JP2016068707A - Lighting circuit and vehicular lighting fixture using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting circuit enabling a preferable gradually changing lighting in a low cost.SOLUTION: A control voltage generation part 30, when instructed to start lighting a light source 2, generates a control voltage Vthat increases with time. A drive circuit 20 supplies a lamp current Icorresponding to the control voltage Vto the light source. A potential of one end of a capacitor C11 is fixed, and the voltage between its both ends is the control voltage V. A charging circuit 32 supplies a variable charging current Ic to the capacitor C11. The charging circuit 32 reduces the charging current Ic more as the control voltage Vbecomes greater.SELECTED DRAWING: Figure 2

Description

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

  Conventionally, halogen lamps and HID (High Intensity Discharge) lamps have been mainstream as light sources for vehicle lamps, particularly headlamps, but in recent years they have been replaced by LEDs (light-emitting diodes) and laser diodes (semiconductor lasers). Development of a vehicular lamp using a semiconductor light source such as

  The human eye has a logarithmic characteristic with respect to ambient brightness, and therefore, the darker the environment, the more sensitive to changes in brightness. When the lamp brightness is gradually increased (gradual lighting), when the lamp light quantity is small, the degree of change in the light quantity decreases, and as the lamp light quantity increases, Natural lighting is possible. FIG. 1A shows a desirable waveform (referred to as an ideal waveform) of the amount of light at the time of turning on / off. Similarly, when the brightness of the lamp is gradually reduced (gradual light extinction), the degree of change in the amount of light is increased when the amount of light in the lamp is large, and the degree of change in the amount of light is reduced as the amount of light in the lamp is reduced. Is preferred.

JP 2004-241142 A Japanese Patent Laid-Open No. 10-335074 JP 2013-69448 A

In order to change the amount of light according to the ideal waveform of FIG. 1A, a control voltage _VCNT having the ideal waveform of FIG. 1A is generated, and a current corresponding to the control voltage _VCNT is supplied to the semiconductor light source. It is necessary to supply. However, the control voltage _VCNT having the ideal waveform shown in FIG. 1A can be generated by using a microcomputer or the like, but a microcomputer, a D / A converter, or the like is required, and the cost of the circuit increases.

On the other hand, if you want to generate a voltage waveform that increases or decreases with time in an analog circuit, charge the capacitor using a constant current source and take out the voltage across the capacitor, or charge the capacitor using a resistor. A method of taking out the voltage between both ends of the capacitor is widely used. However, when a combination of a constant current source and a capacitor is used, the slope of the control voltage _VCNT generated in the capacitor is constant as shown in FIG. 1B, and the ideal waveform in FIG. 1A cannot be obtained. . When a combination of a resistor and a capacitor is used, the control voltage V _CNT generated in the capacitor changes exponentially according to the CR time constant as shown in FIG. An ideal waveform cannot be obtained.

  The present invention has been made in such a situation, and one of the exemplary purposes of an embodiment thereof is to provide a lighting circuit capable of preferably performing gradual change lighting at low cost.

  One embodiment of the present invention relates to a lighting circuit for a light source. The lighting circuit includes a control voltage generation unit that generates a control voltage that increases with time when a lighting start of the light source is instructed, and a drive circuit that supplies a lamp current corresponding to the control voltage to the light source. The control voltage generator is a capacitor in which a potential at one end is fixed and a voltage between both ends is a control voltage, and a charging circuit that supplies a variable charging current to the capacitor, and the control voltage reaches a predetermined voltage value. And a charging circuit that increases the charging current as the control voltage increases.

  According to this aspect, the period until the control voltage reaches a predetermined voltage value, that is, the period until it reaches the predetermined light amount, the charging current increases as the control voltage increases, that is, the light amount increases. Ascending rate, that is, the rate of increase in the amount of light increases, and preferable gradual change lighting is possible.

  The charging circuit may include a current mirror circuit whose output side is connected to a capacitor, and a variable impedance circuit which is connected to the input side of the current mirror circuit and whose impedance decreases as the control voltage increases.

  The charging circuit may include a current mirror circuit whose output side is connected to a capacitor, and a variable current source which is connected to the input side of the current mirror circuit and whose current amount increases as the control voltage increases.

The charging circuit includes a current mirror circuit whose output side is connected to a capacitor, a first resistor connected to the input side of the current mirror circuit, a first transistor and a second transistor provided in series in a path parallel to the first resistor. A signal corresponding to the control voltage may be input to the control terminal of the first transistor.
In this case, in addition to the current mirror circuit, it is possible to perform gradual change lighting with a simple configuration of one transistor and two resistance elements and a small circuit area, and it is possible to reduce costs because an operational amplifier is unnecessary.

The charging circuit is provided between a power source line and a control terminal of the first transistor, a third resistor provided between the control terminal of the first transistor and the ground line, and a control voltage is input to the control terminal, A second transistor having a polarity complementary to the one transistor may be further included.
In this case, by adding the third resistor and the second transistor, the voltage between the base emitters (between the gate and source) of the first transistor and the second transistor cancels out. Therefore, a preferable waveform is obtained even in a region where the control voltage is low. Can be obtained.

The charging circuit is connected to a capacitor, a first current source that sources a first current to the capacitor, and a second current source that is connected to the capacitor and sinks a second current from the capacitor. And a second current source that reduces the two currents.
The capacitor is charged with a differential current between the first current and the second current. Therefore, as the control voltage increases, the differential current increases, and gradually changing lighting is possible.

  The charging circuit includes a current mirror circuit whose output side is connected to one end of the capacitor, a first resistor connected to the input side of the current mirror circuit, and a first transistor provided in series between one end of the capacitor and the ground line And a second resistor, a third resistor provided between the control terminal of the first transistor and the ground line, a fourth resistor having one end connected to the power supply line, and provided between the fourth resistor and the third resistor. And a second transistor having a control voltage input to the control terminal.

The lighting circuit may further include a discharge resistor and a discharge transistor connected in series so as to form a discharge path parallel to the capacitor. The discharging transistor and the charging circuit may be configured to be switched on and off in accordance with a lighting instruction signal from the outside.
When the light is turned off, the charging circuit is turned off and the discharging transistor is turned on, so that the control voltage can be gradually lowered with a preferable waveform, and the gradually changing light can be turned off.

The lighting circuit may further include a comparison circuit that compares a voltage corresponding to the control voltage with a predetermined threshold voltage, and may be configured to output a lamp current forced stop signal indicating the comparison result.
When the laser diode is driven by the comparison circuit, it can be detected that the control voltage is smaller than the threshold value corresponding to the oscillation threshold current of the laser diode. By referring to the current forced stop signal, it is possible to prevent a wasteful current from flowing in the laser diode in the non-oscillation state.

  Another aspect of the present invention relates to a vehicular lamp. The vehicular lamp may include a light source and any one of the lighting circuits described above that drive the light source.

  According to an aspect of the present invention, preferable gradual change lighting is possible at low cost.

FIGS. 1A to 1C are diagrams showing light intensity waveforms when the light is turned on and off. It is a circuit diagram which shows the basic composition of the vehicle lamp which concerns on embodiment. FIGS. 3A and 3B are circuit diagrams illustrating a specific configuration example of the control voltage generation unit. 4A and 4B are specific configuration examples of the control voltage generation unit. FIGS. 5A and 5B are operation waveform diagrams of the control voltage generation unit in FIGS. 4A and 4B, respectively. 6A and 6B are circuit diagrams showing another configuration of the control voltage generation unit. FIGS. 7A to 7C are diagrams illustrating a dimming method that can be combined with the control voltage generation unit. It is a circuit diagram of the control voltage generation part which supports gradual change lighting in addition to gradual change lighting. It is a figure which shows the electric current characteristic of a laser diode. It is a circuit diagram of the control voltage generation part which concerns on a modification. It is a perspective view of a lamp unit provided with the vehicular lamp concerning an embodiment.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected to each other in addition to the case where the member A and the member B are physically directly connected. It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as their electric It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

  Further, in this specification, electrical signals such as voltage signals and current signals, or symbols attached to circuit elements such as resistors and capacitors indicate the respective voltage values, current values, resistance values, and capacitance values as necessary. It shall represent.

  FIG. 2 is a circuit diagram showing a basic configuration of the vehicular lamp 1 according to the embodiment. The vehicular lamp 1 includes a lighting circuit 10 and a light source 2. The light source 2 is a semiconductor light source such as an LED or a laser diode. The lighting circuit 10 supplies a lamp current corresponding to the target luminance to the light source 2 to cause the light source 2 to emit light.

The lighting circuit 10 includes a control voltage generation unit 30 and a drive circuit 20, and performs gradual lighting that gradually increases the luminance when the light source 2 transitions from a light-off state to a light-on state. The drive circuit 20 receives the battery voltage V _BAT from the battery 4 via the switch 6 and supplies the lamp current I _LD corresponding to the control voltage V _CNT to the light source 2. The configuration of drive circuit 20 is not particularly limited. For example, it is configured by a DC / DC converter that boosts or lowers voltage _VBAT from the battery. The dimming method by the drive circuit 20 is not particularly limited, and analog dimming for controlling the current amount may be performed, or PWM adjustment for changing the on / off time ratio while keeping the current amount (amplitude) constant. You may do light.

The control voltage generation unit 30 generates a control voltage _VCNT and supplies it to the drive circuit 20. When the start of lighting of the light source 2 is instructed, the control voltage generation unit 30 increases the control voltage _VCNT with time. The control voltage generation unit 30 includes a capacitor C11 and a charging circuit 32. For example, in the off state, the power supply voltage V _CC of the power supply line is zero, the lighting is instructed, when the switch 6 is turned on the power supply voltage V _CC is increased toward a predetermined level (e.g. 3.5V or 5V).

One end of the capacitor C11 is grounded, and its potential is fixed. The voltage across the capacitor C11 is the control voltage _VCNT . The charging circuit 32 supplies a variable charging current Ic to the capacitor C11. Charging circuit 32, the control voltage _{V CNT} is to reach a predetermined voltage value _{V MAX,} the control voltage _{V CNT} increases the charging current Ic as large. The charging circuit 32 can be understood as a V / I conversion circuit (transconductance circuit) that converts the control voltage _VCNT into a current Ic corresponding thereto.

The above is the basic configuration of the lighting circuit 10. According to the lighting circuit 10, the period until the control voltage V _CNT reaches the predetermined voltage value V _MAX , that is, the period until it reaches the predetermined light amount, the larger the control voltage V _CNT , that is, the larger the light amount, The charging current Ic is increased, and therefore, the rate of increase of the control voltage _VCNT , that is, the rate of increase of the amount of light is increased, and preferable gradual change lighting as shown in FIG. The present invention extends to various circuits grasped as the block diagram of FIG. 2, but some specific examples of the configuration will be described below.

3A and 3B are circuit diagrams illustrating a specific configuration example of the control voltage generation unit 30. FIG. The charging circuit 32 in FIG. 3A includes a current mirror circuit 34 and a variable current source 36. The output side of the current mirror circuit 34 is connected to the capacitor C11. The variable current source 36 is connected to the input side of the current mirror circuit 34, and is configured such that the current amount Ia increases as the control voltage _VCNT increases. The charging current Ic of the capacitor C11 is given by Ic = K × Ia using the mirror ratio (current amplification factor) K of the current mirror circuit 34.

The configuration of the current mirror circuit 34 is not particularly limited. For example, the current mirror circuit 34 includes a pair of PNP-type bipolar transistors whose bases are connected in common. In this configuration, the control voltage V _CNT fluctuates with a predetermined voltage value V _MAX ≈V _CC −V _BE as an upper limit, and after reaching the voltage value V _MAX , the predetermined voltage value V _MAX is maintained. . V _BE is the base-emitter voltage (≈0.6 V) of the bipolar transistor. The emitter resistors R21 and R22 are inserted to increase the accuracy and stability of the current mirror circuit, but may be omitted. A P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) may be used instead of the bipolar transistor.

The control voltage generation unit 30 can also grasp as shown in FIG. A variable impedance circuit 38 is connected to the input side of the current mirror circuit 34. The variable impedance circuit 38 is configured such that the impedance decreases as the control voltage _VCNT increases. The current Ia is given by the following equation using the base-emitter voltage V _BE of the transistor Q21 and the impedance Rv of the variable impedance circuit 38.
V _CC = Ia × (R21 + Rv) + V _BE
Therefore, the current Ia is given by the following equation, and the current Ia increases as the impedance Rv decreases.
Ia = (V _CC −V _BE ) / (R21 + Rv)
When R21 << Rv, the following approximate expression holds.
Ia≈ (V _CC −V _BE ) / Rv

4A and 4B are specific configuration examples of the control voltage generation unit 30. FIG. The variable current source 36 of FIG. 4A includes a first resistor R11, a second resistor R12, and a first transistor Q11. The first resistor R11 is connected to the input side of the current mirror circuit 34. The first transistor Q11 and the second resistor R12 are provided in series on a path parallel to the first resistor R11. The first transistor Q11 is an NPN bipolar transistor, and a signal corresponding to the control voltage _VCNT is input to its control terminal (base). The first transistor Q11 may be an N-channel MOSFET.

Assuming that the voltage between the base and the emitter of the first transistor Q11 is V _BE , the voltage V _R12 across the second resistor _R12 is V _CNT −V _BE . Therefore, the current I _Q11 flowing through the first transistor Q11 and the second resistor R12 is given by the following equation, and thus the current I _Q11 increases substantially linearly with respect to the control voltage _VCNT .
_{I Q11 = (V CNT -V BE} ) / R12

Input current Ia of the current mirror circuit 34 is a current _{I R11} that flows through the first resistor R11 total current _{I Q11} of the first transistor Q11. If the resistance value of the resistor R21 can be ignored, I _R11 = (V _CC −V _BE ) / R11, and the following equation is obtained.
Ia = (V _CC −V _BE ) / R11 + (V _CNT −V _BE ) / R12
Since the first term on the right side can be regarded as a constant, the current Ia changes substantially linearly with respect to the control voltage _VCNT .

FIG. 5A is an operation waveform diagram of the control voltage generation unit 30 in FIG. Since the first transistor Q11 is off in the state of V _BE <0.6V, immediately after the start of lighting (t≈0), Ia = I _R11 and the control voltage V _CNT increases with a substantially constant slope. When V _CNT > 0.6 V at time t1, a current starts to flow between the collector and emitter of the first transistor Q11, and the current Ia starts to increase linearly with respect to the control voltage V _CNT . As a result, the higher the control voltage V _CNT , that is, the higher the amount of light, the faster the change speed, and the preferable gradual change lighting shown in FIG. When the control voltage V _CNT reaches a predetermined voltage value V _MAX , the light amount is maintained at a predetermined amount corresponding to the voltage value V _MAX .

According to the control voltage generation unit 30 of FIG. 4A, in addition to the current mirror circuit 34, two resistors and one transistor are used, and a low-cost, small area and preferable control voltage without using an operational amplifier. A waveform of _VCNT can be generated.

  It can be understood that the first resistor R11, the second resistor R12, and the first transistor Q11 correspond to the variable impedance circuit 38 of FIG. 4B.

The variable current source 36 of FIG. 4B further includes a second transistor Q12 and a third resistor R13 in addition to that of FIG. Third resistor R13 is provided between the control terminal (base) of the power supply line _{V CC} and the first transistor Q11. The second transistor Q12 is a PNP type, that is, has a polarity complementary to that of the first transistor Q11, and is provided between the control terminal of the first transistor Q11 and the ground line. The control voltage _VCNT is input to the base of the second transistor Q12.

FIG. 5B is an operation waveform diagram of the control voltage generation unit 30 in FIG. In FIG. 4B, the voltage V _R12 across the second resistor R12 is V _CNT + V _BE −V _BE = V _CNT , and the current I _{Q11 of the} transistor _Q11 is I _Q11 = V _CNT / R12. Therefore, since the current Ia begins to increase immediately after the start of lighting, the waveform in the region where the light amount is small (V _CNT ≈0) can be improved as compared with the configuration of FIG.

FIG. 6A is a circuit diagram illustrating another configuration of the control voltage generation unit 30. The charging circuit 32 includes a first current source CS1 and a second current source CS2. The first current source CS1 sources the first current I _CS1 to the capacitor C11. The second current source CS2 sinks the second current _{I CS2} from the capacitor C11. The second current source CS2 in other words, draw some or all of the charging current (first _{current) I CS1} to the capacitor C11 from the first current source CS1 to another path. The second current source CS2 is configured to decrease the second current _ICS2 as the control voltage _VCNT increases.

In this case, the capacitor C11 is charged with the differential current Ic (= I _CS1 −I _CS2 ) between the first current I _CS1 and the second current I _CS2 , and thus the differential current Ic increases as the control voltage V _CNT increases. Thus, the gradual change lighting as shown in FIG.

FIG. 6B is a specific circuit diagram of the control voltage generation unit 30 in FIG. The first current source CS1 includes a current mirror circuit 34 and a first resistor R31. If the voltage drop of R21 is ignored, the first current _ICS1 can be regarded as substantially constant.
I _CS1 ≒ (V _CC -V _BE ) / R31

The second current source CS2 includes a first transistor Q31, a second transistor Q32, a second resistor R32, a third resistor R33, and a fourth resistor R34. The first transistor Q31 and the second resistor R32 are provided in series between one end of the capacitor C11 and the ground line. The third resistor R33 is provided between the control terminal (base) of the first transistor Q31 and the ground line. One end of the fourth resistor R34 is connected to the power supply line. The second transistor Q32 is provided between the fourth resistor R34 and the third resistor R33, and a control voltage _VCNT is input to a control terminal (base) thereof.

The voltage (voltage drop) V _R34 across the fourth resistor R34 and its current I _R34 are given by the following equations.
V _R34 = V _CC- (V _CNT + V _BE )
I _R34 = V _R34 / R34 = {V _CC − (V _CNT + V _BE )} / R 34

The base voltage of the transistor Q31 (the voltage drop of the third resistor R33) is V _R33 = I _R34 × R33, and the voltage drop V _R32 of the second resistor _R32 is V _R32 = V _R33 -V _BE .
Therefore, the current _ICS2 flowing through the first transistor Q31 and the second resistor R32 is given by the following equation.
I _CS2 = (V _R33 −V _BE ) / R32 = (I _R34 × R33−V _BE ) / R32
= {(V _CC -V _CNT -V _BE ) / R34 × R33-V _BE } / R32

Therefore, as the control voltage V _CNT increases, the current I _CS2 decreases and the charging current I _C increases.

The configuration example of the control voltage generation unit 30 has been described above. Next, dimming control based on the control voltage _VCNT generated by the control voltage generator 30 will be described. 7A to 7C are diagrams illustrating a dimming method that can be combined with the control voltage generation unit 30. FIG. FIG. 7A shows the drive circuit 20. The drive circuit 20 includes a step-down DC / DC converter 22, a current sensor 24, and a pulse modulator 26. The drive circuit 20 controls the light amount of the light source 2 by analog dimming. Current sensor 24 includes a sensing resistor Rs which is provided on a path of lamp current I _LD, it amplifies the voltage drop across the sense resistor Rs, an amplifier AMP for generating a current detection signal I _S. Pulse modulator 26, as the current detection signal _{I S} is coincident with the control voltage _{V CNT,} switching the DC / DC converter 22.

The configuration of the pulse modulator 26 is not particularly limited, and a known technique may be used. For example, the pulse modulator 26 includes an error amplifier 50, a PWM comparator 52, an oscillator 54, and a driver 56. The error amplifier 50 amplifies an error between the current detection signal _IS and the control voltage _VCNT . The PWM comparator 52 compares the error signal V _ERR with the triangular wave or sawtooth wave periodic signal V _OSC1 generated by the oscillator 54 and converts it into a pulse signal S _PWM having a duty ratio corresponding to the error signal V _ERR . The driver 56 switches the switch M11 of the DC / DC converter 22 according to the pulse signal _{S PWM.}

According to the driving circuit 20 can generate the lamp current _{I LD} which is proportional to the control voltage _{V CNT.} Then, by changing the control voltage V _CNT according to the waveform shown in FIG. 1A, preferable gradual lighting can be realized.

The drive circuit 20 in FIG. 7B performs analog dimming as in FIG. The drive circuit 20 includes a current source 60 and a DC / DC converter 22 provided in series with the light source 2. A driving voltage generated by the DC / DC converter 22 is supplied to the anode of the light source 2. The current source 60 is a V / I conversion circuit, and converts the control voltage _VCNT into a lamp current _ILD corresponding thereto. For example, current source 60 includes a transistor Q41 and a resistor R41. The control voltage _VCNT is input to the control terminal (base) of the transistor Q41. The lamp current I _LD generated by the current source 60 is I _LD = (V _CNT −V _BE ) / R 41.

The drive circuit 20 in FIG. 7C controls the light amount of the light source 2 by PWM dimming (also referred to as burst dimming). The drive circuit 20 includes a current source 60, a burst signal generator 62, and a dimming switch 64. The burst signal generator 62 receives the control voltage _VCNT and generates a dimming pulse S1 having a duty ratio proportional thereto. The burst signal generator 62 includes, for example, an oscillator 66 and a comparator 68. The oscillator 66 generates a sawtooth wave or triangular wave periodic signal V _OSC2 having a frequency of about several tens of Hz to several hundreds of Hz. The comparator 68 compares the periodic signal V _OSC and the control voltage _VCNT , and generates a dimming pulse S1 having a duty ratio corresponding to the control voltage _VCNT . The current source 60 generates a certain amount of lamp current _ILD . The dimming switch 64 is turned on and off in accordance with the dimming pulse signal S1, thereby realizing PWM dimming. Note dimmer switch 64 is not necessarily provided on a path of lamp current I _LD, built to the current source 60, on the current source 60 may be switchable off.

So far, the gradual change lighting has been described, but the gradual change extinction will be described below. FIG. 8 is a circuit diagram of the control voltage generation unit 30a that supports gradually changing lighting in addition to gradually changing lighting. The control voltage generator 30a changes the control voltage _VCNT according to the lighting instruction signal S30. The lighting instruction signal S30 corresponds to lighting at a low level and turning off at a high level. The lighting instruction signal S30 is given from a host microcontroller or the like.

  The control voltage generator 30a includes a discharge transistor Q51, a discharge resistor R51, a charge stop transistor Q52, and a turn-off control circuit 70 in addition to the control voltage generator 30 shown in FIG. 3A or 3B.

  Discharging transistor Q51 and discharging resistor R51 are connected in series to form a discharging path from capacitor C11 to ground. The discharging transistor Q51 is off when the lighting instruction signal S30 instructs to turn on, and is turned on when turning off. For example, the lighting instruction signal S30 divided by the resistors r60 and r61 is input to the base of the discharging transistor Q51.

The charge stopping transistor Q52 is provided to operate the charging circuit 32 when the lighting instruction signal S30 instructs to turn on, and to stop the charging circuit 32 when instructing to turn off. Charging stop transistor Q52 is specifically provided between the base and the power supply line V _CC of the transistors Q21, Q22, turns on when (high level) the lighting instruction signal S30 instructs the off, current mirror circuit 34 Stop.

  The extinguishing control circuit 70 switches on / off the charging stop transistor Q52 in response to the lighting instruction signal S30. For example, the extinguishing control circuit 70 includes resistors r62, r63, r64, r65 and a transistor q53, but the configuration is not particularly limited.

Next, the operation of the control voltage generation unit 30a will be described.
While the lighting instruction signal S30 is at a high level, both the charge stop transistor Q52 and the discharge transistor Q51 are on, and the control voltage _VCNT is 0V. When the lighting instruction signal S30 becomes low level, both the transistors Q52 and Q51 are turned off. The operation at this time is the same as that of the control voltage generation unit 30 of FIG. 3, and the control voltage _VCNT increases in accordance with the waveform of FIG. 5A or 5B, and gradually changing lighting is performed.

  Thereafter, when the lighting instruction signal S30 is switched to the high level in order to turn off the lamp, both the transistors Q52 and Q51 are turned on. As a result, the charging circuit 32 stops, the charging current Ic becomes zero, and the capacitor C11 is discharged through the resistor R51 and the transistor Q51. The discharge speed at this time is given by a CR time constant τ (= C11 × R51), and preferable gradual light extinction can be realized.

Subsequently, a modification example in which the laser diode 3 is used as a light source will be described. FIG. 9 is a diagram showing current characteristics of the laser diode 3. The laser diode 3 does not oscillate in a region where the lamp current I _LD is lower than the threshold current I _TH . That is, supplying lamp current I _LD smaller than threshold current I _TH to laser diode 3 consumes useless power.

FIG. 10 is a circuit diagram of a control voltage generation unit 30b according to a modification. When the control voltage V _CNT becomes lower than the threshold voltage V _TH corresponding to the threshold current I _TH , the control voltage generation unit 30b can output a signal (lamp current forced stop signal) S31 notifying the outside. Composed. In gradual light extinction in which the control voltage _VCNT is lowered by discharge according to the CR time constant, it is difficult to completely define the timing when the light is extinguished. Therefore, by adding the control voltage generation unit 30b, it is possible to accurately define the timing at which the light is completely turned off and to notify the outside.

Control voltage generation unit 30b includes a comparison circuit 72 that compares a detection signal corresponding to control voltage _VCNT of capacitor C11 with a predetermined threshold value. FIG. 10 shows a configuration in which a comparison circuit 72 is added to the control voltage generation unit 30 of FIG. Specifically, the comparison circuit 72 compares the base voltage V _BQ11 (= V _CNT + V _BE ) of the transistor Q11 with a predetermined threshold voltage V _TH1 . For example, the comparison circuit 72 includes a transistor q71 and resistors r71, r72, r73. In this case, when the base voltage (V _CNT + V _BE ) × r72 / (r71 + r72) of the transistor q71 falls below the threshold value, the transistor q71 is turned off, and the lamp current forced stop signal S31 becomes high level. Top controller (not shown), the lamp current forced stop signal S31 transits to the high level, and forcibly zeros the lamp current I _LD. Alternatively the drive circuit 20 of FIG. 2, the lamp current forced stop signal S31 transits to the high level, and forcibly zeros the lamp current I _LD. According to this modification, wasteful power consumption can be reduced. Naturally, the discharge transistor Q51, the discharge resistor R51, the charge stop transistor Q52, and the turn-off control circuit 70 of FIG. 8 may be added to the control voltage generation unit 30 of FIG. The comparison circuit 72 may be configured by a voltage comparator using an operational amplifier.

  Finally, the use of the vehicular lamp 1 will be described. FIG. 11 is a perspective view of a lamp unit (lamp assembly) 500 including the vehicular lamp 1 according to the embodiment. The lamp unit 500 includes a transparent cover 502, a high beam unit 504, a low beam unit 506, and a housing 508. The vehicle lamp 1 described above can be used for the high beam unit 504, for example. The vehicular lamp 1 includes one or a plurality of light sources 2. Instead of or in addition to the high beam unit 504, the vehicular lamp 1 may be used for the low beam unit 506.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Vehicle lamp, 2 ... Light source, 3 ... Laser diode, 4 ... Battery, 6 ... Switch, 10 ... Lighting circuit, 20 ... Drive circuit, 22 ... DC / DC converter, 24 ... Current sensor, 26 ... Pulse modulator , 30 ... control voltage generator, C11 ... capacitor, 32 ... charging circuit, 34 ... current mirror circuit, 36 ... variable current source, 38 ... variable impedance circuit, 50 ... error amplifier, 52 ... PWM comparator, 54 ... oscillator, 56 DESCRIPTION OF SYMBOLS ... Driver 60 ... Current source 62 ... Burst signal generator 64 ... Dimming switch 70 ... Light-off control circuit 72 ... Comparison circuit R11 ... First resistor R12 ... Second resistor R13 ... Third resistor Q11 ... first transistor, Q12 ... second transistor, CS1 ... first current source, CS2 ... second current source, R31 ... first resistor, R32 ... second resistor, R 3 ... 3rd resistor, R34 ... 4th resistor, Q31 ... 1st transistor, Q32 ... 2nd transistor, Q51 ... Discharge transistor, R51 ... Discharge resistor, Q52 ... Charge stop transistor, 70 ... Light-off control circuit, 500 ... Lamp unit, 502. Cover, 504. High beam unit, 506. Low beam unit, 508.

Claims (10)

A light source lighting circuit,
When an instruction to start lighting the light source is given, a control voltage generator that generates a control voltage that increases with time,
A drive circuit for supplying a lamp current corresponding to the control voltage to the light source;
With
The control voltage generator is
A capacitor in which a potential at one end is fixed and a voltage between both ends is the control voltage;
A charging circuit for supplying a variable charging current to the capacitor, the charging circuit increasing the charging current as the control voltage increases until the control voltage reaches a predetermined voltage value;
A lighting circuit comprising: The charging circuit is
A current mirror circuit whose output side is connected to the capacitor;
A variable impedance circuit connected to the input side of the current mirror circuit, the impedance of which decreases as the control voltage increases;
The lighting circuit according to claim 1, comprising: The charging circuit is
A current mirror circuit whose output side is connected to the capacitor;
A variable current source connected to the input side of the current mirror circuit, the current amount of which increases as the control voltage increases;
The lighting circuit according to claim 1, comprising: The charging circuit is
A current mirror circuit whose output side is connected to the capacitor;
A first resistor connected to the input side of the current mirror circuit;
A first transistor and a second resistor provided in series in a path parallel to the first resistor;
4. The lighting circuit according to claim 1, wherein a signal corresponding to the control voltage is input to a control terminal of the first transistor. 5. The charging circuit is
A third resistor provided between a power supply line and the control terminal of the first transistor;
A second transistor provided between the control terminal of the first transistor and a ground line, the control voltage being input to the control terminal, and a second transistor having a polarity complementary to the first transistor;
The lighting circuit according to claim 4, further comprising: The charging circuit is
A first current source connected to the capacitor and sourcing a first current to the capacitor;
A second current source connected to the capacitor and sinking a second current from the capacitor, wherein the second current source decreases the second current as the control voltage increases;
The lighting circuit according to claim 1, comprising: The charging circuit is
A current mirror circuit whose output side is connected to one end of the capacitor;
A first resistor connected to the input side of the current mirror circuit;
A first transistor and a second resistor provided in series between one end of the capacitor and a ground line;
A third resistor provided between the control terminal of the first transistor and the ground line;
A fourth resistor having one end connected to the power line;
A second transistor provided between the fourth resistor and the third resistor and having the control voltage input to a control terminal;
The lighting circuit according to claim 1, comprising: A discharge resistor and a discharge transistor connected in series so as to form a discharge path in parallel with the capacitor;
The lighting circuit according to any one of claims 1 to 7, wherein the discharging transistor and the charging circuit are configured to be able to be switched on and off in accordance with a lighting instruction signal from the outside.   9. A comparison circuit for comparing a voltage corresponding to the control voltage with a predetermined threshold voltage is further provided, and a lamp current forced stop signal indicating a comparison result can be output. The lighting circuit in any one. A light source;
The lighting circuit according to any one of claims 1 to 9, which drives the light source;
A vehicular lamp characterized by comprising:

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