battery chargers, again
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From: Vladimir Vassilevsky on 30 Sep 2009 17:30 Joerg wrote: > John Larkin wrote: > >> I'm working on a smallish board that has four switchers in one corner >> and an ADC that's looking for a 1 nV spectral line in the other, range >> of interest straddling all the switcher frequencies. I'm planning on >> spread-spectrum wobulating all the switchers, just in case. >> > > Since you wrote spectral line, how about rotating the switchers through > three different frequencies and have the ADC always look in the quiet > bands? Besides, you can cancel the components that are correlated with the rate of the rotation of the switchers. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: Joerg on 30 Sep 2009 17:31 Jan Panteltje wrote: > On a sunny day (Wed, 30 Sep 2009 13:01:31 -0700) it happened Joerg > <invalid(a)invalid.invalid> wrote in <7ihrovF320ev9U2(a)mid.individual.net>: > >>> All depends, 10mV is fine with me:-) >>> >>> You really got to come up with some numbers, else it all makes no sense, >>> >> Ok, this is the number I typically need: Not being able to show the >> ripple on a scope when set to 2mV/div. Good enough? >> >> Seriously, 10mV piping out would be disastrous when doing things like >> ultrasound experiments. > > LOL I have done quite interesting ultrasound Doppler experimensts. > If your circuit is so bad that it cannot tolerate 10 mV ripple on the supply line, > then I suggest you change to gardening. > So, then, how many beamformers, audio Dopplers and color flow modules have you brought from blank sheet to market? Experiments, revenue product, two different things. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 30 Sep 2009 17:33 Vladimir Vassilevsky wrote: > > > Joerg wrote: > >> John Larkin wrote: >> >>> I'm working on a smallish board that has four switchers in one corner >>> and an ADC that's looking for a 1 nV spectral line in the other, range >>> of interest straddling all the switcher frequencies. I'm planning on >>> spread-spectrum wobulating all the switchers, just in case. >>> >> >> Since you wrote spectral line, how about rotating the switchers >> through three different frequencies and have the ADC always look in >> the quiet bands? > > Besides, you can cancel the components that are correlated with the rate > of the rotation of the switchers. > That's how we do it in ultrasound. The first time I suggested it (and it works!) I said "... and that will be just software", almost causing a coffee mug from an attending SW engineer to come flying at me. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jan Panteltje on 30 Sep 2009 17:37 On a sunny day (Wed, 30 Sep 2009 14:31:10 -0700) it happened Joerg <invalid(a)invalid.invalid> wrote in <7ii112F31qi8nU3(a)mid.individual.net>: >Jan Panteltje wrote: >> On a sunny day (Wed, 30 Sep 2009 13:01:31 -0700) it happened Joerg >> <invalid(a)invalid.invalid> wrote in <7ihrovF320ev9U2(a)mid.individual.net>: >> >>>> All depends, 10mV is fine with me:-) >>>> >>>> You really got to come up with some numbers, else it all makes no sense, >>>> >>> Ok, this is the number I typically need: Not being able to show the >>> ripple on a scope when set to 2mV/div. Good enough? >>> >>> Seriously, 10mV piping out would be disastrous when doing things like >>> ultrasound experiments. >> >> LOL I have done quite interesting ultrasound Doppler experimensts. >> If your circuit is so bad that it cannot tolerate 10 mV ripple on the supply line, >> then I suggest you change to gardening. >> > >So, then, how many beamformers, audio Dopplers and color flow modules >have you brought from blank sheet to market? Experiments, revenue >product, two different things. Try readng what I wrote.
From: Joerg on 30 Sep 2009 17:40
John Larkin wrote: > On Wed, 30 Sep 2009 16:04:00 -0500, Vladimir Vassilevsky > <nospam(a)nowhere.com> wrote: > >> >> John Larkin wrote: >> >> >>> I'm working on a smallish board that has four switchers in one corner >>> and an ADC that's looking for a 1 nV spectral line in the other, >> The 1nV over the background of how many nV/root(Hz) ? > > About 1. That's our target noise floor. The existing system is > ballpark 100 nv/rtHz with huge birdies all over the place. > > Never let scientists design electronics. > >>> range >>> of interest straddling all the switcher frequencies. >> Synchronize the switchers away from the particular frequency of interest? > > The signals can be all over the place. > >>> I'm planning on >>> spread-spectrum wobulating all the switchers, just in case. >> So the dirt will be in band for sure? > > Yup. Operating range is audio to many MHz, all at once. We digitize at > 64 Ms/s and FFT and see what's there. > How many MHz is "many"? And how much power does the biggest of the switchers have to deliver? >> How about combining the results of two measurements with the different >> switcher frequencies? > > That might be interesting. Actually, we could determine the birdie > level from occasionally running with a null sample, and subtract that > out if it's not huge. But the main plan is to keep things clean. > >>> People should use delta-sigma in switchers instead of PWM. >> No problem except the switching losses will be an order of magnitude >> higher. Delta sigma has the spurious products, also. > > Yeah, I suppose so. Spread-spectrum will have to do. It has its own > complications. If I triangle-modulate all the switcher frequencies, I > don't want the triangle to appear on the power rails either. That > could easily happen. Spice? Breadboard? Take a chance? Go linear with > big heat sinks? > It almost sounds like linear is the best option if you can stomach the dissipation. Or triple banding but that doesn't work if you must keep a full spectrum view at all times at full bandwidth. If that's the case and you want switchers you'd have to run them above the upper end of your spectral range. Some ISM frequency like 13.56MHz or 27.12MHz so you don't get into trouble with the federales. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |