JP2018098165A - Lighting circuit and vehicular lamp - Google Patents

Abstract

A lighting circuit capable of switching light sources at high speed is provided.
A lighting circuit 200 controls turning on / off of a light source 102. The drive circuit 202 generates a drive current I _DRV to be supplied to the light source 102. The clamp circuit 210 clamps the voltage between both ends of the light source 102 to a clamp level in a period in which the light source 102 should be turned off. The clamp level is defined to be greater than zero and lower than the threshold voltage for turning on / off the light source 102.
[Selection] Figure 2

Description

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

  Light sources such as LDs (laser diodes) and LEDs (light emitting diodes) are used in various applications such as vehicular lamps, projectors, backlights for liquid crystal panels, illumination devices, and optical communication technologies.

FIG. 1 is a circuit diagram of a conventional lighting circuit. The lighting circuit 1100 includes a drive circuit 1102 and a bypass switch 1104. The drive circuit 1102 supplies the light source 1002 with a drive current I _DRV stabilized to a predetermined amount. The bypass switch 1104 is connected in parallel with the light source 1002.

When the bypass switch 1104 is OFF, the drive current I _DRV flows to the light source 1002, so that the light source 1002 emits light. When the bypass switch 1104 is on, the drive current I _DRV flows to the bypass switch 1104, and thus the light source 1002 is turned off. Therefore, by switching the bypass switch 1104, the light source 1002 can be switched on / off.

International Publication No. 2016/104319

  For example, when the light source is used as a vehicular lamp or a backlight, the light source 1002 is switched at a frequency that cannot be perceived by human eyes, and light control can be performed by changing the duty ratio. A switching frequency used for general PWM (Pulse Width Modulation) dimming is on the order of several tens of Hz to several hundreds of Hz, and can be realized in the lighting circuit 1100 of FIG.

  However, in the lighting circuit 1100 of FIG. 1, it is difficult to switch the light source 1002 at a frequency higher than several kHz.

  The present invention has been made in such a situation, and one of exemplary purposes of an embodiment thereof is to provide a lighting circuit capable of switching a light source at high speed.

  One embodiment of the present invention relates to a lighting circuit for a light source. The lighting circuit includes a driving circuit that generates a driving current to be supplied to the light source, and a clamp that is defined such that the voltage across the light source is higher than zero and lower than the threshold voltage for turning on / off in a period during which the light source should be turned off. A clamp circuit for clamping to a level.

The voltage across the light source during the lighting period is V _ON , and the clamp level is V _CL . In this aspect, since the voltage between both ends is clamped to the clamp level V _CL during the light source extinction period, the change width ΔV of the voltage between both ends when switching from the extinction to the lighting is V _ON −V _CL . By bringing the V _CL to the threshold voltage V _TH of the point off, it is possible to reduce the fluctuation width ΔV when switched from off to on, thus it is possible to light the light source in a short time. In addition, since the load fluctuation when viewed from the drive circuit can be reduced, the restriction on the design of the drive circuit can be relaxed.

The clamp circuit may immediately reduce the voltage across the light source to substantially zero in response to an instruction to turn off the light source and then clamp to the clamp level.
Thereby, the light source can be turned off in a short time after the light source is turned off.

The clamp circuit may include a first switch and a clamp resistor provided in series on a first path parallel to the light source. When the resistance value of the first path is R ₁ , the threshold voltage of the light source is V _TH , and the drive current is I _DRV , 0 <R ₁ × I _DRV <V _TH may be satisfied.

The clamp circuit may include a first switch provided on a first path parallel to the light source. When the resistance value of the first path is R ₁ , the threshold voltage of the light source is V _TH , and the drive current is I _DRV , 0 <R ₁ × I _DRV <V _TH may be satisfied.

The clamp circuit may further include a second switch provided on a second path parallel to the light source. The second switch may be turned on immediately after an instruction to turn off the light source, and may be turned off prior to the instruction to turn on the light source.
Thereby, switching from lighting to extinguishing can be performed at high speed.

  The clamp circuit is a shunt transistor provided between both ends of the light source, and a transistor control that generates a voltage at the control terminal of the shunt transistor so that the voltage between the both ends of the light source becomes a clamp level during a period when the light source should be turned off. And a circuit.

  The transistor control circuit may include a feedback circuit that brings the voltage across the light source close to the clamp level by feedback. By configuring a so-called shunt regulator with the feedback circuit and the shunt transistor, the voltage across the light source can be clamped.

  The transistor control circuit may include a constant voltage circuit provided between the control terminal of the shunt transistor and one end on the high potential side.

  The transistor control circuit further includes a third switch provided between the control terminal of the shunt transistor and one end on the low potential side of the light source, or between the control terminal of the shunt transistor and the low voltage terminal to which a predetermined low voltage is supplied. May be included. By turning on the third switch, the shunt transistor can be immediately turned off (or turned on), and the light source can be turned on (turned off) instantaneously.

  The transistor control circuit further includes a fourth switch provided between the control terminal of the shunt transistor and one end on the high potential side of the light source, or between the control terminal of the shunt transistor and a high voltage terminal to which a predetermined high voltage is supplied. May be included. By turning on the fourth switch, the shunt transistor can be immediately turned on (or turned off), and the light source can be turned off (lighted) instantaneously.

  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.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  Further, the description of this item (means for solving the problem) does not explain all the essential features of the present invention, and therefore a sub-combination of these described features can also be the present invention. .

  According to an aspect of the present invention, the light source can be switched at high speed.

It is a circuit diagram of the conventional lighting circuit. It is a block diagram of an illuminating device provided with the lighting circuit which concerns on embodiment. It is a figure which shows the I / V characteristic of a light source. FIG. 3 is an operation waveform diagram of the lighting circuit of FIG. 2. It is an operation | movement waveform diagram of the lighting circuit of FIG. It is an operation | movement waveform diagram of a lighting circuit provided with a 2nd function. FIG. 3 is a circuit diagram of a first configuration example of the lighting circuit of FIG. 2. FIG. 3 is a circuit diagram of a second configuration example of the lighting circuit of FIG. 2. FIGS. 9A and 9B are circuit diagrams showing a specific configuration example of the clamp circuit of FIG. FIGS. 10A to 10E are circuit diagrams showing modifications of the clamp circuit. FIG. 4 is a circuit diagram of a third configuration example of the lighting circuit of FIG. 2. FIG. 12 is a circuit diagram illustrating a first configuration example of the clamp circuit of FIG. 11. FIG. 13 is an operation waveform diagram of the clamp circuit of FIG. 12. FIG. 12 is a circuit diagram illustrating a second configuration example of the clamp circuit 210C of FIG. 11. FIGS. 15A to 15D are diagrams illustrating a vehicular lamp including a lighting circuit. FIGS. 16A and 16B are circuit diagrams of a vehicular lamp including a lighting circuit. It is a block diagram of an illuminating device provided with a several light source.

  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 block diagram of the lighting device 100 including the lighting circuit 200 according to the embodiment. The lighting device 100 includes a light source 102 and a lighting circuit 200. The light source 102, LED, LD, a semiconductor light source such as an organic EL, emits light at a brightness corresponding to the driving current (forward current) _{I F} supplied. The light source 102 may be an LED bar including a plurality of LEDs connected in series. The lighting circuit 200 generates a drive current I _DRV stabilized at a constant current (target current), supplies the drive current I _DRV to the light source 102 and turns off the light source 102 during a period in which the light source 102 should be turned on. In the period, the current flowing through the light source 102 is suppressed to be equal to or lower than the lighting threshold.

The lighting circuit 200 includes a drive circuit 202 and a clamp circuit 210. The clamp circuit 210 clamps the voltage V _F across the light source 102 to the clamp level V _CL during a period in which the light source 102 should be turned off. The clamp level V _CL is defined to be greater than zero and lower than the threshold voltage V _{TH for} turning on and off the light source 102. More specifically, the clamp circuit 210, a point enabled (activated) in response to the control signals S ₁ for instructing the turn off of the light source 102, disabled (inactivated) is switchably configured. Control signals S ₁ may be generated inside the lighting circuit 200 may be supplied from the outside.

Clamp circuit 210, a control signal S ₁ it is, becomes disabled when a first level (lighting level), the light source 102 and the driving circuit 202 enters a state that does not act electrically. The clamp circuit 210 may be in a disabled state and in a high impedance state.

Clamp circuit 210, a control signal _{S 1} is, becomes an enable state when it is in the second level (off level), the voltage across _{V F} of the light source 102 is clamped to the clamp level _{V CL.} This is called the first function.

FIG. 3 is a diagram illustrating the I / V characteristics of the light source 102. The horizontal axis voltage across the light source 102, that is, the forward voltage V _F, the vertical axis represents the forward current I _F. When the light source 102 is an LED, the forward current _IF is substantially zero in the region where the forward voltage V _F is lower than the on-voltage V _ON , and the light source 102 can be regarded as extinguished. In the forward voltage V _F is higher than the ON voltage V _ON region, the forward current I _F increases with the forward voltage V _F, the light source 102 emits light with luminance corresponding to the forward current I _F. Therefore, when the light source 102 is an LED, the threshold voltage V _TH can be associated with the _ON voltage V _ON .

Note that the threshold voltage V _TH is a boundary between the light-on state and the light-off state of the light source 102. The light-off state here does not require that the photons emitted from the light source 102 are completely zero. . For example, when the light quantity of the light source 102 is controlled in multiple gradations, a state in which a sufficiently smaller number of photons than the light quantity corresponding to 1LSB is emitted can be regarded as an extinguished state. Alternatively, a state in which fewer photons than the amount of light that can be perceived by humans can be regarded as a light-off state.

In FIG. 3, when V _ON = V _TH , the clamp level V _CL is set between 0 V and the on-voltage V _ON .

The above is the configuration of the lighting circuit 200. Next, the operation will be described.
FIG. 4 is an operation waveform diagram of the lighting circuit 200 of FIG. Prior to time t ₀ , the control signal S ₁ is at a lighting level (high level), and the clamp circuit 210 is in a disabled state (DIS). Forward current _{I F} of this time the light source 102 is equal to the driving current _{I DRV} for driving circuit 202 generates the light source 102 emits light with a brightness corresponding to the driving current _{I DRV.} The forward voltage V _F is a voltage level V _ON corresponding to the drive current I _DRV .

When the control signals _{S 1} at time _{t 0} is shifted to OFF level (low level), the clamp circuit 210 becomes the enable state (EN). The clamp circuit 210 is enabled, the voltage across (forward voltage) _{V F} of the light source 102 is clamped to the clamp level _{V CL.} Due to the operation delay of the clamp circuit 210, the forward voltage V _F decreases toward the clamp level V _CL with a certain slope, and the forward current I _F of the light source 102, that is, the luminance, also decreases with time. Difference of the driving current _{I DRV} and the forward current _{I F} of the light source 102 is generated, it is noted that flow to the clamp circuit 210.

When the forward voltage V _F crosses the threshold voltage V _{TH at} time t ₁ , the forward current _IF becomes zero and the light source 102 is turned off. Thereafter, the forward voltage _{V F} reaches the clamp level _{V CL} to time _{t 2, the} then to maintain the same voltage level.

When the control signals _{S 1} at time _{t 3} is shifted to the lighting level (high level), the clamp circuit 210 is disabled (DIS). The clamp circuit 210 is disabled, the clamping of the forward voltage _{V F} of the light source 102 is released, the drive current _{I DRV} flowing in the clamping circuit 210 in the OFF period, flows to the light source 102, the forward voltage _{V F} It is going to increase toward the original voltage level V _oN. Between V _CL <time _t 3 ~t ₄ is _V F _{<V TH,} the forward current _{I F} is substantially zero, the light source 102 is turned off.

Forward voltage _{V F} is a time _{t 4} after crossing the threshold voltage _{V TH,} first forward current _{I F} flows, the luminance of the light source 102 is increased. Then at time _{t 5,} all of the drive current _{I DRV} becomes to flow to the light source 102, the forward current _{I F} is equal to the driving current _{I DRV.}

  The above is the operation of the lighting circuit 200. The advantage of the lighting circuit 200 becomes clear by comparison with the lighting circuit 1100 of FIG. FIG. 5 is an operation waveform diagram of the lighting circuit 1100 of FIG.

Control signals _{S 1} prior to time _{t 10} is turned level (high level), the bypass switch 1104 is off, the driving current _{I DRV} for driving circuit 202 generates flows to the light source 1002, light source 1002, driving Light is emitted at a luminance corresponding to the current I _DRV . The forward voltage V _F is a voltage level V _ON corresponding to the drive current I _DRV .

When the control signals _{S 1} at time _{t 10} transitions to off level (low level), the bypass switch 1104 is turned on. Accordingly, the driving current _{I DRV} flowing in the light source 1002 flows through the bypass switch 1104, the forward current _{I F} decreases before.

When a forward voltage _{V F} crosses the threshold voltage _{V TH} at time _{t 11,} the forward current _{I F} becomes zero, the light source 1002 is turned off. Thereafter, the forward voltage _{V F} is reduced to zero (0V) at time _{t 12.}

When the control signal S ₁ transitions to the lighting level (high level) at time t ₁₃ , the bypass switch 1104 is turned off, and the drive current I _DRV that was flowing in the bypass switch 1104 during the extinguishing period flows to the light source 1002, and the forward voltage V _F increases toward the original voltage level V _ON . 0 _<Between time _t 13 _{~t 14} is V F _{<V TH,} the forward current _{I F} is substantially zero, the light source 1002 is turned off.

After the time _{t 14} to the forward voltage _{V F} crosses the threshold voltage _{V TH,} first forward current _{I F} flows, the luminance of the light source 1002 increases. Then at time _{t 15,} all of the drive current _{I DRV} becomes to flow to the light source 1002, the forward current _{I F} is equal to the driving current _{I DRV.}

The above is the operation of the lighting circuit 1100 in FIG. In the lighting circuit 1100 of FIG. 1, a period from time t ₁₃ when the control signal S ₁ transitions to the lighting level to time t ₁₄ when the forward voltage V _F reaches the threshold voltage V _TH (referred to as an unlit period). ) Τ ₀ and forward current _IF are zero, and the light source 1002 cannot be turned on.

As the cycle (switching cycle T _P ) of the control signal S ₁ becomes shorter, in other words, as the switching frequency becomes higher, the ratio of the lighting impossible period τ ₀ to the cycle T _P becomes higher. In other words, the switching period T _P is restricted by the lighting non period tau _0.

In addition, the length of the non-lighting period τ ₀ in FIG. 5 is obtained by using the rate of increase of the forward voltage V _F (slew rate SR ₀ ).
τ ₀ = V _TH / SR ₀
Can be approximated.

Returning to FIG. In FIG. 4, times t _{3 to} t ₄ correspond to the unlit period τ ₁ . The length of the lighting non period tau _1, using the rate of rise of the forward voltage V _F (slew rate SR _1),
τ ₁ = (V _TH −V _CL ) / SR ₁
Can be approximated. If the slew rates in FIG. 4 and FIG. 5 are the same (SR ₀ = SR ₁ ), the unlit period τ _{1 in} FIG. 4 is shorter than the unlit period τ _{0 in} FIG.

  As described above, according to the lighting circuit 200 of FIG. 2, since the unlightable period τ when the light source 102 is switched from being turned off to lighting can be shortened, high-speed switching is possible.

  In addition, since the load variation when viewed from the drive circuit 202 can be reduced, the design restrictions of the drive circuit 202 can be relaxed, and thus the design of the drive circuit 202 is facilitated.

  For example, the drive circuit 202 can be configured by a switching converter (switch mode power supply) whose output current is controlled at a constant current. A constant current output switching converter is required to have a function of keeping the output current constant regardless of fluctuations in the output voltage. In applications where the output voltage fluctuates at a high speed and with a large amplitude, the response speed required for the switching converter becomes very fast, and its design becomes extremely difficult. Due to the first function of the clamp circuit 210, the fluctuation range of the output voltage is reduced, so that there is an advantage that the design of the switching converter becomes easy. Although it is possible to configure the drive circuit 202 with a linear power supply, the same merit can be enjoyed even in this case.

Lighting non period tau ₁ is shorter the smaller the fluctuation width ΔV of the forward voltage _{V F (= V TH -V CL} ) in the lighting period and the extinction period. Therefore, in order to increase the switching frequency, it is preferable to set the clamp level V _CL as high as possible within a range not exceeding the threshold voltage V _TH . From this point of view, it is desirable that the clamp level V _CL is set to be higher than 1/3 of the threshold voltage V _TH , more preferably higher than 1/2 of the threshold voltage V _TH .

On the other hand, too high a clamp level V _CL, the variations and temperature variations in the threshold voltage V _TH, there is a possibility that the light source 102 is turned on erroneously at turn-off period. From this point of view, it is desirable that the clamp level V _CL is set lower than 4/5 of the threshold voltage V _TH , more preferably lower than 3/4 of the threshold voltage V _TH .

Next, a more preferable function (second function) of the clamp circuit 210 will be described. The clamp circuit 210 immediately reduces the voltage V _F across the light source 102 to substantially zero in response to an instruction to turn off the light source 102 (ie, the negative edge of the control signal S ₁ ). Thereafter, the clamp circuit 210 clamps the voltage V _F between both ends to the clamp level V _CL before the light source 102 is turned on (first function).

FIG. 6 is an operation waveform diagram of the lighting circuit having the second function. When the control signal _{S 1} is switched to off level at time _{t 0,} the voltage across _{V F} of the light source 102 is reduced immediately to zero (0V). Accordingly, forward current I _F decreases immediately to zero.

Then, at time _{t 2} when _the control signal _{S 1} is prior to the time _{t 3} when switched to the lighting level, the voltage across _{V F} of the light source 102 is returned to the clamp level _{V CL.}

  Thus, according to the clamp circuit 210 having the second function, the light source 102 can be turned off at high speed.

  The present invention is understood as the block diagram and circuit diagram of FIG. 2 or extends to various devices and circuits derived from the above description, and is not limited to a specific configuration. In the following, more specific configuration examples and modifications will be described in order to help understand the essence and circuit operation of the invention and clarify them, not to narrow the scope of the present invention.

(First configuration example)
FIG. 7 is a circuit diagram of a first configuration example (200A) of the lighting circuit 200 of FIG. The clamp circuit 210A has the first function described above. The clamp circuit 210 </ b> A includes a first switch SW <b> ₁ and a clamp resistor 214 provided in series on a first path 212 parallel to the light source 102. On the first switch SW ₁ is in the enabled state of the clamp circuit 210A, first off switch SW ₁ corresponding to the disable state of the clamp circuit 210A.

When the resistance value of the first path 212 is R ₁ and the drive current generated by the drive circuit 202 is I _DRV , the voltage across the first path 212 is R ₁ × I _{DRV in} the enabled state. That is, the clamp level V _CL is given by the following equation.
V _CL = R ₁ × I _DRV
Therefore, it suffices if 0 <R ₁ × I _DRV <V _TH is satisfied.
Resistance _{R 1} of the first path 212, a resistance value of the clamp resistor 214 is the sum of the first resistance of the switch SW _1.

The clamp circuit 210A may further include a controller 220. The controller 220 controls ON / OFF of the first switch SW ₁ based on the control signal S ₁ . The controller 220 Specifically, the control signal S ₁ is to first turn off the switch SW ₁ at the time of lighting level, the control signal S ₁ is turned on first switch SW ₁ when the off-level.

  According to the lighting circuit 200A of FIG. 7, the operation of FIG. 4 can be realized.

(Second configuration example)
FIG. 8 is a circuit diagram of a second configuration example (200B) of the lighting circuit 200 of FIG. The clamp circuit 210B has the first function and the second function described above. Clamp circuit 210B, in addition to the clamp circuit 210A of FIG. 7, further comprising a second switch SW ₂ which is provided on the light source 102 in parallel with the second path 216.

Controller 220 turns off period of the light source 102 (the control signal _{S 1} is off level) to turn on the first switch SW ₁ in the light source 102 lighting period (control signal _{S 1} is turned Level) first turns off the switch SW ₁ at the To do. Further, the controller 220 immediately turns on the second switch SW ₂ in response to an instruction to turn off the light source 102 (that is, a corresponding edge of the control signal S ₁ ), and then turns on the second switch SW ₂ prior to the instruction to turn on the light source 102. Turn off. For example, when the lighting level is high, the controller 220 is triggered by the negative edge of the control signal S _1, while very short, the second switch SW ₂ may be turned on. Alternatively controller 220, between negative edge of the control signals _{S 1} for a predetermined time, it may be turned on second switch SW _2.

  According to the lighting circuit 200B of FIG. 8, the operation of FIG. 5 can be realized.

FIGS. 9A and 9B are circuit diagrams showing a specific configuration example of the clamp circuit 210B of FIG. Both the first switch SW ₁ and the second switch SW ₂ are N-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The first switch SW _1, may be a second switch SW ₂ is constituted by a bipolar transistor or IGBT (Insulated Gate Bipolar Transistor).

Reference is made to FIG. #S ₁ is an inversion signal of the control signal S ₁ , and is a signal whose extinguishing level is high and the lighting level is low. The first driver 222 drives the first switch SW ₁ based on the control signal #S ₁ . Differentiator 226 differentiates the control signal _{S 1.} For example, the differentiator 226 may be configured with a high-pass filter, and may include, for example, a capacitor provided on the signal path. The output of the differentiator 226 is increased by positive edge of the control signal #S _1, immediately returns to zero. The second driver 224 drives the second switch SW ₂ based on the output of the differentiator 226.

In FIG. 9A, the differentiator 226 and the second driver 224 may be interchanged.
In FIG. 9 (a), the second driver 224 is omitted, the output of the first driver 222 is supplied as it is to the first gate of the switch SW _1, the second with the output of the first driver 222 via the differentiator 226 it may be supplied to the gate of the switch SW _2.

Reference is made to FIG. The first driver 223 drives the first switch SW ₁ based on the control signal S ₁ . The edge detector 228 detects an edge corresponding to the turn-off instruction of the control signal S ₁ (a positive edge when the turn-off level is low), and generates an edge detection signal S ₂ that is high for a predetermined time from the detected edge. To do. The second driver 224, second drives the switch SW ₂ in accordance with the edge detection signal _{S 2.}

FIGS. 10A to 10E are circuit diagrams showing modifications of the clamp circuit 210. FIG. Here, only the portion related to the first function is shown. Clamp resistance 10 clamping circuit 210 (a) is omitted, as the first switch SW _1, may be used MOSFET having a large on-resistance _{R ON} corresponding to the resistance value of the clamp resistor. That is, the _ON resistance R _ON becomes the resistance value R ₁ of the first path 212, and R _ON × I _DRV becomes the clamp level V _CL .

In the clamp circuit 210 of FIG. 10 (b), on the first path 212 includes a diode 215 the first switch SW ₁ is provided in series. A substantially constant forward voltage V _C is generated in the diode 215 when the drive current I _DRV flows. When the on-resistance of the first switch SW ₁ is sufficiently small, V _CL = V _C is satisfied. When the on-resistance R _ON of the first switch SW ₁ is large, V _CL = V _C + I _DRV × R _ON .

In the clamp circuit 210 of FIG. 10 (c), on the first path 212 includes a Zener diode 217 the first switch SW ₁ is provided in series. A substantially constant Zener voltage _VZ is generated in the Zener diode 217 when the drive current I _DRV flows. When the on-resistance of the first switch SW ₁ is sufficiently small, V _CL = V _Z is established. When the on-resistance R _ON of the first switch SW ₁ is large, V _CL = V _Z + I _DRV × R _ON .

In the clamp circuit 210 in FIG. 10 (d), when the resistance value of the clamp resistor 214 and _{R 1,} is a _{V CL = V C + (R} 1 + R ON) I DRV. In the clamp circuit 210 shown in FIG. _10E , V _CL = V _Z + (R ₁ + R _ON ) I _DRV where R ₁ is the resistance value of the clamp resistor 214.

  In summary, the clamp circuit 210 can be configured by any combination of a resistor, a diode, and a Zener diode.

(Third configuration example)
FIG. 11 is a circuit diagram of a third configuration example (200C) of the lighting circuit 200 of FIG. The clamp circuit 210C has the first function and the second function described above. The clamp circuit 210 </ b> C includes a shunt transistor M <b> ₃ provided on the first path 212 parallel to the light source 102, and a transistor control circuit 230. Transistor control circuit 230, when the control signal S ₁ is in the off state level, i.e. defined in the enabled state of the clamp circuit 210C, the voltage across the light source 102 is lower than the threshold voltage V _TH of off point of greater source than zero It is such that the clamp level is to adjust the voltage (gate voltage, base voltage) of the control terminal of the shunt transistor M ₃ and V _CNT. Shunt transistor _M 3 represents may be a MOSFET, may be a bipolar transistor, it may be IGBT (Insulated Gate Bipolar Transistor). Transistor control circuit 230, when the control signal _{S 1} is in the on state level, that is, in the disabled state of the clamp circuit 210C, turns off the shunt transistor _{M 3.}

FIG. 12 is a circuit diagram showing a first configuration example of the clamp circuit 210C of FIG. The transistor control circuit 230 in FIG. 12 includes a feedback circuit 232, a third switch SW ₃ , and a fourth switch SW ₄ .

The feedback circuit 232 receives the clamp level target voltage V _REF and the feedback voltage V _FB indicating between both ends of the light source 102, and brings the voltage V _F between both ends of the light source 102 close to the clamp level V _CL by feedback. The configuration of the feedback circuit 232 is not limited, and may be configured by an analog error amplifier, or may be configured by a digital feedback circuit (PI controller or PID controller) and an A / D converter. Feedback circuit 232 and shunt transistor _{M 3} are, can be regarded as a shunt regulator.

The third switch SW ₃ is provided between the low voltage terminal 233 which a predetermined low voltage V _L and the control terminal (gate) of the shunt transistor M ₃ is supplied. The third switch SW ₃ may be provided between the control terminal (gate) of the shunt transistor M ₃ and one end (cathode) on the low potential side of the light source 102 as shown in FIG.

The fourth switch SW ₄ is provided between the high-voltage terminal 234 of a predetermined high voltage V _H and the control terminal (gate) of the shunt transistor M ₃ is supplied. The fourth switch SW ₄ may be provided between the control terminal (gate) of the shunt transistor M ₃ and one end (anode) on the high potential side of the light source 102 as shown in FIG.

The control signal S ₁ includes a signal S _1A for instructing on / off of the feedback circuit 232, a signal S _1B for instructing on / off of the third switch SW ₃ , and a signal S for instructing on / off of the fourth switch SW _4. Includes _1C . The feedback circuit 232 is configured to be enabled when the signal S _1A is at a high level and disabled when the signal S _1A is at a low level.

FIG. 13 is an operation waveform diagram of the clamp circuit 210C of FIG. Control signals S ₁ prior to time t ₀ is illuminated level (high level). Specifically, the control signals S _1A , S _1B , S _1C are generated so that the feedback circuit 232 is disabled, the third switch SW ₃ is turned on, and the fourth switch SW ₄ is turned off. Thus the gate voltage _{V CNT} of shunt transistor _{M 3} are low voltage _{V L,} and the shunt transistor _{M 3} are turned off. This corresponds to the disabled state (DIS) of the clamp circuit 210C. Forward current _{I F} of this time the light source 102 is equal to the driving current _{I DRV} for driving circuit 202 generates the light source 102 emits light with a brightness corresponding to the driving current _{I DRV.} The forward voltage V _F is a voltage level V _ON corresponding to the drive current I _DRV .

Control signals _{S 1} transitions to off level (low level) at time _{t 0.} The control signals S _1A , S _1B , S _1C are generated so that the feedback circuit 232 is disabled, the third switch SW ₃ is turned off, and the fourth switch SW ₄ is turned on. Thus the gate voltage _{V CNT} of shunt transistor _{M 3} are changed immediately to the high voltage _{V H,} shunt transistor _{M 3} is turned on. Thus the forward current I _F is immediately reduced to zero, the light source 102 is turned off.

Followed time _{t 2, the} control signal _{S 1A, S 1B, S 1C,} the feedback circuit 232 is enabled, the third switch SW ₃ is turned off, the fourth switch SW ₄ is produced so that the off-state. By the feedback control of the feedback circuit 232, the voltage across _{V F} of the light source 102 so as to approach the clamp level _{V CL,} the gate voltage _{V CNT} is adjusted.

Control signal _{S 1} is shifted to the lighting level (high level) at time _{t 3.} The control signals S _1A , S _1B and S _1C are generated so that the feedback circuit 232 is disabled, the third switch SW ₃ is turned on, and the fourth switch SW ₄ is turned off. By turning on the third switch SW _3, turns off the shunt transistor _{M 3,} clamp the forward voltage _{V F} of the light source 102 is released, the drive current _{I DRV} flowing in the shunt transistor _{M 3} in extinction period, the light source 102 the flow, the forward voltage V _F, gradually increases towards the original voltage level V _oN.

Forward voltage _{V F} is a time _{t 4} after crossing the threshold voltage _{V TH,} first forward current _{I F} flows, the luminance of the light source 102 is increased. Then at time _{t 5,} all of the drive current _{I DRV} becomes to flow to the light source 102, the forward current _{I F} is equal to the driving current _{I DRV.}

  The above is the operation of the clamp circuit 210C in FIG. According to the clamp circuit 210C, the first function and the second function described above can be realized.

In FIG. 12, when it is possible to transistor control circuit 230 shifts the output voltage V _CNT to the high voltage V _H Fast may omit the fourth switch SW _4. Further, when it is possible to transition to the transistor control circuit 230 is a high speed the output voltage V _CNT to the low voltage V _L may be omitted third switch SW _3.

FIG. 14 is a circuit diagram showing a second configuration example of the clamp circuit 210C of FIG. A clamp circuit 210C in FIG. 14 includes a constant voltage circuit 236 instead of the feedback circuit 232 in FIG. Constant voltage circuit 236 is provided between the one end of the control terminal (gate) and the high potential side of the shunt transistor M ₃ (drain), for holding the voltage between the gate and the drain of the shunt transistor M ₃ constant. However, the capability of the constant voltage circuit 236 is lower than the capabilities of the third switch SW ₃ and the fourth switch SW ₄ , and therefore when either the third switch SW ₃ or the fourth switch SW ₄ is on, the constant voltage circuit 236 The effect disappears.

The configuration of the constant voltage circuit 236 is not particularly limited. For example, the constant voltage circuit 236 may include a plurality (n) of diodes connected in series and a resistor. In this case, the clamp level V _CL is
V _CL = (V _{th (gs)} + Vf × n + V _R ).
Vf is the forward voltage of the _{diode, V th (gs)} is the threshold voltage between the gate and the source of the shunt transistor _{M 3.}

In FIG. 14, the high voltage V _H is the anode voltage of the light source 102 (the drain voltage of the shunt transistor M ₃ ), and the low voltage V _L is the cathode voltage of the light source 102 (the source voltage of the shunt transistor M ₃ ). As shown in FIG. 12, the high voltage V _H may be an arbitrary predetermined voltage, and the low voltage V _L may be grounded.

Next, the operation of the clamp circuit 210C in FIG. 14 will be described. Operation waveform diagram is similar to that ignores the control signal S1 _A 13. According to the clamp circuit 210C of FIG. 14, the same effect as that of the clamp circuit 210C of FIG. 12 can be obtained.

(Use)
Next, the application of the lighting circuit 200 will be described. 2 can be used as a vehicular lamp. FIGS. 15A to 15D are diagrams showing a vehicular lamp including the lighting circuit 200. FIG. A vehicle lamp 300 </ b> A in FIG. 15A is a scan-type lamp that scans light emitted from the light source 302. The vehicular lamp 300A includes a lighting circuit 200, a light source 302, and a scanning device 304. The scanning device 304 includes a motor and a reflector (blade). Light emitted from the light source 302 is reflected by the blade and scanned in front of the vehicle. By synchronizing the light emitted from the light source 302 or switching at high speed in synchronization with the periodic movement of the blade, an arbitrary light distribution pattern can be realized or road surface drawing can be performed.

  The vehicle lamp 300B in FIG. 15B is also a scan-type lamp that scans the emitted light of the light source 302. The vehicular lamp 300 </ b> B includes a lighting circuit 200, a light source 302, and a scanning device 306. The scanning device 306 includes a motor and a galvanometer mirror.

  A vehicle lamp 300C in FIG. 15C includes a lighting circuit 200, a light source 302, and a pattern forming device 308. The pattern forming apparatus 308 is a DMD (digital mirror device) including a plurality of pixels. Each pixel of the DMD can be switched on and off individually. The light emitted from the light source 302 is reflected by the pattern forming device 308, and the reflected light has a pattern corresponding to the state of the DMD pixel.

  15D includes a lighting circuit 200, a light source 302, and an actuator 310 that controls the direction of the light source 302. The emitted light from the light source 302 can be scanned by periodically changing the direction of the light source 302 by the actuator 310.

  FIGS. 16A and 16B are circuit diagrams of a vehicular lamp including the lighting circuit 200. FIG. A vehicle lamp 300E of FIG. 16A includes a first light source 312, a second light source 314, and a lighting circuit 200. For example, the first light source 312 is a low beam, and the second light source 314 is a high beam. The lighting circuit 200 includes a drive circuit 202 and a clamp circuit 210. The second light source 314 corresponds to the light source 102 described above, and the clamp circuit 210 is connected between both ends of the second light source 314.

The vehicle lamp 300F in FIG. 16B includes a plurality of N light sources 316_1 to 316_N and a lighting circuit 200. The plurality of light sources 316 illuminate different positions in front of the vehicle. The lighting circuit 200 includes a drive circuit 202 and a plurality of clamp circuits 210_1 to 210_N. Each clamp circuit 210_i is connected between both ends of the corresponding light source 316_i. Each clamp circuit 210_i receives a control signal _{S1_i} instructing to turn on / off the corresponding light source 316_i.

  In the description so far, the lighting device 100 including the single light source 102 has been described. However, the present invention can also be applied to driving a plurality of light sources.

  FIG. 17 is a block diagram of an illumination device 100D including a plurality of light sources 102. The lighting device 100D includes a plurality of light sources 102_1 to 102_N and its lighting circuit 200D. The light source 102 is, for example, an LED or an LD, and the plurality of light sources 102_1 to 102_N are connected in series.

The lighting circuit 200D includes a plurality of shunt transistors M ₃ , a drive circuit 202, a plurality of interface circuits 204_1 to 204_N, an oscillator 206, and a microcomputer 208.

Each shunt transistor M ₃ are, are connected across the corresponding light source 102. The respective interface circuits 204, drives the shunt transistor _{M 3} corresponding. The interface circuit 204 corresponds to the clamp circuit 210C in FIG.

  The microcomputer 208 is a controller that controls the lighting circuit 200D in an integrated manner, and controls turning on / off of each of the light sources 102_1 to 102_N based on information from an ECU (not shown) on the vehicle side.

Focus on the light source 102_1, the interface circuit 204_1, and the microcomputer 208. The interface circuit 204 includes a third switch SW ₃ , a fourth switch SW ₄ , a regulator 240, and a charge pump 242. The regulator 240 and the microcomputer 208 correspond to the feedback circuit 232 in FIG. That is, the feedback circuit 232 includes a digital control unit and an analog output unit. The former corresponds to the microcomputer 208 and the latter corresponds to the regulator 240. The microcomputer 208, as the feedback voltage V _FB obtained by dividing the drain voltage of the shunt transistor M ₃ and is fed back, the feedback voltage V _FB is closer to a target voltage that defines the clamp level V _CL, the voltage command Generate the value S _REF . The regulator 240 generates a control voltage V _CNT corresponding to the voltage command value S _REF at the control terminal of the shunt transistor M ₃ . The charge pump 242 receives a clock signal from the oscillator 206, performs a boosting operation, and generates a high voltage _{V H.}

  According to this illumination device 100D, the lighting on / off of the plurality of light sources 102_1 to 102_N can be controlled independently. The interface circuit 204 can be configured by the arbitrary clamp circuit 210 described above.

  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.

100 ... lighting device, 102 ... light source, 200 ... lighting circuit, 202 ... driving circuit, 204 ... interface circuit, 206 ... oscillator, 208 ... microcomputer, 210 ... clamping circuit, 212 ... first path, SW 1 _... first switch, 214 ... clamp resistance, 216 ... second path, SW 2 _... second switch, 220 ... controller, 230 ... transistor control circuit, M 3 _... shunt transistor, 232 ... feedback circuit, 233 ... low-voltage terminal, 234 ... high voltage terminal , SW ₃ ... third switch, SW ₄ ... fourth switch, 240 ... regulator, 242 ... charge pump, 236 ... constant voltage circuit, 300 ... vehicle lamp.

Claims (14)

A light source lighting circuit,
A drive circuit for generating a drive current to be supplied to the light source;
A clamp circuit that clamps the voltage across the light source to a clamp level that is defined to be greater than zero and lower than a threshold voltage for turning on / off the light source in a period in which the light source is to be turned off;
A lighting circuit comprising:   2. The clamp circuit according to claim 1, wherein the clamp circuit immediately decreases the voltage across the light source to substantially zero in response to an instruction to turn off the light source, and then clamps the clamp to the clamp level. Lighting circuit. The clamp circuit includes a first switch and a clamp resistor provided in series on a first path parallel to the light source,
The resistance value _{R 1} of the first path, the threshold voltage _{V TH} of the light source, the drive current when the _{I DRV,}
0 <R ₁ × I _DRV <V _TH
The lighting circuit according to claim 1, wherein: The clamp circuit includes a first switch provided on a first path parallel to the light source,
The resistance value _{R 1} of the first path, the threshold voltage _{V TH} of the light source, the drive current when the _{I DRV,}
0 <R ₁ × I _DRV <V _TH
The lighting circuit according to claim 1, wherein: The clamp circuit further includes a second switch provided on a second path in parallel with the light source,
5. The lighting circuit according to claim 1, wherein the second switch is turned on immediately after an instruction to turn off the light source is turned on and turned off prior to the instruction to turn on the light source. The clamp circuit is
A shunt transistor provided between both ends of the light source;
A transistor control circuit for generating a voltage at a control terminal of the shunt transistor so that a voltage between both ends of the light source becomes the clamp level in a period in which the light source is to be turned off;
The lighting circuit according to claim 1, further comprising:   The lighting circuit according to claim 6, wherein the transistor control circuit includes a feedback circuit that brings a voltage across the light source close to the clamp level by feedback.   The lighting circuit according to claim 6, wherein the transistor control circuit includes a constant voltage circuit provided between a control terminal of the shunt transistor and one end on a high potential side.   The transistor control circuit is provided between the control terminal of the shunt transistor and one end on the low potential side of the light source, or between the control terminal of the shunt transistor and a low voltage terminal to which a predetermined low voltage is supplied. The lighting circuit according to claim 6, further comprising a third switch.   The transistor control circuit is provided between the control terminal of the shunt transistor and one end on the high potential side of the light source, or between the control terminal of the shunt transistor and a high voltage terminal to which a predetermined high voltage is supplied. The lighting circuit according to claim 6, further comprising a fourth switch. A light source lighting circuit,
A drive circuit for generating a drive current to be supplied to the light source;
A first switch and a clamp resistor provided in series on a first path in parallel with the light source;
A second switch provided on a second path parallel to the light source and the first path;
A controller for controlling the first switch and the second switch;
A lighting circuit comprising: The controller is
Turning on the first switch in the light-off period of the light source; turning off the first switch in the light-up period of the light source;
The lighting circuit according to claim 10, wherein the second switch is immediately turned on in response to an instruction to turn off the light source, and the second switch is turned off prior to the instruction to turn on the light source. A light source;
The lighting circuit according to any one of claims 1 to 11, which drives the light source;
A vehicular lamp characterized by comprising:   The vehicular lamp according to claim 12, wherein the light source includes a plurality of light sources.

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