JP2008130513A - Led lighting circuit and illumination fixture using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformize light output from numerous LEDs in an LED lighting circuit used for an illumination fixture or the like, and to suppress electric power consumption for that uniformization. <P>SOLUTION: Currents from DC-DC converter 35 to LED module 32 are detected by a current detection resistor R2, and compared with the reference voltage Vref from the reference voltage source 38 in a comparing circuit 37, and by controlling the DC-DC converter 35 with a first control circuit 36 coping with it, the currents flowing into the LED module 32 are constant current controlled in a package, and furthermore, in individual LED load circuits U1 to U3, control elements Q1 to Q3 constituting current mirror circuits are installed in series, and the light output is uniformized, and its reference current is prepared by the LED load circuit U1, and the power consumption is reduced. Moreover, from terminal voltages of the control elements Q1 to Q3, a wire disconnection is detected by comparators CP11 to CP31, and a short circuit is detected by the comparators CP12 to CP32, then in response to it an abnormality circuit is isolated by switching elements SW1 to SW3. <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. 5 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. 6 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. 7 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 in which a DC power source is driven to light at a constant current with respect 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. In the circuit, a control element that is provided in series with each of the LED load circuits, configures a current mirror circuit and interlocks the energization current value in each of the LED load circuits, and the sum of the ON voltages of the LEDs in each of the LED load circuits Including a control element having a 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 each of the LED load circuits Detecting means for detecting an abnormality in the system, and disconnecting the corresponding LED load circuit when the detecting means detects an abnormality. Characterized in that it comprises means to, and a power supply control means for reducing the load current of the circuit component that is separated by the disconnection unit to the DC power supply.

  According to the above configuration, in an LED lighting circuit used for a lighting fixture or the like, a direct current power source is defined for an LED module in which a plurality of LED load circuits including one or a plurality of series-connected LEDs are arranged in parallel with each other. In lighting driving with current, control elements that constitute a current mirror circuit are provided in series with each LED load circuit, and in these control elements, including the sum of the ON voltages Vf of the LEDs in each LED load circuit, Using the circuit with the highest voltage drop due to the LED current as a reference, 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, so that each LED Try to balance between load circuits. 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. Furthermore, the presence or absence of abnormality in the system of each LED load circuit is monitored by the detection means, and when the abnormality is detected, the control means is disconnected from the corresponding LED load circuit and the DC power source. Reduce the load current of the circuit.

  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 detection means detects that an abnormality such as disconnection or short circuit has occurred in any of the LED load circuits, the disconnecting means disconnects the LED load circuit, and the power supply control means is disconnected. Since the DC power supply is operated at a constant current by reducing the load current for the circuit, excessive current flows into the remaining LED load circuit and it is lit in an overload state, and the failure spreads in a chain. This can be prevented.

  Moreover, in the LED lighting circuit of the present invention, the detection means detects a short circuit of the LED in the corresponding LED load circuit from an increase in the voltage between the terminals of the control element.

  According to the above configuration, since the series circuit including the LED load circuit and the corresponding control element is connected between the output terminals of the DC power supply, when the LED in the LED load circuit is short-circuited, the corresponding control element is shared. Since the power voltage increases, it is possible to detect the short circuit.

  Furthermore, in the LED lighting circuit of the present invention, the detection means detects a short circuit of the LED in the corresponding LED load circuit from the temperature rise of the control element.

  According to the above configuration, since the series circuit including the LED load circuit and the corresponding control element is connected between the output terminals of the DC power supply, when the LED in the LED load circuit is short-circuited, the corresponding control element is shared. Since the power voltage increases and the power loss in the control element increases, the short circuit can be detected from the temperature increase caused by the power loss.

  In the LED lighting circuit of the present invention, the detecting means detects disconnection of the LED in the corresponding LED load circuit because the connection point between the control element and the LED load circuit is an open voltage. It is characterized by that.

  According to the above configuration, since the series circuit composed of the LED load circuit and the corresponding control element is connected between the output terminals of the DC power supply, since the connection point thereof becomes an open voltage, the corresponding LED load Disconnection of the LED in the circuit can be detected.

  Furthermore, in the LED lighting circuit according to the present invention, the disconnecting means includes a switch element connected in series with each of the LED load circuits.

  According to the above configuration, when an abnormality is detected, the switch element interposed in series in the system of the LED load circuit is opened, so that the load current does not flow to the LED load circuit in which the abnormality has occurred. The LED load circuit can be disconnected from other LED load circuits.

  In the LED lighting circuit according to the present invention, the disconnecting means may include a switch element interposed between a control terminal of a control element serving as a reference of a current mirror and a control terminal of the remaining control element. .

  According to the above configuration, when an abnormality is detected, the switch element corresponding to the system of the LED load circuit is opened, and when the control element is a transistor, the base current does not flow, and the transistor is a MOS transistor Thus, no gate voltage is applied to the LED load circuit, and thus the load current does not flow to the LED load circuit in which an abnormality has occurred, so that the LED load circuit can be disconnected from other LED load circuits.

  Furthermore, in the LED lighting circuit of the present invention, the DC power source is a DC-DC converter, and current detection means for detecting a total current value flowing through each LED load circuit, and a detection result from the current detection means. A reference voltage source and a comparator for comparison, and control means for feedback-controlling the DC power supply so that a sum of energization current values to the LED module becomes a predetermined value in accordance with an output from the comparator It is characterized by comprising.

  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, even if abnormality, such as a disconnection and a short circuit, occurs with low loss, it prevents that it spreads in a chain. It is possible to realize a lighting fixture that can

  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. When the DC power supply is driven to light at a constant current, control elements constituting a current mirror circuit are provided in series with the LED load circuits, and the LED ON voltage Vf in each LED load circuit is provided in these control elements. The control element corresponding to the LED load circuit has a diode structure based on the circuit with the highest voltage drop due to the LED current, including the sum of the currents, and the energization current values of the control elements of the remaining circuit are linked via the control terminal. By keeping the balance between the LED load circuits, the abnormality in the system of each LED load circuit Whether monitors by the detection means, when the abnormality is detected, the control means may disconnect the corresponding LED load circuit, reducing the load current of the circuit component that is separated into the DC power supply.

  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 detection means detects that an abnormality such as disconnection or short circuit has occurred in any of the LED load circuits, the disconnecting means disconnects the LED load circuit, and the power supply control means is disconnected. Since the DC power supply is operated at a constant current by reducing the load current for the circuit, excessive current flows into the remaining LED load circuit and it is lit in an overload state, and the failure spreads in a chain. This can be prevented.

  Furthermore, as described above, the LED lighting circuit of the present invention includes a DC-DC converter as the DC power supply, and a current detection unit that detects a total current value flowing through each LED load circuit, and the current detection unit. A reference voltage source and a comparator for comparing the detection results of the DC power supply, and feedback control of the DC power supply so that the sum of energization current values to the LED module becomes a predetermined value according to the output from the comparator And control means for performing the configuration.

  Therefore, a current value from the DC power source to each LED load circuit is detected, and based on the detection result, the DC power source is controlled by feedback so that the sum of the current values becomes a predetermined value. Since the control is performed, the loss in 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 as mentioned above.

  Therefore, it is possible to make the light output from a large number of LEDs uniform, and with low loss, even if an abnormality such as disconnection or short circuit occurs, it is possible to prevent the light from spreading in a chain 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. 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 first control circuit 36 for controlling the switching of the switching element Q0 are provided. A boost chopper circuit configured as described above.

  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 first control circuit 36. The first 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.

  It should be noted that the switch elements SW1 to SW3 are connected in series with the LED load circuits U1 to U3, and the presence or absence of abnormality such as disconnection or short circuit of the system of the LED load circuits U1 to U3 is compared with the comparators CP11 to CP11. When the abnormality is detected, the second control circuit 39 shuts off the switch elements SW1 to SW3 and disconnects the corresponding LED load circuit, and the DC-DC This is to reduce the load current corresponding to the circuit separated by the converter 35.

  Specifically, the inter-terminal voltages (shared voltage) of the control elements Q1 to Q3 are input in common to the inverting input terminals of the comparators CP11 to CP31 and the non-inverting input terminals of the comparators CP12 to CP32. The reference voltage Vref1 from the reference voltage source 41 is commonly input to the non-inverting input terminals of the comparators CP11 to CP31, and the reference voltage Vref2 from the reference voltage source 42 is input to the inverting input terminals of the comparators CP12 to CP32. Are entered in common.

  Here, LEDD1 is blue, its ON voltage Vf is 3.2V, the number of series LEDD1 in each LED load circuit U1 to U3 is 5, and the constant current output of DC-DC converter 35 is 60 mA, that is, each LED Table 1 shows the relationship between the voltage (shared voltage) between the terminals of the control elements Q1 to Q3 and the power loss with respect to the number of short-circuited LEDs D1 when the current flowing through the load circuits U1 to U3 is 20 mA.

  Therefore, if the reference voltage Vref1 for detecting disconnection is set to 0.5 V, for example, and the reference voltage for short circuit detection is set to Vref2 = 3.5 V, for example, the voltage between terminals of the control elements Q1 to Q3 (shared voltage) is When the open voltage is equal to or lower than the reference voltage Vref1, the comparators CP11 to CP31 determine that the corresponding LED load circuits U1 to U3 are disconnected, and output a high level to the second control circuit 39. Further, when the inter-terminal voltage (shared voltage) of the control elements Q1 to Q3 rises to the high side due to the short circuit of the LEDD1 and becomes equal to or higher than the reference voltage Vref2, the comparators CP12 to CP32 are short-circuited to the corresponding LED load circuits U1 to U3. It is determined that this has occurred, and a high level is output to the second control circuit 39.

  In response to this, the second control circuit 39 cuts off the switch elements SW1 to SW3 of the system in which an abnormality has occurred and switches the reference voltage Vref for the comparator 37. Specifically, the reference voltage Vref from the reference voltage source 38 is applied to a series circuit by voltage dividing resistors R01, R02, R03, and the voltage at each end is changed to individual contacts 43a, 43b, 43c, The common contact 43e of the changeover switch 43 is input to the reference voltage input terminal of the comparator 37 as the reference voltage Vref ′. Here, R01 = R02 = R03.

  When there is no system in which an abnormality has occurred, the second control circuit 39 causes the changeover switch 43 to conduct to the individual contact 43a, and outputs the reference voltage Vref from the reference voltage source 38 as the reference voltage Vref ′. The rated DC current of 60 mA is output to the DC-DC converter 35. On the other hand, when there is a system in which an abnormality has occurred, according to the number of systems, the changeover switch 43 is conducted to the individual contact 43b or 43c, and the reference voltage Vref ′ is used as a reference from the reference voltage source 38. A voltage that is 2/3 or 1/3 of the voltage Vref is output. Here, disconnection detection and short circuit detection do not occur simultaneously in the same system, and as described above, the second control circuit 39 determines the number of systems in which an abnormality has occurred (comparators CP11 to CP31; CP12 to CP32 high). The change-over switch 43 may be switched according to the number of outputs).

  However, if disconnection occurs in the LED load circuit U1 which is a reference current generating circuit (CP11 output is high), the current control operation completely turns off the light, so the second control circuit 39 conducts the changeover switch 43 to the individual contact 43d. Then, the GND level is output as the reference voltage Vref ′, and the current output of the DC-DC converter 35 is stopped. Further, when a short circuit occurs in the LED load circuit U1 which is a reference current generating circuit (CP12 output is high), as shown in Table 1, the power loss in the control element Q1 of the LED load circuit U1 increases. Since the heat is generated, the switch element SW1 may be shut off and completely turned off, or the switch element SW1 may be turned on without being cut off, and the reference voltage Vref ′ is also short-circuited for the LED load circuit U1. It may not be lowered.

  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. Further, since the LED load circuit (U1 in the example of FIG. 1) having the highest sum of the ON voltages Vf of the LEDs D1 is used as a 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 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. 6 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. 7 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 constant current control is performed and when constant voltage control is performed when the constant current circuits d1 to d3 shown in FIGS. 7 and 8 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. 7 and 8, 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.

  Furthermore, when the comparators CP12 and CP22 detect that an abnormality such as disconnection or short circuit has occurred in any of the LED load circuits U1 to U3, for example, U2, the second control circuit 39 causes the corresponding switch element to When the LED load circuit U2 in which the abnormality has occurred is disconnected by shutting off SW2, the DC-DC converter 35 is caused to perform a constant current operation by reducing the load current corresponding to the disconnected LED load circuit U2. Further, it is possible to prevent an excessive current from flowing into the remaining LED load circuits U1 and U3 to light up in an overload state, and the failure to spread in a chain manner.

  Therefore, the comparators CP11 to CP31; CP12 to CP32, the reference voltage sources 41 and 42, and the second control circuit 39 constitute abnormality detection means, the switch elements SW1 to SW3 constitute disconnection means, and the second The control circuit 39, the voltage dividing resistors R01, R02, R03 and the switch 43 constitute power supply control means.

[Embodiment 2]
FIG. 3 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, the short circuit detection is performed by the temperature sensors S2 and S3. That is, since a series circuit including the LED load circuits U2 and U3 and the corresponding control elements Q2 and Q3 is connected between the output terminals of the DC-DC converter 35, the LED D1 in the LED load circuits U2 and U3 is short-circuited. Since the voltage to be shared by the control elements Q2 and Q3 to be increased increases and the power loss in the control elements Q2 and Q3 increases, the second control circuit 59 detects the short circuit from the temperature increase caused thereby.

  In the present embodiment, the switch is used so that the LED load circuit U1 as the reference current generation circuit is completely turned off by the current mirror operation as described above, and is not turned off even if a short circuit occurs. The element SW1 is not provided, and the corresponding control element Q1 is not provided with a temperature sensor. Further, the change-over switch 43 'is not provided with the GND individual contact 43d to be completely turned off.

  In this way, an abnormality can be detected from a temperature rise due to a short circuit.

[Embodiment 3]
FIG. 4 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 circuits 31 and 51 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, the disconnection of the LED load circuits U2 and U3 due to abnormality detection is performed by stopping the current mirror operation. Specifically, the switch elements SW2 and SW3 are not provided between the LED load circuits U2 and U3 and the control elements Q2 and Q3. Instead, the base and collector of the control element Q1 and the control elements Q2 and Q3 The switch elements SW2 and SW3 are provided between the base elements of the control elements Q2 and SW3. When an abnormality occurs, the second control circuit 69 cuts off the switch elements SW2 and SW3 so that the base currents of the control elements Q2 and Q3 flow. The corresponding LED load circuits U2 and U3 can be disconnected.

  Even with this configuration, the abnormal circuit can be disconnected.

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. 6 and FIG. 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 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, 51, 61 LED lighting circuit 32 LED module 33 Commercial power supply 34 Rectifier bridge 35 DC-DC converter 36 First control circuit 37 Comparison circuit 38, 41, 42 Reference voltage source 39, 59, 69 Second control circuit 43 , 43 'change-over switch C2 smoothing capacitors CP11, CP21, CP31; CP12, CP22, CP32 comparator D diode D1 LED
L choke coil Q0 switching elements Q1-Q3 control elements R1, R2 resistors R01, R02, R03 voltage dividing resistors R21-R23 current-voltage conversion resistors S2, S3 temperature sensors SW1-SW3 switch elements U1-U3 LED load circuit

Claims (8)

In an LED lighting circuit in which a DC power source is driven to be lit at a constant current for 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;
Detecting means for detecting an abnormality in the system of each LED load circuit;
When an abnormality is detected by the detecting means, a disconnecting means for disconnecting a corresponding LED load circuit;
An LED lighting circuit comprising: a power supply control means for reducing a load current corresponding to a circuit separated from the DC power supply by the disconnecting means.   2. The LED lighting circuit according to claim 1, wherein the detection unit detects a short circuit of the LED in the corresponding LED load circuit from an increase in a voltage between terminals of the control element.   The LED lighting circuit according to claim 1, wherein the detection unit detects a short circuit of the LED in the corresponding LED load circuit from the temperature rise of the control element.   The detection unit detects disconnection of an LED in a corresponding LED load circuit because a connection point between the control element and the LED load circuit is an open voltage. The LED lighting circuit according to any one of the above.   5. The LED lighting circuit according to claim 1, wherein the disconnecting unit includes a switch element connected in series with each of the LED load circuits. 6.   5. The switch unit according to claim 1, wherein the separating means includes a switch element interposed between a control terminal of a control element serving as a reference of a current mirror and a control terminal of a remaining control element. LED lighting circuit according to. The DC power supply is a DC-DC converter,
Current detection means for detecting a total current value flowing through each LED load circuit;
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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