[time-nuts] need power trans. for HP3325

[Didier Juges]

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