US20030196787A1

US20030196787A1 - Passive thermal regulator for temperature sensitive components

Info

Publication number: US20030196787A1
Application number: US10/126,293
Authority: US
Inventors: William Mahoney
Original assignee: Scientific Atlanta LLC
Current assignee: Cisco Technology Inc; Scientific Atlanta LLC
Priority date: 2002-04-19
Filing date: 2002-04-19
Publication date: 2003-10-23

Abstract

The present invention is directed towards a passive thermal regulator that is suitable for use in electronic devices, such as optical nodes and amplifiers. The thermal regulator regulates hot and cold temperatures surrounding temperature sensitive components. The thermal regulator includes a heat pipe filled with water, a plastic insulator, and a copper slug inserted into the insulator. The thermal regulator transfers heat to and from the temperature sensitive component by absorbing heat in the copper slug. When the temperature is excessively hot, the heat pipe absorbs the heat from the copper slug and conducts the heat to the dissipation end of the heat pipe. When the temperature is excessively cold, the water in the heat pipe freezes, thereby reducing conduction of the heat. The plastic insulator prohibits the heat absorbed by the copper slug from dissipating into the housing and surrounding air, thereby allowing the heat to transfer to the component.

Description

FIELD OF THE INVENTION

This invention relates generally to communications system, and more specifically to a passive thermal regulator that is suitable for use in a variety of cable television transmission equipment including temperature sensitive components for regulating the temperature of the temperature sensitive components.

BACKGROUND OF THE INVENTION

Components, such as integrated circuits (ICs), have temperature ratings, such as from 0° Celcius (C) to 90° C. Products in which the components operate need to take into consideration these operating temperature ratings. Typically, products include heat sinks or other cooling devices to cool the components. Heating devices for components, however, are less prevalent in products. Consequently, when the temperature of the components falls outside of its temperature range, either too hot or too cold, the component(s) may not operate as required.

What is needed, therefore, is a cooling and heating device, i.e., a thermal regulator, that regulates the temperature of components in order to keep the component within its operating range. Additionally, the thermal regulator needs to be economical in order to not increase the overall costs of manufacturing the product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a simplified communications system. [0004]
FIG. 2 illustrates a top side of a housing including the components for an assembly of a thermal regulator in accordance with the present invention. [0005]
FIG. 3 illustrates a bottom side of the housing illustrating the backside of a printed circuit board. [0006]
FIG. 4 illustrates dimples in the Cu slug to secure it to the inserted heat pipe in accordance with the present invention.[0007]

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention will be described more fully hereinafter with reference to the accompanying drawings in which like numerals represent like elements throughout the several figures, and in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, the embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For example, the present invention is detailed and explained relative to an optical node included within a communications system; however, the present invention is not limited to optical nodes and can include all electronic devices that includes temperature sensitive components. Furthermore, the present invention is not limited to the physical structures of the elements as illustrated and detailed within the specification. A preferred embodiment of the present invention is described more fully hereinbelow. [0008]
Electronic devices, such as optical nodes and amplifiers, are used in the distribution networks of communication systems, for example, a cable television system. FIG. 1 is a block diagram illustrating a [0009] simplified communications system 100. A headend 105 transmits forward signals including, for example, video, voice, and data signals, over a communication medium 110, such as an optical fiber. An optical node 115 then converts the optical signal to an electrical radio frequency (RF) signal for transmission to amplifiers 120 via a second communication medium 123, such as coaxial cable. The amplifiers 120 amplify the signal for further transmission through the distribution network. Splitters 125 may be used to divert a portion of the RF signal to different branches in the system 100. Alternatively, the amplifiers 120 may have an auxiliary port that also diverts the RF signal. Taps 130 further divert portions of the RF signal to subscriber equipment 135, such as set-top boxes or cable modems. Typically, the system 100 accommodates both forward signals and reverse signals, which are signals beginning at the subscriber equipment 135 to be transmitted to the headend 105. It will be appreciated that only one main branch of the system 100 is shown; however, there are typically several main branches emanating from the headend 105.
The [0010] optical nodes 115 and the amplifiers 120 typically have an external temperature range from −40° C. to 60° C. Great care is taken to design the product using internal components that can operate within this temperature range. Some design examples are: heat sinks within the products to transfer heat; fins molded into the housings to radiate internally generated heat; and high temperature plastics used throughout the product to operate around the high temperatures. The other extreme, however, hasn't included heaters or other heating devices to warm the internal components when there are cold conditions.
Currently an internal component, such as an integrated circuit (IC), used within the [0011] optical node 115 and/or amplifier 120 products is extremely temperature sensitive to both the cold temperatures and the hot temperatures. The IC has an operating temperature range from 0° C. to 90° C. Accordingly, the design of the product needs to take into consideration both the hot and, maybe more importantly, the cold temperature rating of the component by looking at the internally generated temperatures of the product and the surrounding outside temperatures. The temperature of the component needs to be regulated in order to maintain the integrity of the component. The present invention, therefore, addresses regulating the temperature of the IC. It will be appreciated that the present invention addresses regulating any temperature sensitive component.
FIG. 2 illustrates a [0012] top side 200 of an open housing 210 and also including the components for assembling a thermal regulator in accordance with the present invention. FIG. 3 illustrates a bottom side 300 of the open housing 210 and also illustrating the backside of a printed circuit board 315. Referring to FIG. 2 in conjunction with FIG. 3, an electronic device, such as an optical node or amplifier, includes a temperature sensitive component 310 that is typically soldered onto a printed circuit board (pcb) 315, the backside of which is illustrated positioned and secured into the bottom side 300 of housing 210, which can be, for example, an aluminum housing.
On the top side of the [0013] housing 200, the assembled thermal regulator is positioned in close proximity to the temperature sensitive component 310. As illustrated in FIG. 2, the unassembled thermal regulator in accordance with the present invention includes three pieces: a copper (Cu) heat pipe 225 that can be purchased from a vendor such as Thermacore; a plastic insulator 230, and a Cu slug 235. Assembly of the thermal regulator begins with inserting the plastic insulator 230 down into a circular cutout of an internal divider 238 that is approximately the size of the temperature sensitive component 310. A top portion 240 of the plastic insulator 230 rests on the top of the internal divider 238. The Cu slug 235 is then inserted into the plastic insulator 230. The heat pipe 225 is then inserted into cutouts in the housing 210. As shown, the internal portion 237 of the heat pipe 225 is inserted into a cutout in the housing until the tip touches a raised ledge in the groove on the bottom of the housing 210. The heat pipe 225 is in direct contact with the Cu slug 235 and approximately ½ inch of the aluminum housing 210 at the outer tip. By isolating the heat pipe 225 from the aluminum housing 210, the thermal path is controlled and limited by the heat pipe 225 only thus minimizing any temperature effects from auxiliary conduction or convection in the housing 210. The cutout is designed to ensure that, when positioned, the heat pipe 225 sits perpendicularly against the temperature sensitive component 310. Referring to FIG. 4, the Cu slug 235 is dimpled 400 to secure it to the heat pipe 225 and create a tight thermal interface between the Cu slug 235 and the heat pipe 225. In the preferred embodiment of the present invention, a copper heat sink is also integrated into the temperature sensitive component by the vendor in order to facilitate heat transfer away from the component.
After assembly of the thermal regulator in the housing and during operation, the thermal regulator regulates the temperature of the temperature [0014] sensitive component 310 in accordance with the present invention. More specifically, during excessive hot temperatures, the Cu slug 235 absorbs the heat from the component 310 via the Cu heat sink and facilitates the heat transfer to the Cu heat pipe 225. The water-filled Cu heat pipe 225 then absorbs this heat that has been transferred to the slug 235 as well as the heat surrounding the component 310. It will also be appreciated that the Cu heat pipe 225 has a much higher thermal conductivity than the Al housing 210 and the internal divider 238, thereby further facilitating the heat transfer from the slug 235 and the component 310 to the Cu heat pipe 225. Accordingly, the Cu heat pipe 225 receives the excess heat and the enclosed water and conducts the heat to the dissipation end 245, which is the end located at the outside cutout of the housing 210. In this manner, the component 310 is temperature regulated, thereby protecting the component 310 from any excessive hot temperatures. It will be appreciated that using a larger diameter heat pipe 225 or larger Cu slug 235 can dissipate more heat.
During excessive cold temperatures, the [0015] Cu slug 235 again absorbs the heat generated by and surrounding the component 310. However, since the surrounding temperatures are excessively cold, the water inside the Cu heat pipe 225 freezes, thereby reducing conduction of the heat by the heat pipe 225. Furthermore, the plastic insulator 230 prohibits the Cu slug 235 from dissipating any excessive heat to the heat pipe 225 or surrounding air. Accordingly, when conduction in the heat pipe 225 is reduced along with the aid of the plastic insulator 230 prohibiting heat dissipation, the component 310 is then able to absorb the heat that is being stored in the Cu slug 235. Additionally, if surrounding temperatures are known to get extremely cold, the Cu heat pipe 225 can be made longer, which facilitates even less conduction and more heat absorption by the component 310 from the Cu slug 235.
In summary, the assembled thermal regulator regulates the temperature of a temperature sensitive component by transferring the heat generated by and surrounding the component either away from the component during hot temperatures or to the component during cold temperatures.[0016]

Claims

What is claimed is:

1. A thermal regulator comprising:

a heat pipe in close proximity to a temperature sensitive component;

a plastic insulator having a cutout placed physically on top of the heat pipe; and

a copper slug inserted into the cutout of the plastic insulator being in close proximity to the temperature sensitive component for transferring heat from the temperature sensitive component and for transferring the heat to the heat pipe when the temperature surrounding the temperature sensitive component is excessively hot, and for transferring heat to the temperature sensitive component when the temperature is excessively cold.

2. The thermal regulator of claim 1, wherein the heat pipe includes water, and wherein the water freezes when the temperature surrounding the temperature sensitive component drops below 0° Celcius.

3. The thermal regulator of claim 2, wherein when the water freezes in the heat pipe and conduction of the heat decreases, the plastic insulator prohibits the dissipation of heat from the copper slug, thereby allowing heat to transfer from the copper slug to the temperature sensitive component.

4. The thermal regulator of claim 1, wherein the temperature sensitive component includes a copper heat sink, and wherein the copper slug transfers heat to and from the copper heat sink.

5. An electronic device for receiving and transmitting signals, the electronic device including temperature sensitive components each having a copper heat sink and a thermal regulator for regulating the temperature surrounding the temperature sensitive component, the electronic device comprising:

an input port for receiving the signals;

a housing for enclosing the temperature sensitive components;

a thermal regulator in close proximity to the copper heat sinks for regulating the temperature of the temperature sensitive components, the thermal regulator comprising:

a heat pipe including water;

a plastic insulator placed on the opposite side to the temperature sensitive component on the heat pipe; and

a copper slug inserted into the plastic insulator and in close proximity to the copper heat sink for transferring heat from the copper heat sink and for transferring the heat to the heat pipe when the temperature surrounding the temperature sensitive component exceeds a hot temperature rating of the temperature sensitive component, and for transferring heat to the copper heat sink when the temperature surrounding the temperature sensitive component exceeds the cold temperature rating.

6. The electronic device of claim 5, wherein, when the water freezes in the heat pipe, the plastic insulator prohibits the dissipation of heat from the copper slug into the housing and surrounding air, thereby allowing heat to transfer from the copper slug to the temperature sensitive component.