance detection circuit 40 activates switch 50 to bypass parallel LED branches 30A and 30B. Such a bypass is detected by the LED driver 10, and voltage and current adjustments are made to maintain the nominal current in the first LED branch 20. In this case, the main light source is maintained optimally, and the decorative light source is switched off.
[0030] Next, a first detailed embodiment is disclosed in relation to Figure 4. In this first embodiment, each parallel LED branch 30A or 30B includes a pickup point located between the LEDs. Preferably, the pickup point is located in the center of each parallel LED branch 30A or 30B, but it can be located at any location having a voltage that depends on whether current flows through the parallel LED branch 30A or 30B. For the sake of simplicity of comparison, it is preferable that the pickup point is located at the same location in both parallel LED branches 30A and 30B.
[0031] In Figure 4, the imbalance detection circuit 40 includes two comparators 60A and 60B and a control circuit 70. Each comparator 60A or 60B includes a first input, a second input, and an output. The control circuit 70 includes a first input, a second input, and an output. The first input of comparator 60A is connected to the pickup point of parallel LED branch 30A, and the second input of comparator 60A is connected to the pickup point of parallel LED branch 30B. The first input of comparator 60B is connected to the pickup point of parallel LED branch 30B, and the second input of comparator 60B is connected to the pickup point of parallel LED branch 30A. The outputs of comparators 60A and 60B are connected to the first and second inputs of the control circuit 70, respectively. The output of the control circuit 70 is connected to the control terminal of switch 50.
[0032] Comparators 60A and 60B can be operational amplifiers used in comparator mode, hysteresis comparators, Schmitt triggers, or any other type of circuit that compares a first voltage to another voltage and activates an output if the voltage of the first input is higher than the voltage of the second input. Thus, each comparator 60A or 60B compares the voltage at one pickup point of the two parallel LED branches 30A and 30B to the voltage at the other pickup point of the two parallel LED branches 30B or 30A, and provides an activated output signal if the voltage at one pickup point of the two parallel LED branches 30A and 30B is higher than the voltage at the other pickup point of the two parallel LED branches 30B or 30A.
[0033] The control circuit 70 is a logic circuit with memory function. After power is turned on to the control circuit, the output of the control circuit 70 is inactive, and the switch 50 remains open. When one of the first and second inputs of the control circuit 70 receives an activation signal, the output of the control circuit 70 is activated, and the switch 50 is closed and maintained.
[0034] The circuit in Figure 4 uses a comparator circuit and a logic control circuit, and requires a power supply to function, and a power supply near the parallel LED branch is required, which is impractical. The circuit in Figure 5 has the same functionality as Figures 2 and 3, but shows a second embodiment in which the power is directly supplied by the current supplied to the LEDs.
[0035] The circuit in Figure 5 compares the current between two parallel LED branches 30A and 30B. To measure the current, each of the parallel LED branches 30A and 30B includes sense resistors 31A and 31B connected in series with the LEDs. Sense resistors 31A and 31B are identical and located at the same ends of the parallel LED branches 30A and 30B. One terminal of each sense resistor 31A and 31B is connected to the ground voltage, and the other terminal of each sense resistor 31A and 31B is connected to the pickup point. Thus, the sense resistors convert the current into voltage, which can be compared by any type of comparator.
[0036] The example in Figure 5 provides an improvement over the circuit in Figure 4, which can function with only an LED supply. Each of the comparators 60A and 60B includes a transistor 61A or 61B, which is, for example, an NPN bipolar transistor. The base of each transistor 61A or 61B corresponds to the first input of each comparator 60A or 60B. The emitter of each transistor 61A or 61B corresponds to the second input of each comparator 60A or 60B. The collector of each transistor 61A or 61B corresponds to the output of each comparator 60A or 60B. In order to trigger transistors 61A and 61B, the difference between the pickup points of the two parallel LED branches must be higher than the trigger voltage between the base and emitter of each transistor 61A or 61B. The sense resistors 31A and 31B have sufficiently high resistance to provide a voltage higher than the threshold voltage of transistors 61A and 61B when crossed by the maximum current flowing through the parallel LED branches 30A and 30B in the event of a failure, and this maximum current corresponds to the nominal current of the first LED branch 20.
[0037] In Figure 5, the control circuit 70 includes a first transistor 71 and a second transistor 72. The first transistor 71 is, for example, a PNP bipolar transistor, and the second transistor is, for example, an NPN bipolar transistor. The base of the first transistor 71 is connected to the collectors of transistors 61A and 61B. The emitter of the first transistor 71 is connected to the ends of the two parallel LED branches 30A and 30B opposite the ground voltage. The collector of the first transistor 71 is connected to the base of the second transistor 72. The emitter of the second transistor 72 is connected to the ground voltage. The collector of the second transistor 72 corresponds to the output of the control circuit 70.
[0038] Switch 50 includes a switching transistor 51, which is, for example, a PNP bipolar transistor. The base of the switching transistor 51 is connected to the collector of the second transistor 72. The emitter of the switching transistor 51 is connected to the ends of two parallel LED branches 30A and 30B opposite to the ground voltage. The collector of the switching transistor 51 is connected to the pickup point of one of the two parallel LED branches, 30B.
[0039] Under normal use (i.e., no LED failures), the currents in the two parallel LED branches 30A and 30B are the same, causing the same voltage at the pickup points of each parallel LED branch 30A and 30B. Transistors 61A and 61B are blocked, and no current is drawn to the base of the first transistor 71, thus blocking transistor 71. Because the collector of the first transistor 71 has high impedance, no voltage is applied to the base of the second transistor 72, thus blocking it as well. Because the collector of the second transistor 72 has high impedance, the switching transistor 51 is blocked.
[0040] As mentioned above, in the event of an LED failure, for example, the current in parallel LED branch 30B stops, and the current in parallel LED branch 30A doubles to reach the nominal current of the first LED branch 20. Transistor 61A turns on, drawing current to the base of the first transistor 71, which also turns on. When the first transistor 71 turns on, the second transistor 72 turns on, turning on the switching transistor 51. When the switching transistor 51 turns on, the voltage at the ends of parallel LED branches 30A and 30B is not sufficient to maintain the on state of the LEDs. Therefore, all the nominal current flows through transistor 51 and sense resistor 31B. Transistor 61A is blocked, and transistor 61B turns on, maintaining the on state of the first transistor 71, the second transistor 72, and the switching transistor 51.
[0041] In the event of an LED failure, all nominal current is diverted through all transistors and sense resistor 31B, and the current balance between the transistors is automatically achieved. The power consumed is equal to the nominal current multiplied by the voltage at the transistor's current balance. However, some of the power is consumed by the sense resistors 31A and 31B. In particular, the size of the sense resistors 31A and 31B is set such that when crossed by the nominal current, they provide a voltage higher than the threshold voltage of transistors 61A and 61B. However, this voltage must be higher than the sum of the voltage across sense resistor 31A or 31B crossed by the emitter current of transistor 61A or 61B when transistor 61A or 61B is turned on, and the threshold voltage of transistor 61A or 61B. One solution to reduce this voltage is to reduce the emitter current when transistors 61A and 61B are turned on. For this reason, the control circuit 70 may have an input resistor 73 connected in series with its input between the base of the first transistor 71 and the collectors of transistors 61A and 61B. Such an input resistance 73 reduces the current flowing through the sense resistor 31B, and preferably the resistance of the input resistance 73 is sufficiently high so that it is negligible compared to the resistances of the sense resistors 31A and 31B.
[0042] The use of input resistor 73 also has the advantage of reducing the base current of the first transistor 71 and thus reducing the power consumed by the first and second transistors 71 and 72, and allows for the selection of smaller transistors than the switching transistor 51.
[0043] As those skilled in the art will understand, there is a switching time required to bypass parallel LED branches 30A and 30B. This switching time is not critical when the LED driver provides pure DC current. However, it is well known that pulse signals are used to facilitate current and / or voltage regulation by the LED driver. In the case of pulse signals, the switching time is repeated with each pulse, and such repetitions cause repeated overcurrents in the LEDs of parallel LED branches 30A or 30B through which current flows. To prevent such repetitions, Figure 6 proposes a modification of the circuit in Figure 5 that stores LED failures between pulses of the power supply.
[0044] The circuit in Figure 6 replicates all the elements of Figure 5. Furthermore, the control circuit 70 includes a memory capacitor 74 connected between the collector of the first transistor 71 and the ground voltage, which is charged through the collector of the first transistor 71 and discharged through the base of the second transistor 72. Such a memory capacitor 74 can maintain a voltage at the base of the second transistor 72 between two pulses of current supply, thereby keeping the switching transistor 51 on. To use a small memory capacitor 74, the control circuit 70 includes a discharge resistor 75 connected in series between the collector of the first transistor 71 and the base of the second transistor 72, through which the memory capacitor 74 is connected to the base of the second transistor 72. Because the memory capacitor 74 is discharged through the discharge resistor 75, it becomes easy to adjust the capacitance value of the memory capacitor 74 to match the time period of the power supply pulse.
[0045] As mentioned above, if an LED failure causes the parallel LED branch 30B to turn off, transistor 61A causes switching transistor 51 to switch, but transistor 61B is charged to maintain the ON state of switching transistor 51. This switching from transistor 61A to transistor 61B can cause a problem commonly known as a "glitch," which depends on the switching time of the transistors. To avoid this problem, an improvement related to Figure 7 is provided based on the circuit in Figure 6.
[0046] Each comparator 60A or 60B may include stabilizing resistors R1 and R2 and a stabilizing capacitor C1. Stabilizing resistors R1 and C1 are connected in parallel to the base and emitter of transistors 61A and 61B. Stabilizing resistor R2 is connected between the base of transistor 61A, or 61B respectively, and the pickup point of the parallel LED branch 30B, or 30A respectively. The control circuit 70 may include stabilizing resistors R3 and R4 and stabilizing capacitors C3 and C4. Stabilizing resistor R3 and C3 are connected in parallel to the base and emitter of the first transistor 71. Stabilizing resistor R4 and C4 are connected in parallel to the base and emitter of the second transistor 72. The switch 50 may include stabilizing resistors R5 and R6 and a stabilizing capacitor C5. The stabilizing resistors R1, R2, R3, R4, R5, and R6 and the stabilizing capacitors C1, C3, C4, and C5 add switching delays to transistors 61A, 61B, 71, 72, and 51 to prevent potential glitches during the propagation state of the transistors, and are used in particular when switching transistor 51 turns on and changes the polarization voltage of all other transistors 61A, 61B, 71, and 72.
[0047] The control circuit 70 may include a charging resistor 76 connected in series between the collector of the first transistor 71 and the discharge resistor 75, and a memory capacitor element 74 connected to the node between the charging resistor 76 and the discharge resistor 75. The memory capacitor element 74 is charged through the charging resistor 76, preventing a sudden abnormal increase in voltage between the switching of the first transistor 71 and the switching of the switching transistor 51.
[0048] The present invention describes an LED circuit having two parallel LED branches 30A and 30B, but it can be used with more parallel LED branches, even though increasing the number of parallel LED branches reduces the overcurrent of other parallel LED branches in the event of an LED failure. A variation of the LED arrangement according to the present invention is shown in Figure 8, illustrating how to adapt the invention to more than two parallel LED branches. Figure 8 differs from Figure 5 in that a third parallel LED branch 30C and a third comparator 60C are added. Comparators 60A, 60B, and 60C are connected in a ring to the parallel LED branches 30A, 30B, and 30C. That is, the first inputs of comparators 60A, 60B, and 60C are connected to the pickup points of the parallel LED branches 30A, 30B, and 30C, respectively, and the second inputs of comparators 60A, 60B, and 60C are connected to the pickup points of the parallel LED branches 30C, 30A, and 30B, respectively. Those skilled in the art can observe that only one additional comparator 60X is needed for each additional parallel LED branch 30X.
[0049] Those skilled in the art can create other circuit variations without departing from the scope of the present invention. The improvements shown in Figures 6 and 7 can be used in the arrangement of Figure 8. The circuits in Figures 4 to 8 show preferred circuit embodiments using bipolar transistors, and those skilled in the art can combine comparators 60A, 60B and 60C with another control circuit 70. Also, all NPN transistors can be replaced with PNP transistors, and PNP transistors can be replaced with NPN transistors, in which case the resistors are located at the ends corresponding to the highest voltage of the parallel LED branches 30A, 30B and 30C. The switching transistor 51 can also be replaced with a MOSFET. Furthermore, although the example of use related to Figure 2 relates to the position lights of automotive headlights, those skilled in the art will understand that the present invention is not limited to headlights or taillights or turn signals or position lights or daytime running lamps, and is not limited to automotive applications.
Claims
1. A lighting circuit in which a first branch (20) of a light-emitting diode (hereinafter referred to as LED) is connected in series with a second branch (30) of an LED having at least two parallel LED branches (30A, 30B, 30C), wherein each parallel LED branch has two ends, and one of the ends is connected to a reference voltage, and the lighting circuit further comprises: An imbalance detection circuit (40) is connected to at least two parallel LED branches (30A, 30B, 30C) and measures the voltage and / or current difference between the parallel LED branches (30A, 30B, 30C), and activates a control signal when a difference is detected. A switch (50) for short-circuiting the parallel LED branches (30A, 30B, 30C) when the aforementioned control signal is activated, A lighting circuit including a light.
2. The imbalance detection circuit (40) is configured to detect LED failures in the second LED branch (30). The lighting circuit according to claim 1.
3. The system is configured to keep the first LED branch (20) in the ON state and to switch the second LED branch (30) off based on a detected LED failure. The lighting circuit according to claim 2.
4. The imbalance detection circuit (40) includes at least two comparators (60A, 60B, 60C) and a control circuit (70), where each parallel LED branch (30A, 30B, 30C) includes a pickup point located at the same position in all parallel LED branches (30A, 30B, 30C), and each comparator (60A, 60B, 60C) measures the voltage of one pickup point among the at least two parallel LED branches (30A, 30B, 30C) to measure the voltage of another pickup point among the at least two parallel LED branches (30A, 30B, 30C). The control circuit (70) is connected to the outputs of all the comparators (60A, 60B, 60C) and provides a control signal that is activated when the output of the comparator (60A, 60B, 60C) is higher than the output of another parallel LED branch (30C, 30A, 30B) when the output of the comparator (60A, 60B, 60C) is higher than the output of another parallel LED branch (30C, 30A, 30B), the comparators are connected to each of the parallel LED branches (30A, 30B, 30C), and the control circuit (70) is connected to the outputs of all the comparators (60A, 60B, 60C), and provides a control signal that is activated when one of the outputs of the comparators (60A, 60B, 60C) is activated. A lighting circuit according to any one of claims 1 to 3.
5. Each parallel LED branch (30A, 30B, 30C) includes a sense resistor (31A, 31B, 31C) connected in series with the LED, wherein one terminal of the sense resistor (31A, 31B, 31C) corresponding to the end of the parallel LED branch (30A, 30B, 30C) is connected to the reference voltage, and the other terminals of the sense resistor (31A, 31B, 31C) are connected to the pickup point. The lighting circuit according to claim 4.
6. Each comparator (60A, 60B, 60C) includes a transistor (61A, 61B, 61C) connected to the control circuit, with its base connected to one pickup point of the at least two parallel LED branches (30A, 30B, 30C) and its emitter connected to another pickup point of the at least two parallel LED branches (30A, 30B, 30C), the collector of which becomes the output of the comparator (60A, 60B, 60C), and the sense resistor (31A, 31B, 31C) having a resistance determined to provide a voltage higher than the threshold voltage of the transistor (61A, 61B, 61C) of each comparator (60A, 60B, 60C) when the sense resistor (31A, 31B, 31C) is crossed by the current flowing through that parallel LED branch (30A, 30B, 30C) when one of the parallel LED branches is off. The lighting circuit according to claim 5.
7. The control circuit (70) includes a first transistor (71) and a second transistor (72), wherein the base of the first transistor (71) is connected to the output of all comparators (60A, 60B, 60C), the emitter of the first transistor (71) is connected to one end of the at least two parallel LED branches (30A, 30B, 30C), the collector of the first transistor (71) is connected to the base of the second transistor (72), the emitter of the second transistor (72) is connected to the reference voltage at the other end of the at least two parallel LED branches (30A, 30B, 30C), and the collector of the second transistor (72) is the output of the control circuit (70). A lighting circuit according to any one of claims 4 to 6.
8. The control circuit (70) includes an input resistor (73) connected in series with its input, and the sense resistors (31A, 31B, 31C) have sufficiently high resistances so that their resistances are negligible compared to the resistances of the input resistor (73). The lighting circuit according to claim 6 or claim 5 and claim 7.
9. The control circuit (70) includes a memory capacitive element (74) connected between the collector of the first transistor (71) and the ends of the at least two parallel LED branches (30A, 30B, 30C) connected to the reference voltage, which is charged through the collector of the first transistor (71) and discharged through the base of the second transistor (72). The lighting circuit according to claim 7 or claim 8.
10. The current is supplied by an LED driver (10) using pulse-width modulation (PWM), and the size of the memory capacitive element (74) is determined to maintain a sufficient voltage at the base of the second transistor (72) to keep the control signal activated for at least one PWM cycle. The lighting circuit according to claim 9.
11. The control circuit (70) includes a discharge resistor (75) connected in series between the collector of the first transistor (71) and the base of the second transistor (72), and the memory capacitance element (74) is connected to the base of the second transistor (72) through the discharge resistor (75). The lighting circuit according to claim 9 or claim 10.
12. A lighting circuit according to any one of claims 5 to 11, wherein the switch (50) includes a switching transistor (51) whose base is connected to the output of the control circuit (70), whose emitter is connected to one end of the parallel LED branches (30A, 30B, 30C), and whose collector is connected to one pickup point of the at least two parallel LED branches (30A, 30B, 30C), A lighting circuit according to any one of claims 5 to 11.
13. The reference voltage is ground, the transistors (61A, 61B, 61C) of each comparator (60A, 60B, 60C) and the second transistor (72) are NPN type transistors, and the first transistor (71) and the switching transistor (51) are PNP type transistors. A lighting circuit according to any one of claims 5 to 12.
14. The first LED branch (20) corresponds to the light source for the position light, and the second LED branch (30) corresponds to the light source for backlighting the logo inside the automobile vehicle. A lighting circuit according to any one of claims 1 to 13.
15. Automotive lighting device including a position light and a light source for backlighting a logo mounted on an automobile vehicle, wherein the automotive lighting device includes an LED driver and a lighting circuit according to any one of claims 1 to 13, the first LED branch corresponding to the position light and the second LED branch corresponding to the light source for backlighting the logo.