Light-emitting element drive circuit

Abstract

A light emitting element drive circuit (1) includes: a first buffer (6) provided between a transmission terminal (1B) and a communication unit (2), with the transmission terminal on an output side and the communication unit on an input side; and a determining unit (32) for determining connection / non-connection of a control unit (15) on the basis of a first signal (S1) at an output terminal of the first buffer, and a second signal (S2) at an input terminal of the first buffer. If the determining unit determines non-connection of the control unit, processing by the communication unit of a signal received from a reception terminal (1A) is disabled, and a light adjustment signal generating unit (31) generates a light adjustment signal (Spwm) on the basis of a pulse signal (Sp) input to the reception terminal or the transmission terminal.

Description

[Technical Field]

[0001] The present disclosure relates to a light-emitting element drive circuit. [Background technology]

[0002] 2. Description of the Related Art Various light emitting element drive circuits for driving light emitting elements such as LEDs (light emitting diodes) have been developed.

[0003] Conventional LED drive circuits include a current driver that passes current through an LED. Some conventional LED drive circuits use PWM (Pulse Width Modulation) control of the current driver based on communication with an external processor (see, for example, Patent Document 1). With PWM control, the current driver is turned on and off based on a PWM signal. This allows PWM dimming of the LED. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-28866 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-described conventional LED drive circuit, if an external processor is not used, communication with the processor cannot be performed, and light emission control of the LED cannot be performed.

[0006] An object of the present disclosure is to provide a light emitting element drive circuit that can control the light emission of a light emitting element without increasing the number of terminals even when an external control unit is not used. [Means for solving the problem]

[0007] For example, the light emitting element drive circuit according to the present disclosure may include: a receiving terminal and a transmitting terminal that can be connected to an external control unit; a communication unit configured to receive a reception signal from the control unit via the reception terminal and to transmit a transmission signal to the control unit via the transmission terminal; a dimming signal generating unit that generates a dimming signal; a constant current circuit that supplies current to the light emitting element and is controlled to be turned on and off based on the dimming signal; a first buffer provided between the transmission terminal and the communication unit, the first buffer having the transmission terminal as an output side and the communication unit as an input side; a determination unit that determines whether the control unit is connected or not based on a first signal at an output terminal of the first buffer and a second signal at an input terminal of the first buffer; and When the determination unit determines that the control unit is connected, processing of the signal received from the receiving terminal by the communication unit is enabled, and the dimming signal generation unit generates the dimming signal based on a command from the communication unit. If the determination unit determines that the control unit is not connected, the processing by the communication unit of the signal received from the receiving terminal is disabled, and the dimming signal generation unit is configured to generate the dimming signal based on the pulse signal input to the receiving terminal or the transmitting terminal. [Effects of the Invention]

[0008] According to the light-emitting element drive circuit of the present disclosure, it is possible to control the light emission of the light-emitting element without using an external control unit, without increasing the number of terminals. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a schematic block configuration of an LED drive circuit according to the first embodiment. [Figure 2] FIG. 2 is a diagram showing a state in which an MCU is connected to the LED drive circuit according to the first embodiment and the LED drive circuit is used. [Figure 3]FIG. 3 is a diagram showing a state in which the LED drive circuit according to the first embodiment is used without being connected to an MCU. [Figure 4] FIG. 4 is a diagram showing a schematic block configuration of an LED drive circuit according to the second embodiment. [Figure 5] FIG. 5 is a diagram showing a state in which an MCU is connected to the LED drive circuit according to the second embodiment and the LED drive circuit is used. [Figure 6] FIG. 6 is a diagram showing a state in which the LED drive circuit according to the second embodiment is used without being connected to an MCU. [Figure 7] FIG. 7 is a diagram showing a schematic block configuration of an LED drive circuit according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] <1. Comparative Example> Before describing an exemplary embodiment of the present invention, a comparative example will be described first. Fig. 7 is a diagram showing a schematic block configuration of an LED drive circuit 10 according to the comparative example.

[0011] 7 includes a UART 11, a logic unit 12, and a constant current circuit 13. The LED drive circuit 10 also includes an RX terminal 10A, a TX terminal 10B, an LED terminal 10C, and a ground terminal 10D as external terminals for establishing electrical connection with the outside.

[0012] The UART (Universal Asynchronous Receiver / Transmitter) 11 is a circuit that performs bidirectional conversion between serial signals and parallel signals. An MCU (Micro Control Unit) 15 is provided outside the LED drive circuit 10. The MCU 15 can be connected to an RX terminal 10A and a TX terminal 10B. The UART 11 receives a reception signal Srx from the MCU 15 via the RX terminal 10A. The UART 11 transmits a transmission signal Stx to the MCU 15 via the TX terminal 10B. In other words, the UART 11 is a communication unit configured to be able to communicate with the MCU 15.

[0013] The constant current circuit 13 is a circuit for supplying a constant LED current ILED to the LED 20 provided outside the LED drive circuit 10. The anode of the LED 20 is connected to a terminal to which a power supply voltage Vcc is applied. The cathode of the LED 20 is connected to an LED terminal 10C. The ground terminal 10D is connected to a terminal to which a ground potential is applied. The constant current circuit 13 is provided to connect between the LED terminal 10C and the ground terminal 10D. The LED 20 is not limited to a configuration in which multiple LED elements are connected in series as shown in FIG. 7, but may also be, for example, a single LED element.

[0014] The UART 11 processes the signal Srx received from the MCU 15 and issues a command to the logic unit 12. The logic unit 12 receives the command and generates a PWM signal Spwm. The PWM signal Spwm is a pulse signal having levels corresponding to the on-period and off-period. The constant current circuit 13 is on / off controlled based on the PWM signal pwm. When the constant current circuit 13 is on, the LED current ILED flows, and when the constant current circuit 13 is off, the LED current ILED does not flow. This enables PWM dimming of the LED 20 according to the on-duty of the PWM signal Spwm (= the ratio of the on-period to the pulse period).

[0015] However, if such an LED drive circuit 10 does not use the MCU 15, it is not possible to communicate with the MCU 15 and therefore is not able to control the light emission of the LED 20. In other words, the use of the MCU 15 is essential, and the LED drive circuit 10 cannot be used stand-alone.

[0016] Therefore, it is possible to add terminals to enable the LED drive circuit 10 to be used as a standalone circuit, but increasing the number of terminals in the LED drive circuit 10 would lead to an increase in the number of terminals in an IC (integrated circuit) package in which the LED drive circuit 10 is modularized, which is undesirable.

[0017] 2. First Embodiment <2-1. LED drive circuit configuration> Various embodiments designed to solve the above problems will be described below. Fig. 1 is a diagram showing a schematic block configuration of an LED drive circuit 1 according to a first embodiment.

[0018] 1 includes a UART 2 (communication unit), a logic unit 3, a constant current circuit 4, and buffers 5 and 6. The LED drive circuit 1 also includes an RX terminal 1A (receiving terminal), a TX terminal 1B (transmitting terminal), an LED terminal 1C, and a ground terminal 1D for establishing electrical connection with the outside.

[0019] An external MCU (controller) (not shown in FIG. 1) (described later in FIG. 2) can be connected to the RX terminal 1A and the TX terminal 1B. The RX terminal 1A is connected to UART2 via a buffer 5. The input side of the buffer 5 is the RX terminal 1A side, and the output side of the buffer 5 is the UART2 side. UART2 can receive a receive signal from the MCU via the RX terminal 1A and the buffer 5.

[0020] The TX terminal 1B is connected to UART2 via a buffer 6. The input side of the buffer 6 is the UART2 side, and the output side of the buffer 6 is the TX terminal 1B side. UART2 can transmit a transmit signal to the MCU via the buffer 6 and the TX terminal 1B.

[0021] The logic unit 3 includes a PWM signal generating unit 31 (a dimming control unit) and a determining unit 32.

[0022] The PWM signal generation unit 31 is configured to be able to generate a PWM signal Spwm (dimming signal) upon receiving a command from UART 2. The PWM signal generation unit 31 is also connected to the output terminal of the buffer 5. As a result, in the standalone mode, the PWM signal generation unit 31 generates the PWM signal Spwm based on the signal output from the buffer 5. The standalone mode is a mode in which the LED drive circuit 1 is used without being connected to an MCU.

[0023] The determination unit 32 is configured to be able to monitor a first signal S1 (signal at node N1) at the output terminal of the buffer 6 and a second signal S2 (signal at node N2) at the input terminal of the buffer 6. Based on the first signal S1 and the second signal S2, the determination unit 32 determines whether or not an MCU is connected to the LED drive circuit 1. If the determination unit 32 determines that an MCU is not connected, it transitions the LED drive circuit 1 to standalone mode.

[0024] A buffer may be provided between the node N1 and the determination unit 32, with the node N1 side as the input side and the determination unit 32 side as the output side.

[0025] The connection configuration of the constant current circuit 4 and the LED 20 is the same as that of the comparative example. The constant current circuit 4 is provided to connect between the LED terminal 1C and the ground terminal 1D. The constant current circuit 4 is on / off controlled based on the PWM signal Spwm.

[0026] <2-2. Normal mode> The operation of the LED drive circuit 1 configured as above will now be described. Figure 2 is a diagram showing the state when the LED drive circuit 1 is used by connecting the MCU 15 to the LED drive circuit 1. That is, Figure 2 shows the state when the LED drive circuit 1 is used in normal mode.

[0027] As shown in FIG. 2, by connecting MCU 15 to RX terminal 1A and TX terminal 1B, UART 2 can receive a receive signal Srx from MCU 15 via RX terminal 1A and buffer 5, and can transmit a transmit signal Stx to MCU 15 via buffer 6 and TX terminal 1B.

[0028] The reception signal Srx received by UART2 from MCU15 and the transmission signal Stx transmitted from UART2 to MCU15 are both signals consisting of high and low levels. Initially, UART2 receives the reception signal Srx and then transmits the transmission signal Stx. At this time, the determination unit 32 monitors the first signal S1 and the second signal S2, and when it detects that the first signal S1 is at a high level while the second signal S2 is being output from UART2, it determines that the MCU15 is connected to the LED drive circuit 1. As a result, the determination unit 32 transitions the LED drive circuit 1 to normal mode.

[0029] At this time, the determination unit 32 enables the processing of the received signal Srx by the UART2. As a result, the UART2 issues a command to the PWM signal generation unit 31 based on the processing of the received signal Srx. The PWM signal generation unit 31 receives the command and generates a PWM signal Spwm. The constant current circuit 4 is on / off controlled based on the PWM signal Spwm. In this way, in the normal mode, PWM dimming of the LED 20 is performed based on the received signal Srx from the MCU 15.

[0030] <2-3. Standalone mode> Fig. 3 is a diagram showing a state in which the LED drive circuit 1 is used without connecting the MCU 15 to the LED drive circuit 1. In other words, Fig. 3 is a diagram showing a case in which the LED drive circuit 1 is used in stand-alone mode.

[0031] As shown in FIG. 3, when the LED drive circuit 1 is used in standalone mode, the RX terminal 1A and the TX terminal 1B are shorted outside the LED drive circuit 1, and a pulse signal Sp is input to the RX terminal 1A and the TX terminal 1B.

[0032] In this case, initially, the determination unit 32 monitors the first signal S1 and the second signal S2. When the second signal S2 is not being output, the determination unit 32 detects that the first signal S1 is at a high level due to the pulse signal Sp, and determines that an MCU is not connected to the LED drive circuit 1. As a result, the determination unit 32 transitions the LED drive circuit 1 to the standalone mode.

[0033] At this time, the determination unit 32 disables processing by UART2 of the signal (here, pulse signal Slp) received from the RX terminal 1A. At the same time, the determination unit 32 instructs the PWM signal generation unit 31 to operate in standalone mode. In response to this instruction, the PWM signal generation unit 31 generates a PWM signal Spwm based on the signal output from the buffer 5. At this time, the PWM signal Spwm is generated by through processing. That is, the PWM signal Spwm is at a high level during a period in which the pulse signal Sp is at a high level, and at a low level during a period in which the pulse signal Sp is at a low level.

[0034] The constant current circuit 4 is on / off controlled based on the PWM signal Spwm. Therefore, in the standalone mode, PWM dimming of the LED 20 is performed based on the pulse signal Sp.

[0035] As described above, according to this embodiment, even when the MCU 15 is not used, the LED drive circuit 1 can be operated in a standalone manner by shorting the RX terminal 1A and the TX terminal 1B and inputting the pulse signal Sp, thereby controlling the light emission of the LED 20. In this case, there is no need to add a new terminal to the LED drive circuit 1, and an increase in the number of terminals can be avoided.

[0036] 3. Second Embodiment 4 is a diagram showing a schematic block configuration of an LED drive circuit 1X according to the second embodiment. Here, differences in the configuration of the LED drive circuit 1X shown in FIG. 4 from the first embodiment (FIG. 1) will be described.

[0037] The LED drive circuit 1X has a buffer 7. The input terminal of the buffer 7 is connected to a node N1. The output terminal of the buffer 7 is connected to a determination unit 32. In the LED drive circuit 1X, unlike the first embodiment, the PWM signal generation unit 31 is connected to the output terminal of the buffer 7, not the output terminal of the buffer 5.

[0038] The operation of the LED drive circuit 1X configured as above will be described. Fig. 5 is a diagram showing a state in which the LED drive circuit 1X is used by connecting an MCU 15 to the LED drive circuit 1X. That is, Fig. 5 is a diagram showing a case in which the LED drive circuit 1X is used in normal mode.

[0039] Initially, UART2 receives the reception signal Srx and then transmits the transmission signal Stx. At this time, the determination unit 32 monitors the first signal S1 and the second signal S2. The determination unit 32 monitors the first signal S1 via the buffer 7. If the determination unit 32 detects that the first signal S1 is at a high level while the second signal S2 is being output from UART2, it determines that the MCU 15 is connected to the LED drive circuit 1X. This causes the determination unit 32 to transition the LED drive circuit 1X to normal mode. The subsequent operations are the same as those in the first embodiment. This allows the LED drive circuit 1X to operate in normal mode while connected to the MCU 15.

[0040] Fig. 6 is a diagram showing a state in which the LED drive circuit 1X is used without connecting the MCU 15 to the LED drive circuit 1X. That is, Fig. 6 is a diagram showing a case in which the LED drive circuit 1X is used in a stand-alone mode.

[0041] As shown in Figure 6, when the MCU 15 is not connected, the RX terminal 1A is left open and an external pulse signal Sp is input to the TX terminal 1B. Initially, the determination unit 32 monitors the first signal S1 and the second signal S2. When the second signal S2 is not being output, the determination unit 32 detects that the first signal S1 is at a high level due to the pulse signal Sp, and determines that an MCU is not connected to the LED drive circuit 1X. This causes the determination unit 32 to transition the LED drive circuit 1X to standalone mode.

[0042] At this time, the determination unit 32 disables processing of the signal received from the RX terminal 1A by UART2. At the same time, the determination unit 32 instructs the PWM signal generation unit 31 to operate in standalone mode. In response to this instruction, the PWM signal generation unit 31 generates a PWM signal Spwm based on the pulse signal Sp input via the TX terminal 1B and the buffer 7. At this time, the PWM signal Spwm is generated by through processing, as in the first embodiment.

[0043] Therefore, like the first embodiment, the LED drive circuit 1X according to this embodiment can also operate in a stand-alone mode and can control the light emission of the LED 20. Also, like the first embodiment, there is no need to add any additional terminals.

[0044] Here, by using a buffer 7 with high responsiveness, the pulse signal Sp can be transmitted to the PWM signal generating unit 31 with good responsiveness, and the characteristics of the LED current ILED can be improved. However, considering that the buffer 5 used in the normal mode (FIG. 5) also needs to have high responsiveness, in the first embodiment (FIG. 1), the highly responsive buffer used to generate the PWM signal Spwm can be used as the buffer 5 in common between the normal mode and the standalone mode.

[0045] <4. IC Package> The LED 20 and the LED drive circuit 1 (or 1X) are packaged, for example, in a single package. In this case, the IC package is configured by sealing an IC chip on which the LED 20 is integrated and an IC chip on which the LED drive circuit 1 (or 1X) is integrated with a sealing material (such as resin). Furthermore, the IC package has terminals (lead frames) for establishing electrical connection with the outside. The IC chip on which the LED 20 is integrated, the IC chip on which the LED drive circuit 1 (or 1X) is integrated, and the terminals are connected by bonding wires or the like.

[0046] As mentioned above, the LED driver circuit 1 (or 1X) does not require any additional terminals, making it particularly effective in IC packages with the above configurations where increasing the number of terminals is difficult due to standards.

[0047] The LED and the LED drive circuit may be packaged in separate packages.

[0048] <5.Other> Although exemplary embodiments have been described above, the embodiments can be modified in various ways within the spirit and scope of the present invention.

[0049] For example, the communication unit that communicates with the MCU in the LED drive circuit is not limited to UART, and may be one that communicates via SPI (Serial Peripheral Interface) or I2C (Inter-Integrated Circuit), for example.

[0050] <6. Notes> As described above, for example, the light-emitting element drive circuit (1) according to the present disclosure has the following features: a receiving terminal (1A) and a transmitting terminal (1B) that can be connected to an external control unit (15); a communication unit (2) configured to be able to receive a reception signal from the control unit via the reception terminal and to be able to transmit a transmission signal to the control unit via the transmission terminal; a dimming signal generating unit (31) that generates a dimming signal (Spwm); a constant current circuit (4) that supplies current to the light emitting element (20) and is on / off controlled based on the dimming signal; a first buffer (6) provided between the transmission terminal and the communication unit, with the transmission terminal as an output side and the communication unit as an input side; a determination unit (32) that determines whether the control unit is connected or not based on a first signal (S1) at an output terminal of the first buffer and a second signal (S2) at an input terminal of the first buffer; and When the determination unit determines that the control unit is connected, processing of the signal received from the receiving terminal by the communication unit is enabled, and the dimming signal generation unit generates the dimming signal based on a command from the communication unit. When the determination unit determines that the control unit is not connected, the processing by the communication unit of the signal received from the receiving terminal is disabled, and the dimming signal generation unit is configured to generate the dimming signal based on a pulse signal (Sp) input to the receiving terminal or the transmitting terminal (first configuration).

[0051] In addition, in the above first configuration, a second buffer (5) may be provided between the receiving terminal and the communication unit, with the receiving terminal as the input side and the communication unit as the output side, and the output end of the second buffer may be connected to the dimming signal generating unit, and when the control unit is not connected, the receiving terminal and the transmitting terminal may be short-circuited (second configuration).

[0052] In addition, in the second configuration, a third buffer may be further provided between the node (N1) to which the transmitting terminal and the output terminal of the first buffer are connected and the judgment unit, the third buffer having the node side as its input side and the judgment unit side as its output side (third configuration).

[0053] In addition, in the above first configuration, a fourth buffer (7) having the node side as its input side and the judgment unit side as its output side may be further provided between a node (N1) to which the transmission terminal and the output end of the first buffer are connected and the judgment unit, and the output end of the fourth buffer may be connected to the dimming signal generation unit (fourth configuration).

[0054] In any one of the first to fourth configurations, the dimming signal may be a PWM signal (fifth configuration).

[0055] In any one of the first to fifth configurations, the communication unit may be a UART (Universal Asynchronous Receiver / Transmitter) (sixth configuration).

[0056] In any one of the first to sixth configurations, the control unit may be an MCU (Micro Control Unit) (seventh configuration).

[0057] In any one of the first to seventh configurations, the light emitting element may be an LED (light emitting diode) (eighth configuration).

[0058] Moreover, the IC package according to the present disclosure is configured by packaging the light-emitting element drive circuit of the eighth configuration and the LED in one package. [Industrial Applicability]

[0059] The invention disclosed in this specification can be used, for example, in LED drive circuits for various applications. [Explanation of symbols]

[0060] 1,1X LED driver circuit 1A RX terminal 1B TX terminal 1C LED terminal 1D Ground Terminal 2 UART 3 Logic section 4 Constant current circuit 5,6,7 buffers 10 LED driving circuit 10A RX terminal 10B TX terminal 10C LED terminal 10D Ground terminal 11 UART 12 Logic section 13 Constant current circuit 20 LED 31 PWM signal generation section 32 Judgment section

Claims

1. a receiving terminal and a transmitting terminal that can be connected to an external control unit; a communication unit configured to receive a reception signal from the control unit via the reception terminal and to transmit a transmission signal to the control unit via the transmission terminal; a dimming signal generating unit that generates a dimming signal; a constant current circuit that supplies current to the light emitting element and is controlled to be turned on and off based on the dimming signal; a first buffer provided between the transmission terminal and the communication unit, the first buffer having the transmission terminal as an output side and the communication unit as an input side; a determination unit that determines whether the control unit is connected or disconnected based on a first signal at an output terminal of the first buffer and a second signal at an input terminal of the first buffer; and When the determination unit determines that the control unit is connected, processing of the signal received from the receiving terminal by the communication unit is enabled, and the dimming signal generation unit generates the dimming signal based on a command from the communication unit. When the determination unit determines that the control unit is not connected, processing of the signal received from the receiving terminal by the communication unit is disabled, and the dimming signal generation unit generates the dimming signal by through processing based on the pulse signal input to the receiving terminal, When the control unit is not connected, the receiving terminal and the transmitting terminal are short-circuited, and the pulse signal is input to the receiving terminal and the transmitting terminal.

2. a second buffer is further provided between the receiving terminal and the communication unit, the second buffer having the receiving terminal as an input side and the communication unit as an output side; The light-emitting element drive circuit according to claim 1 , wherein an output terminal of the second buffer is connected to the dimming signal generating unit.

3. 3. The light-emitting element drive circuit according to claim 2, further comprising a third buffer between the node to which the transmission terminal and the output terminal of the first buffer are connected and the determination unit, the third buffer having the node side as its input side and the determination unit side as its output side.

4. a receiving terminal and a transmitting terminal that can be connected to an external control unit; a communication unit configured to receive a reception signal from the control unit via the reception terminal and to transmit a transmission signal to the control unit via the transmission terminal; a dimming signal generating unit that generates a dimming signal; a constant current circuit that supplies current to the light emitting element and is controlled to be turned on and off based on the dimming signal; a first buffer provided between the transmission terminal and the communication unit, the first buffer having the transmission terminal as an output side and the communication unit as an input side; a determination unit that determines whether the control unit is connected or disconnected based on a first signal at an output terminal of the first buffer and a second signal at an input terminal of the first buffer; and When the determination unit determines that the control unit is connected, processing of the signal received from the receiving terminal by the communication unit is enabled, and the dimming signal generation unit generates the dimming signal based on a command from the communication unit. When the determination unit determines that the control unit is not connected, processing of the signal received from the receiving terminal by the communication unit is disabled, and the dimming signal generation unit generates the dimming signal by through processing based on the pulse signal input to the transmitting terminal, When the control unit is not connected, the receiving terminal is open and the pulse signal is input to the transmitting terminal.

5. a fourth buffer is further provided between the node to which the transmission terminal and the output terminal of the first buffer are connected and the determination unit, the fourth buffer having an input side on the node side and an output side on the determination unit side; The light-emitting element drive circuit according to claim 4 , wherein an output terminal of the fourth buffer is connected to the dimming signal generating unit.

6. 6. The light-emitting element drive circuit according to claim 1, wherein the dimming signal is a PWM signal.

7. 7. The light-emitting element drive circuit according to claim 1, wherein the communication unit is a UART (Universal Asynchronous Receiver / Transmitter).

8. The light-emitting element drive circuit according to claim 1 , wherein the control unit is an MCU (Micro Control Unit).

9. 9. The light-emitting element drive circuit according to claim 1, wherein the light-emitting element is an LED (light-emitting diode).

10. 10. An IC package comprising the light-emitting element drive circuit according to claim 9 and the LED packaged together.

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