[time-nuts] FE-5680A thermal management

Murray Greenman Murray.Greenman at rakon.com
Mon Jun 8 14:42:47 EDT 2009


I agree with Chuck. I have both an FE-5650A and an FE-5680A. With the
former I was concerned about the heat, and so ran it only for short
periods, until I understood what was going on. I had the impression from
the data sheet that there were different heatsink options for different
temperature ranges, and I now believe this led me astray.

With the FE-5680A I had the opportunity to study things in more detail.
There is no temperature range specification that I could find, and no
particular advice in the manual regarding installation. I ran the unit
from regulated 15V DC, and monitored the supply current. With no extra
cooling, the steady state current was about 700mA. With air blown over
it, the current increased. With the unit placed in a poly bag, the
current decreased to about 650mA. By the way, the current also decreased
when operated from 17V DC.

This tells me that the whole structure is part of the thermal package,
and we should not attempt to force down the case temperature just
because the unit runs hot. My experience with high performance OCXOs
tells me that the thermal environment is carefully designed, and part of
the calibration process - if you modify this environment (by cooling or
extra insulation) you modify the thermal environment, and are at risk of
modifying the performance.

I'd leave well alone, and run the unit in an open, breeze-free

Murray ZL1BPU

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