TO220 heatsink with thick base and fins?

[cupoftea]

Hi
For space reasons, we want a heatsink which is like one of these...

https://uk.farnell.com/fischer-elektronik/sk-95-25-to-220/heat-sink-to-220-36-c-w/dp/4621554

..with one of these screwed to the back of it...

https://uk.farnell.com/wakefield-solutions/274-2ab/heat-sink-to-220/dp/1703177

...but just one part, instead of two.
Why do such things not exist?

 

[D.A.(Tony)Stewart]

WHy not use https://uk.farnell.com/fischer-elektronik/fk-214-sa-cb/heat-sink-to-220-sot-32-15-c-w/dp/4621256

 

[cupoftea]

Thanks, the back bit isnt thick enough. You need a thick back right up against the FET to take the heat out of the FET.

 

[D.A.(Tony)Stewart]

Alum has a higher heat velocity than the FET. I merely compared 'C/W specs and saw this was better in a similar size.

 

[FvM]

What's exactly the available room? Can't you use a heatsink like Fischer SK469 or SK437

 

[D.A.(Tony)Stewart]

36 °C/W, TO-220, 25 mm, 25 mm, 6.5 mm​

50 °C/W, TO-220, 13.2 mm, 12.7 mm, 19.1 mm​

15 °C/W, SOT-32, TO-220, 25.4 mm, 13 mm, 30 mm​

14 °K/W ................. 16 mm, 16 mm, 50 mm

The Rth specs assume lots of space around the heatsink, which you do not appear to have, so do not under-design it. Parallel heatsinks are not like parallel resistors for Rth.

But my guess (?) is you are just trying to add mass to absorb power-on transient.

 

[cupoftea]

Thanks, we are indeed space constrained.
The SK 469 35 STS looks best, as we have 36mm height available
The PCB is vertical mounted so the verticality of the heatsink will be violated, and it will be horizontal.

 

[crutschow]

The PCB is vertical mounted so the verticality of the heatsink will be violated, and it will be horizontal.

Then for best heatsink operation you need to mount the heat sink flat on the PCB so the fins run vertically.

 

[D.A.(Tony)Stewart]

Lack of convection air flow degrades the Rth significantly and raises the internal ambient.