JP4347636B2 - Discharge lamp lighting device - Google Patents

Description

  The present invention relates to a technique for simplifying the structure of an AC conversion transformer used in a discharge lamp lighting device, reducing the size and cost, and improving reliability.

  In a lighting circuit for a discharge lamp such as a metal halide lamp, as a configuration suitable for miniaturization and high frequency, for example, an output boosted by one-step voltage conversion in a DC-AC conversion circuit is supplied to the discharge lamp. The configuration is known (for example, see Patent Document 1).

  In the form provided with the AC conversion transformer, the output converted to AC by boosting the DC input is supplied to the discharge lamp, and a starting signal (so-called starter pulse) is generated when the discharge lamp is started up. Applied.

Japanese Patent Laid-Open No. 7-169583

  By the way, with the conventional configuration, it is difficult to make the AC conversion transformer into a simple structure, and there is a problem in power loss when the discharge lamp is turned on, a withstand voltage of the circuit element, and the like.

  For example, in order to obtain a high voltage required for discharge with respect to a start signal to a discharge lamp, it is necessary to increase the turns ratio of the transformer. This is a cause of hindering cost reduction and cost reduction.

  Therefore, the present invention aims to simplify the structure of an AC conversion transformer that constitutes a DC-AC conversion circuit in a discharge lamp lighting device, to achieve downsizing and cost reduction, and to improve the reliability of the circuit. And

  The present invention includes a DC-AC conversion circuit that receives a DC input and performs AC conversion and boosting, and a starting circuit for supplying a starting signal to the discharge lamp, and controls the power output from the DC-AC converting circuit. Thus, the discharge lamp lighting device that controls the lighting of the discharge lamp has the following configuration.

A structure in which an AC conversion transformer constituting a DC-AC conversion circuit is provided, the primary winding and the secondary winding of the AC conversion transformer are insulated , and a discharge lamp is connected to both ends of the secondary winding. When the discharge lamp is lit, the primary current flows through the primary winding so that the AC output converted by the AC conversion transformer is supplied from the secondary winding to the discharge lamp. to the AC output, the starting signal boosted by the AC conversion transformer is supplied to the discharge lamp from the secondary winding are superimposed.

Of the primary windings of the AC conversion transformer, the AC conversion is performed with the first winding portion connected between the output terminals of the starting circuit and the number of turns smaller than that of the primary winding. A dedicated winding that is attached to the transformer and connected to the output terminal of the starting circuit is formed using a metal foil and wound around the core of the AC conversion transformer .

  Therefore, according to the present invention, by strengthening the electromagnetic coupling between the first winding portion or the dedicated winding and the secondary winding, a high voltage necessary for discharge can be obtained without increasing the turns ratio. it can.

  According to the present invention, by increasing the coupling ratio of the transformer when supplying the activation signal to the discharge lamp, the transformer can be reduced in size and the circuit loss can be reduced. Further, since it is not necessary to increase the withstand voltage of the circuit elements, it is advantageous for cost reduction, and the circuit burden when the discharge lamp is turned on can be reduced and the reliability can be improved.

  Furthermore, by adopting a configuration in which the first winding portion or the dedicated winding is formed in a cylindrical shape and wound around the outer periphery of the core or the secondary winding, the first winding portion or The integrity of the dedicated winding and the secondary winding can be increased to increase the coupling rate. The length of the first winding portion or the dedicated winding in the direction of the central axis can be set as the coil of the secondary winding. The coupling rate can be further increased by making it equal to or longer than the length.

  Using copper foil with excellent conductivity for the first winding part or dedicated winding is advantageous in terms of workability and cost, and by using a nickel-based core as the core material, the winding and the core are separated. It can be adhered as much as possible.

  And by providing a flange part in the edge part of the insulating member arrange | positioned between a primary winding and a secondary winding, creeping distance can be lengthened and insulation strength can be raised.

  The present invention can be applied to lighting circuits for various discharge lamps used in automobile illumination light sources such as metal halide lamps, and can achieve the following objects.

Contriving the structure of the AC conversion transformer that constitutes the DC-AC conversion circuit to simplify the insulation structure of the transformer when starting the discharge lamp, thereby contributing to the miniaturization and cost reduction of the circuit. To improve the reliability of the circuit by strengthening the coupling of the AC conversion transformer when the start signal is generated and reducing the circuit load and loss when the discharge lamp is turned on.

  FIG. 1 shows an example of a basic configuration according to the present invention. A discharge lamp lighting device 1 includes a DC-AC conversion circuit 3 and a starting circuit 4 that receive power from a DC power source 2 in the circuit configuration. .

  The DC-AC conversion circuit 3 is provided for receiving DC input from a battery or the like and performing AC conversion and boosting. In this example, two switching elements 5H and 5L and control means 6 for driving them to perform switching control are provided. In other words, one end of the switching element 5H on the higher stage side is connected to the power supply terminal, and the other end of the switching element is grounded via the switching element 5L on the lower stage side. Alternately on / off. In the figure, the elements 5H and 5L are simply indicated by switch symbols, but semiconductor switching elements such as field effect transistors (FETs) and bipolar transistors are used.

  The DC-AC conversion circuit 3 has an AC conversion transformer 7 and has a structure in which the primary circuit and the secondary circuit are insulated. In this example, a circuit configuration using a resonance phenomenon between the resonance capacitor 8 and the inductor or inductance component 9 is used. That is, as a configuration form, for example, there are the following three types.

(I) Form using resonance between resonance capacitor 8 and inductance element (II) Form using resonance between resonance capacitor 8 and leakage (leakage) inductance of AC conversion transformer 7 (III) Resonance capacitor 8 And a form of using the resonance between the inductance element and the leakage inductance of the AC converting transformer 7.

  First, in the above (I), an inductance element 9 such as a resonance coil is attached, for example, one end of the element is connected to the resonance capacitor 8, and the capacitor is connected to a connection point between the switching elements 5H and 5L. To do. And the structure which connected the other end of the inductance element 9 to the primary winding 7p of the transformer 7 for AC conversion is mentioned.

  In the above (II), by using the inductance component 9 of the AC conversion transformer 7, it is not necessary to add a resonance coil or the like. That is, one end of the resonance capacitor 8 may be connected to the connection point between the switching elements 5H and 5L, and the other end of the capacitor may be connected to the primary winding 7p of the AC conversion transformer 7.

  In the above (III), a series combined reactance of the inductance element 9 and the leakage inductance can be used.

  In any form, the series resonance of the resonance capacitor 8 and the inductive element (inductance component or inductance element) is used, and the driving frequency of the switching elements 5H and 5L is defined to a value equal to or higher than the series resonance frequency. Are alternately turned on / off, the sine wave lighting of the discharge lamp 10 connected to the secondary winding 7s of the AC conversion transformer 7 can be performed. In the drive control of each switching element by the control means 6, it is necessary to drive each element reciprocally so that both switching elements are not turned on (depending on on-duty control or the like). As for the series resonance frequency, this is denoted as “f”, the capacitance of the resonance capacitor 8 is “Cr”, the inductance of the inductance element 9 is “Lr”, and the primary inductance of the transformer 7 is “Lp1”. For example, in the above-described form (III), “f = f1 = 1 / (2 · π · √ (Cr · (Lr + Lp1))” before lighting of the discharge lamp, and “f = F2≈1 / (2 · π · √ (Cr · Lr)) ”(f1 <f2).

  Regardless of the configuration of the control means 6 in the application of the present invention, for example, a circuit for controlling the no-load output voltage before the discharge lamp is lit, a transient input power and a steady state after the discharge lamp is lit The control voltage is defined by providing a circuit for controlling the input power at V, and a pulse signal obtained by converting the voltage to V (voltage) -F (frequency) is shaped to be applied to the switching elements 5H and 5L. A configuration form that is transmitted as a control signal can be used.

  In order to stably control the discharge lamp, it is desirable to increase the frequency value after the discharge lamp is turned on with respect to the drive frequency of the switching elements 5H and 5L than the frequency value before the start signal is generated. In a state before the discharge lamp is lit by application of the start signal, the secondary circuit of the AC conversion transformer 7 is opened, so that the transformer can be equivalently regarded as a choke coil. Therefore, the series resonance frequency in this state is f1, and the frequency value is smaller than f2 at the time of lighting, and the switching element is controlled with a driving frequency near f1 at the time of startup. After the discharge lamp is turned on, the switching element is controlled with a driving frequency located near the series resonance frequency f2 determined by the capacitance of the resonance capacitor 8 and the inductance of the inductance element or the leakage inductance of the AC conversion transformer 7. To do.

  In power control, it is preferable to perform switching control at a drive frequency higher than the series resonance frequency, and when the drive frequency is matched with the series resonance frequency, the maximum power can be extracted, so that the power is released as the initial power. By supplying to the electric lamp, the light emission of the discharge lamp can be promoted to promptly shift to the steady state. When switching control is performed with a drive frequency lower than the series resonance frequency, the combined impedance of the capacitance of the resonance capacitor and the inductance enters the capacitive region and falls into a state that is difficult to control. It is desirable to control the drive frequency so as to avoid such a state.

  The starting circuit 4 is provided to supply a starting signal to the discharge lamp 10, and the output of the starting circuit 4 at the time of starting is boosted by the AC conversion transformer 7 and applied to the discharge lamp 10 (AC The start signal is superimposed on the converted output and supplied to the discharge lamp.)

  In this example, one of the output terminals of the starting circuit 4 is connected in the middle of the primary winding 7p of the AC conversion transformer 7, and the other output terminal is connected to one end (ground side terminal) of the primary winding 7p. However, the present invention is not limited to this, and both output terminals of the starting circuit 4 are connected in the middle of the primary winding 7p of the AC conversion transformer 7, or as in the lighting device 1A shown in FIG. In the conversion transformer 7, a dedicated winding 7 a other than the primary winding and the secondary winding is provided, and each output terminal of the starting circuit 4 is connected to the dedicated winding 7 a.

  Further, in order to generate a pulse voltage having a peak value necessary for starting the discharge lamp 10 on the secondary side of the AC converting transformer 7, a voltage as high as possible is supplied to the capacitor in the starting circuit 4. In this example, one of the input terminals of the starting circuit 4 is connected between the resonance capacitor 8 and the inductance element 9 (in the case of (II), the primary winding 7p). Then, the other input terminal is connected to the ground side line to use the resonance voltage. In addition to this, a form for obtaining the input voltage to the starting circuit from the secondary side of the transformer for AC conversion, and an auxiliary winding constituting the transformer together with the inductance element 9 are provided, and the auxiliary winding to the starting circuit is provided. The form etc. which obtain these input voltages are mentioned.

  The starter circuit 4 is not limited in its configuration, for example, it is configured using a plurality of rectifier elements, capacitors, and switch elements. As the switch elements, self-breakdown elements such as spark gaps and varistors, thyristors, A semiconductor element having a control terminal such as an IGBT (insulated gate bipolar transistor) or FET can be used.

  By the way, as described above, the AC conversion transformer 7 has a DC-AC conversion function and a startup signal boosting function. The latter is shown in FIG. 1 in each output of the startup circuit 4 in the primary winding 7p. When the terminal is connected and the first winding portion located between the output terminals is “7p1” and the other winding portion (second winding portion) is “7p2”, the winding As the turn ratio determined by the number of turns of the portion 7p1 and the number of turns of the secondary winding 7s increases, it becomes easier to obtain a high voltage necessary for discharge. However, when the discharge lamp is turned on, the number of turns “n1” of the primary winding 7p, the number of turns “n2” of the secondary winding 7s, and the secondary current “I2” (lamp) are connected to the primary side of the AC conversion transformer 7. Since the primary current “I1” determined by the current) flows (I1≈ (n2 / n1) · I2), the smaller the turn ratio between the primary winding 7p and the secondary winding 7s, the smaller the I1, the loss. Less is. Further, when the turn ratio between the winding portions 7p1 and 7p2 is too large, it is necessary to increase the withstand voltage of the resonance capacitor, inductor, switching element, etc. (for example, the turn ratio of 7p1 to 7p2 is “1: 4”). If the output of the starting circuit is 1 kV (kilovolt), a withstand voltage of 4 kV is required.)

  From the above, in order to generate a sufficient starting voltage for starting the discharge lamp and reduce the circuit loss at the time of lighting and the withstand voltage of the used element, the winding portions 7p1 and 7s at the time of generating the starting signal are used. It is desirable to strengthen the coupling of the two and make the turn ratio of both as small as possible. As an example, if the number of turns of 7p, 7s, and 7p1 is 4T, 40T, and 1T (turns), respectively, and the output voltage of the starting circuit is 1 kV, 20 kV can be output, the coupling between 7p1 and 7s is strengthened. Thus, if 20 kV can be output even if the number of turns of 7s is 25T, the number of turns of 7p can be reduced to 3T. As a result, the turn ratio of 7p1 and 7p and the turn ratio of 7p and 7s can be reduced. Both can be reduced.

  In the conventional method using a wire winding having a general circular section, the secondary terminal voltage of the transformer when the start signal is generated is an ideal value (that is, a voltage proportional to the turn ratio). Therefore, it is necessary to increase the turns ratio of the transformer, and the loss when the discharge lamp is turned on also increases.

  Therefore, in the present invention, the following transformer structure is adopted.

(A) Regarding the winding portions 7p1 and 7p2 constituting the primary winding 7p of the AC conversion transformer 7, the cross-sectional shape of the winding portion 7p1 cut along a plane orthogonal to the winding direction of the winding is made flat, (B) Dedicated to the output terminal of the starting circuit 4 connected to the AC conversion transformer with a smaller number of turns than the primary winding 7p of the AC conversion transformer 7 A structure in which the winding 7a is provided (see FIG. 2), and the cross-sectional shape cut by a plane perpendicular to the winding direction is flattened, and the thickness is smaller than that of the primary winding 7p.

  By using such a structure, the coupling between the windings can be strengthened, and a voltage necessary for starting the discharge lamp can be obtained with a smaller turn ratio.

  In the above (A), for example, when a flat wire, a metal foil, a thin metal plate, or the like is used for the winding portion 7p1, the following configuration is exemplified.

(A1) Form in which the primary winding 7p is arranged outside the insulating member and the secondary winding 7s is arranged inside (see FIGS. 3 and 4)
(A2) A configuration in which the primary winding 7p is arranged inside the insulating member and the secondary winding 7s is arranged outside (see FIGS. 5 and 6).

  First, the form (A1) will be described. The AC conversion transformer 7A shown in FIG. 3 is configured by using an insulating member 11 constituting a coil bobbin and a pair of cores 12 and 12 having an E-shaped block shape.

  The insulating member 11 has a cylindrical portion 11a and disc-shaped flange portions 11b and 11b provided at both ends thereof, and a primary winding 7p is wound around the outer side of the cylindrical portion 11a.

  The winding portion 7p1 of the primary winding 7p is formed using a metal foil or a thin metal plate, and has terminal portions 13 and 14 for connection to the output terminal of the starting circuit 4. For example, a copper foil that is excellent in conductivity, inexpensive, and easy to process is used, and is wound in a cylindrical shape on the outer periphery of the cylindrical portion 11a. In addition, one output terminal of the starting circuit 4 is connected to the terminal portion 13, and one end portion of the winding portion 7 p 2 is connected to the terminal portion 13. Further, the other output terminal (ground side terminal) of the starting circuit 4 is connected to the terminal portion 14. For the terminal portions 13 and 14, for example, a method in which a lead-out portion (connection piece or the like) is formed in advance on a metal foil or a thin metal plate and the portion is bent at the time of winding is used.

  A coated wire is used for the winding portion 7p2 of the primary winding 7p, and is arranged in a coiled state on the outer periphery of the winding portion 7p1.

  The secondary winding 7s is formed in a coil shape using a covered wire, and is disposed inside the cylindrical portion 11a. And the coil part of secondary winding 7s is wound around each core in the state where it was extrapolated to the middle leg parts (column part) 12a and 12a of cores 12 and 12, respectively.

  FIG. 4 schematically shows a cross-sectional structure of the AC conversion transformer 7A.

  The middle legs 12a and 12a of the cores 12 and 12 are connected to each other, the secondary winding 7s is wound on the outer side, and the cylindrical portion 11a of the insulating member 11 is positioned on the outer side. And the winding part 7p1 is wound around the outer periphery of this cylindrical part 11a, and also the winding part 7p2 is wound on the outer side.

  Thus, in this example, each part (7p1, 7p2) of the primary winding 7p is wound around the outer periphery of the core 12 and the secondary winding 7s.

  In order to strengthen the coupling between the windings and obtain the starting voltage with a smaller turn ratio, the core 12, the winding portion 7p1, and the secondary winding 7s are integrally configured with a sufficiently close positional relationship. Therefore, it is preferable to make the cross section of the winding portion 7p1 as flat as possible so as to improve the integrity with the secondary winding 7s. In this example, while using metal foil (copper foil), it has the same winding direction as the secondary winding 7s with respect to the cylindrical portion 11a of the insulating member 11 so as to surround the core 12 and the secondary winding 7s. Metal foil is wrapped.

  The coupling can be further strengthened by defining the length of the winding portion 7p1 in the central axis direction to be equal to or longer than the coil length of the secondary winding 7s. That is, when a metal foil is used for the winding portion 7p1, its width (width in the vertical direction in FIGS. 3 and 4) is equal to or equal to the length in the longitudinal direction of the secondary winding 7s (coil length). It is preferable to make it larger.

  In this example, a configuration in which one output terminal of the starting circuit 4 is connected to the first turn from the ground-side terminal of the primary winding 7p is shown. Accordingly, the number of turns of the winding portion 7p1 is set to 1, and the copper foil of the portion surrounds most of the secondary winding 7s and the middle leg portion 12a of the core 12. As a result, the coupling ratio between the winding portion 7p1 and the secondary winding 7s can be increased, and a high voltage pulse can be generated with a minimum necessary turn ratio. The copper foil may be wound for more than 2 turns, but in this case, insulation between the first turn and the second turn cannot be taken. Is required. Therefore, a one-turn configuration is preferable from the viewpoint of simplifying the configuration.

  Moreover, it is desirable to use a nickel-based core as the core material. In other words, since the coupling between the windings is very important, using a charged core material (a material with low impedance) requires an insulating structure between the core and the windings, and that much winding is required. The wire is separated from the core, causing the coupling to deteriorate. By using a nickel-based core, such an insulating structure becomes unnecessary.

  Flange portions 11b and 11b are provided at the end of the insulating member 11 disposed between the primary winding 7p and the secondary winding 7s of the AC conversion transformer 7A. This ensures the dielectric strength. be able to. That is, when the winding portion 7p1 and the secondary winding 7s are wound with the same width in the vertical direction of FIGS. 3 and 4, the high voltage (starting voltage) generated when starting the discharge lamp is accompanied. In order to reduce the risk of discharge to the winding portion, it is necessary to increase the creepage distance and increase the insulation strength. In order to block the discharge path, the flange portion 11b is preferably provided between the winding portions 7p1 and 7p2 and the secondary winding 7s. In this example, the flange portions 11b and 11b are provided at both ends of the insulating member 11, but the present invention is not limited to this, and only at one end (the end on the side where discharge can occur due to the generation of a high voltage pulse). A flange portion may be provided.

  Next, the form (A2) will be described. The AC conversion transformer 7B shown in FIGS. 5 and 6 is different from the transformer 7A as follows.

The secondary winding 7s is wound around the outer peripheral surface of the cylindrical portion 11a of the insulating member 11. The winding portion 7p1 of the primary winding 7p has a cylindrical shape and is connected to this and wound around the outer periphery. The winding portion 7p2 is disposed inside the cylindrical portion 11a of the insulating member 11. The winding portion 7p1 is wound around the middle leg portions 12a and 12a of the cores 12 and 12.

  That is, in this example, the secondary winding 7s is arranged outside the insulating member 11, and the primary winding 7p is arranged inside the insulating member 11. Therefore, except for the difference in size and size such that the coil diameter of the secondary winding 7s is larger than the outer diameter of the cylindrical portion 11a and the winding diameters of the winding portions 7p1 and 7p2 are smaller than the inner diameter of the cylindrical portion 11a. Since the basic configuration and function of each part are the same as in the case of the transformer 7A, the same reference numerals as those assigned to the respective parts of the transformer are used in the figure.

  FIG. 6 schematically shows a cross-sectional structure of the AC conversion transformer 7B.

  The middle leg portions 12a and 12a of the cores 12 and 12 are connected to each other, the winding portion 7p1 of the primary winding 7p is wound around the outer side, and the winding portion 7p2 is wound around the outer side. And the cylindrical part 11a of the insulating member 11 is located in the outer side, and the secondary winding 7s is wound around the outer periphery of this cylindrical part 11a.

  Thus, in this example, each part (7p1, 7p2) of the primary winding 7p is wound around the outer periphery of the cores 12, 12.

  Also in this example, a copper foil is used for the winding portion 7p1 including the terminal portions 13 and 14, and the length in the central axis direction is not less than the coil length of the secondary winding 7s. The use of a nickel-based core as the core material and the meaning of the flange portion 11b are as described above.

  Next, the structure (B) will be described.

  As shown in FIG. 2, each output terminal of the starting circuit 4 can be connected to a dedicated winding 7a having a smaller number of turns than the primary winding 7p to boost the output voltage, and the output voltage of the starting circuit 4 is dedicated. A start signal applied to the winding 7a and boosted according to the turn ratio of the dedicated winding 7a and the secondary winding 7s is applied to the discharge lamp 10 to light the discharge lamp.

  In this embodiment, a rectangular wire, a metal foil, a thin metal plate, or the like is used for the dedicated winding 7a, and the same configuration form as the above (A1) and (A2) can be mentioned. That is, the differences from the configurations of FIGS. 3 to 6 are as follows.

The winding portion 7p1 corresponds to the dedicated winding 7a, and the winding portion 7p2 corresponds to the primary winding 7p. The terminal portions 13 and 14 of the dedicated winding 7a are connected to the output terminals of the starting circuit 4. (There is no need to connect the dedicated winding 7a and the primary winding 7p).

  Thus, since it is not necessary to connect the output terminal of the starting circuit 4 in the middle of the primary winding 7p, the wiring process is simplified.

  In the above description, an example in which the present invention is applied to a configuration (EER) in which an E-shaped block-shaped core is combined has been shown. However, the present invention is not limited to this and can be applied to configurations using various transformers. Of course.

It is a figure which shows the circuit structural example which concerns on this invention. It is a figure which shows the circuit structural example which connected the output terminal of the starting circuit to the exclusive winding. FIG. 4 shows an example of the configuration of an AC conversion transformer together with FIG. It is a schematic sectional drawing. FIG. 6 shows another example of the configuration of the AC conversion transformer, and this figure is an exploded perspective view of the main part. It is a schematic sectional drawing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 1A ... Discharge lamp lighting device, 3 ... DC-AC conversion circuit, 4 ... Start-up circuit, 7, 7A, 7B ... Transformer for AC conversion, 7p ... Primary winding, 7p1 ... First winding part, 7p2 ... Second winding part, 7s ... secondary winding, 7a ... dedicated winding, 11 ... insulating member, 11b ... flange, 12 ... core

Claims (4)

A discharge lamp comprising a DC-AC conversion circuit for receiving AC input and performing AC conversion and boosting, and an activation circuit for supplying an activation signal to the discharge lamp, and controlling electric power output from the DC-AC conversion circuit In the discharge lamp lighting device that controls the lighting of
An AC conversion transformer that constitutes the DC-AC conversion circuit is provided, a primary winding and a secondary winding of the AC conversion transformer are insulated , and the discharge lamp is connected to both ends of the secondary winding. has a structure, supplied to the discharge lamp converted AC output by the AC conversion transformer by primary current flows in the primary winding from the secondary winding when lit the discharge lamp is, with respect to the AC output at the time of startup of the discharge lamp, the starting signal boosted by the AC conversion transformer is supplied to the discharge lamp from said secondary winding are superimposed,
And among the primary windings of the transformer for AC conversion, each output terminal of the starting circuit is connected, and the first winding part located between the output terminals or the number of turns less than the primary winding A dedicated winding attached to the AC conversion transformer and connected to the output terminal of the starter circuit is formed using a metal foil and wound around the core of the AC conversion transformer around the core. that <br/> discharge lamp lighting device, characterized in that. In the discharge lamp lighting device according to claim 1 ,
The discharge lamp lighting device, wherein a length of the first winding portion or the dedicated winding in a central axis direction is equal to or longer than a coil length of a secondary winding of the AC conversion transformer. In the discharge lamp lighting device according to claim 1 or 2 ,
A discharge lamp lighting device using a nickel-based core as a core material of the AC conversion transformer. In the discharge lamp lighting device according to any one of claims 1 to 3 ,
A discharge lamp lighting device, wherein a flange portion is provided at an end portion of an insulating member disposed between a primary winding and a secondary winding of the AC conversion transformer.

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