Vehicle lamp and lighting circuit

Abstract

The first constant current circuit (210) is arranged in series with a plurality of light emitting elements (112) between the input terminal (IN) and the ground terminal (GND), and can switch between the on and off states according to the first enable signal (EN1). The second constant current circuit (210) is arranged in series with a part of the plurality of light emitting elements (112) between the input terminal (IN) and the ground terminal (GND), and can switch between the on and off states according to the second enable signal (EN2). The control circuit (220) is in the third voltage range where the input voltage (V IN ) is lower than the first threshold (V TH1 ) and higher than the second threshold (V TH2 ). The lower the input voltage (V IN ), the lower the duty factor of the first enable signal (EN1) and the higher the duty factor of the second enable signal (EN2).

Description

Technical Field

[0001] The present disclosure relates to a lamp used in an automobile or the like. Background Art

[0002] As a light source used in a vehicle lamp, a light bulb has been generally used in the past. In recent years, however, semiconductor light sources such as LEDs (light emitting diodes) have been widely adopted. In particular, a semiconductor light source that can be replaced with a normal component in case of a failure such as a wire break is called an LED socket, as in the case of a commonly used light bulb type in the past.

[0003] The LED socket includes a plurality of LEDs connected in series. Patent Document 1 discloses a technique for driving three LEDs connected in series using two systems of current control modules. Specifically, the first current control module is connected in such a way as to supply a driving current to all three LEDs, and the second current control module is connected in such a way as to supply a driving current to two of the three LEDs on the low potential side. In a state where the power supply voltage (input voltage) supplied to the LED socket is sufficiently high, the first current control module is made effective to turn on all the LEDs. When the number of LEDs is set to n = 3 and the forward voltage of the LED is set to Vf, if the input voltage V IN is lower than n × Vf, it is impossible to maintain the lighting of all the LEDs. Therefore, if the input voltage V IN is lower than a certain threshold value, the first current control module is made ineffective and the second current control module is made effective. Thereby, two of the plurality of LEDs on the low potential side are maintained lit.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2016-197711 Summary of the Invention

[0007] In the circuit described in Patent Document 1, the amount of light changes sharply before and after the switching of the effective current control module, which causes flickering.

[0008] Several aspects of the present disclosure have been made in view of the related problems.

[0009] One exemplary object of one aspect of the present disclosure is to provide a lighting circuit that suppresses a sharp change in the amount of light as the input voltage changes.

[0010] One exemplary object of one aspect of the present disclosure is to provide a lighting circuit that can maintain the lighting state of a light source when the light source is disconnected.

[0011] One exemplary object of another aspect of the present disclosure is to provide a light source module capable of suppressing a decrease in light amount in a low voltage state.

[0012] Method for solving technical problems

[0013] 1. One aspect of the present disclosure relates to a lighting circuit that drives a semiconductor light source including a first part composed of m (m≥1) light emitting elements connected in series and a second part composed of n (n≥1) light emitting elements. The lighting circuit includes: a first constant current circuit provided in series with the first part and the second part between an input terminal and a ground terminal, capable of switching between a conductive state and a cutoff state according to a first enable signal; a second constant current circuit provided in series with the second part between the input terminal and the ground terminal, capable of switching between a conductive state and a cutoff state according to a second enable signal; and a control circuit that (i) sets the duty factor of the first enable signal to 100% and the duty factor of the second enable signal to 0% in a first voltage range where the input voltage at the input terminal is higher than a first threshold, (ii) sets the duty factor of the first enable signal to 0% and the duty factor of the second enable signal to 100% in a second voltage range where the input voltage is lower than a second threshold, and (iii) decreases the duty factor of the first enable signal and increases the duty factor of the second enable signal as the input voltage decreases in a third voltage range where the input voltage is lower than the first threshold and higher than the second threshold.

[0014] 2. One aspect of the present disclosure relates to a lighting circuit that drives a semiconductor light source including a first part composed of m (m≥1) light emitting elements connected in series and a second part composed of n (n≥1) light emitting elements. The lighting circuit includes: a first constant current circuit provided in series with the first part and the second part between an input terminal and a ground terminal, generating a first output current having an amount of current corresponding to a first analog dimming signal; a second constant current circuit provided in series with the second part between the input terminal and the ground terminal, generating a second output current having an amount of current corresponding to a second analog dimming signal; and a control circuit that generates the first analog dimming signal and the second analog dimming signal according to the input voltage at the input terminal. The control circuit generates the first analog dimming signal and the second analog dimming signal such that (i) the first output current becomes a specified first target amount and the second output current becomes zero in a first voltage range where the input voltage at the input terminal is higher than a first threshold, (ii) the second output current becomes a specified second target amount and the first output current becomes zero in a second voltage range where the input voltage is lower than a second threshold, and (iii) the first output current decreases from the first target amount to zero and the second output current increases from zero to the second target amount as the input voltage decreases in a third voltage range where the input voltage is lower than the first threshold and higher than the second threshold.

[0015] 3. One aspect of the present disclosure relates to a lighting circuit for driving a semiconductor light source. The semiconductor light source includes a first part composed of m (m≧1) light-emitting elements connected in series, and a second part composed of n (n≧1) light-emitting elements. The lighting circuit includes: a first constant-current circuit provided in series with the first part and the second part between an input terminal and a ground terminal, 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 part between the input terminal and the ground terminal, generating a second output current in an enabled state; and a control circuit controlling the enabling and disabling of each of the first constant-current circuit and the second constant-current circuit. In a state where the first part is open-circuited, the control circuit enables the second constant-current circuit, disables the first constant-current circuit, and sets the second output current to a second current amount greater than the first current amount.

[0016] 4. A light source module according to one aspect 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 receiving an input voltage and supplying a driving current stabilized to a target current to the LED string; and a bypass circuit provided in parallel with a bypassed portion including m (m≦n) adjacent LEDs in the LED string, injecting a bypass current corresponding to the input voltage. The luminous flux of the (n−m) LEDs arranged in a portion other than the bypassed portion is greater than the luminous flux of the m LEDs arranged in the bypassed portion.

[0017] In addition, any combination of the above components, and a solution in which components or expressions are mutually replaced between methods, devices, systems, etc. is also effective as a solution of the present invention.

[0018] Advantages of the Invention

[0019] According to one aspect of the present disclosure, a sharp change in light quantity due to a change in the input voltage can be suppressed. In addition, according to one aspect, a decrease in light quantity in a low-voltage state can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a circuit diagram of a vehicle lamp according to Embodiment 1.

[0021] Figure 2 shows Figure 1 the input voltage dependency of the vehicle lamp.

[0022] Figure 3 shows Figure 1 the operation of the vehicle lamp.

[0023] Figure 4 is a circuit diagram of a vehicle lamp including the lighting circuit of Example 1.1.

[0024] Figure 5 It is a circuit diagram of a vehicle lamp having the lighting circuit of Embodiment 1.2.

[0025] Figure 6 It is a diagram for explaining the operation of the vehicle lamp of Modification 1.1.

[0026] Figure 7 For (a) to (c) of OUT# it is a waveform diagram of the output current I.

[0027] Figure 8 It is a circuit diagram of a vehicle lamp having the lighting circuit of Modification 1.2.

[0028] Figure 9 It is a circuit diagram of a vehicle lamp having the lighting circuit of Modification 1.3.

[0029] Figure 10 It is a circuit diagram of a vehicle lamp having the lighting circuit of Modification 1.4.

[0030] Figure 11 It is a circuit diagram of the constant current circuit of Modification 1.5.

[0031] Figure 12 It is a circuit diagram of the vehicle lamp of Embodiment 2.

[0032] Figure 13 It shows Figure 12 the input voltage correlation of the vehicle lamp.

[0033] Figure 14 It shows Figure 12 the operation of the vehicle lamp.

[0034] Figure 15 It is a circuit diagram of a vehicle lamp having the lighting circuit of Embodiment 2.1.

[0035] Figure 16 It shows Figure 15 a structural example of the control circuit.

[0036] Figure 17 It is a diagram for explaining the operation of the vehicle lamp of Modification 2.1.

[0037] Figure 18 It is a diagram for explaining the operation of the lighting circuit of Modification 2.2.

[0038] Figure 19 It is a circuit diagram of the lighting circuit of Modification 2.2.

[0039] Figure 20 It is Figure 19 a circuit diagram of the control circuit.

[0040] Figure 21 It is a circuit diagram of a vehicle lamp having the lighting circuit of Modification 2.3.

[0041] Figure 22 It is a circuit diagram of a vehicle lamp having the lighting circuit of Modification 2.4.

[0042] Figure 23 It is a circuit diagram of a vehicle lamp having the lighting circuit of Modification 2.5.

[0043] Figure 24 It shows Figure 23 a circuit diagram of a specific structural example of the vehicle lamp.

[0044] Figure 25 It is a circuit diagram of the vehicle lamp of Embodiment 3.1.

[0045] Figure 26 It shows Figure 25 a diagram of the state of the vehicle lamp.

[0046] Figure 27 It is an equivalent circuit diagram showing the first state.

[0047] Figure 28 It is an equivalent circuit diagram showing the second state.

[0048] Figure 29 It is an equivalent circuit diagram showing the third state.

[0049] Figure 30 It is an equivalent circuit diagram showing the fourth state.

[0050] Figure 31 It is a circuit diagram of the constant current circuit of the first structural example.

[0051] Figure 32 It is a circuit diagram of the constant current circuit of the second structural example.

[0052] Figure 33 It is a circuit diagram showing a specific structural example of the lighting circuit.

[0053] Figure 34 It is Figure 33 the first operation waveform diagram of the vehicle lamp.

[0054] Figure 35 It is Figure 33 the second operation waveform diagram of the vehicle lamp.

[0055] Figure 36 It is a block diagram of the vehicle lamp of Embodiment 3.2.

[0056] Figure 37is a diagram showing Figure 36 the state of a vehicle lamp.

[0057] Figure 38 is a circuit diagram of a vehicle lamp having the lighting circuit of Modification 3.1.

[0058] Figure 39 is a circuit diagram of a vehicle lamp having the lighting circuit of Modification 3.2.

[0059] Figure 40 is a block diagram of an existing vehicle lamp.

[0060] Figure 41 is a block diagram of the vehicle lamp of Embodiment 4.1.

[0061] Figure 42 is for explaining Figure 41 the operation of the vehicle lamp.

[0062] Figure 43 is a circuit diagram of the vehicle lamp of Embodiment 4.2.

[0063] Figure 44 is for explaining Figure 43 the operation of the vehicle lamp.

[0064] Figure 45 is a circuit diagram of the vehicle lamp of Embodiment 4.3.

[0065] Figure 46 is for explaining Figure 45 the operation of the vehicle lamp.

[0066] Figure 47 is a diagram for comparing and explaining the operations of the vehicle lamp with n = 4, m = 2 and the vehicle lamp with n = 4, m = 1.

[0067] Figure 48 The (a) and (b) of

[0068] Figure 49 are circuit diagrams showing structural examples of a bypass circuit. Detailed Description of the Invention

[0069] (Embodiment 1)

[0070] (Outline of Embodiment 1)

[0071] Describe the outline of Embodiment 1. This outline serves as a preface to the subsequent detailed description. For the purpose of a basic understanding of the embodiment, it briefly explains some concepts of one or more embodiments, without limiting the scope of the invention or disclosure. In addition, this outline is not an all-inclusive summary of all conceivable embodiments and does not limit the essential components of the embodiment. For convenience, "one embodiment" is sometimes used to refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed in this specification.

[0072] This outline is not an extensive overview of all conceivable embodiments, and its intention is not to identify the key or important elements of all embodiments, nor to delimit the scope of a part or all of the solutions. Its sole purpose is to present, in a simplified form, some concepts of one or more embodiments as a preface to the more detailed description presented later.

[0073] 1. A lighting circuit in one embodiment drives a semiconductor light source, which includes: a first part composed of m (m≧1) light-emitting elements connected in series, and a second part composed of n (n≧1) light-emitting elements. The lighting circuit includes: a first constant-current circuit, which is arranged in series with the first part and the second part between an input terminal and a ground terminal and can switch between a conducting state and a cutoff state according to a first enable signal; a second constant-current circuit, which is arranged in series with the second part between the input terminal and the ground terminal and can switch between a conducting state and a cutoff state according to a second enable signal; and a control circuit, (i) in a first voltage range where the input voltage at the input terminal is higher than a first threshold, setting the duty factor of the first enable signal to 100% and the duty factor of the second enable signal to 0%, (ii) in a second voltage range where the input voltage is lower than a second threshold, setting the duty factor of the first enable signal to 0% and the duty factor of the second enable signal to 100%, (iii) in a third voltage range where the input voltage is lower than the first threshold and higher than the second threshold, the lower the input voltage, the lower the duty factor of the first enable signal and the higher the duty factor of the second enable signal.

[0074] According to this embodiment, a sharp change in the light quantity accompanying the change in the input voltage can be suppressed.

[0075] Alternatively, in one embodiment, the duty factors of the first enable signal and the second enable signal in the third voltage range are set such that the slope of the change in the total emitted light quantity of the light source with respect to the change in the input voltage is 5% / 0.1V or less. Thus, it is possible to make it difficult for people to feel the change in the light quantity caused by a short-term change in the input voltage.

[0076] Alternatively, in one embodiment, the second output current generated in the on state of the second constant current circuit is more than the first output current generated in the on state of the first constant current circuit. Thus, it is possible to suppress the reduction in the overall light amount of the light source as the input voltage decreases.

[0077] Alternatively, in one embodiment, the sum of the duty factors of the first enable signal and the second enable signal is 100%.

[0078] Alternatively, in one embodiment, the first enable signal and the second enable signal are signals that are in antiphase with each other.

[0079] Alternatively, in one embodiment, at the timing of switching the on and off states of the first constant current circuit and the second constant current circuit, their output currents change gradually. Thus, electromagnetic noise can be suppressed.

[0080] Alternatively, in one embodiment, the first constant current circuit generates a first output current proportional to the voltage level of the first enable signal, and the second constant current circuit generates a second output current proportional to the voltage level of the second enable signal.

[0081] Alternatively, in one embodiment, at least one of the rising edge and the falling edge of the pulsed first enable signal and second enable signal generated in the third voltage range is slowed down. Thus, electromagnetic noise can be suppressed.

[0082] (Detailed description of Embodiment 1)

[0083] Regarding Embodiment 1, it will be described with reference to the drawings. The same or equivalent components, elements, and processes shown in each figure are labeled with the same reference numerals, and repeated descriptions are appropriately omitted. In addition, the embodiment is an illustration rather than a limitation of the invention, and all features or their combinations described in the embodiment do not necessarily represent the essence of the invention.

[0084] In this specification, the state where "Component A is connected to Component B" includes the case where Component A and Component B are physically directly connected, and also includes the case where Component A and Component B are indirectly connected via other components that do not substantially affect their electrical connection state or do not impair the functions or effects achieved through their coupling.

[0085] Similarly, the state where "Component C is disposed between Component A and Component B" means that in addition to the cases of directly connecting Component A and Component C or directly connecting Component B and Component C, it also includes the case of being indirectly connected via other components without substantially affecting their electrical connection state or without impairing the functions or effects achieved through their coupling.

[0086] In addition, in this specification, electrical signals such as voltage signals and current signals, or reference numerals assigned to circuit elements such as resistors and capacitors, represent their respective voltage values, current values, or resistance values and capacitance values as needed.

[0087] Figure 1 is a circuit diagram of the vehicle lamp 100 of Embodiment 1. A DC voltage (input voltage) V from the battery 2 is supplied to the vehicle lamp 100 via the switch 4. IN .

[0088] The vehicle lamp 100 includes a semiconductor light source 110 and its lighting circuit 200. A preferred 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 can be attached to and detached from a lamp body (not shown). The LED socket aims for a long service life and strongly aims for low cost because it is a consumable.

[0089] The semiconductor light source 110 is a light emitting element string including (m + n) light emitting elements 112 connected in series. In the present embodiment, the light emitting element 112 is, for example, a white LED, and m + n = 3. The plurality of light emitting elements 112 are chips having substantially the same characteristics, and the light output when the same current is supplied is substantially equal.

[0090] The semiconductor light source 110 is divided into a first part 114 composed of m light emitting elements 112_1 on the high potential side and a second part 116 composed of n light emitting elements 112_2 and 112_3 on the low potential side.

[0091] The lighting circuit 200 may be an IC (Integrated Circuit) integrated on one semiconductor substrate or may be composed of a combination of 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. A power supply voltage (input voltage V) from the battery is supplied to the input terminal IN, and the ground terminal GND is grounded. The anode of the first part 114 of the semiconductor light source 110 is connected to the output terminal OUT1, and the cathode of the first part 114 is connected to the output terminal OUT2. The anode of the second part 116 of the semiconductor light source 110 is connected to the output terminal OUT2, and the cathode of the second part 116 is connected to the output terminal OUT3. The output terminal OUT3 is connected to the ground terminal GND. IN ), and the ground terminal GND is grounded.

[0092] 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 part 114 via the output terminal OUT1, and its input is connected to the input terminal IN. That is, the first constant current circuit 210_1 is provided in series with a plurality of 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 able to switch between a conducting state and a cutoff state according to the first enable signal EN1. When the first constant current circuit 210_1 is in the conducting state, it generates a first output current I REF1 that is stabilized to a specified current amount I OUT1 .

[0093] The output of the second constant current circuit 210_2 is connected to the anode of the second part 116 via the output terminal OUT2, and its input is connected to the input terminal IN. That is, the second constant current circuit 210_2 is provided in series with the second part 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 able to switch between a conducting state and a cutoff state according to the second enable signal EN2. When the second constant current circuit 210_2 is in the conducting state, it generates a second output current I REF2 that is stabilized to a specified current amount I OUT2 . In the present embodiment, it is set that I REF1 =I REF2 =I REF .

[0094] The drive current Id1 flowing in the first part 114 is the first output current I OUT1 from the first constant current circuit 210_1. The drive current Id2 flowing in the second part 116 is the total current of the first output current I OUT1 from the first constant current circuit 210_1 and the second output current I OUT2 from the second constant current circuit 210_2.

[0095] An input voltage V IN is supplied to the control circuit 220. In a first voltage range where the input voltage V IN is higher than a first threshold V TH1 , the control circuit 220 sets the duty factor dc1 of the first enable signal EN1 to 100% and sets the duty factor dc2 of the second enable signal EN2 to 0%. In addition, in (ii) a case where the input voltage V IN is lower than a second threshold V TH2In the 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%. In addition, in (iii) the input voltage V IN Below the first threshold V TH1 , higher than the second threshold V TH2 In the third voltage range, the input voltage V IN The lower the value, the lower the duty cycle dc1 of the first enable signal EN1 is, and the higher the duty cycle dc2 of the second enable signal EN2 is.

[0096] V TH2 It is determined by the number n of light emitting elements included in the second portion 116. In this example, to satisfy n=2, V TH2 >n×Vf.

[0097] Figure 2 It shows Figure 1 FIG. 1 is a diagram showing the input voltage dependency of the vehicle lamp 100. The duty factors dc1 and dc2 are changed complementarily so as to total 100%.

[0098] dc1 + dc2 = 100%

[0099] Figure 2 The first output current I OUT1 , the second output current I OUT2 Indicates the effective value (time average), which is I OUT1 =I REF ×dc1、I OUT2 =I REF ×dc2.

[0100] The current Id1 flowing in the first portion 114 is related to the first output current I OUT1 are equal, so the input voltage V IN The lower the current Id1 is, the OUT1 =dc1×I REF The smaller it is.

[0101] The driving current Id2 flowing in the second portion 116 is the first output current I OUT1 With the second output current I OUT2 The total is expressed as formula (1).

[0102] Id2=I OUT1 +I OUT2 =dc1×I REF +dc2×I REF …(1)

[0103] When dc1+dc2=100%, Id2=I REF。

[0104] Let the amount of light when the current amount I flows through the light-emitting element 112 of one chip be U. The amount of light (dotted line) of the first part 114 is 1×U in the range of V REF < V TH1 < V IN and 0 in the range of V IN < V TH2 and varies in the range of 0 to 1×U in the range of V TH2 < V IN < V TH1 < V

[0105] The current Id2 flowing through the second part 116 is fixed at I IN irrespective of the input voltage V REF , so the amount of light for two chips (dash-dotted line) is 2×U.

[0106] The total amount of light (solid line) of the semiconductor light source 110 is the sum of the amounts of light of the first part 114 and the second part 116, which is 3×U in the range of V TH1 < V IN , 2×U in the range of V IN < V TH2 , and varies in the range of 2×U to 3×U in the range of V TH2 < V IN < V TH1 < V

[0107] In the region of V TH2 < V IN < V TH1 < V IN , it is preferable that the slopes of the duty factors dc1 (and dc2) are designed so that the slope of the emitted light amount of the entire semiconductor light source 110 with respect to the change in the input voltage V IN is 5% / 0.1V or less. Thus, it is possible to make it difficult for a person to feel the change in the light amount caused by the short-term change in the input voltage V

[0108] The above is the structure of the vehicle lamp 100. Next, its operation will be described. Figure 3 is a diagram showing Figure 1 the operation of the vehicle lamp 100.

[0109] Figure 3 shows a state where the input voltage V IN decreases with time. Before time t0, V IN > V TH1 , the duty factor dc1 of the first enable signal EN1 is 100%, the duty factor dc2 of the second enable signal EN2 is 0%, and only the first constant current circuit 210_1 is effective.

[0110] Supply a drive current Id1 = I to the light-emitting element 112_1 of the first part 114 OUT1 = I REF Supply the same amount of drive current Id2 = I to the light-emitting elements 112_2 and 112_3 of the second part 116 OUT1 = I REF .

[0111] Set the light quantity when supplying I to one (1 chip) light-emitting element 112 as U. Before time t0, the light quantity (dotted line) of the first part 114 is 1×U, and the light quantity (dash-dotted line) of the second part 116 is for 2 chips, so it is 2×U. The overall light quantity (solid line) of the semiconductor light source 110 is 3×U REF .

[0112] After time t0, as the input voltage V IN decreases, the duty factor dc1 of the first enable signal EN1 decreases, and the duty factor dc2 of the second enable signal EN2 increases

[0113] Moreover, the overall light quantity of the semiconductor light source 110 decreases from 3×U to 2×U after time t0. After time t1, the overall light quantity of the semiconductor light source 110 maintains 2×U

[0114] The above is the operation of the vehicle lamp 100. According to this vehicle lamp 100, corresponding to the change in the input voltage V IN , the two constant current circuits 210_1 and 210_2 operate while gradually changing. Thereby, it is possible to prevent a sharp change in the overall light quantity of the semiconductor light source 110 and suppress flicker

[0115] Next, a specific structural example of the vehicle lamp 100 will be described

[0116] (Example 1.1)

[0117] Figure 4 is a circuit diagram of the vehicle lamp 100A equipped with the lighting circuit 200A of Example 1.1. The constant current circuits 210_1 and 210_2 are similarly configured and include a series transistor Qsr, a limiting resistor Rs, a gate resistor Rg, an error amplifier EA1, transistors Q41, Q42, and resistors R41 to R44. The EN pin of this constant current circuit 210 is low-level effective

[0118] The target amount I OUT# of the output current I REF# in the constant current circuit 210_# (# = 1, 2) is expressed by Equation (2)

[0119] I REF# = V REF / Rs…(2)

[0120] Transistors Q41 and Q42 and resistors R41 to R44 are added to switch the constant current circuit 210 between on (enabled) and off (disabled). When a high input is applied to the enable pin, transistors Q41 and Q42 are turned on, while transistor Qsr is turned off, disabling the constant current circuit 210.

[0121] The control circuit 220 includes resistors R31, R32, a pulse width modulator 221, and an inverter 228. The input voltage V IN The pulse width modulator 221 generates a pulse width modulator with the same voltage as the divided 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 amplifies the divided input voltage V IN , generating a detection voltage Vs. The oscillator 224 generates a periodic signal V of a triangle wave or a sawtooth wave. OSC The PWM comparator 226 compares the detection voltage Vs with the periodic signal V OSC , outputs the second enable signal EN2. The inverter 228 inverts the second enable signal EN2 to generate the first enable signal EN1.

[0122] (Example 1.2)

[0123] Figure 5 This is a circuit diagram of a vehicle lamp 100B including a lighting circuit 200B according to Example 1.2.

[0124] In the lighting circuit 200B, the constant current circuit 210_# (#=1, 2) generates a current I proportional to the enable signal EN# input to the enable terminal EN. REF The output current I OUT# .

[0125] The error amplifier EA2, transistor Q42, and resistor R46 form a voltage / current conversion circuit to convert the enable signal EN# into a current signal I EN# Set the voltage level of the enable signal EN# to V EN# When the current signal I EN# For I EN# =V EN# / R46. The current signal I EN# When the current flows through resistor R45, a voltage V EN# Ratio-to-reference voltage V REF# Output current I OUT# The target current I REF#It can be expressed by Equation (2) that a current I proportional to the enable signal EN# is generated. OUT# .

[0126] In addition, in Embodiment 1.2, it is necessary to stabilize the high-level voltages of the enable signals EN1 and EN2 to a specified voltage level.

[0127] Describe a modification related to Embodiment 1.

[0128] (Modification 1.1)

[0129] In Modification 1.1, the target amount I of the second output current I generated when the second constant current circuit 210_2 is in the conducting state OUT2 is greater than the target amount I of the first output current I generated when the first constant current circuit 210_2 is in the conducting state REF2 . OUT1 The target amount I of REF1 .

[0130] I REF1 < I REF2

[0131] Figure 6 FIG. is a diagram illustrating the operation of the vehicle lamp of Modification 1.1.

[0132] In Modification 1.1, the drive current Id2 flowing into the second part 116 is expressed by Equation (3).

[0133] Id2 = I OUT1 + I OUT2 = dc1 × I REF1 + dc2 × I REF2 …(3)

[0134] Since I REF1 < I REF2 holds, the drive current Id2 increases as the input voltage V IN decreases.

[0135] Let the light amount when the current amount I REF flows through the light-emitting element 112 of one chip be U. In addition, let I REF1 = I REF , I REF2 = 1.5 × I REF .

[0136] Similar to Embodiment 1 ( Figure 2 ), the light amount (dashed line) of the first part 114 is 1 × U in the range of V TH1 < V IN , 0 in the range of V IN < V TH2 and 0 in the range of VTH2 <V IN <V TH1 In the range of , it changes in the range of 0 to 1×U.

[0137] On the other hand, the current Id2 flowing in the second portion 116 increases with the input voltage V IN The light quantity of the second part 116 (single-dot chain line) is V TH1 <V IN The range is 2×U, and the V IN <V TH2 The range is 3×U, in V TH2 <V IN <V TH1 In the range of , it varies in the range of 2×U~3×U.

[0138] The total light intensity of the semiconductor light source 110 is the sum of the light intensity of the first part 114 and the light intensity of the second part 116, which can suppress the input voltage V IN The overall light intensity changes.

[0139] When the number of chips in the first part 114 is m and the number of chips in the second part 116 is n, REF2 ≒(m+n) / n×I REF1 The current amount is determined in this manner, thereby reducing the overall light intensity variation of the semiconductor light source 110.

[0140] In addition, the vehicle lamp 100 of the modification 1.1 can be used with Figure 4 The same structure. By setting Figure 4 The resistors Rs of the constant current circuits 210_1 and 210_2 can generate different current amounts.

[0141] (Variant 1.2)

[0142] At the timing of switching on and off of the first constant current circuit 210_1 and the second constant current circuit 210_2, their output currents I OUT1 , I OUT2 Gradient. Figure 7 (a) to (c) are the gradual output current I OUT# Waveform diagram. Figure 7 (a) is the output current I OUT# The rise and fall are both gradual. Figure 7 (b) is only the output current I OUT# The rising gradient. Figure 7 (c) is only the output current I OUT# By making the output current I OUT# Gradual change can suppress electromagnetic noise.

[0143] Figure 8 This is the circuit diagram of the vehicle lamp 100C with the lighting circuit 200C having Variation Example 1.2. The basic structure of the lighting circuit 200C is the same as that of Figure 5 the lighting circuit 200B. The control circuit 220 includes low-pass filters 230 and 232. The low-pass filter 230 removes the high-frequency components of the output of the pulse width modulator 221 and generates a second enable signal EN2 with both the rising edge and the falling edge being slowed down. The low-pass filter 232 removes the high-frequency components of the output of the inverter 228 and generates a first enable signal EN1 with both the rising edge and the falling edge being slowed down. According to this structure, as Figure 7 shown in (a) of OUT# .

[0144] (Variation Example 1.3)

[0145] In the embodiment, the case where the light-emitting element 112 is a white LED is described, but it is not limited thereto. The light-emitting element 112 can also be a red LED. Figure 9 This is the circuit diagram of the vehicle lamp 100D with the lighting circuit 200D having Variation Example 1.3. In this vehicle lamp 100D, m = 2, n = 2, and V TH2 is determined in such a way as to satisfy V TH2 > 2 × Vf.

[0146] (Variation Example 1.4)

[0147] Figure 10 This is the circuit diagram of the vehicle lamp 100E with the lighting circuit 200E having Variation Example 1.4. In this Variation Example 1.4, the first constant current circuit 210_1 and the second constant current circuit 210_2 are of the current sinking type. The vehicle lamp 100E can be understood as having a structure that is the high-low inversion of Figure 1 the vehicle lamp 100. The constant current circuit can be formed by inverting the high and low of Figure 5 the constant current circuit.

[0148] (Variation Example 1.5)

[0149] Figure 11 This is the circuit diagram of the constant current circuit of Variation Example 1.5. This constant current circuit is of the current sinking type and includes transistors Q1, Q2 and resistors R1, R2. The output current I OUT of this constant current circuit is expressed as

[0150] I OUT = V BE / R1

[0151] .

[0152] It is possible toFigure 11 The structure is high-low inverted, forming a current extraction type.

[0153] (Variant Example 1.6)

[0154] In the previous description, 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, but chips with different characteristics can also be used.

[0155] For example, it is also possible to make the characteristics of the m chips included in the first part 114 consistent with each other, and make the characteristics of the n chips included in the second part 116 consistent with each other. In this case, the luminous flux (light amount) of each of the n light-emitting elements 112 included in the second part 116 can be greater than the luminous flux of each of the m light-emitting elements 112 included in the first part 114. The luminous flux of the light-emitting element 112 represents the luminous flux when driven by the same driving current I LED when driven.

[0156] Even for LED chips with the same product number supplied by the same supplier, due to manufacturing errors, there will be deviations in the luminous flux when the same driving current is supplied. Suppliers of LED chips sometimes label the grades of LED chips according to the luminous flux for sale. At this time, chips of a higher grade with a larger luminous flux can be used as the second part 116, and chips of a lower grade with a smaller luminous flux can be used as the first part 114. Or, it can also be that the manufacturer of vehicle lamps, rather than the supplier of LED chips, grades a large number of LED chips purchased according to the luminous flux.

[0157] Or, it can also be that when LED chips with different product numbers and different luminous fluxes are provided by the same supplier, chips with a larger product number and a larger luminous flux are used as the second part 116, and chips with a smaller product number and a smaller luminous flux are used as the first part 114.

[0158] Or, it can also be that chips with the same product number provided by the first supplier are used as the first part 114, and chips with a larger luminous flux provided by the second supplier are used as the second part 116.

[0159] Let the light amount (luminous flux) when the current amount I REF flows through one LED chip included in the first part 114 be U. In addition, let the light amount (luminous flux) when the same current amount I REF flows through one LED chip included in the second part 116 be α×U. α is a coefficient greater than 1, and can be set to about α = 1.3, and more preferably set to α = 1.5 is better.

[0160] In this Variant Example 1.6, as Figure 2 shown, it is assumed that an output current I OUT1, I OUT2 . At this time, in the normal voltage region where V IN > V TH1 , the total luminous flux (light quantity) of the semiconductor light source 110 is 1×U + 2×α×U. In the low voltage region where V IN < V TH2 , the total luminous flux (light quantity) of the semiconductor light source 110 is 2×α×U. Therefore, the light quantity in the low voltage region is 2α / (1 + 2α) times that in the normal voltage region. Therefore, the larger α is, the more the ratio of light quantity reduction can be suppressed.

[0161] (Modification Example 1.7)

[0162] In the embodiment, the light emitting element 112 is described as an LED, but an LD (laser diode) or an organic EL element etc. can also be adopted.

[0163] (Modification Example 1.8)

[0164] A bipolar transistor and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) can be replaced. At this time, just change the base, collector, and emitter to the gate, drain, and source. In addition, the NPN type (N-channel) can be replaced with the PNP type (P-channel).

[0165] (Embodiment 2)

[0166] (Outline of Embodiment 2)

[0167] A lighting circuit according to an embodiment drives a semiconductor light source, which includes a first part composed of m (m≥1) light-emitting elements connected in series and a second part composed of n (n≥1) light-emitting elements. The lighting circuit includes: a first constant-current circuit provided in series with the first part and the second part between an input terminal and a ground terminal to generate 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 part between the input terminal and the ground terminal to generate a second output current having a current amount corresponding to a second analog dimming signal; and a control circuit configured to generate the first analog dimming signal and the second analog dimming signal based on an input voltage of the input terminal. The control circuit generates the first analog dimming signal and the second analog dimming signal such that in a first voltage range where (i) the input voltage of the input terminal is higher than a first threshold, the first output current becomes a specified first target amount and the second output current is zero; in a second voltage range where (ii) the input voltage is lower than a second threshold, the second output current is a specified second target amount and the first output current is zero; and in a third voltage range where (iii) the input voltage is lower than the first threshold and higher than the second threshold, corresponding to a decrease in the input voltage, the first output current gradually decreases from the first target amount to zero and the second output current increases from zero to the second target amount.

[0168] According to this embodiment, a sharp change in the light amount due to a change in the input voltage can be suppressed.

[0169] In one embodiment, the first analog dimming signal and the second analog dimming signal in the third voltage range may be generated such that a slope of a change in the overall emitted light amount of the light source with respect to a change in the input voltage is 5% / 0.1V or less. Thereby, it is possible to make it difficult for a person to feel a change in the light amount caused by a short-term change in the input voltage.

[0170] In one embodiment, the second target amount may be larger than the first target amount. Thereby, a decrease in the overall light amount of the light source as the input voltage decreases can be suppressed.

[0171] In one embodiment, a conversion gain of the first output current of the first constant-current circuit with respect to the first analog dimming signal may be equal to a conversion gain of the second output current of the second constant-current circuit with respect to the second analog dimming signal. A sum of voltage levels of the first analog dimming signal and the second analog dimming signal may also be constant.

[0172] In one embodiment, the conversion gain of the second output current of the second constant current circuit with respect to the second analog dimming signal can be greater than the conversion gain of the first output current of the first constant current circuit with respect to the first analog dimming signal. The sum of the voltage levels of the first analog dimming signal and the second analog dimming signal can be constant. At this time, since the second target quantity is more than the first target quantity, it is possible to suppress the decrease in the overall light quantity of the light source as the input voltage decreases.

[0173] (Detailed description of Embodiment 2)

[0174] Figure 12 is a circuit diagram of the vehicle lamp 100 according to Embodiment 2. A DC voltage (input voltage) V from the battery 2 is supplied to the vehicle lamp 100 via the switch 4 IN .

[0175] The vehicle lamp 100 includes a semiconductor light source 110 and its lighting circuit 200. A preferred 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 can be detached from an unillustrated lamp body. The LED socket aims for a long service life, and since it is a consumable item, it also strongly aims for low cost.

[0176] The semiconductor light source 110 is a light emitting element string including (m + n) light emitting elements 112 connected in series. In the present embodiment, the light emitting element 112 is, for example, a white LED, and m + n = 3. The plurality of light emitting elements 112 are chips having substantially the same characteristics, and the light quantities when the same current is supplied are substantially equal.

[0177] The semiconductor light source 110 is divided into a first part 114 composed of m high-potential-side light emitting elements 112_1, and a second part 116 composed of n low-potential-side light emitting elements 112_2 and 112_3.

[0178] The lighting circuit 200 can also be an IC (Integrated Circuit) integrated on one semiconductor substrate, or can be composed of a combination of 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. A power supply voltage (input voltage V) from the battery is supplied to the input terminal IN IN ), and the ground terminal GND is grounded. The anode of the first part 114 of the semiconductor light source 110 is connected to the output terminal OUT1, and the cathode of the first part 114 is connected to the output terminal OUT2. The anode of the second part 116 of the semiconductor light source 110 is connected to the output terminal OUT2, and the cathode of the second part 116 is connected to the output terminal OUT3. The output terminal OUT3 is connected to the ground terminal GND.

[0179] 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 part 114 via the output terminal OUT1, and its input is connected to the input terminal IN. That is, the first constant current circuit 210_1 is provided in series with a plurality of 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 a dimming terminal ADIM and generates a first output current I corresponding to the first analog dimming signal V input to the dimming terminal ADIM. DIM OUT1 .

[0180] The output of the second constant current circuit 210_2 is connected to the anode of the second part 116 via the output terminal OUT2, and its input is connected to the input terminal IN. That is, the second constant current circuit 210_2 is provided in series with the second part 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 generates a second output current I corresponding to the second analog dimming signal V input to the dimming terminal ADIM. ADIM2 OUT2 .

[0181] The first constant current circuit 210_1 and the second constant current circuit 210_2 can be understood as voltage / current (V / I) conversion circuits, and their respective input-output characteristics can also be generalized by the following equations.

[0182] I OUT1 = K1 × (V ADIM1 - V OFS1 )

[0183] I OUT2 = K2 × (V ADIM2 - V OFS2 )

[0184] K1 and K2 are V / I conversion gains, and V, V are offsets. OFS1 , V OFS2

[0185] The drive current Id1 flowing in the first part 114 is the first output current I from the first constant current circuit 210_1. OUT1 . The drive current Id2 flowing in the second part 116 is the total current of the first output current I from the first constant current circuit 210_1 and the second output current I from the second constant current circuit 210_2. OUT1 OUT2

[0186] The input voltage V is supplied to the control circuit 220​​IN , generate a first analog dimming signal V IN and a second analog dimming signal V ADIM1 . ADIM2 .

[0187] The control circuit 220 generates a first analog dimming signal V ADIM1 and a second analog dimming signal V ADIM2 such that in (i) a first voltage range where the input voltage V IN is higher than a first threshold V TH1 , the first output current I OUT1 becomes a specified first target amount I REF1 , and the second output current I OUT2 is zero.

[0188] In addition, the control circuit 220 generates a first analog dimming signal V ADIM1 and a second analog dimming signal V ADIM2 such that in (ii) a second voltage range where the input voltage V IN is lower than a second threshold V TH2 , the second output current I OUT2 becomes a specified second target amount I REF2 , and the first output current I OUT1 is zero.

[0189] In addition, the control circuit 220 generates a first analog dimming signal V ADIM1 and a second analog dimming signal V ADIM2 such that in (iii) a third voltage range where the input voltage V IN is lower than the first threshold V TH1 and higher than the second threshold V TH2 , according to the decrease of the input voltage V IN , the first output current I OUT1 decreases from the first target amount I REF1 towards zero, and the second output current I OUT2 increases from zero towards the second target amount I REF2 .

[0190] The second threshold V TH2 is specified according to the number n of light-emitting elements included in the second part 116. In this example, with n = 2, it is determined in such a way that V TH2 > n × Vf.

[0191] Figure 13 is a graph showing the input voltage correlation of the vehicle lamp 100 Figure 12 . Here, let K1 = K2 = K, V OFS1 = V OFS2 = 0, IREF1 = I REF2 = I REF is established. When the peak voltages of the first analog dimming signal V ADIM1 and the second analog dimming signal V ADIM2 are set to V MAX , the following relationship holds.

[0192] I REF = K × V MAX

[0193] The current Id1 flowing in the first part 114 is equal to the first output current I OUT1 . Therefore, the lower the input voltage V IN , the smaller the current Id1 becomes according to I OUT1 = K × V ADIM1 .

[0194] The drive current Id2 flowing in the second part 116 is the sum of the first output current I OUT1 and the second output current I OUT2 , and is expressed by Equation (1).

[0195] Id2 = I OUT1 + I OUT2 = K × (V ADIM1 + V ADIM2 )...(1)

[0196] V ADIM1 + V ADIM2 = V MAX is established, then Id2 = I REF , and it becomes a constant value independent of the input voltage V IN .

[0197] When the amount of current I REF flowing through one (1 chip) light-emitting element 112 is set as U. The amount of light (dotted line) of the first part 114 is 1 × U in the range of V TH1 < V IN , 0 in the range of V IN < V TH2 , and varies in the range of 0 to 1 × U in the range of V TH2 < V IN < V TH1 .

[0198] The current Id2 flowing in the second part 116 is constant with I IN regardless of the input voltage V REF , so the amount of light (dash-dotted line) for two chips becomes 2 × U.

[0199] The total light quantity (solid line) of the semiconductor light source 110 is the sum of the light quantities of the first part 114 and the second part 116. At V TH1 <V IN In the range, it is 3×U. At V IN <V TH2 In the range, it is 2×U. At V TH2 <V IN <V TH1 In the range, it changes in the range of 2×U to 3×U.

[0200] At V TH2 <V IN <V TH1 In the region, it is preferable that the slopes of the analog dimming signals V ADIM1 、V ADIM2 are designed such that the slope of the emitted light quantity of the entire semiconductor light source 110 with respect to the change in the input voltage V IN is 5% / 0.1V or less. Thus, it is possible to make it difficult for a person to feel the change in the light quantity caused by the short-term change in the input voltage V IN .

[0201] The above is the structure of the vehicle lamp 100. Next, its operation will be described. Figure 14 is a diagram showing Figure 12 the operation of the vehicle lamp 100.

[0202] Figure 14 shows a state where the input voltage V IN decreases with time. Before the time t0, it is V IN >V TH1 , V ADIM1 =V MAX , V ADIM2 =0, I OUT1 =I REF , I OUT2 =0.

[0203] A drive current Id1 = I OUT1 =I REF is supplied to the light-emitting element 112_1 of the first part 114. The same amount of drive current Id2 = I OUT1 =I REF is also supplied to the light-emitting elements 112_2 and 112_3 of the second part 116.

[0204] The light quantity when I REF is supplied to the light-emitting element 112 is set to U. Before the time t0, the light quantity (dashed line) of the first part 114 is 1×U, and the light quantity (dash-dotted line) of the second part 116 is 2 chip portions, so 2×U. The total light quantity (solid line) of the semiconductor light source 110 is 3×U.

[0205] After time t0, as the input voltage V IN decreases, the voltage level of the first analog dimming signal V ADIM1 decreases toward 0V, and conversely, the voltage level of the second analog dimming signal V ADIM2 increases toward V MAX .

[0206] Moreover, the total luminous flux of the semiconductor light source 110 decreases from 3×U to 2×U after time t0. After time t1, the total luminous flux of the semiconductor light source 110 is maintained at 2×U.

[0207] The above is the operation of the vehicle lamp 100. According to this vehicle lamp 100, corresponding to the change in the input voltage V IN , the two constant current circuits 210_1 and 210_2 operate while gradually changing. Thereby, it is possible to prevent a sudden change in the total luminous flux of the semiconductor light source 110 and suppress flicker.

[0208] Next, a specific structural example of the vehicle lamp 100 will be described.

[0209] (Embodiment 2.1)

[0210] Figure 15 is a circuit diagram of a vehicle lamp 100G including the lighting circuit 200G of Embodiment 2.1. The constant current circuits 210_1 and 210_2 are similarly configured and each includes a V / I conversion circuit 212 and a current amplification circuit 214.

[0211] The V / I conversion circuit 212 converts the analog dimming signal V ADIM# into a current signal I ADIM# . The V / I conversion circuit 212 includes a transistor Q2, a resistor R2, and an error amplifier EA2. The current signal I ADIM# is I ADIM# = V ADIM# / R3.

[0212] The current amplification circuit 214 amplifies the current signal I ADIM# and generates an output current I OUT# . The current amplification circuit 214 includes resistors R1, R2, a transistor Q1, and an error amplifier EA1.

[0213] When this current signal I ADIM# flows through the resistor R2, a voltage drop V ADIM# proportional to the voltage V R2 is generated in the resistor R2.

[0214] V R2 = V ADIM# / R3 × R2…(2)

[0215] The error amplifier EA1, the transistor Q1, and the resistor R2 form a V / I conversion circuit that generates an output current I corresponding to the voltage drop V across the resistor R2. R2 OUT# .

[0216] I REF# = V R2 / R1…(3)

[0217] From equations (2) and (3), the input-output characteristics of the constant current circuit 210_# can be obtained as equation (4).

[0218] I REF# = V R2 / R1 = V ADIM# / R3 × R2 / R1…(4)

[0219] That is, the conversion gain K of the constant current circuit 210_# is given by equation (5). #

[0220] K # = R2 / (R1 × R3)…(5)

[0221] The lighting circuit 200G includes a constant voltage power supply 201. The constant voltage power supply 201 receives an input voltage V and generates a stabilized voltage V that is stabilized at a specified voltage level. This stabilized voltage V is supplied to the control circuit 220. The peak voltages of the analog dimming signals V, V generated by the control circuit 220G can be specified according to the stabilized voltage V. IN REG . REG ADIM1 ADIM2 MAX REG .

[0222] Figure 16 Figure 15 IN IN ADIM1 .

[0223] The non-inverting amplifier 240 generates a first analog dimming signal V that varies linearly with respect to the input voltage V. REG IN '. The non-inverting amplifier 240 includes an error amplifier EA3, resistors R6, R7. The input-output characteristics of the non-inverting amplifier 240 are given by equation (6).​​

[0224] V ADIM1 = (R6 + R7) / R6 × V IN ' - (R7 / R6) × V REG …(6)

[0225] The inverting amplifier 242 of the post-stage inverts and amplifies the first analog dimming signal V ADIM1 to generate a second analog dimming signal V ADIM2 .

[0226] According to this structure, the first analog dimming signal V as shown in Figure 13 and the second analog dimming signal V ADIM1 can be generated. ADIM2 . [[ID=Z6]]

[0227] Describe the modification related to Embodiment 2.

[0228] (Modification 2.1)

[0229] In Modification 2.1, the target value I of the second output current I generated by the second constant current circuit 210_2 OUT2 is more than the target value I of the first output current I generated by the first constant current circuit 210_1 REF2 . OUT1 The target value I REF1 .

[0230] I REF1 < I REF2

[0231] In this example, the peak voltages of the two analog dimming signals V ADIM1 and V ADIM2 are equal, and are K1 < K2. In this way, I REF1 < I REF2 is satisfied.

[0232] Figure 17 is a diagram showing the operation of the vehicle lamp of Modification 2.1. In Modification 2.1, the drive current Id2 flowing in the second part 116 is expressed by Equation (7).

[0233] Id2 = I OUT1 + I OUT2 = K1 × V ADIM1 + K2 × V ADIM2 …(7) [[ID=Z5]]

[0234] I REF1 < I REF2 holds, so the drive current Id2 increases as the input voltage V IN decreases.

[0235] The amount of current I flowing through the light-emitting element 112 of one chip is set to 1. In addition, let I REF = I REF1 = I REF and I REF2 = 1.5 × I REF .

[0236] Similar to Embodiment 2 ( Figure 13 ), the light amount (dashed line) of the first part 114 is 1 in the range of V TH1 < V IN , 0 in the range of V IN < V TH2 , and varies in the range of 0 to 1 in the range of V TH2 < V IN < V TH1 .

[0237] On the other hand, the current Id2 flowing through the second part 116 increases as the input voltage V IN decreases. The light amount (dash-dot line) of the second part 116 is 2 in the range of V TH1 < V IN , 3 in the range of V IN < V TH2 , and varies in the range of 2 to 3 in the range of V TH2 < V IN < V TH1 .

[0238] The total light amount of the semiconductor light source 110 is the sum of the light amounts of the first part 114 and the second part 116. Therefore, the change in the total light amount with respect to the change in the input voltage V IN can be suppressed.

[0239] When the number of chips of the first part 114 is m and the number of chips of the second part 116 is n, by determining the current amount in a manner that satisfies I REF2 ≒ (m + n) / n × I REF1 , the variation in the total light amount of the semiconductor light source 110 can be reduced.

[0240] (Modification Example 2.2)

[0241] Figure 18 is a diagram for explaining the operation of the lighting circuit 200H of Modification Example 2.2. In Modification Example 2.2, the first analog dimming signal V ADIM1 varies in the range of 0 to V MAX / 2, and the second analog dimming signal V ADIM2 varies in the range of V MAX / 2 to V MAX .

[0242] In addition, the input-output characteristics of the constant current circuits 210_1 and 220_2 are expressed by Equations (8) and (9).

[0243] I OUT1 = K × V ADIM1 …(8)

[0244] I OUT2 = K × (V ADIM2 − V MAX / 2) …(9)

[0245] holds.

[0246] Through this Modification Example 2.2, it is also possible to achieve the same input voltage correlation of the light quantity as Figure 13 that.

[0247] Figure 19 is the circuit diagram of the lighting circuit 200H of Modification Example 2.2. The first constant current circuit 210_1 can be configured in the same manner as the Figure 15 circuit. The second constant current circuit 210_2 includes, in addition to the structural elements of the Figure 15 , an error amplifier EA4, and resistors R8 and R9. The resistors R8 and R9 divide the stabilized voltage V REG . The error amplifier EA4 is a buffer (voltage follower) that maintains the potential of one end on the low potential side of the resistor R3 at V REG / 2.

[0248] V ADIM2 is applied to one end on the high potential side of the resistor R3, and V REG / 2 is applied to the other end on the low potential side. Therefore, the voltage across the two ends of the resistor R3 is V ADIM2 − V REG / 2 , and thus, the current I ADIM2 flowing through the resistor R3 and the transistor Q2 is expressed by Equation (10).

[0249] I ADIM2 = (V ADIM2 − V REG / 2) / R3 …(10)

[0250] Thus, the input-output characteristics of Equation (9) can be achieved.

[0251] Figure 20 is Figure 19 the circuit diagram of the control circuit 220H. The control circuit 220H includes resistors R4 and R5, a non-inverting amplifier 240, and an inverting amplifier 242H. The structure of the non-inverting amplifier 240 is the same as that of the Figure 16 circuit.

[0252] 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 into a current signal I1. The V / I conversion circuit 244 includes a transistor Q3, an error amplifier EA5, and a resistor R10. A stabilization voltage V REG is applied to one end of the resistor R11, and the V / I conversion circuit 244 is connected to the other end. A second analog dimming signal V ADIM2 is extracted from the connection node between the resistor R11 and the V / I conversion circuit 244. In addition, the first analog dimming signal V ADIM1 can be extracted from the output of the non-inverting amplifier 240 or from the connection node between the resistor R11 and the transistor Q3.

[0253] According to Figure 20 the control circuit 220H, analog dimming signals V Figure 18 as shown in ADIM1 V ADIM2 can be generated.

[0254] (Modification Example 2.3)

[0255] In Embodiment 2, the case where the light-emitting element 112 is a white LED is described, but it is not limited thereto. The light-emitting element 112 can also be a red LED. Figure 21 is a circuit diagram of a vehicle lamp 100I having the lighting circuit 200I of Modification Example 2.3. In this vehicle lamp 100I, m = 2, n = 2, and V TH2 is determined in such a way that V TH2 > 2 × Vf.

[0256] (Modification Example 2.4)

[0257] Figure 22 is a circuit diagram of a vehicle lamp 100J having the 200J of Modification Example 2.4. In this modification example, the primary V / I conversion circuits of the first constant current circuit 210_1 and the second constant current circuit 210_2 are omitted, and they have negative V / I conversion gains K1, K2 (<0). When the analog dimming signal V ADIM# generated by the control circuit 220 is at the maximum voltage level V IN , the output current I OUT# is zero, and the lower the analog dimming signal V ADIM# , the larger the output current I OUT# .

[0258] (Modification Example 2.5)

[0259] Figure 23This is a circuit diagram of a vehicle lamp 100K having the lighting circuit 200K of Modification 2.5. In this Modification 2.5, the first constant current circuit 210_1 and the second constant current circuit 210_2 are of the current-sinking type. The vehicle lamp 100K can be understood as being configured by inverting the high and low of the Figure 22 vehicle lamp 100J.

[0260] Figure 24 This is a circuit diagram showing a specific structural example of the Figure 23 vehicle lamp 100K. The constant current circuits 210_1 and 210_2 are of the current-sinking type and have a structure in which the Figure 22 constant current circuits 210_1 and 210_2 are inverted in terms of high and low. Figure 22 The V / I conversion gains K1 and K2 of the constant current circuits 210_1 and 210_2 of

[0261] (Modification 2.6)

[0262] In the previous description, 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. However, chips with different characteristics can also be used.

[0263] For example, the characteristics of the m chips included in the first part 114 can be made consistent with each other, and the characteristics of the n chips included in the second part 116 can be made consistent with each other. In this case, the luminous flux (light amount) of each of the n light-emitting elements 112 included in the second part 116 can also be greater than the luminous flux of each of the m light-emitting elements 112 included in the first part 114. The luminous flux of the light-emitting element 112 represents the luminous flux when driven by the same drive current I LED is used for driving.

[0264] Even for LED chips supplied from the same supplier with the same product number, due to manufacturing errors, there will be deviations in the luminous flux when the same drive current is supplied. Suppliers of LED chips sometimes label the grades of LED chips according to the luminous flux for sale. At this time, chips of a higher luminous flux grade can be used for the second part 116, and chips of a lower luminous flux grade can be used for the first part 114. Or, instead of the supplier of the LED chips, the manufacturer of the vehicle lamp can grade a large number of LED chips purchased according to the luminous flux.

[0265] Or, when LED chips with different luminous fluxes and different product numbers are provided from the same supplier, chips with a larger product number of luminous flux can be used for the second part 116, and chips with a smaller product number of luminous flux can be used for the first part 114.

[0266] Alternatively, it is also possible to use the chips with the same product number provided by the first supplier as the first part 114, and use the chips with a larger luminous flux provided by the second supplier as the second part 116.

[0267] Let the light quantity (luminous flux) when the current amount I flowing through one LED chip included in the first part 114 be U. In addition, let the light quantity (luminous flux) when the same current amount I flows through one LED chip included in the second part 116 be α×U. α is a coefficient greater than 1, and can be set to about α = 1.3, and more preferably set to α = 1.5. REF Let the light quantity (luminous flux) when the current amount I flowing through one LED chip included in the first part 114 be U. In addition, let the light quantity (luminous flux) when the same current amount I flows through one LED chip included in the second part 116 be α×U. α is a coefficient greater than 1, and can be set to about α = 1.3, and more preferably set to α = 1.5. REF Let the light quantity (luminous flux) when the current amount I flowing through one LED chip included in the first part 114 be U. In addition, let the light quantity (luminous flux) when the same current amount I flows through one LED chip included in the second part 116 be α×U. α is a coefficient greater than 1, and can be set to about α = 1.3, and more preferably set to α = 1.5.

[0268] In this modification 2.6, as Figure 13 shown, set to generate the output currents I OUT1 、I OUT2 . At this time, in the normal voltage region where V IN >V TH1 , the total luminous flux (light quantity) of the semiconductor light source 110 is 1×U + 2×α×U. In the low voltage region where V IN <V TH2 , the total luminous flux (light quantity) of the semiconductor light source 110 is 2×α×U. Therefore, the light quantity in the low voltage region is 2α / (1 + 2α) times that in the normal voltage region. Therefore, the larger α is, the more the ratio of light quantity reduction can be suppressed.

[0269] (Modification 2.7)

[0270] In the second embodiment, the light emitting element 112 is described as an LED, but an LD (laser diode) or an organic EL element etc. can also be used.

[0271] (Modification 2.8)

[0272] The bipolar transistor and the MOSFET (Metal Oxide Semiconductor Field Effect Transistor) can be replaced. At this time, just change the base, collector, and emitter to the gate, drain, and source. In addition, the NPN type (N-channel) can be replaced with the PNP type (P-channel).

[0273] (Modification 2.9)

[0274] The constant current circuits 210_1 and 210_2 can be constituted by a current D / A converter. At this time, the analog dimming signals V ADIM1 、V ADIM2 are digital signals, and the control circuit 220 can be constituted by a digital circuit.

[0275] (Embodiment 3)

[0276] (Summary of Embodiment 3)

[0277] A lighting circuit of an embodiment drives a semiconductor light source. The semiconductor light source includes a first part composed of m (m≥1) light emitting elements connected in series, and a second part composed of n (n≥1) light emitting elements. The lighting circuit includes: a first constant current circuit provided in series with the first part and the second part 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 part between the input terminal and the ground terminal, and generating a second output current in an enabled state; and a control circuit controlling enabling and disabling of each of the first constant current circuit and the second constant current circuit. In a state where the first part is broken, the control circuit enables the second constant current circuit, disables the first constant current circuit, and sets the second output current to a second current amount greater than the first current amount.

[0278] According to this structure, in the case where the first part is broken, lighting of the semiconductor light source can be maintained by switching from the first constant current circuit to the second constant current circuit. Moreover, by driving the second part with a second current amount greater than normal, it is possible to suppress a significant decrease in the light amount (luminous flux) in the broken state compared to the light amount in the normal state.

[0279] In one embodiment, the second current amount may be equal to or less than (m + n) / n times the first current amount and less than the rated current of the second part.

[0280] In one embodiment, the lighting circuit may further include a bypass switch provided in parallel with the second part. The first constant current circuit can switch the first output current to a third current amount greater than the first current amount and the first current amount. The control circuit can turn on the bypass switch, enable the first constant current circuit, disable the second constant current circuit, and set the first output current to the third current amount in a state where the second part is broken.

[0281] According to this configuration, in the case where the second part is broken, on the basis of turning on the bypass switch, lighting of the semiconductor light source can be maintained by switching from the second constant current circuit to the first constant current circuit. And by driving the first part with a third current amount greater than normal, it is possible to prevent a significant decrease in the light amount (luminous flux) in the broken state compared to the light amount in the normal state.

[0282] In one embodiment, the third current amount may be equal to or less than (m + n) / m times the first current amount and less than the rated current of the first part.

[0283] In one embodiment, the second constant current circuit may also be enabled when the semiconductor light source is in a non-disconnected state and the input voltage is lower than a specified threshold. The second output current at this time may be a second current amount. Thereby, the variation in the amount of light in the non-disconnected state can be suppressed.

[0284] In one embodiment, the second constant current circuit may also be enabled when the semiconductor light source is in a non-disconnected state and the input voltage is lower than a specified threshold. The second output current at this time may be a first current amount.

[0285] The lighting circuit according to one embodiment includes: a first constant current circuit disposed in series with a first part and a second part between an input terminal and a ground terminal, generating a first output current of a third current amount greater than or equal to the first current amount in an enabled state; a second constant current circuit disposed in series with the second part between the input terminal and the ground terminal, generating a second output current in an enabled state; a control circuit controlling the enabling and disabling of the first constant current circuit and the second constant current circuit respectively; and a bypass switch disposed in parallel with the second part. The control circuit sets the bypass switch to be conductive, sets the first constant current circuit to be enabled, the second constant current circuit to be disabled, and the first output current to be the third current amount in the case of a disconnection state of the second part.

[0286] According to this structure, in the case of a disconnection of the second part, on the basis of setting the bypass switch to be conductive, by switching from the second constant current circuit to the first constant current circuit, the lighting of the semiconductor light source can be maintained. Moreover, by driving the first part with a third current amount greater than normal, it is possible to prevent the amount of light (luminous flux) in the disconnection state from significantly decreasing compared to the amount of light in the normal state.

[0287] 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 part.

[0288] (Detailed description of Embodiment 3)

[0289] [[ID=1 It is a circuit diagram of the vehicle lamp 100 of Embodiment 3.1. A DC voltage (input voltage) V from the battery 2 is supplied to the vehicle lamp 100 via the switch 4. IN .

[0290] The vehicle lamp 100 includes a semiconductor light source 110 and its lighting circuit 200. A preferred 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, having a shape that can be detached from an unillustrated lamp body. The LED socket aims for long life, and since it is a consumable, it also strongly aims for low cost.

[0291] The semiconductor light source 110 is a string of light-emitting elements including (m + n) light-emitting elements 112 connected in series. In the present embodiment, the light-emitting element 112 is, for example, a white LED, and m + n = 3. The plurality of light-emitting elements 112 are chips having substantially the same characteristics, and the light output when the same current is supplied is substantially equal.

[0292] The semiconductor light source 110 is divided into a first part 114 composed of m light-emitting elements 112_1 on the high-potential side and a second part 116 composed of n light-emitting elements 112_2 and 112_3 on the low-potential side.

[0293] The lighting circuit 200 can be an IC (Integrated Circuit) integrated on a semiconductor substrate or can be constituted 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. A power supply voltage (input voltage V IN ) from a battery is supplied to the input terminal IN, and the ground terminal GND is grounded. The anode of the first part 114 of the semiconductor light source 110 is connected to the output terminal OUT1, and the cathode of the first part 114 is connected to the output terminal OUT2. The anode of the second part 116 of the semiconductor light source 110 is connected to the output terminal OUT2, and the cathode of the second part 116 is connected to the output terminal OUT3. The output terminal OUT3 is connected to the ground terminal GND.

[0294] 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 part 114 via the output terminal OUT1, and its input is connected to the input terminal IN via a reverse connection prevention diode D1. That is, the first constant current circuit 210_1 is provided in series with the plurality of 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 able to switch between enabled and disabled according to a first enable signal EN1 input to the enable terminal EN. In the enabled state, a first output current I OUT1 .

[0295] The output of the second constant current circuit 210_2 is connected to the anode of the second part 116 via the output terminal OUT2, and its input is connected to the input terminal IN via the diode D1. That is, the second constant current circuit 210_2 is provided in series with the second part 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 switch between enabled and disabled according to the second enable signal EN2 input to the enable terminal EN, and generate a second output current I in the enabled state. OUT2 。

[0296] The first output current I OUT1 can be switched according to the first current amount I REF1 or a third current amount I REF1 more than the first current amount I. REF3 The amount of the first output current I OUT1 is controlled according to the first current control signal CNT_CUR1.

[0297] Preferably, the third current amount I REF3 is close to (m + n) / m times the first current amount I REF1 within the range not exceeding the rated current of the first part 114.

[0298] The second output current I OUT2 can be switched according to the first current amount I REF1 or a second current amount I REF1 more than the first current amount I. REF2 The amount of the second output current I OUT2 is controlled according to the second current control signal CNT_CUR2.

[0299] Preferably, the second current amount I REF2 is close to (m + n) / n times the first current amount I REF1 within the range not exceeding the rated current of the second part 116.

[0300] The bypass switch 230 is connected in parallel with the second part 116 and switches between conduction and cutoff according to the control signal CNT_SW generated by the control circuit 220.

[0301] The control circuit 220 is configured to be able to detect disconnection of each of the first part 114 and the second part 116. An input voltage V IN is supplied to the control circuit 220, and according to the input voltage V IN and the detection results of disconnection of the first part 114 and the second part 116, the enable / disable of each 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 The respective amounts of current, and the conduction and cutoff of the bypass switch 230.

[0302] Next, the control of the control circuit 220 will be specifically described. An input voltage V that supplies a voltage level sufficient to drive the (m + n) light-emitting elements 112 of the semiconductor light source 110 IN The state is called the normal voltage state, and the state that is not like this is called the low voltage state. In addition, the state in which neither the first part 114 nor the second part 116 is broken is called the non-broken state. For example, the state where V IN ≧ (m + n) × Vf is the normal voltage state.

[0303] First, the control in the non-broken state will be described. In the non-broken state, the bypass switch 230 is cutoff.

[0304] In (i) the normal voltage state and the non-broken state, the first constant current circuit 210_1 is enabled, and the second constant current circuit 210_2 is disabled. In addition, the first output current I OUT1 is the first amount of current I REF1 . At this time, the light-emitting elements 112_1 to 112_3 are driven by the output current I REF1 of the first amount of current I OUT1 , and all three chips are lit.

[0305] In (ii) the low voltage state and the non-broken 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 is the first amount of current I REF1 . At this time, the light-emitting elements 112_2 and 112_3 are driven by the output current I REF1 of the first amount of current I OUT2 , and two chips are lit.

[0306] Next, the control in the broken state will be described.

[0307] In (iii) the broken state of the first part 114, 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 is the second amount of current I REF2 . In addition, the bypass switch 230 is cutoff. At this time, the light-emitting elements 112_2 and 112_3 are driven by the output current I REF2 of the second amount of current I OUT2 , and two chips are lit.

[0308] In the case of a disconnection state of the second part 116 in (iv), 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 is the third current amount I REF3 . At this time, the light-emitting element 112_1 is driven by the output current I REF3 of the third current amount I OUT1 , and one chip is lit.

[0309] ​ is a diagram showing ​ the state of the vehicle lamp 100. The vehicle lamp 100 can obtain four states φ1 to φ4. The control circuit 220 selects one from the four states φ1 to φ4 according to the input voltage V IN and the presence or absence of a disconnection, and changes the state of the lighting circuit 200.

[0310] The above is the structure of the vehicle lamp 100. Next, its operation will be described.

[0311] ​ is an equivalent circuit diagram showing the first state φ1. In the first state, three light-emitting elements 112_1 to 112_3 are lit by the first output current I REF1 of the first target amount I OUT1 .

[0312] ​ is an equivalent circuit diagram showing the second state φ2. In the second state, two light-emitting elements 112_2 and 112_3 are lit by the second output current I REF1 of the first target amount I OUT2 .

[0313] ​ is an equivalent circuit diagram showing the third state φ۳. In the third state, two light-emitting elements 112_2 and 112_3 are lit by the second output current I REF2 of the second target amount I OUT2 .

[0314] ​ is an equivalent circuit diagram showing the fourth state φ4. In the fourth state, one light-emitting element 112_1 is lit by the first output current I REF3 of the third target amount I OUT1 .

[0315] The above is the operation of the vehicle lamp 100. According to the vehicle lamp 100, the lighting state can be maintained in the case where one of the first part 114 and the second part 116 is disconnected.

[0316] At this time, it is assumed that

[0317] I REF2 I = (m + n) / n × I REF1 = 3 / 2 × I REF1

[0318] I REF3 I = (m + n) / m × I REF1 = 3 × I REF1

[0319] is established. If the luminous flux when the first target amount I of current flows through one light-emitting element 112 is set as U, then the luminous flux when the second target amount I of current flows through one light-emitting element 112 REF1 is 1.5U, and the luminous flux when the third target amount I of current flows through one light-emitting element 112 REF2 is expressed as 3U. REF3 The total luminous flux of the semiconductor light source 110 in the first state φ1 is U × 3 = 3U. The total luminous flux of the semiconductor light source 110 in the second state φ2 is U × 2 = 2U. The total luminous flux of the semiconductor light source 110 in the third state φ3 is 1.5U × 2 = 3U. The total luminous flux of the semiconductor light source 110 in the fourth state φ4 is 3U × 1 = 3U.

[0320] That is, even in the case of disconnection, it is possible to achieve the same level of luminous flux as in the case of non-disconnection. Actually, by limiting the rated current of the light-emitting element 112, I

[0321] < 1.5 × I REF2 , I REF1 < 3 × I REF3 , but by making I REF1 as large as possible compared to I REF2 , it is possible to suppress the reduction of the light quantity. REF3 <{

[0322] ​ is the circuit diagram of the constant current circuit 210 of the first structural 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 generates a reference voltage V that is converted in a binary manner according to the current control signal CNT_CUR# REF .

[0323] The V / I conversion circuit 212 converts the reference voltage V REF into a reference current I REF . The V / I conversion circuit 212 includes a transistor Q2, a resistor R2, and an error amplifier (operational amplifier) EA2. The relationship of I REF = V REF / R2 holds.

[0324] The current amplification circuit 214 amplifies the reference current IREF The output current I OUT# is output. The current amplification circuit 214 includes a resistor R1, a resistor R3, a transistor Q1, and an error amplifier EA1. I OUT# is represented by the following formula.

[0325] I OUT# = I REF × R3 / R1

[0326] To switch between enabling and disabling, transistors Q3, Q4, and resistor R4 are provided. Transistor Q3 is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and is provided between the current amplification circuit 214 and the input terminal. When the enable signal EN# is high, transistor Q4 conducts, the gate voltage of transistor Q3 is low, and transistor Q3 conducts. This state is the enabled state of the constant current circuit 210_#. When the enable signal EN# is low, transistor Q4 is cutoff, the gate voltage of transistor Q3 is high, and transistor Q3 is cutoff. This state is the disabled state of the constant current circuit 210_#.

[0327] ​ is the circuit diagram of the constant current circuit 210 of the second structural example. ​ The current amplification circuit 214 of ​ adds transistors Q6, resistors R8, and R9 to the current amplification circuit 214 of

[0328] and can switch between conduction and cutoff. The enable signal \EN# is negative logic (\ represents negative logic, indicated by a bar in the figure). When the enable signal \EN# is low, transistor Q5 is cutoff. Thereby, the base-emitter voltage of transistor Q6 is zero, transistor Q6 is cutoff, and the current amplification circuit 214 becomes a conducting state.

[0329] When the enable signal \EN# is high, transistor Q5 conducts. Thereby, transistor Q6 conducts, the gate-source voltage of transistor Q1 of the current amplification circuit 214 is lower than the threshold voltage, and transistor Q1, that is, the current amplification circuit 214, becomes a cutoff state.

[0330] ​ is the circuit diagram showing a specific structural 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 of ​ The input switch 213 corresponds to

[0331] The input voltage monitoring circuit 222 monitors the input voltage V IN , and compares it with a specified threshold voltage V TH . The input voltage monitoring circuit 222 generates a first enable signal EN1 and a second enable signal EN2 such that when V IN > V TH , the first constant current circuit 210_1 becomes enabled and the second constant current circuit 210_2 becomes disabled. Conversely, when V IN < V TH , the first constant current circuit 210_1 becomes disabled and the second constant current circuit 210_2 becomes enabled.

[0332] For example, the input voltage monitoring circuit 222 includes a Zener diode ZD21 and resistors R21 to R23. When the input voltage V IN exceeds the threshold voltage V TH based on the Zener voltage, the Zener diode ZD21 conducts, the base of the transistor Q21 becomes high, and the transistor Q21 conducts. As a result, the gate of the input switch 213, that is, the first enable signal \EN1, is low, the input switch 213 of the first constant current circuit 210_1 conducts, 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 is cut off, and the second constant current circuit 210_2 becomes disabled.

[0333] When the input voltage V IN is lower than the threshold voltage V TH , no current flows through the Zener diode ZD21, the base of the transistor Q21 is low, and the transistor Q21 is cut off. As a result, the gate of the input switch 213, that is, the first enable signal \EN1, is high, the input switch 213 of the first constant current circuit 210_1 is cut off, and the first constant current circuit 210_1 becomes disabled. At this time, the second enable signal \EN2 is low, the input switch 213 of the second constant current circuit 210_2 conducts, and the second constant current circuit 210_2 becomes enabled.

[0334] In addition, the input voltage monitoring circuit 222 can be constituted by a voltage comparator. In this case, the voltage comparator can also be a hysteresis comparator. Thereby, it is possible to prevent flickering when the input voltage V IN varies near the threshold voltage V TH .

[0335] The resistor Rs1 and the comparator COMP1 are provided for detecting a disconnection of the semiconductor light source 110. The output of the comparator COMP1 is high when a normal first output current I OUT1 flows and low when it does not flow.

[0336] In addition, the resistor Rs2 and the comparator COMP2 are provided for open-circuit detection of the second part 116. The output of the comparator COMP2 is high when the normal second output current I OUT2 flows, and low when it does not flow.

[0337] The outputs of the two comparators COMP1 and COMP2 are input into the logic gate NAND1. The output A of the logic gate NAND1 becomes low in the state where the current I OUT1 , I OUT2 does not flow. The timer circuit 224 sets its output B to high after a predetermined time τ1 has elapsed since the output A of the logic gate NAND1 became low and the semiconductor light source 110 was open-circuited, and the subsequent flip-flop FF1 is set. The reset terminal of the flip-flop FF1 is input with a power-on reset signal POR and is reset at the start of the lighting circuit 200.

[0338] The output C of the flip-flop FF1 is supplied as a second current control signal CNT_CUR2 to the second constant current circuit 210_2. In addition, the output C of the flip-flop FF1 is supplied to the tri-state buffer 228. The output G of the tri-state buffer 228 is in a high impedance state when the signal C is low, and takes the level corresponding to its input F when the signal C is high.

[0339] The inverted output \C of the flip-flop FF1 and the output A of the logic gate NAND1 are input into the logic gate NAND2. When the output D of the logic gate NAND2 is low, the timing of the timer circuit 226 starts, 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 as a control signal CNT_SW to the gate of the bypass switch 230. In addition, the output F of the flip-flop FF2 is supplied as a second current control signal CNT_CUR2 to the second constant current circuit 210_2. When the output F is high, the current of the second constant current circuit 210_2 increases.

[0340] ​ is ​ the first operation waveform diagram of the vehicle lamp 100. At time t0, an input voltage V TH higher than the threshold voltage V IN is supplied. The first enable signal EN1 becomes low, and the first output current I OUT1 of the first constant current circuit 210_1 is supplied to the semiconductor light source 110.

[0341] After the lighting circuit 200 is started, the power-on reset POR becomes valid, and the output F of the flip-flop FF2 becomes low. Therefore, the first current control signal CNT_CUR1 becomes low, and the target value of the first output current I OUT1 becomes the first current amount IREF1 In addition, the control signal CNT_SW is low, so the bypass switch 230 is off.

[0342] In response to the power-on reset POR being made valid, the output C of the flip-flop FF1 goes low. As a result, the second current control signal CNT_CUR2 goes low, and the target value of the second output current I OUT2 becomes the first current amount I REF1 . The output G of the tri-state buffer 228 becomes high impedance.

[0343] Assume that at time t1, the first part 114 is broken. Thus, the first output current I no longer flows OUT1 , the output A of the logic gate NAND1 goes low, and at time t2 after the elapse of the specified time τ1, the signals B and C go high. As a result, the tri-state buffer 228 is enabled, and its output G becomes low as the input F. As a result, the second enable signal \EN2 goes low, and the second constant current circuit 210_2 becomes enabled. The signal C, that is, the second current control signal CNT_CUR2 goes high, so the second output current I OUT2 is boosted to the second current amount I REF2 . The second output current I OUT2 flows in the second part 116, so that the output A of the logic gate NAND1 returns high.

[0344] ​ is ​ the second operation waveform diagram of the vehicle lamp 100. At time t0, an input voltage V TH higher than the threshold voltage V IN is supplied. Assume that at time t1, a break occurs in the second part 116.

[0345] Thus, the first output current I no longer flows OUT1 , the output A of the logic gate NAND1 goes low, and at time t2 after the elapse of the specified time τ1 therefrom, the signals B and C go high. As a result, the tri-state buffer 228 is enabled, and its output G becomes low as the input F. As a result, the second enable signal \EN2 goes low, and the second constant current circuit 210_2 becomes enabled. The signal C, that is, the second current control signal CNT_CUR2 goes high, so that the target amount of the second output current I OUT2 is increased to the second current amount I REF2 . Among them, the second part 116 is broken, so that the second output current I cannot flow OUT2 , and the output A of the logic gate NAND1 remains low.

[0346] At time t2, when both signals A and C are low, the output D of logic gate NAND2 becomes low. After a specified time τ2 has elapsed from this point, signal E becomes high, the flip-flop FF2 is set, and signal F becomes high. As a result, the output G of the tri-state buffer 228 becomes high, the first enable signal \EN1 becomes low, and the first constant current circuit 210_1 enters an enabled state. Additionally, based on the high-level signal F, the bypass switch 230 conducts, and the target amount of the first output current I OUT1 is increased to the third current amount I REF3 .

[0347] After time t3, the first output current I REF3 that has been increased to the third current amount I OUT1 flows in the path including the first part 114 and the bypass switch 230. As a result, the outputs A and D of logic gates NAND1 and NAND2 become high.

[0348] The above is ​ the operation of the vehicle lamp 100.

[0349] According to ​ the vehicle lamp 100, when a disconnection occurs, regardless of the magnitude relationship between the input voltage V IN and the threshold value V TH , by enabling the second constant current circuit 210_2 once, the second part 116 can be driven by the increased second output current I OUT2 . Additionally, when the semiconductor light source 110 is not lit, by turning on the bypass switch 230 and enabling the first constant current circuit 210_1, the first part 114 can be driven by the increased first output current I OUT1 .

[0350] (Embodiment 3.2)

[0351] ​ is a block diagram of the vehicle lamp 100A of Embodiment 3.2. In Embodiment 3.2, the target amount of the output current I OUT2 of the second constant current circuit 210_2 is fixed at the second target amount I REF2 . Therefore, the second current control signal CNT_CUR2 for the second constant current circuit 210_2 is omitted.

[0352] ​ is a diagram showing ​ the state of the vehicle lamp 100A. The current amount of the second constant current circuit 210_2 in the low voltage state (second state φ2) when there is no disconnection is different from that in the second state φ2 of Embodiment 3.1, and the others are the same.

[0353] In Embodiment 3.2, it is assumed that IREF2 =(m + n) / n × I REF1 = 3 / 2 × I REF1 In addition, when the current flowing through one light-emitting element 112 is I REF1 the amount of light is set as U. At this time, the total luminous flux of the semiconductor light source 110 in the first state φ1 is U × 3 = 3U. The total luminous flux of the semiconductor light source 110 in the second state φ2 is 1.5U × 2 = 3U. That is, when there is no disconnection, the amount of light can be kept constant regardless of the voltage level of the input voltage VIN.

[0354] Actually, due to the limitation of the rated current of the light-emitting element 112, it becomes I REF2 < 1.5 × I REF1 However, by making I as large as possible REF2 the reduction of the amount of light can be suppressed.

[0355] Describe the modification examples related to Embodiment 3.1 and Embodiment 3.2.

[0356] (Modification Example 3.1)

[0357] In Embodiment 3.1 or 3.2, the case where the light-emitting element 112 is a white LED is described, but it is not limited thereto. The light-emitting element 112 can also be a red LED. ​ is a circuit diagram of the vehicle lamp 100I equipped with the lighting circuit 200I of Modification Example 3.1. In this vehicle lamp 100I, m = 2, n = 2, and V TH is determined in such a way as to satisfy V TH > n × Vf.

[0358] (Modification Example 3.2)

[0359] ​ is a circuit diagram of the vehicle lamp 100K equipped with the lighting circuit 200K of Modification Example 3.2. In this Modification Example 3.2, the first constant current circuit 210_1 and the second constant current circuit 210_2 are configured in a current-sinking type.

[0360] (Modification Example 3.3)

[0361] In Embodiment 3.1 or 3.2, the light-emitting element 112 is described as an LED, but an LD (laser diode), an organic EL element, etc. can also be used.

[0362] (Modification Example 3.4)

[0363] A bipolar transistor and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) can be replaced. At this time, the base, collector, and emitter can be changed to the gate, drain, and source. In addition, an NPN type (N-channel) can be replaced with a PNP type (P-channel).

[0364] (Embodiment 4)

[0365] (Summary of Embodiment 4)

[0366] A light source module according to an 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 driving current stabilized to a target current to the LED string; and a bypass circuit provided in parallel with a bypassed portion including m (m≦n) adjacent LEDs in the LED string and injecting a bypass current corresponding to the input voltage. The luminous flux of the (n−m) LEDs arranged in a portion other than the bypassed portion is greater than the luminous flux of the m LEDs arranged in the bypassed portion.

[0367] According to this structure, compared with the case where all n LEDs have the same luminous flux, a decrease in the amount of light in a low voltage state can be suppressed.

[0368] In one embodiment, the LED may be red, n = 4, and m = 2. According to this structure, when the input voltage decreases, two LEDs are bypassed, and even when the load of the battery increases during idling stop, the LED string can be prevented from going out. Therefore, when this light source module is used for a rear identification lamp, it is possible to prevent the LED string from accidentally going out during vehicle parking and sending incorrect information to the following vehicle.

[0369] In one embodiment, the LED may be white or blue, n = 3, and m = 1.

[0370] In one embodiment, the luminous flux of the (n−m) LEDs may be 1.3 times or more the luminous flux of the m LEDs. More preferably, the luminous flux of the (n−m) LEDs may be 1.5 times or more the luminous flux of the m LEDs. When the bypass current is changed corresponding to the input voltage, since the change in luminous flux with respect to the change in input voltage is reduced, flicker can be suppressed.

[0371] In one embodiment, the bypass circuit may further include a current source that generates a bias current whose current amount increases as the input voltage decreases.

[0372] In one embodiment, it is preferable to set the slope of the bypass current with respect to the input voltage such that the slope of the luminous flux of the LED string with respect to the change in the input voltage is 5% / 0.1V or less. Thus, it is possible to make it difficult for a person to feel the change in the emitted light amount caused by a short-term change in the input voltage.

[0373] In one embodiment, the bypass circuit may further include a bypass switch that conducts when the input voltage is lower than a specified threshold value.

[0374] (Detailed description of Embodiment 4)

[0375] (Embodiment 4.1)

[0376] ​ FIG. is a block diagram of a vehicle lamp 500A according to Embodiment 4.1. A DC voltage (input voltage) V from a battery 2 is supplied to the vehicle lamp 500A via a switch 4. IN . 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 plurality of LEDs 504_1 to 504_3 may be LED chips.

[0377] 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 has a shape that can be attached to and detached from a lamp body (not shown), similar to a conventional automotive bulb. The LED socket aims for a long lifespan and strongly aims for low cost because it is a consumable.

[0378] In the present embodiment, the plurality of LEDs are white and may be position lamps or DRLs (Daytime Running Lamps). Alternatively, the plurality of LEDs may be blue. The lighting circuit 600 includes a reverse connection protection diode 602, an LED driver circuit 610, a bypass circuit 620, and an open circuit detection circuit 630.

[0379] The LED driver circuit 610 receives the input voltage V via the reverse connection protection diode 602 IN , and supplies a driving current I that is stabilized to a target amount I REF to the LED string 502. LED . The LED driver circuit 610 may be constituted by any one of (i) a constant current linear regulator, (ii) a step-down switching converter with a constant current output, (iii) a combination of a step-down switching converter with a constant voltage output and a constant current circuit, and (iv) a resistor.

[0380] The bypass circuit 620 is connected in parallel with m = 1 (504_3) of the plurality of LEDs 504_1 to 504_3. The LED 504_3 is referred to as the bypassed portion 503. The bypass circuit 620 can switch between an enabled state and a disabled state. In the enabled state, a bypass current I IN corresponding to the input voltage V BYPASS flows in. When the bypass current I BYPASS flows, the current flowing in the bypassed portion 503 is I LED −I BYPASS . When I BYPASS = 0, a drive current I LED is supplied to the bypassed portion 503 and it lights up. When I BYPASS = I LED , the bypassed portion 503 goes out.

[0381] The disconnection detection circuit 630 is configured to be able to detect a disconnection of the bypassed portion 503. When the disconnection detection circuit 630 detects a disconnection fault of the bypassed portion 503, it sets the bypass circuit 620 to the disabled state. In the disabled state of the bypass circuit 620, the bypass current I BYPASS is 0 and no current is injected anymore.

[0382] The method of disconnection detection of the disconnection detection circuit 630 is not particularly limited. For example, it can be that when the voltage drop of the bypassed portion 503, that is, the voltage V A of node A exceeds the threshold voltage m×Vf = Vf, it is determined that there is a disconnection fault in the bypassed portion 503. Vf is the forward voltage of the LED 504.

[0383] For example, the disconnection detection circuit 630 may also include a voltage comparator that compares the voltage of node A with the threshold voltage V OPEN . The threshold voltage V OPEN can also be set to be slightly higher than m×Vf = Vf.

[0384] In the present embodiment, the luminous fluxes of the (n−m) = 2 LEDs 504_1 and 504_2 arranged in the portion other than the bypassed portion 503 are greater than the luminous flux of the m = 1 LED 504_3 arranged in the bypassed portion 503. The luminous flux of the LED represents the luminous flux when driven by the same drive current I LED .

[0385] Even for LED chips supplied by the same supplier with the same product number, due to manufacturing errors, there are deviations in luminous flux when the same drive current is supplied. Sometimes, the supplier of LED chips labels the grades of LED chips according to the luminous flux for sale. At this time, chips with a larger luminous flux grade can be used as LED504_1 and 504_2, and chips with a smaller luminous flux grade can be used as LED504_3. Or, it can also be that the manufacturer of the vehicle lamp 500A, rather than the supplier of the LED chips, grades a large number of LED chips purchased according to the luminous flux.

[0386] Or, it can also be that when LED chips with different product numbers and different luminous fluxes are provided by the same supplier, chips with a larger product number of luminous flux are used as LED504_1 and 504_2, and chips with a smaller product number of luminous flux are used as the first part of LED504_3.

[0387] Or, it can also be that chips with the same product number provided by the first supplier are used as LED504_1 and 504_2, and chips with a larger luminous flux provided by the second supplier are used as LED504_3.

[0388] The luminous fluxes of (n - m) = 2 LED504_1 and 504_2 are preferably α = 1.3 times or more of the luminous flux of m = 1 LED504_3. More preferably, the luminous fluxes of (n - m) = 2 LED504_1 and 504_2 are α = 1.5 times or more of the luminous flux of m = 1 LED504_3.

[0389] The total luminous flux in the normal voltage state is (n - m) × α + m, and the total luminous flux in the low voltage state is (n - m) × α. Therefore, the reduction ratio of the total luminous flux in the low voltage state relative to the normal voltage state is (n - m) × α / {(n - m) × α + m} times. When α > 1, the relationship (n - m) × α / {(n - m) × α + m} > (n - m) / n holds.

[0390] ​ It is a diagram ​ showing the operation of the vehicle lamp 500A. The horizontal axis represents the input voltage V IN . The upper part represents the bypass current I BYPASS . The lower part represents the total luminous flux (relative value) of the LED string 502.

[0391] The bypass current I BYPASS is 0 when the input voltage V IN is higher than the first threshold V TH1 , and is the same as I IN when the input voltage V TH2 is lower than the second threshold V LEDare equal. At V TH2 <V IN <V TH1 range, the bypass current I BYPASS increases from 0 to I IN as the input voltage V LED decreases. The second threshold voltage V TH2 is defined according to (n - m)×Vf + Vf(D). Vf(D) is the forward voltage of the diode for reverse connection protection.

[0392] In addition, it is preferable to set the slope of the bypass current I BYPASS with respect to the input voltage VIN such that the slope of the emitted light quantity (total luminous flux) of the LED string 502 with respect to the change in the input voltage V IN is 5% / 0.1V or less. Thus, it is difficult for people to feel the change in the emitted light quantity caused by the short-term change in the input voltage V IN .

[0393] When the input voltage V IN is lower than the third threshold voltage V TH3 , both I LED and I BYPASS become zero.

[0394] For comparison, in ​ the operation of a conventional vehicle lamp is shown by a single-dot chain line. In a conventional vehicle lamp, it is assumed that the luminous fluxes of three LEDs when the drive current I LED flows are equal to 1. At this time, the total luminous flux in the normal voltage state (V IN >V TH1 ) is 3, and the total luminous flux in the low voltage state (V IN <V TH2 ) is 2, and it is reduced to 2 / 3 times (=66%) of the normal voltage state in the low voltage state.

[0395] In this embodiment, the luminous flux of LED504_3 when the drive current I LED flows is set to 1, and the luminous fluxes of LED504_1 and 504_2 are set to α(>1). At this time, the total luminous flux in the normal voltage state (V IN >V TH1 ) is 2α + 1, and the total luminous flux in the low voltage state (V IN <V TH2 ) is 2α, and it is 2α / (2α + 1) times of the normal voltage state in the low voltage state.

[0396] When α > 1, the relationship 2α / (2α + 1) > 2 / 3 holds. Thus, according to this embodiment, a decrease in light quantity in a low voltage state can be suppressed. For example, when α = 1.3, in this embodiment, the ratio of light quantity decrease is 2.6 / 3.6 times (= 72%), and when α = 1.5, in this embodiment, the ratio of light quantity decrease is 3 / 4 times (= 75%), which is improved compared to 66% in the prior art.

[0397] The battery voltage is unstable. Thus, in the range of V TH2 < V IN < V TH1 , if the input voltage V IN changes, the total luminous flux will change and flicker will occur. In the embodiment, compared with the prior art, the ratio (slope) of the change in luminous flux with respect to the change in the input voltage in this range can be reduced. Therefore, the variation range of the luminous flux with respect to the same amplitude variation of the input voltage V IN can be reduced.

[0398] Next, the operation of the disconnection detection circuit 630 will be described. In a state where a normal input voltage V IN (> V TH1 ), I BYPASS = 0. At this time, when the bypassed portion 503 is disconnected, no current I LED flows through the LED string 502, and the LED string 502 goes out. On the other hand, when the bypassed portion 503 is disconnected, the input voltage V IN decreases. The bypassed portion 503 as the disconnection position is bypassed by the bypass circuit 620, and the LED string 502 lights up, which is not preferable. In this embodiment, the disconnection detection circuit 630 is provided. When a disconnection occurs, by setting the bypass circuit 620 to non - enabled, I BYPASS = 0, and the LED string can be turned off regardless of the voltage level of the input voltage V IN .

[0399] (Embodiment 4.2)

[0400] ​ is a circuit diagram of the vehicle lamp 500B according to Embodiment 4.2. The vehicle lamp 500B according to Embodiment 4.2 is, for example, a rear identification lamp such as a brake lamp, a tail lamp, or a rear fog lamp. The LED string 502 includes n = 4 red LEDs 504_1 to 504_4.

[0401] 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 plurality of LEDs 504_1 to 504_4. The bypass circuit 620 can switch between an enabled state and a non - enabled state. In the enabled state, current is drawn from the LED string 502 corresponding to the input voltage VIN The corresponding bypass current I BYPASS . The bypass current I BYPASS When flowing, the current flowing in the bypassed portion 503 is I LED -I BYPASS . I BYPASS When I = 0, a drive current I is supplied to the bypassed portion 503 LED and the lamp is lit. When I BYPASS = I LED , the bypassed portion 503 is turned off.

[0402] ​ It is a diagram for explaining ​ the operation of the vehicle lamp 500B. The input voltage dependency of the bypass current I BYPASS is the same as the case shown in ​ . The second threshold V TH2 is defined by (n - m)×Vf + Vf(D) = 3Vf + Vf(D).

[0403] For comparison ​ the operation of a conventional vehicle lamp is shown by a one-dot chain line. In a conventional vehicle lamp, it is assumed that the drive current I LED flows and the luminous fluxes of four LEDs are equal to 1. At this time, the total luminous flux in the normal voltage state (V IN > V TH1 ) is 4, and the total luminous flux in the low voltage state (V IN < V TH2 ) is 3, and it is reduced to 3 / 4 times ( = 75%) of the normal voltage state in the low voltage state.

[0404] In the present embodiment, the luminous flux of the LED504_4 when the drive current I LED flows is set to 1, and the luminous fluxes of the LEDs 504_1 to 504_3 are set to α (> 1). At this time, the total luminous flux in the normal voltage state (V IN > V TH1 ) is 3α + 1, and the total luminous flux in the low voltage state (V IN < V TH2 ) is 3α, and it is 3α / (3α + 1) times that in the normal voltage state in the low voltage state.

[0405] When α > 1, the relationship 3α / (3α + 1) > 3 / 4 holds. Thus, according to the present embodiment, a decrease in the light quantity in the low voltage state can be suppressed. For example, when α = 1.3, in the present embodiment, the ratio of the light quantity decrease is 3.9 / 4.9 times (≒ 80%), when α = 1.5, the ratio of the light quantity decrease in the present embodiment is 4.5 / 5.5 times (≒ 82%), which is improved compared to 75% in the past.

[0406] The battery voltage is unstable, so that within the range of V TH2 <V IN <V TH1 if the input voltage V IN changes, the total luminous flux will change and flicker will occur. In the embodiment, compared with the prior art, the ratio (slope) of the change in luminous flux with respect to the change in input voltage within this range can be reduced. Therefore, the variation range of the luminous flux with respect to the same amplitude variation of the input voltage V IN can be reduced.

[0407] (Embodiment 4.3)

[0408] ​ is the circuit diagram of the vehicle lamp 500C of Embodiment 4.3. Similar to Embodiment 4.2, the vehicle lamp 500C of Embodiment 4.3 is a rear identification lamp such as a brake lamp, a taillight, or a rear fog lamp. The LED string 502 includes n = 4 red LEDs 504_1 to 504_4.

[0409] In Embodiment 4.3, the number m of LEDs included in the bypass portion 503 is 2. The bypass circuit 620 is connected in parallel with m = 2 (504_3, 504_4) of the plurality of LEDs 504_1 to 504_4. The bypass circuit 620 can switch between an enabled state and a disabled state. In the enabled state, a bypass current I IN corresponding to the input voltage V BYPASS flows in. When the bypass current I BYPASS flows, the current flowing in the bypass portion 503 is I LED −IB YPASS . When I BYPASS = 0, a drive current I LED is supplied to the bypass portion 503 to turn on the light. When I BYPASS = I LED , the bypass portion 503 is turned off.

[0410] ​ is a diagram for explaining ​ the operation of the vehicle lamp 500C. The second threshold V TH2 is defined according to (n - m)×Vf + Vf(D) = 2Vf + Vf(D).

[0411] For comparison, ​ the operation of a conventional vehicle lamp is shown by a one-dot chain line. In the conventional vehicle lamp, it is assumed that the luminous fluxes of the 4 LEDs when the drive current I LED flows are equal to 1. At this time, in the normal voltage state (V IN> V TH1 ), the total luminous flux is 4, and in the low voltage state (V IN < V TH2 ), the total luminous flux is 2, and it is reduced to 2 / 4 times (=50%) of the normal voltage state in the low voltage state.

[0412] In this embodiment, the luminous fluxes of LED504_3 and LED504_4 when the flow drive current I LED is applied are set to 1, and the luminous fluxes of LED504_1 and 504_2 are set to α (>1). At this time, in the normal voltage state (V IN > V TH1 ), the total luminous flux is 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 of the normal voltage state.

[0413] When α > 1, the relationship of 2α / (2α + 2) > 2 / 4 holds. Thus, according to this embodiment, the reduction of the light quantity in the low voltage state can be suppressed. For example, when α = 1.3, in this embodiment, the reduction ratio of the light quantity is 2.6 / 4.6 times (≒57%), and when α = 1.5, in this embodiment, the reduction ratio of the light quantity is 3 / 5 times (=60%), which is improved compared with 50% in the past.

[0414] The battery voltage is unstable. Thus, in the range of V TH2 < V IN < V TH1 , if the input voltage V IN changes, the total luminous flux will change and flicker will occur. In the embodiment, compared with the prior art, the ratio (slope) of the change of the luminous flux with respect to the change of the input voltage in this range can be reduced. Therefore, the change amplitude of the luminous flux with respect to the same amplitude change of the input voltage V IN can be reduced.

[0415] ​ The vehicle lamp 500C compared with ​ the vehicle lamp 500B also has further advantages. ​ It is a diagram for comparing the operations of the vehicle lamp 500C with n = 4 and m = 2 and the vehicle lamp 500B with n = 4 and m = 1. Here, in order to focus on the further advantages, it is assumed that the luminous fluxes of the 4 LEDs are equal (i.e., α = 1).

[0416] As ​ shown, when there is 1 LED in the bypassed part, the input voltage V INWhen the voltage is lower than a certain voltage V1, one of the four LEDs is bypassed through the bypass circuit, and thus the light quantity is reduced to 75%. Also, the input voltage V IN When the voltage is lower than voltage V2 (for example, 1.8V × 3 + 0.8V = 6.2V), the light quantity drops to 0.

[0417] In contrast, as ​ shown, when two of the LEDs in the bypassed part, if the input voltage V IN is lower than the voltage V1, the light quantity is reduced to 50%, but even if the input voltage V IN is further reduced, the light quantity remains at 50%. Also, when the input voltage V IN is reduced to voltage V3, the light quantity becomes 0%.

[0418] In recent years, in order to improve fuel consumption, the number of vehicles with an idle stop function has increased. The brake light needs to be lit during the vehicle's stop, that is, during the occurrence of idle stop. During the idle stop period, since the alternator is stopped, when the load on the battery increases, the battery voltage, that is, the input voltage V IN of the vehicle lamp 500 drops significantly. For example, during the idle stop period, when the air conditioner is operating and the engine is restarted by operating the steering wheel, the load current of the battery increases.

[0419] In ​ the vehicle lamp 500B, when the battery voltage V BAT is lower than 6.2V, the LED string 10 goes out. When the brake light goes out, the following vehicle may mistakenly think that the vehicle in front has started.

[0420] In contrast, according to ​ the vehicle lamp 500C, even if the input voltage V BAT is reduced to 6.2V, two LEDs 504_3 and 504_4 are bypassed, so the LED string 502 can be prevented from going out. Therefore, when the vehicle lamp 500C is used as a rear identification lamp, during the vehicle's stop, the LED string 502 that is not intended can be prevented from going out and transmitting wrong information to the following vehicle.

[0421] ​ (a) and (b) of ​ are circuit diagrams showing a structural example of the bypass circuit 620. ​ The bypass circuit 620 in (a) of ​ includes a voltage comparator 622 and a transistor (switch) 624. The voltage comparator 622 compares the input voltage V IN with the threshold voltage V TH , and if V IN < V TH , the transistor 624 conducts. It is also possible to follow the input voltage V INDecrease. The gate voltage of transistor 624 decreases slowly. The current flowing through transistor 624 is the bypass current I BYPASS . Instead of voltage comparator 622, an amplifier can also be used. Instead of voltage comparator 622, a pulse width modulator can also be provided, which generates a PWM (Pulse Width Modulation) signal having a duty factor corresponding to the input voltage V IN , and drives the gate of transistor 624 according to the PWM signal.

[0422] ​ The bypass circuit 620 of (b) includes a variable current source 626. The variable current source 626 generates a bypass current I of an amount of current corresponding to the input voltage V IN . BYPASS .

[0423] Next, the use of the vehicle lamp 500 will be described. ​ (a) to (d) are diagrams showing an example of the vehicle lamp 500, namely, an LED socket. ​ (a) is a perspective view of the appearance of the LED socket 700. ​ (b) shows the front view of the LED socket 700, ​ (c) shows the top view of the LED socket 700, ​ (d) shows the bottom view of the LED socket 700.

[0424] The housing 702 has a shape that can be detached from a lamp body (not shown). At the central part, a plurality of LEDs 504 are installed, which are covered by a transparent sealing resin 704. On the substrate 710, the components of the lighting circuit 600 are installed. The plurality of LEDs 504 are red LED chips and are used as brake lights.

[0425] In an LED socket that uses both a brake light and a tail light, adjacent to the plurality of LEDs 504, a light-emitting element for the tail light is installed, and on the substrate 710, a lighting circuit for the tail light is installed.

[0426] On the bottom surface side of the housing 702, three pins 721, 722, and 723 are exposed. For pin 723, the input voltage V is supplied via a switch IN , and the ground voltage is supplied to pin 721. Pin 722 is supplied with a high input voltage when the tail light is lit. Pins 721 to 723 penetrate the inside of the housing 702, and one ends thereof are connected to the wiring pattern of the substrate 710.

[0427] Modifications associated with Embodiments 4.1 to 4.3 will be described.

[0428] The number n of all LEDs or the number of LEDs in the bypassed part is not limited to the values described in the embodiments.

[0429] In addition, in Embodiments 4.1 to 4.3, a configuration in which there is one bypass circuit is described, but two or more bypass circuits may be provided. For example, as a ​ modification, a second bypass circuit is added in parallel with LED504_2. After the first bypass circuit 620 is enabled, if the input voltage V IN further decreases, the second bypass circuit can be set to be enabled.

[0430] (Use)

[0431] Next, the use of the vehicle lamp described in Embodiments 1 to 4 will be described. ​ (a) to (d) of are diagrams showing an example of a vehicle lamp, an LED socket. ​ (a) of is a perspective view of the appearance of the LED socket 700. ​ (b) of shows the front view of the LED socket 700, ​ (c) of is the top view of the LED socket 700, ​ (d) of shows the bottom view of the LED socket 700.

[0432] The housing 702 has a shape that can be detached from a lamp body (not shown). At the central part, a plurality of LEDs 504 are mounted and covered with a transparent sealing resin 704. On the substrate 710, the components of the lighting circuit 600 are mounted. The plurality of LEDs 504 are red LED chips and are used as brake lights.

[0433] On the bottom surface side of the housing 702, a plurality of pins 721, 722, 723 are exposed. One of the plurality of pins (for example, 721) corresponds to ​ the ground terminal GND. In addition, another one (for example, 723) is supplied with the battery voltage via a switch when the brake light is lit. When the LED socket 700 is also used as a tail light, for another pin (722), the battery voltage is supplied via a switch when the tail light is lit.

[0434] The embodiments only show the principles and applications of the present invention. For the embodiments, various modifications or configuration changes are allowed without departing from the idea of the present invention defined in the claims.

[0435] [Industrial Applicability]

[0436] The present invention relates to a lamp used in an automobile or the like.

[0437] [Explanation of Reference Numerals]

[0438] 2 Battery

[0439] 4 switches

[0440] 100 vehicle lamps

[0441] IN input terminal

[0442] GND ground terminal

[0443] 110 semiconductor light source

[0444] 112 light-emitting element

[0445] 114 first part

[0446] 116 second part

[0447] 200 lighting circuit

[0448] 210 constant current circuit

[0449] 220 control circuit

[0450] 221 pulse width modulator

[0451] 222 amplifier

[0452] 224 oscillator

[0453] 226 PWM comparator

[0454] 228 inverter

[0455] 500 vehicle lamps

[0456] 502 LED string

[0457] 503 bypassed part

[0458] 504 LED

[0459] 600 lighting circuit

[0460] 602 diode

[0461] 610 LED driver circuit

[0462] 620 bypass circuit

[0463] 630 open-circuit detection circuit

Claims

1. A lighting circuit is a lighting circuit for driving a semiconductor light source including a first part composed of m light-emitting elements connected in series and a second part composed of n light-emitting elements, where m ≧ 1, n ≧ 1, and is characterized in that Comprising: A first constant current circuit, which is arranged in series with the first part and the second part between the input terminal and the ground terminal and can switch between the conducting state and the cutoff state according to a first enabling signal; A second constant current circuit, which is arranged in series with the second part between the input terminal and the ground terminal and can switch between the conducting state and the cutoff state according to a second enabling signal; And A control circuit, (i) in a first voltage range where the input voltage of the input terminal is higher than a first threshold, setting the duty factor of the first enabling signal to 100% and setting the duty factor of the second enabling signal to 0%, (ii) in a second voltage range where the input voltage is lower than a second threshold, setting the duty factor of the first enabling signal to 0% and setting the duty factor of the second enabling signal to 100%, (iii) in a third voltage range where the input voltage is lower than the first threshold and higher than the second threshold, the lower the input voltage, the lower the duty factor of the first enabling signal and the higher the duty factor of the second enabling signal.

2. The lighting circuit according to claim 1, wherein The duty factors of the first enabling signal and the second enabling signal in the third voltage range are set such that the slope of the change in the total emitted light amount of the light source with respect to the input voltage is 5% / 0.1V or less.

3. The lighting circuit according to claim 1, wherein The second output current generated when the second constant current circuit is in the conducting state is more than the first output current generated when the first constant current circuit is in the conducting state.

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

5. The lighting circuit according to claim 1, wherein The first enabling signal and the second enabling signal are signals that are inverted with respect to each other.

6. The lighting circuit according to any one of claims 1 to 5, wherein At the timing of switching between the conducting and cutoff states of the first constant current circuit and the second constant current circuit, their output currents change gradually.

7. The lighting circuit according to any one of claims 1 to 5, wherein The first constant current circuit generates a first output current whose current amount is adjusted according to a first analog dimming signal, 8. The lighting circuit according to claim 7, wherein At least one of the rising edge and the falling edge of the pulsed first enabling signal and the second enabling signal generated in the third voltage range is gentle.

9. A lighting circuit is a lighting circuit for driving a semiconductor light source including a first part composed of m light-emitting elements connected in series and a second part composed of n light-emitting elements, where m ≧ 1, n ≧ 1, and is characterized in that Comprising: A first constant current circuit, which is arranged in series with the first part and the second part between the input terminal and the ground terminal and generates a first output current with an adjusted current amount according to a first analog dimming signal, A second constant current circuit is provided in series with the second part between the input terminal and the ground terminal, and generates a second output current with an adjusted current amount according to a second analog dimming signal, and a control circuit generates the first analog dimming signal and the second analog dimming signal according to the input voltage of the input terminal; the control circuit generates the first analog dimming signal and the second analog dimming signal such that (i) in a first voltage range where the input voltage of the input terminal is higher than a first threshold, the first output current becomes a specified first target amount and the second output current becomes zero, (ii) in a second voltage range where the input voltage is lower than a second threshold, the second output current becomes a specified second target amount and the first output current becomes zero, and (iii) in a third voltage range where the input voltage is lower than the first threshold and higher than the second threshold, corresponding to the decrease in the input voltage, the first output current decreases from the first target amount to zero and the second output current increases from zero to the second target amount.

10. The lighting circuit according to claim 9, wherein the first analog dimming signal and the second analog dimming signal in the third voltage range are generated such that the slope of the change in the total emitted light amount of the light source with respect to the change in the input voltage is 5% / 0.1V or less.

11. The lighting circuit according to claim 9 or 10, wherein the second target amount is more than the first target amount.

12. The lighting circuit according to claim 9 or 10, wherein the conversion gain of the first output current of the first constant current circuit with respect to the first analog dimming signal is equal to the conversion gain of the second output current of the second constant current circuit with respect to the second analog dimming signal.

13. The lighting circuit according to claim 9 or 10, wherein the conversion gain of the second output current of the second constant current circuit with respect to the second analog dimming signal is greater than the conversion gain of the first output current of the first constant current circuit with respect to the first analog dimming signal.

14. The lighting circuit according to claim 12, wherein the sum of the voltage levels of the first analog dimming signal and the second analog dimming signal is constant.

15. A lighting circuit is a lighting circuit for driving a semiconductor light source including a first part composed of m light-emitting elements connected in series and a second part composed of n light-emitting elements, where m ≧ 1, n ≧ 1, and is characterized in that, Comprising: a first constant current circuit provided in series with the first part and the second part between the input terminal and the ground terminal, and generating a first output current with a first current amount in an enabled state, a second constant current circuit provided in series with the second part between the input terminal and the ground terminal, and generating a second output current in an enabled state, and a control circuit controlling the enabling and disabling of the first constant current circuit and the second constant current circuit respectively; in a state where the first part is open-circuited, the control circuit enables the second constant current circuit, disables the first constant current circuit, and sets the second output current to a second current amount that is more than the first current amount.

16. The lighting circuit according to claim 15, wherein the second current amount is not more than (m + n) / n times the first current amount and is less than the rated current of the second part.

17. The lighting circuit according to claim 15, wherein it further includes a bypass switch arranged in parallel with the second part, the first constant current circuit can switch the first output current according to the first current amount and a third current amount larger than the first current amount, in a disconnection state of the second part, the control circuit turns on the bypass switch, enables the first constant current circuit, disables the second constant current circuit, and sets the first output current to the third current amount.

18. The lighting circuit according to claim 17, wherein the third current amount is not more than (m + n) / m times the first current amount and is less than the rated current of the first part.

19. The lighting circuit according to any one of claims 15 to 18, wherein in a non-disconnection state of the semiconductor light source and when the input voltage of the input terminal is lower than a specified threshold value, the second constant current circuit is enabled and the second output current is the second current amount.

20. The lighting circuit according to any one of claims 15 to 18, wherein in a non-disconnection state of the semiconductor light source and when the input voltage of the input terminal is lower than a specified threshold value, the second constant current circuit is enabled and the second output current is the first current amount.

21. A lighting circuit is a lighting circuit for driving a semiconductor light source including a first part composed of m light-emitting elements connected in series and a second part composed of n light-emitting elements, where m ≧ 1 and n ≧ 1, and is characterized in that, comprising: a first constant current circuit, arranged in series with the first part and the second part between an input terminal and a ground terminal, and generating a first output current of a first current amount or a third current amount larger than the first current amount in an enabled state, a second constant current circuit, arranged in series with the second part between the input terminal and the ground terminal, and generating a second output current in an enabled state, a control circuit, controlling the enabling and disabling of each of the first constant current circuit and the second constant current circuit, and a bypass switch, arranged in parallel with the second part; in a disconnection state of the second part, the control circuit turns on the bypass switch, enables the first constant current circuit, disables the second constant current circuit, and sets the first output current to the third current amount.

22. The lighting circuit according to claim 21, wherein the third current amount is not more than (m + n) / m times the first current amount and is less than the rated current of the first part.

23. A vehicle lamp, wherein it includes the lighting circuit according to any one of claims 1 to 22.

24. The vehicle lamp according to claim 23, wherein it is an LED (light emitting diode) socket.

25. A light source module, characterized in that, comprising: an LED string, including n same-color LEDs (light emitting diodes) connected in series, where n ≧ 2, an LED driver circuit, receiving an input voltage and supplying a driving current stabilized to a target current to the LED string, and A bypass circuit is provided in parallel with a bypassed portion including m adjacent LEDs among the LED string, and a bypass current corresponding to the input voltage is injected, where m ≤ n; The luminous flux of the n - m LEDs arranged in a portion other than the bypassed portion is greater than the luminous flux of the m LEDs arranged in the bypassed portion.

26. The light source module according to claim 25, characterized in that The LED is red, n = 4, m = 2.

27. The light source module according to claim 25, characterized in that The LED is white or blue, n = 3, m = 1.

28. The light source module according to any one of claims 25 to 27, characterized in that The luminous flux of the n - m LEDs is 1.3 times or more the luminous flux of the m LEDs.

29. The light source module according to any one of claims 25 to 27, characterized in that The luminous flux of the n - m LEDs is 1.5 times or more the luminous flux of the m LEDs.

30. The light source module according to any one of claims 25 to 27, characterized in that The bypass circuit includes a current source that generates a bias current whose current amount increases as the input voltage decreases.

31. The light source module according to claim 30, characterized in that The slope of the bypass current with respect to the input voltage is set such that the slope of the change in the total luminous flux of the LED string with respect to the input voltage is 5% / 0.1V or less.

32. The light source module according to any one of claims 25 to 27, characterized in that The bypass circuit includes a bypass switch that becomes conductive when the input voltage becomes lower than a specified threshold.

33. The light source module according to any one of claims 25 to 27, characterized in that It is an LED socket.

34. The light source module according to any one of claims 25 to 27, characterized in that It further includes an anti-reverse protection diode provided between the input terminal of the LED driver circuit and the battery.

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