WO2000016476A1

WO2000016476A1 - System and method for output power compensation for actual device temperature

Info

Publication number: WO2000016476A1
Application number: PCT/US1999/020938
Authority: WO
Inventors: Steven J. Laureanti; Veli-Pekka Ketonen
Original assignee: Nokia Networks Oy
Priority date: 1998-09-14
Filing date: 1999-09-13
Publication date: 2000-03-23
Also published as: EP1112616A1; AU6035699A

Abstract

An output power adjustment system including an electrical device with a thermal resistance, a temperature sensor adjacent the electrical device, for sensing a temperature thereof, and a controller for adjusting a power dissipation of the electrical device using the temperature and the thermal resistance to control an inner temperature of the electrical device. The system may be used with an RF power amplifier. A linear relationship between the junction temperature, casing temperature and power dissipation is used together with a determined thermal resistance of the device. A method of controlling a temperature of an electrical device includes sensing an outer temperature thereof, and controlling a power dissipation using the outer temperature and a thermal resistance. The system and method allow the junction temperature to be maintained at a substantially constant level.

Description

SYSTEM AND METHOD FOR OUTPUT POWER COMPENSATION FOR ACTUAL DEVICE TEMPERATURE

BACKGROUND OF THE INVENTION

1 Field of the Invention This invention relates in general to systems and methods for controlling temperature in electrical devices, and more particularly to systems and methods for output power compensation for actual device temperature

2 Description of Related Art

Virtually all electπcal devices generate some amount of heat Furthermore, every electrical device is more or less sensitive to excessive tempeiatures The tolerable temperatures vary depending on the kind of electπcal device, and the kind of operations being performed Electπcal devices are often provided with a temperature range by the manufacturer, or at least a maximum temperature, regulating the electπcal dev ice should be used Since electrical devices may require cooling m order to operate properly, they are usually provided with what may generally be called coolmg devices Such cooling devices may, for example, allow ambient air to flow through passages m the electrical device, or as another example actively force coolmg air through at least parts of the electncal device An electrical de\ ice may, for example, be provided with a heat sink substantially surrounding the electrical device, whereby energy dissipating from the electπcal device in form of heat is absorbed in the heat sink while allowing the heat sink to remain substantially at a constant temperature As another example, a fan provided close to the electπcal device may force an air flow toward the electrical device, thereby increasing the heat dissipation from the device and maintaining a tolerable temperature in the electrical device __ A critical device such as an RF power amplifier device will experience a catastrophic failure if its case/flange temperature exceeds its maximum value for an extended period of time One application of this failure may occur in a cellular base station that utilized both forced air flow coolmg and conventional air flow cooling When a failure is introduced m the forced air flow coolmg system such as a mechanical fan failure, clogged air intake, or harsh environmental conditions, the ambient air inside the cellular base station will increase This increase in ambient air will force the case/flange temperature of the RF power amplifier device to increase above the maximum value and cause a catastrophic failure All of these types of failures will directly reduce usability and network operator income It can be seen that there is a need for systems and methods which compensate an output power of an electrical device for its actual temperature

It can also be seen that there is a need for a system and method for output power compensation for actual device temperature which maintain a junction temperature of the device substantially constant

SUMMARY OF THE INVENTION To overcome the limitations in the prior art descπbed above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a system and method for output power compensation for actual device temperature.

The present invention solves the above-described problems by providing a system and method for controlling a temperature of an electπcal device, using a temperature of the device and a thermal resistance of the device.

A system m accordance with the pπnciples of the present invention includes an electπcal device having a thermal resistance, a temperature sensor adjacent the electπcal device, for sensing a temperature of the electπcal device, and a controller connected to the electπcal device and to the temperature sensor The controller adjusts a power dissipation of the electπcal device using the temperature and the thermal resistance to control an inner temperature of the electπcal device A method in accordance with the pπnciples of the present invention includes sensing an outer temperature of an electπcal device duπng operation, and controlling a power dissipation of the electπcal device using the outer temperature and a thermal resistance of the electπcal device

These and vaπous other advantages and features of novelty which characteπze the invention are pointed out with particulaπty in the claims annexed hereto and form a part hereof However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, m which there are illustrated and descπbed specific examples of an apparatus in accordance with the ention

BRIEF DESCRIPTION OF THE DRAWINGS Referring now to the drawings in which like reference numbers represent corresponding parts thioughout

Fig. 1 schematically illustrates an embodiment of a system in accordance with the principles of the invention,

Fig 2 is an exemplary diagram showing the effects on junction temperature at increasing casing temperature without power compensation; and

Fig 3 is an exemplary diagram showing junction temperature at increasing casing temperat e. when dissipated power is adjusted

DET AILED DESCRIPTION OF THE INVENTION In the follow ing description of the exemplary embodiment, teference is made to the accompanying diawmgs which form a part hereof, and m which is shown by way of illustration the specific embodiment in w hich the invention may be practiced It is to be understood that other embodiments may be utilized as structural changes may be made ithout departing from the scope of the present invention

The present invention provides new systems and methods foi controlling temperature of electrical devices.

Fig 1 illustrates schematically an embodiment of a system in accordance with the pimciples of the present invention The system 100 includes a device 101 , which generally is an electric device In some applications the device 101 is, or includes, a power amplifier Well-known power amplifiers may be used with embodiments of the invention

In a particular embodiment, the system 100 is included in a cellular base station in an RF network, with the device 101 being at least part of an RF power amplifier device Such RF networks typically include a plurality of cellular base stations, located at different geographical precisions, for controlling RF transmissions in the network Each one of such cellular base stations is generally enclosed in its own casing, provided with forced and/or unforced air cooling, for example as descπbed above

The device 101 is typically provided with external pow er supply from a remote power source (not show n) as is w ell-known The device 101 may also be connected with data communication cables, antennas, etc. to perfoπn desired functions a particular application A temperature sensor 103 is positioned adjacent the dev ice 101 Well-know n temperatm e sensors may be used with embodiments of the inv ention. The temperature sensoi 103 will be used for sensing a temperature of the device 101. in order to adjust a power dissipation of the device 101 __ The temperature sensor 103 is connected to a controller 120 for controlling the power dissipation of the device 101 Many kinds of well-known controllers may be used with embodiments of the invention. The controller 120 is connected to the sensor 103 using, for example, well-known techniques. The controller 120 may be positioned inside the device 101 as indicated in Fig 1 In other embodiments, the controller 120 may be positioned outside the dev ice 101

The controller 120 will receive temperature measurements from the temperature sensor 103 and adjust settings m the device 101 using the temperature measurements to control the power dissipation of the device 101

The device 101 and temperature sensor 103 are located in a surrounding 105 The surrounding will generally include other pans, devices, circuitry or components of the application where the device 101 is being used For example, the surrounding 105 may be a printed circuit board, where the device 101 is mounted on the printed circuit board. Different well-known printed circuit boards may be used with embodiments of the invention For example, if the device 101 is a RF power amplifier device, it may be mounted on the printed circuit board 105 inside a cellulai base station

The device 101 and the temperature sensor 103 may be provided with a heat sink 107 Different well-known heat sinks mav be used with embodiments of the invention. The heat sink 107 at least partially surrounds the dev ice 101 and temperature sensor 103 and is used to absorb energy in the form of heat dissipating from the device 101 For example, the heat sink 107 may be manufactured from a metal, and be provided with extending fins (not shown) to facilitate the performance of its desired function In embodiments utilizing a heat sink 107, the temperature_^ sensor 103 may, for example be mounted directly on the device 101 , or adjacent to the dev ice 101 on the heat sink 107

The system 100 may be provided with one or more forms of coolmg As descπbed above, a heat sink 107 may be used to absorb energy from the device 101 Forced air coolmg may also be used, for example in the form of a fan providing a forced an flow adjacent the device 101 The forced air coolmg is schematically illustrated by the box 109 in Fig 1 Many different kinds of well-known forced air coolmg may be used with embodiments of the invention

The system 100 may be provided with unforced air coolmg, schematically illustrated by the box 1 1 1 m Fig 1 Different kinds of well-known unforced air coolmg may be used with embodiments of the invention For example, the system 100 may be provided with air intakes and outlets for allowing ambient air to circulate adjacent the device 101

The use of an embodiment of the present invention, where the device 101 includes an RF power amplifier device will now be descπbed ith further reference to Fig 2 Duπng operation of a power amplifier, heat will develop m a junction of

the po er amplifier, and the device is said to have a junction temperature T, The manufacturer of the power amplifier typically pro ides a maximum tolerable junction temperature for the power amplifier, which should not be exceeded to ensure safe and reliable operation of the amplifier The maximum tolerable junction temperature will typically be selected in consideration of the particular RF power amplifier device and/or its intended use and/or the desired reliability For example, the junction temperature T mav be set to a maximum of 200°C in some applications Due to practical circumstances and in order to increase the reliability of the RF __ power amplifier, a derating v alue is typically associated with this maximum temperature

A casing temperature T_c of the power amplifier may be measured, for example, by the temperature sensor 103 located on or adjacent the device 101 The lelationship between the junction temperature T and the casing temperature T_c is

7) = ^_Λll x ^_/r ] + T_e (1)

wherein P_dlSb is a power dissipation from the power amplifier, and R_ϋ is the

thermal resistance between the junction of the power amplifier and the casing For embodiments in accordance with the invention, it can be assumed that the thermal

resistance R_{υ c} is substantially constant and not unilaterally proportional to the

effects of the operating junction temperature T, The thermal resistance R_{ti c} may,

for example, be determined experimentally by measuπng T , T_c and P_dlbS and using equation (1 ) As long as the assumption of substantially constant thermal resistance

is valid, the value of R_{0 c} may be used in controlling the junction temperature T,

If the dissipated power is measured m watts (W), the thermal resistance should be a value measured in °C/W, in order for their product to have the unit of

temperature Knowing the casing temperature T_c, the thermal resistance R_{υ t} and the power dissipation P_dlbb, the junction temperature T may be calculated according to equation 1

In case of insufficient coolmg of the device 101 , the casing temperature will increase Such a situation may arise due to malfunction in the forced air coolmg __ 109, obstructions in air inlets of the system 100, or extreme environmental conditions such as excessive ambient temperature

Figure 2 is an exemplary graph 200 showing junction temperature T, 210, measured casing temperatme T_c 212, and power dissipation P_dlbS 214 In this example, the casing temperature T_t 212 is increasing, and the power dissipation P_dlb 214 is not compensated for the increase The casing temperature T_c 212 is indicated along the abscissa of the graph, showing the range between 60°C and 170°C The power dissipation P_dlss 214 remains substantially constant as illustrated by the line 220 The junction temperature T 210 is linearly dependent on the casing temperature T_c 212, as indicated by line 222 For example, it can be seen that while the casing temperature T 212 increases from 65°C to 165°C, the junction temperature T, 210 inci eases from 130°C to 230°C on the left ordinate

A maximum junction temperature of 200°C was mentioned above for an exemplary device In an embodiment using a power amplifier with such a maximum junction temperature, the increase m casing temperature T_c 212 in the last example would imply a junction temperature T_; 210 above the maximum temperature By decreasing an output power of the power amplifier, and thereby decreasing the power dissipation P_dιss 214, an increase in the junction temperature T, 210 may be limited or avoided Fig 3 is an exemplary graph 300 showing junction temperature T_j 310, measured casing temperature T_L 312, and adjusted power dissipation P_{dl b} 314 In this example, the power dissipation P_dlbS 314 is adjusted to decrease substantially linearly with increasing casing temperature T_c 312, as indicated by line 320

Referring also to Fig 1. the power dissipation P_dlss 314 is adjusted by the _ controller 120 receiving the measured casing temperature T_c 312 from the temperature sensor 103 The controller 120 may, for example, be connected to the device 101 such that it may control the level of output power from the device 101

The controller 120 may, for example, access the equation ( 1 ) where P_d]bi and R_θ

are known, and use it together ith the measured casing temperature The equation ( 1 ) may be provided in a memory m the controller 120, or the controller 120 may access it when needed, using well-known techniques

Using equation (1), the junction temperature T_j 310 can be determined once the casing temperature T_c 312, the adjusted power dissipation P_dιss 314. and the

thermal resistance Rπ,_c are known As indicated by line 320 in the exemplary Fig 3,

the junction temperature T 310 may be held substantially constant For example, while the casing temperature T_c 312 increases from 60 to 170°C, the power dissipation P_dlss 314 is adjusted to successively lower values, resulting in the junction temperature T, 310 remaining substantially constant at about 180°C Thus, the increasing casing temperature T_c 312, caused for example by malfunctioning coolmg devices, is compensated by a decrease in the output power P_dlSb 314 of the device

The foregoing description of the exemplary embodiment of the invention has been presented for the purposes of illustration and description It is not intended to be exhaustive or to limit the invention to the precise form disclosed Many modifications and variations are possible in light of the above teaching It is intended that the scope of the invention be limited not with this detailed description, but rather by the claims appended hereto.

Claims

WHAT IS CLAIMED IS

1 An output power adjustment system for controlling a temperature of an electrical device, the system composing an electocal device, having a thermal resistance, ΓÇö a temperature sensor adjacent the electrical device, for sensing a temperature of the elect╧Çcal device, and a controller connected to the elect╧Çcal device and to the temperature sensor, the controller adjusting a pow er dissipation of the elect╧Çcal device using the temperature and the thermal resistance to control an inner temperature of the elect╧Çcal device

2 The system according to claim 1 , further including a heatsmk substantially su╧Çounding the elect╧Çcal device

3 The system according to claim 2, wherein the temperature sensor is positioned on the heatsink

4 The system according to claim 1 , wherein the electrical device includes a power amplifier

5 The system according to claim 4, wherein the thermal resistance is determined between a junction and a casing of the power amplifier

6. The system according to claim 5, wherein the controller adjusts the power dissipation using the equation

. ^ ^P^ ^x Ro,- l + o wherein T_; is a junction temperature of the power amplifier, P_d╬╣ss is the power dissipation, R_╬╕ is the thermal resistance between the junction and the casing, and

T_c is the temperature of the electrical device.

7. The system according to claim 1, wherein the controller adjusts the 0 power dissipation such that the inner temperature remains substantially constant.

8. A power amplifier system comprising: a power amplifier device, having a thermal resistance value between a junction and a casing of the power amplifier device; a temperature sensor adjacent the power amplifier device, for sensing an outer temperature of the power amplifier device; and a controller connected to the power amplifier device and to the temperature sensor, the controller adjusting a power dissipation from the power amplifier device using the outer temperature and the thermal resistance to control an inner temperature of the power amplifier device.

9 The system according to claim 8, wherein the controller adjusts the power dissipation using the equation

T. = ,. R, Z

wherein T_t is ajunction temperature of the power amplifier device, P_dns is the power dissipation, R₀ is the thermal resistance between ajunction and a casing of the power amplifier device, and T_c is the temperature of the power amplifier device

10 The system according to claim 8, wherein the controller adjusts the power dissipation such that the inner temperature remains substantially constant

11 A method of controlling a temperature of an electrical device, the method comprising sensing an outer temperature of the electrical device du╧Çng operation, and controlling a power dissipation of the electrical device using the outer temperature and a thermal resistance of the elect╧Çcal device

12 The method according to claim 1 1, wherein controlling the power dissipation includes using the equation

T. ╧ï, ^p- + 71

herein T_t is ajunction temperature of the elect╧Çcal device, P_╧Äss is the power dissipation, R is the thermal resistance between ajunction and a casing of the electrical device, and T_c is the temperature of the electrical device

13 The method according to claim 1 1 , further including controlling the power dissipation such that the inner temperature remains substantially constant

14. The method according to claim 11. further including the power dissipation to be less than a maximum tolerable inner temperature of the electrical device.