DIY Bench Power Supply 11

[SeanB]

DIY Bench Power Supply #11 - Heat Transfer between Transistor and Heatsink / Thermal Resistance Pt2

https://www.youtube.com/watch?v=BtibOjcZQQ8

[birrbert]

Excellent and detailed video! Thank you!

Martin, is there any chance to test another power transistor, e.g. MJ15003, suggested kindly by a user in my variable PSU topic? The 2N3055 is a stable component, proven over some decades, but in some regards it's old technology; certainly if I compare its junction to case thermal resistance with the MJ15003: 1.52 C/W versus 0.70 C/W. This is just one example, meaning that there could be even newer and more efficient power transistors out there.

PS: I'm not taking into consideration prices at this point, but I agree that it's a strong factor when it comes to making the final decision on which component to go for in a particular project.

[hlipka]

Its always better to have the fan blowing cool air to the heatsink than trying to suck the hot air from it. Only if you have the heatsink inside of a case it makes sense to have a second fan sucking air from the case (and then the fans should be designed so more air is blown outwards than cool air is sucked inwards - that will create a nice airflow inside of the case). Try it this way, and probably you will see another 5°C temperature reduction.

[steve30]

I'd be interested to see the differences between the fan blowing and the fan sucking. I have always wondered why some products have the fan sucking and why some have the fan blowing.

[SeanB]

Not much difference, the best way is to have the air flowing and creating enough turbulence to not have a boundary layer against the metal. Too little and there is a layer of still air which does not transfer heat, and too much means the turbulence impeded air flow and thus slows it down.