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 < [email protected]> 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 <[email protected]> wrote: > > > > > >> On Aug 30, 2016, at 8:48 PM, Cube Central <[email protected]> > 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 -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
