[time-nuts] need power trans. for HP3325
Didier Juges
didier at cox.net
Mon Mar 26 00:16:55 UTC 2007
Dr Bruce Griffiths wrote:
> Didier Juges wrote:
>
>> Even though you may have to be careful about noise, and assuming the
>> operating voltages are not exotic, you can probably find an
>> off-the-shelf switching supply that will fit where the transformer and
>> linear supplies were, with lots of room to spare, and significantly
>> reduced heat dissipation. I am thinking about doing that with the 5370,
>> considering how hot the rear heat sink runs.
>>
>> Didier KO4BB
>>
>>
>>
>
> Didier
>
> Replacing the HP5370 power supply with switching regulators will be a
> somewhat challenging exercise in ensuring that switching regulator noise
> doesn't degrade the 5370 performance. Even verifying this will be
> challenging. If you don't burn yourself on the external heatsink there
> should be no problem with reliability of the linear regulators.
>
> Bruce
>
>
Bruce,
I am not too concerned about reliability. Power transistors are designed
to run hot. I am concerned about burning myself on the heat sink (it
measures well over 60 degree C here), and overall power consumption and
heat dissipation in the shack, because the instrument is typically
running a lot of time. I have installed it on top of the short rack I
made for my main instruments to maximize air flow, but as a result, the
heat sink is quite exposed. Also, my shack is above the garage, and
therefore the air conditioning is not too effective there (3 walls,
ceiling and floor face non A/C spaces).
I have not looked in detail, but I suspect the voltage drop across the
linear regulators is a little too high and probably could be reduced.
I may also look at simply putting a switching pre-regulator in front of
the existing linear regulators (or at least the worst offender, I am
sure the 5V supply must be loaded pretty well) to reduce the voltage
drop and the heat, while keeping the good regulation and low noise of
the linears. I have a box of LT1074 integrated switching regulators
which require only a handfull of components to make a complete switching
supply.
A small fan would address the high temperature, but would not help with
power consumption and dissipation. That would be an easy fix though.
Didier
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