Light source module and lighting circuit

Abstract

The present invention provides a light source module and a lighting circuit. Provides a rear identification lamp capable of improving safety. An LED string (502) includes four LEDs (504_1 to 504_4) connected in series. An LED driving circuit (610) receives a battery voltage (V IN ), supplying a current stabilized to a target current (I REF ) driving current (I LED The bypass circuit (620) is connected in parallel with the bypassed portion (503) including two adjacent LEDs (504_3, 504_4) in the LED string (502), and is fed with a voltage equal to the battery voltage (V IN ) corresponding to the bypass current (I BYPASS ).

Description

Technical Field

[0001] The present invention relates to a lamp used in a vehicle such as an automobile. Background Art

[0002] As a light source used in vehicle lamps, bulbs have been often used in the past, but in recent years, semiconductor light sources such as LEDs (light emitting diodes) have been widely used.

[0003] Figure 1 1 is a block diagram of a conventional vehicle lamp 1. The vehicle lamp 1 receives a DC voltage (input voltage V IN ). The LED string (LED strip) 10 includes a plurality of n LEDs 12 connected in series. The brightness of the LED string 10 depends on the driving current I flowing therein. LED The lighting circuit 20 includes an LED driving circuit 22, which drives the driving current I LED Stabilize to the target value I corresponding to the target brightness REF .

[0004] When the current flowing through LED 12 is stabilized to the target amount I REF The driving current I LED When the forward voltage is set to Vf0, the voltage between the two ends of the LED string 10 (called the minimum lighting voltage) is V MIN = Vf0×n. When n=3, V MIN ≈11V. In other words, if the output voltage V OUT Lower than the minimum lighting voltage V MIN , then the driving current I LED Unable to maintain target amount I REF , multiple LEDs 12 are off.

[0005] In the LED sockets sold as replacements for conventional automobile bulbs, the LED drive circuit 22 is formed of a constant current series regulator or a constant current output buck converter or resistor because of the requirement for low cost. In this case, the output voltage V of the LED drive circuit 22 is OUT Lower than the input voltage V IN . Input voltage V IN When the battery is fully charged, it is 13V. As it discharges, it is not uncommon for it to drop below 10V. Therefore, if the battery voltage V BAT Reduced (called low voltage state), the output voltage V OUT Lower than the minimum lighting voltage V MIN In this case, LED 12 goes out.

[0006] In order to prevent the LED string 10 from turning off in a low voltage state, a bypass switch 24 and a bypass control circuit 26 are provided. The bypass switch 24 is connected in parallel to one LED 12_n on the lowest potential side. The bypass control circuit 26 IN Below a certain threshold V TH When the voltage is low, the bypass switch 24 is turned on. In this state, the minimum lighting voltage V MIN =Vf0×(n-1), maintain V IN >V MIN That is, the remaining LEDs 12_1 to 12_(n-1) can be kept lit at the expense of the LED 12_n being turned off.

[0007] Patent Document 1: Japanese Patent Publication No. 2016-197711 Summary of the invention

[0008] The inventors of the present invention Figure 1 The lighting circuit 20 is applied to rear marker lights such as brake lights, tail lights, and rear fog lights. The following problems are found. When the voltage drop of the red LED is set to 2.4V and n=4, V MIN =2.4V×4=9.6V. When the forward voltage of the reverse connection protection diode 30 is set to 0.8V, the threshold voltage V TH becomes 9.6V+0.8V+α. When the margin α is set to 1V, it becomes V TH =11.4V. Therefore, at V IN When the voltage is greater than 11.4V, the LED string 10 lights up normally.

[0009] In addition, if V BAT If the voltage is lower than 11.4V, the current flows to the bypass switch 24, and the LED 12_4 on the lowest potential side is bypassed. The minimum lighting voltage at this time is V MIN =1.8V×3=5.4V. Therefore, the LED string 10 can be kept lit until V BAT =5.4V+0.8V=around 6.2V.

[0010] In recent years, in order to improve fuel efficiency, the number of vehicles equipped with an idling stop function has been increasing. The brake lights need to be turned on when the vehicle is parked, in other words, when idling stop occurs. During idling stop, the AC generator stops, so if the load on the battery increases, the battery voltage drops significantly. For example, during idling stop, if the air conditioner is activated or the steering device is operated and the engine is restarted, the load current of the battery 2 increases. As a result, when the battery voltage V BAT Lower than the minimum lighting voltage V MIN=6.2V, the LED string 10 turns off. If the brake lights are off, the following vehicle will mistakenly believe that the preceding vehicle has started.

[0011] The present invention has been made in view of such a problem, and an object of the present invention is to provide a rear marker lamp capable of improving safety.

[0012] One embodiment of the present invention relates to a light source module. The light source module comprises: an LED string including four LEDs (light emitting diodes) connected in series; an LED driving circuit receiving a battery voltage and supplying a driving current stabilized to a target current to the LED string; and a bypass circuit provided in parallel with a bypassed portion including two adjacent LEDs in the LED string and receiving a bypass current corresponding to the battery voltage.

[0013] Another embodiment of the present invention relates to a lighting circuit for driving an LED string including four LEDs (light emitting diodes) connected in series. The lighting circuit includes: an LED driving circuit that receives a battery voltage and supplies a driving current stabilized to a target current to the LED string; and a bypass circuit that is provided in parallel with a bypassed portion including two adjacent LEDs in the LED string and receives a bypass current corresponding to the battery voltage.

[0014] Optional combinations of the above-described constituent elements, and configurations in which constituent elements of the present invention and methods, apparatuses, systems, and the like are replaced with each other may also be additional modes of the present invention.

[0015] According to one aspect of the present invention, safety can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a block diagram of a conventional vehicle lamp.

[0017] Figure 2 This is a block diagram of a vehicle lamp including a lighting circuit according to an embodiment.

[0018] Figure 3 It is a diagram for explaining the operation of the light source module.

[0019] Figure 4 (a) is a diagram showing an example of the input voltage dependency of the emitted light amount. Figure 4 (b) is a diagram showing an example of input-output characteristics of the bypass circuit.

[0020] Figure 5 (a) Figure 5 (b) is a circuit diagram showing a configuration example of a bypass circuit.

[0021] Figure 6 (a)~ Figure 6 (d) is a diagram showing an LED socket as an example of a vehicle lamp. DETAILED DESCRIPTION

[0022] (Overview of Embodiments)

[0023] One embodiment disclosed in this specification relates to a light source module. The light source module comprises: an LED string including four LEDs (light emitting diodes) connected in series; an LED driving circuit receiving a battery voltage and supplying a driving current stabilized to a target current to the LED string; and a bypass circuit arranged in parallel with a bypassed portion including two adjacent LEDs in the LED string and receiving a bypass current corresponding to the battery voltage.

[0024] According to this structure, when the battery voltage drops, the two LEDs are bypassed, so even when the battery load increases during idling stop, the LED string can be prevented from being extinguished. Therefore, when the light source module is used for the rear marker light, it can be prevented that the LED string is accidentally extinguished during parking of the vehicle and a wrong message is transmitted to the following vehicle.

[0025] The light source module is also provided with a disconnection detection circuit, which disables the bypass circuit when a disconnection of the bypassed part is detected. In the case of a disconnection of the bypassed part, if the current bypass is performed in a reduced voltage state, an undesirable situation occurs in which the LED string is turned off under a normal battery voltage but is turned on under a reduced voltage state. Therefore, by providing a disconnection detection circuit, the LED string can be turned off regardless of the voltage level of the battery voltage when a disconnection occurs.

[0026] The disconnection detection circuit may determine that the bypassed portion is disconnected when the voltage drop of the bypassed portion exceeds Vf×2.

[0027] The slope of the bypass current with respect to the battery voltage can be set so that the slope of the emission light amount of the four LEDs with respect to the change in the battery voltage is less than 5% / 0.1 V. This makes it difficult for people to feel the change in the emission light amount caused by the short-term change in the battery voltage.

[0028] (Implementation Method)

[0029] Hereinafter, the present invention will be described with reference to the accompanying drawings based on preferred embodiments. The same or equivalent components, parts, and processes shown in the respective drawings are marked with the same reference numerals, and repeated descriptions are appropriately omitted. In addition, the embodiments do not limit the invention but are merely illustrative, and all the features and combinations thereof described in the embodiments are not necessarily the essence of the invention.

[0030] In this specification, "the state in which component A is connected to component B" includes, in addition to the case in which component A and component B are directly physically connected, a case in which component A and component B are indirectly connected through other components that do not substantially affect the above-mentioned electrical connection state or impair the functions and effects of their combination.

[0031] Similarly, for the state in which "component C is arranged between component A and component B", in addition to the case in which component A and component C or component B and component C are directly connected, it also includes the case in which they are indirectly connected through other components that do not have a substantial impact on the above-mentioned electrical connection state or do not damage the functions and effects achieved by their combination.

[0032] In this specification, reference numerals attached to electrical signals such as voltage signals and current signals, or circuit elements such as resistors and capacitors, represent voltage values, current values, or resistance values ​​and capacitance values, respectively, as required.

[0033] Figure 2 4 is a block diagram of a vehicle lamp 500 including a lighting circuit 600 according to an embodiment. A DC voltage (input voltage) V is supplied from a battery 2 via a switch 4 to the vehicle lamp 500. IN The vehicle lamp 500 includes an LED string 502 and a lighting circuit 600. The LED string 502 includes four LEDs 504_1 to 504_4 connected in series. The vehicle lamp 500 is, for example, a rear marker lamp such as a brake lamp, a tail lamp, or a rear fog lamp, and the LED string 502 includes red LEDs.

[0034] A preferred embodiment of the vehicle lamp 500 is a light source module in which the LED string 502 and the lighting circuit 600 are housed in one package. For example, the vehicle lamp 500 is an LED socket having a shape that can be detached from a lamp body (not shown) like a conventional automobile light bulb. The LED socket is not only required to have a long life, but also to be low-cost because it is a consumable.

[0035] The lighting circuit 600 includes a diode 602 for reverse connection protection, an LED driving circuit 610 , a bypass circuit 620 , and a disconnection detection circuit 630 .

[0036] The LED driving circuit 610 receives an input voltage V via a reverse connection protection diode 602. IN , supplying the LED string 502 with a stable target amount I REF The driving current I LED The LED driving circuit 610 can be composed of any one of (i) a constant current linear regulator, (ii) a buck switching converter with a constant current output, or (iii) a combination of a buck switching converter with a constant voltage output and a constant current circuit, or (iv) a resistor.

[0037] The bypass circuit 620 is connected in parallel with two (504_3, 504_4) of the plurality of LEDs 504_1 to 504_4. The LEDs 504_3 and 504_504_4 are also referred to as bypassed portions 503. The bypass circuit 620 can be switched between an effective state and an ineffective state. In the effective state, the bypass circuit 620 receives a voltage V IN The corresponding bypass current I BYPASS . The bypass current I BYPASS When the current flowing through the bypassed portion 503 becomes I LED -I BYPASS . in I BYPASS = 0, the bypassed portion 503 emits light with the same brightness as the remaining LEDs 504_1 and 504_2. BYPASS =I LED When , the bypassed part 503 is extinguished.

[0038] The disconnection detection circuit 630 is configured to detect disconnection of the bypassed portion 503. When the disconnection detection circuit 630 detects disconnection of the bypassed portion 503, the bypass circuit 620 is disabled. In the disabled state of the bypass circuit 620, the bypass current I BYPASS Becomes 0 and no current can be input.

[0039] The method of disconnection detection in the disconnection detection circuit 630 is not particularly limited. For example, the voltage drop of the bypassed portion 503, that is, the voltage V of the node A may be detected. A When the threshold voltage Vf×2 is exceeded, it is determined that the bypassed portion 503 has a disconnection fault. Vf is the forward voltage of the LED string 502.

[0040] For example, the disconnection detection circuit 630 may also include a circuit that compares the voltage at the node A with the threshold voltage V OPEN The voltage comparison circuit can also be used to compare the threshold voltage V OPEN Set to be slightly higher than Vf×2.

[0041] Figure 3 1 is a diagram for explaining the operation of the vehicle lamp 500. The horizontal axis represents the input voltage V IN , the vertical axis represents the light intensity (relative value) of LED string 502. Figure 1 This is the action when the bypassed part is set to 1.

[0042] In the case where the bypassed part is 1, when the input voltage V IN When the input voltage V1 is lower than a certain value, one of the four LEDs is bypassed by the bypass circuit, so the light quantity decreases toward 75%. Then, when the input voltage V INWhen the voltage V2 is lower than a certain value (for example, 1.8V×3+0.8V=6.2V), the light amount drops to zero.

[0043] On the other hand, according to this embodiment, when the input voltage V IN When the voltage is lower than V1, the light intensity decreases toward 50%, but even if the input voltage V IN If the input voltage V IN When the voltage is further reduced to V3, the light amount becomes 0%.

[0044] The above is the operation of the vehicle lamp 500. According to the vehicle lamp 500, when the battery voltage V BAT When lowered, since the two LEDs 504_3 and 504_4 are bypassed, even when the battery load increases during idling stop, the LED string 502 can be prevented from being turned off. Therefore, when the vehicle lamp 500 is used as a rear marker lamp, the LED string 502 can be prevented from being accidentally turned off during parking of the vehicle and transmitting an erroneous message to the following vehicle.

[0045] Next, the operation of the disconnection detection circuit 630 will be described. BAT In the state, become I BYPASS = 0. At this time, if the bypassed part 503 is disconnected, the current I LED No current flows through the LED string 502, and the LED string 502 turns off. On the other hand, if the bypassed portion 503 is disconnected, the battery voltage V BAT (Input voltage V IN ) is reduced, the broken part, i.e. the bypassed part 503, is bypassed through the bypass circuit 620, and the LED string 502 is lit, which is not preferred.

[0046] In this embodiment, a disconnection detection circuit 630 is provided, and when a disconnection occurs, the bypass circuit 620 is disabled and the circuit is turned on. BYPASS =0, regardless of the battery voltage V BAT (V IN ) voltage level, the LED string will be turned off.

[0047] The bypass current I BYPASS Relative to the battery voltage V BAT When the slope of the change is large, the battery voltage V BAT A small change in the bypass current I BYPASS The slope of the light emission intensity of the four LEDs is designed to be less than 5% / 0.1 V with respect to the change in the battery voltage. This makes it difficult for people to feel the change in the light intensity caused by the short-term change in the battery voltage.

[0048] Figure 4 (a) is a diagram showing an example of the input voltage dependency of the emitted light amount. Figure 4 (b) is a diagram showing an example of input-output characteristics of the bypass circuit 620. Figure 4 In (a) and (b), the horizontal axis is the input voltage V IN .also, Figure 4 The vertical axis of (a) represents the value obtained by normalizing the emission light amounts Iv of the four LEDs with the maximum light amount being 100%. Figure 4 The vertical axis of (b) represents the bypass current I BYPASS With driving current I LED The target amount I REF is the value normalized to 100%. In this example, IN >10.3V I BYPASS = 0, the emitted light amount Iv is 100%. IN Bypass current I when <10.3V BYPASS Increases, current bypass begins, and the emitted light quantity Iv decreases at a gradient of 5% / 0.1V or less. Then, when the input voltage V IN =8.8V, I BYPASS =100%, the emitted light amount Iv decreases to 50%.

[0049] Figure 5 (a) and (b) are circuit diagrams showing configuration examples of the bypass circuit 620. Figure 5 The bypass circuit 620 of (a) includes a voltage comparison circuit 622 and a transistor (switch) 624. The voltage comparison circuit 622 converts the input voltage V IN With the threshold voltage V TH For comparison, at V IN <V TH When the input voltage V IN The gate voltage of transistor 624 decreases gradually. The current flowing through transistor 624 becomes the bypass current I BYPASS An amplifier may be used instead of the voltage comparison circuit 622. A circuit generating a voltage having a voltage equal to the input voltage V may be used instead of the voltage comparison circuit 622. IN A pulse width modulator (PWM) signal of a corresponding duty cycle drives the gate of the transistor 624 based on the PWM signal.

[0050] Figure 5 The bypass circuit 620 of (b) includes a variable current source 626. The variable current source 626 generates a current proportional to the input voltage V INThe corresponding bypass current I BYPASS .

[0051] Next, the purpose of the vehicle lamp 500 will be described. Figure 6 (a) to (d) are diagrams showing an LED socket as an example of the vehicle lamp 500 . Figure 6 (a) is a perspective view of the appearance of the LED socket 700 . Figure 6 (b) shows a front view of the LED socket 700. Figure 6 (c) shows a top view of the LED socket 700. Figure 6 (d) shows a bottom view of the LED socket 700 .

[0052] The frame 702 has a shape that can be detached from the lamp body (not shown). A plurality of LEDs 504 are mounted in the center, and the plurality of LEDs 504 are covered with a transparent sealing resin 704. Components for lighting the circuit 600 are mounted on the substrate 710. The plurality of LEDs 504 are red LED chips and are used as brake lights.

[0053] In the LED socket used for both the stop light and the tail light, a light emitting element for the tail light is mounted adjacent to the plurality of LEDs 504 , and a lighting circuit for the tail light is mounted on the substrate 710 .

[0054] Three pins 721, 722, and 723 are exposed on the bottom surface of the housing 702. An input voltage V is supplied to the pin 721 via a switch. IN , ground voltage is supplied to pin 722. When the tail lamp is turned on, high level input voltage is supplied to pin 723. Pins 721 to 723 pass through the interior of the housing 702, and one end of the pins 721 to 723 is connected to the wiring pattern of the substrate 710.

[0055] Although the present invention has been described using specific words based on the embodiments, the embodiments merely represent the principles and applications of the present invention, and a large number of modifications and changes in configuration may be made to the embodiments without departing from the scope of the concept of the present invention defined in the claims.

[0056] The present international application claims the benefit of priority based on Japanese Patent Application No. 2020-047976, filed on March 18, 2020, the entire contents of which are incorporated herein by reference.

[0057] The above description of the specific embodiments of the present invention is provided for the purpose of illustration. These descriptions are not intended to be exhaustive or limit the present invention to the embodiments described. For those skilled in the art, it is obvious that a large number of variations and changes can be made with reference to the above-mentioned descriptions.

[0058] Description of Reference Numerals

[0059] 500 Vehicle lighting

[0060] 502 LED string

[0061] 503 bypassed part

[0062] 504 LED

[0063] 600 Lighting Circuit

[0064] 602 diode

[0065] 610 LED driver circuit

[0066] 620 Bypass Circuit

[0067] 630 disconnection detection circuit

Claims

1. A light source module, characterized in that: have: An LED string includes four LEDs connected in series, wherein the LEDs are light emitting diodes; An LED driving circuit receives a battery voltage and supplies a driving current stabilized to a target current to the LED string; a bypass circuit, which is provided in parallel with a bypassed portion including two adjacent LEDs in the LED string and receives a bypass current corresponding to the battery voltage; and A line break detection circuit, which disables the bypass circuit when a line break of the bypassed part is detected; When the bypass current is 100%, the light emission of the four LEDs is reduced to 50%, wherein the value of the bypass current of 100% is the value obtained by standardizing the bypass current with the target amount of the driving current as 100%, and the value of the light emission of the four LEDs of 50% is the value obtained by standardizing the light emission of the four LEDs with the maximum light amount as 100%.

2. The light source module according to claim 1, characterized in that: The disconnection detection circuit determines that the bypassed portion is disconnected when the voltage drop of the bypassed portion exceeds Vf×2. The Vf is the forward voltage of the four LEDs connected in series.

3. The light source module according to claim 1 or 2, characterized in that: The light source module is an LED socket.

4. The light source module according to claim 1 or 2, characterized in that: The invention further comprises a reverse connection protection diode provided between an input terminal of the LED drive circuit and a battery.

5. A lighting circuit for driving an LED string comprising four LEDs (light emitting diodes) connected in series, characterized in that: have: An LED driving circuit receives a battery voltage and supplies a driving current stabilized to a target current to the LED string; A bypass circuit is provided in parallel with a bypassed portion including two adjacent LEDs in the LED string, and receives a bypass current corresponding to the battery voltage; as well as A line break detection circuit, which disables the bypass circuit when a line break of the bypassed part is detected; When the bypass current is 100%, the light emission of the four LEDs is reduced to 50%, wherein the value of the bypass current of 100% is the value obtained by standardizing the bypass current with the target amount of the driving current as 100%, and the value of the light emission of the four LEDs of 50% is the value obtained by standardizing the light emission of the four LEDs with the maximum light amount as 100%.

6. The lighting circuit according to claim 5, characterized in that: The disconnection detection circuit determines that the bypassed portion is disconnected when the voltage drop of the bypassed portion exceeds Vf×2. The Vf is the forward voltage of the four LEDs connected in series.

7. The lighting circuit according to claim 5 or 6, characterized in that: The lighting circuit further includes a reverse connection protection diode, and the diode is provided between an input terminal of the LED drive circuit and a battery.

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