JP2016201341A - Lightning circuit and lamp fitting for vehicles using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fluctuation in quantity of light immediately after the start of lighting.SOLUTION: A lightning circuit 20 drives a semiconductor light source 12. A start voltage generation part 40 generates, at the start of lighting, a start voltage Vthat gently changes with time from an initial voltage Vdepending on a temperature. A drive circuit 30 supplies a lamp current Idepending on a start voltage Vto the semiconductor light source 12.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a vehicular lamp used in an automobile or the like.

  Conventionally, halogen lamps and HID (High Intensity Discharge) lamps have been mainstream as light sources for vehicle lamps, particularly headlamps, but in recent years they have been replaced by LEDs (light-emitting diodes) and laser diodes (semiconductor lasers). Development of a vehicular lamp using a semiconductor light source such as

Japanese Patent Laid-Open No. 2004-330819 JP 2006-278361 A JP 2008-193054 A JP 2006-278361 A JP 2013-251131 A

Laser diodes and LEDs have a temperature characteristic in which the amount of emitted light is negative. When constant current control for supplying a constant lamp current (drive current) to these semiconductor light sources is performed, the amount of light changes as the temperature of the semiconductor light sources changes. FIG. 1 is a waveform diagram immediately after the semiconductor light source is turned on. Supply of a constant lamp current _ILD is started at time t0. As time elapses, the temperature of the semiconductor light source rises due to heat generated by the semiconductor light source itself, and the amount of light emitted from the semiconductor light source decreases with time. This change in the amount of light is determined by the temperature of the light source and the thermal time constant at which the light source is dissipated, but since the time constant is on the order of a few tens of seconds, the change in the amount of light is perceptible to the human eye, Reduce.

  In addition, when applied to automotive headlamps, the upper and lower limits of the lamp light amount are specified. Therefore, when designing based on a state in which the light amount is large immediately after startup, it is necessary to set the light amount in a steady state lower. . In addition, the tolerance of light quantity must be strictly selected, which increases the cost.

  The present invention has been made in such a situation, and one of the exemplary purposes of an aspect thereof is to provide a lighting circuit capable of suppressing fluctuations in the amount of light immediately after the start of lighting.

  One embodiment of the present invention relates to a lighting circuit for a semiconductor light source. The lighting circuit has a start voltage generator that generates a start voltage that increases according to a waveform determined based on a temperature rise curve after lighting, from an initial voltage that depends on temperature at the start of lighting, and a start voltage that depends on the start voltage. A driving circuit for supplying a lamp current to the semiconductor light source.

  According to this aspect, the lamp current rises with time by changing the start voltage with a time constant or a time scale determined based on a temperature rise curve. By canceling the increase in the amount of light caused by the increase in the lamp current and the decrease in the amount of light due to the increase in the temperature of the semiconductor light source, fluctuations in the amount of light immediately after the start of lighting can be suppressed. In addition, by setting the initial value of the start voltage according to the temperature, it is possible to obtain a substantially constant amount of light regardless of the temperature at the time of startup.

The start voltage generation unit includes a capacitor, an initialization circuit that charges the capacitor with an initial voltage depending on temperature at the start of lighting, a charging resistor provided between a reference voltage line to which a reference voltage is applied and the capacitor, And the voltage of the capacitor may be a start voltage.
In this configuration, the start voltage has a waveform that increases according to the time constant of CR, and a waveform that closely mimics the temperature rise curve can be obtained.

  The initialization circuit includes a temperature sensor, and includes a temperature detection circuit that generates a temperature detection voltage corresponding to the temperature detected by the temperature sensor, and a charging circuit that applies an initial voltage corresponding to the temperature detection voltage to the capacitor. But you can.

  The charging circuit may be a current source type buffer circuit. Thereby, after the initial voltage is set by the initialization circuit, the initialization circuit can be electrically disconnected from the capacitor.

The temperature detection circuit includes a thermistor and a fixed resistor provided in series between the reference voltage line and the ground, and an arithmetic circuit that generates a temperature detection voltage by performing arithmetic processing on the voltage at the connection point of the thermistor and the fixed resistor. May be included. The arithmetic processing may be any combination of attenuation, inverting amplification, non-inverting amplification, and level shift.
By providing the arithmetic circuit, the relationship between the initial voltage and the temperature can be appropriately designed.

The drive circuit includes a constant current converter that supplies a lamp current to the semiconductor light source, a converter controller that controls the constant current converter so that a detected value of the lamp current matches a target value corresponding to the voltage of the analog dimming terminal, , May be included. The start voltage may be input to the analog dimming terminal.
Thereby, the lamp current can be changed according to the start voltage.

The lighting circuit according to an aspect further includes a low-temperature derating circuit that operates on the analog dimming terminal so that the target value of the lamp current decreases as the temperature decreases in a low-temperature state where the temperature is lower than a predetermined low-temperature threshold. May be.
By providing the low-temperature derating circuit, it is possible to prevent the amount of heat generated by the semiconductor laser from becoming excessive in a steady low-temperature state where the ambient temperature is low, and the reliability can be improved.

  In one aspect, the lighting circuit operates on the analog dimming terminal of the converter controller so that the target value of the lamp current decreases as the temperature rises in a high temperature state where the temperature is higher than a predetermined high temperature threshold, or the converter A high temperature derating circuit acting on the PWM dimming terminal of the controller may be further provided.

The high temperature derating circuit may act on the analog dimming terminal. The lighting circuit may further include a forced extinction circuit that compares the voltage of the analog dimming terminal with a predetermined threshold voltage and forcibly turns off the drive circuit based on the comparison result.
Thereby, the misdetection of COD (Catastrophic Optical Damage) can be prevented.

  Another aspect of the present invention relates to a vehicular lamp. The vehicular lamp may include a semiconductor light source and any one of the lighting circuits described above that drive the semiconductor light source.

  According to an aspect of the present invention, it is possible to suppress fluctuations in the amount of light immediately after starting lighting.

It is a wave form diagram immediately after lighting of a semiconductor light source. It is a circuit diagram which shows the basic composition of the vehicle lamp which concerns on 1st Embodiment. It is a circuit diagram which shows the specific structural example of a vehicle lamp. It is an operation | movement waveform diagram at the time of the lighting start of a vehicle lamp. FIG. 5A is an operation waveform diagram of the vehicular lamp at a high temperature and a low temperature, and FIG. 5B is an operation waveform diagram of the comparative technique. 6A and 6B are circuit diagrams of a start voltage generation unit according to a modification. It is a circuit diagram of the vehicular lamp concerning the 2nd modification. It is a circuit diagram of the vehicular lamp which concerns on 2nd Embodiment. It is a figure which shows a temperature derating characteristic.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected to each other in addition to the case where the member A and the member B are physically directly connected. It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as their electric It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

  Further, in this specification, electrical signals such as voltage signals and current signals, or symbols attached to circuit elements such as resistors and capacitors indicate the respective voltage values, current values, resistance values, and capacitance values as necessary. It shall represent.

(First embodiment)
FIG. 2 is a circuit diagram showing a basic configuration of the vehicular lamp 10 according to the first embodiment. The vehicular lamp 10 includes a lighting circuit 20 and a semiconductor light source 12. The semiconductor light source 12 is an LED or a laser diode and has negative temperature characteristics. In the present embodiment, the semiconductor light source 12 is a laser diode. The lighting circuit 20 supplies the semiconductor light source 12 with a lamp current _ILD corresponding to the target luminance (light quantity) to cause the semiconductor light source 12 to emit light.

The lighting circuit 20 includes a start voltage generation unit 40 and a drive circuit 30. The start voltage generator 40 includes a temperature sensor 42 such as a thermistor, and measures the device temperature (or ambient temperature) T of the semiconductor light source 12. When the start voltage generation unit 40 receives an instruction to start lighting the semiconductor light source 12, the start voltage generation unit 40 generates a start voltage V _START that increases with time from the initial voltage V _INIT depending on the temperature T obtained by the temperature sensor 42. The start voltage V _START has a waveform determined based on a rising curve of the temperature T after lighting. Since the temperature T rises on a time scale (time constant) of several seconds to several tens of seconds, the start voltage V _START is also raised on the same time scale (time constant).

The drive circuit 30 supplies the semiconductor light source 12 with a lamp current I _LD corresponding to the start voltage V _START at the start of lighting. In the present embodiment, the start voltage V _START is supplied to the analog dimming (ADIM) terminal of the drive circuit 30. The drive circuit 30 outputs a start voltage V _START that is substantially proportional to the voltage at the ADIM terminal.

FIG. 3 is a circuit diagram illustrating a specific configuration example of the vehicular lamp 10. The start voltage generation unit 40 includes a capacitor C1, a charging resistor R1, and an initialization circuit 44. One end of the capacitor C1 is grounded. The initialization circuit 44 charges the capacitor C1 with an initial voltage V _INIT depending on the temperature T at the start of lighting. The charging resistor R1 is provided between the reference voltage line 46 to which the reference voltage _VREF is applied and the capacitor C1. The voltage across the capacitor C1 becomes the start voltage _VSTART .

The initialization circuit 44 includes a thermistor 43 that is a temperature sensor 42. The temperature detection circuit 50 generates a temperature detection voltage V _TEMP corresponding to the resistance value of the thermistor 43. The thermistor 43 has a resistance value R _TH having a negative temperature coefficient (NTC) and is provided close to the semiconductor light source 12. For example, the temperature detection circuit 50 includes a fixed resistor R2 in addition to the thermistor 43, and outputs the voltage of those connection nodes.
V _TEMP = R2 / (R _TH + R2) × V _REF
The temperature voltage V _TEMP has a positive temperature characteristic that increases as the temperature increases.

The charging circuit 52 applies an initial voltage V _INIT corresponding to the temperature detection voltage V _TEMP to the capacitor C1. The charging circuit 52 can be configured by a current source type buffer circuit that can source (discharge) current but cannot sink (sink) current.

The drive circuit 30 includes a constant current converter 32 and a converter controller 34. The constant current converter 32 has a general step-down DC / DC converter topology. The current sense resistor R _S is inserted on the path of the lamp current I _LD .

The converter controller 34 includes a current sense amplifier 35, an error amplifier 36, a PWM comparator 37, and a driver 38. The current sense amplifier 35 amplifies the voltage (voltage drop) across the current sense resistor _RS and generates a current feedback signal _VIS . The error amplifier 36 amplifies an error between the current feedback signal V _IS and the start voltage V _START that is a target value thereof, and generates an error signal V _ERR . The PWM comparator 37 is a pulse modulator, compares the ramp signal (or sawtooth wave signal) having a predetermined frequency with the error signal _VERR , and generates a pulse signal _SPWM corresponding to the comparison result. The driver 38 switches the switching element M1 of the constant current converter 32 based on the pulse signal _SPWM .

The above is the configuration of the vehicular lamp 10. Next, the operation will be described.
FIG. 4 is an operation waveform diagram at the start of lighting of the vehicular lamp 10. FIG. 4 shows, in order from the top, the start voltage V _START , the temperature T, the lamp current I _LD , and the amount of light. The alternate long and short dash line of the lamp current I _LD and the amount of light indicates the waveform obtained with the conventional vehicular lamp 10.

When lighting is instructed at time t 0, start voltage V _START immediately increases to initial voltage V _{INIT having} a voltage level corresponding to temperature T detected by temperature sensor 42. Then, the start voltage V _START gradually increases with time based on the time constant of the charging resistor R1 and the capacitor C1. On the other hand, the temperature T of the semiconductor light source 12 also increases gradually with time, and the waveform of the start voltage V _{START and} the waveform of the temperature T are approximate. The lamp current I _LD increases in response to the start voltage V _START .

The operation of the vehicular lamp 10 has been described above.
According to the vehicular lamp 10, the temporal change in the light amount immediately after the start of lighting is canceled by canceling the light amount increase due to the increase in the lamp current _ILD and the light amount decrease due to the temperature increase of the semiconductor light source 12. Can be suppressed.

Next, the advantage of giving the initial voltage V _INIT temperature dependence will be described. This advantage becomes clear by comparison with comparative techniques. In the comparative technique, the initial value V _INIT of the start voltage V _START is a fixed value without depending on the temperature T. FIG. 5B is an operation waveform diagram of the comparative technique. The solid line indicates the high temperature, and the alternate long and short dash line indicates the low temperature. If the initial voltage V _INIT is constant without depending on the temperature, a certain amount of light can be obtained at a certain temperature (in FIG. 5B, the low temperature of the one-dot chain line), but another temperature (FIG. 5). In (b), the amount of light becomes relatively small at a high temperature (solid line). That is, the amount of light varies depending on the temperature of lighting disclosure.

Based on this, the vehicular lamp 10 according to the embodiment will be described. FIG. 5A is an operation waveform diagram of the vehicular lamp 10 at a high temperature and a low temperature. The initial voltage V _INIT is high when the temperature is high, and the initial voltage V _INIT is low when the temperature is low. As a result, the amount of light immediately after the start of lighting can be made uniform without depending on the temperature.

Subsequently, a modification of the first embodiment will be described.
(First modification)
The configuration of the start voltage generation unit 40 is not limited to that of FIG. The start voltage generator 40 of FIG. 3, the temperature detection voltage _{V TEMP,} as it has been used as an initial voltage _{V INIT,} the voltage range of the temperature detection voltage _{V TEMP,} depending such as temperature characteristics, amplifies the temperature detection voltage _{V TEMP,} The initial voltage V _INIT may be generated by attenuation, level shift, or the like.

6A and 6B are circuit diagrams of a start voltage generation unit 40 according to a modification. The start voltage generation unit 40 in FIG. 6A further includes an arithmetic circuit 54. The configuration of the temperature detection circuit 50 is the same as that shown in FIG. The arithmetic circuit 54 is configured by a combination of an operational amplifier OA1 and resistors R _{11 to} R ₁₄ , and input / output thereof is given by the following expression.
V _INIT = R ₁₃ (R ₁₃ + R ₁₂ ) V _TEMP / R ₁₁ (R ₁₃ + R ₁₄ ) −R ₁₂ / R ₁₁ · V _REF
If R ₁₁ = R ₁₃ and R ₁₂ = R ₁₄ , the initial voltage V _INIT is given by the following equation.
V _INIT = R ₁₂ / R ₁₁ × (V _TEMP −V _REF )
The arithmetic circuit 54 can be understood as an analog subtractor.

In the start voltage generator 40 of FIG. 6B, the fixed resistor R3 of the temperature detection circuit 50 is inserted on the high potential side. The thermistor 43 has a negative temperature coefficient (NTC). The polarity of the temperature detection voltage V _TEMP is opposite to that of FIG. Therefore, the arithmetic circuit 54 inverts and amplifies the temperature detection voltage V _TEMP ′ to generate an initial voltage V _INIT .
V _INIT = R ₁₃ (R ₁₃ + R ₁₂ ) V _REF / R ₁₁ (R ₁₃ + R ₁₄ ) −R ₁₂ / R ₁₁ · V _TEMP
If R ₁₁ = R ₁₃ and R ₁₂ = R ₁₄ , the initial voltage V _INIT is given by the following equation.
V _INIT = R ₁₂ / R ₁₁ × (V _REF −V _TEMP )

The circuit format of the arithmetic circuit 54 is not particularly limited, and any combination of a voltage dividing circuit, a level shifter, a non-inverting amplifier, an inverting amplifier, an adder, a subtractor, etc. is obtained so as to obtain a desired relationship between V _TEMP and V _INIT Can be configured.

  As the thermistor 43, a posistor having a positive temperature coefficient (PTC) may be used. In this case, the amplification polarity of the arithmetic circuit 54 is opposite to that in FIGS. 6A and 6B and FIG.

(Second modification)
The control of the lamp current by the start voltage generator 40 can be used in combination with the gradual change lighting control and other derating controls. FIG. 7 is a circuit diagram of the vehicular lamp 10c according to the second modification.

The vehicle lamp 10c further includes a gradual change lighting controller 60 and a voltage clamper 70 in addition to the vehicle lamp 10 of FIG. Gradually changing the lighting controller 60, the time of lighting of the semiconductor light source 12, and generates a gradual change signal V _SS to increase slowly with time. Change the time of this gradual change signal _{V SS} is shorter than a change time of the start voltage _{V START,} for example, about 0.2 to 5 seconds. For example, the gradual change lighting controller 60 can be configured based on a combination of a capacitor C2 and a current source 62 that charges the capacitor C2. The drive circuit 30 outputs a lamp current I _LD corresponding to the voltage of the analog dimming (ADIM) terminal. Analog dimming is also called DC dimming. The gradual change signal _{V SS} is input to the ADIM terminal. The start voltage V _START is input to the voltage clamper 70. Voltage clamper 70, a voltage of ADIM terminal clamps so as not to exceed the start voltage _{V START.} The other voltage clamper 72 receives a derating signal V _DERATE depending on the temperature and the power supply voltage. The voltage clamper 72 clamps the voltage at the ADIM terminal so as not to exceed the derating signal V _DELETE .

  According to this configuration, gradual change lighting, gradual change extinction, and derating control can be used in combination with the start control by the start voltage generator 40. It will be understood by those skilled in the art that these controls can be used in combination with other circuit configurations different from those in FIG.

(Third Modification)
The configuration of the constant current converter 32 is not limited to that of FIG. The constant current converter 32 may be a synchronous rectification step-down converter, a boost converter, or a step-up / down converter. Alternatively, an insulating converter using a transformer may be used, and the circuit topology is not particularly limited.

(Fourth modification)
Further, the configuration of the converter controller 34 and the modulation method are not limited to those shown in FIG. For example, instead of the pulse width modulation method, a controller for hysteresis control (Bang-Bang control) may be used, or other control such as a pulse frequency modulation method may be employed.

(5th modification)
In the embodiment, the start voltage V _START is generated by the CR circuit, but the present invention is not limited to this. For example, instead of the charging resistor R1, a start voltage _VSTART having another preferable waveform may be generated using a variable current source.

(Second Embodiment)
In the first embodiment, the technology for suppressing the light amount fluctuation accompanying the transient temperature fluctuation after the lighting is started has been described. In the second embodiment, temperature derating control for steady temperature fluctuation will be described.

When the lamp current of the semiconductor light source 12 is stabilized at a target amount that does not depend on the temperature in a steady state, the following problems occur depending on the temperature.
-Since semiconductor lasers are vulnerable to high temperatures, reliability is impaired when the ambient temperature is high.
-Since the optical output of the semiconductor laser has a negative temperature characteristic with respect to temperature, the light quantity increases excessively at low temperatures and the reliability is impaired.

  In the second embodiment, a vehicular lamp 10d that can solve these problems will be described. FIG. 8 is a circuit diagram of the vehicular lamp 10d according to the second embodiment.

The vehicular lamp 10d includes a low temperature derating circuit 80 and a high temperature derating circuit 90. The temperature detection circuit 50 is shared by the low temperature derating circuit 80, the high temperature derating circuit 90, and the start voltage generation unit 40. The temperature detection circuit 50 generates a temperature detection voltage V _TEMP . The configuration of the temperature detection circuit 50 in FIG. 8 is the same as that of the temperature detection circuit 50 of the start voltage generation unit 40 in FIG.

The low temperature derating circuit 80 reduces the lamp current I _LD by acting on the dimming voltage (dimming voltage) of the ADIM terminal in a low temperature state. The low temperature derating circuit 80 includes an arithmetic circuit 82 and a voltage clamper 84. The arithmetic circuit 82 receives the temperature detection voltage V _TEMP and generates a low temperature derating signal V _LT . The voltage clamper 84 clamps the voltage of the ADIM terminal so as not to exceed the voltage level of the low temperature derating signal _VLT . This voltage clamper 84 corresponds to the voltage clamper 72 of FIG. The voltage level of the low temperature derating signal V _LT decreases as the temperature decreases in a temperature range lower than a certain low temperature threshold value T _L.

Hot derating circuit 90, by acting on the dimming voltage ADIM terminal in a high temperature state, to reduce the lamp current I _LD. The high temperature derating circuit 90 includes an arithmetic circuit 92 and a voltage clamper 94. The arithmetic circuit 92 receives the temperature detection voltage V _TEMP and generates a high temperature derating signal V _HT . Hot derating signal V _HT is the higher temperature range than a high temperature threshold T _H, the higher the temperature, the voltage level drops. Voltage clamper 94, a voltage of ADIM terminal clamps so as not to exceed the voltage level of the high-temperature derating signal V _HT.

The arithmetic circuits 82 and 92 can be configured similarly to the arithmetic circuit 54 of FIG. The temperature dependence of the low-temperature derating signal V _LT is determined based on the resistance values R _{21 to} R ₂₄ . Temperature dependence of the high-temperature derating signal _{V HT} is determined based on the resistance value _R 31 _{to R 34.} However, the arithmetic circuits 82 and 92 may have different circuit configurations. The configuration of the voltage clampers 84 and 94 is not limited to that shown in FIG. 8, and another circuit may be used.

Next, the operation of the lighting circuit 20d will be described. FIG. 9 is a diagram showing temperature derating characteristics. The lamp current I _LD is normalized with the current level corresponding to the dimming voltage V _DIM being 1. Temperature derating does not occur in the temperature range of T _{L to} T _H.

The range of T _{H <T H,} the lamp current _{I LD} as the temperature T is high is reduced. As a result, the heat generation of the semiconductor light source 12 is suppressed, the temperature of the semiconductor light source 12 can be prevented from exceeding the maximum rating, and the reliability can be improved. Since high temperature derating is care for heat generation, power consumption may be reduced by shortening the energization time by PWM dimming instead of analog dimming (DC dimming).

On the other hand, in the range of T < _TL, the lamp current I _LD decreases as the temperature T decreases. And reduction of the lamp current I _LD by low temperature derating, the amount of light increases due to the temperature drop of the semiconductor light sources 12 is canceled. Thereby, it can prevent that light quantity increases too much in a low-temperature state, and reliability is impaired.

  Here, the low-temperature derating is care for preventing the amount of light emitted from the laser from becoming excessive. Laser diodes are very fast in tracking optical output against current changes, and PWM dimming as a low-temperature derating causes excessive emission light and zero current to be repeated. Must not. Therefore, it is desirable to perform the low temperature derating in a form that acts on the ADIM terminal as shown in FIG.

  Next, still another feature of the lighting circuit 20d will be described. Laser diodes have a failure mode in which they do not emit light, although they do not appear in the electrical characteristics of COD (Catastrophic Optical Damage). Considering a vehicular lamp that uses a laser diode as a light source, it is necessary to detect this failure and transmit it to the vehicle side. It is necessary to add a circuit configuration for determining a COD abnormality. If the lamp current of the laser diode is reduced to near zero due to high temperature derating, COD may be erroneously detected.

In order to solve this problem, a forced turn-off circuit 100 is provided. The forced turn-off circuit 100 compares the voltage V _ADIM at the ADIM terminal with a predetermined threshold voltage V _TH and detects that the amount of light from the semiconductor light source 12 is significantly reduced due to high temperature derating. When the light quantity of the semiconductor light source 12 becomes extremely small, the reset signal RST is asserted (for example, high level). When the reset signal RST is asserted, the converter controller 34 forcibly stops the operation of the constant current converter 32 and sets the lamp current _ILD to zero.

As described above, by providing the forced light-off circuit 100, the semiconductor light source 12 is forcibly turned off when entering the region where the light amount of the semiconductor light source 12 is significantly reduced due to high temperature derating, thereby preventing erroneous detection of COD. it can. In order to prevent the forced lighting circuit 100 from chattering between the lighting state and the forced lighting state, it is desirable that the threshold voltage V _TH has hysteresis (V _THH , V _THL ).

  Finally, modified examples related to the first and second embodiments will be described.

In the embodiment, the case where the driving circuit 30 generates the lamp current I _LD proportional to the voltage of the ADIM terminal has been described, but the present invention is not limited to this. The drive circuit 30 may increase the lamp current I _LD as the voltage at the ADIM terminal is lower. In this case, the start voltage V _START of the start voltage generator 40 and the polarities of the outputs of the low temperature derating circuit 80 and the high temperature derating circuit 90 may be reversed.

  Some of the start voltage generation unit 40, the low temperature derating circuit 80, the high temperature derating circuit 90, and the forced turn-off circuit 100 described in the first and second embodiments may be selectively mounted. For example, the start voltage generator 40 may be omitted from the vehicular lamp 10d in FIG. Alternatively, a low temperature derating circuit 80 may be added to the vehicular lamp 10 of FIG.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Vehicle lamp, 12 ... Semiconductor light source, 20 ... Lighting circuit, 30 ... Drive circuit, 32 ... Constant current converter, 34 ... Converter controller, 35 ... Current sense amplifier, 36 ... Error amplifier, 37 ... PWM comparator, 38 ... Driver, 40 ... start voltage generation unit, 42 ... temperature sensor, C1 ... capacitor, R1 ... charging resistor, 43 ... thermistor, 44 ... initialization circuit, 46 ... reference voltage line, 50 ... temperature detection circuit, 52 ... charging circuit, 54 ... Arithmetic circuit, 60 ... Gradual change lighting controller, 70, 72 ... Voltage clamper, 80 ... Low temperature derating circuit, 82 ... Arithmetic circuit, 84 ... Voltage clamper, 90 ... High temperature derating circuit, 92 ... Arithmetic circuit, 94 ... Voltage clamper, 100 ... Forced extinction circuit.

Claims (9)

A lighting circuit for a semiconductor light source,
A start voltage generator that generates a start voltage that gradually changes with time from an initial voltage that depends on temperature at the start of lighting;
A driving circuit for supplying a lamp current corresponding to the start voltage to the semiconductor light source;
A lighting circuit comprising: The start voltage generator is
A capacitor;
An initialization circuit that charges the capacitor at the initial voltage depending on the temperature at the start of lighting;
A charging resistor provided between a reference voltage line to which a reference voltage is applied and the capacitor;
The lighting circuit according to claim 1, wherein the voltage of the capacitor is the start voltage. The initialization circuit includes:
A temperature detection circuit including a temperature sensor and generating a temperature detection voltage corresponding to the temperature detected by the temperature sensor;
A charging circuit that applies the initial voltage according to the temperature detection voltage to the capacitor;
The lighting circuit according to claim 2, comprising: The temperature detection circuit includes:
A thermistor and a fixed resistor provided in series between the reference voltage line and ground;
An arithmetic circuit that performs arithmetic processing on a voltage at a connection point between the thermistor and the fixed resistor to generate the temperature detection voltage;
The lighting circuit according to claim 3, further comprising: The drive circuit is
A constant current converter for supplying a lamp current to the semiconductor light source;
A converter controller that controls the constant current converter so that a detection value of the lamp current matches a target value corresponding to a voltage of an analog dimming terminal;
Including
The lighting circuit according to claim 1, wherein the start voltage is input to the analog dimming terminal.   6. A low-temperature derating circuit that operates on the analog dimming terminal so that the target value decreases as the temperature decreases in a low-temperature state where the temperature is lower than a predetermined low-temperature threshold. Lighting circuit according to.   In a high temperature state where the temperature is higher than a predetermined high temperature threshold, the target value decreases as the temperature rises, or the analog dimming terminal of the converter controller acts or the PWM dimming terminal of the converter controller The lighting circuit according to claim 5, further comprising a high-temperature derating circuit that operates on the lighting circuit. The high temperature derating circuit acts on the analog dimming terminal,
The said lighting circuit is further provided with the forced light extinction circuit which compares the voltage of the said analog dimming terminal with a predetermined threshold voltage, and forcibly turns off the said drive circuit based on the comparison result. The lighting circuit described. A semiconductor light source;
The lighting circuit according to any one of claims 1 to 8, which drives the semiconductor light source;
A vehicular lamp characterized by comprising:

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