JP2016091730A - Lamp fitting for vehicle and lighting circuit for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting circuit capable of achieving temperature derating control suitable for a semiconductor light source.SOLUTION: A temperature detection circuit 50 includes a first temperature detection element 52 and generates first temperature information ST1 indicating a temperature T1. A microcontroller 60 receives from an ECU 6 a light quantity command S1 that instructs the quantity of light for a semiconductor light source 10 and receives the first temperature information ST1, and outputs a dimming signal S2 based on the light quantity command S1 and the first temperature information ST1. A switching converter 30 supplies a power to the semiconductor light source 10. A drive IC 40 receives a dimming voltage Vdepending on the dimming signal S2, and controls the switching converter 30 so that a current Iflowing in the semiconductor light source 10 approaches a target value depending on the dimming voltage V.SELECTED DRAWING: Figure 1

Description

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

  In recent years, semiconductor light sources such as LEDs (light emitting diodes) and LDs (laser diodes) have been adopted as light sources for vehicle lamps such as high beams, low beams, and rear combination lamps. Semiconductor light sources have advantages over conventional light sources such as HID (High Intensity Discharge) lamps and halogen lamps from the viewpoints of energy efficiency, ease of maintenance, design diversity, and the like.

  The semiconductor light source has a rated temperature that is acceptable to maintain its reliability, and the lighting circuit that drives the semiconductor light source has a junction temperature, device temperature, or device temperature so that the temperature of the semiconductor light source does not exceed the rated temperature. When the ambient temperature rises, it has a function (temperature derating function) that reduces the drive current, that is, reduces the amount of light and suppresses further temperature rise. Patent Documents 1 to 3 disclose related technologies.

  Further, when the environmental temperature becomes high, the temperature of the electronic components in the lighting circuit may exceed the rated temperature due to heat generation of the light source, or the resin parts near the light source may approach the softening point and be deformed. The temperature derating described above is also useful for suppressing these problems.

JP 2006-114279 A JP 2010-141137 A JP 2012-160277 A

  In the temperature derating control described in Patent Documents 1 to 3, a thermistor is incorporated in an analog circuit, and the target value of the current supplied to the semiconductor light source is changed by the analog circuit. Therefore, the relationship between temperature and current (light quantity) (referred to as derating characteristics) is limited to the range that can be realized with an analog circuit, and is not necessarily the optimal derating characteristic for protecting semiconductor light sources and lighting circuits. There was room for improvement.

  In addition, the rated temperature of the semiconductor light source varies from device to device. Further, when the shape of the heat sink, the substrate, or the housing is changed, the temperature of the semiconductor light source when it is turned on with the same amount of light also differs. Therefore, in the conventional temperature derating control by the analog circuit, if the device of the semiconductor light source and the peripheral structure are changed, it is necessary to redesign the derating circuit, which requires enormous time and cost.

  With respect to light sources such as conventional HID lamps and halogen lamps, the rated temperature is specified and a derating function is required.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and one of the exemplary purposes of an aspect thereof is to provide a lighting circuit capable of realizing temperature derating control suitable for a light source.

  One embodiment of the present invention relates to a lighting circuit for a light source. The lighting circuit includes a first temperature detection element, receives a temperature detection circuit for generating first temperature information indicating temperature, and a light amount command for instructing the light amount of the light source from the host controller, receives the first temperature information, A microcontroller that outputs a dimming signal based on the command and the first temperature information, a switching converter that supplies power to the light source, a dimming voltage corresponding to the dimming signal, and the current flowing through the light source becomes the dimming voltage And a drive circuit that controls the switching converter so as to approach the corresponding target value.

  In this aspect, a microcontroller is inserted between the host microcomputer that controls the lamps comprehensively based on the vehicle information and the drive circuit of the switching converter. A commercially available microcontroller uses an A / D converter provided as a standard function, converts analog first temperature information from the first temperature detection element into a digital value, and generates a dimming signal by digital signal processing. Thus, the relationship between the temperature and the dimming signal, that is, the relationship between the temperature and the light amount can be set based on an arbitrary function or table. As a result, temperature derating control suitable for the light source can be realized only by changing the software without being restricted by temperature derating control by an analog circuit.

In a range in which the temperature indicated by the first temperature information is higher than a predetermined first threshold value and lower than a predetermined second threshold value set higher than the first threshold value, The amount of light indicated by the dimming signal may be reduced substantially linearly so that the amount of light becomes zero.
According to this aspect, the temperature derating suitable for the light source can be realized by optimizing the combination of the first threshold value, the second threshold value, and the inclination.

The microcontroller may not reflect the temperature information in the dimming signal in a range in which the temperature indicated by the first temperature information is higher than the third threshold set higher than the second threshold.
When the temperature indicated by the first temperature information exceeds the third threshold value by setting the third threshold value higher than the range that the first temperature information can take when the temperature detection circuit operates normally, It can be estimated that an abnormality has occurred in the temperature detection circuit or a failure has occurred. Therefore, in this case, the lighting of the light source can be maintained by stopping the temperature derating control based on the first temperature information.

  The microcontroller: (i) the first temperature in a range where the temperature indicated by the first temperature information is higher than a predetermined first threshold and lower than a predetermined second threshold set higher than the first threshold. The amount of light indicated by the dimming signal is reduced in accordance with the temperature indicated by the information, and (ii) the dimming is performed in a range where the temperature indicated by the first temperature information is higher than the third threshold set higher than the second threshold The first temperature information may not be reflected in the optical signal.

The lighting circuit according to an aspect may further include a high-temperature shutdown circuit that includes the second temperature detection element and reduces the dimming voltage when the temperature indicated by the second temperature detection element is higher than a predetermined fourth threshold value. .
As a result, the temperature derating control by the microcontroller and the protection by the high temperature shutdown circuit are doubled, so that the reliability of the circuit can be improved.

  Further, in a non-operating state of the microcontroller, the drive circuit may be configured to light the light source with a predetermined light amount that does not depend on the dimming signal. In this case, even if the temperature derating control by the microcontroller is invalidated, the light source can be protected by the high temperature shutdown circuit.

  The fourth threshold value may have hysteresis. This prevents chattering and enables stable control.

The dimming signal may be pulse-modulated so as to have a duty ratio corresponding to the target light amount. The lighting circuit may further include a filter circuit that smoothes the dimming signal and generates a dimming voltage. The high temperature shutdown circuit may change the dimming voltage by changing the amplitude of the input signal of the filter circuit.
Temperature derating control by the microcontroller is realized by changing the duty ratio of the dimming signal according to the temperature. And by changing the amplitude of the input signal (dimming signal) of the filter circuit by the high-temperature shutdown circuit, the temperature derating control by the microcontroller and the protection by the high-temperature shutdown circuit can coexist, and the reliability is improved. Can do.

The lighting circuit may be further provided with a level shifter that is provided in the previous stage of the filter circuit and shifts the amplitude of the dimming signal. The level shifter may include a voltage dividing circuit. The high-temperature shutdown circuit includes a second resistor and a first switch connected in series in parallel with the first resistor constituting the voltage dividing circuit, and compares the temperature indicated by the second temperature detection element with the fourth threshold value. The switch may be turned on / off accordingly.
In this case, the voltage dividing ratio of the voltage dividing circuit changes according to whether the first switch is on or off. Therefore, the amplitude of the output pulse of the level shifter can be changed according to the comparison result between the temperature and the fourth threshold value.

The lighting circuit of a certain aspect may further include a hard temperature derating circuit that includes the third temperature detection element and decreases the dimming voltage as the temperature indicated by the third temperature detection element is higher.
This hard temperature derating circuit is equivalent to the temperature derating by the conventional analog circuit, and is inferior to the temperature derating by the microcontroller in terms of the degree of freedom of the relationship between the temperature and the light quantity, but is used as an auxiliary. Thus, the reliability of the lamp can be increased.

The microcontroller is configured to output a selection signal having a first level in its operating state and a second level in its non-operating state. The hard temperature derating circuit receives the selection signal, and the selection signal is at the first level. When the selection signal is at the second level, it is turned on, and the dimming voltage may be lowered as the temperature indicated by the third temperature detecting element is higher in the on state.
As a result, the hard temperature derating circuit can be protected while the microcontroller is stopped, and the hard temperature derating circuit is disabled while the microcontroller is operating, and the temperature derating by the microcontroller is adopted to achieve the optimum temperature. Control can be realized.

The dimming signal may be pulse-modulated so as to have a duty ratio corresponding to the target light quantity. The lighting circuit may further include a filter circuit that smoothes the dimming signal and generates a dimming voltage. The hard temperature derating circuit may change the dimming voltage by changing the amplitude (voltage level) of the input signal of the filter circuit.
Temperature derating control by the microcontroller is realized by changing the duty ratio of the dimming signal according to the temperature. Then, by changing the input amplitude of the filter circuit by the hard temperature derating circuit, the temperature derating control by the microcontroller and the protection by the hard temperature derating circuit can coexist, and the reliability can be improved.

The lighting circuit may be further provided with a level shifter that is provided in the previous stage of the filter circuit and shifts the amplitude of the dimming signal. The level shifter may include a voltage dividing circuit. The thermistor that is the third temperature detection element may be provided in parallel with the first resistor constituting the voltage dividing circuit.
Thereby, when the resistance value of the thermistor changes according to temperature, the voltage dividing ratio of the voltage dividing circuit changes, and the amplitude of the output pulse of the level shifter can be changed.

The hard temperature derating circuit may further include a second switch connected in series with a thermistor that is a third temperature detection element.
In this case, the hard temperature derating circuit can be turned off (invalidated) by turning off the second switch.

The drive circuit may include a thermal shutdown circuit, and stop the control of the switching converter when the temperature detected by the thermal shutdown circuit exceeds a predetermined sixth threshold value.
Reliability can be further improved by using the temperature protection function by the drive circuit in combination.

  The sixth threshold value may have hysteresis. This prevents chattering and enables stable control.

The microcontroller may monitor the power supply voltage supplied thereto, and reduce the amount of light indicated by the dimming signal when the power supply voltage falls below a predetermined seventh threshold value.
If the input power of the switching converter is constant, the input current of the switching converter increases as the power supply voltage decreases. Since the input current flows through the switching transistor or the like and becomes a loss, it causes an increase in the amount of heat generated in the circuit. Therefore, the lower the power supply voltage, the lower the amount of light, thereby reducing the heat generation of the switching converter and the heat generation of the light source.

The drive circuit may detect a current flowing through the switching transistor of the switching converter, and control the switching converter so that the current supplied to the light source decreases when the detected current becomes higher than a predetermined eighth threshold value. .
By monitoring the input current of the switching converter by the drive circuit, it is possible to estimate the power consumption of the switching converter, and hence its temperature, and to control the switching converter so as to suppress the temperature rise.

The dimming signal is pulse-modulated so as to have a duty ratio corresponding to the target light amount, and the lighting circuit may further include a filter circuit that smoothes the dimming signal and generates a dimming voltage. The microcontroller may be configured to be able to correct the relationship between the duty ratio and the light quantity command.
As a result, it is possible to cancel variations in hardware inserted between the drive circuit and the driver circuit.

  The light source may be a semiconductor light source. The lighting circuit may be driven by a plurality of semiconductor light sources. The microcontroller and the first temperature detection element may be provided in common for the plurality of semiconductor light sources. The switching converter and the drive circuit may be provided for each semiconductor light source. The microcontroller may be configured to receive a light amount command for instructing the light amount of each of the plurality of semiconductor light sources from the host controller and output a plurality of dimming signals. Each drive circuit receives a dimming voltage corresponding to the corresponding dimming signal, and controls the corresponding switching converter so that the current flowing through the corresponding semiconductor light source approaches the target value corresponding to the corresponding dimming voltage. May be.

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

According to still another aspect of the present invention, a vehicular lamp includes a high-beam first semiconductor light source, a first drive module that turns on the first semiconductor light source, and a cooling fan. The first drive module includes any one of the lighting circuits described above. The microcontroller of the lighting circuit of the first drive module monitors the number of rotations of the cooling fan, and if the state where the number of rotations falls below a predetermined threshold value continues for a predetermined time, the amount of light indicated by the dimming signal for the first semiconductor light source May be reduced.
According to this aspect, the failure of the cooling fan can be detected based on the number of rotations of the cooling fan, and the temperature rise can be suppressed by reducing the amount of light when the cooling fan fails.

The vehicular lamp may further include a second semiconductor light source for additional low beam and a second drive module that turns on the second semiconductor light source. The microcontroller may assert a failure diagnosis signal indicating a failure of the cooling fan when the state where the rotation speed falls below a predetermined threshold value continues for a predetermined time. In response to the assertion of the failure diagnosis signal, the second drive module may maintain the light emission while reducing the light amount of the second semiconductor light source.
By maintaining the light emission of the light amount of the second semiconductor light source for the additional low beam when the cooling fan fails, it is possible to prevent the visibility from being deteriorated.

The microcontroller and the host controller may be connected via a LIN (Local Interconnect Network), and the microcontroller may notify the host controller of a cooling fan failure via the LIN.
Thereby, the host controller can perform processing such as notifying the user of a failure of the cooling fan or leaving a log.

  According to an aspect of the present invention, temperature derating control suitable for a light source can be realized.

It is a block diagram of the vehicular lamp which concerns on 1st Embodiment. 2 (a) is a diagram showing an example of the temperature derating characteristic, FIG. 2 (b) is a diagram showing a drive current _{I LED} relationship between the command current _{I CMD.} FIG. 3A is a diagram showing an example of temperature derating by the high temperature shutdown circuit, and FIG. 3B is a diagram showing an example of hard temperature derating by the hard temperature derating circuit. It is a circuit diagram which shows the structural example of the lighting circuit which concerns on 1st Embodiment. It is a wave form diagram which shows soft temperature derating control. It is a wave form diagram which shows high temperature shutdown operation | movement. It is a wave form diagram which shows hard temperature derating operation | movement. It is a circuit diagram of the lighting circuit which concerns on 2nd Embodiment. And current amount (light intensity) I _LED dimming signal indicates a diagram showing an example of the relationship between the power supply voltage V _IG. FIGS. 10A and 10B are diagrams for explaining power supply voltage derating by the driving IC. It is a circuit diagram which shows the structural example of the lighting circuit which concerns on 2nd Embodiment. It is a block diagram of the vehicular lamp which concerns on 3rd Embodiment.

  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. 1 is a block diagram of a vehicular lamp 1 according to the first embodiment. The vehicular lamp 1 includes a semiconductor light source 10 and a lighting circuit 20. For example, the semiconductor light source 10 includes one or a plurality of light emitting elements 12 connected in series. The light emitting element 12 is an LED or an LD. In the present embodiment, it is assumed that the light emitting element 12 is an LED. The lighting circuit 20 is also referred to as an LDM (LED Driving Module).

The voltage V _BAT (also referred to as + B) of the battery 2 is supplied to the Hi terminal of the lighting circuit 20 via the headlight switch 3. In the present embodiment, the semiconductor light source 10 is a high beam light source. Therefore, a voltage supplied via the headlight switch 3 is referred to as a Hi (high beam) voltage V _Hi . Further, the voltage V _{BAT of the} battery 2 is supplied to the IG terminal of the lighting circuit 20 via the ignition switch 4. A voltage supplied to the IG terminal is referred to as an IG (ignition) voltage V _IG . The GND terminal of the lighting circuit 20 is grounded.

  A control command (referred to as a light quantity command S1) from an ECU (Electronic Control Unit) 6 that is a host controller is input to the interface (I / F) terminal of the lighting circuit 20, and the lighting circuit 20 is a semiconductor based on the light quantity command S1. The light quantity of the light source 10 is controlled. The ECU 6 and the microcontroller 60 are connected by a bus compliant with, for example, the LIN (Local Interconnect Network) standard.

Next, the configuration of the lighting circuit 20 will be described.
The lighting circuit 20 includes a voltage regulator 22, a switching converter 30, a drive IC 40, a temperature detection circuit 50, a microcontroller 60, a high temperature shutdown circuit 70, and a hard temperature derating circuit 80.

The voltage regulator 22 receives the IG voltage V _IG and generates a constant voltage V _REG stabilized to about 5V. The temperature detection circuit 50 includes a first temperature detection element 52, and generates first temperature information ST1 indicating the temperature. For example, as the first temperature detection element 52, a thermistor whose resistance value changes according to temperature is preferably used. The temperature detection circuit 50 includes a thermistor 52 and a resistor 54 provided in series between a constant voltage line to which a constant voltage V _REG is supplied and a ground line. The constant voltage V _REG may be a voltage generated by a voltage regulator built in the microcontroller 60. The temperature detection circuit 50 outputs the potential at the connection point between the thermistor 52 and the resistor 54 as first temperature information ST1 having a voltage level corresponding to the temperature. The resistance value of the thermistor 52 may have a positive temperature characteristic or a negative temperature characteristic. For example, when a thermistor 52 having a negative temperature is used, the voltage level of the first temperature information ST1 increases as the temperature increases. The first temperature detection element 52 is preferably disposed in the immediate vicinity of the semiconductor light source 10.

As the microcontroller 60, a commercially available general-purpose one can be used. A constant voltage V _REG is supplied to the power supply (VDD) terminal of the microcontroller 60, and the GND pin is grounded. The commercially available microcontroller 60 incorporates an A / D converter (not shown) that converts a voltage input to a certain pin (referred to as a TH pin) into a digital value. The voltage of the first temperature information ST1 from the temperature detection circuit 50 is input to the TH pin.

  The microcontroller 60 has a built-in general-purpose interface circuit with an external controller. One or a plurality of pins (hereinafter referred to as CTRL pins) of the microcontroller 60 are connected to the ECU 6 via a communication line (bus) so that data can be transmitted and received between them. For example, this bus may conform to the LIN (Local Interconnect Network) standard. A light amount command S <b> 1 from the ECU 6 is input to the CTRL pin of the microcontroller 60.

  The microcontroller 60 generates a dimming signal S2 based on the light quantity command S1 and the first temperature information ST1, and outputs it from the dimming (DIM) pin. The signal format of the dimming signal S2 is not particularly limited. For example, it may be a pulse-modulated signal having a duty ratio corresponding to the amount of light as described later, or an analog voltage having a voltage level corresponding to the amount of light. There may be.

The switching converter 30 receives the battery voltage (Hi voltage V _Hi ) and supplies power to the semiconductor light source 10. For example, the switching converter 30 is a step-up DC / DC converter.

A driving IC (Integrated Circuit) 40 is a functional IC configured to be able to control the switching converter 30. The internal configuration of the drive IC 40 is not particularly limited, and a commercially available or custom designed IC can be used. A high voltage V _Hi is supplied to the power supply (VDD) pin of the drive IC 40, and its GND pin is grounded.

A dimming voltage V _DIM corresponding to the dimming signal S <b> 2 generated by the microcontroller 60 is input to the dimming (DIM) pin of the driving IC 40. In FIG. 1, the DIM pin of the microcontroller 60 and the DIM pin of the driving IC 40 are shown to be directly connected by a single wiring. However, the present invention is not limited to this, and the microcontroller 60 is between them. An analog circuit serving as an interface of the driving IC 40 may be inserted.

A current detection signal S3 indicating an LED current (drive current) I _LED flowing in the semiconductor light source 10 is input to the current detection (CS) pin of the drive IC 40. The drive IC 40 controls the switching converter 30 based on the current detection signal S3 so that the current I _LED flowing through the semiconductor light source 10 approaches the target value I _REF corresponding to the dimming voltage V _DIM input to the DIM pin. . In this embodiment, the target value I _REF is proportional to the dimming voltage V _DIM for easy understanding. A switching pulse S4 is output from the switching output (OUT) pin of the driving IC 40, and a switching transistor (not shown) of the switching converter 30 is switched in response to the switching pulse S4. For example, when the dimming voltage V _DIM is 0 V, the target value I _REF of the drive current I _LED is 0 A, and the target value L _REF increases as the dimming voltage V _DIM increases.

With the above configuration, the current I _LED flowing through the semiconductor light source 10 and the light amount of the semiconductor light source 10 are controlled according to the dimming signal S2 generated by the microcontroller 60.

  That is, the microcontroller 60 converts the analog first temperature information ST1 from the first temperature detection element 52 into a digital value, and generates the dimming signal S2 by digital signal processing, whereby the temperature and the dimming signal S2 are converted. The relationship, that is, the relationship between temperature and light quantity (current) can be set based on an arbitrary function or table. As a result, temperature derating control suitable for a semiconductor light source (hereinafter also referred to as soft temperature derating control) can be realized only by changing the software without being restricted by temperature derating control by an analog circuit.

  The rated temperature of the semiconductor light source 10 varies depending on the type of device and the vendor. Further, when the shape of the heat sink, the substrate, or the housing is changed, the temperature of the semiconductor light source 10 when the light is lit with the same light amount also changes. That is, in the temperature derating control by the conventional analog circuit, if the device of the semiconductor light source 10 or the surrounding structure is changed, it is necessary to redesign the derating circuit, and enormous time and cost are required. On the other hand, according to the lighting circuit 20 according to the embodiment, it is sufficient to rewrite the table and function in software, so that the lighting circuit 20 can be used as a common platform for many types.

  Next, temperature derating control by the microcontroller 60 will be described in detail. FIG. 2A is a diagram illustrating an example of the temperature derating characteristic.

The microcontroller 60 has a first threshold value Ta1 to a third threshold value Ta3 that satisfy Ta <Tb <Tc. In the microcontroller 60, a derating current (allowable maximum current) I _DR corresponding to the temperature T1 indicated by the first temperature information ST1 is determined. Derating current I _DR takes a maximum value I _MAX (for example, 0.8 A) when temperature T1 is lower than first threshold value Ta, and is higher than first threshold value Ta and lower than second threshold value T2. , The value decreases from the maximum value I _MAX to the minimum value I _MIN .

The microcontroller 60 determines the current amount of the drive current I _LED to be supplied to the semiconductor light source 10 based on the smaller one of the current amount indicated by the light amount command S1 (referred to as the command current _ICMD ) and the derating current _IDR. The dimming signal S2 is generated. 2 (b) is a diagram showing a drive current _{I LED} relationship between the command current _{I CMD.}

More specifically, a T1 _<I DR _{= I} MAX in Ta (= 0.8A), _{I DR} in the range of Ta <T1 <Tb decreases linearly between _I MIN _{~I MAX,} Tb < In the range of T1, I _DR = I _MIN . In FIG. 2A, I _MIN = 0A, Ta = 100 ° C., and Tb = 130 ° C. As a matter of course, I _MIN , Ta, and Tb may be determined in consideration of the rated current of the semiconductor light source 10 and the heat radiation design.

  Thereby, the optimum soft temperature derating for the semiconductor light source 10 can be realized by changing the combination of the first threshold value Ta, the second threshold value Tb, and the inclination in software.

Further, the microcontroller 60 does not reflect the temperature information T1 in the dimming signal S2 in a range where the temperature T1 indicated by the first temperature information ST1 is higher than the third threshold value Tc, that is, stops the soft temperature derating. This can be realized by setting I _DR = I _{MAX in} the range of T1> Tc.

  The third threshold value Tc is set higher than a range that the first temperature information ST1 can take when the temperature detection circuit 50 operates normally. In FIG. 2A, Tc = 150 ° C. Accordingly, when the temperature T1 indicated by the first temperature information ST1 exceeds the third threshold value Tc, it can be estimated that an abnormality has occurred in the temperature detection circuit 50 or a failure has occurred. Therefore, in this case, the soft temperature derating control based on the first temperature information ST1 is stopped, and the dimming signal S2 is generated based only on the light amount command S1, whereby the semiconductor light source 10 can be kept on.

Returning to FIG. One feature of the lighting circuit 20 is that it includes a high-temperature shutdown circuit 70. The high-temperature shutdown circuit 70 includes a second temperature detection element (not shown), and reduces the dimming voltage V _DIM when the temperature T2 indicated by the second temperature detection element is higher than a predetermined fourth threshold value Td. The thermistor is used for the second temperature detection element in the same manner as the first temperature detection element 52. In the present embodiment, the high temperature shutdown circuit 70 pulls down the dimming voltage V _DIM to the low potential side and reduces the current I _LED when T2> Td.

FIG. 3A is a diagram illustrating an example of temperature derating by the high-temperature shutdown circuit 70. The fourth threshold value Td has hysteresis and transitions between two values of Td _L and Td _H. This prevents chattering. It is assumed that the current amount indicated by the light quantity command S1 is I _CMD = 0.8A. The high temperature shutdown circuit 70 does not change the dimming voltage V _DIM in the range of T2 <Td, and therefore I _LED = 0.8 A is maintained. The high temperature shutdown circuit 70 decreases the voltage level of the dimming voltage V _DIM so that I _LED = I _CMD × α in the range of Td <T2. α is a predetermined coefficient. For example, when α = 0.2, the value decreases to I _LED = 0.16A. In a modification, the high temperature shutdown circuit 70 may reduce the dimming voltage V _DIM to 0 V so that the current I _LED becomes zero when T2> Td.

  According to this configuration, since the soft temperature derating control by the microcontroller 60 and the protection by the high temperature shutdown circuit 70 are doubled, the reliability of the circuit can be improved.

Returning to FIG. The microcontroller 60 can be switched between an operating state and a non-operating state. Specifically, when the ignition switch 4 is off, no power is supplied to the microcontroller 60, so that it is in a non-operating state. In the non-operating state of the microcontroller 60, the dimming voltage V _DIM is at a non-zero predetermined level. At this time, the driving IC 40 can turn on the semiconductor light source 10 with a predetermined light amount that does not depend on the dimming signal S2.

  In a platform where the operation and non-operation states of the microcontroller 60 can be switched, the soft temperature derating control is invalidated when the microcontroller 60 is stopped. Even in the state, the semiconductor light source 10 can be protected by the high-temperature shutdown circuit 70.

One feature of the lighting circuit 20 is that it includes a hard temperature derating circuit 80. The hard temperature derating circuit 80 includes a third temperature detection element (not shown), and decreases the dimming voltage V _DIM as the temperature T3 indicated by the third temperature detection element is higher (referred to as hard temperature derating control).

  FIG. 3B is a diagram illustrating an example of hard temperature derating by the hard temperature derating circuit 80. The temperature at which the hard temperature derating control is started (the fifth threshold value Te) may be about 75 ° C., for example. The basic concept of the hard temperature derating circuit 80 is based on temperature derating by a conventional analog circuit. From the viewpoint of the degree of freedom of the relationship between the temperature T3 and the light amount (current), the soft temperature by the microcontroller 60 is used. Inferior to derating. In the present embodiment, the reliability of the lamp can be improved by using the hardware temperature derating circuit 80 as an auxiliary.

As described above, the microcontroller 60 can be switched between operation and non-operation. The microcontroller 60 outputs from the selection (SEL) pin a selection signal S5 that is at a first level (for example, high level) in its operating state and at a second level (for example, low level) in its non-operating state. The hard temperature derating circuit 80 receives the selection signal S5, is turned off when the selection signal S5 is at the first level, and is turned on when the selection signal S5 is at the second level. In the on state, the third temperature detection element indicates The higher the temperature T3, the lower the dimming voltage V _DIM . The hard temperature derating circuit 80 does not affect the dimming voltage V _DIM in the off state.

  As a result, when the microcontroller 60 is stopped, the hard temperature derating circuit 80 can protect the circuit. When the microcontroller 60 is operating, the hard temperature derating circuit 80 is disabled and the soft temperature derating by the microcontroller 60 is adopted. Thus, optimum temperature control can be realized.

The drive IC 40 includes a thermal shutdown circuit 42. When the temperature T4 detected by the thermal shutdown circuit 42 exceeds a predetermined sixth threshold value Tf, the drive IC 40 stops the control of the switching converter 30. As a result, the drive current I _LED becomes zero, and the temperature rise is suppressed. The sixth threshold value Tf may have hysteresis. This prevents chattering and enables stable control.

  Thus, reliability can be further improved by using the temperature protection function by the drive IC 40 together with the soft temperature derating control, the high temperature shutdown control, and the hard temperature derating control.

  The above is the basic configuration of the lighting circuit 20 according to the first embodiment. The present invention extends to various circuits grasped from the block diagram of FIG. 1 and the above description, and a specific configuration example will be described below.

FIG. 4 is a circuit diagram showing a configuration example of the lighting circuit 20 according to the first embodiment. The switching converter 30 is a step-up DC / DC converter (boost converter), and boosts the input voltage V _Hi to generate an output voltage _VOUT . The switching converter 30 includes a switching transistor M1, an inductor L1, a rectifier diode D1, an input capacitor C1, and an output capacitor C2. Since the topology of the switching converter 30 is general, the description thereof is omitted. The switching converter 30 supplies an input voltage V _Hi to the cathode of the semiconductor light source 10 and an output voltage _VOUT to the anode of the semiconductor light source 10.

The current sense resistor 34, in order to detect the driving current _{I LED,} is inserted on the path of the drive current _{I LED.} A voltage drop V _CS proportional to the drive current I _LED is generated in the current sense resistor 34. The CS + pin and CS− pin of the drive IC 40 are connected to both ends of the current sense resistor 34, and the current detection signal S3 is input thereto.

  The microcontroller 60 includes an A / D converter 62, a soft derating circuit 66, and a pulse modulator 68. The A / D converter 62 converts the first temperature information ST1 input to the TH pin into a digital value S6. The soft derating circuit 66 generates a digital current command value (duty command value) S7 that indicates the light amount of the semiconductor light source 10, that is, the current amount, based on the temperature T1 indicated by the digital value S6 and the light amount command S1.

The dimming signal S2 is a pulse signal that is pulse-modulated so as to have a duty ratio corresponding to a target light amount (current amount). The pulse modulator 68 of the microcontroller 60 performs pulse modulation (for example, pulse width modulation) on the current command value S7 and converts it to a dimming signal S2. In FIG. 4, the dimming signal S2 is a negative logic signal, and the off-duty ratio, which is the ratio of the low level interval to the period, indicates the target value of the drive current I _LED . The frequency of the dimming signal S2 is several hundred Hz to several kHz, and is set to 1 kHz as an example.

  The soft derating circuit 66 and the pulse modulator 68 are not functional circuit blocks that can be distinguished from other circuits, but functional blocks realized by a combination of various hardware resources and software programs built in the microcontroller 60. Is understood.

  For example, the soft derating circuit 66 can be configured by a combination of an arithmetic processing unit (processor) built in the microcontroller 60 and a software program stored in the ROM.

  The pulse modulator 68 can be configured by a combination of an oscillator and a counter in hardware. Alternatively, the pulse modulator 68 can also be configured by a combination of a configuration that generates a digital periodic signal having a sawtooth wave or a ramp waveform and a digital comparator that compares the digital periodic signal with the current command value S7 and slices it.

  Thus, the dimming signal S2 subjected to pulse modulation is output from the DIM pin of the microcontroller 60.

Between the DIM pin of the driving IC 40 and the DIM pin of the microcontroller 60, a smoothing circuit 90 for converting the dimming signal S2 into an analog dimming voltage V _DIM is provided. The smoothing circuit 90 includes a level shifter 92 and a filter circuit 94. The level shifter 92 shifts the amplitude level of the dimming signal S2 so as to match the input range of the DIM pin of the driving IC 40, and inverts the logical level of the dimming signal S2 as necessary. As described above, when the microcontroller 60 generates the dimming signal S2 in the negative logic system, the smoothing circuit 90 logically inverts the dimming signal S2 and inputs it to the filter circuit 94.

The power supply voltage V _DD supplied to the smoothing circuit 90 may be generated by a voltage regulator built in the driving IC 40. The power supply voltage V _DD may be generated by a voltage source (not shown), but is preferably generated using the Hi voltage V _Hi instead of the IG voltage V _IG . As a result, the high temperature shutdown circuit 70 and the hard temperature derating circuit 80 can function even when the IG voltage V _IG is not supplied. Smoothing circuit 90 includes transistors Q11-Q13 and resistors R11-R14. The resistors R11 and R12 form a voltage dividing circuit 96. The high level voltage of the dimming signal S2 after passing through the level shifter 92 is V _DD × R12 / (R11 + R12), and the low level voltage is 0V. The configuration of the level shifter 92 is not particularly limited.

The filter circuit 94 smoothes the dimming signal S8 that has passed through the level shifter 92 and converts it to an analog dimming voltage V _DIM . The dimming voltage V _DIM is given by the following equation (1) when the duty ratio of the dimming signal S2 is β%.
V _DIM = β / 100 × V _DD × R12 / (R11 + R12) (1)
The filter circuit 94 may be an RC filter including a capacitor C11 and a resistor R15. Those skilled in the art will appreciate that various variations of the configuration of the smoothing circuit 90 can exist.

Here, when the power supply voltage V _DD and the resistors R11 and R12 vary or the design is changed, the relationship between the duty ratio β and the dimming voltage V _DIM changes. Therefore, it is desirable that the pulse modulator 68 of the microcontroller 60 can correct the relationship between the duty ratio of the dimming signal S2 and the light amount command S1. Thereby, the variation of the hardware (smoothing circuit 90) can be canceled, and when the duty ratio β of the dimming signal S2 is changed in the range of 0 to 100%, the drive current I _LED is reduced to the minimum value 0A. It can be changed in the range of ~ maximum value.

Subsequently, the high temperature shutdown circuit 70 is referred to. The thermistor and the resistor 74, which are the second temperature detection element 72, are connected in series between the power supply voltage V _DD and the ground, and the potential V12 at the connection point becomes the second temperature information ST2 indicating the temperature T2. Resistors R21 and R22 divide the power supply voltage V _DD to generate a threshold voltage V _TH . This threshold voltage V _TH corresponds to the fourth threshold value Td shown in FIG. Voltage comparator 76 by comparing the voltage V12 and the voltage _{V TH,} is compared with the temperature T2 of the fourth threshold value Td. When T2> Td, the output S9 of the voltage comparator 76 is high level, and when T2 <Td, the output S9 is low level.

As shown in FIG. 3A, hysteresis is set for the fourth threshold value Td. Therefore, the resistor R32 and the transistor Q21 are connected in series in parallel with the resistor R22. And the transistor Q21 is turned on when the output S9, the high level, and decreases the threshold voltage _{V TH,} the fourth threshold value becomes Td _L, the output S9 to transistor Q21 is turned off at a low level, the threshold voltage V _TH is increased, the fourth threshold value becomes Td _H. The method for setting the hysteresis is not limited to this, and a known technique may be used.

The high-temperature shutdown circuit 70 changes the dimming voltage V _DIM by changing the pulse voltage Vp input to the filter circuit 94, in other words, the amplitude of the output signal of the level shifter 92. For this purpose, the high-temperature shutdown circuit 70 includes a first switch M21 and a first resistor R24 connected in series in parallel with the resistor R12 constituting the voltage dividing circuit 96.

When T2 <Td, the output of the voltage comparator 76 is at a low level, and the first switch (transistor) M21 is off. Therefore, the first resistor R24 does not affect the smoothing circuit 90. When T2> Td, the output of the voltage comparator 76 becomes high level and the transistor M21 is turned on. Therefore, the first resistor R24 is connected in parallel with the resistor R12. If the impedance of the parallel connection of the resistors R12 and R24 is R12 ′, the dimming voltage V _DIM is β / 100 × V _DD × R12 ′ / (R11 + R12 ′) when the duty ratio of the dimming signal S2 is β%. ) That is, the voltage division ratio of the output stage of the level shifter 92 is reduced, and the amplitude of the pulse voltage Vp is reduced. Thereby, the dimming voltage V _DIM is lowered, and a high-temperature shutdown function can be realized.

Subsequently, the hard temperature derating circuit 80 is referred to.
The hard temperature derating circuit 80 changes the dimming voltage V _DIM by changing the input voltage Vp of the filter circuit 94 as in the high temperature shutdown circuit 70. For this purpose, the hard temperature derating circuit 80 includes a thermistor which is a third temperature detection element 82 connected in series and a second switch M31 in parallel with the resistor R12.

  The switch control circuit 84 turns off the second switch M31 when the selection signal S5 is at a high level, that is, when the microcontroller 60 is operating. As a result, the thermistor 82 does not affect the smoothing circuit 90. That is, the hard temperature derating function is disabled.

The switch control circuit 84 turns on the second switch M31 when the selection signal S5 is at a low level, that is, when the microcontroller 60 is stopped (non-operating state). Thereby, the thermistor 82 is connected in parallel with the transistor R12. As a result, the voltage dividing ratio of the voltage dividing circuit 96 changes in accordance with the resistance value of the thermistor 82, that is, the temperature. As the temperature increases, the input voltage Vp of the filter circuit 94 decreases and the dimming voltage V _DIM decreases. be able to.

Next, the operation of the lighting circuit 20 in FIG. 4 will be described. First, soft temperature derating control by the microcontroller 60 will be described. FIG. 5 is a waveform diagram showing soft temperature derating control. FIG. 5 shows temperature T1, current command value (duty command value) S7, inverted signal of dimming signal S2, dimming voltage V _DIM , and drive current I _LED . In FIG. 5, the duty ratio corresponding to the current amount _ICMD indicated by the light quantity command S1 is 75%. When the temperature T1 is lower than the first threshold value Ta, the duty ratio of the dimming signal S2 is 75% determined according to the light amount command S1. When the temperature T1 exceeds the first threshold value Ta, the duty ratio of the dimming signal S2 decreases as the temperature T1 increases, and when the temperature T1 reaches the second threshold value Tb, the duty of the dimming signal S2 The ratio is 0%. The dimming voltage V _DIM is a voltage obtained by smoothing the dimming signal S2, and thus has a voltage level corresponding to the duty ratio of the dimming signal S2. The drive current I _LED decreases as the dimming voltage V _DIM decreases.

Next, the high temperature shutdown operation by the high temperature shutdown circuit 70 will be described. FIG. 6 is a waveform diagram showing a high temperature shutdown operation. FIG. 6 shows the temperature T2, the output of the voltage comparator 76, the inverted signal of the dimming signal S2, the input voltage Vp of the filter circuit 94, the dimming voltage V _DIM , and the drive current I _LED . Also in FIG. 6, the duty ratio corresponding to the current amount _ICMD indicated by the light amount command S1 is 75%. When the temperature T2 is lower than the fourth threshold value Td _H, the duty ratio of the dimming signal S2 is 75% determined in accordance with the amount command S1, the drive current _{I LED} is maintained to the amount of current _{I CMD.} Temperature T3 is is the signal S9 exceeds the fourth threshold value Td _H becomes high level, the resistor R12 and the first resistor R24 are connected in parallel, voltage dividing ratio of the voltage dividing circuit 96 is reduced. As a result, the amplitude of the input pulse Vp of the filter circuit 94 decreases. As a result, the dimming voltage V _DIM and the drive current I _LED decrease (shutdown state).

When the drive current I _LED decreases, the amount of heat generation decreases, and the temperature T3 starts to decrease. When the temperature T3 is below the fourth threshold value Td _L, becomes the output S9 of the voltage comparator 76 to the low level, the amplitude of the input pulse Vp of the filter circuit 94 returns to the original, the dimming voltage _{V DIM} and the drive current I _LED increases and returns from shutdown state.

Next, hard temperature derating by the hard temperature derating circuit 80 will be described. FIG. 7 is a waveform diagram showing a hard temperature derating operation. FIG. 7 shows temperature T3, dimming signal S2, input voltage Vp and dimming voltage V _{DIM of} filter circuit 94, and drive current I _LED .

While the microcontroller 60 is not operating, the second switch M31 is turned on, the thermistor 82 as the third temperature detecting element is connected to the voltage dividing circuit 96, and the hardware temperature derating circuit 80 is turned on. In the non-operating state of the microcontroller 60, the dimming signal S2 is not a pulse but a constant level (fixed to a low level), and therefore the input voltage Vp of the filter circuit 94 is also a non-pulse constant. Specifically, when the microcontroller 60 is not operating, the dimming signal S2 is at a low level, the transistor Q2 is off, the transistor Q13 is on, and the transistor Q11 is on. The dimming voltage V _{DIM at} this time is given by the following equation (2). R12 ′ is a parallel combined resistance of the resistor R12 and the thermistor 82.
V _DIM = Vp≈V _DD × R12 ′ / (R11 + R12 ′) (2)
This is equivalent to the duty ratio of the dimming signal S2 being 100% in the operating state of the microcontroller 60. When the temperature T3 increases, the impedance of the combined resistor R12 ′ decreases, the dimming voltage V _DIM decreases, and the drive current I _LED decreases. Thereby, hard temperature derating can be realized.

(Second Embodiment)
FIG. 8 is a circuit diagram of the lighting circuit 20 according to the second embodiment. In the first embodiment, the temperature derating for changing the current I _LED according to the temperature has been described. However, in the second embodiment, the current I _LED according to the power supply voltage (IG voltage or Hi voltage). The power supply voltage derating for changing the voltage will be described. Of course, the power supply voltage derating can be used alone or in combination with the temperature derating. FIG. 8 shows only the configuration related to the power supply voltage derating.

The microcontroller 60 monitors the power supply voltage supplied thereto, that is, the IG voltage _VIG , and when the power supply voltage _VIG becomes lower than a predetermined seventh threshold value Va, the light amount indicated by the dimming signal S2 is reduced.

The voltage detection circuit 100 includes resistors 102 and 104, divides the IG voltage V _IG , and inputs the divided voltage to one pin (voltage sense VS) connected to the A / D converter of the microcontroller 60. An A / D converter (not shown) built in the microcontroller 60 converts the voltage of the VS pin into a digital value. The microcontroller 60 reduces the amount of light indicated by the dimming signal S2 as the voltage _VIG decreases based on the digital value corresponding to the IG voltage _VIG . Power supply voltage derating by the microcontroller 60 is referred to as soft power supply voltage derating.

FIG. 9 is a diagram illustrating an example of the relationship between the current amount (light quantity) I _LED indicated by the dimming signal S2 and the power supply voltage _VIG .

The microcontroller 60 instructs the drive IC 40 as it is in the current amount I _CMD (for example, 0.8 A) indicated by the light amount command S1 in the range where the power supply voltage V _IG indicated by the voltage at the VS pin is higher than the seventh threshold value Va. .

When the power supply voltage V _IG indicated by the voltage of the VS pin becomes lower than the seventh threshold voltage Va, the microcontroller 60 reduces the current amount (light quantity) indicated by the dimming signal S2 to I as the power supply voltage V _IG decreases. Decrease from _CMD . If the power supply voltage V _IG is lowered to some extent, the microcontroller 60 becomes inoperable. In this case, as described above, the dimming voltage V _DIM becomes a predetermined voltage level that does not depend on the dimming signal S2, and the driving IC 40 supplies a predetermined amount of driving current I _LED to the semiconductor light source 10.

If the input power of the switching converter 30 is constant, the input current I _L1 of the switching converter 30 increases as the power supply voltage V _IG (V _Hi ) decreases. Since the input current I _L1 flows through the switching transistor (M1 in FIG. 4) or the like and becomes a loss, it causes an increase in the amount of heat generated in the circuit. Therefore, the lower the power supply voltage V _IG , the lower the light amount (drive current I _LED ), thereby reducing the input power of the switching converter 30 and thus the input current I _L1. Can be reduced.

Moreover, the state where the IG voltage V _IG is low is a state where the battery voltage V _BAT upstream is lowered, and it is grasped that the battery is abnormal or the other load is consuming large electric power. Therefore, the reliability of the system can be improved by reducing the power consumption of the vehicular lamp 1 as the IG voltage V _IG decreases.

The power supply voltage derating by the microcontroller 60 is similar to the soft temperature derating described in the first embodiment, such as the relationship between the power supply voltage V _IG and the current I _LED , that is, threshold value, curve shape, slope, etc. These parameters can be arbitrarily defined by software. Therefore, according to the lighting circuit 20, optimal derating control can be easily realized according to the characteristics of components and devices used in the semiconductor light source 10 and the switching converter 30.

Returning to FIG. The drive IC 40 also has a power supply voltage derating function. Specifically the driving IC40, the current detection signal S10 showing the input current _{I L1} of the switching converter 30 is input. The drive IC 40 controls the switching converter 30 so that the current I _LED supplied to the semiconductor light source 10 decreases when the detected current _IL1 becomes higher than a predetermined eighth threshold value Ib. It should be noted that the input current I _M1 is different from the drive current I _LED indicated by the current detection signal S3.

10A and 10B are diagrams for explaining power supply voltage derating by the driving IC 40. FIG. FIG. 10A shows the relationship between the power supply voltage V _IG and the drive current I _LED . As shown in FIG. 10A, the relationship of I _LED with respect to V _IG is preferably optimized according to the number of light emitting elements 12 constituting the semiconductor light source 10. More specifically, when the number (number) of chips of the light emitting element 12 is small, the inclination of derating control is reduced, and the inclination of derating control is increased as the number of chips of the light emitting element 12 increases. Is preferred. (I) to (iii) of FIG. 10B show cases where the number of chips is 2, 3, and 4. Under the same driving current I _LED , the heat generation amount of the entire semiconductor light source 10 increases as the number of chips of the light emitting element 12 increases. Further, as the number of chips increases, the mounting density of the chips increases, and the junction temperature tends to rise locally. Therefore, an optimum power supply voltage derating can be realized by increasing the derating slope as the number of chips increases.

The power supply voltage derating by the drive IC 40 depends on the circuit constants of the switching converter 30 and is an indirect power supply voltage derating using the input current I _LIN . From the viewpoint of accuracy, it is inferior to the soft power supply voltage derating by the microcontroller 60. However, the soft power supply voltage derating functions only during the operation of the microcontroller 60, whereas the power supply voltage derating by the driving IC 40 always functions. Can do.

  The above is the basic configuration of the lighting circuit 20 according to the second embodiment. The present invention extends to various circuits grasped from the block diagram of FIG. 10 and the above description, and a specific configuration example will be described below.

  FIG. 11 is a circuit diagram illustrating a configuration example of the lighting circuit 20 according to the second embodiment. The description of the same configuration as in FIG. 4 is omitted.

In connection with power supply voltage derating control by the microcontroller 60, the microcontroller 60 includes an A / D converter 63, a soft derating circuit 66, and a pulse modulator 68. The A / D converter 63 converts the voltage at the VS pin into a digital value S11. The soft derating circuit 66 generates a digital current command value (duty command value) S7 that indicates the light amount of the semiconductor light source 10, that is, the current amount, based on the power supply voltage V _IG indicated by the digital value S11 and the light amount command S1. . The pulse modulator 68 performs pulse width modulation on the current command value S7 and outputs a dimming signal S2 from the DIM pin. The power supply voltage derating by the microcontroller 60 may be directly performed based on the Hi voltage V _Hi instead of the IG voltage V _IG .

Next, power supply voltage derating control by the drive IC 40 will be described. The current sense amplifier 43 converts / amplifies the detection voltage V _CS1 indicating the drive current I _LED into a ground reference voltage. The modulator 44 generates a pulse signal S11 whose duty ratio is adjusted so that the detection voltage V _CS1 approaches the dimming voltage V _DIM . The driver 45 switches the switching transistor M1 of the switching converter 30 based on the pulse signal S11.

The switching converter 30 includes a current sense resistor R _CS2 provided on the path of the input current _IL1 , specifically, between the source of the switching transistor M1 and the ground line. An input current I _L1 (I _M1 ) flows through the current sense resistor R _CS2 during the ON period of the switching transistor M1, and a voltage drop V _CS2 proportional to the input current I _L1 is generated. The voltage drop V _CS2 is input to the drive IC 40 as the current detection signal S10. The comparator 46 compares the voltage Vb corresponding to the above-described eighth threshold value Ib with the detection signal V _CS2 , and forcibly turns off the switching transistor M 1 with pulse-by-pulse when V _CS2 > Vb.

FIG. 10B is a waveform diagram illustrating power supply voltage derating control by the driving IC 40. (I) shows a waveform during normal operation, and (ii) shows a waveform when the power supply voltage _VIG drops. For ease of understanding, assuming that the output power and conversion efficiency of the lighting circuit 20 are constant, the input power is also constant. If the input voltage V _Hi (ie, V _IG ) is sufficiently high under the assumption that the input power of the lighting circuit 20 is constant, the average of the input current I _L1 is small as shown in (i), and the input voltage V _Hi When (that is, V _IG ) decreases, the average of the input current I _L1 increases as shown in (ii). That is, the peak of the current I _M1 flowing in the ON section of the switching transistor M1 also increases.

When the power supply voltage V _IG further decreases, the current I _M1 tends to further increase in order to keep the input power constant. However, when the current I _M1 reaches the eighth threshold value Ib, the switching transistor M1 is forcibly turned off and the on-time is insufficient, so that the current I _M1 and consequently the input current I _L1 reaches a peak. Thus, as the power supply voltage V _IG (V _Hi ) increases, the input power of the lighting circuit 20 is limited so as to decrease, and the output power and thus the drive current I _LED decreases. With the above operation, power supply voltage derating control shown in FIG. The power supply voltage derating by the driving IC 40 is grasped as an overcurrent protection circuit or a current limiting circuit.

(Third embodiment)
In the third embodiment, a vehicular lamp 1 using the lighting circuit according to the first or second embodiment will be described. FIG. 12 is a block diagram of the vehicular lamp 1 according to the third embodiment.

  In this embodiment, the vehicular lamp 1 includes an ECU 6, a plurality of high beam semiconductor light sources 10_1 to 10_N (N is an integer of 2 or more), a high beam first drive module 20A, an additional low beam semiconductor light source 10B, A second drive module 20B for additional low beam and a cooling fan 8 are provided. The vehicle lamp 1 further includes a low beam light source and a lighting circuit thereof, which are omitted here.

  The drive module 20A may be the lighting circuit 20 according to the first and second embodiments, and the basic configuration thereof is as described above. The driving module 20A targets a plurality of semiconductor light sources 10_1 to 10_N as driving targets. The microcontroller 60 and the first temperature detection element 52 are provided in common for the plurality of semiconductor light sources 10_1 to 10_N. The switching converter 30 and the drive circuit 40 are provided for each semiconductor light source 10. The microcontroller 60 receives light amount commands S1_1 to S1_N for instructing the light amounts of the plurality of semiconductor light sources 10_1 to 10_N from the ECU 6 that is a host controller, and outputs a plurality of light control signals S2_1 to S2_N.

  When the drive module 20A of FIG. 12 includes the lighting circuit 20 of FIG. 4, the circuit block that generates the output S9 in the high-temperature shutdown circuit 70 is provided in common for the plurality of semiconductor light sources 10, and includes the resistor R24 and the transistor M21. It may be provided for each semiconductor light source 10.

Each drive circuit 40_i (1 ≦ i ≦ N) receives the dimming voltage V _DIM corresponding to the corresponding dimming signal S2_i, and the current flowing through the corresponding semiconductor light source 10_i corresponds to the corresponding dimming voltage V _DIMi The corresponding switching converter 30_i is controlled so as to approach the target value.

  The cooling fan 8 is provided to cool the semiconductor light sources 10_1 to 10_N. Specifically, the cooling fan 8 is disposed to face a heat sink that is thermally coupled to the semiconductor light source 10, and air-cools the heat sink. The cooling fan 8 outputs an FG (Frequency Generation) signal having a frequency corresponding to the rotational speed. The microcontroller 60 receives this FG signal and monitors the rotational speed of the cooling fan 8.

  The microcontroller 60 monitors the number of revolutions of the cooling fan 8, and when the state where the number of revolutions falls below a prescribed threshold value continues for a prescribed time, the light quantity indicated by the dimming signals S2 to S2_N for the first semiconductor light sources 10_1 to 10_N Reduce. For example, the light amount of the first semiconductor light source 10 may be reduced to 0%. The predetermined time is determined to be longer than the time required for the rotation speed to stabilize after the cooling fan 8 is started, and may be, for example, several tens of seconds to several minutes, more specifically about 120 seconds. Further, the threshold value is set lower than the rotational speed of the stationary cooling fan 8, and may be, for example, 1000 to 2000 rpm, more specifically about 1500 rpm (FG frequency is 50 Hz or less).

  Thereby, a failure of the cooling fan 8 can be detected and estimated, and when the cooling capacity is reduced, the heat generation amount of the semiconductor light source 10 can be suppressed to protect the circuit.

  Further, the microcontroller 60 asserts (for example, high level) a failure diagnosis signal S12 that indicates a failure of the cooling fan 8 when the state where the rotational speed falls below a predetermined threshold value continues for a predetermined time. In response to the assertion of the failure diagnosis signal S12, the second drive module 20B that drives the additional low beam semiconductor light source 10B reduces the light amount of the second semiconductor light source 10B, for example, lights up with a light amount of 30% under normal conditions. Let

  If the amount of light from the semiconductor light source 10 is reduced when the cooling fan 8 fails, the front of the vehicle becomes dark. Therefore, it is possible to prevent the visibility from decreasing by maintaining the light emission without reducing the light amount of the semiconductor light source 10B to zero.

  As described above, the microcontroller 60 and the ECU 6 are connected via a LIN (Local Interconnect Network), and the microcontroller 60 notifies the ECU 6 of a failure of the cooling fan 8 via the LIN. As a result, processing such as notifying the user of a failure of the ECU 6 or the cooling fan 8 or leaving a log is possible.

  The vehicle is equipped with two left and right vehicle lamps 1. When the failure of the cooling fan 8 is detected in one vehicle lamp 1, the ECU 6 notifies the microcontroller 60 of the other vehicle lamp 1. Receiving the notification, the microcontroller 60 does not decrease the light amount of the high-beam semiconductor light source 10 and turns on the light amount of the additional low-beam semiconductor light source 10B at 30% as in the failure side.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. is there. Hereinafter, such modifications will be described.

(First modification)
As the semiconductor light source 10, a semiconductor light source such as an LD (laser diode) or an organic EL (electroluminescence) may be used in addition to the LED.

(Second modification)
In the embodiment, the switching converter 30 is configured as a boost converter, but the present invention is not limited thereto. For example, the switching converter 30 may include a step-down switching converter (Buck converter) and a flyback type or forward type step-up / step-down switching converter provided in the preceding stage. Alternatively, the switching converter 30 may be a Cuk converter or a Zeta converter.

(Third Modification)
The specific algorithm for soft temperature derating is not limited to that described above. For example, the derating characteristic of FIG. 2A is defined as a temperature-dependent coefficient K (0 ≦ K ≦ 1), and the microcontroller 60 determines the amount of current as I _CMD × K = I _LED , and dimming The signal S2 may be generated.

(Fourth modification)
In the first embodiment, the hard temperature derating circuit 80 is stopped when the microcontroller 60 is not operating. However, the hard temperature derating circuit 80 may be always operated. In this case, the duty ratio of the input signal (input pulse) Vp of the filter circuit 94 changes according to the temperature T1, and the amplitude of the input signal (input pulse) Vp of the filter circuit 94 changes according to the temperature T3. Both soft temperature derating and hard temperature derating will function.

(5th modification)
In the embodiment, the vehicular lamp having the semiconductor light source has been described. However, the present invention is also effective in a vehicular lamp including an HID lamp or a halogen lamp as a light source. For example, in a vehicular lamp having a conventional HID lamp, in order to prevent the electronic components in the lighting circuit from exceeding the rated temperature due to heat generated from the light source when the environmental temperature is high, temperature derating and input voltage derating are performed. The present invention is also applicable to such vehicular lamps. In this case, it goes without saying that the configuration of the switching converter 30 is changed to a format suitable for driving the HID.

The present specification discloses the following technical ideas in addition to those described in the claims.
1. The dimming signal is pulse-width modulated so as to have a duty ratio corresponding to the target light quantity. The lighting circuit further includes a filter circuit that smoothes the dimming signal and generates the dimming voltage. The hard temperature derating circuit changes the dimming voltage by changing the amplitude or voltage level of the input signal of the filter circuit.

  2. The lighting circuit is further provided with a level shifter that is provided in a preceding stage of the filter circuit and shifts the amplitude of the dimming signal. The level shifter includes a voltage dividing circuit. The thermistor that is the third temperature detection element is provided in parallel with the first resistor constituting the voltage dividing circuit.

  3. The hard temperature derating circuit further includes a second switch connected in series with the third temperature detection element.

4). The drive circuit includes a thermal shutdown circuit, and stops the control of the switching converter when the temperature detected by the thermal shutdown circuit exceeds a predetermined sixth threshold value.
5. The sixth threshold value has hysteresis.

  6). The microcontroller monitors the power supply voltage supplied thereto, and reduces the amount of light indicated by the dimming signal when the power supply voltage falls below a predetermined seventh threshold value.

7). The drive circuit detects the current flowing through the switching transistor of the switching converter, and controls the switching converter so that the current supplied to the light source decreases when the detected current becomes higher than a predetermined eighth threshold value. .
8). The dimming signal is pulse-width modulated so as to have a duty ratio corresponding to the target light quantity. The lighting circuit further includes a filter circuit that smoothes the dimming signal and generates the dimming voltage. The microcontroller is configured to be able to correct the relationship between the duty ratio and the light quantity command.

  9. The light source is a semiconductor light source. The lighting circuit drives a plurality of semiconductor light sources. The microcontroller and the first temperature detection element are provided in common for the plurality of semiconductor light sources. The switching converter and the drive circuit are provided for each semiconductor light source. The microcontroller is configured to receive a light amount command for instructing the light amount of each of the plurality of semiconductor light sources from the host controller and output the plurality of light control signals. Each drive circuit receives a dimming voltage according to the corresponding dimming signal, and controls the corresponding switching converter so that the current flowing through the corresponding semiconductor light source approaches the target value according to the corresponding dimming voltage. To do.

  10. Moreover, the lighting circuit disclosed in this specification can be grasped as follows. Discloses another embodiment of a semiconductor light source lighting circuit. The lighting circuit receives a light amount command instructing the light amount of the semiconductor light source from a host controller, and outputs a pulse-modulated dimming signal having a duty ratio corresponding to the light amount command, and an amplitude of the dimming signal A level shifter for level-shifting, a filter circuit for smoothing the output of the level shifter to generate a dimming voltage, a switching converter for supplying power to the semiconductor light source, and a current flowing through the semiconductor light source according to the dimming voltage In order to approach the target value, the drive circuit for controlling the switching converter, and at least one of temperature, a current of a predetermined path of the lighting circuit or a voltage of a predetermined node of the lighting circuit is detected, and according to the detected value, And a derating circuit that changes the amplitude of the output of the level shifter.

  11. The vehicular lamp disclosed in the present specification can be grasped as follows. The vehicular lamp includes a first semiconductor light source for high beam, a first drive module that turns on the first semiconductor light source, and a cooling fan. The first drive module includes the lighting circuit described above. The microcontroller of the lighting circuit of the first drive module monitors the number of rotations of the cooling fan, and when the state where the number of rotations is below a predetermined threshold value continues for a predetermined time, the dimming with respect to the first semiconductor light source Reduce the amount of light indicated by the signal.

  12 The vehicular lamp further includes a second semiconductor light source for an additional low beam, and a second drive module that turns on the second semiconductor light source. The microcontroller asserts a failure diagnosis signal indicating a failure of the cooling fan when a state where the rotation speed falls below a predetermined threshold value continues for a predetermined time, and the second drive module detects the failure diagnosis signal. In response to the assertion, the light emission of the second semiconductor light source is reduced while the light emission is maintained.

  13. The microcontroller and the host controller are connected via a LIN (Local Interconnect Network). The microcontroller notifies the host controller of the failure of the cooling fan via the LIN.

  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 1 ... Vehicle lamp, 2 ... Battery, 3 ... Headlight switch, 4 ... Ignition switch, 6 ... ECU, 8 ... Cooling fan, 10 ... Semiconductor light source, 12 ... Light emitting element, 20 ... Lighting circuit, 30 ... Switching converter, 34 ... current sense resistor, 40 ... drive IC, 42 ... thermal shutdown circuit, 43 ... current sense amplifier, 44 ... modulator, 45 ... driver, 46 ... comparator, 50 ... temperature detection circuit, 52 ... first temperature detection element, 54 ... resistor 60 ... microcontroller 62, 63 ... A / D converter 66 ... soft derating circuit 68 ... pulse modulator 70 ... high temperature shutdown circuit 72 ... second temperature detecting element 74 ... resistor 76 ... voltage comparator, 80 ... hard temperature derating circuit, 82 ... third temperature detection element, 90 ... flat , 92... Level shifter, 94... Filter circuit, 96... Voltage dividing circuit, 100... Voltage detection circuit, S1... Light intensity command, S2 ... dimming signal, S3. Temperature information, ST2 ... second temperature information.

Claims (10)

A light source lighting circuit,
A temperature detection circuit including a first temperature detection element and generating first temperature information indicating the temperature;
A microcontroller that receives a light amount command for instructing the light amount of the light source from a host controller, receives the first temperature information, and outputs a dimming signal based on the light amount command and the first temperature information;
A switching converter for supplying power to the light source;
A drive circuit that receives the dimming voltage according to the dimming signal and controls the switching converter so that a current flowing through the light source approaches a target value according to the dimming voltage;
A lighting circuit comprising:   The microcontroller has the second temperature in a range where the temperature indicated by the first temperature information is higher than a predetermined first threshold and lower than a predetermined second threshold set higher than the first threshold. The lighting circuit according to claim 1, wherein the light quantity indicated by the dimming signal is substantially linearly reduced so that the light quantity becomes zero at a threshold value.   The microcontroller does not reflect the temperature information in the dimming signal in a range in which the temperature indicated by the first temperature information is higher than a third threshold set higher than the second threshold. The lighting circuit according to claim 2. The microcontroller is
(I) The first temperature information is within a range in which the temperature indicated by the first temperature information is higher than a predetermined first threshold and lower than a predetermined second threshold set higher than the first threshold. The light intensity indicated by the dimming signal is reduced according to the temperature indicated by
(Ii) The first temperature information is not reflected in the dimming signal in a range in which the temperature indicated by the first temperature information is higher than a third threshold set higher than the second threshold. The lighting circuit according to claim 1.   2. A high-temperature shutdown circuit that includes a second temperature detection element and that reduces the dimming voltage when a temperature indicated by the second temperature detection element is higher than a predetermined fourth threshold value. To 5. The lighting circuit according to any one of 4. The dimming signal is pulse-modulated to have a duty ratio according to the target light amount,
The lighting circuit further includes a filter circuit that smoothes the dimming signal and generates the dimming voltage,
The lighting circuit according to claim 5, wherein the high-temperature shutdown circuit changes the dimming voltage by changing an amplitude of an input signal of the filter circuit. The lighting circuit is further provided with a level shifter that is provided in a preceding stage of the filter circuit and that level-shifts the amplitude of the dimming signal,
The level shifter includes a voltage dividing circuit,
The high-temperature shutdown circuit includes a first resistor and a first switch connected in series in parallel with the first resistor constituting the voltage dividing circuit, and the temperature indicated by the second temperature detection element and the fourth threshold value The lighting circuit according to claim 6, wherein the switch is controlled to be turned on / off in accordance with the comparison result.   8. The device according to claim 1, further comprising a hard temperature derating circuit that includes a third temperature detection element, and lowers the dimming voltage as the temperature indicated by the third temperature detection element is higher. The lighting circuit described. The microcontroller is configured to output a selection signal that is at a first level in its operating state and at a second level in its non-operating state;
The hard temperature derating circuit receives the selection signal, and is turned off when the selection signal is at the first level, and is turned on when the selection signal is at the second level. The lighting circuit according to claim 8, wherein the dimming voltage is lowered as the temperature indicated by the detection element is higher. A semiconductor light source;
A lighting circuit according to any one of claims 1 to 9,
A vehicular lamp characterized by comprising:

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