Semiconductor integrated circuit for driving light emitting element, light emitting element driving device, light emitting device, and vehicle

Abstract

This semiconductor integrated circuit for driving a light emitting element constitutes at least a part of a light emitting element driving device configured to change the number of lights of a plurality of light emitting elements connected in series. The semiconductor integrated circuit for driving a light emitting element has a variable resistance control unit configured to increase a resistance value of a variable resistor connected in series to the plurality of light emitting elements immediately before and at the same time as a timing when the number of lights is reduced.

Description

[Technical Field]

[0001] The invention disclosed in this specification relates to a semiconductor integrated circuit for driving a light-emitting element, and also to a light-emitting element driving device, and a light-emitting device and a vehicle using the same. [Background technology]

[0002] Automobile headlamps are configured to be able to switch between a state in which they function as passing headlamps that emit low beams, and a state in which they function as driving headlamps that emit high beams that can reach further ahead than low beams.

[0003] An example of a light-emitting device used as an automobile headlamp is disclosed in Patent Document 1. The light-emitting device (LED lighting circuit) disclosed in Patent Document 1 has a plurality of light-emitting elements connected in series, and is configured so that when the light-emitting device is used as a driving headlamp, all of the light-emitting elements are turned on, and when the light-emitting device is used as a passing headlamp, some of the light-emitting elements are short-circuited and only the remaining light-emitting elements are turned on. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-47047 A (paragraphs 0029 to 0033) Summary of the Invention [Problem to be solved by the invention]

[0005] In the light-emitting device (LED lighting circuit) disclosed in Patent Document 1, when switching from a driving headlight to a passing headlight, the output voltage of the DC-DC converter that drives the light-emitting element drops. This drop in output voltage causes the charge stored in the output capacitor of the DC-DC converter to be released from the output capacitor, causing the output current of the DC-DC converter to temporarily become an overcurrent, which in turn causes a temporary overcurrent to flow through the LEDs that are not short-circuited. In other words, when switching from a driving headlight to a passing headlight, the LEDs that are not short-circuited are damaged.

[0006] In Patent Document 1, when switching from a driving headlight to a passing headlight, the LED is short-circuited in two stages, thereby reducing the output voltage of the DC-DC converter described above in two stages and reducing the overcurrent.

[0007] However, the light-emitting device (LED lighting circuit) disclosed in Patent Document 1 only reduces the degree of overcurrent and does not fundamentally solve the problem of overcurrent. Therefore, the value of the predetermined output voltage Va obtained by the first-stage output voltage reduction and the value of the maintenance time t1 for maintaining the predetermined output voltage Va must be experimentally optimized through a trial-and-error process to ensure that the overcurrent is reduced to the desired value. Because the optimal values of Va and t1 change depending on changes in LED specifications or individual variations in LEDs, it was difficult to guarantee that the light-emitting device (LED lighting circuit) disclosed in Patent Document 1 would reduce the overcurrent to the desired value.

[0008] In addition to the switching from high beam to low beam described above, when controlling vehicle lamps, for example, by controlling the sequential lighting of multiple light-emitting elements, the sequential lighting of multiple light-emitting elements, the animation lighting of multiple light-emitting elements arranged in a matrix, or the lighting of multiple light-emitting elements in ADB (Adaptive Driving Beam), there is a risk that the number of lit light-emitting elements will decrease and a large current will flow through the light-emitting elements. [Means for solving the problem]

[0009] The semiconductor integrated circuit for driving a light-emitting element disclosed in this specification constitutes at least a part of a light-emitting element driving device configured to vary the number of lit light-emitting elements among a plurality of light-emitting elements connected in series, and the semiconductor integrated circuit for driving a light-emitting element has a variable resistance control unit configured to increase the resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with the timing to reduce the number of lit light-emitting elements.

[0010] The light-emitting element driving device disclosed in this specification includes a variable unit configured to vary the number of lit light-emitting elements among a plurality of light-emitting elements connected in series, and a variable resistance control unit configured to increase the resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with the timing for reducing the number of lit light-emitting elements.

[0011] The light emitting device disclosed in this specification includes the light emitting element driving device configured as described above and the plurality of light emitting elements.

[0012] The vehicle disclosed in this specification has a light emitting device having the above-described configuration. [Effects of the Invention]

[0013] The semiconductor integrated circuit for driving a light-emitting element, the light-emitting element driving device, the light-emitting device, and the vehicle disclosed in this specification can prevent a large current from flowing through the light-emitting element when the number of lit light-emitting elements is reduced. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a light emitting device. [Figure 2] FIG. 2 is a time chart showing waveforms of the output voltage of the DC / DC converter, the voltage applied to the light-emitting diode, and the LED current. [Figure 3]FIG. 3 is a time chart showing waveforms of the output voltage of the DC / DC converter, the voltage applied to the light-emitting diode, and the LED current when a discharge circuit and a clamp element are not provided. [Figure 4] FIG. 4 is a time chart showing the state of the light-emitting diode. [Figure 5] FIG. 5 is a diagram illustrating an example of the configuration of an LED switch circuit. [Figure 6] FIG. 6 is an external view (front) of a vehicle on which a light emitting device is mounted. [Figure 7] FIG. 7 is an external view (rear view) of a vehicle on which a light emitting device is mounted. [Figure 8] FIG. 8 is an external view of the LED headlight module. [Figure 9] FIG. 9 is an external view of the LED turn lamp module. [Figure 10] FIG. 10 is an external view of the LED rear lamp module. [Figure 11] FIG. 11 is a diagram showing a modified example of the light emitting device. DETAILED DESCRIPTION OF THE INVENTION

[0015] In this specification, a MOS field effect transistor refers to a field effect transistor whose gate structure is composed of at least three layers: a layer made of a conductor or a semiconductor such as polysilicon with a low resistance, an insulating layer, and a P-type, N-type, or intrinsic semiconductor layer. In other words, the gate structure of a MOS field effect transistor is not limited to a three-layer structure of metal, oxide, and semiconductor.

[0016] <Light-emitting device> Fig. 1 is a diagram showing an example of the configuration of a light-emitting device. The light-emitting device shown in Fig. 1 has a light-emitting element driving IC 100. The light-emitting device shown in Fig. 1 has light-emitting diodes Z0 to Z7 which are light-emitting elements, and a light-emitting element driving device that drives the light-emitting elements. The light-emitting element driving device has the light-emitting element driving IC 100.

[0017] The light emitting device shown in FIG. 1 includes a coil L1, an N-channel MOS field effect transistor (hereinafter referred to as an NMOS transistor) M1 which is a switching element, a Schottky barrier diode D1, and an output capacitor C1.

[0018] The coil L1, the NMOS transistor M1, the Schottky barrier diode D1, and the output capacitor C1 constitute a step-up / step-down DC / DC converter. IN DC output voltage V OUT Convert to.

[0019] The light emitting device shown in FIG. 1 includes sense resistors R1 and R2, a P-channel MOS field effect transistor (hereinafter referred to as a PMOS transistor) M2 which is a variable resistor, light emitting diodes Z0 to Z7, a diode D2, capacitors C2 to C4, and resistors R3 and R4.

[0020] The light-emitting element driving IC 100 is a semiconductor integrated circuit device (so-called LED driver IC) that integrates a constant voltage circuit 1, a communication interface 2, a control logic circuit 3, an LED (Light Emitting Diode) switch circuit 4, operational amplifiers 5 and 6, an adder 7, an error amplifier 8, an oscillator 9, a slope circuit 10, a comparator 11, a boost drive circuit 12, an operational amplifier 13, an adder 14, a discharge circuit 15, a clamp element 16, and diodes D3 and D4. The light-emitting element driving IC 100 also has terminals VIN, GL, PGND, IS, SNSP, SNSN, PGATE, BOOT, PSW, CH8-CH0, TX, RX, COMP, and RT for establishing electrical connection with the outside.

[0021] Input voltage V INis connected to the terminal VIN, one end of the coil L1, one end of the output capacitor C1, and the cathode of the diode D2. The other end of the coil L1 is connected to the drain of the NMOS transistor M1 and the anode of the Schottky barrier diode D1. The source of the NMOS transistor M1 is connected to one end of the sense resistor R1 and the terminal IS. The other end of the sense resistor R1 is connected to the ground potential and the terminal PGND. The gate of the NMOS transistor M1 is connected to the terminal GL. A square wave switch voltage V SW The switch voltage V SW is supplied to one end of a capacitor C2, the other end of which is connected to the terminal BOOT.

[0022] The cathode of the Schottky barrier diode D1 is connected to the other end of the output capacitor C1, one end of the sense resistor R2, the terminal SNSP, and the terminal OUT. The other end of the output capacitor C1 is connected to the output voltage V OUT occurs. The output voltage V OUT is the switch voltage V SW The output voltage V OUT is supplied to one end of a capacitor C3, the other end of which is connected to a terminal PSW.

[0023] The other end of the sense resistor R2 is connected to the source of the PMOS transistor M2 and the terminal SNSN. The gate of the PMOS transistor M2 is connected to the terminal PGATE. The drain of the PMOS transistor M2 is connected to the terminal CH8. The LED drive current I LED flows through the sense resistor R2 and the PMOS transistor M2 and is supplied to the light-emitting diodes that are to be lit among the light-emitting diodes Z0 to Z8.

[0024] The anode of light-emitting diode Zm is connected to terminal CH(m+1), and the cathode of light-emitting diode Zm is connected to terminal CHm, where m is an integer between 0 and 7. In addition, the anode of diode D2 is connected to terminal CH0. If terminal CH0 is shorted to ground, terminals VIN and GND are shorted, and a large current flows from terminal VIN. If at least one of terminals CH1 to CH7 is shorted to ground, diode D2 prevents current from flowing via the parasitic diode of the switch in LED switch circuit 4. Diode D2 can be, for example, a Schottky barrier diode.

[0025] One end of the clock frequency setting resistor R3 is connected to the terminal RT, and the other end of the resistor R3 is connected to the ground potential.

[0026] One end of the resistor R4 is connected to the terminal COMP, and the other end of the resistor R4 is connected to the ground potential via a phase compensation capacitor C4.

[0027] The constant voltage circuit 1 regulates the input voltage V supplied to the VIN terminal. IN Using a constant voltage V REG and supplies it to each part of the light-emitting element driving IC 100.

[0028] The communication interface 2 receives a signal input from the outside to a terminal RX, and transmits a signal output from the control logic circuit 3 to the outside via a terminal TX. An example of the communication interface is a UART (Universal Asynchronous Receiver / Transmitter) interface. An example of the signal received by the communication interface 2 is an instruction signal that instructs the lighting state of the light-emitting diodes Z0 to Z7. An example of the signal transmitted by the communication interface 2 is an abnormality notification signal that notifies the occurrence of an abnormality.

[0029] The control logic circuit 3 controls the LED switch circuit 4 based on the signal received by the communication interface 2. The control logic circuit 3 also controls the LED switch circuit 4 based on the input voltage V IN The partial pressure V obtained by dividing DIV and the value of the second voltage V2 corresponding to the target current are set. By changing the value of the second voltage V2, so-called DC dimming is performed.

[0030] The LED switch circuit 4 selects light-emitting diodes to be lit from among the light-emitting diodes Z0 to Z7 under the control of the control logic circuit 3. In other words, the control logic circuit 3 and the LED switch circuit 4 vary the number of light-emitting diodes Z0 to Z7 to be lit. The LED switch circuit 4 turns off the switch connected in parallel to the light-emitting diode to be lit, and turns on the switch connected in parallel to the light-emitting diode to be extinguished. The LED switch circuit 4 uses the voltage supplied to the terminal PSW as a power supply voltage. The cathode of the diode D4 is connected to the terminal PSW, the anode of the diode D4 and the cathode of the diode D3 are connected to the terminal BOOT, and a constant voltage V REG is supplied.

[0031] Op-amp 5 is the voltage divider V DIV and the second voltage V2, whichever is smaller. DIV When the input voltage V becomes smaller than the second voltage V2, IN As the LED current I LED The output voltage of the operational amplifier 5 is supplied to the inverting input terminal of the error amplifier 8.

[0032] The non-inverting input terminal of the operational amplifier 6 is connected to the terminal SNSP, and the inverting input terminal of the operational amplifier 6 is connected to the terminal SNSN. The operational amplifier 6 outputs a voltage according to the voltage across the sense resistor R2.

[0033] The output voltage of the operational amplifier 6 is offset by an adder 7 so as to increase it by 0.166 V. The first voltage V1 generated by the adder 7 is supplied to the non-inverting input terminal of the error amplifier 8 and the non-inverting input terminal of the operational amplifier 13. The first voltage V1 is the output current of the DC / DC converter, i.e., the LED current I LED The voltage is based on

[0034] The error amplifier 8 generates an error voltage V according to the difference between the first voltage V1 and the output voltage of the operational amplifier 5. ERR Generate.

[0035] An oscillator 9 generates a clock signal CK. The clock frequency of the clock signal CK is determined by the resistance value of a resistor R3 connected to a terminal RT. The clock signal CK is supplied to a slope circuit 10 and a boost driver circuit 12.

[0036] The slope circuit 10 generates a triangular or sawtooth waveform slope voltage V using a clock signal CK. SLP Generates a slope voltage V SLP The slope of varies depending on the voltage supplied to the terminal IS, that is, the source voltage of the NMOS transistor M1.

[0037] Comparator 11 detects the error voltage V ERR and slope voltage V SLP The comparison result is supplied to the boost driver circuit 12.

[0038] The boost driver circuit 12 generates a gate signal for the NMOS transistor M1 based on the clock signal CK and the output of the comparator 11, and supplies the gate signal to the gate of the NMOS transistor M1 via the terminal GL.

[0039] With the above circuit configuration, the voltage divider V DIV is not smaller than the second voltage V2, the DC / DC converter LED is feedback controlled so that it approaches the target current.

[0040] The operational amplifier 13 increases the resistance value of the PMOS transistor M2 connected in series to the light-emitting diodes Z0 to Z7 just before the timing to decrease the number of lit light-emitting diodes Z0 to Z7 in accordance with an instruction from the control logic circuit 3. The operational amplifier 13 increases the resistance value of the PMOS transistor M2 connected in series to the light-emitting diodes Z0 to Z7 just before the timing to decrease the number of lit light-emitting diodes Z0 to Z7. OUT is used as the power supply voltage.

[0041] The control logic circuit 3 knows in advance how to control the lighting states of the light-emitting diodes Z0 to Z7, and can therefore instruct the operational amplifier 13 to increase the resistance value of the PMOS transistor M2 just before the timing to reduce the number of lit light-emitting diodes Z0 to Z7.

[0042] As the resistance value of the PMOS transistor M2 increases, the LED current I LED It is possible to suppress the increase of

[0043] The light-emitting element driver IC100 controls the LED current I LED and increases the resistance of the PMOS transistor M2 based on the detection result. LED Therefore, the light-emitting element driving IC 100 increases the resistance value of the PMOS transistor M2 before the LED current I LED In other words, the light-emitting element driving IC 100 can increase the resistance value of the PMOS transistor M2 more quickly than a configuration in which an increase in the LED current I LED and increases the resistance of the PMOS transistor M2 based on the detection result. LED This can more effectively suppress the increase in

[0044] Figure 2 shows the output voltage V of the DC / DC converter. OUT , the voltage V applied to the light-emitting diode Z7 CH8 , and LED current ILED 2 is a time chart showing the waveforms of the light emitting diodes Z0 to Z7 when the number of light emitting diodes Z0 to Z7 that are turned on is reduced by one. The dotted lines in FIG. 2 show the timing at which the control logic circuit 3 reduces the number of light emitting diodes Z0 to Z7 that are turned on.

[0045] The output voltage V OUT and voltage V CH8 However, the resistance of the PMOS transistor M2 has increased beforehand, and the LED current I LED is limited, so the output voltage V OUT and voltage V CH8 LED current I during the period when the difference between LED The increase in

[0046] In this embodiment, the operational amplifier 13 increases the resistance value of the PMOS transistor M2 from 10 μs before the timing to decrease the number of light-emitting diodes Z0 to Z7 to several tens of μs after the timing to decrease the number of light-emitting diodes Z0 to Z7, more than during other periods (steady state). The extent to which the resistance value of the PMOS transistor M2 is increased is determined by the output voltage V OUT The resistance of the PMOS transistor M2 may be increased until the PMOS transistor M2 is temporarily turned off, or may be increased while the PMOS transistor M2 is on. In steady state, the operational amplifier 13 turns the PMOS transistor M2 fully on to minimize loss in the PMOS transistor M2.

[0047] The time immediately before the timing to reduce the number of light-emitting diodes Z0 to Z7 is not limited to 10 μs, and is set to, for example, a range of 1 μs to 100 μs. Furthermore, instead of increasing the resistance value of the PMOS transistor M2 immediately before the timing to reduce the number of light-emitting diodes Z0 to Z7, the resistance value of the PMOS transistor M2 may be increased simultaneously with the timing to reduce the number of light-emitting diodes Z0 to Z7.

[0048] The time period immediately after the timing to reduce the number of light-emitting diodes Z0 to Z7 that are turned on is not limited to 10 μs, but is preferably set in the range of 1 μs to 100 μs, for example. Note that the set time immediately before the timing to reduce the number of light-emitting diodes Z0 to Z7 that are turned on and the set time immediately after the timing to reduce the number of light-emitting diodes Z0 to Z7 that are turned on may be the same as in this embodiment, or may be different from each other as in this embodiment.

[0049] The second voltage V2 is offset by the adder 14 so as to increase it by 0.2 V. The second voltage V2 after being offset by the adder 14 is supplied to the inverting input terminal of the operational amplifier 13.

[0050] The operational amplifier 13 controls the PMOS transistor M2 in accordance with the difference between the first voltage V1 and the second voltage V2 that has been offset by the adder 14. Therefore, the operational amplifier 13 controls the LED current I LED becomes larger than the target current by a predetermined value or more, the resistance value of the PMOS transistor M2 is increased to control the LED current I LED The predetermined value can be adjusted by changing the offset voltage value (0.2 V in this embodiment) in the adder 14. LED When the current exceeds the target current by a predetermined value or more, the above-mentioned steady state is excluded.

[0051] In this embodiment, the adder 14 applies an offset to the second voltage V2. However, instead of or in addition to the adder 14 applying an offset to the second voltage V2, an adder that applies an offset to the first voltage V1 may be provided, and the first voltage V1 after the offset is applied may be supplied to the non-inverting input terminal of the operational amplifier 13. In this modification, the operational amplifier 13 also outputs the LED current I LED becomes larger than the target current by a predetermined value or more, the resistance value of the PMOS transistor M2 is increased to control the LED current I LED In this modification, the predetermined value can be adjusted by, for example, changing the value of the offset voltage applied to the first voltage V1, or by, for example, changing at least one of the value of the offset voltage applied to the first voltage V1 and the value of the offset voltage applied to the second voltage V2.

[0052] The discharge circuit 15 draws current from the output terminal of the error amplifier 8 when the operational amplifier 13 increases the resistance value of the PMOS transistor M2 compared to the steady state. As a result, when the resistance value of the PMOS transistor M2 increases compared to the steady state, the error voltage V ERR decreases, the boost driver circuit 12 reduces the LED current I LED The switching of the NMOS transistor M1 is controlled so as to reduce the loss in the PMOS transistor M2 when the resistance value of the PMOS transistor M2 is higher than that in the steady state.

[0053] The value of the current drawn by the discharge circuit 15 is not particularly limited. For example, the value of the current drawn by the discharge circuit 15 is set based on the control state of the terminal PGATE. In this case, the discharge circuit 15 may include a current mirror circuit and draw a mirror current of the current flowing through the terminal PGATE from the output terminal of the error amplifier 8. Alternatively, for example, the discharge circuit 15 may include a constant current circuit and draw a constant current from the output terminal of the error amplifier 8. Alternatively, for example, the discharge circuit 15 may include a variable current circuit and set the value of the output current of the variable current circuit based on the circuit constants of externally connected discrete components, signals received by the communication interface 2, etc., and draw the output current of the variable current circuit from the output terminal of the error amplifier 8.

[0054] The clamp element 16 clamps the error voltage V ERR The clamp element 16 may be, for example, a Zener diode. The discharge circuit 15 draws current to clamp the lower limit of the error voltage V ERR If the LED current I drops too much, the LED current I LED By providing the clamp element 16, the LED current I LED It is possible to prevent shortage of

[0055] FIG. 3 shows the output voltage V of the DC / DC converter when the discharge circuit 15 and the clamp element 16 are not provided. OUT , the voltage V applied to the light-emitting diode Z7 CH8 , and LED current I LED 3 is a time chart showing the waveforms of the light-emitting diodes Z0 to Z7. Like Fig. 2, Fig. 3 is a time chart showing the case where the number of light-emitting diodes Z0 to Z7 that are turned on is reduced by one. Like the dotted lines in Fig. 2, the dotted lines in Fig. 3 also show the timing at which the control logic circuit 3 reduces the number of light-emitting diodes Z0 to Z7 that are turned on.

[0056] In Figure 3, the output voltage V OUT and voltage V CH8, and the period during which the loss in the PMOS transistor M2 is large is longer than in FIG. 2. Therefore, it is preferable to provide the discharge circuit 15 as in this embodiment. It is even more preferable to provide the clamp element 16 as in this embodiment, so that the LED current I LED It is desirable to prevent shortage of

[0057] The control logic circuit 3 is capable of PWM (Pulse Width Modulation) dimming. Specifically, when performing PWM dimming, the control logic circuit 3 generates a PWM signal and switches on and off a switch connected in parallel to the light-emitting diode to be lit based on the PWM signal. In other words, when PWM dimming is being performed, the light-emitting diode to be lit is not always lit, but is switched on and off based on the PWM signal.

[0058] The control logic circuit 3 sets the duty of the PWM signal based on the signal received by the communication interface 2, for example.

[0059] It is desirable that the control logic circuit 3 and the LED switch circuit 4 include a mode (phase shift mode) that staggers the timing at which the light-emitting diodes Z0 to Z7 switch from on to off. When implementing the phase shift mode and PWM dimming to light up all of the light-emitting diodes Z0 to Z7, the control logic circuit 3 and the LED switch circuit 4 should light up the light-emitting diodes Z0 to Z7 according to the time chart shown in FIG.

[0060] The dotted lines in Fig. 4 indicate the timing when any of the light-emitting diodes Z0 to Z7 switches from on to off. The black areas in Fig. 4 indicate off periods, and the white areas in Fig. 4 indicate on periods.

[0061] FIG. 5 is a diagram showing an example of the configuration of the LED switch circuit 4. As shown in FIG.

[0062] The LED switch circuit 4 has switches SW0 to SW7. The switches SW0 to SW7 are individually controlled to be turned on / off by the control logic circuit 3. One end of the switch SW0 is connected to the terminal CH0. The other end of the switch SW0 and one end of the switch SW1 are connected to the terminal CH1. The other end of the switch SW1 and one end of the switch SW2 are connected to the terminal CH2. The other end of the switch SW2 and one end of the switch SW3 are connected to the terminal CH3. The other end of the switch SW3 and one end of the switch SW4 are connected to the terminal CH4. The other end of the switch SW4 and one end of the switch SW5 are connected to the terminal CH5. The other end of the switch SW5 and one end of the switch SW6 are connected to the terminal CH6. The other end of the switch SW6 and one end of the switch SW7 are connected to the terminal CH7. The other end of the switch SW7 is connected to the terminal CH8.

[0063] The LED switch circuit 4 has a comparator 41 for detecting a ground fault at the terminal CH0. The comparator 41 is a hysteresis comparator that compares the voltage applied to the terminal CH0 with a threshold voltage and outputs the comparison result. If the voltage applied to the terminal CH0 is equal to or higher than the threshold voltage, the output signal of the comparator 41 becomes low level (a level indicating a normal state), and if the voltage applied to the terminal CH0 is lower than the threshold voltage, the output signal of the comparator 41 becomes high level (a level indicating a ground fault at the terminal CH0). The threshold voltage used by the comparator 41 is set to a 0th threshold voltage V TH0 and the first threshold voltage V TH1 The output signal of the comparator 41 is sent to the control logic circuit 3.

[0064] The LED switch circuit 4 has a comparator 42 for detecting a ground fault at the terminal CH2. The comparator 42 is a hysteresis comparator that compares the voltage applied to the terminal CH2 with a threshold voltage and outputs the comparison result. If the voltage applied to the terminal CH2 is equal to or higher than the threshold voltage, the output signal of the comparator 42 becomes low level (a level indicating a normal state), and if the voltage applied to the terminal CH2 is lower than the threshold voltage, the output signal of the comparator 42 becomes high level (a level indicating a ground fault at the terminal CH2). The threshold voltage used by the comparator 42 is set to a second threshold voltage V TH2 and the third threshold voltage V TH3 The output signal of the comparator 42 is sent to the control logic circuit 3.

[0065] The LED switch circuit 4 has a comparator 43 for detecting a ground fault at the terminal CH4. The comparator 43 is a hysteresis comparator that compares the voltage applied to the terminal CH4 with a threshold voltage and outputs the comparison result. If the voltage applied to the terminal CH4 is equal to or higher than the threshold voltage, the output signal of the comparator 43 becomes low level (a level indicating a normal state), and if the voltage applied to the terminal CH4 is lower than the threshold voltage, the output signal of the comparator 43 becomes high level (a level indicating a ground fault at the terminal CH4). The threshold voltage used by the comparator 43 is set to a fourth threshold voltage V TH4 and the fifth threshold voltage V TH5 The output signal of the comparator 43 is sent to the control logic circuit 3.

[0066] The LED switch circuit 4 has a comparator 44 for detecting a ground fault at the terminal CH6. The comparator 44 is a hysteresis comparator that compares the voltage applied to the terminal CH6 with a threshold voltage and outputs the comparison result. If the voltage applied to the terminal CH6 is equal to or higher than the threshold voltage, the output signal of the comparator 44 becomes low level (a level indicating a normal state), and if the voltage applied to the terminal CH6 is lower than the threshold voltage, the output signal of the comparator 44 becomes high level (a level indicating a ground fault at the terminal CH6). The threshold voltage used by the comparator 44 is set to a sixth threshold voltage V TH6 and the seventh threshold voltage V TH7 The output signal of the comparator 44 is sent to the control logic circuit 3.

[0067] The LED switch circuit 4 has a comparator 45 for detecting a ground fault at the terminal CH8. The comparator 45 is a hysteresis comparator that compares the voltage applied to the terminal CH8 with a threshold voltage and outputs the comparison result. If the voltage applied to the terminal CH8 is equal to or higher than the threshold voltage, the output signal of the comparator 45 becomes low level (a level indicating a normal state), and if the voltage applied to the terminal CH8 is lower than the threshold voltage, the output signal of the comparator 45 becomes high level (a level indicating a ground fault at the terminal CH8). The threshold voltage used by the comparator 45 is an eighth threshold voltage V TH8 and the ninth threshold voltage V TH9 The output signal of the comparator 45 is sent to the control logic circuit 3.

[0068] In this embodiment, the output signals of the comparators 41 to 45 are transmitted to the control logic circuit 3, but the logical sum of the output signals of the comparators 41 to 45 may also be transmitted to the control logic circuit 3. If the logical sum of the output signals of the comparators 41 to 45 is at a high level, at least one of the terminals CH0, CH2, CH4, CH6, and CH8 has a ground fault. In this embodiment, the comparators 41 to 45 form a ground fault detection unit, but for example, only the comparator 41 may be provided, or conversely, a comparator for detecting a ground fault at the terminal CH1 may be added.

[0069] When a ground fault is detected by the ground fault detector, the control logic circuit 3 operates as a protection unit that stops the supply of current to the light-emitting diodes Z0 to Z7. For example, when a ground fault is detected by the ground fault detector, the control logic circuit 3 controls the boost drive circuit 12 to stop the operation of the DC / DC converter. This makes it possible to prevent a current from continuing to flow through the PMOS transistor M2 when a ground fault occurs, thereby preventing continuous loss in the PMOS transistor M2.

[0070] The LED switch circuit 4 has an open-circuit detection circuit DETm that detects an open circuit in the light-emitting diode Zm. The open-circuit detection circuit DETm detects an open circuit in the light-emitting diode Zm when the voltage across the light-emitting diode Zm is greater than a predetermined value (a value slightly greater than the forward voltage of the light-emitting diode Zm) while the switch SWm is off, where m is an integer between 0 and 7.

[0071] The detection results of the open detection circuits DET0 to DET7 are sent to the control logic circuit 3. When at least one of the open detection circuits DET0 to DET7 detects an open state in an LED, the control logic circuit 3 turns on one of the switches SW0 to SW7 that is connected in parallel to the LED in which the open state was detected, thereby forming a bypass path that bypasses the LED in which the open state was detected. This makes it possible to prevent all of the light-emitting diodes Z0 to Z7 from turning off even if some of the light-emitting diodes Z0 to Z7 become open.

[0072] However, when a bypass path is formed due to open circuit detection, the number of lit light-emitting diodes Z0 to Z7 decreases, and the LED current I LED Therefore, the control logic circuit 3 increases the resistance value of the PMOS transistor M2 at the same time that an open circuit is detected by at least one of the open circuit detection circuits DET0 to DET7. LED In order to form a bypass path as quickly as possible when an open circuit is detected, in this embodiment, the resistance value of the PMOS transistor M2 is not increased before the bypass path is formed, but the timing to start increasing the resistance value of the PMOS transistor M2 and the timing to start forming the bypass path are set to be the same. However, as in the circuit example shown in FIG. 1, if the response of the DC / DC converter is slow and some of the light-emitting diodes Z0 to Z7 become open, the output voltage V of the DC / DC converter may not increase. OUT In the case of a configuration in which the voltage Vcc does not rise easily, when it is detected that some of the light-emitting diodes Z0 to Z7 are open, the resistance value of the PMOS transistor M2 may be increased first, and then a bypass path may be formed.

[0073] <Application> The above-described light emitting device can be suitably used, for example, as shown in Figures 6 and 7, as a headlight (including high beam / low beam / parking lamp / fog lamp, etc., as appropriate) X11 of a vehicle X10, a light source for daylight running (DRL) X12, a tail lamp (including parking lamp, back lamp, etc., as appropriate) X13, a stop lamp X14, and a turn lamp X15.

[0074] The above-described light emitting device may be provided as a module (such as the LED headlight module Y10 in FIG. 8, the LED turn lamp module Y20 in FIG. 9, and the LED rear lamp module Y30 in FIG. 10). Also, the light emitting device may be provided in the form of a driving device with a light emission number control function, which is a semi-finished product obtained by removing external components such as light emitting diodes and light emitting element driving ICs from the above-described light emitting device.

[0075] <Other> The above-described embodiments should be considered to be illustrative in all respects and not restrictive. The technical scope of the present invention is indicated by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0076] In the above embodiment, a configuration using a light-emitting diode as the light-emitting element has been described as an example, but the configuration of the present invention is not limited to this, and for example, an organic EL (electro-luminescence) element can also be used as the light-emitting element.

[0077] In the above embodiment, a configuration using a PMOS transistor as a variable resistor has been described as an example, but the configuration of the present invention is not limited to this, and it is also possible to use, for example, an active element other than a PMOS transistor.

[0078] In the above embodiment, a single light-emitting diode is connected between terminal CH(m+1) and terminal CHm. However, multiple light-emitting diodes may be connected between terminal CH(k+1) and terminal CHk (k is an integer between 0 and 7). However, when multiple light-emitting diodes are connected between terminal CH(k+1) and terminal CHk, the multiple light-emitting diodes are treated as one group and switched on and off on a group-by-group basis. Care must also be taken to ensure that the voltage VCH8 applied to terminal CH8 does not exceed the rated value. FIG. 11 shows an example of a configuration in which multiple light-emitting diodes are connected between terminal CH(k+1) and terminal CHk. In the modified example shown in FIG. 11, two light-emitting diodes are connected between terminal CH(k+1) and terminal CHk for k=0, 1, 2, and 3.

[0079] In the above embodiment, nine terminals, terminals CH0 to CH8, are connectable to light-emitting diodes, but the number of terminals connectable to light-emitting diodes is not limited to nine and may be any number other than nine.

[0080] In the above embodiment, the light emitting device is configured to include a single light emitting element driving IC 100, but the portion corresponding to the light emitting element driving IC 100 may be configured with multiple ICs. For example, the portions corresponding to the communication interface 2, the control logic circuit 3, and the LED switch circuit 4 may be ICs separate from the light emitting element driving IC 100.

[0081] The semiconductor integrated circuit for driving light-emitting elements described above is a semiconductor integrated circuit for driving light-emitting elements that constitutes at least a part of a light-emitting element driving device configured to vary the number of lit light-emitting elements among a plurality of light-emitting elements connected in series, and has a configuration (first configuration) that has a variable resistance control unit configured to increase the resistance value of the variable resistors connected in series to the plurality of light-emitting elements immediately before or simultaneously with the timing to reduce the number of lit light-emitting elements.

[0082] Furthermore, in the semiconductor integrated circuit for driving a light-emitting element of the first configuration, the light-emitting element driving device may include a DC / DC converter that converts an input voltage into an output voltage, and a switching control unit that controls a switching element in the DC / DC converter based on an error voltage output from an error amplifier that amplifies the difference between a first voltage based on the output current of the DC / DC converter and a second voltage corresponding to a target current, and is configured to supply the output current of the DC / DC converter to a light-emitting element to be turned on among the plurality of light-emitting elements, and the semiconductor integrated circuit for driving a light-emitting element may have a configuration (second configuration) including a discharge unit that is configured to draw current from the output terminal of the error amplifier when the variable resistance control unit increases the resistance value of the variable resistor above that in steady state.

[0083] Furthermore, the semiconductor integrated circuit for driving a light-emitting element having the second configuration may have a configuration (third configuration) that includes a clamp element that clamps the lower limit of the error voltage.

[0084] Also, the above 2nd or 3rd In the semiconductor integrated circuit for driving a light-emitting element having the above configuration, an offset processing unit configured to apply an offset to at least one of the first voltage and the second voltage may be provided, and the variable resistance control unit may be configured to adjust the resistance value of the variable resistor based on the difference between the first voltage and the second voltage after the offset processing unit applies an offset to at least one of the first voltage and the second voltage (fourth configuration).

[0085] Furthermore, the semiconductor integrated circuit for driving light-emitting elements of any of the first to fourth configurations may have a variable section configured to vary the number of lit elements, and the variable section may be configured to include a mode that staggers the timing at which the plurality of light-emitting elements switch from lit to extinguished. (Fifth configuration)

[0086] Furthermore, in a semiconductor integrated circuit for driving a light-emitting element of any of the first to fifth configurations, a sixth configuration may be provided which includes a ground fault detection unit configured to detect a ground fault at at least one location on the series circuit of the plurality of light-emitting elements, and a protection unit configured to stop the supply of current to the plurality of light-emitting elements when a ground fault is detected by the ground fault detection unit.

[0087] Furthermore, in a semiconductor integrated circuit for driving light-emitting elements of any of the first to sixth configurations, the semiconductor integrated circuit may have an open detection unit configured to detect an open circuit in units of multiple groups for the multiple light-emitting elements, and a bypass unit configured to form a bypass path that bypasses a light-emitting element among the multiple light-emitting elements that has been detected as open by the open detection unit, and the variable resistance control unit may be configured to increase the resistance value of the variable resistor at the same time as an open circuit is detected by the open detection unit (seventh configuration).

[0088] The light-emitting element driving device disclosed in this specification has a configuration (8th configuration) that includes a variable unit configured to vary the number of lit light-emitting elements among a plurality of light-emitting elements connected in series, and a variable resistance control unit configured to increase the resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with the timing of reducing the number of lit light-emitting elements.

[0089] The light emitting device disclosed in this specification has a configuration (ninth configuration) including the light emitting element driving device of the eighth configuration and the plurality of light emitting elements.

[0090] The vehicle disclosed in this specification has a configuration (tenth configuration) that includes the light emitting device of the ninth configuration. [Explanation of symbols]

[0091] 1 Constant voltage circuit 2. Communication Interface 3 Control logic circuit 4 LED switch circuit 5, 6, 13 Op-amps 7, 14 adder 8 Error Amplifier 9. Oscillators 10 Slope Circuit 11 Comparator 12 Boost driver circuit 15 Discharge circuit 16 Clamping element 100 Light emitting element driving IC BOOT, CH0~CH8, COMP, GL, IS, PGATE, PGND, PSW, RT, RX, SNSN, SNSP, TX, VIN terminal C1 Output capacitor C2~C4 capacitors L1 coil M1 NMOS transistor M2 PMOS transistor 100 Light emitting element driving IC SW0~SW7 switches X10 vehicle X11 headlight X12 Day and Night Running Light X13 tail lamp X14 Stop lamp X15 Turn Lamp Z0~Z7 light emitting diodes

Claims

1. A variable resistance control unit configured to increase the resistance value of a variable resistor connected in series to a plurality of light-emitting elements immediately before or simultaneously with a timing to reduce the number of lit light-emitting elements of the plurality of light-emitting elements connected in series; a discharge unit configured to draw current from an output terminal of the error amplifier when the variable resistance control unit increases the resistance value of the variable resistance from a steady state; and a current based on the error voltage output from the error amplifier is supplied to a light-emitting element among the plurality of light-emitting elements, an output current of a DC / DC converter that converts an input voltage into an output voltage is supplied to a light-emitting element among the plurality of light-emitting elements, the error amplifier is configured to amplify a difference between a first voltage based on an output current of the DC / DC converter and a second voltage corresponding to a target current; A semiconductor integrated circuit for driving a light emitting element, in which a switching element in the DC / DC converter is controlled based on the error voltage.

2. 2. The semiconductor integrated circuit for driving a light-emitting element according to claim 1, further comprising a clamping element for clamping the lower limit of the error voltage.

3. an offset processing unit configured to apply an offset to at least one of the first voltage and the second voltage; 3. The semiconductor integrated circuit for driving a light-emitting element according to claim 1, wherein the variable resistance control unit is configured to adjust the resistance value of the variable resistance based on the difference between the first voltage and the second voltage after the offset processing unit applies an offset to at least one of the first voltage and the second voltage.

4. a variable resistance control unit configured to increase a resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with a timing to reduce the number of light-emitting elements that are turned on in the plurality of light-emitting elements that are connected in series; A variable unit configured to vary the number of lights; and The semiconductor integrated circuit for driving a light-emitting element is configured so that the variable section includes a mode for shifting timings at which the plurality of light-emitting elements switch from on to off.

5. a variable resistance control unit configured to increase a resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with a timing to reduce the number of light-emitting elements that are turned on in the plurality of light-emitting elements that are connected in series; a ground fault detection unit configured to detect a ground fault at at least one point on the series circuit of the plurality of light emitting elements; a protection unit configured to stop supplying current to the plurality of light-emitting elements when a ground fault is detected by the ground fault detection unit; A semiconductor integrated circuit for driving a light-emitting element, comprising:

6. a variable resistance control unit configured to increase a resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with a timing to reduce the number of light-emitting elements that are turned on in the plurality of light-emitting elements that are connected in series; an open-circuit detection unit configured to detect an open circuit in units of a plurality of groups for the plurality of light-emitting elements; a bypass unit configured to form a bypass path that bypasses a light-emitting element detected as open by the open detection unit among the plurality of light-emitting elements; and The variable resistance control section is configured to increase the resistance value of the variable resistor at the same time that an open circuit is detected by the open circuit detection section.

7. a variable unit configured to vary the number of lit light-emitting elements among the plurality of light-emitting elements connected in series; a variable resistance control unit configured to increase a resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with the timing of decreasing the number of light-emitting elements; a discharge unit configured to draw current from an output terminal of the error amplifier when the variable resistance control unit increases the resistance value of the variable resistance from a steady state; and a current based on the error voltage output from the error amplifier is supplied to a light-emitting element among the plurality of light-emitting elements, The light-emitting element driving device is configured so that the variable unit includes a mode for shifting the timing at which the plurality of light-emitting elements switch from on to off.

8. a variable unit configured to vary the number of lit light-emitting elements among the plurality of light-emitting elements connected in series; a variable resistance control unit configured to increase a resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with the timing of decreasing the number of light-emitting elements; and The light-emitting element driving device is configured so that the variable unit includes a mode for shifting the timing at which the plurality of light-emitting elements switch from on to off.

9. a variable unit configured to vary the number of lit light-emitting elements among the plurality of light-emitting elements connected in series; a variable resistance control unit configured to increase a resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with the timing of decreasing the number of light-emitting elements; a ground fault detection unit configured to detect a ground fault at at least one point on the series circuit of the plurality of light emitting elements; a protection unit configured to stop supplying current to the plurality of light-emitting elements when a ground fault is detected by the ground fault detection unit; A light emitting element driving device having the above structure.

10. a variable unit configured to vary the number of lit light-emitting elements among the plurality of light-emitting elements connected in series; a variable resistance control unit configured to increase a resistance value of a variable resistor connected in series to the plurality of light-emitting elements immediately before or simultaneously with the timing of decreasing the number of light-emitting elements; an open-circuit detection unit configured to detect an open circuit in units of a plurality of groups for the plurality of light-emitting elements; a bypass unit configured to form a bypass path that bypasses a light-emitting element detected as open by the open detection unit among the plurality of light-emitting elements; and The light-emitting element driving device, wherein the variable resistance control unit is configured to increase the resistance value of the variable resistance at the same time as an open circuit is detected by the open circuit detection unit.

11. A light emitting element driving device according to any one of claims 7 to 10; the plurality of light-emitting elements; A light emitting device comprising:

12. A vehicle comprising the light emitting device according to claim 11.

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