JP2015168305A - Lighting fixture for vehicle and drive device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive device capable of surely detecting open failure.SOLUTION: An abnormality detection circuit 60 comprises: an open detection circuit 62 which is disposed in parallel to a bypass circuit 40 and a light emitter 12, and determines whether detection voltage Vs exceeds or not a threshold of open failure. A charging circuit 64 charges a capacitor C1 by voltage based on the detection voltage Vs, when the detection voltage Vs exceeds a first threshold based on the threshold of open failure. A time constant of a discharge path 66 of electric charge of the capacitor C1 is longer than period of PWM dimming.

Description

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

  In general, a vehicular lamp can be switched between a low beam and a high beam. The low beam illuminates the neighborhood with a predetermined illuminance, and the light distribution regulation is determined so as not to give glare to the oncoming vehicle and the preceding vehicle, and is mainly used when traveling in an urban area. On the other hand, the high beam illuminates a wide area in front and a distant area with a relatively high illuminance, and is mainly used when traveling at high speed on a road with few oncoming vehicles and preceding vehicles. Therefore, although the high beam is more visible to the driver than the low beam, there is a problem that glare is given to the driver or pedestrian of the vehicle existing in front of the vehicle.

  In recent years, ADB (Adaptive Driving Beam) technology has been proposed that dynamically and adaptively controls a high-beam light distribution pattern based on the state around the vehicle. The ADB technology reduces glare given to a vehicle or pedestrian by detecting the presence of a preceding vehicle, an oncoming vehicle or a pedestrian in front of the vehicle, and dimming a region corresponding to the vehicle or pedestrian. is there.

  A vehicle lamp having an ADB function will be described. FIG. 1 is a block diagram of a vehicular lamp having an ADB function according to a comparative technique. This comparison technique should not be recognized as a known technique.

  The vehicular lamp 1r includes a light source 10 and a driving device 20r. In ADB, the high beam irradiation area is divided into a plurality of N (N is a natural number) sub-areas. The light source 10 includes a plurality of light emitting elements 12_1 to 12_N associated with N sub-regions. Each light emitting element 12 is a semiconductor device such as an LED (light emitting diode) or an LD (laser diode), and is arranged so as to irradiate a corresponding sub-region. The drive device 20r changes the light distribution of the high beam by controlling on (lighting) and off (light extinction) of each of the plurality of light emitting elements 12_1 to 12_N. Alternatively, the driving device 20r adjusts the effective luminance by PWM (pulse width modulation) control of the light emitting element 12 at a high frequency.

The driving device 20r includes a current source 30, a plurality of bypass circuits 40_1 to 40_N, and a controller 50. The current source 30 receives a battery voltage V _BAT (also referred to as an input voltage _VIN ) from the battery 2 via the switch 4, and stabilizes the drive current I _DRV flowing through the light source 10 to a certain target amount.

The plurality of bypass circuits 40_1 to 40_N are associated with the plurality of light emitting elements 12_1 to 12_N. The bypass circuit 40 is configured to be switched on and off. When the i-th bypass circuit 40_i is turned on, the drive current I _DRV flows to the bypass circuit 40_i instead of the light emitting element 12_i. When the light emitting element 12_i is turned off and the bypass circuit 40_i is turned off, the drive current I _DRV is Lights through the light emitting element 12_i.

  An upstream processor (for example, an electronic control unit ECU) 6 that controls the vehicular lamp 1r determines a sub-region to be irradiated with a high beam based on a state in front of the vehicle, and instructs the controller 50 of the driving device 20r. The controller 50 controls the states of the bypass circuits 40_1 to 40_N based on the control command from the processor 6. Specifically, the light emitting element 12 corresponding to the sub-region to be irradiated is selected, the bypass circuit 40 parallel to the selected light emitting element 12 is turned off, and the bypass circuit 40 parallel to the remaining light emitting elements 12 is turned on. State.

  The light source 10 and the driving device 20r are connected via wiring. When this wiring is cut (open failure), the light emitting element 12 cannot be turned on, or the light emitting element 12 cannot be actively controlled to be turned off. Therefore, means for detecting an abnormality such as a short circuit failure or an open failure is mounted on the driving device 20r.

When a certain bypass circuit 40_i is off and the drive current I _DRV flows through the corresponding light emitting element 12_i and is normally lit, the voltage drop (forward voltage) of the light emitting element 12_i is within a predetermined voltage range (normal voltage). Range). Conversely, when an open fault or a short fault occurs, the voltage drop deviates from the normal voltage range. Therefore, it is possible to detect an abnormality by monitoring the detection voltage Vs between both ends of each light emitting element 12 (that is, the forward voltage Vf of the light emitting element 12).

  Specifically, when an open failure occurs in which the wiring connecting the cathode of the light-emitting element 12_i and the node ND_i or the wiring connecting the anode of the light-emitting element 12_i and the node ND_ (i-1) is disconnected, the voltage across the bypass circuit 40_i Becomes higher than the normal voltage range. On the other hand, when a short circuit failure occurs in which the cathode and anode of the light emitting element 12_i are short-circuited, the voltage across the bypass circuit 40_i becomes lower than the normal voltage range. Note that the open failure and the short failure include a case where the light emitting element itself is in an open state or a short state.

For example, when the typical value of the forward voltage Vf of the light emitting element 12 when a predetermined drive current I _DRV flows is 4V, the upper limit V _THH of the normal voltage range is 5.5V, and the lower limit V _THL is about 1.5V. By doing so, it is possible to detect a short circuit failure and an open failure.

JP 2014-017463 A

  As described above, for the purpose of dimming, the control signal S1 for each bypass circuit 40 may be subjected to pulse width modulation so as to have a duty ratio corresponding to the target luminance. 2A to 2D are operation waveform diagrams of the vehicular lamp 1r when PWM dimming is performed. FIG. 2A shows a control signal S1 subjected to pulse width modulation, and FIGS. 2B to 2D show waveforms of the detection voltage Vs at the time of normal operation, open failure, and short failure, respectively. It is.

During the _{on-time T ON} of the bypass circuit 40_i (off period of the light emitting element 12_I) is normal, abnormal detection voltage Vs regardless is almost zero. Therefore, abnormality determination in the drive device 20r with PWM dimming is (i) whether the detection period is limited to the _OFF time T _OFF of the bypass circuit 40, or (ii) abnormality determination only when the abnormality lasts for a long time, Must be one of the following.

  Here, the former method (i) requires a signal line and a transistor for timing control. In order to turn on and off the transistor, an appropriate control voltage should be applied to its gate (base). In the vehicle lamp 1r of FIG. 1, the bypass circuit 40 and the abnormality detection circuit are floating with respect to the ground. Therefore, it is necessary to shift the control voltage to an appropriate voltage level for each bypass circuit 40, resulting in an increase in circuit scale.

  Therefore, the present inventors examined an abnormality detection circuit that employs the method (ii). FIG. 3 is a circuit diagram of the abnormality detection circuit 60r_i according to the comparative technique examined by the present inventors.

The abnormality detection circuit 60r_i includes a comparison circuit 61r and a filter circuit 80r. The comparison circuit 61r compares the detection voltage Vsi with the two threshold voltages V _THH and V _THL . The comparison circuit 61r has an open collector type output stage including the transistor Q11, and is configured such that the transistor Q11 is turned on when V _THL <Vsi <V _{THH and} the transistor Q11 is turned off when Vsi <V _THL or V _THH <Vsi. The

Therefore, the output S3 of the comparator circuit 61r becomes a low level voltage in a normal state, a high impedance at the open failure, short-circuit failure or bypass circuit 40_i within the on-time T _ON.

Filter circuit 80r _generates a V THL <Vsi _<low level voltage _{V L} becomes the _{V THH,} Vsi _{<V THL} or _V THH <abnormality detection signal S2_i that the high level voltage _{V CC} in Vsi. When the output S3 of the comparison circuit 61r transitions to the low level voltage _VL , the output S2_i immediately transitions to the low level, and (ii) when the output S3 of the comparison circuit 61r transitions to the high impedance, The output S2_i is configured to gradually transition to a high level.

  4A and 4B are operation waveform diagrams of the abnormality detection circuit 60r of FIG. 3 in a normal state and an abnormal state. As shown in FIG. 4A, in the normal state, the output S3 of the comparison circuit 61r becomes a low level voltage every PWM dimming period (PWM period), and the output S2 of the filter circuit 80r is reset to a low level. Is done. Therefore, the output S2 of the filter circuit 80r is within the low level L region and does not enter the high level H region indicating an abnormal state.

  As shown in FIG. 4B, it is assumed that an abnormal state (here, a short failure) occurs at time t0. At this time, the output S3 of the comparison circuit 61r maintains the high impedance state, and the output S2 of the filter circuit 80r continues to rise without being reset to the low level. If the abnormal state continues and the output S2 of the filter circuit 80r enters the high level H region indicating the abnormal state at time t1, it is determined as an abnormal state.

  As a result of studying the abnormality detection circuit 60r of FIG. 3, the present inventors have recognized the following problems.

(First issue)
When the load power of the driving device 20 is sharply switched, the bypass circuit 40 is turned on and off to prevent the current flowing through the light source 10 from overshooting and undershooting or to suppress radio noise. It may be performed slowly (also called a soft switch). FIG. 5A is an operation waveform diagram of the abnormality detection circuit 60r when the bypass circuit 40 is soft-switched in an abnormal state. When the bypass circuit 40 is soft switched, the detection voltage Vsi is normal during the turn-on period (rise time Tr) and the turn-off period (fall time Tf) of the bypass circuit 40 when an abnormal state (here, an open failure) occurs. It will be included in the voltage range. As a result, at the rise time Tr and fall time Tf, the output S3 of the comparison circuit 61r becomes low level, and the output of the filter circuit 80r is reset to low level. Thereby, even in the abnormal state, the abnormality detection signal S2 does not enter the high level region H and cannot be determined as an abnormal state.

(Second problem)
In FIG. 3, a failure mode in which the wiring L2 is disconnected will be considered.
When the wiring L2 is disconnected when the bypass circuit 40_i is off and 40_ (i + 1) is on, the current flowing through the light-emitting element 12_ (i + 1) is bypassed regardless of whether the bypass circuit 40_ (i + 1) is on. The drive current I _DRV flows through the light emitting elements 12_i and 12_ (i + 1). Therefore, the voltage between both ends of the light emitting elements 12_i and 12_ (i + 1) is 2 × Vf. When the bypass circuit 40_ (i + 1) is on, Vsi≈2 × Vf and Vs (i + 1) ≈0.

Consider a state in which the bypass circuits 40_i and 40_ (i + 1) are simultaneously turned off. At this time, if the impedances of the abnormality detection circuits 60r_i and 60r_ (i + 1) are Zi and Z (i + 1), the following equations are established.
Vsi = 2 × Vf × Zi / {Zi + Z (i + 1)}
Vs (i + 1) = 2 × Vf × Z (i + 1) / {Zi + Z (i + 1)}

  Therefore, if Zi≈Z (i + 1), Vsi≈Vs (i + 1) ≈Vf.

  FIG. 5B is an operation waveform diagram of the abnormality detection circuit 60r when the wiring L2 is disconnected. When adjacent bypass circuits 40_i and 40_ (i + 1) are switched with different duty ratios and their off times overlap, the detection voltages Vsi and Vs (i + 1) are normal voltages during the off overlap time. It will be included in the range, making it impossible to determine abnormality.

  This problem occurs not only when ADB control is performed, but also when the vehicular lamp 1r shown in FIG. 1 is used for luminance control.

  The present invention has been made in view of the problems, and one of exemplary purposes of an embodiment thereof is to provide a vehicular lamp and a driving device thereof that can solve at least one of the above-described problems.

  An aspect of the present invention relates to a drive device that is used with a light source including a plurality of light emitting elements connected in series and constitutes a vehicular lamp. The driving device is associated with a current source that supplies a driving current to the light source and N (N is a natural number) light emitting elements among the plurality of light emitting elements, and each of the driving devices is provided in parallel with the corresponding light emitting element. By switching in a cycle, the corresponding light emitting elements are associated with the N bypass circuits configured to be dimmable and the N light emitting elements, and each is based on the detection voltage between both ends of the corresponding bypass circuit. And N abnormality detection circuits configured to detect the abnormality. The abnormality detection circuit includes an open detection circuit that determines whether or not the corresponding detection voltage exceeds an open failure threshold. The open detection circuit includes a capacitor and a charging circuit that charges the capacitor with a voltage corresponding to the detection voltage when a corresponding detection voltage exceeds a first threshold value corresponding to the open failure threshold value. The time constant of the capacitor charge discharge path is configured to be longer than a predetermined period.

  According to this aspect, when an open failure occurs, the open failure can be reliably detected even when an event occurs in which the detection voltage Vs returns to the normal voltage range within the PWM dimming period.

  The first electrode of the capacitor may be commonly connected to the first end of the corresponding bypass circuit. The charging circuit is provided between the second electrode of the capacitor and the second end of the corresponding bypass circuit, does not conduct in the first direction flowing out of the capacitor, and the corresponding detection voltage has a first threshold value. When it exceeds, it may be configured to conduct in the second direction flowing into the capacitor.

  The charging circuit may include a Zener diode and a first diode provided in series between the second electrode of the capacitor and the corresponding second end of the bypass circuit.

  The abnormality detection circuit may further include an output stage that compares the voltage of the capacitor with a predetermined second threshold value, and the output state transitions according to the comparison result.

  The output stage may include a bipolar transistor and a first resistor provided between the base of the bipolar transistor and the first electrode of the capacitor. The first resistor and the base emitter of the bipolar transistor may form a discharge path, and on / off of the bipolar transistor may be associated with the comparison result.

  In the charging circuit, the Zener diode is disposed on the side close to the second end of the bypass circuit, and the bypass circuit includes a bypass transistor provided in parallel with the corresponding light emitting element and a cathode connected to a control terminal of the bypass transistor. And a second diode having an anode connected to the anode of the Zener diode.

  The abnormality detection circuit may further include a short detection circuit that determines whether or not the corresponding detection voltage falls below a short failure threshold.

  The anomaly detection circuit is a filter circuit that filters the output of the anomaly detection circuit. The anomaly detection signal that is output from the anomaly detection circuit is shifted relatively quickly to a level indicating normality, and is relatively It may further include a filter circuit that makes the transition to a low speed.

  Another aspect of the present invention relates to a vehicular lamp. The vehicular lamp includes a light source including a plurality of light emitting elements connected in series, and the driving device according to any one of the above-described aspects that drives the light source.

  According to an aspect of the present invention, an open failure can be reliably detected.

It is a block diagram of the vehicular lamp which has the ADB function which concerns on a comparison technique. 2A to 2D are operation waveform diagrams of the vehicular lamp when PWM dimming is performed. It is a circuit diagram of the abnormality detection circuit which concerns on the comparison technique which the present inventors examined. 4A and 4B are operation waveform diagrams of the abnormality detection circuit of FIG. 3 in a normal state and an abnormal state. FIG. 5A is an operation waveform diagram of the abnormality detection circuit when the bypass circuit is soft-switched in the abnormal state, and FIG. 5B is an operation waveform diagram of the abnormality detection circuit when the adjacent light emitting elements are turned on with different duty ratios. It is a block diagram of the vehicular lamp which concerns on 1st Embodiment. 1 is a circuit diagram showing a basic configuration of an abnormality detection circuit according to a first embodiment. FIG. 8A and 8B are operation waveform diagrams at the time of an open failure of the abnormality detection circuit of FIG. It is an operation | movement waveform diagram of the abnormality detection circuit when the wiring LA is disconnected. FIG. 5 is a circuit diagram of an abnormality detection circuit according to a second embodiment. It is a circuit diagram of a drive device provided with an abnormality detection circuit. It is a perspective view of a lamp unit (lamp assembly) provided with the vehicle lamp of FIG. It is a circuit diagram of an abnormality detection circuit according to a first modification. It is a circuit diagram of an abnormality detection circuit according to a second modification. FIGS. 15A and 15B are circuit diagrams of modifications of the charging circuit.

  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. 6 is a block diagram of the vehicular lamp 1 according to the first embodiment. The vehicular lamp 1 includes a light source 10 and a driving device 20. The light source 10 includes a plurality of light emitting elements 12_1 to 12_N connected in series. The driving device 20 is used together with the light source 10 and constitutes the vehicular lamp 1. The light emitting element 12 is, for example, an LED (light emitting diode).

  The drive device 20 includes a current source 30, N (N is a natural number) bypass circuits 40_1 to 40_N, a controller 50, and N abnormality detection circuits 60_1 to 60_N.

The current source 30 supplies a driving current I _DRV corresponding to the target luminance to the light source 10. For example, current source 30 includes a step-up or step-down converter and its control circuit. Control circuit detects a driving current I _DRV, the detected driving current I _DRV is to approach the target amount may be feedback-controlled switching states of the converter. The type of the converter and the current control method are not particularly limited, and a known technique may be used.

  The N bypass circuits 40_1 to 40_N are associated with N light emitting elements 12 among the plurality of light emitting elements 12. In the present embodiment, a case where bypass circuits 40 are provided for all the light emitting elements 12 will be described. The bypass circuit 40_i is provided in parallel with the corresponding light emitting element 12_i. The bypass circuit 40_i can be switched between an on state and an off state according to the control signal S1_i, and is configured to form a bypass path parallel to the light emitting element 12_i in the on state.

  The abnormality detection circuits 60_1 to 60_N are associated with N light emitting elements. The i-th abnormality detection circuit 60_i is configured to be able to detect an abnormality based on the detection voltage Vsi between both ends of the corresponding bypass circuit 40_i (that is, the corresponding light emitting element 12_i).

  In a normal lighting control period, the controller 50 controls the N bypass circuits 40_1 to 40_N to be turned on / off based on the lighting / extinguishing instructions of the N light emitting elements 12_1 to 12_N. More specifically, the controller 50 performs pulse width modulation on the control signal S1_i in accordance with the target luminance of the light emitting element 12_i, and switches the bypass circuit 40_i in the PWM cycle, thereby dimming the light emitting element 12_i.

The abnormality detection circuit 60_i is configured to be able to determine whether there is an abnormality based on the detection voltage Vsi between both ends of the corresponding bypass circuit 40_i. Specifically, an open failure is detected by comparing the detection voltage Vsi with an open failure threshold (upper threshold voltage) V _THH .

  The above is the overall configuration of the driving device 20. Next, the configuration of the abnormality detection circuit 60 will be described.

  FIG. 7 is a circuit diagram showing a basic configuration of the abnormality detection circuit 60 according to the first embodiment. Although only the i-th abnormality detection circuit 60_i is shown in FIG. 7, the N abnormality detection circuits 60 are similarly configured. Hereinafter, as long as there is no hindrance in the description, subscripts for distinguishing the plurality of abnormality detection circuits 60 are omitted.

  The abnormality detection circuit 60 includes an open detection circuit 62. A wiring connected to the cathode of the light emitting element 12 is referred to as a cathode line LK, and a line connected to the anode of the light emitting element 12 is referred to as an anode line LA. The i-th cathode line LK is the (i + 1) -th anode line LA. The first end E1 of the bypass circuit 40 is connected to the cathode line LK, and the second end E2 is connected to the anode line LA.

Open detection circuit 62, the detection voltage Vs compared to the upper threshold voltage V _THH, the detection voltage Vs is based on whether or not exceeds the upper threshold voltage V _THH, it detects an open failure.

The open detection circuit 62 includes a capacitor C1, a charging circuit 64, a discharge path 66, and an output stage 68. The first electrode E1 of the capacitor C1 is commonly connected to the first terminal E1 of the corresponding bypass circuit 40 via the cathode line LK. The discharge path 66 charges the capacitor C1 with a voltage corresponding to the detection voltage Vs when the detection voltage Vs exceeds the first threshold value V _TH1 corresponding to the upper threshold voltage V _THH .

  The open detection circuit 62 has a discharge path 66 for the charge of the capacitor C1, and the time constant of the discharge path 66 is configured to be longer than the PWM cycle.

For example, the charging circuit 64 is provided between the second electrode E2 of the capacitor C1 and the second terminal E2 of the bypass circuit 40. Charging circuit 64, a second flowing into capacitor C2 when not conducting the first direction flowing from the capacitor C1, and the detection voltage Vs exceeds a first threshold value V _TH1 corresponding to the upper threshold voltage V _THH Configured to conduct in a direction.

For example, charging circuit 64 includes a Zener diode ZD1 and a first diode D1 connected in series. The first diode D1 is provided to prevent backflow in the first direction. The zener diode ZD1 and the first diode D1 may be interchanged.
In this configuration, V _TH1 ≈Vz + Vf. Vz is a Zener voltage, and Vf is a forward voltage of the diode. Then, when the _{Vs> V TH1,} conducts the charging circuit 64, the capacitor C1 is charged with a voltage corresponding to the detection voltage Vs Vs- (Vz + Vf).

The output stage 68 compares the capacitor voltage V _C1 with a predetermined second threshold value, and its output state transitions according to the comparison result. Specifically, the output stage 68 includes a first bipolar transistor Q1 and a first resistor R1, and has an open collector type in which the collector of the first bipolar transistor Q1 serves as an output. A voltage of the capacitor C1 (referred to as a capacitor voltage) V _C1 is input to the base of the first bipolar transistor Q1 via the resistor R1. The first bipolar transistor Q1 is turned on when the capacitor voltage V _C1 (= Vs− (Vz + Vf)) exceeds the second threshold value Vbe (≈0.7 V).
The open failure threshold value V _THH of the open detection circuit 62 is given by the following equation, and the comparison result is associated with the on / off state of the transistor Q1.
V _THH = Vbe + Vz + Vf
The collector voltage of the first bipolar transistor Q1 is set as a signal S4.

  The first resistor R1 and the base emitter of the first bipolar transistor Q1 form a charge discharge path 66 of the capacitor C1. That is, the time constant of the discharge path 66 is set according to the resistance value of the first resistor R1 and the transistor size of the first bipolar transistor Q1.

  The above is the configuration of the open detection circuit 62. The abnormality detection circuit 60 outputs an abnormality detection signal S2 corresponding to whether the first bipolar transistor Q1 is on or off.

  Next, the operation of the abnormality detection circuit 60 in FIG. 7 will be described. 8A and 8B are operation waveform diagrams at the time of open failure of the abnormality detection circuit 60 of FIG. FIG. 8A shows a case where the soft switch is not performed, and FIG. 8B shows a case where the soft switch is performed.

Reference is made to FIG. Prior to time t0, the state is normal. An open failure occurs at time t0. When the bypass circuit 40 is turned off at time t1, the detection voltage Vs exceeds the threshold value _VTHH . At this time, since the detection voltage Vs exceeds the first threshold value _VTH1 , the charging circuit 64 becomes conductive and the capacitor C1 is charged.

When the bypass circuit 40 is turned on at time t2, the detection voltage Vs becomes 0V, and the charging circuit 64 is cut off. Then, the electric charge of the capacitor C1 is discharged through the discharge path 66, and the capacitor voltage V _C1 decreases with time. The inclination at this time depends on the time constant of the discharge path 66, and is longer than the PWM cycle _TPWM . In other words, after the charging circuit 64 is charged capacitor C1 conducts, maximum time over the PWM period _{T PWM,} even as the discharge by the discharge route 66 is performed, the capacitor voltage _{V C1} is below the threshold value Vbe There is a time constant so that there is no such thing.

  As a result, the transistor Q1 remains on, and it can be determined that an open failure has occurred.

Next, a case where a soft switch is performed will be described with reference to FIG. When the detection voltage Vs exceeds the threshold value V _TH1 at time t1, the charging circuit 64 becomes conductive, the capacitor voltage V _C1 rises, and the first bipolar transistor Q1 is turned on. Thereafter, the capacitor voltage V _C1 maintains a level higher than the threshold value Vbe without being affected by the soft switch, and the first bipolar transistor Q1 continues to be turned on.

  As described above, according to the abnormality detection circuit 60 according to the first embodiment, an open failure can be detected even when a soft switch is performed.

  Next, detection of an open failure when the wiring LA or LK in FIG. 7 is disconnected will be described. FIG. 9 is an operation waveform diagram of the abnormality detection circuit 60 when the wiring LA is disconnected. The waveforms of the control signal S1 and the detection voltage Vs are the same as those in FIG.

The detection voltage Vsi is included in the normal voltage range in the i-th abnormality detection circuit 60 during the overlap T _OFF of the adjacent off time. As a result, the charging circuit 64 is cut off, and the capacitor voltage V _c1 i decreases during this time. However, since the capacitor voltage V _C1 i does not fall below the threshold value Vbe, the first bipolar transistor Q1 is kept on and an open failure can be detected.

The above is the operation of the abnormality detection circuit 60.
According to the abnormality detection circuit 60, it is possible to reliably detect an open failure even when a soft switch is performed. Further, even when the light emitting elements 12 adjacent to each other are dimmed with different duty ratios and their lighting sections (bypass switch off periods) overlap, it is possible to reliably detect the disconnection failure of the anode wiring and the cathode wiring. .

  In other words, when an open failure occurs, the open failure can be reliably detected even when an event occurs in which the detection voltage Vs returns to the normal voltage range within the PWM dimming period.

(Second Embodiment)
In the first embodiment, the abnormality detection circuit 60 that detects only open failure detection has been described. In the second embodiment, an abnormality detection circuit 60 capable of detecting a short fault in addition to an open fault will be described.

FIG. 10 is a circuit diagram of the abnormality detection circuit 60 according to the second embodiment.
The abnormality detection circuit 60 detects a short circuit failure by comparing the detection voltage Vs with a short circuit failure threshold value (a lower threshold voltage) V _THL set lower than the upper threshold value V _THH. . When the abnormality detection circuit 60_i determines that an abnormal state in which a short failure or an open failure has occurred, the abnormality detection signal S2_i is asserted (for example, high level). The abnormality detection circuit 60 includes a short detection circuit 70 in addition to the open detection circuit 62.

The short detection circuit 70 determines whether or not the detection voltage Vs is lower than the short failure threshold V _THL . For example, the short detection circuit 70 includes a second bipolar transistor Q2, a second resistor R2 to a fourth resistor R4.

The emitter of the second bipolar transistor Q2 is connected to the cathode of the light emitting element 12 via the fourth resistor R4. The second resistor R2 and the third resistor R3 divide the detection voltage Vs and supply it to the base of the second bipolar transistor Q2. The resistance values of the resistors R2 and R3 are determined so as to satisfy the following expression.
V _THL × R3 / (R2 × R3) = Vbe
Vbe is a threshold voltage between the base and emitter of the bipolar transistor, and has a predetermined value near 0.7 V, for example.

Thus, when _{Vs> V THL,} the base voltage Vb ₂ of the second bipolar transistor Q2 is turned on it becomes higher than the threshold Vbe. On the other hand, when Vs <V _THL , Vb ₂ <Vbe and the second bipolar transistor Q2 is turned off. With this configuration, Vs and V _THL can be compared.

The collector of the first bipolar transistor Q1 of the open detection circuit 62 is connected to the base of the second bipolar transistor Q2.
When Vs> V _{THH and} the first bipolar transistor Q1 is turned on, the base of the second bipolar transistor Q2 is pulled down, and the second bipolar transistor Q2 is turned off. That is, the second bipolar transistor Q2 is turned on in a normal state where V _THL <Vs <V _THH , and turned off in an abnormal state where Vs <V _THL or Vs> V _THH .

  Thus, ON / OFF of the second bipolar transistor Q2 is associated with the determination result by the abnormality detection circuit 60.

  The abnormality detection circuit 60 may further include a filter circuit 80 that filters the abnormality detection signal S2 that is the output thereof. The filter circuit 80 causes the abnormality detection signal S2 to transition to a level indicating normal (low level) at a relatively high speed, and to change to a level indicating abnormality (a high level) at a relatively low speed. For example, the filter circuit 80 includes a capacitor C2, diodes D11 and D12, and a resistor R5. One end of the capacitor C2 is connected to the cathode line LK, and the other end is pulled up to the high level voltage Vcc by the resistor R5. The other end of the capacitor C2 is connected to the collector of the second bipolar transistor Q2 via the diode D11.

  When the detection voltage Vs is included in the normal voltage range, the second bipolar transistor Q2 is turned on. Therefore, the capacitor C2 is discharged through the diode D11, the second bipolar transistor Q2, and the resistor R4, and the abnormality detection signal S2 transits to a low level. By reducing the impedance of the discharge path, the abnormality detection signal S2 can be shifted to a level indicating normal (low level) at a relatively high speed.

When the detection voltage Vs deviates from the normal voltage range, the second bipolar transistor Q2 is turned off. Therefore, the capacitor C2 is pulled up to the high level voltage Vcc by the resistor R5, and the capacitor voltage _VC2 rises. Since the rising speed depends on the impedance of the resistor R5, by increasing the impedance of the resistor R5, the abnormality detection signal S2 can be shifted relatively slowly to a level (high level) indicating abnormality.

  By providing the filter circuit 80, abnormality detection can be stabilized.

  Next, a preferable configuration of the drive device 20 using the abnormality detection circuit 60 according to the embodiment will be described.

FIG. 11 is a circuit diagram of the drive device 20 including the abnormality detection circuit 60.
The bypass circuit 40 includes a bypass transistor M1 provided in parallel with the light emitting element 12 and a second diode D2. The cathode of the second diode D2 is connected to the control terminal (gate) of the bypass transistor M1, and the anode of the second diode D2 is connected to the anode of the Zener diode ZD1.

  In this configuration, the Zener diode ZD1, the second diode D2, and the diode between the gate and source of the bypass transistor M1 function as a clamp circuit. That is, when an open failure occurs, the detection voltage Vs can be clamped so as not to exceed Vz + Vf + Vth, and the reliability of the circuit can be improved. Vth is a threshold voltage between the gate and the source of the MOSFET.

  Finally, the use of the vehicular lamp 1 will be described. FIG. 12 is a perspective view of a lamp unit (lamp assembly) 500 including the vehicular lamp 1 of FIG. The lamp unit 500 includes a transparent cover 502, a high beam unit 504, a low beam unit 506, and a housing 508. The vehicle lamp 1 described above can be used for the high beam unit 504, for example. The plurality of light emitting elements 12 are arranged, for example, in a row in the horizontal direction so as to irradiate different regions. Then, in the traveling state of the vehicle, a region to be irradiated is adaptively selected by a vehicle-side controller, for example, an ECU (electronic control unit). The vehicle lamp 1 receives data indicating an area to be irradiated, and the vehicle lamp 1 turns on the light source 10 (light emitting element 12) corresponding to the instructed area.

  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)
FIG. 13 is a circuit diagram of the abnormality detection circuit 60 according to the first modification. In this modification, the first bipolar transistor Q1 is replaced with a MOSFET. Instead of the discharge path using the base emitter of the first bipolar transistor Q1, a resistor R6 connected in parallel with the capacitor C1 forms a discharge path 66. The time constant is adjusted according to the resistance value of the resistor R6.

(Second modification)
FIG. 14 is a circuit diagram of an abnormality detection circuit 60 according to the second modification. In this modification, the collector of the first bipolar transistor Q1 of the open detection circuit 62 is connected to the collector of the third bipolar transistor Q3 of the short detection circuit 70. The base of the third bipolar transistor Q3 is connected to the collector of the second bipolar transistor Q2. The abnormality detection signal S2 becomes high impedance when the detection voltage Vs is included in the normal voltage range, and becomes low level when it deviates from the normal voltage range.

(Third Modification)
The configuration of the charging circuit 64 is not limited to that described above, and it will be understood by those skilled in the art that various modified examples having equivalent functions may exist. 15A and 15B are circuit diagrams of modified examples of the charging circuit 64. FIG. The charging circuit 64 in FIG. 15A includes a plurality of stacked diodes D3 instead of or in addition to the Zener diode ZD1. In this configuration, the threshold value V _TH1 can be adjusted according to the number of stages of the diode D3. The charging circuit 64 in FIG. 15B includes a switch SW1 and a comparison unit 65. The comparing means 65 compares the detection voltage Vs with the threshold value V _TH1 and makes the switch SW1 conductive when Vs> V _TH1 .

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

(5th modification)
In the lamp unit 500 of FIG. 12, the case where the vehicle lamp 1 of FIG. 3 is used for the high beam unit 504 has been described, but the vehicle lamp 1 may be used for the low beam unit 506 instead of or in addition thereto. .

  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, 4 ... Switch, 6 ... Processor, 10 ... Light source, 12 ... Light emitting element, 20 ... Drive apparatus, 30 ... Current source, 40 ... Bypass circuit, 42 ... Gate drive circuit, 50 ... Controller 60. Abnormality detection circuit 62 Open detection circuit 64 Charge circuit C1 Capacitor 66 Discharge path 68 Output stage Q1 First bipolar transistor R1 First resistor 70 Short detection Circuit, Q2 ... second bipolar transistor, R2 ... second resistor, R3 ... third resistor, R4 ... fourth resistor, 80 ... filter circuit, 500 ... lamp unit, 502 ... cover, 504 ... high beam unit, 506 ... low beam unit 508: A housing.

Claims (7)

A drive device that is used together with a light source including a plurality of light emitting elements connected in series and constitutes a vehicular lamp,
A current source for supplying a driving current to the light source;
Of the plurality of light emitting elements, the light emitting elements are associated with N light emitting elements (N is a natural number), and each of the light emitting elements is provided in parallel with the corresponding light emitting element, and the corresponding light emitting element is dimmed by switching with a predetermined period N bypass circuits configured as possible,
N abnormality detection circuits that are associated with the N light emitting elements and configured to be able to detect an abnormality based on a detection voltage between both ends of the corresponding bypass circuit;
With
The abnormality detection circuit includes an open detection circuit that determines whether or not the corresponding detection voltage has exceeded an open failure threshold;
The open detection circuit includes:
A capacitor;
A charging circuit that charges the capacitor with a voltage according to the detection voltage when the corresponding detection voltage exceeds a first threshold value according to the open failure threshold value;
And a time constant of the discharge path of the capacitor charge is configured to be longer than the predetermined period. A first electrode of the capacitor is connected in common with a first end of a corresponding bypass circuit;
The charging circuit is provided between a second electrode of the capacitor and a second end of the bypass circuit corresponding to the charging circuit. The charging circuit does not conduct in the first direction flowing out of the capacitor, and the corresponding detection voltage is the first voltage. 2. The driving device according to claim 1, wherein the driving device is configured to conduct in a second direction flowing into the capacitor when a threshold value is exceeded.   3. The driving device according to claim 2, wherein the charging circuit includes a Zener diode and a first diode provided in series between a second electrode of the capacitor and a second end of the bypass circuit corresponding to the second electrode.   4. The abnormality detection circuit further includes an output stage that compares the voltage of the capacitor with a predetermined second threshold value, and an output state transitions according to the comparison result. The drive device described in 1. The output stage is
A bipolar transistor;
A first resistor provided between a base of the bipolar transistor and a first electrode of the capacitor;
Including
5. The driving device according to claim 4, wherein the first resistor and a base emitter of the bipolar transistor form the discharge path, and ON / OFF of the bipolar transistor is associated with the comparison result. 6. In the charging circuit, the Zener diode is disposed on the side close to the second end of the bypass circuit,
The bypass circuit is:
A bypass transistor provided in parallel with the corresponding light emitting element;
A second diode having a cathode connected to a control terminal of the bypass transistor and an anode connected to an anode of the Zener diode;
The drive device according to claim 3, comprising: A light source including a plurality of light emitting elements connected in series;
The driving device according to any one of claims 1 to 6, which drives the light source;
A vehicular lamp characterized by comprising:

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