How to calculate what heatsink to use.

Exo

Active Member

• Apr 26, 2005

• #1

How must one read the datasheet to calculate what heatsink to use?

For example, say i'm using a LM7805
https://www.electro-tech-online.com/custompdfs/2005/04/LM7512CPDF.pdf

And i'm inputting 17V and using a current of 0.5A
That would make 17 - 5 = 12V * 0.5A = 6W of dissipation.

Now, what factors and graphs in the datasheet should i use and how to see what kind of heatsink to use.

 

David Bridgen

Member

• Apr 26, 2005

• #2

The first two graphs on page 5, "Typical Performance Characteristics," of the data sheet are the ones to use.

With 6W dissipation a heatsink with a thermal resistance of no more than 10degC/W is necessary.

See **broken link removed** for a thorough treatise.

 

Someone Electro

New Member

• Apr 27, 2005

• #3

whith that heat sink it wod heat up to 80 C° (at 20 C° sourundings)is its in a case or somting it cod heat up to 100 C°

meaby an 5 C°/W wod do by heating up only to 50 C° (or in a caseing up to 70C°)

 

David Bridgen

Member

• Apr 27, 2005

• #4

Someone Electro said:

whith that heat sink it wod heat up to 80 C° (at 20 C° sourundings)is its in a case or somting it cod heat up to 100 C°

Click to expand...

Yes.
No problem.

 

Exo

Active Member

• Apr 27, 2005

• #5

Thank you for your answer David.