JP2005332586A - Lighting dimmer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control illumination brightness at night with a high resolution by attenuating light through reduction of a constant current value supplied to a light source for illumination at night and making duty control in this state of light attenuation, in a lighting dimmer for controlling illumination brightness of measuring instruments or the like of a vehicle by duty control. <P>SOLUTION: A constant-current circuit 2 drives at constant current a light source for illumination 1 consisting of a plurality of light-emitting diodes D1 to D8 with a constant-current value set in accordance with a constant-current value controlled voltage Vb. A constant value switching circuit 4 changes the constant-current value controlled voltage Vb to a voltage lower than at the daytime, when a light-attenuation signal is outputted from a light control part (a CPU part) at a night-time light control. With this, the constant current drive value of the light source for illumination is reduced down to around 20% of that of the daytime. A PWM drive circuit 3 controls a period during which the constant current value controlled voltage Vb is supplied to the constant-current circuit 2, in accordance with a PWM signal outputted from the light control part (the CPU part) 7. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an illumination dimming device that adjusts the illumination brightness of a vehicle instrument or the like by duty control. More specifically, the illumination control is such that duty control is performed by reducing power supplied to an illumination light source at night or the like. The present invention relates to an optical device.

In general, in a vehicle, illumination brightness of a combination meter or the like can be adjusted by duty control at night or the like. Based on the fact that the night lamp switch was turned on, a current limiting resistor was inserted in series with the illuminating lamp, so that the brightness was reduced to the brightness corresponding to the night, and the illumination brightness could be adjusted by duty control. The thing is known (refer patent documents 1-3). Also, in the daytime, the lamp for lighting and the variable resistor for dimming are connected in series, the brightness of the dimming lamp can be adjusted from 0 to 100%, and when the light switch is turned on at night, There is known an illumination dimmer in which a dropper resistor is interposed in series with the lamp so that the luminance of the illumination lamp can be adjusted between 0 and 20% within the maximum range of the dimming variable resistor ( (See Patent Document 4).
Japanese Utility Model Publication No. 5-16485 Japanese Patent Laid-Open No. 10-59066 JP 2000-180217 A JP 7-242146 A

  When the brightness of the illumination light source can be varied from 0% (lights off) to 100% (maximum brightness during the daytime) by duty control, the brightness adjustment range at night may be about 0% to 20%. Is difficult to adjust in fine steps. For example, even if the duty of the PWM signal is controlled in units of 1%, it can be adjusted only with a resolution of 1% with respect to the maximum luminance in the daytime.

  Therefore, at night, by providing a current limiting resistor (dropper resistor) in series with the illumination light source, the current supplied to the illumination light source can be reduced, and duty control can be performed with the current reduced. Has been made traditionally.

  However, in order to reduce the light to about 20% of the maximum daytime luminance by providing a current limiting resistor (dropper resistor) in series with the illumination light source, the allowable power is relatively large in the current limiting resistor (dropper resistor). It is necessary to use something. In addition, when a vehicle battery is used as the illumination power source, it is necessary to provide a circuit or the like for preventing the illumination luminance from fluctuating due to fluctuations in battery voltage. For this reason, it is difficult to reduce the size of the illumination light control device.

  The present invention has been made to solve such a problem. By driving the illumination light source at a constant current, the illumination brightness does not fluctuate due to the fluctuation of the battery voltage, and the constant current value is reduced at night. An object of the present invention is to provide an illumination dimming device capable of adjusting the nighttime illumination brightness with high resolution by controlling the constant current drive period based on the duty ratio of the PWM signal.

  In order to solve the above problems, an illumination dimming device according to the present invention switches an illumination light source, a constant current circuit that drives the illumination light source with a constant current, and switches a constant current value of the constant current circuit in at least two stages. A constant current value switching circuit and a PWM drive circuit that controls a constant current drive period of the illumination light source by the constant current circuit according to the duty of the PWM signal.

  The illumination light source can be composed of one or a plurality of light emitting diodes. The constant current circuit is composed of a transistor having a current value setting resistor connected to the emitter side and an illumination light source connected to the collector side, and the constant current value switching circuit changes the voltage supplied to the base of the transistor. The constant current value supplied to the illumination light source may be switched.

  By driving the illumination light source at a constant current, the illumination brightness does not vary even if the power supply voltage of the illumination power source varies. By switching the constant current value in two stages, the illumination brightness can be reduced at night. And by performing duty control in a state where the constant current value is reduced, it is possible to adjust nighttime illumination brightness with high resolution.

  Hereinafter, the best mode for carrying out the invention will be described based on examples.

  FIG. 1 is a diagram showing a circuit configuration of an illumination dimmer according to an embodiment of the present invention. The illumination dimming device shown in FIG. 1 includes an illumination light source 1 composed of a plurality of light emitting diodes D1 to D8, a constant current circuit 2 that drives each of the light emitting diodes D1 to D8 at a constant current, and a constant current of each of the light emitting diodes D1 to D8. PWM drive circuit 3 that controls the current drive period according to the duty of the PWM signal, constant current value switching circuit 4 that changes the constant current value of constant current circuit 2 based on the dimming signal, illuminance sensor 5, and dimming A dimming control unit (CPU unit) 7 that outputs a dimming signal and a PWM signal based on an input from the operation unit 6, and a constant voltage power source that outputs a stabilized power supply VCC upon receiving power from an in-vehicle battery 8 Circuit 9.

  Each of the light emitting diodes D1 to D8 is for illuminating various instruments provided on an instrument panel (not shown), operation / display units of various in-vehicle facilities, and the like. A battery power source VBB is used as a power source for illumination. In the present embodiment, two sets of three light-emitting diodes connected in series and one set of two light-emitting diodes connected in series are provided, and each set is driven at a constant current. Therefore, the constant current circuit 2 is provided with a constant current circuit composed of NPN transistors Q1, Q2, Q3 and emitter resistors R1, R2, R3 corresponding to each of the three sets of light emitting diode series connection circuits. In this constant current circuit 2, a constant current value flowing through the light emitting diode is set by a constant current value control voltage Vb supplied to the base of the NPN transistor and an emitter resistance value. Here, if the constant current value control voltage is Vb, the emitter resistance value is Re, and the base-emitter voltage of the NPN transistor is Vbe, the constant current value Iled supplied to the light emitting diode is Iled = (Vb−Vbe). / Re relationship.

  Thus, by driving each of the light emitting diodes D1 to D8 at a constant current, the current supplied to each of the light emitting diodes D1 to D8 does not fluctuate even if the power supply voltage of the battery 8 fluctuates. Luminance does not vary with variation.

  The PWM drive circuit 3 is composed of an electronic switch circuit using transistors and the like, and the constant current value control voltage Vb, which is the output of the constant current value switching circuit 4, is constant current while the logic level of the PWM signal is H level. The ground potential is supplied to the base of each NPN transistor of the constant current circuit 2 while the logic level of the PWM signal is L level.

  While the constant current value control voltage Vb is supplied, the constant current circuit 2 drives the light emitting diodes D1 to D8 with a constant current value set based on the constant current value control voltage Vb. When the constant current value control voltage Vb is not supplied, no current is supplied to the light emitting diodes D1 to D8. Thereby, the average value of the current supplied to each of the light emitting diodes D1 to D8 is controlled based on the duty of the PWM signal, and the luminance of each of the light emitting diodes D1 to D9 can be adjusted.

  The constant current value switching circuit 4 changes the constant current value control voltage Vb supplied to the bases of the NPN transistors Q1 to Q3 of the constant current circuit 2 between non-dimming and dimming. The constant current value switching circuit 4 is basically configured by a constant voltage circuit using a PNP transistor Q41. In a state where the dimming signal is not output (the dimming signal is at the L level), the electronic switch circuit S41 configured by the transistor circuit is off (non-conducting state). The base potential of the PNP transistor Q41 at this time is determined by the divided voltage of the resistor R41 and the resistor R42, and a voltage higher than the base potential of the PNP transistor Q41 by the emitter-base voltage of the PNP transistor Q41 is connected to the emitter resistor R43. It is output from the connection point with the emitter of the PNP transistor Q41.

  In the state where the dimming signal is output (the dimming signal is at the H level), the electronic switch circuit S41 is on (conducting state). At this time, the base potential of the PNP transistor Q41 is determined by the divided voltage of the resistor R41 and the parallel combined resistor of the resistor R42 and the resistor R44. Therefore, the constant current value control voltage Vb output from the constant current value switching circuit 4 is a lower voltage when dimming than when it is not dimmed.

  In the present embodiment, the constant current driving value of the constant current circuit (that is, the driving current value of the light emitting diode) is, for example, about 100 mA based on the constant current value control voltage Vb (non-dimming) at the time of non-dimming. The constant current value control voltage Vb is set so that the constant current drive value of the constant current circuit (that is, the drive current value of the light emitting diode) is about 21 mA, for example, based on the constant current value control voltage Vb during light (during dimming). I try to switch.

  The dimming control unit (CPU unit) 7 is configured using a microcomputer system, and is controlled by a dimming stage setting unit 71, dimming control unit 72, daytime dimming by a control program stored in a ROM (not shown) or the like. An optical duty table 73, a nighttime light control duty table 74, a PWM signal generation unit 75, and various determination / processing means are configured.

  The dimming operation unit 6 includes a switch or the like for setting the dimming stage. The dimming stage up / down operation signal is supplied to the dimming stage setting unit 71 via an input interface circuit (not shown). The dimming level setting unit 71 sets the dimming level based on the up / down operation of the dimming level. The set dimming stage is supplied to the PWM signal generation unit 75 and the dimming control unit 72. In the present embodiment, the dimming brightness can be adjusted in 16 levels including turning off.

  The illuminance detection signal according to the ambient brightness detected by the illuminance sensor 5 is converted into digital data via an A / D converter (not shown) in the dimming control unit (CPU unit) 7, and the dimming control unit 72. The dimming control unit 72 determines whether it is daytime or nighttime based on the ambient brightness detected by the illuminance sensor 5. The judgment result of daytime / nighttime is supplied to the PWM signal generation unit. When it is determined that it is nighttime, the dimming control unit 72 outputs a dimming signal via an output interface circuit (not shown). In the present embodiment, the dimming control unit 72 does not output a dimming signal when the dimming stage is set to the maximum even at night. Thereby, the illumination brightness can be maximized by setting the dimming step to the maximum even at night.

  The determination at night may be made based on the fact that the night light switch is turned on. Moreover, a switch for performing dimming may be provided, and it may be determined that the night is based on the dimming switch being turned on. In such a case, it is not necessary to provide the illuminance sensor 5.

  The daytime dimming duty table 73 stores daytime dimming duty data in association with each dimming stage. The night-time dimming duty table 74 stores night-time dimming duty data in association with each dimming stage. In the present embodiment, each dimming duty data is stored in a rewritable nonvolatile memory such as an EEPROM. Note that the daytime dimming duty table 73 is not required in the case of a specification in which the illumination luminance is fixed (no dimming is performed) during the daytime.

  The PWM signal generation unit 75 reads the duty data at the dimming stage set from the corresponding dimming duty tables 73 and 74 based on the daytime / nighttime determination result, generates a PWM signal of the read duty, and is not illustrated. A PWM signal is output via the output interface circuit.

  FIG. 2 is a diagram illustrating the dimming characteristics at night of the illumination dimming apparatus according to the present embodiment. In the present embodiment, the dimming stage can be adjusted to 16 stages from step 0 to step 15. In step 15, which is the maximum luminance, the dimming signal is not output even at night (the dimming signal is off), the current of the light source (light emitting diode) is set to 100 mA, and the dimming duty is set to 95%. Thereby, the relative luminance is set to 95. Here, the value obtained by multiplying the current (I) of the light source (light emitting diode) and the dimming duty (D) on the assumption that the luminance of the light source (light emitting diode) is directly proportional to the current of the light source (light emitting diode). Is the relative luminance (L).

  If the dimming stage is step 14 or less at night, a dimming signal is output (dimming signal on). Thereby, duty control by the PWM signal is performed with the current of the light source (light emitting diode) reduced to 21 mA. In step 14, the light control duty is set to 95% and the relative luminance is set to 20. In step 13, the dimming duty is set to 71% and the relative luminance is set to 15. In step 2, the light control duty is set to 3% and the relative luminance is set to 0.63. In step 1, the light control duty is set to 2% and the relative luminance is set to 0.42. In step 0, the dimming duty is 0% (output of the PWM signal is stopped), and the light is turned off.

  FIG. 3 is a diagram for explaining dimming characteristics when dimming is performed without dimming at night (conventional). When dimming is performed with only the dimming duty while the current of the light source (light emitting diode) is fixed at 100 mA, the change in relative luminance is 1 even if the dimming duty is changed in units of 1%. A sufficient resolution cannot be obtained in the luminance region.

  On the other hand, as shown in FIG. 2, the current of the light source (light emitting diode) is reduced from 100 mA to 21 mA, and the duty control is performed in a state where the illumination luminance is lowered, so that the dimming duty is in units of 1%. The change of the relative luminance when changed with is 0.21, and a high resolution can be obtained in the low luminance region.

  FIG. 4 is a diagram showing a main configuration of an illumination dimming device according to another embodiment of the present invention, and FIG. 5 is a diagram showing a main configuration of an illumination dimming device according to still another embodiment of the present invention. . As shown in FIG. 4, an illumination light source corresponding to each unit such as a meter unit, a warning light unit, an odometer unit, an operation display / operation unit of an in-vehicle audio device, an operation display / operation unit of a car air conditioner, etc. 1 and 11 and constant current circuits 2 and 12 may be provided, respectively, so that luminance corresponding to each part can be obtained. Further, as shown in FIG. 5, the illumination light sources 1 and 11, the constant current circuits 2 and 12, the PWM drive circuits 3 and 13, and the constant current value switching circuits 4 and 14 are provided for each part, and for each part. A plurality of corresponding PWM signals may be generated to realize different dimming characteristics (brightness change characteristics) and different dimming characteristics (differentiating the maximum brightness at night for each part). .

  Note that in this embodiment mode, an example in which a light-emitting diode is used as an illumination light source has been described, but a lamp may be used as the illumination light source. Moreover, the illumination dimming device according to the present invention is not only used for adjusting the illumination brightness of a vehicle meter, but also for adjusting the brightness of a self-luminous meter display or warning light display provided on an instrument panel or the like. Applicable.

It is a figure which shows the circuit structure of the illumination light control apparatus which concerns on one Example of this invention. It is a figure which shows the light control characteristic at night of the illumination light control apparatus which concerns on a present Example. It is a figure explaining the light control characteristic at the time of performing light control without dimming at night (conventional). It is a figure which shows the principal part structure of the illumination light control apparatus which concerns on the other Example of this invention. It is a figure which shows the principal part structure of the illumination light control apparatus which concerns on the further another Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Light source for illumination 2,12 Constant current circuit 3,13 PWM drive circuit 4,14 Constant current value switching circuit 5 Illuminance sensor 6 Dimming operation part 7 Dimming control part (CPU part)
8 Battery 9 Constant voltage power supply circuit 71 Dimming stage setting unit 72 Dimming control unit 73 Dimming duty table for daytime 74 Dimming duty table for nighttime 75 PWM signal generation unit D1 to D8 Light emitting diodes Q1 to Q3 NPN transistor Q41 PNP transistors constituting constant current value switching circuit R1 to R3 Emitter resistors constituting constant current circuit R41 to R43 Resistors constituting constant current value switching circuit S41 Electronic switch Vb for switching constant current value control voltage Vb Constant current control voltage

Claims (3)

  An illumination light source, a constant current circuit that drives the illumination light source with a constant current, a constant current value switching circuit that switches the constant current value of the constant current circuit in at least two stages, and the illumination light source of the constant current circuit An illumination dimming device comprising: a PWM drive circuit that controls a constant current drive period according to a duty of a PWM signal.   The illumination light control device according to claim 1, wherein the illumination light source includes one or a plurality of light emitting diodes.   The constant current circuit includes a transistor having a current value setting resistor connected to the emitter side and the illumination light source connected to the collector side, and the constant current value switching circuit changes a voltage supplied to the base of the transistor. The illumination light control device according to claim 1, wherein the constant current value supplied to the illumination light source is switched.

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