battery chargers, again
in [Design]
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From: Rich Grise on 1 Oct 2009 13:55 On Wed, 30 Sep 2009 14:29:06 -0700, John Larkin wrote: > ... could easily happen. A. Spice? B. Breadboard? C. Take a chance? D. Go linear with big heat sinks? > D. Good ol' American Brute Force; sorta kill two birdies with one stone? ;-P Cheers! Rich
From: Joerg on 1 Oct 2009 16:10 John Larkin wrote: > On Wed, 30 Sep 2009 14:40:06 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> 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? > > 20-ish. And just a couple of watts. I need 5, 3.3, 2.5, 1.8, 1.2, and > -5. All from +12. > Theoretically you could run it at 27.12MHz but that's nasty. If you can't stomach the dissipation of linears then you may be stuck with some spectral dodging scheme like the one I described. We do that in ultrasound sometimes but there I could always get a few clock control lines from some a DSP or FPGA. If I bought the digital and SW guys some beers that night ... -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 1 Oct 2009 16:13 John Larkin wrote: > On Wed, 30 Sep 2009 14:23:38 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> 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. > > It will take a big spectral spike and make it into wide and low hump. > If the psd gets below my 1 nv/rtHz noise floor, it's as good as gone. > >> Since you wrote spectral line, how about rotating the switchers through >> three different frequencies and have the ADC always look in the quiet bands? > > No, we've got to digitize in one burst and see what's there. The next > shot may be different chemicals, and we need all the data. > Nasty situation ... If you can confine them all to a corner and the loads don't change too rapidly you could LC-filter the dickens out of every rail. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 1 Oct 2009 16:22 Jan Panteltje wrote: > On a sunny day (Wed, 30 Sep 2009 15:40:50 -0700) it happened Joerg > <invalid(a)invalid.invalid> wrote in <7ii53oF31ev0lU1(a)mid.individual.net>: > >>> You are weaseling away from the subject of 10 mV ripple on supply lines. >> >> No. I said 10mV ripple on supply lines do matter in ultrasound, it's way >> too much when you must listen to the wee rumbles in the aortoa of an >> incredibly obese person. I've got well over 20 years in that business. >> >> Anyhow, if I bought a lab bench the supply that had 10mV ripple on the >> output it would go back same day. This is not to diss you PIC solution, >> that can very well have its place and certainly for experiments with >> digital stuff. Just not with what I usually do. FYI, one of my recent >> switchers (30W) has 600uV of ripple under full load. > > Indeed. > It matters *how* you use the lab supply. > Normally chips, preamps, things that need ultra low ripple have the filtering right next to it, > RC for example, and you are not going to connect you bench power supply directly to those, > but to the normal power input of the board. > > As far as radiation from the supply leads goes, well apart from the usual ferrites and small value caps to ground, > I am sure there are many applications like yours that could pick it up, especially when you open the box when you > are measuring something. > So that would require some extra filtering in the power supply. > When we talk *industrial*, you see supplies specified at any ripple value, from 5 % to some milli volts. > There are zillions of different models. > Often you see 24V, if it is for relays then the ripple value is insignificant. > In an industrial environment there usually are very high electrical noise levels, from relays, motors, machines, what not. > > So it all depends what it is for, and how you use it. > Some very advanced companies with top of the line ultra high speed products, their executives use the power supplies > to charge their car battery. > In such a case the ripple is not very important either. > Ok, you mentioned it was a lab bench supply, not industrial. But you should be ok if you normally don't do too sensitive analog stuff or have another supply for that. A serious LC filter will also help but only if no fast load changes. > I dreamt up a simple circuit to add to the PIC switcher to make it a true current mode controller. > It only uses 2 transistors and 3 resistors, so ultra cheap :-) > > > +12V U out > | | > [ ] R0 [ ] R1 > | | > ------------- | > | | | > e e | > +5V ref -- b b-------------------------| > c c | > | | | > | [ ] R4 | > | | | > | | to current | > | [ ]<---> comparator [ ] R2 > | | | > /// /// /// > > The way this works is that it lowers the voltage of the current limiter setpoint when the output voltage rises above it's setpoint. > With 0V on the pot the current limit is at it's lowest value. > The output voltage will be regulated at 5 x R2 / (R1 + R2), or you need 5V over R2 for equilibrium. > > R0 can be a current source too of course, or you could use an opamp. > You can make it as sophisticated as you want. > Have not tried this yet, maybe in a next one :-) > It also frees up one more PIC pin, that input can then be used for other goodies. > Ok, other than freeing up a pin I can't see much advantage in tapping into the current sense here. But if the numer of free pins is close to zilch right now that'll be different. Pretty soon you've arrive at the usual discrete solution. Hint: My PIC was often a CD40106, with current mode control :-) > So, when are we going to see some circuits or code from you Joerg? > When I retire. Obviously I cannot share schematics of designs I do for customers here. So for now I'll have to limit myself to trying to help folks who got stuck, or ask when I get stuck. But even when I retire I am not so sure about doing much in electronics. A friend and I have mulled over reviving an old passion of ours, brewing beer :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 1 Oct 2009 16:31
On Thu, 01 Oct 2009 13:10:44 -0700, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Wed, 30 Sep 2009 14:40:06 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> 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? >> >> 20-ish. And just a couple of watts. I need 5, 3.3, 2.5, 1.8, 1.2, and >> -5. All from +12. >> > >Theoretically you could run it at 27.12MHz but that's nasty. If you >can't stomach the dissipation of linears then you may be stuck with some >spectral dodging scheme like the one I described. We do that in >ultrasound sometimes but there I could always get a few clock control >lines from some a DSP or FPGA. If I bought the digital and SW guys some >beers that night ... I've got a couple of switcher eval boards around. Maybe I should fire some up and experiment with FMing the switcher freqs and see what that does to the spectrum and to the output voltage. Or better yet have somebody do it for me. John |