Lighting fixture, lighting circuit, and semiconductor device

Abstract

To provide a lighting fixture, a lighting circuit, and a semiconductor device that can prevent a light-emitting element from turning off when the input voltage fluctuates, even when the characteristics of the light-emitting element fluctuate due to manufacturing variations or temperature environments.SOLUTION: A lighting circuit 3 includes a third constant current driver 6 that generates an LED current IOUT, and a first constant current driver 4 that generates a first bypass current IREFBYP1 that is lower than the LED current IOUT and has a lower current driving capability than the third constant current driver 6. The first constant current driver 4 is disposed in a current path that passes through a light emitting element 21a and bypasses light emitting elements 21b and 21c.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a lighting fixture, a lighting circuit, and a semiconductor device.

Background Art

[0002] Conventional lighting circuits disclosed in Patent Document 1 and lighting fixtures using light-emitting elements such as LEDs (Light Emitting Diodes) are used, for example, as vehicle lighting fixtures. When the amount of light is insufficient with only one chip of the light-emitting element, a plurality of light-emitting elements are connected in series and used. In a lighting fixture in which a plurality of light-emitting elements are connected in series, when the input voltage of the lighting circuit for lighting the light-emitting elements decreases and becomes equal to or lower than the forward voltage drop (VF voltage) of the light-emitting elements, the light-emitting elements turn off. In the case of a vehicle lighting fixture, the input voltage of the lighting circuit decreases during an idle stop function or the like.

[0003] Therefore, a lighting circuit has been proposed in which a bypass circuit is provided, the bypass circuit is connected according to the input voltage, and control is performed to reduce the number of light-emitting elements (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the VF voltage of the light-emitting elements has a large manufacturing variation and also changes with environmental changes such as temperature. Therefore, in the prior art, the problem that the light-emitting elements turn off due to a decrease in the input voltage has not been completely solved.

[0006] The present disclosure provides a lighting fixture, a lighting circuit, and a semiconductor device that can prevent the light-emitting element from turning off when the input voltage fluctuates, even if the characteristics of the light-emitting element vary due to manufacturing variations or temperature environment.

Means for Solving the Problems

[0007] The lighting fixture of the present disclosure is a lighting fixture including a plurality of light-emitting elements connected in series, and a lighting circuit that receives an input voltage and supplies an LED current set for the light-emitting element. The lighting circuit includes a constant current driver that generates the LED current, and a bypass constant current driver that generates a bypass current lower than the LED current and has a lower current driving ability than the constant current driver. The bypass constant current driver is disposed in a current path that passes through one or more of the light-emitting elements and bypasses one or more of the light-emitting elements.

Effects of the Invention

[0008] The lighting fixture of the present disclosure can prevent the light-emitting element from turning off when the input voltage fluctuates because the number of lit light-emitting elements automatically switches even if the characteristics of the light-emitting element vary due to manufacturing variations or temperature environment.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described based on the accompanying drawings.

[0011] (First Embodiment) Referring to FIG. 1, the lighting fixture 1 of the first embodiment includes a light emitting unit 2 and a lighting circuit 3 that causes the light emitting unit 2 to emit light.

[0012] The light emitting unit 2 includes three light emitting elements 21a, 21b, and 21c connected in series. The light emitting elements 21a, 21b, and 21c can be configured by LEDs (Light Emitting Diodes).

[0013] The lighting circuit 3 includes an LED current setting terminal SET, a first sink current input terminal SNK1, a second sink current input terminal SNK2, and a third sink current input terminal SNK3.

[0014] The input voltage Vin from the battery BT is input to the anode of the light emitting element 21a, and the connection point between the cathode of the light emitting element 21a and the anode of the light emitting element 21b is connected to the first sink current input terminal SNK1. The connection point between the cathode of the light emitting element 21b and the anode of the light emitting element 21c is connected to the second sink current input terminal SNK2, and the cathode of the light emitting element 21c is connected to the third sink current input terminal SNK3.

[0015] The lighting circuit 3 includes a first constant current driver 4, a second constant current driver 5, a third constant current driver 6, an LED current setting circuit 31, and a reference power supply circuit 32. The first constant current driver 4 and the second constant current driver 5 constitute a bypass function unit 10. The first constant current driver 4 provides a current path for bypassing the light emitting elements 21b and 21c. The second constant current driver 5 provides a current path for bypassing the light emitting element 21c. Part or all of the lighting circuit 3 can be configured as a driver IC, which is a semiconductor device integrated on a substrate.

[0016] The first constant current driver 4 is a sink-type (sucking type) constant current circuit that sucks in the first sink current I SNK1 from the first sink current input terminal SNK1. The first constant current driver 4 includes, for example, an operational amplifier 41 and an N-type MOSFET 42.

[0017] For the N-type MOSFET 42, the drain terminal on the sink current input side is connected to the first sink current input terminal SNK1, and the source terminal on the reference potential side is grounded via a shunt resistor R SHU which is a current detection circuit. The operational amplifier 41 has the first reference voltage V REFBYP1 generated by the reference power supply circuit 32 input to its non-inverting input terminal, and the inverting input terminal is connected to the connection point between the N-type MOSFET 42 and the shunt resistor R SHU .

[0018] The second constant current driver 5 is a sink-type (sucking type) constant current circuit that sucks in the second sink current I SNK2 from the second sink current input terminal SNK2. The second constant current driver 5 includes, for example, an operational amplifier 51 and an N-type MOSFET 52.

[0019] For the N-type MOSFET 52, the drain terminal on the sink current input side is connected to the second sink current input terminal SNK2, and the source terminal on the reference potential side is grounded via a shunt resistor R SHU which is a current detection circuit. The operational amplifier 51 has the second reference voltage V generated by the reference power supply circuit 32 input to its non-inverting input terminalREFBYP2 is input, and the inverting input terminal is connected to the connection point between the N-type MOSFET 52 and the shunt resistor R SHU .

[0020] The second sink current I SNK2 sucked in by the second constant current driver 5 is SNK2 I REFBYP2 = V SHU / R SHU . Since the shunt resistor R SNK2 has a fixed value, the second sink current I REFBYP2 is determined by the second reference voltage V

[0021] The third constant current driver 6 is a sink-type (sucking type) constant current circuit, and sucks in the third sink current I SNK3 from the third sink current input terminal SNK3. The third constant current driver 6 includes, for example, an operational amplifier 61 and an N-type MOSFET 62.

[0022] For the N-type MOSFET 62, the drain terminal on the sink current input side is connected to the LED current input terminal SNK3, and the source terminal on the reference potential side is grounded via the shunt resistor R SHU . The operational amplifier 61 has the third reference voltage V REFOUT generated by the reference power supply circuit 32 input to the non-inverting input terminal, and the inverting input terminal is connected to the connection point between the N-type MOSFET 62 and the shunt resistor R SHU .

[0023] The LED current setting circuit 31 outputs an LED current setting signal LIS for setting the LED current I SET to the reference power supply circuit 32 according to the resistance value of the external resistor R OUT connected to the LED current setting terminal SET.

[0024] Based on the LED current setting signal LIS from the LED current setting circuit 31, the reference power supply circuit 32 sets the drive current of the third constant current driver 6 so that the LED current is I OUT and the third reference voltage VREFOUT is generated and supplied to the non-inverting input terminal of the operational amplifier 61. The drive current (LED current I OUT ) of the third constant current driver 6 is I OUT = V REFOUT / R SHU . Since the shunt resistor R SHU has a fixed value, the LED current I OUT is determined by the third reference voltage V REFOUT generated by the reference power supply circuit 32.

[0025] Also, the reference power supply circuit 32 generates a second reference voltage V OUT such that the drive current of the second constant current driver 5 is a second bypass current I REFBYP2 lower than the LED current I OUT (for example, 98% of the LED current I REFBYP2 ) and supplies it to the non-inverting input terminal of the operational amplifier 51. The drive current (second bypass current I REFBYP2 ) of the second constant current driver 5 is I REFBYP2 = V REFBYP2 / R SHU . Since the shunt resistor R SHU has a fixed value, the second bypass current I REFBYP2 is determined by the second reference voltage V REFBYP2 generated by the reference power supply circuit 32.

[0026] Furthermore, the reference power supply circuit 32 generates a first reference voltage V REFBYP2 such that the drive current of the first constant current driver 4 is a first bypass current I REFBYP1 lower than the second bypass current I OUT (for example, 96% of the LED current I REFBYP1 ) and supplies it to the non-inverting input terminal of the operational amplifier 41. The drive current (first bypass current I REFBYP1 ) of the first constant current driver 4 is I REFBYP1 = V REFBYP1 / R SHU . Since the shunt resistor R SHU has a fixed value, the first bypass current I REFBYP1 is determined by the first reference voltage VREFBYP1 It is determined by

[0027] The reference voltage is the relationship with the first reference voltage V REFBYP1 <the second reference voltage V REFBYP2 <the third reference voltage V REFOUT That is. And the first constant current driver 4, the second constant current driver 5, and the third constant current driver 6 have their reference potential side terminals grounded through a common current detection circuit (shunt resistor R SHU ). Therefore, there is a difference in the current driving capabilities of the first constant current driver 4, the second constant current driver 5, and the third constant current driver 6, and the relationship is first constant current driver 4 < second constant current driver 5 < third constant current driver 6.

[0028] The operation of the lighting circuit 3 will be described in detail with reference to FIG. 2. FIG. 2(a) shows the LED current I flowing through the light emitting element 21a LEDa . FIG. 2(b) shows the first sink current I sucked in by the first constant current driver 4 SNK1 . FIG. 2(c) shows the LED current I flowing through the light emitting element 21b LEDb . FIG. 2(d) shows the second sink current I sucked in by the second constant current driver 5 SNK2 . FIG. 2(e) shows the LED current I flowing through the light emitting element 21c LEDc . FIG. 2(f) shows the third sink current I sucked in by the third constant current driver 6 SNK3 .

[0029] When the input voltage Vin rises and exceeds V1, as shown in FIG. 2(a), the LED current I starts to flow in the current path of the light emitting element 21a - the first sink current input terminal SNK1 - the first constant current driver 4 LEDa . The LED current I LEDa bypasses the light emitting elements 21b and 21c and is sucked in from the first sink current input terminal SNK1 as the first sink current I SNK1 . V1 is the forward voltage VFa of the light emitting element 21a when the current starts to flow.

[0030] When the input voltage Vin rises and reaches V2, the LED current ILEDa and the first sink current I SNK1 As shown in FIGS. 2(a) and 2(b), reaches the drive current of the first constant current driver 4 (the first bypass current I REFBYP1 ). V2 is the forward voltage VFa when the first bypass current I REFBYP1 flows through the light emitting element 21a. The first sink current I SNK1 sucked in by the first constant current driver 4 is not more than the first bypass current I REFBYP1 . Therefore, until the input voltage Vin further rises and reaches V3, the LED current I LEDa = the first bypass current I REFBYP1 is maintained.

[0031] When the input voltage Vin rises and exceeds V3, as shown in FIG. 2(c), the LED current I LEDb starts to flow through the current path of the light emitting element 21a - the light emitting element 21b - the second sink current input terminal SNK2 - the second constant current driver 5. The LED current I LEDb bypasses the light emitting element 21c and is sucked in from the second sink current input terminal SNK2 as the second sink current I SNK2 . V3 is the voltage obtained by adding the forward voltage VFa when the first bypass current I REFBYP1 flows through the light emitting element 21a and the forward voltage VFb of the light emitting element 21b when the current starts to flow.

[0032] Since the reference potential side terminals of the first constant current driver 4 and the second constant current driver 5 are common, the current driving ability of the second constant current driver 5 is higher than that of the first constant current driver 4. Therefore, when the input voltage Vin rises from V3, the current path of the LED current I LEDa flowing through the light emitting element 21a transitions to the second constant current driver 5 as shown in FIGS. 2(b) and 2(d), and no current flows through the first constant current driver 4.

[0033] When the input voltage Vin rises and reaches V4, the LED current I LEDb and the second sink current I SNK2As shown in FIGS. 2(c) and 2(d), it reaches the drive current of the second constant current driver 5 (the second bypass current I REFBYP2 ). When the input voltage Vin is V4, the first sink current I SNK1 becomes zero, and the LED current I LEDa becomes the second bypass current I REFBYP2 . V2 is the forward voltage VFa when the second bypass current I REFBYP2 flows through the light emitting element 21a, and the forward voltage VFb when the second bypass current I REFBYP2 flows through the light emitting element 21b, and is the voltage obtained by adding them. The second sink current I SNK2 absorbed by the second constant current driver 5 does not exceed the second bypass current I REFBYP2 . Therefore, until the input voltage Vin further rises to reach V5, the state of the LED current I LEDa = LED current I LEDb = second bypass current I REFBYP2 is maintained.

[0034] When the input voltage Vin rises and exceeds V5, as shown in FIG. 2(e), the LED current I LEDc starts to flow through the current path of the light emitting element 21a - light emitting element 21b - light emitting element 21c - third sink current input terminal SNK3 - third constant current driver 6. The LED current I LEDc is absorbed from the third sink current input terminal SNK3 as the third sink current I SNK3 as shown in FIG. 2(f). V5 is the forward voltage VFa when the second bypass current I REFBYP2 flows through the light emitting element 21a, the forward voltage VFb when the second bypass current I REFBYP2 flows through the light emitting element 21b, and the forward voltage VFc of the light emitting element 21b when the current starts to flow, and is the voltage obtained by adding them.

[0035] Since the reference potential side terminals of the second constant current driver 5 and the third constant current driver 6 are common, the current driving ability of the third constant current driver 6 is higher than that of the second constant current driver 5. Therefore, when the input voltage Vin rises from V5, the LED current I LEDbThe current path transitions to the third constant current driver 6 and no longer flows through the second constant current driver 5, as shown in FIGS. 2(d) and 2(f).

[0036] When the input voltage Vin rises to reach V6, the LED current I LEDc and the third sink current I SNK3 reach the drive current of the third constant current driver 6 (LED current I OUT ), as shown in FIGS. 2(e) and 2(f). When the input voltage Vin is at V6, the second sink current I SNK2 becomes zero, and the LED current I LEDa and the LED current I LEDb become the LED current I OUT . V6 is the voltage obtained by adding the forward voltage VFa when the LED current I OUT flows through the light emitting element 21a, the forward voltage VFb when the LED current I OUT flows through the light emitting element 21b, and the forward voltage VFc when the LED current I OUT flows through the light emitting element 21c. The third sink current I SNK3 sucked in by the third constant current driver 6 does not exceed the LED current I OUT . Therefore, even if the input voltage Vin further rises, the LED current I LEDa = LED current I LEDb = LED current I LEDc = LED current I OUT is maintained. That is, when the input voltage Vin is V6 or higher, the set LED current I OUT flows through all the light emitting elements 21a, 21b, and 21c of the light emitting unit 2, and all three lights of the light emitting unit 2 are in the fully lit state.

[0037] As described above, even when the input voltage Vin fluctuates, the lighting fixture 1 switches the number of lit light emitting elements 21a, 21b, 21c and the current path according to the characteristics of the light emitting elements 21a, 21b, 21c. This operation is the same when the input voltage Vin drops from the normal operating state. Therefore, even if the characteristics (forward voltage) of the light emitting elements 21a, 21b, 21c vary due to manufacturing variations or temperature environment, it is possible to prevent the light emitting unit 2 from going out and to smoothly change the luminous intensity when the number of light emitting elements changes.

[0038] (Second Embodiment) As shown in FIG. 3, the lighting fixture 1a of the second embodiment includes a lighting circuit 3a. The lighting circuit 3a is composed of a first constant current driver 4a, a second constant current driver 5a, and a third constant current driver 6a, which are source-type (output-type) constant current circuits.

[0039] The lighting circuit 3a includes a voltage input terminal VIN to which an input voltage Vin from the battery BT is input, and an LED current setting terminal SET. The lighting circuit 3a includes a first source current output terminal SOURCE1, a second source current output terminal SOURCE2, and a third source current output terminal SOURCE3.

[0040] The anode of the light emitting element 21a is connected to the third source current output terminal SOURCE3. The connection point between the cathode of the light emitting element 21a and the anode of the light emitting element 21b is connected to the second source current output terminal SOURCE2. The connection point between the cathode of the light emitting element 21b and the anode of the light emitting element 21c is connected to the first source current output terminal SOURCE1. The cathode of the light emitting element 21c is grounded.

[0041] The first constant current driver 4a and the second constant current driver 5a constitute a bypass function unit 10a. The first constant current driver 4a provides a current path for bypassing the light emitting elements 21a and 21b. The second constant current driver 5a provides a current path for bypassing the light emitting element 21a. Part or all of the lighting circuit 3a can be configured as a driver IC, which is a semiconductor device integrated on a substrate.

[0042] The first constant current driver 4a is a source-type (output-type) constant current circuit that outputs a first source current I SOURCE1 from the first source current output terminal SOURCE1. The first constant current driver 4a includes, for example, an operational amplifier 41a and a P-type MOSFET 42a.

[0043] The P-type MOSFET 42a has a source terminal on the reference potential side, which is a shunt resistor R that is a current detection circuitSHU is connected to the voltage input terminal VIN via SHU , and the drain terminal on the source current output side is connected to the first source current output terminal SOURCE1. The operational amplifier 41a has the negative electrode of the first reference voltage VREFBYP1 generated by the reference power supply circuit 32 input to the non-inverting input terminal, and the inverting input terminal is connected to the connection point between the P-type MOSFET 42a and the shunt resistor R SHU and.

[0044] The second constant current driver 5a is a source type (ejector type) constant current circuit, and ejects the second source current I SOURCE2 from the second source current output terminal SOURCE2. The second constant current driver 5a includes, for example, an operational amplifier 51a and a P-type MOSFET 52a.

[0045] The source terminal of the P-type MOSFET 52a on the reference potential side is connected to the voltage input terminal VIN via the shunt resistor R which is a current detection circuit SHU and the drain terminal on the source current output side is connected to the second source current output terminal SOURCE2. The operational amplifier 51a has the negative electrode of the second reference voltage VREFBYP2 generated by the reference power supply circuit 32 input to the non-inverting input terminal, and the inverting input terminal is connected to the connection point between the P-type MOSFET 52a and the shunt resistor R SHU and.

[0046] The third constant current driver 6a is a source type (ejector type) constant current circuit, and ejects the third source current I SOURCE3 from the third source current output terminal SOURCE3. The third constant current driver 6a includes, for example, an operational amplifier 61a and a P-type MOSFET 62a.

[0047] The source terminal of the P-type MOSFET 62a on the reference potential side is the shunt resistor R which is a current detection circuit SHUis connected to the voltage input terminal VIN through, and the drain terminal on the source current output side is connected to the third source current output terminal SOURCE3. The operational amplifier 61a has the negative electrode of the third reference voltage VREFOUT generated by the reference power supply circuit 32 input to the non-inverting input terminal, and the inverting input terminal is connected to the connection point between the P-type MOSFET 62a and the shunt resistor RSHU.

[0048] The LED current setting circuit 31 outputs an LED current setting signal LIS for setting the LED current I OUT to the reference power supply circuit 32 according to the resistance value of the external resistor RSET connected to the LED current setting terminal SET.

[0049] Based on the LED current setting signal LIS from the LED current setting circuit 31, the reference power supply circuit 32 generates a third reference voltage V OUT such that the drive current of the third constant current driver 6a becomes the LED current I REFOUT and supplies it to the non-inverting input terminal of the operational amplifier 61a. The drive current (LED current I OUT ) of the third constant current driver 6a is I OUT = V REFOUT / R SHU . Since the shunt resistor R SHU has a fixed value, the LED current I OUT is determined by the third reference voltage V REFOUT generated by the reference power supply circuit 32.

[0050] Also, the reference power supply circuit 32 generates a second reference voltage V OUT such that the drive current of the second constant current driver 5a is a second bypass current I REFBYP2 lower than the LED current I OUT (for example, 98% of the LED current I REFBYP2 ) and supplies it to the non-inverting input terminal of the operational amplifier 51a. The drive current (second bypass current I REFBYP2 ) of the second constant current driver 5a is I REFBYP2 = V REFBYP2 / R SHU . Since the shunt resistor R SHUSince is a fixed value, the second bypass current I REFBYP2 is the second reference voltage V generated by the reference power supply circuit 32. REFBYP2 is determined.

[0051] Furthermore, the reference power supply circuit 32 is configured such that the drive current of the first constant current driver 4a is equal to or smaller than the second bypass current I REFBYP2 The first bypass current I REFBYP1 (For example, LED current I OUT The first reference voltage V REFBYP1 is generated and supplied to the non-inverting input terminal of the operational amplifier 41a. REFBYP1 ) is I REFBYP1 =V REFBYP1 / R SHU The shunt resistance R SHU Since is a fixed value, the first bypass current I REFBYP1 is the first reference voltage V generated by the reference power supply circuit 32. REFBYP1 is determined.

[0052] The reference voltage is the first reference voltage V REFBYP1 <Second reference voltage V REFBYP2 <Third reference voltage V REFOUT The first constant current driver 4a, the second constant current driver 5a, and the third constant current driver 6a are connected to a current detection circuit (including a shunt resistor R SHU ) is connected to the voltage input terminal VIN. Therefore, there is a difference in the current driving capabilities of the first constant current driver 4a, the second constant current driver 5a, and the third constant current driver 6a, and the relationship is first constant current driver 4a<second constant current driver 5a<third constant current driver 6a.

[0053] The operation of the lighting circuit 3a will be described in detail with reference to Fig. 4. Fig. 4(a) shows the LED current I LEDc FIG. 4(b) shows the first source current I SOURCE1 FIG. 4(c) shows the LED current ILEDb is shown. FIG. 4(d) shows the second source current I discharged by the second constant current driver 5a SOURCE2 is shown. FIG. 4(e) shows the LED current I flowing through the light emitting element 21a LEDa is shown. FIG. 4(f) shows the third source current I discharged by the third constant current driver 6a SOURCE3 is shown.

[0054] When the input voltage Vin rises and exceeds V1, as shown in FIG. 4(a), in the current path of the first constant current driver 4a - the first source current output terminal SOURCE1 - the light emitting element 21c, the LED current I LEDc starts to flow. The LED current I LEDc bypasses the light emitting elements 21a and 21b and is discharged from the first source current output terminal SOURCE1 as the first source current I SOURCE1 as shown in FIG. 4(b). V1 is the forward voltage VFc of the light emitting element 21c when the current starts to flow.

[0055] When the input voltage Vin rises and reaches V2, the LED current I LEDc and the first source current I SOURCE1 reach the drive current (the first bypass current I REFBYP1 ) of the first constant current driver 4a as shown in FIGS. 4(a) and (b). V2 is the forward voltage VFc of the light emitting element 21c when the first bypass current I REFBYP1 flows through it. Since the first source current I SOURCE1 discharged by the first constant current driver 4a does not exceed the first bypass current I REFBYP1 , the state of the LED current I LEDc = the first bypass current I REFBYP1 is maintained until the input voltage Vin further rises and reaches V3.

[0056] When the input voltage Vin rises and exceeds V3, as shown in FIG. 4(c), in the current path of the second constant current driver 5a - the second source current output terminal SOURCE2 - the light emitting element 21b - the light emitting element 21c, the LED current I LEDb starts to flow. The LED current I LEDb bypasses the light emitting element 21a and, as shown in FIG. 4(d), is the second sink current ISNK2 is emitted from the second source current output terminal SOURCE2. V3 is the forward voltage VFc when the first bypass current I REFBYP1 flows through the light emitting element 21c, and the forward voltage VFb of the light emitting element 21b when the current starts to flow, added together.

[0057] Since the reference potential side terminals of the first constant current driver 4a and the second constant current driver 5a are common, the current driving ability of the second constant current driver 5a is higher than that of the first constant current driver 4a. Therefore, when the input voltage Vin rises and V3 also rises, the current path of the LED current I LEDc transitions to the second constant current driver 5a as shown in FIGS. 4(b) and (d), and no longer flows through the first constant current driver 4a.

[0058] When the input voltage Vin rises and reaches V4, the LED current I LEDb and the second source current I SOURCE2 reach the drive current (the second bypass current I REFBYP2 ) of the second constant current driver 5a as shown in FIGS. 4(c) and (d). At the input voltage Vin of V4, the first source current I SOURCE1 becomes zero, and the LED current I LEDc becomes the second bypass current I REFBYP2 . V4 is the forward voltage VFc when the second bypass current I REFBYP2 flows through the light emitting element 21c, and the forward voltage VFb when the second bypass current I REFBYP2 flows through the light emitting element 21b, added together. The second source current I SOURCE2 emitted by the second constant current driver 5a does not exceed the second bypass current I REFBYP2 . Therefore, until the input voltage Vin further rises and reaches V5, the state where the LED current I LEDc = the LED current I LEDb = the second bypass current I REFBYP2 is maintained.

[0059] When the input voltage Vin rises and exceeds V5, as shown in FIG. 4(e), the LED current I flows through the current path of the third constant current driver 6a - the third source current output terminal SOURCE3 - the light emitting element 21a - the light emitting element 21b - the light emitting element 21c. LEDa begins to flow. The LED current I LEDa is discharged from the third source current output terminal SOURCE3 as the third source current I SOURCE3 as shown in FIG. 4(f). V5 is the forward voltage VFc when the second bypass current I REFBYP2 flows through the light emitting element 21c, the forward voltage VFb when the second bypass current I REFBYP2 flows through the light emitting element 21b, and the forward voltage VFa of the light emitting element 21a when the current starts to flow, added together.

[0060] Since the reference potential side terminals of the second constant current driver 5a and the third constant current driver 6a are common, the current driving ability of the third constant current driver 6a is higher than that of the second constant current driver 5a. Therefore, when the input voltage Vin rises from V5, the current path of the LED current I LEDb flowing through the light emitting element 21b transitions to the third constant current driver 6a and no longer flows through the second constant current driver 5a, as shown in FIGS. 4(d) and (f).

[0061] When the input voltage Vin rises and reaches V6, the LED current I LEDa and the third source current I SOURCE3 reach the driving current (LED current I OUT ) of the third constant current driver 6a, as shown in FIGS. 4(e) and (f). When the input voltage Vin is at V6, the second source current I SOURCE2 becomes zero, and the LED current I LEDc and the LED current I LEDb become the LED current I OUT . V6 is the forward voltage VFc when the LED current I OUT flows through the light emitting element 21c, the forward voltage VFb when the LED current I OUT flows through the light emitting element 21b, and the forward voltage when the LED current I OUTis the forward voltage VFa when flowing and the voltage obtained by adding. The third source current I discharged by the third constant current driver 6a SOURCE3 is the LED current I OUT Since it does not exceed the above, even if the input voltage Vin further increases, the LED current I LEDc = LED current I LEDb = LED current I LEDa = LED current I OUT The state of is maintained. That is, when the input voltage Vin is V6 or more, the set LED current I OUT flows through all the light-emitting elements 21a, 21b, 21c of the light-emitting unit 2, and the light-emitting unit 2 is in a state where all three lights are lit.

[0062] As described above, even when the input voltage Vin fluctuates, the lighting fixture 1a switches the number of lit light-emitting elements 21a, 21b, 21c and the current path according to the characteristics of the light-emitting elements 21a, 21b, 21c. This operation is the same when the input voltage Vin drops from the normal operating state. Therefore, Even if the characteristics (forward voltage) of the light-emitting elements 21a, 21b, 21c vary due to manufacturing variations or temperature environment, it is possible to prevent the light-emitting unit 2 from going out and to smoothly change the luminous intensity when the number of light-emitting elements changes.

[0063] (Third Embodiment) Referring to FIG. 5, the lighting fixture 1b of the third embodiment includes a lighting circuit 3b. The lighting circuit 3b includes a voltage input terminal VIN and a constant current driver control circuit 7 in addition to the configuration of the lighting circuit 3 of the first embodiment.

[0064] When the input voltage Vin exceeds V4 at which the first sink current I SNK1 becomes zero, the constant current driver control circuit 7 stops the first constant current driver 4, and when the input voltage Vin is the second sink current I SNK2When V6 becomes zero or exceeds it, the second constant current driver 5 is stopped. Referring to FIG. 6, the constant current driver control circuit 7 includes, for example, a first comparator 71 and a second comparator 72. When the light emitting unit 2 is mounted in a vehicle, it is necessary to turn off the light in case of a failure (open failure). The constant current driver control circuit 7 can turn off the failed (open failed) light emitting unit 2.

[0065] The first comparator 71 compares the input voltage Vin with the reference voltage V ref1 (=V4), and when the input voltage Vin exceeds the reference voltage V ref1 , it outputs a stop signal at the Hi level and stops the first constant current driver 4.

[0066] When the light emitting element 21b has an open failure, the light emitting element 21a will continue to light with the first constant current driver 4 as the current path. Therefore, when the input voltage Vin exceeds V4, the constant current driver control circuit 7 stops the first constant current driver 4. As a result, when the light emitting element 21b is faulty (open fault), the constant current driver control circuit 7 can turn off the light emitting unit 2 when the input voltage Vin exceeds V4. Note that when the light emitting element 21a has an open failure, the light emitting unit 2 will not light.

[0067] The second comparator 72 compares the input voltage Vin with the reference voltage V ref2 (=V6), and when the input voltage Vin exceeds the reference voltage V ref2 , it outputs a stop signal at the Hi level and stops the second constant current driver 5.

[0068] When the light emitting element 21c has an open failure, the light emitting elements 21a and 21b will continue to light with the second constant current driver 5 as the current path. Therefore, when the input voltage Vin exceeds V6, the constant current driver control circuit 7 also stops the second constant current driver 5. As a result, when the light emitting element 21c is faulty (open fault), the constant current driver control circuit 7 can turn off the light emitting unit 2 when the input voltage Vin exceeds V6.

[0069] (Fourth Embodiment) Referring to FIG. 7, the lighting fixture 1c of the fourth embodiment includes a lighting circuit 3c. The lighting circuit 3c includes a voltage input terminal VIN, a current replenishment control circuit 8, and a current replenishment circuit 9 in addition to the configuration of the lighting circuit 3 of the first embodiment.

[0070] When the input voltage Vin is between V2 and V4, the current replenishment control circuit 8 determines the level of the replenishment current I SNK1 to replenish the first sink current I REP sucked in from the first sink current input terminal SNK1, and outputs the determined level to the current replenishment circuit 9 as a replenishment current setting signal PIS. When the input voltage Vin is between V2 and V4, the current replenishment control circuit 8 determines the level of the replenishment current I REP based on the LED current setting signal LIS from the LED current setting circuit 31, and subtracts the first bypass current I OUT from the LED current I REFBYP1 to determine the value. For example, when the first bypass current I REFBYP1 is 96% of the LED current I OUT , the level of the replenishment current I REP is determined to be 4% of the LED current I OUT .

[0071] When the input voltage Vin is between V4 and V6, the current replenishment control circuit 8 determines the level of the replenishment current I SNK2 to replenish the second sink current I REP sucked in from the second sink current input terminal SNK2, and outputs the determined level to the current replenishment circuit 9 as a replenishment current setting signal PIS. When the input voltage Vin is between V4 and V6, the current replenishment control circuit 8 determines the level of the replenishment current I REP based on the LED current setting signal LIS from the LED current setting circuit 31, and subtracts the second bypass current I OUT from the LED current I REFBYP2 to determine the value. For example, when the second bypass current I REFBYP2 is 98% of the LED current I OUT , the level of the replenishment current I REP is determined to be 2% of the LED current I OUT .

[0072] The current replenishment control circuit 8 outputs a current path switching signal SS for instructing switching in the current path to the current replenishment circuit 9 according to the input voltage Vin. When Vin is between V2 and V4, the current replenishment control circuit 8 instructs connection to the first sink current input terminal SNK1. When the input voltage Vin is between V4 and V6, the current replenishment control circuit 8 instructs connection to the second sink current input terminal SNK2.

[0073] The current replenishment circuit 9 is a constant current circuit that generates a replenishment current I SNK1 or a second sink current I SNK2 as a drive current for replenishing the REP When the input voltage Vin is between V2 and V4, the current replenishment circuit 9 generates, as a drive current, a replenishment current I OUT whose level is the value obtained by subtracting the first bypass current I REFBYP1 from the LED current I REP When the input voltage Vin is between V4 and V6, the current replenishment circuit 9 generates, as a drive current, a replenishment current I OUT whose level is the value obtained by subtracting the second bypass current I REFBYP2 from the LED current I REP

[0074] The current replenishment circuit 9 can be configured by, for example, a sink type (sucking type) constant current circuit. Referring to FIG. 8, the current replenishment circuit 9 includes, for example, an operational amplifier 91, an N-type MOSFET 92, and a switching switch 93.

[0075] For the N-type MOSFET 92, the drain terminal on the sink current input side is connected to the first sink current input terminal SNK1 or the second sink current input terminal SNK2 via the switching switch 93. The source terminal of the N-type MOSFET 92 on the reference potential side is grounded via a shunt resistor R SHUa which is a current detection circuit. The non-inverting input terminal of the operational amplifier 91 receives a reference voltage V REFREP generated and set by the replenishment current setting signal PIS, and the inverting input terminal is connected to the connection point between the N-type MOSFET 92 and the shunt resistor R SHUa ​​

[0076] Reference voltage V REFREP is set to a voltage such that when the input voltage Vin is between V2 and V4, the drive current of the current replenishment circuit 9 is the LED current I OUT - First bypass current I REFBYP1 based on the replenishment current setting signal PIS. The reference voltage V REFREP is set to a voltage such that when the input voltage Vin is between V4 and V6, the drive current of the current replenishment circuit 9 is the LED current I OUT - Second bypass current I REFBYP2 based on the replenishment current setting signal PIS.

[0077] The switching switch 93 connects the drain terminal of the N-type MOSFET 92 and the first sink current input terminal SNK1 based on the current path switching signal SS when the input voltage Vin is between V2 and V4. The switching switch 93 connects the drain terminal of the N-type MOSFET 92 and the second sink current input terminal SNK2 based on the current path switching signal SS when the input voltage Vin is between V4 and V6.

[0078] When the input voltage Vin of the lighting fixture 1c is between V2 and V4, the replenishment current I REP generated by the current replenishment circuit 9 is replenished to the first sink current I SNK1 . The level of the replenishment current I REP replenished when the input voltage Vin is between V2 and V4 is the LED current I OUT - First bypass current I REFBYP1 . Therefore, as shown in FIG. 9, the LED current I LEDa flowing through the light emitting element 21a is the same LED current I OUT as when all lights are lit even when the input voltage Vin is between V2 and V4. When the input voltage Vin of the lighting fixture 1c is between V4 and V6, the replenishment current I REP generated by the current replenishment circuit 9 is replenished to the second sink current I SNK2 . The level of the replenishment current I REP replenished when the input voltage Vin is between V4 and V6 is the LED current I OUT - Second bypass current I REFBYP2Therefore, as shown in FIG. 9, the LED currents I flowing through the light-emitting elements 21a and 21b LEDa , I LEDb are the same as the LED current I when all the lights are on even when the input voltage Vin is between V4 and V6. OUT That is.

[0079] As described above, this embodiment includes a plurality of light-emitting elements 21a, 21b, and 21c connected in series, and a lighting circuit 3 that receives an input voltage Vin and supplies an LED current I set for the light-emitting elements 21a, 21b, and 21c. OUT The lighting circuit 3 includes a constant current driver (third constant current driver 6) that generates an LED current I, and a bypass constant current driver (first constant current driver 4, second constant current driver 5) that generates a bypass current (first bypass current I OUT , second bypass current I OUT ) lower than the LED current I. The bypass constant current driver (first constant current driver 4, second constant current driver 5) is arranged in a current path that passes through one or more of the light-emitting elements 21a and 21b and bypasses one or more of the light-emitting elements 21b and 21c. REFBYP1 , second bypass current I REFBYP2 ) and has a lower current driving ability than the constant current driver. With this configuration, even if the characteristics (forward voltage) of the light-emitting elements 21a, 21b, and 21c vary due to manufacturing variations or temperature environment, the number of lit light-emitting elements 21a, 21b, and 21c automatically switches in the lighting fixtures 1 to 1c. Therefore, it is possible to prevent the light-emitting elements from turning off when the input voltage Vin fluctuates.

[0080] Also, in this embodiment, the reference potential side terminals of the constant current driver (third constant current driver 6) and the bypass constant current driver (first constant current driver 4, second constant current driver 5) are connected to a common current detection circuit (shunt resistor R SHU ). With this configuration, the lighting fixtures 1 to 1c can have a difference in current driving ability between the constant current driver (third constant current driver 6) and the bypass constant current driver (first constant current driver 4, second constant current driver 5).

[0081] Furthermore, in the present embodiment, a plurality of bypass constant current drivers (first constant current driver 4, second constant current driver 5) having different current driving capabilities are provided, and the first constant current driver 4 having a low current driving capability is arranged in a current path passing through a smaller number of the light emitting elements than the second constant current driver 5. With this configuration, the lighting fixtures 1 to 1c can stepwise control the number of lit light emitting elements 21a, 21b, 21c.

[0082] Furthermore, in the present embodiment, the constant current driver (third constant current driver 6) and the bypass constant current drivers (first constant current driver 4, second constant current driver 5) are of the same type of sink type or source type constant current circuits. With this configuration, since the constant current driver (third constant current driver 6) and the bypass constant current drivers (first constant current driver 4, second constant current driver 5) can be made of the same type, a difference in current driving capability can be provided only by changing the reference voltage.

[0083] Furthermore, the third embodiment includes a constant current driver control circuit 7 that stops the bypass constant current drivers (first constant current driver 4, second constant current driver 5) when the input voltage Vin exceeds a set voltage. With this configuration, when the light emitting elements 21b and 21c of the lighting fixture 1b are faulty (open fault), the light emitting unit 2 can be turned off when the input voltage Vin exceeds the set voltages V4 and V6.

[0084] Furthermore, the fourth embodiment includes a current replenishing circuit 9 that generates a replenishing current I REFBYP1 which, when added to the bypass currents (first bypass current I REFBYP2 ), second bypass current I OUT ), results in the LED current I REP and supplies it to the light emitting elements 21a, 21b. With this configuration, the lighting fixture 1c can be lit with the LED current I OUT even when the number of lit elements in the light emitting unit 2 is small.

[0085] Note that the present invention is not limited to the above-described embodiments, and it is obvious that each embodiment can be appropriately modified within the scope of the technical idea of the present invention. Also, the number, position, shape, etc. of the above-described constituent members are not limited to the above embodiments, and can be set to appropriate numbers, positions, shapes, etc. for implementing the present invention. Note that the same reference numerals are assigned to the same constituent elements in each figure.

Explanation of Reference Numerals

[0086] 1, 1a, 1b, 1c Lighting fixture 2 Light emitting part 3, 3a, 3b, 3c Lighting circuit 4, 4a First constant current driver 5, 5a Second constant current driver 6, 6a Third constant current driver 7 Constant current driver control circuit 8 Current replenishment control circuit 9 Current replenishment circuit 10, 10a Bypass function part 21a, 21b, 21c Light emitting element 31 LED current setting circuit 32 Reference power supply circuit 41, 41a, 51, 51a, 61, 61a, 91 Operational amplifier 42, 52, 62, 92 N-type MOSFET 42a, 52a, 62a P-type MOSFET 71 First comparator 72 Second comparator 93 Switch Vin Input voltage

Claims

1. A lighting fixture comprising a plurality of light-emitting elements connected in series, and a lighting circuit that receives an input voltage and supplies an LED current set for the light-emitting elements, wherein the lighting circuit comprises a constant current driver that generates the LED current, and a bypass constant current driver that generates a bypass current lower than the LED current and has a lower current driving ability than the constant current driver, wherein the bypass constant current driver is arranged in a current path that passes through one or more of the light-emitting elements and bypasses one or more of the light-emitting elements. The lighting fixture is characterized by this.

2. The lighting fixture according to claim 1, wherein reference potential side terminals of the constant current driver and the bypass constant current driver are connected to a common current detection circuit.

3. The lighting fixture according to claim 1 or 2, further comprising a plurality of the bypass constant current drivers having different current driving abilities, wherein the bypass constant current driver with lower current driving ability is arranged in a current path passing through a smaller number of the light-emitting elements.

4. The lighting fixture according to claim 1 or 2, wherein the constant current driver and the bypass constant current driver are of the same type of sink or source type constant current circuit.

5. The lighting fixture according to claim 1 or 2, further comprising a constant current driver control circuit that stops the bypass constant current driver when the input voltage exceeds a set voltage.

6. The lighting fixture according to claim 1 or 2, further comprising a current replenishment circuit that generates a replenishment current which, when added to the bypass current, becomes the LED current according to the input voltage and supplies the replenishment current to the light-emitting elements.

7. A lighting circuit that receives an input voltage and supplies an LED current flowing through a plurality of light-emitting elements connected in series, comprising a constant current driver that generates the LED current, and a bypass constant current driver that generates a bypass current lower than the LED current and has a lower current driving ability than the constant current driver, wherein the bypass constant current driver is arranged in a current path that passes through one or more of the light-emitting elements and bypasses one or more of the light-emitting elements. The lighting circuit is characterized by this.

8. A semiconductor device, characterized in that the lighting circuit according to claim 7 is integrated on a substrate.

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