JP2008130296A - Led lighting circuit and illumination fixture using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To homogenize light output from numerous LEDs, and to suppress power consumption for the homogenization in an LED lighting circuit used for an illumination fixture or the like. <P>SOLUTION: By detecting a current from a DC-DC converter 35 to an LED module 32 by a current detecting resistor R2, comparing it with the reference voltage Vref from the reference voltage source 38 by a comparing circuit 37, and controlling the DC-DC converter 35 in response to the comparison result, a control circuit 36 collectively constant current controls a current to flow into the LED module 32. Furthermore, in the respective LED load circuits U1 to U3 constituting the LED module 32, control elements Q1 to Q3 constituting a current mirror circuit are installed in series, homogenize the light output, and achieve low power consumption by making its reference current by the LED load circuit U1. Moreover, when a disconnection detecting circuit 42 detects disconnection of the LED load circuit U1, an impedance circuit 42 is inserted and light-out of other LED load circuits U2, U3 due to disappearance of the reference current is prevented. <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 having 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 configures a current mirror circuit to interlock the energization current value in each LED load circuit, including the sum of the ON voltages of LEDs in each LED load circuit Such a control element that has a diode structure and a reference current circuit for the current mirror so that the LED load circuit with the highest voltage drop due to LED current becomes the reference current circuit for the current mirror. Provided in parallel with the LED load circuit, the energization current value when the LED in the LED load circuit is disconnected as the reference current Characterized in that it comprises an impedance circuit to maintain so that.

  According to the above configuration, in an LED lighting circuit used in a lighting fixture or the like, a DC power supply is energized 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. Are provided in series with each of the LED load circuits, and control elements constituting a current mirror circuit are provided, and in those control elements, including the sum of the ON voltages Vf of the LEDs in each of the LED load circuits, the LED current depends on the LED current. With the circuit having the highest voltage drop as a reference, the control element corresponding to the LED load circuit has a diode structure, and the energizing current values of the control elements of the remaining circuits are linked via the control terminal, so that each LED load circuit is connected. To balance. 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 circuit is provided in parallel with the LED load circuit that is the reference current circuit, and the impedance circuit bypasses the current that should flow through the LED load circuit when the LED in the corresponding LED load circuit is disconnected. The reference current of the current mirror circuit is maintained.

  Therefore, the current balance between the LED load circuits is uniformly controlled by the current mirror circuit, so that the light output from a large number of LEDs can be made uniform. In addition, since the LED load circuit having the highest sum of the ON voltages Vf is used as the circuit for generating the reference current of the current mirror circuit, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to that is eliminated. It can be lost. Furthermore, even if a disconnection occurs in the LED of the LED load circuit serving as the reference current circuit, the reference current continues to flow, and it is possible to prevent light extinction from reaching other LED load circuits.

  Further, in the LED lighting circuit of the present invention, the impedance circuit is provided in parallel with the LED load circuit, which is a reference current circuit of the current mirror by connecting switch elements in series, and the reference current circuit of the current mirror In relation to the LED load circuit, a disconnection detecting means for detecting disconnection of the LED and turning on the switch element is further provided.

  According to said structure, while providing a disconnection detection means, the said impedance circuit is provided with the switch element in series, and when a disconnection is detected, the said switch element is turned ON and an impedance circuit is inserted.

  The disconnection detecting means includes, for example, a Zener diode and a control means for turning on the switch element when an increase in the voltage between the terminals of the LED load circuit due to the disconnection of the LED exceeds the Zener voltage of the Zener diode. Or a current detection means such as a current detection resistor or a light emitting diode provided in series with an LED load circuit serving as a reference current circuit for the current mirror, and the current detection means detects a current interruption due to the disconnection of the LED. And a control means such as a control transistor or a phototransistor for turning on the switch element.

  Therefore, it is possible to prevent loss due to the impedance circuit and to prepare for disconnection with low power consumption.

  Furthermore, in the LED lighting circuit of the present invention, the impedance circuit is provided in parallel with the LED load circuit, which is a reference current circuit of the current mirror with a switch element connected in series, and the output voltage of the DC power supply A disconnection detecting means for detecting disconnection of the LED from a rise in output or a decrease in output current; and a latch means for continuing to turn on the switch element once the disconnection detecting means detects the disconnection. To do.

  According to the above configuration, the disconnection detecting means and the latch means are provided, and the impedance circuit is provided with a switch element in series so that the disconnection is detected once the output voltage of the DC power supply increases or the output current decreases. Then, the switch element is turned on and an impedance circuit is inserted.

  Therefore, it is possible to prevent loss due to the impedance circuit and to prepare for disconnection with low power consumption.

  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. The control circuit is a control element that is provided in series with each LED load circuit, and forms a current mirror circuit to interlock the energization current value in each LED load circuit, and the sum of the ON voltages of the LEDs in each LED load circuit In addition, such a control element having a corresponding diode structure so that the LED load circuit having the highest voltage drop due to the LED current becomes the reference current circuit of the current mirror, and the reference current circuit of the current mirror A disconnection detecting means provided in association with the LED load circuit to detect disconnection of the LED in the LED load circuit; Provided in association with a control element corresponding to an LED load circuit other than the LED load circuit serving as a reference current circuit of the current mirror, and when a disconnection is detected by the disconnection detection means, one of those control elements And a short-circuit means capable of switching to a diode connection.

  According to the above configuration, in an LED lighting circuit used in a lighting fixture or the like, a DC power supply is energized 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. Are provided in series with each of the LED load circuits, and control elements constituting a current mirror circuit are provided, and in those control elements, including the sum of the ON voltages Vf of the LEDs in each of the LED load circuits, the LED current depends on the LED current. Using the circuit with the highest voltage drop as a reference, the control element in the circuit has a diode structure, and the energizing current value of the control element of the remaining circuit is linked via the control terminal, thereby balancing the LED load circuits. Try to take. 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, in connection with the LED load circuit that has become the reference current circuit, a disconnection detecting means for detecting disconnection of the LED in the LED load circuit is provided, and other than the LED load circuit that becomes the reference current circuit of the current mirror In connection with the control element corresponding to the LED load circuit, a short-circuit unit capable of short-circuiting between the base and the collector or between the gate and the drain is provided, and when the disconnection is detected by the disconnection detection unit, the short-circuit unit is Switch one of the control elements to a diode connection.

  Therefore, the current balance between the LED load circuits is uniformly controlled by the current mirror circuit, so that the light output from a large number of LEDs can be made uniform. In addition, since the LED load circuit having the highest sum of the ON voltages Vf is used as the circuit for generating the reference current of the current mirror circuit, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to that is eliminated. It can be lost. Furthermore, when the LED of the LED load circuit serving as the reference current circuit is disconnected, one of the control elements corresponding to the other LED load circuits is diode-connected, and the constant current operation is continuously performed. It is possible not to reach other LED load circuits.

  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, while being able to equalize the light output from many LED, 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. Then, when energizing from a DC power supply, control elements constituting a current mirror circuit are provided in series with the LED load circuits, and the sum of the ON voltages Vf of the LEDs in the LED load circuits is set in these control elements. Including the LED load circuit with the highest voltage drop due to the LED current, the control element corresponding to the LED load circuit has a diode structure, and the energization current values of the control elements of the remaining circuits are linked via the control terminal. As a result, the LED load circuits are balanced, and the reference current circuit LE An impedance circuit is provided in parallel with the load circuit, and when the LED in the corresponding LED load circuit is disconnected, the impedance circuit bypasses the current that should flow through the LED load circuit and maintains the reference current of the current mirror circuit. To do.

  Therefore, the current balance between the LED load circuits is uniformly controlled by the current mirror circuit, so that the light output from a large number of LEDs can be made uniform. In addition, since the LED load circuit having the highest sum of the ON voltages Vf is used as the circuit for generating the reference current of the current mirror circuit, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to that is eliminated. It can be lost. Furthermore, even if a disconnection occurs in the LED of the LED load circuit serving as the reference current circuit, the reference current continues to flow, and it is possible to prevent light extinction from reaching other LED load circuits.

  Further, as described above, the LED lighting circuit of the present invention is provided with the disconnection detecting means, the switch circuit is provided in series with the impedance circuit, and the switch element is turned on when the disconnection is detected. Insert an impedance circuit.

  Therefore, the loss due to the impedance circuit is always suppressed, and it is possible to prepare for the disconnection with low power consumption.

  Furthermore, as described above, the LED lighting circuit of the present invention is provided with the disconnection detecting means and the latch means, and the impedance circuit is provided with a switch element in series to increase the output voltage of the DC power supply or the output current. From this decrease, once a disconnection is detected, the switch element is turned on and an impedance circuit is inserted.

  Therefore, the loss due to the impedance circuit is always suppressed, and it is possible to prepare for the disconnection with low power consumption.

  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. In contrast, when energizing from a DC power supply, control elements constituting a current mirror circuit are provided in series with the LED load circuits, and in these control elements, the ON voltage Vf of the LED in the LED load circuits is set. By taking the circuit with the highest voltage drop due to LED current, including the sum, as a reference, the control element in the circuit has a diode structure, and the energization current value of the control element of the remaining circuit is linked via the control terminal, Try to balance each LED load circuit and related to the LED load circuit that became the reference current circuit A disconnection detecting means for detecting disconnection of the LED in the LED load circuit, and the base in relation to a control element corresponding to an LED load circuit other than the LED load circuit serving as a reference current circuit of the current mirror; A short-circuit means capable of short-circuiting between the collector and the gate and the drain is provided, and when the disconnection is detected by the disconnection detection means, the short-circuit means switches one of the control elements to a diode connection.

  Therefore, the current balance between the LED load circuits is uniformly controlled by the current mirror circuit, so that the light output from a large number of LEDs can be made uniform. In addition, since the LED load circuit having the highest sum of the ON voltages Vf is used as the circuit for generating the reference current of the current mirror circuit, a circuit for generating only the reference current is unnecessary, and the circuit loss corresponding to that is eliminated. It can be lost. Furthermore, when the LED of the LED load circuit serving as the reference current circuit is disconnected, one of the control elements corresponding to the other LED load circuits is diode-connected, and the constant current operation is continuously performed. It is possible not to reach other LED load circuits.

  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, the light output from many LEDs can be made uniform, and a low-loss lighting fixture can be realized.

[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 31, an LED module 32 is configured by connecting three LED load circuits U <b> 1 to U <b> 3 in which a large number of LEDs D <b> 1 are connected in series 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. Among these control elements Q1 to Q3, a circuit having the highest voltage drop due to the LED current including the sum of the LED ON voltages Vf in the corresponding LED load circuits U1 to U3 (in the example of FIG. 1) With reference to U1), the control element (Q1 in the example of FIG. 1) in the circuit has a diode structure, and the control elements (U2, U3 in the example of FIG. 1) of the remaining circuit (U1 in FIG. 1) via the control terminal (FIG. 1) In the example, the LED load circuits U1 to U3 are balanced by linking the energization current values of Q2 and Q3).

  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 circuit 41 is provided in parallel with the LED load circuit (U1 in the example of FIG. 1) serving as the reference current circuit, and the LED D10 in the corresponding LED load circuit U1 is disconnected. In this case, the current to flow through the LED load circuit U1 is bypassed to maintain the reference current of the current mirror circuit.

  Specifically, the impedance circuit 41 is composed of an element or a circuit capable of generating a constant current, such as a resistor, a constant current circuit, a Zener diode, and a series circuit of a Zener diode and a resistor. Q4 is connected in series and provided in parallel to the LED load circuit U1. Further, in connection with the LED load circuit U1, a disconnection detection circuit 42 for detecting the disconnection of the LED D10 in the circuit and turning on the switch element Q4 is provided.

  The disconnection detection circuit 42 serving as disconnection detection means detects the terminal voltage of the LED load circuit U1, that is, the collector voltage of the control element Q1, and a Zener diode ZD provided in parallel with the LED load circuit U1. In addition, the series circuit of the voltage dividing resistors R11 and R12 includes a capacitor C11 provided in parallel with the resistor R12, and the connection point between the voltage dividing resistor R11, the voltage dividing resistor R12, and the capacitor C11 is a transistor. It is connected to the base of the element Q4. When the terminal voltage of the LED load circuit U1, that is, the collector voltage of the control element Q1, rises to a predetermined voltage higher than the sum of the ON voltages Vf of the LEDs due to the disconnection of the LEDD10, the Zener diode ZD is turned on and the switching element Q4 is turned on. And the current flows through the impedance circuit 41 instead of the disconnected LED load circuit U1. Therefore, the voltage dividing resistors R11 and R12 and the capacitor C11 constitute a control means for controlling the switch element Q4 in response to the detection result of the Zener diode ZD.

  With this configuration, control is performed so that the sum of energization current values from the DC-DC converter 35 to the LED load circuits U1 to U3 is constant by collective constant current control based on the detection result of the resistor R2. Since the current balance between the LED load circuits U1 to U3 is uniformly controlled by the current mirror circuit, the light output from the multiple LEDs D1 can be made uniform. In addition, the circuit that generates the reference current of the current mirror circuit (Q1 in the example of FIG. 1) uses the LED load circuit (U1 in the example of FIG. 1) having the highest sum of the ON voltages Vf of the LEDs D1. This eliminates the need for a circuit for generating only the reference current and eliminates the circuit loss. 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. 10 described above, but an insulation type 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.

  2 shows a case where the DC-DC converter 35 performs only the constant current control based on the detection result of the resistor R2 as described above and the case where only the constant voltage control of the voltage VDC as shown in FIG. 11 is performed. The loss due to the control elements Q1 to Q3 will be described in detail. FIG. 2 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. 11 and 12 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 apparent from FIG. 2, 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 FIGS. 11 and 12 described above, the constant current control is more effective in 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.

  Further, by configuring as in the present embodiment, even if the LEDD 10 of the LED load circuit U1 serving as the reference current circuit is disconnected, the reference current continues to flow through the impedance circuit 41, and the extinction is not performed. It is possible not to reach the LED load circuits U2 and U3. Furthermore, the impedance circuit 41 is provided in parallel to the LED load circuit U1 that is connected in series with the switch element Q4 and serves as a reference current circuit for the current mirror, and the disconnection detection circuit 42 detects the disconnection of the LEDD10. In this case, since the switching element Q4 is turned on and inserted, the loss due to the impedance circuit 41 can be suppressed constantly, and the power can be prepared with low power consumption.

  As another means for detecting disconnection in the disconnection detection circuit 42, instead of the Zener diode ZD, an LED lighting circuit 31a shown in FIG. 3 is connected in series with the LED load circuit U1 serving as the reference current circuit. A light-emitting diode D11 or the like can be used like the provided current-voltage conversion resistor R13 or the LED lighting circuit 31b shown in FIG.

  Specifically, in the disconnection detection circuit 42a of FIG. 3, a resistor R14 and a control transistor Q5 are connected in series between power supply lines, and the voltage obtained by the current-voltage conversion resistor R13 is applied to the base of the transistor Q5. The output from the collector is applied to the base of the switch element Q4. Accordingly, the transistor Q5 is turned on while the current flows through the LED load circuit U1, the switch element Q4 is turned off, and the impedance circuit 41 is disconnected. On the other hand, when the current stops flowing to the LED load circuit U1 due to disconnection, the transistor Q5 is turned off, the switch element Q4 is turned on, and the impedance circuit 41 is inserted.

  Similarly, in the disconnection detection circuit 42b of FIG. 4, the resistor R14 and the control phototransistor Q6 are connected in series between the power supply lines, and the phototransistor Q6 constitutes the light emitting diode D11 and the photocoupler PC. The output from the collector is given to the base of the switch element Q4. Therefore, the phototransistor Q6 is turned on while the current flows through the LED load circuit U1, the switch element Q4 is turned off, and the impedance circuit 41 is disconnected. On the other hand, when the current stops flowing to the LED load circuit U1 due to disconnection, the phototransistor Q6 is turned off, the switch element Q4 is turned on, and the impedance circuit 41 is inserted.

[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 the LED lighting circuit 51, when the constant current feedback control is performed on the DC-DC converter 35, the current detection resistor R2 is inserted into the LED load circuit U1 which is the reference current generating circuit. is there. In this case, the loss due to the resistor R2 can be reduced (in the example of FIG. 5, 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.

[Embodiment 3]
FIG. 6 is a block diagram showing a configuration of an LED lighting circuit 61 according to still 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 this LED lighting circuit 61, control elements Q2 and Q3 corresponding to the LED load circuits U2 and U3 other than the LED load circuit U1 which is the reference current generating circuit are connected to the reference current by the disconnection detection circuit 42. When the disconnection of the LED load circuit U1, which is the creation circuit, is detected, the switch switching control circuit 62 is provided with switches SW2, SW3 that can switch the corresponding control elements Q2, Q3 to diode connection. .

  Therefore, in response to the occurrence of the disconnection, when the disconnection detection circuit 42 turns on one of the switches SW2 and SW3 (SW2 in the example of FIG. 6) as the short-circuit means, the ON side of the switch is continuously turned on. Constant current operation is performed in the LED load circuit (U2 in the example of FIG. 6), and the current balance with the remaining LED load circuit (U3 in the example of FIG. 6) is maintained. In this way, the remaining LED load circuit can continue to be lit while maintaining a uniform current value while preventing the extinction from reaching other LED load circuits (U2 and U3 in the example of FIG. 6).

[Embodiment 4]
7 and 8 are block diagrams showing configurations of LED lighting circuits 71 and 81 according to another embodiment of the present invention. These LED lighting circuits 71 and 81 are 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, the disconnection detection circuit 42c first detects the disconnection of the LED D10 from the decrease in the output current of the DC-DC converter 35. Specifically, the thyristor Q7 is connected in series with the impedance element 41, the cathode of the Zener diode ZD is connected to the high-side terminal of the current detection resistor R2, and the anode of the Zener diode ZD is connected to the switch element from the resistor R15. Connected to the base of Q4, the emitter of the switch element Q4 is connected to the low-side terminal of the current detection resistor R2. The collector of the control element Q4 is connected to the gate of the thyristor Q7 through a bias resistor R20.

  Therefore, when the LEDD10 is not disconnected, the voltage between the terminals of the current detection resistor R2 is high, the Zener diode ZD and the switch element Q4 are turned on, the gate of the thyristor Q7 becomes low level, and the thyristor Q7 is turned off. When the impedance circuit 41 is not inserted and the LED D10 is disconnected, the terminal voltage of the current detection resistor R2 is lowered, the Zener diode ZD and the control element Q4 are turned off, and the gate of the thyristor Q7 becomes high level. Is turned ON, and the impedance circuit 41 is inserted. Once the thyristor Q7 is turned on, this state is maintained until the power supply is stopped. Therefore, the thyristor Q7 becomes a latch means. The resistor R15 is provided so that the Zener diode ZD and the switch element Q4 do not absorb the voltage drop at the current detection resistor R2 for constant current feedback control.

  On the other hand, in the LED lighting circuit 81, the disconnection detection circuit 82 detects the disconnection of the LEDD 10 from the increase in the output voltage VDC of the DC-DC converter 35. Specifically, the disconnection detection circuit 82 is a comparator that compares the voltage of the voltage dividing resistors R21, R22 interposed between the output terminals of the DC-DC converter 35 and the connection point thereof with a predetermined reference voltage Vref1. 83 and a reference voltage source 84, and the output of the comparator 83 is applied to the gate of the thyristor Q7.

  Therefore, when the LEDD10 is not disconnected, the output voltage VDC becomes a specified voltage, the comparator 83 outputs a low level, the thyristor Q7 is turned OFF, the impedance circuit 41 is not inserted, and the LEDD10 is disconnected. The output voltage VDC becomes higher than the specified voltage, the comparator 83 outputs a high level, the thyristor Q7 is turned on, and the impedance circuit 41 is inserted. Once the thyristor Q7 is turned on, the state is maintained until the power supply is stopped, as in FIG.

  Even if it does in this way, even if the disconnection arises in LEDD10 of the LED load circuit U1 used as a reference | standard, it can prevent turning off completely, suppressing the loss by the impedance circuit 41 constantly.

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 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. In the LED lighting circuit shown in FIG. 1, it is a block diagram which shows the other example of a disconnection detection circuit. FIG. 10 is a block diagram showing still another example of a disconnection detection circuit in the LED lighting circuit shown in FIG. 1. 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 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 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, 31b, 51, 61, 71, 81 LED lighting circuit 32 LED module 33 Commercial power supply 34 Rectifier bridge 35 DC-DC converter 36 Control circuit 37 Comparison circuit 38 Reference voltage source 41 Impedance circuits 42, 42a, 42b, 42c , 82 Disconnection detection circuit 62 Switch switching control circuit C2 Smoothing capacitor D Diode D1, D10 LED
D11 Light-emitting diode L Choke coil PC Photocoupler Q0 Switching element Q1-Q3 Control element Q4 Switch element Q5 Transistor Q6 Phototransistor Q7 Thyristor R1, R2; R11, R12, R14 Resistor R13 Current-voltage conversion resistance R21, R22 Voltage dividing resistance SW2, SW3 switch U1-U3 LED load circuit ZD Zener diode

Claims (8)

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 configures a current mirror circuit to interlock the energization current value in each LED load circuit, including the sum of the ON voltages of LEDs in each LED load circuit Such a control element in which the corresponding one is a diode structure so that the LED load circuit with the highest voltage drop due to the LED current becomes the reference current circuit of the current mirror;
An impedance circuit that is provided in parallel with an LED load circuit serving as a reference current circuit of the current mirror, and maintains an energization current value at the time of disconnection of the LED in the LED load circuit so as to be a reference current; LED lighting circuit. The impedance circuit is provided in parallel with the LED load circuit, which is a reference current circuit of the current mirror with a switch element connected in series,
2. The LED lighting circuit according to claim 1, further comprising: a disconnection detecting unit that detects disconnection of the LED and turns on the switch element in association with an LED load circuit serving as a reference current circuit of the current mirror. .   The disconnection detecting means comprises a Zener diode and a control means for turning on the switch element when an increase in the voltage between the terminals of the LED load circuit due to the disconnection of the LED becomes equal to or higher than the Zener voltage of the Zener diode. The LED lighting circuit according to claim 2, wherein:   The disconnection detection means includes a current detection means provided in series with an LED load circuit serving as a reference current circuit of the current mirror, and when the current detection means detects a current interruption due to the disconnection of the LED, the disconnection detection means 3. The LED lighting circuit according to claim 2, further comprising a control means for turning on. The impedance circuit is provided in parallel with the LED load circuit, which is a reference current circuit of the current mirror with a switch element connected in series,
Disconnection detecting means for detecting disconnection of the LED from an increase in output voltage or a decrease in output current of the DC power supply, and latch means for continuously turning on the switch element once the disconnection detecting means detects the disconnection. The LED lighting circuit according to claim 1, further comprising: 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 configures a current mirror circuit to interlock the energization current value in each LED load circuit, including the sum of the ON voltages of LEDs in each LED load circuit Such a control element in which the corresponding one is a diode structure so that the LED load circuit with the highest voltage drop due to the LED current becomes the reference current circuit of the current mirror;
Disconnection detecting means provided in association with an LED load circuit serving as a reference current circuit of the current mirror, and detecting disconnection of the LED in the LED load circuit;
Provided in association with a control element corresponding to an LED load circuit other than the LED load circuit serving as a reference current circuit of the current mirror, and when a disconnection is detected by the disconnection detection means, one of those control elements And a short-circuit means capable of switching to diode connection. 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 7. The LED lighting circuit according to any one of Items 1 to 6.   The LED lighting circuit of any one of the said Claims 1-7 is used, The lighting fixture characterized by the above-mentioned.

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