Small-size active cooling system for LED lamp.

July 26, 2010
Date Announced: 26 Jul 2010 Vancouver, BC — MP Lighting, a designer and manufacturer of innovative LED fixtures, continues the successful development in the thermal management of the LED sources of light for indoor and outdoor application. With emphasis on art design the size and weight of cooling system for LED fixture is becoming critical and right answers could be find in active cooling system provided forced air through construction of LED lamp.Recently in MP Lighting R&D Lab was tested small-size active cooling system based on two innovation principles: use of an original NTC thermistor matrix for the direct control of the current through fan; and the application of special heat sink for LED , which contains the elements for forming of turbulent airflow around the heat sink – vortex generators.The thermistor matrix consist of array of thermistors which are connected electrically in serial-parallel way and placed on PCB with special shape and layout. The use of such of matrix makes it possible to realize simple, reliable and small system control loop, in which NTC thermistors carry out at the same time the role of both the temperature sensor and the regulator of current through the cooler - fan. For constructing the matrix were used SMD the thermistors from Mitsubishi (series TC05-2S with the dimensions of 1x0,5x0.25 mm), what ensured the arrangement of thermistor matrix close to LED and good thermal connection between the object of control, the sensors and the heat sink.The heat sink of original construction was made from sheet of aluminum with a thickness of 0, 7 mm; it has the weight only of 11 grams, the total area (for two sides) of heat transfer surface 86 sq. cm. Because of the relatively simple shape and the configuration this heat sink in the mass production can be made by the method of punching from the sheet of metal. The overall dimensions of entire assembling (fan, heat sink, thermistor matrix and LED itself) are around 40 x 40 x 40 mm; the total weight is no more than 40 grams, which provides very good initial conditions for art design of LED lamp.During the testing of cooling system the CITIZEN LED was used as thermal load. It was running under 12 Wt electrical power and was fitted to heat sink directly (the fan was fitted on opposite side of LED assembly). As the cooler in the prototype of LED lamp the DELTA fan was applied, model AFB0412SHB, 12Vdc; 0,25A but just some part of output power was used in the operating of cooling system what reduce the noise of fan significantly.The results of the tests of cooling system are represented in the graph 1, from which it follows that it is capable of automatically stabilizing the temperature of LED lamp at level 40 degrees Celsius, and of ensuring the value of the coefficient of convective heat transfer in the construction of LED lamp around 170 Wt/*Cxm^2 (it is obtained by the original calculation methodology from the heat sink transient function). In this case the average power, consumed by cooling system comprises around 6% of the net power of LED lamp, which is enough acceptable for the practical applications at the stage of the prototyping.

Alexander Kornich R&D Lab Manager MP Lighting

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