JP2010171199A - Light emitting diode driving device and lighting instrument using the same, in-cabin lighting device, and lighting device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress power loss in regular illumination by suppressing abrupt variation of a current flowing to a light emission portion by suppressing generation of an excess current at the start of supply of a voltage. <P>SOLUTION: A light emitting diode driving device includes a current limiting resistance portion 7 having a plurality of current limiting resistances R4a to R4c connected in parallel to each other, and a plurality of switch elements Tra to Trc individually opening and closing paths where currents flow to the plurality of current limiting resistances. The switch elements are controlled to close only the path of Tra at the start of supply of the voltage and to close other paths one after another thereafter in accordance with the elapsed time. Namely, the composite resistance R1 of the current limiting portion 7 is large at the start of supply of the voltage, so generation of an excess current is suppressed. Thereafter, the composite resistance R1 sequentially decreases as the respective paths are closed and the current flowing to the light emission portion 3 gradually increases. Finally, the resistance value R1 of the current limiting resistance portion 7 is made small by closing all the paths to suppress the power loss in regular illumination. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light emitting diode driving device, and a lighting fixture, a vehicle interior lighting device, and a vehicle lighting device using the same.

  In recent years, the use of light emitting diodes for vehicle lamps has become widespread due to advantages such as low power consumption and long life. These vehicle lamps include a light-emitting unit having a plurality of light-emitting diodes connected in series, and a driving device that converts a DC voltage supplied from an in-vehicle battery into a necessary voltage of the light-emitting unit and stably outputs it. It has been. For example, a flyback type DC-DC converter is used for this driving device, and the DC-DC converter is PWM-controlled to drive the light emitting unit while keeping the current flowing through the light emitting unit substantially constant.

  However, in the driving device as described above, an overcurrent flows in the light emitting portion immediately after the voltage supply is started, and there is a possibility that the bonding wire of the light emitting diode is broken or the chip is deteriorated. In order to avoid this, for example, a method in which a current limiting resistor is connected in series with the light emitting unit in a path between the light emitting unit and the DC-DC converter to limit the current flowing through the light emitting unit can be considered. However, in this method, since power is always consumed by the current limiting resistance, power loss always occurs during steady driving.

  Therefore, conventionally, for example, a light emitting diode driving device described in Patent Document 1 is provided as a driving device that suppresses the occurrence of overcurrent while suppressing power loss. This is connected to a DC-DC converter, a control unit for PWM control of the DC-DC converter, a shunt resistor for detecting a current flowing in the light emitting unit, and a path between the DC-DC converter and the light emitting unit. A protection circuit and a control circuit that controls the protection circuit with reference to a current flowing through the shunt resistor are provided. Here, the protection circuit is a parallel circuit composed of a path having a current limiting resistor and a bypass path through which a current flows without passing through the current limiting resistor. The bypass path is appropriately opened and closed by a switch element included in the path. Is done.

  The above control circuit is configured so that the bypass path is opened and only the path through the current limiting resistor is formed before the current starts to flow or when the current flowing through the shunt resistor is larger than a predetermined value. When the current flowing through is smaller than a predetermined value, the switch element is controlled so as to form a bypass path. Therefore, in this conventional example, since the current is limited by the current limiting resistor immediately after the voltage supply is started, it is possible to prevent an excessive current from flowing to the light emitting unit, and the current flows through the bypass path during steady driving. Thus, unnecessary power loss due to current limiting resistance can be suppressed.

JP 2007-126041 A

  However, in the conventional example described in Patent Document 1, the resistance value of the current limiting resistor needs to be large to some extent in order to suppress the occurrence of overcurrent. For this reason, when a current flows through the current limiting resistor, a certain amount of power loss occurs. Further, when closing the bypass path in the protection circuit, the current flowing through the light emitting unit may change greatly, and the luminous flux of the light emitting unit may change abruptly.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to make a rapid change in luminous flux and unnecessary power loss while suppressing the occurrence of overcurrent at the start of voltage supply with a simple circuit configuration. LED driving device capable of suppressing power loss during steady driving, and a lighting fixture, a vehicle interior lighting device, and a vehicle lighting device including the light emitting diode driving device having the above characteristics There is to do.

  In order to achieve the above object, the invention according to claim 1 is characterized in that an output terminal electrically connected to a light emitting unit having a plurality of light emitting diodes connected in series and a DC voltage supplied from a DC power source are provided. A voltage conversion unit that converts the DC voltage necessary for driving the light emitting unit and applies the voltage to the output terminal; a current limiting resistor unit connected to a path between the output terminal and the voltage conversion unit; A current control unit that controls the current limiting resistor, and the current limiting resistor opens and closes a plurality of current limiting resistors connected in parallel to each other and a path through which current flows through the current limiting resistors. And the current control unit gradually increases the number of switch elements that close the path according to the elapsed time from the start of DC voltage supply by the DC power supply. And

  According to the first aspect of the present invention, at the start of voltage supply, the resistance value of the current limiting resistor is relatively increased, thereby suppressing the occurrence of overcurrent. By closing a plurality of parallel paths sequentially, the value of the combined resistance is sequentially decreased, and the current flowing through the light emitting unit is gradually increased, so that a rapid change in the luminous flux can be suppressed. In addition, unnecessary power loss in the current limiting resistor can be suppressed by sequentially decreasing the resistance value of the current limiting resistor. Further, during steady driving, power loss in the current limiting resistor can be suppressed by closing all the paths in the current limiting resistor.

  According to a second aspect of the present invention, in the first aspect of the present invention, the current limiting resistor includes a bypass path through which a current flows without passing through the current limiting resistance, and a switch element that opens and closes the path. The switch element is controlled, and the bypass path is closed after a predetermined elapsed time.

  According to the second aspect of the present invention, current flows through the bypass path of the current limiting resistor during steady driving, thereby further suppressing power loss in the current limiting resistor.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, there is provided detection means for detecting a voltage between the output terminals, and the current control unit refers to the detected voltage value to close the path. The timing of increasing the number of switch elements formed is adjusted.

  According to invention of Claim 3, the change of an electric current can be controlled according to the state of a light emission part, and a light emission part can be protected.

  According to a fourth aspect of the present invention, in the first or second aspect of the present invention, there is provided detection means for detecting the temperature of the light emitting section, and the current control section refers to the value of the detected temperature to close the path. The timing of increasing the number of switch elements is adjusted.

  According to invention of Claim 4, the change of an electric current can be controlled according to the state of a light emission part, and a light emission part can be protected.

  In order to achieve the above object, a light emitting diode driving apparatus according to any one of claims 1 to 4, a light emitting unit having a plurality of light emitting diodes connected in series, and the light emission A diode driving device and an instrument main body for holding the light emitting unit are provided.

  According to the invention of claim 5, it is possible to provide a luminaire having the same effect as that of the invention of claims 1 to 4.

  In order to achieve the above object, a sixth aspect of the present invention includes the light emitting diode driving device according to any one of the first to fourth aspects and a plurality of light emitting diodes connected in series, and is disposed in the vehicle interior. And a light emitting portion that is provided.

  According to the sixth aspect of the present invention, it is possible to provide a vehicle interior lighting device that exhibits the same effect as the first to fourth aspects of the present invention.

  In order to achieve the above object, a seventh aspect of the present invention includes the light emitting diode driving device according to any one of the first to fourth aspects and a plurality of light emitting diodes connected in series. And a light emitting unit that emits light.

  According to the seventh aspect of the invention, it is possible to provide a vehicular illumination device that has the same effect as the first to fourth aspects of the invention.

  The present invention has a simple circuit configuration, suppresses the occurrence of overcurrent at the time of voltage supply start, suppresses a rapid change in luminous flux and unnecessary power loss, and suppresses power loss during steady driving. It is possible to provide a light emitting diode driving device that can be used, and a lighting fixture, a vehicle interior lighting device, and a vehicle lighting device including the light emitting diode driving device having the above-described features.

It is a schematic circuit block diagram of Embodiment 1 of the light-emitting-diode drive device based on this invention. It is a schematic circuit block diagram of Embodiment 2 of the light-emitting-diode drive device based on this invention. It is a schematic circuit block diagram of Embodiment 3 of the light-emitting-diode drive device based on this invention. It is a schematic circuit block diagram of Embodiment 4 of the light-emitting-diode drive device based on this invention. It is a schematic circuit block diagram of Embodiment 5 of the light-emitting-diode drive device based on this invention.

(Embodiment 1)
FIG. 1 shows a schematic circuit configuration diagram of Embodiment 1 of a light emitting diode driving apparatus according to the present invention.

  The light-emitting diode driving device according to the present embodiment includes output terminals A and B connected to the light-emitting unit 3 and a voltage conversion unit connected to a DC power source (for example, a battery mounted on an automobile) 1 via a power switch SW. 2, a voltage detector 4 that detects the output voltage V 2 of the voltage converter 2, a current detector 5 that detects the output current, a controller 6 that controls the operation of the voltage converter 2, and a current detector 5 A current limiting resistor unit 7 connected to the path between the output terminals B and a current control unit 70 for controlling the operation of the current limiting resistor unit 7 are provided.

    The voltage conversion unit 2 is a flyback type DC-DC converter, and includes a switching element Q1 made of a power MOSFET or the like, a transformer T, a rectifying diode D1, and a smoothing capacitor C0. One end of the primary side of the transformer T is connected to the positive electrode of the DC power source 1 via the power switch SW, and the other end is connected to the negative electrode of the DC power source 1 via the switching element Q1 and grounded. One end of the secondary side of the transformer T is connected to the anode side of the rectifying diode D1, and the cathode side of the rectifying diode D1 is connected to one end of the capacitor C0 and one output terminal of the DC-DC converter. It has become. The other end of the secondary side of the transformer T is connected to the other end of the capacitor C0 and grounded, and further serves as the other output end of the DC-DC converter.

  The voltage detection unit 4 includes resistors R1 and R2 connected in series between output terminals of the voltage conversion unit 2, and a detection voltage Vx (= V2 × R2 / () obtained by dividing the output voltage V2 from the voltage conversion unit 2. R1 + R2)) is output to the control unit 6. One end of the voltage detector 4 is connected to the output terminal A.

  The current detection unit 5 includes a detection resistor R3 connected to a path between the voltage detection unit 4 and the current limiting resistor unit 7, and a voltage drop Vy (=) generated at both ends of the detection resistor R3 as a detection value of the output current I0. R3 × I0) is output to the control unit 6.

  The control unit 6 includes a reference current setting unit 61, a calculation unit 62, a PWM control unit 63, and a driver unit 64. The reference current setting unit 61 refers to the detection voltage Vx input from the voltage detection unit 4 and outputs a voltage Vb corresponding to the reference current Ib to the calculation unit 62. Here, the reference current Ib is the magnitude of the output current I0 when a desired light beam is obtained by the light emitting unit 3. The calculation unit 62 outputs a difference Vd (= Vy−Vb) between the voltage drop Vy and the voltage Vb corresponding to the reference current to the PWM control unit 63. The PWM control unit 63 includes a transmitter that generates a triangular wave reference signal therein, compares the difference Vd input from the calculation unit 62 with the reference signal, and turns on when the reference signal is greater than the difference Vd. PWM signal which is turned off when is smaller than the difference Vd is output to the driver unit 64. The driver unit 64 turns on / off the switching element Q1 in the voltage conversion unit 2 in accordance with the PWM signal supplied from the PWM control unit 63. That is, the control unit 6 performs the PWM control of the switching element Q1 to drive the voltage conversion unit 2 at a constant current so that the output current I0 matches the reference current Ib.

  The current-limiting resistor unit 7 is composed of a parallel circuit in which three paths composed of a series connection of one fixed resistor R4x and one transistor Trx (x = a, b, c; random order) are connected in parallel to each other. One end of the current limiting resistor 7 is connected to the current detector 5, and the other end is connected to the output terminal B. Further, the current control unit 70 controls the opening and closing of each parallel path of the current limiting resistor unit 7 by controlling the base current of the transistor Trx (x = a, b, c) which is a switch element.

  Hereinafter, the magnitude of each resistance value is R4a> R4b> R4c. When the power switch SW is turned on, the current control unit 70 controls each of the transistors Tra, Trb, and Trc so as to close only the path of the transistor Tra and open the paths of the transistors Trb and Trc. At this time, the magnitude Rl of the combined resistance of the current limiting resistor 7 is R4a. Therefore, if the resistance value R4a is set to a sufficiently large value, it is possible to suppress an excessive inrush current from flowing through the light emitting unit 3 when the power is turned on. Thereafter, the current control unit 70 sequentially closes the paths of the transistors Trb and Trc as time elapses from when the power is turned on, for example. As a result, the combined resistance Rl of the current limiting resistor 7 decreases sequentially, and the current flowing through the light emitting unit 3 gradually increases, so that a rapid change in the luminous flux of the light emitting unit 3 can be suppressed. Moreover, unnecessary power loss in the current limiting resistor 7 can be suppressed by sequentially reducing the combined resistance of the current limiting resistor 7. The final combined resistance Rs of the current limiting resistor section 7 is Rs = 1 / (1 / R4a + 1 / R4b + 1 / R4c), and can be reduced to a sufficiently small value by reducing the resistance value R4c. Therefore, at the time of steady driving, it is possible to drive the light emitting unit 3 while suppressing power loss in the current limiting resistance unit 7.

  As described above, in this embodiment, the current control unit 70 suppresses the occurrence of overcurrent at the start of voltage supply with a simple circuit configuration in which the transistors Tra, Trb, and Trc are sequentially turned on over time. In addition, it is possible to suppress a sudden change in luminous flux and unnecessary power loss, and to suppress power loss during steady driving.

(Embodiment 2)
FIG. 2 shows a schematic circuit configuration diagram of Embodiment 2 of the present invention.

  The present embodiment is based on the configuration of the first embodiment, and omits one of the fixed resistors R4c in the current limiting resistor section 7. As a result, power consumption in the current limiting resistor unit 7 during steady driving is eliminated, so that the light emitting unit 3 can be driven with further reduced power loss than in the first embodiment.

Since other configurations and operations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.
(Embodiment 3)
In FIG. 3, the schematic circuit block diagram of Embodiment 3 of this invention is shown.

  The present embodiment is based on the configuration of the first embodiment, and the current detection unit 5 is also used as the current limiting resistance unit 7 to suppress power loss during steady driving. In the present embodiment, the combined resistance Rl of the current limiting resistor 7 that also serves as the current detector 5 changes when closing the path corresponding to the transistors Trb and Trc. Therefore, in this embodiment, the voltage drop Vy ′ detected by the current limiting resistor unit 7 and the combined resistance Rl of the current limiting resistor unit 7 when the voltage drop Vy ′ is measured are input to the detection current setting unit 65. The output current I0 = Vy ′ / R1 is calculated. In the present embodiment, the final value Rs of the combined resistance Rl of the current limiting resistor unit 7 is made equal to the resistance value R3 of the current detection unit 5 in the first embodiment (Rs = 1 / (1 / R4a + 1 / R4b + 1 / R4c). ) = R3), the combined resistance of the path through which the output current I0 flows can be made equal to the state in which the current limiting resistor section 7 is not provided.

Since other configurations and operations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.
(Embodiment 4)
FIG. 4 shows a schematic circuit configuration diagram of Embodiment 4 of the present invention.

  The present embodiment is based on the configuration of the first embodiment, and is newly provided with a Vf detector 71 that detects the voltage Vf between the output terminals AB and outputs it to the current controller 70. The current control unit 70 refers to the detection voltage Vf input from the Vf detection unit 71, determines the timing for closing each parallel path in the current limiting resistor unit 7, and controls each transistor of the current limiting resistor unit 7. . That is, in this embodiment, the timing for reducing the combined resistance Rl of the current limiting resistor 7 is determined with reference to the voltage drop in the light emitting unit 3. In the present embodiment, for example, even when the forward voltage of the light emitting unit 3 drops due to deterioration of the light emitting diode, the light emitting unit is reduced by reducing the combined resistance Rl of the current limiting resistor unit 7 in accordance with the forward voltage. 3 can obtain the predetermined light-emission characteristics while protecting the light-emitting diodes constituting the light-emitting diode 3.

  Since other configurations and operations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

Further, instead of the first embodiment, it is of course possible to configure this embodiment based on the configuration of the second or third embodiment.
(Embodiment 5)
FIG. 5 shows a schematic circuit configuration diagram of Embodiment 5 of the present invention.

  The present embodiment is based on the configuration of the first embodiment, and is newly provided with a temperature detection unit 8 and a temperature calculation unit 80 that detect the temperature of the light emitting unit 3. For example, the temperature detection unit 8 includes a thermistor temperature measuring element, and the temperature calculation unit 80 calculates the temperature of the light emitting unit 3 from a change in the resistance value of the thermistor temperature measuring element. In the present embodiment, the current control unit 70 determines the timing for closing each parallel path in the current limiting resistor unit 7 according to the temperature of the light emitting unit 3 calculated by the temperature calculating unit 80, and the current limiting resistor unit 7. Each of the transistors is controlled. That is, in this embodiment, the timing for reducing the combined resistance Rl of the current limiting resistor 7 is determined with reference to the temperature of the light emitting unit 3. In general, light emitting diodes tend to have a reduced withstand capability at high temperatures. Therefore, in the present embodiment, when the light emitting unit 3 is at a high temperature, the light emitting diode constituting the light emitting unit 3 can be protected by decreasing the combined resistance Rl of the current limiting resistor 7 more slowly than at normal temperature.

  Since other configurations and operations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  Further, instead of the first embodiment, it is of course possible to configure the present embodiment based on the configuration of the second or third embodiment.

  Further, by combining the above-described Embodiment 4 and Embodiment 5 and detecting the voltage drop and temperature in the light-emitting section 3 and determining the timing for reducing the combined resistance Rl of the current-limiting resistance section 7, the light-emitting section 3 is The light emitting diode can be driven while protecting.

  In the embodiment shown above, the fixed resistance of the current limiting resistor unit 7 is three R4a, R4b, and R4c and the number of parallel paths is three, but the number of fixed resistors and the number of parallel paths are two. Or four or more may be sufficient. Further, the resistance part of each parallel path may be configured by connecting a plurality of fixed resistors in series, and among the paths parallel to each other in the current limiting resistor part 7, there is a path that does not include a transistor. Also good.

  The light-emitting unit 3 is not limited to a circuit in which two series circuits composed of four light-emitting diodes are connected in parallel as shown in the figure, but a plurality of light-emitting diodes connected in series and parallel. I just need it.

    Further, using the light emitting diode driving device and the light emitting unit 3 of the above embodiment, a lighting fixture is configured together with the fixture body that holds both, or the light emitting unit 3 is provided in the vehicle interior to provide a vehicle interior lighting device, The light emitting unit 3 may be disposed as a vehicle head lamp or tail lamp so as to radiate light to the surroundings to provide a vehicle lighting device.

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Voltage conversion part 3 Light emission part 4 Voltage detection part 5 Current detection part 6 Control part 7 Current limiting resistance part 70 Current control part

Claims (7)

An output terminal electrically connected to a light emitting unit having a plurality of light emitting diodes connected in series and a DC voltage supplied from a DC power source are converted into a DC voltage necessary for driving the light emitting unit. And a voltage converter that is applied to the output terminal, a current limiting resistor connected to a path between the output terminal and the voltage converter, and a current controller that controls the current limiting resistor.
The current limiting resistor unit includes a plurality of current limiting resistors connected in parallel to each other, and a plurality of switch elements that individually open and close paths through which current flows through the current limiting resistors.
The light-emitting diode driving device, wherein the current control unit gradually increases the number of switch elements that close the path according to an elapsed time from the start of supply of a DC voltage by a DC power supply. The current limiting resistor has a bypass path for passing a current without passing through a current limiting resistor and a switch element for opening and closing the path, and the current controller controls the switch element, and after a predetermined elapsed time 2. The light emitting diode driving device according to claim 1, wherein the bypass path is closed.   Detection means for detecting a voltage between the output terminals is provided, and the current control unit refers to the detected voltage value and adjusts the timing for increasing the number of switch elements that close the path. The light emitting diode driving device according to claim 1 or 2.   And a detecting unit configured to detect a temperature of the light emitting unit, wherein the current control unit refers to a value of the detected temperature and adjusts a timing for increasing the number of switch elements that close the path. The light emitting diode drive device according to claim 1.   5. A light emitting diode driving device according to claim 1, a light emitting portion having a plurality of light emitting diodes connected in series, and the light emitting diode driving device and a fixture main body for holding the light emitting portion. A lighting apparatus characterized by that.   A vehicle interior comprising the light emitting diode driving device according to any one of claims 1 to 4 and a light emitting section having a plurality of light emitting diodes connected in series and disposed in the vehicle interior. Lighting equipment.   5. A vehicle comprising: the light emitting diode driving device according to claim 1; and a light emitting unit that has a plurality of light emitting diodes connected in series and emits light around the vehicle. Lighting equipment.

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