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

[Павел Шатов]

On 26.03.2015 1:19, Fredrik Thulin wrote:
> 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).

Excuse me, I can't understand. What has plenty of noise? Charge pump 
output or noise circuit output?

>> 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.

I recommended SEPIC (LTM8045?) regulator exactly for this purpose. You 
don't need to increase input voltage and can leave it at 12V nominal. If 
you are not sure what output voltage you need, then you can use 
adjustable LDO (LT1761?) in the second stage.

--
With best regards,
Pavel Shatov