Power dissipation of 7805

[hayowazzup]

Hi all

I am trying to find out the max power dissipation of this voltage regulator

http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS007744.PDF

on page 7 it says

Typical thermal resistance values for the packages are:
Z Package: Rth(J-C) e 60 §C/W, Rth(J-A) e 230 §C/W

Does anyone know what it means?

and is the actual Power dissipating on the regulator equal to (Vin - Vout)*I?

 

[alexan_e]

I am trying to find out the max power dissipation of this voltage regulator

Check the first two graphs in page 8.

and is the actual Power dissipating on the regulator equal to (Vin - Vout)*I?

Correct

Alex

 

[hayowazzup]

Hi Alex,

I am trying to take out 5V from 24V using Z package, to supply the microcontroller.
Using the equation, the power dissipation is around 5W, do you think it will work with a heat sink mounted on?

 

[alexan_e]

The graph gives a max of 4W with an infinite heatsink and an ambient temperature or 0 degree Celcious, so no it can't work.

Your input/output difference in high so you should consider a switching regulator, for example LM2596 or LM2676 , this will increase efficiency and reduce the generated heat.

Alex