JP2017085676A - Lighting control device for lamp body for vehicle, and lamp body system for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress overcurrent at a voltage variation time and to perform lighting control due to PWM control at a normal time.SOLUTION: The present invention relates to a device for performing lighting control of a lamp body for vehicle. The device comprises: a booster circuit part 20 which boosts a power supply voltage and generates a drive voltage; a voltage comparator part which outputs a first signal in the case where the power supply voltage is higher than a comparative voltage, and outputs a second signal in the case where the power supply voltage is equal to or lower than the comparative voltage; a lighting control PWM signal output part which outputs a lighting control PWM signal of a predetermined duty ratio while the first signal is outputted, and outputs a lighting control PWM signal of which the ON period is made become 100% substantially, while the second signal is outputted; a lighting control circuit 30 which performs PWM control on the drive voltage on the basis of the lighting control PWM signal and supplies the drive voltage to the lamp body for vehicle; and a drive voltage control part which controls the generation of the drive voltage due to the booster circuit part in such a manner that a current to flow to the lamp body for vehicle becomes a substantially fixed value while the first signal is outputted, and that a magnitude of the current becomes smaller than the fixed value while the second signal is outputted.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lighting control technique for a vehicle lamp (for example, a headlamp).

  Some vehicle lamps such as headlamps are configured using light emitting elements such as LEDs. In order to drive such a vehicular lamp, a DC voltage is required. Therefore, a voltage obtained by using a battery mounted on the vehicle as a power source is boosted or lowered by a DC-DC converter. A magnitude voltage is generated. This DC-DC converter requires feedback control for making the voltage or current constant. Although feedback control may be realized using an analog circuit, in a vehicle application, since a plurality of vehicle lamps are controlled, control to make a voltage or current constant using PWM control by a microcomputer is performed. (See, for example, Patent Documents 1 and 2).

  In addition, in a vehicle lamp, not only lighting on / off control but also control to increase / decrease the illuminance at the time of lighting according to the situation around the vehicle is desired. Such illuminance control is effective by increasing or decreasing the amount of current supplied to the vehicular lamp using a DC-DC converter, or by performing PWM control while keeping the current level constant. There is a method of increasing or decreasing the magnitude of current.

  By the way, the voltage supplied from the battery of the vehicle may fluctuate abruptly when the engine of the vehicle is started, when the engine is stopped, or when other in-vehicle devices are started. In such voltage fluctuations, particularly when the voltage drops rapidly, a phenomenon may occur in which overcurrent is output to the vehicular lamp when PWM control with a constant current is performed.

  FIG. 5 is a waveform diagram for explaining overcurrent at the time of voltage drop. As shown in the figure, when the battery voltage temporarily decreases, the output current supplied to the vehicle lamp increases. At this time, if dimming is performed by PWM control, the PWM signal changes from the off period to the on period, and thus a larger overcurrent is generated. Thereafter, when the battery voltage recovers, the output current decreases. At this time, since dimming is performed by PWM control, the output current further decreases when the PWM signal changes from the on period to the off period. In order to prevent the overcurrent as described above, it is necessary to stop the dimming by the PWM control, but in this case, there is a disadvantage that it is difficult to control the illuminance.

Japanese Patent No. 3302386 JP 2004-327152 A

  A specific aspect of the present invention has an object to provide a technique capable of suppressing overcurrent due to fluctuations in power supply voltage and performing dimming by PWM control in normal times.

  A lighting control device according to one aspect of the present invention is (a) a device for controlling lighting of a vehicular lamp including one or more light emitting elements, and (b) a DC power supply voltage. (C) a first signal is output when the power supply voltage is greater than a predetermined reference value, and the power supply voltage is less than or equal to the reference value. A voltage comparator that outputs a second signal different from the first signal; and (d) a dimming PWM signal having a predetermined duty ratio when the first signal is output from the voltage comparator; A dimming PWM signal output unit for outputting the dimming PWM signal with an on period being substantially 100% when the second signal is output from the voltage comparing unit; and (e) the dimming PWM signal. The drive is based on the dimming PWM signal output from the output unit. A dimming circuit unit that PWM-controls the voltage and supplies the voltage to the vehicular lamp; and (f) when the first signal is output from the voltage comparison unit, the current flowing through the vehicular lamp is almost equal. When the second signal is output from the voltage comparison unit, the driving voltage by the boosting circuit unit is set so that the magnitude of the current flowing through the vehicle lamp is smaller than the constant value. And a drive voltage control unit that controls generation of the lighting control device.

  According to the above configuration, it is possible to suppress overcurrent due to fluctuations in the power supply voltage and to perform dimming by PWM control during normal times.

  In the above lighting control device, for example, the dimming circuit unit includes a transistor provided in a current path between the boosting circuit unit and the vehicle lamp, and the dimming PWM signal is connected to a control terminal of the transistor. Is preferably entered. It is also preferable that the booster circuit unit is a chopper type booster DC-DC converter. Moreover, it is also preferable that the said light emitting element is LED.

  A vehicle lamp system according to an aspect of the present invention is a vehicle lamp system including any one of the lighting control devices described above and a vehicle lamp controlled by the lighting control device.

  According to the above configuration, it is possible to obtain a vehicular lamp system that can suppress overcurrent due to fluctuations in power supply voltage and can perform dimming by PWM control in normal times.

FIG. 1 is a circuit diagram illustrating a configuration of a lighting control device for a vehicle lamp according to an embodiment. FIG. 2 is a waveform diagram of an example when the power supply voltage is lowered. FIG. 3 is a block diagram for explaining in detail an example of the internal configuration of the microcomputer of the lighting control device. FIG. 4 is a diagram for explaining a method for setting the comparison voltage. FIG. 5 is a waveform diagram for explaining overcurrent at the time of voltage drop.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a circuit diagram illustrating a configuration of a lighting control device for a vehicle lamp according to an embodiment. The illustrated lighting control device receives a supply of a DC power supply voltage from a vehicle battery via terminals 40 and 41, and controls the lighting state of the LED unit 100 as a vehicle lamp. The resistor elements 11 and 12, the booster circuit unit 20, and the dimming circuit unit 30 are configured. The LED unit 100 includes, for example, a plurality of LEDs, and is used as a vehicle headlamp unit. A vehicle lamp system is configured including the lighting control device and the LED unit 100.

  The microcomputer 10 is a microcomputer having a built-in comparator, and controls the operations of the booster circuit unit 20 and the dimming circuit unit 30. The microcomputer 10 has three input ports 10a, 10b, and 10c and two output ports 10d and 10e. The function of each input port and output port will be described later.

  The resistance elements 11 and 12 constitute a voltage detection circuit unit, and are directly connected by connecting one end of each other. The other end of the resistance element 11 is connected to a terminal 40 on the high potential side, and the other end of the resistance element 12 is connected to a terminal 41 on the reference potential (GND) side. The resistance element 11 is used to divide the power supply voltage (for example, + 12V) supplied via the terminals 40 and 41, and the resistance element 12 is used to detect the power supply voltage in the microcomputer 10.

  The booster circuit unit 20 is a circuit unit for boosting the power supply voltage, and includes a coil element (inductor element) 21, a field effect transistor 22, a diode 23, a capacitor element (capacitor element) 24, a resistor element 25, and a current detection amplifier. 26. Among these, the coil element 21, the field effect transistor 22, the diode 23, and the capacitor element 24 constitute a chopper type boost DC-DC converter (boost chopper circuit).

  The coil element 21, the diode 23, and the resistance element 25 are connected in series in this order. One end side of the coil element 21 is connected to the terminal 40, and one end side of the resistance element 25 is the field effect transistor 31 of the dimming circuit unit 30. Connected with.

  The field effect transistor 22 has a gate terminal connected to the output port 10 d of the microcomputer 10, a drain terminal connected to a node between the coil element 21 and the diode 23, and a source terminal connected to the terminal 41.

  One end side of the capacitor element 24 is connected to the node between the diode 23 and the resistance element 25, and the other end side is connected to the terminal 41.

  One end side of the resistance element 25 is connected to the diode 23, and the other end side is connected to the field effect transistor 31 of the dimming circuit unit 30. The resistance element 25 is for detecting the magnitude of the current supplied from the booster circuit unit 20 to the dimming circuit unit 30.

  The current detection amplifier 26 is connected to both ends of the resistance element 25 and amplifies the voltage across the resistance element 25. The output terminal of the current detection amplifier 26 is connected to the input port 10 c of the microcomputer 10. The output voltage of the current detection amplifier 26 reflects the magnitude of the current supplied to the dimming circuit unit 30.

  The dimming circuit unit 30 is for performing dimming control of the LED unit 100, and includes a field effect transistor 31.

  The field effect transistor 31 has a gate terminal connected to the output port 10 e of the microcomputer 10, a drain terminal connected to the resistance element 25 of the booster circuit unit 20, and a source terminal connected to one end side of the LED unit 100. The other end side of the LED unit 100 is connected to the terminal 41.

  The configuration of the lighting control device of the present embodiment is as described above. Next, the operation will be described in detail. Below, operation | movement in case a power supply voltage is a normal value is demonstrated first, and operation | movement in case a power supply voltage falls next is demonstrated.

(1) Operation when the power supply voltage is in the normal range The lighting control device supplies a constant current to the LED unit 100 by the booster circuit unit 20 under the control of the microcomputer 10 when the magnitude of the power supply voltage is within the predetermined normal range. Thus, the LED unit 100 is dimmed (illuminance control) by generating a drive voltage and PWM-controlling the field effect transistor 31 in the dimming circuit unit 30.

  The magnitude of the current supplied from the booster circuit unit 20 to the LED unit 100 is fed back from the current detection amplifier 26 to the microcomputer 10 via the input port 10c, and the microcomputer 10 boosts the current so that the current becomes constant. The circuit unit 20 is controlled. Specifically, the microcomputer 10 appropriately sets the duty ratio of the output current PWM signal output from the output port 10d to the gate of the field effect transistor 22 of the booster circuit unit 20. By controlling the conduction period and the non-conduction period of the field effect transistor 22 according to the duty ratio of the output current PWM signal, the energy accumulated in the coil element 21 of the booster circuit unit 20 increases or decreases, thereby boosting the voltage. The magnitude of the voltage generated from the circuit unit 20 is controlled. The voltage / current supplied from the booster circuit unit 20 to the LED unit 100 is smoothed by the capacitor element 24.

(2) Operation when power supply voltage drops FIG. 2 is a waveform diagram of an example when the power supply voltage drops. When the power supply voltage decreases and falls outside the normal range at time t1, the lighting control device controls the microcomputer 10 to control the magnitude of the current (output current) supplied from the booster circuit unit 20 to the LED unit 100 by a certain amount. The duty ratio of the dimming PWM signal used for PWM control in the dimming circuit unit 30 is set to 100% on-duty (lighting 100%). When the power supply voltage returns to the normal range at time t2, the magnitude of the current supplied to the LED unit 100 is returned to the original constant value, and the duty ratio of the dimming PWM signal is also set to a value that matches the desired illuminance. .

  Specifically, the microcomputer 10 compares the voltage input from the input port 10b with a predetermined comparison voltage by a built-in comparator. Here, the voltage input from the input port 10b is one end voltage of the resistance element 12 obtained by dividing by the resistance elements 11 and 12, and reflects the magnitude of the power supply voltage.

  When the voltage input to the input port 10b is equal to or lower than the comparison voltage, that is, when the power supply voltage is out of the normal range, the comparator of the microcomputer 10 outputs an ON signal (FLT signal). In response to the ON signal, the microcomputer 10 sets the dimming PWM signal output from the output port 10e to an ON duty of 100%. By supplying this dimming PWM signal to the gate of the field effect transistor 31 of the dimming circuit unit 30, the lighting state of the LED unit 100 is 100% lighting, that is, the state where the current is supplied and is lit during the entire period. It becomes.

  At this time, the microcomputer 10 receives the ON signal from the comparator, and outputs the output current PWM signal output from the built-in output current control PWM unit to the booster circuit unit 20 via the output port 10d. Is set so that the magnitude of the current supplied to is reduced.

  Thereafter, when the voltage input to the input port 10b becomes larger than the comparison voltage, that is, when the power supply voltage returns to the normal range, the comparator of the microcomputer 10 outputs an off signal (FLT release signal). In response to this off signal, the microcomputer 10 sets the dimming PWM signal output from the output port 10e to a duty ratio that matches the desired illuminance. By supplying this dimming PWM signal to the gate of the field effect transistor 31 of the dimming circuit unit 30, the lighting state of the LED unit 100 is supplied with current in a period corresponding to the duty ratio, and is lit at a desired illuminance. It will be in the state.

  At this time, the microcomputer 10 receives the OFF signal from the comparator, and outputs the output current PWM signal output from the built-in output current control PWM unit to the booster circuit unit 20 via the output port 10d. Is set so that the magnitude of the current supplied to becomes the original constant value.

  FIG. 3 is a block diagram for explaining in detail an example of the internal configuration of the microcomputer of the lighting control device. The microcomputer 10 shown in FIG. 3 includes analog-to-digital converters (ADC) 51 and 58, a comparison voltage setting unit 52, a comparator 53, an output current value setting unit 54, a voltage drop output current setting unit 55, an output current control unit 56, An output current PWM unit 57, a lighting rate setting unit 59, and a dimming PWM unit 60 are included. Such a microcomputer 10 can be realized by using various commercially available products. For example, the dsPIC series (for example, dsPIC33FJ09GS302, dsPIC33FJ64GS606, dsPIC33FJ64GS610) from Microchip, C2000 series from Texas Instruments, RL series from Renesas Electronics, 78K0 series, etc.

  The ADC 51 converts the voltage input from the input port 10a (one end voltage of the resistance element 12) into digital data. The ADC 58 converts the voltage (output voltage of the current detection amplifier 26) input from the input port 10c into digital data.

  The comparison voltage setting unit 52 sets a comparison voltage to be applied to the comparator 53 based on the digital data voltage output from the ADC 51. This comparison voltage is for determining whether or not the power supply voltage has decreased below a certain value (abnormality determination value). Since the power supply voltage constantly fluctuates, this comparison voltage is set while calculating at a constant cycle (for example, 40 μsec) corresponding to the conversion cycle of the ADC 51.

  FIG. 4 is a diagram for explaining a method for setting the comparison voltage. Depending on various set values, for example, when the power supply voltage decreases from 12 (V) to 9 (V), the output current increases from 1 (A) to about 1.3 (A). The fluctuation range of the power supply voltage at this time is 3 (V). Such a relationship between the fluctuation range (variation value) of the power supply voltage and the output current is substantially proportional within a certain range (see FIG. 4). The inclination at this time is determined by the output current, the load (LED unit 100), and the response speed (responsiveness) of PI control, and the illustrated relationship is an example.

  In the example shown in FIG. 4, if the reference value for determining that the output current is an overcurrent is 2 (A), the allowable fluctuation range of the power supply voltage at that time is 6 (V). Therefore, the comparison voltage setting unit 52 prepares in advance a relationship between the fluctuation range of the power supply voltage and the output current as shown in FIG. 4 and sets the comparison voltage to be supplied to the comparator 53 using the table. . For example, when the voltage input from the ADC 51 is 12 (V), 6 (V) obtained by subtracting 6 (V), which is an allowable value of the fluctuation range of the power supply voltage, from 12 (V). Set the value as the comparison voltage. Similarly, for example, when the voltage input from the ADC 51 is 11 (V), 5 (obtained by subtracting 6 (V), which is an allowable value for the fluctuation range of the power supply voltage, from 11 (V). A value V) is set as a comparison voltage. The comparison voltage setting unit 52 according to the present embodiment refers to the table corresponding to the voltage output from the ADC 51 every fixed period (for example, 4 μsec) corresponding to the conversion period of the ADC 51 in this way, thereby obtaining the comparison voltage. Set.

  In this embodiment, since the power supply voltage is divided using the resistance elements 11 and 12, the voltage of the digital data output from the ADC 51 does not necessarily indicate the value of the power supply voltage as it is. For this purpose, the relationship between the fluctuation range of the power supply voltage and the current in the table may be adjusted as appropriate.

  The comparator 53 compares the comparison voltage set by the comparison voltage setting unit 52 with the voltage input from the input port 10b (hereinafter referred to as “input voltage”), and when the input voltage becomes equal to or lower than the comparison voltage. The FLT signal which is an ON signal is output. The output terminal of the comparator 53 is connected to the dimming PWM unit 60. In the dimming PWM unit 60, when the FLT signal is input, the dimming PWM signal is automatically set to the on-duty 100%.

  The output current value setting unit 54 sets the target output current value when controlling the current supplied to the LED unit 100 when the magnitude of the power supply voltage is within the normal range (normal time), thereby controlling the output current. To the unit 56.

  When the magnitude of the power supply voltage falls below the normal range, the output current setting unit 55 at the time of voltage reduction sets the output current value that has been reduced from the normal time, and outputs it to the output current control unit 56. The output current value lowered from the normal time is set according to the lighting rate set in the lighting rate setting unit 59 and the magnitude of the voltage of the digital data output from the ADC 51.

  When the ON signal is output from the comparator 53, the voltage drop output current setting unit 55 uses this as an interrupt signal to determine that the magnitude of the power supply voltage has fallen below the normal range, and the voltage drop Set the output current target value. Further, when the OFF signal is output from the comparator 53, the output current value setting unit 54 uses this as an FLT release signal to set the target value of the output current at the normal time.

  The output current control unit 56 receives digital data (of the current detection amplifier 26) fed back from the ADC 58 so that the target value of the output current set by the output current value setting unit 54 or the output current setting unit 55 at the time of voltage drop is obtained. PI (Proportional Action; Integral Action) control is performed based on the output voltage. Specifically, the output current control unit 56 sets the duty ratio of the output current PWM signal generated in the output current PWM unit 57.

  The output current PWM unit 57 generates an output current PWM signal based on the duty ratio set by the output current control unit 56. This output current PWM signal is supplied to the gate of the field effect transistor 22 via the output port 10d.

  The lighting rate setting unit 59 sets the duty ratio of the dimming PWM signal generated in the dimming PWM unit 60 according to the lighting rate for dimming the LED unit 100. This duty ratio is also output to the voltage drop output current setting unit 55.

  The dimming PWM unit 60 generates a dimming PWM signal based on the duty ratio set by the lighting rate setting unit 59. The dimming PWM signal is supplied to the gate of the field effect transistor 31 of the dimming circuit unit 30 through the output port 10e.

  According to the embodiment as described above, it is possible to suppress overcurrent due to fluctuations in the power supply voltage and to perform dimming by PWM control during normal times.

  Note that the present invention is not limited to the contents of the above-described embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, in the above-described embodiment, the case where the lighting control device is configured using a microcomputer with a built-in comparator is illustrated, but the comparator may be provided outside the microcomputer.

DESCRIPTION OF SYMBOLS 10: Microcomputer 11, 12, 25: Resistance element 20: Boosting circuit part 21: Coil element 22, 31: Field effect transistor 23: Diode 24: Capacitor element 26: Current detection amplifier 30: Dimming circuit part 40, 41: Terminal 100: LED unit

Claims (5)

An apparatus for performing lighting control of a vehicular lamp including one or more light emitting elements,
A booster circuit that boosts a DC power supply voltage to generate a drive voltage;
A voltage comparison unit that outputs a first signal when the power supply voltage is greater than a predetermined reference value, and that outputs a second signal different from the first signal when the power supply voltage is equal to or less than the reference value;
When the first signal is output from the voltage comparison unit, a dimming PWM signal having a predetermined duty ratio is output, and when the second signal is output from the voltage comparison unit, the ON period is substantially set. A dimming PWM signal output unit for outputting the dimming PWM signal, which is 100%,
A dimming circuit unit that PWM-controls the drive voltage based on the dimming PWM signal output from the dimming PWM signal output unit and supplies the drive voltage to the vehicle lamp;
When the first signal is output from the voltage comparison unit, the current flowing through the vehicular lamp becomes a substantially constant value, and when the second signal is output from the voltage comparison unit, the vehicle A drive voltage control unit that controls generation of the drive voltage by the booster circuit unit so that the magnitude of the current flowing through the lamp body is smaller than the constant value;
Including a lighting control device. The dimming circuit unit includes a transistor provided in a current path between the booster circuit unit and the vehicle lamp, and the dimming PWM signal is input to a control terminal of the transistor.
The lighting control device according to claim 1. The step-up circuit unit is a chopper type step-up DC-DC converter.
The lighting control device according to claim 1 or 2. The light emitting element is an LED;
The lighting control apparatus of any one of Claims 1-3.   A vehicle lamp system comprising the lighting control device according to claim 1 and the vehicle lamp controlled by the lighting control device.

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