WO2012089863A1

WO2012089863A1 - Symmetrical flow temperature control apparatus for electronic devices with a cylindrical geometry

Info

Publication number: WO2012089863A1
Application number: PCT/ES2011/000373
Authority: WO
Inventors: Francisco Javier RÍOS GOMEZ; Jorge ROMERO SÁNCHEZ; Raquel FERNÁNDEZ RAMOS; José Franncisco MARTÍN CANALES; Francisco Javier MARTÍN MARTÍN
Original assignee: Universidad De Málaga
Priority date: 2010-12-27
Filing date: 2011-12-23
Publication date: 2012-07-05
Also published as: ES2362232A1; ES2362232B2

Abstract

Symmetrical thermal flow temperature control apparatus for electronic devices with a cylindrical geometry, comprising: - a metal block (18) which accommodates the electronic device (19); - four Peltier cells (16) which exchange heat with the block (18); - a heat exchanger which exchanges heat with the Peltier cells (16), comprising a frame (15) in contact with the Peltier cells (16) and four heat sinks (5) attached to each outer side of the frame (15); - a temperature sensor (11) for the block; - a temperature sensor (6) for the heat exchanger; - a controller (31) for the Peltier cells for controlling the current which flows through the Peltier cells (16) and the direction of flow thereof; - data processing means (30), which apparatus receives the temperatures of the block (18) and of the heat exchanger and controls the current in the Peltier cells (16) and the direction of flow thereof in order to keep the temperature of the block (18) under control.

Description

Symmetric flow thermoregulator device for electronic devices with cylindrical geometry

Field of the Invention

The invention presented is framed in the field of mechanical and electronic industry for thermal control and regulation applications in electronic components and devices.

Background of the invention

In general terms, electronic devices have varied geometric shapes. The integrated circuits have a parallelepiped shape and contain many active devices that produce heat, their distribution being dependent on their arrangement. Discrete devices can have a cylindrical or rectangular shape at the crystalline level and are normally encapsulated in cylindrical shapes. The discrete power devices contain gels or thermoconducting liquids that bathe the crystalline structure causing the heat transferred to be distributed homogeneously over the cylindrical capsule that contains them.

On the other hand, passive coolers based on heat exchange fins by air convection can have cylindrical geometry (hugging the equally cylindrical capsule), rectangular or circular with fins with a flat shape where it contacts the discrete or integrated circuit of similar form.

There are no solid-state heat pumps that adapt to a geometry (their shapes are rectangular, circular or annular), always obeying the presentation of two opposite faces in the space for the cold focus and the hot focus. Therefore, it is necessary to use these devices forming spatial structures that allow adapting the characteristics of the generated flows.

The spatial thermal standardization in radial or axial geometries applied to devices with the same geometry allows them to minimize the mechanical stresses generated by thermal gradients, stabilize their electrical characteristics and increase their durability.

W. Koechner, in his book 'Solid State Laser Engineering' 2006 Springer, suggests the use of symmetrical thermoregulatory devices for cooling high-power gas-based lasers in order to standardize their electrical and mechanical behavior. One of the most common problems in electronic engineering is to find solutions to the problem of thermoregulation of electronic circuits and components that must maintain specific thermal conditions for their operation. Semiconductor devices, by their nature, are strongly dependent on temperature. When semiconductors are used in sensors and actuators, a thermal control strategy should be designed to ensure that they remain in the proper thermal operating ranges.

On the other hand, a thermal change involves not only a deviation from the electrical characteristics of the device, but also a phenomenon of aging and mechanical alteration. A semiconductor device subjected to extreme temperatures, undergoes alterations in carrier injection levels and its non-linear behavior induces to force the electric targets in inadequate thermal zones. If, in addition, the thermal changes are not isotropic in the semiconductor, irregular thermal gradients occur that cause the appearance of stresses and deformations in the crystalline structure altering the durability and functional characteristics.

In general, an electronic device working at its point of operation tends to warm above room temperature generating a heat flow to the outside. This thermal gradient reaches an equilibrium condition that keeps the device at a stable temperature that will be adequate or not. Any change in environmental conditions causes a change in the gradient tending towards a new equilibrium condition and at another temperature. The semiconductor propagates heat by conduction to the substrate, terminals, capsule, heat exchanger medium (thermal radiator, if it exists) and by simple or forced convection, to the surrounding air. For a given air temperature, a stable thermal gradient not necessarily uniform and a stable device temperature will also be achieved. The purpose of a thermal regulator is to ensure that the temperature of the device or its thermal state is in the optimal position, maximizing its performance and durability without causing mechanical deformations.

The use of devices based on thermoelectric phenomena, allows us to go beyond the simple search for thermal exchange. These devices allow us to generate heat flows between two zones, hot and cold, by the application of an electric current.

In this invention a thermal regulating apparatus is presented that makes use of peltier cells in a geometric configuration that generates a controlled heat flow symmetrically along an axis. A cylindrical device located on this axis undergoes a homogeneous heat exchange generating flow with axial symmetry. Thus the associated thermal gradient is uniform in all planes perpendicular to the axis of the cylinder. This invention is specially designed for the heat treatment of electronic devices with cylindrical shape. That is, the semiconductor active elements must have a cylindrical shape such as optoelectronic devices such as VCSEL laser diodes or avalanche photodiodes.

A peltier cell is a thermoelectric device that functions as a small heat pump. The peltier cell has two faces. A direct current applied to a peltier cell causes a heat flow that cools one side and heats the other. When a peltier cell is connected to a suitable voltage source, a heat flow is generated that decreases until a maximum temperature difference is reached. If heat is supplied to the cold face, it will absorb a maximum amount of heat when the temperature equality between the two faces is reached again. Like mechanical refrigerators, a peltier cell is governed by the same fundamentals and principles of thermodynamics. The hot face of a peltier cell normally uses an heat exchanger or heat sink that, by convection, exchanges heat with the surrounding air. To increase heat exchange, forced ventilation is usually used with fans that propel the air over the heatsink.

Analytically, if T _c is the cold face temperature and T _h the hot face temperature (temperature expressed in ° K), the heat flow absorbed or heat transfer rate Q _c by the cold face in watts is given by:

Q _C = (ST _C I) - (¿/ ² - K) - Κ - ΔΤ (1) where 5 is the Seebeck coefficient evaluated on the hot and cold faces, / the electric current flowing through the cell (in amps) , R the thermal resistance of the cell (in ohms), K the thermal conductance of the cell (in watts / ° K), evaluated on the hot and cold faces and ΔΓ = T _h - T _c the temperature difference between the two faces. On the other hand, the heat flux ceded Q _h by the hot face, in watts, is given by:

Qh = Qe + Pc (2) where P _{c is} the power consumed by the cell in watts.

The temperature difference ΔΓ between the cold face and the hot face of the peltier cell is an essential variable for determining the heat transferred. The greater this difference, the greater the heat can be extracted. When this difference is zero, heat is not transferred and the hot and cold face temperatures equalize. If a target temperature outside the range set by ΔΓ is set in a regulation process, the regulation cannot be performed.

Regulation is an engineering field that studies the control of a process in a specific state. A thermal regulator is a system that allows constant temperature to be maintained in a target element within known ranges. The most stable regulated systems are those that are configured in closed loop. The target output variable is compared with a reference value defining an error parameter as the difference between these two values. Depending on this error variable, the regulator changes the target output until the error is at a certain value. In this invention, the regulation strategies or algorithms are carried out by means of a microcontroller that is part of the closed control loop. The microcontroller reads the input variables from temperature sensors and acts on the output variables (peltier cells and fans), after executing the regulation algorithm.

Description of the invention

In this invention a thermoregulator apparatus with symmetric thermal flux based on peltier cells for electronic devices with cylindrical geometry is presented.

The object of this invention is to keep the temperature of an electronic device with cylindrical geometry in a constant value throughout the space that surrounds it so that the absorption or transfer of heat in that space is carried out in a homogeneous way thus achieving the stability of its electrical characteristics, non-mechanical deformation and increased durability.

The apparatus consists of a metallic heat-conducting die that houses in its central axis the cylindrical capsule of the electronic device to be thermally controlled. Said die is in an adiabatic cavity connected to four peltier cells on four of its sides. The thermal exchange of the die is mainly done at through the faces of the four peltier cells that absorb or give heat to the die. The other side of each of the peltier cells is connected to a heat sink that exchanges heat with the surrounding air forced by fans.

The geometry that makes up the assembly allows to guarantee, as shown by simulation, that the heat flow generated in the die has a radial shape and with axisymmetric symmetry around the axis that contains the cylindrical capsule of the electronic device.

The air flow injected by the fans is driven by a microcontroller through a driver controlling their motors.

Peltier cells yield or absorb heat from the die by controlling the current flowing through them. Said control is carried out by a microcontroller and a driver with an electronic circuit that allows to exchange the direction of the current in the cells. Thus, the hot and cold faces of the cells can be exchanged by changing the direction of the current.

The die has a temperature sensor that measures its average temperature and whose value is read by the microcontroller. The temperature of this sensor is equal, in the first approximation, to the temperature of the face of the peltier cell that is in contact with the die.

The heat exchanger has a temperature sensor that measures its average temperature and whose value is read by the microcontroller. The temperature of this sensor is equal, in the first approximation, to the temperature of the face of the peltier cell that is in contact with the heatsink.

The maintenance of an objective temperature in the die is carried out by the closed loop assembly: temperature sensors, microcontroller, acting on the current and its direction in the peltier cells and acting on the volume of air injected into the heatsink by the fans.

The basic thermoregulation algorithm on the die, without subtracting generality, is as follows:

1. Set the target temperature of the die.

2. Set the value of the error variable.

3. Read the temperature of the dice.

4. Read the temperature of the heatsink.

5. Calculate the thermal range of the peltier cell ΔΓ.

5.1. If the target temperature is within the thermal range, continue. 5.2. If the target temperature is not attainable and the fans are not activated, activate the fans. Go to 3.

5.3. If the fans are not activated even if the target temperature is achieved, change the target temperature of the die to a value that is within the range of action except for a lower or upper limit in the range (it is a safety measure to not reach the maximum limits and minimums of the strip guaranteeing the possible non-linear dispersions that may occur). Go to 3.

5.4. If the temperature of the die exceeds the upper and lower margins of a safety threshold, disconnect the device to be thermoregulated. Get out.

Compare the temperature of the die with the target temperature.

Act on the peltier cells by heating or cooling the die until the thermal difference reaches the error variable.

Return to step 2.

Temporary periods of reading and acting must verify the stability criteria of the known control theory for the system time constant. Brief description of the drawings

A series of drawings that help to better understand the invention and that expressly relate to an embodiment of said invention which is presented as a non-limiting example thereof is described very briefly below.

Figures 1 A and 1 B show two views of the thermoregulator apparatus object of the present invention.

Figures 2A and 2B represent two views of the thermoregulator apparatus mounted on a laser transmitter.

Figure 3 represents a middle cross section of the thermoregulatory apparatus allowing to see the interior parts such as the die, the peltier cells and the heat exchanger.

Figure 4 shows an exploded view of the thermoregulatory apparatus with all its components. Figures 5A and 5B show two types of dice for two types of standard capsules T05 and T046 associated in this embodiment with a VCSEL laser and an avalanche photodiode respectively.

Figures 6A and 6B show, for the dice of Figures 5A and 5B respectively, the simulation result of the corresponding thermal gradients showing their symmetrical character around the axis of the die.

Figure 7 shows the schematic diagram of the driver and the control unit of the direction of the current in the peltier cells.

Figure 8 shows, finally, the functional block diagram that forms the control loop of the thermoregulator apparatus object of this invention.

Detailed description of the invention

In this invention a thermoregulator apparatus with symmetric thermal flux based on peltier cells for electronic devices with cylindrical geometry is presented. The symmetric flow thermoregulator apparatus 1, shown in different views in Figures 1A and 1 B, is constituted by a front support 2 and a rear support 3 of low thermal conductivity polycarbonate containing an adiabatic cavity supported by a frame, four heatsinks thermal 5 and four fans 4. In the presented embodiment, the thermoregulatory apparatus 1 and without subtracting generality, thermally controls a laser diode that is focused through an optical system consisting of a focusing tube 7 and an aspherical lens 8, all the assembly mounted by means of fixing means 12 (in the preferred embodiment, inserts) to a transmitter 14, as shown in Figures 2A and 2B, with electronic circuits for accessing terminals 13 of peltier cells and temperature sensors 6.

Figures 3 and 4 respectively represent a cross-section and an exploded view of the thermoregulatory apparatus in which all the components it possesses and their arrangement are shown. The frame 15 made of aluminum separates two spaces, one exterior and one interior, the interior containing the metal die 18 made of brass, four peltier cells 16 and the thermal insulators comprising lateral insulators 17 between peltier cells, back cover 20, rear closure 21, anterior lid 22 and anterior closure 23, which form an adiabatic cavity on die 18 in which the thermal exchange is mainly carried out through the faces of the peltier cells 16. On the axis of die 18 is the electronic device with cylindrical symmetry 19 (a laser diode in the presented embodiment), whose terminals they are accessible from the outside by the socket 9 being the laser beam transmitted from the opposite side through the focusing tube 7 and aspherical lens with support 8. The outer space that delimits the frame 15 together with the aluminum heat sinks 5 constitutes the heat exchanger through forced air provided by the fans 4. The fastening screws of the adiabatic cavity 26 are made of insulating plastic (nylon), while the rest 27, (28) and 29 (and 28) are made of steel. The frame 15 is attached to the front 2 and rear 3 brackets with the screws 27 and washers 25. The fans 4 are screwed to the front 2 and rear 3 brackets with the 28 screws. The temperature sensors 11 and 6 stick together, respectively , to die 18 (whereby the temperature sensor 11 constitutes the temperature sensor of the die) and to the frame 15 (whereby the temperature sensor 6 constitutes the temperature sensor of the heat exchanger). To maximize thermal contact, high conductivity glues and thermal pastes have been used. Thus, the peltier cells 16 are glued to the frame 15 on their inner faces (those of the frame). The die 18 has a solidarity contact with the faces of the peltier cells 16 by thermal paste (the die contacts thermal paste and is not glued with thermal glue). The die can be removed from the frame by removing the screws. The frame 15 is glued with thermal glue with a face of the peltier cells 16. The focusing tube 7 is glued to the die 18 with a thermal insulating glue in order to avoid thermal exchange with the optical system.

Figures 5A and 5B show two types of dice for two types of standard capsules T05 and T046 associated in this embodiment with a VCSEL laser and an avalanche photodiode respectively. Figures 6A and 6B show, respectively, the thermal gradient in the die for capsule cavity T05 and the thermal gradient in the die for capsule cavity T046, the result of a simulation, showing its symmetrical character around the axis of the die. In fact, the thermal gradient generated by the cylindrical surface from a die with four of its contiguous faces at constant temperature has radial geometry. The diffusive effects of heat within the die, considering it large enough (19mm sideways in the presented embodiment), make it possible for a thermal gradient initially perpendicular to the faces of the die, to end up forming a radial distribution in a cylinder located on its central axis.

Figure 7 shows the schematic of the driver or controller of the peltier cells 31 capable of controlling the direction of the electric current flowing through it. The peltier cell 16, is connected by each of its ends to the output of two CMOS inverters built with MOSFET transistors (M1-M3, M2-M4) of power (> 10 A). The current flowing through its sources converges on a common node to which the NMOS transistor of power M5 is connected and the peltier cell 16 can be controlled in On-Off mode through the base of the bipolar transistor Q3 connected to data processing means (preferably a microcontroller 30) through an output C, whereby if the output C = 0 (logical 0) the peltier cell 16 is in operation and if the output C = 1 (logical 1) the peltier cell 16 is off . The bases of the bipolar transistors Q1 and Q2, also connected to microcontroller 30 through outputs A and B, complement the corresponding doors of their associated CMOS inverters. Since the inputs of CMOS inverters are complementary, when one of them is activated the other is deactivated and vice versa. An analysis of currents of this topology, considering the transistor M5 in conduction, demonstrates that when the pair M1-M3 is activated (M2-M4 deactivated), transistors M1 and M4 enter conduction. Thus the current flows from left to right according to the direction M1->16-> M4, which occurs if the output A = 0 (0 logical) and the output B = 1 (1 logical). On the contrary, when the M1-M3 pair is deactivated (M2-M4 activated), the transistors M2 and M3 enter conduction generating a current from right to left according to the direction M2->16-> M3, which occurs if the output A = 1 (1 logical) and the output B = 0 (0 logical). Therefore, this circuit allows the direction of the current flowing through a peltier cell to be exchanged, causing its hot and cold faces to exchange their role according to this direction. This ability of the presented thermoregulator makes it possible to achieve the desired temperature target in shorter times than with conventional thermostat control methods, since thanks to this exchange, die heat is injected and extracted forcibly contributing to the increase in the natural speed of diffusion of heat in the material.

Figure 8 shows the diagram of functional blocks in closed loop for thermal control of the thermoregulator object of this invention. The temperature sensors 1 1 (die temperature sensor) and 6 (heatsink / rack temperature sensor) provide the microcontroller 30 with the temperatures of each of the faces of the peltier cell (interior and exterior, respectively) allowing to calculate the variable ΔΓ = T _h - T _c . On the other hand, the microcontroller 30 can act by generating PWM type pulses in the peltier cell controller 31, with control of the direction of the current in the peltier cells, creating the average current that causes heat transfer from one side to the other. of this. Controller 31 closes a first loop of control. A second loop is created in the operation of the microcontroller 30 on the fans 4, which act by exchanging forced air with the fins of the heat sink 5. According to the characteristics of the cell used in the presented embodiment, the maximum thermal difference with transfer of Null heat is ΔΓ = 66 ° C. Likewise, the maximum heat flux transferred, unlike zero temperature, is 28 watts. The fans generate a maximum air flow of 0.63 m ³ / min. The heat resistance of the heatsink is 7 ° C / W down to a minimum of approximately 2 ° C / W with maximum forced air flow. Considering the algorithm described above, the experimental measurements show that in environments with thermal differences not less than approximately 22 ° C, a die temperature can be found that remains constant regardless of the thermal changes that may occur. These results are valid for application in Mediterranean and Central European climates considering that the thermal changes that occur between day and night, on average, do not exceed 20 ° C.

Peltier cells are connected in series and act all at once. Similarly, the four fans 4 are activated all at once, that is, or all or none are activated.

Claims

1. - Symmetric thermal flux thermoregulator apparatus for electronic devices with cylindrical geometry, characterized in that it comprises:

- a metallic die (18) in charge of housing in its central axis the electronic device (19) of cylindrical geometry to be thermally regulated;

- four peltier cells (16), each with a first face in contact with each external side of the metal die (18), responsible for exchanging heat with the die (18);

- a heat exchanger responsible for exchanging heat with the peltier cells (16), comprising four heat sinks (5), each in thermal contact with the second face of each peltier cell (16);

- means for measuring the temperature of the die (11);

- temperature measuring means of the heat exchanger (6);

- a peltier cell controller (31), which allows the control of the current flowing through the peltier cells (16) and its direction of circulation;

- data processing means (30), responsible for receiving the temperatures of the die (18) and the heat exchanger and controlling through the peltier cell controller (31) the current of the peltier cells (16) and their sense of circulation to maintain the temperature of the die (18) regulated.

2. - Thermoregulatory apparatus according to claim 1, wherein the heat exchanger comprises a frame (15), the four peltier cells (16) each being attached by the second face to each internal side of the frame (15) and the four heat sinks (5) adhered each to each outer side of the frame (15).

3. - Thermoregulator apparatus according to claim 2, wherein the temperature measuring means of the heat exchanger comprises a temperature sensor (6) adhered to the frame (15).

4. - Thermoregulatory apparatus according to any of the preceding claims, wherein the means for measuring the temperature of the die comprises a temperature sensor (11) adhered to the die (18).

5. - Thermoregulatory apparatus according to any of the preceding claims, further comprising four fans (4), each facing each heatsink (5), the data processing means (30) being in charge of controlling said fans (4) .

6. - Thermoregulator apparatus according to claim 5, wherein the data processing means (30) are configured to effect the thermoregulation of the die (18) in closed loop, for which said data processing means (30) are configured to :

set the target temperature of the die (18);

b- set the value of the error variable;

c- obtain the temperature of the die (18);

d- obtain the temperature of the heat exchanger;

e- calculate the thermal strip of action of the peltier cells (16);

* If the target temperature of the die is not attainable and the fans (4) are not activated, activate them and re-measure the temperature of the die (18) and the exchanger to calculate again the thermal operating range ΔΤ;

^* If the fans (4) are activated and the target temperature is not achieved, change the target temperature of the die and re-measure the temperature of the die (18) and the heat exchanger to calculate the operating thermal range ΔΤ again;

f- if the target temperature of the die (18) is within the thermal range of action, compare the temperature of the die (18) with the target temperature; g- act on the peltier cells (16), heating or cooling the die (18) as appropriate until the thermal difference between the target temperature of the die (18) and the measured temperature of the die (18) reaches the value of the variable previously set error;

h- set the value of the error variable again and repeat the process.

7. - Thermoregulatory apparatus according to any of the preceding claims, further comprising a plurality of thermal insulators (17,20,21, 22,23) that form an adiabatic cavity on the metal die (18).

8. - Thermoregulatory apparatus according to any of the preceding claims, comprising an anterior support (2) and a posterior support (3) of low thermal conductivity, which supports inside the metal die (18) and the heat exchanger.

9. - Thermoregulator apparatus according to claim 8, wherein the electronic device (19) with cylindrical geometry is a laser diode (19) of a laser transmitter (14), the thermoregulator apparatus comprising:

- a focusing tube (7) and a spherical lens (8) mounted on the front support (2) to focus the laser diode beam (19), and

- fixing means (12) on the rear support (3) for fixing the laser transmitter (14).

10. - Thermoregulator apparatus according to claim 8, wherein the electronic device with cylindrical geometry is an avalanche photodiode of a laser receiver, the thermoregulator apparatus comprising:

- a focusing tube (7) and a spherical lens (8) mounted on the anterior support (2) to focus the beam received by the avalanche photodiode, and

- fixing means (12) on the back support (3) for fixing the laser receiver.