Abstract:
A temperature control device for controlling temperature of an object substance, the temperature control device includes: a pulse width modulator for changeably providing current directions of a providing current; a low pass filter; a Peltier device electrically connected to the pulse width modulator via the low pass filter; and a diode placed the low pass filter in parallel.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2007-337394, filed on Dec. 27, 2007, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    This art relates to a temperature control device for controlling a temperature. 
       BACKGROUND 
       [0003]    Temperature control devices for controlling the temperature of an object substance, which needs to be temperature controlled, such as a sheet mounted on one of an optical communication device, a medical apparatus, and a wheeled vehicle (see Japanese Laid-open Patent Publication No. 07-20950) have been conventionally available. Such a temperature control device is briefly described with reference to  FIG. 3A ,  FIG. 3B ,  FIG. 4A  and  FIG. 4B .  FIG. 3A  and  FIG. 3B  illustrate a structure of a conventional temperature control device  10 .  FIG. 4A  and  FIG. 4B  illustrate a structure of a Peltier device  50 . 
         [0004]    As illustrated in  FIG. 3A  and  FIG. 3B , the conventional temperature control device  10  includes a Pulse Width Modulator (PWM)  20 , a first low-pass filter  31 , a second low-pass filter  32 , and a Peltier device  50 . Each of the first low-pass filter and the second low-pass filter  32  is arranged and connected between the PWM  20  and the Peltier device  50  in a state that allows a current output from the PWM  20  to be conducted therethrough, and removes an alternating current component contained in the current output from the PWM  20 . 
         [0005]    The conventional temperature control device  10  then heats an object substance  58 , arranged next to the Peltier device  50 , with the Peltier device  50  when the current output from the PWM  20  in a predetermined direction (for example, an X direction) flows through the first low-pass filter  31 , the Peltier device  50 , and the second low-pass filter  32  in that order as shown in a portion  FIG. 3A . 
         [0006]    More in detail, the conventional temperature control device  10  causes the current output from the PWM  20  in the predetermined direction (for example, in the X direction) to flow through a p-type lower electrode  55 , a p-type semiconductor  53 , an upper electrode  52 , an n-type semiconductor  54 , and an n-type lower electrode  56  in that order in the Peltier device  50  as shown in a portion  FIG. 4A . The conventional temperature control device  10  then absorbs heat via a lower substrate  57 , and discharges heat via an upper substrate  51 , by means of holes in the p-type semiconductor  53  and electrons in the n-type semiconductor  54 , thereby heating an object substance  58  arranged adjacent to the upper substrate  51 . 
         [0007]    A heating efficiency of the Peltier device  50  is now discussed further. A magnitude of the current flowing in the X direction is represented by the following equation (1). Here, “I” represents the magnitude of the current. Also, “I(0)” represents the magnitude of a direct current component of the “I.” Further, “A(n)” and “B(n) represent coefficients of an alternating current component of the “I.” Further, “n” represents a natural number. Further, “ω” represents an angular frequency. Further, “t” represents a time length. Further, “Σ” represent a sequence of numbers with respect to “n.” Further, “*” represents a multiplication operation. 
         [0000]        I=I   0 Σ( A ( n )*sin( nωt )+ B ( n )*cos( nωt )   (1) 
         [0008]    Then, it can be assumed that equation (2) including equation (2-1), equation (2-2), and equation (2-3) holds true. Here, “n(1)” and “n(2)” represent predetermined natural numbers. 
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         [0009]    Equation (1) is integrated with reference to t of from “0 (zero)” to “τ” sufficiently large in comparison with “I”, and then if equation (2) is substituted into the integration results, equation (3) including the following equations (3-1) and (3-2) are calculated. 
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         [0010]    Also, a relationship between an amount of heat added by the Peltier device  50  and the magnitude of the current is represented by the following equation (4). Here, “Q(x)” represents the heat added. Further, “Π(pi)” represents a Peltier coefficient. Further, “S” represents a thermal resistance when heat is absorbed via the lower substrate  57  and when heat is discharged via the upper substrate  51 . Further, “ΔT” represents a temperature difference between the upper substrate  51  and the lower substrate  57 . Further, “R” represents an electrical resistance of the Peltier device  50 . 
         [0000]        Q ( x )=Π* I−S             T +(½) I   2   R    (4) 
         [0011]    If equation (4) is integrated with respect to t from “0 (zero)” to “τ,” the following equation (5) results from equation (4). 
         [0000]      ∫  Q ( x ) dt=Π*∫ Idt−S             T  τ+(½) R*∫ I   2   dt    (5) 
         [0012]    If equation (3) is substituted in equation (5), equation (5) may be modified into the following equation (6). 
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         [0013]    A third term of the right side of equation (6) means that the Joule heat caused by the alternating current component (heat generation caused by the electrical resistance) is contained. More specifically, when the object substance  58  is heated by the Peltier device  50 , the alternating current component contained in the current flowing in the X direction contributes to the heating efficiency. 
         [0014]    On the other hand, the conventional temperature control device  10  cools the object substance  58 , arranged adjacent to the Peltier device  50 , with the Peltier device  50  if a current output from the PWM  20  in a direction opposite from the predetermined direction (for example, in a Y direction) is conducted through the second low-pass filter  32 , the Peltier device  50 , and the first low-pass filter  31  in that order as shown in a portion  FIG. 3B . 
         [0015]    More in detail, the conventional temperature control device  10  causes the current to flow through the n-type lower electrode  56 , the n-type semiconductor  54 , the upper electrode  52 , the p-type semiconductor  53 , and the p-type lower electrode  55  in that order in the Peltier device  50  in the opposite direction from the PWM  20  opposite from the predetermined direction (for example, in the Y direction) as shown in a portion  FIG. 4B . In this case, the conventional temperature control device  10  discharges heat via the lower substrate  57  and absorbs heat via the upper substrate  51  by means of holes in the p-type semiconductor  53  and electrons in the n-type semiconductor  54 , thereby cooling the object substance  58  arranged adjacent to the upper substrate  51 . 
         [0016]    A cooling efficiency of the Peltier device  50  is also described. A relationship between an amount of heat absorbed by the Peltier device  50  and a magnitude of a current is represented by the following equation (7). Here, “Q(y)” represents the absorbed heat amount. 
         [0000]      ∫  Q ( y ) dt=Π*∫ I−S             T  τ−(½) R*∫ I   2   dt    (7) 
         [0017]    In the same manner as described with reference to the heating efficiency of the Peltier device  50 , equation (7) may be modified into the following equation (8). 
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         [0018]    A third term of equation (8) means that the Joule heat caused by an alternating current component is contained. More specifically, when an object substance  58  is cooled by the Peltier device  50 , the alternating current component contained in the current flowing in the Y direction means a drop in the cooling efficiency. 
         [0019]    The related art described above has a problem that the alternating current component contained in the current is not effectively used. More specifically, the conventional temperature control device  10  has a problem that since the conventional temperature control device  10  typically has an apparatus structure including a low-pass filter, the alternating current component contained in the current is removed and the alternating current component contributing to the heating efficiency is not effectively used. 
       SUMMARY 
       [0020]    According to an aspect of the embodiment, a temperature control device for controlling temperature of an object substance, the temperature control device includes: a pulse width modulator for changeably providing current directions of a providing current; a low pass filter; a Peltier device electrically connected to the pulse width modulator via the low pass filter; and a diode placed the low pass filter in parallel. 
         [0021]    Additional objects and advantages of the invention (embodiment) will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
         [0022]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1A  and  FIG. 1B  illustrate a summary and features of a temperature control device of a first embodiment. 
           [0024]      FIG. 2  is a block diagram illustrating a structure of a temperature control device. 
           [0025]      FIG. 3A  and  FIG. 3B  illustrate a structure of a conventional temperature control device. 
           [0026]      FIG. 4A  and  FIG. 4B  illustrate a structure of a Peltier device  50 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    The embodiments of the temperature control device are described below in detail with reference to the accompanying drawings. In the discussion of the embodiments, the present embodiments are applied to a temperature control device controlling a temperature of a laser element mounted on a semiconductor laser for use in an optical communication apparatus, 
       Embodiment 1 
       [0028]    In the following discussion of an embodiment 1, a summary and features of the temperature control device  10  of the embodiment 1, a structure of the temperature control device  10 , and a process flow of the temperature control device  10  are described in that order, and advantages of the embodiment 1 are described finally. 
         [0029]    The summary and features of the temperature control device  10  of the embodiment 1 is described first with reference to  FIG. 1A  and  FIG. 1B .  FIG. 1A  and  FIG. 1B  illustrate the summary and features of the temperature control device  10  of the embodiment 1. 
         [0030]    The temperature control device  10  of the embodiment 1 includes a Pulse Width Modulator (PWM)  20 , a first low-pass filter  31  (a smoothing circuit), a second low-pass filter  32 , and a Peltier device  50 . Each of the first low-pass filter  31  and the second low-pass filter  32  is arranged and connected between the PWM  20  and the Peltier device  50  in a state that allows a current output from the PWM  20  to be conducted therethrough, and remove an alternating current component contained in the current output from the PWM  20 . 
         [0031]    The temperature control device  10  of the embodiment 1 controls the temperature of the laser element so that the laser element arranged adjacent to the Peltier device  50  is heated by the Peltier device  50  if a current output from the PWM  20  in an X direction is conducted through the first low-pass filter  31 , the Peltier device  50 , and the second low-pass filter  32  in that order as shown in a portion  FIG. 1A  and so that the laser element arranged adjacent to the Peltier device  50  is cooled by the Peltier device  50  if a current output from the PWM  20  in a Y direction opposite from the X direction is conducted through the second low-pass filter  32 , the Peltier device  50 , and the first low-pass filter  31  in that order as shown in a portion  FIG. 1B . 
         [0032]    Under such an arrangement, the main feature of the temperature control device  10  of the embodiment 1 is that the temperature control device  10  of the embodiment 1 further includes a first diode (rectifier) connected in parallel with the first low-pass filter  31  and a second diode connected in parallel with the second low-pass filter  32 . 
         [0033]    The temperature control device  10  of the embodiment 1 causes the current output from the PWM  20  in the X direction not to flow and to bypass the first low-pass filter  31  and the second low-pass filter  32  when the current is conducted through the first low-pass filter  31 , the Peltier device  50 , and the second low-pass filter  32  in that order, and causes the current output from the PWM  20  in the Y direction to flow through the second low-pass filter  32  and the first low-pass filter  31  when the current is conducted through the second low-pass filter  32 , the Peltier device  50 , and the first low-pass filter  31  in that order. 
         [0034]    More specifically, the temperature control device  10  of the embodiment 1 causes the current output from the PWM  20  in the X direction to flow through the first low-pass filter  31 , the Peltier device  50 , and the second low-pass filter  32  in that order as shown in a portion  FIG. 1A  when the laser element arranged adjacent to the Peltier device  50  is to be heated. The temperature control device  10  thus causes the alternating current component contributing to the heating efficiency to input to the Peltier device  50 . 
         [0035]    Also, the temperature control device  10  of the embodiment 1 causes the current output from the PWM  20  in the Y direction to flow through the second low-pass filter  32 , the Peltier device  50 , and the first low-pass filter  31  in that order as shown in a portion  FIG. 1B  when the laser element arranged adjacent to the Peltier device  50  is to be cooled. The temperature control device  10  thus removes the alternating current component lowering the cooling efficiency from the current input to the Peltier device  50 . 
         [0036]    In this way, the temperature control device  10  of the embodiment 1 can effectively utilize the alternating current component contained in the current. 
       Structure of the Temperature Control Device 
       [0037]    Next, the structure of the temperature control device  10  of  FIG. 1A  and  FIG. 1B  are described with reference to  FIG. 2 .  FIG. 2  is a block diagram illustrating the structure of the temperature control device  10 . As illustrated in  FIG. 2 , the temperature control device  10  includes a PWM  20 , a first low-pass filter  31 , a second low-pass filter  32 , a first diode  41 , a second diode  42 , and a Peltier device  50 . 
         [0038]    The PWM  20  out of these elements controls and outputs a current input from a power supply. More specifically, the PWM  20  outputs the current in an X direction to heat the laser element. Also, the PWM  20  outputs the current in a Y direction to cool the laser element. 
         [0039]    The first low-pass filter  31  is arranged and connected between the PWM  20  and the Peltier device  50  in a state that a current output from the PWM  20  is conducted therethrough, and removes an alternating current component from the current output from the PWM  20 . More specifically, the first low-pass filter  31  receives the current output from the PWM  20  and flowing in the Y direction, removes the alternating current component, and outputs power to the Peltier device  50 . 
         [0040]    The second low-pass filter  32  arranged and connected between the PWM  20  and the Pettier device  50 , in a state that a current output from the PWM  20  is conducted therethrough, in a path different from the path of the first low-pass filter  31 , and removes the alternating current component contained in the current output from the PWM  20 . More specifically, the second low-pass filter  32  receives the current output from the PWM  20 , conducted through the Peltier device  50  and flowing in the Y direction, removes the alternating current component, and outputs power to the PWM  20 . 
         [0041]    When the current output from the PWM  20  in the X direction is conducted through the first low-pass filter  31 , the Peltier device  50 , and the second low-pass filter  32  in that order, the first diode  41 , connected in parallel with the first low-pass filter  31 , causes the current not to flow through, thus, to bypass the first low-pass filter  31 . 
         [0042]    More specifically, the first diode  41  is a PN junction diode or the like, which is manufactured by joining a p-type semiconductor  53  and an n-type semiconductor  54 . When receiving the current output from the X direction from the PWM  20 , the first diode  41  becomes smaller in electrical resistance (low-impedance), and tends to allow the current in the X direction to flow easily therethrough. As a result, the first diode  41  causes the current not to flow through, thus, to bypass the first low-pass filter  31 . The first diode  41  outputs the received current to the Peltier device  50 . 
         [0043]    On the other hand, when the current output from the PWM  20  in the Y direction is conducted through the second low-pass filter  32 , the Peltier device  50 , and the first low-pass filter  31  in that order, the first diode  41  causes the current to flow through the first low-pass filter  31 . 
         [0044]    More specifically, the first diode  41  becomes higher in electrical resistance (high impedance) when receiving the current output from the PWM  20 , flowing through the Peltier device  50  in the Y direction. The first diode  41  conducts less current flowing therethrough in the Y direction, thereby causing the first low-pass filter  31  to conduct the current. 
         [0045]    The second diode  42  is connected in parallel with the second low-pass filter  32 . When the current output from the PWM  20  in the X direction is conducted through the first low-pass filter  31 , the Peltier device  50 , and the second low-pass filter  32  in that order, the second diode  42  causes the current not to flow through, thus to bypass the second low-pass filter  32 . 
         [0046]    More specifically, the second diode  42  becomes lower in electrical resistance (low impedance) when receiving the current output from the Peltier device  50  in the X direction. The second diode  42  tends to conduct the current in the X direction to flow easily, thereby causing the current not to flow through, thus to bypass the second low-pass filter  32 . The second diode  42  outputs the received current to the Peltier device  50 . A lower electrical resistance of the second diode  42  reduces an electrical resistance which the current from the PWM  20  in the X direction and then flowing back to the PWM  20  is subject to, and means that the alternating current component in the current in the X direction more easily flows therethrough. 
         [0047]    On the other hand, when the current output from the PWM  20  in the Y direction is conducted through the second low-pass filter  32 , the Peltier device  50 , and the first low-pass filter  31  in that order, the second diode  42  causes the second low-pass filter to conduct the current. 
         [0048]    More specifically, the second diode  42  becomes higher in electrical resistance (high impedance) when receiving the current output from the PWM  20  in the Y direction. The second diode  42  causes less current in the Y direction to flow therethrough, thereby allowing the second low-pass filter  32  to conduct the current, 
         [0049]    The Peltier device  50  controls the temperature of the laser element by heating the laser element adjacent thereto when the current output from the PWM  20  is conducted through the first low-pass filter  31 , the Peltier device  50 , and the second low-pass filter  32  in that order, and by cooling the laser element adjacent thereto when the current output from the PWM  20  is conducted through the second low-pass filter  32 , the Peltier device  50 , and the first low-pass filter  31  in that order 
         [0050]    More specifically, the Peltier device  50  heats the laser element adjacent thereto when receiving the current output from the PWM  20  in the X direction which has flown through the first diode but bypassed the first low-pass filter  31 . On the other hand, the Pettier device  50  cools the laser element adjacent thereto when receiving the current output from the PWM  20  in the Y direction from which the alternating current component has been removed by the second low-pass filter  32 . 
       Advantages of the Embodiment 1  
       [0051]    Since the current is set not to flow but bypass the first low-pass filter  31  to heat the object substance  58  in accordance with the embodiment 1 as described above, the alternating current component contained in the current is effectively utilized. 
         [0052]    If the current is output from the PWM  20  in the X direction, for example, at 50% of the output thereof, the Joule heat (heat generation caused by an electrical resistance) caused by the alternating current component indicated by the third term of the above described equation (6) equals the Joule heat caused by the direct current component, and the contribution of the Joule heat in the heating efficiency is advantageously doubled. 
         [0053]    For example, if a power consumption of the Peltier device  50  is “0.2 W (watt)” with “R=5Ω (ohms) and “I(0)=0.2 A (ampere) in the third term of the above equation (6) during heating, the alternating current component generating the Joule heat corresponding to half of consumption power is effectively and advantageously utilized. 
       Embodiment 2  
       [0054]    The embodiment 1 has been discussed, and the present invention may be implemented in a variety of embodiments other than the above-described embodiment. Another embodiment is described as an embodiment 2. 
         [0055]    In accordance with the embodiment 1, for example, the temperature control device  10  including the first low-pass filter  31 , the second low-pass filter  32 , and the Peltier device  50  further includes the first diode  41  and the second diode  42 . The present invention is not limited to this embodiment. For example, a temperature control device  10  may include additionally the first diode  41  but excludes the second diode  42 . In the temperature control device  10 , the current to be conducted through the first low-pass filter  31 , the Peltier device  50 , and the second low-pass filter  32  in that order may be set not to flow through and bypass the first low-pass filter  31 . 
         [0056]    The bypassing of the alternating current component in the temperature control device  10  of the embodiment 1 can fluctuate the temperature of the laser element. However, if the current from the PWM  20  is controlled and output with a period shorter than a thermal time constant of the laser element, the temperature of the laser element can be finely controlled. 
         [0057]    The specific names and the controlled object substance  58  described above in the specification and illustrated in the drawings may be modified as appropriate unless otherwise noted. Also, the illustrated elements represent the functional concepts thereof, and are not necessarily physically constructed exactly as illustrated. For example, the structure of the first low-pass filter  31  and the second low-pass filter  32 , illustrated in  FIG. 2 , and the structure of the Peltier device  50  of  FIG. 4A  and  FIG. 4B  are not limited to those illustrated, and can be modified as appropriate unless otherwise noted. 
         [0058]    The above-described structures of the temperature control device  10  are only embodiments, and the temperature control device  10  and the size of each element of the temperature control device  10  can be modified as appropriate and embodied. 
         [0059]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.