• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    An illumination circuit (10) for a light source (2) comprises a driver circuit (20) and an overcurrent protection circuit (30). The driver circuit supplies energy to the light source. The overcurrent protection circuit is inserted between the driving circuit and the light source. The overcurrent protection circuit limits the lamp current flowing in the light source so that the lamp current does not exceed an overcurrent threshold value. The overcurrent protection circuit (30) comprises a transistor (M31), an induction coil (L31), a rectifier (D31), a current detector (32) and an overcurrent protection controller (34). . The current detector generates a current detection signal as a function of the lamp current. The overcurrent protection controller controls the ON / OFF state of the transistor based on the current detection signal and the overcurrent threshold value. The transistor, the induction coil and the rectifier are arranged in a T-shape.
    公开号:FR3025868A1
    申请号:FR1558696
    申请日:2015-09-16
    公开日:2016-03-18
    发明作者:Tomoyuki Ichikawa
    申请人:Koito Manufacturing Co Ltd；
    IPC主号:
    专利说明:

    [0001] BACKGROUND Exemplary embodiments of the invention relate to a vehicle lamp for use in an automobile or the like and relate in particular to an overcurrent protection circuit. Associated Technique Hitherto halogen lamps and high intensity discharge (HID) lamps have been used predominantly as light sources for vehicle lamps and in particular for headlights. The recent advent of semiconductor light sources such as light-emitting diodes (LEDs) is progressing as an alternative.
    [0002] JP 2004-140885 A (corresponding to US 2004/0070374 A1) describes for example a vehicle lamp including a laser diode (also called "semiconductor laser") and a phosphor instead of LEDs to further improve visibility. In JP 2004-140885 A, the phosphor is irradiated with ultraviolet light which is an excitation light emitted by a laser diode. The phosphor generates white light when it receives ultraviolet light. The white light generated by the phosphor is emitted in front of the vehicle lamp so as to form a specific light distribution pattern. Figure 1 is a circuit diagram of a vehicle lamp ir studied by the inventor. A light source 2 comprises a laser diode 3. A lighting circuit 10r comprises an upconverter (DC-DC boost converter) which receives and raises a supply voltage VBAT from a battery. A driving circuit 20r comprises an induction coil L21, a switching transistor M21, a rectifying diode D21 and an output capacitor C21. A controller 22 executes a feedback control for the duty cycle of the switching transistor M21 so that the ILD current flowing in the laser diode 3 corresponds to a target current. The laser diode 3 has a low ability to withstand overcurrent. There is a problem in that the reliability of the laser diode 3 can degrade if it is delivered an overcurrent. Overcurrent can occur in the vehicle lamp for example under the following circumstances. Given the maintainability, there is a case where the laser diode 3 is connected to the lighting circuit 10r so as to be replaceable. More specifically, the laser diode 3 can be connected to the illumination circuit 10 via a connector. There is a problem that, if the connection point of the connector can fluctuate between a contact state and a non-contact state (instability), the charge stored in the output capacitor C21 of the driver circuit 20r can flow. in the laser diode 3 when the connection point is restored to the contact state, which can generate an overcurrent. In the normal state without disturbance, the driver 20r performs a switching operation with a given fixed duty cycle. When the supply voltage VBAT increases rapidly, it is necessary to immediately decrease the duty cycle to keep constant the driving current (lamp current) IL1 flowing in the laser diode 3. There is, however, a problem in because of the delay of the feedback loop, switching occurs with a large duty cycle just prior to fluctuation of the supply voltage, an excessive amount of energy is stored in the induction coil and energy is delivered to the laser diode 3 as overcurrent. These problems do not occur only in the upconverters, but can also occur in a circuit system which controls the laser diode 3 by using a power source having a topology including an inductor or transformer and an output capacitor, such as a buck converter (DC-DC converter), a Cuk converter, a Zeta converter, a flyback converter or a direct converter.
    [0003] Similar problems can also occur in a circuit system that controls the laser diode 3 using a linear regulator. Overcurrent protection is also important in the case where an LED is used as a light source 2 instead of a laser diode 3.
    [0004] SUMMARY The inventor has sought to insert an overcurrent protection circuit (OCP) between the driver 20r and the laser diode 3, so as to suppress overcurrent. Figs. 2A and 2B are OCP circuit circuit diagrams studied by the inventor. In the circuits of FIGS. 2A and 2B, a transistor 180 is disposed in the current path of the ILD lamp and the resistance value of the transistor 180 increases continuously with the increase of the lamp current ID. That is, transistor 180 acts as a variable resistance element.
    [0005] The OCP circuit 30r of FIG. 2A comprises the transistor 180 and a resistor R31, which are arranged in the path of the lamp current ILD, and an error amplifier 182. A power source 184 generates a voltage of VTH threshold. The error amplifier 182 amplifies the error between the voltage drop Vs appearing across the sense resistor R31 and the threshold voltage VTH and then outputs the amplified error to the gate of the transistor 180. OCP circuit 30r, in the state where Vs <VTH, the output voltage (gate voltage of transistor 180) VG of error amplifier 182 is lowered so as to approach the voltage of the mass (0V). Transistor 180 is thus fully switched in the ON state. The ILD lamp current increases in the overcurrent state. If Vs> VTH, then the output voltage VG of the error amplifier 180 increases, the gate-source voltage of the transistor 180 approaches zero, the resistance value of the transistor 180 increases and the lamp current 25 ILI ) is deleted. However, the phase compensation for stabilizing the control system introduces a significant response delay in the error amplifier 182. Thus, when there is a sudden change in the normal lighting state (Vs <VTH ) in the overcurrent state (Vs> VTH), the gate voltage VG of the transistor 180 can not instantaneously increase from a passing level (0V) to a blocked level, so that an overcurrent flows. In the OCP circuit 30s of FIG. 2B, the voltage drop Vs of the sense resistor 31 is introduced between the base and the emitter of the bipolar transistor 186. The potential VG at the connection point between transistor 186 and FIG. a resistor 188 is input to the gate of the transistor 180. In the normal light state, the transistor 186 is BLOCKED and no current flows through the resistor 188. As a result, the voltage of the transistor 188 is BLOCKED. gate VG of the transistor 190 is decreased and the transistor 180 is made completely PASSING. In the overcurrent state, transistor 186 is turned ON, current flows through resistor 188, gate voltage VG of transistor 180 increases, the resistance value of transistor 180 increases, and overcurrent can be suppressed. However, there is not a big difference between the lamp current IL1) in the normal lighting state and the maximum nominal current of the laser diode 3 (i.e., the threshold value overcurrent protection) in the vehicle lamp. As a result, the voltage drop Vs of the detection resistor R31 is large in the normal lighting state and the power loss is important. On the other hand, the overcurrent threshold value fluctuates with temperature because the voltage between the base and the emitter of the bipolar transistor 186 has temperature dependent characteristics. Examples of embodiments of the invention have been made in view of the above circumstances and some of the exemplary embodiments provide a lighting circuit capable of suppressing overcurrents delivered to the light source. (1) According to an exemplary embodiment, a lighting circuit for a light source comprises a driver circuit and an overcurrent protection circuit. The driver delivers energy to the light source. The overcurrent protection circuit is inserted between the driving circuit and the light source. The overcurrent protection circuit limits the lamp current flowing in the light source so that the lamp current does not exceed an overcurrent threshold value. The overcurrent protection circuit includes a transistor, an inductor, a rectifier, a current detector, and an overcurrent protection controller. The current detector generates a current detection signal as a function of the lamp current. The overcurrent protection controller controls the ON / OFF state of the transistor 35 based on the current detection signal and the overcurrent threshold value. The transistor, the induction coil and the rectifier are arranged in a T-shape. In this overcurrent protection circuit, the transistor is switched to the ON state in the normal lighting state where the lamp current is less than the overcurrent threshold value. On the other hand, in an overcurrent state where the lamp current is greater than the overcurrent threshold value, the transistor is switched to the PASSING state and the current path from the driver to the light source is interrupted. That is, the transistor is used as a switch rather than as a variable resistance element. A high-speed overcurrent protection circuit can thus be realized. On the other hand, a small loss of power can be achieved in the normal lighting state. In addition, the induction coil can suppress fluctuations in the lamp current. Accordingly, even if a delay occurs in making the transistor GO, the overcurrent can be suppressed. In addition, the counter-electromotive force that is generated when the transistor is switched to the PASSING state can be limited by the rectifier. (2) In the lighting circuit according to (1), if the current detection signal exceeds an upper threshold value which is determined according to the overcurrent threshold value, the overcurrent protection controller can switch the transistor in the BLOCKED state. If the current detection signal falls below a lower threshold value which is determined according to the overcurrent threshold value, the overcurrent protection controller can switch the transistor to the ON state. (3) In the lighting circuit according to (2), the overcurrent protection controller may include a hysteresis comparator and an amplifier. The hysteresis comparator receives the current detection signal at a first input terminal thereof. The hysteresis comparator receives a predetermined threshold value voltage on a second terminal thereof. The hysteresis comparator generates a protection signal indicating the result of the comparison. The amplifier controls the transistor according to the protection signal. (4) In the lighting circuit according to (1), if the current detection signal exceeds a threshold value level which is determined as a function of the overcurrent threshold value, the Overcurrent protection can immediately switch the transistor to the BLOCKED state. If the current detection signal falls below the threshold value level, the overcurrent protection controller can switch the transistor to the ON state after a predetermined delay time has elapsed. (5) In the lighting circuit according to (4), the overcurrent protection controller may include a comparator and a first sequencer circuit. The comparator receives the current detection signal at a first input terminal thereof. The comparator receives a predetermined threshold value voltage on a second input terminal thereof. The comparator generates a protection signal that is set when the current detection signal exceeds the threshold value voltage. The first sequencer circuit delays an edge corresponding to the transition of the delay time of a level set to a canceled level of the protection signal. (6) In the lighting circuit according to any one of (1) to (5), the transistor and the induction coil may be arranged in series between the positive output of the driving circuit and the positive electrode. of the light source. The rectifier may be disposed between (i) the point of connection between the transistor and the induction coil and (ii) a power source line which connects the negative output of the driver circuit and the negative electrode of the light source. (7) In the lighting circuit according to (3), the transistor may be a p-channel MOSFET. The overcurrent protection controller may further include a voltage source. The voltage source receives a voltage from the driver. The voltage source generates a voltage that is obtained by shifting the received voltage by a specific value on the low potential side. The voltage source delivers the generated voltage to a lower-side power source terminal of the amplifier. (8) In the lighting circuit according to any one of (1) to (5), the transistor and the induction coil may be arranged in series between the negative output of the driving circuit and the negative electrode of the light source. The rectifier may be disposed between (i) the point of connection between the transistor and the induction coil and (ii) a power source line which connects the positive output of the driver to the positive electrode. of the light source. (9) In the lighting circuit according to any one of (1) to (8), the overcurrent protection controller may include a LATCH latch circuit which sets the transistor in the BLOCKED state when a state remains for a predetermined time when the transistor makes repeated switching between the states PASSING and BLOCKED. If a fault occurs in a switching transistor, due to a short circuit in the case where the driver is a switching converter, if a fault occurs in an output transistor due to a short circuit in the case where the driving circuit is a linear regulator or if a feedback circuit of the driving circuit has a fault, the control of the driving current delivered to the light source is lost and the overcurrent state becomes continued. When the overcurrent condition has remained continuous for a long time, the exemplary embodiment assumes that there is a circuit failure and sets the transistor of the overcurrent protection circuit in the BLOCKED state. The light source is thus extinguished and the security can be improved. (10) In the lighting circuit according to (9), the LATCH latch circuit can monitor a signal to request PASSER / BLOCK switching of the transistor. (11) In the lighting circuit according to any one of (9) to (10), the LATCH latch circuit may include a switch detector, a second sequencer circuit and a FORCE LOCK circuit. The switching detector generates a switching detection signal that adopts a first state when the transistor is set in the PASSING state and a second state when the transistor repeatedly switches between the PASSING and BLOCKED states. The second sequencer circuit sets the suspend signal when the second state of the switch detection signal has continued for the specific time. The FORCE LOCK circuit forcibly switches the transistor to the BLOCKED state when the suspend signal is set. (12) The lighting circuit according to any one of (1) to (11) may further include an abnormality detector. The anomaly detector optically monitors the light source. The anomaly detector 3025868 8 sets an abnormality detection signal when the intensity of the light source exceeds a permitted level in a low luminance mode in which the light source is turned on at a lower intensity than the normal level. The transistor is switched to the ON state when the abnormality detection signal is set. (13) According to another exemplary embodiment, a lighting circuit for a light source comprises a driving circuit, an abnormality detector and a protection circuit. The driver circuit supplies power to the light source. The anomaly detector 10 optically monitors the light source. The anomaly detector sets an abnormality detection signal when the intensity of the light source exceeds a permitted level in a low luminance mode in which the light source is turned on at a lower intensity than a normal level. The protection circuit limits the supply of the light source from the driving circuit when the fault signal is set. With this configuration, strong light emission can be prevented under conditions and / or in use situations where the intensity of the light needs to be reduced.
    [0006] The low luminance mode may for example be a test mode in which light is emitted light by the light source 2 for the purposes of light axis adjustments, testing or maintenance. Operator safety during maintenance can be improved. (14) The illumination circuit according to (13) may further include an emission light detector which optically detects whether or not the light source is lit normally. The abnormality detector may set the abnormality detection signal when the emission light detector indicates normal illumination in the low luminance mode. With semiconductor light sources such as laser diodes, there is sometimes a failure mode in which light ceases to be emitted (catastrophic optical deterioration (COD)) even though its electrical characteristics are normal. Accordingly, an emitted light detector which optically detects the light emitted by the laser diode can be used in a vehicle lamp including a laser diode. A detection threshold value of the emitted light detector may be set higher than permitted in the low light mode. The output of the emitted light detector can thus also be used in anomaly detection by a fault detector. On the other hand, the increase of the surface area of the circuit can be suppressed. (15) According to yet another exemplary embodiment, a vehicle lamp comprises a light source and the lighting circuit according to any one of (1) to (14) which drives the light source. The light source may include a laser diode and a phosphor. The laser diode emits excitation light. The phosphor emits fluorescence when excited by the excitation light. The light source generates a white output light including the spectrum of excitation light and fluorescence. According to the exemplary embodiments described above, a circuit may be protected against sudden overcurrent. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and its advantages will be better understood on reading the following detailed description. The description refers to the following drawings, which are given by way of example. Figure 1 is a circuit diagram of a lighting circuit of a light source investigated by the inventor; Figs. 2A and 2B are OCP circuit circuit diagrams studied by the inventor; Fig. 3 is a circuit diagram of a vehicle lamp according to a first exemplary embodiment; Fig. 4 is a circuit diagram showing an example of a specific configuration of an OCP circuit; Fig. 5 is a circuit diagram showing an example of a specific configuration of the OCP circuit of Fig. 4; Fig. 6A shows operating waveforms of the illumination circuit of Fig. 1; Figure 6B shows functional waveforms of the lighting circuits of Figures 3 to 5; Fig. 7 is a circuit diagram of an OCP circuit according to a second exemplary embodiment; Figure 8 shows operating waveforms during the recovery of the contact point of a connector of the lighting circuit of Figure 7; Fig. 9 is a circuit diagram showing an example of a specific configuration of the OCP circuit of Fig. 7; Fig. 10 is a circuit diagram of a lighting circuit provided with an OCP circuit according to a third exemplary embodiment; Figs. 11A and 11B are circuit diagrams showing exemplary OCP circuit configurations of Fig. 10; Fig. 12 is a circuit diagram of a lighting circuit provided with an OCP circuit according to a fourth exemplary embodiment; Figs. 13A and 13B are block diagrams of a BLOCK LOCK circuit; Fig. 14 is a circuit diagram of the BLOCK LOCK circuit; Figs. 15A and 15B explain the operation of a BLOCK lock circuit; Fig. 16 is a block diagram of a vehicle lamp according to a fifth exemplary embodiment; Fig. 17 is a circuit diagram showing an example of a specific configuration of a lighting circuit of the fifth exemplary embodiment; and Fig. 18 is a perspective view of a lamp unit provided with a vehicle lamp according to an exemplary embodiment.
    [0007] DETAILED DESCRIPTION Examples of embodiments of the invention will be described below with reference to the accompanying drawings. Identical or equivalent components, organs and treatments shown in the respective drawings are given the same reference numbers and a redundant explanation thereof will be omitted. In addition, the modes of realization are merely examples and do not limit the invention. All the features described in the following exemplary embodiments and combinations thereof are not always essential to the invention.
    [0008] In the present description, "element A is in a state where element A is connected to element B" includes the case where element A and element B are directly physically connected together and the case where Element A is the element B are indirectly connected together via another element to the extent that (i) there is no appreciable impact on their electrical connection state or (ii) it does not There is no degradation of the functionality and effects provided by their mutual connection. Similarly, a "C element is in a state where element C is disposed between element A and element B" includes the case where element A is directly connected to element B, the case where the element B is directly connected to the element C and the case where an indirect connection is made via another element to the extent that (i) there is no significant impact on their connection state or (ii) there is no degradation of the functionality and effects presented by their mutual connection. In the present description, symbols assigned to electrical signals such as voltage and current signals, and circuit elements such as resistors and capacitors, respectively represent voltage values and current values or values. resistance values and capacitance values, as appropriate. Those skilled in the art will understand that it is possible to replace bipolar transistors, MOSFETs and insulated gate bipolar transistors (IGBTs) with one another by permuting p-channel transistors (pnp type) and transistors. to n-channel (npn type) and to electrically invert the power source and the mass. (First exemplary embodiment) Fig. 3 is a circuit diagram of a vehicle lamp 1 according to a first exemplary embodiment. The vehicle lamp 35 1 comprises a light source 2 and a lighting circuit 10 which drives the light source 2.
    [0009] The light source 2 may for example include a laser diode 3 and a phosphor (not shown in the drawings). The laser diode 3 emits excitation light. The phosphor emits a fluorescent light when excited by the excitation light. The light source is configured to generate white light output including the excitation light and fluorescent light spectra. Alternatively, the light source 2 may include a white LED or a combination of red, green and blue LEDs. When a switch 6 is switched from PASSING to BLOCKED, a voltage VBAT from a battery 4 is applied to the lighting circuit 10 which raises and supplies the voltage VBAT to the light source 2. The lighting circuit 10 comprises a driving circuit 20 and an OCP circuit 30. The driving circuit 20 executes feedback control for the power supply supplied to the light source 2. In the first exemplary embodiment, the circuit driver 20 is a current control upconverter (boost converter). The driving circuit 20 comprises an induction coil L21, a switching transistor M21, a rectifying diode D21, an output capacitor 21 and a controller 22. The controller 22 detects an ILD lamp current delivered to the source of the power supply. light 2, generates a gate pulse whose duty cycle is set to approach a target current IREF which is given as a function of the target luminance of the light source 2 and drives the switching transistor M21. The output voltage See generated at the terminals of the output capacitor C21 is supplied to the light source 2 via the OCP circuit 30. The OCP circuit 30 is inserted between the driver 20 and the driver. 2. The OCP circuit 30 limits the ILD current flowing in the light source 2, so that the ILD current does not exceed an overcurrent threshold value ITH. The overcurrent threshold value ITH is set to be greater than the maximum value of the target current IREF and to be smaller than the maximum nominal current of the laser diode 3. The OCP circuit 30 comprises a transistor M31, a coil of induction L31, a rectifier D31, a current detector 32 and an OCP controller 34. The transistor M31, the induction coil L31 and the rectifier D31 are arranged in the shape of a T. In the first example of 302 In an embodiment, transistor M31 and induction coil L31 are arranged in series on the path of a power source line Lp which connects a positive electrode output OUTP of driver circuit 20. and a positive electrode (anode) of the light source 2. The rectifier D31 is disposed between (i) the connection point N1 between the transistor M31 and the induction coil L31 and (ii) a source line of LN power supply, which connects an OUTN negative electrode output of the driver 20 and a negative electrode (cathode) of the light source 2. Although a diode is suitably used as the rectifier D31, a TEC can be used instead of a diode and it is possible to switch the TEC complementary to the transistor M31. The current detector 32 generates a current detection signal Is a function of the lamp current ILD flowing in the light source 2. The OCP controller 34 controls the ON / OFF switching of the transistor M31 based on the current signal. current detection Is and the overcurrent threshold value ITH. More specifically, the OCP controller 34 switches the M31 transistor to the BLOCKED state if the current detection signal Is exceeds an upper threshold value ITHH which is determined as a function of the overcurrent threshold value ITH. On the other hand, the OCP controller 34 switches the transistor M31 to the ON state if the current detection signal Is is less than a lower threshold value ITHL which is determined according to the overcurrent threshold value. TH. The following is the basic configuration of the vehicle lamp 1. Fig. 4 is a circuit diagram showing an example of a specific configuration of the OCP circuit 30. The current detector 32 has the detection resistor R31 for the The detection resistor R31 is arranged on the path of the line of the power source Lp along which the output voltage VouT is delivered by the drive circuit 20 of the power supply. previous floor. The amplifier 36 amplifies the voltage drop Vs across the detection resistor R31. The output of the amplifier 36 consists of the current detection signal Is which varies linearly with respect to the lamp current ILD. Note that the amplifier 36 of Figure 4 or Figure 5 may be omitted. In addition, the detection resistor R31 may be placed on the line of the LN power source instead of the line of the power source Lp. The sense resistor R31 may be used as the current detection resistor for detecting the ILD lamp current when feedback control is performed for the ILD lamp current in a normal lighting state. The OCP controller 34 mainly comprises a hysteresis comparator 38 and a level shifter 40. A first (+) input terminal of the hysteresis comparator 38 receives the current detection signal Is. The input (-) of the hysteresis comparator 38 receives the predetermined threshold value VTH. The level shifter 40 appropriately shifts the level of the output signal (also referred to as a "protection signal") of the hysteresis comparator 38 and controls the ON / OFF state of the transistor M31.
    [0010] The upper threshold value ITHH and the lower threshold value ITHL are set in the hysteresis comparator 38 as a function of the threshold value VTH. If Is <ITHH, the hysteresis comparator 38 sets its SoCP output high. If Is <ITHL, the hysteresis comparator 38 sets its output S o at the low level. The level shifter 40 also switches the transistor M31 to the ON state when the protection signal Socp is high. On the other hand, the level shifter 40 switches the transistor M31 to the ON state when the protection signal S0 is low. Transistor M31 is, for example, a p-channel MOSFET. When the protection signal S0) is low, the level shifter 40 sets the gate voltage VG of the transistor M31 low to thereby switch the transistor M31 to the ON state. On the other hand, when the protection signal Socp is high, the level shifter 40 sets the gate voltage VG of the transistor M31 high to thereby switch the transistor M31 to the BLOCKED state. The reliability is affected if the gate-source voltage of the transistor M31 exceeds its maximum value when a low voltage is applied to the gate of the transistor M31. Thus, the level shifter 40 comprises an amplifier 42 and a voltage source 44. The voltage source 44 receives the voltage VouT of the driver 20, generates a voltage VL which is obtained by shifting down the Voltage 302 of a predetermined amount and supplies the voltage VL to the lower-side power source terminal of the amplifier 42. The output at the low level of the amplifier 42 becomes the voltage VL. FIG. 5 is a circuit diagram showing an example of a specific configuration of the OCP circuit 30 of FIG. 4. The hysteresis comparator 38 comprises an operational amplifier 0A41 and resistors R41 to R43. The hysteresis comparator 38 enters the driving circuit 42 via a transistor Q41 and a resistor R44. A capacitor C41 and resistor R45 are inserted for the purposes of high speed switching of transistor Q41. The voltage source 44 comprises a Zener diode ZD1, a capacitor C42, a transistor Q42 and a resistor R46. VL = VOUT Vz VF is generated by the voltage source 44, where Vz represents the Zener voltage and VF represents the base-emitter voltage of the transistor Q42. The amplifier 42 comprises transistors Q43 to Q45, a diode D41 and a resistor R47. The voltage VL from the voltage source 44 is supplied to the lower-side power source terminal of the amplifier 42. The transistor Q43 can be switched at a higher speed due to the Schottky limitation by the diode D41. The amplification of current through transistors Q45 and Q42 makes it possible to switch transistor M31 to a higher speed. The respective configurations of the level shifter 40, the current detector 32 and the hysteresis comparator 38 are not limited to the example shown in FIG. 5. As will be understood by one skilled in the art, there are various modified examples and modified examples are also included within the scope of the invention. The OCP circuit 30, the lighting circuit 10 including the OCP circuit 30 and the vehicle lamp 1 including the OCP circuit 30 have been described above. The operation of the OCP circuit 30, the lighting circuit 10 and the vehicle lamp 1 will be described below. FIG. 6B shows functional waveforms of the illumination circuit 10. For the purposes of clarifying the effect of the OCP circuit 30, FIG. 6A shows functional waveforms of the illumination circuit 10r. FIG. 1 does not include the OCP circuit 30. The upper portions of FIGS. 6A and 6B show waveforms at the moment when the connector between the lighting circuit 10 and the light source 2 is connected. brought from a contactless state to a contact state. On the other hand, the lower portions of Figs. 6A and 6B show waveforms that occur when the voltage of the VBAT power supply drops rapidly from 9 V to 16 V. Referring to the upper portions of Figs. 6A and 6B. As shown in FIG. 6A, in the case where the OCP circuit 30 is not provided, when the connector is brought back from the non-contact state to the contact state, the lamp current ILD becomes an overcurrent. a maximum value of 8 A. On the other hand, as shown in FIG. 6B, the supply of the OCP circuit 30 makes it possible to maintain the lamp current ILD between the upper threshold value ITHH and the lower threshold value ITFIL and overcurrent can be suppressed. Reference is then made to the lower portions of Figures 6A and 6B.
    [0011] As shown in FIG. 6A, in the case where the OCP circuit 30 is not provided, when the voltage of the power source VBAT increases rapidly from 9V to 16V, the lamp current ILD becomes a In contrast, as shown in FIG. 6B, the supply of the OCP circuit 30 makes it possible to maintain the lamp current ILD between the upper threshold value ITFIFI and the lower threshold value. ITHL and overcurrent can be suppressed. The operation of the lighting circuit 10 has been described above. Thus, according to the lighting circuit 10, the transistor M31 is switched to the ON state in the normal lighting state where the lamp current ILD is less than the overcurrent threshold value ITH. On the other hand, in the overcurrent state where the lamp current ILD is greater than the overcurrent threshold value ITH, the transistor M31 is switched to the ON state to thereby interrupt the current path of the driver circuit. 20 to the light source 2. That is, since the transistor M31 is used as a switch instead of being a variable resistance element, overcurrent protection can be provided. high speed. In addition, since the transistor M31 is fully switched in the ON state in the normal lighting state, it is also possible to reduce the power loss.
    [0012] In addition, the supply of the L31 induction coil makes it possible to suppress the fluctuations of the ILD lamp current. Consequently, even in the case where a delay occurs in the BLOCKED state of transistor M31, overcurrent can be suppressed. In addition, when the M31 transistor is switched in the PASSING state, the counter-electromotive force can also be limited by the rectifier D31.
    [0013] In addition, the current detection signal Is corresponding to the lamp current ILD is compared with the two threshold values ITHH, exhibiting hysteresis, and the transistor M31 is switched according to the result of the comparison. This provides stabilized protection against overcurrent.
    [0014] In this lighting circuit 10, since the threshold values ITH (ITHH, ITHL) are set higher than the target current TREF, the OCP circuit 30 does not operate in the normal lighting state. Accordingly, priority is given to the current control feedback loop of the driving circuit 20. (Second exemplary embodiment) Fig. 7 is a circuit diagram of an OCP circuit according to a second example embodiment. An OCP circuit 60 comprises a transistor M61, an induction coil L61, a rectifier D61, a current detector 62 and an OCP controller 64. The transistor M61, the induction coil L61 and the rectifier D61 are arranged in T-shape in a manner similar to the first exemplary embodiment. In the second exemplary embodiment, the transistor M61 and the induction coil L61 are arranged in series on the path of the line of the LN power source. A transistor, controlled to be switched ON / OFF in a complementary manner to transistor M61, may be used in place of rectifier D61. The current detector 62 detects the lamp current ILD and generates the current detection signal Is as a function of the lamp current ILD. The OCP controller 64 controls the ON / OFF state of the M61 transistor based on the current detection signal Is and the over-current threshold value ITH. More specifically, in the second exemplary embodiment, if the current detection signal Is exceeds the overcurrent threshold value ITH, the OCP controller 64 immediately switches the transistor M61 to the BLOCKED state. If the current detection signal Is drops below the overcurrent threshold value ITH, the OCP controller 64 switches the transistor M61 to the ON state after a given delay time has elapsed. has passed. The OCP controller 64 includes a comparator 66 and a first sequencer circuit 68. The comparator 66 compares the current detection signal Is with the overcurrent threshold value ITH. If Is> the OCP controller 64 generates a protection signal set S o (for example, high). When the protection signal Su) makes a transition from a canceled level to a set level, the first sequencer circuit 68 immediately switches the transistor M61 to the BLOCKED state without delay. Conversely, when the protection signal Soc makes a transition from the level set to the canceled level, the first sequencer circuit 68 switches the transistor M61 into the PASSING state after a delay of the delay time T. The first sequencer circuit 68 can be considered as a delay circuit which is effective for one edge of the positive edge and the negative edge of the protection signal Socp and has no effect for the other edge. Fig. 8 shows waveforms of the illumination circuit 10 when the contact of the connector of the illumination circuit 10 of Fig. 7 is restored. The contact is restored at time t0. A charge stored in the output capacitor C1 of the driver circuit 20 thus flows in the light source 2 and the lamp current ILD increases sharply. If the lamp current Tu) exceeds the threshold value TH, the protection signal S0 is set (high in this case) and the transistor M61 is immediately switched to the ON state. When the transistor M61 is switched to the ON state, the lamp current ILL) begins to decrease through the induction coil L61 and the diode D61 and quickly becomes smaller than the threshold value ITH and the protection signal Soc is canceled. The edges corresponding to the protection signal Soc effecting a transition from the state set to the canceled state (negative edges) are delayed by the first sequencer circuit 68. The transistor M61 is switched back to the PASSING state after the delay time 1 'has elapsed. When the transistor M61 is switched to the ON state, the lamp current ILD begins to increase. The OCP circuit 60 repeats this operation, which limits the ILD lamp current to values below the overcurrent threshold value ITH. The slope of the ILL lamp current decrease. ) during the delay time i depends on the induction coil L61 and the voltage VLD 5 across the laser diode 3, and is given by VLD / L61. Accordingly, the value of the decrease of the ILD lamp current during the delay time C is equal to T x VLD / L61. Therefore, since the delay time T is determined so as to satisfy ILow = ITH TX VLD / L61> IREF, the overcurrent protection operates in the normal lighting state and the transistor M61 can be prevented from switching . Thus, the transition to the ON state of the transistor M61 is delayed by the OCP controller 64 of the second exemplary embodiment, thereby limiting the ILD lamp current to values between the threshold values ITH. and ILow. Fig. 9 is a circuit diagram showing a specific example of configuration of the OCP circuit 60 of Fig. 7. The current detector 62 has a resistor R62 for current detection. Resistor R62 is disposed in the ILD lamp current path. The voltage drop across the resistor R62 constitutes the current detection signal I. Similar to the first exemplary embodiment, an amplifier that amplifies the voltage drop across the resistor R62 can be added. The resistor R62 is disposed on the line of the LN power source which connects the negative electrode output OUTN of the driver circuit 20 of the previous stage and the negative electrode terminal (cathode) of the source of the 2. Similar to the first exemplary embodiment, the resistor R62 can be arranged on the line of the power source L. Resistors R63 to R67 and an operational amplifier 0A61 constitute a hysteresis comparator and correspond to the Comparator 66 shown in Figure 7. Note that this hysteresis serves to prevent instability and that the hysteresis here is different in the technical sense of that of the first exemplary embodiment. The first sequencer circuit 68 includes a resistor R68, a transistor M62 and a capacitor C61. The capacitor C61 can use the gate capacitance of the transistor M61. When the SOCP protection signal 302 is set (high), the transistor M62 is switched in the PASSING state, the capacitor C61 is discharged immediately, the gate-source voltage of the transistor M61 becomes zero, the transistor M61 is switched in the ON state and the overcurrent protection is activated. When the protection signal Sccp is canceled (low level), the transistor M62 is switched into the ON state. The capacitor C61 is charged through the resistor R68 with a given time constant. After a delay time i corresponding to the flow of the time constant, the gate-source voltage of the transistor M61 exceeds the value of the threshold voltage of a TEC, the transistor M61 is switched to the PASSING state and overcurrent protection is disabled. A diode D62 is provided for the purpose of limiting the back EMF of the inductor L61 when the connection line between the lighting circuit 10 and the light source 2 and in particular the connector, is in an offline state. The second exemplary embodiment has the following advantageous effect with respect to the first exemplary embodiment.
    [0015] In the second exemplary embodiment, when the lamp current ILD exceeds the given threshold value ITH, the transistor M61 is switched to the PASSING state. After that, when the lamp current ILL drops to a level ILow which is lower than the threshold value ITH, the transistor M61 is switched to the ON state. In this sense, the second exemplary embodiment is similar to the first exemplary embodiment. However, the first and second exemplary embodiments are different in that, while the first exemplary embodiment sets the lower ILOW level by using the lower threshold value ITHL of the hysteresis comparator, the second example of In the OCP circuit 30 of FIG. 4, it is necessary to compare the ILD lamp current with the lower threshold value ITHL by means of the comparator. hysteresis 38 in a state where transistor M31 is in the BLOCKED state. As a result, the sense resistor R31 can not be arranged on the ground terminal (OUTN) side of the transistor M31.
    [0016] Therefore, in order for the hysteresis comparator 38 to perform the voltage comparison using the ground voltage as a reference, it is necessary for the amplifier 36 to convert the voltage drop Vs into a detection signal. current Is which is based on the voltage of the mass serving as a reference. However, since the high-speed amplifier 36 is generally expensive, the cost can be significant in the OCP circuit 30 of FIG. 4. By contrast, in the second exemplary embodiment, since the sequencing in which the transistor M61 is set to the ON state is determined by the first sequencer circuit 68, it is not necessary that the ILD lamp current be detected during the time that the M61 transistor is in the BLOCKED state. That is, the detection resistor R62 of the ILD lamp current can be arranged on the ground terminal side (OUTN) as shown in FIG. 9. Thus, the current detection signal Is which is based on FIG. The reference ground voltage can be generated even without the amplifier 36 of FIG. 4. As a result, the cost can be reduced. (Third Embodiment) Fig. 10 is a circuit diagram of an illumination circuit 10 provided with an OCP circuit according to a third exemplary embodiment. An OCP circuit 50 is inserted between a driver circuit 20 and a laser diode 3 in the third exemplary embodiment. The OCP circuit 50 comprises a current detector 52, a comparator 54, a sequencer circuit 56, a branching transistor M51 and a current limiting resistor R51. The current detector 52 detects an ILD lamp current and generates a current detection signal Is dependent on the lamp current ILD. The comparator 54 compares the current detection signal Is with the overcurrent threshold value ITH and generates a set protection signal (for example, at high level) Soc when Is> ITH. It is preferable that the comparator 54 is a hysteresis comparator. The current limiting resistor R51 is arranged in the path of the lamp current Tu. The branching transistor M51 is arranged in parallel with the current limiting resistor R51. Bypass transistor M51 is switched to the ON state for a period during which the protection signal S0 is canceled. On the other hand, the branching transistor M51 is switched to the ON state during a period during which the protection signal Soep is set. The sequencer circuit 56 is inserted between the bypass transistor M51 and the comparator 54. When the protection signal Socp makes a transition from a canceled state to a set state, the sequencer circuit 56 immediately switches the bypass transistor M51 into the BLOCKED state without delay. Conversely, when the protection signal Soc makes a transition from the level set to the canceled level, the sequencer circuit 56 switches the bypass transistor M51 into the ON state after a specific time delay has elapsed. The sequencer circuit 56 may be considered as a delay circuit which takes effect for one edge of the positive edge and the negative edge of the protection signal Su and has no effect for the other edge.
    [0017] When an overcurrent state of ILD> ITH is detected, the OCP circuit 50 according to the third exemplary embodiment immediately switches the transistor M51 to the BLOCKED state and the overcurrent can be suppressed. Conversely, when the state is returned to a normal illumination state of ILD <ITH, the bypass transistor M51 is switched to the ON state after a time delay has elapsed, the limiting resistance of R51 current is bypassed and the light source 2 can be attacked with a small loss of power. When the lighting circuit 10 and the connector of the light source 2 are in a non-contact state (separated), the output voltage V0D-r of the driver 20 becomes a predetermined voltage Vocv. Assuming that VL represents the output voltage of the driving circuit 20 in the normal lighting state, a maximum current MAX that flows in the light source 2 when the connection point of the connector is restored is obtained by (Vocv - VL) / R51. Accordingly, the laser diode 3 can be suitably protected by determining the resistance value of the resistor R51 so that the maximum current MAX does not exceed the maximum rated current (current allowed) of the laser diode 3. Figs. 11A and 11B are circuit diagrams showing configuration examples of the OCP circuit of Fig. 10.
    [0018] 302 5 8 6 8 23 The OCP circuit 50 of Figure 11A will be described below. The current detector 52 has a resistor R52 for the current detection. The resistor R52 is arranged in the path of the lamp current Io. The voltage drop across the resistor R52 constitutes the current detection signal Is. Similar to the first exemplary embodiment, an amplifier that amplifies the voltage drop across the resistor R52 can be added. The resistor R52 is disposed on a power source line LN which connects the negative electrode output OUTN of the driver circuit 20 of the preceding stage and the negative electrode (cathode) of the light source 2. Note that the resistor R52 may be disposed on a power source line Lp similarly to the first exemplary embodiment. An operational amplifier 0A51, resistors R53 to R56 and a transistor M52 constitute a hysteresis comparator and correspond to the comparator 54 of Fig. 10. The level set of the protection signal Soc of Fig. 11A is the low level. The sequencer circuit 56 comprises a resistor R57, a transistor Q51 and a capacitor C51. When the protection signal Socp is set (low level), the transistor Q51 is switched into the ON state, the capacitor C51 discharges immediately, the gate-source voltage of the bypass transistor M51 becomes zero, the bypass transistor M51 is switched to the ON state and overcurrent protection is enabled. When the protection signal S0 is canceled (high level), the transistor Q51 is switched to the ON state. The capacitor C51 is charged with a given time constant through the resistor R57 and after a delay time corresponding to the flow of the time constant, the gate-source voltage of the bypass transistor M51 exceeds the voltage of the set value. As a threshold of a TEC, the M51 bypass transistor is switched to the ON state and the overcurrent protection is disabled. The OCP circuit 50 of FIG. 11A can reliably enable current limitation on a small scale, with a small number of components and low cost.
    [0019] When an overcurrent is detected, the OCP circuit 50 of FIG. 11A immediately switches off the M51 bypass transistor. However, it is difficult to cancel the delay. Because of this delay, a problem may arise such that the lamp current ILD exceeds the maximum rated current (current allowed) of the laser diode 3 before the bypass transistor M51 is switched to the ON state. Then, the OCP circuit 50 of Fig. 11B further comprises an induction coil L51 which is arranged in series with the current limiting resistor R51. The rapid fluctuations of the ILD lamp current are thus suppressed. A diode D51 is also arranged in parallel with the induction coil L51. The diode D1 can absorb (block) the counter-electromotive force generated by the adduction coil L51. (Fourth Embodiment) Fig. 12 is a circuit diagram of a lighting circuit provided with the OCP circuit according to a fourth exemplary embodiment. The differences between the illumination circuit 10a of Fig. 12 and the illumination circuit 10 of Fig. 7 will be described. An OCP controller 64a of an OCP circuit 60a further includes a LATCH latch circuit 70 in addition to the comparator 66 and the first sequencer circuit 68. As described above, in the OCP circuit 60, the Transistor M61 is continuously in the ON state in the normal state in which Is <ITH. An overcurrent state in which Is exceeds ITH also gives rise to a state in which transistor M61 is repeatedly switched into the ON / LOCKED state (called "switch state").
    [0020] In the switching state in which the transistor M61 repeatedly switches to the ON / OFF state for a predetermined period of time T2, the LATCH latch circuit 70 sets (locks in LOCK) the gate signal of the transistor M61 to a latch. low level so as to set the transistor M61 in the BLOCKED state. The predetermined time T2 can be for example in a range from a few hundred milliseconds to several seconds. More specifically, the predetermined time T2 may be for example 0.2 seconds. The LATCH latch circuit 70 determines whether transistor M61 is in the fixed PASSING state and whether transistor M61 is switched or not, by monitoring a signal (hereinafter called "gate control signal") S10 which requires the transition to the ON / OFF state of transistor M61. The gate control signal S10 may be the protection signal S0, may be the gate signal of the transistor M61, that is to say the output signal of the first sequencer circuit 68 or may be an internal signal of the first circuit. Sequencer 68. The following advantageous effects are achieved by providing the LATCH latch circuit 70. When a failure occurs in which the switching transistor is short-circuited or the feedback circuit fails in the event that the driver 20 is a switching converter (in particular, a down converter), as described above, it becomes impossible to control the ILD lamp current delivered to the laser diode 3 and the overcurrent state continues. In this exemplary embodiment, the BLOCK 70 latch circuit is provided. When the overcurrent condition occurs for a long time, it is assumed that the circuit fails and the M61 of the OCP circuit 60 is set in the BLOCKED state. The laser diode 3 is thus deactivated and the security can be improved. Fig. 13A is a block diagram of the LATCH latch circuit 70. The LATCH latch circuit 70 includes a switch detector 72, a second sequencer circuit 74, a latch circuit 76, and a BLOCK LOCK circuit 78. The detector switching circuit 72 generates a switching detection signal S11 such that (i) if the transistor M61 remains in the ON state, the switching detection signal S11 is in a first state (for example, high) and ( ii) if the switching transistor M61 is in the switching state where the transistor M61 is repeatedly switched in the PASSING / BLOCKING state, the switching detection signal S11 is in a second state (for example, at the low).
    [0021] As described above, the switching detector 72 can monitor any of the protection signal S0, the gate signal of the transistor M61 and the internal signal of the first sequencer circuit 68. If the switching detection signal S11 is is found in the second state (low level) continuously for a predetermined duration T2, the second sequencer circuit 74 sets the suspension signal S12. If the suspend signal S12 is set, the lock circuit 76 locks this state. If the set suspension signal S12 is latched, the FORCE LOCK circuit 78 forcibly secures the transistor M61 in the BLOCKED state. For example, the FORCE LOCK circuit 78 may include a switch which is disposed between the gate of the M61 transistor and the ground. If the set suspension signal S12 is locked, the blocking circuit 76 may output a BLOCKED signal at the high level S13. If the BLOCKED signal S13 is high, the switch can be switched to the PASSING state. Fig. 13B shows a modified example of the FORCE LOCK circuit 78. The FORCE LOCK circuit 78 may be configured as a logic gate which performs logic operations for an SG gate signal which controls the M61 transistor ON / OFF state. and for the output S13 of the latch 76A and outputs the resulting output SG 'to the gate of the transistor M61. When for example the latch circuit 76 is configured so that a LOW BLOCKED signal S13 is output during a period during which the positioned suspend signal S12 is latched, the logic gate may be a logic gate. OR negative. Fig. 14 is a circuit diagram of the LATCH latch circuit 70. The gate control signal SG (S10) is applied to the input of the I / O terminal of the BLOCK 70 latch circuit. for example, where the LATCH latch circuit 70 is disposed in the OCP circuit 60 of Figure 9, the drain of the transistor M62 (the gate of the transistor M61) is connected to the I / O terminal.
    [0022] The switching detector 72 mainly comprises a low pass filter 80 and an output stage 82. The low pass filter 80 removes the high frequency components associated with the switching of the gate control signal S10 so as to smooth the gate control signal S10. The low pass filter 80 comprises a capacitor C3, a charging circuit 84 and a discharge circuit 86. One end of the capacitor C3 is connected to ground and the other end is connected to a transistor Tr5 which constitutes the charging circuit. . The discharge circuit 86 is disposed between the other end of the capacitor C3 and the ground. The output stage 82 has two inverter stages in series. The first inverter stage comprises a transistor Tr6 and a resistor R4.
    [0023] The second inverter stage comprises a transistor Tr7 and resistors R5, R6. The second sequencer circuit 74 mainly comprises a capacitor C4 and a comparator 88. The resistors R7, R8 and the capacitor C5 divide the supply voltage Vcc and generate a reference voltage (reference value voltage) VTH. The output of the switching detector 72 is connected to the capacitor C4. A diode D2 constitutes a voltage setting device. The comparator 88 compares the voltage Vc4 of the capacitor C4 to the reference voltage VTH.
    [0024] A low pass filter including a resistor R9 and a capacitor C6 is connected to the output of the comparator 88. The latch circuit 76 includes a bistable multivibrator circuit (also referred to as a latch or latch) 90. The bistable multivibrator circuit 90 may include transistors Tr9 to Tr10 and resistors R10 to R11. Since the configuration and operation of the bistable multivibrator 90 is known, its description will be omitted. The configuration of the bistable multivibrator 90 is not particularly limited, and a flip-flop D, a latch D, or the like can be used as the bistable multivibrator 90. The output of the bistable multivibrator 90 is output to the bistable multivibrator circuit 90. FORCED BLOCK 78. The latch circuit 76 further includes a power-on reset circuit 92. The power-on reset circuitry 92 resets the flip-flop 90 to an initial state when the source voltage is turned on. Vcc power supply is applied as input. The power-up reset circuit 92 comprises, for example, resistors R12 to R14 and transistors Tr11, Tr12. The FORCE LOCK circuit 78 includes a transistor Tr13 disposed between (i) a line 94 which transmits the gate control signal S10 and (ii) ground. The transistor Tr13 is switched to the ON state when the output S13 of the latch circuit 76 is high. When the transistor Tr13 is switched to the ON state, the gate control signal S10 is set low and the transistor M61 is forcibly switched to the BLOCKED state.
    [0025] The operation of the BLOCK 70 latch circuit will then be described.
    [0026] Figs. 15A and 15B are diagrams for explaining the operation of the LATCH latch circuit 70. Fig. 15A shows an overcurrent protection operation. In the normal state, before a time t0, the drive current ILD is held at a target current IREF. The gate control signal S10 remains high at this time. As a result, the transistor Tr5 is in the BLOCKED state, the transistor Tr6 is in the BLOCKED state and Tr7 is in the PASSING state. The charge of the capacitor C4 is thus discharged through the transistor Tr7 and the voltage Vc4 is maintained at 0 V.
    [0027] When the mode goes into an overcurrent state at time t0, drive current IL1) increases. In the overcurrent state, the gate control signal S10 of the transistor M61 oscillates and the transistor M61 switches over. The drive current ILD is thus maintained so as not to exceed the threshold value 'TH.
    [0028] When the gate control signal S10 switches, the transistor Tr5 switches. The voltage Vo across the capacitor C3 increases accordingly, the transistor Tr6 switches to the PASSING state and the transistor Tr7 switches to the LOCKED state. When the transistor Tr7 switches to the LOCKED state, the capacitor C4 is charged across the resistor R5 and the capacitor voltage Vc4 increases with time. Then, when the voltage of the capacitor Vc4 exceeds the threshold voltage VTH at a time t1 after the predetermined time T2 has elapsed, the output of the comparator 88 goes high and the transistor Tr8 switches to the PASSING state. The bistable multivibrator circuit 90 is therefore locked in a state where the transistor Tr10 is in the BLOCKED state and the transistor Tr9 is in the PASSING state. Thus, the BLOCKED signal S13 is set high. The transistor Tr13 is therefore switched to the ON state, the gate control signal S10 goes low and the transistor M61 is forcibly switched to the BLOCKED state. The power-on reset operation at the time the power source is inputted will then be described with reference to FIG. 15B. When the power source is inputted at time t0, the voltage of the power supply Vcc 35 begins to increase. The operation of the circuit is unstable between time t0 and time t1.
    [0029] The voltage that is obtained by dividing the voltage of the power source Vcc by the resistors R13, R14 is fed to the base of the transistor Tr12. From time t1 to time t2, the base-emitter voltage of transistor Tr12 is less than 0.6V and transistor Tr12 is accordingly in the BLOCKED state. At this time, the voltage of the supply source Vcc is delivered to the base of the transistor Tri 1 through the resistor R12, this base voltage S14 is maintained at around 0.6 V and the transistor Trl 1 is switched in. the passing state. The BLOCKED signal S13 is thus reset to the low level.
    [0030] The voltage of the power supply Vcc increases from the beginning of the time t2. When the base voltage of the transistor Tr12 exceeds 0.6 V, the transistor Tr12 switches to the PASSING state and the transistor Tri 1 switches to the BLOCKED state. The resetting of the bistable multivibrator circuit 90 is thus deactivated. Thus, the laser diode 3 can be started from a state where the FORCE LOCK is disabled by the power-on reset when the power source is inputted. (Fifth exemplary embodiment) Fig. 16 is a block diagram of a vehicle lamp 20b according to a fifth exemplary embodiment. The driver circuit 20 may be a constant current switching converter. In this exemplary embodiment, the light source 2 comprises the laser diode 3 and a phosphor. The driver 20 has a plurality of selectable modes. The driving circuit 25 causes the light diode 3 to emit light with a different intensity in each mode. The driver circuit 20 is capable for example of switching between a first mode and a second mode. In the first mode, the driving circuit 20 causes light emission by the laser diode 3 with a normal intensity. In the second mode, the driving circuit 20 causes the laser diode 3 to emit light at a lower intensity than the normal intensity. The first mode may for example be a mode of travel in which the driving circuit 20 causes the light source 2 to emit light with sufficient intensity to illuminate ahead of the vehicle 35 during a normal journey. The second mode may be a test mode in which the driving circuit 20 causes a low light emission by the light source 2 for the purposes of light axis adjustments, testing or maintenance. An electronic control unit (ECU) 8 supplies the driving circuit 20 with a SMODE mode signal indicating the current mode. The ECU 8 can be installed on the vehicle side or can be installed on the vehicle lamp side. It is assumed that the second mode is a test mode in which light is to be emitted with low luminance. In this case, if the light source 2 emits light with a high luminance, there is a problem that glare may occur to nearby workers and the like. Similarly, it is assumed alternatively that the second mode is one in which light must be emitted with low luminance while the vehicle is moving. In this case, if the light source 2 emits light with high luminance, glare may be caused to an oncoming vehicle and a pedestrian. That is, it is an abnormal state for the light source 2 to emit light with high luminance in the second mode. To solve these problems, a fault detector 100 and a protection circuit 110 are provided in the vehicle lamp 1b.
    [0031] The anomaly detector 100 optically monitors the light source 2. When the intensity of the light source 2 exceeds a permitted level in a low luminance mode in which the light source 2 is illuminated with a lower intensity than the light source 2 At normal intensity, the anomaly detector 100 sets the anomaly detection signal S20.
    [0032] The vehicle lamp 1b requires a function to generate a diagnostic signal which warns the vehicle side ECU of a light failure of the light source 2. There is a failure mode in which the laser diode 3 does not emits no light (catastrophic optical deterioration (COD)) even though the electrical characteristics of the laser diode 3 are normal. Consequently, the simple monitoring of the electrical characteristics is not sufficient to detect a failure of the laser diode 3. There is a case in which a light emission detector 102 is provided, optically detecting the light emitted by the laser diode 3. The light emission detector 102 comprises a photodiode, a phototransistor, a CMOS sensor, a charge coupled device or the like. The light emission detector 100 can determine whether or not the light source 2 is lit normally. If the light emitting detector 102 detects that the light source 2 is not lit in the normal mode, the light emitting detector 102 sets the signal ScoD (for example, high). On the other hand, the signal Som is canceled (low level) during normal lighting. The signal Scot) is transmitted on the vehicle side as a diagnostic signal. In an exemplary preferred embodiment, the light emission detector 102 may also be used to detect an abnormal state in the second mode. That is, the detection threshold value of the light emitting detector 102 is set to be higher than the permitted level in the low luminance mode and the anomaly detector 100 is referenced at the output. Som of the light emitting detector 102. Thus, the output Som of the light emitting detector 102 can be used in the anomaly detection performed by the anomaly detector 100. More specifically, when the signal Scop is canceled in the second mode, the anomaly detector 100 can determine the abnormal state. Since an emission light detector is not needed in the second mode, the increase in the surface area of the circuit can be suppressed. Another emission light detector for detecting an abnormality in the second mode may also be provided in addition to the light emitting detector 102 for detecting COD. In this case, the allowed levels (threshold values) can be set individually. If the abnormality detection signal S20 is set, the protection circuit 110 limits the supply of the driver 20 to the light source 2. Examples of power limitation include the interruption of the power supply. diet, the decrease in diet and the like. The protection circuit 110 may be configured, for example, to include a switch 112 disposed in the path of the drive current ID and to interrupt supply of the power supply to the light source 2 by switching the switch 112 in BLOCKED state.
    [0033] The configuration of the vehicle lamp 1b according to the fifth exemplary embodiment has been described above. The operation of the vehicle lamp 1b will then be described. When the SMODE mode signal indicates the second mode, the driver 20 delivers a small drive current ILD to the light source 2. The light source 2 then emits light with a luminance dependent on the small current ILD attack. In the case where the light source 2 uses a combination of the laser diode 3 and the phosphor, if an anomaly occurs, such as the detachment of the phosphor, the excitation light of the laser diode 3 is emitted as it is. If the light source 2 is normal, the light emitting detector 102 detects only a weak light at a level below the permitted level of the second mode. Thus, the Scot signal must be positioned. If, however, the light source 2 is abnormal, the light-emitting detector 102 then detects light with sufficient intensity for the Saxo signal to be canceled. If the SMODE mode signal indicates the second mode and the signal Sax) is canceled, the fault detector 100 sets the abnormality detection signal S20. The switch 112 of the protection circuit 110 is accordingly switched to the ON state and the light emission by the laser diode 3 is immediately stopped.
    [0034] In this manner, the illumination circuit 10b of FIG. 16 prevents the excitation light from escaping as it is when the laser diode 3 is turned on in the test mode in a state where an abnormality occurs in the phosphor and prevents close workers and the like from being enlightened. As a result, security can be improved.
    [0035] Fig. 17 is a circuit diagram showing an example of a specific configuration of a lighting circuit 10b according to the fifth exemplary embodiment. The anomaly detector 100 can be configured by a combination of logic gates. If the high level of the SMODE mode signal corresponds to the second mode, the fault detector 100 may include an inverter 120 and an AND gate 122. The inverter 120 inverts the signal Som. The output of the inverter 120 is set (high level) when the laser diode 3 emits light exceeding the permitted level. The AND gate 122 performs the logical sum of the SMODE mode signal and the inverter 120 output and outputs the output as an abnormality detection signal S20. Note that the assignment of the high / low level to each signal may be varied and in this case inverters may be added or omitted or OR gates may be replaced by AND gates. The illumination circuit 10c of FIG. 17 may be considered as a combination of the illumination circuit 10b of FIG. 16 and the illumination circuit 10a of FIG. 12. In addition to the OCP circuit 60a of FIG. 12, the protection circuit 110 also comprises a logic gate 114. The transistor M61 corresponds to the switch 112 of FIG. 16. An overcurrent detector 116 corresponds to the current detector 62 and the comparator 66 of FIG. 16. The logic gate 114 10 applies a start trip to the first sequencer circuit 68 when the protection signal Socp is set or when the abnormality detection signal S20 is set. The logic gate 114 may be for example a gate OÙ. It should be noted that the configuration of the protection circuit 110 is not limited to that of FIG. 17. The protection circuit 110 may include, for example, the OCP circuit 30 of FIG. 2 or FIGS. include the OCP circuit 60 of Figures 7 and 9 or may include the OCP circuit 50 of Figures 10 and 11. Alternatively, the protection circuit 110 may simply include the switch 112 alone as shown in Figure 16 when a combination with the overcurrent protection function is not required. An application of the lamp for vehicle 1 will finally be described. Fig. 18 is a perspective view of a lamp unit (lamp assembly) 500 provided with the vehicle lamp 1 according to the exemplary embodiment. The lamp unit 500 comprises a transparent cover 502, a high beam unit 504, a dipped beam unit 506 and a housing 508. The vehicle lamp 1 described above can be used for example in the unit. The vehicle lamp 1 may include one or more light sources 2. The vehicle lamp 1 may also be used in the dipped beam unit 506 in place of the light unit 504 or in addition to it. The invention has been explained above based on the exemplary embodiments. However, these exemplary embodiments are merely examples and one skilled in the art will understand that various modified examples are possible by combining the respective configuration elements and the respective processing processes, these modified examples also belonging to the present invention. scope of the invention. Such modified examples will be described below. (First modified example) In the exemplary embodiments, the driver 20 is a switching converter. However, the invention is not limited thereto. A linear regulator or a combination of a switching converter and a linear regulator can be used. The advantageous effects described for each of the exemplary embodiments can also be achieved. (Second modified example) The LATCH latch circuit 70 described in the fourth exemplary embodiment is also applicable to the OCP circuits 30 of FIGS. 3 and 5. In this case, replacing the transistor M61, the latch circuit of FIG. BLOCK 70 may be configured to set the transistor M61 in the BLOCKED state when a state remains for the predetermined time T2 during which the transistor M31 performs a repeated switching between the PASSING and BLOCKED states. Alternatively, BLOCK LOCK circuit 70 may be combined with OCP circuit 50 of FIGS. 10, 11A and 11B. An explanation of the invention has been given in specific terms based on its exemplary embodiments. However, the exemplary embodiments merely illustrate the principles and application of the invention. A large number of modified examples and alternative arrangements can be made on the exemplary embodiments within a scope that does not depart from the spirit of the invention as defined by the claims.
    权利要求:
    Claims (15)
    [0001]
    REVENDICATIONS1. An illumination circuit (10, 10a) for a light source (2), the illumination circuit (10, 10a) comprising: a driver (20) which supplies energy to the light source ( 2); and an overcurrent protection circuit (30, 60, 60a) which is inserted between the driver (20) and the light source (2) and which limits the lamp current (ILD) flowing in the source of the light. light (2) so that the lamp current (ILD) does not exceed an overcurrent threshold value (ITH), wherein the overcurrent protection circuit (30, 60, 60a) comprises: a transistor (M31 , M61), an induction coil (L31, L61), a rectifier (D31, D61), a current detector (32, 62) which generates a current detection signal (Is) as a function of the lamp current ( ILD), and an overcurrent protection controller (34, 64, 64a) which controls the ON / OFF state of the transistor (M31, M61) based on the current detection signal (Is) and on the overcurrent threshold value (ITH), the transistor (M31, M61), the induction coil (L31, L61) and the rectifier (D31, D61) are arranged in a T-shape.
    [0002]
    The illumination circuit (10) according to claim 1, wherein if the current detection signal (Is) exceeds an upper threshold value (ITHH) which is determined according to the overcurrent threshold value (ITH). the overcurrent protection controller (34) switches the transistor (M31) to the BLOCKED state, and if the current detection signal (Is) drops below a lower threshold value (ITHL) which is determined according to the overcurrent threshold value (ITH), the overcurrent protection controller (34) switches the transistor (M31) to the ON state.
    [0003]
    The illumination circuit (10) according to claim 2, wherein the overcurrent protection controller (34) comprises: a hysteresis comparator (38) which receives the current detection signal (Is) on a first terminal input thereof, receives a predetermined threshold value voltage (VTH) on a second input terminal thereof, and generates a protection signal (Socp) indicating the result of the comparison, and an amplifier (42), which controls the transistor (M31) according to the protection signal (Socp).
    [0004]
    The illumination circuit (10, 10a) according to claim 1, wherein if the current detection signal (Is) exceeds a threshold value level which is determined according to the overcurrent threshold value (ITH). the overcurrent protection controller (64) immediately switches the transistor (M61) to the BLOCKED state, and if the current detection signal (Is) drops below the threshold value level, the protection controller against overcurrent (64) switches the transistor (M61) to the ON state after a predetermined delay time (t) has elapsed.
    [0005]
    The illumination circuit (10, 10a) according to claim 4, wherein the overcurrent protection controller (64) comprises a comparator (66) which receives the current detection signal (Is) on a first terminal input signal, which receives a predetermined threshold value voltage on a second input terminal thereof, and generates a protection signal (Socp) which is set when the current detection signal (Is) exceeds the threshold value voltage, and a first sequencer circuit (68) which delays an edge, corresponding to the transition of the delay time (t) of a level set to a canceled level, of the protection signal (SOCP). .
    [0006]
    The illumination circuit (10) according to any one of claims 1 to 5, wherein: the transistor (M31) and the induction coil (L31) are arranged in series between the positive output of the circuit of etching (20) and the positive electrode of the light source (2), and the rectifier (D31) is disposed between (i) the point of connection between the transistor (M31) and the induction coil (L31) and (ii) a power source line (Lp) which connects the negative output of the driver (20) and the negative electrode of the light source (20).
    [0007]
    The illumination circuit (10) of claim 3, wherein the transistor (M31 is a p-channel MOSFET) and the overcurrent protection controller (34) further comprises a voltage source (44) receiving a voltage (VouT) from the driving circuit (20), which generates a voltage which is obtained by shifting the received voltage by a specific value on the low potential side, and which delivers the generated voltage (VL) to a source terminal supplying the lower side of the driver (42).
    [0008]
    The lighting circuit (10a) according to any one of claims 1 to 5, wherein the transistor (M61) and the induction coil (L61) are arranged in series between the negative output of the driving circuit ( 20) and the negative electrode of the light source (2); and the rectifier (D61) is disposed between (i) the point of connection between the transistor (M61) and the induction coil (L61) and (ii) a power source line (Lp) which connects the positive output from the driving circuit (20) to the positive electrode of the light source (2).
    [0009]
    The illumination circuit (10a) according to any one of claims 1 to 8, wherein the overcurrent protection controller (64a) comprises a LOCK latch circuit (70) which secures the transistor (M61) in the BLOCKED state when a state remains for a predetermined duration (i2) where the transistor (M61) makes repeated switching between the PASSING and BLOCKED states.
    [0010]
    The illumination circuit (10a) of claim 9, wherein the LATCH latch circuit (70) monitors a signal to request PASSER / BLOCK switching of the transistor (M61).
    [0011]
    The illumination circuit (10a) according to any one of claims 9 to 10, wherein the LATCH latch circuit (70) comprises a switching detector (72) which generates a switching detection signal. (S11) which adopts a first state when the transistor (M61) is set in the ON state, and a second state when the transistor (M61) repeatedly switches between the PASSING and BLOCKED states; a second sequencer circuit (74) which positions a suspension signal (S12) when the second state of the switching detection signal (S11) has continued for the specific time (r2), and a forced LOCK circuit (78). ) that forcibly switches the transistor (M61) to the BLOCKED state when the suspend signal (S12) is set.
    [0012]
    The illumination circuit (10, 10a) according to any one of claims 1 to 11, further comprising an abnormality detector (100) which optically monitors the light source (2) and which positions a light source signal. abnormality detection (S20) when the intensity of the light source (20) exceeds a permitted level in a low luminance mode in which the light source (2) is illuminated at a lower intensity than the normal level, in wherein the transistor (M31, M61) is switched to the ON state when the abnormality detection signal (S20) is set.
    [0013]
    A lighting circuit (10b) for a light source (2), the lighting circuit (10b) comprising: a driver (20) which supplies energy to the light source (2) ); an abnormality detector (100) which optically monitors the light source (2) and which positions an abnormality detection signal (S20) when the intensity of the light source (20) exceeds a permitted level in a low luminance mode in which the light source (2) is illuminated at a lower intensity than a normal level; and a protection circuit (110) which limits the supply of the light source (2) from the driver (20) when the abnormality signal (S20) is set. 35
    [0014]
    The illumination circuit (10b) according to claim 13, further comprising: an emission light detector (102) which optically detects whether or not the light source (2) is normally lit, wherein Anomaly detector (100) sets the abnormality detection signal (S20) when the emission light detector (102) indicates normal illumination in the low luminance mode.
    [0015]
    A vehicle lamp (1, 1a, 1b) comprising: a light source (2); and the lighting circuit (10, 10a, 10b) according to any one of claims 1 to 14 which drives the light source (2). 10
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    法律状态:
    2016-08-05| PLFP| Fee payment|Year of fee payment: 2 |
    2017-07-28| PLFP| Fee payment|Year of fee payment: 3 |
    2018-08-01| PLFP| Fee payment|Year of fee payment: 4 |
    2018-09-21| PLSC| Publication of the preliminary search report|Effective date: 20180921 |
    2019-08-20| PLFP| Fee payment|Year of fee payment: 5 |
    2020-07-28| PLFP| Fee payment|Year of fee payment: 6 |
    2021-07-27| PLFP| Fee payment|Year of fee payment: 7 |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2014187991|2014-09-16|
    JP2014263103|2014-12-25|
    JP2015147799A|JP6591814B2|2014-09-16|2015-07-27|Lighting circuit and vehicle lamp using the same|
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