Load drive device, lighting device, and vehicle

Abstract

To control a rise delay and an overshoot of a load current.SOLUTION: A load drive device (3A) includes: a first transistor (M1) configured to be connected in series to a load (2); a first current detection unit (R1) configured to detect a current flowing through the first transistor; a second transistor (M2); a current source (CS2); a second current detection unit (R2) configure to detect a total current of a current flowing through the second transistor and a current output from the current source; an error amplifier (AMP1) configure to output a voltage according to an error between a reference voltage and a current detection result; and a selection unit (SW1a to SW2b) configured to select whether to use the current detection result as an output of the first current detection unit and to supply a voltage output from the error amplifier to a control terminal of the first transistor, or to use the current detection result as an output of the second current detection unit and to supply the voltage output from the error amplifier to a control terminal of the second transistor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention disclosed herein relates to a load driving device, a lighting device, and a vehicle. [Background technology]

[0002] Conventionally, various light-emitting element driving devices have been developed that drive light-emitting elements by modulating the light intensity of the light-emitting elements using PWM (Pulse Width Modulation) (see, for example, Patent Document 1).

[0003] The light-emitting element driving device disclosed in Patent Document 1 generates an extended PWM signal by extending the period during which the input PWM signal is at the first level, and drives the light-emitting element by PWM dimming based on the extended PWM signal. The light-emitting element driving device disclosed in Patent Document 1 can appropriately drive the light-emitting element even when the dimming rate is low, i.e., the period during which the input PWM signal is at the first level is short. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-73492 A

[0005] [overview] However, the light-emitting element driving device disclosed in Patent Document 1 does not fundamentally solve the problem of the delayed rise of the load current (the current flowing through the light-emitting element) when the input PWM signal switches from the second level to the first level.

[0006] The load driving device disclosed in this specification comprises a first transistor configured to be connected in series with a load, a first current detection unit configured to detect a current flowing through the first transistor, a second transistor, a current source, a second current detection unit configured to detect a total current of a current flowing through the second transistor and a current output from the current source, an error amplifier configured to output a voltage corresponding to an error between a reference voltage and a current detection result, and a selection unit configured to select whether to use the current detection result as an output of the first current detection unit and supply the output voltage of the error amplifier to a control terminal of the first transistor, or to use the current detection result as an output of the second current detection unit and supply the output voltage of the error amplifier to a control terminal of the second transistor.

[0007] The lighting device disclosed in this specification includes a load driving device having the above-described configuration and the load which is a light-emitting element.

[0008] The vehicle disclosed in this specification includes the load driving device having the above-described configuration and the load. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a lighting device according to a first embodiment. [Diagram 2] FIG. 2 is a timing chart for explaining the operation of the LED driver IC. [Diagram 3] FIG. 3 is a timing chart for explaining the operation of the LED driver IC when the set value of the LED current is large. [Figure 4] FIG. 4 is a timing chart for explaining the operation of the LED driver IC when the set value of the LED current is small. [Diagram 5] FIG. 5 is a diagram showing a schematic configuration of an illumination device according to the second embodiment. [Figure 6] FIG. 6 is a diagram showing a schematic configuration of an illumination device according to a third embodiment. [Figure 7]FIG. 7 is a diagram showing a schematic configuration of an illumination device according to a fourth embodiment. [Figure 8] FIG. 8 is an external view of the vehicle.

[0010] [Detailed Description] In this specification, MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) refers to a field effect transistor whose gate structure is composed of at least three layers: "a layer made of a conductor or a semiconductor such as polysilicon with a low resistance value," "an insulating layer," and "a P-type, N-type, or intrinsic semiconductor layer." In other words, the gate structure of a MOSFET is not limited to a three-layer structure of a metal, an oxide, and a semiconductor.

[0011] First Embodiment FIG. 1 is a diagram showing a schematic configuration of a lighting device according to a first embodiment. The lighting device 1A shown in FIG. 1 includes an LED (Light Emitting Diode) 2 and an LED driver IC (Integrated Circuit) 3A that drives the LED 2. The LED 2 is an example of a load. The LED 2 is also an example of a light-emitting element. The LED driver IC 3A is an example of a load driving device. Although four LEDs 2 are shown in FIG. 1, the number of LEDs 2 is not limited. The LEDs 2 driven by the load driving device 3A may be a single LED or a multiple number other than four.

[0012] The LED driver IC3A includes an internal power supply circuit 31, current sources CS1 and CS2, resistors R0 to R2, transistors M1 and M2, an error amplifier AMP1, switches SW1a, SW1b, SW2a, and SW2b, and an inverter INV1. The LED driver IC3A also includes terminals T1 to T6 for establishing electrical connections with the outside.

[0013] Four LEDs 2 and a resistor R3 are externally connected to the LED driver IC3A.

[0014] A power supply voltage Vcc is applied to a terminal T1 from outside the LED driver IC 3A. The internal power supply circuit 31 generates an internal power supply voltage Vreg based on the power supply voltage Vcc supplied from the terminal T1.

[0015] The terminal T2 receives a PWM signal Spwm from outside the LED driver IC3A. The terminal T2 supplies the PWM signal Spwm to the inverter INV1, the switch SW1a, and the switch SW1b. The inverter INV1 generates an inverted PWM signal Spwm, which is an inverted signal of the PWM signal Spwm supplied from the terminal T2, and supplies the inverted PWM signal Spwm to the switch SW2a and the switch SW2b. Unlike this embodiment, the LED driver IC3A may have a built-in PWM signal generating circuit configured to generate a PWM signal, and the PWM signal generating circuit may generate a PWM signal based on a duty value supplied from the LED driver IC3A.

[0016] A power supply voltage Vcc is applied to the anode of the series-connected body formed of four LEDs 2. The cathode of the series-connected body formed of four LEDs 2 is connected to a terminal T3 outside the LED driver IC3A.

[0017] The terminal T4 is connected to the ground potential outside the LED driver IC3A.

[0018] The internal power supply voltage Vreg is applied to a first terminal of the current source CS1. A second terminal of the current source CS1 is connected to the non-inverting input terminal of the error amplifier AMP1 and a first terminal of the resistor R0. A second terminal of the resistor R0 is connected to the terminal T4.

[0019] An output terminal of the error amplifier AMP1 is connected to a first terminal of the switch SW1a and a first terminal of the switch SW2a, and an inverting input terminal of the error amplifier AMP1 is connected to a first terminal of the switch SW1b and a first terminal of the switch SW2ab.

[0020] The drain of the transistor M1, which is an n-channel MOSFET, is connected to the terminal T3. The gate of the transistor M1 is connected to the second terminal of the switch SW1a. The source of the transistor M1 is connected to the first terminal of the resistor R1 and the second terminal of the switch SW1b. The second terminal of the resistor R1 is connected to the terminal T4.

[0021] The internal power supply voltage Vreg is applied to the drain of the transistor M2, which is an n-channel MOSFET, and to a first terminal of the current source CS2. The gate of the transistor M2 is connected to the second terminal of the switch SW2a. The source of the transistor M2 and the second terminal of the current source CS2 are connected to a first terminal of the resistor R2 and a second terminal of the switch SW2b. The second terminal of the resistor R2 is connected to the terminal T4.

[0022] The switches SW1a and SW1b are turned on when the PWM signal Spwm is at a high level, and turned off when the PWM signal Spwm is at a low level. The switches SW2a and SW2b are turned on when the inverted PWM signal Spwm is at a high level, and turned off when the inverted PWM signal Spwm is at a low level.

[0023] A first end of the resistor R3 is connected to a terminal T5 outside the LED driver IC3A. A second end of the resistor R3 is connected to the ground potential. The terminal T6 receives digital data D1 from outside the LED driver IC3A by communication such as SPI (Serial Peripheral Interface), I2C, etc. The digital data D1 is data related to the setting of DC (Direct Current) dimming. The terminal T6 supplies the digital data D1 to a logic circuit (not shown) provided inside the LED driver IC3A. The logic circuit generates a signal according to the digital data D1 and supplies it to a digital-to-analog converter (DAC) 32. The DAC 32 converts the signal received from the logic circuit into analog data A1 and supplies the analog data A1 to a current source CS1.

[0024] The current source CS1 sets the maximum value of the current Iin output from the current source CS1 based on the resistance value of the resistor R3, and sets the value of the current Iin output from the current source CS1 based on the analog data A1 within a range equal to or less than the maximum value. Note that, unlike this embodiment, the LED driver IC3A may not include the terminal T6, and the current source CS1 may set the value of the current Iin output from the current source CS1 based on the resistance value of the resistor R3.

[0025] The resistor R0 converts the current Iin output from the current source CS1 into a reference voltage Vin that is proportional to the current Iin.

[0026] A current ILED flowing through LED2 (hereinafter referred to as LED current ILED) flows into the transistor M1 and becomes a current I1 flowing through the transistor M1.

[0027] The resistor R1 detects the current flowing through the transistor M1. The resistor R2 detects the sum of the current I2 flowing through the transistor M2 and the current IADD output from the current source CS2. The error amplifier AMP1 outputs a voltage Vampout according to the error between the reference voltage Vin and the current detection result.

[0028] The resistance value of the resistor R2 is greater than the resistance value of the resistor R1, which allows the size of the transistor M2 to be smaller than the size of the transistor M1, and allows the current I2 flowing through the transistor M2 to be smaller than the current I1 flowing through the transistor M1.

[0029] The switches SW1a, SW1b, SW2a, and SW2b select whether to output the current detection result as the output of the resistor R1 (the voltage at the first end of the resistor R1) and supply the voltage Vampout to the gate of the transistor M1, or to output the current detection result as the output of the resistor R2 (the voltage at the first end of the resistor R2) and supply the voltage Vampout to the gate of the transistor M2. When the PWM signal Spwm is at a HIGH level, the switches SW1a, SW1b, SW2a, and SW2b output the current detection result as the output of the resistor R1 and supply the voltage Vampout to the gate of the transistor M1. On the other hand, when the PWM signal Spwm is at a LOW level, the switches SW1a, SW1b, SW2a, and SW2b output the current detection result as the output of the resistor R2 and supply the voltage Vampout to the gate of the transistor M2.

[0030] Figure 2 is a timing chart for explaining the operation of the LED driver IC3A. From the top, Figure 2 depicts the waveform of the PWM signal Spwm, the state of the switches SW1a and SW1b, the state of the switches SW2a and SW2b, the waveform of the voltage Vampout, and the waveform of the LED current ILED. Note that the thick dotted lines in Figure 2 show the waveforms of the voltage Vampout and the LED current ILED in a hypothetical configuration in which the LED driver IC3A does not include the current source CS2.

[0031] When the PWM signal Spwm is at a high level, the switches SW1a and SW1b are turned on, driving the transistor M1 and LED2. On the other hand, when the PWM signal Spwm is at a low level, the switches SW2a and SW2b are turned on, driving the transistor M2. As a result, the error amplifier AMP1 operates both when the PWM signal Spwm is at a high level and when the PWM signal Spwm is at a low level. This reduces the rise delay of the LED current ILED when the PWM signal Spwm switches from a low level to a high level, compared to a case in which the LED driver IC3A does not include the current source CS2, the resistor R2, the transistor M2, and the switches SW2a and SW2b.

[0032] Ideally, due to the pairing of the transistors M1 and M2, the value of the current detection result supplied to the inverting input terminal of the error amplifier AMP1 immediately before the PWM signal Spwm switches from a LOW level to a HIGH level matches the value of the current detection result supplied to the inverting input terminal of the error amplifier AMP1 immediately after the PWM signal Spwm switches from a LOW level to a HIGH level. As a result, ideally, the fluctuation of the voltage Vampout when the PWM signal Spwm switches from a LOW level to a HIGH level becomes zero.

[0033] However, in reality, the pairing of the transistors M1 and M2 is not completely matched, so the fluctuation of the voltage Vampout when the PWM signal Spwm switches from a low level to a high level does not become zero. The LED driver IC3A is configured with a current source CS2, so it is possible to reduce the fluctuation of the voltage Vampout when the PWM signal Spwm switches from a low level to a high level.

[0034] When the PWM signal Spwm is at a low level, in addition to the current I2 flowing through the transistor M2, the current IADD output from the current source CS2 also flows into the resistor R2, so the gate voltage of the transistor M2 can be low. As a result, when the PWM signal Spwm is at a low level, the voltage Vampout is lower than the thick dotted line. This reduces the fluctuation of the voltage Vampout when the PWM signal Spwm switches from a low level to a high level, and reduces the overshoot of the LED current ILED (excess of the set value ISET) compared to the thick dotted line.

[0035] As described above, the LED driver IC3A can control the rise delay and overshoot of the LED current ILED.

[0036] However, an appropriate value of the current IADD output from the current source CS2 varies depending on the set value ISET of the LED current ILED.

[0037] 3 is a timing chart for explaining the operation of the LED driver IC3A when the set value ISET of the LED current ILED is large. In the LED driver IC3A, the current IADD output from the current source CS2 is kept constant, so when the set value ISET of the LED current ILED is large, the current IADD output from the current source CS2 is insufficient. As a result, the voltage Vampout does not decrease sufficiently when the PWM signal Spwm is at a low level, and the overshoot of the LED current ILED is also not reduced sufficiently.

[0038] 4 is a timing chart for explaining the operation of the LED driver IC3A when the set value ISET of the LED current ILED is small. In the LED driver IC3A, the current IADD output from the current source CS2 is constant, so when the set value ISET of the LED current ILED is small, the current IADD output from the current source CS2 becomes excessive. As a result, the voltage Vampout drops excessively when the PWM signal Spwm is at a low level, and the rise delay of the LED current ILED is not reduced sufficiently.

[0039] <Second embodiment> 5 is a diagram showing a schematic configuration of an illumination device according to embodiment 2. In embodiment 2, descriptions of parts similar to those in embodiment 1 will be omitted as appropriate.

[0040] The lighting device 1B shown in Fig. 5 includes an LED 2 and an LED driver IC3B that drives the LED 2. In the LED driver IC3B, a current source CS2 outputs a current IADD that changes according to a reference voltage VIN. This allows the LED driver IC3B to appropriately reduce the rise delay and overshoot of the LED current ILED regardless of whether the set value ISET of the LED current ILED is large or small.

[0041] In this embodiment, the current source CS2 includes an error amplifier AMP2, a resistor R4, and transistors M3 to M5.

[0042] A reference voltage Vin is supplied to a non-inverting input terminal of the error amplifier AMP2. A gate of the transistor M3, which is an n-channel MOSFET, is connected to the output terminal of the error amplifier AMP2.

[0043] The source of the transistor M3 and a first end of the resistor R4 are connected to the inverting input terminal of the error amplifier AMP2. The second end of the resistor R4 is connected to the ground potential. Although the connection line connecting the second end of the resistor R4 and the terminal T4 is omitted in FIG. 5, the second end of the resistor R4 is actually connected to the terminal T4.

[0044] The resistor R4 converts the current flowing through the transistor M3 into a voltage proportional to the current flowing through the transistor M3, and supplies the voltage to the inverting input terminal of the error amplifier AMP2.

[0045] Due to feedback control by the error amplifier AMP2, the current flowing through the transistor M3 changes according to the reference voltage VIN.

[0046] The drain of the transistor M3 is connected to the gate and drain of the transistor M4, which is a p-channel MOSFET, and the gate of the transistor M5, which is a p-channel MOSFET. An internal power supply voltage Vreg is applied to the sources of the transistors M4 and M5. The drain of the transistor M5 is connected to the source of the transistor M2, a first terminal of the resistor R2, and a second terminal of the switch SW2b. The current mirror circuit formed by the transistors M4 and M5 outputs a current IADD, which is a mirror current of the current flowing through the transistor M3. Therefore, the current IADD output from the current source CS2 is a current that changes according to the reference voltage VIN.

[0047] <Third embodiment> 6 is a diagram showing a schematic configuration of an illumination device according to embodiment 3. In embodiment 3, descriptions of parts similar to those in embodiment 2 will be omitted as appropriate.

[0048] The lighting device 1C shown in FIG. 6 includes an LED 2 and an LED driver IC3C that drives the LED 2.

[0049] In this embodiment, the LED driver IC3C includes a switch SW3, so that it is possible to switch between detecting the total current of the current I2 flowing through the transistor M2 and the current IADD output from the current source CS2 by the resistor R2, or detecting the current I2 flowing through the transistor M2.

[0050] The switch SW3 switches between electrical connection and electrical disconnection between the current source CS2 and the resistor R2. The LED driver IC3C includes a terminal T7. For example, when the terminal T7 is in an open state as shown in FIG. 6, the switch SW3 is turned on by the pull-up resistor R5, and when the terminal T7 is connected to a ground potential outside the LED driver IC3C, the switch SW3 is turned off.

[0051] For example, in general, there is a tendency to place more importance on reducing the overshoot of the LED current ILED than on the rise delay of the LED current ILED. In cases where the rise delay of the LED current ILED is more important than reducing the overshoot of the LED current ILED, the switch SW3 can be turned off.

[0052] <Fourth embodiment> 7 is a diagram showing a schematic configuration of an illumination device according to embodiment 4. In embodiment 4, descriptions of parts similar to those in embodiment 2 will be omitted as appropriate.

[0053] The lighting device 1D shown in FIG. 7 includes an LED 2 and an LED driver IC 3D that drives the LED 2.

[0054] In this embodiment, since the current source CS2 can be switched between an enabled state and a disabled state, the resistor R2 can be switched between detecting the total current of the current I2 flowing through the transistor M2 and the current IADD output from the current source CS2, or detecting the current I2 flowing through the transistor M2.

[0055] The LED driver IC3D includes a terminal T7. For example, when the terminal T7 is open as shown in Fig. 7, the current source CS2, more specifically the error amplifier AMP2, is enabled by the pull-up resistor R5, and when the terminal T7 is connected to the ground potential outside the LED driver IC3C, the current source CS2, more specifically the error amplifier AMP2, is disabled.

[0056] For example, there is a general tendency to place more importance on reducing the overshoot of the LED current ILED than on the rise delay of the LED current ILED. However, if the rise delay of the LED current ILED is more important than reducing the overshoot of the LED current ILED, the error amplifier AMP2 can be disabled.

[0057] <Application Examples> The above-described lighting devices 1A to 1D are used, for example, as backlight devices for a liquid crystal display device (vehicle-mounted display) mounted on a vehicle 4 shown in Fig. 8. The above-described lighting devices 1A to 1D can expand the dimming range by reducing the rise delay of the LED current, and are therefore suitable as backlight devices for vehicle-mounted displays that require brightness adjustment between daytime driving and nighttime driving or driving in a tunnel or the like.

[0058] <Other> In addition to the above-described embodiment, various modifications can be made to the configuration of the invention without departing from the spirit of the invention. The above-described embodiment should be considered to be illustrative in all respects and not restrictive, and the technical scope of the present invention is indicated by the claims, not the description of the above-described embodiment, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0059] For example, in the above embodiment, a PWM signal is used, but a pulse modulated signal other than a PWM signal may be used. Examples of pulse modulated signals other than a PWM signal include a PFM (Pulse Frequency Modulation) signal and a PDM (Pulse Density Modulation) signal.

[0060] For example, in the above embodiment, the load is an LED (one example of a light-emitting element), but the load may be something other than a light-emitting element.

[0061] <Additional Notes> Regarding the present disclosure, specific configuration examples of which have been shown in the above-mentioned embodiments, additional notes will be provided.

[0062] A load driving device (3A to 3D) disclosed herein has a configuration (first configuration) including a first transistor (M1) configured to be connected in series to a load (2), a first current detection unit (R1) configured to detect a current flowing through the first transistor, a second transistor (M2), a current source (CS2), a second current detection unit (R2) configured to detect a total current of a current flowing through the second transistor and a current output from the current source, an error amplifier (AMP1) configured to output a voltage corresponding to an error between a reference voltage and a current detection result, and a selection unit (SW1a, SW1b, SW2a, SW2b) configured to select whether to use the current detection result as the output of the first current detection unit and supply the output voltage of the error amplifier to a control terminal of the first transistor, or to use the current detection result as the output of the second current detection unit and supply the output voltage of the error amplifier to a control terminal of the second transistor.

[0063] In the load driving device of the first configuration described above, the current source may be configured to output a current that changes depending on the reference voltage (second configuration).

[0064] In the load driving device of the first or second configuration described above, the second current detection unit may be configured to be switchable between detecting the total current or detecting the current flowing through the second transistor (third configuration).

[0065] In the load driving device of the third configuration, the current source may be configured to be switchable between an enabled state and a disabled state (fourth configuration).

[0066] The load driving device of the third configuration may be configured (fifth configuration) to include a switch (SW3) configured to switch between electrical connection and electrical interruption between the current source and the second current detection unit.

[0067] In the load driving device of any of the above first to fifth configurations, the selection section may be configured to perform selection based on a pulse modulated signal (sixth configuration).

[0068] In the load driving device having any of the first to sixth configurations, the resistance value of the second current detection section may be greater than the resistance value of the first current detection section (seventh configuration).

[0069] The lighting device (1A to 1D) of the present disclosure has a configuration (eighth configuration) including a load driving device of any one of the first to seventh configurations above, and the load being a light emitting element.

[0070] A vehicle (4) of the present disclosure has a configuration (ninth configuration) including the load driving device of any one of the first to seventh configurations and the load. [Explanation of symbols]

[0071] 1A~1D Lighting equipment 2 LED 3A~3D LED driver IC 31 Internal power supply circuit 32 DAC AMP1, AMP2 Error amplifiers CS1, CS2 current source INV1 Inverter M1~M5 Transistors R0~R4 resistance R5 Pull-up resistor SW1a, SW1b, SW2a, SW2b, SW3 switches T1~T7 terminals

Claims

1. a first transistor configured to be connected in series with a load; a first current detector configured to detect a current through the first transistor; A second transistor; A current source; a second current detection unit configured to detect a total current of a current flowing through the second transistor and a current output from the current source; an error amplifier configured to output a voltage corresponding to an error between a reference voltage and a current detection result; a selection unit configured to select whether to use the current detection result as an output of the first current detection unit and to supply an output voltage of the error amplifier to a control terminal of the first transistor, or to use the current detection result as an output of the second current detection unit and to supply an output voltage of the error amplifier to a control terminal of the second transistor; A load driving device comprising:

2. The load driver according to claim 1 , wherein the current source is configured to output a current that varies depending on the reference voltage.

3. 2. The load driving device according to claim 1, wherein the second current detection section is capable of switching between detecting the total current and detecting the current flowing through the second transistor.

4. 4. The load driver according to claim 3, wherein the current source is switchable between an enabled state and a disabled state.

5. The load driving device according to claim 3 , further comprising a switch configured to switch between an electrical connection and an electrical interruption between the current source and the second current detection unit.

6. The load driver according to claim 1 , wherein the selection section is configured to make a selection based on a pulse modulated signal.

7. 2. The load driving device according to claim 1, wherein a resistance value of the second current detection unit is greater than a resistance value of the first current detection unit.

8. A load driving device according to any one of claims 1 to 7, The load is a light emitting element; A lighting device comprising:

9. A load driving device according to any one of claims 1 to 7, The load; A vehicle equipped with:

Images