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Heat sink calculations

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ljcox

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I'm trying to determine whether I need a heat sink for a BD682 Darlington transistor.
The data sheet states Pc 14W @ Tc = 25C.
Rja junction to ambient 88C/W
Tj max junction temperature 150C
Rjc junction to case 3.12 C/W
Rja junction to ambient 100C/W

The maximum power that the device will have to dissipate is 560 mW.

Do I need a heat sink? I did an internet search but the results were much more complicated than I need.

The Silicon Chip magazine gave an example of a heat sink calculation for a MOSFET which is relatively simple but I became confused when I tried to do it for the BD682.

Any assistance will be appreciated.
 

Hi,

You have all the necessary values - except max ambient temperature .... so why not calculate it on your own?
The formulas can ve found all over the internet. Show your calculations.

Why there are two different values for junction to ambient?

Klaus
 

KlausST said:
Hi,

You have all the necessary values - except max ambient temperature .... so why not calculate it on your own?
The formulas can ve found all over the internet. Show your calculations.

Why there are two different values for junction to ambient?

Klaus
Click to expand...

Thanks Klaus.
I tried to find the info on the internet but the ones I found calculated the thermal resistance of a heat sinks which is not what I want.

The reason why there are 2 values for junction to ambient is because the Fairchild data sheet said 88C/W and the SGS Thompson one said 100C/W.
 

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