Lighting circuit and vehicle lamp

A lighting circuit which lights a semiconductor light source, the lighting circuit includes a drive circuit configured to receive a PWM signal from a controller, to generate a drive current to the semiconductor light source, and to switch the drive current according to the PWM signal. When a non-input state of the PWM signal exceeds a predetermined time, the lighting circuit is configured to assert an abnormality detection signal and to output the abnormality detection signal to the controller.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2016-150246 filed on Jul. 29, 2016, the entire content of which is incorporated herein by reference.

BACKGROUND

Technical Field

The present invention relates to a lighting circuit for a lamp used for an automobile or the like and a vehicle lamp including the lighting circuit.

Halogen lamps or HID (High Intensity Discharge) lamps have been mainly used as a light source of a vehicle lamp, particularly, a headlamp. However, in recent years, instead of these lamps, development for a vehicle lamp using a semiconductor light source such as an LED (light emitting diode) or an LD (semiconductor laser) has been advanced.

As a method of controlling the amount of light of a semiconductor light source, an analog dimming in which the amount (amplitude or peak value) of a drive current (lamp current) is changed and a PWM (Pulse Width Modulation) dimming in which a drive current is switched and a duty ratio of the switching is changed have been known.FIG. 1is a block diagram of a lamp system200R studied by the present inventors. The lamp system200R includes an external controller202, a battery204, a switch206, and a vehicle lamp300R. The external controller202is also referred to as an ECU (Electronic Control Unit) and includes a microcomputer (processor) for controlling the vehicle lamp300R.

The ECU202turns on the switch206when turning on the vehicle lamp300R. In this way, a battery voltage VBATis supplied to the vehicle lamp300R. Further, the ECU202generates a PWM signal indicating the amount of light of the vehicle lamp300R in conjunction with the turn on of the switch26and inputs the PWM signal to the vehicle lamp300R.

The vehicle lamp300R includes a semiconductor light source302and a drive circuit304. When the semiconductor light source302is an LED, the drive circuit304is also referred to as an LDM (LED Driver Module). The drive circuit304includes a constant current output switching converter and a controller for the switching converter. The drive circuit304switches a lamp current ILAMPsupplied to the semiconductor light source302according to the PWM signal. Further, when an abnormality of the vehicle lamp300R is detected, the drive circuit304asserts a diagnostic signal DG and notifies it to the ECU202.

In this lamp system200R, the ECU202and the vehicle lamp300R are electrically connected by a wire harness210. When an abnormality such as disconnection occurs in this wire harness210, the PWM signal is not supplied to the drive circuit304, and thus, the amount of light of the semiconductor light source302becomes uncontrollable. For this reason, an abnormality detection function of the wire harness210is required.

In order to solve the above problem, a return line212is provided in the wire harness210and a PWM signal bypassing the inside of the drive circuit304is returned to the ECU202. The ECU202compares the transmitted PWM signal and the returned PWM signal. When these signals coincide (match), it can be determined as a normal state. When these signals do not coincide (unmatch), it can be determined as an abnormal state.

However, in the abnormality detection method ofFIG. 1, the return line212is necessary and an extra pin for return is necessary on the side of the ECU202or the drive circuit304. Therefore, the connection of the lamp system200R becomes complicated.

SUMMARY

Exemplary embodiments of the invention provide a lighting circuit and a vehicle lamp which can provide an improved abnormality detection technique.

A lighting circuit which lights a semiconductor light source, according to an exemplary embodiment, comprises

a drive circuit configured to receive a PWM signal from a controller, to generate a drive current to the semiconductor light source, and to switch the drive current according to the PWM signal,

wherein, when a non-input state of the PWM signal exceeds a predetermined time, the lighting circuit is configured to assert an abnormality detection signal and to output the abnormality detection signal to the controller.

According to this aspect, a unit which detects an abnormality of the PWM signal is provided on the side of the lighting circuit, and the detection result is notified to the controller. As a result, the return line of the wire harness becomes unnecessary.

A supply start of the PWM signal by the controller and a start of power supply to the lighting circuit by the controller may be synchronized. In this way, the lighting circuit can measure the non-input state of the PWM signal by using the supply of power as a trigger.

An abnormality detection signal indicating an abnormality of the lighting circuit and an abnormality detection signal indicating an abnormality of the PWM signal may be logically synthesized and supplied to the controller via a single signal line.

The drive circuit may include a converter and a converter controller configured to control the converter according to the PWM signal. The converter controller may include a timer circuit configured to detect the non-input state of the PWM signal continuing for a predetermined time.

The timer circuit may be provided outside the converter controller.

The converter controller may comprise a regulator configured to generate a power supply voltage used in the lighting circuit, and to shut down the power supply voltage when the non-input state of the PWM signal continuing for the predetermined time is detected, so that the abnormality detection signal supplied to the controller is in an asserted state.

Another aspect of the present invention relates to a vehicle lamp. The vehicle lamp may include a semiconductor light source, and the lighting circuit according to one of the above aspects.

According to an aspect of the present invention, it is possible to detect an abnormality of the PWM signal.

DETAILED DESCRIPTION

Hereinafter, based on preferred embodiments, the present invention will be described with reference to the drawings. The same or similar constituent elements, members or processes shown in each drawing are denoted by the same reference numerals, and the repeated explanations are omitted as appropriate. Further, the embodiment is not intended to limit the invention but is an example. All the features described in the embodiment and combinations thereof are not necessarily essential to the invention.

In the present specification, a state represented by the phrase “a member A is connected to a member B” includes a state in which the member A is indirectly connected to the member B via another member that does not substantially affect the electric connection state therebetween or that does not impair the function or effect exhibited by their connection, in addition to a state in which the member A is physically and directly connected to the member B.

Similarly, a state represented by the phrase “a member C is provided between a member A and a member B” includes a state in which the member A is indirectly connected to the member C or the member B is indirectly connected to the member C via another member that does not substantially affect the electric connection state therebetween or that does not impair the function or effect exhibited by their connection, in addition to a state in which the member A is directly connected to the member C or a state in which the member B is directly connected to the member C.

Further, in the present specification, the symbols attached to electrical signals such as voltage signals and current signals or circuit elements such as resistors and capacitors respectively represent voltage values and current values or resistance values and capacitance values, as necessary.

FIG. 2is a block diagram of a lamp system200including a lighting circuit400according to an embodiment. The lamp system200includes an ECU (controller)202, a battery204, a switch206and a vehicle lamp300. The ECU202, the battery204and the switch206are basically the same as inFIG. 1.

The ECU202and the vehicle lamp300(lighting circuit400) are connected by two wire harnesses214(214a,214b). A PWM signal generated by the ECU202is transmitted to the wire harness214a. Further, a diagnostic signal DG generated by the vehicle lamp300is transmitted to the wire harness214b. The diagnostic signal DG is an abnormality detection signal that indicates abnormality or failure occurring in the vehicle lamp300or the wire harness214or the like.

The vehicle lamp300includes a semiconductor light source302and the lighting circuit400. The lighting circuit400receives a PWM signal from the ECU202, generates a drive current (lamp current) ILAMPto the semiconductor light source302, and switches the drive current ILAMPaccording to the PWM signal.

When a non-input state of the PWM signal exceeds a predetermined time (determination time τ), the lighting circuit400asserts the abnormality detection signal, i.e., the above-described diagnostic signal DG and outputs the abnormality detection signal to the ECU202. The assert may be a high level, a lower level, or a high impedance state. The determination time τ may be determined to be somewhat longer than the period of the PWM signal. Typically, since the PWM signal is on the order of several hundred Hz (period is several ms), the determination time τ can be set to several ten ms to several hundred ms.

The lighting circuit400functionally includes a drive circuit410, an abnormality detection circuit420, and an OR circuit430. The drive circuit410has a constant current output and its drive current ILAMPcan be switched according to the PWM signal. The drive circuit410asserts an abnormality detection signal DG2when an abnormality is detected in the lighting circuit400or in the semiconductor light source302. This abnormality detection signal DG2is transmitted to the ECU202as the above-described diagnostic signal DG

The abnormality detection circuit420detects an abnormality of the PWM signal, more specifically, an abnormality such as a ground fault or disconnection of the wire harness214a. Specifically, when the non-input state of the PWM signal continues for the determination time τ, the abnormality detection circuit420asserts an abnormality detection signal DG1. The abnormality detection circuit420can be configured by a timer circuit.

Meanwhile, inFIG. 2, the abnormality detection circuit420and the OR circuit430are not necessarily hardware separate from the drive circuit410but may be integrated with (or incorporated in) the drive circuit410.

The start of power supply to the lighting circuit400by the ECU202, in other words, the turn-on timing of the switch206is synchronized with the supply start of the PWM signal. That is, the ECU202starts supplying the PWM signal at the same time as the turn-on of the switch206or after a lapse of a predetermined time from the turn-on of the switch206based on the activation time of the lighting circuit400. In this case, the abnormality detection circuit420may start monitoring the PWM signal as soon as a power supply voltage VBATis supplied to the vehicle lamp300(lighting circuit400), and thus, the vehicle lamp300(lighting circuit400) becomes operable.

The abnormality detection signal DG2indicating an abnormality of the lighting circuit400and the abnormality detection signal DG1indicating an abnormality of the PWM signal may be logically synthesized and supplied to the ECU202via a single signal line (wire harness)214b. The OR circuit430logically synthesizes (logically sums) the two abnormality detection signals DG1, DG2to generate the diagnostic signal DG The OR circuit430does not necessarily include an OR gate and may be configured such that the diagnostic signal DG is asserted when at least one of the two abnormality detection signals DG1, DG2is asserted. Further, the OR circuit430may have an open-collector type output stage or an open-drain type output stage, or may have a driver (buffer) for driving the wire harness214b.

Hereinabove, the configuration of the lamp system200including the lighting circuit400has been described. Subsequently, an operation of the lamp system200will be described.FIGS. 3A and 3Bare operation waveform diagrams of the lamp system200shown inFIG. 2in a normal state and in an abnormal state. A vertical axis and a horizontal axis of a waveform or a time chart as used in the present specification are appropriately enlarged or reduced for ease of understanding. Further, each waveform shown is also simplified or exaggerated or emphasized for ease of understanding.

A signal SW indicating ON/OFF of the switch206, the PWM signal, the diagnostic signal DG and the lamp current ILAMPare shown inFIG. 3. In the PWM signal, the low level corresponds to the turn on, and the high level corresponds to the turn off. Meanwhile, although the waveform of the lamp current ILAMPis actually switched according to the PWM signal, the average value thereof is shown inFIG. 3A.

Referring toFIG. 3A, an operation of the lamp system in a normal state will be described. Prior to time t0, the switch206is in an off state and the PWM signal is at the high level (turn off). At time t0, the ECU202turns on the switch206in order to turn on the semiconductor light source302. When the ECU202turns on the switch206, a battery voltage (power supply voltage) VBATis supplied to the vehicle lamp300, and the drive circuit410and the abnormality detection circuit420become operable. The ECU202generates the PWM signal together with the turn on of the switch206. A duty ratio of the PWM signal may be gradually increased in order to gently increase the luminance of the semiconductor light source302. The average value of the lamp current ILAMPvaries according to the duty ratio of the PWM signal.

Referring toFIG. 3B, an operation of the lamp system in an abnormal state will be described. At time t0, in order to turn on the semiconductor light source302, the ECU202turns on the switch206and generates the same PWM signal as inFIG. 3A. By the way, due to the disconnection of the wire harness214a, the PWM signal received by the lighting circuit400is at a constant level (as an example, high level). The abnormality detection circuit420starts measurement at time t1. At time t2after the determination time τ elapses, the abnormality detection signal DG2(DG) is asserted and notified to the ECU202.

Hereinabove, the operation of the lamp system200has been described. According to this lamp system200, a unit which detects an abnormality of the PWM signal is provided on the side of the lighting circuit400, and the detection result is notified to the ECU202. Therefore, the return line of the wire harness shown inFIG. 1becomes unnecessary. That is, since the number of the wire harnesses can be reduced by one, the lamp system200can be simplified.

The present invention is not limited to specific configurations but extends to various devices and circuits which are grasped as the block diagram or circuit diagram inFIG. 2or which are derived from the above description. Hereinafter, more specific configuration examples or embodiments will be described in order to aid understanding of the essence of the invention and the operation of circuit and to clarity them, not to narrow the scope of the present invention.

FIG. 4is a block diagram of a configuration example of the vehicle lamp300. The lighting circuit400includes a converter412, a converter controller414, the OR circuit430and a circuit block440. The converter412is a step-down converter and includes a switching transistor M1, a synchronous rectification transistor M2, an inductor L1and a smoothing capacitor C1. Note that the topology of the converter412is not limited thereto. Here, a bootstrap circuit for driving the switching transistor M1on the high side is omitted.

The converter controller414is a function IC for controlling the converter412, and mainly includes a pulse generator416and a driver418. The power supply voltage VBATis inputted to an input (VIN) of the converter controller414, a detection signal corresponding to the lamp current ILAMPis inputted to a CS (current detection) pin, and the PWM signal from the ECU202is inputted to a PWM pin. An LX (switching) pin is connected to the inductor L1. The pulse generator416generates a pulse signal S1so that a detection signal Vcs approaches a target value. The pulse generator416may be configured by a pulse width modulator using an error amplifier or a pulse frequency modulator, or may be a controller for hysteresis control (Bang-Bang control).

The driver418switches the transistors M1, M2based on the pulse signal S1. Further, the driver418blocks the lamp current ILAMPduring the period when the PWM signal instructs the turning off.

The converter controller414includes a timer circuit422and an internal power supply circuit424. The internal power supply circuit424is, for example, a linear regulator. The internal power supply circuit424receives the voltage VBATof the VIN pin and generates a stabilized power supply voltage VCC_M. The power supply voltage VCC_Mis outputted from the VCC pin of the converter controller414to the outside and is supplied to various circuits (not shown) outside the converter controller414.

The timer circuit422receives the PWM signal and asserts the abnormality detection signal DG1when the non-input state continues for the determination time τ. The internal power supply circuit424stops in response to the assert of the abnormality detection signal DG1. Meanwhile, the entire converter controller414may be shut down in response to the assert of the abnormality detection signal DG1. When the internal power supply circuit424is stopped, the power supply voltage VCC_Mbecomes zero. The timer circuit422and the internal power supply circuit424correspond to the abnormality detection circuit420inFIG. 2. The power supply voltage VCC_Malso serves as the abnormality detection signal DG1.

The circuit block440is provided outside or inside the converter controller414and performs some kind of signal processing. Further, the circuit block440asserts the abnormality detection signal DG2when an abnormality of the lighting circuit400is detected.

InFIG. 4, the assert of the abnormality detection signals DG1, DG2is assigned to a low level. Further, the assert of the diagnostic signal DG is in an open state and the negate is in a low level.

When the abnormality detection signal DG2is asserted, i.e., becomes a low level, a transistor M13is turned off and the diagnostic signal DG becomes an open state. Further, when the abnormality detection signal DG1is asserted, i.e., when the power supply voltage VCC_Mbecomes a low level, a transistor Q11of the OR circuit430is turned off, a transistor Q12of the OR circuit430is turned on, the transistor M13is turned off, and the diagnostic signal DG becomes an open state. When both the abnormality detection signals DG1, DG2are negated (in a high level), the transistor M13is turned on and the diagnostic signal DG becomes a low level.

FIG. 5is a block diagram showing another configuration example of the lamp system200. The vehicle lamp300is composed of three lamps of a main low beam, an additional low beam and a high beam, and includes semiconductor light sources302_1to302_3corresponding thereto. A drive module410_Lo for the low beam includes two drive circuits450_1,450_2, each of which turns on the corresponding semiconductor light source302_1,302_2for the low beam.

A drive module410_Hi for the high beam turns on the semiconductor light source302_3for the high beam. The drive module410_Hi includes a lamp ECU452and a drive circuit450_3.

The vehicle lamp300and the vehicle ECU203are connected to each other via a path216such as LIN (Local Interconnect Network) or CAN (Controller Area Network) and the wire harness214b. The lamp ECU452receives, from the vehicle ECU203, a control signal S3including ON/Off of a plurality of semiconductor light sources302and command values of luminance and the like. The luminance of the additional low beam is variable, and the control signal S3includes data indicating the luminance of the additional low beam. The lamp ECU452generates a PWM signal having a duty ratio corresponding to the data. The PWM signal is supplied to the drive circuit450_2via the wire harness214a. The drive circuit450_2includes the timer circuit422. When the non-input state of the PWM signal is detected to be longer than the determination time τ, the drive circuit450_2asserts the abnormality detection signal DG1. Further, the drive circuit450_1(and450_2) asserts the abnormality detection signal DG2when an abnormality is detected. The OR circuit430transmits the diagnostic signal DG based on the abnormality detection signals DG1, DG2to the vehicle ECU via the wire harness214b.

That is, it can be understood that, in the lamp system200inFIG. 5, the function of the ECU202inFIG. 2is divided into the vehicle ECU203and the lamp ECU452. In other words, in the present invention, the physical arrangement of the controller (ECU), the lighting circuit400and the abnormality detection circuit420is not particularly limited.

FIG. 6is a block diagram showing yet another configuration example of the lamp system200. Since a basic configuration of the lighting circuit400is the same as inFIG. 4, the lighting circuit400is shown in a simplified manner. The vehicle lamp300includes the lamp ECU320. The lamp ECU320includes a switch322and a CPU (controller)324. The switch322corresponds to the switch206inFIG. 2, and the CPU324corresponds to the ECU202inFIG. 2. The CPU324is connected to the vehicle ECU203via the path216and receives the control signal S3. When the control signal S3instructs the turning on, the CPU324turns on the switch322and supplies the power supply voltage VBATto the lighting circuit400. Further, the CPU324generates a PWM signal having a duty ratio corresponding to the command value of the luminance of the semiconductor light source302and transmits the PWM signal to the lighting circuit400via the wire harness214a. Further, when the non-input state of the PWM signal is detected, the lighting circuit400asserts the diagnostic signal DG The diagnostic signal DG is inputted to the CPU324via the wire harness214b.

Although the present invention has been described using specific words and phrases and based on the embodiment, the embodiment merely illustrates the principle and application of the present invention. Many modifications and changes of arrangement are permitted to the embodiment without departing from the spirit of the present invention defined in the claims.

In the above embodiment, the case where the drive circuit410is constituted by the step-down convert has been described. However, the present invention is not limited thereto. For example, the drive circuit410may be a step-up/step down converter, or may be a combination of the step-up converter and the step-down converter, or may be a linear regular or a constant current circuit.

The semiconductor light source302is not limited to the LED, and may be an LD or an organic EL (Electro Luminescence).