Light emitting element driving device

Abstract

To provide a light-emitting element drive device capable of directly monitoring a current flowing a constant current circuit for driving a light-emitting element.SOLUTION: A light-emitting element drive device (20) includes a constant current circuit (121), and a current detection part (130), the constant current circuit includes a first transistor (M1) including a first end to be connected to external terminal (LED1 to 4), a second end, and a control end, and a drive amplifier (121A) including a current setting resistor (R) to be connected to the second end of the first transistor, a first input end to be connected to a first node (N1) at which the first transistor and the current setting resistor are connected, a second input end to which a current setting voltage (VA) is applied, and an output end to be connected to the control end of the first transistor, the current detection part generates a current detection signal (Vdet) based on a feedback voltage (Vfb) generated at the first node.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a light emitting element driving device. [Background technology]

[0002] Conventionally, LEDs (light emitting diodes) are known as an example of light emitting elements, and LEDs with low power consumption and long life are used for various purposes. A conventional example of an LED driving device for driving an LED is disclosed in Patent Document 1.

[0003] The LED driving device of Patent Document 1 includes an LED terminal configured to be connectable to a cathode of an LED, and a constant current driver connected to the LED terminal. The constant current driver causes a constant LED current to flow through the LED.

[0004] Furthermore, the LED driving device of Patent Document 1 has a function of detecting abnormalities such as an open circuit or a ground fault at an LED terminal based on the voltage at the LED terminal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-21117 Summary of the Invention [Problem to be solved by the invention]

[0006] Recently, there has been a demand for the above-mentioned LED driving device to be able to monitor whether the current set in the constant current driver is flowing normally. The LED driving device of Patent Document 1 is provided with the above-mentioned abnormality detection function, but it detects the state of the current flowing in the constant current driver in a pseudo manner based on the voltage of the LED terminal, and does not make it possible to directly monitor the current flowing in the constant current driver.

[0007] In view of the above circumstances, an object of the present disclosure is to provide a light emitting element driving device that is capable of directly monitoring the current flowing in a constant current circuit that drives a light emitting element. [Means for solving the problem]

[0008] For example, a light emitting element driving device according to the present disclosure includes: an external terminal configured to be connectable to a first end of a light emitting element; a constant current circuit connected to the external terminal; a current detection unit configured to detect a current flowing through the constant current circuit; Equipped with The constant current circuit is a first transistor including a first terminal connected to the external terminal, a second terminal, and a control terminal; a current setting resistor connected to the second terminal of the first transistor; a drive amplifier including a first input terminal connected to a first node where the first transistor and the current setting resistor are connected, a second input terminal to which a current setting voltage is applied, and an output terminal connected to the control terminal of the first transistor; and The current detection section is configured to convert the current flowing through the light emitting element into a voltage signal based on the feedback voltage generated at the first node, and generate a current detection signal. [Effects of the Invention]

[0009] According to the light emitting element driving device of the present disclosure, it is possible to directly monitor the current flowing in the constant current circuit that drives the light emitting element. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an LED driving device according to an exemplary embodiment. [Figure 2] FIG. 2 is a circuit diagram showing a configuration including a current monitor unit according to the first embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example of a detection state of a current flowing through a constant current circuit. [Figure 4] FIG. 4 is a diagram showing a configuration including a modified example of the current monitor unit according to the first embodiment. [Figure 5] FIG. 5 is a circuit diagram showing a configuration including a current monitor unit according to the second embodiment. [Figure 6] FIG. 6 is a circuit diagram showing a configuration including a current monitor unit according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] <1. LED driver configuration> Fig. 1 is a diagram showing the configuration of an LED driving device 20 according to an exemplary embodiment. The LED driving device 20 shown in Fig. 1 drives LED arrays 31 to 34 of multiple systems (four systems in this embodiment, for example).

[0012] The LED driving device 20 is a semiconductor device that integrates an internal voltage generating unit 1, an oscillator unit 2, a slope generating unit 3, a PWM (Pulse Width Modulation) comparator 4, a DC / DC control logic unit 5, a driver 6, an error amplifier 7, a selector 8, a reference voltage generating unit 9, a protection circuit unit 10, an LED current setting unit 11, a constant current driver 12, and a current monitoring unit 13.

[0013] The LED driving device 20 also has external terminals for establishing electrical connection with the outside, including a VCC terminal, an OUTL terminal, a CSL terminal, LED1 terminal to LED4 terminal, an OVP terminal, a GND terminal, an ISET terminal, a FAIL terminal, and a COMP terminal.

[0014] An output stage 25 is arranged outside the LED driver 20 to generate an output voltage Vout from an input voltage Vin by DC / DC conversion and supply the output voltage Vout to the anodes of the LED arrays 31 to 34. The output stage 25 has a switching element SW, a diode D1, an inductor L1, and an output capacitor Co. The switching element SW is driven and controlled by the LED driver 20, thereby controlling the output stage 25. The output stage 25 and the LED driver 20 form a DC / DC converter. In this embodiment, a step-up DC / DC converter is particularly configured as the DC / DC converter.

[0015] The application terminal of the input voltage Vin is connected to one terminal of the inductor L1. The other terminal of the inductor L1 is connected to the anode of the diode D1 and the drain of the switching element SW, which is composed of an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET). The source of the switching element SW is connected to the ground terminal via the current detection resistor Rcsl. The gate of the switching element SW is connected to the OUTL terminal. The cathode of the diode D1 is connected to one terminal of the output capacitor Co. The other terminal of the output capacitor Co is connected to the ground terminal. An output voltage Vout is generated at one terminal of the output capacitor Co.

[0016] The switching element SW may be included in the LED driving device 20.

[0017] The anodes of the LED arrays 31 to 34 are connected to one end of the output capacitor Co, which generates the output voltage Vout. Each of the LED arrays 31 to 34 is made up of a plurality of LEDs connected in series. The cathodes of the LED arrays 31 to 34 are connected to the LED1 terminal to the LED4 terminal, respectively.

[0018] The LED arrays 31 to 34 are not limited to being connected in series, but may be configured with LEDs connected in series and parallel, or may be configured with only one LED. The number of drivable LED arrays (number of systems) is also not limited to four, but may be, for example, six. The number of drivable LED systems may be one.

[0019] Next, the internal configuration of the LED driving device 20 will be described.

[0020] The internal voltage generator 1 generates and outputs an internal voltage Vreg (for example, 5V) from a power supply voltage Vcc applied to a VCC terminal. The internal voltage Vreg is used as a power supply voltage for an internal circuit included in the LED driving device 20. The internal voltage Vreg may be output to the outside from an external terminal, the REG terminal.

[0021] The oscillator 2 generates a predetermined clock signal and outputs it to the slope generator 3 .

[0022] The slope generating unit 3 generates a slope signal (triangular wave signal) Vslp based on the clock signal input from the oscillator 2 and outputs this to the PWM comparator 4. The slope generating unit 3 also has a function of providing an offset to the slope signal Vslp in accordance with the CSL terminal voltage obtained by converting the current flowing through the switching element SW using the current detection resistor Rcsl.

[0023] The PWM comparator 4 compares the error signal Verr input to the non-inverting input terminal (+) with the slope signal Vslp input to the inverting input terminal (-) to generate an internal PWM signal pwm, which is output to the DC / DC control logic unit 5.

[0024] The DC / DC control logic unit 5 generates a drive signal for the driver 6 based on the internal PWM signal pwm.

[0025] Based on the drive signal input from the DC / DC control logic unit 5, the driver 6 generates a gate voltage of the switching element SW in the form of pulses between the internal voltage Vreg and the ground voltage.

[0026] The switching element SW is turned on / off based on a gate voltage input from the driver 6.

[0027] LED terminal voltages Vled1 to Vled4 are applied to the LED1 to LED4 terminals as the cathode voltages of the LED arrays 31 to 34, respectively. A selector 8 selects the lowest voltage from the LED terminal voltages Vled1 to Vled4 and outputs it to the inverting input terminal (−) of the error amplifier 7.

[0028] A reference voltage Vref generated by a reference voltage generator 9 is applied to the non-inverting input terminal (+) of the error amplifier 7. The error amplifier 7 outputs an error amplifier output current (source current or sink current) according to the difference between the minimum voltage applied to the inverting input terminal (-) and the reference voltage Vref.

[0029] The output terminal of the error amplifier 7 is connected to the COMP terminal. The COMP terminal is connected to the ground terminal via an external phase compensation resistor Rpc and capacitor Cpc, which are connected in series. An error voltage Verr is generated at the COMP terminal. The error voltage Verr is applied to the non-inverting input terminal (+) of the PWM comparator 4.

[0030] The protection circuit section 10 includes a TSD section, an OCP section, an OVP section, an LED open detection circuit (OPEN), an LED short detection circuit (SHORT), an output short protection circuit (SCP), and a UVLO section.

[0031] When the junction temperature of the LED driver 20 reaches, for example, 175°C or higher, the TSD unit commands the DC / DC control logic unit 5 to turn off DC / DC switching, and commands the constant current driver 12 to turn off all LED systems. Note that the TSD unit restores circuit operation when the junction temperature of the LED driver 20 reaches, for example, 150°C.

[0032] The OCP unit monitors the CSL terminal voltage (input current detection voltage) detected as a voltage signal by the current detection resistor Rcsl from the current flowing through the switching element SW, and activates overcurrent protection when the CSL terminal voltage exceeds, for example, 0.3 V. When activating overcurrent protection, the OCP unit commands the DC / DC control logic unit 5 to turn off DC / DC switching.

[0033] The OVP unit monitors the OVP terminal voltage and activates overvoltage protection when the OVP terminal voltage exceeds, for example, 1.21 V. When overvoltage protection is activated, it commands the DC / DC control logic unit 5 to turn off DC / DC switching.

[0034] The LED open detection circuit (OPEN) detects open abnormalities in the terminals LED1 to LED4. When the current monitor unit 13 (described later) detects an undercurrent state and the OVP terminal voltage is, for example, 1.21 V or higher, the LED open detection circuit activates LED open detection and latches off only the LED array in which open detection has been detected (the constant current circuit 121 of the corresponding system in the constant current driver 12 is turned off).

[0035] In the LED short detection circuit (SHORT), when any of the LED terminal voltages Vled1 to Vled4 is, for example, 5.0 V or higher, the built-in counter starts operating, and after approximately 3.56 ms, the circuit is latched and only the LED array that has been detected as shorted is latched off (the constant current circuit 121 of the corresponding system in the constant current driver 12 is turned off).

[0036] In the output short-circuit protection circuit (SCP), when the OVP terminal voltage falls to, for example, 0.1 V or less, the built-in counter starts operating and latches after approximately 3.56 ms has elapsed, issuing a command to the DC / DC control logic unit 5 to turn off DC / DC switching and a command to the constant current driver 12 to turn off all LED systems. This allows the output short-circuit protection circuit to protect the anode side (DC / DC output terminal side) of the LED arrays 31 to 34 when a ground fault occurs.

[0037] Furthermore, in the output short-circuit protection circuit, when an insufficient current abnormality is detected by the current monitor unit 13 described below and the OVP terminal voltage is lower than, for example, 1.21 V, the built-in counter starts operating and latches after approximately 3.56 ms has elapsed, issuing a command to the DC / DC control logic unit 5 to turn off DC / DC switching and a command to the constant current driver 12 to turn off all LED systems. This allows the output short-circuit protection circuit to protect the cathode sides of the LED arrays 31 to 34 when a ground fault occurs.

[0038] When the power supply voltage Vcc becomes, for example, 4.1 V or less, or when the internal voltage Vreg becomes, for example, 4.0 V or less, the UVLO unit commands the DC / DC control logic unit 5 to turn off the DC / DC switching and commands the constant current driver 12 to turn off all the LED systems.

[0039] The protection circuit unit 10 outputs an abnormality detection signal from a FAIL terminal to the outside based on the abnormality detection states of the LED open detection circuit, the LED short detection circuit, and the output short circuit protection circuit (SCP). The FAIL terminal has an open drain configuration.

[0040] The LED current setting unit 11 sets a constant current value corresponding to the resistance value of an LED current setting resistor Riset externally connected to an ISET terminal (current setting terminal) in the constant current driver 12. The specific configuration of the LED current setting unit 11 will be described later.

[0041] The constant current driver 12 has four constant current circuits 121 arranged between each of the LED1 to LED4 terminals and a GND terminal connected to the ground terminal. The constant current circuits 121 generate the LED current I LED flows through the LED arrays 31 to 34 of the corresponding system. As will be described later, DC dimming of the LEDs can be performed by varying the constant current value set by the LED current setting unit 11. Also, a PWM dimming function may be provided that controls the on / off of the constant current circuit 121 based on a PWM dimming signal.

[0042] The current monitor unit 13 is a circuit that monitors the current flowing in the constant current circuit 121 of each system, and outputs the monitoring result to the protection circuit unit 10. Note that specific configurations of the constant current circuit 121 and the current monitor unit 13 will be described later.

[0043] 2. DC / DC controller Next, the DC / DC controller 201 (a circuit block including the oscillator 2, slope generator 3, PWM comparator 4, DC / DC control logic unit 5, driver 6, and error amplifier 7) provided in the LED driver 20 will be described in detail.

[0044] The error amplifier 7 generates an error amplifier output current according to the difference between the reference voltage Vref and the lowest value of the LED terminal voltages Vled1 to Vled4 selected by the selector 8. The error amplifier output current is a source current when the lower voltage is lower than the reference voltage Vref, and is a sink current when the lower voltage is higher than the reference voltage Vref.

[0045] The PWM comparator 4 compares the error voltage Verr with the slope signal Vslp to generate an internal PWM signal pwm. The internal PWM signal pwm goes high if the error voltage Verr is higher than the slope signal Vslp, and goes low if the error voltage Verr is lower than the slope signal Vslp.

[0046] The control logic unit 5 controls the on / off of the switching element SW based on the internal PWM signal pwm. Specifically, the control logic unit 5 turns on the switching element SW when the internal PWM signal pwm is at a high level. Conversely, the control logic unit 5 turns off the switching element SW when the internal PWM signal pwm is at a low level.

[0047] As a result, the feedback control unit, which is made up of the error amplifier 7, PWM comparator 4, control logic unit 5, and driver 6, performs feedback control to output a switching pulse from the OUTL terminal to the switching element SW so as to match the minimum value of the LED terminal voltages Vled1 to Vled4 with the reference voltage Vref. In other words, the DC / DC controller 201 has the above-mentioned feedback control unit.

[0048] When the switching element SW is turned on, a current flows from the input voltage Vin application terminal to the ground terminal via the switching element SW, and energy is stored in the inductor L1. At this time, the diode D1 is in a reverse bias state, so no current flows from the output capacitor Co to the switching element SW. If a charge has been stored in the output capacitor Co, the LED current I LED will be played.

[0049] When the switching element SW is turned off, the energy stored in the inductor L1 is released and the current becomes the LED current I LED The current flows into the LED arrays 31 to 34 as a current, and also flows into the output capacitor Co, charging the output capacitor Co.

[0050] By repeating the above operation, the output voltage Vout obtained by boosting the input voltage Vin is supplied to the anodes of the LED arrays 31 to 34. At this time, the cathode voltage of the LED array in the system with the highest forward voltage is controlled to the reference voltage Vref, and the cathode voltages of the LED arrays in the other systems are controlled to voltages equal to or higher than the reference voltage Vef.

[0051] 3. First embodiment of current monitor unit Next, the constant current circuit 121 and the current monitor unit 13 will be described in more detail. Fig. 2 is a circuit diagram showing an example configuration of the constant current circuit 121 and the current monitor unit 13. The current monitor unit 13 shown in Fig. 2 is the current monitor unit 13 according to the first embodiment. Note that Fig. 2 also shows the configuration of the LED current setting unit 11.

[0052] The configuration in Fig. 2 is representatively shown for one system of LEDs, and in reality, the configuration in Fig. 2 is provided for the number of systems of LEDs to be provided (four systems in the example in Fig. 1). However, the LED current setting unit 11 and voltage dividing resistors RA, RB, and RC, which will be described later, may be common to the systems of LEDs.

[0053] As shown in FIG. 2, the constant current circuit 121 has a drive amplifier (error amplifier) ​​121A, a transistor M1, and a current setting resistor R. A current setting reference voltage VA is applied to a non-inverting input terminal (+) of the drive amplifier 121A. The output terminal of the drive amplifier 121A is connected to the gate of a transistor M1 configured as an NMOS transistor (N-channel MOSFET). The drain of the transistor M1 is connected to an LED terminal (one of the LED1 terminal to LED4 terminal). The source of the transistor M1 is connected to one terminal of the current setting resistor R at a node N1. The other terminal of the current setting resistor R is connected to the ground terminal. The node N1 is connected to the inverting input terminal (-) of the drive amplifier 121A.

[0054] The driving amplifier 121A amplifies the error between the current setting reference voltage VA and the feedback voltage Vfb generated at the node N1 and outputs the amplified error to the gate of the transistor M1, thereby controlling the feedback voltage Vfb to be equal to the current setting reference voltage VA.

[0055] 2, the current monitor unit 13 includes a current detection unit 130. The current detection unit 130 is configured to be able to detect a current Im1 flowing through the transistor M1.

[0056] The current detection unit 130 has a transistor M2, a current mirror 131, and an IV conversion (current-voltage conversion) resistor R3. The gate of the transistor M2, which is an NMOS transistor, is connected to the output terminal of the drive amplifier 121A. The source of the transistor M2 is connected to a node N1. The drain of the transistor M2 is connected to the input terminal of the current mirror 131. The output terminal of the current mirror 131 is connected to one terminal of the IV conversion resistor R3. The other terminal of the IV conversion resistor R3 is connected to the ground terminal.

[0057] In the constant current circuit 121, a current Ir of Ir=Vfb / R flows through the current setting resistor R due to the feedback voltage Vfb generated at the node N1 and the current setting resistor R. The current Ir is a current obtained by combining the current Im1 flowing through the transistor M1 and the current Im2 flowing through the transistor M2. In the normal state, Im1=LED current I LED This becomes:

[0058] If the size ratio of the transistor M1 to the transistor M2 is M1:M2, the currents Im1 and Im2 are expressed as follows: Im1=Ir×(M1 / (M1+M2))=(Vfb / R)×(M1 / (M1+M2)) Im2=Ir×(M2 / (M1+M2))=(Vfb / R)×(M2 / (M1+M2))

[0059] The output current I131 output from the current mirror 131 to the IV conversion resistor R3 is I131=Im2. Therefore, the current detection signal Vdet obtained by IV converting the output current I131 by the IV conversion resistor R3 is expressed as follows: Vdet=I131×R3=Im2×R3=(Vfb / R)×(M2 / (M1+M2))×R3

[0060] That is, the current Im1 flowing through the transistor M1 is detected by the current Im2 flowing through the transistor M2 based on the feedback voltage Vfb, and the current Im2 is IV converted by the current mirror 131 and the IV conversion resistor R3 to obtain the current detection signal Vdet, so that the current Im1 flowing through the constant current circuit 121 is directly monitored by the current detection signal Vdet. Note that the current Im2 can be reduced by making the size of the transistor M2 smaller than the size of the transistor M1.

[0061] The current setting reference voltage VA is generated by an LED current setting unit 11. The LED current setting unit 11 includes an error amplifier 11A, a transistor 11B, a current mirror 11C, and resistors R1 and R2.

[0062] A reference voltage αVref is applied to the non-inverting input terminal (+) of the error amplifier 11A. The reference voltage αVref is variable. The output terminal of the error amplifier 11A is connected to the gate of a transistor 11B, which is an NMOS transistor. The source of the transistor 11B is connected to one end of a resistor R1 at a node N2. The other end of the resistor R1 is connected to the ground terminal. The node N2 is connected to the inverting input terminal (-) of the error amplifier 11A.

[0063] The drain of the transistor 11B is connected to the input terminal of the current mirror 11C. The output terminal of the current mirror 11C is connected to one terminal of the resistor R2. The other terminal of the resistor R2 is connected to the ground terminal.

[0064] The feedback voltage generated at node N2 is controlled to be V1=αVref. As a result, the current flowing through resistor R1 becomes I1=V1 / R1=αVref / R1. Because the current I2 output from current mirror 11C to resistor R2 is I1, the current setting reference voltage VA obtained by IV conversion of current I2 using resistor R2 is expressed as follows: VA=I2×R2=I1×R2=(αVref / R1)×R2

[0065] In the constant current circuit 121, the feedback voltage Vfb is controlled to be equal to VA, and therefore the current Im1 flowing through the transistor M1 is expressed as follows: Im1=(VA / R)×(M1 / (M1+M2))

[0066] By making the reference voltage αVref variable, the current setting reference voltage VA becomes variable, and the current Im1, i.e., the LED current I LED This makes it possible to vary the LED current, enabling DC dimming. Resistor R1 corresponds to the LED current setting resistor Riset (Figure 1) externally connected to the ISET terminal mentioned above. Therefore, the value of the current setting reference voltage VA can be set using the LED current setting resistor Riset. Furthermore, by trimming resistor R2, the current setting reference voltage VA can be set to the desired value even if the reference voltage αVref varies.

[0067] Since the feedback voltage Vfb is controlled to be equal to VA, the current detection signal Vdet is expressed as follows: Vdet=(Vfb / R)×(M2 / (M1+M2))×R3 =(VA / R)×(M2 / (M1+M2))×R3 =(((αVref / R1)×R2) / R)×(M2 / (M1+M2))×R3

[0068] 2, the current monitor unit 13 includes window comparators CP1 and CP2 and voltage dividing resistors RA, RB, and RC. The window comparators CP1 and CP2 are provided to detect whether the current Im1 is flowing normally as set.

[0069] The application terminal of the reference voltage αVref is connected to one terminal of a voltage dividing resistor RA. The other terminal of the voltage dividing resistor RA is connected to one terminal of a voltage dividing resistor RB. The other terminal of the voltage dividing resistor RB is connected to one terminal of a voltage dividing resistor RC. The other terminal of the voltage dividing resistor RC is connected to the ground terminal.

[0070] The non-inverting input terminal (+) of the window comparator CP1 is applied with a current detection signal Vdet. The inverting input terminal (-) of the window comparator CP1 is connected to the node NA to which the resistors RA and RB are connected. The comparison reference voltage Vref_cp1 generated at the node NA is Vref_cp1 = αVref × ((RB + RC) / (RA + RB + RC)). The window comparator CP1 compares the current detection signal Vdet with the comparison reference voltage Vref_cp1 and outputs the comparison result as a comparison output signal Cpout1.

[0071] The non-inverting input terminal (+) of the window comparator CP2 is applied with a current detection signal Vdet. The inverting input terminal (-) of the window comparator CP2 is connected to the node NB to which the resistors RB and RC are connected. The comparison reference voltage Vref_cp2 generated at the node NB is Vref_cp2 = αVref × (RC / (RA + RB + RC)). That is, Vref_cp2 < Vref_cp1. The window comparator CP2 compares the current detection signal Vdet with the comparison reference voltage Vref_cp2 and outputs the comparison result as a comparison output signal Cpout2.

[0072] Here, Vdet = (((αVref / R1) × R2) / R) × (M2 / (M1 + M2)) × R3 = αVref × K Let it be so. That is, the value of K is set according to the values of R1, R2, R, M1, M2, and R3.

[0073] Then, the voltage dividing resistors RA, RB, and RC are set so that Vref_cp1 > αVref × K and Vref_cp2 < αVref × K. As a result, it is detected by the window comparators CP1 and CP2 that the current detection signal Vdet is not less than Vref_cp2 and not more than Vref_cp1, so that the current detection signal Vdet is within the allowable range and it is detected that the current Im1 is flowing normally as set.

[0074] As an example, the detection state of current Im1 when K=0.5, Vref_cp1=αVref×0.7, and Vref_cp2=αVref×0.3 is shown in Fig. 3. As shown in Fig. 3, when αVref×0.3≦Vdet≦αVref×0.7, Vref is within the allowable range and current Im1 is in a normal state.

[0075] On the other hand, if Vdet<αVref×0.3, the current Im1 is in an undercurrent state. This state occurs, for example, when an LED terminal is open or has a ground fault, resulting in Ir=Im1=Im2=0.

[0076] Furthermore, if Vdet>αVref×0.7, the current Im1 is in an overcurrent state. This state occurs, for example, when an abnormality occurs in the drive amplifier 121A or the transistor M1, causing an abnormality in the feedback voltage Vfb, or when a short circuit occurs in the resistor R1 in the LED current setting unit 11, causing an abnormality in the current setting reference voltage VA.

[0077] Although the value of K is not limited to 0.5, it is preferable to set K=0.5 in order to ensure a range for detecting abnormalities in an undercurrent state and an overcurrent state, as shown in FIG.

[0078] 2, the reference voltage αVref for generating the current setting voltage VA and the reference voltage αVref for generating the comparison reference voltages Vref_cp1 and Vref_cp2 are common, but they do not necessarily have to be common. However, considering that variations in the reference voltage αVref may occur, it is preferable to commonize the reference voltage αVref.

[0079] The comparison output signals Cpout1 and Cpout2 output from the window comparators CP1 and CP2 can be output to the protection circuit unit 10. As described above, the LED open detection circuit (OPEN) or the output ground fault protection circuit (SCP) in the protection circuit unit 10 can activate open protection or ground fault protection when it determines that an abnormality in an undercurrent state has occurred based on the comparison output signals Cpout1 and Cpout2. Furthermore, the protection circuit unit 10 may activate protection by, for example, turning off the constant current circuit 121 of the corresponding system when it determines that an abnormality in an overcurrent state has occurred based on the comparison output signals Cpout1 and Cpout2.

[0080] 4 is a diagram showing a modification of the current monitor unit 13 according to the first embodiment. The current monitor unit 13 shown in FIG. 4 includes a resistor R4. The source of the transistor M2 is connected to one end of the resistor R4. The other end of the resistor R4 is connected to the ground terminal. If the value of the resistor R4 is made much larger than the value of the current setting resistor R, the current Im1 can be detected by the current detection signal Vdet, as in the first embodiment.

[0081] 4. Second embodiment of current monitor unit Fig. 5 is a diagram showing a second embodiment of the current monitor unit 13. The current monitor unit 13 according to the second embodiment shown in Fig. 5 includes a PMOS transistor (P-channel MOSFET) 13A and a constant current source 13B.

[0082] The gate of the PMOS 13A is connected to a node N1 in the constant current circuit 121. The constant current source 13B is connected between the application terminal of the internal voltage Vreg and the source of the PMOS transistor 13A. The drain of the PMOS transistor 13A is connected to the ground terminal.

[0083] With this configuration, the current detection signal Vdet generated at the source of the PMOS transistor 13A is Vdet=Vfb+Vgs, where Vgs is the gate-source voltage of the PMOS transistor 13A.

[0084] The current Im1 flowing through the transistor M1 is expressed as Im1=Vfb / R, so the current Im1 can be directly monitored by the current detection signal Vdet. Under normal conditions, Vdet=VA+Vgs=(αVref / R1)×R2+Vgs. In particular, the current monitor unit 13 of this embodiment can reduce the number of elements used.

[0085] 5. Third embodiment of current monitor unit Fig. 6 is a diagram showing a third embodiment of the current monitor unit 13. The current monitor unit 13 according to the third embodiment shown in Fig. 6 has an A / D converter (hereinafter referred to as an ADC (analog to digital converter)) 13C instead of the window comparators CP1 and CP2 in the first embodiment.

[0086] The ADC 13C is configured as a so-called flash type or successive approximation type. The current detection signal Vdet is input to the analog input terminal of the ADC 13C. The reference voltage αVref is input to the reference voltage input terminal of the ADC 13C. The ADC 13C outputs the digital value of the current detection signal Vdet as the digital output Dout, with the reference voltage αVref as the maximum digital value (all bits 1).

[0087] As a result, as described above, if Vdet=αVref×K (K is, for example, 0.5) in the normal state, the ADC 13C outputs a digital output Dout having a digital value according to αVref×K.

[0088] According to this embodiment, the current detection signal Vdet, that is, the state of the current Im1, can be detected more accurately than in the first embodiment that uses the window comparators CP1 and CP2.

[0089] <6.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.

[0090] <7. Notes> As described above, for example, the light-emitting element driving device (20) according to the present disclosure includes external terminals (LED1 to LED4) configured to be connectable to first ends of the light-emitting elements (31 to 34); a constant current circuit (121) connected to the external terminal; a current detection unit (130) configured to be able to detect a current flowing through the constant current circuit; Equipped with The constant current circuit is a first transistor (M1) including a first terminal connected to the external terminal, a second terminal, and a control terminal; a current setting resistor (R) connected to the second end of the first transistor; a drive amplifier (121A) including a first input terminal connected to a first node (N1) to which the first transistor and the current setting resistor are connected, a second input terminal to which a current setting voltage (VA) is applied, and an output terminal connected to the control terminal of the first transistor; and The current detection unit is configured to convert the current flowing through the light emitting element into a voltage signal based on a feedback voltage (Vfb) generated at the first node, and generate a current detection signal (Vdet) (first configuration).

[0091] In the first configuration, the current detection unit (130) a second transistor (M2) including a control terminal connected to the output terminal of the driving amplifier (121A), a first terminal connected to the first node, and a second terminal; a first current mirror (131) including an input terminal connected to the second terminal of the second transistor and an output terminal; an IV conversion resistor (R3) connected to the output terminal of the first current mirror; (second configuration).

[0092] In the second configuration, the size of the second transistor (M2) may be smaller than the size of the first transistor (M1) (third configuration).

[0093] In any one of the first to third configurations, the current setting voltage (VA) is generated based on a first reference voltage (αVref), The light-emitting element driving device (20) may be configured to include window comparators (CP1, CP2) that compare the current detection signal (Vdet) with comparison reference voltages (Vref_cp1, Vref_cp2) obtained by dividing a second reference voltage (αVref) (fourth configuration).

[0094] In the fourth configuration, the first reference voltage and the second reference voltage may be a common voltage (αVref) (fifth configuration).

[0095] In the fourth or fifth configuration, in the normal state, the current detection signal may be Vdet, the first reference voltage may be αVref, and Vdet=αVref×0.5 may be satisfied (sixth configuration).

[0096] In addition, in any one of the first to third configurations, the current setting voltage (VA) is generated based on a third reference voltage (αVref), The light-emitting element driving device (20) may be configured to include an A / D converter (13C) including an analog input terminal to which the current detection signal (Vdet) is input and a reference voltage input terminal to which a fourth reference voltage (αVref) is input (seventh configuration).

[0097] In the seventh configuration, the third reference voltage and the fourth reference voltage may be a common voltage (αVref) (eighth configuration).

[0098] In the seventh or eighth configuration, in the normal state, the current detection signal may be Vdet, the third reference voltage may be αVref, and Vdet=αVref×0.5 may be satisfied (ninth configuration).

[0099] In the first configuration, the current detection section (130) may have a PMOS transistor (13A) including a gate connected to the first node (N1) (tenth configuration).

[0100] In addition, in any one of the first to tenth configurations, the light-emitting element driving device (20) includes a current setting unit (11) that generates the current setting voltage (VA), The current setting unit a third transistor (11B) including a control terminal, a first terminal, and a second terminal; an error amplifier (11A) including: a first input terminal to which a reference voltage (αVref) is input; a second input terminal to which a voltage (V1) generated at a second node (N2) to which the first terminal of the third transistor and a first resistor (R1) are connected; and an output terminal connected to the control terminal of the third transistor; a second current mirror (11C) including an input terminal connected to the second terminal of the third transistor and an output terminal; a second resistor (R2) connected to the output terminal of the second current mirror; (eleventh configuration).

[0101] In the eleventh configuration, the reference voltage (αVref) may be variable (twelfth configuration).

[0102] In any one of the first to twelfth configurations, a DC / DC controller (201) that controls an output voltage (Vout) to be supplied to a second terminal of the light-emitting element (31 to 34) based on a voltage of the external terminal (LED1 to LED4); The configuration may also include a protection circuit unit (10) that detects at least one of an open circuit abnormality in the external terminal and a ground fault abnormality in the external terminal based on the current detection signal (Vdet) and the output voltage, and provides protection (13th configuration). [Industrial Applicability]

[0103] The present disclosure can be used, for example, as a means for driving LEDs for various applications. [Explanation of symbols]

[0104] 1 Internal voltage generator 2 Oscillator 3 Slope generation section 4 PWM Comparators 5 DC / DC control logic section 6 Drivers 7 Error Amplifier 8 Selectors 9 Reference voltage generation section 10 Protection circuit section 11 LED current setting section 11A Error Amplifier 11B transistor 11C Current Mirror 12 Constant Current Driver 13 Current monitor section 13A PMOS transistor 13B constant current source 20 LED driver 25 output stage 31~34 LED array 121 Constant current circuit 121A driver amplifier 131 Current mirror 201 DC / DC Controller CP1,CP2 window comparators Co Output Capacitor Cpc capacitor D1 Diode L1 inductor M1, M2 transistors SW Switching element N1, N2, NA, NB nodes R current setting resistor R1,R2 resistance R3 IV conversion resistor R4 resistance RA, RB, RC voltage dividing resistors Rcsl Current detection resistor Riset LED current setting resistor Rovp1, Rovp2 voltage dividing resistors Rpc Phase compensation resistor

Claims

1. an external terminal configured to be connectable to a first end of the light emitting element; a constant current circuit connected to the external terminal; a current detection unit configured to detect a current flowing through the constant current circuit; a current setting unit configured to generate a current setting voltage; Equipped with The constant current circuit is a first transistor including a first end connected to the external terminal, a second end, and a control end; a current setting resistor connected to the second end of the first transistor; a driver amplifier including: a first input terminal connected to a first node where the first transistor and the current setting resistor are connected; a second input terminal to which the current setting voltage is applied; and an output terminal connected to the control terminal of the first transistor; and the current detection unit converts a current flowing through the light emitting element into a voltage signal based on a feedback voltage generated at the first node, and generates a current detection signal; The current detection unit a second transistor including a control terminal connected to the output terminal of the driver amplifier, a first terminal connected only to the first node, and a second terminal; a first current mirror including an input terminal connected to the second terminal of the second transistor and an output terminal; an I-V conversion resistor connected to the output terminal of the first current mirror; and The light emitting element driving device, wherein the voltage input to the current setting unit and the voltage input for generating a comparison reference voltage to be compared with the current detection signal are the same first reference voltage.

2. The light-emitting element driving device according to claim 1 , wherein the size of the second transistor is smaller than the size of the first transistor.

3. the current setting voltage is generated based on the first reference voltage; 3. The light emitting element driving device according to claim 1, further comprising a window comparator that compares the current detection signal with the comparison reference voltage obtained by dividing the first reference voltage.

4. 4. The light-emitting element driving device according to claim 3, wherein, in a normal state, Vdet=αVref×0.5, where Vdet is the current detection signal and αVref is the first reference voltage.

5. the current setting voltage is generated based on the first reference voltage; The light-emitting element driving device according to claim 1 or 2, further comprising an A / D converter including an analog input terminal to which the current detection signal is input and a reference voltage input terminal to which the first reference voltage is input as the comparison reference voltage.

6. 6. The light-emitting element driving device according to claim 5, wherein, in a normal state, Vdet=αVref×0.5 is satisfied, where Vdet is the current detection signal and αVref is the first reference voltage.

7. The current setting unit a third transistor including a control end, a first end, and a second end; an error amplifier including: a first input terminal to which the first reference voltage is input; a second input terminal to which a voltage generated at a second node to which the first terminal of the third transistor and a first resistor are connected; and an output terminal connected to the control terminal of the third transistor; a second current mirror including an input terminal connected to the second terminal of the third transistor and an output terminal; a second resistor connected to the output terminal of the second current mirror; The light emitting element driving device according to claim 1 , further comprising:

8. The light emitting element driving device according to claim 7 , wherein the first reference voltage is variable.

9. a DC / DC controller that controls generation of an output voltage to be supplied to a second terminal of the light-emitting element based on a voltage at the external terminal; a protection circuit unit that detects at least one of an open circuit abnormality of the external terminal and a ground fault abnormality of the external terminal based on the current detection signal and the output voltage, and performs protection; The light emitting element driving device according to claim 1 , comprising:

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