[Cryptech Tech] Updated version of alpha board drawing and description available

[Fredrik Thulin]

On Wednesday, March 25, 2015 11:24:55 PM Павел Шатов wrote:
...
> I want to clarify one thing regarding power supply. How is Fredrik's
> circuit powered now? 

I've deferred the real power solution for the avalanche noise circuit until 
now. Provisionally, I've been using two cascaded LMC7660IM charge pumps to get 
a total of 15v (-15v to be precise). This has plenty of noise in the range of 
125 mV. Old screenshot of this from my scope is attached (yellow input A/C 
coupled).

> If it requires very clean power, then dedicated
> two-stage power regulator should be used to power it. This is the common
> approach used to power critical analog components. The first stage is a
> switching regulator, the second stage is a low-dropout linear regulator.
> You can use SEPIC converter with 12.5V output as the first stage
> followed by LDO regulator with 12.0V output as the second stage.

Yes, I've acquired three different 12v LDOs to try this approach. I think/hope 
12v is enough to get the avalanche effect - I tested different voltages a long 
time ago and 10 was too little (get too low frequency noise) but I think 12 
was enough. Have to test to know for sure.

Anyway, that is why we upped the input voltage from 12 to > 12 in the diagram. 
Before testing I don't feel confident to say 12 will be enough though. What I 
know for sure is that 15 is enough.

/Fredrik
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