JP2013246379A - Light source drive device and head-up display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the occurrence of a noise while satisfactorily controlling the luminance of a light source.SOLUTION: A light source drive device 100 comprises: a driving circuit 102 for supplying a driving current to a light source 12 to drive it; control means 101 for generating an analog light control signal to supply it to the driving circuit 102 if target luminance is a first threshold value or more, and generating a PWM light control signal to supply it to the driving circuit 102 if the target luminance is less than the first threshold value; and frequency change means 103 for changing a frequency of an on-off signal generated by the driving circuit 102. The frequency change means 103 changes the frequency of the on-off signal if the target luminance is a second threshold value or more, and does not change the frequency of the on-off signal if the target luminance is less than the second threshold value T2.

Description

  The present invention relates to a light source driving device and a head-up display device.

  As a conventional light source driving device, for example, there is one disclosed in Patent Document 1. The light source driving device according to Patent Document 1 is applied to, for example, a display device mounted on a vehicle, and includes a driving circuit that drives a light source, and a control unit that supplies a driving signal to the light source driving unit, and a desired target. The light source is driven and controlled to emit light with luminance, and the light source is driven by combining analog dimming control and pulse width modulation control (PWM control) according to the target luminance.

JP 2004-284508 A

  In the light source driving apparatus as disclosed in Patent Document 1, the driving circuit performs a constant frequency oscillation to generate an on / off signal that determines the timing for supplying a driving current for driving the light source. Unnecessary electromagnetic waves).

  As a measure for suppressing the above-described noise, a method of changing the operating frequency of an on / off signal generated by a drive circuit by modulation is known. However, when the frequency is changed in this way, when the light source is driven at low luminance by reducing the duty ratio of the drive signal by PWM control, the drive signal (PWM dimming signal) supplied from the control means to the drive circuit is reduced. Since the cycle of the on / off signal whose frequency is changed may be longer with respect to the on period, the desired drive current is not supplied to the light source, resulting in variations in luminance control. (See FIGS. 8A to 8C). If the frequency of the signal generated by the drive circuit is not changed in this way, the problem of variation in luminance control can be avoided, but this time, noise cannot be reduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light source driving device and a head-up display device including the light source driving device that can reduce the generation of noise while favorably controlling the luminance of the light source. .

In order to achieve the above object, a light source driving apparatus according to the first aspect of the present invention includes:
Light source driving means for driving the light source by supplying a driving current to the light source;
Control means for controlling the light source driving means so that the light source emits light at a desired target luminance, and when the value indicating the target luminance is equal to or greater than a predetermined first threshold, the driving current is A first drive signal adjusted to have a value corresponding to the target luminance is generated and supplied to the light source driving means. When the value indicating the target luminance is smaller than the first threshold, the driving is performed. A control unit that generates a second drive signal that is adjusted to have a constant current value and has a pulse width changed in accordance with the target luminance, and supplies the second drive signal to the light source driving unit;
Generating means for generating an on / off signal superimposed on the second driving signal and supplying the on / off signal to the light source driving means;
Frequency changing means for changing the frequency of the on / off signal generated by the generating means,
The frequency changing means changes the frequency of the on / off signal when the value indicating the target luminance is equal to or higher than a predetermined second threshold, and the value indicating the target luminance is smaller than the second threshold. If the frequency of the on-off signal is not changed,
The light source driving means includes
When the first drive signal is supplied, a drive current is supplied to the light source based on the first drive signal, the second drive signal is supplied, and a value indicating the target luminance is obtained. If it is equal to or greater than the second threshold, a drive current is supplied to the light source based on the second drive signal and the on / off signal whose frequency is changed by the frequency changing means, and the second drive signal is When the value indicating the target luminance is smaller than the second threshold, the light source is based on the second drive signal and the on / off signal whose frequency is not changed by the frequency changing means. Supply drive current to
It is characterized by that.

In order to achieve the above object, a head-up display device according to a second aspect of the present invention provides:
The light source driving device, and the light source,
By causing display light representing a predetermined image emitted from the light source to reach the transparent plate, the observer is allowed to visually recognize a virtual image of the predetermined image superimposed on the front landscape through the transparent plate.

  According to the present invention, it is possible to reduce the generation of noise while favorably controlling the luminance of the light source.

It is a conceptual diagram which shows how the head-up display apparatus which concerns on one Embodiment of this invention is mounted in the vehicle, and how a virtual image is formed. (A) is a schematic block diagram of a head-up display apparatus. (B) is a schematic sectional drawing of the liquid crystal display device with which a head-up display apparatus is provided. It is a block diagram which mainly shows the structure of a light source drive device. It is a flowchart of the light source drive control process which a control means performs. (A)-(c) is a timing chart in case a light source drive device drives a light source by PWM control. (A) And (b) is a figure for demonstrating how a control means adjusts a duty ratio and a drive current. (C) is a figure for demonstrating the ON / OFF timing of a switch control signal in case a 2nd threshold value is larger than a 1st threshold value. (D) is a figure for demonstrating the ON / OFF timing of a switch control signal in case a 2nd threshold value is smaller than a 1st threshold value. (A) And (b) is a figure for demonstrating the control method of the light source which concerns on a modification. (A)-(c) is a figure for demonstrating the problem which generate | occur | produced conventionally, when driving a light source with low brightness | luminance by PWM control.

  A light source driving device according to an embodiment of the present invention will be described with reference to the drawings.

  The light source driving device 100 (see FIG. 3) according to the present embodiment is configured as a part of the HUD device 1 shown in FIG. The HUD device 1 is provided in the dashboard of the vehicle 2 and reflects the light (display light L) representing the display image for notifying vehicle information by the windshield 3 (windshield), thereby displaying the display image. Is a device that allows the user 4 (mainly, the driver of the vehicle 2) to visually recognize the virtual image V. Thereby, the user 4 can recognize vehicle information, without deflecting a gaze from the front during a driving | operation.

As shown in FIGS. 2A, 2B, and 3, the HUD device 1 includes a liquid crystal display device 10, an optical system 20, an illuminance sensor 30, a circuit board 40 including a light source driving device 100, and a housing. 50.
As illustrated in FIG. 3, the light source driving device 100 includes a control unit 101, a driving circuit 102, and a frequency changing unit 103.

  The liquid crystal display device 10 displays a display image for reporting vehicle information, that is, emits light (display light L) representing the display image. The liquid crystal display device 10 is composed of, for example, a known transmissive liquid crystal display device, and includes a liquid crystal panel 11 and a light source 12.

  The liquid crystal panel 11 includes a pair of substrates 11a and 11b (made of glass, plastic, etc.) facing each other and transparent electrodes 11c and 11d (ITO (Indium Tin Oxide) formed on the surfaces facing each other of the substrates 11a and 11b. And the like, and an alignment film (not shown) that covers each of the transparent electrodes 11c and 11d, and a space formed by the substrates 11a and 11b and a sealing material (not shown) that joins both the substrates. A liquid crystal layer 11e and a pair of polarizing plates 11f and 11g arranged so as to sandwich the substrates 11a and 11b from the outside.

  When a voltage is applied to the liquid crystal layer 11e through the transparent electrodes 11c and 11d under the control of the control means 101, the birefringence of the liquid crystal molecules included in the liquid crystal layer 11e changes. Using this change, the liquid crystal panel 11 displays a predetermined display image. The display image is displayed by transmissive display using light from the light source 12 provided behind the liquid crystal panel 11.

  The liquid crystal panel 11 includes a known liquid crystal panel such as a TN (Twisted Nematic) type, a VA (Vertical Alignment) type, a STN (Super-Twisted Nematic) type, and a ferroelectric type. Further, the liquid crystal panel 11 may be either a TFT (Thin Film Transistor) type or a passive drive type, or may be a segment display type or a dot matrix type. The polarizing plates 11f and 11g are appropriately arranged according to the type of liquid crystal panel 11 (TN type or the like) and the display mode (negative / positive display) so that the transmission axes of each are orthogonal or parallel to each other. (Cross Nicol or Parallel Nicol arrangement).

  The light source 12 includes one or a plurality of LEDs (Light Emitting Diodes), and is disposed on the back side of the liquid crystal panel 11. The light source 12 emits light as appropriate under the control of the control unit 101 and illuminates the liquid crystal panel 11 from the back side. The liquid crystal display device 10 performs transmissive display using light from the light source 12. That is, the light source 12 functions as a backlight in the liquid crystal display device 10. As a result, light representing the display image (display light L) is emitted.

  The optical system 20 is an optical system provided between the optical path of the liquid crystal display device 10 and the windshield 3 so that the display image of the liquid crystal display device 10 is formed as a virtual image V at a desired position and in a desired size. is there. The optical system 20 according to this embodiment includes two reflecting members, a plane mirror 21 and a concave mirror 22.

  The plane mirror 21 is disposed at a position for receiving the display light L from the liquid crystal display device 10 and has a reflection surface 21 a that efficiently reflects the incident display light L toward the concave mirror 22. The flat mirror 21 is formed by evaporating a metal such as Al on a plate-like base material made of, for example, resin, glass or the like, and a reflective surface 21a is formed by the deposited film.

  The concave mirror 22 emits the reflected light toward the windshield 3 by reflecting the display light L reflected by the plane mirror 21 by the concave surface 22a. As a result, the size of the virtual image V to be connected becomes a size obtained by enlarging the display image. The concave mirror 22 is formed by evaporating a metal such as Al on a plate-like base material made of, for example, resin, glass or the like, and a concave surface 22a which is a reflection surface is formed by the deposited film.

  The illuminance sensor 30 shown in FIG. 3 detects the illuminance of external light, and includes a phototransistor, a photodiode, and the like. The illuminance sensor 30 is disposed at an appropriate position where external light can be received (for example, a position where a hole is provided in a part of the housing 50 and external light entering from the hole can be received). Illuminance information shown is supplied to the control means 101.

  The circuit board 40 is a printed circuit board in which a predetermined wiring pattern is formed on a plate-like base material made of a resin containing glass fiber. The circuit board 40 is disposed, for example, on the side opposite to the display light L emission side of the liquid crystal display device 10. A light source driving device 100 and a light source 12 are mounted on the circuit board 40. The circuit board 40 is electrically connected to each of the liquid crystal panel 11 and the illuminance sensor 30 through, for example, an unillustrated FPC (Flexible Printed Circuit).

  The control means 101 shown in FIG. 3 comprises ICs (Integrated Circuits) such as a microcontroller and a graphic controller, and various types of vehicles transmitted from an external device (not shown) such as a vehicle ECU (Electronic Control Unit) via a communication line. A drive signal for acquiring information and displaying measured values such as vehicle speed and fuel consumption on the liquid crystal panel 10 and a drive signal for driving the light source 12 are output to the liquid crystal display device 11 as appropriate. As a result, the liquid crystal display device 10 is driven to display a predetermined display image.

In particular, in the present embodiment, the control unit 101 has a desired brightness according to dimming information supplied from an operation unit (not shown) by manual operation of the user 4 or illuminance information supplied from the illuminance sensor 30. A drive signal for driving the light source 12 is appropriately supplied to the light source 12 by pulse width modulation control (PWM dimming method) or current value control (analog dimming method) so that the light source 12 emits light. Specifically, the control unit 101 sets a target luminance for determining the output of the light source 12 according to dimming information or illuminance information, and the drive current supplied to the light source 12 becomes a value corresponding to the target luminance. Drive signal adjusted in this way (hereinafter referred to as an analog dimming signal) or a drive signal adjusted so that the value of the drive current is constant and the pulse width is changed in accordance with the target luminance (hereinafter referred to as the target luminance). , Which is referred to as a PWM dimming signal (see FIG. 5A), and is supplied to the drive circuit 102.
The control means 101 outputs a switch control signal (see FIGS. 6C and 6D) to control a switch means 103b described later.
How the control means 101 controls the driving of the light source 12 will be described later in detail.

  The microcontroller constituting the control means 101 is executed in response to a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores a program defining a procedure of processing by the CPU, an appropriate numerical input by the user, and the like. And storage means including a RAM (Random Access Memory) or the like for temporarily storing programs and necessary information. In the ROM, programs for executing light source drive control processing described later are stored in advance, and the CPU reads and executes these programs.

The drive circuit 102 is composed of, for example, an IC of a switching regulator type LED driver, and performs a switching operation by an internal oscillation circuit to control a drive current supplied to the light source 12.
Specifically, the drive circuit 102 outputs an input voltage from a power source (not shown) as an on / off signal (pulse) as shown in FIG. This on / off signal is superimposed on the supplied PWM dimming signal, and the pulse width of the on / off signal is appropriately changed so that the output has a desired power. Thus, in the PWM dimming method, when both the PWM dimming signal (see FIG. 5A) and the on / off signal (see FIG. 5B) supplied from the control means 101 are turned on, FIG. A driving current as shown in c) is supplied to the light source 12.
On the other hand, in the analog dimming method, the drive circuit 102 supplies a drive current to the light source 12 based on the analog dimming signal supplied from the control means 101.

  The frequency changing unit 103 changes the frequency of the on / off signal when a predetermined condition is satisfied, and includes a signal generating unit 103a and a switch unit 103b.

  The signal generation unit 103a includes a resistor, an oscillation circuit, and the like, and outputs a signal (frequency modulation signal) that changes the frequency of the switching operation of the drive circuit 102 (frequency of the on / off signal).

The switch means 103b is composed of a transistor such as an FET (Field Effect Transistor) and a switch element such as an IC including the transistor, and is based on a switch control signal (see FIGS. 6C and 6D) supplied from the control means 101. Thus, it is controlled whether or not the input signal from the signal generation means 103a is output to the drive circuit 102.
Specifically, when the switch control signal indicates ON, the switch unit 103b outputs an input signal from the signal generation unit 103a to the drive circuit 102. As a result, the frequency of the on / off signal changes (that is, modulates). On the other hand, when the switch control signal indicates OFF, the switch unit 103b does not cause the drive circuit 102 to output the input signal from the signal generation unit 103a. The on / off timing of the switch control signal and the operation of the switch means 103b will be described in detail later.

  The housing 50 shown in FIG. 2A accommodates the liquid crystal display device 10, the optical system 20, the illuminance sensor 30, and the circuit board 40, and is, for example, a box having an upper opening made of hard resin. The opening 51 of the housing 50 is provided to secure the optical path of the display light L. That is, the display light L reflected by the concave mirror 22 reaches the windshield 3 through the opening 51. In addition, you may provide the transparent window (For example, consisting of translucent resin, such as an acryl) which covers the opening part 51 of the housing 50. FIG.

  The HUD device 1 having the above configuration enables a driver to visually recognize a predetermined display image as a virtual image V. Briefly describing a series of flows of the mechanism that enables this, i) Under the control of the control means 101, the liquid crystal display device 10 displays a predetermined display image, that is, emits display light L. ii) The display light L is reflected by the optical system 20 (plane mirror 21 and concave mirror 22), and the reflected light is emitted toward the windshield 3. In this way, the HUD device 1 emits the display light L. iii) The display light L emitted from the HUD device 1 is reflected by the windshield 3 so that a virtual image V of the display image is formed in front of the windshield 3 as seen from the driver as shown in FIG. This is the flow.

  By the way, in the HUD device mounted on the vehicle, the required luminance range of the display light is extremely wide compared to other displays. This is because, in the daytime, it is necessary to make the display light brighter than the outside light, and there is a loss of the amount of light that allows the display light L to pass through the windshield (or combiner). On the other hand, at night, when visually recognizing the situation outside the vehicle, low brightness and delicate light control is required so that the user is not dazzled.

  Therefore, in the HUD device 1 according to the present embodiment, when the target luminance is smaller than a predetermined threshold (first threshold T1 described later), that is, on the low luminance side, the light source 12 is driven and controlled by the PWM dimming method. When the luminance is equal to or higher than the first threshold T1, that is, on the high luminance side, the light source 12 is driven and controlled by the analog dimming method.

Further, in the HUD device 1, the frequency of the on / off signal is changed (the frequency is modulated) by the frequency changing means 103 in order to reduce noise due to frequency vibration of the oscillation circuit of the drive circuit 102.
In this case, if the frequency of the on / off signal is always modulated, as described above, when dimming control is performed by the PWM dimming method on the low luminance side, as shown in FIGS. In addition, since the period of the on / off signal whose frequency is changed may be longer with respect to the on period of the PWM dimming signal, a desired drive current is not supplied to the light source, resulting in variations in luminance control. Will occur.

However, in the HUD device 1 according to the present embodiment, the control unit 101 executes the light source drive control process described below, and stops the frequency modulation operation when the predetermined condition is satisfied, thereby While controlling the luminance of 12 well (while controlling light control well), the generation of noise is reduced as much as possible.
From here, the light source drive control process peculiar to this embodiment is demonstrated with reference to the flowchart of FIG.

(Light source drive control processing)
For example, the control unit 101 starts the light source drive control process on condition that the HUD device 1 is powered on.
First, the control means 101 sets a target luminance for determining the output of the light source 12 based on the dimming information from the operation unit and the illuminance information from the illuminance sensor 30 (step S1).
For example, when setting the target luminance based on the illuminance information from the illuminance sensor 30, when a plurality of threshold values are stored in the control unit 101 in advance and the illuminance of external light indicated by the illuminance information is greater than a certain threshold value, When the luminance of the light source 12 is increased by a predetermined frequency and the illuminance of external light indicated by the illuminance information is smaller than a certain threshold, the luminance of the light source 12 is decreased by a predetermined frequency.

  Subsequently, the control means 101 determines whether or not the set target luminance is smaller than a predetermined value (first threshold value T1, see FIGS. 6A and 6B) stored in advance (step). S2).

When the target brightness is smaller than the first threshold T1 (step S2; Yes), the control unit 101 generates a PWM dimming signal and supplies it to the drive circuit 102 (step S3).
Specifically, the control means 101 determines a duty ratio for obtaining the set target luminance, and a pulse signal having the duty ratio (so that the value of the drive current supplied to the light source 12 is constant). A drive signal that is adjusted and whose pulse width is changed in accordance with the target luminance is generated and supplied to the drive circuit 102. The drive signal (PWM dimming signal) here corresponds to the left side of the first threshold value T1 in the graphs shown in FIGS. For example, the duty ratio is set to be 100% when the target brightness is the first threshold T1, and 0% when the target brightness is 0.

On the other hand, when the target luminance is equal to or higher than the first threshold T1 (step S3; No), the control unit 101 generates an analog dimming signal and supplies it to the drive circuit 102 (step S4).
Specifically, the control unit 101 supplies the drive circuit 102 with a drive signal adjusted so that the pulse duty ratio is constant and the drive current is a value corresponding to the set target luminance. The driving signal (analog light control signal) here corresponds to the right side including the first threshold value T1 in the graphs shown in FIGS.
Each adjustment value (duty ratio or current value) corresponding to the target luminance is set using a calculation program or table data stored in advance in the storage means of the control means 101.

When executing the processing of steps S3 to S4, the control means 101 determines whether or not the set target luminance is smaller than the second threshold value T2 stored in advance (step S5).
Here, the second threshold value T2 is determined as a value at which the noise generated from the drive circuit 102 is equal to or less than a specified value (specification of the vehicle 2 on which the HUD 1 is mounted or a value according to the ISO standard). As will be described later, the second threshold value T2 triggers whether or not to change the frequency of the on / off signal. The second threshold value T2 is determined in the range where the noise is below a specified value. If it is possible to provide a sufficiently reliable product without changing noise by changing the frequency of the on / off signal, and the noise is assumed to exceed the reference value, the frequency of the on / off signal This is because noise can be reduced by changing.

  Note that the second threshold value T2 may be smaller than the first threshold value T1, or may be equal to or greater than the first threshold value T1. When the second threshold value T2 is smaller than the first threshold value T1 (see (1) shown in FIG. 6B), for example, the second threshold value T2 is determined in consideration of the duty ratio of the PWM dimming signal. Good. Further, when the second threshold T2 is equal to or greater than the first threshold T1 (see (2) shown in FIG. 6B), the driving current supplied to the light source 12 may be determined (FIG. 6B). ) (Refer to the driving current A).

When the target luminance is smaller than the second threshold T2 (step S5; Yes), the control unit 101 supplies a switch control signal indicating OFF to the switch unit 103b, and uses the input signal from the signal generation unit 103a as the drive circuit 102. (Step S6).
On the other hand, when the target luminance is equal to or higher than the second threshold T2 (step S5; No), the control unit 101 supplies a switch control signal indicating ON to the switch unit 103b, and the input circuit from the signal generation unit 103a is driven. It outputs to 102 (step S7).
The ON / OFF timing of the switch control signal at this time will be described with reference to FIGS. 6C and 6D. When the second threshold T2 is smaller than the first threshold T1 (FIG. 6). (See (1) shown in FIG. 6B) is as shown in FIG. 6C, and when the second threshold T2 is equal to or greater than the first threshold T1 (see (2) shown in FIG. 6B). As shown in FIG.

  The control means 101 will return a process to step S1, if the process of step S6 thru | or S7 is performed.

  When the control unit 101 executes the above processing, the drive circuit 102 supplies i) a drive current to the light source 12 based on the analog dimming signal when the analog dimming signal is supplied, and ii) PWM When the dimming signal is supplied and the value indicating the target luminance is equal to or higher than the second threshold T2, the light source 12 is driven based on the PWM dimming signal and the on / off signal whose frequency is changed by the frequency changing unit 103. Iii) When the PWM dimming signal is supplied and the value indicating the target luminance is smaller than the second threshold T2, the frequency is not changed by the PWM dimming signal and the frequency changing unit 103. A drive current is supplied to the light source 12 based on the on / off signal.

According to the light source driving device 100 according to the present embodiment, since the second threshold value T2 is set as described above, the frequency of the on / off signal is not changed in the luminance range in which noise is predicted to be equal to or less than the specified value. Therefore, it can be avoided that a desired drive current is not supplied to the light source 12 as shown in FIG. 8C, and the frequency of the on / off signal is changed in a luminance range where noise is predicted to exceed the specified value. , Noise can be reduced. Therefore, it is possible to reduce the generation of noise while favorably controlling the luminance of the light source 12.
This effect is realized by the light source driving device 100 and the HUD device 1 having the following configuration.

  The light source driving device 100 generates an on / off signal superimposed on a PWM dimming signal (an example of a second driving signal), and supplies a driving current to the light source 12 to drive the light source 12 (generating unit). And an example of a light source driving unit) and a control unit 101 that controls the driving circuit 102 so that the light source 12 emits light at a desired target luminance, and a value indicating the target luminance is a first threshold value T1 that is determined in advance. In the above case, an analog dimming signal (an example of the first drive signal) adjusted so that the drive current has a value corresponding to the target brightness is generated and supplied to the drive circuit 102, and the target brightness is set. Is smaller than the first threshold value T1, a PWM dimming signal in which the value of the drive current is adjusted to be constant and the pulse width is changed according to the target luminance is generated. Drive circuit 102 A control unit 101 that supplies the signal, and a frequency changing unit 103 that changes the frequency of the on / off signal generated by the drive circuit 102, and the frequency changing unit 103 has a second threshold value with a predetermined value indicating the target luminance. When the frequency is equal to or greater than T2, the frequency of the on / off signal is changed. When the value indicating the target luminance is smaller than the second threshold T2, the frequency of the on / off signal is not changed, and the drive circuit 102 When the dimming signal is supplied, the driving current is supplied to the light source 12 based on the analog dimming signal, the PWM dimming signal is supplied, and the value indicating the target luminance is equal to or greater than the second threshold T2. Supplies a drive current to the light source 12 based on the PWM dimming signal and the on / off signal whose frequency is changed by the frequency changing means 103, and the PWM dimming signal is supplied, and , If the value indicating the target luminance is smaller than the second threshold T2 supplies the driving current to the light source 12 based on the OFF signal is not frequency changes by the PWM dimming signal and the frequency changing means 103.

  In the light source driving apparatus 100, the frequency changing unit 103 includes a signal generating unit 103a that generates a signal for changing the frequency of the on / off signal, and a value indicating the target luminance under the control of the control unit 101. When the threshold value T2 is greater than or equal to the threshold value T2, the signal generated by the signal generation unit 103a is output to the drive circuit 102. When the value indicating the target luminance is smaller than the second threshold value T2, the signal generated by the signal generation unit 103a Switch means 103b (an example of output control means) that does not output the signal to the drive circuit 102.

  The HUD device 1 includes a light source driving device 100 and a light source 12, and causes the user 4 to cause the display light L representing a predetermined image emitted from the light source 12 to reach the windshield 3 (an example of a transparent plate). The virtual image V of the predetermined image is visually recognized through the windshield 3 with the scenery in front.

(Modification)
In addition, this invention is not limited to said embodiment, A various deformation | transformation is possible. An example of modification is shown below.

In the above description, an example in which the drive circuit 102 and the signal generation unit 103a are separate bodies has been described, but the present invention is not limited to this.
An LED driver IC with a frequency modulation function may be adopted as the drive circuit. In this case, whether the frequency of the on / off signal is changed by switching whether or not the external parts (resistors, capacitors, etc.) connected to enable the frequency modulation function of the LED driver IC are connected by the switch means. You can control whether or not. That is, the drive circuit in this case has a light source control unit and a signal generation unit as functional units.

In the above description, an example in which only the analog dimming method is performed at the first threshold value T1 or more is shown, but the present invention is not limited thereto.
For example, as shown in FIGS. 7A and 7B, the control unit 101 outputs a PWM dimming signal in a range where the target luminance value is smaller than the first threshold T1, and is equal to or higher than the first threshold T1. In addition, within a range less than a predetermined value (see (3) shown in FIGS. 7A and 7B), a signal in which both the drive current and the pulse width are adjusted according to the target luminance is output, and is equal to or greater than the predetermined value. In this range, an analog dimming signal may be output. The duty ratio in this case is, for example, 0% when the target luminance is 0, 80% when the first threshold value T1, and 100 when the predetermined value (see (3) shown in FIG. 7A). %, And so on.
Even in such a case, when the value indicating the target luminance is equal to or greater than the first threshold T1, the control unit 101 generates a drive signal adjusted so that the drive current becomes a value corresponding to the target luminance. It can be said that.

  In the above description, the example in which the light source 12 is the backlight of the liquid crystal display device 10 is shown, but the present invention is not limited to this. The light source may be a light source provided in a self-luminous display device.

  In the above description, the example in which the optical system 20 is configured by two reflecting members has been described, but the present invention is not limited thereto. The optical system may be configured by one or three or more reflecting members, or may be configured to directly irradiate the windshield 3 with the display light L from the liquid crystal display device 10 without including the optical system 20.

  In the above description, the display image L is reflected by the windshield 3 of the vehicle 2 to cause the user 4 to visually recognize the display image. However, the present invention is not limited to this. The HUD device may include a dedicated combiner (an example of a transparent plate), and the display image may be visually recognized by reflecting the display light L with the combiner. Further, the HUD device is not provided in the dashboard, but may be a stationary type that can be installed on the dashboard.

  In the above embodiment, an example of a vehicle on which the HUD device is mounted is a vehicle, but the present invention is not limited to this. The HUD device may be mounted on another vehicle such as a motorcycle, a construction machine, an agricultural machine, a ship, an aircraft, or the like.

  In addition, this invention is not limited by the above embodiment and drawing. Changes (including deletion of constituent elements) can be added to the embodiments and the drawings as appropriate without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... HUD apparatus 2 ... Vehicle 3 ... Windshield (an example of a transparent plate)
DESCRIPTION OF SYMBOLS 4 ... User L ... Display light V ... Virtual image 10 ... Liquid crystal display device 11 ... Liquid crystal panel 12 ... Light source 20 ... Optical system 21 ... Plane mirror 22 ... Concave mirror 30 ... Illuminance sensor 40 ... Circuit board 50 ... Housing 100 ... Light source drive device 101 ... Control unit 102... Drive circuit (an example of light source control unit and generation unit)
103 ... Frequency changing means 103a ... Signal generating means 103b ... Switching means (an example of output control means)

Claims (3)

Light source driving means for driving the light source by supplying a driving current to the light source;
Control means for controlling the light source driving means so that the light source emits light at a desired target luminance, and when the value indicating the target luminance is equal to or greater than a predetermined first threshold, the driving current is A first drive signal adjusted to have a value corresponding to the target luminance is generated and supplied to the light source driving means. When the value indicating the target luminance is smaller than the first threshold, the driving is performed. A control unit that generates a second drive signal that is adjusted to have a constant current value and has a pulse width changed in accordance with the target luminance, and supplies the second drive signal to the light source driving unit;
Generating means for generating an on / off signal superimposed on the second driving signal and supplying the on / off signal to the light source driving means;
Frequency changing means for changing the frequency of the on / off signal generated by the generating means,
The frequency changing means changes the frequency of the on / off signal when the value indicating the target luminance is equal to or higher than a predetermined second threshold, and the value indicating the target luminance is smaller than the second threshold. If the frequency of the on-off signal is not changed,
The light source driving means includes
When the first drive signal is supplied, a drive current is supplied to the light source based on the first drive signal, the second drive signal is supplied, and a value indicating the target luminance is obtained. If it is equal to or greater than the second threshold, a drive current is supplied to the light source based on the second drive signal and the on / off signal whose frequency is changed by the frequency changing means, and the second drive signal is When the value indicating the target luminance is smaller than the second threshold, the light source is based on the second drive signal and the on / off signal whose frequency is not changed by the frequency changing means. Supply drive current to
A light source driving device characterized by that. The frequency changing means is
Signal generating means for generating a signal for changing the frequency of the on / off signal;
Under the control of the control means, when the value indicating the target brightness is equal to or greater than the second threshold, the signal generated by the signal generation means is output to the light source driving means, and the value indicating the target brightness is An output control unit that does not output the signal generated by the signal generation unit to the light source driving unit when smaller than the second threshold;
The light source driving device according to claim 1. The light source driving device according to claim 1 or 2, and the light source,
A head-up display device that causes a viewer to visually recognize a virtual image of the predetermined image through the transparent plate by causing display light representing the predetermined image emitted from the light source to reach the transparent plate.

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