Vehicle lighting fixture and lighting circuit

Abstract

A first constant current circuit (210) is provided in series with a plurality of light emitting elements (112) between an input terminal (IN) and a ground terminal (GND), and is capable of switching between ON and OFF states in accordance with a first enable signal (EN1). A second constant current circuit (210) is provided in series with some of the plurality of light emitting elements (112) between the input terminal (IN) and the ground terminal (GND), and is capable of switching between ON and OFF states in accordance with a second enable signal (EN2). In a third voltage range in which an input voltage (VIN) is lower than a first threshold (VTH1) and is higher than a second threshold (VTH2), a control circuit (220) reduces the duty cycle of the first enable signal (EN1) and increases the duty cycle of the second enable signal (EN2) the lower the input voltage (VIN).

Description

[Technical field]

[0001] The present disclosure relates to a lamp for use in an automobile or the like. [Background technology]

[0002] Traditionally, light bulbs have been widely used as light sources for vehicle lighting, but in recent years, semiconductor light sources such as LEDs (light emitting diodes) have come to be widely adopted. In particular, semiconductor light sources that allow replacement with a normal light source in the event of a breakdown such as a broken wire, like the conventional general-purpose light bulb type, are called LED sockets.

[0003] The LED socket is equipped with a number of LEDs connected in series. Patent Document 1 discloses a technique for driving three LEDs connected in series using two current control blocks. Specifically, the first current control block is connected to supply drive current to all three LEDs, and the second current control block is connected to supply drive current to the two LEDs on the lower potential side among the three LEDs. When the power supply voltage (input voltage) supplied to the LED socket is sufficiently high, the first current control block is enabled and all LEDs are turned on. When the number of LEDs is n=3 and the forward voltage of the LEDs is Vf, the input voltage V IN If the input voltage V falls below n × Vf, it will not be possible to maintain the illumination of all the LEDs. IN When the current falls below a certain threshold, the first current control block is disabled and the second current control block is enabled, thereby keeping the two LEDs on the low potential side lit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-197711 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the circuit described in Patent Document 1, the amount of light changes suddenly before and after switching of the active current control block, which causes flickering.

[0006] Some aspects of the present disclosure have been made in light of these problems.

[0007] An exemplary object of an embodiment of the present disclosure is to provide a lighting circuit that suppresses abrupt changes in light intensity caused by fluctuations in input voltage.

[0008] An exemplary object of an embodiment of the present disclosure is to provide a lighting circuit capable of maintaining a light source in a lit state even when the light source is disconnected.

[0009] An exemplary object of another aspect of the present disclosure is to provide a light source module capable of suppressing a decrease in the amount of light in a low voltage state. [Means for solving the problem]

[0010] 1. An aspect of the present disclosure relates to a lighting circuit for driving a semiconductor light source including a first section consisting of m (m≧1) light emitting elements and a second section consisting of n (n≧1) light emitting elements connected in series. The lighting circuit includes a first constant current circuit provided in series with the first section and the second section between an input terminal and a ground terminal and switchable between on and off states in response to a first enable signal, a second constant current circuit provided in series with the second section between the input terminal and a ground terminal and switchable between on and off states in response to a second enable signal, and (i) a constant current circuit provided in series with the second section when the input voltage of the input terminal is In a first voltage range above the first threshold, the duty cycle of the first enable signal is 100% and the duty cycle of the second enable signal is 0%; (ii) in a second voltage range below the second threshold, the duty cycle of the first enable signal is 0% and the duty cycle of the second enable signal is 100%; and (iii) when the input voltage is below the second threshold, the duty cycle of the first enable signal is 0% and the duty cycle of the second enable signal is 100%. and a control circuit that reduces the duty cycle of the first enable signal and increases the duty cycle of the second enable signal as the input voltage becomes lower within a third voltage range that is lower than the first threshold value and higher than the second threshold value.

[0011] 2. An aspect of the present disclosure relates to a lighting circuit for driving a semiconductor light source including a first section consisting of m (m≧1) light-emitting elements and a second section consisting of n (n≧1) light-emitting elements connected in series. The lighting circuit includes a first constant current circuit provided in series with the first section and the second section between an input terminal and a ground terminal, the first constant current circuit generating a first output current having a current amount corresponding to a first analog dimming signal, a second constant current circuit provided in series with the second section between the input terminal and a ground terminal, the second constant current circuit generating a second output current having a current amount corresponding to a second analog dimming signal, and a control circuit generating the first analog dimming signal and the second analog dimming signal based on an input voltage of the input terminal. The control circuit (i) controls the first and second analog dimming signals to be generated based on an input voltage of the input terminal within a first voltage range in which the input voltage of the input terminal is higher than a first threshold value. (ii) in a second voltage range in which the input voltage is lower than the second threshold value, the second output current becomes a predetermined second target amount and the first output current becomes zero; (iii) in a second voltage range in which the input voltage is lower than the first threshold value, the second output current becomes a predetermined second target amount and the first output current becomes zero; In a third voltage range higher than the second threshold, the first analog dimming signal and the second analog dimming signal are generated so that the first output current decreases from the first target amount toward zero and the second output current increases from zero toward the second target amount in response to a decrease in the input voltage.

[0012] 3. An aspect of the present disclosure relates to a lighting circuit for driving a semiconductor light source. The semiconductor light source includes a first portion consisting of m (m≧1) light-emitting elements connected in series, and a second portion consisting of n (n≧1) light-emitting elements. The lighting circuit includes a first constant current circuit provided in series with the first portion and the second portion between an input terminal and a ground terminal, and generating a first output current of a first current amount in an enabled state, a second constant current circuit provided in series with the second portion between the input terminal and a ground terminal, and generating a second output current in an enabled state, and a control circuit for controlling the enable and disable of the first constant current circuit and the second constant current circuit. In a disconnection state of the first portion, the control circuit enables the second constant current circuit and disables the first constant current circuit, and sets the second output current to a second current amount greater than the first current amount.

[0013] 4. A light source module according to an embodiment of the present disclosure includes an LED string including n (n≧2) LEDs (light emitting diodes) of the same color connected in series, an LED driver circuit that receives an input voltage and supplies a drive current stabilized to a target current to the LED string, and a bypass circuit that is provided in parallel with a bypassed portion including adjacent m (m≦n) LEDs of the LED string and sinks a bypass current according to the input voltage. The luminous flux of (nm) LEDs arranged in a portion other than the bypassed portion is greater than the luminous flux of m LEDs arranged in the bypassed portion.

[0014] Any combination of the above components, or mutual substitution of components or expressions between methods, devices, systems, etc. are also valid aspects of the present invention. Effect of the Invention

[0015] According to an aspect of the present disclosure, it is possible to suppress a sudden change in the amount of light caused by a fluctuation in the input voltage, and also to suppress a decrease in the amount of light in a low-voltage state. [Brief description of the drawings]

[0016] [Figure 1]1 is a circuit diagram of a vehicle lamp according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing the input voltage dependency of the vehicle lamp of FIG. [Diagram 3] 2A to 2C are diagrams illustrating the operation of the vehicular lamp of FIG. 1. [Figure 4] 1 is a circuit diagram of a vehicle lamp including a lighting circuit according to Example 1.1. [Diagram 5] FIG. 1 is a circuit diagram of a vehicle lamp including a lighting circuit according to an embodiment 1.2. [Figure 6] 10A to 10C are diagrams illustrating the operation of a vehicle lamp according to Modification 1.1. [Figure 7] 7(a) to 7(c) are waveform diagrams of the gradually changing output current IOUT#. [Figure 8] FIG. 11 is a circuit diagram of a vehicle lamp including a lighting circuit according to Modification 1.2. [Figure 9] FIG. 11 is a circuit diagram of a vehicle lamp including a lighting circuit according to Modification 1.3. [Figure 10] FIG. 11 is a circuit diagram of a vehicle lamp including a lighting circuit according to Modification 1.4. [Figure 11] FIG. 13 is a circuit diagram of a constant current circuit according to Modification 1.5. [Figure 12] FIG. 11 is a circuit diagram of a vehicle lamp according to a second embodiment. [Figure 13] FIG. 13 is a diagram showing the input voltage dependency of the vehicle lamp of FIG. 12. [Figure 14] 13A to 13C are diagrams illustrating the operation of the vehicle lamp of FIG. 12. [Figure 15] FIG. 2 is a circuit diagram of a vehicle lamp including a lighting circuit according to an embodiment 2.1. [Figure 16] 16 is a circuit diagram showing a configuration example of a control circuit in FIG. 15. [Figure 17] 10A to 10C are diagrams illustrating the operation of a vehicle lamp according to Modification 2.1. [Figure 18] FIG. 13 is a diagram illustrating the operation of the lighting circuit according to Modification 2.2. [Figure 19] FIG. 13 is a circuit diagram of a lighting circuit according to Modification 2.2. [Figure 20] FIG. 20 is a circuit diagram of the control circuit of FIG. 19. [Figure 21] FIG. 11 is a circuit diagram of a vehicle lamp including a lighting circuit according to Modification 2.3. [Figure 22] FIG. 11 is a circuit diagram of a vehicle lamp including a lighting circuit according to Modification 2.4. [Figure 23] FIG. 11 is a circuit diagram of a vehicle lamp including a lighting circuit according to Modification 2.5. [Figure 24] FIG. 24 is a circuit diagram showing a specific configuration example of the vehicle lamp of FIG. 23. [Diagram 25] FIG. 3 is a circuit diagram of a vehicle lamp according to embodiment 3.1. [Figure 26] 26A and 26B are diagrams illustrating the state of the vehicle lamp of FIG. 25. [Figure 27] FIG. 4 is an equivalent circuit diagram showing a first state. [Figure 28] FIG. 4 is an equivalent circuit diagram showing a second state. [Figure 29] FIG. 11 is an equivalent circuit diagram showing a third state. [Diagram 30] FIG. 13 is an equivalent circuit diagram showing a fourth state. [Diagram 31] 1 is a circuit diagram of a constant current circuit according to a first configuration example. [Diagram 32] FIG. 11 is a circuit diagram of a constant current circuit according to a second configuration example. [Diagram 33] FIG. 2 is a circuit diagram showing a specific example of the configuration of a lighting circuit. [Diagram 34] FIG. 34 is a first operational waveform diagram of the vehicular lamp of FIG. 33. [Diagram 35] FIG. 34 is a second operational waveform diagram of the vehicular lamp of FIG. 33. [Diagram 36] FIG. 3 is a block diagram of a vehicle lamp according to embodiment 3.2. [Figure 37] 37A and 37B are diagrams illustrating the state of the vehicle lamp of FIG. 36. [Figure 38] FIG. 3 is a circuit diagram of a vehicle lamp including a lighting circuit according to Modification 3.1. [Figure 39] FIG. 3 is a circuit diagram of a vehicle lamp including a lighting circuit according to Modification 3.2. [Diagram 40] FIG. 1 is a block diagram of a conventional vehicle lamp. [Diagram 41]FIG. 4 is a block diagram of a vehicle lamp according to embodiment 4.1. [Diagram 42] 42A to 42C are diagrams illustrating the operation of the vehicular lamp of FIG. 41. [Diagram 43] FIG. 4 is a circuit diagram of a vehicle lamp according to embodiment 4.2. [Diagram 44] 44 is a diagram for explaining the operation of the vehicle lamp of FIG. 43. [Diagram 45] FIG. 4 is a circuit diagram of a vehicle lamp according to embodiment 4.3. [Diagram 46] 46A to 46C are diagrams illustrating the operation of the vehicular lamp of FIG. 45. [Figure 47] 1 is a diagram illustrating the operation of a vehicle lamp with n=4 and m=2 in comparison with the operation of a vehicle lamp with n=4 and m=1 in comparison. FIG. [Figure 48] 48(a) and (b) are circuit diagrams showing configuration examples of the bypass circuit. [Figure 49] 49(a) to (d) are diagrams showing an LED socket, which is an example of a vehicle lamp. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] (Embodiment 1) (Overview of the first embodiment) An overview of the first embodiment will be described. This overview is intended to briefly explain some concepts of one or more embodiments for the purpose of a basic understanding of the embodiments as a prelude to the detailed description that follows, and is not intended to limit the scope of the invention or disclosure. In addition, this overview is not a comprehensive overview of all possible embodiments, and does not limit essential components of the embodiments. For convenience, the term "one embodiment" may be used to refer to one embodiment (example or modification) or multiple embodiments (examples or modifications) disclosed in this specification.

[0018] This summary is not an extensive overview of all possible embodiments, and is not intended to identify key or critical elements of all embodiments or to delineate the scope of some or all aspects. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

[0019] 1. A lighting circuit according to one embodiment drives a semiconductor light source including a first portion consisting of m (m≧1) light-emitting elements and a second portion consisting of n (n≧1) light-emitting elements, which are connected in series. The lighting circuit includes a first constant current circuit provided in series with the first and second portions between an input terminal and a ground terminal, the first constant current circuit being switchable between on and off states in response to a first enable signal, a second constant current circuit provided in series with the second portion between the input terminal and a ground terminal, the second constant current circuit being switchable between on and off states in response to a second enable signal, and a second constant current circuit provided in series with the second portion between the input terminal and a ground terminal, the second constant current circuit being switchable between on and off states in response to a second enable signal. (ii) in a second voltage range where the input voltage is below the second threshold, the duty cycle of the first enable signal is 0% and the duty cycle of the second enable signal is 100%; and (iii) in a second voltage range where the input voltage is below the first threshold, the duty cycle of the first enable signal is 0% and the duty cycle of the second enable signal is 100%. and a control circuit configured to decrease the duty cycle of the first enable signal and increase the duty cycle of the second enable signal as the input voltage decreases in a third voltage range that is lower than the first threshold value and higher than the second threshold value.

[0020] According to this embodiment, it is possible to suppress abrupt changes in the amount of light caused by fluctuations in the input voltage.

[0021] In one embodiment, the duty cycle of the first enable signal and the duty cycle of the second enable signal in the third voltage range may be determined so that the slope of the total light output of the light source with respect to the change in the input voltage is equal to or less than 5% / 0.1 V. This makes it difficult for humans to sense the fluctuation in the light output caused by short-term fluctuations in the input voltage.

[0022] In one embodiment, the second output current generated by the second constant current circuit in the ON state may be greater than the first output current generated by the first constant current circuit in the ON state, thereby suppressing a decrease in the overall light amount of the light source due to a decrease in the input voltage.

[0023] In one embodiment, the duty cycle of the first enable signal and the duty cycle of the second enable signal may sum to 100%.

[0024] In one embodiment, the first enable signal and the second enable signal may be inverted signals.

[0025] In one embodiment, the output currents of the first constant current circuit and the second constant current circuit may be gradually changed when the first constant current circuit and the second constant current circuit are switched on and off, thereby making it possible to suppress electromagnetic noise.

[0026] In one embodiment, the first constant current circuit may generate a first output current proportional to the voltage level of the first enable signal, and the second constant current circuit may generate a second output current proportional to the voltage level of the second enable signal.

[0027] In one embodiment, at least one of a positive edge and a negative edge of the pulse-shaped first enable signal and the pulse-shaped second enable signal generated in the third voltage range may be rounded, thereby suppressing electromagnetic noise.

[0028] (Detailed Description of the First Embodiment) The first embodiment will be described with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, the embodiments are illustrative and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0029] In this specification, "a state in which component A is connected to component B" includes not only a case in which component A and component B are directly physically connected to each other, but also a case in which component A and component B are indirectly connected to each other via other components that do not substantially affect the electrical connection state between them or that do not impair the function or effect achieved by their combination.

[0030] Similarly, "a state in which component C is provided between components A and B" includes not only the case in which components A and C, or components B and C, are directly connected to each other, but also the case in which they are indirectly connected to each other via other components that do not substantially affect the electrical connection between them or that do not impair the functions or effects achieved by their combination.

[0031] In this specification, symbols attached to electrical signals such as voltage signals and current signals, or circuit elements such as resistors and capacitors, represent the respective voltage values, current values, resistance values, or capacitance values ​​as necessary.

[0032] 1 is a circuit diagram of a vehicle lamp 100 according to the first embodiment. The vehicle lamp 100 receives a DC voltage (input voltage) V IN is supplied.

[0033] The vehicle lamp 100 includes a semiconductor light source 110 and its lighting circuit 200. A suitable embodiment of the vehicle lamp 100 is an LED socket in which the semiconductor light source 110 and the lighting circuit 200 are housed in one package, and has a shape that allows it to be attached to and detached from a lamp body (not shown). The LED socket is required to have a long life, and since it is a consumable item, it is strongly required to reduce the cost.

[0034] The semiconductor light source 110 is a light emitting element string including (m+n) light emitting elements 112 connected in series. In this embodiment, the light emitting elements 112 are, for example, white LEDs, where m+n=3. The multiple light emitting elements 112 are chips having substantially the same characteristics, and the light amounts when the same current is supplied are substantially equal.

[0035] The semiconductor light source 110 is divided into a first portion 114 consisting of m light emitting elements 112_1 on the high potential side, and a second portion 116 consisting of n light emitting elements 112_2 and 112_3 on the low potential side.

[0036] The lighting circuit 200 may be an IC (Integrated Circuit) integrated on a single semiconductor substrate, or may be configured by combining a plurality of discrete elements. The lighting circuit 200 has an input terminal IN, a ground terminal GND, and three output terminals OUT1 to OUT3. The input terminal IN receives a power supply voltage (input voltage V IN ) is supplied to the first portion 114 of the semiconductor light source 110, and the ground terminal GND is grounded. The anode of the first portion 114 of the semiconductor light source 110 is connected to the output terminal OUT1, and the cathode of the first portion 114 is connected to the output terminal OUT2. The anode of the second portion 116 of the semiconductor light source 110 is connected to the output terminal OUT2, and the cathode of the second portion 116 is connected to the output terminal OUT3. The output terminal OUT3 is connected to the ground terminal GND.

[0037] The lighting circuit 200 includes a first constant current circuit 210_1, a second constant current circuit 210_2, and a control circuit 220. The output of the first constant current circuit 210_1 is connected to the anode of the first portion 114 via an output terminal OUT1, and the input of the first constant current circuit 210_1 is connected to the input terminal IN. In other words, the first constant current circuit 210_1 is provided in series with the multiple light emitting elements 112_1 to 112_3 between the input terminal IN and the ground terminal GND. The first constant current circuit 210_1 has an enable terminal EN, and is configured to be switchable between an on state and an off state in response to a first enable signal EN1. In an on state, the first constant current circuit 210_1 supplies a predetermined amount of current I REF1 The first output current I OUT1 Generate.

[0038] The output of the second constant current circuit 210_2 is connected to the anode of the second portion 116 via the output terminal OUT2, and the input of the second constant current circuit 210_2 is connected to the input terminal IN. In other words, the second constant current circuit 210_2 is provided in series with the second portion 116 of the semiconductor light source 110 between the input terminal IN and the ground terminal GND. The second constant current circuit 210_2 has an enable terminal EN, and is configured to be switchable between an on state and an off state in response to a second enable signal EN2. In the on state, the second constant current circuit 210_2 supplies a predetermined amount of current I REF2 The second output current I O UT2 In this embodiment, I REF1 =I REF2 =I REF Let us assume that.

[0039] The driving current Id1 flowing through the first portion 114 is a first output current I OUT1 The driving current Id2 flowing through the second portion 116 is a first output current I OUT1 and the second output current I from the second constant current circuit 210_2. OUT2 is the total current.

[0040] The control circuit 220 receives an input voltage V IN The control circuit 220 is supplied with an input voltage V IN is the first threshold V TH1 In a first higher voltage range, the duty cycle dc1 of the first enable signal EN1 is 100% and the duty cycle dc2 of the second enable signal EN2 is 0%. IN is the second threshold V TH2 In a lower second voltage range, the duty cycle dc1 of the first enable signal EN1 is set to 0% and the duty cycle dc2 of the second enable signal EN2 is set to 100%. Power voltage V IN is the first threshold V TH1 Lower, the second threshold V TH2 In the third higher voltage range, the input voltage V INis lower, the duty cycle dc1 of the first enable signal EN1 is decreased and the duty cycle dc2 of the second enable signal EN2 is increased.

[0041] V TH2 is determined based on the number n of light-emitting elements included in the second portion 116. In this example, n=2, and V TH2 > n × Vf.

[0042] Fig. 2 is a diagram showing the input voltage dependency of the vehicular lamp 100 of Fig. 1. The duty cycles dc1 and dc2 vary complementarily so that the sum of them is 100%. dc1+dc2=100%

[0043] The first output current I in Figure 2 OUT1 , the second output current I OUT2 indicates the effective value (time average value), and I OUT1 =I REF ×dc1, I OUT2 =I REF ×dc2.

[0044] The current Id1 flowing through the first portion 114 is the first output current I OUT1 Therefore, the input voltage V IN The lower the current Id1, the lower the I OUT1 =dc1×I REF It decreases according to.

[0045] The drive current Id2 flowing through the second portion 116 is equal to the first output current I OUT1 and the second output current I OUT2 and is expressed by equation (1). Id2=I OUT1 +I OUT2 =dc1×I REF +dc2×I REF …(1)

[0046] When dc1+dc2=100%, Id2=I REF It becomes.

[0047] A current amount I REF The amount of light when the light flows is U. The amount of light in the first portion 114 (dashed line) is V TH1 <V IN In the range of 1×U, V IN <V TH2 0 in the range of V TH2 <V IN <V TH1 In the range of , it varies from 0 to 1 × U.

[0048] The current Id2 flowing through the second portion 116 is IN Regardless I REF Since this is constant, the amount of light for two chips (dashed line) is 2×U.

[0049] The total light amount of the semiconductor light source 110 (solid line) is the sum of the light amounts of the first portion 114 and the second portion 116, and V TH1 <V IN In the range of 3 × U, V IN <V TH2 In the range of 2×U, V TH2 <V IN <V TH1 In this range, it changes in the range of 2×U to 3×U.

[0050] V TH2 <V IN <V TH1 In the region, the slope of the duty cycle dc1 (and dc2) is the input voltage V IN It is recommended to design the input voltage V so that the slope of the change in V is 5% / 0.1V or less. IN This makes it harder for humans to sense fluctuations in light intensity caused by short-term fluctuations in the

[0051] The above is the configuration of the vehicular lamp 100. Next, a description will be given of the operation of the vehicular lamp 100. Fig. 3 is a diagram showing the operation of the vehicular lamp 100 of Fig. 1.

[0052] Figure 3 shows the input voltage V INThe figure shows how V decreases over time. Before time t0, IN >V TH1 The duty cycle dc1 of the first enable signal EN1 is 100%, the duty cycle dc2 of the second enable signal EN2 is 0%, and only the first constant current circuit 210_1 is enabled.

[0053] The light emitting element 112_1 in the first portion 114 is driven by a driving current Id1=I OUT1 =I REF The light emitting elements 112_2 and 112_3 in the second portion 116 are also supplied with the same amount of driving current Id2=I OUT1 =I REF is supplied.

[0054] One (one chip) light emitting element 112 is REF is supplied is denoted as U. Before time t0, the light amount of first portion 114 (dashed line) is 1×U, the light amount of second portion 116 (dotted line) is for two chips, so is 2×U, and the light amount of semiconductor light source 110 as a whole (solid line) is 3×U.

[0055] After time t0, the input voltage V IN As the duty cycle dc1 of the first enable signal EN1 decreases, the duty cycle dc2 of the second enable signal EN2 increases.

[0056] After time t0, the total light amount of semiconductor light source 110 decreases from 3×U to 2×U. After time t1, the total light amount of semiconductor light source 110 remains at 2×U.

[0057] The above is the operation of the vehicle lamp 100. According to this vehicle lamp 100, the input voltage V I N In response to the fluctuation of the current, the two constant current circuits 210_1 and 210_2 operate in a gradual alternation. This makes it possible to prevent a sudden change in the overall light amount of the semiconductor light source 110, thereby suppressing flickering.

[0058] Next, a specific configuration example of the vehicle lamp 100 will be described.

[0059] Example 1.1 4 is a circuit diagram of a vehicle lamp 100A including a lighting circuit 200A according to Example 1.1. The constant current circuits 210_1 and 210_2 are configured similarly and include a series transistor Qsr, a limiting resistor Rs, a gate resistor Rg, an error amplifier EA1, transistors Q41 and Q42, and resistors R41 to R44. The EN pin of the constant current circuit 210 is active low.

[0060] Output current I in constant current circuit 210_# (#=1, 2) OUT# Target amount I REF# is expressed by equation (2). I REF# =V REF / Rs …(2)

[0061] Transistors Q41 and Q42 and resistors R41 to R44 are added to switch on (enable) and off (disable) the constant current circuit 210. When a high is input to the enable pin, the transistor Q41 turns on, the transistor Q42 turns on, the transistor Qsr turns off, and the constant current circuit 210 is disabled.

[0062] The control circuit 220 includes resistors R31 and R32, a pulse width modulator 221, and an inverter 228. The resistors R31 and R32 control the input voltage V IN The pulse width modulator 221 divides the input voltage V IN For example, the pulse width modulator 221 includes an amplifier 222, an oscillator 224, and a PWM comparator 226. The amplifier 222 generates a pulse signal having a duty cycle according to the divided input voltage V IN The oscillator 224 amplifies the signal Vs and generates a detection voltage Vs. OSC The PWM comparator 226 generates the detection voltage Vs and the periodic signal V OSCand outputs the second enable signal EN2. The inverter 228 inverts the second enable signal EN2 to generate the first enable signal EN1.

[0063] (Example 1.2) FIG. 5 is a circuit diagram of a vehicle lamp 100B including a lighting circuit 200B according to the embodiment 1.2.

[0064] In the lighting circuit 200B, a constant current circuit 210_# (#=1, 2) outputs a current I proportional to an enable signal EN# input to an enable terminal EN. REF Output current I OUT# Generate.

[0065] The error amplifier EA2, transistor Q42, and resistor R46 form a voltage / current conversion circuit, which converts the enable signal EN# into a current signal I EN# The voltage level of the enable signal EN# is converted to V EN# Then, the current signal I EN# I EN# =V EN# / R46. This current signal I EN# When a current flows through resistor R45, the voltage V EN# A reference voltage V proportional to REF# The output current I OUT# The target current I REF# Since it is expressed by equation (2), the current I OUT# can be generated.

[0066] In the embodiment 1.2, it is necessary to stabilize the high level voltages of the enable signals EN1 and EN2 at predetermined voltage levels.

[0067] A modification related to the first embodiment will be described.

[0068] (Variation 1.1) In the modification 1.1, the second output current I generated by the second constant current circuit 210_2 in the ON state is OUT2 Target amount I REF2is the first output current I generated by the first constant current circuit 210_2 in the ON state. OUT1 Target amount I REF1 More. I REF1 REF2

[0069] FIG. 6 is a diagram illustrating the operation of the vehicular lamp according to Modification 1.1.

[0070] In the modification 1.1, the drive current Id2 flowing through the second portion 116 is expressed by the formula (3). Id2=I OUT1 +I OUT2 =dc1×I REF1 +dc2×I REF2 …(3) I REF1 REF2 Since the above holds, the drive current Id2 is IN It increases as decreases.

[0071] A current amount I REF The amount of light when I flows is U. REF1 =I REF , I REF2 =1.5×I REF Let us assume that.

[0072] As in the first embodiment (FIG. 2), the amount of light in the first portion 114 (dashed line) is V TH1 <V IN In the range of 1×U, V IN <V TH2 0 in the range of V TH2 <V I N <V TH1 In the range of , it varies from 0 to 1 × U.

[0073] On the other hand, the current Id2 flowing through the second portion 116 is IN The amount of light in the second portion 116 (dashed line) increases as V TH1 <V IN In the range of 2×U, V​​IN <V TH2 In the range of 3 × U, V TH2 <V IN <V T H1 In this range, it changes in the range of 2×U to 3×U.

[0074] The total light amount of the semiconductor light source 110 is the sum of the light amount of the first portion 114 and the light amount of the second portion 116. Therefore, when the input voltage V IN This can suppress the overall change in light quantity due to fluctuations.

[0075] If the number of chips in the first portion 114 is m and the number of chips in the second portion 116 is n, then I REF 2≒(m+n) / n×I REF1 By determining the amount of current so as to satisfy the above, it is possible to reduce the fluctuation in the amount of light from semiconductor light source 110 as a whole.

[0076] The vehicular lamp 100 according to the modified example 1.1 can be configured in the same manner as in Fig. 4. By individually setting the resistances Rs of the constant current circuits 210_1 and 210_2 in Fig. 4, different amounts of current can be generated.

[0077] (Variation 1.2) At the timing when the first constant current circuit 210_1 and the second constant current circuit 210_2 are switched on and off, their output currents I OUT1 ,I OUT2 7(a) to (c) show the gradually changing output current I OUT# FIG. 7(a) shows the waveform of the output current. I OUT# The output current (b) changes gradually as the rising edge and the falling edge of the I OUT# Only the rising edge of the output current changes gradually. I OUT# Only the falling edge of the output current I OUT# By gradually changing the frequency, electromagnetic noise can be suppressed.

[0078] FIG. 8 is a circuit diagram of a vehicle lamp 100C including a lighting circuit 200C according to modification 1.2. The basic configuration of the lighting circuit 200C is the same as that of the lighting circuit 200B of FIG. 5. The control circuit 220 includes low-pass filters 230 and 232. The low-pass filter 230 removes high-frequency components from the output of the pulse width modulator 221, and generates a second enable signal EN2 in which both the positive and negative edges are blunted. The low-pass filter 232 removes high-frequency components from the output of the inverter 228, and generates a first enable signal EN1 in which both the positive and negative edges are blunted. With this configuration, as shown in FIG. 7(a), the output current I OUT# can be generated.

[0079] (Variation 1.3) In the embodiment, the light emitting element 112 is a white LED, but this is not limited thereto. The light emitting element 112 may be a red LED. FIG. 9 is a circuit diagram of a vehicle lamp 100D including a lighting circuit 200D according to modification 1.3. In this vehicle lamp 100D, m=2, n=2, and V TH2 V TH2 > 2×Vf.

[0080] (Variation 1.4) Fig. 10 is a circuit diagram of a vehicle lamp 100E including a lighting circuit 200E according to a modified example 1.4. In this modified example 1.4, the first constant current circuit 210_1 and the second constant current circuit 210_2 are configured as current sink types. The vehicle lamp 100E can be understood as having a configuration in which the vehicle lamp 100 in Fig. 1 is inverted. The constant current circuit 210 can be configured by inverting the constant current circuit in Fig. 5.

[0081] (Variation 1.5) 11 is a circuit diagram of a constant current circuit according to modification 1.5. This constant current circuit is a current sink type and includes transistors Q1 and Q2 and resistors R1 and R2. The output current I OUT teeth, I OUT =V BE / R1 It is expressed as:

[0082] It is also possible to invert the configuration of FIG. 11 to form a current source type.

[0083] (Variation 1.6) In the explanation so far, the multiple light-emitting elements 112 are chips having substantially the same characteristics, and the amount of light emitted when the same current is supplied is substantially equal, but chips with different characteristics may also be used.

[0084] For example, the characteristics of the m chips included in the first portion 114 may be uniform, and the characteristics of the n chips included in the second portion 116 may be uniform. In this case, the luminous flux (light amount) of each of the n light-emitting elements 112 included in the second portion 116 may be greater than the luminous flux of each of the m light-emitting elements 112 included in the first portion 114. The luminous flux of the light-emitting elements 112 is uniform when the same driving current I LED This refers to the luminous flux when driven by

[0085] Even LED chips with the same product number supplied by the same vendor will have different luminous fluxes when supplied with the same drive current due to manufacturing variations. LED chip vendors may rank LED chips based on luminous flux before selling them. In this case, chips with a higher luminous flux rank may be used for the second portion 116, and chips with a lower luminous flux rank may be used for the first portion 114. Alternatively, a manufacturer of vehicle lamps, rather than a vendor of LED chips, may rank a large number of LED chips that it purchases based on luminous flux.

[0086] Alternatively, when LED chips with different part numbers having different luminous flux are provided by the same vendor, the chip with the part number having the larger luminous flux may be used for the second portion 116 and the chip with the part number having the smaller luminous flux may be used for the first portion 114.

[0087] Alternatively, first portion 114 may use chips of the same part number provided by a first vendor, and second portion 116 may use chips with a higher luminous flux provided by a second vendor.

[0088] A current amount I REF The amount of light (luminous flux) when the same current I flows through one LED chip included in the second portion 116 is defined as U. R EF The amount of light (luminous flux) when the light flows is defined as α×U. α is a coefficient larger than 1, and can be set to about α=1.3, and more preferably, α=1.5.

[0089] In this modification 1.6, as shown in FIG. 2, the output current I OUT1 ,I OUT2 In this case, V IN >V TH1 In the normal voltage region, the total luminous flux (light amount) of the semiconductor light source 110 is 1×U+2×α×U. IN <V TH2 In this low voltage region, the total luminous flux (light amount) of the semiconductor light source 110 is 2×α×U. Therefore, the light amount in the low voltage region is 2α / (1+2α) times that in the normal voltage region. Therefore, the larger α is, the more the rate of decrease in the light amount can be suppressed.

[0090] (Variation 1.7) In the embodiment, the light emitting element 112 is described as an LED, but an LD (laser diode) or an organic EL element may also be used.

[0091] (Variation 1.8) Bipolar transistors and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) can be interchanged. In this case, the base, collector, and emitter are replaced by the gate. The term "NPN" can be replaced with "PNP" (P channel).

[0092] (Embodiment 2) (Overview of the second embodiment)

[0093] A lighting circuit according to one embodiment drives a semiconductor light source including a first portion consisting of m (m≧1) light-emitting elements and a second portion consisting of n (n≧1) light-emitting elements connected in series. The lighting circuit includes a first constant current circuit provided in series with the first and second portions between an input terminal and a ground terminal, the first constant current circuit generating a first output current having a current amount corresponding to a first analog dimming signal, a second constant current circuit provided in series with the second portion between the input terminal and a ground terminal, the second constant current circuit generating a second output current having a current amount corresponding to a second analog dimming signal, and a control circuit generating the first analog dimming signal and the second analog dimming signal based on an input voltage of the input terminal. The control circuit (i) controls the first output current to be a first constant current circuit in a first voltage range in which the input voltage of the input terminal is higher than a first threshold value. (ii) in a second voltage range in which the input voltage is lower than the second threshold, the second output current becomes a predetermined second target amount and the first output current becomes zero; (iii) in a second voltage range in which the input voltage is lower than the first threshold and the second threshold, the second output current becomes a predetermined second target amount and the first output current becomes zero. The first analog dimming signal and the second analog dimming signal are generated such that, in a third voltage range higher than the first voltage range, the first output current decreases from the first target amount toward zero and the second output current increases from zero toward the second target amount in response to a decrease in the input voltage.

[0094] According to this embodiment, it is possible to suppress abrupt changes in the amount of light caused by fluctuations in the input voltage.

[0095] In one embodiment, the first and second analog dimming signals in the third voltage range may be generated so that the slope of the total light output of the light source with respect to the change in the input voltage is 5% / 0.1 V or less, thereby making it difficult for humans to sense the fluctuation in the light output caused by short-term fluctuations in the input voltage.

[0096] In one embodiment, the second target amount may be greater than the first target amount, which makes it possible to suppress a decrease in the amount of light of the entire light source due to a decrease in the input voltage.

[0097] In one embodiment, the conversion gain of the first output current of the first constant current circuit for the first analog dimming signal may be equal to the conversion gain of the second output current of the second constant current circuit for the second analog dimming signal. The sum of the voltage levels of the first analog dimming signal and the second analog dimming signal may be constant.

[0098] In one embodiment, the conversion gain of the second output current of the second constant current circuit for the second analog dimming signal may be greater than the conversion gain of the first output current of the first constant current circuit for the first analog dimming signal. The sum of the voltage levels of the first analog dimming signal and the second analog dimming signal may be constant. In this case, the second target amount is greater than the first target amount, so that the decrease in the light amount of the entire light source due to the decrease in the input voltage can be suppressed.

[0099] (Detailed Description of the Second Embodiment) 12 is a circuit diagram of a vehicle lamp 100 according to the second embodiment. The vehicle lamp 100 receives a DC voltage (input voltage) V IN is supplied.

[0100] The vehicle lamp 100 includes a semiconductor light source 110 and its lighting circuit 200. A suitable embodiment of the vehicle lamp 100 is an LED socket in which the semiconductor light source 110 and the lighting circuit 200 are housed in one package, and has a shape that allows it to be attached to and detached from a lamp body (not shown). The LED socket is required to have a long life, and since it is a consumable item, it is strongly required to reduce the cost.

[0101] The semiconductor light source 110 is a light emitting element string including (m+n) light emitting elements 112 connected in series. In this embodiment, the light emitting elements 112 are, for example, white LEDs, where m+n=3. The multiple light emitting elements 112 are chips having substantially the same characteristics, and the light amounts when the same current is supplied are substantially equal.

[0102] The semiconductor light source 110 is divided into a first portion 114 consisting of m light emitting elements 112_1 on the high potential side, and a second portion 116 consisting of n light emitting elements 112_2 and 112_3 on the low potential side.

[0103] The lighting circuit 200 may be an IC (Integrated Circuit) integrated on a single semiconductor substrate, or may be configured by combining a plurality of discrete elements. The lighting circuit 200 has an input terminal IN, a ground terminal GND, and three output terminals OUT1 to OUT3. The input terminal IN receives a power supply voltage (input voltage V IN ) is supplied to the first portion 114 of the semiconductor light source 110, and the ground terminal GND is grounded. The anode of the first portion 114 of the semiconductor light source 110 is connected to the output terminal OUT1, and the cathode of the first portion 114 is connected to the output terminal OUT2. The anode of the second portion 116 of the semiconductor light source 110 is connected to the output terminal OUT2, and the cathode of the second portion 116 is connected to the output terminal OUT3. The output terminal OUT3 is connected to the ground terminal GND.

[0104] The lighting circuit 200 includes a first constant current circuit 210_1, a second constant current circuit 210_2, and a control circuit 220. The output of the first constant current circuit 210_1 is connected to the anode of the first portion 114 via an output terminal OUT1, and the input of the first constant current circuit 210_1 is connected to the input terminal IN. That is, the first constant current circuit 210_1 is provided in series with the multiple light emitting elements 112_1 to 112_3 between the input terminal IN and a ground terminal GND. The first constant current circuit 210_1 has a dimming terminal ADIM, and a first analog dimming signal V DIM The first output current I OUT1 Generate.

[0105] The output of the second constant current circuit 210_2 is connected to the anode of the second portion 116 via the output terminal OUT2, and the input of the second constant current circuit 210_2 is connected to the input terminal IN. That is, the second constant current circuit 210_2 is provided in series with the second portion 116 of the semiconductor light source 110 between the input terminal IN and the ground terminal GND. The second constant current circuit 210_2 has a dimming terminal ADIM, and receives a second analog dimming signal VADIM2 The second output current I OU T2 Generate.

[0106] The first constant current circuit 210_1 and the second constant current circuit 210_2 are a voltage / current (V / I) It can be understood as a conversion circuit, and its respective input / output characteristics can be generalized by the following equation. I OUT1 =K1×(V ADIM1 -V OFS1 ) I OUT2 =K2×(V ADIM2 -V OFS2 )

[0107] K1 and K2 are the V / I conversion gains, and V OFS1 , V OFS2 is the offset.

[0108] The driving current Id1 flowing through the first portion 114 is a first output current I OUT1 The driving current Id2 flowing through the second portion 116 is a first output current I OUT1 and the second output current I from the second constant current circuit 210_2. OUT2 is the total current.

[0109] The control circuit 220 receives an input voltage V IN is supplied, and the input voltage V IN Based on the first analog dimming signal V ADIM1 and the second analog dimming signal V ADIM2 Generate.

[0110] The control circuit 220 controls (i) the input voltage V IN is the first threshold V TH1 Higher first voltage range In the range, the first output current I OUT1 is the first target quantity I REF1 The second output current I OUT2 The first analog dimming signal V ADIM1and the second analog dimming signal V ADIM2 Generate.

[0111] The control circuit 220 also controls (ii) the input voltage V IN is the second threshold V TH2 In a second lower voltage range, the second output current I OUT2 is the predetermined second target quantity I REF2 The first output current I OUT1 The first analog dimming signal V ADIM1 and the second analog dimming signal V ADIM2 Generate.

[0112] The control circuit 220 also controls the input voltage V IN is the first threshold V TH1 Lower, first 2. Threshold V TH2 In the third higher voltage range, the input voltage V IN As the first output current I OUT1 is the first target quantity I REF1 to zero, and the second output current I OUT2 From zero to the second target quantity I REF2 The first analog dimming signal V ADIM1 and the second analog dimming signal V ADIM2 Generate.

[0113] Second threshold V TH2 is determined based on the number n of light-emitting elements included in the second portion 116. In this example, n=2, and V TH2 > n × Vf.

[0114] FIG. 13 is a diagram showing the input voltage dependency of the vehicular lamp 100 of FIG. 12. Here, K1=K2=K, V OFS1 =V OFS2 =0, I REF1 =I REF2 =I REF The first analog dimming signal V ADIM1 and the second analog dimming signal V AD IM2 The peak voltage of VMAX Then, the following relationship holds: I REF =K×V MAX

[0115] The current Id1 flowing through the first portion 114 is the first output current I OUT1 Therefore, the input voltage V IN The lower the current Id1, the lower the I OUT1 =K×V ADIM1 It decreases according to.

[0116] The drive current Id2 flowing through the second portion 116 is equal to the first output current I OUT1 and the second output current I OUT2 and is expressed by equation (1). Id2=I OUT1 +I OUT2 =K×(V ADIM1 +V ADIM2 ) …(1)

[0117] V ADIM1 +V ADIM2 =V MAX When this holds, Id2=I REF and the input voltage V IN It is a constant amount that does not depend on

[0118] A current amount I REF The amount of light when the light flows is U. The amount of light in the first portion 114 (dashed line) is V TH1 <V IN In the range of 1×U, V IN <V TH2 0 in the range of V TH2 <V IN <V TH1 In the range of , it varies from 0 to 1 × U.

[0119] The current Id2 flowing through the second portion 116 is IN Regardless I REF Since this is constant, the amount of light for two chips (dashed line) is 2×U.

[0120] The total light amount of the semiconductor light source 110 (solid line) is the sum of the light amounts of the first portion 114 and the second portion 116, and V TH1 <V IN In the range of 3 × U, V IN <V TH2 In the range of 2×U, V TH2 <V IN <V TH1 In this range, it changes in the range of 2×U to 3×U.

[0121] V TH2 <V IN <V TH1 In the region, the analog dimming signal V ADIM1 ,V AD IM2 The slope of the input voltage V IN It is recommended to design the input voltage V so that the slope of the change in V is 5% / 0.1V or less. IN This makes it harder for humans to sense fluctuations in light intensity caused by short-term fluctuations in the

[0122] The above is the configuration of the vehicular lamp 100. Next, a description will be given of the operation of the vehicular lamp 100. Fig. 14 is a diagram showing the operation of the vehicular lamp 100 in Fig. 12.

[0123] Figure 14 shows the input voltage V IN The figure shows how V decreases over time. Before time t0, IN >V TH1 and V ADIM1 =V MAX , V ADIM2 = 0, and I OUT1 =I REF ,I OUT2 =0.

[0124] The light emitting element 112_1 in the first portion 114 is driven by a driving current Id1=I OUT1 =I REF The light emitting elements 112_2 and 112_3 in the second portion 116 are also supplied with the same amount of driving current Id2=I OUT1 =I REF is supplied.

[0125] The light emitting element 112 is REF is supplied is denoted as U. Before time t0, the light amount of first portion 114 (dashed line) is 1×U, the light amount of second portion 116 (dotted line) is for two chips, so is 2×U, and the light amount of semiconductor light source 110 as a whole (solid line) is 3×U.

[0126] After time t0, the input voltage V IN As the first analog dimming signal V ADIM1 The voltage level of the second analog dimming signal V ADIM2 The voltage level of V MAX increases towards

[0127] After time t0, the total light amount of semiconductor light source 110 decreases from 3×U to 2×U. After time t1, the total light amount of semiconductor light source 110 remains at 2×U.

[0128] The above is the operation of the vehicle lamp 100. According to this vehicle lamp 100, the input voltage V I N In response to the fluctuation of the current, the two constant current circuits 210_1 and 210_2 operate in a gradual alternation. This makes it possible to prevent a sudden change in the overall light amount of the semiconductor light source 110, thereby suppressing flickering.

[0129] Next, a specific configuration example of the vehicle lamp 100 will be described.

[0130] Example 2.1 15 is a circuit diagram of a vehicle lamp 100G including a lighting circuit 200G according to Example 2.1. The constant current circuits 210_1 and 210_2 are configured in the same manner, and each includes a V / I conversion circuit 212 and a current amplification circuit 214.

[0131] The V / I conversion circuit 212 converts the analog dimming signal V ADIM# current signal I ADIM# The V / I conversion circuit 212 includes a transistor Q2, a resistor R2, and an error amplifier EA2. ADIM#I ADIM# =V ADIM# / R3.

[0132] The current amplifier circuit 214 outputs a current signal I ADIM# is amplified and the output current I OUT# The current amplifier circuit 214 includes resistors R1 and R2, a transistor Q1, and an error amplifier EA1.

[0133] This current signal I ADIM# When current flows through resistor R2, a voltage V ADIM# Voltage drop V proportional to R2 occurs. V R2 =V ADIM# / R3×R2 …(2)

[0134] The error amplifier EA1, transistor Q1, and resistor R2 form a V / I conversion circuit. The voltage drop V R2 Output current I according to OUT# Generate. I REF# =V R2 / R1 …(3)

[0135] From equations (2) and (3), equation (4) can be obtained as the input / output characteristic of the constant current circuit 210_#. I REF# =V R2 / R1=V ADIM# / R3×R2 / R1 …(4) That is, the conversion gain K of the constant current circuit 210_# # is given by equation (5). K # =R2 / (R1×R3) …(5)

[0136] The lighting circuit 200G includes a constant voltage source 201. The constant voltage source 201 receives an input voltage V IN The regulated voltage V REG This stabilization voltage V REG is supplied to the control circuit 220. The analog dimming signal V ADIM1 ,VADIM2 Peak voltage V MAX is the regulated voltage V REG It can be prescribed based on.

[0137] Fig. 16 is a circuit diagram showing a configuration example of the control circuit 220G of Fig. 15. The control circuit 220G includes resistors R4 and R5, a non-inverting amplifier 240, and an inverting amplifier 242. The input voltage V I N is divided by resistors R4 and R5. The non-inverting amplifier 240 receives the input voltage V IN The first analog dimming signal V changes linearly with ADIM1 Generate.

[0138] The non-inverting amplifier 240 outputs a regulated voltage V REG Based on the reference, the input voltage after division V IN The non-inverting amplifier 240 includes an error amplifier EA3 and resistors R6 and R7. The input / output characteristics of the non-inverting amplifier 240 are given by equation (6). V ADIM1 =(R6+R7) / R6×V IN '-(R7 / R6)×V REG …(6)

[0139] The inverting amplifier 242 in the latter stage receives the first analog dimming signal V ADIM1 is inverted and amplified to generate the second analog dimming signal V ADIM2 Generate.

[0140] According to this configuration, the first analog dimming signal V ADIM1 and the second analog dimming signal V ADIM2 can be generated.

[0141] A modification related to the second embodiment will be described.

[0142] (Variation 2.1) In the modification 2.1, the second output current I generated by the second constant current circuit 210_2 is OUT2 Target amount I REF2 is the first output current I generated by the first constant current circuit 210_2. OUT1 Target amount IREF1 More. I REF1 REF2

[0143] In this example, two analog dimming signals V ADIM1 and V ADIM2 The peak voltages of K1 are equal. <K2となっている。こうすることにより、I REF1 REF2 is satisfied.

[0144] 17 is a diagram illustrating the operation of the vehicular lamp according to Modification 2.1. In Modification 2.1, the drive current Id2 flowing through the second portion 116 is expressed by equation (7). Id2=I OUT1 +I OUT2 =K1×V ADIM1 +K2×V ADIM2 …(7) I REF1 REF2 Since the above holds, the drive current Id2 is IN It increases as decreases.

[0145] A current amount I REF The amount of light when I flows is 1. REF1 =I REF , I REF2 =1.5×I REF Let us assume that.

[0146] As in the second embodiment (FIG. 13), the amount of light in the first portion 114 (dashed line) is V TH1 <V IN 1 in the range of V IN <V TH2 0 in the range of V TH2 <V IN <V TH1 It varies in the range of 0 to 1.

[0147] On the other hand, the current Id2 flowing through the second portion 116 is IN The amount of light in the second portion 116 (dashed line) increases as V​​​TH1 <V IN 2 in the range of V IN <V TH2 3 in the range of V TH2 <V IN <V TH1 Within this range, it changes within a range of 2 to 3.

[0148] The total light amount of the semiconductor light source 110 is the sum of the light amount of the first portion 114 and the light amount of the second portion 116. Therefore, when the input voltage V IN This can suppress the overall change in light quantity due to fluctuations.

[0149] If the number of chips in the first portion 114 is m and the number of chips in the second portion 116 is n, then I REF 2≒(m+n) / n×I REF1 By determining the amount of current so as to satisfy the above, it is possible to reduce the fluctuation in the amount of light from semiconductor light source 110 as a whole.

[0150] (Variation 2.2) 18 is a diagram illustrating the operation of a lighting circuit 200H according to Modification 2.2. In Modification 2.2, the first analog dimming signal V ADIM1 is 0 to V MAX / 2, and the second analog dimming signal V ADIM2 V MAX / 2~V MAX The change ranges from .

[0151] The input / output characteristics of the constant current circuits 210_1 and 220_2 are expressed by equations (8) and (9). I OUT1 =K×V ADIM1 …(8) I OUT2 =K×(V ADIM2 -V MAX / 2) …(9) holds true.

[0152] This modification 2.2 also makes it possible to realize the input voltage dependency of the light amount similar to that shown in FIG.

[0153] 19 is a circuit diagram of a lighting circuit 200H according to the modified example 2.2. The first constant current circuit 210_1 can be configured similarly to that in FIG. 15. The second constant current circuit 210_2 includes an error amplifier EA4 and resistors R8 and R9 in addition to the components in FIG. 15. The resistors R8 and R9 are connected to a stabilizing voltage V REG The error amplifier EA4 is a buffer (voltage follower) that divides the potential at one end of the low potential side of resistor R3 by V REG Maintain at / 2.

[0154] The high potential end of resistor R3 is connected to V ADIM2 is applied to the other end on the low potential side, V RE G Therefore, the voltage across resistor R3 is V ADIM2 -V REG / 2 Therefore, the current I ADIM2 is expressed by equation (10). I ADIM2 =(V ADIM2 -V REG / 2 ) / R3 …(10) This makes it possible to realize the input / output characteristics of equation (9).

[0155] Fig. 20 is a circuit diagram of the control circuit 220H of Fig. 19. The control circuit 220H includes resistors R4 and R5, a non-inverting amplifier 240, and an inverting amplifier 242H. The configuration of the non-inverting amplifier 240 is similar to that of Fig. 16.

[0156] The inverting amplifier 242H includes a V / I conversion circuit 244 and a resistor R11. The V / I conversion circuit 244 converts the first analog dimming signal V ADIM1 The V / I conversion circuit 244 includes a transistor Q3, an error amplifier EA5, and a resistor R10. One end of the resistor R11 is connected to a stabilizing voltage V REG is applied to the resistor R11, and the other end is connected to the V / I conversion circuit 244. A second analog dimming signal V ADIM2 The first analog dimming signal V ADIM1may be taken from the output of the non-inverting amplifier 240, or from the connection node between the resistor R11 and the transistor Q3.

[0157] According to the control circuit 220H of FIG. 20, the analog dimming signal V ADIM 1,V ADIM2 can be generated.

[0158] (Variation 2.3) In the second embodiment, the light emitting element 112 is a white LED, but this is not limited thereto. The light emitting element 112 may be a red LED. FIG. 21 is a circuit diagram of a vehicle lamp 100I including a lighting circuit 200I according to a modified example 2.3. In this vehicle lamp 100I, m=2, n=2, and V TH2 V TH2 > 2×Vf.

[0159] (Variation 2.4) 22 is a circuit diagram of a vehicle lamp 100J including a 200J according to the modified example 2.4. In this modified example, the first constant current circuit 210_1 and the second constant current circuit 210_2 omit the V / I conversion circuit in the first stage and have negative V / I conversion gains K1, K2 (<0). ADIM# is the maximum voltage level V IN When the output current I OUT# becomes zero, and the analog dimming signal V ADIM# The lower the output current I OUT# increases.

[0160] (Variation 2.5) Fig. 23 is a circuit diagram of a vehicle lamp 100K including a lighting circuit 200K according to a modified example 2.5. In this modified example 2.5, the first constant current circuit 210_1 and the second constant current circuit 210_2 are configured as current sinks. The vehicle lamp 100K can be understood as having a configuration in which the vehicle lamp 100J in Fig. 22 is inverted.

[0161] Fig. 24 is a circuit diagram showing a specific configuration example of the vehicle lamp 100K of Fig. 23. The constant current circuits 210_1 and 210_2 are of a current sink type and have a configuration obtained by inverting the constant current circuits 210_1 and 210_2 of Fig. 22. The V / I conversion gains K1 and K2 of the constant current circuits 210_1 and 210_2 of Fig. 22 are positive.

[0162] (Variation 2.6) In the explanation so far, the multiple light-emitting elements 112 are chips having substantially the same characteristics, and the amount of light emitted when the same current is supplied is substantially equal, but chips with different characteristics may also be used.

[0163] For example, the characteristics of the m chips included in the first portion 114 may be uniform, and the characteristics of the n chips included in the second portion 116 may be uniform. In this case, the luminous flux (light amount) of each of the n light-emitting elements 112 included in the second portion 116 may be greater than the luminous flux of each of the m light-emitting elements 112 included in the first portion 114. The luminous flux of the light-emitting elements 112 is uniform when the same driving current I LED This refers to the luminous flux when driven by

[0164] Even LED chips with the same product number supplied by the same vendor will have different luminous fluxes when supplied with the same drive current due to manufacturing variations. LED chip vendors may rank LED chips based on luminous flux before selling them. In this case, chips with a higher luminous flux rank may be used for the second portion 116, and chips with a lower luminous flux rank may be used for the first portion 114. Alternatively, a manufacturer of vehicle lamps, rather than a vendor of LED chips, may rank a large number of LED chips that it purchases based on luminous flux.

[0165] Alternatively, when LED chips with different part numbers having different luminous flux are provided by the same vendor, the chip with the part number having the larger luminous flux may be used for the second portion 116 and the chip with the part number having the smaller luminous flux may be used for the first portion 114.

[0166] Alternatively, first portion 114 may use chips of the same part number provided by a first vendor, and second portion 116 may use chips with a higher luminous flux provided by a second vendor.

[0167] A current amount I REF The amount of light (luminous flux) when the same current I flows through one LED chip included in the second portion 116 is defined as U. R EF The amount of light (luminous flux) when the light flows is defined as α×U. α is a coefficient larger than 1, and can be set to about α=1.3, and more preferably, α=1.5.

[0168] In this modification 2.6, as shown in FIG. 13, the output current I OUT1 ,I OUT2 In this case, V IN >V TH1 In the normal voltage region, the total luminous flux (light amount) of the semiconductor light source 110 is 1×U+2×α×U. IN <V TH2 In this low voltage region, the total luminous flux (light amount) of the semiconductor light source 110 is 2×α×U. Therefore, the light amount in the low voltage region is 2α / (1+2α) times that in the normal voltage region. Therefore, the larger α is, the more the rate of decrease in the light amount can be suppressed.

[0169] (Variation 2.7) In the second embodiment, the light emitting element 112 is described as an LED, but an LD (laser diode) or an organic EL element may also be used.

[0170] (Variation 2.8) Bipolar transistors and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) can be interchanged. In this case, the base, collector, and emitter are replaced by the gate. The term "NPN" can be replaced with "PNP" (P channel).

[0171] (Variation 2.9) The constant current circuits 210_1 and 210_2 may be configured with a current D / A converter. In that case, the analog dimming signal V ADIM1 ,V ADIM2 becomes a digital signal, and the control circuit 220 can be configured as a digital circuit.

[0172] (Embodiment 3) (Overview of the Third Embodiment) A lighting circuit according to an embodiment drives a semiconductor light source. The semiconductor light source includes a first portion consisting of m (m≧1) light emitting elements connected in series, and a second portion consisting of n (n≧1) light emitting elements. The lighting circuit includes a first constant current circuit provided in series with the first portion and the second portion between an input terminal and a ground terminal, and generating a first output current of a first current amount in an enabled state, a second constant current circuit provided in series with the second portion between the input terminal and a ground terminal, and generating a second output current in an enabled state, and a control circuit that controls enabling and disabling of the first constant current circuit and the second constant current circuit. In a disconnection state of the first portion, the control circuit enables the second constant current circuit and disables the first constant current circuit, and sets the second output current to a second current amount greater than the first current amount.

[0173] According to this configuration, when the first portion is disconnected, the semiconductor light source can be kept on by switching from the first constant current circuit to the second constant current circuit. Then, by driving the second portion with the second current amount that is larger than normal, it is possible to prevent the light amount (luminous flux) in the disconnected state from being significantly reduced compared to the light amount in the normal state.

[0174] In one embodiment, the second current amount may be less than or equal to (m+n) / n times the first current amount and less than the rated current of the second portion.

[0175] In one embodiment, the lighting circuit may further include a bypass switch provided in parallel with the second portion. The first constant current circuit may be capable of switching the first output current between a first current amount and a third current amount greater than the first current amount. The control circuit may turn on the bypass switch in a disconnection state of the second portion, enable the first constant current circuit, disable the second constant current circuit, and set the first output current to the third current amount.

[0176] According to this configuration, when the second portion is disconnected, the semiconductor light source can be kept lit by switching from the second constant current circuit to the first constant current circuit after turning on the bypass switch. Then, by driving the first portion with a third current amount that is larger than normal, it is possible to prevent the light amount (luminous flux) in the disconnected state from being significantly reduced compared to the light amount in the normal state.

[0177] In one embodiment, the third current amount may be less than or equal to (m+n) / m times the first current amount and less than the rated current of the first portion.

[0178] In one embodiment, the second constant current circuit may be enabled when the semiconductor light source is in an open state and the input voltage is lower than a predetermined threshold. The second output current may be a second current amount at this time. This makes it possible to suppress fluctuations in the amount of light in the open state.

[0179] In one embodiment, the second constant current circuit may be enabled when the semiconductor light source is in an open state and the input voltage is lower than a predetermined threshold value, and the second output current at this time may be the first current amount.

[0180] A lighting circuit according to one embodiment includes a first constant current circuit provided in series with a first portion and a second portion between an input terminal and a ground terminal and configured to generate a first output current having a first current amount or a third current amount greater than the first current amount in an enabled state, a second constant current circuit provided in series with the second portion between the input terminal and a ground terminal and configured to generate a second output current in an enabled state, a control circuit that controls enabling and disabling of the first constant current circuit and the second constant current circuit, and a bypass switch provided in parallel with the second portion. In a disconnection state of the second portion, the control circuit turns on the bypass switch to enable the first constant current circuit and disable the second constant current circuit, and sets the first output current to the third current amount.

[0181] According to this configuration, when the second portion is broken, the semiconductor light source can be kept lit by switching from the second constant current circuit to the first constant current circuit after turning on the bypass switch. By driving the first portion with a third current amount that is larger than normal, it is possible to prevent the light amount (luminous flux) in the broken state from decreasing significantly compared to the light amount in the normal state.

[0182] In one embodiment, the third current amount may be less than or equal to (m+n) / m times the first current amount and less than the rated current of the first portion.

[0183] (Detailed Description of the Third Embodiment) 25 is a circuit diagram of a vehicle lamp 100 according to embodiment 3.1. The vehicle lamp 100 receives a DC voltage (input voltage) V IN is supplied.

[0184] The vehicle lamp 100 includes a semiconductor light source 110 and its lighting circuit 200. A suitable embodiment of the vehicle lamp 100 is an LED socket in which the semiconductor light source 110 and the lighting circuit 200 are housed in one package, and has a shape that allows it to be attached to and detached from a lamp body (not shown). The LED socket is required to have a long life, and since it is a consumable item, it is strongly required to reduce the cost.

[0185] The semiconductor light source 110 is a light emitting element string including (m+n) light emitting elements 112 connected in series. In this embodiment, the light emitting elements 112 are, for example, white LEDs, where m+n=3. The multiple light emitting elements 112 are chips having substantially the same characteristics, and the light amounts when the same current is supplied are substantially equal.

[0186] The semiconductor light source 110 is divided into a first portion 114 consisting of m light emitting elements 112_1 on the high potential side, and a second portion 116 consisting of n light emitting elements 112_2 and 112_3 on the low potential side.

[0187] The lighting circuit 200 may be an IC (Integrated Circuit) integrated on a single semiconductor substrate, or may be configured by combining a plurality of discrete elements. The lighting circuit 200 has an input terminal IN, a ground terminal GND, and three output terminals OUT1 to OUT3. The input terminal IN receives a power supply voltage (input voltage V IN ) is supplied to the first portion 114 of the semiconductor light source 110, and the ground terminal GND is grounded. The anode of the first portion 114 of the semiconductor light source 110 is connected to the output terminal OUT1, and the cathode of the first portion 114 is connected to the output terminal OUT2. The anode of the second portion 116 of the semiconductor light source 110 is connected to the output terminal OUT2, and the cathode of the second portion 116 is connected to the output terminal OUT3. The output terminal OUT3 is connected to the ground terminal GND.

[0188] The lighting circuit 200 includes a first constant current circuit 210_1, a second constant current circuit 210_2, a control circuit 220, and a bypass switch 230. The output of the first constant current circuit 210_1 is connected to the anode of the first portion 114 via an output terminal OUT1, and the input of the first constant current circuit 210_1 is connected to the input terminal IN via a diode D1 for preventing reverse connection. In other words, the first constant current circuit 210_1 is provided in series with the multiple light emitting elements 112_1 to 112_3 between the input terminal IN and the ground terminal GND. The first constant current circuit 210_1 has an enable terminal EN, and is configured to be switchable between enabled and disabled in response to a first enable signal EN1 input to the enable terminal EN, and in the enabled state, a first output current I OUT1 Generate.

[0189] The output of the second constant current circuit 210_2 is connected to the anode of the second portion 116 via an output terminal OUT2, and the input of the second constant current circuit 210_2 is connected to the input terminal IN via a diode D1. That is, the second constant current circuit 210_2 is provided in series with the second portion 116 of the semiconductor light source 110 between the input terminal IN and the ground terminal GND. The second constant current circuit 210_2 has an enable terminal EN and is configured to be switchable between enabled and disabled states according to a second enable signal EN2 input to the enable terminal EN, and in the enabled state outputs a second output current I OUT2 Generate.

[0190] First output current I OUT1 is the first current I REF1 Or, the first current I REF1 The third current I is greater than REF3 The first output current I OUT1 The amount of current is controlled in response to a first current control signal CNT_CUR1.

[0191] 3rd current amount I REF3 is the first current amount I REF1 It is preferable that the number of n is close to (m+n) / m times the number of n.

[0192] Second output current I OUT2is the first current I REF1 Or, the first current I REF1 The second current I is larger REF2 The second output current I OUT2 The amount of current is controlled in response to a second current control signal CNT_CUR2.

[0193] 2nd current amount I REF2 is the first current amount I REF1 It is desirable to have a value close to (m+n) / n times the original value.

[0194] The bypass switch 230 is connected in parallel to the second portion 116 and is switched on and off in response to a control signal CNT_SW generated by the control circuit 220.

[0195] The control circuit 220 is configured to be able to detect a break in each of the first portion 114 and the second portion 116. The control circuit 220 is connected to an input voltage V IN is supplied, and the input voltage V IN Based on the results of the detection of the disconnection of the first portion 114 and the second portion 116, the enable / disable of the first constant current circuit 210_1 and the second constant current circuit 210_2 and the first output current I OUT1 , the second output current I OUT2 It controls the amount of current flowing through each of these, as well as the on / off state of the bypass switch 230.

[0196] Next, the control by the control circuit 220 will be specifically described. IN A state in which V is supplied is called a normal voltage state, and a state in which V is not supplied is called a low voltage state. A state in which no disconnection occurs in either the first portion 114 or the second portion 116 is called a non-disconnection state. For example, V IN The state where it satisfies ≧(m+n)×Vf is the normal voltage state.

[0197] First, the control in the non-disconnected state will be described. In the non-disconnected state, the bypass switch 230 is off.

[0198] (i) When the voltage is normal and the line is not broken, the first constant current circuit 210_1 is enabled; The second constant current circuit 210_2 is disabled. Also, the first output current I OUT1 The first current I REF1 At this time, the light emitting elements 112_1 to 112_3 are supplied with the first current amount I R EF1 Output current I OUT1 Powered by, all three chips light up.

[0199] (ii) In a low voltage state and an unbroken line state, the first constant current circuit 210_1 is disabled and the second constant current circuit 210_2 is enabled. The second output current I OUT2 The first current I REF1 At this time, the light emitting elements 112_2 and 112_3 are supplied with the first current amount I R EF1 Output current I OUT2 It is driven by and two chips are lit up.

[0200] Next, control of the disconnection state will be described.

[0201] (iii) When the first portion 114 is in a disconnected state, the first constant current circuit 210_1 is disabled. The second constant current circuit 210_2 is enabled, and the second output current I OUT2 The second current I REF2 In addition, the bypass switch 230 is turned off. At this time, the light emitting elements 112_2 and 112_3 are supplied with the second current amount I REF2 Output current I OUT2 It is driven by and two chips are lit up.

[0202] (iv) When the second portion 116 is in a disconnection state, the first constant current circuit 210_1 is enabled, the second constant current circuit 210_2 is disabled, and the bypass switch 230 is turned on. In addition, the first output current I OUT1 The third current I REF3 At this time, the light emitting element 112_1 receives a third current amount I REF3 Output current IOUT1 is driven and one chip lights up.

[0203] Fig. 26 is a diagram showing the states of the vehicular lamp 100 of Fig. 25. The vehicular lamp 100 can take four states φ1 to φ4. The control circuit 220 controls the input voltage V IN Depending on the presence or absence of a break, one of four states φ1 to φ4 is selected to change the state of the lighting circuit 200.

[0204] The above is the configuration of the vehicular lamp 100. Next, the operation will be described.

[0205] FIG. 27 is an equivalent circuit diagram showing the first state φ1. In the first state, the first target quantity I REF 1st output current I OUT1 As a result, the three light emitting elements 112_1 to 112_3 are turned on.

[0206] FIG. 28 is an equivalent circuit diagram showing the second state φ2. In the second state, the first target quantity I REF 1's second output current I OUT2 This causes the two light emitting elements 112_2 and 112_3 to light up.

[0207] FIG. 29 is an equivalent circuit diagram showing the third state φ3. In the third state, the second target quantity I REF The second output current I OUT2 This causes the two light emitting elements 112_2 and 112_3 to light up.

[0208] FIG. 30 is an equivalent circuit diagram showing the fourth state φ4. In the fourth state, the third target quantity I REF 3. First output current I OUT1 This causes one light emitting element 112_1 to light up.

[0209] The above is the operation of the vehicular lamp 100. According to this vehicular lamp 100, even if one of the first portion 114 and the second portion 116 is broken, the light can be maintained in a lit state.

[0210] now, I REF2=(m+n) / n×I REF1 =3 / 2×I REF1 I REF3 =(m+n) / m×I REF1 =3×I REF1 It is assumed that the first target amount I REF1 When the driving current of the second target amount I flows through one light emitting element 112, the luminous flux of the second target amount I REF2 The luminous flux when the driving current is 1.5U, the third target quantity I REF3 The luminous flux when a drive current of 1U is flowing is expressed as 3U.

[0211] The total luminous flux of the semiconductor light source 110 in the first state φ1 is U×3 units=3U. The total luminous flux of the semiconductor light source 110 in the second state φ2 is U×2 units=2U. The total luminous flux of the semiconductor light source 110 in the third state φ3 is 1.5U×2 units=3U. The total luminous flux of the semiconductor light source 110 in the fourth state φ4 is 3U×1 unit=3U.

[0212] In other words, even when the light emitting element 112 is broken, the same level of luminous flux as when the light emitting element 112 is not broken can be achieved. REF2 <1.5×I REF1 , I REF3 <3×I REF1 However, it is preferable to use I REF2 and I REF3 By making it as large as possible, the decrease in the amount of light can be suppressed.

[0213] 31 is a circuit diagram of a constant current circuit 210 according to a first configuration example. The constant current circuit 210 includes a V / I conversion circuit 212, a current amplification circuit 214, and a variable voltage source 216. The variable voltage source 216 outputs a reference voltage V REF Generate.

[0214] The V / I conversion circuit 212 converts the reference voltage V REF The reference current I REF The V / I conversion circuit 212 includes a transistor Q2, a resistor R2, and an error amplifier (op-amp) EA2.REF =V REF / R2 relationship holds.

[0215] The current amplifier circuit 214 outputs a reference current I REF is amplified and the output current I OUT# The current amplifier circuit 214 includes resistors R1 and R3, a transistor Q1, and an error amplifier EA1. OUT# is expressed by the following formula: I OUT# =I REF ×R3 / R1

[0216] To switch between enable and disable, transistors Q3 and Q4 and a resistor R4 are provided. The transistor Q3 is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and is provided between the current amplifier circuit 214 and the input terminal. When the enable signal EN# is high, the transistor Q4 is turned on, the gate voltage of the transistor Q3 is low, and the transistor Q3 is turned on. This state is the enable state of the constant current circuit 210_#. When the enable signal EN# is low, the transistor Q4 is turned off, the gate voltage of the transistor Q3 is high, and the transistor Q3 is turned off. This state is the disable state of the constant current circuit 210_#.

[0217] Fig. 32 is a circuit diagram of a constant current circuit 210 according to the second configuration example. A current amplifier circuit 214 in Fig. 32 is configured by adding a transistor Q6 and resistors R8 and R9 to the current amplifier circuit 214 in Fig. 31, and is switchable between on and off.

[0218] The enable signal \EN# is negative logic (\ represents negative logic, and is shown by a bar in the figure). When the enable signal \EN# is low, the transistor Q5 is turned off. This causes the base-emitter voltage of the transistor Q6 to become zero, the transistor Q6 is turned off, and the current amplifier circuit 214 is turned on.

[0219] When the enable signal \EN# is high, the transistor Q5 is turned on, which turns on the transistor Q6, causing the gate-source voltage of the transistor Q1 in the current amplifier circuit 214 to become lower than the threshold voltage, and the transistor Q1, i.e., the current amplifier circuit 214, is turned off.

[0220] Fig. 33 is a circuit diagram showing a specific configuration example of the lighting circuit 200. The constant current circuits 210_1 and 210_2 include a variable current source 211 and an input switch 213. The variable current source 211 corresponds to the V / I conversion circuit 212, the current amplification circuit 214, and the variable voltage source 216 in Fig. 31. The input switch 213 corresponds to the transistor Q3 in Fig. 31.

[0221] The input voltage monitoring circuit 222 monitors the input voltage V IN is monitored and a predetermined threshold V TH The input voltage monitoring circuit 222 compares V IN >V TH On the other hand, when V I N <V TH At this time, the first enable signal EN1 and the second enable signal EN2 are generated so that the first constant current circuit 210_1 is in a disabled state and the second constant current circuit 210_2 is in an enabled state.

[0222] For example, the input voltage monitoring circuit 222 includes a Zener diode ZD21 and resistors R21 to R23. IN is the Zener voltage-based threshold V TH, the Zener diode ZD21 becomes conductive, the base of the transistor Q21 becomes high, and the transistor Q21 becomes conductive. As a result, the gate of the input switch 213, i.e., the first enable signal \EN1, becomes low, the input switch 213 of the first constant current circuit 210_1 turns on, and the first constant current circuit 210_1 becomes enabled. At this time, the second enable signal \EN2 is high, the input switch 213 of the second constant current circuit 210_2 turns off, and the second constant current circuit 210_2 becomes disabled.

[0223] Input voltage V IN is the threshold value V TH In the lower state, no current flows through the Zener diode ZD21, the base of the transistor Q21 goes low, and the transistor Q21 turns off. As a result, the gate of the input switch 213, i.e., the first enable signal \EN1, goes high, the input switch 213 of the first constant current circuit 210_1 turns off, and the first constant current circuit 210_1 is in a disabled state. At this time, the second enable signal \EN2 is low, the input switch 213 of the second constant current circuit 210_2 turns on, and the second constant current circuit 210_2 is in an enabled state.

[0224] The input voltage monitoring circuit 222 may be configured with a voltage comparator. In this case, the voltage comparator may be a hysteresis comparator. I N is the threshold value V TH This helps prevent flickering when nearby fluctuations occur.

[0225] The resistor Rs1 and the comparator COMP1 are provided to detect an open circuit in the semiconductor light source 110. The output of the comparator COMP1 is a normal first output current I OUT1 When it flows, it is high, and when it does not flow, it is low.

[0226] The resistor Rs2 and the comparator COMP2 are provided to detect an open circuit in the second portion 116. The output of the comparator COMP2 is a normal second output current I OUT2When it flows, it is high, and when it does not flow, it is low.

[0227] The outputs of the two comparators COMP1 and COMP2 are input to the logic gate NAND1. The output A of the logic gate NAND1 is a current I OUT1 ,I OUT2 When no current flows, the output of the timer circuit 224 goes low when the output A of the logic gate NAND1 goes low and a predetermined time τ1 has elapsed since the semiconductor light source 110 was disconnected, and the timer circuit 224 sets its output B to high and sets the flip-flop FF1 in the subsequent stage. The power-on reset signal POR is input to the reset terminal of the flip-flop FF1, and the flip-flop FF1 is reset when the lighting circuit 200 is started up.

[0228] An output C of the flip-flop FF1 is supplied to the second constant current circuit 210_2 as a second current control signal CNT_CUR2. The output C of the flip-flop FF1 is also supplied to a tri-state buffer 228. An output G of the tri-state buffer 228 has high impedance when the signal C is low, and takes a level according to its input F when the signal C is high.

[0229] The inverted output \C of the flip-flop FF1 and the output A of the logic gate NAND1 are input to the logic gate NAND2. When the output D of the logic gate NAND2 becomes low, the timer circuit 226 starts timing, and after a predetermined time τ2 has elapsed, its output E becomes high, the subsequent flip-flop FF2 is set, and the output F of the flip-flop FF2 becomes high. The output F of the flip-flop FF2 is input to the gate of the bypass switch 230 as a control signal CNT_SW. In addition, the output F of the flip-flop FF2 is supplied to the second constant current circuit 210_2 as a second current control signal CNT_CUR2. When the output F becomes high, the current of the second constant current circuit 210_2 increases.

[0230] 34 is a first operational waveform diagram of the vehicular lamp 100 of FIG. 33. At time t0, the threshold voltage V TH Higher input voltage V INThe first enable signal EN1 goes low, and the first output current I OUT1 is supplied to the semiconductor light source 110.

[0231] Immediately after the lighting circuit 200 is started, the power-on reset POR is asserted, and the output F of the flip-flop FF2 becomes low. Therefore, the first current control signal CNT_CUR1 becomes low, and the first output current I OUT1 The target value of the first current I REF1 In addition, since the control signal CNT_SW is low, the bypass switch 230 is off.

[0232] In response to the assertion of the power-on reset POR, the output C of the flip-flop FF1 goes low. Therefore, the second current control signal CNT_CUR2 goes low, and the second output current I OUT2 The target value of the first current I REF1 The output G of the tri-state buffer 228 is in a high impedance state.

[0233] Assume that the first portion 114 is broken at time t1. Then, the first output current I OUT1 stops flowing, output A of logic gate NAND1 goes low, and at time t2 after a predetermined time τ1 has elapsed, signals B and C go high. This enables tri-state buffer 228, and its output G goes low, the same as input F. As a result, the second enable signal \EN2 goes low, and second constant current circuit 210_2 is enabled. Because signal C, i.e., second current control signal CNT_CUR2, is high, second output current I OUT2 is the second current I REF2 The second output current I OUT2 flows to the second portion 116, causing the output A of logic gate NAND1 to return high.

[0234] 35 is a second operational waveform diagram of the vehicular lamp 100 of FIG. 33. At time t0, the threshold voltage V TH Higher input voltage V INIt is assumed that a disconnection occurs in the second portion 116 at time t1.

[0235] Then the first output current I OUT1 stops flowing, output A of logic gate NAND1 goes low, and then, at time t2 after a predetermined time τ1 has elapsed, signals B and C go high. This enables tri-state buffer 228, and its output G goes low, the same as input F. This causes the second enable signal \EN2 to go low, and the second constant current circuit 210_2 is enabled. Because signal C, i.e., second current control signal CNT_CUR2, is high, the second output current I OUT2 The target amount of the second current I REF2 However, since the second portion 116 is open, the second output current I OUT2 cannot flow and output A of logic gate NAND1 remains low.

[0236] When signals A and C both go low at time t2, output D of logic gate NAND2 goes low, and then after a predetermined time τ2 has elapsed, signal E goes high, flip-flop FF2 is set, and signal F goes high. As a result, output G of tri-state buffer 228 goes high, first enable signal EN1 goes low, and first constant current circuit 210_1 is enabled. In addition, bypass switch 230 is turned on based on signal F at a high level, and first output current I OUT1 The target amount of the third current I REF3 will be boosted to.

[0237] After time t3, the third current amount I REF3 The first output current I OUT1 flows through a path that includes the first portion 114 and the bypass switch 230. As a result, the outputs A and D of the logic gates NAND1 and NAND2 go high.

[0238] The above is the operation of the vehicular lamp 100 in FIG.

[0239] According to the vehicle lamp 100 of FIG. 33, when a disconnection occurs, the input voltage V IN Regardless of the magnitude relationship between the threshold value VTH and the second constant current circuit 210_2, the boosted second output current I OUT2 If the semiconductor light source 110 still does not light up, the bypass switch 230 is turned on to enable the first constant current circuit 210_1, thereby driving the second portion 116 with the boosted first output current I O UT1 The first portion 114 can be driven by

[0240] (Embodiment 3.2) 36 is a block diagram of a vehicle lamp 100A according to embodiment 3.2. In embodiment 3.2, the output current I OUT2 The target amount is the second target amount I R EF2 Therefore, the second current control signal CNT_CUR2 for the second constant current circuit 210_2 is omitted.

[0241] Fig. 37 is a diagram showing the state of the vehicular lamp 100A of Fig. 36. The amount of current of the second constant current circuit 210_2 in the non-disconnected low voltage state (second state φ2) is different from that in the second state φ2 of embodiment 3.1, but the rest is the same.

[0242] In embodiment 3.2, I REF2 =(m+n) / n×I REF1 =3 / 2×I RE F1 In addition, one light emitting element 112 has I REF1 The amount of light when the input voltage V IN This allows the light output to remain constant regardless of the voltage level.

[0243] In reality, due to the constraints of the rated current of the light emitting element 112, IREF2 <1.5×I REF1 However, it is preferable to use I REF2 By making it as large as possible, the decrease in the amount of light can be suppressed.

[0244] Modifications related to embodiment 3.1 and embodiment 3.2 will be described.

[0245] (Variation 3.1) In the embodiment 3.1 or 3.2, the light emitting element 112 is a white LED, but this is not limited thereto. The light emitting element 112 may be a red LED. FIG. 38 is a circuit diagram of a vehicle lamp 100I including a lighting circuit 200I according to the modified example 3.1. In this vehicle lamp 100I, m=2, n=2, and V TH V TH > n × Vf.

[0246] (Variation 3.2) 39 is a circuit diagram of a vehicle lamp 100K including a lighting circuit 200K according to Modification 3.2. In this Modification 3.2, the first constant current circuit 210_1 and the second constant current circuit 210_2 are configured as current sink types.

[0247] (Variation 3.3) In the embodiment 3.1 or 3.2, the light emitting element 112 is described as an LED, but an LD (laser diode) or an organic EL element may also be used.

[0248] (Variation 3.4) Bipolar transistors and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) can be interchanged. In this case, the base, collector, and emitter are replaced by the gate. The term "NPN" can be replaced with "PNP" (P channel).

[0249] (Embodiment 4) (Outline of the fourth embodiment) A light source module according to one embodiment includes an LED string including n (n≧2) LEDs (light emitting diodes) of the same color connected in series, an LED driver circuit that receives an input voltage and supplies a drive current stabilized to a target current to the LED string, and a bypass circuit that is provided in parallel with a bypassed portion including adjacent m (m≦n) LEDs of the LED string and sinks a bypass current according to the input voltage. The luminous flux of (nm) LEDs arranged in a portion other than the bypassed portion is greater than the luminous flux of m LEDs arranged in the bypassed portion.

[0250] According to this configuration, it is possible to suppress a decrease in the amount of light in a low voltage state, compared to a case in which all of the n LEDs have the same luminous flux.

[0251] In one embodiment, the LEDs may be red, n=4, and m=2. With this configuration, when the input voltage drops, two LEDs are bypassed, so that the LED string can be prevented from turning off even if the load on the battery increases during idling stop. Therefore, when this light source module is used for a rear marker lamp, it is possible to prevent the LED string from being unintentionally turned off while the vehicle is stopped, which would send an incorrect message to the following vehicles.

[0252] In one embodiment, the LEDs may be white or blue, and n=3, m=1.

[0253] In one embodiment, the luminous flux of the (nm) LEDs may be 1.3 times or more that of the m LEDs. More preferably, the luminous flux of the (nm) LEDs may be 1.5 times or more that of the m LEDs. When the bypass current is changed according to the input voltage, the change in luminous flux with respect to the fluctuation of the input voltage becomes small, so that flickering can be suppressed.

[0254] In one embodiment, the bypass circuit may include a current source that generates a bias current whose magnitude increases as the input voltage decreases.

[0255] In one embodiment, the slope of the bypass current versus input voltage is set so that the slope of the luminous flux of the LED string versus input voltage change is 5% / 0.1 V or less, which makes it difficult for humans to sense fluctuations in the amount of emitted light caused by short-term fluctuations in the input voltage.

[0256] In one embodiment, the bypass circuit may include a bypass switch that turns on when the input voltage falls below a predetermined threshold.

[0257] (Detailed Description of the Fourth Embodiment) (Embodiment 4.1) 41 is a block diagram of a vehicle lamp 500A according to embodiment 4.1. The vehicle lamp 500A receives a DC voltage (input voltage) V IN is supplied. The vehicle lamp 500A includes an LED string 502 and a lighting circuit 600. The LED string 502 includes n=3 LEDs 504_1 to 504_3 connected in series. The LEDs 504_1 to 504_3 may be LED chips.

[0258] A preferred embodiment of the vehicle lamp 500A 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 500A is an LED socket having a shape that can be attached to and detached from a lamp body (not shown), similar to a conventional automobile light bulb. The LED socket is required to have a long life, and is also required to be low-cost because it is a consumable item.

[0259] In this embodiment, the LEDs are white and may be clearance lamps or DRLs (Daytime Running Lamps). Alternatively, the LEDs may be blue. The lighting circuit 600 includes a diode 602 for reverse connection protection, an LED driver circuit 610, a bypass circuit 620, and a disconnection detection circuit 630.

[0260] The LED driver circuit 610 receives the input voltage V IN5, the LED string 502 receives the target amount I REF The drive current I LED The LED driver circuit 610 includes: (i) a constant current linear regulator; or (iii) a constant voltage output step-down switching converter. It can be constructed either by a combination of a constant current inverter and a constant current circuit, or by a resistor.

[0261] The bypass circuit 620 is connected in parallel with m=1 (504_3) of the multiple LEDs 504_1 to 504_3. The LED 504_3 is also referred to as a bypassed portion 503. The bypass circuit 620 can be switched between an enabled state and a disabled state, and in the enabled state, IN Bypass current I according to BYPASS from the LED string 502. BYPASS When the current I flows through the bypassed portion 503, LED -I BYPASS It becomes. BYPASS When I = 0, the bypassed portion 503 receives a driving current I LED is supplied and lights up, and I BYPASS =I LE D At this time, the bypassed portion 503 is turned off.

[0262] The disconnection detection circuit 630 is configured to be able to detect a disconnection in the bypassed portion 503. When the disconnection detection circuit 630 detects a disconnection fault in the bypassed portion 503, the disconnection detection circuit 630 disables the bypass circuit 620. The bypass circuit 620 in the disabled state flows a bypass current I BYP ASS becomes 0 and is no longer able to sink current.

[0263] The method of detecting a disconnection 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 AHowever, if the threshold voltage m×Vf=Vf is exceeded, it may be determined that an open circuit fault has occurred in the bypassed portion 503. Vf is the forward voltage of the LED 504.

[0264] For example, the open circuit detection circuit 630 may detect the voltage of node A as a threshold voltage V OPEN The input may include a voltage comparator for comparing the threshold voltage V OPEN may be set slightly higher than m×Vf=Vf.

[0265] In this embodiment, the luminous flux of the (nm)=2 LEDs 504_1 and 504_2 arranged in a portion other than the bypassed portion 503 is greater than the luminous flux of the m=1 LED 504_3 arranged in the bypassed portion 503. The luminous flux of the LEDs is LED This refers to the luminous flux when driven by

[0266] Even LED chips of the same product number supplied by the same vendor have different luminous fluxes when supplied with the same drive current due to manufacturing variations. LED chip vendors may rank LED chips based on luminous flux before selling them. In this case, chips with a higher luminous flux ranking may be used for LEDs 504_1 and 504_2, and chips with a lower luminous flux ranking may be used for LED 504_3. Alternatively, instead of the LED chip vendor, the manufacturer of the vehicle lamp 500A may rank a large number of LED chips purchased based on luminous flux.

[0267] Alternatively, when LED chips with different product numbers having different luminous fluxes are provided by the same vendor, a chip with a product number having a larger luminous flux may be used for LEDs 504_1 and 504_2, and a chip with a product number having a smaller luminous flux may be used for LED 504_3.

[0268] Alternatively, chips with the same product number provided by a first vendor may be used for LEDs 504_1 and 504_2, and a chip provided by a second vendor may be used for LED 504_3.

[0269] The luminous flux of the (nm)=2 LEDs 504_1 and 504_2 is preferably α=1.3 times or more the luminous flux of the (nm)=2 LEDs 504_3. More preferably, the luminous flux of the (nm)=2 LEDs 504_1 and 504_2 is α=1.5 times or more the luminous flux of the (nm)=1 LEDs 504_3.

[0270] The total luminous flux in the normal voltage state is (nm)×α+m, and the total luminous flux in the low voltage state is (nm)×α, so the rate of decrease in the total luminous flux in the low voltage state compared to the normal voltage state is (nm)×α / {(nm)×α+m} times. When α>1, the relationship (nm)×α / {(nm)×α+m}>(nm) / n holds.

[0271] FIG. 42 is a diagram for explaining the operation of the vehicle lamp 500A of FIG. 41. The horizontal axis represents the input voltage V IN The upper row shows the bypass current I BYPASS The lower row shows the total luminous flux (relative value) of the LED string 502.

[0272] Bypass current I BYPASS is the input voltage V IN is the first threshold V TH1 At higher voltages, it is 0 and at higher voltages, V IN is the second threshold V TH2 In the lower state I LE D is equal to V TH2 <V IN <V TH1 In the range of the bypass current I BYPASS is the input voltage V IN As the value of I decreases, the LED The second threshold V TH2 is (nm) × Vf + Vf (D) It is specified based on Vf (D) is the forward voltage of the diode for reverse polarity protection.

[0273] The bypass current I BYPASS Input voltage V IN The slope of the input voltage VIN It is recommended to set the slope of the input voltage V to 5% / 0.1V or less. IN This makes it difficult for humans to sense fluctuations in the amount of emitted light caused by short-term fluctuations in the amount of emitted light.

[0274] Input voltage V IN is the third threshold voltage V TH3 If it is lower, I LED ,I BYPAS S Both are zero.

[0275] For comparison, the operation of a conventional vehicle lamp is shown by a dashed line in FIG. 42. In the conventional vehicle lamp, the driving current I LED The luminous flux of the three LEDs when current is flowing is assumed to be equal to 1. In this case, the normal voltage state (V IN >V TH1 ) total luminous flux is 3, low voltage state (V IN <V TH2 ) the total luminous flux is 2, and at low voltage it decreases to 2 / 3 (=66%) of that at normal voltage.

[0276] In this embodiment, the driving current I LED The luminous flux of the LED 504_3 when current is flowing is 1, and the luminous flux of the LEDs 504_1 and 504_2 is α (>1). In this case, in the normal voltage state (V IN >V TH1 ) has a total luminous flux of 2α+1, and in the low voltage state (V IN <V TH2 ) the total luminous flux is 2α, and in the low voltage state it is 2α / (2α+1) times that in the normal voltage state.

[0277] When α>1, the relationship 2α / (2α+1)>2 / 3 holds, so this embodiment can suppress the reduction in light intensity in a low voltage state. For example, when α=1.3, the ratio of the reduction in light intensity is 2.6 / 3.6 times (=72%) in this embodiment, and when α=1.5, the ratio of the reduction in light intensity is 3 / 4 times (=75%) in this embodiment, which is an improvement over the conventional 66%.

[0278] The battery voltage is unstable, so VTH2 <V IN <V TH1 In the range of input voltage V IN When the input voltage V changes, the total luminous flux changes, resulting in flickering. In the embodiment, the ratio (slope) of the change in luminous flux to the change in input voltage in this range can be made smaller than in the conventional technology. IN Therefore, the fluctuation width of the light flux for the same amplitude fluctuation can be reduced.

[0279] Next, the operation of the disconnection detection circuit 630 will be described. IN (>V TH1 ) is supplied, I BYPASS At this time, if the bypassed portion 503 is disconnected, the current I LED current stops flowing, and the LED string 502 goes out. On the other hand, if the bypassed part 503 is disconnected, and the input voltage VIN drops, the bypassed part 503, which is the disconnected part, is bypassed by the bypass circuit 620, and the LED string 502 lights up, which is not preferable. In this embodiment, a disconnection detection circuit 630 is provided, and when a disconnection occurs, the bypass circuit 620 is disabled and the LED string 502 goes out. BYPASS By setting = 0, the input voltage V IN This allows the LED string to remain off regardless of the voltage level at

[0280] (Embodiment 4.2) 43 is a circuit diagram of a vehicle lamp 500B according to embodiment 4.2. The vehicle lamp 500B according to embodiment 4.2 is a rear marker lamp such as a stop lamp, a tail lamp, or a rear fog lamp, and the LED string 502 includes n=4 red LEDs 504_1 to 504_4.

[0281] The number m of LEDs included in the bypassed portion is 1. The bypass circuit 620 is connected in parallel with m=1 (504_4) of the multiple LEDs 504_1 to 504_4. The bypass circuit 620 can be switched between an enabled state and a disabled state, and in the enabled state, the input voltage VIN Bypass current I according to BYPASS from the LED string 502. BYPASS When the current I flows through the bypassed portion 503, LED -I BYPASS It becomes. BYPASS When I = 0, the bypassed portion 503 receives a driving current I LED is supplied and lights up, and I BYPASS =I LE D At this time, the bypassed portion 503 is turned off.

[0282] 44 is a diagram illustrating the operation of the vehicular lamp 500B of FIG. B YPASS The input voltage dependence of the second threshold V TH2 is (nm) × Vf + Vf (D) =3Vf+Vf (D) It is prescribed based on.

[0283] For comparison, the operation of a conventional vehicle lamp is shown by a dashed line in FIG. 44. In the conventional vehicle lamp, the driving current I LED The luminous flux of the four LEDs when current is flowing is assumed to be equal to 1. In this case, the normal voltage state (V IN >V TH1 ) total luminous flux is 4, low voltage state (V IN <V TH2 ) the total luminous flux is 3, and at low voltage it drops to 3 / 4 times (=75%) that at normal voltage.

[0284] In this embodiment, the driving current I LED The luminous flux of the LED 504_4 when current is flowing is 1, and the luminous flux of the LEDs 504_1 to 504_3 is α (>1). In this case, in the normal voltage state (V IN >V TH1 ) has a total luminous flux of 3α+1, and in the low voltage state (V IN <V TH2 ) the total luminous flux is 3α, and in the low voltage state it is 3α / (3α+1) times that in the normal voltage state.

[0285] When α>1, the relationship 3α / (3α+1)>3 / 4 holds, so this embodiment can suppress the reduction in light intensity in a low voltage state. For example, when α=1.3, the ratio of the reduction in light intensity is 3.9 / 4.9 times (≒80%) in this embodiment, and when α=1.5, the ratio of the reduction in light intensity is 4.5 / 5.5 times (≒82%) in this embodiment, which is an improvement over the conventional 75%.

[0286] The battery voltage is unstable, so V TH2 <V IN <V TH1 In the range of input voltage V IN When the input voltage V changes, the total luminous flux changes, resulting in flickering. In the embodiment, the ratio (slope) of the change in luminous flux to the change in input voltage in this range can be made smaller than in the conventional technology. IN Therefore, the fluctuation width of the light flux for the same amplitude fluctuation can be reduced.

[0287] (Embodiment 4.3) 45 is a circuit diagram of a vehicle lamp 500C according to embodiment 4.3. The vehicle lamp 500C according to embodiment 4.3 is a rear marker lamp such as a stop lamp, tail lamp, or rear fog lamp, as in embodiment 4.2, and the LED string 502 includes n=4 red LEDs 504_1 to 504_4.

[0288] In the embodiment 4.3, the number m of LEDs included in the bypassed portion 503 is 2. The bypass circuit 620 is connected in parallel with m=2 LEDs (504_3, 504_4) among the plurality of LEDs 504_1 to 504_4. The bypass circuit 620 can be switched between an enabled state and a disabled state, and in the enabled state, the input voltage V IN Bypass current I according to BYPASS from the LED string 502. BYPASS When the current I flows through the bypassed portion 503, LED -I BY PASS It becomes. BYPASS When I = 0, the bypassed portion 503 receives a driving current ILE D is supplied and lights up, and I BYPASS =I LED At this time, the bypassed portion 503 is turned off.

[0289] 46 is a diagram illustrating the operation of the vehicular lamp 500C of FIG. T H2 is (nm) × Vf + Vf (D) =2Vf+Vf (D) It is prescribed based on.

[0290] For comparison, the operation of a conventional vehicle lamp is shown by a dashed line in FIG. 46. In the conventional vehicle lamp, the driving current I LED The luminous flux of the four LEDs when current is flowing is assumed to be equal to 1. In this case, the normal voltage state (V IN >V TH1 ) total luminous flux is 4, low voltage state (V IN <V TH2 ) the total luminous flux is 2, and at low voltage it drops to 2 / 4 times (=50%) that at normal voltage.

[0291] In this embodiment, the driving current I LED The luminous flux of LED504_3 and LED504_4 when current is flowing is 1, and the luminous flux of LED504_1 and LED504_2 is α (>1). In this case, in the normal voltage state (V IN >V TH1 ) has a total luminous flux of 2α+2, and in the low voltage state (V IN <V TH2 ) the total luminous flux is 2α, and in the low voltage state it is 2α / (2α+2) times that in the normal voltage state.

[0292] When α>1, the relationship 2α / (2α+2)>2 / 4 holds, so this embodiment can suppress the reduction in light intensity in a low voltage state. For example, when α=1.3, the ratio of the reduction in light intensity is 2.6 / 4.6 times (≈57%) in this embodiment, and when α=1.5, the ratio of the reduction in light intensity is 3 / 5 times (=60%) in this embodiment, which is an improvement over the conventional 50%.

[0293] The battery voltage is unstable, so V TH2 <V IN <V TH1 In the range of input voltage V IN When the input voltage V changes, the total luminous flux changes, resulting in flickering. In the embodiment, the ratio (slope) of the change in luminous flux to the change in input voltage in this range can be made smaller than in the conventional technology. IN Therefore, the fluctuation width of the light flux for the same amplitude fluctuation can be reduced.

[0294] The vehicular lamp 500C of Fig. 45 has further advantages over the vehicular lamp 500B of Fig. 43. Fig. 47 is a diagram for explaining the operation of the vehicular lamp 500C with n=4 and m=2 in comparison with the vehicular lamp 500B with n=4 and m=1. Here, in order to focus on further advantages, the luminous fluxes of the four LEDs are assumed to be equal (i.e., α=1).

[0295] As shown in Figure 43, when there is one LED in the bypassed section, the input voltage V IN However, when the input voltage falls below a certain voltage V1, one of the four LEDs is bypassed by the bypass circuit, and the light output decreases toward 75%. IN When the voltage falls below a certain voltage V2 (for example, 1.8V x 3 + 0.8V = 6.2V), the light intensity drops to 0.

[0296] In contrast, when there are two LEDs in the bypassed section as shown in Figure 45, the input voltage V I N When the input voltage V falls below V1, the light intensity decreases toward 50%. IN Even if the input voltage V IN When the voltage drops to V3, the light output becomes 0%.

[0297] In recent years, the number of vehicles equipped with an idling stop function to improve fuel efficiency has increased. The stop lamp needs to be turned on when the vehicle is stopped, in other words, when the idling stop occurs. During the idling stop, the alternator stops, so if the load on the battery increases, the battery voltage, that is, the input voltage V of the vehicle lamp 500, IN For example, if the air conditioner is turned on or the steering wheel is operated to restart the engine during idling stop, the load current of the battery increases.

[0298] In the vehicle lamp 500B of FIG. 43, the battery voltage V BAT When the voltage drops below 6.2V, the LED string 10 is turned off. When the stop lamp is turned off, the following vehicle mistakenly recognizes that the preceding vehicle has started moving.

[0299] In contrast, according to the vehicle lamp 500C of FIG. 45, the input voltage V BAT Even if the voltage drops to 6.2 V, the two LEDs 504_3 and 504_4 are bypassed, so that the LED string 502 can be prevented from being turned off. Therefore, when the vehicle lamp 500C is used as a rear marker lamp, it is possible to prevent the LED string 502 from being turned off unintentionally while the vehicle is stopped, thereby preventing an erroneous message from being sent to a following vehicle.

[0300] 48(a) and (b) are circuit diagrams showing an example of the configuration of a bypass circuit 620. The bypass circuit 620 in FIG. 48(a) includes a voltage comparator 622 and a transistor (switch) 624. The voltage comparator 622 detects an input voltage V IN is the threshold voltage V TH Compared to V IN <V TH When this happens, the transistor 624 is turned on. The input voltage V IN As the voltage at the gate of the transistor 624 decreases, the current flowing through the transistor 624 may be reduced gradually by the bypass current I BYPASS Instead of the voltage comparator 622, an amplifier may be used.IN A pulse width modulator may be provided to generate a PWM (Pulse Width Modulation) signal having a duty cycle according to the input signal, and the gate of the transistor 624 may be driven based on the PWM signal.

[0301] The bypass circuit 620 of FIG. 48(b) includes a variable current source 626. The variable current source 626 is connected to an input voltage V IN Bypass current I BYPASS Generate.

[0302] Next, applications of the vehicle lamp 500 will be described. Fig. 400(a)-(d) are diagrams showing an LED socket, which is an example of the vehicle lamp 500. Fig. 400(a) is a perspective view of the exterior of the LED socket 700. Fig. 400(b) is a front view of the LED socket 700, Fig. 400(c) is a plan view of the LED socket 700, and Fig. 400(c) is a bottom view of the LED socket 700.

[0303] The housing 702 has a shape that allows it to be detachably attached to a lamp body (not shown). Multiple LEDs 504 are mounted in the center and are covered with transparent sealing resin 704. Components of the lighting circuit 600 are mounted on the substrate 710. The multiple LEDs 504 are red LED chips and are used as a stop lamp.

[0304] In the LED socket used both for a stop lamp and a tail lamp, a light emitting element for a tail lamp is mounted adjacent to the plurality of LEDs 504, and a lighting circuit for the tail lamp is mounted on the substrate 710.

[0305] Three pins 721, 722, and 723 are exposed on the bottom side of the housing 702. The pin 723 is connected to an input voltage V IN is supplied to pin 721, and a ground voltage is supplied to pin 722. An input voltage that becomes high when the tail lamp is turned on is supplied to pin 722. Pins 721 to 723 pass through the inside of housing 702, and one end of each is connected to the wiring pattern of substrate 710.

[0306] Modifications related to embodiments 4.1 to 4.3 will be described.

[0307] The total number n of LEDs and the number of LEDs in the bypassed portion are not limited to the values ​​described in the embodiment.

[0308] In addition, in the embodiments 4.1 to 4.3, a configuration in which one bypass circuit is provided has been described, but two or more bypass circuits may be provided. For example, as a modification of FIG. 41, a second bypass circuit is added in parallel with the LED 504_2, and after the first bypass circuit 620 becomes active, the input voltage V IN If the voltage drops further, a second bypass circuit may be activated.

[0309] (Application) Next, applications of the vehicle lamp 100 described in the first to fourth embodiments will be described. Figures 49(a) to (d) are diagrams showing an LED socket, which is an example of the vehicle lamp 100. Figure 49(a) is a perspective view of the exterior of the LED socket 700. Figure 49(b) shows a front view of the LED socket 700, Figure 49(c) shows a plan view of the LED socket 700, and Figure 49(c) shows a bottom view of the LED socket 700.

[0310] The housing 702 has a shape that allows it to be detachably attached to a lamp body (not shown). Multiple LEDs 504 are mounted in the center and are covered with transparent sealing resin 704. Components of the lighting circuit 600 are mounted on the substrate 710. The multiple LEDs 504 are red LED chips and are used as a stop lamp.

[0311] A plurality of pins 721, 722, and 723 are exposed on the bottom side of the housing 702. One of the plurality of pins (for example, 721) corresponds to the ground terminal GND in FIG. 1. Another one (for example, 723) is supplied with the battery voltage via a switch when the stop lamp is turned on. When the LED socket 700 is also used as a tail lamp, the other pin (722) is supplied with the battery voltage via a switch when the tail lamp is turned on.

[0312] The embodiments merely illustrate the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments without departing from the spirit of the present invention defined in the claims. [Industrial Applicability]

[0313] The present invention relates to a lamp for use in an automobile or the like. [Explanation of symbols]

[0314] 2 Battery 4 Switch 100 Vehicle lighting fixtures IN Input terminal GND Grounding terminal 110 Semiconductor light source 112 Light emitting element 114 Part 1 116 Part 2 200 Lighting circuit 210 Constant current circuit 220 Control circuit 221 Pulse Width Modulator 222 Amplifier 224 Oscillator 226 PWM Comparator 228 Inverter 500 Vehicle lighting fixtures 502 LED String 503 Bypassed Part 504 LED 600 Lighting circuit 602 Diode 610 LED driver circuit 620 Bypass Circuit 630 Disconnection detection circuit

Claims

1. A lighting circuit for driving a semiconductor light source including a first section including m (m≧1) light-emitting elements connected in series and a second section including n (n≧1) light-emitting elements, a first constant current circuit provided in series with the first portion and the second portion between an input terminal and a ground terminal, the first constant current circuit being switchable between an on state and an off state in response to a first enable signal; a second constant current circuit provided in series with the second portion between the input terminal and the ground terminal, the second constant current circuit being switchable between an on state and an off state in response to a second enable signal; (i) in a first voltage range in which an input voltage of the input terminal is higher than a first threshold, a duty cycle of the first enable signal is 100% and a duty cycle of the second enable signal is 0%, (ii) in a second voltage range in which the input voltage is lower than a second threshold, a duty cycle of the first enable signal is 0% and a duty cycle of the second enable signal is 100%, and (iii) in a third voltage range in which the input voltage is lower than the first threshold and higher than the second threshold, a control circuit which decreases the duty cycle of the first enable signal and increases the duty cycle of the second enable signal as the input voltage becomes lower. A lighting circuit comprising:

2. 2. The lighting circuit according to claim 1, wherein the duty cycle of the first enable signal and the duty cycle of the second enable signal in the third voltage range are determined so that a slope of a change in the input voltage of the total amount of light emitted from the light source is 5% / 0.1 V or less.

3. 3. The lighting circuit according to claim 1, wherein the second output current generated by the second constant current circuit in the on state is greater than the first output current generated by the first constant current circuit in the on state.

4. 4. The lighting circuit according to claim 1, wherein a sum of a duty cycle of the first enable signal and a duty cycle of the second enable signal is 100%.

5. 5. The lighting circuit according to claim 1, wherein the first enable signal and the second enable signal are mutually inverted signals.

6. 6. The lighting circuit according to claim 1, wherein the output currents of the first constant current circuit and the second constant current circuit change gradually at the timing when the first constant current circuit and the second constant current circuit are switched on and off.

7. 6. The lighting circuit according to claim 1, wherein the first constant current circuit generates a first output current proportional to a voltage level of the first enable signal, and the second constant current circuit generates a second output current proportional to a voltage level of the second enable signal.

8. 8. The lighting circuit according to claim 7, wherein at least one of a positive edge and a negative edge of the pulse-like first enable signal and the pulse-like second enable signal generated in the third voltage range is dull.

9. A vehicle lamp comprising the lighting circuit according to any one of claims 1 to 8.

10. 10. The vehicle lamp according to claim 9, which is an LED (light emitting diode) socket.

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