Does anyone have experience using diamond shaped top-mount TO-3 heatsinks like the Aavid PF523 or Fischer Elektronik AKK 127?
Since these heatsinks are anodized or lacquered and mount on top of the transistor, it seems like screws would not be able to establish an electrical connection to the collector/case as they typically might.
I'm not sure if there's space between the transistor top and the heatsink to place a ring terminal connector, or if this would then create a gap in the transistor-heatsink interface and interfere with heat transfer.
Assuming that the TO-3's are attached to a T-bracket and then a PCB mounted underneath the bracket, I'm curious if anyone knows the ideal method and required components for installing these heatsinks. I've reached out to Aavid, but thought I'd also see if anyone here has used this style of heatsink as an additional measure for keeping TO-3s cool.
Since these heatsinks are anodized or lacquered and mount on top of the transistor, it seems like screws would not be able to establish an electrical connection to the collector/case as they typically might.
I'm not sure if there's space between the transistor top and the heatsink to place a ring terminal connector, or if this would then create a gap in the transistor-heatsink interface and interfere with heat transfer.
Assuming that the TO-3's are attached to a T-bracket and then a PCB mounted underneath the bracket, I'm curious if anyone knows the ideal method and required components for installing these heatsinks. I've reached out to Aavid, but thought I'd also see if anyone here has used this style of heatsink as an additional measure for keeping TO-3s cool.
Maybe those are technically acting as heat sinks by adding some surface area, but I feel their real purpose is 'don't touch hot/live part.'
The top is a cover, the junction is on the flat plate, which is the normal heat sink attachment place.
The heat will not be transferred efficiently to the top.
The top heat sink is not a practical solution, and is purely a cosmetic / safety usage.
The heat will not be transferred efficiently to the top.
The top heat sink is not a practical solution, and is purely a cosmetic / safety usage.
The die is not attached to the cover, so I doubt these are designed for high power situations. The base is the "heat spreader" and this needs to be sinked via a nice thick piece of aluminium connected to the main heatsink for high power use. I use these heatsinks for TO-3 BJTs that are not drawing too many amps - https://za.rs-online.com/web/p/heatsinks/1764162/ or these space permitting - WA208 14 | Heatsink, 2.2K/W, 97x75x25mm | RS Components, but at a total minimum these - KL 151-3 | Heatsink, 6K/W, 46 x 46 x 25mm | RS Components
Correct, the thermal resistance from the die to the flange ends making contact with the top heatsink will be much higher than the usual quoted Theta JC.
Considering that they are inside the equipment and probably have cluttered air flow around them, 20 C/W is a more realistic value in practice
Considering that they are inside the equipment and probably have cluttered air flow around them, 20 C/W is a more realistic value in practice