[time-nuts] FE-5680A heat sink

Neville Michie namichie at gmail.com
Tue Jun 9 01:40:42 EDT 2009

some light might be shed on the heatsink problem by reading the data  
sheet for the LPRO 101 (Symmetricom)
The units will have similar issues to cope with.
The LPRO has temperature controlled lamp and filter, at different  
temperatures above 80C.
Its power consumption is shown in a chart and is reduced as the  
temperature rises because the heating power needed becomes less.
It must have a 17V internal series regulator, because total power  
consumption falls down to the minimum of 18V.
MTBF is listed as 380kh at 20C, 320kh at 30C, 253kh at 40C, 189k at  
50C and 134k at 60C.
These are values that you would expect for most solid state boards.
My solution was to put the device onto a finned heat sink in an  
aluminum box with a tiny 12V brushless fan, (40mm)
which runs on 8 volts and is switched by a thermistor in the heatsink  
to keep the baseplate at 40C.
This seems to be a good trade-off with MTBF, and the 10 MHZ xtal will  
run at a constant temperature of 40C + or - 0.05.
I have not yet assembled the gear to measure how much its performance  
is improved.
cheers, Neville Michie

On 09/06/2009, at 2:18 PM, Mark Sims wrote:

> Also see my post from June of last year where I had measured the  
> heat sink rise over ambient of several rubidium oscillators in free  
> air...  the FEI-5650 was very close to it's operating limit if  
> operated in free air and not attached to something:
> http://www.febo.com/pipermail/time-nuts/2008-June/031695.html
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