[Elecraft] KLPA3A power transistor thermal stress concerns

[Clay Autery]

If anyone requires someone to assist in REALLY getting "nutty" about 
thermal control/dissipation on electronic components, I'd be happy to 
oblige from my experience.
I have had some fairly extensive hand-on experience.  Once upon a time, 
I invented Arctic Silver thermal compound and adhesive. Before, during, 
and after that time I spent thousands of hours working on custom thermal 
control solutions.

It's.... an addiction.

73,
Clay KY5G


On 10/27/2017 6:00 PM, Don Wilhelm wrote:
> Bill is entirely correct.
> Once in my prior career, I did a study of Mean Time Between Failure 
> for IC circuits (same applies to transistors).  That study had to 
> consider the case temperature of the IC (or transistor) with respect 
> to the junction temperature.
> The specification for the IC or transistor package will include a 
> thermal resistance parameter, which must be considered to obtain the 
> maximum temperature for the case of the device.
>
> Bill's comment about the screw tightness is entirely correct - the 
> heat of the device case must be transferred to the heatsink in an 
> efficient manner.
>
> 73,
> Don W3FPR
>
> On 10/27/2017 6:07 PM, Nr4c wrote:
>> Yes. But I believe that is Junction temperature, not case on heatsink 
>> temp.  Remember the case bottom is heatsink for those. Make sure 
>> screws are tight.
>>
>> Sent from my iPhone
>> ...nr4c. bill
>>
>>
>>> On Oct 27, 2017, at 12:19 PM, N2TK, Tony <tony.kaz at verizon.net> wrote:
>>>
>>> 50C is not hot for a transistor. Commercial transistors are usually 
>>> speced to 85C. JANS (space) transistors are speced to 125C and 
>>> actually baked without bias for 320 hours at 200C. The hFE is 
>>> measured before and after to check for change.