WO2019187279A1 - Light-emitting element drive device - Google Patents

Abstract

A light-emitting apparatus X1 has: a light-emitting element light source 200 formed by connecting a plurality of light-emitting elements 201-203 (for example, light-emitting diodes) in series; and a light-emitting element drive device 100 that drives the light-emitting element light source 200. The light-emitting element drive device 100 has: a current driver 101 that generates an output current Iout flowing in the light-emitting element light source 200 and that is connected between the application end of a power supply voltage Vin and the ground end; and a bypass functioning unit 112 that bypasses at least one of the plurality of light-emitting elements 201-203 constituting the light-emitting element light source 200 so as to decrease the number of series stages of the light-emitting elements in which the output current Iout flows when the power supply voltage Vin decreases.

Description

Light emitting element driving device

The invention disclosed in this specification relates to a light emitting element driving device.

Conventionally, various light-emitting element driving devices for driving light-emitting elements such as light-emitting diodes (hereinafter referred to as LEDs [light emitting diodes]) have been developed.

Note that Patent Document 1 can be cited as an example of the related art related to the above.

Japanese Patent Application Laid-Open No. 2011-244677

However, when a light emitting element light source formed by connecting a plurality of light emitting elements in series is to be driven, in the conventional light emitting element driving device, when the power supply voltage decreases to near the total forward voltage drop of the light emitting element light source, the light emitting element There was a problem that the light source was turned off.

The invention disclosed in the present specification provides a light emitting element driving device capable of maintaining the lighting of the light emitting element light source even when the power supply voltage is lowered in view of the above-described problems found by the inventors of the present application. The purpose is to do.

A light-emitting element driving device disclosed in the present specification includes a current driver that generates an output current that flows to a light-emitting element light source connected between a power supply voltage application terminal and a ground terminal, and when the power supply voltage decreases. A bypass function unit that bypasses at least one of the plurality of light emitting elements constituting the light emitting element light source and reduces the number of series stages of the light emitting elements through which the output current flows (first configuration) is provided.

In the light emitting element driving device having the first configuration, the bypass function unit compares the power supply voltage or a divided voltage thereof with a predetermined threshold voltage to generate a comparison signal, and the comparison signal And a switch that switches whether or not to bypass at least one of the plurality of light-emitting elements.

Further, in the light emitting element driving device having the second configuration, the comparator may be a hysteresis comparator (third configuration).

Further, in the light emitting element driving apparatus having the first configuration, the bypass function unit gradually changes the output current flowing through the light emitting element to be bypassed when switching the number of series stages of the light emitting elements through which the output current flows. A configuration (fourth configuration) is preferable.

Further, in the light emitting element driving device having the fourth configuration, the bypass function unit passes through the light emitting element to be bypassed among the output currents based on a control current corresponding to the power supply voltage or a divided voltage thereof. A configuration (fifth configuration) in which the set value of the branch current not to be variably controlled is good.

In the light emitting element driving device having the fifth configuration, the control current starts to flow when the power supply voltage or the divided voltage becomes higher than a predetermined threshold voltage (sixth configuration). Good.

In the light emitting element driving device having the fifth or sixth configuration, the set value of the branch current decreases from the maximum value larger than the target value of the output current as the control current increases. A configuration (seventh configuration) is preferable.

In the light emitting element driving apparatus having any one of the fifth to seventh configurations, the bypass function unit generates the control current so that a terminal voltage of a bypass control terminal through which the control current flows matches a threshold voltage. The control current generator may be configured (eighth configuration).

In the light emitting element driving device having the eighth configuration, the terminal voltage is a voltage obtained by subtracting a voltage drop corresponding to the control current from the power supply voltage or the divided voltage (ninth configuration). ).

Further, in the light emitting element driving device having the eighth or ninth configuration, the bypass function unit includes a first coefficient multiplying unit that multiplies a reference coefficient for determining a target value of the output current by a first coefficient, A second coefficient multiplier that multiplies the control current by a second coefficient, a subtractor that subtracts the output signal of the second coefficient multiplier from the output signal of the first coefficient multiplier, and the output signal of the subtractor according to the output signal And a current source that generates a branch current (a tenth configuration).

Further, in the light emitting element driving device having the eighth or ninth configuration, the bypass function unit includes a reference voltage generation unit that generates a reference voltage corresponding to a target value of the output current, and a response corresponding to the branch current. A current detection unit that generates a sense voltage; an offset applying unit that applies an offset voltage corresponding to the control current to the sense voltage; and the branch so that the sense voltage to which the offset voltage is applied matches the reference voltage It may be configured to further include a branch current generation unit that generates a current (an eleventh configuration).

In the light emitting element driving device having any one of the eighth to eleventh configurations, the first end is connected to the power supply voltage application end and the second end is connected to the divided voltage application end. A first resistor connected to the divided voltage application terminal, a second resistor connected to the ground terminal, and a first terminal connected to the divided voltage application terminal. A configuration in which a third resistor having two ends connected to the bypass control terminal is externally attached (a twelfth configuration) may be employed.

In the light emitting element driving apparatus having any one of the eighth to twelfth configurations, the bypass control terminal may be configured to be adjacent to the power supply voltage input terminal (a thirteenth configuration).

In the light emitting element driving apparatus having any one of the eighth to thirteenth configurations, the external terminal through which the branch current flows is adjacent to at least one of the output terminal and the ground terminal of the output current (fourteenth configuration). ).

Further, in the light emitting element driving apparatus having any one of the first to fourteenth configurations, the current driver may be configured to be a current source type (fifteenth configuration).

Further, in the light emitting element driving apparatus having any one of the first to fourteenth configurations, the current driver may be configured to be a current sink type (sixteenth configuration).

The light-emitting device disclosed in this specification includes a light-emitting element light source formed by connecting a plurality of light-emitting elements in series and any of the first to sixteenth configurations, and drives the light-emitting element light source. A light emitting element driving device (a seventeenth configuration).

In the light emitting device having the seventeenth configuration, the light emitting element may be a light emitting diode or an organic EL element (eighteenth configuration).

The light emitting device having the seventeenth or eighteenth configuration further includes a substrate on which a wiring pattern for mounting the light emitting element light source and the light emitting element driving device is laid, and a socket for mounting the substrate. It is preferable to have the configuration (19th configuration).

Further, the vehicle disclosed in the present specification has a configuration (twentieth configuration) having a light emitting device having any one of the seventeenth to nineteenth configurations.

According to the light emitting element driving device disclosed in the present specification, it is possible to keep the light emitting element light source on even if the power supply voltage decreases.

The figure which shows the whole structure of the vehicle provided with LED light-emitting device. The figure which shows 1st Embodiment of a bypass function part. Timing chart showing an example of bypass operation in the first embodiment The figure which shows 2nd Embodiment of a bypass function part. Timing chart showing an example of bypass operation in the second embodiment The figure which shows the element addition example of LED light-emitting device The figure which shows 3rd Embodiment of a bypass function part. Timing chart showing an example of bypass operation in the third embodiment The figure which shows the 1st example of a setting of external resistance (Iout = 100mA) The figure which shows the 2nd setting example of external resistance (Iout = 600mA) The figure which shows 4th Embodiment of a bypass function part. The figure which shows terminal arrangement of an LED drive device Top view of socket type LED module Plan view showing another layout of LED chip External view of vehicle equipped with LED light emitting device (front) External view of vehicle equipped with LED light emitting device (back) External view of LED headlamp module External view of LED turn lamp module External view of LED rear lamp module

<Overall configuration>
FIG. 1 is a diagram illustrating an overall configuration of a vehicle including an LED light emitting device. The vehicle X in the figure includes an LED light emitting device X1, a battery X2, and power switches X3a and X3b.

The LED light emitting device X1 is an in-vehicle lamp that is lit by receiving the supply of the power supply voltage Vin from the battery X2. Examples of the light emitting device X1 include a headlamp, a daytime running lamp, a tail lamp, a stop lamp, or a turn lamp.

The battery X2 is a power source of the vehicle X, and a lead storage battery or a lithium ion battery is preferably used.

The power switches X3a and X2b are respectively connected between the light emitting device X1 and the battery X2, and are turned on / off in response to a control signal from a controller (not shown).

<LED light emitting device>
Next, the internal configuration of the LED light emitting device X1 will be described. The LED light-emitting device X1 includes an LED driving device 100 and an LED light source 200, and various discrete components externally attached to the LED driving device 100 include resistors R1 to R4, capacitors C1 to C3, and diodes D1 to D3. Negative characteristic thermistor NTC.

The LED driving device 100 has a plurality of external terminals (in this figure, VIN pin, PBUS pin, SWCNT pin, CRT pin, DISC pin, GND pin as means for establishing electrical connection with the outside of the device. , ISET pin, THD pin, SW pin, and IOUT pin). The VIN pin is a power supply voltage input terminal. The PBUS pin is an abnormality detection input / output terminal. The SWCNT pin is a power supply voltage monitoring terminal. The CRT pin is a CR timer setting terminal. The DISC pin is a CR timer discharge terminal. The GND pin is a ground terminal. The ISET pin is a reference current setting terminal. The THD pin is a temperature derating setting terminal. The SW pin is a bypass switch connection terminal. The IOUT pin is an output current output terminal.

The positive terminal of the battery X2 is connected to the first terminal of each of the power switches X3a and X3b. The negative terminal of the battery X2 is connected to the ground terminal. The second end of the power switch X3a is connected to the anode of the diode D1. The second end of the power switch X3b is connected to the anodes of the diodes D2 and D3. The cathodes of the diodes D1 and D2 are connected to the VIN pin. The cathode of the diode D3 is connected to the CRT pin. The diodes D1 to D3 connected in this way function as a backflow prevention diode for interrupting a backflow current from the light emitting device X1 to the battery X2.

Resistors R1 and R2 are connected in series between the VIN pin and the ground terminal. A connection node between the resistors R1 and R2 is connected to the SWCNT pin. The resistors R1 and R2 connected in this way function as a voltage dividing circuit that generates a monitoring voltage Vm (= Vin × {R2 / (R1 + R2)}) corresponding to the power supply voltage Vin. The resistor R3 is connected between the CRT pin and the DISC pin, and functions as a part of the CR timer 106. The resistor R4 is connected between the ISET pin and the ground terminal, and functions as a part of the reference current setting unit 109.

The capacitor C1 is connected between the VIN pin and the ground terminal, and functions as an input smoothing capacitor. The capacitor C2 is connected between the IOUT pin and the ground terminal, and functions as an output smoothing capacitor. The capacitor C3 is connected between the CRT pin and the ground terminal, and functions as a part of the CR timer 106.

The negative characteristic thermistor NTC is connected between the THD pin and the ground terminal, and functions as a part of the reference current setting unit 109 (temperature detection element).

The LED driving device 100 is a silicon monolithic semiconductor integrated circuit device (so-called LED driver IC) that operates by receiving the supply voltage Vin from the battery X2 and generates an output current Iout to be supplied to the LED light source 200.

The LED light source 200 is an LED string including a plurality of LED chips connected in series (in this figure, LED chips 201 to 203). When the LED chips 201 to 203 are viewed individually, each can be understood as a single LED element, or can be understood as a light emitting element assembly in which a plurality of LED elements are combined in series or in parallel. .

In the LED light emitting device X1 of the present embodiment, the anode of the LED light source 200 (= the anode of the LED chip 201 arranged on the highest potential side) is the IOUT pin (= the output terminal of the output current Iout) of the LED driving device 100. )It is connected to the. On the other hand, the cathode of the LED light source 200 (= the cathode of the LED chip 203 arranged on the lowest potential side) is connected to the ground terminal. The anode of the LED chip 203 (= the cathode of the LED chip 202) is connected to the SW pin of the LED driving device 100, and the reason will be described later.

In the vehicle X, in the PWM [pulse width modulation] dimming mode, the power switch X3a is turned on and the power switch X3b is turned off. As a result, in the PWM dimming mode, the power supply voltage Vin is applied from the battery X2 to the VIN pin via the power switch X3a and the diode D1. Further, the CRT pin is in an open state with respect to the battery X2. On the other hand, in the DC dimming mode, the power switch X3a is turned off and the power switch X3b is turned on. As a result, in the DC dimming mode, the power supply voltage Vin is applied from the battery X2 to the VIN pin via the power switch X3b and the diode D2. A DC voltage (= battery voltage VB) is applied to the CRT pin from the battery X2 via the power switch X3b and the diode D3.

<LED drive device>
Next, the internal configuration of the LED driving device 100 will be described with reference to FIG. The LED driving device 100 includes a current driver 101, a reference voltage generation unit 102, an open mask function unit 103, an overvoltage mute unit 104, a protect bus function unit 105, a CR timer 106, an LED open detection unit 107, LED short detection unit 108, reference current setting unit 109, ISET open / short detection unit 110, control logic unit 111, bypass function unit 112, N-channel MOS (metal oxide semiconductor) field effect transistors N1 and N2 And current sources CS1 and CS2 and switches SW1 and SW2 are integrated. Further, although not explicitly shown in the drawing, the LED driving device 100 also has other circuit parts (such as UVLO [under voltage locked out] function part and TSD [thermal shutdown] function part) integrated therein.

The current driver 101 performs constant current control of the output current Iout so that the output current Iout flowing through the LED light source 200 matches a predetermined target value. Although not explicitly shown in the figure, the current driver 101 includes, for example, an output transistor provided on a current path through which the output current Iout flows, a sense resistor that converts the output current Iout into a feedback voltage, a feedback voltage, and a reference voltage. And an operational amplifier that performs linear drive of the output transistor so that they match. Note that the target value of the output current Iout can be arbitrarily set according to the reference current Iset.

The reference voltage generation unit 102 generates a predetermined reference voltage VREG (for example, 5V) from the power supply voltage Vin (for example, 5.5V to 20V), and outputs this to each unit of the LED driving device 100.

When the power supply voltage Vin is lower than a predetermined threshold voltage, the open mask function unit 103 notifies the detection result to the control logic unit 111 and masks the detection result of the LED open detection unit 107. With such an open mask function, for example, it is possible to eliminate erroneous detection of LED open when the power supply voltage Vin rises.

When the power supply voltage Vin exceeds a predetermined threshold voltage (for example, 16 V), the overvoltage mute unit 104 reduces the reference current Iset (and thus the output current Iout) according to the difference value between the two (in excess of Vin). Thus, the reference current setting unit 109 is controlled. Such overvoltage mute processing can suppress abnormal heat generation of the LED driving device 100.

The protect bus function unit 105 shares the abnormality detection results among the plurality of LED driving devices 100 and reflects them in the abnormality protection operation by the control logic unit 111. For example, when a certain abnormality (LED open, LED short, UVLO, temperature abnormality, etc.) is detected in the LED driving device 100, the protect bus function unit 105 outputs an abnormality detection signal to the outside via the PBUS pin. Further, when an abnormality detection signal is externally input via the PBUS pin, the protect bus function unit 105 transfers this to the control logic unit 111. By such an operation, for example, if an abnormality is detected in one LED driving device, a cooperative protection operation can be realized such that all the LED driving devices are stopped.

The CR timer 106 pulses the PWM dimming signal S1 to the control logic unit 111 in order to perform PWM dimming of the LED light source 200 in the PWM dimming mode (X3b off) in which no DC voltage is applied to the CRT pin. . For example, the CR timer 106 performs on / off control of the switch SW1 and the transistors N1 and N2 using the PWM dimming signal S1, and periodically switches charging / discharging of the capacitor C3, thereby changing the terminal voltage of the CRT pin to a triangle. Driving in a wave form is performed to drive the PWM dimming signal S1. Note that the time average value of the output current Iout (and hence the luminance of the LED light source 200) changes according to the on-duty of the PWM dimming signal S1. The cycle and on-duty of the PWM dimming signal S1 can be arbitrarily set by adjusting the resistance value of the resistor R3 and the capacitance value of the capacitor C3.

On the other hand, the CR timer 106 fixes the logic level of the PWM dimming signal S1 in the DC dimming mode (X3b ON) in which a DC voltage is applied to the CRT pin. At this time, the control logic unit 111 performs constant current control of the output current Iout.

As described above, if the LED driving device 100 has the CR timer 106 built-in, PWM dimming without a microcomputer can be realized, so that the cost of the LED light emitting device X1 can be reduced. Further, the CR timer 106 has a function of outputting a PWM signal as a PWM dimming signal S1 to the control logic unit 111 when a PWM signal is externally input to the CRT pin. It is possible to cope with.

The LED open detection unit 107 compares the terminal voltage of the IOUT pin (= output voltage Vout) with a predetermined threshold voltage (for example, Vin−0.05 V) to determine whether or not an open abnormality of the LED light source 200 has occurred. The detection result is notified to the control logic unit 111.

The LED short detection unit 108 compares the terminal voltage (= output voltage Vout) of the IOUT pin with a predetermined threshold voltage (for example, 0.6 V / 0.8 V), and the LED light source 200 has a short circuit abnormality (for example, ground fault). Is detected, and the detection result is notified to the control logic unit 111. Note that in this specification, “ground fault” refers to a short circuit to the ground terminal or a low potential terminal equivalent thereto.

The reference current setting unit 109 generates a reference current Iset for setting a target value for the output current Iout. The reference current Iset can be arbitrarily set by adjusting the resistance value of the resistor R4. The reference current setting unit 109 also has a temperature derating function for adjusting the reference current Iset according to the resistance value of the negative characteristic thermistor NTC.

The ISET open / short detection unit 110 detects whether an open / short has occurred in the ISET pin by comparing the terminal voltage of the ISET pin with a predetermined threshold voltage, and the detection result is controlled by the control logic unit 111. Notify

The control logic unit 111 is a main body that comprehensively controls the operation of the entire LED driving device 100. For example, the control logic unit 111 detects detections obtained by various abnormality detection units (overvoltage mute unit 104, protect bus function unit 105, LED open detection unit 107, LED short detection unit 108, ISET open / short detection unit 110). It has a function of variably controlling the current value of the output current Iout according to the result and switching its output availability.

The bypass function unit 112 monitors the monitoring voltage Vm (= divided voltage of the power supply voltage Vin) input to the SWCNT pin, and cannot ensure the total forward voltage drop Vf_total of the LED light source 200 when the power supply voltage Vin decreases (= the LED light source 200). When the power supply voltage Vin decreases to the voltage value), the output current Iout flows by bypassing at least one of the plurality of LED chips 201 to 203 (the LED chip 203 in this figure) constituting the LED light source 200. The total number of LED chips in series is reduced, and the total forward voltage drop Vf_total of the LED light source 200 is lowered.

For example, by reducing the number of LED chips in series from “3” to “2”, the total forward voltage drop Vf_total of the LED light source 200 can be reduced from “3 Vf” to “2 Vf” (where Vf is the LED chip) 201-203 forward voltage drop).

By incorporating such a bypass function unit 112, it is possible to keep the LED light source 200 on even if the power supply voltage Vin decreases. The configuration and operation of the bypass function unit 112 will be described in detail later.

Transistors N1 and N2 are connected between the DISC pin and the ground terminal, and are on / off controlled by the CR timer 106.

The current source CS1 and the switch SW1 are connected in series between the application terminal of the reference voltage VREG and the CRT pin. The current source CS1 generates a source current for charging the capacitor C3. As described above, the switch SW1 is turned on / off in response to the PWM dimming signal S1 output from the CR timer 106.

The current source CS2 and the switch SW2 are connected in series between the VIN pin and the IOUT pin. The current source CS2 generates a source current (for example, 1 mA) for preventing the LED short detection unit 108 from malfunctioning. For example, the switch SW1 is turned on when the terminal voltage of the IOUT pin (= output voltage Vout) becomes lower than a predetermined threshold voltage (for example, 0.8 V).

<Bypass function unit (first embodiment)>
FIG. 2 is a diagram illustrating a first embodiment of the bypass function unit 112. The bypass function unit 112 of the present embodiment includes a comparator 112a and a switch 112b (in this embodiment, an N-channel MOS field effect transistor).

The comparator 112a includes a monitoring voltage Vm (= divided voltage of the power supply voltage Vin) input to the inverting input terminal (−) and a threshold voltage VthL / VthH (where VthL <VthH) input to the non-inverting input terminal (+). ) To generate a comparison signal Sa. The comparison signal Sa falls from the high level to the low level when Vm> VthH (for example, VthH = 2.0 V) when the power supply voltage Vin increases. On the other hand, the comparison signal Sa rises from a low level to a high level when Vm <VthL (for example, VthL = 1.8 V) when the power supply voltage Vin decreases.

As described above, by using a hysteresis comparator having hysteresis in the threshold voltage VthL / VthH as the comparator 112a, the logic level of the comparison signal Sa is not unnecessarily switched even when noise or the like is superimposed on the monitoring voltage Vm. Therefore, it is possible to improve the operational stability of the bypass function unit 112.

If the power supply voltage Vin is within the input dynamic range of the comparator 112a, the resistors R1 and R2 may be omitted and the power supply voltage Vin may be directly input to the comparator 112a.

The switch 112b is connected between the SW pin and the ground terminal, and is turned on / off in accordance with the comparison signal Sa to turn on at least one of the LED chips 201 to 203 (the LED chip 203 in the example of this figure). Switches whether to bypass.

More specifically, when the comparison signal Sa is at a low level, the switch 112b is turned off, so that the LED chip 203 is not bypassed. At this time, the output current Iout output from the IOUT pin flows through the first current path to the ground terminal via all the LED chips 201 to 203.

On the other hand, when the comparison signal Sa is at the high level, the switch 112b is turned on, so that the LED chip 203 is bypassed. At this time, the output current Iout output from the IOUT pin flows into the second current path from the cathode of the LED chip 202 to the SW pin and reaching the ground terminal.

Hereinafter, the first output current flowing through the first current path is referred to as IoutA, and the second output current flowing through the second current path is referred to as IoutB. Note that a relationship of Iout = IoutA + IoutB is established between the output current Iout output from the IOUT pin, the first output current IoutA, and the second output current IoutB.

FIG. 3 is a timing chart showing an example of the bypass operation in the first embodiment. The power supply voltage Vin, the output current Iout, the first output current IoutA, and the second output current IoutB are depicted in order from the top. ing.

For example, when the power supply voltage Vin rises, while Vin <VthH × {(R1 + R2) / R2}, that is, while Vm <VthH, the comparison signal Sa becomes high level and the switch 112b is turned on. As a result, the LED light source 200 is in a state where the LED chip 203 is bypassed. At this time, the output current Iout flows through the second current path via the SW pin instead of the first current path via the LED chip 203. Therefore, IoutA = 0 and IoutB = Iout.

As described above, while the power supply voltage Vin is low, the LED chip 203 is bypassed, the number of series stages of the LED chips through which the output current Iout flows is reduced, and the total forward drop voltage Vf_total of the LED light source 200 is reduced. The lighting of 200 is maintained.

Thereafter, when the power supply voltage Vin rises sufficiently and Vin> VthH × {(R1 + R2) / R2}, that is, Vm> VthH, the comparison signal Sa falls to the low level, and the switch 112b is turned off. As a result, the LED light source 200 is in a state where the LED chip 203 is not bypassed. At this time, the output current Iout flows through the first current path via the LED chip 203 instead of the second current path via the SW pin. Therefore, IoutB = 0 and IoutA = Iout.

As described above, when the power supply voltage Vin becomes high, the LED light source 200 is turned on with the maximum luminance by releasing the bypass of the LED chip 203 and causing all the LED chips 201 to 203 to emit light.

After the power supply voltage Vin once rises, the comparison signal Sa is maintained at a low level while Vin> VthL × {(R1 + R2) / R2}, that is, Vm> VthL, and the switch 112b is turned off. Will remain. As a result, since the bypass release state of the LED chip 203 is continued, the LED light source 200 is continuously lit at the maximum luminance.

However, when the power supply voltage Vin further decreases and Vin <VthL × {(R1 + R2) / R2}, that is, Vm <VthL, the comparison signal Sa rises to a high level and the switch 112b is turned on. As a result, the LED chip 203 is bypassed again, and the total forward voltage drop Vf_total of the LED light source 200 is lowered, so that the LED light source 200 is kept on.

As described above, the bypass function unit 112 compares the power supply voltage Vin with the bypass release voltage VthH × {(R1 + R2) / R2} and the bypass start voltage VthL × {(R1 + R2) / R2}. Bypass control is performed. Note that both the bypass release voltage and the bypass start voltage can be arbitrarily set by adjusting the resistance values of the resistors R1 and R2 externally attached to the SWCNT pin.

<Bypass function unit (second embodiment)>
FIG. 4 is a diagram illustrating a second embodiment of the bypass function unit 112. The bypass function unit 112 of the present embodiment includes operational amplifiers AMP1 to AMP3, N-channel MOS field effect transistors M1 to M3, current mirrors CM1 and CM2, a current control unit CTRL, and resistors Ra to Rd. The LED driving device 100 is provided with an ISINK pin, a SET pin, and an RVIN pin instead of the SW pin and the SWCNT pin of FIG. Note that the anode of the LED chip 203 (= the cathode of the LED chip 202) is connected to the ISINK pin. Further, resistors RSET and RVIN are externally attached to the SET pin and the RVIN pin, respectively. Below, the connection relationship of each element in the LED drive device 100 is demonstrated concretely.

A predetermined reference voltage VREF (for example, a band gap voltage) is input to the non-inverting input terminal (+) of the operational amplifier AMP1. The inverting input terminal (−) of the operational amplifier AMP1 is connected to the SET pin and the source and back gate of the transistor M1. The output terminal of the operational amplifier AMP1 is connected to the gate of the transistor M1. The drain of the transistor M1 is connected to the current input terminal of the current mirror CM1. The current output terminal of the current mirror CM1 is connected to the current input terminal of the current mirror CM2. The current output terminal of the current mirror CM2 is connected to the first current input terminal (= input terminal of the internal current Ia) of the current control unit CTRL.

The resistors Ra and Rb are connected in series between the input terminal of the power supply voltage Vin and the ground terminal. The non-inverting input terminal (+) of the operational amplifier AMP2 is connected to a connection node between the resistors Ra and Rb. The inverting input terminal (−) of the operational amplifier AMP2 is connected to the RVIN pin and the source and back gate of the transistor M2. The output terminal of the operational amplifier AMP2 is connected to the gate of the transistor M2. The drain of the transistor M2 is connected to the second current input terminal (= input terminal of the internal current Ib) of the current control unit CTRL.

The first end of the resistor Rc is connected to the current output end (= output end of the internal current Ic) of the current control unit CTRL. A second end of the resistor Rc is connected to the ground end. The non-inverting input terminal (+) of the operational amplifier AMP3 is connected to the first terminal of the resistor Rc. The inverting input terminal (−) of the operational amplifier AMP3 is connected to the first terminal of the resistor Rd and the source and back gate of the transistor M3. The second end of the resistor Rd is connected to the ground end. The output terminal of the operational amplifier AMP3 is connected to the gate of the transistor M3. The drain of transistor M3 is connected to the ISINK pin.

In the bypass function unit 112 of the present embodiment, the operational amplifier AMP1 controls the gate of the transistor M1 so that its two input terminals are imaginarily short-circuited. Therefore, the drain current of the transistor M1 has a current value (= VREF / RSET) corresponding to the reference voltage VREF and the resistor RSET.

The current mirror CM1 is connected between the application terminal of the internal power supply voltage VREG and the transistor M1, and mirrors an input current (= drain current of the transistor M1) to output current (= source flowing into the current mirror CM2). Current).

The current mirror CM2 is connected between the current output terminal and the ground terminal of the current mirror CM1, and mirrors the input current (= source current flowing from the current mirror CM1) to output current (= current control unit CTRL). , Which is a sink current drawn from, and corresponds to the internal current Ia).

If the coefficient for setting Ia (= the mirror ratio of the current mirrors CM1 and CM2) is α, the current value of the internal current Ia is obtained by Ia = α × VREF / RSET.

As described above, the operational amplifier AMP1, the transistor M1, the resistor RSET, and the current mirrors CM1 and CM2 function as a first internal current generation unit that generates a fixed-value internal current Ia.

On the other hand, the operational amplifier AMP2 controls the gate of the transistor M2 so that its two input terminals are imaginarily short-circuited. Accordingly, the drain current of the transistor M2 (= the sink current drawn from the current control unit CTRL and corresponding to the internal current Ib) becomes a current value (= β × Vin / RVIN) corresponding to the power supply voltage Vin and the resistance RVIN. . Note that β in the formula is a coefficient for setting Ib, and can be expressed as a voltage dividing ratio of the resistors Ra and Rb (= Rb / (Ra + Rb)).

As described above, the operational amplifier AMP2, the transistor M2, the resistor RVIN, and the resistors Ra and Rb function as a second internal current generator that generates an internal current Ib having a variable value corresponding to the power supply voltage Vin.

The current control unit CTRL generates an internal current Ic (= Ia−Ib) by subtracting the internal current Ib from the internal current Ia.

The operational amplifier AMP3 controls the gate of the transistor M3 so that its two input terminals are imaginary short-circuited. Accordingly, the drain current of the transistor M3 (= the sink current drawn from the ISINK pin and corresponding to the second output current IoutB) is a current value (= Ic × Rc / Rd) corresponding to the internal current Ic and the resistors Rc and Rd. )

As described above, the operational amplifier AMP3, the transistor M3, and the resistors Rc and Rd function as a current sink unit that draws the second output current IoutB corresponding to the internal current Ic from the ISINK pin.

FIG. 5 is a timing chart showing an example of the bypass operation in the second embodiment. Similarly to FIG. 3, the power supply voltage Vin, the output current Iout, the first output current IoutA, and the second The output current IoutB is depicted.

For example, when the power supply voltage Vin is raised, if Vin is lower than a predetermined set voltage (= VREF × (RVIN / RSET) × (α / β)), Ia> Ib and IoutB> 0. At this time, if the coefficients α and β are set so that IoutB> Iout, all the output current Iout flows into the ISINK pin, so that IoutA = 0. That is, in the LED light source 200, the LED chip 203 is completely bypassed, and only the LED chips 201 and 202 are lit (see period (1) in the drawing).

Thereafter, when the power supply voltage Vin reaches a voltage value (= VREF × (RVIN / RSET) × (α / β) − (Rd / Rc) × (RVIN / β) × Iout) where IoutB = Iout) The output current IoutB starts to decrease. Thereafter, as the power supply voltage Vin increases, the second output current IoutB gradually decreases, and the first output current IoutA increases in a complementary manner by the amount of the decrease (period ( See 2)).

Furthermore, when the power supply voltage Vin rises and Vin> VREF × (RVIN / RSET) × (α / β), the bypass of the LED chip 203 is completely released. At this time, all of the output current Iout flows through the first current path via the LED chip 203 instead of the second current path via the ISINK pin. Therefore, IoutB = 0 and IoutA = Iout (see period (3) in the figure).

Contrary to the above, when the power supply voltage Vin decreases, when Vin <VREF × (RVIN / RSET) × (α / β), the first output current IoutA starts to decrease, and the decrease is the first. The output current IoutB of 2 begins to increase complementarily.

After that, when the power supply voltage Vin is further decreased to VREF × (RVIN / RSET) × (α / β) − (Rd / Rc) × (RVIN / β) × Iout, the LED chip 203 is completely bypassed. Return to state. Therefore, IoutA = 0 and IoutB = Iout.

As described above, the bypass function unit 112 of the second embodiment controls whether to bypass the LED chip 203 and switches the number of LED chips in series in which the output current Iout flows, from the cathode of the LED chip 202. By performing linear control of the second output current IoutB drawn into the SW pin, the first output current IoutA that fluctuates complementarily to the second output current IoutB (= the output current flowing through the LED chip 203 to be bypassed) ) Is gradually changed. That is, complementary linear cross control of the first output current IoutA and the second output current IoutB is performed.

In the case of the bypass function unit 112 of the present embodiment, when the bypass state of the LED chip 203 is switched, the luminance change of the LED light source 200 is moderate as compared to the first embodiment (FIG. 2). The user does not feel uncomfortable.

<LED light emitting device (element addition example)>
FIG. 6 is a diagram illustrating an example of adding elements of the LED light emitting device X1. The LED light-emitting device X1 of this configuration example further includes resistors R5 to R7 based on FIG. The resistor R5 is connected between the anode of each of the diodes D2 and D3 and the ground terminal. The resistor R6 is connected between the THD pin and the ground terminal. The resistor R7 is connected between the THD pin and the negative characteristic thermistor NTC.

<Bypass function unit (third embodiment)>
FIG. 7 is a diagram illustrating a third embodiment of the bypass function unit 112 (and the LED driving device 100 including the bypass function unit 112). The LED drive device 100 of the present embodiment has basically the same configuration as that of the first embodiment (FIG. 1), but some components are not illustrated.

In addition, for some components, the respective codes are changed (IOUT → OUT, ISET → SET, SW → ISLINK, SWCNT → BPCNT, IoutB → Isink, R1 → RBP1, R2 → RBP2, R4 → RSET. ). However, each function is basically unchanged.

Also, a resistor RBP3 is newly provided between the connection node between the resistors RBP1 and RBP2 (= applied end of the divided voltage Vin_div) and the BPCNT pin. The connection relationship between the resistors RBP1 to RBP3 will be specifically described. A first end of the resistor RBP1 is connected to an application end of the power supply voltage Vin. A second end of the resistor RBP1 and a first end of each of the resistors RBP2 and RBP3 are connected to an application end of the divided voltage Vin_div (= Vin × {RBP2 / (RBP1 + RBP2)}). A second end of the resistor RBP2 is connected to the ground end. A second end of the resistor RBP3 is connected to the BPCNT pin.

Hereinafter, the bypass function unit 112 having a new configuration will be described mainly. The bypass function unit 112 of the present embodiment includes an operational amplifier 112A, a P-channel MOS field effect transistor 112B, coefficient multiplication units 112C and 112D, a subtraction unit 112E, and a current source 112F.

The inverting input terminal (−) of the operational amplifier 112A is connected to the BPCNT pin (= corresponding to a bypass control terminal). The non-inverting input terminal (+) of the operational amplifier 112A is connected to the application terminal of the threshold voltage VBP. The output terminal of the operational amplifier 112A is connected to the gate of the transistor 112B. The source and back gate of transistor 112B are connected to the BPCNT pin. The drain of the transistor 112B is connected to the input terminal of the coefficient multiplier 112D.

The operational amplifier 112A and the transistor 112B connected in this way function as a control current generation unit that generates the control current IBPCTL so that the terminal voltage Vin_div2 of the BPCTL pin matches the threshold voltage VBP.

Note that the control current IBPCTL flows from the application end of the divided voltage Vin_div to the transistor 112B via the resistor RBP3. Accordingly, the terminal voltage Vin_div2 is a voltage obtained by subtracting the voltage drop at the resistor RBP3 corresponding to the control current IBPCTL from the divided voltage Vin_div (= Vin_div−IBPCTL × RBP3).

The coefficient multiplication unit 112C multiplies the reference current Iset for determining the target value of the output current Iout by a coefficient Ksink (= Isink current setting coefficient).

The coefficient multiplier 112D multiplies the control current IBPCNT by the coefficient G sink (= I sink current gain).

The subtractor 112E subtracts the output signal of the coefficient multiplier 112D from the output signal of the coefficient multiplier 112C.

The current source 112F is a sink current I sink that is drawn from the cathode of the LED chip 202 to the ISINK pin in accordance with the output signal of the subtractor 112E (= corresponding to the branch current that does not pass through the bypassed LED chip 203 in the output current Iout) Is generated.

The set value of the sink current I sink and the maximum value I sink_max thereof, and the control current IBPCNT can be calculated by the following equations (1a), (1b), and (1c), respectively.

As can be seen from the above equation, the bypass function unit 112 of the present embodiment can variably control the set value of the sink current Isink based on the control current IBPCTL corresponding to the power supply voltage Vin or the divided voltage Vin_div.

If the bypass function unit 112 is not used, the ISINK pin may be connected to GND, and the BPCNT pin may be connected to a resistor pull-down or GND.

FIG. 8 is a timing chart showing an example of the bypass operation in the third embodiment. In order from the top, the power supply voltage Vin, the divided voltage Vin_div and the terminal voltage Vin_div2, the output current Iout, the control current IBPCNT, the sink current Isink, and , The output current IoutA (= Iout−Isink) is depicted.

Before time t1, the power supply voltage Vin is not sufficiently increased, and the terminal voltage Vin_div2 (the same value as the divided voltage Vin_div at this time) is lower than the threshold voltage VBP. Therefore, since the output signal of the operational amplifier 112A sticks to the upper limit value (= high level potential) of the output dynamic range, the transistor 112B is in a full-off state, and the control current IBPCTL does not flow at all (IBPCTL = 0). As a result, the set value of the sink current I sink is the maximum value I sink_max (= see the above equation (1b)).

Here, the maximum value I sink_max may be set to a value larger than the target value of the output current Iout. According to such setting, the output current Iout can be entirely covered by the sink current Isink, so that the output current IoutA flowing through the LED chip 203 is maintained at a zero value.

That is, in the LED light source 200, the LED chip 203 is completely bypassed, and only the LED chips 201 and 202 are lit. Thus, while the power supply voltage Vin is low, the LED chip 203 can be bypassed to reduce the number of LED chips connected in series, and the total forward voltage drop Vf_total of the LED light source 200 can be reduced. The LED light source 200 can be kept on.

After that, when the terminal voltage Vin_div2 (= divided voltage Vin_div) exceeds the threshold voltage VBP at time t1, as the power supply voltage Vin increases, the output signal of the operational amplifier 112A decreases, so that the control current IBPCTL flows through the transistor 112B. start. As a result, the set value of the sink current I sink decreases from the maximum value I sink_max as the control current IBPCNT increases.

However, since the set value of the sink current I sink is still higher than the target value of the output current I out at the time t1, the output current I out is all covered by the sink current I sink. As a result, the output current IoutA flowing through the LED chip 203 remains at a zero value.

Further, when the control current IBPCTL starts to flow, the terminal voltage Vin_div2 becomes a voltage obtained by subtracting the voltage drop at the resistor RBP3 corresponding to the control current IBPCTL from the divided voltage Vin_div (= Vin_div−IBPCTL × RBP3). Thereafter, the terminal voltage Vin_div2 is maintained at a voltage value (or a voltage value substantially equal to) the threshold voltage VBP.

Furthermore, when the power supply voltage Vin rises and the set value of the sink current I sink becomes lower than the target value of the output current Iout at time t2, it is impossible to cover all of the output current Iout with the sink current I sink. As a result, after time t2, the sink current I sink gradually decreases as the power supply voltage Vin increases, and the output current IoutA increases complementarily by the decrease.

Thereafter, when the sink current I sink does not flow at time t3 due to a further increase in the power supply voltage Vin, the output current Iout flows as the output current IoutA, that is, the bypass of the LED chip 203 is completely released. Become.

Thus, in the bypass function unit 112 of the present embodiment, the sink current I sink drawn from the cathode of the LED chip 202 to the ISINK pin and the LED chip 203 to be bypassed, as in the second embodiment (FIG. 4). Complementary linear cross control with the output current IoutA flowing through the

In the case of the bypass function unit 112 of the present embodiment, the power supply voltage Vin starting to decrease the set value of the sink current I sink by appropriately adjusting the resistance values of the external resistors RBP1, RBP2, and RBP3, and the sink Both the slope when the set value of the current I sink is lowered (the power supply voltage Vin at which the sink current I sink does not flow) can be arbitrarily set. Hereinafter, a specific example will be described.

FIG. 9 is a diagram illustrating a first setting example (Iout = 100 mA) of the resistors RBP1, RBP2, and RBP3. The horizontal axis represents the power supply voltage Vin [V], and the vertical axis represents the set value [mA] of the sink current I sink. In the following description, VBPstart corresponds to the power supply voltage Vin at which the set value of the sink current I sink starts to decrease. Further, ΔVBP [V] indicates an increase width of the power supply voltage Vin required from when the set value of the sink current I sink starts to decrease to the zero value.

First, consider the case where VBPstart = 6V and ΔVBP = 4V are set as indicated by the solid line (1). In this case, adjustment may be made to RBP1 = 46.7 kΩ, RBP2 = 30.0 kΩ, and RBP3 = 96.5 kΩ, respectively.

Next, consider the case where VBPstart = 6V and ΔVBP = 1V are set as indicated by a small broken line (2). In this case, RBP1 = 18.9 kΩ, RBP2 = 10.0 kΩ, and RBP3 = 18.8 kΩ may be adjusted.

Next, consider the case where VBPstart = 9V and ΔVBP = 4V are set as indicated by the large broken line (3). In this case, RBP1 = 30.6 kΩ, RBP2 = 10.0 kΩ, and RBP3 = 64.8 kΩ may be adjusted.

Finally, consider the case where VBPstart = 9V and ΔVBP = 1V are set as indicated by the alternate long and short dash line (4). In this case, adjustment may be made to RBP1 = 33.9 kΩ, RBP2 = 10.0 kΩ, and RBP3 = 8.99 kΩ, respectively.

FIG. 10 is a diagram illustrating a second setting example (Iout = 600 mA) of the resistors RBP1, RBP2, and RBP3. As in FIG. 9, the horizontal axis represents the power supply voltage Vin [V], and the vertical axis represents the set value [mA] of the sink current Isink.

First, consider the case where VBPstart = 6V and ΔVBP = 4V are set as indicated by the solid line (1). In this case, RBP1 = 15.6 kΩ, RBP2 = 10.0 kΩ, and RBP3 = 13.0 kΩ may be adjusted.

Next, consider the case where VBPstart = 6V and ΔVBP = 1V are set as indicated by a small broken line (2). In this case, adjustment may be made to RBP1 = 10.58 kΩ, RBP2 = 5.6 kΩ, and RBP3 = 0.57 kΩ, respectively.

Next, consider the case where VBPstart = 9V and ΔVBP = 4V are set as indicated by the large broken line (3). In this case, RBP1 = 30.6 kΩ, RBP2 = 10.0 kΩ, and RBP3 = 4.52 kΩ may be adjusted.

Finally, consider the case where VBPstart = 9V and ΔVBP = 1V are set as indicated by the alternate long and short dash line (4). In this case, RBP1 = 11.18 kΩ, RBP2 = 3.30 kΩ, and RBP3 = 0.24 kΩ, respectively.

<Bypass function unit (fourth embodiment)>
FIG. 11 is a diagram illustrating a fourth embodiment of the bypass function unit 112. The bypass function unit 112 of the present embodiment is a configuration embodying the third embodiment (FIG. 7), and includes the previous operational amplifier 112A and the transistor 112B, as well as coefficient multiplication units 112C and 112D, a subtraction unit 112E, As the components corresponding to the current source 112F, an operational amplifier 112G, a current source 112H, an N-channel MOS field effect transistor 112I, and resistors RA, RB, and RC are included.

The first end of the current source 112H is connected to the power supply end. The second end of the current source 112H and the first end of the resistor RA are connected to the non-inverting input terminal (+) of the operational amplifier 112G. A second end of the resistor RA is connected to the ground end. The inverting input terminal (−) of the operational amplifier 112G is connected to the drain of the transistor 112B and the first terminal of the resistor RC. The output terminal of the operational amplifier 112G is connected to the gate of the transistor 112I. The drain of transistor 112I is connected to the ISINK pin. The source and back gate of the transistor 112I are connected to the first end of the resistor RB and the second end of the resistor RC. A second end of the resistor RB is connected to the ground end.

The current source 112H generates a reference current Iset (or a constant current corresponding thereto) for determining a target value of the output current Iout. The resistor RA is a current / voltage conversion element that converts the reference current Iset into a reference voltage Vref. As described above, the current source 112H and the resistor RA function as a reference voltage generation unit that generates the reference voltage Vref (= Iset × RA) corresponding to the target value of the output current Iout.

The resistor RB is a current / voltage conversion element that converts the sink current I sink into the sense voltage Vs. Thus, the resistor RB functions as a current detection unit that generates the sense voltage Vs (= I sink × RB) corresponding to the sink current I sink.

The resistor RC generates an offset voltage Vofs (= IBPCTL × RC) corresponding to the control current IBPCTL, and functions as an offset applying unit that adds this to the sense voltage Vs. When the offset voltage Vofs ′ (= IBPCTL × RB) generated between both ends of the resistor RB in accordance with the control current IBPCTL cannot be ignored, the resistors RB and RC may be understood as the offset applying unit. .

The operational amplifier 112G and the transistor 112I function as a sink current generator that generates the sink current I sink so that the offset sense voltage (Vs + Vofs) matches the reference voltage Vref.

For example, when the power supply voltage Vin is low and the control current IBPCTL is not flowing, the sink current Isink is generated so that the sense voltage Vs to which no offset is applied matches the reference voltage Vref. This state corresponds to a state where the set value of the sink current I sink is set to the maximum value I sink_max and the output current IoutA does not flow at all, that is, the LED chip 203 is completely bypassed.

On the other hand, when the power supply voltage Vin rises and the control current IBPCTL starts to flow, the offset voltage Vofs corresponding to the current value is added to the sense voltage Vs and fed back to the operational amplifier 112G. As a result, the feedback loop reaches equilibrium with a smaller sink current I sink. This state corresponds to a state where the set value of the sink current I sink is lowered from the maximum value I sink_max, that is, a state where complementary linear cross control of the sink current I sink and the output current I outA is performed.

Finally, when the power supply voltage Vin rises until the offset voltage Vofs corresponding to the control current IBPCTL exceeds a predetermined reference voltage Vref, the sink current I sink no longer flows. This state is a state where all the output current Iout flows as the output current IoutA, that is, a state where the bypass of the LED chip 203 is completely released.

<Terminal arrangement>
FIG. 12 is a diagram showing a terminal arrangement of the LED driving device 100 in FIGS. 7 and 11. The LED driving device 100 is sealed in a VSON (Very-thin Small Outline No Lead) package, and has ten external terminals (VIN pin, BPCNT as means for establishing electrical connection with the outside of the device). Pin, PBUS pin, CRT pin, DISC pin, THD pin, SET pin, GND pin, ISINK pin, and OUT pin).

The VIN pin (pin 1) is a power supply voltage input terminal. The BPCNT pin (pin 2) is a current bypass function setting terminal at the time of power reduction. The PBUS pin (pin 3) is an abnormal state flag output / output current off control input terminal. The CRT pin (pin 4) and the DISC pin (pin 5) are CR timer setting terminals, respectively. The THD pin (pin 6) is a temperature derating setting terminal. The SET pin (pin 7) is an output current setting terminal. The GND pin (8 pin) is a ground terminal. The ISINK pin (pin 9) is a current sink terminal. The OUT pin (10 pin) is a current output terminal.

In addition, since the BPCNT pin (pin 2) is a resistance voltage dividing input terminal for the power supply voltage Vin, it is desirable to provide it adjacent to the VIN pin (pin 1).

Also, since both the OUT pin (10 pin) and the ISINK pin (9 pin) are terminals connected to the LED light source 200, it is desirable to provide them adjacent to each other. By adopting such a pin arrangement, even if the OUT pin and the ISINK pin are short-circuited, only a part of the LED light source 200 (= LED chips 201 and 202 connected between OUT and ISINK) is turned off. The drive device 100 is not destroyed. When the power supply voltage Vin rises, the lowermost LED chip 203 is lit.

Also, it is desirable to provide the ISINK pin (9 pins) adjacent to the GND pin (8 pins). If such a pin arrangement is adopted, even if the ISINK pin and the GND pin are short-circuited, a part of the LED light source 200 (= LED chips 201 and 202 connected between OUT and ISINK) is lit.

Further, the LED driving device 100 is provided with a heat radiation pad EXP-PAD on the lower surface of the package. Note that the heat dissipation pad EXP-PAD may be GND-connected.

<Socket type LED module>
FIG. 13 is a plan view showing a socket-type LED module Y as an example of realizing the LED light-emitting device X1 described so far. The socket type LED module Y of this configuration example is, for example, an in-vehicle lighting fixture, and includes a substrate 300, an LED chip 400 (corresponding to the above-described LED chips 201 to 203), a white resin 480, a reflector 600, a terminal 800, Various electronic components (LED driving device 100, resistors R1 to R7, capacitors C1 to C3, diodes D1 to D3, negative characteristic thermistor NTC) and a socket 900 are provided.

The substrate 300 has a base material and a wiring pattern formed thereon (see the hatched area in the figure). The substrate has a rectangular shape and is made of, for example, a glass epoxy resin. The wiring pattern is a conductive member laid on the surface of the base material for mounting the LED chip 400 and various electronic components, and is made of, for example, a metal such as Cu or Ag. On the upper surface of the substrate 300, the LED driving device 100, resistors R1 to R7, capacitors C1 to C3, diodes D1 to D3, and a negative characteristic thermistor NTC are mounted. Each electronic component is connected by a wiring pattern laid on the upper and lower surfaces of the substrate 300 to form a circuit, and is for lighting the LED chip 400 in a desired light emitting state.

In the following, the up, down, left, and right directions of the page are defined as the up, down, left, and right directions of the substrate 300, the component arrangement direction parallel to the up and down direction of the substrate 300 is defined as the vertical direction, The direction is defined as horizontal, and the arrangement of electronic components (depicted by a thin broken frame in the drawing) will be described.

The LED driving device 100 is arranged in the upper left area of the substrate 300 so that the arrangement direction of the pins is horizontal.

The resistor R1 is disposed sideways on the upper right side of the LED driving device 100 in the upper central region of the substrate 300. The resistor R2 is disposed sideways on the upper side of the LED driving device 100 (left side of the resistor R1) in the upper left region of the substrate 300. The resistor R <b> 3 is arranged vertically on the left side of the LED driving device 100 in the upper left region of the substrate 300. The resistor R <b> 4 is disposed laterally below the LED driving device 100 in the upper left region of the substrate 300. The resistor R5 is disposed horizontally on the right side of the diode D2 in the lower left region of the substrate 300. The resistor R <b> 6 is disposed sideways on the left side of the LED driving device 100 in the upper left region of the substrate 300. The resistor R7 is disposed in the horizontal direction on the lower left side of the LED driving device 100 (below the resistor R6) in the upper left region of the substrate 300. Negative characteristic thermistor NTC is arranged vertically below resistor R7 in the left center region of substrate 300.

The capacitor C <b> 1 is arranged vertically on the right side of the LED driving device 100 in the upper center region of the substrate 300. The capacitor C <b> 2 is disposed sideways on the right side of the LED driving device 100 in the upper center region of the substrate 300. The capacitor C3 is arranged in the vertical direction on the left side of the resistor R3 and above the resistor R6 in the upper left region of the substrate 300.

The diode D1 is arranged vertically in the lower right region of the substrate 300. The diode D <b> 2 is arranged in the vertical direction in the lower left region of the substrate 300. The diode D3 is arranged vertically in the left center region of the substrate 300 on the left side of the negative characteristic thermistor NTC. The diode D3 is smaller than the diodes D1 and D2.

Note that the type, number and location of electronic components are not limited to the above.

The reflector 600 is made of, for example, a white resin, and is fixed to the central region of the substrate 300 so as to surround the LED chip 400. The reflector 600 is for reflecting upward the light emitted from the LED chip 400 to the side. A reflecting surface 601 is formed on the reflector 600. The reflective surface 601 surrounds the LED chip 400. Although it is difficult to understand in FIG. 13, the reflective surface 601 moves away from the LED chip 400 in the direction perpendicular to the thickness direction of the substrate 300 as it is separated from the substrate 300 in the thickness direction of the substrate 300. It is inclined to. That is, the reflecting surface 601 has a tapered shape in which a cross section orthogonal to the thickness direction of the substrate 300 increases toward the opening side of the reflector 600.

The LED chip 400 is a light source of the socket type LED module Y and emits red light, for example. In this configuration example, the three LED chips 400 are mounted on the substrate 300 so as to be surrounded by the reflector 600. In the drawing, three LED chips 400 are respectively arranged at positions corresponding to the vertices of the equilateral triangle. However, the layout of the LED chip 400 is not limited to this, and for example, as shown in FIG. 14, the three LED chips 400 may be arranged in a line along the left-right direction of the substrate 300. .

In this configuration example, the case where the LED chip 400 emits red light has been described. However, the emission color of the LED chip 400 is not limited thereto.

The white resin 480 is made of a white resin material that does not transmit light from the LED chip 400 and corresponds to an example of an opaque resin. As can be understood from FIG. 13, the white resin 480 surrounds the LED chip 400, and the outer peripheral edge reaches the reflecting surface 601 of the reflector 600. For this reason, in FIG. 13, the region extending from the LED chip 400 to the reflection surface 601 in the vertical direction and the horizontal direction in the drawing is filled with the white resin 480.

The terminal 800 is a metal wire serving as an electrode, and is provided through the substrate 300 and the socket 900. One end of the terminal 800 is connected to a part of the wiring pattern by, for example, solder.

The socket 900 is a component that mounts the substrate 300 and is attached to, for example, an automobile. The socket 900 is made of, for example, a synthetic resin, and is formed by, for example, injection molding. The socket 900 includes a mounting portion 910 for mounting the substrate 300 and an attachment portion for attachment to an automobile or the like. The mounting portion 910 has a cylindrical shape with one opening, and the substrate 300 is mounted on the inner bottom surface of the mounting portion 910. A heat radiating plate 950, which is a circular plate made of, for example, aluminum, is fixed to the inner bottom surface of the mounting portion 910. The substrate 300 is mounted on the mounting portion 910 of the socket 900 by bonding the lower surface to the upper surface of the heat sink 950 with an adhesive.

Next, the operation of the socket type LED module Y will be described.

The white resin 480 covers the entire annular region from the support substrate of the LED chip 400 to the reflection surface 601 of the reflector 600. Therefore, the area surrounded by the reflective surface 601 is covered with the white resin 480 except for the area occupied by the LED chip 400. Thereby, more light from the semiconductor layer of the LED chip 400 can be reflected. This is suitable for increasing the brightness of the socket type LED module Y. In addition, it is not necessary to separately perform a process for suitably reflecting light in the region surrounded by the reflection surface 601 of the substrate 300.

By providing the reflector 600 having the reflective surface 601, the direction directly above the socket-type LED module Y can be illuminated more brightly.

In the socket type LED module Y, the LED chips 400 serving as the light source are concentrated in one place. Therefore, even if any one of the LED chips 400 is bypassed by using the bypass function unit 112 when the power supply voltage Vin is decreased, only the brightness of one LED chip is decreased. It will never go out.

In particular, in-vehicle lamps are required to comply with the law that the lighting state must be maintained even when the power supply voltage Vin decreases. In view of this, it can be said that the LED driving device 100 including the bypass function unit 112 is very suitable as a driving subject of the in-vehicle lamp.

In the case where priority is given to uniform light emission of the socket type LED module Y, for example, in FIG. On the other hand, if priority is given to the ease of laying the printed wiring, for example, in FIG. 14, the LED chip disposed at the end may be targeted for bypass.

<Application>
The LED driving device 100 described so far includes, for example, as shown in FIGS. 15 and 16, a headlamp (including a high beam / low beam / small lamp / fog lamp, etc.) X11 of a vehicle X10, a daytime running lamp. (DRL [daylight running lamps]) X12, tail lamps (including small lamps and back lamps as appropriate) X13, stop lamps X14, turn lamps X15 and the like can be incorporated and used.

The LED driving device 100 includes a module (socket-type LED module Y in FIGS. 13 to 14, LED headlamp module Y10 in FIG. 17, LED turn lamp module Y20 in FIG. 19 may be provided as an LED rear lamp module Y30 of FIG. 19, or may be provided as an IC unit independently of the LED light source 200.

<Other variations>
In the above embodiment, the configuration using a light emitting diode as a light emitting element has been described as an example. However, the configuration of the present invention is not limited thereto, and for example, an organic EL [electro- It is also possible to use a luminescence] element.

In the above-described embodiment, the case where the current driver 101 is of a current source type (= an output format in which the output current Iout flows from the power supply terminal to the anode of the LED light source 200) is taken as an example. However, the present invention is not limited to this, and even when the current driver 101 is a current sink type (= an output type that draws the output current Iout from the cathode of the LED light source 200 toward the ground terminal), Introduction is effective.

In the above embodiment, among the three LED chips 201 to 203 constituting the LED light source 200, the LED chip 203 arranged on the lowest potential side is set as a bypass target. It is also possible to make a bypass target.

Also, for example, a plurality of threshold voltages Vth1 and Vth2 (where Vth1 <Vth2) to be compared with the power supply voltage Vin are prepared. When Vin <Vth1, both the LED chips 202 and 203 are bypassed, and Vth1 <Vin When Vth2, the bypass of the LED chip 202 is released and only the LED chip 203 is bypassed, and when Vin> Vth2, the bypass of both the LED chips 202 and 203 is released. It is also possible.

As described above, various technical features disclosed in the present specification can be variously modified within the scope of the technical creation in addition to the above-described embodiment. For example, mutual replacement of a bipolar transistor and a MOS field effect transistor and logic level inversion of various signals are arbitrary. That is, the above-described embodiment should be considered as illustrative in all points and not restrictive, and the technical scope of the present invention is not limited to the above-described embodiment, and It should be understood that all modifications that fall within the meaning and range are included.

The invention disclosed in the present specification can be used, for example, in an in-vehicle light emitting element driving device to maintain lighting of a light emitting element light source even when a power supply voltage is lowered.

100 LED driving device (light emitting element driving device)
DESCRIPTION OF SYMBOLS 101 Current driver 102 Reference voltage generation part 103 Open mask function part 104 Overvoltage mute part 105 Protect bus function part 106 CR timer 107 LED open detection part 108 LED short detection part 109 Reference current setting part 110 ISET open / short detection part 111 Control logic Unit 112 bypass function unit 112a comparator 112b switch 112A operational amplifier 112B P channel type MOS field effect transistor 112C, 112D coefficient multiplication unit 112E subtraction unit 112F current source 112G operational amplifier 112H current source 112I N channel type MOS field effect transistor 200 LED light source (light emitting element) light source)
201, 202, 203 LED element (light emitting element)
300 Substrate 400 LED chip 480 White resin 600 Reflector 601 Reflecting surface 800 Terminal 900 Socket 910 Mounting portion 950 Heat sink R1-R4, R5-R7 Resistor C1-C3 Capacitor D1-D3 Diode NTC Negative characteristic thermistor N1, N2 N-channel type MOS Field effect transistor CS1, CS2 Current source SW1, SW2 Switch AMP1 to AMP3 Operational amplifier CM1, CM2 Current mirror CTRL Current control unit M1 to M3 N-channel MOS field effect transistor Ra to Rd, RA, RB, RC, RSET, RVIN, RBP1 3 Resistance X Vehicle X1 LED light emitting device X2 Battery X3a, X3b Power switch X10 Vehicle X11 Headlamp X 2 daytime running lamp X13 tail lamp X14 stop lamp X15 turn lamp Y socket type LED module Y10 LED headlamp module Y20 LED turn lamp module Y 30 LED Rear lamp module

Claims (20)

1. A current driver that generates an output current that flows to a light emitting element light source connected between a power supply voltage application terminal and a ground terminal;
   A bypass function unit that bypasses at least one of a plurality of light-emitting elements constituting the light-emitting element light source when the power supply voltage decreases, and reduces the number of series stages of light-emitting elements through which the output current flows;
   A light-emitting element driving device comprising:
2. The bypass function unit is
   A comparator that compares the power supply voltage or a divided voltage thereof with a predetermined threshold voltage to generate a comparison signal;
   A switch for switching whether or not to bypass at least one of the plurality of light emitting elements according to the comparison signal;
   The light-emitting element driving device according to claim 1, comprising:
3. 3. The light emitting element driving device according to claim 2, wherein the comparator is a hysteresis comparator.
4. 2. The light emitting element driving device according to claim 1, wherein the bypass function unit gradually changes an output current flowing through a light emitting element to be bypassed when switching a series number of light emitting elements through which the output current flows. .
5. The bypass function unit variably controls a set value of a branch current that does not pass through the light-emitting element to be bypassed among the output currents based on a control current corresponding to the power supply voltage or a divided voltage thereof. The light emitting element drive device according to claim 4.
6. The light emitting element driving device according to claim 5, wherein the control current starts to flow when the power supply voltage or the divided voltage becomes higher than a predetermined threshold voltage.
7. 7. The light emitting element drive according to claim 5, wherein the set value of the branch current decreases from a maximum value larger than a target value of the output current as the control current increases. apparatus.
8. The bypass function unit includes a control current generation unit configured to generate the control current so that a terminal voltage of a bypass control terminal through which the control current flows matches a predetermined threshold voltage. The light-emitting element driving device according to claim 7.
9. 9. The light emitting element driving device according to claim 8, wherein the terminal voltage is a voltage obtained by subtracting a voltage drop corresponding to the control current from the power supply voltage or the divided voltage.
10. The bypass function unit is
    A first coefficient multiplier for multiplying a reference current for determining a target value of the output current by a first coefficient;
    A second coefficient multiplier for multiplying the control current by a second coefficient;
    A subtractor for subtracting the output signal of the second coefficient multiplier from the output signal of the first coefficient multiplier;
    A current source that generates the branch current according to an output signal of the subtracting unit;
    The light-emitting element driving device according to claim 8, further comprising:
11. The bypass function unit is
    A reference voltage generation unit that generates a reference voltage according to a target value of the output current;
    A current detection unit that generates a sense voltage according to the branch current;
    An offset applying unit that gives the sense voltage an offset voltage corresponding to the control current;
    A branch current generation unit that generates the branch current so that the sense voltage to which the offset voltage is applied matches the reference voltage;
    The light-emitting element driving device according to claim 8, further comprising:
12. A first resistor connected to the power supply voltage application terminal and a second terminal connected to the divided voltage application terminal; a first terminal connected to the divided voltage application terminal; A second resistor having two ends connected to the ground end and a third resistor having the first end connected to the divided voltage application end and the second end connected to the bypass control terminal are externally attached. The light-emitting element driving device according to any one of claims 8 to 11, wherein:
13. The light-emitting element driving device according to any one of claims 8 to 12, wherein the bypass control terminal is adjacent to an input terminal of the power supply voltage.
14. 14. The light emitting element driving apparatus according to claim 8, wherein the external terminal through which the branch current flows is adjacent to at least one of an output terminal and a ground terminal of the output current.
15. 15. The light-emitting element driving device according to claim 1, wherein the current driver is a current source type.
16. The light-emitting element driving device according to any one of claims 1 to 14, wherein the current driver is a current sink type.
17. A light emitting element light source formed by connecting a plurality of light emitting elements in series;
    The light emitting element driving device according to any one of claims 1 to 16, which drives the light emitting element light source;
    A light emitting device comprising:
18. The light emitting device according to claim 17, wherein the light emitting element is a light emitting diode or an organic EL element.
19. A substrate on which a wiring pattern for mounting the light emitting element light source and the light emitting element driving device is laid;
    A socket for mounting the substrate;
    The light-emitting device according to claim 17 or 18, further comprising:
20. A vehicle comprising the light-emitting device according to any one of claims 17 to 19.

Images