JP2006245307A - Light source apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress heat generation of a driver IC for driving a heat-generating element. <P>SOLUTION: A plurality of element arrays L1-Ln in which a plurality of LEDs 26 are connected in series are each driven by a driver IC 28. The driver IC 28 is provided with a plurality of constant current driving channels Ch, and the driving channels Ch are each allocated to each of the element arrays L1-Ln. A protective transistor Q for protecting the driver IC 28 is provided between the driver IC 28 and each of the element arrays L1-Ln. In the protective transistor Q, a predetermined voltage Vreg is applied to its base terminal to make an output voltage of an emitter terminal constant, irrespective of a voltage to be applied to a collector terminal. A difference voltage between a forward voltage VFL of the element array L and a driving voltage Vd is applied to the collector terminal, and even if its value is large, since the protective transistor Q limits an input voltage into the driver IC 28, heat generation of the driver IC can be suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a light source device in which a plurality of light emitting elements are arranged.

  A light source device (for example, see Patent Documents 1 and 2 below) having an LED array in which a plurality of LEDs (Light Emitting Diodes) as light emitting elements are arranged is known, and is used for various applications such as lighting and displays. ing. The LED array is configured, for example, by connecting element columns in which m LEDs are connected in series to n columns in parallel. A driver IC for driving the LED array is connected to the LED array. The driver IC includes, for example, a lighting control circuit that controls lighting for each column based on a driving signal, and a constant current driving circuit that is driven by passing a constant current through each element column. The constant current drive circuit includes, for example, the same number of drive lines as the number of each element row, and each drive line is connected to each element row. By using this constant current drive circuit, even if the applied drive voltage is larger than a predetermined value, the current flowing through each element row can be made constant.

The LED generates a voltage drop when a current flows in the forward direction (from the anode to the cathode), and this voltage drop is called a forward voltage drop (hereinafter abbreviated as VF). The forward voltage drop (hereinafter abbreviated as VFL) of the entire element array is a total value of VF of individual LEDs constituting the element array. Even if a voltage equal to or lower than the VFL is applied to the element array, it does not light, so the drive voltage Vd is set to a value higher than the VFL. Specifically, since the actual VF of each LED varies, a margin allowing for variation is added to the average value of the VF of a plurality of LEDs, and this value is summed by the number of LEDs in the element array. The value is set as the drive voltage Vd.
JP 7-321623 A JP-A-9-141932

  However, the difference between the drive voltage Vd and the actual VFL results in power loss and is wasted by the driver IC. When wasteful power consumption occurs in the driver IC, heat generation increases correspondingly, and a local temperature rise or the like occurs internally. In the worst case, there is a problem that the IC is destroyed.

  An object of the present invention is to provide a light source device in which heat generation of a driver IC can be suppressed.

  The light source device of the present invention includes at least one light emitting element array in which a plurality of light emitting elements are connected in series, and each light emission even when a drive voltage applied from a power source to the anode of the light emitting element array exceeds a predetermined value. A driver IC having at least one constant current drive channel that is driven by passing a constant current through the element array; and a collector terminal connected to a cathode of the light emitting element array, provided for each of the constant current drive channels, An emitter terminal is connected to the driver IC, and a base terminal is provided with a transistor to which a predetermined voltage is applied.

  The voltage applied to the base terminal is preferably determined based on a forward voltage of the light emitting element array.

  A switch for turning on / off a voltage applied to the base terminal may be provided. Further, the light emitting element rows may be connected in parallel, for example. Each constant current drive channel drives at least one light emitting element array.

  The plurality of light emitting element arrays may be composed of a plurality of types of light emitting element arrays having different emission colors. A power supply path switching unit may be provided that is disposed between the anode of each of the plurality of types of light emitting element arrays and a power source, and selectively switches a power supply path to each of the light emitting element arrays for each type. Furthermore, drive voltage switching means for changing the drive voltage of each light emitting element array for each type may be provided.

  A plurality of types of light emitting element rows may be alternately arranged. One constant current drive channel may be shared by a plurality of different types of light emitting element arrays.

  According to the present invention, at least one light emitting element array in which a plurality of light emitting elements are connected in series, and each light emitting element even when a drive voltage applied from a power source to the anode of the light emitting element array exceeds a predetermined value. A driver IC having at least one constant current drive channel that is driven by passing a constant current through the column; a collector terminal connected to the cathode of the light emitting element column; Since the emitter terminal is connected to the IC and the base terminal includes a transistor to which a predetermined voltage is applied, a light source device that can suppress the heat generation of the driver IC can be provided.

  FIG. 1 shows a color thermal printer 10 using the light source device of the present invention as a light fixing light source. The color thermal printer 10 takes in image data from, for example, a memory card storing image data taken by a digital camera or a personal computer, and prints the image on color thermal recording paper 11.

  As is well known, the recording paper 11 is formed by providing, on the support, three thermosensitive coloring layers that color each color of Y (yellow), M (magenta), and C (cyan) in order from the upper layer. . The color thermosensitive recording paper 11 has the highest thermal sensitivity of the yellow thermosensitive coloring layer as the uppermost layer and the lowest thermal sensitivity of the cyan thermosensitive coloring layer as the lowermost layer.

  Each of the yellow and magenta thermosensitive coloring layers is provided with a light fixing property by light in a specific wavelength range so that the uncolored portion of the upper thermosensitive coloring layer is not colored when the deep thermosensitive coloring layer is heated. Each thermosensitive coloring layer is photofixed by irradiating light of each wavelength after the image is thermally recorded. The yellow thermosensitive coloring layer loses its coloring ability when irradiated with yellow fixing light, which is blue-violet light with an emission peak wavelength of about 420 nm, and the magenta thermosensitive coloring layer has a near ultraviolet ray with an emission peak wavelength of about 365 nm. When the magenta fixing light is irradiated, the coloring ability is lost.

  The color thermal printer 10 performs thermal recording of a full-color image and photofixing of the thermal recording color thermal recording paper 11 while reciprocating the recording paper 11 in the feed direction and the return direction.

  The system controller 21 includes a CPU, a ROM, a RAM, and the like, and comprehensively controls each unit of the printer based on an operation signal from the operation unit. The power supply circuit 22 supplies power supplied from a commercial power supply connected via an outlet to each part of the printer 10.

  On the conveyance path of the color thermal recording paper 11, a thermal head 12 and a platen roller 13 that is arranged at a position facing the thermal head 12 and supports the color thermal recording paper 11 from the back side are arranged. As is well known, the thermal head 12 includes a heating element array 12a in which a large number of heating elements are arranged in a line along the main scanning direction (width direction of the color thermal recording paper). The heating element array 12a is brought into pressure contact with the color thermosensitive recording paper 11, and each thermosensitive coloring layer is heated, whereby images of each color of yellow, magenta, and cyan are thermally recorded.

  The system controller 21 reads the image data fetched into the memory line by line, generates drive data from the line data, and sends the drive data to the thermal head 12. Based on this drive data, the thermal head 12 is driven, and each heating element generates printing heat energy corresponding to the gradation of each pixel. This printing heat energy is applied to the color thermal recording paper 11 and the recording paper 11 is colored.

  On the downstream side in the forward direction of the thermal head 12, a conveyance roller pair 14 and an optical fixing device 16 serving as an optical fixing light source are arranged. The conveyance roller pair 14 nips the fed color thermal recording paper 11 and conveys it in the sub-scanning direction. During this conveyance, the color thermal recording paper 11 passes through the thermal head 12 and the optical fixing device 16 to perform thermal recording and optical fixing.

  The conveyance roller pair 14 is driven by a drive motor 18. For example, a stepping motor is used as the drive motor 18 and is connected to the system controller 21 via the motor driver 19. The system controller 21 controls the rotation amount and rotation speed of the drive motor. Through the control of the drive motor 18, the transport amount and transport speed of the color thermal recording paper 11 are controlled.

  The optical fixing device 16 is arranged on the downstream side of the thermal head 12 in the feeding direction, and is unique to each recorded thermosensitive coloring layer on which an image of each color of yellow or magenta is thermally recorded by the head 12. Light fixing is performed by irradiating fixing light in various wavelengths.

  As shown in FIG. 2, the optical fixing device 16 includes a substrate 24 on which a wiring pattern is formed, and a light emitting element array in which a plurality of LEDs 26 are arranged in a matrix on the substrate 24. Three LEDs 26 arranged in a line along the sub-scanning direction are connected in series, and these constitute one set of element rows L, and this element row L is arranged in a plurality of rows in the main scanning direction. Yes. The element rows L1 to Ln are connected in parallel. A driver IC 28 (see FIG. 4) for driving the element rows L1 to Ln is mounted on the substrate 24, and is unitized together with the element rows L1 to Ln. The driver IC 28 controls lighting of the element rows L1 to Ln based on the drive signal input from the system controller 21.

  As the LED 26, as shown by the solid line in the graph of FIG. 3, a blue LED that includes yellow fixing light and magenta fixing light in the emission wavelength and whose emission peaks are around 365 nm (magenta fixing light) and 420 nm is used.

  The filter 17 (see FIG. 1) is an ultraviolet cut filter having a characteristic of cutting light in the ultraviolet region of about 400 nm or less, as indicated by a broken line in the graph of FIG. The filter 17 is inserted between the optical fixing device 16 and the conveyance path so as to be detachable between an insertion position facing the light emitting surface of the optical fixing device 16 and a retracted position retracted from the insertion position. It has been.

  When performing the light fixing (Y light fixing) of the yellow thermosensitive coloring layer, the filter 17 moves to the insertion position. As a result, of the light emitted from the optical fixing device 16, light in the ultraviolet region including magenta fixing light is cut, and only the yellow fixing light transmitted through the filter 17 is irradiated onto the color thermal recording paper 11. For this reason, only the yellow thermosensitive coloring layer is photofixed, and the unrecorded magenta thermosensitive coloring layer is not photofixed. When performing light fixing (M light fixing) of the magenta thermosensitive coloring layer, the filter 17 is moved to the retracted position, and the yellow fixing light and the magenta fixing light are irradiated from the optical fixing device 16 to the color thermosensitive recording paper 11. . In the M light fixing, since the Y light fixing has already been completed, there is no problem even if the color thermal recording paper 11 is irradiated with the yellow fixing light.

  FIG. 4 is an explanatory diagram showing an outline of the electrical configuration of the optical fixing device 16. A system controller 21 and a power supply circuit 22 that supplies power are connected to the optical fixing device 16. On the substrate 24 of the optical fixing device 16, an LED array composed of the element rows L1 to Ln and a driver IC 28 for driving the LED array are provided. The system controller 21 inputs drive signals (strobe signal, latch signal, drive data, clock signal) to the driver IC 28. The driver IC 28 drives the element rows L1 to Ln based on this drive signal.

  The driver IC 28 has constant current drive channels (hereinafter referred to as drive channels) Ch1 to Chn that are driven by passing a constant current through the element arrays L1 to Ln. Each of the drive channels Ch1 to Chn includes a constant current circuit 31 and a switching transistor Tr. The constant current circuit 31 is connected to the cathode side of the element array L, and is a constant current source that allows a constant current to flow through the element array L regardless of the voltage applied from the power supply circuit 22 to the anode of the element array L. The switching transistor Tr is turned on / off based on the drive signal, and controls energization of the element row L. Each drive channel Ch1 to Chn is provided for each element row L1 to Ln.

  Each output terminal of the AND gate array 41 is connected to the base terminals of the switching transistors Tr1 to Trn. Each element row L1 to Ln is pulse-driven by a periodically generated pulse signal. For example, the system controller 21 outputs a strobe signal that defines the maximum lighting frequency of each of the element arrays L1 to Ln to the AND gate array 41. This strobe signal is a pulse train having a predetermined pulse width and composed of a plurality of pulse signals generated at a predetermined cycle. The maximum lighting frequency of each of the element rows L1 to Ln and the maximum lighting time per driving pulse are defined by this strobe signal. A shift register 43 is connected to each input terminal of the AND gate array 41 via a latch array 42. The system controller 21 controls the lighting frequency for each element row L1 to Ln by outputting drive data for each element row L1 to Ln.

The drive data is binary data “1” or “0”, and is output in accordance with the pulse period of the strobe signal. Drive data for all the element rows L1 to Ln is serially input to the shift register 43 in synchronization with the clock signal. The drive data for each element array is shifted in the shift register 43 and converted into parallel drive data. The parallel drive data is transferred to the latch array 42 in synchronization with the clock signal.
The latch array 42 holds the transferred drive data. The drive data held in the latch array 42 is input to the AND gate array 41 in synchronization with the latch signal. The AND gate array 41 outputs a “H (high level)” signal when the drive data is “1” while the strobe signal is at a high level. When an “H” signal is output from the AND gate array 41, the switching transistors Tr1 to Trn are turned on, and the element rows L1 to Ln are turned on. When the drive data is “0”, since a “L (low level)” signal is output, the switching transistors Tr1 to Trn are not turned on, and the element rows L1 to Ln are not lit. The lamp control unit 31 controls the lighting frequency for each element row by changing the drive data output for each element row.

  In this way, the luminance of each element row L1 to Ln is adjusted by controlling the lighting frequency for each element row L1 to Ln. Thereby, for example, the illuminance of each of the element rows L1 to Ln is corrected so that the illuminance distribution in the main scanning direction is uniform. The illuminance unevenness of each of the element rows L1 to Ln may be detected in an inspection process before shipment, or an illuminance sensor that detects the illuminance of each of the element rows L1 to Ln in the vicinity of the optical fixing device in the printer or in the optical fixing device itself. (Not shown) may be provided, and the illuminance unevenness may be detected by the illuminance sensor.

  Further, protection transistors Q1 to Qn are provided between the element rows L1 to Ln and the drive channels Ch1 to Chn. The collector terminals of the protection transistors Q1 to Qn are connected to the cathodes of the element rows L1 to Ln, and the emitter terminals are connected to the driver IC 28. The base terminal is connected to the power supply circuit 22 and is supplied with a specified voltage Vreg. These protection transistors Q1 to Qn protect the driver IC by limiting the drive voltage applied to the driver IC 28.

  A drive voltage Vd is applied to the anodes of the element rows L1 to Ln. A voltage obtained by subtracting VFL of the element row L from the drive voltage Vd is input to the collector terminals of the protection transistors Q1 to Qn. The output voltage from the emitter terminal is determined by the base voltage applied to the base terminal regardless of the input voltage applied to the collector terminal. For this reason, since the output voltage from the emitter terminal can be made constant regardless of the input voltage to the collector terminal, the drive voltage of the driver IC can be stabilized.

  As described above, since there is a variation in the VFL of each of the element rows L1 to Ln, the drive voltage Vd is set to a higher value that anticipates the variation. For this reason, when the difference between the drive voltages Vd and VFL exceeds the minimum drive voltage required to drive the driver IC 28, the surplus is wasted by the driver IC 28. The variation in VF of one LED may reach 1 V at the maximum, and if the number of LEDs included in the element array is large, the variation in VFL increases accordingly. If the variation in VFL is large, the drive voltage Vd is set with a large margin so that the difference between the drive voltages Vd and VFL becomes very large depending on the column. This not only results in power loss, but also increases the heat generation of the driver IC 28, causing the IC to be destroyed in the worst case.

  The specified voltage Vreg is set so that the output voltage from the emitter terminal of the protection transistor Q becomes an optimum voltage (optimum driving voltage) for driving the driver IC 28. If the drive voltage necessary for driving the driver IC 28 is, for example, about 0.7V, 0.1V to 0.3V is added to this to obtain the optimum drive voltage. The specified voltage Vreg is set to 1.5 V, for example, so that this optimum driving voltage is applied to the driver IC 28.

  Hereinafter, the operation of the above configuration will be described. When a print instruction is given, printing is started. The recording paper 11 is fed, and a yellow image is first thermally recorded by the thermal head 12. When the yellow image is recorded, the recorded portion is sent to the optical fixing device 16, and the yellow image is optically fixed. At the time of this light fixing, since the filter 17 is at the insertion position, the recording paper 11 is irradiated only with the yellow fixing light. A drive voltage Vd is applied from the power supply circuit 22 to each of the element rows L1 to Ln. When a drive signal is given from the system controller 21 to the driver IC 28, the switching transistors Tr1 to Trn are turned on according to the drive signal, and a constant current flows through the element rows L1 to Ln to light them. At this time, since the protective transistors Q1 to Qn limit the input voltage to the driver IC 28, heat generation of the driver IC 28 is suppressed.

  When the yellow light fixing is completed, the color thermal recording paper 11 is once conveyed in the returning direction until the recording start position reaches the thermal head 12. Thereafter, thermal recording of the magenta image is started while being conveyed in the feeding direction again. The filter 17 moves to the retracted position during this return conveyance. When the magenta image is thermally recorded, the recorded portions are sequentially sent to the optical fixing device 16 and the magenta image is optically fixed. In the magenta fixing, similarly to the yellow fixing, the input voltage to the driver IC 28 is limited by the protection transistors Q1 to Qn, so that the heat generation of the driver IC 28 is suppressed.

  After the magenta light fixing is completed, the color thermal recording paper 11 is conveyed again in the returning direction, and then a cyan image is thermally recorded during conveyance in the third feeding direction. As a result, the recording of the full-color image is completed and the sheet is discharged.

  In the above-described embodiment, the example in which each element array is configured by one type of LED has been described. However, an LED array is configured by using two types of LEDs having different emission colors as in the optical fixing device 51 illustrated in FIG. May be.

  On the substrate 52 of the optical fixing device 51, a Y element array Ly to which a plurality of Y LEDs 53 that emit Y fixing light are connected in series and a plurality of Y LEDs 54 that emit M fixing light are connected in series. M element rows Lm are provided, and the element rows Ly and Lm are alternately arranged. The adjacent element rows Ly and Lm for Y and M are connected in parallel in a total of two rows, one each, and this is regarded as one group, one drive channel for each group. Ch1 to Chn are assigned. The Y element row Ly and the M element row Lm are not lit simultaneously but are selectively lit. In this way, the filter 17 used in the first embodiment is not necessary.

  SW1 is connected to the anodes of the Y element row Ly and the M element row Lm. SW1 is a switch for switching a power feeding path from the power supply circuit 22 to each of the element arrays Ly and Lm. When a switching signal is input to SW1 by the system controller 21, the Y element array Ly and the M element array Lm are switched. The power feeding path is selectively switched. The system controller 21 sends a control signal to the power supply circuit 22 to control switching between the drive voltage Vdy of the Y element array Ly and the drive voltage Vdm of the M element array Lm. The power supply circuit 22 supplies the drive voltages Vdy and Vdm to the Y element row Ly and the M element row Lm, respectively, based on a control signal from the system controller 21. A plurality of types of LEDs having different emission wavelengths (emission colors) have different VFs. Therefore, the power loss can be suppressed by changing the drive voltage Vd according to the type.

  The current detection circuit 56 detects the current supplied from the power supply circuit 22 to the optical fixing device 51, and connects the cutoff signal to the base terminal of the protection transistor Q when the current exceeds a predetermined value. Output to SW2. SW2 is a cutoff switch that turns off when receiving a cutoff signal and stops the voltage output to the protection transistor Q. As a result, the protection transistor Q is turned off, and the light emission of the optical fixing device 51 is stopped. As a result, an abnormal current flows from the power supply circuit 22 and the optical fixing device 51 is prevented from being destroyed. Thus, by providing the protection transistor Q and combining it with the SW2 and the current detection circuit 56, the current cutoff circuit can be configured easily.

  Alternatively, the luminance of each element row may be adjusted by inputting a luminance adjustment pulse of each element row from the system controller 21 to SW2 and duty-controlling the protection transistor Q. When a brightness adjustment pulse is input to SW2, SW2 is turned on / off in response to the pulse, and the protection transistor Q is also turned on / off. Thereby, the element row L is driven according to the luminance adjustment pulse.

  As shown in the first embodiment, the luminance adjustment is often performed based on a drive signal input to the driver IC 28. However, the drive signal input to the driver IC 28 is often disturbed by noise, causing the driver IC 28 to malfunction. Such malfunction can be prevented by adjusting the brightness with the protection transistor Q separately from the driver IC 28. This also simplifies the control by the driver IC 28, and thus contributes to a reduction in cost by simplifying the configuration.

  In addition, the number (three) of LED which comprises the element row | line | column shown in the said example is an example, These numbers can be changed suitably. In addition, the configuration in which one drive channel is shared by two types of LEDs (for Y and M) has been described, but it may be shared by three or more types of LEDs, or may be shared by more than that. Moreover, although LED was demonstrated to the example as a light emitting element, various light emitting elements, such as EL (Electro Luminescence) element, can be used besides this, for example.

  In the above embodiment, the light source device of the present invention has been described as an example used in a light fixing device of a thermal printer. It can be used for various applications such as a warning device (for example, an on-vehicle stop lamp). The type (light emission color) of the light emitting element is appropriately selected according to such applications.

1 is a configuration diagram illustrating an outline of a color thermal printer. FIG. It is explanatory drawing of the light emission surface of an optical fixing device. It is a graph which shows the spectral characteristic of LED, and the transmission characteristic of a filter. It is a block diagram which shows the electric structure which controls an optical fixing device. It is explanatory drawing in the case of sharing one drive channel with two types of element rows.

Explanation of symbols

1 Color Thermal Printer 16 Light Fixer 21 System Controller 22 Power Supply Circuit 26 LED
28 Driver IC
Ch1 to Chn Constant current drive channel L1 to Ln Element array Tr1 to Trn Switching transistor Q1 to Qn Protection transistor

Claims (10)

At least one light emitting element array in which a plurality of light emitting elements are connected in series;
A driver IC having at least one constant-current drive channel that drives by driving a constant current through each light-emitting element row even if a drive voltage applied from a power source to the anode of the light-emitting element row exceeds a predetermined value;
A light source provided for each of the constant current drive channels, having a collector terminal connected to the cathode of the light emitting element array, an emitter terminal connected to the driver IC, and a transistor to which a predetermined voltage is applied to the base terminal. apparatus.   The light source device according to claim 1, wherein the voltage applied to the base terminal is determined based on a forward voltage of the light emitting element array.   3. The light source device according to claim 1, further comprising a switch for turning on / off a voltage applied to the base terminal.   The light-emitting device according to claim 1, wherein the light-emitting element rows are connected in parallel in a plurality of rows.   5. The light source device according to claim 4, wherein each of the constant current drive channels drives at least one light emitting element array.   The light source device according to claim 5, wherein the plurality of light emitting element arrays include a plurality of types of light emitting element arrays having different emission colors.   The power supply path switching means is provided between the anode of each of the plurality of types of light emitting element arrays and a power source, and selectively switches a power supply path to each of the light emitting element arrays for each type. 6. The light source device according to 6.   8. The light source device according to claim 7, further comprising drive voltage switching means for changing a drive voltage of each light emitting element row for each type.   9. The light source device according to claim 7, wherein the plurality of types of light emitting element arrays are alternately arranged. 10. The light source device according to claim 9, wherein one constant current drive channel is shared by a plurality of light emitting element arrays of different types.

Images