battery chargers, again
in [Design]
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From: John Larkin on 30 Sep 2009 16:28 On Wed, 30 Sep 2009 13:01:31 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jan Panteltje wrote: >> On a sunny day (Wed, 30 Sep 2009 11:17:34 -0700) it happened Joerg >> <invalid(a)invalid.invalid> wrote in <7ihlm2F3179urU2(a)mid.individual.net>: >> >>>> Are you referring to the loop filter? >>>> There is no loop filter. >>>> >>> No, to the output filter. You can't possibly let the ripple just saunter >>> out the banana jacks of a bench supply and pollute whatever it find >>> downstream. >> >> 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. 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. People should use delta-sigma in switchers instead of PWM. John
From: Vladimir Vassilevsky on 30 Sep 2009 17:04 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) ? > range > of interest straddling all the switcher frequencies. Synchronize the switchers away from the particular frequency of interest? > I'm planning on > spread-spectrum wobulating all the switchers, just in case. So the dirt will be in band for sure? How about combining the results of two measurements with the different switcher frequencies? > 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. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: Jan Panteltje on 30 Sep 2009 17:22 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. !
From: Joerg on 30 Sep 2009 17:23 John Larkin wrote: > On Wed, 30 Sep 2009 13:01:31 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jan Panteltje wrote: >>> On a sunny day (Wed, 30 Sep 2009 11:17:34 -0700) it happened Joerg >>> <invalid(a)invalid.invalid> wrote in <7ihlm2F3179urU2(a)mid.individual.net>: >>> >>>>> Are you referring to the loop filter? >>>>> There is no loop filter. >>>>> >>>> No, to the output filter. You can't possibly let the ripple just saunter >>>> out the banana jacks of a bench supply and pollute whatever it find >>>> downstream. >>> 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. > > 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. > Spread spectrum just smears the noise so it looks lower (and is to some extent but not a lot). Like throwing excess junk under the sofa and pretending it ain't there no more. Since you wrote spectral line, how about rotating the switchers through three different frequencies and have the ADC always look in the quiet bands? > People should use delta-sigma in switchers instead of PWM. > You could completely oversize them and run in pulse-skipping mode but it wouldn't help much. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 30 Sep 2009 17:29
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 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? John |