Light-emitting element driving device

Abstract

A light-emitting element driving device includes: a receiver that receives a predetermined communication signal transmitted via a communication line; a generator that generates a reference signal based on a start time point of a start bit in the predetermined communication signal; and a determiner that determines, based on the reference signal, a timing for switching a light-emitting element from extinction to illumination. The predetermined communication signal is a signal in which a start bit having a first logic level is transmitted from a transmitter at a predetermined period, and in which data bits following each start bit do not have a second logic level for a predetermined number of times or more.

Description

Technical Field

[0001] The present invention relates to a light emitting element driving device. Background Art

[0002] Conventionally, a light emitting element driving device having multiple channels is known (for example, see Patent Document 1). When a single light emitting element driving device cannot provide a desired number of channels, a plurality of light emitting element driving devices are used to construct a lighting system.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2011-107259 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] Here, if on / off control or dimming control is performed on a channel-by-channel basis, a plurality of light emitting element driving devices need to be operated synchronously, because otherwise the lighting system operates in a lighting pattern different from a desired lighting pattern.

[0008] For example, by feeding a common clock signal to the light-emitting element driving devices so that the light-emitting element driving devices operate based on the clock signal, a plurality of light-emitting element driving devices can be operated in synchronization with each other. However, in order to feed the common clock signal to the light-emitting element driving devices, a port for feeding the clock signal to each light-emitting element driving device needs to be provided, which increases the size and cost of the light-emitting element driving devices.

[0009] In view of the above circumstances, the present invention is intended to provide a light emitting element driving device that can operate in synchronization with another light emitting element driving device without using a clock signal common to them.

[0010] Means of solving the problem

[0011] According to one aspect of the present disclosure, a light-emitting element driving device includes: a receiver configured to receive a predetermined communication signal transmitted via a communication line; a generator configured to generate a reference signal based on a start time point of a start bit in the predetermined communication signal; and a determiner configured to determine a timing for switching a light-emitting element from extinction to illumination based on the reference signal. The predetermined communication signal is a signal in which a start bit having a first logic level is transmitted from a transmitter at a predetermined period, and data bits following each start bit do not have a second logic level for a predetermined number of times or more (a first configuration).

[0012] In the light-emitting element driving device according to the above-mentioned first configuration, preferably, the generator includes: a first detector, which is configured to detect that the period during which the communication line is at the second logic level has continued for a first predetermined time; and a second detector, which is configured to detect a first logic occurrence time point at which the first logic level first appears on the communication line after the period during which the communication line is at the second logic level has continued for the first predetermined time, as the starting time point of the start bit (second configuration).

[0013] In the light-emitting element driving device according to the above-mentioned second configuration, preferably, the second detector is configured so that if the period in which the communication line is at the first logic level does not last for a second predetermined time after the first logic occurrence time point, the second detector does not exceptionally detect the first logic occurrence time point as the starting time point of the start bit (third configuration).

[0014] In the light emitting element drive device according to the third configuration described above, preferably, the second predetermined time is shorter than the first predetermined time (fourth configuration).

[0015] In the light emitting element driving device according to any one of the first to fourth configurations described above, preferably, the predetermined communication signal includes dimming information of the light emitting element (fifth configuration).

[0016] In the light emitting element driving device according to any one of the first to fifth configurations described above, preferably, the predetermined communication signal is a UART (Universal Asynchronous Receiver / Transmitter) communication signal (sixth configuration).

[0017] According to another aspect of the present disclosure, the light-emitting system includes a plurality of light-emitting element driving devices configured according to any one of the first to sixth configurations, and the light-emitting system also includes a communication line, a transmitter, and at least the same number of light-emitting elements as the number of the light-emitting element driving devices (seventh configuration).

[0018] According to still another aspect of the present disclosure, a vehicle includes the lighting system according to the seventh configuration described above (eighth configuration).

[0019] Effects of the Invention

[0020] According to the present invention, it is possible to provide a light emitting element driving device that can operate in synchronization with other light emitting element driving devices without using a clock signal common to them. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a diagram showing a lighting system according to one embodiment;

[0022] Figure 2 is a diagram showing one configuration example of a light emitting element driving device;

[0023] Figure 3 is a timing chart showing the operation of the light emitting element driving device;

[0024] Figure 4 is another timing chart showing the operation of the light emitting element driving device;

[0025] Figure 5 is another timing diagram showing the operation of the light emitting element driving device;

[0026] Figure 6 is a diagram showing a structural example of a light emitting element circuit;

[0027] Figure 7 is an exterior view of the vehicle. DETAILED DESCRIPTION

[0028] Figure 1 is a diagram illustrating a lighting system according to one embodiment. Figure 1 The illustrated lighting system 1 includes a microcomputer 2, a communication bus 3, light emitting element driving devices 4A to 4D, light emitting element circuits 5A_1 to 5A_8, 5B_1 to 5B_8, 5C_1 to 5C_8, and 5D_1 to 5D_8, and DC-DC converters 6A to 6D.

[0029] The microcomputer 2 performs dimming control for each channel of the light-emitting element driving devices 4A to 4D via the communication bus 3. The microcomputer 2 can control each of the light-emitting element driving devices 4A to 4D by specifying an address. For example, when a 2-bit address is used, the microcomputer 2 can individually control up to four light-emitting element driving devices. For example, when a 3-bit address is used, the microcomputer 2 can individually control up to eight light-emitting element driving devices.

[0030] The microcomputer 2 performs dimming control on each channel of the light-emitting element driving devices 4A to 4D by controlling the on-duty ratio of PWM (pulse width modulation). In a modified version of this embodiment, a dimming control method other than PWM dimming can be used. For example, the microcomputer 2 can perform dimming control by controlling the value of the DC current flowing through each channel of the light-emitting element driving devices 4A to 4D.

[0031] Communication bus 3 is a communication line for transmitting a predetermined communication signal. The predetermined communication signal is a signal in which a start bit having a first logic level is transmitted from microcomputer 2, serving as a transmitter, at a predetermined interval, and in which data bits following each start bit do not have a second logic level for a predetermined number of times or more. For example, a UART communication signal or the like can be used as the predetermined communication signal. In a UART communication signal, the first logic level is a low level, and the second logic level is a high level.

[0032] As the communication bus 3 , for example, a CAN (Controller Area Network) bus or the like can be used.

[0033] The light-emitting element driver 4A has a first channel 1ch to an eighth channel 8ch, and drives the light-emitting element circuits connected to the first channel 1ch to the eighth channel 8ch for each channel according to the dimming control of the microcomputer 2. The cathode of the light-emitting element circuit 5A_k is connected to the kth channel kch (where k represents a natural number greater than or equal to 1 and less than or equal to 8) of the light-emitting element driver 4A.

[0034] The light emitting element driving devices 4B to 4D have similar configurations to the light emitting element driving device 4A except for the addresses to which they are assigned.

[0035] The light-emitting element circuits 5A_k to 5D_k are circuits in which a plurality of LEDs (light-emitting diodes) are connected in series. In a modified version of this embodiment, the light-emitting element circuits 5A_k to 5D_k may each include a single LED. Alternatively, any other type of light-emitting element, such as an organic EL (electroluminescence) light-emitting element, may be used instead of any LED.

[0036] The DC-DC converter 6A converts the input voltage VIN into the output voltage VOUT1 and feeds the output voltage VOUT1 to the anode of the light-emitting element circuit 5A_k. The DC-DC converter 6B converts the input voltage VIN into the output voltage VOUT2 and feeds the output voltage VOUT2 to the anode of the light-emitting element circuit 5B_k. The DC-DC converter 6C converts the input voltage VIN into the output voltage VOUT3 and feeds the output voltage VOUT3 to the anode of the light-emitting element circuit 5C_k. The DC-DC converter 6D converts the input voltage VIN into the output voltage VOUT4 and feeds it to the anode of the light-emitting element circuit 5C_k. It is generally assumed that the output voltages VOUT1 to VOUT4 have equal voltage values. However, for example, if the number of light-emitting elements constituting the light-emitting element circuit 5A_k is different from the number of light-emitting elements constituting the light-emitting element circuit 5B_k, the output voltages VOUT1 and VOUT2 may be given different voltage values. In a modified version of this embodiment, at least two of the DC-DC converters 6A to 6D may be integrated.

[0037] Next, refer to Figure 2 and Figure 3 , the light emitting element driving device 4A will be described. Figure 2 is a diagram showing one configuration example of a light emitting element driving device 4A. Figure 3 1 is a timing chart showing the operation of the light emitting element driving device 4A.

[0038] The light emitting element driving device 4A includes a terminal 40 , a receiver 41 , a generator 42 , a determiner 43 , and current sources 44_1 to 44_8 .

[0039] Terminal 40 is connected to the communication bus 3 (see Figure 1 ).

[0040] The receiver 41 receives the UART communication signal sent via the communication bus 3 (see Figure 1 Receiver 41 stores the address of light-emitting element driver 4A in a nonvolatile manner, extracts information related to light-emitting element driver 4A from the UART communication signal based on the address of light-emitting element driver 4A, and stores the extracted information in register 431 in determiner 43. In this embodiment, receiver 41 extracts the PWM dimming on-duty ratio for each channel of light-emitting element driver 4A.

[0041] The receiver 41 in the light-emitting element driving device 4B stores the address of the light-emitting element driving device 4B in a nonvolatile manner. The receiver 41 in the light-emitting element driving device 4C stores the address of the light-emitting element driving device 4C in a nonvolatile manner. The receiver 41 in the light-emitting element driving device 4D stores the address of the light-emitting element driving device 4D in a nonvolatile manner.

[0042] The generator 42 generates a reference signal based on the start time point of the start bit in the UART communication signal. The generator 42 includes a counter 421 and a falling edge detector 422.

[0043] When the communication bus 3 (see Figure 1 ) is at a high level, the counter 421 continues to count, and when the communication bus 3 (see Figure 1 ) becomes low, stops counting and resets the count value.

[0044] The counter 421 senses the communication bus 3 (see Figure 1) has been at a high level for a first predetermined time PT1. In a UART communication signal, a data bit never has a high level nine or more times in a row; therefore, the first predetermined time PT1 is set to the period during which the data bit has a high level nine times in a row, and the value obtained by dividing the first predetermined time PT1 by the period of the internal clock signal of the light-emitting element driving device 4A is used as the threshold value of the count value. Therefore, the counter 421 can sense that the UART communication has been completed.

[0045] When the communication bus 3 (see Figure 1 ) is at a high level for a first predetermined time PT1, the counter 421 changes the enable signal fed to the falling edge detector 422 to a high level.

[0046] The falling edge detector 422 senses a falling edge as a start time point of a start bit in UART communication only during a period in which the enable signal is at a high level, and the falling edge is a signal received by the communication bus 3 (see FIG. Figure 1 ) appears a low level on the communication bus 3 (see Figure 1 ) has been at a high level for a period of time PT1, a low level first appears on the communication bus 3 (see Figure 1 ) as the start time point of the start bit in UART communication.

[0047] Then, after the falling edge detector 422 detects the falling edge, the counter 421 immediately switches the enable signal from a high level to a low level.

[0048] The falling edge detector 422 feeds a reference signal SREF, which is a pulse signal appearing at a start time point of a start bit in UART communication, to the PWM signal generator 432 in the determiner 43 .

[0049] The determiner 43 determines a time point to switch the light emitting element circuits 5A_1 to 5A_8 from off to on based on the reference signal SREF The determiner 43 includes a register 431 and a PWM signal generator 432 .

[0050] As described above, register 431 stores the PWM dimming on-duty ratio of each channel of light emitting element driving device 4A. In this embodiment, the PWM dimming on-duty ratio is represented by an integer (ie, 8-bit data) whose setting value is 0 or greater but 255 or less.

[0051] The PWM signal generator 432 generates a PWM signal SPWMk (where k represents a natural number greater than or equal to 1 but less than or equal to 8) based on the PWM dimming conduction duty cycle of the kth channel stored in the register 431 and the reference signal SREF. For example, in the period between time points t1 and t2, the PWM signal generator 432 calculates the lighting time of each channel of the light-emitting element driving device 4A using the PWM dimming conduction duty cycle of each channel transmitted by the UART signal S1, and reflects the calculation result after the time point (t3) when the next pulse appears in the reference signal SREF. Specifically, the transition to the lighting time can occur at a time point after time point t3 when the extinguishing time (the time length obtained by subtracting the above-mentioned lighting time from the known period of UART communication) has passed. The above-mentioned lighting time can be calculated by multiplying the period of UART communication by the above-mentioned set value and then dividing the result by 255.

[0052] The current source 44_k is connected to the cathode of the light emitting element circuit 5A_k (see Figure 1 ), and PWM driving is performed by a PWM signal SPWMk (where k represents a natural number greater than or equal to 1 but less than or equal to 8). When the PWM signal SPWMk is at a high level, the current source 44_k is turned on and drives the light-emitting element circuit 5A_k. Conversely, when the PWM signal SPWMk is at a low level, the current source 44_k is turned off and does not drive the light-emitting element circuit 5A_k.

[0053] Since the light emitting element driving device 4A operates as described above and the light emitting element driving devices 4B to 4D also operate in a similar manner to the light emitting element driving device 4A, all the light emitting element driving devices 4A to 4D operate in synchronization with the reference signal SREF. Therefore, without using a clock signal common to the light emitting element driving devices 4A to 4D, Figure 1 The light emission pattern of the illustrated light emitting system 1 is adjusted to a desired light emission pattern (the light emission pattern that the microcomputer 2 instructs the light emitting element driving devices 4A to 4D to use).

[0054] Even when the PWM dimming on-duty cycle is equal between channels, the timing of switching from extinction to lighting does not have to be synchronized. Figure 4 As shown, the timing of switching from extinction to light emission can be shifted by a predetermined offset time Δ. Figure 3 and Figure 4 In the embodiment, the PWM dimming conduction duty cycle between each channel is equal, but needless to say, the PWM dimming conduction duty cycle between each channel may be different. In addition, in each channel, the PWM dimming conduction duty cycle can be changed for each PWM period.

[0055] Although the above description deals with the case where there is no abnormality in the voltage level of the communication bus 3 (see Figure 1 ), but there may be a case where an abnormality occurs in the voltage level of the communication bus 3 due to a malfunction in the microcomputer 2, the influence of noise, or the like (see Figure 1 ).

[0056] For example, if the communication bus 3 (see Figure 1 ) becomes a low level period L1, the generator 42 will not mistakenly recognize the starting time point of the period L1 as the starting time point of the start bit in the UART signal (see Figure 5 ).

[0057] However, if the communication bus 3 (see Figure 1 ) becomes a low level period L1, the generator 42 mistakenly recognizes the starting time point of the period L1 as the starting time point of the start bit in the UART signal.

[0058] To prevent this misidentification, when the communication bus 3 (see Figure 1 ) is at a low level during the period of communication bus 3 (see Figure 1 ) does not continue for a second predetermined time after the time point at which the low level appears on the communication bus 3 (see Figure 1 ) is detected as the starting time point of the start bit in the UART communication. For example, a filter circuit capable of eliminating a low-level signal that only lasts for the second predetermined time or shorter can be provided in the falling edge detector 422.

[0059] The second predetermined time is set to be shorter than the first predetermined time PT1. More specifically, the second predetermined time is set to be shorter than the communication bus 3 corresponding to the start bit in the UART communication (see Figure 1 Otherwise, the start time point of the start bit in UART communication cannot be correctly detected.

[0060] Although there is no particular limitation on the arrangement of the light emitting element circuits 5A_1 to 5A_8, 5B_1 to 5B_8, 5C_1 to 5C_8, and 5D_1 to 5D_8, they may be arranged, for example, in a manner similar to that described above. Figure 6 The matrix shown allows Figure 1 The lighting system 1 shown displays an animated 8 x 4 dot picture.

[0061] Although Figure 1 The use of the light emitting system shown is not particularly limited, but it can be applied to, for example Figure 7The vehicle X10 shown in FIG. The vehicle X10 includes display units X11 to X13. The display unit X11 is provided at the left rear end of the vehicle X10, the display unit X12 is provided below a hatchback door X14 of the vehicle X10, and the display unit X13 is provided at the right rear end of the vehicle X10. For example, by using light-emitting element circuits 5A_1 to 5A_8 as the display unit X11, light-emitting element circuits 5B_1 to 5B_8 and light-emitting element circuits 5C_1 to 5C_8 as the display unit X12, and light-emitting element circuits 5D_1 to 5D_8 as the display unit X13, even if the display units X11 and X12 are physically separated by the hatchback door X14 and the display units X12 and X13 are physically separated by the hatchback door X14, it is possible to use the display units X11 to X13 for an integrated display.

[0062] The present invention can be implemented in any manner other than the above-described embodiment, and any modifications can be made within the scope of the present invention. The embodiments disclosed herein should be considered to be illustrative and not restrictive in every respect, and the technical scope of the present invention is not limited by the description of the embodiments given above, but by the scope of the appended claims, and should be understood to include any modifications within the meaning and scope equivalent to the claims.

[0063] Explanation of symbols

[0064] 1 Lighting system

[0065] 2 Microcomputer

[0066] 3 Communication bus

[0067] 4A to 4D Light-emitting element driver

[0068] 5A_1 to 5A_8 Light-emitting element circuit

[0069] 5B_1 to 5B_8 Light-emitting element circuit

[0070] 5C_1 to 5C_8 Light-emitting element circuit

[0071] 5D_1 to 5D_8 Light-emitting element circuit

[0072] 6A to 6D DC-DC Converters

[0073] 40 terminals

[0074] 41 Receiver

[0075] 42 Generator

[0076] 421 Counter

[0077] 422 Falling Edge Detector

[0078] X10 Vehicle

[0079] X11 to X13 display unit

[0080] X14 hatchback

Claims

1. A light emitting element driving device, comprising: a receiver configured to receive a predetermined communication signal transmitted through the communication line; a generator configured to generate a reference signal based on a start time point of a start bit in the predetermined communication signal; as well as a determiner configured to determine a timing for switching the light emitting element from extinction to illumination based on the reference signal, in, The predetermined communication signal is a signal in which a start bit having a first logic level is transmitted from a transmitter at a predetermined cycle, and data bits following each start bit do not have a second logic level continuously for a predetermined number of times or more, in, The generator includes: a first detector configured to detect that a period in which the communication line is at the second logic level has continued for a first predetermined time; and a second detector configured to: after the period in which the communication line is at the second logic level has continued for the first predetermined time, detect a first logic occurrence time point at which the first logic level first appears on the communication line as a start time point of the start bit, and in, The second detector is configured to, if the period in which the communication line is at the first logic level does not continue for a second predetermined time after the first logic occurrence time point, exceptionally not detect the first logic occurrence time point as the start time point of the start bit.

2. The light emitting element driving device according to claim 1, in, The second predetermined time is shorter than the first predetermined time.

3. The light emitting element driving device according to claim 1, in, The predetermined communication signal includes dimming information for the light emitting element.

4. The light emitting element driving device according to claim 1, in, The predetermined communication signal is a universal asynchronous receiver / transmitter communication signal.

5. A lighting system, comprising a plurality of light emitting element driving devices according to any one of claims 1 to 4, further comprising: Communication lines; transmitter; as well as There are at least as many light emitting elements as the number of the light emitting element driving devices.

6. A vehicle comprising the lighting system according to claim 5.

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