This invention relates in general 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 Related Art.

Virtually all electrical devices generate some amount of heat. Furthermore, every electrical device is more or less sensitive to excessive temperatures. The tolerable temperatures vary depending the kind of electrical device, the kind of operations being performed. devices are often provided with a temperature range by the manufacturer, or at least a maximum temperature. regulating the device should be used.

Since electrical devices may require cooling in order to operate properly, they usually provided with whatmay generally called cooling Such cooling devicesmay) example, allow ambient air to flow through passages the electrical device, or as another example force cooling air through at least parts of the electrical device.

An electrical device may, for example, be provided with a heat sink substantially surrounding electrical device, whereby energydissipating from the electrical device in form of heat is absorbed in the heat sink while allowing heat

sink to remain substantially at a constant temperature. As another example, a fan provided close to the electrical device may force an air flow the electrical device, therebyincreasing the dissipation from the device and maintaining a tolerable temperature in the electrical _ A critical device such as an RF 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 in a cellular base station that utilized both forced air flow cooling conventional air flow cooling.

When a failure is introduced in the air flow cooling 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 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 described above, to overcome other limitations that will apparent upon reading and understanding present specification. present invention discloses a system and method for output power compensation for actual temperature.

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

A system in accordance with the principles the present invention includes an electrical device having a thermal resistance, a temperature sensor adjacent the electrical device, for sensing temperature of the electrical device, and a controller connected to the electrical device and to the temperature sensor. The controller adjusts a power dissipation of the electrical device using the temperature and the thermal resistance to control an inner temperature of the electrical device.

A method in accordance with the principles of the present invention includes sensing outer temperature of an electrical deviceduring and controlling a power dissipation of the electrical device using the outer temperature and a thermal resistance of the electrical device.

These and various otheravantages features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However. a better understanding of the invention, its advantages, and the objects obtained by use, reference should be made to the drawings which form a further part hereof, and to accompanying matter, in which there are illustrated anddescribed examples of an apparatus in accordance with the invention.

BRIEF DESCRIPTION OFTHE DRAWINGS Referring now the drawings inwhich like reference represent corresponding parts throughout: Fig. 1 schematically illustrates embodiment of a system in accordance with the principles of the invention ; Fig. 2 is an exemplary diagram showing effects on junction temperature at increasing casing without power compensation ; and Fig. is an exemplarydiagram showing junction at increasing casina temperature. wllen power is adjusted.

DETAILED OF THE INVENTION In the following description of the exemplary embodiment, is made to the accompanying drawings which form part hereof, in which shown bv wav ofillustration specific embodiment which the invention may practiced.

It is be understood that other embodiments may utilized as structural changes may be without departing from scope of the present invention.

The presentinvention new systems and methods for controlling temperature of electrical devices.

Fig. 1 illustratesschematically embodiment of a system in accordance with the principles of the present invention. The system 100 a device 101, which generally an electric device. In some applications the device 101 or includes, a power amplifier. NVell-known amplifiers may used with embodiments of the invention.

In a particular embodiment, the system100 included in a cellular base station in an RF network, with device 101 at least part of an RF power amplifier Such RF networks typically include a plurality cellular base stations, located at different geographical for controlling RF transmissions in the network. Each one of such cellular base stations is generally enclosed in its own provided with forcedand/or air cooling, for example described above.

The device 101 istypically with external power supply a remote power source (not shown) is well-known. device 101 also be connected with data communication cables,antennas, to perform desired functions a particular application.

A temperature sensor 103 is positioned adjacent the devicel01. Well-linow temperature may be used with of the invention. The temperature sensor 103 will be used for sensing atemperature the device 101, in order to adjust a power dissipation ofthe device 101.

The temperature sensor 103 is connected a controller 120 forcontrolling the power dissipation of the device 101. Manykinds ofwell-known controllersmay be used with embodiments of the invention. The controller120 connected to the sensor 103 using, for well-known techniques. The controller120 be positioned inside device 101 as indicated in Fig. I. In other embodiments, the controller 120 be positioned outside device 101.

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

The device101 temperature sensor 103 located in a surrounding 105.

The surrounding willgenerally other parts. devices,circuit or components of the application where the device 101 isbeing For example, the surrounding 105 be a printed circuit where the device 101 mounted on the printed circuit board. Different well-known printed circuit boards may be used witll embodiments of the invention. For example, if the device 101 a RF power amplifier device, it may be mounted on the printed circuit board 105 a cellular base station.

The device 101 the temperature sensor 103 may be provided with a heat sink Different well-known heat sinks may used with of the invention. Theheat sink at least partially surrounds device 101 and

temperature sensor 103 and is used to absorb energy the form heat dissipating from the device 101. example, the heat sink 107 may bemanufactured a metal, and be provided with extending fins (not shown) to facilitate the performance of its desired function. In embodiments utilizing a heat sink107, thetemperature sensor 103 may, for example. mounted directly on the device 101, adjacent to the device101 the heat sink 107.

The system 100 be provided with one or more forms of cooling. As described above, a heat sink 107 may be used to absorb energy from the device 101.

Forced air cooling may be used, for example the form of a fan providing a forced air flow the device 101. forced air cooling schematically illustrated by the box 109 Fig. 1. different kinds of well-known forced air cooling may be used with embodiments of the invention.

The system 100 be provided with unforced air cooling, schematically illustrated by the box 111 inFig. 1. kinds of well-known unforced air cooling be used with embodiments of the invention. For example, system 100 may provided with air intakes and outlets for allowing 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 described with further reference to Fig. 2. operation of a power amplifier, heat develop in a junction of the power amplifier, and the device is said to have a junction temperatureT,. The manufacturer of the power amplifier typically provides a maximum tolerable junction temperature the power amplifier, which should not be exceeded to ensure safe and reliable operation of the amplifier. The maximum tolerablejunction

temperature will be selected in consideration of the particular RF power amplifier device and/or its intended use and/or desired reliabilitv. example, thejunction temperature T, be set to a maximum of 200°C some applications.

Due to practical circumstances and in order to increase the reliabilitv the RF _ power amplifier, a derating value is typically with this maximum temperature.

A casing temperature T, the power amplifier may be measured, for example, by the temperature sensor 103 located on or adjacent the device 101. The relationship between the junction temperature Tj the casing temperatureT, is wherein PdjSs a power dissipation from the power amplifier, and Ru ils the thermal resistance between the junction the power amplifier and the casing. For embodiments in accordance with the invention, it can be assumed that the thermal resistance 7<issubstantially and not unilaterally to the effects of the operating junction temperatureTj. The resistance Ra . may, for example, be determined experimentally by measuring Tj, Tc andPdjSs and using equation (1). long as the assumption of substantially constant thermal resistance is valid, the value of 7< may used in controlling the junction temperature T,.

If the dissipated power is measured in watts (W), the thermal resistance should be a value measured in °C/W, order for their product to have the unit of temperature. Knowing the casing temperatureTc, thermal resistance Roi,, and

the power dissipation P ; ss, tlle junction temperatureT, may calculated according to equation 1.

In case of insufficient cooling of the device 101, the casing temperature will increase. Such a situation may due to malfunction in the forced air _ 109, obstructions in air inlets of the system 100, or extreme environmental conditions such asexcessive temperature.

Figure 2 is an exemplary graph 200 showing junction temperatureT, 210, measured casing temperature T, 212, power dissipation Pdiss 214. this example, the casing temperatureT, is increasing, andthe dissipation Pdiss 214 is not compensated for the increase. The casing temperature T, is indicated along the abscissa of the graph, showing the range between 60°C and170°C. The power dissipation Pdjs5214 substantially constant as illustrated by the line 220. The junction temperatureT is linearly dependent on the casing temperature Toc212, indicated by line 222. For example, it can be seen that while the casing temperature T, increases from 65°C to165°C, junction temperature T, increases from 130°C to230°C the left ordinate.

A maximum junction temperature of 200°C mentioned above for an exemplary device. In an embodiment using a power amplifier with such a maximum junction temperature, the increase in casing temperature Tu 212 the last example would imply a junction temperature T, above the maximum temperature.

By decreasing an output power of the power amplifier, and thereby decreasing the power dissipation Piu, , 214, increase in the junction temperatureTj 210 may be limited avoided. Fig. 3 is an exemplary graph 300 showing junction temperature Tj 310, casing temperature T, 312, adjusted power

dissipation Pdiss 314. In this example, the power dissipation Pdiss 314 is adjusted to decrease substantially linearly with increasing casing temperature Tc 312, as indicated by line 320.

Referring to Fig. 1, the dissipation P, i,, 3 14 adjusted by _ controller 120 the measured casing temperature Tc 312 from the temperature sensor 103. The controller 120 may, for example, be connected to the device 101 that it may control the level of output power from the 101.

The controller 120 may, for example, access the equation (1) where Pii, , and7< are known, use it together the measured casing The equation (1) be provided in a memory in the controller 120, or the controller 120 may access it when needed, using well-known techniques.

Using equation (1), the junction temperatureT, 310 be determined once the casing temperatureT, the adjusted power dissipation Pdiss 314, and the thermal resistance R, are As indicated by line 320 in the exemplary Fig. 3, the junction temperature Tj 310 may be substantially constant. For example, while the casing temperatureT, 312 increases 60 to 170°C, power dissipation P 314 is to successively lower values, resulting the junction temperature Tj 310 substantially constant at about 180°C. the increasing casing temperatureT, caused for example by malfunctioning cooling devices, is compensated by a decrease in the output power P ; S, 314 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. is intended that the scope of the invention be limited not with this detailed description, but rather by the claims appended hereto.