Light-emitting element drive device, light emission control device, and light emission device

Abstract

This light-emitting element drive device (1) comprises, for example: a current sense amplifier (16) configured so as to generate a current detection signal (Vcso), which corresponds to the difference between a sense voltage (Vsns) corresponding to an inductor current (IL) (in addition to an output current (ILED) supplied to a light-emitting element (2)) and a prescribed current setting signal (for example, an offset voltage corresponding to a setting current (ISET)); an error amplifier (17) configured so as to generate an error signal (Vc) such that a direct current component of the current detection signal (Vcso) assumes a value of zero; a comparator (18) configured so as to generate a setting signal (SET) by comparing the current detection signal (Vcso) and the error signal (Vc); and a driver (11) configured so as to perform feedback control of the output current (ILED) in accordance with the setting signal (SET).

Description

Light emitting element driving device, light emitting control device, light emitting device

[0001] The invention disclosed in this specification relates to a light emitting element driving device, and a light emitting control device and a light emitting device using the same.

[0002] 2. Description of the Related Art Various light emitting element driving devices have been proposed so far for supplying a constant output current to a light emitting element.

[0003] An example of the related prior art is disclosed in Japanese Patent Application Laid-Open No. 2003-222299.

[0004] Japanese Patent Application Laid-Open No. 2021-044283

[0005] However, in the conventional light emitting element driving device, there is room for further study regarding the operation for restoring lighting when the load is opened.

[0006] For example, the light-emitting element driving device disclosed in this specification includes a current sense amplifier configured to generate a current detection signal corresponding to the difference between a sense voltage corresponding to the output current supplied to the light-emitting element and a predetermined current setting signal, an error amplifier configured to generate an error signal so that the DC component of the current detection signal becomes zero, a comparator configured to compare the current detection signal with the error signal to generate a set signal, and a driver configured to perform feedback control of the output current according to the set signal.

[0007] Still other features, elements, steps, advantages, and characteristics will become more apparent from the detailed description that follows and the accompanying drawings related thereto.

[0008] According to the invention disclosed in this specification, it is possible to provide a light-emitting element driving device that can quickly and safely perform a lighting recovery operation when a load is opened, as well as a light-emitting control device and a light-emitting device that use the same.

[0009] FIG. 1 is a diagram illustrating a lighting recovery operation (continuous operation) when an LED is open. FIG. 2 is a diagram illustrating an example of an operation mode required for lighting recovery. FIG. 3 is a diagram illustrating an example of a general operation mode for lighting recovery. FIG. 4 is a diagram illustrating a first embodiment of an LED lamp module. FIG. 5 is a diagram illustrating an example of a circuit configuration in the first embodiment. FIG. 6 is a diagram illustrating an example of signal transmission in the first embodiment. FIG. 7 is a diagram illustrating an example of a control block in the first embodiment. FIG. 8 is a diagram illustrating how an error signal in the first embodiment depends on a set current. FIG. 9 is a diagram illustrating an example of a lighting recovery operation in the first embodiment. FIG. 10 is a diagram illustrating the responsiveness of an output current in the first embodiment. FIG. 11 is a diagram illustrating a second embodiment of an LED lamp module. FIG. 12 is a diagram illustrating an example of a circuit configuration in the second embodiment. FIG. 13 is a diagram illustrating an example of signal transmission in the second embodiment. FIG. 14 is a diagram illustrating an example of a control block in the second embodiment. FIG. 15 is a diagram illustrating how an error signal in the second embodiment does not depend on a set current. FIG. 16 is a diagram illustrating an example of a lighting recovery operation in the second embodiment. FIG. 17 is a diagram showing the response of the output current in the second embodiment.

[0010] <Lighting Restoration Operation When an LED [Light Emitting Diode] is Open> Fig. 1 is a diagram showing the lighting restoration operation (continuation operation) when an LED is open. The LED lamp module Z in this figure is an example of a light emitting device used, for example, as a head lamp, tail lamp, or turn lamp of a vehicle, and includes an LCU [Light Control Unit] 10 (corresponding to a light emission control device), an LED string 2 (corresponding to a light emitting element), and a matrix manager 3 (corresponding to a switch control device).

[0011] The LCU 10 includes an LED driver IC 1 (corresponding to a light emitting element driving device) and supplies an output current I LED to the LED string 2 .

[0012] The LED string 2 includes a plurality of LED elements connected in series, and emits light at a brightness corresponding to the output current ILED.

[0013] The matrix manager 3 includes a plurality of switch elements SW connected in parallel to each of the plurality of LED elements that form the LED string 2, and by turning on / off each switch element, the number of series stages (number of lit LED elements) of the LED elements can be arbitrarily switched.

[0014] Incidentally, as is clear from comparing the left and right sides of this figure, the LED lamp module Z equipped with the matrix manager 3 can maintain a lighting state even when an open circuit fault occurs in the LED string 2.

[0015] Specifically, in the case of the LED lamp module Z shown in this figure, by forcibly turning on the switch element SW connected in parallel to the LED element with the open fault, a path for the output current ILED to flow bypassing the open fault location in the LED string 2 can be secured, and the LED string 2 can be restored to the lit state.

[0016] Other circumstances in which an open load may occur include poor connector contact due to vibrations while the vehicle is running, disconnection of the output wire harness, or plugging and unplugging of a connector during maintenance work.

[0017] 2 is a diagram showing an example of an operation mode required when restoring lighting from an LED open fault. As shown in this diagram, the LCU 10 (especially the LED driver IC 1, which is its main component) is required to continue operating even in the event of an LED open fault, and to quickly increase the output current ILED to the current setting value (target value) after establishing a bypass path around the open fault location, thereby quickly restoring the LED string 2 to a lighting state.

[0018] 3 is a diagram showing a typical operation mode when restoring illumination from an LED open fault. As shown in this diagram, in the typical operation mode when restoring illumination, the LCU 10 is shut down once the LED open fault is detected and then restarted. Therefore, due to a startup delay of the LCU 10, it takes a considerable amount of time for the illumination of the LED string 2 to return to normal.

[0019] The reason why the LCU 10 needs to be restarted when the lighting is restored from an LED open fault will be explained below, using a typical circuit configuration of the LCU 10 as an example.

[0020] 4 is a diagram showing a first embodiment of an LED lamp module Z (= a general circuit configuration to be compared with the second embodiment described later). As described above, the LED lamp module Z of this embodiment includes an LCU 10 and an LED string 2. For convenience, the matrix manager 3 described above is not shown in the figure.

[0021] The LCU 10 includes an LED driver IC1 and various discrete components (in this figure, an inductor L1, a sense resistor Rs, and a capacitor Co) externally attached to the LED driver IC1.

[0022] The LED driver IC1 is a semiconductor integrated circuit device that steps down the power system input voltage Vi and supplies power to the LED string 2 (i.e., generates the output current ILED). The LED driver IC1 has multiple external terminals (such as a SW pin, an SNSP pin, and an SNSN pin) as means for establishing electrical connections with the outside of the IC. The SW pin is a switch output terminal. The SNSP pin is a first current sense terminal (+). The SNSN pin is a second current sense terminal (-).

[0023] The SW pin is connected to a first end of the inductor L1. The second end of the inductor L1 is connected to a first end of the sense resistor Rs. The second end of the sense resistor Rs and the first end of the capacitor Co are both connected to the anode of the LED string 2. The cathode of the LED string 2 and the second end of the capacitor Co are both connected to the ground end. The first end (high potential end) of the sense resistor Rs is connected to the SNSP pin. The second end (low potential end) of the sense resistor Rs is connected to the SNSN pin.

[0024] Among the above-mentioned discrete components, the inductor L1 and the capacitor Co, together with the driver 11 (particularly the upper switch 11H and the lower switch 11L included in the driver 11) integrated into the LED driver IC1, form a step-down switch output stage.

[0025] Furthermore, the sense resistor Rs converts the inductor current IL flowing through the inductor L1 into a sense voltage Vsns.

[0026] The LED driver IC 1 integrates a driver 11, an on-time setting unit 14, a slope signal generating unit 15, an error amplifier 17, a comparator 18, a current setting unit 1X, input resistors R1P and R1N, and a capacitor Cc. Of course, the LED driver IC 1 may also integrate other components (such as a temperature detection circuit and various protection circuits) besides those mentioned above.

[0027] The driver 11 includes an upper switch 11H and a lower switch 11L. The upper switch 11H is connected between a PIN pin (the terminal to which the input voltage Vi is applied) and a SW pin. On the other hand, the lower switch 11L is connected between the SW pin and a PGND pin. NMOSFETs (N-channel type metal oxide semiconductor field effect transistors) can be suitably used as the upper switch 11H and the lower switch 11L, respectively.

[0028] The upper switch 11H and the lower switch 11L connected in this manner form a half-bridge type (synchronous rectification) switch output stage that outputs a rectangular wave switch voltage Vsw from the SW pin. In other words, the upper switch 11H corresponds to the output element, and the lower switch 11L corresponds to the synchronous rectification element. Note that, when a diode rectification type switch output stage is used, a rectifier diode can be used instead of the lower switch 11L.

[0029] The driver 11 performs feedback control of the inductor current IL (and therefore the output current ILED) using a bottom detection type fixed on-time method by complementarily turning on / off the upper switch 11H and the lower switch 11L in response to a set signal SET and a reset signal RST, so that the output current ILED matches a predetermined current setting value (target value).

[0030] More specifically, the driver 11 turns on the upper switch 11H and turns off the lower switch 11L at the rising timing of the set signal SET, and turns off the upper switch 11H and turns on the lower switch 11L at the rising timing of the reset signal RST.

[0031] However, the term "complementary" in this specification should be understood in a broad sense to include not only the case where the on / off states of the upper switch 11H and the lower switch 11L are completely reversed, but also the case where a simultaneous off period (so-called dead time) is provided to prevent through current.

[0032] In this way, if a nonlinear control method (for example, a bottom detection fixed on-time method) with excellent high-speed response is adopted as the output feedback control method for the LED driver IC1, it will be possible to continue to stably supply a constant output current ILED even if the number of LED elements connected in series (number of lights up) fluctuates due to the function of the matrix manager 3.

[0033] The on-time setting unit 14 generates a pulse in the reset signal RST when a predetermined on-time Ton has elapsed since the generation of a pulse in the set signal SET. In other words, the on-time setting unit 14 raises the reset signal RST to a high level when a predetermined on-time Ton has elapsed since the rising edge of the set signal SET (and thus the on-time of the upper switch 11H). The on-time setting unit 14 may also have a function to arbitrarily set the on-time Ton. The on-time setting unit 14 may also have a function to vary the on-time Ton based on the terminal voltages of the PIN pin and the SNSN pin so as to suppress fluctuations in the switching frequency Fsw.

[0034] The slope signal generator 15 generates a slope signal Vslp containing information (AC component) of the inductor current IL from the sense voltage Vsns applied between the non-inverting input terminal (+) and the inverting input terminal (-). The slope signal Vslp increases as the inductor current IL increases, and decreases as the inductor current IL decreases.

[0035] The non-inverting input terminal (+) of the error amplifier 17 is connected to the SNSP pin via an input resistor R1P. The inverting input terminal (-) of the error amplifier 17 is connected to the SNSN pin via an input resistor R1N. A capacitor Cc is connected between the output terminal of the error amplifier 17 and the ground terminal. The error amplifier 17 connected in this manner outputs a current corresponding to the voltage between the SNSP pin and the SNSN pin (= the sense voltage Vsns generated across the sense resistor Rs), and generates the error signal Vc by charging and discharging the capacitor Cc.

[0036] The comparator 18 generates a set signal SET by comparing the slope signal Vslp input to its inverting input terminal (-) with the error signal Vc input to its non-inverting input terminal (+). The set signal SET goes low when Vc<Vslp and goes high when Vc>Vslp. Therefore, the lower the error signal Vc, the later the rise timing of the set signal SET (and therefore the turn-on timing of the upper switch 11H), and the higher the error signal Vc, the earlier the rise timing of the set signal SET.

[0037] The current setting unit 1X sets the input offset value of the error amplifier 17 (and thus the current setting value of the output current ILED) by passing a reference current through the input resistor R1P or R1N.

[0038] 5 is a diagram showing an example of a specific circuit configuration of the LED driver IC 1 according to the first embodiment. Note that components already described are assigned the same reference numerals as those in FIG. 4, and redundant explanations will be omitted. The following description will focus on new components and changes.

[0039] The LED driver IC1 of this configuration example integrates the previously mentioned slope signal generating unit 15, error amplifier 17, comparator 18, input resistors R1P and R1N, and capacitor Cc, as well as a current sense amplifier 16, and resistors R21, R22, and Ro.

[0040] In addition, in the LED driver IC1 of this configuration example, current limiting resistors RpP and RpN are connected between the first end (high potential end) of the sense resistor Rs and the SNSP pin, and between the second end (low potential end) of the sense resistor Rs and the SNSN pin, respectively.

[0041] The error amplifier 17 outputs a current corresponding to the difference between the analog dimming signal Vdcdim (corresponding to a predetermined current setting signal) input to its non-inverting input terminal (+) and the current detection signal VISET input to its inverting input terminal (-), and generates an error signal Vc by charging and discharging a capacitor Cc. Therefore, the error signal Vc rises when VISET<Vdcdim and falls when VISET>Vdcdim. A resistor ro is connected in parallel with the capacitor Cc between the output terminal and ground terminal of the error amplifier 17. The capacitor Cc is used for phase compensation. The resistor ro is the output impedance of the error amplifier 17 and does not exist as an actual element.

[0042] The slope signal generating unit 15 is a gm amplifier that receives a current supply from the PIN pin and can detect the sense voltage Vsns that appears between the SNSP and SNSN pins without drawing current from them. A resistor R22 is connected between the output terminal of the slope signal generating unit 15 and the ground terminal.

[0043] The current sense amplifier 16 receives power from the PIN pin and amplifies the sense voltage Vsns to generate the current detection signal VISET. The non-inverting input terminal (+) of the current sense amplifier 16 is connected to the SNSP pin via an input resistor R1P. The inverting input terminal (-) of the current sense amplifier 16 is connected to the SNSN pin via an input resistor R1N. The output terminal of the current sense amplifier 16 (= the terminal to which the current detection signal VISET is applied) is connected to the first terminal of a resistor R21 and also to the inverting input terminal (-) of the error amplifier 17. The second terminal of the resistor R21 is connected to ground.

[0044] The current sense amplifier 16 also includes a first feedback current path configured to pass a first feedback current i31 between its output terminal and its non-inverting input terminal (+), and a second feedback current path configured to pass a second feedback current i31' between its output terminal and the SNSN pin. The second feedback current i31' may be a copy (mirror current) of the first feedback current i31, or may be a copy of the first feedback current i31 with an offset.

[0045] With this configuration, even if current limiting resistors RpP and RpN are externally attached to the SNSP pin and the SNSN pin, respectively, it is possible to reduce the differential input current difference of the current sense amplifier 16 (and thus the gain error of the current sense amplifier 16), thereby eliminating the degradation of current detection accuracy (particularly temperature drift) in the LED driver IC1.

[0046] Furthermore, by attaching the external current limiting resistors RpP and RpN, the electrostatic protection diodes (not shown) built into the SNSP pin and the SNSN pin can be protected from surge currents. Therefore, external surge protection diodes are no longer necessary, which reduces the cost of the LED lamp module Z and also makes it possible to reduce the component mounting area on the board.

[0047] However, the LED driver IC1 of this configuration example requires two floating amplifiers (slope signal generator 15 and current sense amplifier 16) that can amplify the sense voltage Vsns rail-to-rail (between the power supply potential and the ground potential). Therefore, it should be noted that the circuit area becomes large. Note that "floating" in this specification means floating from the ground potential (potentially separated).

[0048] FIG. 6 is a diagram showing an example of signal transmission in the LED driver IC1 of the first embodiment (= a block diagram rewritten from FIG. 5 ). The symbol Gcs denotes the gain of the slope signal generating unit 15. The symbol Gsns denotes the gain of the current sense amplifier 16. The symbol gm denotes the transconductance of the error amplifier 17 (= the value converted from the amplifier input voltage to the amplifier output current). The symbol ΔVsns denotes the sense voltage Vsns. The symbol X denotes the current setting value (target value) of the output current ILED. The symbol ΔVc denotes the error signal Vc. The symbol ΔD denotes the off-duty of the lower switch 11L (control of the bottom value of the inductor current IL → control of the off-period). The symbol ro denotes the resistance value of the resistor ro (= the output impedance of the error amplifier 17). The symbol Cc denotes the capacitance value of the capacitor Cc. The symbol s denotes the complex number s (= jω).

[0049] As can be seen from this diagram, the signal transmission system in the LED driver IC1 of the first embodiment has a first-order characteristic with the inductor current IL (=average inductor current IL_ave+current ripple component ΔIL) as the control point.

[0050] 7 is a diagram showing an example of a control block in the LED driver IC1 of the first embodiment. The control block A in this diagram is a functional rewrite of the error amplifier 17 in FIG. 4, and includes a subtractor A1 and an amplifier A2.

[0051] The subtractor A1 subtracts the set current ISET from the current information of the inductor current IL (=average inductor current IL_ave+current ripple component ΔIL) to generate a current error signal. Note that in a balanced state of the output current ILED, the average inductor current IL_ave matches the set current ISET. Therefore, the current error signal output from the subtractor A1 corresponds to the current ripple component ΔIL of the inductor current IL.

[0052] The amplifier A2 generates a control voltage by integrating and amplifying the current error signal (=current ripple component ΔIL) output from the subtractor A1.

[0053] The comparator 18 compares the current information of the inductor current IL (=slope signal Vslp) with the control voltage (=error signal Vc).

[0054] FIG. 8 is a diagram showing how the error signal Vc in the LED driver IC1 of the first embodiment depends on the set current ISET.

[0055] In the LED driver IC1 of the first embodiment, a comparison control is performed between the bottom value of the inductor current IL (more precisely, the bottom value of the slope signal Vslp corresponding to the current information of the inductor current IL) and the error signal Vc so that the difference between the inductor current IL (more precisely, the average inductor current IL_ave) and the set current ISET becomes zero.

[0056] Here, when the set current ISET is increased, the error signal Vc increases following the set current ISET, and the bottom value of the inductor current IL also increases, resulting in the average inductor current IL_ave converging to the increased set current ISET.

[0057] As described above, in the LED driver IC1 of the first embodiment, the error signal Vc depends on the set current ISET, and therefore the upper limit value VcH of the error signal Vc (= the upper limit clamp value in the event of an LED open failure) must be set to a value higher than the maximum value of the error signal Vc (= the error signal Vc when the set current ISET is set to its maximum value).

[0058] 9 is a diagram showing an example of the lighting recovery operation in the LED driver IC1 of the first embodiment. The upper part of the diagram shows the behavior of the inductor current IL, and the lower part of the diagram shows the behavior of the slope signal Vslp and the error signal Vc.

[0059] When an open circuit fault occurs in the LED string 2, the inductor current IL stops flowing, and the sense voltage Vsns is not generated (output feedback control is not active). If the LED driver IC1 continues to operate in this state, the slope signal Vslp drops to low level (GND level), and the error signal Vc rises to the upper limit value VcH (outside the steady-state control range).

[0060] Thereafter, when the open fault location in the LED string 2 is bypassed by, for example, the matrix manager 3 (FIG. 1) described above, the inductor current IL starts to flow again, and the LED string 2 returns to the lit state.

[0061] However, when the LED returns to normal operation after the open circuit fault, the error signal Vc is stuck at the upper limit VcH, which is higher than the normal operating point (i.e., the signal level according to the set current ISET). Therefore, an excessive inductor current IL (so-called overcurrent) is generated until the error signal Vc returns from the upper limit VcH to the normal operating point.

[0062] One possible measure to prevent such an overcurrent from occurring is to shut down the LED driver IC1 once when an LED open fault is detected and then restart it (see FIG. 3 above). However, with this measure, a considerable amount of time is required to restore the illumination of the LED string 2 due to the startup delay of the LED driver IC1. Therefore, it is difficult to satisfy the market demand for immediate restoration of the illumination of the LED string 2.

[0063] FIG. 10 is a diagram showing the responsiveness of the output current ILED in the LED driver IC1 of the first embodiment, depicting, from top to bottom, the error signal Vc, the inductor current IL, and the set current ISET.

[0064] As mentioned above, in the LED driver IC1 of the first embodiment, the error signal Vc depends on the set current ISET. Referring to this figure, as the set current ISET increases, the error signal Vc first rises, and the inductor current IL follows suit, converging to the target value. The time T1 required for the inductor current IL to converge to the target value is approximately several hundred μs.

[0065] As described above, in the LED driver IC1 of the first embodiment, the response of the inductor current IL (and therefore the output current ILED) to the set current ISET is poor.

[0066] <Second Embodiment> Fig. 11 is a diagram showing a second embodiment of an LED lamp module Z. The LED lamp module Z of this embodiment is based on the first embodiment (Figs. 4 and 5) described above, but has been modified in the internal configuration (particularly the output feedback system) of the LED driver IC 1. Therefore, the same reference numerals as in Fig. 4 are used for the components already described, and redundant explanations will be omitted, with the focus being placed on new components and changes.

[0067] 5, the current sense amplifier 16 generates a current detection signal Vcso (corresponding to the current detection signal VISET in FIG. 5) corresponding to the difference between a sense voltage Vsns corresponding to the inductor current IL (and therefore the output current ILED) and a predetermined current setting signal (for example, an offset voltage corresponding to the set current ISET). Note that a resistor R21 connected to the output terminal of the current sense amplifier 16 is connected between the output terminal of the current sense amplifier 16 and the application terminal of the reference voltage Vref.

[0068] Furthermore, in the LED driver IC1 of this embodiment, the aforementioned slope signal generating unit 15 is removed, and a current detection signal Vcso is output from the output terminal of the current sense amplifier 16 to the inverting input terminals (−) of the error amplifier 17 and the comparator 18.

[0069] The error amplifier 17 outputs an error signal Vc corresponding to the difference between the current detection signal Vcso input to its inverting input terminal (-) and the reference voltage Vref input to its non-inverting input terminal (+). In other words, the error amplifier 17 generates the error signal Vc so that the DC component of the current detection signal Vcso becomes zero.

[0070] The comparator 18 generates a set signal SET by comparing the current detection signal Vcso input to its inverting input terminal (-) with the error signal Vc input to its non-inverting input terminal (+). The set signal SET is at a low level when Vc<Vcso and at a high level when Vc>Vsco. Therefore, the lower the error signal Vc, the later the rise timing of the set signal SET (and therefore the on timing of the upper switch 11H), and the higher the error signal Vc, the earlier the rise timing of the set signal SET.

[0071] The driver 11 turns on the upper switch 11H and turns off the lower switch 11L at the rising timing of the set signal SET, and turns off the upper switch 11H and turns on the lower switch 11L at the rising timing of the reset signal RST.

[0072] That is, when the current detection signal Vcso drops to the error signal Vc, the driver 11 turns on the upper switch 11H and turns off the lower switch 11L, and when a predetermined on-time Ton has elapsed since the on-timing of the upper switch 11H, the driver 11 turns off the upper switch 11H and turns on the lower switch 11L.

[0073] In this way, the driver 11 turns on / off the upper switch 11H and the lower switch 11L complementarily in response to the set signal SET and the reset signal RST, thereby performing feedback control of the inductor current IL (and therefore the output current ILED) using a bottom detection type fixed on-time method so that the output current ILED matches a predetermined current setting value (target value).

[0074] The LED driver IC1 of this embodiment further includes a clamper 1Y that limits the error signal Vc to a predetermined upper limit value VcH or less. The clamper 1Y may be an operational amplifier having a non-inverting input terminal (+) to which the upper limit value VcH of the error signal Vc is applied, and an inverting input terminal (-) and an output terminal connected to the terminal to which the error signal Vc is applied.

[0075] Fig. 12 is a diagram showing an example of a specific circuit configuration of the LED driver IC1 in the second embodiment. Note that components already described are assigned the same reference numerals as in Fig. 11, and redundant explanations will be omitted. The following description will focus on new components and changes.

[0076] In the LED driver IC1 of this configuration example, in addition to the previously mentioned current sense amplifier 16, error amplifier 17, comparator 18, input resistors R1P and R1N, and capacitor Cc, a bias amplifier 1A, a VI converter 1B, transistors P1a and P1b (for example, PMOSFETs [P-channel type MOSFETs]), resistors R31a, R31b, R32a, R32b, R33, R34a, R34b, and Ro are integrated.

[0077] In addition, in the LED driver IC1 of this configuration example, current limiting resistors RpP and RpN are connected between the first end (high potential end) of the sense resistor Rs and the SNSP pin, and between the second end (low potential end) of the sense resistor Rs and the SNSN pin, respectively, as in the case of FIG.

[0078] The VI converter 1B is a functional block that converts a voltage signal (=analog dimming signal Vdcdim) into a current signal (=first reference current i41 and second reference current i41').

[0079] As shown in the figure, in the LED driver IC1 of this embodiment, a first reference current i41 needs to flow through the VI converter 1B to generate the reference voltage (=scaled analog dimming signal Vdcdim×R1P / R33) for the current sense amplifier 16. Therefore, the LED driver IC1 of this embodiment includes a first reference current path configured to flow the first reference current i41 between the SNSP pin and the first output terminal of the VI converter 1B.

[0080] However, in a configuration in which the first reference current i41 flows only through the current-limiting resistor RpP externally attached to the SNSP pin, the reference voltage of the current sense amplifier 16 will deviate by the voltage across the current-limiting resistor RpP. Therefore, the LED driver IC1 of this embodiment includes a second reference current path configured to pass a second reference current i41' between the SNSN pin and the second output terminal of the VI converter 1B. The first reference current i41 and the second reference current i41' may have the same value, or an arbitrary offset may be applied between them.

[0081] In this manner, with the configuration in which the first reference current i41 required to generate the reference voltage of the current sense amplifier 16 is corrected by the second reference current i41′, even if current limiting resistors RpP and RpN are externally attached to the SNSP pin and the SNSN pin, respectively, the gain of the VI converter 1B (and therefore the reference voltage of the current sense amplifier 16) is uniquely determined according to the ratio between the input resistor R1P and the resistor R33, making it possible to eliminate degradation in current detection accuracy (particularly temperature drift) in the LED driver IC1.

[0082] The current sense amplifier 16 amplifies the sense voltage Vsns to generate a differential current detection signal ΔVcso (=VcsoP-VcsoN). The non-inverting input terminal (+) of the current sense amplifier 16 is connected to the SNSP pin via an input resistor R1P. The inverting input terminal (-) of the current sense amplifier 16 is connected to the SNSN pin via an input resistor R1N. The first differential output terminal of the current sense amplifier 16 is connected to the first terminal of a resistor R31a and also to the inverting input terminal (-) of an error amplifier 17. The second differential output terminal of the current sense amplifier 16 is connected to the first terminal of a resistor R31b and also to the non-inverting input terminal (+) of the error amplifier 17. The second terminals of the resistors R31a and R31b are both connected to ground. Resistors R32a and R32b are connected in series between the non-inverting input terminal (+) and the inverting input terminal (-) of the current sense amplifier 16, and the drive voltage of the current sense amplifier 16 is supplied from the connection node between them.

[0083] The error amplifier 17 outputs a current corresponding to a current detection signal ΔVcso differentially input between the non-inverting input terminal (+) and the inverting input terminal (-), and generates an error signal Vc by charging and discharging a capacitor Cc. A resistor ro is connected in parallel with the capacitor Cc between the output terminal and the ground terminal of the error amplifier 17. The capacitor Cc is used for phase compensation. The resistor ro is the output impedance of the error amplifier 17 and does not exist as an actual element.

[0084] The gate of the transistor P1a is connected to the first differential output terminal of the current sense amplifier 16. The drain of the transistor P1a is connected to the ground terminal. The source of the transistor P1a is connected to the first terminal of the resistor R34a. The second terminal of the resistor R34a is connected to the inverting input terminal (-) of the comparator 18. The transistor P1a connected in this manner functions as a first voltage follower (first source follower) connected between the first differential output terminal of the current sense amplifier 16 and the inverting input terminal (-) of the comparator 18.

[0085] The gate of the transistor P1b is connected to the second differential output terminal of the current sense amplifier 16. The drain of the transistor P1b is connected to the ground terminal. The source of the transistor P1b is connected to the first terminal of the resistor R34b. The second terminal of the resistor R34b is connected to the non-inverting input terminal (+) of the comparator 18. The transistor P1b connected in this manner functions as a second voltage follower (second source follower) connected between the second differential output terminal of the current sense amplifier 16 and the non-inverting input terminal (+) of the comparator 18.

[0086] The bias amplifier 1A determines the operating points of the first voltage follower and the second voltage follower by outputting differential currents to the resistors R34a and R34b, respectively, according to the difference between the error signal Vc input to the non-inverting input terminal (+) and the bias voltage Vbias input to the inverting input terminal (-).

[0087] Referring to this figure, the inverting input terminal (-) of the comparator 18 receives a subtraction signal (=VcsoP+Vgs(P1a)-(Vc-Vbias)) obtained by subtracting the error signal Vc from the output signal (=VcsoP+Vgs(P1a)) of the first voltage follower.

[0088] On the other hand, the non-inverting input terminal (+) of the comparator 18 receives an addition signal (=VcsoN+Vgs(P1b)+(Vc-Vbias)) obtained by adding the error signal Vc to the output signal (=VcsoN+Vgs(P1b)) of the second voltage follower.

[0089] Therefore, in the comparator 18, when (VcsoP-Vc)-(VcsoN+Vc)>0, that is, when ΔVcso-2Vc>0, the logical level of the set signal SET is switched. To further explain, the bottom value of the inductor current IL is detected at the point where the current information ΔVcso reaches the control voltage Vc.

[0090] If the difference between the inductor current IL and its target value is sensed, the differential input difference of the current sense amplifier 16 becomes zero (the DC error is zero), and no current difference occurs between the SNSP pin and the SNSN pin. As a result, there is no need to supply power to the current sense amplifier 16 from the PIN pin, and a Δ zero bias current can be achieved. Furthermore, the slope signal generator 15 can be integrated into the current sense amplifier 16, allowing for a smaller circuit size.

[0091] FIG. 13 is a diagram showing an example of signal transmission in the LED driver IC1 of the second embodiment (= a block diagram redrawn from the aforementioned FIG. 12). The symbol Gsns denotes the gain of the current sense amplifier 16. The symbol gm denotes the transconductance of the error amplifier 17 (= the value converted from the amplifier input voltage to the amplifier output current). The symbol ΔVsns denotes the sense voltage Vsns. The symbol X denotes the current setting value (target value) of the output current ILED. The symbol ΔVc denotes the error signal Vc. The symbol ΔD denotes the off-duty of the lower switch 11L (control of the bottom value of the inductor current IL → control of the off-interval). The symbol ro denotes the resistance value of the resistor ro (= the output impedance of the error amplifier 17). The symbol Cc denotes the capacitance value of the capacitor Cc. The symbol s denotes the complex number s (= jω).

[0092] As can be seen from this diagram, the signal transmission system in the LED driver IC1 of the second embodiment is a system in which only the current ripple component ΔIL of the inductor current IL is a control point. Furthermore, in this signal transmission system, a high-speed path can be generated for the current error component (= the difference between the output current ILED and the current setting value).

[0093] Fig. 14 is a diagram showing an example of a control block in the LED driver IC1 of the second embodiment. The control block B in this figure is a functional rewrite of the current sense amplifier 16 and the error amplifier 17 in Fig. 12, and includes a subtractor B1 and an amplifier B2.

[0094] The subtractor B1 subtracts the set current ISET from the current information of the inductor current IL (=average inductor current IL_ave+current ripple component ΔIL) to generate a current error signal. Note that in a balanced state of the output current ILED, the average inductor current IL_ave matches the set current ISET. Therefore, the current error signal output from the subtractor A1 corresponds to the current ripple component ΔIL of the inductor current IL.

[0095] The amplifier B2 generates a control voltage by integrating and amplifying the current error signal (=current ripple component ΔIL) output from the subtractor B1.

[0096] Up to this point, the present embodiment is the same as the first embodiment (FIG. 7), except that the comparator 18 compares the current ripple component ΔIL of the inductor current IL with the control voltage (=error signal Vc).

[0097] FIG. 15 is a diagram showing how the error signal Vc in the LED driver IC1 of the second embodiment does not depend on the set current ISET.

[0098] In the LED driver IC1 of the second embodiment, the DC component of the current error signal (= current detection signal Vcso) becomes zero through feedback control, that is, the current detection signal Vcso fluctuates based on a fixed operating point, and so a comparison control is performed between the bottom value of the current detection signal Vcso and the error signal Vc.

[0099] Therefore, even if the set current ISET is increased, the error signal Vc does not increase in response to the set current ISET. In other words, in the LED driver IC1 of the second embodiment, the error signal Vc does not depend on the set current ISET. As a result, it is possible to set the upper limit value VcH of the error signal Vc (= the upper limit clamp value in the event of an LED open fault) to a value lower than that of the first embodiment (= a value close to the normal operating point).

[0100] 16 is a diagram showing an example of the lighting recovery operation in the LED driver IC1 of the second embodiment. The upper part of the diagram shows the behavior of the inductor current IL, and the lower part of the diagram shows the behavior of the current detection signal Vcso and the error signal Vc.

[0101] When an open circuit fault occurs in the LED string 2, the inductor current IL stops flowing, and the sense voltage Vsns is not generated (output feedback control is not active). If the LED driver IC1 continues to operate in this state, the current detection signal Vcso drops to low level (GND level), and the error signal Vc rises to the upper limit value VcH.

[0102] Thereafter, when the open fault location in the LED string 2 is bypassed by, for example, the matrix manager 3 (FIG. 1) described above, the inductor current IL starts to flow again, and the LED string 2 returns to the lit state.

[0103] Note that when the LED returns to normal operation after an open LED fault, the error signal Vc remains at the upper limit VcH. However, in the LED driver IC1 of the second embodiment, the upper limit VcH of the error signal Vc (= the upper limit clamp value during an open LED fault) can be set to a lower value (= a value close to the normal operating point) than in the first embodiment. This allows the error signal Vc to quickly return to the normal operating point, significantly reducing the occurrence of excessive inductor current IL (so-called overcurrent).

[0104] Therefore, since there is no need to shut down the LED driver IC1 as a measure to prevent overcurrent, the operation to restore lighting from an LED open fault can be performed quickly and safely.

[0105] FIG. 17 is a diagram showing the responsiveness of the output current ILED in the LED driver IC1 of the second embodiment, depicting, from top to bottom, the error signal Vc, the inductor current IL, and the set current ISET.

[0106] As mentioned above, in the LED driver IC1 of the second embodiment, the error signal Vc does not depend on the set current ISET. Therefore, even if the set current ISET is increased, the error signal Vc does not change, and the inductor current IL converges to the target value without delay. Note that the time T2 required for the inductor current IL to converge to the target value is only a few microseconds.

[0107] In this way, the LED driver IC1 of the second embodiment can not only quickly and safely restore illumination in the event of an LED open fault, but also significantly improve the responsiveness of the inductor current IL (and therefore the output current ILED) to the set current ISET.

[0108] <Summary> The various embodiments described above will be summarized below.

[0109] For example, the light-emitting element driving device disclosed in this specification is configured (first configuration) to include a current sense amplifier configured to generate a current detection signal corresponding to the difference between a sense voltage corresponding to the output current supplied to the light-emitting element and a predetermined current setting signal, an error amplifier configured to generate an error signal so that the DC component of the current detection signal becomes zero, a comparator configured to compare the current detection signal with the error signal to generate a set signal, and a driver configured to perform feedback control of the output current in accordance with the set signal.

[0110] The light emitting element driving device according to the first configuration may be configured (second configuration) further comprising a clamper configured to limit the error signal to a predetermined upper limit value or less.

[0111] In the light-emitting element driving device according to the first or second configuration, the first differential output terminal and the second differential output terminal of the current sense amplifier may be connected to the inverting input terminal and the non-inverting input terminal of the error amplifier, respectively (third configuration).

[0112] The light-emitting element driving device according to the third configuration may further include a first voltage follower configured to be connected between the first differential output terminal of the current sense amplifier and the inverting input terminal of the comparator, and a second voltage follower configured to be connected between the second differential output terminal of the current sense amplifier and the non-inverting input terminal of the comparator, and the error signal may be subtracted from the output signal of the first voltage follower and added to the output signal of the second voltage follower (fourth configuration).

[0113] In the light emitting element driving device according to any one of the first to fourth configurations, the driver may be configured as a half-bridge type including an upper switch and a lower switch (fifth configuration).

[0114] In the light-emitting element driving device according to the fifth configuration, the driver may be configured (sixth configuration) to turn on the upper switch and turn off the lower switch when the current detection signal drops to the error signal, and to turn off the upper switch and turn on the lower switch when a predetermined on-time has elapsed since the on-timing of the upper switch.

[0115] The light-emitting element driving device according to the sixth configuration may further include an on-time setting unit configured to generate a pulse in the reset signal at a point when the on-time has elapsed since a pulse was generated in the set signal, and the driver may be configured (seventh configuration) to perform feedback control of the output current using a bottom-detection type fixed on-time method in accordance with the set signal and the reset signal.

[0116] Furthermore, for example, the light emitting control device disclosed in this specification is configured (eighth configuration) to include a light emitting element driving device having any of the first to seventh configurations described above, an inductor and a capacitor configured to form a switch output stage together with a switch element included in the driver, and a sense resistor configured to convert the inductor current flowing through the inductor into the sense voltage.

[0117] Furthermore, for example, the light emitting device disclosed in this specification is configured (ninth configuration) to include a light emitting control device having the eighth configuration described above and a light emitting element configured to receive the output current from the light emitting control device.

[0118] The light emitting device according to the ninth configuration may be configured (tenth configuration) further including a switch control device configured to arbitrarily switch the number of series stages of the light emitting elements.

[0119] <Other Modifications> In addition to the above-described embodiments, the various technical features disclosed in this specification can be modified in various ways without departing from the spirit of the technical creation. In other words, the above-described embodiments should be considered to be illustrative and not restrictive in all respects, and the technical scope of the present invention is defined by the claims, and should be understood to include all modifications that fall within the meaning and scope equivalent to the claims.

[0120] 1 LED driver IC (light emitting element driving device) 10 LCU (light emitting control device) 2 LED string (light emitting element) 3 Matrix manager (switch control device) 11 Driver 11H Upper switch (NMOSFET) 11L Lower switch (NMOSFET) 14 On time setting unit 15 Slope signal generating unit 16 Current sense amplifier 17 Error amplifier 18 Comparator 1X Current setting unit 1Y Clamper 1A Bias amplifier 1B V-I converter A, B Control block A1, B1 Subtractor A2, B2 Amplifier Cc, Co Capacitor L1 Inductor P1a, P1b Transistor (PMOSFET) R1P, R1N Input resistor R21, R22, R31a, R31b, R32a, R32b, R33, R34a, R34b, ro Resistor RpP, RpN Current limiting resistor Rs Sense resistor SW Switch element Z LED lamp module (light emitting device)

Claims

1. a current sense amplifier configured to generate a current detection signal corresponding to a difference between a sense voltage corresponding to an output current supplied to a light emitting element and a predetermined current setting signal; an error amplifier configured to generate an error signal such that a DC component of the current detection signal has a zero value; a comparator configured to compare the current sense signal with the error signal to generate a set signal; a driver configured to perform feedback control of the output current in response to the set signal; A light-emitting element driving device comprising:

2. 2. The light emitting element driving device according to claim 1, further comprising a clamper configured to limit the error signal to a predetermined upper limit value or less.

3. 2 . The light-emitting element driving device according to claim 1 , wherein a first differential output terminal and a second differential output terminal of the current sense amplifier are respectively connected to an inverting input terminal and a non-inverting input terminal of the error amplifier.

4. a first voltage follower configured to be connected between the first differential output terminal of the current sense amplifier and the inverting input terminal of the comparator; a second voltage follower configured to be connected between the second differential output of the current sense amplifier and the non-inverting input of the comparator; Further equipped with 4. The light-emitting element driving device according to claim 3, wherein the error signal is subtracted from the output signal of the first voltage follower and added to the output signal of the second voltage follower.

5. 2. The light-emitting element driving device according to claim 1, wherein the driver is of a half-bridge type including an upper switch and a lower switch.

6. 6. The light-emitting element driving device of claim 5, wherein the driver turns on the upper switch and turns off the lower switch when the current detection signal drops to the error signal, and turns off the upper switch and turns on the lower switch when a predetermined on-time has elapsed since the on-timing of the upper switch.

7. an on-time setting unit configured to generate a pulse in a reset signal at a time when the on-time has elapsed since a pulse was generated in the set signal; 7. The light-emitting element driving device according to claim 6, wherein the driver performs feedback control of the output current by a bottom detection type fixed on-time method in response to the set signal and the reset signal.

8. A light emitting element driving device according to any one of claims 1 to 7, an inductor and a capacitor configured to form a switched output stage with a switch element included in the driver; a sense resistor configured to convert an inductor current flowing through the inductor to the sense voltage; A light emission control device comprising:

9. A light emission control device according to claim 8 , A light-emitting element configured to receive the output current from the light-emitting control device; A light emitting device comprising:

10. The light emitting device according to claim 9 , further comprising a switch control device configured to arbitrarily switch the number of series stages of the light emitting devices.