# Power dissapation?

Discussion in 'The Projects Forum' started by Porkchop, Feb 5, 2007.

1. ### Porkchop Thread Starter Member

Feb 5, 2007
17
0
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

2. ### mrmeval Distinguished Member

Jun 30, 2006
833
2
Hard to follow what you're saying with the abbreviations. Can you add the part numbers and a a pointer to the datasheets?

3. ### kubeek AAC Fanatic!

Sep 20, 2005
4,590
777
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.

4. ### Porkchop Thread Starter Member

Feb 5, 2007
17
0
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.

5. ### Porkchop Thread Starter Member

Feb 5, 2007
17
0
Smashing thank you. I did get that result but i assumed it to be far to low tbh

Going off this it looks like i might be better having it on a seportat heat sink, i think i might actually be heating it up lol

Thanks guys!