Light emitting element driving device, light emitting device, and vehicle

Abstract

This light emitting element driving device comprises: an error amplifier configured to output a voltage corresponding to the difference between a reference voltage and a voltage corresponding to the current flowing to a light emitting element, and to switch between operation and non-operation according to a control signal; a drive unit configured to drive, on the basis of the voltage output from the error amplifier, a switching element of a voltage supply unit configured to supply a voltage to the light emitting element; and a suppression unit configured to suppress a rise in the voltage output from the error amplifier when the error amplifier switches from non-operation to operation.

Description

Light emitting element driving device, light emitting device, and vehicle

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

[0002] 2. Description of the Related Art Conventionally, a light emitting device having a PWM (Pulse Width Modulation) dimming switch has been proposed (see, for example, Patent Document 1).

[0003] JP 2013-132107 A

[0004] By eliminating the PWM dimming switch from the light emitting device, the number of components can be reduced, leading to lower costs.

[0005] However, when the PWM dimming switch is removed from the light emitting device, there may be disadvantages due to the elimination of the PWM dimming switch, and therefore it is desirable to take measures to address these disadvantages.

[0006] The light-emitting element driving device disclosed in this specification includes an error amplifier, a driving unit, and a suppressing unit. The error amplifier outputs a voltage corresponding to the difference between a voltage corresponding to a current flowing through a light-emitting element and a reference voltage, and is configured to be switched between operating and non-operating states in response to a control signal. The driving unit is configured to drive a switching element of a voltage supply unit configured to supply voltage to the light-emitting element based on the output voltage of the error amplifier. The suppressing unit is configured to suppress an increase in the output voltage of the error amplifier when the error amplifier switches from non-operating to operating.

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

[0008] The vehicle disclosed in this specification has a light emitting device having the above-described configuration.

[0009] According to the invention disclosed in this specification, it is possible to suppress overshoot of the current flowing through the light emitting element.

[0010] FIG. 1 is a diagram showing an example of the configuration of a light-emitting device. FIG. 2 is a diagram showing current and voltage waveforms. FIG. 3 is a diagram showing an example of the configuration of a PWM dimming signal generation unit provided in an LED driver IC. FIG. 4 is a diagram showing an example of the configuration of a PWM dimming signal generation unit provided in an LED driver IC. FIG. 5 is a diagram showing the waveform of a current flowing through a light-emitting diode. FIG. 6 is an external view (front) of a vehicle on which a light-emitting device is mounted. FIG. 7 is an external view (rear) of a vehicle on which a light-emitting device is mounted. FIG. 8 is an external view of an LED headlight module. FIG. 9 is an external view of an LED turn lamp module. FIG. 10 is an external view of an LED rear lamp module.

[0011] In this specification, a MOS (Metal Oxide Semiconductor) field effect transistor refers to a field effect transistor whose gate structure is composed of at least three layers: a layer made of a conductor or a semiconductor such as polysilicon with a low resistance value, an insulating layer, and a P-type, N-type, or intrinsic semiconductor layer. In other words, the gate structure of a MOS field effect transistor is not limited to a three-layer structure of a metal, an oxide, and a semiconductor.

[0012] In this specification, the reference voltage means a voltage that is constant under ideal conditions, but in reality it is a voltage that may fluctuate slightly due to temperature changes and the like.

[0013] <Light-emitting device> Fig. 1 is a diagram showing an example of the configuration of a light-emitting device. The light-emitting device 100 shown in Fig. 1 has light-emitting diodes Z1 to Z3 which are light-emitting elements, and an LED (Light Emitting Diode) driver IC (Integrated Circuit) 101 which is a light-emitting element driving device that drives the light-emitting elements.

[0014] In addition to the light emitting diodes Z1 to Z3, a capacitor C1, an inductor L1, an output capacitor C2, and a sense resistor R1 are externally connected to the LED driver IC101.

[0015] The LED driver IC 101 has a terminal PINP, a terminal BOOT, a terminal SW, a terminal PINN, a terminal SNSP, and a terminal SINN for establishing electrical connection with the outside.

[0016] A first end of the capacitor C1 is connected to the terminal BOOT, and a second end of the capacitor C1 and a first end of the inductor L1 are connected to the terminal SW.

[0017] The second end of the inductor L1 is connected to the anode of the light-emitting diode Z1, the first end of the output capacitor C2, and the ground potential.

[0018] The cathode of light-emitting diode Z1 is connected to the anode of light-emitting diode Z2, and the cathode of light-emitting diode Z2 is connected to the anode of light-emitting diode Z3.

[0019] The cathode of the light-emitting diode Z2 is connected to the terminal SNSP and to the first end of the sense resistor R1.

[0020] A second end of the sense resistor R1 is connected to the terminal SINN and a second end of the output capacitor C2.

[0021] The LED driver IC 101 includes a constant voltage circuit 1, a control circuit 2, an operational amplifier 3, an adder 4, an error amplifier 5, an oscillator 6, a slope circuit 7, a comparator 8, drivers 9 and 10, N-channel MOS transistors 11 and 12, a delay unit 13, and a diode D1.

[0022] The constant voltage circuit 1 generates a constant voltage VDRV using an input voltage VIN supplied to a terminal PINP, and supplies the constant voltage VDRV to various parts of the LED driver IC 101, including the anode of a diode D1. The cathode of the diode D1 is connected to a terminal BOOT. A bootstrap circuit formed by the diode D1 and a capacitor C1 generates a voltage VBOOT at the terminal BOOT that is higher than the voltage VSW applied to a terminal SW.

[0023] A gate signal G1 is output from the output terminal Q of the control circuit 2. A gate signal G2 is output from the inverting output terminal Q of the control circuit 2. The control circuit 2 sets the gate signal G1 by a signal supplied to the set terminal SET, and resets the gate signal G1 by a signal supplied to the reset terminal RST. The control circuit 2 operates when the PWM dimming signal PWMDIM is at a HIGH level, and does not operate when the PWM dimming signal PWMDIM is at a LOW level. When the control circuit 2 is not operating, both the gate signals G1 and G2 are at a LOW level.

[0024] The non-inverting input terminal of the operational amplifier 3 is connected to the terminal SNSP, and the inverting input terminal of the operational amplifier 3 is connected to the terminal SINN. The operational amplifier 3 outputs a voltage corresponding to the voltage across the sense resistor R1.

[0025] The output voltage of the operational amplifier 3 is offset by the adder 4 so as to increase it by 0.2 V. The feedback voltage VFB generated by the adder 4 is supplied to the inverting input terminal of the error amplifier 5. The feedback voltage VFB is a voltage based on the current ILED flowing through the light-emitting diodes Z1 to Z3.

[0026] The error amplifier 5 generates an error voltage VERR corresponding to the difference between the feedback voltage VEB and a reference voltage VISET. The reference voltage VISET is a voltage for setting the value of the current ILED flowing through the light-emitting diodes Z1 to Z3. The higher the reference voltage VISET, the larger the value of the current ILED flowing through the light-emitting diodes Z1 to Z3.

[0027] The oscillator 6 generates a clock signal CK, which is supplied to a slope circuit 7 and a set terminal SET of the control circuit 2.

[0028] The slope circuit 7 generates a slope voltage VSLP by adding a voltage corresponding to ripple information of the current IL flowing through the inductor L1 to a triangular or sawtooth ramp waveform voltage using the clock signal CK.

[0029] The comparator 8 compares the error voltage VERR with the slope voltage VSLP, and supplies the comparison result to the reset terminal RST of the control circuit 2 .

[0030] The driver 9 amplifies the gate signal G1 and supplies the amplified drive signal to the gate of the MOS transistor 11. The positive power supply terminal of the driver 9 is supplied with the voltage VBOOT, and the negative power supply terminal of the driver 9 is supplied with the voltage VSW.

[0031] The driver 10 supplies a drive signal obtained by amplifying the gate signal G2 to the gate of the MOS transistor 12. A voltage VDRV is supplied to the positive power supply terminal of the driver 10, and the voltage applied to the terminal PINN is supplied to the negative power supply terminal of the driver 10.

[0032] The drain of the MOS transistor 11 is connected to the terminal PINP. The source of the MOS transistor 11 and the drain of the MOS transistor 12 are connected to the terminal SW. The source of the MOS transistor 12 is connected to the terminal PINN.

[0033] A voltage supply unit composed of MOS transistors 11 and 12, an inductor L1, and an output capacitor C2 supplies a voltage to light-emitting diodes Z1 to Z3.

[0034] The delay unit 13 will be described later.

[0035] The LED driver IC 101 is a negative-polarity step-up / step-down DC / DC converter type LED driver IC. In the light-emitting device 100, energy is stored in the inductor L1 when the MOS transistor 11 is on and the MOS transistor 12 is off. In the light-emitting device 100, when the MOS transistor 11 is off and the MOS transistor 12 is on, the current IL flowing through the inductor L1 negatively charges the output capacitor C2.

[0036] When the PWM dimming signal PWMDIM is at a high level, the error amplifier 5 operates. When the error amplifier 5 is operating, it outputs an error voltage VERR from its output terminal, which corresponds to the difference between the feedback voltage VEB and the reference voltage VISET. When the error amplifier 5 is operating, the MOS transistors 11 and 12 perform a switching operation, and as shown in Figure 2, the current IL flowing through the inductor L1 has a triangular waveform, and the voltage VSW has a pulse waveform.

[0037] When the PWM dimming signal PWMDIM is at a low level, the error amplifier 5 is inactive. When the error amplifier 5 is inactive, the output terminal of the error amplifier 5 is in a high impedance state.

[0038] The LED driver IC 101 includes a PWM dimming signal generator. 3 and 4 are diagrams showing an example of the configuration of the PWM dimming signal generator provided in the LED driver IC 101.

[0039] 3 and 4 includes a current source 14, resistors 15 and 17, comparators 16 and 18, and an oscillator 19. The LED driver IC 101 further includes a terminal DRV, a terminal DSET, and a terminal GNDIN for establishing electrical connection with the outside.

[0040] The constant voltage VDRV output from the constant voltage circuit 1 is supplied to the terminal DRV, a first terminal of the current source 14, and the positive power supply terminal of the comparator 16. The second terminal of the current source 14 is connected to the terminal DSET and the non-inverting input terminal of the comparator 16.

[0041] The terminal GNDIN is connected to a first end of the resistor 15 and a negative power supply terminal of the comparator 16. The second end of the resistor 15 is connected to an inverting input terminal of the comparator 16.

[0042] The output terminal of the comparator 16 is connected to a first terminal of a resistor 17 and a non-inverting input terminal of a comparator 18. A second terminal of the resistor 17 is connected to a terminal SINN (see FIG. 1). The output signal of the oscillator 19 is supplied to the inverting input terminal of the comparator 18. The output signal of the oscillator 19 is a sawtooth wave signal having a bottom value V1 and a top value V2. The comparator 18 outputs a PWM dimming signal PWMDIM.

[0043] In the configuration shown in FIG. 3 , the frequency of the PWM dimming signal PWMDIM is internally fixed. In the configuration shown in FIG. 3 , a capacitor C3 and resistors R2 and R3 are externally connected to the LED driver IC 101. A first end of the capacitor C3 and a first end of the resistor R2 are connected to the terminal DRV. A second end of the resistor R2 and a first end of the resistor R3 are connected to the terminal DSET. A second end of the capacitor C3 and a second end of the resistor R3 are connected to the terminal GNDIN. In the configuration shown in FIG. 3 , the frequency of the PWM dimming signal PWMDIM is the same as the frequency of the output signal of the oscillator 19. Furthermore, in the configuration shown in FIG. 3 , the on-duty of the PWM dimming signal PWMDIM is determined by the voltage applied to the terminal DSET.

[0044] In the configuration shown in FIG. 4 , the frequency of the PWM dimming signal PWMDIM is determined by a signal input from an external source to the terminal DSET. In the configuration shown in FIG. 4 , a capacitor C3 is externally connected to the LED driver IC 101. The first end of the capacitor C3 is connected to the terminal DRV. The second end of the capacitor C3 is connected to the terminal GNDIN. A PWM signal is supplied to the terminal DSET. When the PWM signal supplied to the terminal DSET is equal to or higher than V2, the PWM dimming signal PWMDIM becomes a high level, and when the PWM signal supplied to the terminal DSET is equal to or lower than V1, the PWM dimming signal PWMDIM becomes a low level. Therefore, in the configuration shown in FIG. 3 , the frequency of the PWM dimming signal PWMDIM is the same as the frequency of the PWM signal supplied to the terminal DSET.

[0045] Next, the delay unit 13 provided in the LED driver IC 101 will be described.

[0046] First, to explain the role of the delay unit 13, we will explain the case where the delay unit 13 is removed from the LED driver IC 101. When the PWM dimming signal PWMDIM is at a low level, the switching operation of the MOS transistors 11 and 12 is stopped, and charge is drained from the output capacitor C2 via the light-emitting diodes Z1 to Z3. As a result, when the PWM dimming signal PWMDIM is at a low level, the output voltage VOUT decreases. When the PWM dimming signal PWMDIM subsequently switches from a low level to a high level, the error amplifier 5 switches from inactive to active. At the time the error amplifier 5 switches from inactive to active, no current flows through the light-emitting diodes Z1 to Z3, so the error voltage VERR output from the error amplifier 5 reaches its maximum. As a result, the output voltage VOUT rises too high, causing an overshoot in the current flowing through the light-emitting diodes Z1 to Z3.

[0047] The delay unit 13 suppresses an increase in the error voltage VERR output from the error amplifier 5 when the error amplifier 5 switches from a non-operating state to an operating state, thereby suppressing an overshoot of the current ILED flowing through the light-emitting diodes Z1 to Z3 when the error amplifier 5 switches from a non-operating state to an operating state, as shown in FIG.

[0048] Specifically, the delay unit 13 is configured to switch the error amplifier 5 from inactive to active with a delay from when the PWM dimming signal PWMDIM switches from a low level to a high level. The delay time of the delay unit 13 may be set to the time required for charging of the output capacitor C2 to be completed and for the feedback voltage VFB to rise to near the reference voltage VISET.

[0049] The time T_charge required for the feedback voltage VFB to rise to near the reference voltage VISET after the charging of the output capacitor C2 is completed can be calculated using the following formula. In the formula, C2 is the capacitance of the output capacitor C2. Also, ΔV in the formula is the difference between the reference voltage VISET and the feedback voltage VFB. Also, I_charge in the formula is the charging current of the output capacitor C2. Also, ILED in the formula is the current flowing through the light-emitting diodes Z1 to Z3. Also, Don in the formula is the on-duty of the MOS transistor 12. T_charge = C2 x ΔV / I_charge At the start of charging I_charge = ILED / (1 - Don) In steady state I_charge = {ILED / (1 - Don)} - ILED

[0050] The delay unit 13 generates a delay time from the timing at which the PWM dimming signal PWMDIM switches from LOW level to HIGH level. If the delay unit 13 is configured with a logic circuit, it becomes easy to generate this delay time.

[0051] For example, the delay time can be fixed by storing the delay time in a register within the logic circuit.

[0052] Furthermore, for example, a detection circuit that detects when the output voltage VOUT reaches a set value may be provided in the LED driver IC 101, and the delay unit 13 may determine the end of the delay using the output of the detection circuit as a trigger.

[0053] For example, by making it possible to rewrite the delay time held by a register in a logic circuit, the delay time can be varied.

[0054] <Applications> As shown in Figs. 6 and 7 , the above-described light-emitting device can be suitably used, for example, as a headlight (including high beam / low beam / small lamp / fog lamp, etc., as appropriate) X11 of a vehicle X10, a light source for daylight running (DRL) X12, a tail lamp (including small lamp, back lamp, etc., as appropriate) X13, a stop lamp X14, and a turn lamp X15.

[0055] The light emitting device described above 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). It may also be provided in the form of a driver 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 light emitting device described above.

[0056] <Others> 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.

[0057] 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.

[0058] In the above embodiment, an LED driver IC of a negative polarity step-up / step-down DC / DC converter type 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 an LED driver that is not negative polarity.

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

[0060] In the above embodiment, a delay in switching the error amplifier 5 from non-operating to operating is used to suppress an increase in the error voltage VERR output from the error amplifier 5 when the error amplifier 5 switches from non-operating to operating. However, a method other than a delay may be used to suppress an increase in the error voltage VERR output from the error amplifier 5 when the error amplifier 5 switches from non-operating to operating.

[0061] For example, instead of the delay unit 13, a clamp circuit that clamps the error voltage VERR output from the error amplifier 5 may be provided. However, because the error voltage VERR output from the error amplifier 5 varies depending on the reference voltage VISET, it is not possible to set a unique clamp voltage. This results in a complex circuit configuration for the clamp circuit.

[0062] Alternatively, for example, a discharge circuit may be provided instead of the delay unit 13. The discharge circuit discharges the error voltage VERR when the PWM dimming signal PWMDIM is at a low level, thereby lowering the error voltage VERR. However, if the error voltage VERR is lowered, it takes time for the error voltage VERR to rise when the PWM dimming signal PWMDIM switches from a low level to a high level. As a result, when the on-duty of the PWM dimming signal PWMDIM is small, the current ILED flowing through the light-emitting diodes Z1 to Z3 cannot be output. In other words, the guaranteed operating range is narrowed.

[0063] The light-emitting element driving device (101) described above is a configuration (first configuration) having an error amplifier (5) configured to output a voltage corresponding to the difference between a voltage corresponding to the current flowing through the light-emitting elements (Z1 to Z3) and a reference voltage, and to switch between operation and non-operation according to a control signal, drive units (2, 9, 10) configured to drive switching elements (11, 12) of voltage supply units (11, 12, L1, C2) configured to supply voltage to the light-emitting elements based on the output voltage of the error amplifier, and a suppression unit (13) configured to suppress an increase in the output voltage of the error amplifier when the error amplifier switches from non-operation to operation.

[0064] The light emitting element driving device having the first configuration can suppress overshoot of the current flowing through the light emitting element.

[0065] In the light-emitting element driving device of the first configuration, the control signal may be a PWM dimming signal (second configuration).

[0066] The light emitting element driving device of the second configuration can increase the versatility of the control signal.

[0067] In the light-emitting element driving device of the first or second configuration, the suppression unit may be configured to switch the error amplifier from inoperative to operative with a delay from the switching of the control signal from the first level to the second level (third configuration).

[0068] The light emitting element driving device of the third configuration can avoid the circuit configuration from becoming complicated and the guaranteed operating range from becoming narrow.

[0069] In the light emitting element driving device of the third configuration, the delay time may be fixed (fourth configuration).

[0070] The light-emitting element driving device having the fourth configuration can realize the suppression section with a simple configuration.

[0071] In the light-emitting element driving device of the third configuration described above, the suppression unit may be configured to continue the delay until the voltage supplied to the light-emitting element from the voltage supply unit reaches a set value (fifth configuration).

[0072] The light emitting element driving device having the fifth configuration can optimize the delay time.

[0073] In the light emitting element driving device of the third configuration, the delay time may be variable (sixth configuration).

[0074] The light emitting element driving device having the sixth configuration can adjust the delay time.

[0075] In the light-emitting element driving device of any one of the third to sixth configurations, the suppression section may be configured as a logic circuit (seventh configuration).

[0076] The light emitting element driving device having the seventh configuration makes it easy to generate a delay time.

[0077] The light emitting device (100) described above has a configuration (eighth configuration) including a light emitting element driving device of any one of the first to seventh configurations and the light emitting element.

[0078] The light emitting device having the eighth configuration can suppress overshoot of the current flowing through the light emitting element.

[0079] The light-emitting device of the eighth configuration may further include a sense resistor (R1) for detecting the current flowing through the light-emitting element, and the light-emitting element and the sense resistor may be directly connected in series (ninth configuration).

[0080] The light emitting device of the ninth configuration does not have a switch provided between the light emitting element and the sense resistor, and therefore can achieve low costs.

[0081] The vehicle (X10) described above has a configuration (tenth configuration) that includes the light emitting device of the eighth or ninth configuration.

[0082] The vehicle having the tenth configuration can suppress overshoot of the current flowing through the light emitting element.

[0083] 1 Constant voltage circuit 2 Logic circuit 3 Operational amplifier 4 Adder 5 Error amplifier 6, 19 Oscillator 7 Slope circuit 8, 16, 18 Comparator 9, 10 Driver 11, 12 MOS transistor 13 Delay section 14 Current source 15, 17, R2, R3 Resistor 100 Light emitting device 101 LED driver IC BOOT, DRV, DSET, GNDIN, PINN, PINP, SINN, SNSP, SW Terminals C1, C3 Capacitor C2 Output capacitor D1 Diode L1 Inductor R1 Sense resistor X10 Vehicle X11 Headlight X12 Daytime and night driving light source X13 Tail lamp X14 Stop lamp X15 Turn lamp Y10 LED headlight module Y20 LED turn lamp module Y30 LED rear lamp module Z1 to Z3 light-emitting diode

Claims

1. an error amplifier configured to output a voltage corresponding to a difference between a voltage corresponding to a current flowing through a light emitting element and a reference voltage, and to switch between operation and non-operation in response to a control signal; a drive unit configured to drive a switching element of a voltage supply unit configured to supply a voltage to the light-emitting element based on an output voltage of the error amplifier; A suppression unit configured to suppress an increase in an output voltage of the error amplifier when the error amplifier switches from a non-operating state to an operating state; A light emitting element driving device having the above configuration.

2. 2. The light emitting element driving device according to claim 1, wherein the control signal is a PWM dimming signal.

3. The light-emitting element driving device according to claim 1 , wherein the suppression unit is configured to switch the error amplifier from a non-operating state to an operating state with a delay from when the control signal switches from the first level to the second level.

4. 4. The light emitting element driving device according to claim 3, wherein the delay time is fixed.

5. The light-emitting element driving device according to claim 3 , wherein the suppression unit continues the delay until the voltage supplied from the voltage supply unit to the light-emitting element reaches a set value.

6. 4. The light emitting element driving device according to claim 3, wherein the delay time is variable.

7. The light-emitting element driving device according to claim 3 , wherein the suppression section is a logic circuit.

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

9. A sense resistor is further provided for detecting a current flowing through the light emitting element. The light emitting device according to claim 8 , wherein the light emitting element and the sense resistor are directly connected in series.

10. A vehicle comprising the light emitting device according to claim 8.