# Power dissapation?

#### Porkchop

Joined Feb 5, 2007
17
Hi guys nice forum

Little question.

I have a regulator and a bridge rectifier mounted on the same heatink.

I have calculated the power dissipated in the regulator and from this i have found the minimum heat sink C/W which is fine.

How do i calculate the rec power though ?

There is 25V sec from the transformer going in. And with a max draw of 7A

Also when i know the power dissipation of the rec how do i account for this in my heat sink thermal resistance calculation. Do i just add the to powers of the reg and rec together

Making Q the total sum?

Thanks

#### mrmeval

Joined Jun 30, 2006
833
Hard to follow what you're saying with the abbreviations. Can you add the part numbers and a a pointer to the datasheets?

#### kubeek

Joined Sep 20, 2005
5,793
power dissipation = voltage drop x current

in case of bridge rectifier it is 2*0.6V x 7A = 8.4W
You just add this number to the heat the regulator makes and recount the heatsink.

#### Porkchop

Joined Feb 5, 2007
17
Sorry. When i say Rec i mean rectifier

When i said Sec i meant the secondary winding of the step down transformer supplying the low voltage AC to the rectifier.

I just want to know how to work out the power dissipated in the rectifier first Please.