It all depends what the -12V rail is for, some have said it directly references the EFC dac. I would hope an ocxo would have a better tuning gain on its efc pin than supply pin but maybe that's not always true.
On Saturday, 22 October 2016, Bob Camp <kb...@n1k.org> wrote: > Hi > > The +12 goes straight to the OCXO. All OCXO’s have a voltage sensitivity. > That sensitivity is much higher than voltage sensitivity is much higher > than > what you see on the other two supply pins. > > Bob > > > On Oct 21, 2016, at 11:06 PM, Scott Stobbe <scott.j.sto...@gmail.com > <javascript:;>> wrote: > > > > Interesting, I would have thought that the +12V input would be extremely > > well regulated since its shared with the oven heater, I*R drops are going > > to show up every where, if your looking for uV levels of stability. > > Just a connector has milliohms of contact resistance, let alone routing > and > > cables... > > > > On Friday, 21 October 2016, Bob Camp <kb...@n1k.org <javascript:;>> > wrote: > > > >> Hi > >> > >>> On Oct 21, 2016, at 7:44 PM, Scott Stobbe <scott.j.sto...@gmail.com > <javascript:;> > >> <javascript:;>> wrote: > >>> > >>> A little more data on the 7912. > >>> > >>> The first plot shows the tempCo of the 7912 measured with ambient > >>> temperature swings "7912_TempCo.png". Which is -150 ppm/degC. > >>> > >>> The second plot is off a 7912 logged for an hour or so, > "7912_1PLC.png", > >>> nothing too interesting here. However the environmental temperature > swing > >>> of about 1 degC/hour is pretty conservative for a DUT sitting in free > >> air. > >>> > >>> Finally, an allan devation plot looking at the normalized stability of > a > >>> 7912 regulator "7912_AllanDeviation.png". Interestingly here, is, how > >> quick > >>> a 15 mK/min temperature swing shoots above the 1/f floor, it's a matter > >> of > >>> seconds. > >>> > >>> Now if your PSRR is 1 ppb/V or better, then all of this is comfortably > >>> below the intrinsic noise of a thunderbolt. > >> > >> The main point is that the internal tempco of the TBolt it’s self is > much > >> larger than > >> the issues surrounding the power supply pins. The +12 is the only one > that > >> is > >> sensitive enough to voltage (change in frequency vs voltage) to > contribute > >> to any > >> significant way to the overall stability. > >> > >> Bob > >> > >>> > >>> On Fri, Oct 21, 2016 at 12:20 AM, Scott Stobbe < > scott.j.sto...@gmail.com <javascript:;> > >> <javascript:;>> > >>> wrote: > >>> > >>>> Nick had mention that the -12V rail on the thunderbolt has the poorest > >>>> PSRR with respect to frequency output, so I first took a look at the > >>>> venerable 7912. > >>>> > >>>> The first data-set was taken with a -13.5 VDC input. Attached is the > 0.1 > >>>> Hz to 10 Hz noise of an essentially quiescently loaded 7912, only a > 10k > >>>> resistor was added as load for preliminary evaluation. With a 60 dB > >> preamp > >>>> the scale of the scope plot is 20 uV/div. The 0.1Hz to 10Hz band noise > >> is > >>>> 15 uVrms, which is about 1.3 ppm rms of the DC mean. > >>>> > >>>> In allan deviation terms, a quiescently loaded 7912 has a spot noise > of > >> 7 > >>>> uV/rtHz at 1 Hz (on the 1/f slope), normalized that's 580 ppb/rtHz. > >>>> Equivalently speaking, the flicker noise floor of an allan deviation > >> plot > >>>> would be sqrt(2*ln(2)) that figure to be 6.8E-7. > >>>> > >>>> Assuming a thunderbolt should be achieving 1/f floor of around 1E-12, > it > >>>> would need a PSRR of at least 1 ppm/V. I'm sure someone has gone to > the > >>>> trouble of actually measuring it. > >>>> > >>>> So from a 0.1 Hz to 10 Hz noise standpoint, the 7912 isn't terrible > >>>> with 1.3 ppm rms noise, considering an LM399 is about 0.1 ppm rms, > only > >> one > >>>> order of magnitude off. > >>>> > >>>> The bad side of a 7912 is in long-term stability and tempCo, the > sample > >> I > >>>> tested had at least a 150 ppm/degC tempCo, which is going to put a > >> serious > >>>> lump/bump in the 10s tau to gps crossover point on an allan deviation > >> plot. > >>>> > >>>> > >>>> > >>>> On Tue, Oct 18, 2016 at 3:05 PM, Scott Stobbe < > scott.j.sto...@gmail.com <javascript:;> > >> <javascript:;>> > >>>> wrote: > >>>> > >>>>> I'm sure I have some 7805s lying around, maybe a 7812/7912. I'm > >>>>> interested to see the 1/f noise of a classic regulator, what load > >> current > >>>>> do you expect? I can bias a 7805 for the same load and measure the > 0.1 > >> to > >>>>> 10 Hz noise. > >>>>> > >>>>> Also if you have a digital scope without a very good builtin FFT, > >> octave > >>>>> would be one solution. > >>>>> > >>>>> On Tue, Oct 18, 2016 at 10:46 AM, Nick Sayer via time-nuts < > >>>>> time-nuts@febo.com <javascript:;> <javascript:;>> wrote: > >>>>> > >>>>>> Just an update. I’ve built the second prototype board (I skipped > over > >>>>>> the first design), and it’s powering my tbolt right now. > >>>>>> > >>>>>> The design calls for 15v in (though it would also work with 13.8v). > >> The > >>>>>> +12 output comes from a D2PAK 7812. For +5, there is an AP1509 buck > >>>>>> converter to make around 6.5 volts, then a DPAK 7805. For -12, there > >> is an > >>>>>> MC34063 configured as an inverter to make around -13.75 volts and > >> then a > >>>>>> DPAK 7912. > >>>>>> > >>>>>> Steady-state, the system appears to be working just fine. The > AP1509’s > >>>>>> inductor and the D2PAK 7812 are just warm to the touch. > >>>>>> > >>>>>> I checked for noise and ripple on the outputs and it’s somewhere > >> around > >>>>>> ±2 mV or so generally. From what I can see on the scope, there’s no > >> ripple > >>>>>> - it’s all high frequency noise. I am not absolutely certain that > the > >> noise > >>>>>> measurement represents real noise or the limits of my measuring > >> ability. > >>>>>> I’m just using the scope probes the scope came with, and 2 mV/div is > >> its > >>>>>> lowest range. > >>>>>> > >>>>>> I haven’t compared the noise with the ex laptop supply that I was > >> using > >>>>>> before, but I’d have to believe it’s cleaner. I don’t really have a > >> way to > >>>>>> check the oscillator’s before and after ADEV. My only other > reference > >> is an > >>>>>> FE5680A, and I think the thunderbolt’s going to be far better at > >> lower tau > >>>>>> (where this all matters). > >>>>>> > >>>>>> I know also that ±2 mV is still one and perhaps two orders of > >> magnitude > >>>>>> higher than some have called for. But before I attempt to reduce the > >> noise > >>>>>> further, I’d like to know that there are real gains to be had. Would > >>>>>> someone with a Thunderbolt and better output noise measuring > >> wherewithal be > >>>>>> willing to take a prototype and compare it with something that does > >> have µV > >>>>>> levels of noise and ripple so I can get an idea of what there is to > >> gain? > >>>>>> If you like, you can make such comparisons public - no secrets here. > >>>>>> > >>>>>>> On Aug 30, 2016, at 10:37 PM, Nick Sayer <nsa...@kfu.com > <javascript:;> > >> <javascript:;>> wrote: > >>>>>>> > >>>>>>> > >>>>>>>> On Aug 30, 2016, at 8:48 PM, Cube Central <cubecent...@gmail.com > <javascript:;> > >> <javascript:;>> > >>>>>> wrote: > >>>>>>>> > >>>>>>>> I would be interested, I think. Planning ahead for if the one I > >> have > >>>>>> for my Thunderbolt fails, I guess. Are there different models or > >> would a > >>>>>> photo of the input ports on mine be useful? > >>>>>>> > >>>>>>> Actually, what I had in mind is to just put a SIP4 header on the > >> board > >>>>>> for the output and people could wire the “last mile” themselves. The > >> input > >>>>>> is a 2.1mm barrel connector. You use whatever 15W 12VDC wall wart is > >> handy > >>>>>> and plug it right in. > >>>>>>> > >>>>>>> What it really amounts to is that you get +12 volts directly from > the > >>>>>> input, then there’s a buck converter to drop the +12 down to +5 and > an > >>>>>> inverter to generate -12 from the +12. Those 3 voltages, plus a > >> ground go > >>>>>> to the SIP4. > >>>>>>> > >>>>>>> So it’s just two switching power supplies to turn a +12 volt only > >>>>>> supply into the three-way that the Thunderbolt wants. > >>>>>>> > >>>>>>> It’d be good for around 1500 mA @ 5V and around 50 mA @ -12 (the > +12 > >>>>>> spec is whatever is left from the source supply’s power spec) - more > >> than > >>>>>> enough for a Thunderbolt. Probably enough for a hard disk or a > >> smallish PC. > >>>>>> _______________________________________________ > >>>>>> time-nuts mailing list -- time-nuts@febo.com <javascript:;> > <javascript:;> > >>>>>> To unsubscribe, go to https://www.febo.com/cgi-bin/m > >>>>>> ailman/listinfo/time-nuts > >>>>>> and follow the instructions there. > >>>>>> > >>>>> > >>>>> > >>>> > >>> <7912_1PLC.png><7912_AllanDeviation.png><7912_ > >> TempCo.png>_______________________________________________ > >>> time-nuts mailing list -- time-nuts@febo.com <javascript:;> > <javascript:;> > >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >>> and follow the instructions there. > >> > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@febo.com <javascript:;> > <javascript:;> > >> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com <javascript:;> > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com <javascript:;> > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.