WO2017086220A1

WO2017086220A1 - Lighting circuit and vehicular lamp

Info

Publication number: WO2017086220A1
Application number: PCT/JP2016/083228
Authority: WO
Inventors: 知幸市川
Original assignee: 株式会社小糸製作所
Priority date: 2015-11-18
Filing date: 2016-11-09
Publication date: 2017-05-26
Also published as: JPWO2017086220A1; JP6783790B2

Abstract

In order to enable accurate abnormality detection in a configuration in which a plurality of light emitting elements connected in series can be selectively lit up, the present invention is provided with: a voltage conversion unit which receives DC voltage and performs voltage conversion and which supplies a drive current to a light source unit including first and second light emitting elements connected in series; a first bypass switch which forms a bypass path through which the drive current bypasses the first light emitting element; an abnormality detection unit which detects an abnormality of the light source unit by an output voltage from the voltage conversion unit being reduced to less than a threshold value; and a control unit which controls the first bypass switch and which changes the threshold value for the abnormality detection unit in accordance with the control state of the first bypass switch. Accordingly, the threshold value for determination of abnormality of the light source unit is adaptively changed in accordance with the number or types of the light emitting elements which are emitting light.

Description

Lighting circuit, vehicle lamp

The present invention relates to a lighting circuit and a vehicular lamp including a lighting circuit and a light source unit, and relates to a technical field for detecting an abnormality such as a short circuit abnormality.

Japanese Unexamined Patent Publication No. 2015-110357

For example, in a vehicular lamp such as a vehicle headlamp or a turn signal lamp, a light-emitting element such as an LED (Light Emitting Diode) or a light-emitting element such as a filament bulb is used.
Patent Document 1 discloses a circuit in which a bypass circuit is provided for each of a plurality of LEDs connected in series, and a part of the LEDs are turned off by turning on the bypass path.

Consider a light source unit in which a plurality of light emitting elements are connected in series. For example, a plurality of LEDs, a laser element such as a plurality of laser diodes, or an LED and a laser element are connected in series.
In this case, if the steady lighting current of each light-emitting element is the same, the light-emitting element is driven by a common converter and the number of light-emitting elements to be lit is changed by turning on / off a bypass switch provided in parallel to each light-emitting element. Or, the light source type can be changed like LED and laser.

Here, an abnormality of each light emitting element, for example, a short circuit failure (including a failure in which the wiring of the lighting circuit output is equivalent to a light source short circuit (such as a short circuit of the harness)), a current leakage of the lighting circuit wiring, a deterioration of the light source, etc. Think about it. In order to detect such an abnormality, it is common to monitor the output voltage of the lighting circuit and determine an abnormality if it is below a threshold value.
However, in a configuration in which a plurality of light emitting elements are connected in series and a light emitting element to be lit can be selected by a bypass switch, the output voltage of the lighting circuit varies depending on the number of light emitting elements to be lit and the type of light emitting elements. Therefore, the threshold value for detecting an abnormality may not always be an appropriate value for detecting an abnormality, and the abnormality detecting function may be deteriorated.

Therefore, an object of the present invention is to make it possible to accurately detect an abnormality in a configuration in which a plurality of light emitting elements connected in series can be selectively lit.

A lighting circuit according to the present invention receives a direct current voltage to perform voltage conversion, and supplies a driving current to a light source unit having first and second light emitting elements connected in series. A first bypass switch that forms a bypass path that bypasses the first light emitting element; an abnormality detection unit that detects an abnormality of the light source unit when an output voltage of the voltage conversion unit is lower than a threshold; and the first And a control unit that changes the threshold value of the abnormality detection unit in accordance with a control state of the first bypass switch.
In this configuration, the abnormality detection unit detects that an abnormality such as a short circuit or a leak has occurred when the output voltage of the voltage conversion unit with respect to the light source unit drops below a threshold value. Here, by controlling the bypass switch, the number and types of light emitting elements to which a driving current is supplied, that is, light emitting elements that emit light, change. Then, the load voltage of the voltage conversion part as the whole light source part also changes. In this case, if a constant threshold value is always used, the abnormality detection sensitivity changes according to the control state of the bypass switch. Therefore, the threshold value of the abnormality detection unit is changed according to the control state of the bypass switch.

The lighting circuit described above includes a second bypass switch that forms a bypass path through which the drive current bypasses the second light emitting element, and the control unit controls the first and second bypass switches. At the same time, it is conceivable to change the threshold value of the abnormality detection unit in accordance with the control state of the first and second bypass switches.
The ON / OFF control of the first and second bypass switches makes the lighting state of the light source unit more diverse. Therefore, the threshold value of the abnormality detection unit is changed according to the combination of ON / OFF control of the first and second bypass switches.

In the lighting circuit described above, the abnormality detection unit compares a voltage dividing circuit that divides the output voltage of the voltage conversion unit, and a first voltage divided by the voltage dividing circuit with a second voltage that is a reference voltage. The voltage converter is configured to stop the voltage conversion in response to an abnormality being detected based on the first voltage being lower than the second voltage, The control unit may change the voltage dividing ratio of the voltage dividing circuit in order to change the threshold value.
That is, the abnormality detection unit performs the process of comparing the output voltage of the voltage conversion unit and the threshold by the process of comparing the divided voltage of the output voltage and the reference voltage. In this case, if the reference voltage is a threshold, changing the voltage dividing ratio indirectly changes the threshold.

In the lighting circuit described above, the abnormality detection unit includes a voltage dividing circuit that divides the output voltage of the voltage conversion unit, and a comparison circuit that compares the first voltage divided by the voltage dividing circuit with the second voltage. And a reference voltage variable circuit that varies the reference voltage to generate the second voltage, and the voltage conversion unit detects an abnormality based on the fact that the first voltage is lower than the second voltage. It is considered that the voltage conversion is stopped in response to the detection, and the control unit instructs the reference voltage variable circuit to generate the second voltage in order to change the threshold value.
The abnormality detection unit performs the process of comparing the output voltage of the voltage conversion unit and the threshold by the process of comparing the divided voltage of the output voltage and the reference voltage. In this case, the threshold value of the reference voltage that functions as the threshold value is changed.

A vehicular lamp according to the present invention is a vehicular lamp that includes a light source unit having first and second light emitting elements connected in series and the lighting circuit.

According to the present invention, by changing the threshold value according to the control state of the bypass switch, the abnormality determination voltage of the light source unit can be adaptively changed according to the number and type of light emitting elements that emit light. Regardless of the control state of the bypass switch, the abnormality detection can be performed with a substantially constant sensitivity. Therefore, the abnormality detection accuracy can be improved.

It is a block diagram of the vehicle lamp of the 1st Embodiment of this invention. It is explanatory drawing of the abnormality detection signal of embodiment. It is a block diagram of the vehicle lamp of 2nd Embodiment. It is a block diagram of the vehicle lamp of 3rd Embodiment. It is a block diagram of the vehicle lamp of 4th Embodiment.

<First Embodiment>
Hereinafter, a lighting circuit 2 according to an embodiment and a vehicular lamp 1 including the lighting circuit 2 will be described with reference to the drawings. FIG. 1 shows a vehicular lamp 1 according to an embodiment and related parts thereof. The vehicular lamp 1 can be suitably applied to various lamps such as a vehicle headlamp, a turn signal lamp, and a backlight.

The vehicle lamp 1 includes a lighting circuit 2 and a light source unit 3. The lighting circuit 2 is composed of various electronic components arranged on a lighting circuit board, for example. The light source unit 3 has a plurality of light emitting elements arranged on a light source substrate. Here, an example in which the

light emitting elements

30 and 31 are connected in series is shown.

In the present embodiment, the light source unit 3 is a light source as a headlamp. As an example, the light emitting element 30 is an LED, and the light emitting element 31 is a laser element such as a laser diode. Therefore, in the following description, the light emitting element 30 is referred to as “LED 30”, and the light emitting element 31 is referred to as “laser element 31”.
In the case of a headlamp, it is conceivable that the LED 30 serves as a diffused light source and the laser element 31 serves as a condensing light source to function as an additional high beam.
In addition, it is an example to make the light source part 3 into the serial structure of LED and a laser element, and other examples, such as setting it as the serial structure only of several LED, or the serial structure only of a laser element, are also considered. In any case, a plurality of light source elements may be connected in series.

The lighting circuit 2 is configured to receive power from the vehicle battery BT between the

terminals

41 and 42. The lighting circuit 2 is connected via a terminal 43 so as to be communicable with an ECU (Electronic Control Unit) 52 that comprehensively performs electrical control provided on the vehicle side.
A switch SWb is inserted between the positive terminal of the battery BT and the terminal 41 of the lighting circuit 2, and lighting / extinguishing of the vehicular lamp 1 is controlled by ON / OFF of the switch SWb. A terminal 42 of the vehicular lamp 1 is connected to the negative electrode side of the battery BT through a ground point.
A configuration is also conceivable in which the power supply voltage line and the ground line from the battery BT are connected to the

terminals

41 and 42 via the ECU 52 so that the ECU 52 can control the power supply to the lighting circuit 2.

In the light source unit 3 in the vehicular lamp 1, the LED 30 and the laser element 31 are connected in series as described above. The LED 30 and the laser element 31 are driven to emit light by being supplied with a drive current Id controlled at a constant current from the lighting circuit 2.

The lighting circuit 2 includes a control unit 11, a DC / DC converter 12, a converter driving unit 13, an abnormality detection unit 14, and bypass switches 15 and 16.

The DC / DC converter 12 is a voltage conversion unit that supplies a drive current Id to the light source unit 3. The DC / DC converter 12 receives the direct current voltage from the battery BT, performs voltage conversion, and generates an output voltage Vd.
The DC / DC converter 12 is a switching regulator, for example. Depending on the relationship between the forward voltage drop of the light source unit 3 and the power supply voltage by the battery BT, any of a step-up type, a step-down type, and a step-up / step-down type can be considered.
The current based on the output voltage Vd appearing on the output side of the DC / DC converter 12 flows to the LED 30 and the laser element 31 of the light source unit 3 as the drive current Id.

The converter drive unit 13 performs the voltage conversion operation of the DC / DC converter 12 and performs constant current control of the drive current Id.
For example, the converter drive unit 13 compares the current value of the drive current Id with the target current value based on the detection signal SId of the output (drive current Id) of the DC / DC converter 12, and the PWM control signal Spwm according to the difference. Is generated. This PWM control signal Spwm is supplied to the switching element of the DC / DC converter 12 to control the voltage conversion operation, thereby realizing a constant current output.

The lighting circuit 2 is provided with

bypass switches

15 and 16 that are connected in parallel to the LED 30 and the laser element 31 connected in series. The bypass switches 15 and 16 are configured by switching elements such as MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), for example.
The lighting circuit 2 is provided with

terminals

44, 45, and 46, and the

terminals

44 and 46 serve as positive / negative terminals on the output side of the DC / DC converter 12. The bypass switches 15 and 16 are connected in series between the

terminals

44 and 46. A connection point between the bypass switches 15 and 16 is led to a terminal 45.

Corresponding to the

terminals

44, 45, 46 of the lighting circuit 2,

terminals

32, 33, 34 are provided on the light source unit 3 side.
The terminal 32 is connected to the anode of the LED 30, and the terminal 34 is connected to the cathode of the laser element 31 (laser diode). A connection point between the LED 30 and the laser element 31 is connected to the terminal 33.
And each terminal 44, 45, 46 is connected with the corresponding terminal in the

terminals

32, 33, 34 as shown in the figure. For example, it is connected by wiring between substrates.
Therefore, the bypass switch 15 is connected in parallel to the LED 30, and the bypass switch 16 is connected in parallel to the laser element 31.

When the bypass switch 15 is turned on, a bypass path BP1 for the LED 30 is formed. In this case, since the drive current Id flows through the bypass BP1 and does not flow through the LED 30, the LED 30 is not lit. When the bypass switch 15 is turned off, the drive current Id flows through the LED 30 and the LED 30 is lit.
When the bypass switch 16 is turned on, a bypass path BP2 for the laser element 31 is formed. In this case, the drive current Id flows through the bypass BP2, and the laser element 31 is not turned on. When the bypass switch 16 is turned off, the drive current Id flows through the laser element 31, and the laser element 31 is turned on.
The bypass switches 15 and 16 are ON / OFF controlled by bypass control signals SB1 and SB2 from the control unit 11.

The control unit 11 is formed of a microcomputer, for example, and controls the converter drive unit 13 and the bypass switches 15 and 16. Further, the threshold value variable control of the abnormality detection unit 14 is performed.
The control unit 11 controls the operation of the converter driving unit 13 for turning on / off the light source unit 3 in accordance with an instruction from the ECU 52. Further, the control unit 11 generates bypass control signals SB1 and SB2 based on an instruction from the ECU 52, and performs ON / OFF control of the bypass switches 15 and 16, respectively. For example, in the case of this configuration, each lighting state can be switched and controlled such that only the LED 30 is turned on, only the laser element 31 is turned on, and both the LED 30 and the laser element 31 are turned on.

Note that the controller 14 can control the lighting state in various ways by controlling the bypass switches 15 and 16 with the bypass control signals SB1 and SB2 during the period in which the DC / DC converter 12 is operated.
That is, the LED 30 is turned off by continuously turning on the bypass switch 15 by the bypass control signal SB1, and not only the LED 30 is turned on by turning off the bypass switch 15 continuously. The LED 30 can be dimmed by turning on / off at 100 Hz). Furthermore, dimming can be performed by changing the on-duty of the on / off control. The same applies to the laser element 31.

The abnormality detection unit 14 includes a voltage dividing circuit 20, a comparator 21, a fail timer 22, and a reference voltage generation circuit 23.

The voltage dividing circuit 20 includes resistors R1 to R4 and switches T1 and T2, and divides the output voltage Vd of the DC / DC converter 12.
The resistors R1 and R2 are connected in series between the output terminal (positive electrode) of the DC / DC converter 12 and the ground. The resistor R3 and the drain-source of the switch T1 are connected in series between the connection point of the resistors R1 and R2 and the ground. Further, the resistor R4 and the drain-source of the switch T2 are connected in series between the connection point of the resistors R1 and R2 and the ground.
The switches T1 and T2 are, for example, MOSFETs, and the signal St1 from the control unit 11 is supplied to the gate of the switch T1, and the signal St2 from the control unit 11 is supplied to the gate of the switch T2. The controller 11 can control ON / OFF of the switches T1 and T2 by signals St1 and St2. When the switch T1 is turned on, the resistor R3 functions as a voltage dividing resistor. Further, when the switch T2 is turned on, the resistor R4 functions as a voltage dividing resistor. Therefore, the voltage dividing ratio of the voltage dividing circuit 20 changes in four ways depending on the ON / OFF combination of the switches T1 and T2.
The switches T1 and T2 may be composed of other elements such as bipolar transistors.

The voltage (divided voltage Vdv) at the connection point of the resistors R1 and R2 is input to the comparator 21. The reference voltage Vref from the reference voltage generation circuit 23 is input to the other end of the comparator 21. The comparison result between the divided voltage Vdv and the reference voltage Vref by the comparator 21 is supplied to the fail timer 22.

The output of the comparator 21 becomes L level when, for example, the divided voltage Vdv is lower than the reference voltage Vref. The L level output of the comparator 21 becomes a signal for detecting that the output voltage Vd of the DC / DC converter 12 has dropped due to a short circuit abnormality or the like. The fail timer 22 outputs an abnormality detection signal SF in response to the L level output of the comparator 21 continuing for a predetermined time.
For example, as shown in FIG. 2, if the L level output period of the comparator 21 is less than the predetermined time Tc, the fail timer 22 is not abnormal, and the L level output period of the comparator 21 continues the predetermined time Tc. At that time, an abnormality detection signal SF for notifying abnormality is output.

The abnormality detection signal SF is supplied to the converter drive unit 13 and the control unit 11. The converter drive unit 13 may stop the operation of the DC / DC converter 12 according to the abnormality detection signal SF. Alternatively, the control unit 11 may instruct the converter driving unit 13 to stop the operation according to the abnormality detection signal SF. Further, depending on the abnormality detection signal SF, the controller 11 may notify the ECU 52 of the abnormality without necessarily stopping the operation of the DC / DC converter 12. Further, the output of the fail timer 22 may be directly supplied to the vehicle side (ECU 52) side.

The operation of the vehicular lamp 1 having the above configuration, particularly the abnormality detection will be described.
As the lighting state of the light source unit 3, the control unit 11 can select lighting of only the LED 30, lighting of only the laser element 31, and lighting of both the LED 30 and the laser element 31 by controlling the bypass switches 15 and 16.
The abnormality detection unit 14 detects an abnormality as a signal for detecting a short circuit of the light source unit 3 (including a failure in which the wiring of the lighting circuit output is equivalent to a light source short circuit (such as a short circuit of a harness)), current leakage, light source deterioration, and the like. The signal SF is output.

Here, in the normal lighting state, the output voltage Vd of the DC / DC converter 12 is about 4 V when only the laser element 31 is turned on. When the LED 30 is a two-chip LED, the output voltage Vd of the DC / DC converter 12 is about 7 V when only the LED 30 is lit. When both the LED 30 (2-chip LED) and the laser element 31 are lit, the output voltage Vd is about 11 V (= 4 V + 7 V). Hereinafter, this example will be described.

When the short circuit abnormality occurs, the output voltage Vd decreases. Therefore, the threshold value Vth for determining short circuit abnormality is set to a certain value, and it is detected that the output voltage Vd is equal to or lower than the threshold value Vth. Here, when the threshold value Vth is set to a constant value, the occurrence of a short circuit abnormality can be detected by setting the threshold value Vth to a voltage value that is impossible for the normal output voltage Vd. In the configuration in which the light source elements connected in series are selectively turned on as in this example, the threshold value Vth must be matched when the output voltage Vd is the lowest. This is to prevent erroneous detection when the output voltage Vd is the lowest.

In the case of the above example, if the output voltage Vd = 4V when the laser element 31 is turned on, the threshold value Vth is set to 2V, for example. If the voltage is higher than 2 V, there is a high possibility of erroneous detection when only the laser element 31 is turned on.
However, it is appropriate to detect the abnormality even when the light source element cannot be normally turned on due to deterioration of the light source or current leakage in the wiring path. In consideration of this, assuming that the threshold value Vth = 2V as described above, when the LED 30 (2-chip LED) is lit (when the output voltage Vd = 7V) or both are lit (when the output voltage Vd = 11V). It will be too low. In these cases, the detection sensitivity to a voltage drop due to deterioration of the light source element, current leakage, or the like becomes dull, and abnormal detection may not be performed appropriately.

Therefore, in this embodiment, the abnormality determination threshold is changed according to the lighting state of the light source unit 3. For example, the threshold value Vth is set to 2V with respect to the output voltage Vd = 4V when only the laser element 31 is turned on. Further, the threshold value Vth is set to 3.5V with respect to the output voltage Vd = 7V when only the LED 30 is turned on. Further, the threshold value Vth is set to 5.5V with respect to the output voltage Vd = 11V when the LED 30 and the laser element 31 are turned on. That is, the threshold value Vth is varied so that the voltage value is 50% of the normal output voltage Vd.

In the case of the embodiment of FIG. 1, such change of the threshold value Vth is indirectly executed by changing the voltage dividing ratio of the voltage dividing circuit 20. For example, each constant is as follows.
Resistance R1 = 15kΩ
Resistance R2 = 10kΩ
Resistor R3 = 8kΩ
Resistance R4 = 3.43kΩ
Reference voltage Vref = 0.8V

When only the laser element 31 is turned on, the control unit 11 turns off the switches T1 and T2. Then, the divided voltage Vdv becomes a voltage obtained by dividing the output voltage Vd by the resistors R1 and R2. When the output voltage Vd = 4V, the divided voltage Vdv = 1.6V.
When only the LED 30 is lit, the control unit 11 turns on the switch T1 and turns off T2. Then, the divided voltage Vdv is a voltage obtained by dividing the output voltage Vd by the resistor R1 and the parallel resistance of the resistors R2 and R3. When the output voltage Vd = 7V, the divided voltage Vdv = 1.6V.
When the LED 30 and the laser element 31 are turned on, the control unit 11 turns off the switch T1 and turns on T2. Then, the divided voltage Vdv is a voltage obtained by dividing the output voltage Vd by the resistor R1 and the parallel resistance of the resistors R2 and R4. When the output voltage Vd = 11V, the divided voltage Vdv = 1.6V.

That is, in any case, the divided voltage Vdv at normal time is 1.6V, which is compared with the reference voltage Vref = 0.8V.
The divided voltage Vdv becomes 0.8V or less, and the output of the comparator 21 becomes a level indicating abnormality.
-When the output voltage Vd is 2 V or less when only the laser element 31 is lit-When the output voltage Vd is 3.5 V or less when only the LED 30 is lit-When the LED 30 and the laser element 31 are lit, the output voltage Vd is 5. This is the case for 5V or less.
After all, it is equivalent to changing the threshold value Vth according to the lighting state of the light source unit 3 so that it is determined that the output voltage Vd is 50% or less of the normal value.
Accordingly, it is possible to appropriately detect a short circuit abnormality, a current leak, and the like regardless of the lighting state of the light source unit 3.
The lighting state of the light source unit 3, that is, the lighting / extinguishing of the LED 30 and the laser element 31, is set by the control unit 11 performing ON / OFF control of the bypass switches 15 and 16 with the bypass control signals SB1 and SB2. Therefore, the control unit 11 may turn ON / OFF the switches T1 and T2 according to the control of the bypass switches 15 and 16.

<Second Embodiment>
A vehicular lamp 1 according to a second embodiment is shown in FIG. The same parts as those in FIG. In this example, the configuration of the abnormality detection unit 14A is different from that of the first embodiment.
The abnormality detection unit 14A includes resistors R1 and R2 as the voltage dividing circuit 20A. The resistors R1 and R2 are connected in series between the output terminal (positive electrode) of the DC / DC converter 12 and the ground. In this case, the output voltage Vd of the DC / DC converter 12 is always divided by the resistors R 1 and R 2, and the divided voltage Vdv is supplied to the comparator 21.

The reference voltage variable circuit 23 </ b> A varies the reference voltage Vref supplied to the comparator 21 in accordance with the control signal Sv of the control unit 11.
Now, assume that R1 = R2 and the divided voltage Vdv = Vd / 2.
The control unit 11 controls the reference voltage Vref generated by the reference voltage variable circuit 23A according to the lighting state of the light source unit 3 so that Vref = Vd / 4.
For example, when only the laser element 31 is turned on (Vd = 4V), the reference voltage Vref = 1V.
When only the LED 30 is lit (Vd = 7V), the reference voltage Vref = 1.75V.
When the LED 30 and the laser element 31 are turned on (Vd = 11V), the reference voltage Vref = 2.75V.
Also in this case, the threshold value Vth is changed according to the lighting state of the light source unit 3 so that it is determined that the output voltage Vd is 50% or less of the normal value.
Accordingly, it is possible to appropriately detect a short circuit abnormality, a current leak, and the like regardless of the lighting state of the light source unit 3.
The control unit 11 may perform variable control of the reference voltage Vref value of the reference voltage variable circuit 23 </ b> A along with control of the bypass switches 15 and 16.

<Third Embodiment>
A vehicle lamp 1 according to a third embodiment is shown in FIG. The same parts as those in FIG. In this example, the bypass switch 15 is eliminated from the configuration of FIG. A bypass switch 16 is provided, and the controller 11 controls the turn-off / lighting of the laser element 31 by turning the bypass switch 16 on and off with a bypass control signal SB2. That is, in this configuration, the lighting state of the light source unit 3 can be switched between lighting of only the LED 30 and lighting of the LED 30 and the laser element 31.

The abnormality detection unit 14 includes a voltage dividing circuit 20B, a comparator 21, a fail timer 22, and a reference voltage generation circuit 23.
The voltage dividing circuit 20B includes resistors R10 to R12 and a switch T3, and divides the output voltage Vd of the DC / DC converter 12.
The resistors R10 and R11 are connected in series between the output terminal (positive electrode) of the DC / DC converter 12 and the ground. Further, a resistor R12 and a drain-source of a switch T3 made of, for example, a MOSFET are connected in series between a connection point of the resistors R10 and R11 and the ground. A signal St3 from the control unit 11 is supplied to the gate of the switch T3. The control unit 11 can control ON / OFF of the switch T3 by a signal St3.

In this configuration, for example, the control unit 11 turns off the switch T3 when only the LED 30 is lit. On the other hand, when the LED 30 and the laser element 31 are turned on, the control unit 11 turns on the switch T3. Thereby, the threshold value Vth for abnormality determination is changed according to the lighting state of the light source unit 3. That is, appropriate abnormality detection is realized in the same way as in the first embodiment.

<Fourth embodiment>
FIG. 5 shows a vehicular lamp 1 according to a fourth embodiment. Note that the same parts as those in FIG. In this example, the bypass switch 15 is eliminated from the configuration of FIG. Therefore, as in the third embodiment of FIG. 4, the lighting state of the light source unit 3 can be switched between lighting of only the LED 30 and lighting of the LED 30 and the laser element 31.
The control unit 11 variably controls the reference voltage Vref generated by the reference voltage variable circuit 23 </ b> A according to the lighting state of the light source unit 3. As a result, the threshold value Vth for abnormality determination is changed according to the lighting state of the light source unit 3. That is, appropriate abnormality detection is realized in the same way as in the second embodiment.

<Summary>
In the above embodiment, the following effects can be obtained.
The lighting circuit 2 according to the first to fourth embodiments receives a DC voltage, performs voltage conversion, and supplies a drive current to the light source unit 3 having the first and second light emitting elements (30, 31) connected in series. A voltage conversion unit (DC / DC converter 12) that supplies Id, a first bypass switch 16 that forms a bypass path BP2 in which the drive current Id bypasses the first light emitting element (for example, the laser element 31), and voltage conversion The abnormality detection unit (14 or 14A) that detects an abnormality of the light source unit 3 when the output voltage Vd of the unit is lower than the threshold value Vth, the first bypass switch 16, and the control of the first bypass switch 16 The control unit 11 changes the threshold value Vth of the abnormality detection unit (14 or 14A) according to the state.
In this way, by changing the threshold value according to the control state of the bypass switch 16, the threshold value Vth for determining the abnormality of the light source unit 3 can be adaptively changed according to the number and type of light emitting elements that emit light. Can do. Therefore, regardless of the control state of the bypass switch 16, abnormality detection can be performed with substantially constant sensitivity, and detection accuracy can be improved. For example, a leak abnormality can always be detected with the same sensitivity. Therefore, the abnormality detection accuracy can be improved.

The lighting circuit 2 of the first and second embodiments includes a second bypass switch 15 that forms a bypass path BP1 in which the drive current Id bypasses the second light emitting element (for example, the LED 30). The control unit 11 controls the first and second bypass switches 16 and 15, and the threshold value of the abnormality detection unit (14 or 14A) according to the control state of the first and second bypass switches 16 and 15. Vth is changed.
That is, the ON / OFF control of the plurality of bypass switches 15 and 16 makes the lighting state of the light source unit 3 more diverse. Therefore, the threshold value Vth of the

abnormality detection units

14 and 14A is changed according to the combination of ON / OFF control of the bypass switches 15 and 16.
Thereby, the threshold value Vth for determining the abnormality of the light source unit 3 can be adaptively changed according to the number and type of light emitting elements emitting light.
In addition, since it is not necessary to take a configuration for monitoring the voltage for each of the plurality of bypass paths, that is, monitoring the voltage at both ends of each light emitting element, the lighting circuit configuration can be simplified, which is advantageous for downsizing and cost reduction. It is. Furthermore, since voltage detection can be performed on the basis of a fixed voltage (for example, ground potential) that is not based on the floating node for detecting an abnormality of each light emitting element, the voltage detection accuracy can be improved.

In the first and third embodiments, the abnormality detection unit 14 divides the output voltage Vd of the voltage conversion unit, and the first voltage (divided voltage) divided by the voltage dividing circuit 20. A comparison circuit (comparator 21) for comparing Vdv) with the second voltage (reference voltage Vref) is provided. The voltage conversion unit (DC / DC converter 12) stops the voltage conversion in response to the detection of an abnormality based on the first voltage (Vdv) being lower than the second voltage (Vref). The controller 11 changes the voltage dividing ratio of the voltage dividing circuit 20 in order to change the threshold value Vth.
That is, the abnormality detection unit 14 performs a process of comparing the output voltage Vd of the voltage converter and the threshold value Vth by a process of comparing the divided voltage Vdv of the output voltage Vd and the reference voltage Vref. In this case, changing the voltage dividing ratio is equivalent to changing the threshold value Vth indirectly. The threshold can be easily changed by changing the partial pressure ratio.

In the lighting circuits of the second and fourth embodiments, the abnormality detection unit 14A includes a voltage dividing circuit 20A that divides the output voltage Vd of the voltage conversion unit, and a first voltage (divided by the voltage dividing circuit 20A). A comparison circuit (comparator 21) that compares the divided voltage Vdv) with the second voltage, and a reference voltage variable circuit 23A that generates the second voltage by changing the reference voltage Vref. The voltage converter (DC / DC converter 12) converts the voltage in response to the detection of an abnormality based on the first voltage (Vdv) being lower than the second voltage (Vref or its variable voltage value). To stop. The controller 11 instructs the reference voltage variable circuit 23A to generate the second voltage (variable value of the reference voltage Vref) in order to change the threshold value Vth.
That is, the abnormality detection unit 14A executes a process of comparing the output voltage Vd of the voltage converter and the threshold value Vth by a process of comparing the divided voltage Vdv of the output voltage Vd and the reference voltage Vref. In this case, the threshold value change can be easily realized by adopting a method of changing the reference voltage Vref.

The abnormality detection unit (14 or 14A) of the first to fourth embodiments includes a comparison circuit (comparator 21) that compares the output voltage Vd of the voltage conversion unit and the threshold value Vth, and an output of the abnormality detection level of the comparison circuit. Has a timer circuit (fail timer 22) for outputting an abnormality detection signal in response to the continuation of a predetermined time. The

abnormality detectors

14 and 14A output the abnormality detection signal SF when the abnormality detection level continues as a comparison result between the output voltage of the voltage converter and the threshold value Vth. As a result, it is possible to avoid erroneous detection of an abnormality due to an instantaneous output voltage change and the like, and to promote accurate abnormality detection.

The configurations of the first and third embodiments for changing the voltage division ratio and the configurations of the second and fourth embodiments for changing the reference voltage Vref are combined to control both the voltage division ratio and the reference voltage Vref. A configuration in which 11 is variable is also possible.

In the embodiment, the threshold Vth is described as an example in which the voltage Vd is 50% of the normal output voltage Vd. However, the voltage value equivalent to 50% is merely an example.
If the threshold value Vth is set to a voltage value such as 60% or 70% of the normal output voltage Vd, the detection sensitivity increases, but conversely the possibility of erroneous detection also increases. If the threshold value Vth is a voltage value such as 40% or 30% of the normal output voltage Vd, the detection sensitivity is lowered, but the possibility of erroneous detection is reduced.
Therefore, it may be determined according to the lighting circuit configuration, lamp type, detection purpose, and the like.

Although an example having the bypass switches 15 and 16 and a configuration having only the bypass switch 16 are illustrated, a configuration having only the bypass switch 15 is also conceivable. That is, the present invention is also effective in the case where a bypass switch is provided for some of a plurality of light source elements connected in series.
Further, a configuration in which a larger number of light emitting elements are connected in series and a bypass switch is provided in all or a part thereof is also conceivable. Also in those cases, the control unit 11 may change the threshold value Vth in the abnormality detection unit 14 together with the control of one or a plurality of bypass switches.

DESCRIPTION OF SYMBOLS 1 ... Vehicle lamp, 2 ... Lighting circuit, 3 ... Light source part, 11 ... Control part, 12 ... DC / DC converter, 13 ... Converter drive part, 14, 14A ... Abnormality detection part, 15, 16 ... Bypass switch, 30 ... Light emitting element (LED) 31. Light emitting element (laser element) 20, 20A... Voltage dividing circuit, 21.

Claims

A voltage conversion unit that receives a direct current voltage, performs voltage conversion, and supplies a drive current to a light source unit having first and second light emitting elements connected in series;
A first bypass switch that forms a bypass path through which the drive current bypasses the first light emitting element;
An abnormality detection unit that detects an abnormality of the light source unit when an output voltage of the voltage conversion unit is lower than a threshold;
And a control unit that controls the first bypass switch and changes the threshold value of the abnormality detection unit in accordance with a control state of the first bypass switch.
A second bypass switch that forms a bypass path for the drive current to bypass the second light emitting element;
The control unit controls the first and second bypass switches, and changes the threshold value of the abnormality detection unit according to a control state of the first and second bypass switches. Lighting circuit.
The abnormality detection unit
A voltage dividing circuit for dividing the output voltage of the voltage converter;
A comparison circuit that compares the first voltage divided by the voltage dividing circuit with a second voltage that is a reference voltage;
The voltage converter is configured to stop the voltage conversion in response to an abnormality being detected based on the first voltage being lower than the second voltage,
The lighting circuit according to claim 1, wherein the control unit changes a voltage dividing ratio of the voltage dividing circuit to change the threshold value.
The abnormality detection unit
A voltage dividing circuit for dividing the output voltage of the voltage converter;
A comparison circuit that compares the first voltage divided by the voltage dividing circuit with a second voltage;
A reference voltage variable circuit that varies the reference voltage to generate the second voltage,
The voltage converter is configured to stop the voltage conversion in response to an abnormality being detected based on the first voltage being lower than the second voltage,
The lighting circuit according to claim 1, wherein the control unit instructs the reference voltage variable circuit to generate the second voltage in order to change the threshold value.
A light source unit having first and second light emitting elements connected in series;
A lighting device for a vehicle, comprising: the lighting circuit according to claim 1.