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COOLING FAN REQUIRES NO ADDITIONAL CURRENT

IP.com Disclosure Number: IPCOM000008073D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-16
Document File: 2 page(s) / 108K

Publishing Venue

Motorola

Related People

Boris C. Dinkoff: AUTHOR [+2]

Abstract

This invention describes a method of powering a cooling fan for electronic equipment that requires no additional current compared to when the fan is not needed. Current drain is kept constant by allow- ing the decrease in transmitter current drain during thermal shutback to be equally diverted to the fan, regardless of power output or temperature. This method provides a continuously variable distribu- tion of current between the transmitter and the cool- ing fan and results in constant current drain on the power system. Minimum variation of transmit power over time is an added benefit compared to other methods of intermittent cooling.

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MOTOROLA Technical Developments

COOLING FAN REQUIRES NO ADDITIONAL CURRENT

by Boris C. Dinkoff and Glenn Mukli

ABSTRACT

  This invention describes a method of powering a cooling fan for electronic equipment that requires no additional current compared to when the fan is not needed. Current drain is kept constant by allow- ing the decrease in transmitter current drain during thermal shutback to be equally diverted to the fan, regardless of power output or temperature. This method provides a continuously variable distribu- tion of current between the transmitter and the cool- ing fan and results in constant current drain on the power system. Minimum variation of transmit power over time is an added benefit compared to other methods of intermittent cooling.

PROBLEM DESCRIPTION

Repeaters and transmitting radio equipment that are mounted in confined spaces require forced air cool- ing to keep thermal cutback protection circuitry from severely lowering output power. This is espe- cially true for long key-down periods encountered in repeaters and other high duty cycle transmit con- ditions. Communications equipment is being designed to be smaller and to have lower current drain, making attractive the use of energy limited power sources such as solar panel arrays, chemical batteries, fossil fuel and wind powered generators, thermopiles, fuel cells, and switching and regulated power supplies. The additional current required to operate a cooling fan in the traditional manner would affect the cost and size of the limited energy source. This directly impacts the customer expecta- tions of transmit time, RF power level and conse- quent signal quality in remote site multi-hop links, and cost and size of solar panel arrays and recharge- able batteries.

Previous solutions have been to use fans that are on continuously, switched on only during maximum

load such as during transmit, or thermostatically controlled. The fan typically requires 200 - 1000 mA current to operate it. If the fan were operated before shutback occurred, the total current drain of the equipment would increase. If the fan were ther- mostatically controlled after shutback had proceed- ed beyond a certain point, power output would fluc- tuate suddenly after the fan started operating, and due to the thermal mass of the RF heatsink the fan would continue to operate a...