JP7515331B2 - Lighting control device, lighting device - Google Patents

Description

This disclosure relates to lighting control devices and lighting devices.

A lighting control method is known in which a plurality of light-emitting element groups (a group of light-emitting elements), each of which includes one or more light-emitting elements, are driven in a time-division manner so that the light emission periods of the groups do not overlap (see, for example, Patent Document 1). This type of lighting control method is also called time-share control.

When using the lighting control method using time-division driving described above, for example, the voltage generated by a DC-DC converter is applied to the light-emitting elements of each group in a time-division manner, and the current flowing during this process is detected and fed back to the DC-DC converter, thereby controlling the voltage applied to the light-emitting elements of each group to an appropriate level. At this time, the accuracy of current detection may decrease, which may result in a decrease in the accuracy of feedback control.

JP 2003-332624 A

One of the objectives of a specific aspect of the present disclosure is to improve the accuracy of feedback control when controlling lighting using time-division driving.

[1] A lighting control device according to one aspect of the present disclosure includes: (a) a lighting control device that supplies power to a plurality of light-emitting element groups in a time-division manner, (b) a power supply unit that is connected to the plurality of light-emitting element groups and supplies power in a pulse waveform; (c) a plurality of switching elements that are connected between each of the plurality of light-emitting element groups and the power supply unit; (d) a current detection circuit that is connected to a current path from the power supply unit to the plurality of light-emitting element groups and detects a current flowing in the current path; (e) an analog-to-digital converter that is connected to the current detection circuit and converts the current detected by the current detection circuit into a digital signal; and (f) an analog-to-digital converter that is connected to the plurality of switching elements and detects a rise and fall of the current. and a controller that controls the opening and closing of each of the plurality of switching elements based on each falling edge time and the digital signal obtained from the analog-to-digital converter, wherein (g) the controller uses the digital signal corresponding to the current in a first period , which is a period that includes at least the period from the rising edge of the current to its peak value but does not include the falling edge of the current, to determine the value of the current in the first period, uses the current value in the first period to determine an average value of the current in the period from the rising edge to the falling edge, and increases or decreases the time that each of the plurality of switching elements is open based on the average current value.
[2] An illumination device according to one aspect of the present disclosure is an illumination device including the lighting control device described above in [1] and a group of multiple light-emitting elements connected to the lighting control device and supplied with power in a time-division manner.

In this disclosure, "connected" can mean either a case where object A and object B are directly connected via wiring or the like, or a case where object A and object B are indirectly connected via wiring or the like with another object C interposed between them.

The above configuration can improve the accuracy of feedback control when controlling lighting using time-division driving.

FIG. 1 is a diagram showing the configuration of a lighting control device according to one embodiment and a group of light emitting elements controlled by this lighting control device. 2A to 2F are timing charts for explaining the basic operation of the lighting control device. 3A and 3B are waveform diagrams showing the relationship between the output voltage of the DC-DC converter and the current flowing through the light-emitting element group. Fig. 4A is a waveform diagram for explaining a current detection method, and Fig. 4B is a waveform diagram for explaining a feedback control method.

Figure 1 is a diagram showing the configuration of a lighting control device according to one embodiment and a group of light-emitting elements controlled by this lighting control device. The illustrated lighting control device 1 receives power from a power source 2 to generate a drive voltage, and supplies this drive voltage (power) to light-emitting element groups 3a and 3b in a time-division manner. The lighting control device 1 of this embodiment controls each of the light-emitting element groups 3a and 3b that constitute various lamps provided on a vehicle. The power source 2 is, for example, a battery provided on the vehicle. The lighting control device 1 and the light-emitting element groups 3a and 3b constitute a vehicle lamp, which is an example of a lighting device. The light-emitting element group 3a is used, for example, to emit a low beam (passing light), and the light-emitting element group 3b is used, for example, to emit a high beam (driving light).

The lighting control device 1 is composed of a DC-DC converter 10, a current detection circuit 11, a controller 12, a lighting time detection circuit 13, and two switching elements 14a and 14b. The lighting time detection circuit corresponds to the "waveform detection circuit."

The DC-DC converter 10 is connected to the power source 2, and generates an output voltage (drive voltage) of a voltage value suitable for driving the light-emitting element group 3a or the light-emitting element group 3b by stepping up or stepping down the DC voltage obtained from the power source 2.

The current detection circuit 11 is connected to the DC-DC converter 10 and generates the signals necessary for the operation of the DC-DC converter 10. It is composed of a resistive element 20, a peak current detection unit 21, and an I/V conversion unit (conversion unit) 22. The current detection circuit 11 is composed of, for example, an integrated circuit.

The resistor element 20 is connected to the wiring (i.e., the current path) that connects the DC-DC converter 10 and each of the light-emitting element groups 3a and 3b.

The peak current detection unit 21 is connected to both ends of the resistive element 20 and detects the maximum current (peak current) flowing through this resistive element 20. In detail, the current detection unit 21 is connected to the DC-DC converter 10 and generates a voltage signal that varies depending on the magnitude of the peak current flowing through the resistive element 20 and supplies this voltage signal to the DC-DC converter 10. The DC-DC converter 10 uses this voltage signal as a feedback signal to adjust the output voltage so that the peak current is kept approximately constant.

The I/V conversion unit 22 obtains the current flowing through the resistive element 20 via the peak current detection unit 21 and converts this current (I) into a voltage (V) signal.

The controller 12 controls the opening and closing of the switching elements 14a and 14b. The controller 12 is realized by using a computer system having, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and executing a predetermined operation program in the computer system. The controller 12 in this embodiment has an analog-to-digital converter (ADC) 23 built in.

The analog-to-digital converter (ADC) 23 is connected to the I/V conversion unit 22 and converts the voltage input from the I/V conversion unit 22 into a digital signal. In this embodiment, the analog-to-digital converter 23 is built into the controller 12, but it may be separate.

The illumination time detection circuit 13 is a circuit for detecting the illumination time of the light-emitting element group 3a or the light-emitting element group 3b, and is connected to the I/V conversion unit 22 and to the controller 12. The illumination time detection circuit 13 has a comparator 24.

One input terminal of the comparator 24 is connected to the I/V conversion unit 22, the other input terminal is connected to the reference power supply 4 that supplies the reference voltage Vrf, and the output terminal is connected to the controller 12. The comparator 24 outputs one of two values with relatively different magnitudes from the output terminal depending on the magnitude relationship between the voltage output from the I/V conversion unit 22 and the reference voltage Vrf. By appropriately setting the reference voltage Vrf, the voltage from the output terminal becomes a first value (e.g., high level) only while a current flows through the resistance element 20, and becomes a second value (e.g., low level) while no current is actually flowing. That is, the lighting time detection circuit 13 of this embodiment including the comparator 24 acts as a waveform detection circuit that detects the rising and falling times of the current. Therefore, the controller 12 can determine the lighting time of the light-emitting element group 3a or the light-emitting element group 3b based on the magnitude of the voltage at the output terminal of the comparator 24.

The switching element 14a has a first input/output terminal connected to the DC-DC converter 10 via the resistive element 20, a second input/output terminal connected to the light-emitting element group 3a, and a control terminal connected to the controller 12. The switching element 14a is controlled to be turned on/off in response to a control signal given to the control terminal from the controller 12. Here, "on" refers to a state in which a current can easily flow between the first input terminal and the second input terminal (open state), and "off" refers to a state in which a current does not substantially flow between the first input terminal and the second input terminal (closed state).

The switching element 14b has a first input/output terminal connected to the DC-DC converter 10 via the resistive element 20, a second input/output terminal connected to the light-emitting element group 3b, and a control terminal connected to the controller 12. The on/off of this switching element 14b is controlled in response to a control signal provided to the control terminal from the controller 12. The meanings of "on" and "off" here are the same as those described above.

In this embodiment, the figure shows field effect transistors as an example of the switching elements 14a and 14b, but the present invention is not limited to this. Each switching element 14a, 14b may be, for example, a bipolar transistor. In this embodiment, the on/off of these switching elements 14a, 14b is controlled in a time-division manner by the controller 12, so that the light-emitting element group 3a and the light-emitting element group 3b are controlled to light up in a time-division manner without lighting up at the same time.

The light-emitting element group 3a includes five light-emitting elements (LEDs) connected in series, one end of which is connected to the DC-DC converter 10, and the other end of which is connected to a reference potential end (so-called GND). The light-emitting element group 3b includes eight light-emitting elements (LEDs) connected in series, one end of which is connected to the DC-DC converter 10, and the other end of which is connected to a reference potential end (so-called GND). In this embodiment, the light-emitting element group 3a and the light-emitting element group 3b are connected in parallel to the DC-DC converter 10. In addition, since the number of light-emitting elements of the light-emitting element group 3a and the light-emitting element group 3b are different from each other, the overall load (resistance value) of each group is different.

Figures 2(A) to 2(F) are timing charts for explaining the basic operation of the lighting control device. In detail, Figure 2(A) is a waveform diagram showing the on/off state of the switching element 14a, Figure 2(B) is a waveform diagram showing the on/off state of the switching element 14b, Figure 2(C) is a waveform diagram showing the on/off state by PWM control of the DC-DC converter 10, Figure 2(D) is a waveform of the current flowing through the light-emitting element group 3a, Figure 2(E) is a waveform of the current flowing through the light-emitting element group 3b, and Figure 2(F) is a waveform of the output voltage of the DC-DC converter 10. In Figures 2(A) and 2(B), the relatively high level of the waveform indicates the "on" of each switching element 14a, 14b, and the relatively low level of the waveform indicates the "off" of each switching element 14a, 14b. In addition, in FIG. 2(C), when the waveform is at a relatively high level, it indicates a state in which a voltage is output from the DC-DC converter 10, and when the waveform is at a relatively low level, it indicates a state in which no voltage is output from the DC-DC converter 10.

As shown in FIG. 2(C), the DC-DC converter 10 is PWM (Pulse Width Modulation) controlled, and generates a pulse-wave voltage by repeatedly turning on and off at a predetermined duty ratio. When the duty of the DC-DC converter 10 is on, if the switching element 14a is turned on (FIG. 2(A)), the output voltage of the DC-DC converter 10 rises after a delay time td1 (for example, 10 μs) and becomes a constant value corresponding to the load of the light-emitting element group 3a (FIG. 2(F)). At this time, the output voltage of the DC-DC converter 10 gradually increases over a certain amount of time until it reaches a constant value, so that the current flowing through the light-emitting element group 3a also gradually increases in response to this and then remains at a constant value (FIG. 2(D)). After that, if the switching element 14a is turned off (FIG. 2(A)), the current flowing through the light-emitting element group 3a becomes substantially zero (FIG. 2(D)). The delay time td1 is provided to put the light-emitting element group 3a into a conductive state before the DC-DC converter 10 starts outputting, thereby preventing abnormal voltage increase in the DC-DC converter 10.

When switching element 14b is turned on after a certain time has elapsed since switching element 14a was turned off (FIG. 2B), the output voltage of DC-DC converter 10 rises after a delay time td2 (e.g., 10 μs) until the PWM signal of DC-DC converter 10 is turned on, and then the output voltage becomes a constant value corresponding to the load of light-emitting element group 3b (FIG. 2F). In this manner, in this embodiment, the output voltage of DC-DC converter 10 is raised after switching element 14b is turned on. The delay time td2 is provided to prevent abnormal voltage increase of DC-DC converter 10, as in the case of delay time td1 described above.

In this embodiment, the load on the light-emitting element group 3b is greater than that on the light-emitting element group 3a, and so the output voltage is also greater. This also increases the time it takes for the output voltage to reach a constant value. The current flowing through the light-emitting element group 3b gradually increases in response to the gradual increase in the output voltage of the DC-DC converter 10, and then remains at a constant value (Figure 2 (E)). After that, when the switching element 14b is turned off (Figure 2 (B)), the current flowing through the light-emitting element group 3b becomes substantially zero (Figure 2 (E)).

If one cycle is defined as the period during which switching element 14a turns on and then turns off, switching element 14b turns on and then turns off, and a certain amount of time passes before switching element 14a turns on again, the length T of one cycle can be set to, for example, about 5000 μs (equivalent to 200 Hz). In this embodiment, the on period of switching element 14a is set relatively longer than the on period of switching element 14b within one cycle.

The peak current value and the target duty of the current flowing through the light-emitting element group 3a are set so that the average value over one period T is, for example, 1.3 A. Similarly, the peak current value and the target duty of the current flowing through the light-emitting element group 3b are set so that the average value over one period T is, for example, 0.05 A. These duties can be set by the on-period and off-period of the switching elements 14a and 14b described above.

The DC-DC converter 10 of this embodiment controls the output voltage so that the peak current is approximately constant. Therefore, in order to increase or decrease the average value of the current flowing through each of the light-emitting element groups 3a and 3b, it is advisable to increase or decrease the time during which the current flows. In this embodiment, the controller 12 variably sets the lengths of the on and off periods of the switching elements 14a and 14b, thereby increasing or decreasing the time during which the current flows through each of the light-emitting element groups 3a and 3b.

Each of Figures 3(A) and 3(B) is a waveform diagram showing the relationship between the output voltage of the DC-DC converter and the current flowing through the light-emitting element group. In each diagram, the upper part shows the output voltage, and the lower part shows the current. The DC-DC converter 10 of this embodiment performs control to automatically switch between three control modes, boost mode, boost/buck mode, and buck mode, depending on the magnitude of the output voltage. Therefore, when the relationship between the input voltage from the power source 2 and the output voltage of the DC-DC converter 10 reaches the control mode switching voltage, a delay occurs in the rise time of the output voltage.

When the control mode does not switch, the output voltage rises linearly (linearly) as shown in the upper part of Figure 3(A) and then remains at a constant value, and the current also follows a similar trend as shown in the lower part of Figure 3(A). In this case, the output voltage of the DC-DC converter 10 can be precisely controlled by detecting the time t during which the current flows (lighting time).

On the other hand, when the control mode is switched, the output voltage does not increase linearly as shown in the upper part of FIG. 3(B), but increases stepwise with a period during which the output voltage does not increase due to the switching of the control mode. Therefore, as shown in the lower part of FIG. 3(B), the current does not immediately reach the peak current (Ipk), and a period of relatively low current is sandwiched between them. In this case, it is difficult to precisely control the output voltage of the DC-DC converter 10 by only detecting the time (lighting time) t during which the current flows. This is because the average value of the current flowing through the light-emitting element group 3a (or 3b) is lower than when the control mode is not switched. For this reason, in this embodiment, the controller 12 controls the time for which each switching element 14a, 14b is turned on based on the rise and fall of the current detected by the lighting time detection circuit 13, thereby controlling the current to approach an appropriate value. The details of this will be described below.

Figure 4 (A) is a waveform diagram for explaining the current detection method. In reality, the current flowing through the resistive element 20 is converted to a voltage by the I/V conversion unit 22, and the magnitude of the current is detected via this voltage, so this voltage waveform is shown in Figure 4 (A). The controller 12 detects the rising time (starting time) of the current based on the voltage level (high/low) of the voltage signal output from the illumination time detection circuit 13. The controller 12 also converts the voltage signal output from the I/V conversion unit 22 to a digital signal by the analog-digital converter 23 at a fixed sampling period Δt and captures it. In the figure, sampling points are shown as black circles for ease of understanding.

During the first period (including the period from when the current rises to the peak current (Ipk) in this embodiment) which includes at least the period from when the current rises to the peak current (Ipk) to when a certain time has passed after the peak current Ipk is reached, the controller 12 acquires the value of the current based on the digital signal obtained by the analog-digital converter 23. During the second period (including at least the period from when the current reaches the peak current (Ipk) to when the current falls (end), the controller 12 detects the time the current flows based on the output voltage of the lighting time detection circuit 13. Specifically, the controller 12 detects the fall time of the current based on the voltage level (high/low) of the voltage signal output from the lighting time detection circuit 13. The time from the start of the second period to when the current falls is the time of the second period. The boundary between the first period and the second period is appropriately set by the controller 12.

In the first period corresponding to the rising edge of the current, the waveform change can be accurately detected by using the digital signal from the analog-digital converter 23. On the other hand, if the waveform change for the entire period combining the first and second periods is detected based on the digital signal from the analog-digital converter 23, the sampling frequency may not be able to follow the steep fall of the current, and the time of the fall of the current (the end of the second period) may not be accurately detected. For this reason, the end of the second period is detected using the illumination time detection circuit 13, which is an analog circuit, and the voltage at the output end of the comparator 23 is treated as a logic signal (digital signal) and taken in from the input port for digital signals of the controller 12, so that the end can be detected more accurately.

The controller 12 integrates the magnitude of the current at each sampling point in the first period based on the sampling period, and also integrates the magnitude of the peak current and the time during which it flows in the second period, and then adds them together and takes the average to obtain the average magnitude of the current (average current) throughout the first and second periods. The controller 12 then compares this average current value with a preset reference value, and increases or decreases the time (conduction time) during which current flows through the light-emitting element group 3a (or 3b) according to the difference, as shown in FIG. 4(B). Specifically, the length of the conduction time is increased or decreased by shifting the end of the conduction time forward or backward as shown in the figure. For example, if the average current value is smaller than the reference value, the conduction time is increased according to the difference. Also, if the average current value is larger than the reference value, the conduction time is shortened according to the difference. Specifically, the controller 12 increases or decreases the conduction time by controlling the length of the on period of each switching element 14a, 14b. This makes it possible to realize accurate feedback control according to the average current value.

As described above, according to this embodiment, it is possible to improve the accuracy of feedback control when controlling the lighting of multiple light-emitting element groups by split driving.

Note that the present disclosure is not limited to the contents of the above-mentioned embodiment, and various modifications can be made within the scope of the gist of the present disclosure. For example, the above-mentioned embodiment illustrates a case where two light-emitting element groups are driven in a time-division manner, but the number of light-emitting element groups may be three or more. The number of light-emitting elements included in each of the light-emitting element groups is also an example, and is not limited to that of the above-mentioned embodiment. In the present disclosure, the number of light-emitting elements included in each of the light-emitting element groups may be at least one or more. Furthermore, the use of the light-emitting element groups is not limited to vehicle lamps, and various lighting devices can be used.

In the above embodiment, feedback control was achieved by increasing or decreasing the time (conduction time) for which current was supplied to each light-emitting element group, but feedback control may also be achieved by increasing or decreasing the peak current. In this case, a control signal is supplied from the controller 12 to the DC-DC converter 10 according to the average current value, and the peak current is increased or decreased by increasing or decreasing the output voltage. Furthermore, such control based on peak current and control based on conduction time may be used in combination. Furthermore, the peak current value and/or average current value of the current supplied to each light-emitting element group may be the same or different.

In addition, in the above embodiment, the current fall timing is detected using an illumination time detection circuit, which is an analog circuit, but if the sampling period of the analog-to-digital converter is sufficiently short, the fall timing may also be detected based on the digital signal obtained from the analog-to-digital converter.

In addition, the DC-DC converter in the above embodiment has three control modes, but it is sufficient if it has at least two control modes. Also, in the above embodiment, a DC-DC converter is used as an example of a power supply unit that supplies pulse waveform power, but the power supply unit is not limited to this.

1: Lighting control device, 2: Power supply, 3a, 3b: Light-emitting element group, 4: Reference power supply, 10: DC-DC converter, 11: Control circuit, 12: Controller, 13: Illumination time detection circuit, 14a, 14b: Switching element, 15: Resistance element, 21: Peak current detection unit, 22: I/V conversion unit, 23: Analog-to-digital converter, 24: Comparator

Claims (8)

A lighting control device that supplies power to a plurality of light-emitting element groups in a time-division manner,
a power supply unit connected to the plurality of light-emitting element groups and supplying power having a pulse waveform;
a plurality of switching elements connected between each of the plurality of light-emitting element groups and the power supply unit;
a current detection circuit connected to a current path from the power supply unit to the plurality of light-emitting element groups and detecting a current flowing through the current path;
an analog-to-digital converter connected to the current detection circuit and converting the current detected by the current detection circuit into a digital signal;
a controller connected to the plurality of switching elements and controlling opening and closing of each of the plurality of switching elements based on the rising and falling timings of the current and the digital signal obtained from the analog-to-digital converter;
Including,
the controller uses the digital signal corresponding to the current in a first period, the first period being a period including at least a period from a rise time of the current to a peak value but not including a fall time of the current, calculates an average value of the current in the period from the rise time to the fall time using the current value in the first period, and increases or decreases a time for which each of the plurality of switching elements is in an open state based on the average current value;
Lighting control device. a waveform detection circuit connected to the current detection circuit and detecting a rise and a fall of the current detected by the current detection circuit;
the controller determines a length of a second period including at least a period from after the first period has elapsed to the falling edge of the current based on an output of the waveform detection circuit, and determines an average value of the current using the length of the second period;
The lighting control device according to claim 1 . the controller determines a first average value of the current in the first period based on the digital signal and a sampling period thereof, determines a second average value of the current in the second period based on a length of time from the end of the first period to a falling edge of the current, and determines an average value of the current based on the first average value and the second average value.
The lighting control device according to claim 2 . The power supply unit is a DC-DC converter that autonomously switches between at least two operation modes among a step-up mode, a step-down mode, and a step-up/step-down mode.
The lighting control device according to any one of claims 1 to 3. The analog-to-digital converter is built into the controller.
The lighting control device according to any one of claims 1 to 4. the current detection circuit includes a resistive element connected on the current path, and a conversion unit that converts a current flowing through the resistive element into a voltage;
The analog-to-digital converter converts the voltage obtained from the conversion unit into a digital signal.
The lighting control device according to any one of claims 1 to 5. The plurality of light-emitting element groups have different loads, and the peak values of currents flowing through the plurality of light-emitting element groups when they are turned on are different from one another.
The lighting control device according to any one of claims 1 to 6. A lighting control device according to any one of claims 1 to 7,
A plurality of light-emitting element groups connected to the lighting control device and supplied with power in a time-division manner;
13. A lighting device comprising:

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