JP2006206001A - Led drive device, lighting system and luminaire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED drive device, a lighting system and a luminaire having a compact, inexpensive and simple configuration capable of reducing the thermal stress in an LED element and consistently irradiating light. <P>SOLUTION: An LED drive circuit 2 comprising a DC power source 1, an LED drive circuit 2, and an LED unit 3 consisting of a plurality of LED elements La connected in series performs the shifting operation to the output characteristic with the output power reduced if the detected value of the LED voltage Vf is reduced, reduces both the output voltage V2 and the LED current IL, and suppresses the heat generation of the LED element La. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an LED driving device, a lighting device, and a lighting fixture.

  In recent years, mass production of white LED elements (light emitting diodes) has been actively carried out, and their uses are diversified. In the field of vehicles, the use in the passenger compartment and the development of headlights and daytime running lamps with higher brightness are being carried out.

  Such an LED element has a long life and quick response compared to an incandescent bulb, can be mounted compactly in structure, and can easily realize various emission colors without a filter depending on the application. Furthermore, when it is used for a lighting device such as a lamp, it can be mounted thinly and three-dimensionally, so that a free design that does not limit the design and shape of the vehicle is possible.

FIG. 10 shows a circuit configuration of a lighting device using a conventional LED driving device. A plurality of LED elements La, La,. . . The LED unit 3 is driven by applying a DC voltage V2 obtained by boosting the voltage V1 of the DC power source 1 by the LED driving circuit 8. The LED drive circuit 100 detects the voltage across the resistor 101 connected in series to the low-voltage output terminal as an output current, and performs constant current control by varying the output voltage V2 based on the detected current value. (For example, see Patent Document 1)
JP 2003-187614 A

  In the above conventional example, the drive current of the LED element La can be kept constant even when the voltage V1 of the DC power supply 1 varies. However, the power consumption in the LED element La varies depending on the change in ambient temperature and the amount of self-heating caused by individual differences in the LED elements La. When the power consumption increases, the heat generated by the LED element La increases, and excessive thermal stress is applied to the LED element La.

  In particular, in the use of the LED element La that achieves high brightness and high output, the drive current is large and the LED element La itself generates a large amount of heat. Reduction of this thermal stress is important, and conventionally, mounting in consideration of heat dissipation of the LED element La has been required to reduce the thermal stress. Further, there is a method of detecting and controlling the temperature of the LED element La, but the temperature detection means and the peripheral circuit of the temperature detection means become complicated.

  Thus, although LED element La itself is small, the members required for heat dissipation, temperature detection, etc. have become large and expensive.

  The present invention has been made in view of the above-described reasons, and an object of the present invention is to reduce the thermal stress of the LED element with a small size, low cost, and a simple configuration, and to stably emit light. It is in providing a lighting device and a lighting fixture.

  The invention of claim 1 includes a DC power supply and an LED drive circuit that supplies a desired DC output generated from the DC power supply to a series circuit of a plurality of LED elements connected between output terminals. The output power is controlled within a predetermined range by changing the output characteristic based on the voltage across the one LED element.

  According to the present invention, since the temperature is detected based on the voltage across one LED element using the LED element as a load, there is no need to provide a separate temperature sensor, and the configuration is simplified and miniaturized. Cost reduction can be achieved. In addition, since high-precision feedback control based on the substantial temperature of the LED element is performed, high reliability can be obtained. Furthermore, since the output control is performed within a predetermined range when the voltage across the LED element changes, it is possible to prevent overpower and overcurrent, and to ensure stable light output without excessive thermal stress of the LED element. . In addition, since there is no power consumption more than necessary, it is possible to extend the life and increase the efficiency. That is, it is possible to reduce the thermal stress of the LED element with a small size, low cost, and simple configuration and to irradiate light stably.

  According to a second aspect of the present invention, in the first aspect, the LED driving circuit includes a booster circuit.

  According to the present invention, by connecting a plurality of LED elements, a sufficient output voltage can be supplied even when an output voltage higher than the voltage supplied from the DC power supply is required.

  According to a third aspect of the present invention, there is provided a voltage detection value obtained by dividing the output voltage of the LED driving circuit, comprising a series circuit of a plurality of resistors connected between the output terminals of the LED driving circuit. An output voltage detection unit that outputs and an output current detection unit that includes a resistor connected in series to the output terminal of the LED drive circuit and outputs a voltage generated in the resistor as a current detection value. The output is controlled based on the detected value and the detected current value.

  According to the present invention, output voltage detection and output current detection can be performed with a simple configuration.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the LED driving circuit generates a desired DC output from the DC power source using a flyback transformer.

  According to the present invention, the LED drive circuit can be constituted by a step-up / step-down circuit, and a voltage obtained by boosting or stepping down the input voltage or an output having the same voltage as the input voltage can be obtained.

  According to a fifth aspect of the present invention, in the third or fourth aspect, the LED driving circuit generates a desired DC output by switching, and a reference value generation that generates a reference value based on the voltage detection value. And a PWM control unit that PWM-controls the switching element based on the detected current value and the reference value.

  According to the present invention, the switching element can be PWM-controlled according to the output of the LED drive circuit, and the output of the LED drive circuit can be controlled with high accuracy.

  According to a sixth aspect of the present invention, an illumination device includes the LED driving device according to any one of the first to fifth aspects, and a series circuit of a plurality of LED elements driven by the LED driving device.

  According to this invention, the illuminating device which can have the same effect as the LED drive device of Claim 1 can be provided.

  According to a seventh aspect of the present invention, a lighting fixture includes the lighting device according to the sixth aspect.

  According to this invention, the lighting fixture which can show | play the effect similar to the illuminating device of Claim 6 can be provided.

  As described above, the present invention has an effect that the thermal stress of the LED element can be reduced with a small size, low cost, and a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a circuit configuration of an illuminating device 7 using the LED driving device 8 of the present embodiment, and includes a DC power source 1 such as a battery, an LED driving circuit 2, and a plurality of LED elements La, La, . . . It is comprised with the LED unit 3 which consists of. As shown in FIG. 2, the DC power supply 1 may include a rectifier 11 and a capacitor 12 that rectify and smooth the output of the AC power supply 10.

  The LED drive circuit 2 converts the voltage V1 of the DC power source 1 into a desired output voltage V2 to generate a plurality of LED elements La, La,. . . Are applied to both ends of the series circuit to drive each LED element La. This output voltage V2 is also the voltage across the LED unit 3. The voltage across both ends (LED voltage) Vf of one LED element La connected to the output terminal on the low voltage side is fed back to the LED drive circuit 2, and the LED drive circuit 2 performs output control based on the LED voltage Vf. Yes.

  Hereinafter, output control of the LED drive circuit 2 will be described. FIG. 3 is a graph showing the change of the LED voltage Vf with respect to the temperature of the LED element La. When the temperature of the LED element La rises, the LED voltage Vf decreases.

  FIG. 4 is a graph showing the characteristics of the output voltage V2 and the LED current IL of the LED drive circuit 2, the characteristic YLa is the voltage-current characteristic of the LED unit 3, and the characteristic Yp is the output characteristic of the LED drive circuit 2. The intersection of the characteristic YLa and the characteristic Yp becomes the operating point A, and the product of the output voltage V2typ and the LED current ILtyp at the operating point A becomes the output power of the LED drive circuit 2. The output voltage V2typ and the LED current ILtyp are typical values in a steady state, and the upper limit value and lower limit value of the output voltage V2 in the characteristic Yp are voltages V2H and V2L. The upper limit value and lower limit value of the LED current IL are ILH, ILL.

  Since the LED voltage Vf decreases as the temperature of the LED element La rises, the voltage-current characteristic of the LED unit 3 becomes a characteristic YLa ′ shifted in the direction in which the output voltage V2 decreases. However, when the output characteristic of the LED drive circuit 2 is the characteristic Yp regardless of the LED voltage Vf, the operating point B is reached, the LED current IL increases, and the LED elements La, La,. . . The amount of heat generated increases. Then, the LED elements La, La,. . . , The LED voltage Vf further decreases, the LED current IL further increases, and the LED elements La, La,. . . It will fall into the vicious circle that the calorific value of will increase further.

  Therefore, when the detected value of the LED voltage Vf decreases, the LED drive circuit 2 performs an operation of shifting the output characteristic to the characteristic Yp ′ in which the output power is reduced from the characteristic Yp, and both the output voltage V2 and the LED current IL operate. The operation is performed at the operating point C of the output voltage V2typ ′ and the LED current ILtyp ′ lower than the point A. Therefore, the power consumption in the LED unit 3 is suppressed, the amount of heat generated by the LED element La is reduced, and the above-described vicious circle is prevented.

  Thus, since temperature detection is performed using the LED element La as a load, it is not necessary to provide a dedicated temperature sensor separately, and the configuration can be simplified, downsized, and reduced in cost.

  Further, by controlling the power supplied to the LED unit 3 based on the LED voltage Vf that changes according to the temperature of the LED element La, it is possible to perform accurate feedback control based on the substantial temperature of the LED element La. High reliability can be obtained.

  In addition, when the LED voltage Vf changes, output control is performed within the allowable power range of the LED element La, so that overpower and overcurrent are prevented and the thermal stress of the LED element La does not become excessive and is stable. Since the optical output can be secured and the power consumption is not more than necessary, it is possible to extend the life and increase the efficiency.

  Furthermore, since the output characteristics of the LED drive circuit 2 and the shift operation of the output characteristics are set in consideration of characteristic variations such as the LED voltage Vf of each LED element La, characteristic variations such as selection of the LED elements La are suppressed. Therefore, the cost increase of the LED element La alone can be suppressed.

  In addition, although about 3 to several tens of LED elements La are connected in series to the LED unit 3, this number may be arbitrarily set according to the application, and the output voltage V2 varies depending on the combination of the LED elements La. .

  Further, although the change in the LED voltage Vf with respect to the temperature of the LED element La shown in FIG. 3 differs depending on the type of the LED element La, in practice, the output characteristics may be shifted in accordance with the characteristics of the LED element La to be used.

(Embodiment 2)
FIG. 5 shows a circuit configuration of the illumination device 7 using the LED driving device 8 of the present embodiment. The basic configuration is the same as that of the first embodiment, and the same components are denoted by the same reference numerals and described. Is omitted.

  The output of the LED drive circuit 2 is provided with an output voltage detection unit 4 composed of a series circuit of resistors 40 and 41 connected between output terminals, and a connection midpoint voltage obtained by dividing the output voltage V2 by the resistors 40 and 41 is provided. And output as an output voltage detection value.

  The LED drive circuit 2 is composed of a booster circuit, a series circuit of an inductor 201 and a diode 202 connected between the input and output terminals on the high voltage side, and an FET connected in parallel to the DC power source 1 via the inductor 201. A switching element 203 such as a transistor, a capacitor 204 connected in parallel to the switching element 203 via a diode 202, a detection value of the LED voltage Vf, and an output voltage detection value from the output voltage detection unit 4 The boosting control unit 205 controls the switching operation 203, and boosts the voltage V1 = 12V of the DC power supply 1 to the output voltage V2 = 24V.

  Also in the present embodiment, as in the first embodiment, the boost control unit 205 shifts the output characteristic based on the LED voltage Vf that changes according to the temperature of the LED element La, and the switching element 203 according to the output characteristic. Is controlled to control the power supplied to the LED unit 3. Further, the boost control unit 205 adds to the same control as in the above embodiment, controls the switching operation of the switching element 203 based on the output voltage detection value from the output voltage detection unit 4, and sets the output voltage V2 to the target voltage. The feedback control is performed so as to match the above, and output control with higher accuracy becomes possible.

  Further, by configuring the LED drive circuit 2 with a booster circuit, the LED unit 3 has a large number of LED elements La, La,. . . Even when the output voltage V2 equal to or higher than the voltage V1 of the DC power supply 1 is necessary, an output voltage V2 sufficient to drive all the LED elements La can be obtained.

(Embodiment 3)
FIG. 6 shows a circuit configuration on the output side of the LED drive circuit 2 of the present embodiment. A resistor is connected in series to the output terminal on the low voltage side of the LED drive circuit 2 of the second embodiment, and the output current detection unit 5 is connected. The voltage across the output current detection unit 5 generated by the LED current IL is input to the boost control unit 205 as an output current detection value.

  In addition to the control of the second embodiment, the boost control unit 205 controls the switching operation of the switching element 203 based on the output current detection value from the output current detection unit 5 to match the additional current IL with the target current. Feedback control is performed, and output control with higher accuracy becomes possible.

(Embodiment 4)
FIG. 7 shows a circuit configuration of the illumination device 7 using the LED drive device 8 of the present embodiment, the basic configuration is the same as that of the first embodiment, and the same configuration is denoted by the same reference numerals and described. Is omitted.

  The output of the LED drive circuit 2 is provided with an output voltage detection unit 4 composed of a series circuit of resistors 40 and 41 connected between output terminals, and a connection midpoint voltage obtained by dividing the output voltage V2 by the resistors 40 and 41 is provided. And output as an output voltage detection value.

  Further, a resistor is connected in series to the output terminal on the low voltage side of the LED drive circuit 2 to configure the output current detector 5, and the voltage across the output current detector 5 generated by the LED current IL is output as an output current detection value. .

  The LED drive circuit 2 includes a step-up / step-down circuit using a flyback transformer 206, and includes a step-up / step-down main circuit unit 200 and a step-up / down control unit 210.

  The step-up / step-down main circuit unit 200 includes a series circuit of a primary winding 206a of a transformer 206 connected between input terminals and a switching element 203 such as an FET or a transistor, and a diode 202 and a transformer 206 connected between output terminals. The circuit is composed of a series circuit with the secondary winding 206 b and a capacitor 204, and the low voltage side end of the primary winding 206 a is connected to the low voltage side end of the secondary winding 206 b through the switching element 203. Further, a switch SW for turning on / off the input of the step-up / step-down main circuit unit 200 is inserted between the high-voltage side output end of the DC power supply 1 and the high-voltage side input end of the step-up / step-down main circuit unit 200.

  The step-up / down control unit 210 includes an amplification circuit unit 211, a PWM control unit 215, a reference value generation circuit 216, a driver circuit 217, and a control power supply 218. The amplification circuit unit 211 includes the output voltage detection unit 4. Are provided with amplifiers 212, 213 and 214 for amplifying the detected output voltage value of LED, the detected value of LED voltage Vf, and the detected output current value of output current detector 5, respectively. The switching operation of the switching element 203 is controlled based on the value and the output current detection value. The control power source 218 is a power source for operating the step-up / step-down control unit 210, and the voltage V 1 is supplied from the DC power source 1.

  When the switching element 203 is turned on, current flows in a closed circuit of the DC power source 1 -primary winding 206 a -switching element 203 -DC power source 1, and energy is accumulated in the transformer 206. Next, when the switching element 203 is turned off, this energy is released in the closed circuit of the secondary winding 206b-diode 202-capacitor 204-secondary winding 206b, and the capacitor 204 is charged. At this time, the voltage induced in the secondary winding 206 b is rectified by the diode 202 and then smoothed by the capacitor 204. The voltage across the capacitor 204 is a voltage obtained by stepping up or down the voltage V1 of the DC power supply 1, or the same voltage as the voltage V1. The switching element 203 is turned on and off at a high frequency, and is stable regardless of the value of the voltage V1. A voltage is generated. The charge of the capacitor 204 is supplied to the LED unit 3 as the output voltage V2 and the LED current I2.

  In the present embodiment, the operation mode is switched based on the output voltage detection value input via the amplifier 212. Here, the operation mode is (1) a start mode in which control is performed to gradually supply power without suddenly supplying power from the LED drive circuit 2 to the LED unit 3 at the start when the switch SW is turned on. (2) When the output voltage V2 is in the range of the upper limit value or less and the lower limit value or more, the LED drive circuit 2 of the LED drive circuit 2 is based on the detected value of the LED voltage Vf input through the amplifier 213 as in the first embodiment. A steady mode in which the output characteristic is shifted and the driver circuit 217 drives the switching element 203 along the output characteristic. (3) When the output voltage V2 rises above the upper limit, supply of the output voltage V2 and the LED current IL (4) An overcurrent control mode for controlling the LED current IL to a constant value when the output voltage V2 falls below the lower limit value. In degrees.

  First, the reference value generation circuit 216 includes a timer unit (not shown), switches the mode based on the output voltage detection value input via the amplifier 212, generates a reference value, and generates the reference value. Output to the PWM control unit 215.

  The PWM control unit 215 is a pulse for setting the on-duty of the switching element 203 according to the mode switched by the reference value generation circuit unit 216, the reference value, and the output current detection value input via the amplifier 214. A width modulation signal is generated, and this pulse width modulation signal is output to the driver circuit 217.

  The driver circuit 217 outputs a drive signal to the switch element 203 during the ON period of the pulse width modulation signal from the PWM control unit 215.

  In the above (3) steady-state mode, the PWM control unit 215 determines the output characteristics of the LED drive circuit 2 based on the detected value of the LED voltage Vf input through the amplifier 213 as in the first embodiment. The generation of the pulse width modulation signal is performed along this output characteristic.

(Embodiment 5)
FIG. 8 shows a circuit configuration of the illumination device 7 using the LED driving device 8 of the present embodiment. The basic configuration is the same as that of the fourth embodiment, and the same components are denoted by the same reference numerals and described. Is omitted.

  In this embodiment, the microcomputer 230 is used for the step-up / step-down control unit 210 of the LED drive circuit 2, and the microcomputer 230 constitutes a PWM control unit 215, a reference value generation circuit 216, an error calculation operation unit 219, and a driver signal generation unit 220. To do. Here, the PWM control unit 215 and the reference value generation circuit 216 have the same functions as those in the fourth embodiment. Then, the miscalculation calculation unit 219 outputs a calculation result based on the reference value from the reference value generation circuit 216 and the output current detection value input via the amplifier 214 to the PWM control unit 215. The PWM control unit 215 generates a pulse width modulation signal based on the calculation result, the detected value of the LED voltage Vf, and the detected output voltage value, and the driver signal generation unit 220 receives the pulse width modulation signal from the PWM control unit 215. In response to the driver signal, the driver circuit 217 drives the switching element 203 (see FIG. 7) in response to the driver signal.

  In the fourth embodiment, the step-up / step-down control unit 210 is configured by an analog circuit. However, in the present embodiment, since each function is processed by software using the microcomputer 230, finer control can be performed.

(Embodiment 6)
FIG. 9 shows a cross-sectional configuration of a lighting fixture using the lighting device according to the first to fifth embodiments. This luminaire is, for example, an in-vehicle illuminator, an in-vehicle illuminator such as a headlamp, an auxiliary lamp, an indoor illuminator, or a display luminaire provided in the vehicle, as shown in FIG. A lamp 6 and a lighting device 7 are provided.

  The lamp 6 includes a body 60 that is in contact with an upper surface CB in the vehicle, a cover 61 that is fitted to the body 60, and a lens body 62. The body 60 is integrally provided with a bottom portion 600 formed in a circular shape by, for example, insulating resin molding, and a cylindrical portion 601 extending downward from the outer peripheral edge of the bottom portion 600. The body 60 houses the lens body 62 and the LED unit 3 in a detachable manner. The cover 61 is integrally provided with a bottom portion 610 formed in a circular shape by, for example, insulating resin molding, and a cylindrical portion 611 extending upward from the outer peripheral edge of the bottom portion 610. Further, the cover 61 is provided with a circular hole 610 a in the center of the bottom 610.

  The lens body 62 is integrally provided with a bottom portion 620 formed in a circular shape by, for example, insulating resin molding, and a cylindrical portion 621 extending upward from the outer peripheral edge of the bottom portion 620. Further, the lens body 62 includes a plurality of lenses 622... At a position in front of the plurality of LED elements La. Each lens 622 controls light emitted from each LED element La.

  The illumination device 7 includes an LED unit 3 and an LED driving device 8. The LED unit 3 includes a substrate 30 and a plurality of (for example, 3 to several tens) LED elements La. The board | substrate 30 is a printed circuit board, a resin substrate, etc., for example, and is formed in circular shape. The plurality of LED elements La are connected in series on the substrate 30. The plurality of LED elements La... Are electrically connected to the LED driving device 8 as shown in FIGS. 1, 5, 7, and 8, and the voltage V2 supplied from the LED driving device 8 and The illumination load emits white light by the LED current IL. The number of LED elements La can be set as appropriate according to the application.

It is a figure which shows the circuit structure of the illuminating device of Embodiment 1 of this invention. It is a figure which shows another circuit structure of DC power supply same as the above. It is a figure which shows the change of the LED voltage with respect to the temperature of an LED element. It is a figure which shows the characteristic of the output voltage of a LED drive circuit, and LED current. It is a figure which shows the circuit structure of the illuminating device of Embodiment 2 of this invention. It is a figure which shows the circuit structure of the illuminating device of Embodiment 3 of this invention. It is a figure which shows the circuit structure of the illuminating device of Embodiment 4 of this invention. It is a figure which shows the circuit structure of the illuminating device of Embodiment 5 of this invention. It is a figure which shows the cross section of the lighting fixture of Embodiment 6 of this invention. It is a figure which shows the circuit structure of the conventional illuminating device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 LED drive circuit 3 LED unit La LED element 7 Illumination device 8 LED drive device

Claims (7)

A direct-current power supply and an LED drive circuit that supplies a desired direct-current output generated from the direct-current power supply to a series circuit of a plurality of LED elements connected between output ends, and the LED drive circuit has both ends of any one of the LED elements An LED driving device characterized by controlling output power within a predetermined range by changing output characteristics based on voltage. The LED driving device according to claim 1, wherein the LED driving circuit includes a booster circuit. An output voltage detection unit configured by a series circuit of a plurality of resistors connected between the output terminals of the LED drive circuit and outputting a voltage detection value obtained by dividing the output voltage of the LED drive circuit; and an output terminal of the LED drive circuit And an output current detection unit that outputs a voltage generated in the resistor as a current detection value, and the LED driving circuit controls the output based on the voltage detection value and the current detection value. The LED driving device according to claim 1 or 2, characterized in that The LED driving device according to claim 1, wherein the LED driving circuit generates a desired DC output from the DC power source using a flyback transformer. The LED driving circuit is based on a switching element that generates a desired DC output by switching, a reference value generation unit that generates a reference value based on the voltage detection value, and the current detection value and the reference value 6. The LED driving device according to claim 3, further comprising: a PWM control unit that performs PWM control of the switching element. An illumination device comprising: the LED driving device according to claim 1; and a series circuit of a plurality of LED elements driven by the LED driving device. A lighting apparatus comprising the lighting device according to claim 6.

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