NS2W095AT Datasheet, PDF (8/19 Pages) NICHIA CORPORATION – TYPE WHITE LED

Nichia STS-DA1-0037
<Cat.No.071122>
(4) Application Design Considerations
· In designing a circuit, the current through each LED must not exceed its absolute maximum rating.
It is recommended to use Circuit B which regulates the current flowing through each LED.
In the meanwhile, when driving LEDs with a constant voltage in Circuit A, the current through
the LEDs may vary due to the variation in forward voltage (VF) of the LEDs. In the worst case,
some LED may be subjected to stresses in excess of the absolute maximum rating.
(A)
(B)
· Thermal design of the end product is of paramount importance. Please consider the heat generation
of the LED when making the system design. The coefficient of temperature increase per input
electric power is affected by the thermal resistance of the circuit board and density of LED placement
on the board, as well as other components. It is necessary to avoid intense heat generation and operate
within the maximum ratings given in this specification.
· Please determine the operating current with consideration of the ambient temperature local to the LED
and refer to the plot of Ambient temperature vs. Allowable Forward Current on CHARACTERISTICS
in this specifications. Please also take measures to remove heat from the area near the LED to improve
the operational characteristics of the LED.
· The equation 1 indicates correlation between Tj and Ta, and the equation 2 indicates correlation
between Tj and Ts.
Tj=Ta + Rja W
1
Tj=Ts + Rjs W
2
Tj = Dice Temperature : °C, Ta = Ambient Temperature : °C,
Ts = Solder Temperature (Cathode Side) : °C,
Rja = Heat resistance from Dice to Ambient temperature : °C /W,
Rjs = Heat resistance from Dice to Ts measuring point ≒ 55°C /W,
W = Inputting Power (IF VF) : W
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