100mV DC supply

On Thu, 13 Jul 2017 19:09:12 -0700 (PDT), pcdhobbs@gmail.com wrote:

>>Really low-noise amps need low-value feedback resistors to keep 
>>Johnson noise down, which implies a lot of opamp current even with no 
>>load. So sometimes one adds a buffer just to drive the feedback 
>>resistors. 
>
>Yup.  300-kelvin resistors are a serious inconvenience when your active devices have 0.01-K noise temperatures. (BF862s are about that good in the flatband.)
>
>Cheers
>
>Phil Hobbs

The NMR amps needed PPM-flat current pulses, so we didn't want thermal
tails in the current shunt amp. Hence the buffer inside the loop.

We made our own current shunts, too. That's a whole nother story.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

On Thu, 13 Jul 2017 18:42:06 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

>On Thursday, July 13, 2017 at 6:16:34 PM UTC-4, Phil Hobbs wrote:
>> On 07/13/2017 12:21 PM, dagmargoodboat@yahoo.com wrote:
>> > On Thursday, July 13, 2017 at 12:13:23 PM UTC-4, John Larkin wrote:
>
>> >> Some opamps, especially RRO types, are c-load stable.
>> >>
>> >> Almost any opamp is c-load stable with enough C!
>> >
>> > I once put a 100,000uF low e.s.r. capacitor on the output of a SMPS.
>> > It cleaned up the load-step response nicely.
>> >
>> >
>> BFC superpowers to the rescue.
>> 
>> Cheers
>> 
>> Phil "use a bigger hammer" Hobbs
>
>Yep. I had to drive through a 300A load step without losing more than
>about a volt, IIRC.
>
>Hey, Wikipedia's disambiguation page for "BFC" lists one possible
>meaning as "Engineering slang for a supercapacitor." :-)
>
>Cheers,
>James Arthur

It must be French. Beaucoup Farads.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

On Thursday, July 13, 2017 at 11:22:37 PM UTC-4, John Larkin wrote:
> On Thu, 13 Jul 2017 18:42:06 -0700 (PDT), dagmargoodboat@yahoo.com
> wrote:
> 
> >On Thursday, July 13, 2017 at 6:16:34 PM UTC-4, Phil Hobbs wrote:
> >> On 07/13/2017 12:21 PM, dagmargoodboat@yahoo.com wrote:
> >> > On Thursday, July 13, 2017 at 12:13:23 PM UTC-4, John Larkin wrote:
> >
> >> >> Some opamps, especially RRO types, are c-load stable.
> >> >>
> >> >> Almost any opamp is c-load stable with enough C!
> >> >
> >> > I once put a 100,000uF low e.s.r. capacitor on the output of a SMPS.
> >> > It cleaned up the load-step response nicely.
> >> >
> >> >
> >> BFC superpowers to the rescue.
> >> 
> >> Cheers
> >> 
> >> Phil "use a bigger hammer" Hobbs
> >
> >Yep. I had to drive through a 300A load step without losing more than
> >about a volt, IIRC.
> >
> >Hey, Wikipedia's disambiguation page for "BFC" lists one possible
> >meaning as "Engineering slang for a supercapacitor." :-)
>
> It must be French. Beaucoup Farads.

Wouldn't that have to be Beau Farads Coup?

It was a monster computer-grade electrolytic, an absolute beast.

My task was helping a COTS Mean Well 24V supply weather a 300A peak impulse
without losing voltage, and without modifying the Mean Well. That didn't
leave many options, so out came the BFC.

I tested the impulse response and monitored the SMPS' switching--the Mean Well
seemed to like it just fine.

Cheers,
James Arthur