Lighting circuit and vehicle lamp

The present application claims the benefit of priority of Japanese Patent Application No. 2016-159700, filed on Aug. 16, 2016, the content of which is incorporated herein by reference.

The present invention relates to a lamp for an automobile or the like.

Halogen lamps and High Intensity Discharge (HID) lamps are conventional mainstream of light sources for vehicle lamps, particularly, for headlamps. In recent years, vehicle lamps are developed to use semiconductor light sources, such as Light Emitting Diodes (LEDs) and Laser Diodes (LDs), instead of these halogen lamps and HID lamps (for example, JP-A-2006-103404).

A vehicle lamp includes a plurality of light sources which are configured to be lit on and off individually. For example, a vehicle lamp includes a low beam light source and a high beam light source. FIGS. 1A and 1B are circuit diagrams of a vehicle lamp including a plurality of light sources which are investigated by the inventors. In FIGS. 1A and 1B , a first light source 302 is for low beam and a second light source 304 is for high beam.

In FIG. 1A , the first light source 302 and the second light source 304 of a vehicle lamp 300 U are configured as individual light emitting units and are respectively connected to a lighting circuit 400 U via wire harnesses 306 , 308 . The first light source 302 , the second light source 304 , the wire harnesses 306 , 308 , and a wire 416 in the lighting circuit 400 U form a series current path.

The lighting circuit 400 U includes a drive circuit 414 , a bypass switch 430 , and a switch driver 432 . The drive circuit 414 is configured by combining (i) a constant current converter or (ii) a constant voltage converter, with a constant current circuit.

When a power-supply voltage V IN is supplied to an LO terminal, the drive circuit 414 supplies a drive current I LAMP (lamp current) to a current path including the first light source 302 and the second light source 304 .

The bypass switch 430 is provided in parallel with the second light source 304 , and the switch driver 432 turns off the bypass switch 430 when an HI terminal is at a high level. In this case, the drive current I LAMP is supplied to the second light source 304 such that the second light source 304 is lit on. The switch driver 432 turns on the bypass switch 430 when the HI terminal is at a low level. In this case, the drive current I LAMP flows through the bypass switch 430 and the second light source 304 is lit off.

In FIG. 1B , a first light source 302 and a second light source 304 of a vehicle lamp 300 V are configured as a single light emitting unit 301 which is connected to a lighting circuit 400 V via a wire harness 305 . In FIG. 1A , the wire harnesses 306 , 308 respectively include two wires, i.e. four wires in total. In FIG. 1B , the wire harness 305 includes three wires, so that the wires, terminals (pins), and the wire 416 in FIG. 1A can be reduced.

The inventors have recognized the following problems after investigating the lighting circuit 400 V of FIG. 1B . Due to poor connection of terminals, wire disconnection or the like, open abnormality may occur in the wire harness 305 . Now, it is assumed that open abnormality occurs in a center wire 310 of the wire harness 305 .

When open abnormality occurs in the wire 310 , the drive current I LAMP flows through the first light source 302 and the second light source 304 , and the second light source 304 cannot be turned off, regardless of ON or OFF of the bypass switch 430 . It is noted that when open abnormality occurs in the wire 312 , problems like those in FIG. 1B would not occur in the vehicle lamp 300 U of FIG. 1A since the second light source 304 is turned off

When open abnormality occurs in the bypass switch 430 , the second light source 304 cannot be turned off either.

Although the combination of the high beam and the low beam has been described here, the same problem may also occur in combination of other light sources.

The present invention has been made in view of the above circumstances, and an aspect of the present invention provides a lighting circuit capable of detecting open abnormality.

According to an aspect of the present invention, there is provided a lighting circuit which is configured to drive a light emitting unit including a first light source and a second light source connected in series. The lighting circuit includes a first pin which is connected to one end of the first light source, a second pin which is connected to a connection node of the first light source and the second light source, a third pin which is connected to one end of the second light source, a drive circuit which is configured to supply a drive current to the light emitting unit, a bypass switch which is provided between the second pin and the third pin, a first resistor which is provided in parallel with the bypass switch between the second pin and the third pin, and an abnormality detection circuit which is configured to detect abnormality based on a detection voltage generated between the second pin and the third pin when an ON signal is applied to the bypass switch.

According to the above configuration, at least one of open abnormality of the wire harness and open abnormality of the bypass switch can be detected.

The abnormality detection circuit may be configured to determine that abnormality occurs when the ON signal is applied to the bypass switch and the detection voltage is smaller than a first threshold which is set near zero.

When open abnormality occurs in the wire (or terminal) in the wire harness connecting the light emitting unit to the second pin, the drive current flows through the second light source. Since the drive current does not flow through the bypass switch or the first resistor, the detection voltage between the second pin and the third pin is near zero. Therefore, open abnormality in the wire connecting the light emitting unit to the second pin can be detected.

The abnormality detection circuit may be configured to determine that abnormality occurs when the ON signal is applied to the bypass switch and the detection voltage is within a voltage range which is based on a forward voltage when the drive current flows through the second light source.

When the wire (or terminal) in the wire harness connecting the light emitting unit to the second pin is normal and open abnormality occurs in the bypass switch, the drive current flows through the second light source, and a forward voltage is generated between the second pin and the third pin. Therefore, open abnormality of the bypass switch can be detected.

The abnormality detection circuit may determine that abnormality occurs when the ON signal is applied to the bypass switch and the detection voltage is smaller than the first threshold or greater than a second threshold.

Therefore, open abnormality of the wire harness and the bypass switch can be detected.

The lighting circuit may further include a second resistor which is provided in series with the bypass switch between the second pin and the third pin. When the drive current is I LAMP , a resistance value of the second resistor is R 2 , and on-resistance of the bypass switch is R ON , and the wire harness and the bypass switch are normal, the detection voltage V DET between the second pin and the third pin is represented by the following Equation (2).

V DET =I LAMP ×( R 2 +R ON )  (2)

That is, since a normal range of the detection voltage can be shifted by taking R 2 as a parameter, it is easy to set thresholds for abnormality determination.

The third pin may be grounded. Therefore, it is easy to compare the detection voltage with the thresholds. In addition, control of the bypass switch can be simplified.

According to another aspect of the present invention, there is provided a vehicle lamp. The vehicle lamp may include a light emitting unit which includes a first light source and a second light source connected in series, the above lighting circuit which is configured to drive the light emitting unit, and a wire harness which includes three wires connecting the light emitting unit to the lighting circuit.

Any combination of the above constituent elements, and the constituent elements and expressions of the present invention mutually replaced by methods, apparatuses, systems, and the like are also within the scope of the present invention.

According to the above configuration, abnormality can be detected.

The above and other aspects of the present invention will become more apparent and more readily appreciated from the following description of illustrative embodiments of the present invention taken in conjunction with the attached drawings, in which:

FIGS. 1A and 1B are circuit diagrams of vehicle lamps including a plurality of light sources which are investigated by the inventors;

FIG. 2 is a block diagram of a vehicle lamp including a lighting circuit according to an embodiment;

FIGS. 3A to 3C are equivalent circuit diagrams of a vehicle lamp;

FIG. 4 is a level diagram of a detection voltage V DET ;

FIG. 5 is a diagram showing a configuration example of an abnormality detection circuit;

FIG. 6 is a circuit diagram of a lighting circuit according to a first modification; and

FIG. 7 is a circuit diagram showing a part of a lighting circuit according to a second modification.

Embodiments of the present invention will be described with reference to the drawings. Identical or equivalent components, members, and processes shown in each drawing are given with same reference numerals, and repeated descriptions are omitted appropriately. The embodiments are not intended to limit the scope of the present invention but are merely illustrative, and all features described in the embodiment and combinations thereof are not essential to the present invention.

In the specification, “a state where a member A is connected to a member B” includes not only a case where the member A and the member B are connected physically and directly, but also a case where the member A and the member B are connected indirectly via other members which do not cause substantial effects on an electrical connection state thereof or do not impair functions or effects due to the connection thereof.

Similarly, “a state where a member C is provided between a member A and a member B” includes not only a case where the member A and the member C, or the member B and the member C, are connected directly, but also a case where the member A and the member C, or the member B and the member C, are connected indirectly via other members which do not cause substantial effects on an electrical connection state thereof or do not impair functions or effects due to the connection thereof.

In the specification, reference numerals given to electrical signals such as voltage signals and current signals, or circuit elements such as resistors and capacitors may represent voltage values and current values, or resistance values and capacitance.

FIG. 2 is a block diagram of a vehicle lamp 300 including a lighting circuit 400 according to an embodiment. The vehicle lamp 300 includes a light emitting unit 301 , a wire harness 305 , and the lighting circuit 400 . The light emitting unit 301 may contain a first light source 302 and a second light source 304 connected in series, and may be mounted on one substrate or configured as one module, but is not limited thereto. For example, the first light source 302 may be a low beam light source and the second light source 304 may be a high beam light source.

The wire harness 305 is detachably connected to the light emitting unit 301 and the lighting circuit 400 . The wire harness 305 includes three wires 309 , 310 , 311 . The first wire 309 connects a first pin P 1 of the lighting circuit 400 to an anode of the first light source 302 , the second wire 310 connects a second pin P 2 of the lighting circuit 400 to a cathode of the first light source 302 and an anode of the second light source 304 , the third wire 311 connects a third pin P 3 of the lighting circuit 400 to a cathode of the second light source 304 . The third pin P 3 is grounded in this embodiment.

The lighting circuit 400 includes the first pin P 1 to the third pin P 3 , a drive circuit 414 , a bypass switch 430 , a switch driver 432 , a first resistor R 1 , and an abnormality detection circuit 460 . The lighting circuit 400 drives the light emitting unit 301 . Specifically, the lighting circuit 400 can be switched between a first mode in which a drive current I LAMP is supplied to the first light source 302 only such that a low beam is lit on and a second mode in which the drive current I LAMP is supplied to the first light source 302 and the second light source 304 such that both low and high beams are lit on.

The lighting circuit 400 further includes a ground (GND) pin, an LO pin, and an HI pin, but is not limited thereto. In this embodiment, when a power-supply voltage V IN is supplied to the LO pin and the HI pin is at a low level, the lighting circuit 400 is switched to the first mode. When the power-supply voltage V IN is supplied to the LO pin and the HI pin is at high level, the lighting circuit 400 is switched to the second mode.

The drive circuit 414 supplies the drive current I LAMP to the light emitting unit 301 . The drive circuit 414 may be configured by combining (i) a constant current output converter or (ii) a constant voltage output converter, with a constant current circuit. The circuit type of the converter is not limited, and a buck type, a boost type, a boost-buck type and the like may be used. Particularly, the drive circuit 414 may be configured by a Buck converter, a Boost converter, a Cuk converter, a Flyback converter or the like. The control method of the converter is also not limited, and a control method using an error amplifier, or a hysteresis control (Bang-Bang control) method may be used.

The bypass switch 430 and the second light source 304 are provided in parallel between the second pin P 2 and the third pin P 3 . For example, the bypass switch 430 can be configured by an N-Channel Metal Oxide Semiconductor Field Effect Transistor (MOSFET).

When a low level is input to the HI pin of the lighting circuit 400 , the switch driver 432 applies a gate signal V G at a high level to a gate of the bypass switch 430 and turns on the bypass switch 430 . When a high level is input to the LO pin of the lighting circuit 400 , the switch driver 432 applies the gate signal V G at a low level to the gate of the bypass switch 430 and turns off the bypass switch 430 .

The first resistor R 1 and the abnormality detection circuit 460 are provided in connection with abnormality detection. The first resistor R 1 , the bypass switch 430 , and the second light source 304 are provided in parallel between the second pin P 2 and the third pin P 3 . A resistance value of the first resistor R 1 is sufficiently higher than on-resistance R ON of the bypass switch 430 and impedance (V F /I) of the second light source 304 such that no current flows through the first resistor R 1 . For example, the resistance value of R 1 is several kΩ.

The abnormality detection circuit 460 detects abnormality according to a detection voltage V DET generated between the second pin P 2 and the third pin P 3 when an ON signal (the gate signal at a high level) is applied to the bypass switch 430 , i.e. in the second mode. Accordingly, information representing ON or OFF of the bypass switch 430 , particularly, a signal of the HI pin or the gate signal V G of the bypass switch 430 , is input to the abnormality detection circuit 460 .

The abnormality detection circuit 460 asserts a diagnostic (DG) signal (for example, makes it to a high level) when abnormality is detected. The DG signal is supplied to a processor (microcomputer) of a vehicle Electronic Control Unit (ECU; not shown) or a processor of a lamp ECU (not shown).

The abnormality detection circuit 460 can detect open abnormality of the wire 310 in the wire harness 305 and open abnormality of the bypass switch 430 . The detection methods will be explained as following.

(Normal State)

FIG. 3A is an equivalent circuit diagram of the vehicle lamp 300 in a normal state. The drive current I LAMP flows through a path including the first pin P 1 , the first light source 302 , the second pin P 2 , and the bypass switch 430 when the wire 310 is normal and the bypass switch 430 is normally turned on. Since R ON <<R 1 , the first resistor R 1 can be ignored and the detection voltage V DET (a normal value V NORM ) between the second pin P 2 and the third pin P 3 is represented by Equation (1).

V NORM =I LAMP ×R ON   (1)

Therefore, the abnormality detection circuit 460 can determine that the vehicle lamp 300 is normal when the detection voltage V DET is within a normal range including the normal value V NORM of Equation (1), otherwise the vehicle lamp 300 is abnormal. Abnormality includes two modes described below.

(Open Abnormality of Wire Harness)

FIG. 3B is an equivalent circuit diagram with the wire harness 305 in an open abnormality state. The drive current I LAMP flows through a path including the first pin P 1 , the first light source 302 , the second light source 304 , and the third pin P 3 when open abnormality occurs in the wire 310 . Since the current does not flow through the bypass switch 430 and the first resistor R 1 , the detection voltage V DET is zero. Therefore, the abnormality detection circuit 460 can determine that open abnormality occurs in the wire harness when the detection voltage V DET is smaller than the first threshold V TH1 which is set near zero. The first threshold V TH1 corresponds to a lower limit of the normal range of the detection voltage V DET , and can be set between 0 V and the normal value V NORM of Equation (1).

(Open Abnormality of Bypass Switch)

FIG. 3C is an equivalent circuit diagram with the bypass switch 430 in an open abnormality state. Similar to FIG. 3B , the drive current I LAMP flows through a path including the first pin P 1 , the first light source 302 , the second light source 304 , and the third pin P 3 when open abnormality occurs in the bypass switch 430 . At this time, a potential of the second pin P 2 is equal to a cathode voltage of the second light source 304 , and a potential of the third pin P 3 is equal to an anode voltage of the second light source 304 , so that the detection voltage V DET is equal to a forward voltage V F of the second light source 304 .

Therefore, the abnormality detection circuit 460 determines that abnormality occurs when the detection voltage V DET is within a voltage range based on the forward voltage V F . The boundary (a second threshold V TH2 ) between the voltage range and an allowable voltage range can be set between the forward voltage V F and the normal value V NORM of Equation (1).

FIG. 4 is a level diagram of the detection voltage V DET . The abnormality detection circuit 460 has two thresholds V TH1 , V TH2 . The first threshold V TH1 is set between the normal value V NORM and 0 V, and the second threshold V TH2 is set between the normal value V NORM and the forward voltage V F of the second light source 304 . The abnormality detection circuit 460 may determine that the bypass switch is normal and negate the DG signal when V TH1 <V DET <V TH2 , and may determine abnormality occurs and assert the DG signal when V DET <V TH1 or V TH2 <V DET .

Since on-resistance R ON of the bypass switch 430 , the drive current I LAMP , and the forward voltage V F have variations, the thresholds V TH1 , V TH2 may be set taking the variations into account.

When the drive current I LAMP is changed for controlling luminance of the light sources, the normal value V NORM takes a value in a range. In this case, the first threshold V TH1 is set between a lower limit of the range and 0 V, and the second threshold V TH2 is set between an upper limit of the range and V F .

There have been described configurations and operations of the vehicle lamp 300 . According to the vehicle lamp 300 of the embodiment, open abnormality of the wire harness 305 , in other words, abnormality that the second light source 304 cannot be turned off, can be detected. Further, according to the vehicle lamp 300 , open abnormality of the bypass switch 430 can be detected.

For example, the vehicle may store abnormality occurrence in logs, and/or inform a driver of the abnormality occurrence when the DG signal is asserted. Whether to light off the first light source 302 and the second light source 304 or to keep them lit on in response to the assertion of the DG signal is decided based on safety-related policies of vehicle manufacturers and/or regions or countries.

Since the third pin P 3 is grounded, the lighting circuit 400 in FIG. 2 can process the detection voltage V DET taking a ground voltage as a reference and the configuration of the circuit can be simplified.

FIG. 5 is a diagram showing a configuration example of the abnormality detection circuit 460 . The abnormality detection circuit 460 includes voltage comparators 462 , 464 and a logic circuit 466 . The voltage comparator 462 compares the detection voltage V DET with the first threshold V TH1 and generates a determination signal S 11 representing a comparison result. The voltage comparator 464 compares the detection voltage V DET with the second threshold V TH2 and generates a determination signal S 12 representing a comparison result. The logic circuit 466 asserts the DG signal when the HI pin (or the gate signal V G ) is in the second mode and at least one of the two determination signals S 11 , S 12 is at a level corresponding to abnormality.

The abnormality detection circuit 460 may be configured by combining discrete elements or may also be integrated into a controller IC for controlling a converter of the drive circuit 414 . Alternatively, a part of the abnormality detection circuit 460 (for example, processing of the logic circuit 466 ) may be mounted in the lamp ECU (processor).

Although the present invention has been described with the specific embodiment, the embodiment merely shows the principle and application of the present invention. Various modifications and configuration changes may be made in the embodiment without departing from the inventive concept as defined in the claims.

(First Modification)

FIG. 6 is a circuit diagram of a lighting circuit 400 a according to a first modification. The lighting circuit 400 a includes a second resistor R 2 in addition to the lighting circuit 400 of FIG. 2 . The second resistor R 2 and the bypass switch 430 are provided in series between the second pin P 2 and the third pin P 3 .

A detection voltage V DET in a normal state (normal value V NORM ′) is represented by Equation (2).

V NORM ′=I LAMP ×( R ON +R 2 )  (2)

Therefore, an abnormality detection circuit 460 a determines that the vehicle lamp 300 is normal when the detection voltage V DET is within a normal range including the normal value V NORM ′ of Equation (2), otherwise the vehicle lamp 300 is abnormal.

According to this modification, since the normal value V NORM ′ of the detection voltage V DET may be shifted by taking resistance value of the second resistor R 2 as a parameter, it is easy to set thresholds for abnormality determination, and detection accuracy may be improved.

(Second Modification)

FIG. 7 is a circuit diagram showing a part of a lighting circuit 400 b according to a second modification. A first resistor R 1 includes resistors R 11 , R 12 connected in series. A detection voltage V DET ′ is obtained by dividing the detection voltage V DET with the resistor R 11 and the resistor R 12 and is generated at a connection node of the two resistors R 11 , R 12 . An abnormality detection circuit 460 b determines abnormality based on the divided detection voltage V DET ′.

When a forward voltage V F is 5V, the maximum of the detection voltage V DET is also 5V, the voltage V DET ′ is generated by dividing the detection voltage V DET , therefore the abnormality detection circuit 460 b may be configured by a 5 V system or 3.5 V system.

(Third Modification)

The abnormality detection circuit 460 may be mainly configured by a digital circuit. In this case, the detection voltage V DET may be converted to a digital signal D DET by an A/D converter, and the digital signal D DET may be compared with a digital threshold corresponding to the two thresholds V TH1 , V TH2 by digital signal processing. In this case, the function of the abnormality detection circuit 460 may be executed by the processor of the lamp ECU. Specifically, as shown in FIG. 7 , the function of the abnormality detection circuit 460 may be easily incorporated into a microcomputer with 5 V or 3 V power supply by utilizing the divided detection voltage V DET ′.

(Fourth Modification)

The abnormality detection circuit 460 may detect only open abnormality of the wire 310 of the wire harness 305 . In this case, the abnormality detection circuit 460 may determine that abnormality occurs when the detection voltage V DET is smaller than the first threshold V TH1 . On the contrary, the abnormality detection circuit 460 may detect only open abnormality of the bypass switch 430 . In this case, the abnormality detection circuit 460 may determine that abnormality occurs when the detection voltage V DET is greater than the second threshold V TH2 .

(Fifth Modification)

The abnormality detection circuit 460 may generate a DG signal such that open abnormality of the wire harness 305 may be distinguished from open abnormality of the bypass switch 305 . For example, the DG signal may be set as a multi-value signal, or transmitted through two lines.

(Other Modifications)

The first light source 302 may be provided on a low potential side and the second light source 304 may be provided on a high potential side. Alternatively, a negative voltage output converter may be used in the drive circuit 414 .

The light sources 302 , 304 are not limited to LED and may be LD or organic Electro Luminescence (EL). Further, the drive circuit 414 is not limited to a switching converter and may be configured by a linear regulator or other circuits. Although two light sources 302 , 304 are connected in series in the embodiment, three or more light sources may be connected in series.

The first light source 302 and the second light source 304 may be a combination different from the combination of a low beam and a high beam. For example, the first light source 302 may be a normal low beam, and the second light source 304 may be an additional low beam.