OVTL09LG3G datasheet(11/14 Pages) TTELEC

11 / 14 page

Issue B.2 07/08

Page 11 of 14

OPTEK reserves the right to make changes at any time in order to improve design and to supply the best product possible.

OPTEK Technology Inc. —

1645 Wallace Drive, Carrollton, Texas 75006

Phone: (972) 323-2200 or (800) 341-4747 FAX: (972) 323-2396 visibleLED@optekinc.com www.optekinc.com

Lednium Series Optimal X

OVTL09LG3x Series

Thermal Resistance

Optek Lednium Series 1-watt Cup – Measured value 2oC/w

(OVTL01LGAxx)

Optek Lednium Series 10-watt Matrix – Measured value 2.5oC/w

(OVTL09LG3xx)

Theory

In line with industry practice, the thermal resistance (Rth) of our LED packages is stated as R

θ j-b, thermal

resistance from the junction region ( j ) of the die, to the board (b) - PCB or other mounting surface. What this

means in a practical sense, is that when operating at rated input (1watt approx.) the junction of a die in a cup prod-

uct will attain a temperature that is 2oC higher than a reference point on the mounting surface beneath it. In the

case of a 10-watt Matrix product, the maximum temperature difference between any junction and the reference

point is 25oC (2.5oC/w x 10w). The thermal path thus quantified is a composite of a number of thermally resistive

elements in a series and or parallel configuration, but lumped together into a single parameter for convenience.

For an end user of LED products then, this constant allows the junction temperature to be determined by a

simple measurement of the temperature of the mounting surface. Optek recommends that the design value of sus-

tained die junction temperature be limited to 80oC. In an ambient temperature of 25oC, the board temperature of a

10-watt device must be constrained below 55oC to comply with this recommendation, and for a 1-watt cup the board

can theoretically operate at up to 78oC.

From the diagram above it can be seen that the heat generated in the junction region follows a somewhat

serial conductive path through the package to the major radiating surface – which in this example is a single sided

PCB. Some additional radiation may occur directly from the upper surface of the package (not shown). This would

be conducted upward from the die surface through the transparent encapsulating material to the package surface

and be radiated from there. To all practical purposes this is a very minor effect. The polymer encapsulants in normal

use are poor conductors of heat.

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