[time-nuts] Anybody want a Thunderbolt power supply

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Sep 1 02:18:34 EDT 2016

It will show up if the value of the voltage setting bypass capacitor is reduced. Both the Johnson and excess noise in this resistor coupled with the current source flicker noise should become evident. The datasheet graphs indicate that the Johnson noise of the voltage setting resistor(33k2 ~22nV/rtHz) isn't significant in comparison with other sources.


    On Thursday, 1 September 2016 5:56 PM, Gerhard Hoffmann <dk4xp at arcor.de> wrote:

 Am 01.09.2016 um 06:07 schrieb Bruce Griffiths:
> I have a quad LT3042 PCB that I must get around to assembling.One potential issue with the LT3042 is the relatively high noise at low frequencies when the capacititve bypassing of the resistor that sets the output voltage is ineffective.

I wonder where that relatively high noise on the LT3042 might hide.


That is maybe 3 nV/RT Hz at 10 Hz, and the limit is probably not the 
LT3042 but
the GR-like noise of my old preamp below 30 Hz. (rises faster than 1/f)
Remember that 0 dB in the plot is 1 nV rt Hz, which is the equivalent 
INPUT noise voltage
of an AD797 or LT1028.

The LT4042 measurement was taken from an ugly dead bug ad-hoc construction.
Deviating from the 4.7u output cap produces some noise peaks @ > 100 KHz.
(but still 30 dB better than the others)
More is less here.

regards, Gerhard

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