[Halld-tagger] specs for microscope readout power supplies

[Richard Jones]

Hello Fernando,

I am spec'ing the Vbias supply capacity at 500mA to allow for the maximum
SiPM draw current that is permitted by the bias voltage supply system.
 Initially we expect the average current to be around 15 mA at full
intensity (2.2 uA electrons on 20 micron diamond) but that it will increase
gradually over time due to radiation damage.  To get the maximum current
spec, I imagine the worst possible circumstances under which the radiation
damage might accumulate faster than expected, and ask how much current
could we sustain across all channels before the resolution and efficiency
degrade significantly due to dark current.  The answer to that is
approximately 800uA per channel, which totals about 400mA from the supply.
 I rounded that up to 500mA.

-Richard Jones


On Thu, Dec 5, 2013 at 4:51 PM, Fernando J Barbosa <barbosa at jlab.org> wrote:

> Hi Richard,
>
> I looked at the specs and the bias supply current seems to be excessive at
> 500mA. What's the reason for this?
>
> Best regards,
> Fernando
>
>
>
> On 12/5/2013 3:33 PM, Richard Jones wrote:
>
>> Hello Alex,
>>
>> Here is a draft of the specs for the microscope readout dc power
>> supplies.  They can be a single unit for each of 3 levels, or a few
>> lower-capacity supplies in tandem with the same total output capacity.
>>  Please request justification for any of the specs.  One thing we do not
>> spec here, but think would be useful, is separate delivery and sense
>> terminals for each output.  We have separate pins on the backplane
>> connector for this purpose.
>>
>> http://zeus.phys.uconn.edu/wiki/index.php/Microscope_
>> Electronics#Power_Supply_Requirements
>>
>> -Richard Jones
>>
>
>
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