High power LED heat dissipation calculation formula

If the junction temperature for TJ, environmental temperature for TA, LED power consumption for PD, RJA and TJ, the relationship between TA and PD to RJA = ( TJ - TA) / PD ( 1) Type in the PD is the unit of W. PD and positive pressure drop VF LED and LED, based on the relationship between the forward current of the IF PD = VF x IF ( 2)

if has LED the temperature of the cooling pads TC, is ( 1) Type can be written as RJA = ( TJ - TC) /PD+( TC- TA) / PD RJC = ( TJ - TC) / PD ( 3) RBA=( TC- TC) / PD ( 4)

in the heat calculation, when choosing the high power LED, can be found from the data sources in the RJC value; When determining the LED forward current IF, VF PD may be calculated according to the LED; If have measure the temperature of TC, the press ( 3) Type can be calculated to TJ. Before measuring the TC to do an experiment board ( Choosing a PCB, determine the certain area) , welding on the LED, and input the IF current, stable, with K type thermocouple thermometer measures LED cooling pad temperature TC.

in the ( 4) Type of TC can be detected and TA, PD can be calculated, the RBA value can be calculated. TJ, if calculated in ( 1) To calculate RJA type can be.

this TJ calculated through test, the method is based on some kind of PCB and heat dissipation area. If the calculated TJ less than requirements ( Or equal to) TJmax, can think selection of PCB and area of appropriate; If calculation to TJ is greater than the required TJmax, best to replace the cooling performance of PCB, or increasing the cooling area of PCB.

in addition, if choose LED RJC value is too large, also can be replaced on the performance better on design and RJC value smaller high-power LED, to meet the calculated TJ TJmax or less. To this point in the calculation example.

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