# Patent

## Title
Temperature control device

## 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.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
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
This art relates to a temperature control device for controlling a temperature.
BACKGROUND
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.
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.
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.
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.
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.

I=I0+Σ(A(n)*sin(nωt)+B(n)*cos(nωt)  (1)

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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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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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.

Q(x)=Π*I−ST+(1⁄2)I2R  (4)

If equation (4) is integrated with respect to t from “0 (zero)” to “τ,” the following equation (5) results from equation (4).

∫Q(x)dt=Π*∫Idt−STτ+(1⁄2)R*∫I2dt  (5)

If equation (3) is substituted in equation (5), equation (5) may be modified into the following equation (6).




  
    
      
        
          
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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.
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.
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.
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.

∫Q(y)dt=Π*∫I−STτ−(1⁄2)R*∫I2dt  (7)

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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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.
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
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.
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.
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
FIG. 1A and FIG. 1B illustrate a summary and features of a temperature control device of a first embodiment.
FIG. 2 is a block diagram illustrating a structure of a temperature control device.
FIG. 3A and FIG. 3B illustrate a structure of a conventional temperature control device.
FIG. 4A and FIG. 4B illustrate a structure of a Peltier device 50.



DESCRIPTION OF EMBODIMENTS
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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,
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
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
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.
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.
For example, if a power consumption of the Peltier device 50 is “0.2 W (watt)” with “R=5 Ω (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
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.
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.
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.
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.
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.
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.

## Claims

1. A temperature control device for controlling temperature of an object substance, the temperature control device comprising:
a pulse width modulator for changeably providing current directions of a providing current;
a first low pass filter;
a second low pass filter;
a Peltier device electrically coupled to the pulse width modulator via the first low pass filter and the second low pass filter, the first low pass filter being arranged between the pulse width modulator and the Peltier device, the second low pass filter being arranged between the pulse width modulator and the Peltier device;
a first diode placed in parallel with the first low pass filter in a forward bias direction between from the pulse width modulator to the Peltier device; and
a second diode placed in parallel with the second low pass filter in a forward bias direction between from the Peltier device to the pulse width modulator.

2. The temperature control device of claim 1, wherein the pulse width modulator applies the current to the Peltier device via the first diode and the second diode so that a laser element adjacent to the Peltier device is heated.

3. The temperature control device of claim 1, wherein the pulse width modulator modulates the current to be smaller period than a thermal time constant of the object substance.

4. A temperature control device for controlling temperature of an object substance, the temperature control device comprising:
a pulse width modulator for changeably providing current directions of a providing current;
a first low pass filter;
a second low pass filter;
a Peltier device electrically coupled to the pulse width modulator via the first low pass filter and the second low pass filter, the first low pass filter being arranged between the pulse width modulator and the Peltier device, the second low pass filter being arranged between the pulse width modulator and the Peltier device; and
a diode placed in parallel with the first low pass filter in a forward bias direction between from the pulse width modulator to the Peltier device.

5. The temperature control device of claim 1, wherein each of the first diode and the second diode is a PN junction diode that becomes a low-impedance when receiving a current having the forward bias direction.

6. The temperature control device of claim 1, wherein the temperature control device operates to control temperature of a laser element arranged adjacent to the Peltier device.

7. The temperature control device of claim 4, wherein the temperature control device operates to control temperature of a laser element arranged adjacent to the Peltier device.

8. An apparatus comprising:
a pulse width modulator for changeably providing current directions of a providing current;
a first low pass filter;
a second low pass filter;
a Peltier device electrically coupled to the pulse width modulator via the first low pass filter and the second low pass filter, the first low pass filter being arranged between the pulse width modulator and the Peltier device, the second low pass filter being arranged between the pulse width modulator and the Peltier device;
a first diode placed in parallel with the first low pass filter; and
a second diode placed in parallel with the second low pass filter.

9. The apparatus of claim 8, wherein the apparatus operates to control temperature of a laser element arranged adjacent to the Peltier device.