JP2015074309A - Led headlight light-control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED headlight light-control circuit capable of changing luminous intensity of headlight for a vehicle stepwise or at a speed in accordance with circumstances without giving discomfort to a visually recognizing person.SOLUTION: A control circuit and a driving part change and control an electric conduction state of a power MOS transistor M1 stepwise by changing a driving control signal given to a gate of the power MOS transistor M1. For example, when the control circuit is driven by using a first linear driving circuit LN11, the light emission luminous intensity of an LED module LM1 can be sharply changed. When the control circuit is driven by using a second linear driving circuit LN21, the light emission luminous intensity of the LED module LM1 can be moderately changed.

Description

  The present invention relates to an LED headlight dimming circuit for dimming a headlamp.

  As this type of dimming circuit, a technique is provided in which the energization time per unit time is varied by PWM control (see, for example, Patent Document 1). According to the technique described in Patent Document 1, PWM control makes it difficult to be affected by noise even in low illuminance.

  By the way, for example, a headlight for a vehicle irradiates the traveling direction of the vehicle to ensure the visibility of the driver particularly at night. At this time, when changing the illuminance of the headlamp to the target illuminance, it is desirable to change the illuminance from the current value to the target value stepwise and at a speed corresponding to the situation. In order to realize such a configuration, a plurality of LEDs are connected in series to the headlamp, a control switch is provided in parallel with a part of the plurality of LEDs, and the part of the LEDs is turned on and off. Is configured to be short-circuitable.

JP 2008-192324 A

  For example, a case is considered in which other LEDs are turned on / off while a part of the light quantity of the LEDs is maintained. When the PWM control method described in Patent Document 1 or the like is applied, the applied voltage applied to the plurality of LEDs fluctuates twice at the PWM on / off timing per one PWM cycle, and the energization current of the LED is the LED Increases or decreases greatly at the on / off timing.

  When the DCDC converter generates and outputs the applied voltage applied to the LED, it takes time for feedback accompanying fluctuations in the output voltage due to the output characteristics of the DCDC converter, and control followability is poor. For this reason, even if the above technique is applied and the PWM on / off duty is changed stepwise by 1% from 10% to 0%, for example, a considerable time is required for the output feedback time of the DCDC converter. For this reason, the change resolution of the PWM on / off duty ratio is restricted, and the viewer feels uncomfortable.

  An object of the present invention is to provide an LED headlamp dimming circuit capable of changing the luminous intensity of a vehicle headlamp at a stepwise and speed according to the situation without giving a sense of incongruity to a viewer. There is.

  According to the first aspect of the present invention, the control switch can control the energization current by changing the drive control signal applied to the control terminal. Therefore, when the drive control signal given to the control terminal of the control switch by the change control circuit is changed, the energization current of the control switch can be changed stepwise by changing the energization state of the control switch step by step. The energizing current flowing through the section can also be changed in stages.

  Then, the energization current of some of the plurality of LEDs can be changed stepwise, and accordingly, the light quantity of the target LED can be adjusted stepwise. Therefore, the luminous intensity of the headlamp can be changed at the stepwise and speed according to the situation. As a result, the luminous intensity of the vehicle headlamp can be changed without causing the viewer to feel uncomfortable. “Stepwise” includes not only discrete steps but also infinite steps. The “energized state” includes a state in which the characteristics of the control switch change from the off state to the on state or from the on state to the off state, as well as the on state and the off state.

The electrical block diagram which shows the structural example of the headlamp light control circuit which concerns on 1st Embodiment of this invention. Explanatory drawing which shows roughly the example of arrangement | positioning of a headlamp LED circuit Timing chart showing an example of dimming method (part 1) Characteristic diagram showing control signal dependence of on-resistance of control switch Timing chart showing an example of dimming method (2) Timing chart schematically showing the result of comparison with the control method of the comparative example Electrical configuration diagram showing a configuration example of a part of a headlight dimming circuit according to a second embodiment of the present invention (part 1) Explanatory diagram schematically showing one form of linear control Timing chart showing an example of dimming method (part 3) Timing chart showing an example of dimming method (4) Timing chart showing an example of light control method (5) Timing chart showing an example of light control method (6) Electrical configuration diagram showing an example of a part of a headlamp dimming circuit (part 2) The electrical block diagram which shows the structural example of the headlamp dimming circuit which concerns on 3rd Embodiment of this invention. Explanatory drawing which shows the usage example of the headlamp light control circuit which concerns on 4th Embodiment of this invention. Block diagram schematically showing an example of the electrical configuration of the headlight dimming circuit

  Hereinafter, some embodiments of the LED headlight dimming circuit will be described with reference to the drawings. In each embodiment, substantially the same or similar parts are denoted by the same reference numerals, and description thereof will be omitted as necessary. In each embodiment, description will be made focusing on characteristic parts.

(First embodiment)
FIG. 1 schematically shows an example of an electrical configuration of a headlamp dimming circuit, and FIG. 2 schematically shows an illumination state of the headlamp dimming circuit. As shown in FIG. 2, this headlamp is used for a passenger such as a driver of a vehicle Ca to visually recognize the front of the vehicle mainly at night. This headlamp is configured by using, for example, a white LED, and a traveling headlamp (hereinafter referred to as a high beam) HB that irradiates a relatively high range HI and a low-profile headlamp (hereinafter referred to as a low headlight) that irradiates a relatively low range LO. Low beam) LB. These headlamps LT are arrange | positioned at the vehicle front left part and the vehicle front right part, for example.

  The high beam HB is mainly used when there is no preceding vehicle that travels forward in order to illuminate a distance in front of the vehicle (for example, 100 m or more) at night, an oncoming vehicle that passes from the front, or a pedestrian. The low beam LB is arranged so as to illuminate slightly below the high beam HB, for example, about 40 m ahead. The low beam LB is used to reduce the influence of light reflection such as fog, snow and the like, leading vehicles traveling in front, oncoming vehicles passing from the front, pedestrians and the like.

  As shown in FIG. 1, the high beam HB and the low beam LB are configured by, for example, connecting at least a plurality of LED modules LM1 and LM2 in series. In the present embodiment, the LED module LM1 constitutes a high beam HB, and the LED module LM2 constitutes a low beam LB.

  Each of these LED modules LM1 and LM2 is configured by connecting a plurality of LEDs directly (and in parallel). A lighting current is supplied from the DCDC converter 1 to the LED modules LM1 and LM2.

  A headlight dimming circuit 2 is connected to these LED modules LM1 and LM2 for adjusting and controlling the lighting state of the headlamp. The headlight dimming circuit 2 includes an N-channel type power MOS transistor M1 connected in parallel to the LED module LM1, a drive unit 31 for driving the power MOS transistor M1, and a P-channel connected in parallel to the LED module LM2. A power MOS transistor M2 of a type, a drive unit 32 for driving the power MOS transistor M2, and a control circuit 4 for controlling the drive units 31 and 32.

  The control circuit 4 of the headlamp dimming circuit 2 is constituted by, for example, a microcomputer, and the LED modules LM1 and LM2 are turned on / off in response to a command signal for turning on / off the headlight for traveling and the low headlight. Controls the off state.

  A MOS transistor M2 is connected between both terminals of the LED module LM2, and a MOS transistor M1 is connected between both terminals of the LED module LM1. Therefore, if the drive unit 32 drives the MOS transistor M2 on, both terminals of the LED module LM2 are short-circuited. On the other hand, if the drive unit 31 drives the MOS transistor M1 on, both terminals of the LED module LM1 are short-circuited.

  The DCDC converter 1 is configured to light up the LED modules L2 and LM1 at a constant current, and is configured to vary the output voltage of the LED modules LM2 and LM1 that perform dimming control. When the control circuit 4 controls, for example, the LED module LM2 to be fully turned on and the LED module LM1 to be turned off in response to the command signal, the MOS transistor M1 is turned on while the MOS transistor M2 is turned off. In such a case, the DCDC converter 1 sets the output voltage only to the energization of the LED module LM2.

  As shown in FIG. 1, since the drive units 31 and 32 have the same electrical configuration, only the electrical connection relationship of the drive unit 31 will be described. In the drawing, the suffix “1” is added to the reference numerals of the components of the drive unit 31 for illustration. The drive unit 32 shows the reference numerals of the corresponding components with the subscript “2” instead of the subscript “1” described above, and a description thereof will be omitted.

  The drive unit 31 includes, for example, 2 (plural) systems of current energization paths and current discharge paths for the gate input capacitance of the MOS transistor M1, and thus includes 2 (plural) systems of linear drive circuits.

  The drive unit 31 includes drive circuits 51 and 61, a P-channel type MOS transistor M51, an N-channel type MOS transistor M61, and a resistor R11. These elements constitute the first linear drive circuit LN11.

  MOS transistors M51 and M61 are connected in series between the supply terminal of the power supply Vcc and the ground, and a resistor R11 is connected between the common connection node N11 and the gate of the MOS transistor M1. A drive circuit 51 is connected to the gate of the MOS transistor M51, and the control circuit 4 is connected to the drive circuit 51. A drive circuit 61 is connected to the gate of the MOS transistor M61, and the control circuit 4 is connected to the drive circuit 61.

  The drive unit 31 includes drive circuits 71 and 81, a P-channel type MOS transistor M71, an N-channel type MOS transistor M81, and a resistor R21, and the second linear drive circuit LN21 is configured by these elements.

  MOS transistors M71 and M81 are connected in series between the supply terminal of the power supply Vcc and the ground, and a resistor R21 is connected between the common connection node N21 and the gate of the MOS transistor M1.

  A drive circuit 71 is connected to the gate of the MOS transistor M71, and the control circuit 4 is connected to the drive circuit 71. A drive circuit 81 is connected to the gate of the MOS transistor M81, and the control circuit 4 is connected to the drive circuit 81.

  The drive unit 31 linearly drives the MOS transistor M1 from, for example, an on state to an off state or from an off state to an on state in accordance with a control signal supplied from the control circuit 4. The resistance values of the resistor R11 and the resistor R21 are set to different resistance values. Since the drive part 32 is the same structure as the drive part 31, the detailed description of the electrical connection relationship is abbreviate | omitted.

  The operation of the above configuration will be described. Here, the LED module LM2 is always in the fully lit state S1, and the LED module LM1 is a dimming method for returning from the fully lit state S1 to the fully lit state S2, and further returning from the fully lit state S2 to the fully lit state S1. explain.

  FIG. 3A schematically shows an example of a dimming method when the first linear drive circuit LN11 of the drive unit 31 is used. In the example shown in FIG. 3A, for example, the drive circuit 71 outputs a drive control signal “H” and the drive circuit 81 outputs “L”, so that the second linear drive circuit LN21 has its output node N21. Is maintained in a high impedance state.

  As shown in FIG. 3A, when the drive circuit 51 outputs “H” and the drive circuit 61 outputs “L” as a drive control signal, the node N11 is in a high impedance state and the gate of the MOS transistor M1 is also in a high impedance state. Retained. Therefore, the drain and source of the MOS transistor M1 are kept open, current is supplied to the LED module LM1, and the LED module LM1 is fully lit (see period A in FIG. 3A).

  Thereafter, when the drive circuit 51 outputs “L” as a drive control signal, the MOS transistor M51 is turned on, and the gate input capacitance of the MOS transistor M1 is charged from the power supply Vcc through the resistor R11. At this time, if the resistance value of the resistor R11 is relatively low (<< resistance value of the resistor R21), the time required for charging the gate input capacitance of the MOS transistor M1 is also relatively short, and the gate voltage of the MOS transistor M1 increases rapidly. To do.

Then, the LED module LM1 is short-circuited between the two terminals by the MOS transistor M1, the current flowing in the LED module LM1 flows to the MOS transistor M1 side, and the LED module LM1 rapidly shifts to the all-off state S2. (Refer to period B in FIG. 3A). At this time, the drain-source current of the MOS transistor M1 is at a maximum current _{I M.}

  Thereafter, when the drive circuit 51 outputs “H” as a drive signal and the drive circuit 61 outputs “H” as a drive signal, the MOS transistor M51 is turned off and the MOS transistor M61 is turned on. At this time, the accumulated power of the gate input capacitance of the MOS transistor M1 is discharged to the ground through the MOS transistor M61.

  As described above, when the resistance value of the resistor R11 is relatively low, the time required for discharging the gate input capacitance of the MOS transistor M1 is also relatively short, and the gate voltage of the MOS transistor M1 rapidly decreases. Then, since both ends of the LED module LM1 are rapidly opened, the LED module LM1 is rapidly energized again, and the LED module LM1 rapidly shifts to the fully lit state S1 (see FIG. (Refer to period C in 3 (a)).

  FIG. 3B schematically shows an example of a dimming method when the second linear drive circuit LN21 of the drive unit 32 is used for driving. In the example shown in FIG. 3B, the control circuit 4 outputs an “H” drive signal to the drive circuit 51 and outputs an “L” drive signal to the drive circuit 61, for example. The output node N11 of the 1 linear drive circuit LN11 is held in a high impedance state.

  As shown in FIG. 3B, when the drive circuit 71 outputs “H” as a drive signal and the drive circuit 81 outputs “L” as a drive signal, the node N21 becomes a high impedance state and the gate of the MOS transistor M1. Are also maintained in a high impedance state. Accordingly, the drain and source of the MOS transistor M1 are kept open, and a current is passed through the LED module LM1 so that the LED module LM1 is in the fully lit state S1 (see period D in FIG. 3B).

  Thereafter, when the drive circuit 71 outputs “L” as a drive signal, the MOS transistor M71 is turned on, and the gate input capacitance of the MOS transistor M1 is charged from the power supply Vcc through the resistor R21. At this time, if the resistance value of the resistor R21 is relatively high (>> resistance value of the resistor R11), the time required for charging the gate input capacitance of the MOS transistor M1 also becomes relatively long, and the gate voltage of the MOS transistor M1 becomes gentle. Rise (eg linearly proportional to time). When the gate voltage of the MOS transistor M1 rises slowly, the drain-source current (energization current) of the MOS transistor M1 gradually rises according to the degree of increase in the gate voltage (see period E in FIG. 3B).

  When the drain-source current of the MOS transistor M1 is gradually increased, the energization current of the LED module LM1 is decreased according to the gentle increase. The drain-source current of the MOS transistor M1 continues to rise until the gate voltage of the MOS transistor M1 reaches approximately the threshold voltage Vth. When the gate voltage reaches the threshold voltage Vth, the drain-source current of the MOS transistor M1 is saturated. As a result, the current becomes almost constant, and the current hardly flows to the LED module LM1 side. Then, the current that has been energized to the LED module LM1 flows to the MOS transistor M1 side, and thus the LED module LM1 is completely turned off S2 (see period F in FIG. 3B).

  Thereafter, when the drive circuit 71 outputs “H” as a drive signal and the drive circuit 81 outputs “H” as a drive signal, the MOS transistor M71 is turned off and the MOS transistor M81 is turned on. At this time, the accumulated power of the gate input capacitance of the MOS transistor M1 is extracted to the ground through the MOS transistor M81.

  As described above, when the resistance value of the resistor R21 is relatively high, the time required for discharging the gate input capacitance of the MOS transistor M1 is also relatively short, and the gate voltage of the MOS transistor M1 gradually decreases (FIG. 3). (Refer to period G in (b)). When the gate voltage of the MOS transistor M1 gradually decreases and the gate voltage reaches the threshold voltage Vth of the MOS transistor M1, the drain-source current of the MOS transistor M1 gradually decreases in accordance with the gentle decrease in the gate voltage. (Refer to the period H in FIG. 3B).

  When the drain-source current of the MOS transistor M1 decreases, the energization current of the LED module LM1 gradually increases in accordance with this gradual decrease. As the energization current increases, the luminous intensity of the LED module LM1 gradually increases. When the drain-source current of the MOS transistor M1 continues to decrease and becomes almost zero, the current flows to the LED module LM1 side. Then, LED module LM1 will be in the all lighting state S1 (refer I period of FIG.3 (b)).

  FIG. 4 shows an example of the gate-source voltage dependence of the on-resistance of the power MOS transistor M1. FIG. 5 shows a modification of the timing chart in place of FIG. As shown in FIG. 4, when the gate-source voltage of the power MOS transistor M1 increases, the on-resistance decreases, and conversely, when the gate-source voltage decreases, the on-resistance increases.

  Therefore, when the total current amount of the MOS transistor M1 and the LED module LM1 is constant, the energization current amount of the LED module LM1 changes according to the change of the on-resistance value of the power MOS transistor M1. Then, the luminous intensity of the LED module LM1 changes in accordance with the amount of energization current.

  Therefore, the control circuit 4 and the drive circuits 71 and 81 adjust the on-resistance of the MOS transistor M1 by linearly driving the LED module LM1 and adjusting the gate voltage of the MOS transistor M1 to 0 or more and less than the threshold voltage Vth, Thereby, the amount of current flowing through the LED module LM1 may be adjusted to adjust the luminous intensity of the LED module LM1.

  That is, for example, when the LED module LM1 is shifted from the fully lit state S1 to the fully lit state S2, or when the LED module LM1 is shifted from the fully lit state S2 to the fully lit state S1, the control process is performed in the dimming state S3 in the middle stage. May be stopped.

As shown in FIG. 5, when the drive circuit 71 outputs “L” as a drive signal, the gate input capacitance of the MOS transistor M1 gradually increases, and the drain-source current of the MOS transistor M1 increases accordingly. However, if the period during which the drive circuit 71 outputs “L” is reduced as compared with the example of FIG. 3B, the gate voltage of the MOS transistor M1 can be adjusted so as not to reach the threshold voltage Vth (FIG. 5). E2 period reference). Then, the conduction current of the MOS transistor M1 remains at the current I _L1 (<maximum current I _M ).

  When the drive circuit 71 holds the “H” output and the drive circuit 81 holds the “L” output, the node N21 is in a high impedance state, and the gate of the MOS transistor M1 is floated. Then, the gate voltage of the MOS transistor M1 can be maintained almost as it is.

  When the gate voltage of the MOS transistor M1 is maintained, the drain-source current of the MOS transistor M1 is also maintained as it is, thereby stabilizing the luminous intensity of the LED module LM1 in the dimming state S3 (see the period F2 in FIG. 5). ). Here, the dimming state S3 indicates a state in which the light intensity is lower than that in the full lighting state S1 and higher than in the light extinction state S2.

  Conversely, when the drive circuit 81 outputs “H” thereafter, the accumulated charge is released from the gate input capacitance of the MOS transistor M1. Then, the gate voltage of the MOS transistor M1 gradually decreases, and the drain-source current of the MOS transistor M1 also decreases accordingly.

  At the same time, the luminous intensity of the LED module LM1 gradually returns from the dimming state S3 to the full lighting state S1 (see the H2 period in FIG. 5). In this way, the LED module LM1 can be held in the dimming state S3 in the middle from the fully lit state S1 to the fully lit state S2, and from the fully lit state S2 to the fully lit state S1.

  FIG. 6 shows a comparison between a control method (comparative example) using the technique shown in the background art column and the control method according to the present embodiment. As shown in FIG. In the control method of the comparative example, the energization current of the LED module LM1 changes rapidly every period of the PWM signal. This is because it is difficult for the DCDC converter 1 to follow the load fluctuation. At this time, the output voltage of the DCDC converter 1 also varies accordingly. On the other hand, in the control method of the present embodiment, the energization current of the LED module LM1 and the output voltage of the DCDC converter 1 fluctuate gently. Thereby, the light quantity can be adjusted smoothly.

<Summary>
According to the present embodiment, the control circuit 4 and the drive unit 31 change and control the energization state of the power MOS transistor M1 stepwise by changing the drive control signal applied to the gate of the power MOS transistor M1, and connect in parallel. The energization current of the LED module LM1 thus adjusted is adjusted. For this reason, the luminous intensity of the LED module LM1 can be changed.

  Therefore, even if the DCDC converter 1 has a large internal feedback delay, the luminous intensity of the headlamp can be changed stepwise and at a speed according to the situation without giving the viewer a sense of incongruity.

  Further, according to the present embodiment, a plurality of drive control signal application paths having different ascending or descending slopes are provided, and the energization state of the power MOS transistor M1 is changed and controlled according to switching of the application paths. Therefore, the rate of change of luminous intensity can be changed.

  In the present embodiment, the resistance R11 and the resistance R21 are set so that their resistance values are different from each other. For example, if the control circuit 4 is driven using the first linear drive circuit LN11, the luminous intensity of the LED module LM1 can be changed abruptly. If the control circuit 4 is driven using the second linear drive circuit LN21, the luminous intensity of the LED module LM1 can be changed gently. For this reason, the time for shifting from the fully lit state S1 to the fully lit state S2 and the time for shifting from the fully lit state S2 to the fully lit state S1 can be changed.

  Thereby, according to a condition, the light quantity of LED can be changed gently or abruptly, and the luminous intensity (illuminance) of a headlamp can be changed without giving a discomfort to a viewer. Thereby, when the control circuit 4 changes the headlight from the current light intensity to the target light intensity, it can be changed stepwise (or steplessly) and at a desired speed.

  Further, when the control circuit 4 and the drive circuits 71 and 81 linearly drive the MOS transistor M1 and adjust the gate voltage of the MOS transistor M1 to a constant value exceeding 0 and less than the threshold voltage Vth, the LED module LM1 is dimmed. Will be able to hold.

(Second Embodiment)
7 to 13 show a second embodiment. The second embodiment differs from the previous embodiment in that the energization state of the control switch is changed stepwise in response to applying a pulse signal to the control switch as a drive control signal. Further, the PWM switch is used as the pulse signal, and the energization state of the control switch is changed and controlled according to the pulse width (duty ratio). The same or similar parts as those in the above-described embodiment are denoted by the same or similar reference numerals, and the description thereof is omitted. Hereinafter, different parts will be described.

  FIG. 7 shows an example of the drive unit 33 of the power MOS transistor M1. Note that the drive unit of the power MOS transistor M2 has a configuration substantially similar to that of the drive unit 33, and is not shown. As shown in FIG. 7, the drive unit 33 includes drive circuits 91 and 101, a P-channel MOS transistor M91, an N-channel MOS transistor M101, a resistor R31, and a capacitor C31, and is configured as a linear drive circuit. . In the present embodiment, the drive unit 33 includes only one current path to be applied to the gate of the MOS transistor M1. Two or more paths may be provided.

  In response to the control signal from the control circuit 4, the drive circuit 91 has an “H” level (duty ratio 100%), an “L” level (duty ratio 0%), and an “H” “L” PWM signal (duty ratio). The ratio 0% <Du <100%) can be applied to the gate of the MOS transistor M91. In response to the control signal of the control circuit 4, the drive circuit 101 is set to “H” level (duty ratio 100%), “L” level (duty ratio 0%), and “H” and “L” PWM signals (duty ratio). The ratio 0% <Du <100%) can be applied to the gate of the MOS transistor M101.

  MOS transistors M91 and M101 are connected in series between the supply terminal of the power supply Vcc and the ground, and a resistor R33 is connected between the common connection node N33 and the gate of the MOS transistor M1. Further, a capacitor C33 is connected between the gate of the MOS transistor M1 and the ground.

  In the present embodiment, a case will be described in which the gate voltage of the MOS transistor M1 is linearly driven by changing the duty ratio of the PWM signal output from the drive circuits 91 and 101 to change the luminous intensity of the LED module LM1.

  When the control circuit 4 and the drive unit 33 gradually increase the gate voltage of the MOS transistor M1 toward a predetermined value (for example, a predetermined value less than the threshold voltage Vth), as shown in FIG. 4 outputs a rising control signal to the drive circuit 91, and the drive circuit 91 outputs a low active PWM signal having a predetermined duty ratio T1 / T (= Du1) to the gate of the MOS transistor M91. Then, the power supply Vcc gradually charges the gate input capacitance of the power MOS transistor M1 and the capacitor C33 through the MOS transistor M91. Then, the gate voltage of the MOS transistor M1 gradually increases. Then, the drain-source current of the MOS transistor M1 increases, and the amount of current flowing through the LED module LM1 decreases. Thereby, the luminous intensity of the LED module LM1 can be reduced.

  On the contrary, when the control circuit 4 and the drive unit 33 gradually lower the gate voltage of the MOS transistor M1 toward a predetermined value (for example, 0), the control circuit 4 is lowered as shown in FIG. The control signal is output to the drive circuit 101, and the drive circuit 101 outputs a high active PWM signal having a predetermined duty ratio T2 / T (= Du2) to the gate of the MOS transistor M101.

  Then, the gate input capacitance of the MOS transistor M1 and the stored power of the capacitor C33 are gradually discharged to the ground through the resistor R33, and the gate voltage of the MOS transistor M1 gradually decreases. As a result, the drain-source current of the MOS transistor M1 decreases, the amount of current flowing through the LED module LM1 increases, and the luminous intensity of the LED module LM1 can be increased.

  In the above description, as shown in FIG. 8A and FIG. 8B, the mode in which the pulse width (duty ratio) of the PWM signal is changed as a parameter has been described. However, the pulse period (frequency) of the PFM signal is set as a parameter. You may apply to the form changed as.

  FIGS. 9A and 9B schematically show an example of a light control method when the drive unit 33 is used. As shown in FIG. 9A, the drive circuit 91 outputs “H” level at which the duty ratio Du1 = 0% as a drive control signal, and the drive circuit 101 at “L” level at which the duty ratio Du2 = 0%. Is output as a drive control signal, the node N33 enters a high impedance state.

  The gate voltage of the MOS transistor M1 is held at the voltage between the terminals of the capacitor C33. If the voltage between the terminals of the capacitor C33 is held at 0, for example, the gate voltage of the MOS transistor M1 is also held at almost 0, so that the drain and source of the MOS transistor M1 are held open. Then, a current is passed through the LED module LM1, and the LED module LM1 is in a fully lit state S1 (see period A3 in FIG. 9A).

When the drive circuit 91 outputs the “L” level at which the duty ratio Du1 = 100% as the drive control signal, the MOS transistor M91 is turned on, and the gate voltage of the MOS transistor M1 rises rapidly. Then, the LED module LM1 rapidly shifts to the fully extinguished state S2 (see the period B3 in FIG. 9A). At this time, the drain-source current of the MOS transistor M1 is at a maximum current _{I M.}

  Thereafter, when the drive circuit 91 outputs “H” at which the duty ratio Du1 = 0% and the drive circuit 101 outputs “H” at the duty ratio Du2 = 100%, the MOS transistor M91 is turned off and the MOS transistor M101 turns on. At this time, the gate input capacitance of the MOS transistor M1 and the stored power of the capacitor C33 are rapidly released to the ground through the MOS transistor M101.

  As a result, the gate voltage of the MOS transistor M1 rapidly decreases, and the drain and source of the MOS transistor M1 rapidly transition to the open state. Then, the LED module LM1 is rapidly energized again, and the LED module LM1 rapidly shifts to the fully lit state S1 (see the period C3 in FIG. 9A).

  Next, with reference to FIG. 9B, a dimming method for dimming by adjusting the duty ratios Du1 and Du2 will be described. As shown in FIG. 9B, when the drive circuit 91 outputs “H” and the drive circuit 101 outputs “L”, the node N33 is in a high impedance state, and the gate voltage of the MOS transistor M1 is between the terminals of the capacitor C33. Voltage. If the voltage between the terminals of the capacitor C33 is almost zero, the drain and source of the MOS transistor M1 are held open, current is supplied to the LED module LM1, and the LED module LM1 is in the fully lit state S1 (FIG. 9B). ) Refer to D3 period).

  Thereafter, when the drive circuit 91 outputs a PWM signal with a duty ratio Du1 = predetermined value DUTY1, the MOS transistor M91 is turned on / off according to the PWM signal, and the gate input capacitance of the MOS transistor M1 and the MOS transistor M1 are turned on during the on period of the MOS transistor M91. Capacitor C33 is gradually charged from power supply Vcc through resistor R33. At this time, as shown in FIG. 8A, the gate voltage of the MOS transistor M1 gradually increases (see the period E3 in FIG. 9B).

  When the gate voltage of the MOS transistor M1 rises gently, the drain-source current of the LED module LM1 continues to rise until the gate voltage of the MOS transistor M1 reaches almost the threshold voltage Vth in accordance with the gentle rise. Reaches the threshold voltage Vth, the drain-source current of the MOS transistor M1 is saturated and becomes almost constant. As a result, almost no current flows to the LED module LM1 side, and the LED module LM1 is in a fully extinguished state S2 (see period F3 in FIG. 9B).

  After that, when the drive circuit 91 outputs “H” level with a duty ratio Du1 = 0% and the drive circuit 101 outputs a PWM signal with the duty ratio Du2 = predetermined value DUTY1, the MOS transistor M101 is turned on / off according to the PWM signal. Then, the gate input capacitance of the MOS transistor M1 and the stored power of the capacitor C33 are extracted to the ground through the MOS transistor M101. Then, the gate voltage gradually decreases (see the G3 period in FIG. 9B).

  When the gate voltage of the MOS transistor M1 gradually decreases, the gate voltage reaches the threshold voltage Vth of the MOS transistor M1, and further decreases, the drain-source current of the MOS transistor M1 gradually increases in accordance with the gentle decrease in the gate voltage. (Refer to the H3 period in FIG. 3B).

  When the drain-source current of the MOS transistor M1 decreases, the energization current of the LED module LM1 gradually increases in accordance with this gradual decrease. As the energization current increases, the luminous intensity of the LED module LM1 gradually increases. When the drain-source current of the MOS transistor M1 continues to decrease and becomes almost zero, the current flows to the LED module LM1 side. Then, LED module LM1 will be in the all lighting state S1 (refer I3 period of FIG.9 (b)). In this manner, the light emission of the LED module LM1 can be controlled as in the above-described embodiment.

  10 and 11 show another dimming method. As shown in FIG. 10, in order to gently decrease the luminous intensity of the LED module LM1, the drive circuit 91 drives the MOS transistor M91 with a PWM signal having a relatively low duty ratio DUTY2 (see the period E3 in FIG. 10). In order to raise the luminous intensity of the module LM1 relatively abruptly, the drive circuit 101 may drive the MOS transistor M101 with a PWM signal having a relatively high duty ratio DUTY3 (> DUTY2) (G3 and H3 in FIG. 10). Period reference).

  As shown in FIG. 11, when the luminous intensity of the LED module LM1 is gradually lowered in the initial stage and rapidly lowered in the final stage, the MOS transistor M91 is driven by the low active PWM signal having a relatively low duty ratio DUTY4. (See period E31 in FIG. 11), and immediately thereafter, the MOS transistor M91 may be driven by a low active PWM signal having a relatively high duty ratio DUTY5 (see period E32 in FIG. 11).

  Similarly to the first embodiment, for example, when the LED module LM1 is shifted from the fully lit state S1 to the fully lit state S2, or when the LED module LM1 is shifted from the fully lit state S2 to the fully lit state S1, etc. The control process may be stopped in the dimming state S3.

In this case, the period during which the drive circuit 91 outputs the drive control signal having the predetermined duty ratio DUTY1 to the gate of the MOS transistor M91 may be reduced as compared with the above. Then, the gate voltage of the MOS transistor M1 can be adjusted so as not to reach the threshold voltage Vth (see the period E4 in FIG. 12). Then, the conduction current of the MOS transistor M1 remains at the current I _L2 (<maximum current I _M ).

  Thereafter, when the drive circuit 91 holds the “H” output and the drive circuit 101 holds the “L” output, the node N33 is in a high impedance state, and the gate voltage of the MOS transistor M1 is almost the same as the voltage across the terminals of the capacitor C33. Can be held at voltage.

  When the gate voltage of the MOS transistor M1 is held, the drain-source current of the MOS transistor M1 is also held as it is, and thereby the luminous intensity of the LED module LM1 is stabilized in the dimming state S3 (see the period F4 in FIG. 12). ).

  Conversely, when the drive circuit 101 outputs a drive control signal having a predetermined duty ratio DUTY1 to the gate of the MOS transistor M101, the stored power is released from the gate input capacitance of the MOS transistor M1 and the capacitor C33. Then, the gate voltage of the MOS transistor M1 gradually decreases, and the drain-source current of the MOS transistor M1 also decreases accordingly. At the same time, the luminous intensity of the LED module LM1 gradually returns from the dimming state S3 to the full lighting state S1 (see the period H4 in FIG. 12). In this way, the LED module LM1 can be held in the dimming state S3 in the middle from the fully lit state S1 to the fully lit state S2, and from the fully lit state S2 to the fully lit state S1.

  FIG. 13 shows a configuration example when a current drive type transistor G1 is used instead of the power MOS transistor M1. As shown in FIG. 13, the drive unit 34 receives a control signal from the control circuit 4 and current-drives the base of the transistor G1. When the common connection node of the MOS transistors M91 and M101 is a node N34, a capacitor C34 is connected between the node N34 and the ground, and a resistor R34 is connected between the node N34 and the base of the transistor G1. ing. With this configuration, the base of the transistor G1 can also be current driven.

<Summary>
According to the present embodiment, the control circuit 4 and the drive unit 33 change the duty ratio (pulse width) of the PWM signal as a drive control signal and apply it to the MOS transistors M91 and M101, and thereby the power MOS transistor M1. The energization state of the LED module LM1 connected in parallel is adjusted by changing and controlling the energization state in a stepwise manner. For this reason, the luminous intensity of the LED module LM1 can be changed. Thereby, there exists an effect similar to the above-mentioned embodiment.

(Third embodiment)
FIG. 14 shows a third embodiment. The third embodiment is different from the first and second embodiments in that a driving unit of the MOS transistor M1 (control switch) is configured using a current source. Parts that are the same as or similar to those in the previous embodiment are given the same or similar reference numerals and description thereof is omitted, and different parts are described below.

  As shown in the headlight dimming circuit 102 in FIG. 14, the drive unit 34 is configured to drive the MOS transistor M <b> 1 according to the control signal of the control circuit 4, and the drive unit 35 controls the control circuit 4. The MOS transistor M2 is configured to be driven according to the signal.

The drive unit 34 includes a plurality (four) of current sources SI11, SI21, SI31, and S41, and a plurality (four) of valid / invalid switching circuits 111, 121, 131, and 141.
Current sources SI11 and SI31 are connected in series between the supply terminal of the power supply Vcc and the ground. Current sources SI21 and SI41 are connected in series between the supply terminal of the power supply Vcc and the ground. The common connection node of these current sources SI11 and SI31 and the common connection node of the current sources SI21 and SI41 are commonly connected to each other and are connected to the gate of the power MOS transistor M1.

  The current amounts when the current sources SI11 and SI31 operate effectively are set to the same amount Iz1, and the current amounts when the current sources SI21 and SI41 operate effectively are set to the same amount Iz2. Here, the current amounts Iz1 and Iz2 are set to different current amounts (for example, Iz1 <Iz2).

  The valid / invalid switching circuit 111 switches validity / invalidity of the current output of the current source SI11. The valid / invalid switching circuit 121 switches validity / invalidity of the current output of the current source SI21. The valid / invalid switching circuit 131 switches validity / invalidity of the current output of the current source SI31. The valid / invalid switching circuit 141 switches validity / invalidity of the current output of the current source SI41.

  Then, for example, it is assumed that all current sources SI11, SI21, SI31, and SI41 are invalidally switched by the valid / invalid switching circuits 111, 121, 131, and 141 according to the control signal of the control circuit 4, respectively.

  Thereafter, when the current source SI11 is effectively switched by the valid / invalid switching circuit 111, the current source SI11 can charge the gate input capacitance of the MOS transistor M1 relatively slowly by the current amount Iz1. When the current source SI21 is effectively switched by the valid / invalid switching circuit 121, the current source SI21 can charge the gate input capacitance of the MOS transistor M1 relatively quickly by the current amount Iz2.

  On the other hand, when the current source SI31 is effectively switched by the valid / invalid switching circuit 131, the current source SI31 can discharge the stored power from the gate input capacitance of the MOS transistor M1 relatively slowly by the current amount Iz1. Further, when the current source S141 is effectively switched by the valid / invalid switching circuit 141, the current source SI41 can discharge the stored power from the gate input capacitance of the MOS transistor M1 relatively rapidly by the current amount Iz2. Thereby, there exists an effect similar to the above-mentioned embodiment.

(Fourth embodiment)
15 and 16 show a fourth embodiment. In this embodiment, a usage example of the control method described in the above embodiment is shown.

  As shown in FIG. 15, for example, one use form of the control method when the vehicle Ca1 passes the oncoming vehicle Ca2 approaching from the front is shown. As shown in FIG. 15, the vehicle Ca1 emits both the headlight for traveling (high beam) and the low headlight (low beam) to irradiate the front of the host vehicle Ca1. In this embodiment, the LED module LM1 will be described as constituting a high beam.

  When the vehicle Ca1 exists at the position L0 and the oncoming vehicle Ca2 exists at the position L1, since the distance L1-L0 is a relatively long distance, neither the high beam HB nor the low beam LB will adversely affect the oncoming vehicle Ca2. . However, when the oncoming vehicle Ca2 moves to the position L2, the distance L2-L0 is shortened, so that the high beam HB may adversely affect the visibility of the driver of the oncoming vehicle Ca2.

  Therefore, when the oncoming vehicle Ca2 moves to the position L2, in particular, the oncoming vehicle Ca2 considers that the headlamp LT is irradiated between the positions L2 and L0, and the vehicle Ca1 is between these positions L2 and L0. It is desirable to have a function of adjusting the amount of light within a predetermined range to be within a certain range.

  FIG. 15 shows a mode in which the output of the high beam HB is controlled to the lowest level at a position where the vehicle Ca1 and the oncoming vehicle Ca2 pass each other. However, the oncoming vehicle Ca2 is practically located in front of the vehicle Ca1. When passing by a predetermined meter (several meters), the output of the high beam HB may be set to the lowest level.

  In order to realize such a configuration, for example, the vehicle Ca1 has an electrical configuration shown in FIG. The circuit configuration shown in FIG. 16 uses the configuration shown in the first embodiment, but is not limited to this, and the configuration shown in the second or third embodiment may be used.

  As shown in FIG. 16, a camera 63 and a light amount sensor 64 are connected to the control circuit 4. The camera 63 acquires an image of a predetermined range in front of the vehicle Ca1 and outputs the image information to the control circuit 4. The control circuit 4 acquires light amount information within a predetermined range in front of the vehicle Ca1 according to the image information. Thereby, the control circuit 4 can acquire light quantity information within a predetermined range shown in FIG. 15 (for example, between the positions L2 and L0). The light quantity sensor 64 detects the light quantity in front of the vehicle Ca 1 and outputs the light quantity information to the control circuit 4. Note that only one of the camera 63 and the light amount sensor 64 may be connected to the control circuit 4, and the control circuit 4 may acquire light amount information from any one of these devices 63 and 64.

  When the control circuit 4 acquires the light amount information from the camera 63 or / and the light amount sensor 64, the control circuit 4 estimates the light amount within a predetermined range. Then, the control circuit 4 decreases the energization current amount of the LED module LM1 constituting the high beam HB so as to keep the estimated light amount within a certain range.

  At this time, the closer the oncoming vehicle Ca2 is to the vehicle Ca1, the greater the amount of light within a predetermined range in front of the vehicle Ca1. Then, the control circuit 4 of the vehicle Ca1 gradually decreases the amount of energization current of the LED module LM1, thereby maintaining the light amount within a predetermined range in front of the vehicle Ca1 within a certain range.

  At this time, the relative traveling speed of the vehicle Ca1 and the oncoming vehicle Ca2 is several to several hundred km / h, and when the vehicles Ca1 and Ca2 pass each other, the total amount of light is changed and controlled as shown in the above embodiment. Each driver can maintain good visibility without feeling uncomfortable. The passing speed may be detected using the camera 63 or / and the light quantity sensor 64, and the light quantity changing speed may be changed according to the detected speed. In the present embodiment, the influence of light projection by the oncoming vehicle Ca2 is considered. However, the present invention is not limited to this, and the influence of other light sources such as street lamps can also be considered.

  According to the present embodiment, when the control circuit 4 acquires the light amount information from the camera 63 or / and the light amount sensor 64, the light amount within a predetermined range is estimated and constant within a predetermined range in front of the vehicle Ca1 and the oncoming vehicle Ca2. Hold. Thereby, the visibility of the driver | operator of vehicle Ca1 and oncoming vehicle Ca2 can be kept favorable, and a driver | operator's concentration can be maintained.

  Moreover, it can also comprise as follows. As shown in FIG. 16, a voltage detector 61 and a current detector 62 are connected to the LED module LM1 of the vehicle Ca1. The voltage detector 61 detects the voltage value between both terminals of the LED module LM1. The current detector 62 detects the amount of LED energization current of the LED module LM1. The current detector 62 detects the current amount of the MOS transistor M1, and subtracts the detected current amount from the current amount of the LED module LM1 in the open state of the MOS transistor M1, thereby detecting the current amount of the LED module LM1. You may do it.

  Only one of the voltage detector 61 and the current detector 62 may be connected to the control circuit 4 so that the control circuit 4 can acquire the voltage value or current amount of the LED module LM1.

  At this time, the control circuit 4 estimates the front light amount of the vehicle Ca1 based on the detection result of the voltage detector 61 and / or the current detector 62, and controls the energization current of the LED module LM1 constituting the high beam HB. Then, the front light quantity of the vehicle Ca1 can be estimated without the camera 63 or the light quantity sensor 64 performing the detection process of the front light quantity of the vehicle Ca1. As described above, when only the detection result of the voltage detector 61 and / or the current detector 62 is used, it is particularly effective when the light amount of another light source (for example, the oncoming vehicle Ca2) is assumed to be small enough to be ignored. It is.

  When the control circuit 4 acquires the light amount information using the camera 63 or the light amount sensor 64, the voltage detector 61 and / or the current detector 62 may or may not be provided. At least one of these devices 61 to 64 may be provided, but two or more of these devices 61 to 64 may be provided in order to further improve the light amount information detection accuracy.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and for example, the following modifications or expansions are possible. The mode of changing the LED module LM1 from off to on and from on to off has been shown, but this may be the LED module LM2, and even if three or more LED modules are connected in series and parallel, The control method described in the above embodiment can be applied.

  Although the configuration in which the power MOS transistors M1 and M2 are applied as control switches is shown, the present invention can be applied to a configuration using various transistors (for example, BJT).

  In the drawings, 1 is a DCDC converter, 2 is a headlight dimmer circuit, 4 is a control circuit (estimating means, light adjusting means), 4 and 31 and 32 are change control circuits, LM1 and LM2 are LED modules (LED series circuit) ), M1 and M2 are power MOS transistors (control switches), HB is a high beam, and LB is a low beam.

Claims (5)

A headlight dimming circuit (2) for a vehicle,
LED series circuit (LM1, LM2) in which a DC voltage is applied by a DCDC converter (11) and a plurality of LEDs are connected in series;
A control switch (M1, M2) connected in parallel to a part of the LED series circuit and capable of changing the energization current stepwise according to the change of the drive control signal applied to the control terminal;
Changing the drive control signal to be supplied to the control terminal of the control switch to change and control the energization state of the control switch in a stepwise manner and adjusting the energization current to a part of the LED series circuit connected in parallel A control circuit (4, 31, 32);
An LED headlamp dimming circuit comprising:   The change control circuit (4, 31, 32) changes the energization state of the control switch stepwise in response to applying a pulse signal as the drive control signal, and the pulse width or / and pulse of the pulse signal. 2. The LED headlamp dimming circuit according to claim 1, wherein the energization state of the control switch is changed and controlled according to a cycle.   The change control circuit (4, 31, 32) includes a plurality of drive control signal application paths having different ascending or descending slopes, and the control switch is configured to switch the plurality of drive control signal applying paths. The LED headlamp dimming circuit according to claim 1, wherein the energization state is changed and controlled. Estimating means (4) for estimating the amount of light in front of the vehicle;
Light adjustment means (4) for adjusting the output light quantity of the headlamp and adjusting the energization state of the control switch by the change control circuit so as to keep the estimated light quantity of the estimation means within a certain range is executable. The LED headlamp dimming circuit according to claim 1, wherein the LED headlamp dimming circuit is provided.   5. The LED headlight dimming circuit according to claim 4, wherein the light adjusting means (4) adjusts an output light amount of a high beam (HB) of the headlamp.

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