JP2008130523A - Led lighting circuit and illumination fixture using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformize the light output from numerous LEDs and to suppress power consumption for its uniformization in an LED lighting circuit used for an illumination fixture or the like. <P>SOLUTION: A current from a DC-DC converter 35 to an LED module 32 is detected by a resistor R2, the detected current is compared with a reference voltage Vref from the reference voltage source 38 in a comparison circuit 37, and the DC-DC converter 35 is controlled by a control circuit 36 in response to its result, thereby totally controlling a load current by a constant current control. Furthermore, in the respective LED load circuits U1 to U3 constituting the module 32, control elements Q1 to Q3 constituting a current mirror are installed in series, an impedance element A is installed in series against the element Q1 to prepare a reference current, and the voltage drop in its system is made to be the maximum. Accordingly, even if there is variance in an ON voltage Vf, current values in the respective circuits U1 to U3 are equally controlled, and the light output can be equalized. Moreover, a circuit to prepare only the reference current is not required, and a loss of that share is eliminated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an LED lighting circuit and a luminaire using the same, and more particularly to a technique for equalizing the currents of LEDs provided in parallel.

  When using a large number of LEDs to obtain the required light output, such as when using the LEDs (light emitting diodes) in the luminaire, a low current LED is more efficient and can be used to obtain the same light output. When subdividing, an excessive power supply voltage is required to light them by connecting them in series. On the other hand, if the plurality of LEDs are connected to each other in parallel and turned on, an excessive current is required. Therefore, in practice, an appropriate series-parallel configuration according to the application is adopted. However, in the case of a blue LED, the ON voltage Vf is about 3 to 3.5 V and varies widely. When combined in series and parallel, a difference in the shunt ratio between the series circuits parallel to each other tends to occur. There is a problem that a difference in brightness between the series circuits tends to occur.

  Specifically, the light output of the LED depends on the energization current value. From this point of view, in the case of the series configuration, the energization current value is the same even if the ON voltage Vf of each LED varies. Therefore, the light output variation of each LED is also small. On the other hand, in the case of the parallel configuration, if the sum of the ON voltages Vf of the LEDs in the series configuration is different, the current value flowing from the collective output of the lighting circuit (power supply circuit) to each series circuit is a circuit with a low ON voltage Vf. As a result, the optical output variation increases for each series circuit.

  FIG. 9 is a block diagram showing a configuration of a typical prior art LED lighting circuit 1. This prior art is disclosed in Patent Document 1. In this LED lighting circuit 1, an LED module 2 is configured by connecting three LED load circuits u <b> 1 to u <b> 3 in which many LED loads are connected in series in parallel. The LED module 2 is supplied with the DC voltage VDC obtained by converting the voltage Vac from the commercial power source 3 into a DC voltage from the noise-cutting capacitor c1 by the rectifier bridge 4 and converting the voltage through the DC-DC converter 5.

  The DC-DC converter 5 rectifies the output current from the choke coil l, the switching element q0 for switching the DC output voltage of the rectifier bridge 4, the choke coil l for storing / releasing the excitation energy by the switching, and the choke coil l. It comprises a smoothing diode d and a smoothing capacitor c2, a resistor r1 for detecting the current flowing through the switching element q0 by converting it into a voltage, and a control circuit 6 for controlling the switching of the switching element q0. A boost chopper circuit.

  On the other hand, constant current circuits q1 to q3 are inserted in series in the LED load circuits u1 to u3 in order to make the energization current values flowing through them equal to each other. The applied voltage (burden voltage) of the constant current circuits q1 to q3 is compared with the reference voltage Vref from the reference voltage source 8 in the comparison circuit 7, and the comparison result is given to the control circuit 6, The circuit 6 controls the constant voltage output of the DC-DC converter 5 so that the voltage applied to each of the constant current circuits q1 to q3 is smaller than the sum of the ON voltages Vf of the series LEDs. Thereby, loss suppression in each of the constant current circuits q1 to q3 is achieved. However, this conventional technique has problems such that the greater the variation in the ON voltage Vf of the LED, the more the overall light output level fluctuates and the loss in the constant current circuits q1 to q3 increases.

  FIG. 10 is a block diagram showing a configuration of another conventional LED lighting circuit 11. This prior art is disclosed in Patent Document 2. In this LED lighting circuit 11, the total energization current value to each LED load circuit u1-u3 is detected by converting the voltage with the resistor r2, and the result of comparing the voltage with the reference voltage Vref in the comparator 17 becomes a constant value. Thus, the DC-DC converter 15 is controlled via the PWM control circuit 16. The DC-DC converter 15 switches the voltage Vdc from the DC power supply 13 by the switching element q0 and applies it to the primary side of the transformer t. The DC voltage VDC obtained by rectifying and smoothing the secondary output by the rectifying and smoothing circuit 14 is provided. Is provided to each of the LED load circuits u1 to u3, thereby constituting a one-stone flyback converter that insulates the power supply side from the load side. And also in this LED lighting circuit 11, the constant current circuits d1-d3 are each provided in series with each LED load circuit u1-u3.

  FIG. 11 is an electric circuit diagram showing a specific example of the constant current circuits d1 to d3. The constant current circuits d1 to d3 include a transistor q11 and a resistor r11 connected in series to the LED load circuits u1 to u3, a resistor r12 connecting between a collector and a base of the transistor q11, and a base of the transistor q11. And a Zener diode dz interposed between the emitters. The collector current of the transistor q11 is made constant under the condition that the sum of the voltage drop of the resistor r11 and the base-emitter voltage Vbe of the transistor q11 substantially matches the Zener voltage of the Zener diode dz.

  As a result, the currents of the LED load circuits u1 to u3 are individually made constant, and the collective output current of the DC-DC converter 15 is also controlled by the constant current as described above. Variations in light output can be significantly suppressed. However, there is a problem that the constant current circuits d1 to d3 have a large loss as compared with the simple constant current circuits q1 to q3 formed of FET source follower circuits.

Therefore, the present inventor has proposed an LED lighting circuit 21 as shown in FIG. According to the prior art, transistors q21 and q22 and resistors r21 and r22 are connected in series with the LED load circuits u1 and u2, respectively, and the transistor q20 and the transistor q20 constituting the current mirror circuit are connected to resistors r23, The terminals r24 and r20 are connected between the terminals of the DC power supply 23. A reference current determined by the voltage VDC from the DC power supply 23 and the resistors r23, r24, r20 and the like flows to the transistor q20, and the current flowing through the transistors q21 and q22 is balanced with the reference current, thereby suppressing variations in optical output. It is supposed to be. Note that, by short-circuiting the resistor r24 by a bypass switch sw provided in parallel with one of the resistors (r24 in this example), the reference current can be increased and the optical output can be increased.
Japanese Patent Laid-Open No. 2002-8409 JP 2004-319583 A JP 2004-39290 A

  Although the method using the mirror circuit as described above is convenient for balancing the currents between the LED load circuits u1 and u2, the reference current fluctuates due to fluctuations in the power supply voltage VDC, and the reference current is generated. There is also a problem that losses occur in the resistors r23, r24, r20 and the transistor q20.

  The objective of this invention is providing the LED lighting circuit which can equalize the light output of many LED with low loss, and a lighting fixture using the same.

  The LED lighting circuit of the present invention is an LED lighting circuit in which an electric current is supplied from a DC power source to an LED module in which a plurality of LED load circuits each composed of one or a plurality of series LEDs are arranged in parallel with each other. A control element that is provided in series with each LED load circuit, and that configures a current mirror circuit to link the energization current value in each LED load circuit, so that any one becomes a reference current circuit for the current mirror. When such a control element having a diode structure and a control element circuit having the diode structure are inserted in series, the ON voltage of the LED is Vf, the variation is σ, and the number of series stages is n. And an impedance element that causes a voltage drop of Vf × n × σ or more with current.

  According to the above configuration, in an LED lighting circuit used for a lighting fixture or the like, a direct current power source is lit for an LED module in which a plurality of LED load circuits composed of one or a plurality of serially arranged LEDs are arranged in parallel with each other. In driving, in series with each LED load circuit, a control element constituting a current mirror circuit is provided, and in these control elements, any one of them has a diode structure to be a reference current circuit of the current mirror, The LED load circuits are balanced by interlocking the energization current values of the control elements of the remaining circuits via the control terminals. Specifically, when the control element is a transistor, the base that is the control terminal and the collector are short-circuited and the bases are connected in common. When the control element is a MOS transistor, the gate and drain which are control terminals are short-circuited and the gates are connected in common. Further, an impedance element that can be realized by a diode or the like is inserted in series with the control element circuit having the diode structure, and the impedance element is set to Vf as the ON voltage of the LED, σ as the variation, and the number of series stages. Where n is a voltage drop of Vf × n × σ or more at the rated current.

  Therefore, even if the LED ON voltage Vf varies, the circuit that creates the reference current of the current mirror circuit is the circuit that has the highest voltage drop due to the LED current, including the sum of the LED ON voltage Vf. In addition, the current value in each LED load circuit can be controlled uniformly, and the light output from a large number of LEDs can be made uniform. In addition, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to the circuit can be eliminated.

  In the LED lighting circuit of the present invention, the impedance element is an LED.

  According to the above configuration, it is possible to set the sum of the ON voltages Vf to be the highest by simply setting a large number of series LED stages of the LED load circuit serving as the reference current circuit of the current mirror. The power consumption by the impedance element can be effectively utilized while being configured.

  Furthermore, the LED lighting circuit of the present invention includes a shorting switch capable of short-circuiting the terminals of the impedance element, the shorting switch being opened, and the control element performing a current mirror operation. The detection means for detecting the sum of the LED ON voltages Vf in the LED load circuit, and the sum of the ON voltages Vf of the LED load circuits in which the control element has the diode structure is the highest in response to the detection result of the detection means. Switching control means for closing the short-circuit switch in the case, and opening the short-circuit switch in the other case.

  According to the above configuration, when the current equalization operation is performed by the current mirror as described above, the circuit having the highest sum of the ON voltages Vf of the LEDs must be the reference current circuit, whereas the impedance element A short-circuit switch for short-circuiting between the terminals of the LED load circuit is provided in advance, and when the detection means actually measures the sum of the ON voltages Vf of the LEDs in each LED load circuit, the switching control means has a diode structure as the control element. When the sum of the ON voltage Vf of the LED load circuit is highest, the short-circuit switch is closed to prevent the impedance element from functioning. Otherwise, the short-circuit switch is opened to function the impedance element.

  Therefore, the impedance element can be made to function only when necessary with respect to aging and the like, and loss in the impedance element can be suppressed.

  Further, the LED lighting circuit of the present invention is an LED lighting circuit in which a current is supplied from a DC power source to an LED module in which a plurality of LED load circuits composed of one or a plurality of series LED's are arranged in parallel with each other. A control element that is provided in series with each of the LED load circuits and that configures a current mirror circuit to link an energization current value in each of the LED load circuits, one of which is a reference current circuit of the current mirror And including such a control element having a diode structure, and an impedance element inserted in parallel to a circuit other than the control element circuit of the diode structure to reduce the impedance of the LED load circuit. To do.

  According to the above configuration, in an LED lighting circuit used for a lighting fixture or the like, a direct current power source is lit for an LED module in which a plurality of LED load circuits composed of one or a plurality of serially arranged LEDs are arranged in parallel with each other. In driving, in series with each LED load circuit, a control element constituting a current mirror circuit is provided, and in these control elements, any one of them has a diode structure to be a reference current circuit of the current mirror, The LED load circuits are balanced by interlocking the energization current values of the control elements of the remaining circuits via the control terminals. Specifically, when the control element is a transistor, the base that is the control terminal and the collector are short-circuited and the bases are connected in common. When the control element is a MOS transistor, the gate and drain which are control terminals are short-circuited and the gates are connected in common. Further, an impedance element for reducing the impedance of the LED load circuit is inserted in parallel to a circuit other than the control element circuit having the diode structure.

  Therefore, even if the LED ON voltage Vf varies, the circuit that creates the reference current of the current mirror circuit is the circuit that has the highest voltage drop due to the LED current, including the sum of the LED ON voltage Vf. Thus, the current value in each LED load circuit can be controlled uniformly, and the light output from a large number of LEDs can be made uniform. In addition, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to the circuit can be eliminated.

  Furthermore, in the LED lighting circuit of the present invention, the DC power source is a DC-DC converter, and the total current value flowing through each LED load circuit or the current flowing through the LED load circuit corresponding to the diode-connected control element. A current detection means for detecting a value, a reference voltage source and a comparator for comparing detection results from the current detection means, and a sum of energization current values to the LED module according to the output from the comparator And a control means for feedback-controlling the DC power supply so that the value becomes a predetermined value.

  According to the above configuration, the current value flowing from the DC power source to each LED load circuit is detected, and the DC current is fed back by feedback so that the sum of the current values becomes a predetermined value based on the detection result. Since the power source is controlled at a constant current, the loss at the control element is small compared to the constant voltage control, and the loss can be reduced.

  Moreover, the lighting fixture of this invention uses the said LED lighting circuit, It is characterized by the above-mentioned.

  According to said structure, even if the ON voltage (Vf) of LED varies extremely, the light output from many LED can be equalize | homogenized and a low-loss lighting fixture can be implement | achieved.

  As described above, the LED lighting circuit of the present invention is an LED lighting circuit used for lighting fixtures, etc., for an LED module in which a plurality of LED load circuits composed of one or a plurality of series LED's are arranged in parallel with each other. Thus, when the DC power supply is lit, a control element constituting a current mirror circuit is provided in series with each LED load circuit, and one of these control elements serves as a reference current circuit for the current mirror. In this way, a diode structure is used, and the energizing current values of the control elements of the remaining circuit are linked via the control terminal so as to balance the LED load circuits, and the control element circuit having the diode structure. An impedance element is inserted in series with the impedance element, and the impedance element sets the ON voltage of the LED to Vf. Was a sigma, when the serial number is n, to produce a Vf × n × sigma or more voltage drop at rated current.

  Therefore, even if the LED ON voltage Vf varies, the circuit that generates the reference current of the current mirror circuit is the circuit that has the highest voltage drop due to the LED current, including the sum of the LED ON voltage Vf. Therefore, the current value in each LED load circuit can be controlled uniformly, and the light output from many LEDs can be made uniform. In addition, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to the circuit can be eliminated.

  Moreover, the LED lighting circuit of this invention uses the said impedance element as LED as mentioned above.

  Therefore, it is possible to set the total sum of the ON voltages Vf to be the highest only by setting a large number of series LED stages of the LED load circuit serving as the reference current circuit of the current mirror, and it can be easily configured. The power consumption by the impedance element can be effectively utilized.

  Furthermore, as described above, in the LED lighting circuit of the present invention, when the current equalization operation is performed by the current mirror as described above, the circuit having the highest sum of the LED ON voltages Vf must be the reference current circuit. On the other hand, a short-circuit switch for short-circuiting between the terminals of the impedance element is provided in advance, and when the detecting means actually measures the sum of the LED ON voltages Vf in each LED load circuit, the switching control means When the total of the ON voltage Vf of the LED load circuit having a diode structure as the control element is the highest, the short-circuit switch is closed to prevent the impedance element from functioning. Otherwise, the short-circuit switch is opened. The impedance element is made to function.

  Therefore, the impedance element can be made to function only when necessary with respect to secular change and the like, and loss in the impedance element can be suppressed.

  Further, as described above, the LED lighting circuit of the present invention is an LED module in which a plurality of LED load circuits composed of one or a plurality of series-connected LEDs are arranged in parallel with each other in an LED lighting circuit used for a lighting fixture or the like. On the other hand, when the DC power supply is driven to light, a control element constituting a current mirror circuit is provided in series with each LED load circuit, and one of these control elements is a reference current circuit of the current mirror. The diode structure is configured so that the energizing current values of the control elements of the remaining circuits are interlocked via the control terminal so as to balance each LED load circuit, and the control element having the diode structure. An impedance element for reducing the impedance of the LED load circuit is inserted in parallel with the circuit other than the above circuit.

  Therefore, even if the LED ON voltage Vf varies, the circuit that generates the reference current of the current mirror circuit is the circuit that has the highest voltage drop due to the LED current, including the sum of the LED ON voltage Vf. Thus, the current value in each LED load circuit can be controlled uniformly, and the light output from a large number of LEDs can be made uniform. In addition, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to the circuit can be eliminated.

  Furthermore, as described above, the LED lighting circuit according to the present invention detects the energization current value from the DC power source to each of the LED load circuits, and based on the detection result, the sum of the energization current values is a predetermined value. Thus, the DC power supply is controlled at a constant current by feedback.

  Therefore, compared with the constant voltage control, the loss in the control element is small, and the loss can be reduced.

  Moreover, the lighting fixture of this invention uses the said LED lighting circuit as mentioned above.

  Therefore, even if the ON voltage (Vf) of the LED varies extremely, it is possible to make the light output from a large number of LEDs uniform and to realize a low-loss lighting fixture.

[Embodiment 1]
FIG. 1 is a block diagram showing a configuration of an LED lighting circuit 31 according to an embodiment of the present invention. In the LED lighting circuit 1, an LED module 32 is configured by connecting three LED load circuits U1 to U3 in which a large number of LEDD1s are connected in series to each other in parallel. The number of series LED loads in each of the LED load circuits U1 to U3 is arbitrary, and may be composed of a single LED.

  Each of the LED load circuits U1 to U3 is configured such that the LEDD1 is mounted on a common heat sink and bonded, and a wavelength conversion phosphor, a light diffusion lens, and the like are attached. The LED module 32 and the LED lighting circuit 31 are used as a lighting fixture. The LED load emits blue or ultraviolet light, and the light from the LED load is wavelength-converted by the phosphor and emitted as white light. . The number of parallel circuits of the LED load circuits U1 to U3 is also arbitrary, and a method for obtaining white light, for example, combining light emitted by the three primary colors of RGB is also arbitrary.

  The LED module 32 is supplied with the DC voltage VDC obtained by converting the voltage Vac from the commercial power source 33 into a direct current from the noise-cutting capacitor C <b> 1 by the rectifier bridge 34 and converting the voltage through the DC-DC converter 35. The DC-DC converter 35 rectifies the output current from the choke coil L, the switching element Q0 that switches the DC output voltage of the rectifier bridge 34, the choke coil L that stores and discharges the excitation energy by the switching, and the like. It comprises a smoothing diode D and a smoothing capacitor C2, a resistor R1 for detecting the current flowing through the switching element Q0 by converting it into a voltage, and a control circuit 36 for controlling the switching of the switching element Q0. A boost chopper circuit.

  The current flowing from the DC-DC converter 35, which is a DC power supply, to the LED module 32 is converted into a voltage value by the current detection resistor R2, and compared with the reference voltage Vref from the reference voltage source 38 in the comparison circuit 37. The comparison result is fed back to the control circuit 36. The control circuit 36 controls the switching frequency and duty of the switching element Q0 in response to the detection results of the resistors R1 and R2. Thus, constant voltage control of the voltage VDC and constant current control of the current flowing to the LED module 32 are performed.

  It should be noted that in the present embodiment, each of the LED load circuits U1 to U3 is provided with control elements Q1 to Q3 constituting a current mirror circuit in series in order to make the current values flowing through them equal to each other. One of the control elements Q1 to Q3 (Q1 in the example of FIG. 1) has a diode structure so as to be a reference current circuit of the current mirror, and the remaining control is performed via the control terminal. It is to balance the LED load circuits U1 to U3 by interlocking the energization current values of the elements (Q2 and Q3 in the example of FIG. 1).

  Specifically, when the control elements Q1 to Q3 are transistors as shown in FIG. 1, the base that is the control terminal and the collector are short-circuited and the bases are connected in common. When the control element is a MOS transistor, the gate and drain which are control terminals are short-circuited and the gates are connected in common.

  Further, it should be noted that an impedance element A is inserted in series into the LED load circuit U1 of the control element Q1 having the diode structure, and the impedance element A has the ON voltage of the LEDD1 as Vf and the variation thereof as σ. When the number of stages is n, the voltage drop Va is not less than Vf × n × σ at the rated current.

  The impedance element A is realized by, for example, one or a plurality of stages of diodes as shown in FIG. 2A, a Zener diode as shown in FIG. 2B, a resistance as shown in FIG. Can do. When the diode shown in FIG. 2 (a) is used, for example, one can cope with a fine variation of 0.7V, and when the Zener diode shown in FIG. 2 (b) is used, the sum of the ON voltage Vf. 2V, and when using a resistor as shown in FIG. 2 (c), a loss always occurs, but it is possible to cope with a finer variation than the diode, and the ON voltage This is suitable when the variation in Vf is small or when the LEDD1 has a small number of stages.

  With this configuration, even if the ON voltage Vf of the LEDD1 varies, the circuit that generates the reference current of the current mirror circuit has a voltage drop due to the LED current including the sum of the ON voltage Vf of the LEDD1. It is the highest circuit, and the current values in the LED load circuits U1 to U3 can be uniformly controlled, so that the light outputs from the multiple LEDs D1 can be made uniform. In addition, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to the circuit can be eliminated. Furthermore, since one of the control elements Q1 to Q3 such as a transistor has a diode structure and is only configured as a mirror circuit, it can be realized with an inexpensive configuration.

  For example, when the number of LED load circuits is three of U1 to U3, each of the LED load circuits U1 to U3 is constituted by five stages of LEDs D1, and the variation of the ON voltage Vf is ± 5%, the resistance In the case of only the collective constant current control based on the detection result of R2, that is, when the control elements Q1 to Q3 are not provided, the current variation between the LED load circuits U1 to U3 is 17.5 to 22.7 mA (described above). The current value of the batch constant current control is 60 mA), whereas the control elements Q1 to Q3 are provided, and the control element Q1 corresponding to the LED load circuit U1 having the highest sum of the ON voltages Vf as described above is used as a reference. As described above, by causing the other control elements Q2 and Q3 to perform the mirror operation, the current variation can be suppressed to 20.0 to 20.1 mA. Similarly, when the variation of the ON voltage Vf is ± 10%, 15.2 to 25.8 mA is obtained only by collective constant current control, and 20.0 to 20.1 mA is obtained by performing the mirror operation. be able to.

  The DC power source of the LED lighting circuit 31 is a DC-DC converter 35 having a choke coil L, as in the LED lighting circuit shown in FIG. 9, but an insulation type DC-DC having a transformer t shown in FIG. A DC converter may be used, and in particular, a DC power supply for the LED module 32 is arbitrary. However, when performing the constant current control by the current mirror operation using the control elements Q1 to Q3, it is preferable to use the constant current control for the DC power supply in the constant voltage control and the constant current control.

  FIG. 3 shows a case where the DC-DC converter 35 performs only constant current control based on the detection result of the resistor R2 as described above and only performs constant voltage control of the voltage VDC as shown in FIG. The loss due to the control elements Q1 to Q3 will be described in detail. FIG. 3 also shows in detail the loss when the constant current control is performed and when the constant voltage control is performed when the constant current circuits d1 to d3 shown in FIGS. 10 and 11 are used. Show. The conditions for the trial calculation are as follows: the current flowing through each LED load circuit U1 to U3, that is, the rated current of LEDD1 is 20 mA, the ON voltage Vf of LEDD1 is 3.2 V, the variation is ± 10%, and the control elements (transistors) Q1 to Q3 Let hfe be 100.

  As is clear from FIG. 3, in the current balance control by the current mirror circuit of the present embodiment, the loss is smaller when there is no variation in the ON voltage Vf, but the constant current control is performed regardless of whether there is a variation in the ON voltage Vf. It is understood that the loss is smaller than the constant voltage control. On the other hand, even in the current balance control using the constant current circuits d1 to d3 shown in FIG. 10 and FIG. 11 described above, the constant current control is more effective for the constant voltage control regardless of whether the ON voltage Vf varies. In comparison, although the loss is small, in the constant current control, the total current amount is limited. Therefore, it is understood that the loss is the same regardless of whether the ON voltage Vf varies. Therefore, constant current control is preferable for the current balance control by the current mirror circuit of the present embodiment, and in ensuring the current balance in any condition compared to the case where the constant current circuits d1 to d3 are used. It is understood that the loss can be greatly reduced.

  In the above description, the emitter area ratios of the control elements (transistors) Q1 to Q3, that is, the rated currents of the LEDs D1 in the LED load circuits U1 to U3 are equal to each other, but may be configured to be different from each other. In this case, the control elements Q1 to Q3 perform control so as to maintain the different set current ratios. Moreover, organic EL (organic LED) is applicable to LEDD1 in this invention.

  The impedance element A can also be realized by an LED. In this case, as shown by the LED lighting circuit 31a in FIG. 4, an extra LEDD10 is provided in the LED load circuit U1a of the LED module 32a, and the LED load It is only necessary to set the number of series LED stages of the circuit U1a to be larger than that of the remaining LED load circuits U2 and U3. For example, when σ = about 10%, one additional LEDD10 is provided until n = 10, and two additional LEDs D10 are provided until n = 20, so that the variation is σ and the number of series stages is n. Correspondingly, the LED load circuit U1a may be set so that the total sum of the ON voltages Vf is always the highest. With this configuration, it is possible to easily configure a configuration that maximizes the sum of the ON voltages Vf, and it is also possible to effectively use the power consumed by the impedance element A.

[Embodiment 2]
FIG. 5 is a block diagram showing a configuration of an LED lighting circuit 51 according to another embodiment of the present invention. The LED lighting circuit 51 is similar to the LED lighting circuit 31 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. It should be noted that in this LED lighting circuit 51, a short-circuit switch SW is provided between the terminals of the impedance element A, the short-circuit switch SW is opened, and the control elements Q1 to Q3 perform a current mirror operation. In this state, the Vf detection circuit 52 detects the sum of the LED ON voltages Vf in the LED load circuits U1 to U3. From the detection result, the switching control circuit 53 has the control element Q1 in the diode structure. The short-circuit switch SW is closed when the sum of the ON voltages Vf of the LED load circuit U1 is the highest, and the short-circuit switch SW is opened otherwise.

  FIG. 6 is a block diagram showing a configuration example of the Vf detection circuit 52 and the switching control circuit 53. As shown in FIG. The Vf detection circuit 52 includes two comparators CP1 and CP2 and an AND gate G that adds their outputs. The terminal voltage of the LED load circuit U1 in which the impedance element A is provided in common is applied to the non-inverting input terminals of the comparators CP1 and CP2, and the impedance element A is not provided in the non-inverting input terminal. Terminal voltages of the LED load circuits U2 and U3 are respectively given. Accordingly, the comparators CP1 and CP2 output a high level when the terminal voltage of the LED load circuit U1 is lower, that is, when the amount of voltage drop from the output voltage VDC of the DC-DC converter 35 is large, and AND A high level is output from the gate G when the voltage drop amount of the LED load circuit U1 is the largest.

  The switching control circuit 53 includes a transistor TR1 to which an output of the AND gate G is applied to a base, a base resistor R11 and a collector resistor R12, and a photocoupler PC driven by the transistor TR1 through the collector resistor R12. It is prepared for. Therefore, when a high level is output from the AND gate G, the transistor TR1 is turned on, the photodiode D11 of the photocoupler PC is turned on, the phototransistor TR2 constituting the short-circuit switch SW is turned on, and the impedance element A is turned on. Bypass.

  With this configuration, when the current equalization operation is performed by the current mirror as described above, the circuit having the highest sum of the ON voltages Vf of the LEDD1 must be the reference current circuit. The Vf detection circuit 52 measures the total of the LED ON voltage Vf in each of the LED load circuits U1 to U3, and the switching control circuit 53 is inserted only when the impedance element A is necessary. Thus, the impedance element A can function only when necessary, and the loss in the impedance element A can be suppressed.

[Embodiment 3]
FIG. 7 is a block diagram showing a configuration of an LED lighting circuit 61 according to another embodiment of the present invention. The LED lighting circuit 61 is similar to the LED lighting circuit 31 described above, and corresponding portions are denoted by the same reference numerals, and description thereof is omitted. It should be noted that in the LED lighting circuit 61, in the LED module 32b, impedance elements A2 and A3 are provided in parallel between terminals of the LED load circuits U2 and U3 in which the control elements Q2 and Q3 do not have the diode structure. That is. The impedance elements A2 and A3 reduce the impedance of the corresponding LED load circuits U2 and U3, and clamp the inter-terminal voltage lower than the inter-terminal voltage of the LED load circuit U1, for example, in FIG. As shown in the figure, a configuration including a Zener diode or a resistance element in series with the Zener diode can be used.

  Even with this configuration, even if there is a variation in the ON voltage Vf of the LEDD1, the LED load circuit U1 that creates the reference current of the current mirror circuit includes the total of the ON voltage Vf of the LEDD1 and includes the LED current. The voltage drop due to is the highest in the circuit, and the current values in the LED load circuits U1 to U3 can be uniformly controlled, and the light output from the multiple LEDs D1 can be made uniform. In addition, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to the circuit can be eliminated.

[Embodiment 4]
FIG. 8 is a block diagram showing a configuration of an LED lighting circuit 71 according to another embodiment of the present invention. The LED lighting circuit 71 is similar to the LED lighting circuit 31 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. It should be noted that in the LED lighting circuit 71, when the constant current feedback control is performed on the DC-DC converter 35, the current detection resistor R2 is set to any one of the LED load circuits U1 to U3 (see FIG. In the example of 8, it is inserted into U1). In this case, the loss due to the resistor R2 can be reduced (in the example of FIG. 8, approximately 1/3 of the example of FIG. 1). Further, even if the LEDD1 is disconnected other than the reference LED load circuit, the remaining circuits can continue to be lit with a constant current value.

  Here, in Japanese Patent Application Laid-Open No. 2006-203044, when adjusting the current of parallel LEDs having different ON voltages Vf, transistors are connected in series and their gates are driven in common, and the ON voltage Vf is small. It is shown that a dummy diode is connected in series with the LED to reduce the difference in the ON voltage Vf. However, in this prior art, the reference current of the current mirror is created separately, and a diode is inserted in order to reduce the difference in the ON voltage Vf. It is inserted so that the difference of the ON voltage Vf becomes large so that a reference current can be created. Therefore, when white light is generated by RGB emission as in this prior art, in this prior art, a diode is inserted into a system of R elements having a small ON voltage Vf (about 2 V). Then, a diode is inserted into a system of B elements having a large ON voltage Vf (about 3 to 3.5 V), which is completely different.

It is a block diagram which shows the structure of the LED lighting circuit which concerns on one Embodiment of this invention. It is a figure which shows an example of the impedance element in the lighting circuit shown in FIG. It is a figure which shows the result of the loss calculation required for balance control of the electric current supplied to a parallel LED load circuit by one Embodiment of this invention shown in FIG. 1, and the prior art shown in FIG. 10 and FIG. It is a block diagram which shows the other structural example in the LED lighting circuit which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the LED lighting circuit which concerns on the other form of implementation of this invention. FIG. 2 is a block diagram illustrating a configuration example of a Vf detection circuit and a switching control circuit in the lighting circuit illustrated in FIG. 1. It is a block diagram which shows the structure of the LED lighting circuit which concerns on other form of implementation of this invention. It is a block diagram which shows the structure of the LED lighting circuit which concerns on the other form of implementation of this invention. It is a block diagram which shows the structure of a typical prior art LED lighting circuit. It is a block diagram which shows the structure of the LED lighting circuit of another prior art. It is an electric circuit diagram which shows the specific example of the constant current circuit in the LED lighting circuit shown in FIG. It is a block diagram which shows the structure of the LED lighting circuit of another prior art.

Explanation of symbols

31, 31a, 51, 61, 71 LED lighting circuit 32, 32a, 32b LED module 33 commercial power supply 34 rectifier bridge 35 DC-DC converter 36 control circuit 37 comparison circuit 38 reference voltage source 52 Vf detection circuit 53 switching control circuit A, A2, A3 Impedance element C2 Smoothing capacitor CP1, CP2 Comparator D Diode D1, D10 LED
D11 Photodiode G AND gate L Choke coil PC Photocoupler Q0 Switching element Q1-Q3 Control element R1, R2 Resistance R11 Base resistance R12 Collector resistance SW Short-circuit switch TR1 Transistor TR2 Phototransistor U1, U1a, U2, U3 LED load circuit

Claims (6)

In an LED lighting circuit in which a current is supplied from a DC power supply to an LED module in which a plurality of LED load circuits composed of one or a plurality of series LEDs are arranged in parallel with each other,
A control element that is provided in series with each LED load circuit, and that configures a current mirror circuit to link the energization current value in each LED load circuit, so that any one becomes a reference current circuit for the current mirror. Such a control element having a diode structure;
When the LED ON voltage is Vf, the variation is σ, and the number of series stages is n, the voltage drop of Vf × n × σ or more is generated at the rated current. An LED lighting circuit comprising an impedance element.   The LED lighting circuit according to claim 1, wherein the impedance element is an LED. A shorting switch capable of short-circuiting between terminals of the impedance element;
Detecting means for detecting the sum of the ON voltages Vf of the LEDs in the LED load circuits in a state where the short-circuit switch is opened and the control element is performing a current mirror operation;
In response to the detection result of the detecting means, the short-circuit switch is closed when the sum of the ON voltage Vf of the LED load circuit having the diode structure as the control element is the highest, and the short-circuit otherwise. 3. The LED lighting circuit according to claim 1, further comprising switching control means for opening the switch. In an LED lighting circuit in which a current is supplied from a DC power supply to an LED module in which a plurality of LED load circuits composed of one or a plurality of series LEDs are arranged in parallel with each other,
A control element that is provided in series with each LED load circuit, and that configures a current mirror circuit to link the energization current value in each LED load circuit, so that any one becomes a reference current circuit for the current mirror. Such a control element having a diode structure;
An LED lighting circuit comprising: an impedance element that is inserted in parallel to a circuit other than the control element circuit having the diode structure and reduces an impedance of the LED load circuit. The DC power supply is a DC-DC converter,
Current detection means for detecting a total current value flowing through each LED load circuit or a current value flowing through the LED load circuit corresponding to the diode-connected control element;
A reference voltage source and a comparator for comparing the detection results from the current detection means;
And a control unit that feedback-controls the DC power supply so that a total sum of energization current values to the LED module becomes a predetermined value in accordance with an output from the comparator. Item 5. The LED lighting circuit according to any one of Items 1 to 4.   A lighting fixture using the LED lighting circuit according to any one of claims 1 to 5.

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